%!PS record-id author year title type journal volume issue firstpage lastpage abstract database species country state locality latitude longitude research-type ecosystem biome focus hypothesis superior-character trophic-level 3 Abhilasha, D.; Joshi, J. 2009 Enhanced fitness due to higher fecundity, increased defence against a specialist and tolerance towards a generalist herbivore in an invasive annual plant journal JOURNAL OF PLANT ECOLOGY-UK 2 2 77 86 Web of Science Conyza canadensis;Arion lusitanicus;Uroleucon erigeronense Switzerland Zürich University of Zürich 47.55 8.6167 Greenhouse;Garden terrestrial Invasion Hyp. Enemy Release;Evolution of Increased Competitive Ability;Novel Weapons;Preadaptation to Climate primary;herbivore 4 Abhilasha, Dipti; Quintana, Naira; Vivanco, Jorge; Joshi, Jasmin 2008 Do allelopathic compounds in invasive Solidago canadensis s.l. restrain the native European flora? journal JOURNAL OF ECOLOGY 96 5 993 1001 1. One mechanism explaining the success of invasive weeds may be the production and release of allelopathic compounds by the invader that, due to a lack of co-evolutionary history, have harmful effects on plant neighbours in the introduced range. 2. We partially tested this hypothesis by growing seven competing native European plant species either with the introduced Solidago canadensis s.l., one of the most successful invasive plants in Europe or on soil pre-cultivated with S. canadensis. We added activated carbon to the soil to neutralize organic chemical compounds with putative allelopathic effects. Furthermore, we added unsterilized soil inocula from the introduced (Switzerland) or native (USA) range to the soil to test potential confounding effects of soil microbes on invasion success. Untreated sterilized soil served as control. 3. Five out of the seven native species were more competitive against the invasive species in soils with activated carbon than without, supporting the allelopathy hypothesis. However, competitive outcomes were also influenced by the two sources of soil inoculum and by interactive effects of soil inoculum and Solidago origin suggesting that soil microbes alter allelopathic effects. 4. Achillea millefolium, the species least affected by the presence of S. canadensis and with no response to the activated carbon treatment is the only species used in this experiment reported to grow within Solidago stands in Europe, whereas the other European species tested tend to grow at the periphery of invasive Solidago stands. 5. Chemical analysis by LC-MS of Solidago root extracts revealed four main secondary chemical compounds with potential allelopathic effects. Root exudates of Solidago showed a significant inhibitory effect on growth of the model plant species Arabidopsis thaliana. The magnitude of inhibition increased with increasing concentration of the extract. Synthesis. Levels of the four compounds were lower in Solidago populations from the invasive range than in populations of the same ploidy level from the native range. This suggests lower investment of invasive plants into these secondary compounds, possibly because of a higher susceptibility of plant competitors in the invasive range to these substances. Web of Science Solidago canadensis Switzerland Zürich University of Zürich 47.55 8.6167 Greenhouse;Garden terrestrial Impacts;Invasion Hyp. Novel Weapons primary 5 Adams, Jonathan M.; Fang, Wei; Callaway, Ragan M.; Cipollini, Don; Newell, Elizabeth 2009 A cross-continental test of the Enemy Release Hypothesis: leaf herbivory on Acer platanoides (L.) is three times lower in North America than in its native Europe journal BIOLOGICAL INVASIONS 11 4 1005 1016 Acer platanoides (Norway maple) is a widespread native tree species in Europe. It has been introduced to North America where it has often established dense stands in both secondary woodlands and relatively undisturbed mature woodlands. In Europe A. platanoides is also extending its original range, but generally seems to exist at much lower densities. One explanation for the 'aggressiveness' of invasive plants such as A. platanoides is that they have left behind pests and diseases which limit their population densities in their native lands (the enemy release hypothesis or ERH). To assess the ERH for Norway maple, a large network of collaborators assessed leaf herbivory rates in populations throughout Europe and North America. We found significantly lower total leaf herbivory (1.6% +/- A 0.19, n = 21 vs. 7.4% +/- A 1.94, n = 34) and lower fungal damage (1.0% +/- A 0.35, n = 13 vs. 3.7% +/- A 0.85, n = 34) in North America than in Europe over a 2 year period, which is consistent with the predictions of the Enemy Release Hypothesis. Across years, the average total leaf herbivory was significantly correlated with average annual temperature of the site (P < 0.05), although this was mostly due to sites in Europe (P < 0.001), and not sites in North America (P > 0.05). Furthermore, only populations in Europe showed very high levels of herbivory (e.g., nine sites had total leaf herbivory ranging from 10.0 to 51.2% in at least 1 year) or leaf fungal damage (only one site in North America showed high levels of fungal damage in 1 year), suggesting the possibility of more frequent episodic outbreaks in the native range. Leaf herbivory and fungal damage are only two aspects of consumer pressure and we do not know whether the differences reported here are enough to actually elicit release from top-down population control, but such large scale biogeographic differences in herbivory contribute towards understanding exotic invasions. Web of Science Acer platanoides Europe, North America Field - Observational terrestrial Deciduous Forest Invasion Hyp. Enemy Release primary 6 Adams, Sheherezade N.; Engelhardt, Katharina A. M. 2009 Diversity declines in Microstegium vimineum (Japanese stiltgrass) patches journal BIOLOGICAL CONSERVATION 142 5 1003 1010 The spread of invasive plant species and their impacts on plant communities have received international attention as global trade and global environmental change enhance the colonization and establishment of introduced species and threaten the integrity of native ecosystems. Because introduced species vary in their impact, studying the relationship between invasion and native communities is necessary to guide allocation of finite management resources. By studying adjacent pairs of invaded and uninvaded plots across an eastern United States forested landscape, we demonstrate Microstegium vimineum was associated with local declines in species richness and cover of native species. Negative impacts of M. vimineum on species richness did not emerge until August when M. vimineum cover and height were greatest, highlighting the value of following study subjects through the growing season. In contrast, native species cover was already lower in invaded plots early in the growing season. M. vimineum invasion was not the only important driver of species richness and community composition within the study region: abiotic environmental gradients, such as soil nitrate concentration and pH, across the six study sites were also important in affecting species richness and cover, but lessened in explanatory power through the growing season. We conclude that M. vimineum has effects on community structure that may have long-term consequences for biodiversity. Studies which track sites through time and consider multiple scales are required as invaders impact multiple biotic and abiotic factors operating at different spatial and temporal scales. (C) 2009 Elsevier Ltd. All rights reserved. Web of Science Microstegium vimineum United States Maryland Chesapeake and Ohio Canal National Historical Park 39.00131 -77.246418 Field - Experimental;Greenhouse terrestrial Deciduous Forest Impacts;Fundamentals primary 7 Ahern, Robert G.; Hawthorne, David J.; Raupp, Michael J. 2009 Founder effects and phenotypic variation in Adelges cooleyi, an insect pest introduced to the eastern United States journal BIOLOGICAL INVASIONS 11 4 959 971 Introduced organisms experience founder effects including genetic bottlenecks that result in significant reductions in genetic variation. Genetic bottlenecks may constrain the evolution of phenotypic traits that facilitate success in novel habitats. We examined the effect of introduction into novel environments on genetic diversity of an insect pest, Adelges cooleyi, which was introduced into the eastern United States during the mid nineteenth century. We compared variation in mitochondrial and nuclear genomes in native and introduced samples to determine the effect of introduction on genetic variation experienced by this insect. We also measured an ecologically important phenotype, variation in host preference, in both native and introduced samples to compare variation in that trait with molecular genetic variation. To further investigate the relationship between genetic and phenotypic variation, we examined the degree to which mtDNA haplotypes provide information about host preference. Adelges cooleyi in eastern North America has significantly reduced genetic and phenotypic variation, but this low variation does not appear to have prevented persistence in a novel environment. Introduced insects appear to have retained host preference phenotypes similar to those of insects found where introductions likely originated. Web of Science Adelges cooleyi Lab Invasion Hyp. Evolution in General 13 Alexander, Jake M.; Edwards, Peter J.; Poll, Myriam; Parks, Catherine G.; Dietz, Hansjoerg 2009 Establishment of parallel altitudinal clines in traits of native and introduced forbs journal ECOLOGY 90 3 612 622 Due to altered ecological and evolutionary contexts, we might expect the responses of alien plants to environmental gradients, as revealed through patterns of trait variation, to differ from those of the same species in their native range. In particular, the spread of alien plant species along such gradients might be limited by their ability to establish clinal patterns of trait variation. We investigated trends in growth and reproductive traits in natural populations of eight invasive Asteraceae forbs along altitudinal gradients in their native and introduced ranges (Valais, Switzerland, and Wallowa Mountains, Oregon, USA). Plants showed similar responses to altitude in both ranges, being generally smaller and having fewer inflorescences but larger seeds at higher altitudes. However, these trends were modified by region-specific effects that were independent of species status ( native or introduced), suggesting that any differential performance of alien species in the introduced range cannot be interpreted without a fully reciprocal approach to test the basis of these differences. Furthermore, we found differences in patterns of resource allocation to capitula among species in the native and the introduced areas. These suggest that the mechanisms underlying trait variation, for example, increasing seed size with altitude, might differ between ranges. The rapid establishment of clinal patterns of trait variation in the new range indicates that the need to respond to altitudinal gradients, possibly by local adaptation, has not limited the ability of these species to invade mountain regions. Studies are now needed to test the underlying mechanisms of altitudinal clines in traits of alien species. Web of Science Cirsium arvense;Cirsium vulgare;Cichorium intybus;Lactuca serriola;Conyza canadensis;Erigeron annuus;Matricaria discoidea;Solidago canadensis; Solidago lepida Switzerland;United States Valais;Oregon Central Alps;Wallowa Mountains 46.1667 7.3333 Field - Experimental terrestrial Mountain Fundamentals;Invasion Hyp. Other primary 14 Alexander, Jake M.; Naylor, Bridgett; Poll, Myriam; Edwards, Peter J.; Dietz, Hansjoerg 2009 Plant invasions along mountain roads: the altitudinal amplitude of alien Asteraceae forbs in their native and introduced ranges journal ECOGRAPHY 32 2 334 344 Studying plant invasions along environmental gradients is a promising approach to dissect the relative importance of multiple interacting factors that affect the spread of a species in a new range. Along altitudinal gradients, factors such as propagule pressure, climatic conditions and biotic interactions change simultaneously across rather small geographic scales. Here we investigate the distribution of eight Asteraceae forbs along mountain roads in both their native and introduced ranges in the Valais (southern Swiss Alps) and the Wallowa Mountains (northeastern Oregon, USA). We hypothesised that a lack of adaptation and more limiting propagule pressure at higher altitudes in the new range restricts the altitudinal distribution of aliens relative to the native range. However, all but one of the species reached the same or even a higher altitude in the new range. Thus neither the need to adapt to changing climatic conditions nor lower propagule pressure at higher altitudes appears to have prevented the altitudinal spread of introduced populations. We found clear differences between regions in the relative occurrence of alien species in ruderal sites compared to roadsides, and in the degree of invasion away from the roadside, presumably reflecting differences in disturbance patterns between regions. Whilst the upper altitudinal limits of these plant invasions are apparently climatically constrained, factors such as anthropogenic disturbance and competition with native vegetation appear to have greater influence than changing climatic conditions on the distribution of these alien species along altitudinal gradients. Web of Science Cirsium arvense;Cirsium vulgare;Cichorium intybus;Lactuca serriola;Conyza canadensis;Erigeron annuus;Matricaria discoidea;Solidago canadensis;Solidago lepida Switzerland;United States Valais;Oregon Southern Alps;Wallowa Mountains 46.1667 7.3333 Field - Experimental terrestrial Mountain Fundamentals;Invasion Hyp. Other primary 15 Alexander, Jake M.; Poll, Myriam; Dietz, Hansjoerg; Edwards, Peter J. 2009 Contrasting patterns of genetic variation and structure in plant invasions of mountains journal DIVERSITY AND DISTRIBUTIONS 15 3 502 512 To assess the population genetic consequences of the colonization of two species with contrasting mating systems, Solidago canadensis and Lactuca serriola, along altitudinal gradients in both their native and introduced ranges. Allegheny Mountains, West Virginia and Wallowa Mountains, Oregon, USA; Valais, southern Switzerland. Leaf material was collected from populations along altitudinal gradients and genotyped at seven microsatellite loci for each species. Differences in variability between native and introduced areas and in relation to altitude were analysed using linear models. Differences in the genetic, geographical and altitudinal structure of populations between areas were analysed by AMOVA, cluster analysis and Mantel tests. Genetic variation within and across populations of S. canadensis was significantly reduced, while populations of L. serriola were significantly more variable, in the introduced area. Genetic diversity decreased significantly with altitude for S. canadensis but not L. serriola. Genetic structure of S. canadensis was similar in both areas, and populations were isolated by geographical but not altitudinal distance. By contrast, population structure of L. serriola was much weaker in the introduced area, and populations were not isolated by distance in either area. Solidago canadensis has experienced a strong genetic bottleneck on introduction to the Valais, but this has not prevented it from colonizing a wide altitudinal range. Variation in neutral markers is therefore not necessarily a good measure for judging the ecological behaviour of a species. By contrast, the greater variability of L. serriola in the introduced area, where it also occurs over a greater altitudinal range, can be explained by increased outcrossing among admixed populations. This suggests that the ecological amplitude of alien species might be enhanced after population admixture in the new range, especially for species with highly structured native populations. However, even genetically depauperate introduced populations can be expected to colonize the same environmental range that they occupy in the native area. Web of Science Solidago canadensis;Lactuca serriola Switzerland;United States;United States Valais;Oregon;West Virginia Central Alps;Wallowa Mountains;Allegheny Mountains 46.1667 7.3333 Field - Observational;Lab terrestrial Mountain Invasion Hyp. Other primary 16 Alford, Ross A.; Brown, Gregory P.; Schwarzkopf, Lin; Phillips, Benjamin L.; Shine, Richard 2009 Comparisons through time and space suggest rapid evolution of dispersal behaviour in an invasive species journal WILDLIFE RESEARCH 36 1 23 28 During a biological invasion, we expect that the expanding front will increasingly become dominated by individuals with better dispersal abilities. Over many generations, selection at the invasion front thus will favour traits that increase dispersal rates. As a result of this process, cane toads (Bufo marinus) are now spreading through tropical Australia about 5-fold faster than in the early years of toad invasion; but how have toads changed to make this happen? Here we present data from radio-tracking of free-ranging cane toads from three populations (spanning a 15-year period of the toads' Australian invasion, and across 1800 km). Our data reveal dramatic shifts in behavioural traits (proportion of nights when toads move from their existing retreat-site to a new one, and distance between those successive retreat-sites) associated with the rapid acceleration of toad invasion. Over a maximum period of 70 years (similar to 50 generations), cane toads at the invasion front in Australia apparently have evolved such that populations include a higher proportion of individuals that make long, straight moves. Web of Science Bufo marinus Australia Queensland -22.16 142.01 Field - Observational terrestrial Tropical Forest Invasion Hyp. Evolution in General;Inherent Superiority Effective Disperser omnivore 17 Allan, Eric; Pannell, John R. 2009 Rapid divergence in physiological and life-history traits between northern and southern populations of the British introduced neo-species, Senecio squalidus journal OIKOS 118 7 1053 1061 Web of Science Senecio squalidus Great Britain;Great Britain Oxford;Edinburg 55.93;51.74 -3.20;-1.26 Field - Experimental;Greenhouse;Garden marine Urban;Old Field Invasion Hyp. Evolution in General;Other primary 22 Arteaga, Manuel A.; Delgado, Juan D.; Otto, Rudiger; Fernandez-Palacios, Jose M.; Arevalo, Jose R. 2009 How do alien plants distribute along roads on oceanic islands? A case study in Tenerife, Canary Islands journal BIOLOGICAL INVASIONS 11 4 1071 1086 Islands are paradigms of the pervasive spread of alien plants, but little work has been done assessing pattern and cause of the distribution of such plants in relation to roads on oceanic islands. We studied richness, composition, and distribution of alien plants and compared them with native species along roads on Tenerife (Canary Islands). We studied a single road transect that sampled two contrasting wind-facing aspects (leeward versus windward) and ran from coastal Euphorbia scrubland through thermophilous scrubland to Makaronesian laurel forest at the top of a mountainous massif. We evaluated the effects of elevation, aspect, distance to urban nuclei, and several road-edge features (including road-edge width and management-implying disturbance intensity), using regression models, analysis of variance, and multivariate ordination methods. Richness of both endemics and native nonendemics was explained by elevation (related to well-defined vegetation belts), steepness of the edge slope, and cover of rocky ground. Despite a short elevational gradient (0-650 m), we found clear altitudinal zonation by biogeographic origin of both nonendemic natives and aliens, and altitudinal distribution of aliens followed the same zonation as that of natives. Alien species' richness was related to management intensity determining edge disturbance, road-edge width, and distance to the nearest urban nuclei (propagule sources). Different variables explained distribution patterns of natives, endemics, and aliens along roadsides on leeward and windward aspects. Altitude and aspect also had a strong influence on the frequency of life strategies (woody species, annuals and biennial/perennial herbs) of roadside plant communities. Due to harsher environmental filters operating on the leeward aspect, alien species were distributed along the altitudinal gradient in apparent consistency with general biogeographical affinities. Tropical/subtropical taxa showed exponential decrease with increasing elevation, Mediterranean taxa showed a unimodal response (i.e., maximum richness at mid elevation, minimum at the extremes of the gradient), and temperate taxa showed linear increase with elevation. Native but nonendemic species followed analogous trends to those of aliens. This suggests climatic matching as a prerequisite for successful invasion of this topographically complex island. Other road traits, such as edge width, slope steepness, soil cover, and road-edge disturbance intensity may play a complementary role, at a more local scale, to shape the distribution of alien plants on these island roads. Web of Science Many Canary Islands Tenerife Anaga massif 28.543965 -16.202259 Field - Observational terrestrial Chaparral/Shrublands Fundamentals;Invasion Hyp. Preadaptation to Climate primary 25 Bailey, John P.; Bimova, Katerina; Mandak, Bohumil 2009 Asexual spread versus sexual reproduction and evolution in Japanese Knotweed s.l. sets the stage for the Battle of the Clones"" journal BIOLOGICAL INVASIONS 11 5 1189 1203 The invasion of NW Europe by a single clone of male-sterile Fallopia japonica var. japonica by purely vegetative reproduction has demonstrated that reproduction by seed and the genetic diversity associated with it may not be an essential feature of plant invasions, at least in the short term. What is less well known is that a significant proportion of the Japanese Knotweed s.l. involved is not F. japonica var. japonica, but the hybrid between it and F. sachalinensis-F. x bohemica. This hybrid is able to backcross to either parent with the potential to replace the missing male F. japonica; by the same process, the hybrid is generating the genetic diversity so conspicuously lacking in F. japonica. In terms of understanding the population structure in a particular country, it is important to be able to identify hybrids and putative back-crosses. We bring together a mixture of published and unpublished information to provide a comprehensive section on morphological and anatomical aids to identification. Regeneration of plants from stem and rhizome fragments varies by taxon, as do responses to control techniques, underlining the importance of correct identification of these plants. In this paper we look closely at this group of taxa, with special emphasis on the role played by hybridization, with an examination of the genetic make up of seedlings produced in the wild or by artificial hybridizations, and the implications that this will have on the future directions of the invasion process. Web of Science Fallopia japonica var. japonica; F. sachalinensis-F. x behemica Europe; USA Czech republic; UK; USA Field - Observational;Review terrestrial Urban;Old Field Invasion Hyp. Hybridization primary 26 Banasiak, Stephen E.; Meiners, Scott J. 2009 Long term dynamics of Rosa multiflora in a successional system journal BIOLOGICAL INVASIONS 11 2 215 224 Long term studies of invasion dynamics are critical in developing a more complete understanding of the factors that influence species spread. To address this issue, the dynamics of the non-native invasive plant, Rosa multiflora, were examined using a 40-year record of successional change. The roles of biotic and abiotic factors in regulating R. multiflora invasion were also assessed. The invasion showed an initial 9-year time lag, followed by a 20-year period of population expansion and an ultimate decline as succession progressed. During all phases of R. multiflora's invasion, there was continuous turnover within plots. Rainfall during the previous season was found to increase R. multiflora colonization during population expansion while tree species inhibited the invader's growth. During expansion and decline of R. multiflora, common associated species were often positively or negatively correlated with changes in R. multiflora cover. Though early population dynamics were regulated by propagule pressure, the major influence on R. multiflora late in succession was canopy closure. Although the invasion of this species was largely self-limiting in this system, the species is likely to persist within late successional systems and may require management intervention. Web of Science Rosa multiflora USA NJ Piedmont region, Buell-Small Succession Study 40.5 -74.5667 Field - Observational terrestrial Deciduous Forest Fundamentals primary 27 Bangle, Dianne N.; Walker, Lawrence R.; Powell, Elizabeth Ann 2008 SEED GERMINATION OF THE INVASIVE PLANT BRASSICA TOURNEFORTII (SAHARA MUSTARD) IN THE MOJAVE DESERT journal WESTERN NORTH AMERICAN NATURALIST 68 3 334 342 In the southwestern United States, Brassica tournefortii (Gouan) is a highly invasive plant that threatens native annuals. We conducted 5 experiments to help define the environmental limits for B. tournefortii germination. We found that this species germinates at a wide range of temperatures (16 degrees C to 32 degrees C), under moderate salt concentrations (up to 3.20 dS . m(-1)), in 24 hours of light or darkness, and after 10 weeks of submergence in water. These germination characteristics make B. tournefortii a potentially vigorous competitor of native annuals in the Mojave Desert. The fact that B. tournefortii can take advantage of and effectively reproduce in habitat altered by Tamarix spp. adds to management concerns for controlling this species. That B. tournefortii seeds remain viable after extended submergence, combined with our observation that B. tournefortii can float across large bodies of water with seed pods intact, indicates that this species is it highly successful invader and may be a threat to natural environments, including remote shoreline habitats. We can no longer assume that shoreline habitats experiencing little to no human contact will be safe from invasions initiated by humans. Web of Science Brassica tournefortii United States Southwestern USA Lab terrestrial Desert Invasion Hyp. Inherent Superiority Broad Tolerances primary 31 Barto, E. Kathryn; Cipollini, Don 2009 Density-Dependent Phytotoxicity of Impatiens pallida Plants Exposed to Extracts of Alliaria petiolata journal JOURNAL OF CHEMICAL ECOLOGY 35 4 495 504 Invasive plants are by definition excellent competitors, either indirectly through competition for resources or directly through allelopathic inhibition of neighboring plants. Although both forms of competition are commonly studied, attempts to explore the interactions between direct and indirect competition are rare. We monitored the effects of several doses of extracts of Alliaria petiolata, a Eurasian invader in North America, on the growth of Impatiens pallida, a North American native, at several planting densities. The density-dependent phytotoxicity model predicts that as plant density increases, individual plant size will decrease, unless a toxin is present in the soil. In this case, individual plant size is predicted to increase as plant density increases, as plants share a limited toxin dose. We tested this model using fractions of an A. petiolata extract enriched in flavonoids or glucosinolates, as well as a combined fraction. The flavonoid-enriched fraction and the combined fraction suppressed I. pallida growth but only when applied at a dose eight times higher than that expected in the field. When treated with a dose equivalent to estimated field exposure levels, I. pallida growth was not distinguishable from that of control plants that received no extract, showing that indirect competition for resources was more important for determining the growth of I. pallida than direct allelopathic inhibition by A. petiolata. This is an important reminder that, even though many plants have the demonstrated potential to exert strong allelopathic effects, those effects may not always be apparent when other forms of competition are considered as well. Web of Science Alliaria petiolata USA Lab terrestrial Invasion Hyp. Novel Weapons primary 33 Bartomeus, Ignasi; Vila, Montserrat 2009 Breeding system and pollen limitation in two supergeneralist alien plants invading Mediterranean shrublands journal AUSTRALIAN JOURNAL OF BOTANY 57 2 109 115 Many widely known invasive plants are well integrated into native plant-pollinator networks. Typically, these invaders have entomophilous flowers which are visited by a diverse array of pollinators. The type of breeding system and the role that pollination services play in the reproductive success of invasive plants have, however, received little attention. We studied the breeding system and pollen limitation of two entomophilous invasive plants, Carpobrotus affine acinaciformis and Opuntia stricta, in different Mediterranean coastal localities in north-eastern Spain. Both species are, to some degree self-compatible; however, because of frequent visitation, open pollination increased the seed set in both species by at least 50%. Whereas O. stricta showed no pollen limitation, some populations of C. aff. acinaciformis had a lower seed set in open-pollinated flowers than in flowers where supplementary hand-pollination ensured out-crossing. This local pollen limitation in C. aff. acinaciformis could be due to the low efficiency of its visitors (mainly beetles) or its hybrid status. On the basis of previous studies on Carpobrotus sp. hybrid complexes, we suggest that the variability among sites in the seed set of open-pollinated flowers is caused by different degrees of hybrid introgression. Not withstanding, we found the C. aff. acinaciformis seed sets studied were higher than those reported in other regions. Further research is needed to assess the invasion potential of these hybrids in Mediterranean shrublands. Web of Science Carpobrotus affine acinaciformis; Opuntia stricta Spain Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Other primary 34 Basky, Zsuzsa; Magyar, D. 2009 Impact of indigenous aphids on development of the invasive common ragweed (Ambrosia artemisiifolia L.) in Hungary journal JOURNAL OF PEST SCIENCE 82 1 19 25 The common ragweed, Ambrosia artemisiifolia is a widespread invasive weed species in Europe. In order to estimate the deteriorative effect of native arthropods on the invasive ragweed the effect of three indigenous aphid species on plant development and pollen production was studied. Common ragweed plants grown in a greenhouse were artificially infested with five apterous individuals of either Aphis fabae, Brachycaudus helichrysi or Myzus persicae at the 4-leaf stage. Feeding by all three aphid species over a 5-week period significantly reduced plant height, the number of male inflorescences, the length of racemes, pollen emission and plant dry mass. Brachycaudus helichrysi produced the largest colonies, followed by A. fabae and M. persicae. In a host plant choice test, B. helichrysi showed significant preference for ragweed over sunflower, whereas A. fabae preferred sunflower and M. persicae did not show any preference. In a Weld experiment, the growth rate of A. fabae on caged ragweed plants was similar to that in the greenhouse, but the final numbers of B. helichrysi and M. persicae after 30 days was ten and seven times lower than under greenhouse conditions, respectively. On exposed Weld plants, B. helichrysi was more abundant than other species. However, no aphid species affected the height or dry mass of either caged or exposed plants during a 30-day period. Under controlled conditions aphids effectively hampered development and pollen production of ragweed, however, under Hungarian Weld conditions the development of ragweed was much more dynamic, therefore no deleterious effect of aphid feeding occurred. Web of Science Ambrosia artemisiifolia Hungary Field - Experimental terrestrial Grassland Invasion Hyp. Other primary 35 Battaglia, Loretta L.; Denslow, Julie S.; Inczauskis, Jason R.; Baer, Sara G. 2009 Effects of native vegetation on invasion success of Chinese tallow in a floating marsh ecosystem journal JOURNAL OF ECOLOGY 97 2 239 246 1. Interactions between resident and exotic species have been shown to control the biotic resistance of communities to invasion. With different life stages of the exotic species, each sequential interaction may dampen or strengthen previous ones, thereby influencing invasion success. 2. We assessed the effects of resident vegetation type on the arrival and performance of Triadica sebifera (Chinese tallow), a widespread invader in freshwater floating marshes, using a combination of field studies and glasshouse experiments. 3. Our results indicated that Triadica abundance was positively associated with native woody species, particularly the native actinorhizal shrub Morella cerifera (wax myrtle). Seed dispersal and germination of Triadica were generally low but suggestive that Morella has weak, facilitative effects on the spread of Triadica by channelling its dispersal by birds into shrub thickets and promoting germination upon arrival. Triadica seedling growth was greatest where light and total inorganic N were higher. Growth of Triadica trees was greater in marsh sites without Morella and did not exhibit any detectable responses to elevated N levels in substrates from Morella thickets. 4. Morella may facilitate the spread of Triadica in floating shrub communities, yet inhibit its growth once established. The few individuals that establish in herbaceous marshes grow faster and may therefore reach maturity sooner than in Morella shrub thickets. 5. Synthesis. Our work suggests that the net effects of facilitation and inhibition by native, resident species on exotics can influence invasion success. In this case, weak, facilitative effects operating in the arrival and establishment phases of invasion are not completely negated by subsequent negative interactions between the same species, enabling the invader to persist. Models that quantify the relative strength and cumulative effects of these interactions are needed to improve predictions of community invasibility. Web of Science Triadica sebifera USA Louisiana Jean Lafitte Natl Historic Park 29.799 -90.123 Field - Experimental;Field - Observational;Greenhouse estuarine Wetland Invasion Hyp. Mutualism Facilitation;Other primary 37 Beaumont, Linda J.; Gallagher, Rachael V.; Thuiller, Wilfried; Downey, Paul O.; Leishman, Michelle R.; Hughes, Lesley 2009 Different climatic envelopes among invasive populations may lead to underestimations of current and future biological invasions journal DIVERSITY AND DISTRIBUTIONS 15 3 409 420 We explore the impact of calibrating ecological niche models (ENMs) using (1) native range (NR) data versus (2) entire range (ER) data (native and invasive) on projections of current and future distributions of three Hieracium species. H. aurantiacum, H. murorum and H. pilosella are native to Europe and invasive in Australia, New Zealand and North America. Differences among the native and invasive realized climatic niches of each species were quantified. Eight ENMs in BIOMOD were calibrated with (1) NR and (2) ER data. Current European, North American and Australian distributions were projected. Future Australian distributions were modelled using four climate change scenarios for 2030. The invasive climatic niche of H. murorum is primarily a subset of that expressed in its native range. Invasive populations of H. aurantiacum and H. pilosella occupy different climatic niches to those realized in their native ranges. Furthermore, geographically separate invasive populations of these two species have distinct climatic niches. ENMs calibrated on the realized niche of native regions projected smaller distributions than models incorporating data from species' entire ranges, and failed to correctly predict many known invasive populations. Under future climate scenarios, projected distributions decreased by similar percentages, regardless of the data used to calibrate ENMs; however, the overall sizes of projected distributions varied substantially. This study provides quantitative evidence that invasive populations of Hieracium species can occur in areas with different climatic conditions than experienced in their native ranges. For these, and similar species, calibration of ENMs based on NR data only will misrepresent their potential invasive distribution. These errors will propagate when estimating climate change impacts. Thus, incorporating data from species' entire distributions may result in a more thorough assessment of current and future ranges, and provides a closer approximation of the elusive fundamental niche. Web of Science Hieracium aurantiacum;Hieracium murorum;Hieracium pilosella Theoretical/Modeling terrestrial Invasion Hyp. Preadaptation to Climate 38 Becerra, Pablo I.; Bustamante, Ramiro O. 2008 The effect of herbivory on seedling survival of the invasive exotic species Pinus radiata and Eucalyptus globulus in a Mediterranean ecosystem of Central Chile journal FOREST ECOLOGY AND MANAGEMENT 256 9 1573 1578 Herbivory may be an important factor affecting seedling survival of exotic species invading new habitats. We evaluated the effect of vertebrate herbivory on the seedling survival of two widely planted and invasive tree species (Pinus radiata and Eucalyptus globulus), in a Mediterranean-type ecosystem of central Chile. An important role of herbivory on seedling survival of these two species in their introduced ranges has previously been documented. However, this has mainly been evaluated in forest plantations where habitat and vegetation conditions differ from wild habitats in which invasion occurs. We planted seedlings with and without protection against vertebrate herbivores in different aspects (a mesic south-facing slope and a xeric north-facing slope) and vegetation cover (open sites and sites with patchy tree cover). We found that regardless of aspect or vegetation cover, herbivory, in this case mainly caused by exotic vertebrates, significantly and negatively affected seedling survival of both species. However, while the effect of herbivory on P. radiata was significant in every vegetation and habitat condition, for E. globulus, the effect of herbivory was significant only for open sites in the mesic habitat. These results suggest that, as observed in forestry plantations, vertebrate herbivory may constrain seedling establishment of these two exotic trees and potentially impede the invasion. However, the importance of herbivory in controlling exotic species may vary depending on the vegetation and habitat conditions in some species such as E. globulus. (C) 2008 Elsevier B.V. All rights reserved. Web of Science Pinus radiata; Eucalyptus globulus Chile -30.5 -70.5 Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Other primary 43 Best, Rebecca J. 2008 Exotic grasses and feces deposition by an exotic herbivore combine to reduce the relative abundance of native forbs journal OECOLOGIA 158 2 319 327 Increased resource availability can facilitate establishment of exotic plant species, especially when coincident with propagule supply. Following establishment, increased resource availability may also facilitate the spread of exotic plant species if it enhances their competitive abilities relative to native species. Exotic Canada geese (Branta canadensis) introduce both exotic grass seed and nutrients to an endangered plant community on the Gulf Islands of southwestern British Columbia, Canada. I used greenhouse experiments to assess the competitive advantage of the exotic grasses relative to native and exotic forbs in this community and to test the impacts of nutrient addition from goose feces on competitive outcomes. I grew experimental communities varying in their proportion of forbs versus exotic grasses, and added goose feces as a nutrient source. I found that both native and exotic forbs produced significantly more biomass in competition with conspecifics than in competition with the grasses, and that the proportional abundance of two out of three native forbs was lowest in the combined presence of exotic grasses and nutrient addition. In a second experiment, I found that in monoculture all species of forbs and grasses showed equal growth responses to nutrients. The exotic species did not convert additional nutrients into additional biomass at a higher rate, but did germinate earlier and grow larger than the native species regardless of nutrient availability. This suggests that the exotic species may have achieved their competitive advantage partly by pre-empting resources in community mixtures. Small and late-germinating native forbs may be particularly vulnerable to competitive suppression from exotic grasses and forbs and may be at an even greater disadvantage if their competitors are benefiting from early access to additional nutrients. In combination, the input of exotic propagules and additional nutrients by nesting geese may compromise efforts to maintain native community composition in this system. Web of Science Branta canadensis; Bromus diandrus; Aira praecox; Vulpia bromoides; Poa annua; Senecio vulgaris Canada British Colombia Gulf Islands 48.683053 -123.383603 Greenhouse terrestrial Savanna Invasion Hyp. Mutualism Facilitation primary;herbivore 44 Best, Rebecca J.; Arcese, Peter 2009 Exotic herbivores directly facilitate the exotic grasses they graze: mechanisms for an unexpected positive feedback between invaders journal OECOLOGIA 159 1 139 150 The ability of an exotic species to establish in a system may depend not only on the invasibility of the native community, but also on its interactions with other exotic species. Though examples of mutually beneficial interactions between exotic species are known, few studies have quantified these effects or identified specific mechanisms. We used the co-invasion of an endangered island ecosystem by exotic Canada geese (Branta canadensis) and nine exotic annual grasses to study the effects of an invading herbivore on the success of invading grasses. On our study islands in southwestern Canada, we found that geese fed selectively on the exotic grasses and avoided native forbs. Counter to current theory suggesting that the grasses should be limited by a selective enemy, however, the grasses increased in proportional abundance under grazing whereas forbs showed declining abundance. Testing potential mechanisms for the effects of grazing on grasses, we found that the grasses produced more stems per area when grazing reduced vegetation height and prevented litter accumulation. Forming dense mats of short stems appeared to be an efficient reproductive and competitive strategy that the Eurasian grasses have evolved in the presence of grazers, conferring a competitive advantage in a system where the native species pool has very few annual grasses and no grazers. Germination trials further demonstrated that selective herbivory by geese enables their dispersal of exotic grass seed between heavily invaded feeding areas and the small islands used for nesting. In summary, the exotic geese facilitated both the local increase and the spatial spread of exotic grasses, which in turn provided the majority of their diet. This unexpected case of positive feedback between exotic species suggests that invasion success may depend on the overall differences between the evolutionary histories of the invaders and the evolutionary history of the native community they enter. Web of Science Branta canadensis; Bromus diandrus; Aira praecox; Vulpia bromoides; Poa annua; Senecio vulgaris Canada British Colombia Gulf Islands 48.683053 -123.383603 Field - Experimental;Field - Observational;Theoretical/Modeling terrestrial Savanna Impacts;Invasion Hyp. Mutualism Facilitation;Propagule Pressure;Ecosystem Engineers primary;herbivore 47 Blanchett, Simon; Leprieur, Fabien; Beauchard, Olivier; Staes, Jan; Oberdorff, Thierry; Brosse, Sebastien 2009 Broad-scale determinants of non-native fish species richness are context-dependent journal PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES 276 127 2385 2394 Web of Science Many Statistical/Meta-analysis lotic Invasion Hyp. Other herbivore;omnivore;predator 49 Blumenthal, Dana; Mitchell, Charles E.; Pysek, Petr; Jarosik, Vojtech 2009 Synergy between pathogen release and resource availability in plant invasion journal PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 106 19 7899 7904 Web of Science Many USA Statistical/Meta-analysis terrestrial Invasion Hyp. Enemy Release;Disturbance primary 50 Blumenthal, Dana Michael 2009 Carbon addition interacts with water availability to reduce invasive forb establishment in a semi-arid grassland journal BIOLOGICAL INVASIONS 11 6 1281 1290 Web of Science Bromus tectorum; Centaurea diffusa; Cirsium arvense; Euphorbia esula; Gypsophila paniculata; Linaria dalmatica USA Wyoming High Plains Grassland Research Station 41 -104 Field - Experimental terrestrial Grassland Invasion Hyp. Plasticity primary 52 Boman, Sanna; Grapputo, Alessandro; Lindstroem, Leena; Lyytinen, Anne; Mappes, Johanna 2008 Quantitative genetic approach for assessing invasiveness: geographic and genetic variation in life-history traits journal BIOLOGICAL INVASIONS 10 7 1135 1145 Predicting the spread of invasive species is a challenge for modern ecology. Although many invasive species undergo genetic bottlenecks during introduction to new areas resulting in a loss of genetic diversity, successful invaders manage to flourish in novel environments either because of pre-adaptations or because important traits contain adaptive variation enabling rapid adaptation to changing conditions. To predict and understand invasion success, it is crucial to analyse these features. We assessed the potential of a well-known invader, the Colorado potato beetle (Leptinotarsa decemlineata), to expand north of its current range in Europe. A short growing season and harsh overwintering conditions are apparent limiting factors for this species' range. By rearing full-sib families from four geographically distinct populations (Russia, Estonia, Poland, Italy) at two fluctuating temperature regimes, we investigated (a) possible differences in survival, development time, and body size among populations and (b) the amount of adaptive variation within populations in these traits. All populations were able to complete their development in cooler conditions than in their current range. A significant genotype-environment interaction for development time and body size suggests the presence of adaptive genetic variation, indicating potential to adapt to cooler conditions. The northernmost population had the highest survival rates and fastest development times on both temperature regimes, suggesting pre-adaptation to cooler temperatures. Other populations had minor differences in development times. Interestingly, this species lacks the classical trade-off between body size and development time which could have contributed to its invasion potential. This study demonstrates the importance of considering both ecological and evolutionary aspects when assessing invasion risk. Web of Science Leptinotarsa decemlineata Russia, Poland, Europe Lab terrestrial Invasion Hyp. Preadaptation to Climate herbivore 53 Botham, M. S.; Rothery, P.; Hulme, P. E.; Hill, M. O.; Preston, C. D.; Roy, D. B. 2009 Do urban areas act as foci for the spread of alien plant species? An assessment of temporal trends in the UK journal DIVERSITY AND DISTRIBUTIONS 15 2 338 345 Given that urban landscapes often act as a point of entry for many non-native species and urban development continues to increase as the human population rapidly expands, an understanding of the interaction between urbanization and non-native plant species is important both in the control of potentially invasive species and in the conservation of native biodiversity. We investigated the spatial and temporal relationship between urban land cover and the distribution of non-native species in Britain using two floristic data sets collected at two different time periods: 1987-88 and 2003-04. UK. Using floristic data collected by the Botanical Society of the British Isles in 1987-88 (Monitoring Scheme) and 2003-04 (Local Change) in conjunction with habitat data obtained from the Land Cover Map of the UK, we conducted multiple regression analyses both within and between years on both groups of species (natives, neophytes and archaeophytes) and individual species. Neophytes (alien species introduced after 1500) were very strongly associated with urban land cover in both time periods and do not appear to be spreading out of urban habitats into the wider countryside. Archaeophytes (alien species introduced before 1500), however, showed a strong association with urban habitats in the earlier 1988 data set but no longer showed this association in the 2004 data set. Analysis at the individual species level showed that a large percentage of alien plant species, particularly archaeophytes, were not strongly associated with urban land cover or were negatively associated with such habitats. Our results suggest that there has been a reduction in the urban association of archaeophytes that is likely to have resulted from the recovery of archaeophytes associated with non-urban (especially arable) habitats, following their decline in mid-20th century, rather than from the movement of aliens into the wider countryside from urban habitats. Web of Science Many UK Statistical/Meta-analysis terrestrial Invasion Hyp. Other primary 54 Boulant, Nadine; Kunstler, Georges; Rambal, Serge; Lepart, Jacques 2008 Seed supply, drought, and grazing determine spatio-temporal patterns of recruitment for native and introduced invasive pines in grasslands journal DIVERSITY AND DISTRIBUTIONS 14 5 862 874 The rate of grassland invasion by trees depends on the ability of the species to invade, i.e. their invasiveness, and on the susceptibility of the environments to invasion, i.e. their invasibility. Knowledge of the invasiveness of native and introduced tree species and of the environmental factors that contribute to invasibility is necessary to understand landscape evolution and assess required management measures. Our main aim was to explore this by estimating the separate effects of propagule pressure and environmental factors on the spatio-temporal patterns of sapling recruitment, a key stage in the tree life cycle. Causse Mejean calcareous plateau (southern France). The effects of seed supply and environmental variables (grazing, geological substrate, and duration or intensity of drought) on the spatio-temporal patterns of sapling recruitment were assessed for the native Scots pine (Pinus sylvestris L.) and the introduced black pine (Pinus nigra Arn. ssp. nigra). Estimates were derived by inverse modelling with data of locations and ages of 4- to 20-year-old saplings and seed-bearing trees in 32 sites. Yearly indices of drought were derived from a soil-water content model. For both species, seed supply was as important as the whole set of environmental factors in explaining sapling recruitment rates. Grazing and the duration of drought from July to August decreased sapling recruitment rates, which were also lower on hard limestone than on dolomite. Dispersal distances and effective fecundities were higher for the introduced P. nigra, which was less susceptible to drought but more affected by grazing than the native P. sylvestris. In grazed grasslands, shrubs facilitated sapling establishment of both species. This study shows how seed supply and environmental factors shape spatio-temporal patterns of sapling recruitment for trees invading grasslands. Implications for landscape evolution and management, of the difference in invasiveness of the two pine species and of the hierarchy of environmental factors in determining invasibility, are discussed. Web of Science Pinus nigra France Aveyron Causse Mejean 44.258282 3.568954 Field - Observational;Theoretical/Modeling;Statistical/Meta-analysis terrestrial Grassland Invasion Hyp. Propagule Pressure;Preadaptation to Climate;Disturbance primary 55 Bradley, Bethany A. 2009 Regional analysis of the impacts of climate change on cheatgrass invasion shows potential risk and opportunity journal GLOBAL CHANGE BIOLOGY 15 1 196 208 Interactions between climate change and non-native invasive species may combine to increase invasion risk to native ecosystems. Changing climate creates risk as new terrain becomes climatically suitable for invasion. However, climate change may also create opportunities for ecosystem restoration on invaded lands that become climatically unsuitable for invasive species. Here, I develop a bioclimatic envelope model for cheatgrass (Bromus tectorum), a non-native invasive grass in the western US, based on its invaded distribution. The bioclimatic envelope model is based on the Mahalanobis distance using the climate variables that best constrain the species' distribution. Of the precipitation and temperature variables measured, the best predictors of cheatgrass are summer, annual, and spring precipitation, followed by winter temperature. I perform a sensitivity analysis on potential cheatgrass distributions using the projections of 10 commonly used atmosphere-ocean general circulation models (AOGCMs) for 2100. The AOGCM projections for precipitation vary considerably, increasing uncertainty in the assessment of invasion risk. Decreased precipitation, particularly in the summer, causes an expansion of suitable land area by up to 45%, elevating invasion risk in parts of Montana, Wyoming, Utah, and Colorado. Conversely, increased precipitation reduces habitat by as much as 70%, decreasing invasion risk. The strong influence of precipitation conditions on this species' distribution suggests that relying on temperature change alone to project future change in plant distributions may be inadequate. A sensitivity analysis provides a framework for identifying key climate variables that may limit invasion, and for assessing invasion risk and restoration opportunities with climate change. Web of Science Bromus tectorum USA Montana; Wyoming; Utah; Colorado Theoretical/Modeling terrestrial Grassland Invasion Hyp. Climate Change primary 56 Bradley, Bethany A.; Oppenheimer, Michael; Wilcove, David S. 2009 Climate change and plant invasions: restoration opportunities ahead? journal GLOBAL CHANGE BIOLOGY 15 6 1511 1521 Rather than simply enhancing invasion risk, climate change may also reduce invasive plant competitiveness if conditions become climatically unsuitable. Using bioclimatic envelope modeling, we show that climate change could result in both range expansion and contraction for five widespread and dominant invasive plants in the western United States. Yellow starthistle (Centaurea solstitialis) and tamarisk (Tamarix spp.) are likely to expand with climate change. Cheatgrass (Bromus tectorum) and spotted knapweed (Centaurea biebersteinii) are likely to shift in range, leading to both expansion and contraction. Leafy spurge (Euphorbia esula) is likely to contract. The retreat of once-intractable invasive species could create restoration opportunities across millions of hectares. Identifying and establishing native or novel species in places where invasive species contract will pose a considerable challenge for ecologists and land managers. This challenge must be addressed before other undesirable species invade and eliminate restoration opportunities. Web of Science Centaurea solstitialis; Tamarix; Euphorbia esula USA Theoretical/Modeling terrestrial Grassland Invasion Hyp. Climate Change primary 58 Bradshaw, Corey J. A.; Giam, Xingli; Tan, Hugh T. W.; Brook, Barry W.; Sodhi, Navjot S. 2008 Threat or invasive status in legumes is related to opposite extremes of the same ecological and life-history attributes journal JOURNAL OF ECOLOGY 96 5 869 883 1. The urgency and scale of the global biodiversity crisis requires the application of generalized predictors of a species' likelihood of going extinct or becoming invasive in non-native areas. A common approach is to correlate species' ecological and life-history characteristics (attributes, traits) with the probability of becoming either threatened (responding negatively to human activity), or invasive (responding positively). The limitation of previous studies is that the fates of becoming threatened or invasive have generally been treated in isolation. 2. Here we consider the problem of threat and invasiveness in unison based on analysis of one of the largest-ever species attributes data bases (8906 species) compiled for a single plant family (Fabaceae). We used generalized linear mixed-effects models (using taxonomic grouping to control for within-family phylogenetic relationships) to correlate species' life-history and ecological traits to three response variables: probability of being (i) threatened or not, (ii) invasive or not, and (iii) threatened or invasive. 3. We found that tall, annual, range-restricted species with tree-like growth forms, inhabiting closed-forest and lowland sites are more likely to be threatened. Conversely, climbing and herbaceous species that naturally span multiple floristic kingdoms and habitat types are more likely to become invasive. 4. Synthesis. These results support the idea that at least for one of the richest plant families, species' life-history and ecological traits correlate with a fate response to anthropogenic global change. Our results show that species do demonstrate particular susceptibility to either fate based on their evolved traits, and that traits generally correlated with invasiveness are also those that correlate with a reduced probability of becoming threatened. Web of Science Many Statistical/Meta-analysis terrestrial Invasion Hyp. Inherent Superiority Superior Competitor primary 59 Branch, George M.; Odendaal, Francois; Robinson, Tamara B. 2008 Long-term monitoring of the arrival, expansion and effects of the alien mussel Mytilus galloprovincialis relative to wave action journal MARINE ECOLOGY-PROGRESS SERIES 370 0 171 183 The Mediterranean mussel Mytilus galloprovincialis is the most widespread marine alien species along the South African coast. Long-term monitoring of the mid-to-low intertidal zone in the Groen-Spoeg area on the west coast between 1988 and 1993 tracked the establishment and expansion of this aggressive invader along a gradient of wave action. Additionally, the effects of M. galloprovincialis on other dominant species were quantified. The rate of increase and abundance of M. galloprovincialis was promoted by exposure to strong wave action. The tube-building polychaete Gunnarea capensis remained the dominant space occupier on sheltered shores but its density was negatively correlated with the M galloprovincialis expansion on semi-exposed and exposed shores. In contrast, the indigenous mussel Aulacomya ater demonstrated no significant changes in density over time as it simply became incorporated into the spreading M. galloprovincialis beds. Overall abundance of the grazing limpet Scutellastra granularis was positively affected by the M. galloprovincialis invasion, although adults and recruits occupying primary space showed a negative correlation with M. galloprovincialis abundance, the strength of which increased with wave exposure. Conversely, adults and recruits occurring on secondary space were positively affected by M galloprovincialis beds, which enhanced settlement, Again the strength of the interaction increased with wave action. Patterns observed in the field therefore indicated that abundance of M. galloprovincialis and its effects on other elements of the fauna were linked with the intensity of wave action. Web of Science Mytilus galloprovincialis South Africa -33.958853 25.651245 Field - Observational marine Intertidal/Near Shore Invasion Hyp. Inherent Superiority Superior Competitor filter 60 Brandt, M.; Van Wilgenburg, E.; Tsutsui, N. D. 2009 Global-scale analyses of chemical ecology and population genetics in the invasive Argentine ant journal MOLECULAR ECOLOGY 18 5 997 1005 Ants are some of the most abundant and ecologically successful terrestrial organisms, and invasive ants rank among the most damaging invasive species. The Argentine ant is a particularly well-studied invader, in part because of the extreme social structure of introduced populations, known as unicoloniality. Unicolonial ants form geographically vast supercolonies, within which territorial behaviour and intraspecific aggression are absent. Because the extreme social structure of introduced populations arises from the widespread acceptance of conspecifics, understanding how this colonymate recognition occurs is key to explaining their success as invaders. Here, we present analyses of Argentine ant recognition cues (cuticular hydrocarbons) and population genetic characteristics from 25 sites across four continents and the Hawaiian Islands. By examining both hydrocarbon profiles and microsatellite genotypes in the same individual ants, we show that native and introduced populations differ in several respects. Both individual workers and groups of nestmates in the introduced range possess less diverse chemical profiles than ants in the native range. As previous studies have reported, we also find that introduced populations possess much lower levels of genetic diversity than populations in the native range. Interestingly, the largest supercolonies on several continents are strikingly similar to each other, suggesting that they arose from a shared introduction pathway. This high similarity suggests that these geographically far-flung ants may still recognize and accept each other as colonymates, thus representing distant nodes of a single, widely distributed supercolony. These findings shed light on the behaviour and sociality of these unicolonial invaders, and pose new questions about the history and origins of introduced populations. Web of Science Linepithema humile USA; Spain; Australia California; Hawaii; North Carolona; Catalonia Field - Observational;Lab terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority Superior Competitor omnivore 62 Brodersen, Craig; Lavergne, Sebastien; Molofsky, Jane 2008 Genetic variation in photosynthetic characteristics among invasive and native populations of reed canarygrass (Phalaris arundinacea) journal BIOLOGICAL INVASIONS 10 8 1317 1325 With the extensive spread of invasive species throughout North America and Europe there is an urgent need to better understand the morphological and physiological characteristics of successful invasive plants and the evolutionary mechanisms that allow introduced species to become invasive. Most ecological studies have focused on morphological differences and changes in community dynamics, and physiological studies have typically explored the differences between native and invasive species. In this study, 15 different genotypes of Phalaris arundinacea from both its native (European) and invasive (North American) range were grown in a common garden experiment to monitor the physiological differences between native and invasive genotypes. Here we present data that suggests high variability exists in the physiological traits among genotypes of P. arundinacea, yet genotypes from the native range are not necessarily physiologically inferior to the hybridized invasive genotypes. Previous work has shown that multiple introductions of P. arundinacea from various European locations to the United States resulted in numerous hybridization events, yielding more genetic variability and phenotypic plasticity in the invasive range. Of the genotypes studied, both morphological and physiological traits of genotypes with French origin were significantly different from the plants from the Czech Republic, North Carolina, and Vermont. The lack of clear differences between native and invasive genotypes indicates that physiological traits may be highly conserved in P. arundinacea and enhanced photosynthetic rates are not indicative of successful invasive genotypes. Instead, morphological traits and defensive secondary compound metabolism may play a more important role in the success of P. arundinacea within its invasive range, and patterns of genetic variation in physiological traits between invasive and native range may be more important than the mean traits of each region when explaining reed canarygrass' invasive potential in North America. Web of Science Phalaris arundinacea USA North Carolina; Vermont Garden terrestrial Riparian Invasion Hyp. Evolution of Increased Competitive Ability primary 64 Broennimann, Olivier; Guisan, Antoine 2008 Predicting current and future biological invasions: both native and invaded ranges matter journal BIOLOGY LETTERS 4 5 585 589 The classical approach to predicting the geographical extent of species invasions consists of training models in the native range and projecting them in distinct, potentially invasible areas. However, recent studies have demonstrated that this approach could be hampered by a change of the realized climatic niche, allowing invasive species to spread into habitats in the invaded ranges that are climatically distinct from those occupied in the native range. We propose an alternative approach that involves fitting models with pooled data from all ranges. We show that this pooled approach improves prediction of the extent of invasion of spotted knapweed (Centaurea maculosa) in North America on models based solely on the European native range. Furthermore, it performs equally well on models based on the invaded range, while ensuring the inclusion of areas with similar climate to the European niche, where the species is likely to spread further. We then compare projections from these models for 2080 under a severe climate warming scenario. Projections from the pooled models show fewer areas of intermediate climatic suitability than projections from the native or invaded range models, suggesting a better consensus among modelling techniques and reduced uncertainty. Web of Science Centaurea maculosa North America; Europe Theoretical/Modeling terrestrial Grassland Fundamentals primary 65 Brown, Carissa D.; Boutin, Celine 2009 Linking past land use, recent disturbance, and dispersal mechanism to forest composition journal BIOLOGICAL CONSERVATION 142 8 1647 1656 Web of Science Many Canada Eastern Ontario Field - Observational terrestrial Deciduous Forest;Coniferous Forest Invasion Hyp. Inherent Superiority;Disturbance Effective Disperser primary 67 Broz, Amanda K.; Manter, Daniel K.; Bowman, Gillianne; Mueller-Schaerer, Heinz; Vivanco, Jorge M. 2009 Plant origin and ploidy influence gene expression and life cycle characteristics in an invasive weed journal BMC PLANT BIOLOGY 9 0 0 Background: Ecological, evolutionary and physiological studies have thus far provided an incomplete picture of why some plants become invasive; therefore we used genomic resources to complement and advance this field. In order to gain insight into the invasive mechanism of Centaurea stoebe we compared plants of three geo-cytotypes, native Eurasian diploids, native Eurasian tetraploids and introduced North American tetraploids, grown in a common greenhouse environment. We monitored plant performance characteristics and life cycle habits and characterized the expression of genes related to constitutive defense and genome stability using quantitative PCR. Results: Plant origin and ploidy were found to have a significant effect on both life cycle characteristics and gene expression, highlighting the importance of comparing appropriate taxonomic groups in studies of native and introduced plant species. We found that introduced populations of C. stoebe exhibit reduced expression of transcripts related to constitutive defense relative to their native tetraploid counterparts, as might be expected based on ideas of enemy release and rapid evolution. Measurements of several vegetative traits were similar for all geocytotypes; however, fecundity of tetraploids was significantly greater than diploids, due in part to their polycarpic nature. A simulation of seed production over time predicts that introduced tetraploids have the highest fecundity of the three geo- cytotypes. Conclusion: Our results suggest that characterizing gene expression in an invasive species using populations from both its native and introduced range can provide insight into the biology of plant invasion that can complement traditional measurements of plant performance. In addition, these results highlight the importance of using appropriate taxonomic units in ecological genomics investigations. Web of Science Centaurea stoebe Switzerland Fribourg Botanical Garden Greenhouse;Lab terrestrial Grassland Invasion Hyp. Enemy Release;Evolution in General;Inherent Superiority Superior Competitor primary 68 Broz, Amanda K.; Manter, Daniel K.; Callaway, Ragan M.; Paschke, Mark W.; Vivanco, Jorge M. 2008 A molecular approach to understanding plant-plant interactions in the context of invasion biology journal FUNCTIONAL PLANT BIOLOGY 35 11 1123 1134 Competition is a major determinant of plant community structure, and can influence the size and reproductive fitness of a species. Therefore, competitive responses may arise from alterations in gene expression and plant function when an individual is confronted with new competitors. This study explored competition at the level of gene expression by hybridising transcripts from Centaurea maculosa Lam., one of North America's most invasive exotic plant species, to an Arabidopsis thaliana (L.) Heynh microarray chip. Centaurea was grown in competition with Festuca idahoensis Elmer, a native species that generally has weak competitive effects against Centaurea; Gaillardia aristata Pursh, a native species that tends to be a much stronger competitor against Centaurea; and alone (control). Some transcripts were induced or repressed to a similar extent regardless of the plant neighbour grown with Centaurea. Other transcripts showed differential expression that was specific to the competitor species, possibly indicating a species-specific aspect of the competitive response of Centaurea. These results are the first to identify genes in an invasive plant that are induced or repressed by plant neighbours and provide a new avenue of insight into the molecular aspects of plant competitive ability. Web of Science Centaurea maculosa USA Northwest Lab terrestrial Grassland Invasion Hyp. Inherent Superiority Superior Competitor primary 70 Bucharova, Anna; van Kleunen, Mark 2009 Introduction history and species characteristics partly explain naturalization success of North American woody species in Europe journal JOURNAL OF ECOLOGY 97 2 230 238 1. The search for general characteristics of invasive species has not been very successful yet. A reason for this could be that current invasion patterns are mainly reflecting the introduction history (i.e. time since introduction and propagule pressure) of the species. Accurate data on the introduction history are, however, rare, particularly for introduced alien species that have not established. As a consequence, few studies that tested for the effects of species characteristics on invasiveness corrected for introduction history. 2. We tested whether the naturalization success of 582 North American woody species in Europe, measured as the proportion of European geographic regions in which each species is established, can be explained by their introduction history. For 278 of these species we had data on characteristics related to growth form, life cycle, growth, fecundity and environmental tolerance. We tested whether naturalization success can be further explained by these characteristics. In addition, we tested whether the effects of species characteristics differ between growth forms. 3. Both planting frequency in European gardens and time since introduction significantly increased naturalization success, but the effect of the latter was relatively weak. After correction for introduction history and taxonomy, six of the 26 species characteristics had significant effects on naturalization success. Leaf retention and precipitation tolerance increased naturalization success. Tree species were only 56% as likely to naturalize as non-tree species (vines, shrubs and subshrubs), and the effect of planting frequency on naturalization success was much stronger for non-trees than for trees. On the other hand, the naturalization success of trees, but not for non-trees, increased with native range size, maximum plant height and seed spread rate. 4. Synthesis. Our results suggest that introduction history, particularly planting frequency, is an important determinant of current naturalization success of North American woody species (particularly of non-trees) in Europe. Therefore, studies comparing naturalization success among species should correct for introduction history. Species characteristics are also significant determinants of naturalization success, but their effects may differ between growth forms. Web of Science Many Europe Review terrestrial Grassland;Deciduous Forest;Coniferous Forest Invasion Hyp. Inherent Superiority;Disturbance Superior Competitor primary 71 Bulleri, Fabio; Bruno, John F.; Benedetti-Cecchi, Lisandro 2008 Beyond competition: Incorporating positive interactions between species to predict ecosystem invasibility journal PLOS BIOLOGY 6 6 1136 1140 Web of Science Theoretical/Modeling Invasion Hyp. Mutualism Facilitation 72 Bullock, James M. 2009 A long-term study of the roles of competition and facilitation in the establishment of an invasive pine following heathland fires journal JOURNAL OF ECOLOGY 97 4 646 656 Web of Science Pinus sylvestris England Dorset County 50.688628 -2.04071 Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Mutualism Facilitation;Disturbance primary 76 Burls, Kevin; McClaugherty, Charles 2008 Landscape Position Influences the Distribution of Garlic Mustard, an Invasive Species journal NORTHEASTERN NATURALIST 15 4 541 556 We investigated the distribution and abundance of Alliaria petiolata, an invasive biennial, with respect to historical land use, and examined environmental conditions to look for correlations with distribution patterns. Sixty currently forested plots in Cuyahoga Valley National Park, OH were chosen based on 1959 land use: agricultural (open) versus forested. Plots were analyzed for Garlic Mustard distribution, abundance, invasion area, and incursion distance. Garlic Mustard distribution did not vary with historical land use, but did vary significantly with distance from rivers and with elevation. Polygon area:perimeter values were also correlated with invasion. These results differ from studies done with Garlic Mustard in New England where historical land use appeared to be a larger factor in distribution. These results suggest the importance of landscape corridors in biological invasions and can be used to identify areas with greater potential for invasive species in this region. Web of Science Alliaria petiolata USA Ohio Cuyahoga Valley National Park 41.2833 -81.5667 Field - Observational terrestrial Deciduous Forest;Old Field Invasion Hyp. Disturbance primary 79 Cadotte, Marc W.; Hamilton, Mark A.; Murray, Brad R. 2009 Phylogenetic relatedness and plant invader success across two spatial scales journal DIVERSITY AND DISTRIBUTIONS 15 3 481 488 Successful invaders often possess similar ecological traits that contribute to success in new regions, and thus under niche conservatism, invader success should be phylogenetically clustered. We asked if the degree to which non-native plant species are phylogenetically related is a predictor of invasion success at two spatial scales. Australia - the whole continent and Royal National Park (south-eastern Australia). We used non-native plant species occupancy in Royal National Park, as well as estimated continental occupancy of these species from herbarium records. We then estimated phylogenetic relationships using molecular data from three gene sequences available on GenBank (matK, rbcL and ITS1). We tested for phylogenetic signals in occupancy using Blomberg's K. Whereas most non-native plants were relatively scarce, there was a strong phylogenetic signal for continental occupancy, driven by the clustering of successful species in Asteraceae, Caryophyllaceae, Poaceae and Solanaceae. However, we failed to detect a phylogenetic signal at the park scale. Our results reveal that at a large spatial scale, invader success is phylogenetically clustered where ecological traits promoting success appear to be shared among close relatives, indicating that phylogenetic relationships can be useful predictors of invasion success at large spatial scales. At a smaller, landscape scale, there was no evidence of phylogenetic clustering of invasion success, and thus, relatedness plays a much reduced role in determining the relative success of invaders. Web of Science Many Australia Royal National Park Statistical/Meta-analysis terrestrial Grassland;Deciduous Forest;Chaparral/Shrublands Invasion Hyp. Preadaptation to Climate primary 80 Cano, Lidia; Escarre, Josep; Blanco-Moreno, Jose M.; Sans, F. Xavier 2008 Assessing the effect of inbreeding and long-distance gene flow on the invasive potential of Senecio pterophorus (Asteraceae) journal AUSTRALIAN JOURNAL OF BOTANY 56 6 539 549 Alien invasive species undergo genetic bottlenecks during the colonisation of new areas that can lead to a loss of genetic variation within populations and to subsequent reproductive constraints. We analysed the self-compatibility and the effects of inbreeding and inter-population gene flow in the fitness of one native and one introduced population of the invasive Senecio pterophorus D.C. Plants were self-pollinated and outcrossed within families, within populations, between local populations and between populations located in the native and introduced range. Self-pollinated individuals from both populations produced almost no seeds, thus revealing self-incompatibility. High family-level variation was observed in the effect of pollination treatment on seed set and total fitness. Overall, in the Spanish population, related crosses produced fewer seeds and lower germination rates than unrelated crosses. In the South African population, inbreeding depression affected the probability of flowering. Heterosis was found to affect seed set in both populations and growth and mean pre-reproductive time in the Spanish population. We discuss the effects of the incompatibility system, inbreeding depression and long-distance gene flow within the introduced population with respect to the invasive potential of S. pterophorus in north-eastern Spain. Web of Science Senecio pterophorus Spain, South Africa Greenhouse;Lab terrestrial Chaparral/Shrublands Invasion Hyp. Evolution in General;Plasticity primary 81 Cano, L.; Escarre, J.; Vrieling, K.; Sans, F. X. 2009 Palatability to a generalist herbivore, defence and growth of invasive and native Senecio species: testing the evolution of increased competitive ability hypothesis journal OECOLOGIA 159 1 95 106 This paper tests the prediction that introduced plants may become successful invaders because they experience evolutionary changes in growth and defence in their new range [evolution of increased competitive ability hypothesis (EICA)]. Interspecific and intraspecific binary feeding choices were offered to the snail Helix aspersa. The choices were between: (1) plants of the invasive Senecio inaequidens and Senecio pterophorus derived from populations in the introduced range (Europe) and plants of three indigenous species (Senecio jacobea, Senecio vulgaris and Senecio malacitanus) from populations in Europe; (2) plants of the invasive S. inaequidens and S. pterophorus from populations in the introduced range (Europe) and from populations in the native range (South Africa). We did not find a clear pattern of preference for indigenous or alien species of Senecio. However, we found that European invasive populations of S. inaequidens and S. pterophorus were less palatable than South African native populations. Moreover, in contrast to the predictions of the EICA hypothesis, the invasive genotypes of both species also showed a higher total concentration of pyrrolizidine alkaloids, and in the case of S. inaequidens we also found higher growth than in native genotypes. Our results are discussed with respect to the refinement of the EICA hypothesis that takes into account the difference between specialist and generalist herbivores and between qualitative and quantitative defences. We conclude that invasive populations of S. inaequidens and S. pterophorus are less palatable than native populations, suggesting that genetic differentiation associated with founding may occur and contribute to the plants' invasion success by selecting the best-defended genotypes in the introduced range. Web of Science Senecio inaequidens; Senecio pterophorus Europe, South Africa Lab Invasion Hyp. Evolution of Increased Competitive Ability primary 82 Capers, Robert S.; Selsky, Roslyn; Bugbee, Gregory J.; White, Jason C. 2009 Species richness of both native and invasive aquatic plants influenced by environmental conditions and human activity journal BOTANY-BOTANIQUE 87 3 306 314 Invasive plants alter community structure, threatening ecosystem function and biodiversity, but little information is available on whether invasive species richness responds to environmental conditions in the same way that richness of native plants does. We surveyed submerged and floating-leaved plants in 99 Connecticut (northeast USA) lakes and ponds, collecting quantitative data on abundance and frequency. We used multiple linear and logistic regression to determine which environmental conditions were correlated with species richness of invasive and native plants. Independent variables included lake area, maximum depth, pH, alkalinity, conductivity, phosphorus concentration, productivity, and dominance (the proportional abundance of the most abundant and frequently found species), plus two estimates of human activity. Species richness of both native and invasive richness was correlated with alkalinity and human activity. Native richness also increased with water clarity, lake area, and productivity; invasive species richness also rose with pH. We found no evidence that richness of one group affected richness of the other. We also investigated patterns of dominance and found that native plants were as likely to become dominant as invasive species. Dominance occurred overwhelmingly in shallow lakes with high productivity. Web of Science Many USA Connecticut Field - Observational lentic Wetland Impacts;Invasion Hyp. Community Species Richness;Disturbance primary 86 Castillo, Jesus M.; Figueroa, Enrique 2009 Effects of abiotic factors on the life span of the invasive cordgrass Spartina densiflora and the native Spartina maritima at low salt marshes journal AQUATIC ECOLOGY 43 1 51 60 We analyzed variations in the life span of the invasive cordgrass Spartina densiflora at low marshes of SW Iberian Peninsula, and identified the abiotic factors limiting the plant in the absence of competition. With these objectives, clump survivorship, flowering, and growth of S. densiflora were studied in two natural populations at different low marsh elevations during more than three years, and at a transplant experiment in comparison with the native Spartina maritima. The life spans of both cordgrasses changed depending on small variations of a few centimeters in elevation. S. maritima, which tolerates better than S. densiflora the stressful abiotic environment of lower marshes, showed a significant lower distribution limit for its perennial habit, with survivorship longer than three years (from 1997 to 2000), than the neophyte (+1.57 m SHZ vs. +2.00 m SHZ). S. densiflora clumps flowered before dying at mostly all elevations, showing low relative growth rates. In contrast, clumps of S. maritima, with non-viable seeds, only flowered when they were three years old at higher elevations in the low marsh. Our results have applications for salt marshes bioengineering projects and to prevent S. densiflora from invading European marshes since our data improve the knowledge of its colonization mechanisms through salt marsh zonation and so identify those portions of restored and native marshes most susceptible to invasion due to the establishment of perennial populations. Web of Science Spartina densiflora Spain Huevla Province Field - Experimental estuarine Wetland Fundamentals primary 90 Cha, Dong H.; Hochwender, Cris G.; Bosecker, Elizabeth M.; Tucker, Rachel E.; Kaufman, Arlen D.; Fritz, Robert S.; Smyth, Rebecca R. 2009 Do exotic generalist predators alter host plant preference of a native willow beetle? journal AGRICULTURAL AND FOREST ENTOMOLOGY 11 2 175 184 1 Selection can favour herbivores that choose host plants benefitting their offspring either by enhancing growth rates or by increasing larval defences against native predators. For exotic predator species that feed on herbivores, their success with invading new habitats may depend upon overcoming defences used by native prey. Whether exotic predators can alter herbivore host choice has remained unexamined. Therefore, we compared the efficacy of larval defence by Chrysomela knabi (a native beetle species) that had fed on two native willow hosts: Salix sericea (a phenolic glycoside (PG)-rich species) and Salix eriocephala (a PG-poor species), when attacked by exotic generalist predators. In addition, the preference and performance of C. knabi on S. sericea and S. eriocephala was examined. 2 Chrysomela knabi preferred and performed better on S. sericea. In a common garden, adult C. knabi were nine-fold more common and oviposited five-fold more frequently on S. sericea than on S. eriocephala. In the laboratory, adult feeding preference on leaf discs and survival rates of larvae were both greater on S. sericea, and time to pupation was shorter. 3 Chrysomela knabi larvae produced significantly more salicylaldehyde when fed S. sericea leaves than when fed S. eriocephala leaves. Additionally, those larvae with greater salicylaldehyde had reduced predation by two exotic generalist predators, Harmonia axyridis larvae and juvenile Tenodera aridifolia sinensis. 4 The results obtained in the present study suggest that selection favoured the preference of C. knabi for PG-rich willow plants because larvae grew and survived better and that selection by common exotic generalist predators would reinforce this preference. Web of Science Harmonia axyridis USA New York Milford Field - Experimental terrestrial Deciduous Forest;Riparian Impacts;Fundamentals herbivore 93 Chaplin, Glen I.; Valentine, John F. 2009 Macroinvertebrate Production in the Submerged Aquatic Vegetation of the Mobile-Tensaw Delta: Effects of an Exotic Species at the Base of an Estuarine Food Web journal ESTUARIES AND COASTS 32 2 319 332 This study, conducted in 1997, reports the first estimates of the impacts of the proliferation of an exotic submerged aquatic vegetation (SAV) species (Myriophyllum spicatum) on macroinvertebrate production via comparisons with two co-occurring native SAV species (Heteranthera dubia and Vallisneria americana) in the tide-influenced Mobile-Tensaw Delta (located in the north-central Gulf of Mexico, 30A degrees 40' N, 87A degrees 55' W). Production of macroinvertebrates was greatest on M. spicatum and H. dubia and least on V. americana. The key determinant of these differences was a greater abundance of amphipods (Gammarus mucronatus) found on the leaves of M. spicatum and H. dubia. Macroinvertebrate production on M. spicatum was three times greater (> 1 kg m(-2) year(-1)) than on either of the native SAV species. No-choice palatability tests showed that these differences could not be attributed to differences in invertebrate grazing on these plants. Instead, it is probable that the high production within the structurally complex M. spicatum and H. dubia was the result of reduced predator foraging efficiency. If true, then the presence of this exotic species probably renders this elevated production inaccessible to most high-order predators. Web of Science Myriophyllum spicatum USA Mobile-Tensaw Delta 30.6667 -87.9167 Field - Experimental;Field - Observational estuarine Wetland Impacts;Invasion Hyp. Inherent Superiority Superior Competitor primary 98 Christen, Douglas C.; Matlack, Glenn R. 2009 The habitat and conduit functions of roads in the spread of three invasive plant species journal BIOLOGICAL INVASIONS 11 2 453 465 Nonnative plant species commonly occur along roadsides, and populations are often assumed to invade by spread along the road axis. To distinguish between the function of roadsides as movement corridors and as habitat, nonnative plant species were surveyed along roads in deciduous forest sites in southeastern Ohio, USA. The importance of road proximity was tested by comparing nonnative species abundance in 100 m transects along roads with transects in undisturbed forest. Nonnative species were most abundant and most frequently observed in roadside sites in valleys. Three common species were chosen for closer scrutiny. In a seed sowing experiment roads and open sites proved to be better locations for the germination and growth of Microstegium vimineum than non-roadside and closed-canopy sites. Tussilago farfara and Rosa multiflora occurred in a small number of disjunct patches suggesting infrequent arrival in the sampled transects. Both species were strongly clustered at scales consistent with diffusive spread by vegetative growth and short-range seed dispersal. Comparisons of distributions parallel and perpendicular to roads showed no evidence for enhanced dispersal along the road axis. Microstegium distributions were correlated with local light availability implying site saturation. Microstegium micro-distributions suggested that spread along the road axis was facilitated by movement of dormant seeds in road maintenance. Thus, roadsides appear to function as both habitat and a conduit for population expansion, with the rate of spread dependent on the life history of the individual species. These results suggest a hierarchical process of regional invasion, with different dispersal mechanisms functioning at different spatial scales. Web of Science Microstegium vimineum; Tussilago farfara; Rosa multiflora USA Ohio Wayne National Forest; Zaleski State Forest; Vinton Furnace Experimental Forest 39.4833; 39.3666; 39.1833 -82.2333; -82.3; -82.3833 Field - Experimental;Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 99 Christenhusz, Maarten J. M.; Toivonen, Tuuli K. 2008 Giants invading the tropics: the oriental vessel fern, Angiopteris evecta (Marattiaceae) journal BIOLOGICAL INVASIONS 10 8 1215 1228 The Oriental vessel fern, Angiopteris evecta (G.Forst.) Hoffm. (Marattiaceae), has its native range in the South Pacific. This species has been introduced into other localities since the 18th century and is now listed as an invasive species in several regions (Jamaica, Hawaii and Costa Rica). The purpose of our study is (1) to trace the distributional history of the species, and (2) to model its potential future range based on climatic conditions. The native range and the history of introduction are based on the existing literature and on 158 specimens from 15 herbaria, together with field observations. As there are taxonomic problems surrounding A. evecta, we limited our analysis to samples from the Pacific, most closely resembling the type from Tahiti. We modelled the potential range using GARP species distribution modelling with basic climatic variables, elevation, and location in relation to the coast. Analysis of past records shows that the species is able to colonise new ecosystems with relative ease. The modelling reveals that the species could be cultivated over a much wider range than where it currently is grown. The escape of cultivated plants into nature is probably due to distance from natural areas and is limited by local ecological factors, such as soil conditions or competitors. The predicted distribution in Asia and Madagascar is similar to the native distribution of the entire genus Angiopteris. It can therefore be assumed that most Angiopteris species have similar climatic preferences, and the absence of A. evecta in this predicted region may be due to dispersal limitation. In the Americas there is no native Angiopteris, but our climatic model predicts a vast potential habitat in tropical America; an invasion of A. evecta should be anticipated here in localities where the species is cultivated. Vessel ferns are known to alter the natural environment, which may reduce local biodiversity. Since A. evecta is not yet widely cultivated, it is advisable to restrict the trade and spread of the species and to discourage its cultivation as an ornamental. The global climate data available for modelling is however not detailed enough to predict the spread of A. evecta on a local or regional scale. Web of Science Angiopteris evecta many Theoretical/Modeling terrestrial Tropical Forest Invasion Hyp. Preadaptation to Climate primary 100 Chytry, Milan; Pysek, Petr; Wild, Jan; Pino, Joan; Maskell, Lindsay C.; Vila, Montserrat 2009 European map of alien plant invasions based on the quantitative assessment across habitats journal DIVERSITY AND DISTRIBUTIONS 15 1 98 107 Recent studies using vegetation plots have demonstrated that habitat type is a good predictor of the level of plant invasion, expressed as the proportion of alien to all species. At local scale, habitat types explain the level of invasion much better than alien propagule pressure. Moreover, it has been shown that patterns of habitat invasion are consistent among European regions with contrasting climates, biogeography, history and socioeconomic background. Here we use these findings as a basis for mapping the level of plant invasion in Europe. European Union and some adjacent countries. We used 52,480 vegetation plots from Catalonia (NE Spain), Czech Republic and Great Britain to quantify the levels of invasion by neophytes (alien plant species introduced after ad 1500) in 33 habitat types. Then we estimated the proportion of each of these habitat types in CORINE land-cover classes and calculated the level of invasion for each class. We projected the levels of invasion on the CORINE land-cover map of Europe, extrapolating Catalonian data to the Mediterranean bioregion, Czech data to the Continental bioregion, British data to the British Isles and combined Czech-British data to the Atlantic and Boreal bioregions. The highest levels of invasion were predicted for agricultural, urban and industrial land-cover classes, low levels for natural and semi-natural grasslands and most woodlands, and the lowest levels for sclerophyllous vegetation, heathlands and peatlands. The resulting map of the level of invasion reflected the distribution of these land-cover classes across Europe. High level of invasion is predicted in lowland areas of the temperate zone of western and central Europe and low level in the boreal zone and mountain regions across the continent. Low level of invasion is also predicted in the Mediterranean region except its coastline, river corridors and areas with irrigated agricultural land. Web of Science Many Europe Field - Observational;Statistical/Meta-analysis terrestrial Grassland;Deciduous Forest;Coniferous Forest;Mountain;Tundra;Chaparral/Shrublands;Urban Invasion Hyp. Other primary 101 Cincotta, C. L.; Adams, J. M.; Holzapfel, C. 2009 Testing the enemy release hypothesis: a comparison of foliar insect herbivory of the exotic Norway maple (Acer platanoides L.) and the native sugar maple (A-saccharum L.) journal BIOLOGICAL INVASIONS 11 2 379 388 Norway maple (Acer platanoides) is a Eurasian introduced tree species which has invaded the North American range of its native congener, sugar maple (A. saccharum). One hypothesis used to explain the success of an invasive species is the enemy release hypothesis (ERH), which states that invasive species are often particularly successful in their new range because they lack the enemies of their native range. In this study, we hypothesized that Norway maple would have less insect damage than sugar maple due to such enemy release. Autumn 2005 and summer 2006 leaves of Norway and sugar maple were collected from six sites in New Jersey and Pennsylvania to compare percent leaf area loss, gall damage, fungal damage, and specific leaf area (cm(2)/g). Although both species had low overall mean levels of leaf damage (0.4-2.5%), in both years/seasons Norway maple had significantly less leaf damage than sugar maple. Insects were also collected to compare insect assemblies present on each tree species. The numbers of insect taxa and individuals found on each species were nearly equivalent. Overall, the results of this study are consistent with the enemy release hypothesis for Norway maple. In addition, sugar maples when surrounded by Norway maples tended to show reduced herbivory. This suggests that the spread of Norway maple in North America, by reducing amounts of insect herbivory, may have further ecosystem-wide impacts. Web of Science Acer platanoides; Acer saccharum USA New Jersey; Pennsylvania 6 sites Field - Observational terrestrial Deciduous Forest Invasion Hyp. Enemy Release primary 103 Cipollini, Kendra A.; McClain, Georgette Y.; Cipollini, Don 2008 Separating above- and belowground effects of Alliaria petiolata and Lonicera maackii on the performance of Impatiens capensis journal AMERICAN MIDLAND NATURALIST 160 1 117 128 Invasive plants can exert their effects on native plants through both above- and belowground mechanisms. In a fully factorial field study, we examined the effects of activated carbon addition and removal of aboveground biomass (i.e., cutting) on the survival, growth and reproduction of transplanted Impatiens capensis seedlings in habitats dominated by either Lonicera maackii (honeysuckle) or Alliaria petiolata (garlic mustard). Activated carbon can adsorb organic molecules, including potential allelochemicals. Cutting of A. petiolata increased Survival and fruit production of I. capensis, while cutting of L. maackii increased survival and tended to increase fruit production. Carbon application tended to increase survival of I. capensis in A. petiolata-dominated plots, but. had no effect in L. maackii-dominated plots. The effects of carbon application on growth and fruit production of I. capensis depended upon the cutting treatment in A. petiolata - dominated plots. In plots where A. petiolata was not cut, carbon application increased height and fruit production. In plots where A. petiolata was cut, carbon application decreased height and tended to decrease fruit production. Impatiens capensis tended to survive longer when in competition with A. petiolata than with L. maackii. While carbon application may benefit native plant growth in the presence of A. petiolata, the addition of activated carbon after removal of aboveground biomass, a Source of both allelochemicals and light competition, may have little benefit as an understory plant restoration tool. Web of Science Alliaria petiolata; Lonicera maackii USA Ohio Frank O. Hazard Arboretum of Wilmington College in Wilmington 39.550648 -83.787231 Field - Experimental terrestrial Deciduous Forest Impacts;Invasion Hyp. Novel Weapons primary 107 Compagnoni, Aldo; Halpern, Charles B. 2009 Properties of native plant communities do not determine exotic success during early forest succession journal ECOGRAPHY 32 3 449 458 Web of Science Crepis capillaris;Cirsium vulgare;Senecio sylvaticus;Lactuca serriola USA Oregon McKenzie River 44.15 -122.54 Field - Experimental terrestrial Coniferous Forest Invasion Hyp. Community Species Richness;Disturbance primary 112 Cowie, Robert H.; Dillon, Robert T., Jr.; Robinson, David G.; Smith, James W. 2009 Alien non-marine snails and slugs of priority quarantine importance in the United States: A preliminary risk assessment journal AMERICAN MALACOLOGICAL BULLETIN 27 2 113 132 Web of Science Many Theoretical/Modeling terrestrial;lentic;lotic Invasion Hyp. Other herbivore 114 Cripps, Michael G.; Hinz, Hariet L.; McKenney, Jessica L.; Price, William J.; Schwarzlaender, Mark 2009 No evidence for an 'evolution of increased competitive ability' for the invasive Lepidium draba journal BASIC AND APPLIED ECOLOGY 10 2 103 112 The 'evolution of increased competitive ability' (EICA) hypothesis states that reduced herbivory ill the introduced range Causes an evolutionary shift in resource allocation from herbivore defense to growth. Therefore, according to EICA, introduced genotypes are expected to grow more vigorously than conspecific native genotypes when cultivated under common standardized conditions. The EICA hypothesis also assumes that herbivores will perform better on introduced genotypes compared to native genotypes, because they are less well defended. However, selection for either defense or growth will depend on the type of defense (quantitative or qualitative) employed by the plant, and whether the plant is released from generalist or specialist herbivores. The predictions of the EICA hypothesis might be reversed if a plant experiences increased generalist herbivore pressure in the introduced range, and therefore invests more ill qualitative defense. We examined this idea with the invasive perennial mustard, Lepidium draba. We grew a total of 16 populations of L. draba from both its native European and introduced western US ranges under common conditions in a greenhouse. We also tested for differences ill plant resistance to the specialist herbivore, Psylliodes wrasei, by conducting a leaf disc feeding bioassay with native and introduced L. draba genotypes. Furthermore, we quantified the generalist herbivore load on L. draba in both ranges in order to assess the selection pressure for increased qualitative defense. Contrary to the original EICA prediction, all plant traits (biomass. number of shoots, length and diameter of longest leaf) tended to be greater for the native, rather than introduced L. draba genotypes. There was no significant difference in the proportion of leaf area consumed by the specialist herbivore between native and introduced genotypes. The generalist herbivore load oil L. draba was significantly greater in the introduced range. Our data Suggest that the EICA hypothesis does not explain the invasion success of L. draba in the US. Instead, we propose that the reduced vigor or introduced genotypes may be due to selection for increased defense against generalist herbivores in the introduced range. (C) 2008 Gesellschaft fur Okologic. Published by Elsevier GmbH. All rights reserved. Web of Science Lepidium draba Field - Observational;Greenhouse terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 116 Culley, Theresa M.; Hardiman, Nicole A. 2009 The role of intraspecific hybridization in the evolution of invasiveness: a case study of the ornamental pear tree Pyrus calleryana journal BIOLOGICAL INVASIONS 11 5 1107 1119 Hybridization between genetically distinct populations of a single species can serve as an important stimulus for the evolution of invasiveness. Such intraspecific hybridization was examined in Pyrus calleryana, a Chinese tree species commonly planted as an ornamental in residential and commercial areas throughout the United States. This self-incompatible species is now escaping cultivation and appearing in disturbed habitats, where it has the potential to form dense thickets. Using genetic techniques incorporating nine microsatellite markers, we show that abundant fruit set on cultivated trees as well as the subsequent appearance of wild individuals result from crossing between genetically distinct horticultural cultivars of the same species that originated from different areas of China. We conclude that intraspecific hybridization can be a potent but little recognized process impacting the evolution of invasiveness in certain species. Web of Science Pyrus calleryana USA Garden;Lab terrestrial Invasion Hyp. Hybridization primary 117 Dafforn, K. A.; Johnston, E. L.; Glasby, T. M. 2009 Shallow moving structures promote marine invader dominance journal BIOFOULING 25 3 277 287 Global increases in urban development have resulted in severe habitat modification in many estuaries. Most are now dominated by artificial structures, which might have a myriad of effects on native species. The provision of extra hard substrata presents additional free space, and recent research suggests non-indigenous epifauna may be able to exploit these artificial structures (particularly pontoons) more effectively than native species. The early development of fouling assemblages was compared on settlement plates attached to fixed or moving experimental structures at depths of 0.5 m and 2 m. Invertebrate invaders as a group were disproportionately more numerous on shallow, moving plates (essentially floating surfaces) than on deeper plates, whereas native epifauna were less numerous than invaders in all treatments. Importantly, however, individual invasive species showed differing effects of movement and depth. Future management strategies should take into account the potential for shallow, moving structures to enhance invader dominance and strongly consider using fixed structures to reduce opportunities for invaders. Web of Science Many Field - Observational estuarine Intertidal/Near Shore Invasion Hyp. Other filter 120 Daneshgar, Pedram; Jose, Shibu 2009 Role of species identity in plant invasions: experimental test using Imperata cylindrica journal BIOLOGICAL INVASIONS 11 6 1431 1440 The role of species richness, functional diversity and species identity of native Florida sandhill understory species were tested with Imperata cylindrica, an exotic rhizomatous grass, in mesocosms. I. cylindrica was introduced 1 year after the following treatments were established: a control with no native species, five monocultures, a grass mix treatment, a forb mix treatment, and a 3-species treatment and a 5-species treatment. Monthly cover, final biomass, root length, root length density (RLD) and specific root length (SRL) of all species were determined for one full growing season. There was a significant negative linear relationship between the cover of native species and I. cylindrica (r (2) = 0.59, P = 0.01) and a negative logarithmic relationship between the biomass of native species and I. cylindrica (r (2) = 0.70, P = 0.003). There was no diversity-invasibility relationship. Grasses proved to be the most resistant functional group providing resistance alone and in mixed functional communities. Repeated measures analysis demonstrated that treatments including Andropogon virginicus were the most resistant to invasion over time (P < 0.001). Significantly greater root length (P = 0.002), RLD (P = 0.011) and SRL (P < 0.001) than all of the native species and I. cylindrica in monocultures and in mixed communities made A. virginicus successful. The root morphology characteristics allowed it to be a great competitor belowground where I. cylindrica was most aggressive. The results suggest that species identity could be more important than species or functional richness in determining community resistance to invasion. Web of Science Imperata cylindrica USA Florida West FL Research & Ed Ctr Univ FL 31.2833 -87.0011 Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority;Community Species Richness Superior Competitor primary 121 Darling, John A.; Kuenzi, Ashley; Reitzel, Adam M. 2009 Human-mediated transport determines the non-native distribution of the anemone Nematostella vectensis, a dispersal-limited estuarine invertebrate journal MARINE ECOLOGY-PROGRESS SERIES 380 0 137 146 Sessile invertebrates are common invaders of estuarine ecosystems. To expand their non-native ranges, these invasive taxa Must contend with the geographically and ecologically discontinuous nature of estuarine habitats, in many cases without the benefit of highly dispersive larval phases. In addition, their population dynamics may reflect contributions from both sexual and asexual reproduction. Here we use genetic methods to explore the Population structure of Nematostella vectensis, a dispersal-limited salt marsh anemone, along the Pacific coast of North America. Analysis of 9 highly polymorphic microsatellite loci reveals that asexual reproduction is critical to both maintenance of local population density and regional population expansion. While high levels of genetic differentiabon among populations (F-ST > 0.3) reflect general restrictions to natural dispersal, the observation of 2 clones distributed across multiple, widely separated sampling sites indicates that long distance dispersal of adult anemones is a major contributor to the spread of N. vectensis. We argue that anthropogenic transport represents the most likely mechanism driving this spread, although rafting may offer an alternative explanation for the observed distribution. Web of Science Nematostella vectensis USA Field - Observational marine Intertidal/Near Shore Invasion Hyp. Inherent Superiority Effective Disperser omnivore 124 Dawson, Wayne; Burslem, David F. R. P.; Hulme, Philip E. 2009 Factors explaining alien plant invasion success in a tropical ecosystem differ at each stage of invasion journal JOURNAL OF ECOLOGY 97 4 657 665 Web of Science Many Tanzania East Usambara Mountains -5.0917 38.6361 Field - Observational;Theoretical/Modeling terrestrial Tropical Forest Invasion Hyp. Inherent Superiority;Propagule Pressure;Preadaptation to Climate Rapid Growth primary 126 Dawson, Wayne; Burslem, David F. R. P.; Hulme, Philip E. 2009 Herbivory is related to taxonomic isolation, but not to invasiveness of tropical alien plants journal DIVERSITY AND DISTRIBUTIONS 15 1 141 147 The enemy release hypothesis is often invoked to explain why some alien plant species become invasive. Here, we investigated relationships between invasiveness, taxonomic isolation and leaf herbivory for tropical alien plant species introduced to a botanical garden in East Africa. Amani Botanical Garden, East Usambara mountains, northeast Tanzania. We measured the proportion of leaves damaged, and the percentage leaf area damaged on individuals of 28 alien plant species. We extracted data on the presence/absence of native congeners and the number of native confamilial species from an inventory of the East Usambara flora. We also obtained data on planting effort for 26 species, from historical records. Linear and generalized linear models were used to analyse the relationships between invasiveness, herbivory and taxonomic isolation. Mean proportion of leaves damaged per species was significantly explained by taxonomic isolation; proportion of leaves damaged increased with the number of native confamilial species and was greater, on average, for species with native congeners than those without native congeners. The mean percentage of leaf area damaged per species could not be explained by any variables considered in this study. There was no relationship between the degree of herbivory or taxonomic isolation and alien plant species invasiveness, but more-invasive species did have a significantly greater planting effort than less-invasive species. The role herbivores play in controlling alien plant invasions has been investigated relatively little in the tropics. In this study, although the amount of herbivory suffered by alien plants was related to taxonomic isolation, we found no evidence for leaf-feeding invertebrates having a significant role in invasion, suggesting that other factors may be responsible for differences in species success. Web of Science Many Tanzania East Usambara Amani Botanical Garden, East Usambara Mountains -5.0917 38.6361 Field - Observational terrestrial Tropical Forest Invasion Hyp. Enemy Release primary 131 Denslow, Julie S.; Space, James C.; Thomas, Philip A. 2009 Invasive Exotic Plants in the Tropical Pacific Islands: Patterns of Diversity journal BIOTROPICA 41 2 162 170 Oceanic islands are good model systems with which to explore factors affecting exotic species diversity. Islands vary in size, topography, substrate type, degree of isolation, native species diversity, history, human population characteristics, and economic development. Moreover, islands are highly vulnerable to exotic species establishment. We used AICc analyses of data on 1132 vascular plant species for 15 countries and 114 islands from the Pacific Island Ecosystems at Risk (PIER) project to examine biological, geographical, and socioeconomic correlates of exotic species richness. PIER provides data on the distribution of naturalized non-native plant species thought to pose environmental or economic risk. We hypothesized that the numbers of PIER-listed species would be positively correlated with island size, habitat diversity, and proximity to major source pools for propagules. Further, we expected numbers of PIER-listed exotic species to be similar among islands in the same country and to be greater where human populations were larger and where economic activity was high. Most species (908) were found on <= 10 islands. Species number was significantly correlated with island and country areas and with native plant species richness. The strongest model revealed by AICc analyses of island data included log (area) and maximum elevation as well as country membership, substrate type, and presence of an airport with paved runway (an index of economic activity). By country, AICc analyses revealed two equivalent models, both of which included log (area) and per capita gross domestic product as well as a measure of population size (either log (population size) or (population density)). Our analyses provide strong evidence of the roles of biogeographic, environmental, and socioeconomic impacts on the distribution and spread of exotic species. Web of Science Many United States; American Samoa; Cook Islands; Fiji; Guam; Kiribati; Marshall Islands; Federated States of Micronesia; Nauru; New Caledonia; Niue; Northern Mariana Islands; Palau; Samoa; Tonga Hawaii Pacific Ocean Field - Observational terrestrial Invasion Hyp. Community Species Richness;Propagule Pressure primary 135 Dillemuth, Forrest P.; Rietschier, Erick A.; Cronin, James T. 2009 Patch dynamics of a native grass in relation to the spread of invasive smooth brome (Bromus inermis) journal BIOLOGICAL INVASIONS 11 6 1381 1391 The effects of invasive species on the patch dynamics (establishment, growth, and local extinction) of native species are not well studied, owing to the need for relatively fine-scale data on the distribution of species. Within the prairie pothole region of the United States and Canada, the grass, Bromus inermis (smooth brome) has become established by invading disturbed prairies, and through repeated introductions for soil retention and animal graze. In this study, the impact of smooth brome on the patch dynamics of a dominant native grass species, Spartina pectinata (prairie cordgrass), was assessed using fine-scale (sub-meter) mapping of the distribution of cordgrass and brome in three prairie fragments from 2000 to 2006. Using GIS spatial analyses, we determined that cordgrass patch growth was two times greater in areas not invaded by smooth brome versus areas that were heavily infested with smooth brome. Among sites and time periods, there was a consistent significant negative relationship between the amount of smooth brome surrounding a patch of cordgrass and the growth of that cordgrass patch. The probability of establishment of a new patch of cordgrass averaged 1.3 times higher in areas of low brome coverage (< 25%) than areas of high brome coverage (> 75%). Conversely, existing cordgrass patches were 7.8 times more likely to go extinct in areas of high than low brome coverage. This is one of only a few field studies to provide evidence of the negative impact of smooth brome on native flora and hopefully will serve as justification for the development of a formal management plan to limit the distribution of this species in tallgrass prairie ecosystems. Web of Science Bromus inermis United States North Dakota Kellys Slough National Wildlife Refuge 47.941848 -97.310368 Field - Observational terrestrial Grassland Impacts;Invasion Hyp. Inherent Superiority Superior Competitor primary 138 Domenech, Roser; Vila, Montserrat 2008 Response of the invader Cortaderia selloana and two coexisting natives to competition and water stress journal BIOLOGICAL INVASIONS 10 6 903 912 Alien species' resistance and adjustment to water stress and plant competition might largely determine the success of invasions in Mediterranean ecosystems because water availability is often limiting biomass production. Two outdoor pot experiments were conducted to test the hypotheses that at the recruitment stage the invader perennial tussock grass Cortaderia selloana is a superior competitor, and that it is more resistant to water stress than the two coexisting native species of the same functional group, Festuca arundinacea and Brachypodium phoenicoides. C. selloana reduced aboveground biomass of target native species, but not more than target native species on each other. Moreover, C. selloana did not resist interspecific competition more than target native species. Under control conditions, C. selloana did not have larger specific leaf area (SLA) and root-shoot ratio (R/S) ratio than target native species, contradicting the general statement that these traits are associated to invasiveness. F. arundinacea was the species which performed best but also the one most affected by water stress. Both C. selloana and B. phoenicoides performed in a similar way under water stress conditions. However, the alien species' capacity to adjust to water stress, indicated by the increase in the root-shoot ratio under moderate and severe water stress, was slightly better than that of B. phoenicoides. Overall, at early recruitment stages, C. selloana is not a better competitor than the coexisting native species. However, it seems to be more resistant to water stress because as water becomes scarce C. selloana maximizes water uptake and minimizes water losses more than the native species. Web of Science Cortaderia selloana Spain Barcelona 41.386597 2.1698 Field - Experimental terrestrial Grassland Invasion Hyp. Inherent Superiority Superior Competitor;Broad Tolerances primary 140 Donnelly, Melinda J.; Walters, Linda J. 2008 Water and boating activity as dispersal vectors for Schinus terebinthifolius (Brazilian pepper) seeds in freshwater and estuarine habitats journal ESTUARIES AND COASTS 31 5 960 968 Schinus terebinthifolius (Brazilian pepper), a native of South America, is currently naturalized in 20 countries worldwide and can alter native systems by displacing flora and forming monotypic stands. The primary described mechanism of seed dispersal is through consumption of fruits by birds and mammals. We evaluated an alternative dispersal method by evaluating the potential for S. terebinthifolius growing in freshwater and estuarine environments to disperse via water currents. Specifically, we: (1) determined the duration fruits remained buoyant in three salinities, (2) estimated the viability of seeds after 7 days in water, (3) estimated the dispersal rate of floating solitary fruits, and (4) examined the role of boat wakes in moving seeds above mean high water at the shoreline. The length of time fruits floated in 0 ppt water (4.9 days) was significantly less than 15 ppt saltwater (6.2 days), and 30 ppt saltwater (6.9 days). After 7 days, over 13% of seeds remained viable in 0 ppt, 15 ppt, and 30 ppt water. By combining mean dispersal rates and the mean number of days fruits floated, we calculated individual fruits could be transported 16.9 km in 0 ppt and over 22 km in 15 and 30 ppt water. To increase germination, seeds must be stranded above the intertidal zone. Wind wakes alone never achieved this result; however, boat wakes plus wind wakes significantly increased the movement of fruits above the intertidal region into drier soils. The use of both vertebrate dispersal vectors and water dispersal may potentially increase the rate of invasion, establishment, and survival of S. terebinthifolius in freshwater and estuarine environments. Web of Science Schinus terebinthifolius USA Florida Canaveral National Seashore 28.934 -80.82 Field - Experimental;Lab estuarine Invasion Hyp. Inherent Superiority Effective Disperser primary 142 Dray, F. Allen, Jr.; Hale, Rebecca E.; Madeira, Paul T.; Bennett, Bradley C.; Center, Ted D. 2009 Concordance between life history traits, invasion history, and allozyme diversity of the Everglades invader Melaleuca quinquenervia journal AQUATIC BOTANY 90 4 296 302 During the century following its initial introduction in 1886, the Australian tree Melaleuca quinquenervia (Myrtaceae) dispersed from a few introduction points to occupy over 200,000 ha, primarily in historic Everglades wetlands of southern Florida. Cellulose acetate gel electrophoresis (CAGE) was used to investigate the allozyme diversity and population genetic structure of 208 individuals in a dozen populations resulting from this invasion. The analyses showed that these populations have a high (82%) rate of polymorphic loci and an average of 2 alleles/locus. There was substantial heterozygosity (mean H-e = 0.356), which concords well with recent studies reporting a greater number of introduction events and sources than generally recognized. The introduction history and distributional patterns within Florida have led to geographic structuring (G(ST) = 0.419) in which the Gulf Coast metapopulation has a greater effective number of alleles and greater heterozygosity than the Atlantic Coast metapopulation. The gene diversity in M. quinquenervia was comparable to other tropical woody species. Its strong population divergence was reminiscent of pioneer species and consistent with its status as a plant invader in Florida. Published by Elsevier B.V. Web of Science Melaleuca quinquenervia United States Florida Everglades Lab terrestrial Wetland Invasion Hyp. Hybridization primary 143 Duke, Stephen O.; Blair, Amy C.; Dayan, Franck E.; Johnson, Robert D.; Meepagala, Kumudini M.; Cook, Daniel; Bajsa, Joanna 2009 Is (-)-Catechin a Novel Weapon of Spotted Knapweed (Centaurea stoebe)? journal JOURNAL OF CHEMICAL ECOLOGY 35 2 141 153 The novel weapons hypothesis states that some invasive weed species owe part of their success as invaders to allelopathy mediated by allelochemicals that are new to the native species. Presumably, no resistance has evolved among the native species to this new allelochemical (i.e., the novel weapon). In their native habitat, however, the plants that co-evolved with these invasive species have theoretically evolved defenses that obviate the allelochemical advantage. Previous studies have claimed that catechin is such a novel weapon of spotted knapweed (Centaurea stoebe = C. maculosa), an invasive species in the non-native habitat of North America. These studies indicated that (-)-catechin is more phytotoxic than (+)-catechin. Other studies have not found sufficient catechin in field soils to support this theory. We report that (-)-catechin and (+)-catechin are essentially equal, but poorly phytotoxic to a variety of plant species in bioassays without soil. In a dose/response experiment with Montana soils, we found the lowest dose for a growth reduction of two native Montana grasses (Koeleria macrantha and Festuca idahoensis) by a racemic mixture of (+/-)-catechin that ranged from about 25 to 50 mM, concentrations, orders of magnitude higher than expected in nature. Autoclaving the soil before adding the catechin did not affect the activity of catechin. We found (-)-catechin to be a potent antioxidant, in contrast to a previous claim that it acts as an allelochemical by causing oxidative stress. Our findings suggest that catechin is not a novel weapon of spotted knapweed and that other allelochemical(s) or alternative mechanisms must be found to explain the success of this species as an invader in North America. Web of Science Centaurea stoebe United States Montana 46.5729 -112.147 Lab terrestrial Grassland Invasion Hyp. Novel Weapons primary 145 Ebeling, Susan K.; Welk, Erik; Auge, Harald; Bruelheide, Helge 2008 Predicting the spread of an invasive plant: combining experiments and ecological niche model journal ECOGRAPHY 31 6 709 719 Rapid evolutionary adjustments to novel environments may contribute to the successful spread of invasive species, and can lead to niche shifts making range dynamics unpredictable. These effects might be intensified by artificial selection in the course of breeding efforts, since many successful plant invaders were deliberately introduced and cultivated as ornamentals. We hypothesized that the invasion success of Buddleja davidii, the ornamental butterfly bush, is facilitated by local adaptation to minimum temperatures and thus, exhibits unpredictable range dynamics. To assess the potential effects of adaptive evolution and artificial selection on the spread of B. davidii, we combined a common garden experiment investigating local adaptation to frost, with ecological niche modelling of the species' native and invasive ranges. We expected that populations naturalized in sub-continental climate are less susceptible to frost than populations from oceanic climate, and that the invasive range does not match predictions based on climatic data from the native range. Indeed, we revealed significant variation among invasive B. davidii populations in frost resistance. However, frost hardiness was not related to geographic location or climatic variables of the populations' home site, suggesting that invasive B. davidii populations are not locally adapted to minimum temperatures. This is in line with results of our ecological niche model that did not detect a niche shift between the species' native range in China, and its invasive range in Europe and North America. Furthermore, our niche model showed that the potential invasive range of B. davidii is still not completely occupied. Together with the frost resistance data obtained in our experiment, the results indicate that climatic conditions are currently not limiting the further spread of the species in Europe and North America. Web of Science Buddleja davidii Germany Halle 51.489664 11.961178 Theoretical/Modeling;Garden terrestrial Chaparral/Shrublands Invasion Hyp. Evolution in General primary 146 Edward, Ezekiel; Munishi, Pantaleo K. T.; Hulme, Philip E. 2009 Relative Roles of Disturbance and Propagule Pressure on the Invasion of Humid Tropical Forest by Cordia alliodora (Boraginaceae) in Tanzania journal BIOTROPICA 41 2 171 178 Current understanding of the vulnerability of tropical forests to plant invasion is limited but is widely believed to increase where forests: (1) suffer marked natural or man-made disturbance; and/or (2) are exposed to high propagule pressure of alien species. This study aimed, for the first time, to address the importance of propagule pressure and disturbance by examining the spread of an introduced tree, Cordia alliodora, from a single plantation into a surrounding mosaic of humid forest in the East Usambara Mountains, Tanzania. By assessing vulnerability to invasion along transects radiating from the plantation, the effects of distance (measure of propagule pressure), and disturbance could be discerned. For all life stages, distance from source population was the strongest correlate of density. A marked influence of disturbance was only evident for C. alliodora seedlings. Spatial variation in the densities of later life stages may be a function of past disturbances, less easy to assess from current surveys, especially following the marked self-thinning between seedling and adult densities. Nevertheless, the evidence suggests that propagule pressure is a more important determinant of Cordia density than disturbance. If this is true for other alien tree species in tropical forests, controlling for introduction effort is essential to assess the drivers of plant invasion. Given an annual population growth rate of ca 3.5 percent, equivalent to the population doubling every 20 yr, C. alliodora poses a significant threat to the East Usambaras as well as other humid forests where it is promoted for agroforestry. Web of Science Cordia alliodora Tanzania Amani Nature Reserve Field - Observational terrestrial Tropical Forest;Subtropical Forest Invasion Hyp. Inherent Superiority;Propagule Pressure;Disturbance Effective Disperser primary 149 Ehrenfeld, Joan G. 2008 Exotic invasive species in urban wetlands: environmental correlates and implications for wetland management journal JOURNAL OF APPLIED ECOLOGY 45 4 1160 1169 1. Wetlands in urban regions are subjected to a wide variety of anthropogenic disturbances, many of which may promote invasions of exotic plant species. In order to devise management strategies, the influence of different aspects of the urban and natural environments on invasion and community structure must be understood. 2. The roles of soil variables, anthropogenic effects adjacent to and within the wetlands, and vegetation structure on exotic species occurrence within 21 forested wetlands in north-eastern New Jersey, USA, were compared. The hypotheses were tested that different vegetation strata and different invasive species respond similarly to environmental factors, and that invasion increases with increasing direct human impact, hydrologic disturbance, adjacent residential land use and decreasing wetland area. Canonical correspondence analyses, correlation and logistic regression analyses were used to examine invasion by individual species and overall site invasion, as measured by the absolute and relative number of exotic species in the site flora. 3. Within each stratum, different sets of environmental factors separated exotic and native species. Nutrients, soil clay content and pH, adjacent land use and canopy composition were the most frequently identified factors affecting species, but individual species showed highly individualistic responses to the sets of environmental variables, often responding in opposite ways to the same factor. 4. Overall invasion increased with decreasing area but only when sites > 100 ha were included. Unexpectedly, invasion decreased with increasing proportions of industrial/commercial adjacent land use. 5. The hypotheses were only partially supported; invasion does not increase in a simple way with increasing human presence and disturbance. 6. Synthesis and applications. The results suggest that a suite of environmental conditions can be identified that are associated with invasion into urban wetlands, which can be widely used for assessment and management. However, a comprehensive ecosystem approach is needed that places the remediation of physical alterations from urbanization within a landscape context. Specifically, sediment, inputs and hydrologic changes need to be related to adjoining urban land use and to the overlapping requirements of individual native and exotic species. Web of Science Many United States New Jersey Field - Observational terrestrial Wetland Invasion Hyp. Community Species Richness;Disturbance primary 150 Eigenbrode, Sanford D.; Andreas, Jennifer E.; Cripps, Michael G.; Ding, Hongjian; Biggam, Russell C.; Schwarzlaender, Mark 2008 Induced chemical defenses in invasive plants: a case study with Cynoglossum officinale L. journal BIOLOGICAL INVASIONS 10 8 1373 1379 The 'evolution of increased competitive ability' (EICA) hypothesis is an extension of optimal defense theory and predicts that reduced pressure from insect herbivores in the introduced range results in evolution of reduced defenses in invading plant populations, allowing greater allocation of resources to competitive traits such as growth rate and reproduction. The EICA hypothesis considered levels of defensive chemistry to be fixed within a particular genotype. In this paper, we propose that if herbivory is reduced in the introduced range, but chemical defenses are inducible in response to herbivory, evolution of reduced defenses and any associated increase competitive ability should not occur. Rather, mean induced and constitutive levels of induced defenses should be similar in introduced and native ranges, but the variance about mean induced levels should be greater in the introduced range. This is predicted because induced levels will occur less frequently in the introduced range where herbivory is reduced, thereby insulating these levels from the stabilizing selection expected in the native range where induced levels occur more frequently. We conducted a preliminary study to examine this by comparing constitutive and induced concentrations of total pyrrolizidine alkaloids (PAs) from native (European) and introduced (western North America) populations of Cynoglossum officinale L. The mean constitutive and induced concentrations of PAs did not differ between continents, but the variability of the induced concentrations was significantly greater for plants from the introduced range. Although our study with C. officinale is provisional due to a small sample size, it supports our predictions for evolution of inducible defenses in introduced ranges where herbivore pressure is reduced. Most chemical defenses in plants have been found to be inducible, so similar patterns may occur widely. If so, this weakens the generality of EICA's predictions concerning chemical defenses. The effects of inducible defenses should be considered in cross-continent comparisons of other invasive plant species. Web of Science Cynoglossum officinale United States Idaho 47.3667 -116.7 Garden terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 152 Elzinga, Jelmer A.; Bernasconi, Giorgina 2009 Enhanced frugivory on invasive Silene latifolia in its native range due to increased oviposition journal JOURNAL OF ECOLOGY 97 5 1010 1019 Web of Science Silene latifolia Switzerland Lausanne 46.5218 6.5802 Field - Experimental terrestrial Grassland Invasion Hyp. Evolution of Increased Competitive Ability primary 153 Engelen, Aschwin; Santos, Rui 2009 Which demographic traits determine population growth in the invasive brown seaweed Sargassum muticum? journal JOURNAL OF ECOLOGY 97 4 675 684 Web of Science Sargassum muticum Portugal Praia do Queimado; Almograve; Zambujeira do Mar 37.849 -8.795 Field - Observational marine Intertidal/Near Shore;Pelagic/Open Ocean Invasion Hyp. Inherent Superiority High Reprod. Output primary 155 Engelkes, Tim; Morrien, Elly; Verhoeven, Koen J. F.; Bezemer, T. Martijn; Biere, Arjen; Harvey, Jeffrey A.; McIntyre, Lauren M.; Tamis, Wil L. M.; van der Putten, Wim H. 2008 Successful range-expanding plants experience less above-ground and below-ground enemy impact journal NATURE 456 127 946 948 Many species are currently moving to higher latitudes and altitudes(1-3). However, little is known about the factors that influence the future performance of range- expanding species in their new habitats. Here we show that range- expanding plant species from a riverine area were better defended against shoot and root enemies than were related native plant species growing in the same area. We grew fifteen plant species with and without non- coevolved polyphagous locusts and cosmopolitan, polyphagous aphids. Contrary to our expectations, the locusts performed more poorly on the range- expanding plant species than on the congeneric native plant species, whereas the aphids showed no difference. The shoot herbivores reduced the biomass of the native plants more than they did that of the congeneric range expanders. Also, the range- expanding plants developed fewer pathogenic effects(4,5) in their root- zone soil than did the related native species. Current predictions forecast biodiversity loss due to limitations in the ability of species to adjust to climate warming conditions in their range(6-8). Our results strongly suggest that the plants that shift ranges towards higher latitudes and altitudes may include potential invaders, as the successful range expanders may experience less control by above- ground or below-ground enemies than the natives. Web of Science Angelica archangelica; Artemisia biennis; Centaurea stoebe; Bidens frondosa; Senecio inaequidens; Solidago gigantea Netherlands Millingerwaard 52.45 6.0167 Greenhouse terrestrial Invasion Hyp. Enemy Release primary 157 Erneberg, Marianne; Strandberg, Beate; Strandberg, Morten; Jensen, Brita Dahl; Weiner, Jacob 2008 EFFECTS OF SOIL DISTURBANCE AND DISEASE ON THE GROWTH AND REPRODUCTION OF LOLIUM PERENNE (POACEAE) INTRODUCED TO SEMI-NATURAL GRASSLANDS journal POLISH JOURNAL OF ECOLOGY 56 4 593 604 We performed manipulative field experiments to investigate the effects of soil disturbance and exposure to a fungal plant pathogen, Puccinia coronata (Corda), on the establishment and spread of two introduced, cultivated genotypes of perennial ryegrass, Lolium perenne (L.). The two cultivars of L. perenne with different levels of susceptibility to R coronata were introduced to grassland sites to investigate whether a plant cultivar selected to resist a pathogen shows better establishment in semi-natural plant communities than a susceptible cultivar. At two sites where L. perenne was already present, the addition of L. perenne seeds had no significant effect on the shoot biomass of the species, indicating that these populations were not seed limited. Exposure to the pathogen resulted in disease, and infected L. perenne populations showed increased shoot biomass over the course of the 3 year experiment and at harvest the final year, but no effect on seed production. Reproductive allocation was not affected by disease exposure in disturbed plots, but decreased in the presence of disease in undisturbed plots. The increased biomass observed in the semi-natural plant communities when exposed to the pathogen contrasts with the reduced biomass observed in garden experiments when the two cultivars of L. perenne were exposed to pathogen attack. The surprising positive effect of R coronata on biomass in semi-natural communities indicates that processes here are more complex than in more intensively managed production systems. Web of Science Lolium perenne Denmark 56.4;56.3833;56.3833;56.3667 9.35;9.35;9.35;9.3167 Field - Experimental terrestrial Grassland Invasion Hyp. Inherent Superiority;Disturbance Superior Competitor primary 159 Eschtruth, Anne K.; Battles, John J. 2009 Assessing the relative importance of disturbance, herbivory, diversity, and propagule pressure in exotic plant invasion journal ECOLOGICAL MONOGRAPHS 79 2 265 280 The current rate of invasive species introductions is unprecedented, and the dramatic impacts of exotic invasive plants on community and ecosystem properties have been well documented. Despite the pressing management implications, the mechanisms that control exotic plant invasion remain poorly understood. Several factors, such as disturbance, propagule pressure, species diversity, and herbivory, are widely believed to play a critical role in exotic plant invasions. However, few studies have examined the relative importance of these factors, and little is known about how propagule pressure interacts with various mechanisms of ecological resistance to determine invasion success. We quantified the relative importance of canopy disturbance, propagule pressure, species diversity, and herbivory in determining exotic plant invasion in 10 eastern hemlock forests in Pennsylvania and New Jersey (USA). Use of a maximum-likelihood estimation framework and information theoretics allowed us to quantify the strength of evidence for alternative models of the influence of these factors on changes in exotic plant abundance. In addition, we developed models to determine the importance of interactions between ecosystem properties and propagule pressure. These analyses were conducted for three abundant, aggressive exotic species that represent a range of life histories: Alliaria petiolata, Berberis thunbergii, and Microstegium vimineum. Of the four hypothesized determinants of exotic plant invasion considered in this study, canopy disturbance and propagule pressure appear to be the most important predictors of A. petiolata, B. thunbergii, and M. vimineum invasion. Herbivory was also found to be important in contributing to the invasion of some species. In addition, we found compelling evidence of an important interaction between propagule pressure and canopy disturbance. This is the first study to demonstrate the dominant role of the interaction between canopy disturbance and propagule pressure in determining forest invasibility relative to other potential controlling factors. The importance of the disturbance-propagule supply interaction, and its nonlinear functional form, has profound implications for the management of exotic plant species populations. Improving our ability to predict exotic plant invasions will require enhanced understanding of the interaction between propagule pressure and ecological resistance mechanisms. Web of Science Alliaria petiolata; Berberis thunbergii; Microstegium vimineum United States Pennsylvania; New Jersey Field - Observational terrestrial Coniferous Forest Invasion Hyp. Enemy Release;Community Species Richness;Propagule Pressure;Disturbance primary 160 Essl, Franz; Dirnboeck, Thomas 2008 Diversity of native and alien vascular plant species of dry grasslands in central Europe journal APPLIED VEGETATION SCIENCE 11 4 441 450 Question: Which factors determine diversity of native and alien vascular plant species in semi-natural dry grasslands? Location: Northern limestone Alps to the Southern rim of the Bohemian massif in northern Austria. Methods: In 70 randomly chosen dry grassland patches (0.008 ha - 7 ha) we sampled a complete inventory of vascular plant species at each site. We analysed the correlation between species diversity of natives. archaeophytes (pre-1500 aliens) and neophytes (post-1500 aliens). We used GLM to study the relationship of species number (natives, neophytes. archaeophytes) to five explanatory variables (altitude. within habitat diversity habitat diversity of adjacent areas, within land-use diversity and land-use derived with a PCA and used in the models. We also tested the influence of minimum residence time (MRT) and the covariables origin, mode of introduction and life form on the number of grassland sites with neophytes with analogous GLMs. Results: Native species diversity species was positively correlated with the species diversity of new. but not old invaders. GLM explains 70% of the variance in the number of native species. Patch size explained the largest part of the variation in the number of native species. PCA axes 1 and 3 were significantly related to the number of native species. Axis 1 was related to on-site habitat and land-use diversity. The GLM of the archaeophyte diversity explains 18% of the variance. Altitude and presence of fields and grassland in the neighbourhood mainly explained archaeophyte species diversity. The GLM of neophyte diversity explains 12% of the variance. The number of neophytes was positively related to that of archaeophytes. Only PCA axis 3. which is mainly influenced by adjacent land-use types. showed a relationship with neophytes. MRT. mode of introduction and region of origin (but not life form) were significantly related to the number of grassland sites invaded by neophytes. explaining 35% of the variance. Conclusion: Most factors governing native species diversity are not significantly related to alien species diversity. Additional determinants of the local scale diversity of alien species exist such as region of origin and historical factors (MRT, mode of introduction). Web of Science Many Austria Field - Observational terrestrial Grassland Invasion Hyp. Community Species Richness primary 161 Essl, Franz; Kobler, Johannes 2009 Spiny invaders - Patterns and determinants of cacti invasion in Europe journal FLORA 204 7 485 494 Web of Science Many Europe Statistical/Meta-analysis terrestrial Invasion Hyp. Preadaptation to Climate;Other primary 162 Fabiszewski, Jerzy; Brej, Teresa 2008 Ecological significance of some kenophytes in Lower Silesian national parks journal ACTA SOCIETATIS BOTANICORUM POLONIAE 77 2 167 174 The paper presents the results of several years investigations (2003-2007) on two invaders: the Himalayans Impatiens glandulifera and Asiatic Reynoutfia japonica. The Sudety Mountains and their national parks are under strong pressure of both species, threatening the local vegetation. The four-year investigations have been carried out in field, glasshouse and in laboratory. lnvasive species have their peculiar life histories which help them to occupy new areas. Those are above all the specific generative reproduction strategies (Impatiens) or vegetative reproduction strategies (Reynoutria). Both strategies secure the reproductive success and to capture more and more highly situated areas of the mountains. Very significant characteristics connected with the expansion of invaders is the excessively over and above the average production of seeds (Impatiens) and a huge annual increment aboveground biomass (Reynoutria). The investigated invasive species are probably not equipped with influence of allelopatic type as of greater importance is their competitive strength. The invaders can eliminate a part of the early spring flora belonging to the geophyte group and impoverish the regional biological diversity. Both the invasive plants enter also into some moist mountain forest communities. Web of Science Impatiens glandulifera; Reynoutria japonica Poland Sudety Mountains Field - Experimental terrestrial;lotic Deciduous Forest;Coniferous Forest;Riparian;Chaparral/Shrublands Invasion Hyp. Inherent Superiority Rapid Growth;High Reprod. Output primary 166 Feng, Yu-Long; Fu, Gai-Lan 2008 Nitrogen allocation, partitioning and use efficiency in three invasive plant species in comparison with their native congeners journal BIOLOGICAL INVASIONS 10 6 891 902 In this study, we hypothesized that invasive species may allocate a higher fraction of leaf nitrogen (N) to photosynthesis than phylogenetically related native species. To test this hypothesis, we determined N allocation and other ecophysiological traits of three invasive species in comparison with their respective native congeners by measuring response curves of photosynthesis to intercellular CO2 concentration. The invasive species of Peperomia and Piper indeed allocated a higher fraction of leaf N to photosynthesis and were more efficient in photosynthetic N (N-P) partitioning than their native congeners. The two invasive species partitioned a higher fraction of N-P to carboxylation and showed a higher use efficiency of N-P, while their native congeners partitioned a higher fraction of N-P to light-harvesting components. The higher N allocation to photosynthesis and the higher N-P partitioning to carboxylation in the two invaders were associated with their higher specific leaf area. Nitrogen allocation and partitioning were the most important factors in explaining the differences in light-saturated photosynthetic rate and photosynthetic N use efficiency (PNUE) between the two invasive species and their native congeners. The differences in N allocation-related variables between the invasive and native species of Amaranthus could not be evaluated in this study due to the method. Except PNUE, resource capture- and use-related traits were not always higher in all three invasive species compared to their native congeners, indicating that different invasive species may have different syndrome of traits associated with its invasiveness. Web of Science Peperomia pellucida; Piper hispidinervium; Amaranthus spinosus China Xishuangbanna Tropical Botanical Garden 21.0017 101.25 Garden terrestrial Invasion Hyp. Inherent Superiority primary 167 Feng, Yu-Long; Lei, Yan-Bao; Wang, Rui-Fang; Callaway, Ragan M.; Valiente-Banuet, Alfonso; Inderjit; Li, Yang-Ping; Zheng, Yu-Long 2009 Evolutionary tradeoffs for nitrogen allocation to photosynthesis versus cell walls in an invasive plant journal PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 106 6 1853 1856 Many studies have shown that individuals from invasive populations of many different plant species grow larger than individuals from native populations and that this difference has a genetic basis. This increased vigor in invasive populations is thought to be due to life history tradeoffs, in which selection favors the loss of costly defense traits, thereby freeing resources that can be devoted to increased growth or fecundity. Despite the theoretical importance of such allocation shifts for invasions, there have been no efforts to understand apparent evolutionary shifts in defense-growth allocation mechanistically. Reallocation of nitrogen (N) to photosynthesis is likely to play a crucial role in any growth increase; however, no study has been conducted to explore potential evolutionary changes in N allocation of introduced plants. Here, we show that introduced Ageratina adenophora, a noxious invasive plant throughout the subtropics, appears to have evolved increased N allocation to photosynthesis (growth) and reduced allocation to cell walls, resulting in poorer structural defenses. Our results provide a potential mechanism behind the commonly observed and genetically based increase in plant growth and vigor when they are introduced to new ranges. Web of Science Ageratina adenophora China Yunnan Province Xishuangbanna Tropical Botanical Garden 21.0017 101.0014 Garden terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 168 Ferreras, A. E.; Torres, C.; Galetto, L. 2008 Fruit removal of an invasive exotic species (Ligustrum lucidum) in a fragmented landscape journal JOURNAL OF ARID ENVIRONMENTS 72 9 1573 1580 We evaluated if fruit removal of an exotic and invasive species-Ligustrum lucidum (Oleaceae)-varies between fragments of different sizes in the Chaco dry forests of Cordoba, Argentina. We considered densities of both L. lucidum and the other ornithochorous plant species that bear fruit simultaneously with L. lucidum, as variables that could influence fruit removal of this species. We sampled three small (0.5-5 ha), two medium fragments (10-30ha), and two continuous forests (more than 1000ha). The percentage of fruits removed per tree was higher in small fragments than in medium or large ones. We did not find significant differences in plant density between fragments of different size neither for L. lucidum nor for the other ornithochorous plant species. During the effective removal period of L. lucidum (i.e., when animals removed fruits), the other ornithochorous plant species did not offer fruits. This region is affected by an increasing fragmentation process, where continuous woodlands have been reduced to small fragments. Considering that the main result is higher fruit removal in small fragments, new studies on the ecology of this species are needed if Chaco dry forests are to be conserved. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved. Web of Science Ligustrum lucidum Argentina Cordoba Chaco region Field - Observational terrestrial Deciduous Forest Invasion Hyp. Mutualism Facilitation primary 169 Fey, Karen; Banks, Peter B.; Oksanen, Lauri; Korpimaki, Erkki 2009 Does removal of an alien predator from small islands in the Baltic Sea induce a trophic cascade? journal ECOGRAPHY 32 3 546 552 Web of Science Mustela vison Finland Field - Experimental terrestrial Chaparral/Shrublands Impacts;Fundamentals predator 170 Ficetola, Gentile Francesco; Thuiller, Wilfried; Padoa-Schioppa, Emilio 2009 From introduction to the establishment of alien species: bioclimatic differences between presence and reproduction localities in the slider turtle journal DIVERSITY AND DISTRIBUTIONS 15 1 108 116 Understanding the factors determining the transition from introduction of aliens to the establishment of invasive populations is a critical issue of the study of biological invasions, and has key implications for management. Differences in fitness among areas of introduction can define the zones where aliens become invasive. The American slider turtle Trachemys scripta has been introduced worldwide, and has negative effects on freshwater communities, but only a subset of introduced populations breed successfully. We used species distribution models to assess the factors influencing the slider distribution in Italy, by analysing bioclimatic features that can cause the transition from presence of feral adults to breeding populations. We also evaluated whether climate change might increase the future suitability for reproduction. Central and Northern Italy. The distribution of slider turtle was obtained from the literature, unpublished reports and field surveys. We used Maxent to build bioclimatic models. Reproductive populations are associated to a clear bioclimatic envelope with warmer climate, more solar radiation and higher precipitations than populations where reproduction is not observed. Several Mediterranean areas currently have climatic features suitable for sliders. Scenarios of climate change predict the expansion of these areas. In the near future (2020), the proportion of populations in areas suitable for reproduction will dramatically increase. Our study shows that bioclimatic differences can determine the areas where aliens become invaders. Management should be focused to these source areas. However, climate change can increase fitness in the future, and therefore the interactions between climate change and fitness can boost the invasiveness of this alien species. Web of Science Trachemys scripta Italy Theoretical/Modeling lentic Invasion Hyp. Preadaptation to Climate;Climate Change omnivore 171 Figueroa, Javier A.; Cavieres, Lohengrin A.; Gomez-Gonzalez, Susana; Molina-Montenegro, Marco A.; Jaksic, Fabian M. 2009 Do heat and smoke increase emergence of exotic and native plants in the matorral of central Chile? journal ACTA OECOLOGICA-INTERNATIONAL JOURNAL OF ECOLOGY 35 2 335 340 We studied the effect of heat shock and wood-fueled smoke on the emergence of native and exotic plant species in soil samples obtained in an evergreen shrubland of central Chile, located on the eastern foothills of the Coastal Range of Lampa. Immediately after collection samples were dried and stored under laboratory condition. For each two transect, 10 samples were randomly chosen, and one of the following treatments was applied: 1) Heat-shock treatment. 2) Plant-produced smoke treatment. 3) Combined heat-and-smoke treatment. 4) Control, corresponding to samples not subjected to treatment. Twenty-three species, representing 12 families, emerged from the soil samples. The best-represented families were Poaceae and Asteraceae. All of the emerged species were herbs, 21 were annuals, and 14 were exotic to Chile. Fire-related triggers used in this study did not increase the emergence and/or abundance of exotic species with respect to natives in soil samples. Interestingly, this study provides evidence that heat-shock can increase the emergence of native herbs. (C) 2009 Elsevier Masson SAS, All rights reserved. Web of Science Many Chile Lampa -33 -70 Greenhouse terrestrial Subtropical Forest Invasion Hyp. Disturbance primary 173 Fisher, Judith L.; Loneragan, William A.; Dixon, Kingsley; Delaney, Julie; Veneklaas, Erik J. 2009 Altered vegetation structure and composition linked to fire frequency and plant invasion in a biodiverse woodland journal BIOLOGICAL CONSERVATION 142 10 2270 2281 Web of Science Many Australia Perth -31.945426 115.772252 Field - Observational;Statistical/Meta-analysis terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 175 Flory, S. Luke; Clay, Keith 2009 Effects of roads and forest successional age on experimental plant invasions journal BIOLOGICAL CONSERVATION 142 11 2531 2537 Web of Science Elaeagnus umbellata; Ligustrum obtusifolium; Lonicera maackii United States Indiana Bloomington 39.320142 -86.412536 Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Disturbance;Other primary 178 Foxcroft, L. C.; Parsons, M.; McLoughlin, C. A.; Richardson, D. M. 2008 Patterns of alien plant distribution in a river landscape following an extreme flood journal SOUTH AFRICAN JOURNAL OF BOTANY 74 3 463 475 The availability of suitable patches and gaps in the landscape is a crucial determinant of invasibility for alien plants. The type and arrangement of patches in the landscape may both facilitate and obstruct alien plant invasions, depending on whether alien species perceive the patches as barriers. In February 2000 tropical weather systems caused an extreme flood with an estimated return interval of 90 to 200 years in the Sabie River, South Africa. The impact of the 2000 flood on the Sabie River landscape provides an array of patches that may provide suitable resources for the establishment of alien plants. This study examines the distribution of alien plants in relation to patchiness of the Sabie River landscape. Our hypothesis was that if certain patches in the river landscape do not represent environmental barriers to alien plant invasion, alien species will occur preferentially in these patch types. The Sabie River within Kruger National Park [KNP] was divided into six patch types (zones, channel types, elevations, geomorphic units, substrates and flood imprint types). We then examined the distribution of native and alien woody and herbaceous density and species richness in patches. The density and species richness of alien plants in the Sabie River in KNP is very low when compared to the density and species richness of native plants. Some patches (bedrock distributary and braid bar geomorphic units) contained higher density and richness of alien plants compared to the other patches examined, indicating that these locations in the river landscape offer the resources necessary for alien plant establishment. Individual alien species are also associated with different parts of the river landscape. Failure of large numbers of alien plants to establish after the 2000 flood is most likely due to a combination of factors-the plant specific barriers imposed by landscape patchiness, the high abundance and richness of native vegetation leading to competition, and for some species certainly, the clearing by the management (Working for Water) programme. (c) 2008 SAAB. Published by Elsevier B. V. All rights reserved. Web of Science Many South Africa Sabie River Field - Observational terrestrial Riparian Invasion Hyp. Disturbance primary 179 Foxcroft, Llewellyn C.; Richardson, David M.; Rouget, Mathieu; MacFadyen, Sandra 2009 Patterns of alien plant distribution at multiple spatial scales in a large national park: implications for ecology, management and monitoring journal DIVERSITY AND DISTRIBUTIONS 15 3 367 378 Spatial scale is critical for understanding and managing biological invasions. In providing direction to managing alien plant invasions, much emphasis is placed on collecting spatially explicit data. However, insufficient thought is often given to how the data are to be used, frequently resulting in the incompatibility of the data for different uses. This paper explores the role of spatial scale in interpreting, managing and monitoring alien plant invasions in a large protected area. Kruger National Park, South Africa. Using 27,000 spatially-explicit records of invasive alien plants for the Kruger National Park (> 20,000 km(2)) we assessed alien plant species richness per cell at nine different scales of resolution. When assessing the patterns of alien plants at the various scales of resolution, almost identical results are obtained when working at scales of quarter-degree grids and quaternary watersheds (the fourth level category in South Africa's river basin classification system). Likewise, insights gained from working at resolutions of 0.1-0.5 km and 1-5 km are similar. At a scale of 0.1 x 0.1 km cells, only 0.4% of the Kruger National Park is invaded, whereas > 90% of the park is invaded when mapped at the quarter-degree cell resolution. Selecting the appropriate scale of resolution is crucial when evaluating the distribution and abundance of alien plant invasions, understanding ecological processes, and operationalizing management applications and monitoring strategies. Quarter-degree grids and quaternary watersheds are most useful at a regional or national scale. Grid cells of 1 to 25 km(2) are generally useful for establishing priorities for and planning management interventions. Fine-scale data are useful for informing management in areas which are small in extent; they also provide the detail appropriate for assessing patterns and rates of invasion. Web of Science Many South Africa Kruger National Park Statistical/Meta-analysis terrestrial Fundamentals primary 182 Friday, James B.; Scowcroft, Paul G.; Ares, Adrian 2008 Responses of native and invasive plant species to selective logging in an Acacia koa-Metrosideros polymorpha forest in Hawai'i journal APPLIED VEGETATION SCIENCE 11 4 471 482 Questions: Is the introduced timber species Fraximus uhdei invasive in Hawai'i? Has logging disturbance facilitated the spread of Fraxinus and other alien species? Location: Windward Mauna Kea, island of Hawai'i. Methods: We surveyed 29 plots which were established before selective logging of the native tree Acacia koa in 1971 to determine if Fraxinus spread beyond the borders of an existing plantation and if other alien species increased. We created gaps in the canopy of the Fraxinus plantation and measured seed rain and regeneration, and we sampled foliar and soil nutrients inside and around the plantation. Results: Basal area of Fraxinus increased front 0.7 m(2).ha(-1) in 1971 to 10.8 m(2).ha (1) in 2000. Fraxinus was not found in plots that were located more than 500 m from those where it occurred in 1971 except along a road, Basal area of Acacia koa decreased after logging but subsequently recovered. Occurrence of the alien vine Passiflora tarminiana and alien grass Ehrharta stipoides decreased. Seedling regeneration of Fraxinus was prolific in gaps but did not occur under the canopy. Basal area of Fraxinus did not correlate with soil nutrient concentrations. Conclusions: Fraxinus was able to regenerate following logging more rapidly than native tree species. Basal area growth of Fraxinus was great enough to offset a decline in native trees and cause an increase in forest productivity. If the Fraxinus plantation is harvested. managers should plan ways of favoring regeneration of the native Acacia which is more valuable both for timber and for conservation. Web of Science Fraximus uhdei USA Hawaii 19.9167 -155.3167 Field - Experimental;Field - Observational terrestrial Subtropical Forest Invasion Hyp. Disturbance primary 183 Friedman, Jonathan M.; Roelle, James E.; Gaskin, John F.; Pepper, Alan E.; Manhart, James R. 2008 Latitudinal variation in cold hardiness in introduced Tamarix and native Populus journal EVOLUTIONARY APPLICATIONS 1 4 598 607 To investigate the evolution of clinal variation in an invasive plant, we compared cold hardiness in the introduced saltcedar (Tamarix ramosissima, Tamarix chinensis, and hybrids) and the native plains cottonwood (Populus deltoides subsp. monilifera). In a shadehouse in Colorado (41 degrees N), we grew plants collected along a latitudinal gradient in the central United States (29-48 degrees N). On 17 occasions between September 2005 and June 2006, we determined killing temperatures using freeze-induced electrolyte leakage and direct observation. In midwinter, cottonwood survived cooling to -70 degrees C, while saltcedar was killed at -33 to -47 degrees C. Frost sensitivity, therefore, may limit northward expansion of saltcedar in North America. Both species demonstrated inherited latitudinal variation in cold hardiness. For example, from September through January killing temperatures for saltcedar from 29.18 degrees N were 5-21 degrees C higher than those for saltcedar from 47.60 degrees N, and on September 26 and October 11, killing temperatures for cottonwood from 33.06 degrees N were > 43 degrees C higher than those for cottonwood from 47.60 degrees N. Analysis of nine microsatellite loci showed that southern saltcedars are more closely related to T. chinensis while northern plants are more closely related to T. ramosissima. Hybridization may have introduced the genetic variability necessary for rapid evolution of the cline in saltcedar cold hardiness. Web of Science Tamarix ramosissima USA Colorado Greenhouse terrestrial Deciduous Forest;Chaparral/Shrublands Invasion Hyp. Hybridization primary 184 Funk, Jennifer L. 2008 Differences in plasticity between invasive and native plants from a low resource environment journal JOURNAL OF ECOLOGY 96 6 1162 1173 1. Phenotypic plasticity is often cited as an important mechanism of plant invasion. However, few studies have evaluated the plasticity of a diverse set of traits among invasive and native species, particularly in low resource habitats, and none have examined the functional significance of these traits. 2. I explored trait plasticity in response to variation in light and nutrient availability in five phylogenetically related pairs of native and invasive species occurring in a nutrient-poor habitat. In addition to the magnitude of trait plasticity, I assessed the correlation between 16 leaf- and plant-level traits and plant performance, as measured by total plant biomass. Because plasticity for morphological and physiological traits is thought to be limited in low resource environments (where native species usually display traits associated with resource conservation), I predicted that native and invasive species would display similar, low levels of trait plasticity. 3. Across treatments, invasive and native species within pairs differed with respect to many of the traits measured; however, invasive species as a group did not show consistent patterns in the direction of trait values. Relative to native species, invasive species displayed high plasticity in traits pertaining to biomass partitioning and leaf-level nitrogen and light use, but only in response to nutrient availability. Invasive and native species showed similar levels of resource-use efficiency and there was no relationship between species plasticity and resource-use efficiency across species. 4. Traits associated with carbon fixation were strongly correlated with performance in invasive species while only a single resource conservation trait was strongly correlated with performance in multiple native species. Several highly plastic traits were not strongly correlated with performance which underscores the difficulty in assessing the functional significance of resource conservation traits over short timescales and calls into question the relevance of simple, quantitative assessments of trait plasticity. 5. Synthesis. My data support the idea that invasive species display high trait plasticity. The degree of plasticity observed here for species occurring in low resource systems corresponds with values observed in high resource systems, which contradicts the general paradigm that trait plasticity is constrained in low resource systems. Several traits were positively correlated with plant performance suggesting that trait plasticity will influence plant fitness. Web of Science Leucaena leucocephala; Psidium cattleianum; Holcus lanatus; Paspalum urvillei; Rubus ellipticus United States Hawaii University of Hawaii, Volcano Agricultural Experiment Station 19.4667 -154.7333 Greenhouse terrestrial Tropical Forest Invasion Hyp. Plasticity primary 185 Fynn, R. W. S.; Wragg, P. D.; Morris, C. D.; Kirkman, K. P.; Naiken, J. 2009 Vegetative traits predict grass species' invasiveness and the invasibility of restored grassland journal AFRICAN JOURNAL OF RANGE & FORAGE SCIENCE 26 2 59 68 Web of Science Paspalum urvillei South Africa KwaZulu-Natal University of Pietermaritzburg, Neil Tainton Arboretum -28.3703 30.4019 Field - Experimental terrestrial Grassland Invasion Hyp. Inherent Superiority Superior Competitor primary 188 Garau, A. M.; Ghersa, C. M.; Lemcoff, J. H.; Baranao, J. J. 2009 Weeds in Eucalyptus globulus subsp maidenii (F. Muell) establishment: effects of competition on sapling growth and survivorship journal NEW FORESTS 37 3 251 264 The effect of herbaceous vegetation on growth and survival was assessed in planted eucalyptus saplings grown under four levels of weed cover. Seedlings of Eucalyptus globulus subsp. maidenii were planted with 0 (W0), 25 (W25), 50 (W50) and 100% (W100) weed cover. Weed species composition and aboveground biomass was determined. Soil water content was evaluated by the gravimetric method. Seedling leaf area, diameter and height were evaluated at planting and during the 3 months following establishment. Tree height, diameter and stem volume was estimated at 12, 24 and 36 months. First year tree survival was recorded. The ratio of cumulative stem growth under W100: cumulative stem growth under W0 was used to measure competitive performance. Regression analysis was used to determine competition thresholds. Weeds seriously threaten the growth of E. globulus subsp. maidenii. Early negative effects of competition on growth were evident as from the second month after establishment, and both seedlings and 1-year-old saplings were more affected than 2- and 3-year-old ones. A 'minimum-response threshold' was determined near 500 kg/ha (corresponding to W25 cover). No clear effect was found between sapling survival and weed biomass. Web of Science Many Argentina Buenos Aires Province Buenos Aires, National University of Lujan -34.566667 -59.083333 Garden terrestrial Deciduous Forest Fundamentals primary 189 Garcia, Pablo; Mateos, Isabel; Arevalo, Valentin 2009 DIURNAL ACTIVITY OF THE AMERICAN MINK (NEOVISON VISON) IN CENTRAL SPAIN journal HYSTRIX-ITALIAN JOURNAL OF MAMMALOGY 20 1 61 68 Web of Science Neovision vision Spain Salamanca River Tormes, Salamanca 40.956 -5.6578 Field - Observational terrestrial Deciduous Forest;Riparian Invasion Hyp. Empty Niche omnivore 190 Gaskin, John F.; Wheeler, Gregory S.; Purcell, Matthew F.; Taylor, Gary S. 2009 Molecular evidence of hybridization in Florida's sheoak (Casuarina spp.) invasion journal MOLECULAR ECOLOGY 18 15 3216 3226 Web of Science Casuarina glauca; Casuarina cunninghamiana; Casuarina equisetifolia United States; Argentina; Australia Florida; California; Hawaii Florida; California; Hawaii; Argentina; Australia Lab terrestrial Deciduous Forest;Subtropical Forest Invasion Hyp. Hybridization primary 191 Gasso, Nuria; Sol, Daniel; Pino, Joan; Dana, Elias D.; Lloret, Francisco; Sanz-Elorza, Mario; Sobrino, Eduardo; Vila, Montserrat 2009 Exploring species attributes and site characteristics to assess plant invasions in Spain journal DIVERSITY AND DISTRIBUTIONS 15 1 50 58 Biological invasions are a major component of global change with increasing effects on natural ecosystems and human societies. Here, we aim to assess the relationship between plant invader species attributes and the extent of their distribution range size, at the same time that we assess the association between environmental factors and plant invader species richness. Spain, Mediterranean region. From the species perspective, we calculated the distribution range size of the 106 vascular plant invaders listed in a recently published atlas of alien plant species in Spain. Range size was used as an estimation of the degree of invasion success of the species. To model variation in range size between species as a function of a set of species attributes, we adopted the framework of the generalized linear mixed models because they allow the incorporation of taxonomic categories as nested random factors to control for phylogenetic relationships. From the invaded site perspective, we determined invader plant species richness as the number of species for each 10 x 10 km Universal Transverse Mercator (UTM) grid. For each grid cell, we estimated variables concerning landscape, topography, climate and human settlement. Then, we performed a generalized linear mixed model incorporating a defined spatial correlation structure to assess the relationship between plant invader richness and the environmental predictors. From the species perspective, wind dispersal and minimum residence time appeared to favour invasion success. From the invaded site perspective, we identified high anthropogenic disturbance, low altitude, short distance to the coastline and dry, hot weather as the main correlates to UTM grid cell invader richness. According to these results, an increasing importance of man-modified ecosystems and global warming in the Mediterranean region should facilitate the expansion of plant invaders, especially wind-dispersed species, leading to the accumulation of invasive species in some sites (i.e. invasion hot spots). Web of Science Many Spain Spain Theoretical/Modeling terrestrial Grassland;Deciduous Forest;Coniferous Forest;Mountain;Chaparral/Shrublands;Urban;Old Field Invasion Hyp. Inherent Superiority;Community Species Richness;Preadaptation to Climate;Disturbance;Climate Change Effective Disperser primary 193 Gettys, L. A.; Haller, W. T.; Mudge, C. R.; Koschnick, T. J. 2008 Effect of temperature and feeding preference on submerged plants by the island apple snail, Pomacea insularum (d'Orbigny, 1839) (Ampullariidae) journal VELIGER 50 3 248 254 The island apple snail (Pomacea insularum (d'Orbigny, 1839)) is a South American snail that became naturalized in Florida waterways in the mid-1970s and has recently spread throughout much of the state. Food Consumption by this herbivorous Snail was determined in 10-day feeding trials at temperatures of 15 to 35 degrees C. Optimum feeding of the exotic submerged plant Hydrilla verticillata (L.f.) Royle (hydrilla) occurred over a wide temperature range (20 to 35 degrees C). However, Snail growth was greatest at temperatures of 20 to 30 degrees C. Free choice plant preference Studies were conducted to determine feeding preferences for native and exotic Submerged plants. One exotic and two native species (H. verticillata, Najas guadalupensis (Spreng.) Magnus (southern naiad) and Chara sp. (stonewort), respectively) were highly preferred by island apple snails, followed by the two native Species potamogeton illinoensis Morong. (Illinois pondweed) and Vallisneria americana Michx. (tapegrass). Leaves of the exotic species Myriophyllum aquaticum (Vell.) Verdc. (parrotsfeather) were eaten after the more preferred plants were consumed and no significant feeding was noted on the exotic species Egeria densa Planch. (Brazilian elodea). While island apple snails have distinct preferences for certain submerged plants, they consumed both native and exotic species, which may significantly affect growth of certain species and will likely change species composition of Submerged plant communities in Florida wherever they are common. Web of Science Pomacea insularum United States Florida Impacts;Fundamentals herbivore 196 Godoy, Oscar; Richardson, David M.; Valladares, Fernando; Castro-Diez, Pilar 2009 Flowering phenology of invasive alien plant species compared with native species in three Mediterranean-type ecosystems journal ANNALS OF BOTANY 103 3 485 494 Flowering phenology is a potentially important component of success of alien species, since elevated fecundity may enhance invasiveness. The flowering patterns of invasive alien plant species and related natives were studied in three regions with Mediterranean-type climate: California, Spain and South Africa's Cape region. A total of 227 invasive-native pairs were compared for seven character types across the regions, with each pair selected on the basis that they shared the same habitat type within a region, had a common growth form and pollination type, and belonged to the same family or genus. Invasive alien plant species have different patterns of flowering phenology from native species in the three regions. Whether the alien species flower earlier, later or at the same time as natives depends on the climatic regime in the native range of the aliens and the proportion of species in the invasive floras originating from different regions. Species invading at least two of the regions displayed the same flowering pattern, showing that flowering phenology is a conservative trait. Invasive species with native ranges in temperate climates flower earlier than natives, those from Mediterranean-type climates at the same time, and species from tropical climates flower later. In California, where the proportion of invaders from the Mediterranean Basin is high, the flowering pattern did not differ between invasive and native species, whereas in Spain the high proportion of tropical species results in a later flowering than natives, and in the Cape region early flowering than natives was the result of a high proportion of temperate invaders. Observed patterns are due to the human-induced sympatry of species with different evolutionary histories whose flowering phenology evolved under different climatic regimes. The severity of the main abiotic filters imposed by the invaded regions (e.g. summer drought) has not been strong enough (yet) to shift the flowering pattern of invasive species to correspond with that of native relatives. It does, however, determine the length of the flowering season and the type of habitat invaded by summer-flowering aliens. Results suggest different implications for impacts at evolutionary time scales among the three regions. Web of Science Many United States, Spain and South Africa California, South African Cape Region and Spanish Mediterranean Region Theoretical/Modeling terrestrial Invasion Hyp. Inherent Superiority;Preadaptation to Climate Broad Tolerances primary 198 Going, Barbara Marie; Hillerislambers, Janneke; Levine, Jonathan M. 2009 Abiotic and biotic resistance to grass invasion in serpentine annual plant communities journal OECOLOGIA 159 4 839 847 Biological invasions severely impact native plant communities, causing dramatic shifts in species composition and the restriction of native species to spatially isolated refuges. Competition from resident species and the interaction between resource limitation and competition have been overlooked as mechanisms of community resistance in refugia habitats. We examined the importance of these factors in determining the resistance of California serpentine plant communities to invasion by three common European grasses, Avena barbata, Bromus diandrus, and Hordeum murinum. We added seeds of each of these grasses to plots subjected to six levels of resource addition (N, P, Ca, H2O, all resources together, and a no-addition control) and two levels of competition (with resident community present or removed). Resource limitation and competition had strong effects on the biomass and reproduction of the three invaders. The addition of all resources together combined with the removal of the resident community yielded individual plants that were fourfold to 20-fold larger and sixfold to 20-fold more fecund than plants from control plots. Competitor removal alone yielded invaders that were twofold to sevenfold larger and twofold to ninefold more fecund. N addition alone or in combination with other resources led to a twofold to ninefold increase in the biomass and fecundity of the invaders. No other resource alone significantly affected native or invader performance, suggesting that N was the key limiting resource during our experiment. We found a significant interaction between abiotic and biotic resistance for Bromus, which experienced increased competitive suppression in fertilized plots. The threefold increase in resident biomass with N addition was likely responsible for this result. Our results confirm that serpentine plant communities are severely N limited, which, in combination with competition from resident species, promotes the resistance of these systems to invasions. Our work suggests that better understanding the relative sensitivities of invaders and residents to the physical environment is critical to predicting how abiotic and biotic factors interact to determine community resistance. Web of Science Avena barbata; Bromus diandrus; Hordeum murinum United States California Sedgwik Reserve 34.739167 -120.005556 Field - Experimental terrestrial Grassland Fundamentals;Invasion Hyp. Inherent Superiority;Fluctuating Resources;Other Superior Competitor primary 200 Gomez-Gonzalez, Susana; Cavieres, Lohengrin A. 2009 Litter burning does not equally affect seedling emergence of native and alien species of the Mediterranean-type Chilean matorral journal INTERNATIONAL JOURNAL OF WILDLAND FIRE 18 2 213 221 Central Chile differs from other areas with Mediterranean-type climate by the scarcity of natural wildfires. The Chilean matorral is highly invaded by alien plant species from other Mediterranean zones of the world, where natural, recurrent wildfires have been one of their ecological features at least since the Pliocene. This suggests that anthropogenic fires in Chile might favour alien plant recruitment, increasing the invasive process. We assessed the effect of litter burning on the emergence of alien and native species from the soil seedbank of a matorral of central Chile. Soil samples were taken from three types of microhabitats: (i) closed matorral; (ii) beneath the canopy of shrubs and trees from an open matorral; (iii) grassland. Each sample was split in two subsamples. One subsample was exposed to fire by burning the litter taken from its corresponding microhabitat, and the other subsample was left unburned and used as a control. Fire intensity, determined by the fuel type, affected more markedly the native seedbank survival than the alien one. The low-intensity fire produced by grassland litter did not significantly affect the emergence of native herbs but increased alien species richness. The high-intensity and the very high-intensity fires produced by litter burning from beneath the canopy of the closed and the open matorral, respectively, negatively affected the seedling emergence of both native and alien species, but did so in a more pronounced manner to native species. Therefore, anthropogenic fires in central Chile may promote the invasion of alien plants with favourable traits (i. e. heat-shock resistance of seeds) that are not present in the native flora. Web of Science Many Chile Santiago province San Carlos de Apoquindo -33.45 -70.42 Field - Experimental;Greenhouse terrestrial Grassland;Chaparral/Shrublands Invasion Hyp. Inherent Superiority;Preadaptation to Climate;Disturbance Superior Competitor;Broad Tolerances primary 201 Gomez-Gonzalez, Susana; Cavieres, Lohengrin A.; Torres, Patricio; Torres-Diaz, Cristian 2009 COMPETITIVE EFFECTS OF THE ALIEN INVASIVE CENTAUREA SOLSTITIALIS L. ON TWO CHILEAN BACCHARIS SPECIES AT DIFFERENT LIFE-CYCLE STAGES journal GAYANA BOTANICA 66 1 71 83 Web of Science Centaurea solstitialis L. Chile Province of Santiago Quebrada de la Plata -33.483333 -70.866667 Field - Experimental;Lab terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority;Other Superior Competitor;High Reprod. Output primary 208 Gurevitch, Jessica; Howard, Timothy G.; Ashton, Isabel W.; Leger, Elizabeth A.; Howe, Katherine M.; Woo, Eliza; Lerdau, Manuel 2008 Effects of experimental manipulation of light and nutrients on establishment of seedlings of native and invasive woody species in Long Island, NY forests journal BIOLOGICAL INVASIONS 10 6 821 831 While earlier studies on the process of invasion often focused on single factors or on the general explanation of 'Cydisturbance,' recent work has attempted to move towards a more mechanistic understanding of the factors that promote plant community invasion. Manipulative experiments provide a means for discerning causal relationships and interactive effects of environmental factors in promoting invasion; such experiments have been conducted in a number of grassland and shrub ecosystems. This study extends multifactor manipulative experiments into forest communities to compare factors influencing early seedling establishment for native and invasive woody plants. In Long Island, NY, invasion patterns are correlated with forest community type (pine barrens or hardwood), light availability, and soil N and Ca. We conducted manipulative field experiments in two different years to determine the relative importance and interaction of experimental gaps and N and Ca addition in pine barrens and hardwood forests in promoting invasion. We used seedlings of seven common native and invasive species in the first experiment, and 16 native and invasive species paired phylogenetically in the second experiment. Light had the strongest effect on plant growth; all plants grew more in gaps. We found no difference in the average growth rates of native and invasive species. Invasives responded more to high resources than did natives, with highest relative growth rates in gaps in the more fertile soils of the hardwood forests. Opportunities for invasion may differ from year to year, with differential success of invaders only in some years and under some environmental conditions. Clearly, to understand the complex interactions between resources and invasion in forests will require many manipulative experiments across a range of environments and using suites of invasive and native species. Web of Science Many United States New York Long Island 40.8869;40.8523;40.874;40.9055;40.9085;40.9429 -72.6449;-72.7322;-72.7145;-73.1517;-73.2105;-72.9491 Field - Experimental terrestrial Deciduous Forest;Coniferous Forest Invasion Hyp. Fluctuating Resources;Disturbance primary 209 Haande, Sigrid; Rohrlack, Thomas; Ballot, Andreas; Roberg, Kjetil; Skulberg, Randi; Beck, Martin; Wiedner, Claudia 2008 Genetic characterisation of Cylindrospermopsis raciborskii (Nostocales, Cyanobacteria) isolates from Africa and Europe journal HARMFUL ALGAE 7 5 692 701 The invasive cyanobacterium Cylindrospermopsis raciborskii is increasingly spreading in temperate freshwater habitats worldwide and is of major concern due to its ability to produce potent toxins. It is, therefore, important to understand the mechanisms behind the dispersal of this species. Different hypotheses have been proposed to explain the phylogeography and mechanisms underlying the recent expansion of C raciborskii into temperate latitudes, but there is still no conclusive evidence whether the obvious ecological success of C raciborskii is due to selection mechanisms, physiological tolerance, climatic change or radiation after the last ice age. In the present study, new isolates of C raciborskii from Europe and Africa were genetically characterised by sequencing the ITS1, PC-IGS, nifH and rpoC1 genes and compared to corresponding sequences of C raciborskii available in GenBank in order to test different phylogeographical hypotheses. The strains were also morphologically examined and screened for production of the hepatotoxic cylindrospermopsin (CYN). We clearly demonstrate a variation among the populations of C raciborskii from different geographical regions. The phylogenetic analyses revealed a clustering of the strains due to geographic origin. The ITS1 and nifH genes separated into American, European and Australian-African groups, whereas the PC-IGS and rpoC1 separated into American and European/Australian/African groups. An analysis of concatenated data supported the division into American, European and African/Australian groups, and even indicated a subdivision into an African and an Australian group. Our findings do not strongly support any of the existing hypotheses on the phylogeography of C raciborskii, and most likely a combination of these hypotheses is the best approach to understand the evolution and dispersal of this species. (c) 2008 Elsevier B.V. All rights reserved. Web of Science Cylindrospermopsis raciborskii France; Germany; Hungary; Portugal; Australia; Senegal; USA; Mexico; Brazil; Uganda Lab lentic Invasion Hyp. Evolution of Increased Competitive Ability;Inherent Superiority;Preadaptation to Climate Broad Tolerances primary 212 Han, M.; Fukushima, M.; Fukushima, T. 2008 A spatial linkage between dams and non-native fish species in Hokkaido, Japan journal ECOLOGY OF FRESHWATER FISH 17 3 416 424 The native and non-native freshwater fish species richness as well as the proportion of native fish species to overall fish species were examined to test a hypothesis of a spatial linkage between the distributions of dams and non-native fishes based on survey data collected in rivers and streams in Hokkaido, Japan. Non-native fish species have steadily increased in Hokkaido since the mid 1970s, as indicated by the decreasing proportion of native fish species per fish survey. Non-native species richness was significantly higher in areas above dams (i.e., reservoirs and their inlet streams) compared to areas without dams. As a result, the proportion of native fish species was lower above dams. This proportion was lower in developed and agricultural areas compared with forest areas, although both native and non-native species richness were higher in areas with development and agriculture. Non-native cyprinids, catfish and snakehead occurred primarily in a particular river basin with the largest drainage area, the longest history of reclamation and highest human population in the island. Non-native salmonids on the other hand, occurred in forest areas at higher elevations and their occurrence was associated with the existence of dams. There was a spatial linkage between the distribution of dams and non-native species, although it was applicable only to salmonids. The management of dams and reservoirs needs a strategy to prevent further expansion of exotic salmonids such as rainbow and brown trout. These species can be a significant threat to native Japanese salmonids as a result of various biological mechanisms. Web of Science Many Japan Hokkaido Hokkaido 41.35;45.55 -139.3333;-148.8833 Field - Observational lentic Riparian Invasion Hyp. Disturbance herbivore;omnivore;predator 213 Han, Xuemei; Dendy, Shauna P.; Garrett, Karen A.; Fang, Liang; Smith, Melinda D. 2008 Comparison of damage to native and exotic tallgrass prairie plants by natural enemies journal PLANT ECOLOGY 198 2 197 210 We surveyed the prevalence and amount of leaf damage related to herbivory and pathogens on 12 pairs of exotic (invasive and noninvasive) and ecologically similar native plant species in tallgrass prairie to examine whether patterns of damage match predictions from the enemy release hypothesis. We also assessed whether natural enemy impacts differed in response to key environmental factors in tallgrass prairie by surveying the prevalence of rust on the dominant C-4 grass, Andropogon gerardii, and its congeneric invasive exotic C-4 grass, A. bladhii, in response to fire and nitrogen fertilization treatments. Overall, we found that the native species sustain 56.4% more overall leaf damage and 83.6% more herbivore-related leaf damage when compared to the exotic species. Moreover, we found that the invasive exotic species sustained less damage from enemies relative to their corresponding native species than the noninvasive exotic species. Finally, we found that burning and nitrogen fertilization both significantly increased the prevalence of rust fungi in the native grass, while rust fungi rarely occurred on the exotic grass. These results indicate that reduced damage from enemies may in part explain the successful naturalization of exotic species and the spread of invasive exotic species in tallgrass prairie. Web of Science Many United States Kansas Konza Prairie Biological Station 39.0833 -96.5833 Field - Experimental terrestrial Grassland Invasion Hyp. Enemy Release primary 214 Hansen, Dennis M.; Mueller, Christine B. 2009 Invasive Ants Disrupt Gecko Pollination and Seed Dispersal of the Endangered Plant Roussea simplex in Mauritius journal BIOTROPICA 41 2 202 208 In Mauritius, the endemic blue-tailed day-gecko Phelsuma cepediana is currently the sole pollinator and seed disperser of the critically endangered endemic plant Roussea simplex (Rousseaceae). The flowers and fruits are often visited by the invasive ant Technomyrmex albipes, which forages on the nectar and fruit pulp, and tends honeydew-producing mealybugs on the fruits. Here, we experimentally explore how the presence of this alien ant species influences geckos foraging at flowers and fruits of R. simplex by removing and excluding ants from flowers and fruits. Gecko visitation rates to ant-free control flowers and fruits, and flowers and fruits where ants had been removed and excluded, were higher than those to ant-infested flowers and fruits. The resulting seed set of ant-infested flowers was greatly reduced, compared to ant-free control flowers. Similarly, for fruits with ants, very few seeds were likely to be ingested and dispersed by the geckos. Thus, T. albipes monopolizes flowers and fruits of R. simplex, and prevents access of pollinating and seed-dispersing P. cepediana geckos by aggressive interference competition. For a critically endangered plant like R. simplex, this double-disruption of two vital mutualistic interactions is of urgent conservation concern. Web of Science Technomyrmex albipes Mauritius Pétrin;Bassin Blanc -20.4058 57.4658 Field - Experimental terrestrial Tropical Forest Invasion Hyp. Inherent Superiority High Reprod. Output herbivore 216 Hao, Jian-Hua; Qiang, Sheng; Liu, Qian-Qian; Cao, Fei 2009 Reproductive traits associated with invasiveness in Conyza sumatrensis journal JOURNAL OF SYSTEMATICS AND EVOLUTION 47 3 245 254 Web of Science Conyza sumatrensis China Jiangsu Nanjing 32.0356 118.8375 Field - Observational terrestrial Urban;Old Field Invasion Hyp. Inherent Superiority High Reprod. Output;Effective Disperser primary 219 Harmon-Threatt, Alexandra N.; Burns, Jean H.; Shemyakina, Lyudmila A.; Knight, Tiffany M. 2009 BREEDING SYSTEM AND POLLINATION ECOLOGY OF INTRODUCED PLANTS COMPARED TO THEIR NATIVE RELATIVES journal AMERICAN JOURNAL OF BOTANY 96 8 1544 1550 Web of Science Many United States of America Missouri Tyson Research Center 38.5269 -90.5603 Field - Experimental terrestrial Deciduous Forest;Old Field Invasion Hyp. Mutualism Facilitation;Inherent Superiority Self Compatible primary 221 He, Wei-Ming; Feng, Yulong; Ridenour, Wendy M.; Thelen, Giles C.; Pollock, Jarrod L.; Diaconu, Alecu; Callaway, Ragan M. 2009 Novel weapons and invasion: biogeographic differences in the competitive effects of Centaurea maculosa and its root exudate (+/-)-catechin journal OECOLOGIA 159 4 803 815 Recent studies suggest that the invasive success of Centaurea maculosa may be related to its stronger allelopathic effects on native North American species than on related European species, one component of the 'novel weapons' hypothesis. Other research indicates that C. maculosa plants from the invasive range in North America have evolved to be larger and better competitors than conspecifics from the native range in Europe, a component of the 'evolution of increased competitive ability' hypothesis. These hypotheses are not mutually exclusive, but this evidence sets the stage for comparing the relative importance of evolved competitive ability to inherent competitive traits. In a competition experiment with a large number of C. maculosa populations, we found no difference in the competitive effects of C. maculosa plants from North America and Europe on other species. However, both North American and European C. maculosa were much better competitors against plants native to North America than congeners native to Romania, collected in areas where C. maculosa is also native. These results are consistent with the novel weapons hypothesis. But, in a second experiment using just one population from North America and Europe, and where North American and European species were collected from a broader range of sites, competitive interactions were weaker overall, and the competitive effects of C. maculosa were slightly stronger against European species than against North American species. Also consistent with the novel weapons hypothesis, (+/-)-catechin had stronger effects on native North American species than on native European species in two experiments. Our results suggest that the regional composition of the plant communities being invaded by C. maculosa may be more important for invasive success than the evolution of increased size and competitive ability. Web of Science Centaurea maculosa United States of America Montana Greenhouse terrestrial Grassland Invasion Hyp. Evolution of Increased Competitive Ability;Novel Weapons primary 222 Hebel, Cassie L.; Smith, Jane E.; Cromack, Kermit, Jr. 2009 Invasive plant species and soil microbial response to wildfire burn severity in the Cascade Range of Oregon journal APPLIED SOIL ECOLOGY 42 2 150 159 Web of Science Bromus tectorum;Brachypodium sylvaticum;Centaurea maculosa United States of America Oregon Booth and Bear Butte 43.928495 -121.630554 Field - Observational;Lab terrestrial Coniferous Forest Invasion Hyp. Mutualism Facilitation;Disturbance primary 227 Herault, Bruno; Bornet, Aurelien; Tremolieres, Michele 2008 Redundancy and niche differentiation among the European invasive Elodea species journal BIOLOGICAL INVASIONS 10 7 1099 1107 Community ecologists implicitly assume redundancy when they aggregate species into functional groups. But there have been remarkably few empirical efforts to investigate the accuracy of this concept in situ. The concept of redundancy could be roughly split into two components: the ecological redundancy (similar response to environmental variations involving similar ecological processes) and the functional redundancy (similar biological trait combinations shaping similar functional processes). Both types of redundancy are tested among the 3 invasive European Elodeas. In 11 sites and during two successive years 2004-2005, the cover growth rate of each Elodea species was monthly recorded. To test ecological redundancy, cover growth rates were related to a large suite of environmental variables. To test functional redundancy, 13 biological traits involved in competitive relationships were measured each month. Firstly, the redundancy hypothesis looks problematic for Elodea ernstiae. Indeed, the later possess numerous biological traits involved in light competition and niche overlap with the other Elodeas is very low. Secondly, ecological and functional redundancy can be successfully applied to Elodea canadensis and Elodea nuttallii. They share a large suite of biological traits leading to wide niche overlaps through the growing season. And the measured environmental variables do not differentially influence their growth rates, which are, in turn, controlled by a similar group of biological traits. In this way, the different invasiveness patterns of E. canadensis and E. nuttallii could be solely due to the ecological drift and their ecological dynamic could follow neutral rules. Web of Science Elodea canadensis;Elodea ernstiae; Elodea nuttallii France Alsace Rhine former floodplain 48.5837 7.7388 Field - Observational lotic Fundamentals primary 232 Herrera, I.; Nassar, J. M. 2009 Reproductive and recruitment traits as indicators of the invasive potential of Kalanchoe daigremontiana (Crassulaceae) and Stapelia gigantea (Apocynaceae) in a Neotropical arid zone journal JOURNAL OF ARID ENVIRONMENTS 73 11 978 986 Web of Science Kalanchoe daigremontiana;Stapelia gigantea Venezuela Cerro Saroche National Park 10.25 -69.85 Field - Observational terrestrial Invasion Hyp. Inherent Superiority High Reprod. Output;Clonal Reproduction primary 233 Herrera, Lorena P.; Laterra, Pedro 2009 Do seed and microsite limitation interact with seed size in determining invasion patterns in flooding Pampa grasslands? journal PLANT ECOLOGY 201 2 457 469 Additive influences of the invasion ability of species (invasiveness) and the characteristics of the habitat which make it invasible (invasibility) cannot fully explain grassland invasion patterns. We tested the hypothesis that different species assemblages of grassland communities may partly result from interactive influences between the relative invasiveness of available species and community invasibility. During 10 months, we evaluated seed and microsite limitation of seedling emergence, survival, and recruitment of plants belonging to species with different seed size (large-seeded species vs. small-seeded species), with in a two-phase community mosaic typical of semi-natural grasslands in the southern flooding Pampa of Argentina. Seeds of large versus small-seeded species were sown either in species-poor patches dominated by a tall tussock grass ('pajonal') or in species-rich patches dominated by short grasses ('matrix'), subjected to different levels of canopy disturbance (cut vs. uncut). Seed addition promoted seedling emergence for 7 out of the 10 species sown, and this effect was higher for large than for small-seeded species. After seed limitations were removed, interactive effects among seed size, community state and canopy disturbance reflected a strong positive influence of seed size on plant recruitment only in cut pajonal patches. Therefore, according to the stage of invasion process, relative species success may depend on non-interactive (seed-size effect on seed limitation to seedling emergence) or interactive influences among species invasibility and community invasiveness (from seedling emergence to plant recruitment). As a general conclusion, different assemblages of species are expected to successfully colonize spatially close grassland patches, according to both the available invasible species (seed size) and the community state and stage (species composition and canopy disturbance). Web of Science Many Argentina southeast Pampa -37 -58 Field - Experimental terrestrial Grassland Invasion Hyp. Community Species Richness;Propagule Pressure;Other primary 234 Hierro, Jose L.; Eren, Ozkan; Khetsuriani, Liana; Diaconu, Alecu; Torok, Katalin; Montesinos, Daniel; Andonian, Krikor; Kikodze, David; Janoian, Levan; Villarreal, Diego; Estanga-Mollica, Maria E.; Callaway, Ragan M. 2009 Germination responses of an invasive species in native and non-native ranges journal OIKOS 118 4 529 538 Studying germination in the native and non-native range of a species can provide unique insights into processes of range expansion and adaptation; however, traits related to germination have rarely been compared between native and non-native populations. In a series of common garden experiments, we explored whether differences in the seasonality of precipitation, specifically, summer drought vs summer rain, and the amount and variation of annual and seasonal precipitation affect the germination responses of populations of an annual ruderal plant, Centaurea solstitialis, from its native range and from two non-native regions with different climates. We found that seeds from all native populations, irrespective of the precipitation seasonality of the region in which they occurred, and non-native populations from regions with dry summers displayed similarly high germination proportions and rates. In contrast, genotypes from the non-native region with predominantly summer rain exhibited much lower germination fractions and rates. Also, percent germination was strongly correlated with variation in precipitation in winter, the season that follows germination for C. solstitialis. Specifically, germination was lower for native and non-native populations experiencing greater variation in winter precipitation. This correlation, however, was greatly influenced by the non-native region with summer rain, which also exhibited the greatest variation in winter precipitation among studied regions. These results suggest that rather than general climatic patterns, the degree of risk experienced at early developmental stages could exert an important control over the germination strategy of C. solstitialis populations in both native and non-native ranges. Also, these findings reveal a largely unique germination response in C. solstitialis genotypes growing in the non-native region with summer rain and high variation in winter precipitation. Our work raises the possibility that rapid adaptive changes in germination strategies may contribute to the success of globally distributed invaders. Web of Science Centaurea solstitialis Greenhouse terrestrial Grassland Invasion Hyp. Evolution in General;Preadaptation to Climate primary 235 Hill, Steven Burton; Kotanen, Peter M. 2009 Evidence that phylogenetically novel non-indigenous plants experience less herbivory journal OECOLOGIA 161 3 581 590 Web of Science Many Canada Ontario Koffler Scientific Reserve 44.0333 -79.5167 Field - Observational;Garden terrestrial Deciduous Forest;Old Field Invasion Hyp. Enemy Release;Other primary 238 Hoffmann, Benjamin D.; Kay, Alice 2009 Pisonia grandis monocultures limit the spread of an invasive ant-a case of carbohydrate quality? journal BIOLOGICAL INVASIONS 11 6 1403 1410 The mechanisms by which invasive species are able to spread into and dominate natural communities are poorly understood and remain a focus of invasion research. In this quest, studying invasions that are limited by a controlling factor will be more informative than will studies documenting unabated spread and impacts. Some ant species are very successful invaders, and research demonstrating abiotic and biotic factors limiting their success has aided the understanding of invasion ecology. We report here a study showing the highly invasive African big headed ant Pheidole megacephala having a novel distribution on coral cays within Australia's Great Barrier Reef. These patterns displayed a clear limitation of its distribution with monocultures of the tree Pisonia grandis. This distribution was contrary to the known environmental limitations of the ant, and the limitation could not be associated with an underlying abiotic determinant of the vegetation type. We present these distributional patterns, and following consideration of all known biotic and abiotic limitations of ant invasions we discuss the potential that the peculiar ecophysiology of P. grandis is the causal factor. Specifically, we suggest that the quality of carbohydrate supply to ants is a limitation to invasive spread in much the same way that carbohydrate quantity is known to affect ant population densities in other ecosystems. Web of Science Pheidole megacephala Australia Queensland Capricornia Cays National Park -23.25 151.9 Field - Observational terrestrial Tropical Forest Invasion Hyp. Preadaptation to Climate herbivore 241 Hong, Lan; Shen, Hao; Ye, Wanhui; Cao, Honglin; Wang, Zhangming 2008 Secondary pollen presentation and style morphology in the invasive weed Mikania micrantha in South China journal BOTANICAL STUDIES 49 3 253 260 Mikania micrantha H.B.K. is a successful invasive weed in many parts of the world. Its reproductive biology, specifically, floral functional morphology, growth and behavior of the style during anthesis, and style morphology, was studied in an open M. micraniha Population in South China during the flowering seasons of 2004 and 2005. Floral biology was studied in detail by examining florets at different developmental stages under a dissecting microscope and a scanning electron microscope. Stigma receptivity and pollen viability was determined by MTT [3-(4,5-dimetliyltliiazol-yl)-2,5-diphenyl-2H-tetrazolium bromide] staining technique. The results show that M. micrantha is protandrous and has a secondary pollen presentation system which characterizes the family Asteraceae. Typically, tile flowering period is 6 days and can be divided into six floral stages (A, B, C, D, E and F) based on style morphology and behaviour, At the beginning of anthesis, tile style bends to break and enter the tube formed. by five fused anthers. Later, the style protrudes the anther tube and moves the pollen out from the anther. During anthesis, two partially overlapping phases, functionally male phase and functionally female phase, can be distinguished. by MTT tests: the former is from stage B to D, and the latter is stage E. The style has two style branches in its terminal part. The sweeping hairs, which act as pollen presenter, are located on the tips and on the upper parts of the style branches forming developed stylar appendages. The stigmatic papillae are separated into two ventro-niarginal bands along each style branch in symmetric arrangement. Tile bending behavior of the style and the sweeping hairs play an important role in presenting pollen to pollinator. Web of Science Mikania micrantha China Guangdong Province Dongguan City Field - Observational terrestrial Old Field Invasion Hyp. Inherent Superiority primary 247 Hull-Sanders, Helen M.; Johnson, Robert H.; Owen, Heather A.; Meyer, Gretchen A. 2009 EFFECTS OF POLYPLOIDY ON SECONDARY CHEMISTRY, PHYSIOLOGY, AND PERFORMANCE OF NATIVE AND INVASIVE GENOTYPES OF SOLIDAGO GIGANTEA (ASTERACEAE) journal AMERICAN JOURNAL OF BOTANY 96 4 762 770 The role of polyploidy in facilitating invasiveness of introduced plants has not been well explored. Examination of traits of diploid and polyploid plants in both their native and introduced ranges can shed light on evolutionary processes occurring post-introduction in invasive plants. We determined the distribution and prevalence of cytotypes of Solidago gigantea in both its native range (USA) and introduced range (Europe). and measured a suite of biochemical, physiological, and reproductive characters for plants from both continents. Tetraploids were the most frequent cytotype encountered on both continents, while hexaploids were found only in the USA. Hexaploids were the most distinctive cytotype. with fewer differences observed between diploids and tetraploids. Comparison of diploids and tetraploids in the USA and Europe showed that traits changed in concert for both cytotypes. Both diploids and tetraploids in Europe had reduced concentrations of three classes of secondary chemical and invested relatively more into rhizomes than into flowers. The same changes occurring in both cytotypes in the introduced range show that altered phenotypes of European plants are not due to Shifts in the proportions of cytotypes but instead occur within them. There was no evidence that polyploids evolve more quickly in the introduced range. Web of Science Solidago gigantea United States Wisconsin University of Wisconsin-Milwaukee Field Station 43.386899 -88.020744 Garden terrestrial Invasion Hyp. Inherent Superiority Superior Competitor primary 252 Isermann, Maike 2008 Classification and habitat characteristics of plant communities invaded by the non-native Rosa rugosa Thunb. in NW Europe journal PHYTOCOENOLOGIA 38 2 133 150 The Japanese Rose (Rosa rugosa) an invasive neophyte in Europe, builds LIP large dominant shrublands especially in coastal areas. To describe the vegetation invaded by R. rugosa 383 releves out of NW Europe with R. rugosa were collected from literature and from vegetation databases. Different plant communities were evaluated by TWINSPAN classification, and two main groups were distinguished: wood- and Shrublands, grass- and heathlands. Rosa rugosa builds up dominant stands that are assigned to the corresponding higher syntaxon. The main variation in vegetation composition Was Studied with a Detrended Correspondence Analysis and related to Ellenberg indicator values. Furthermore, Ellenberg indicator values were used to compare the environmental conditions in different plant communities containing Rosa rugosa. Environmental conditions changed with the development and spread of R. rugosa. Effects of R. rugosa Invasion on species richness of different lifeform groups, native species and neophytes were analysed. The study shows, that the expansion of R. rugosa changes the species composition of the invaded vegetation. Species richness, especially of herbaceous plants, decreased with increasing cover of R. rugosa. Furthermore, Rosa dominated plots have a higher percentage number of neophytes and a lower percentage number of native species than the corresponding not invaded plant communities. In comparison to its native range, R. rugosa establishes In various plant communities, at a wide range of environmental conditions. Therefore it appears that the shrub has a broader environmental niche in its new range. According to the presented environmental gradient, moderate conditions of nutrients, soil pH and water content, and both lighter and dryer sites were preferred. Considering environmental requirements, open dry grasslands as well as heathlands especially with bare patches arc probably very endangered by R. rugosa invasion. Web of Science Rosa rugosa NW Europe Field - Observational;Statistical/Meta-analysis terrestrial Grassland;Deciduous Forest;Chaparral/Shrublands Impacts;Invasion Hyp. Inherent Superiority Broad Tolerances primary 256 James, J. J. 2008 Leaf nitrogen productivity as a mechanism driving the success of invasive annual grasses under low and high nitrogen supply journal JOURNAL OF ARID ENVIRONMENTS 72 10 1775 1784 Invasion of the historically perennial-dominated landscapes in the Great Basin by exotic winter annual grasses is one of the most serious plant invasions in North America. Evidence suggests invasive annuals outperform native perennials under N-poor and N-rich conditions. The objective of this study was to identify key traits contributing to the success of invasive annual grasses in these environments. Three invasive annual grasses, two native perennial grasses and one introduced perennial grass were exposed to three levels of N supply. Root biomass, root length, root N uptake rate, root and leaf morphology, leaf nitrogen productivity (leaf NP) as well as biomass and N allocation were quantified over four harvests. Path analysis indicated that leaf NP was the key trait contributing to variation in N capture among the species. Species with a higher leaf NP produced more root length and consequently captured more N under a range of soil N availability. This suggests variation in leaf NP may be one critical trait determining the ability of the resident plant community to resist establishment of these invaders. Restoration programs may be able to increase weed resistance by specifically selecting for this trait in revegetation efforts. Published by Elsevier Ltd. Web of Science Many United States Oregon Eastern Oregon Agricultural Research Center, Burns 43.592328 -119.055061 Field - Experimental terrestrial Invasion Hyp. Inherent Superiority Superior Competitor primary 257 James, J. J.; Mangold, J. M.; Sheley, R. L.; Svejcar, T. 2009 Root plasticity of native and invasive Great Basin species in response to soil nitrogen heterogeneity journal PLANT ECOLOGY 202 2 211 220 Soil nutrients are heterogeneously distributed in natural systems. While many species respond to this heterogeneity through root system plasticity, little is known about how the magnitude of these responses may vary between native and invasive species. We quantified root morphological and physiological plasticity of co-occurring native and invasive Great Basin species in response to soil nitrogen heterogeneity and determined if trade-offs exist between these foraging responses and species relative growth rate or root system biomass. The nine study species included three perennial bunchgrasses, three perennial forbs, and three invasive perennial forbs. The plants were grown in large pots outdoors. Once a week for 4 weeks equal amounts of (NH4)-N-15 (NO3)-N-15 were distributed in the soil either evenly through the soil profile, in four patches, or in two patches. All species acquired more N in patches compared to when N was applied evenly through the soil profile. None of the species increased root length density in enriched patches compared to control patches but all species increased root N uptake rate in enriched patches. There was a positive relationship between N uptake rate, relative growth rate, and root system biomass. Path analysis indicated that these positive interrelationships among traits could provide one explanation of how invasive forbs were able to capture 2 and 15-fold more N from enriched patches compared to the native grasses and forbs, respectively. Results from this pot study suggest that plant traits related to nutrient capture in heterogeneous soil environments may be positively correlated which could potentially promote size-asymmetric competition belowground and facilitate the spread of invasive species. However, field experiments with plants in different neighbor environments ultimately are needed to determine if these positive relationships among traits influence competitive ability and invader success. Web of Science Many USA Oregon Garden terrestrial Grassland Invasion Hyp. Inherent Superiority Superior Competitor;Rapid Growth primary 259 Jarchow, Meghann E.; Cook, Bradley J. 2009 Allelopathy as a mechanism for the invasion of Typha angustifolia journal PLANT ECOLOGY 204 1 113 124 Web of Science Typha angustifolia United States Minnesota Greenhouse terrestrial Invasion Hyp. Inherent Superiority Superior Competitor primary 260 Jiang, Li-Fen; Luo, Yi-Qi; Chen, Jia-Kuan; Li, Bo 2009 Ecophysiological characteristics of invasive Spartina alterniflora and native species in salt marshes of Yangtze River estuary, China journal ESTUARINE COASTAL AND SHELF SCIENCE 81 1 74 82 Biological invasions represent one of the significant components of global change. A comparative study of invaders and co-occurring natives is a useful approach to gaining insights into the invasiveness of exotic plants. Spartina alterniflora, a C-4 grass, is a widespread invader in the coastal wetlands in China and other regions of the world. We conducted a comparative study of S. alterniflora and native C-3 species, Phragmites australis and Scirpus mariqueter, in terms of their gas exchange and efficiencies in resource utilization. We tested the hypothesis that S. alterniflora has growth-related ecophysiological advantages over the natives in its non-native range, which result in its rapid growth and enhance its invasiveness. Photosynthesis, leaf area index (LAI), specific leaf area (SLA), and the efficiency of resource use (light, water, and nitrogen) were examined monthly for eight months in 2004. Overall, S. alterniflora had greater LAI, higher maximal net photosynthetic rate (Amax), and longer growing season than those of the native species. On average, the efficiencies of S. alterniflora in light, water, and nitrogen utilization were respectively 10.1%, 26.1%, and 33.1% higher than those of P. australis, and respectively 70.3%, 53.5%, 28.3% higher than those of S. mariqueter. However, SLA of S. alterniflora was significantly lower than those of P. australis and S. mariqueter. Although there was no general pattern in the relationship between invasiveness and plant photosynthetic types, in this study, most of the ecophysiological characteristics that gave S. alterniflora a competitive advantage in the Yangtze River estuary were associated with photosynthetic pathways. Our results offer a greater understanding of the relationship between invasiveness and plant photosynthetic type. Our results also indicate that LAI and the length of the photosynthetic season, which vary with habitats, are also important in invasion success. (C) 2008 Elsevier Ltd. All rights reserved. Web of Science Spartina alterniflora China Jiuduansha Islands 31.13 121.58 Field - Observational wetland Invasion Hyp. Inherent Superiority Rapid Growth primary 263 Johnson, Pieter T. J.; Olden, Julian D.; vander Zanden, M. Jake 2008 Dam invaders: impoundments facilitate biological invasions into freshwaters journal FRONTIERS IN ECOLOGY AND THE ENVIRONMENT 6 7 359 365 Freshwater ecosystems are at the forefront of the global biodiversity crisis, with more declining and extinct species than in terrestrial or marine environments. Hydrologic alterations and biological invasions represent two of the greatest threats to freshwater biota, yet the importance of linkages between these drivers of environmental change remains uncertain. Here, we quantitatively test the hypothesis that impoundments facilitate the introduction and establishment of aquatic invasive species in lake ecosystems. By combining data on boating activity water body physicochemistry, and geographical distribution of five nuisance invaders in the Laurentian Great Lakes region, we show that non-indigenous species are 2.4 to 300 times more likely to occur in impoundments than in natural lakes, and that impoundments frequently support multiple invaders. Furthermore, comparisons of the contemporary and historical landscapes revealed that impoundments enhance the invasion risk of natural lakes by increasing their proximity to invaded water bodies, highlighting the role of human-altered ecosystems as 'stepping-stone' habitats for the continued spread of freshwater invaders. Web of Science Myriophyllum spicatum; Dreissena polymorpha; Bythotrephes longimanus; Osmerus mordax; Orconectes rusticus USA Wisconsin 45.341335 -88.487549 Field - Observational lentic Invasion Hyp. Disturbance herbivore;omnivore;filter 264 Jones, Julia P. G.; Rasamy, Jeanne R.; Harvey, Andrew; Toon, Alicia; Oidtmann, Birgit; Randrianarison, Michele H.; Raminosoa, Noromalala; Ravoahangimalala, Olga R. 2009 The perfect invader: a parthenogenic crayfish poses a new threat to Madagascar's freshwater biodiversity journal BIOLOGICAL INVASIONS 11 6 1475 1482 In 2007 an unusual crayfish found in food markets in the capital of Madagascar was preliminarily identified as Procambarus 'Marmorkrebs': a new world taxa and the only decapod known to reproduce by parthenogenesis. We present information on the identity, distribution and ecology of this recent invader and attempt to evaluate the threat it poses to Madagascar's biodiversity and to livelihoods. The species appears to be currently limited to the area close to Antananarivo, but is being sold alive on major transport routes. We present molecular evidence of its taxonomic relationships and confirm that the Procambarus present in Madagascar is indeed the parthenogenic taxa. We investigate its reproductive ecology and find Procambarus 'Marmorkrebs' to have an extremely high fecundity; more than six times that of the native crayfish Astacoides. The limited evidence we have suggests that this species poses a serious threat to freshwater biodiversity and that it is likely to damage human livelihoods (through its impact on fishing and possibly rice agriculture). More research is urgently needed but in the meantime action is needed to reduce the rate of spread before it is too late. Web of Science Procambarus 'Marmorkrebs' Madagascar Antananarivo Field - Observational lentic Riparian Invasion Hyp. Inherent Superiority Rapid Growth;High Reprod. Output omnivore 266 Jorgensen, Rasmus Halfdan; Kollmann, Johannes 2009 Invasion of coastal dunes by the alien shrub Rosa rugosa is associated with roads, tracks and houses journal FLORA 204 4 289 297 Mapping the distribution of invasive alien plant species is significant for testing ecological hypotheses and for guiding effective management. Little is known about the distribution of invasive plants at landscape scale, and the factors controlling their dispersal and establishment are still poorly understood. This is the case for Rosa rugosa, an invasive shrub with negative effects on biodiversity in dune ecosystems of NW Europe. The aim of the study was to identify the factors which determine the distribution of R rugosa in coastal dunes. In a large semi-natural dune area of NW Denmark (2364 ha) all patches of the species (1321, 1.3-59.1 m(2)) were GPS mapped. Patch distribution was GIS analysed, based on aerial photographs and vegetation maps. The distance of R. rugosa from the most conspicuous landscape elements was compared with randomly placed reference points. The species had invaded 0.35% of the dune landscape, and it was present in all vegetation types and all parts of the study area. Rosa rugosa patches were slightly smaller in grey dunes than in white dunes and brown dunes, and some of the largest patches were found close to villages. The occurrence of the shrub was positively correlated with distance to the coastline, to roads, tracks and houses. We conclude that the distribution of R rugosa is determined by both natural and anthropogenic factors. It is further discussed how these factors may control dispersal and establishment of the species, and how the results can be used for improved management of coastal dunes. (C) 2008 Elsevier GmbH. All rights reserved. Web of Science Rosa rugosa Denmark 57.06 8.35 Field - Observational terrestrial Invasion Hyp. Propagule Pressure;Disturbance primary 269 Kalwij, Jesse M.; Robertson, Mark P.; van Rensburg, Berndt J. 2008 Human activity facilitates altitudinal expansion of exotic plants along a road in montane grassland, South Africa journal APPLIED VEGETATION SCIENCE 11 4 491 498 Question: Do antropogenic activities facilitate the distribution of exotic plants along steep altitudinal gradients? Location: Sani Pass road. Grassland biome, South Africa. Methods: On both sides of this road. presence and abundance of exotic plants was recorded in four 25-m long road-verge plots and in parallel 25 m x 2 m adjacent land plots, nested at five altitudinal levels: 1500, 1800, 2100, 2400 and 2700 in a.s.l. Exotic community structure was analyzed using Canonical Correspondence Analysis while a two-level nested Generalized Linear Model was fitted for richness and cover of exotics. We tested the upper altitudinal limits tor all exotics along this road for spatial clustering around four potential propagule sources Using a t-test. Results: Community structure, richness and abundance of exotics were negatively correlated with altitude. Greatest invasion by exotics was recorded for adjacent land at the 1500 in level. Of the 45 exotics, 16 were found at higher altitudes than expected and observations were spatially clustered around potential propagule sources. Conclusions: Spatial clustering of upper altitudinal limits around human inhabited areas suggests that exotics originate from these areas, while exceeding expected altitudinal limits suggests that distribution ranges of exotics are presently underestimated. Excites are generally characterised by a high propagule pressure and/or persistent seedbanks, thus future tarring of the Sani Pass may result in art increase of exotic species richness and abundance. This would initially result from construct ion-related soil disturbance and subsequently from increased traffic. water run-off, and altered fire frequency. We suggest examples of management actions to prevent this. Web of Science Many South Africa Ukhahlamba-Drakensberg Park -29.1739 29.3539 Field - Observational terrestrial Invasion Hyp. Disturbance primary 270 Kandori, Ikuo; Hirao, Toshihiro; Matsunaga, Satoshi; Kurosaki, Tsutomu 2009 An invasive dandelion unilaterally reduces the reproduction of a native congener through competition for pollination journal OECOLOGIA 159 3 559 569 The impact of invasive alien species on native species is of increasing global concern. Invasive plants have various negative effects on natives through competition; however, relatively little is known about competition for pollination. The relationship between Japanese native dandelions (Taraxacum spp.) and invasive congeners may be a typical case of such an interaction. For example, native dandelions are being replaced by invasive congeners, especially in urban and suburban areas of Japan. To explain this phenomenon, we hypothesized that when natives are mixed with attractive invasives, natives may suffer from reduced seed set because invasives deprive natives of pollinators or because pollinators frequently move between species, resulting in interspecific pollen transfer. To test this hypothesis, we studied the effect of the invasive dandelion T. officinale on the pollination and seed set of the native T. japonicum using artificial arrays of monospecific and mixed-species plots as well as natural populations. Taraxacum officinale attracted more pollinator visits, perhaps because it produced more nectar than T. japonicum. The number of pollinator visits to T. japonicum was reduced when the congeners were grown together, and pollinators moved frequently between the two species. The proportion of seed set for T. japonicum was reduced in the presence of T. officinale in both artificial arrays and natural populations. These results support our hypothesis that interspecific competition for pollination plays an important role in the recent replacement of native dandelions by invasive congeners in Japan. Because invasive dandelions are apomicts, negative effects are incurred only by sexual natives. Thus, this system can be recognized as a rare case of interspecific interaction through pollination. Web of Science Taraxacum officinale Japan Nara Prefecture; Osaka Prefecture; Kyoto Prefecture Field - Experimental;Field - Observational terrestrial Urban Invasion Hyp. Mutualism Facilitation;Inherent Superiority;Other Effective Disperser primary 273 Kawakami, Kazuto; Mizusawa, Leiko; Higuchi, Hiroyoshi 2009 Re-established mutualism in a seed-dispersal system consisting of native and introduced birds and plants on the Bonin Islands, Japan journal ECOLOGICAL RESEARCH 24 4 741 748 Web of Science Zosterops japonicus Japan Bonin Islands 26.61 142.16 Field - Observational terrestrial Deciduous Forest Impacts;Fundamentals primary;herbivore 279 King, Joshua R.; Tschinkel, Walter R.; Ross, Kenneth G. 2009 A case study of human exacerbation of the invasive species problem: transport and establishment of polygyne fire ants in Tallahassee, Florida, USA journal BIOLOGICAL INVASIONS 11 2 373 377 Understanding how exotic invasive species are spread is fundamental for ecology and conservation biology. Human transport has become one of the primary modes of dispersal for exotic species. We examined how the multiple queen, or polygyne, social form of the fire ant Solenopsis invicta is spread along roadsides in Tallahassee, Florida, USA. We then determined the likely source of this expanding population, which was a central soil depot. A survey of road maintenance practices in counties of several southeastern states and Texas revealed that the use of a central soil depot is a common practice. Road maintenance therefore may be the primary source for the establishment of new polygyne fire ant populations in this region and elsewhere. Control efforts focused on the soil depots will help to limit further spread of polygyne fire ants and perhaps other invasive organisms, particularly invasive weeds. Web of Science multiple queen, or polygyne, social form of the fire ant Solenopsis invicta United States Florida Tallahassee 30.403675 -84.347878 Field - Observational terrestrial Coniferous Forest;Urban Invasion Hyp. Disturbance herbivore 280 Kinzler, Werner; Kley, Axel; Mayer, Gerd; Waloszek, Dieter; Maier, Gerhard 2009 Mutual predation between and cannibalism within several freshwater gammarids: Dikerogammarus villosus versus one native and three invasives journal AQUATIC ECOLOGY 43 2 457 464 Dikerogammarus villosus, a Ponto-Caspian species, is known to be a particularly successful invader, and is currently the prevailing invasive gammarid in Southern German large waters. Field observations suggest that D. villosus has replaced the native G. pulex and the invasive D. haemobaphes, also a Ponto-Caspian species, in some reaches of the German Danube. Dikerogammarus villosus is also believed to be the reason why Echinogammarus berilloni, a Mediterranean species, and Dikerogammarus bispinosus, a further Ponto-Caspian gammaridean species, could not build significant populations in Southern German rivers. Because intraguild predation (IGP) is regarded as a major force leading to species displacements, we hypothesized that superiority in predation by D. villosus is responsible for the disappearance or limited occurrence of several native and invasive gammarideans in many reaches of Southern German waters. To test this hypothesis, we conducted a series of laboratory IGP experiments with 1:1 combinations in which D. villosus was allowed to prey on other gammarids and vice versa. We also studied the extent of cannibalism within species. Dikerogammarus villosus was a stronger predator than G. pulex and E. berilloni. However, D. villosus was not stronger in predation than its relatives D. haemobaphes and D. bispinosus, although results with the combinations of D. villosus and D. bispinosus were less conclusive, especially in the female-female combination. Cannibalism rate was high in D. haemobaphes compared with other species. We conclude that superiority in IGP experiments could explain the disappearance of G. pulex and the missing or limited occurrence of E. berilloni since the arrival of D. villosus in Southern German rivers. However, the results of IGP experiments do not explain why D. haemobaphes was displaced by D. villosus in many places and why D. bispinosus could not build significant populations in Southern German waters. Possibly specific combinations between mutual predation and cannibalism or factors other than predation could have affected displacement and occurrence patterns of Dikerogammarus species in Southern German waters. Web of Science Dikerogammarus villosus Germany Danube near Deggendorf, Isar mouth 48.830374 12.941895 Lab lotic Invasion Hyp. Inherent Superiority Superior Competitor predator 282 Knight, Tiffany M.; Dunn, Jessica L.; Smith, Lisa A.; Davis, JoAnn; Kalisz, Susan 2009 Deer Facilitate Invasive Plant Success in a Pennsylvania Forest Understory journal NATURAL AREAS JOURNAL 29 2 110 116 Invasive species impose severe biological and economic costs worldwide. In forested ecosystems, invasive species supplant native species, resulting in decreased biodiversity. Furthermore, human-mediated disturbances may stress native forest species and benefit invasive species that thrive in disturbed habitats. Anthropogenic changes to the landscape have caused unprecedented increases in white-tailed deer (Odocoileus virginianus) numbers, which has resulted in the degradation of understory native plant communities. We suggest that deer-mediated disturbance to understory communities facilitates the success of invaders in forests, Many North American forests experience both exotic plant invasion and deer overabundance, but the two problems have never been empirically linked. In this paper, we quantify deer effects on native and exotic understory herbs in a western Pennsylvania forest. We show that the percentage of bare ground and the relative abundances of the invasive herbs, Alliaria petiolata and Microstegium vimineum are significantly greater, while native plants are significantly smaller with a lower proportion flowering in deer access vs. deer exclusion plots. Our data support the idea that invader success is due in part to both preferential foraging by deer on native herbs that reduces their size and flowering status and the creation of open patches when deer are present. We conclude that deer overabundance facilitates the success of invasive species in forested ecosystems and that management will benefit by considering these factors jointly. Web of Science Alliaria petiolata; Microstegium vimineum United States Pennsylvania Allegheny County 40.8671 -80.503 Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 292 Kueffer, Christoph; Kronauer, Lilian; Edwards, Peter J. 2009 Wider spectrum of fruit traits in invasive than native floras may increase the vulnerability of oceanic islands to plant invasions journal OIKOS 118 9 1327 1334 Web of Science Many Republic of Seychelles Mahe -4 55 Field - Observational terrestrial Subtropical Forest Invasion Hyp. Mutualism Facilitation primary 296 Kyle, G. Page; Kulmatiski, Andrew; Beard, Karen H. 2008 INFLUENCE OF POCKET GOPHER MOUNDS ON NONNATIVE PLANT ESTABLISHMENT IN A SHRUBSTEPPE ECOSYSTEM journal WESTERN NORTH AMERICAN NATURALIST 68 3 374 381 Soil disturbances across a wide range of spatial scales have been found to promote the establishment of invasive plant species. This study addresses whether mounds built by northern pocket gophers (Thomomys talpoides) in the shrubsteppe environment 4 north central Washington are facilitating plant invasions into native-dominated fields. Research was conducted in native-dominated plant communities adjacent to ex-arable, nonnative-dominated fields. To determine the effect of mounds on plant growth, we recorded new establishment and persistence of all plant species over 2 growing seasons on 10-19 mound and intermound areas in 10 fields. Normative plant establishment was not affected by mounds, but native plant establishment, particularly of the dominant native Pseudoroegneria spicata was lower on mounds than on intermounds. Early in the growing season, mounds had reduced soil moisture, bulk density, soil strength, N mineralization rates, and total N and C concentrations, and similar extractable NO3- concentrations relative to intermound soils. Our results did not suggest that soil disturbance improved normative growth resulting in competitive suppression of natives; rather, our results suggested that low soil moisture and slow N mineralization rates on mounds in this ecosystem present relatively stressful conditions for native plant growth. Web of Science Many United States Washington Methow Valley 48.37 -107.1 Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Disturbance primary 298 Lach, Lori; Hobbs, Richard J.; Majer, Jonathan D. 2009 Herbivory-induced extrafloral nectar increases native and invasive ant worker survival journal POPULATION ECOLOGY 51 2 237 243 Ascertaining the costs and benefits of mutualistic interactions is important for predicting their stability and effect on community dynamics. Despite widespread designation of the interaction between ants and extrafloral nectaries (EFNs) as a mutualism and over 100 years of studies on ant benefits to plants, the benefits to ants have never been experimentally quantified. The success of invasive ants is thought to be linked to the availability of carbohydrate-rich resources, though reports of invasive ant visits to EFNs are mixed. In two laboratory experiments, we compared worker survival of one native (Iridomyrmex chasei) and two invasive ant species (Linepithema humile and Pheidole megacephala) exposed to herbivorized or non-herbivorized EFN-bearing plants (Acacia saligna) or positive and negative controls. We found that non-herbivorized plants did not produce any measurable extrafloral nectar, and ants with access to non-herbivorized plants had the same survival as ants with access to an artificial plant and water (unfed ants). Ants given herbivorized plants had 7-11 times greater worker survival relative to unfed ants, but there were no differences in survival between native and invasive ants exposed to herbivorized plants. Our results reveal that ants cannot induce A. saligna extrafloral nectar production, but workers of both native and invasive ant species can benefit from extrafloral nectar as much as they benefit from sucrose. Web of Science Linepithema humile; Pheidole megacephala Australia Lab terrestrial Invasion Hyp. Mutualism Facilitation herbivore 299 Lai, Zhao; Kane, Nolan C.; Zou, Yi; Rieseberg, Loren H. 2008 Natural variation in gene expression between wild and weedy populations of Helianthus annuus journal GENETICS 179 4 1881 1890 The molecular genetic changes underlying the transformation of wild plants into agricultural weeds are poorly understood. Here we use a sunflower cDNA microarray to detect variation in gene expression between two wild (non-weedy) Helianthus annuus populations from Utah and Kansas and four weedy H. annuus populations collected from agricultural fields in Utah, Kansas, Indiana, and California. When grown in a common growth chamber environment, populations differed substantially in their gene expression patterns, indicating extensive genetic differentiation. Overall, 165 uni-genes, representing similar to 5% of total genes on the array, showed significant differential expression in one or more weedy populations when compared to both wild populations. This subset of genes is enriched for abiotic/biotic stimulus and stress response proteins, which may underlie niche transitions from teh natural sites to agricultural fields for H. annuus. However, only a small proportion of the differentially expressed genes overlapped in multiple wild vs. weedy comparisons, indicating that most of the observed expression changes are due to local adaptation or neural processes, as opposed to parallel genotypic adaptation to agricultural fields. These results are consistent with an earlier phylogeographic study suggesting that weedy sunflowers have evolved multiple times in different regions of the United States and further indicate that the evolution of weedy sunflowers has been accompained by substantial gene expression divergence in different weedy populations. Web of Science Helianthus annuus United States Utah; Kansas Lab terrestrial Old Field Invasion Hyp. Evolution in General primary 300 Lambdon, Philip W.; Lloret, Francisco; Hulme, Philip E. 2008 How do introduction characteristics influence the invasion success of Mediterranean alien plants? journal PERSPECTIVES IN PLANT ECOLOGY EVOLUTION AND SYSTEMATICS 10 3 143 159 Invasive plant species are becoming increasingly widespread following accelerated anthropogenic activity in the Mediterranean region. Humans have played a central role in the expansion process, and it is important to incorporate such considerations into management plans. Using generalized linear models, our first aim was to describe how the invasion success of 862 prominent alien plant species on Mediterranean islands is related to characteristics of the introduction process: introduction frequency, date and region of origin, range size and purpose of import. The importance of each was measured by the numbers of species present and their average invasiveness. The main findings were: (a) accidental imports and ornamentals accounted for a high proportion of all aliens, although neither group had particularly high average invasiveness; (b) introduction frequency had a comparatively modest influence, with the most commonly-introduced species naturalized only three times more widely than those rarely-introduced; (c) rates of species introduction appear to have increased dramatically in the last century, although aliens which have been present in the region for more than 200 years were most widespread, indicating that it may be centuries before some species fill their potential range; (d) there were small tendencies for successful invaders to originate in the Neotropics or in regions with Mediterranean climate biomes and to have large range sizes. Our second aim was to determine whether the number or average invasiveness of species introduced via a given pathway had the most influence on the overall probability of invasion on a given island. An elasticity analysis suggested that the number of species was substantially the best predictor of the two. This finding arises largely because invasion events are rare and remain unpredictable, and has significant implications for assessing invasion risk. We discuss how substantial sources of error and intrinsic variability in invasiveness within species groups limit the potential for developing accurate risk models. (C) 2008 Rubel Foundation, ETH Zurich. Published by Elsevier GmbH. All rights reserved. Web of Science Many Mediterranean Region Statistical/Meta-analysis terrestrial Invasion Hyp. Propagule Pressure;Other primary 303 Lardies, Marco A.; Bozinovic, Francisco 2008 Genetic variation for plasticity in physiological and life-history traits among populations of an invasive species, the terrestrial isopod Porcellio laevis journal EVOLUTIONARY ECOLOGY RESEARCH 10 5 747 762 Background: Evolutionary interpretations of life-history as well as physiological patterns require distinction between genotypic variations and environmentally induced phenotypic variation. Problem: We investigate the extent to which variation in life history and metabolism have an environmental or a genetic basin in an invasive species. Methods: We used the widely distributed isopod, Porcellio laevis, as a model. To examine the effects of latitudinal gradients in temperature and photoperiod on life-history and physiological traits, we studied three populations located along a latitudinal gradient. We performed two common garden experiments using 20 families from each population. Treatment were: (1) 12 degrees C. 12/12 h light/dark and (2) 20 degrees C, 14/10 h light/dark. Measurements of metabolic rate and life-history traits were performed on females from the F-1 generation. Conclusions: (1) Differences in life-history and metabolic traits among populations mimic the natural pattern of latitudinal variation in a cold environment, where offspring size and reproductive output increase towards higher latitudes and metabolic rate increases towards lower latitudes. (2) There is genetic variation for plasticity in response to the environment, which may be acted upon by natural selection. (3) Our results support the hypothesis that phenotypic plasticity itself is an adaptive response to environmental heterogeneity. Web of Science Porcellio laevis Chile -23.6333;-29.9167;-33.3833 -70.4333;-71.25;-70.7 Lab terrestrial Fundamentals decomposer 305 Laungani, Ramesh; Knops, Johannes M. H. 2009 Species-driven changes in nitrogen cycling can provide a mechanism for plant invasions journal PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 106 30 12400 12405 Web of Science Pinus strobus United States Minnesota Cedar Creek Ecosystem Science Reserve 45.4 -93.2 Garden terrestrial Grassland;Deciduous Forest Invasion Hyp. Inherent Superiority primary 306 Le Cam, Sabrina; Pechenik, Jan A.; Cagnon, Mathilde; Viard, Frederique 2009 Fast versus Slow Larval Growth in an Invasive Marine Mollusc: Does Paternity Matter? journal JOURNAL OF HEREDITY 100 4 455 464 Web of Science Crepidula fornicata France Brittany Bay of Morlaix 48.66 -3.88 Field - Observational;Lab marine Benthic Invasion Hyp. Inherent Superiority Rapid Growth;Effective Disperser filter 309 Lelong, Benjamin; Lavoie, Claude; Theriault, Marius 2009 What are the factors that facilitate the implementation of the common reed (Phragmites australis) along roads in Southern Quebec? journal ECOSCIENCE 16 2 224 237 Web of Science Phragmites australis Canada Quebec Field - Observational terrestrial Old Field Invasion Hyp. Disturbance;Other primary 313 Leunda, P. M.; Oscoz, J.; Elvira, B.; Agorreta, A.; Perea, S.; Miranda, R. 2008 Feeding habits of the exotic black bullhead Ameiurus melas (Rafinesque) in the Iberian Peninsula: first evidence of direct predation on native fish species journal JOURNAL OF FISH BIOLOGY 73 1 96 114 The feeding ecology of the exotic invasive black bullhead Ameiurus melas was conducted in the Iberian Peninsula for the first time. Dietary analysis based on the stomach contents of individuals caught in several Iberian basins was carried out as a first step to evaluate its potential threat for the native Iberian ichthyofauna. Aquatic macroinvertebrates (mainly Chironomidae) dominated the black bullhead's diet in all size-classes and sites, irrespective of natural riverine or artificial lentic habitats. Secondary prey items were responsible for the observed between-sites (microcrustaceans in artificial lentic habitat; oligochaeta and caddisfly larvae in natural riverine habitats) and ontogenetic diet differences (from microcrustaceans to larger prey). These diet variations were also detected in trophic diversity values and feeding strategy plots. Black bullheads consumed plant material, terrestrial prey and co-occurring fish species (native or exotic) and thus they could be considered as generalist or opportunistic, foraging on the most abundant and available prey. There was no positive relationship between black bullhead size (total length) and fish prey size, probably indicating piscivory on dead or dying vulnerable fishes as well as predation on smaller-sized active fishes. The results showed that the black bullhead could negatively affect native Iberian ichthyofauna throughout direct predation and competition. Aspects of potential conservation and management implications of fishes resulting from the undesirable presence of the black bullhead in Iberian water bodies are discussed. (c) 2008 The Authors Journal compilation (c) 2008 The Fisheries Society of the British Isles. Web of Science Ameiurus melas Spain Lab lotic Pelagic/Open Ocean Impacts;Invasion Hyp. Inherent Superiority Broad Tolerances;High Reprod. Output predator 320 Lilleskov, Erik A.; Mattson, William J.; Storer, Andrew J. 2008 Divergent biogeography of native and introduced soil macroinvertebrates in North America north of Mexico journal DIVERSITY AND DISTRIBUTIONS 14 6 893 904 To improve understanding of the biogeographical consequences of species introduction, we examined whether introduced soil macroinvertebrates differ from natives in the relationship between species richness and key environmental predictors, and whether such differences affect the relationship between native and introduced species richness. For North America north of Mexico, we summarized jurisdiction occurrence data for seven macroinvertebrate taxa with strong influences on soil biodiversity or processes. We analysed the relationships of native and introduced species richness to each other using linear regression; to latitude using Gaussian regressions; and, using the residuals of the richness-latitude regressions, to distance from coasts, human population density, and human population size using regression and correlation. We found weak to strong positive relationships between native and introduced species richness. This variation was related to divergent relationships of native and introduced species with latitude, human population density, and distance from coasts. Native species richness declined with increasing latitude for all taxa, as did introduced species richness for taxa with predominantly lower-latitude origins (ants, termites, non-lumbricid earthworms). In contrast, introduced species richness peaked at higher latitudes for four taxa of predominantly Palearctic origins (weevils, ground beetles, lumbricid earthworms, isopods). Partitioning introduced taxa within these groups based on region of origin, we found that Palearctic taxa were distributed at higher latitudes than non-Palearctic taxa. Thus source region appears to strongly influence introduced species richness-latitude relationships. Compared to natives, introduced species exhibited more positive relationships with human population density and negative relationships with distance from coasts, but did not differ in relationships with human population size. Thus coastal, densely populated regions are likely to have a higher proportion of introduced soil macroinvertebrate species. These differences between distribution of native and introduced species tend to weaken positive correlations between native and introduced species richness, especially for taxa dominated by Palearctic introductions. Web of Science Many USA; Canada Field - Observational terrestrial Invasion Hyp. Community Species Richness herbivore;omnivore;decomposer 321 Lilley, Patrick L.; Vellend, Mark 2009 Negative native-exotic diversity relationship in oak savannas explained by human influence and climate journal OIKOS 118 9 1373 1382 Web of Science Many Canada British Columbia Vancouver Island 48.0017 -123.0006 Field - Observational terrestrial Savanna Invasion Hyp. Community Species Richness;Preadaptation to Climate;Disturbance primary 322 Linnebjerg, Jannie F.; Hansen, Dennis M.; Olesen, Jens M. 2009 Gut passage effect of the introduced red-whiskered bulbul (Pycnonotus jocosus) on germination of invasive plant species in Mauritius journal AUSTRAL ECOLOGY 34 3 272 277 In Mauritius, many of the worst invasive plant species have fleshy fruits and rely on animals for dispersal. The introduced red-whiskered bulbul (Pycnonotus jocosus) feeds on many fleshy-fruited species, and often moves from invaded and degraded habitats into higher quality native forests, thus potentially acting as a mediator of continued plant invasion into these areas. Furthermore, gut passage may influence seed germination. To investigate this, we fed fleshy fruits of two invasive plant species, Ligustrum robustum and Clidemia hirta, to red-whiskered bulbuls. Gut passage times of seeds were recorded. Gut-passed seeds were sown and their germination rate and germination success compared with that of hand-cleaned seeds, as well as that of seeds in whole fruits. Gut passage and hand-cleaning had significant positive effects on germination of both species. Gut-passed seeds of both C. hirta and L. robustum germinated faster than hand-cleaned seeds. However, for L. robustum, this was only true when compared with hand-cleaned seeds with intact endocarp; when compared with hand-cleaned seeds without endocarp, there was no difference. For overall germination success, there was a positive effect of gut passage for C. hirta, but not for L. robustum. For both C. hirta and L. robustum, no seeds in intact fruits geminated, suggesting that removal of pulp is essential for germination. Our results suggest that, first, the initial invasion of native forests in Mauritius may not have happened so rapidly without efficient avian seed dispersers like the red-whiskered bulbul. Second, the bulbul is likely to be a major factor in the continued re-invasion of C. hirta and L. robustum into weeded and restored conservation management areas. Web of Science Pycnonotus jocosus; Ligustrum robustum, Clidemia hirta Mauritius Black River Gorges National Park -20.6333 57.75 Field - Experimental terrestrial Tropical Forest Invasion Hyp. Mutualism Facilitation primary;herbivore 323 Liu, Chunhua; Yu, Dan 2009 The bud and root sprouting capacity of Alternanthera philoxeroides after over-wintering on sediments of a drained canal journal HYDROBIOLOGIA 623 1 251 256 Alternanthera philoxeroides (Mart.) Griseb. is one of many aggressive invasive plants that can grow in diverse habitats. Aquatic A. philoxeroides forms dense floating mats over the water surface. However, when water levels decrease during winter, some mats become stranded on exposed sediments and are thus exposed to air. Do the stems of these mats possess the capacity to develop new shoots during the next growing season? In this study, we examined the sprouting of sediment-stranded over-wintering mats of A. philoxeroides. Stems of the over-wintering mats were divided into three types (dry, withered, and fresh stems) depending on moisture content and were immersed in water for 4 weeks to observe the sprouting of axillary buds and roots. The results showed that withered stems yielded much more biomass than dry or fresh stems. Stem moisture content significantly affected the sprouting rate and the length growth rate of buds and roots. Dry stems lacked reproductive capacity. The sprouting rate and length growth rate of the buds and roots were higher in fresh stems than in withered stems. Furthermore, the mean values of the bud sprouting rate and the bud length growth rate were highest during the first week, i.e., most of buds sprouted within 1 week or less. Our results suggest that more than 70% (on a dry weight basis) of the stems in stranded mats possessed rapid sprouting capacity even after over-wintering on the sediment for more than 2 months. This strategy may be an adaptation to the fluctuations inherent in many aquatic habitats, and it possibly explains why A. philoxeroides can flourish even after a dry winter. Web of Science Alternanthera philoxeroides China Hubei Changgang Canal Field - Observational;Lab lentic Invasion Hyp. Inherent Superiority Broad Tolerances;Rapid Growth;Clonal Reproduction primary 324 Liu, Hong; Pemberton, Robert W. 2009 Solitary invasive orchid bee outperforms co-occurring native bees to promote fruit set of an invasive Solanum journal OECOLOGIA 159 3 515 525 Our understanding of the effects of introduced invasive pollinators on plants has been exclusively drawn from studies on introduced social bees. One might expect, however, that the impacts of introduced solitary bees, with much lower population densities and fewer foragers, would be small. Yet little is known about the potential effects of naturalized solitary bees on the environment. We took advantage of the recent naturalization of an orchid bee, Euglossa viridissima, in southern Florida to study the effects of this solitary bee on reproduction of Solanum torvum, an invasive shrub. Flowers of S. torvum require specialized buzz pollination. Through timed floral visitor watches and two pollination treatments (control and pollen supplementation) at three forest edge and three open area sites, we found that the fruit set of S. torvum was pollen limited at the open sites where the native bees dominate, but was not pollen limited at the forest sites where the invasive orchid bees dominate. The orchid bee's pollination efficiency was nearly double that of the native halictid bees, and was also slightly higher than that of the native carpenter bee. Experiments using small and large mesh cages (to deny or allow E. viridissima access, respectively) at one forest site indicated that when the orchid bee was excluded, the flowers set one-quarter as many fruit as when the bee was allowed access. The orchid bee was the most important pollinator of the weed at the forest sites, which could pose additional challenges to the management of this weed in the fragmented, endangered tropical hardwood forests in the region. This specialized invasive mutualism may promote populations of both the orchid bee and this noxious weed. Invasive solitary bees, particularly species that are specialized pollinators, appear to have more importance than has previously been recognized. Web of Science Euglossa viridissima; Solanum torvum United States Florida Field - Observational terrestrial Deciduous Forest Impacts;Invasion Hyp. Mutualism Facilitation primary;herbivore 327 Long, Jeremy D.; Trussell, Geoffrey C.; Elliman, Ted 2009 Linking invasions and biogeography: Isolation differentially affects exotic and native plant diversity journal ECOLOGY 90 4 863 868 The role of native species diversity in providing biotic resistance to invasion remains controversial, with evidence supporting both negative and positive relationships that are often scale dependent. Across larger spatial scales, positive relationships suggest that exotic and native species respond similarly to factors other than diversity. In the case of island habitats, such factors may include island size and isolation from the mainland. However, previous island studies exploring this issue examined only a few islands or islands separated by extreme distances. In this study, we surveyed exotic and native plant diversity on 25 islands separated by <15 km in Boston Harbor. Exotic and native species richness were positively correlated. Consistent with island biogeography theory, species richness of both groups was positively related to area and negatively related to isolation. However, the isolation effect was significantly stronger for native species. This differential effect of isolation on native species translated into exotic species representing a higher proportion of all plant species on more distant islands. The community similarity of inner harbor islands vs. outer harbor islands was greater for exotic species, indicating that isolation had a weaker influence on individual exotic species. These results contrast with recent work focusing on similarities between exotic and native species and highlight the importance of studies that use an island biogeographic approach to better understand those factors influencing the ecology of invasive species. Web of Science Many U.S.A. Massachusetts Boston Harbor 42.355892 -71.050884 Field - Observational terrestrial Grassland;Deciduous Forest;Wetland;Chaparral/Shrublands;Old Field;Intertidal/Near Shore Fundamentals;Invasion Hyp. Inherent Superiority Effective Disperser primary 331 Loomis, Eli S.; Fishman, Lila 2009 A CONTINENT-WIDE CLONE: POPULATION GENETIC VARIATION OF THE INVASIVE PLANT HIERACIUM AURANTIACUM (ORANGE HAWKWEED; ASTERACEAE) IN NORTH AMERICA journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 170 6 759 765 Web of Science Hieracium aurantiacum United States; Canada Lab terrestrial Invasion Hyp. Inherent Superiority Clonal Reproduction primary 333 Losure, David A.; Moloney, Kirk A.; Wilsey, Brian J. 2009 Modes of Crown Vetch Invasion and Persistence journal AMERICAN MIDLAND NATURALIST 161 2 232 242 Plant invasions have been hypothesized to proceed at the local scale (i.e., individual patch or stand) according to one of several distinct spatial patterns. However, few studies have attempted to reconstruct the patterns of perennial herbaceous plant invasions at local scales due to difficulty in determining the age of individuals. We used herb chronology to determine the ages of roots within several crown vetch patches in order to characterize the spatial age structure of these patches. Additionally, we examined both sexual and vegetative crown vetch reproduction, with regard to potential impacts on local spread and persistence, through seed bank sampling and greenhouse experiments. We found little distinct spatial age structuring in crown vetch patches, perhaps due to a lack of older roots caused by rapid ramet turnover within patches. We also found no support for the hypothesis, proposed by several land managers, that crown vetch builds up a large seed bank. However, we did find that even small fragments of crown vetch plants are capable of vegetative regeneration, which may be important in explaining this species' persistence in spite of control measures. Web of Science Coronilla varia United States Iowa 42.1333;42.1167 -94.5667;-96.4 Field - Observational terrestrial Grassland Invasion Hyp. Inherent Superiority Clonal Reproduction primary 336 Loydi, Alejandro; Martin Zalba, Sergio 2009 Feral horses dung piles as potential invasion windows for alien plant species in natural grasslands chapter PLANT ECOLOGY 201 2 471 480 Small scale disturbances could act as patches that provide sites for the colonization of competitively inferior species, promoting the establishment of non-native species in some cases. We analyzed the vegetation associated with feral horse dung piles in montane pampas grasslands in Mid-East Argentina and described the changes following their abandonment, evaluating whether dung piles act as invasion windows, allowing the entrance of alien plant species. We estimated the portion of the study area directly covered by horse manure and dung height was used to estimate the time elapsed after the abandonment of each pile. Vegetation replacement on dung piles of different ages was assessed and compared with grassland controls using discriminant analysis. We used regression analysis to look for changes in vegetation cover, species richness, species diversity and evenness in response to height (age) of the dung piles, and principal component analyses (PCA) to identify groups of plants associated with different successional stages. We compared cover of alien plant species on dung piles with grassland controls using one-way ANOVA. On average, 2.5% of the study area was covered by horse dung. Total vegetation cover, species richness, diversity and evenness increased after the piles were abandoned. Characteristic plant groups were associated with initial, middle and last phases of the studied succession. Vegetation on the dung piles significantly differed from that in grassland controls and two species were consistently associated with dung piles: the invasive Red Star Thistle, Centaurea calcitrapa, and a native grazing-intolerant grass, Nassella clarazii. Non-native species cover was also higher in dung piles than in control plots. Dung piles cover a significant portion of grassland area in our study site, produce significant changes in the vegetation and are associated with some invasive alien plants that could eventually colonize more pristine areas in the vicinity. On the other hand, they might represent refuges for palatable species, since horses seem to avoid them for grazing. Web of Science Many Argentina Ernesto Tornquist Provincial Park Field - Observational terrestrial Grassland Invasion Hyp. Fluctuating Resources;Disturbance primary 338 Lynch, Ryan L.; Chen, Hongjun; Brandt, Laura A.; Mazzotti, Frank J. 2009 Old World Climbing Fern (Lygodium microphyllum) Invasion in Hurricane Caused Treefalls journal NATURAL AREAS JOURNAL 29 3 210 215 Web of Science Lygodium microphyllum United States Florida Arthur R. Marshall Loxahatchee National Wildlife Refuge 26.502224 -80.216846 Field - Observational terrestrial Subtropical Forest Invasion Hyp. Disturbance primary 339 Lyons, Devin A.; Scheibling, Robert E. 2008 Context-dependant survival of the invasive seaweed Codium fragile ssp tomentosoides in kelp bed and urchin barren habitats off Nova Scotia journal AQUATIC BIOLOGY 2 1 17 27 This study examines the fate of the invasive alga Codium fragile ssp. tomentosoides at destructive grazing fronts of the green sea urchin Strongylocentrotus droebachiensis along the margins of algal beds and in barren grounds formed in the wake of these fronts. We monitored the first reported encounter between an urchin front and an algal bed containing C. fragile, and conducted a series of manipulative experiments at a grazing front and in a barrens habitat. Urchin density had a significant effect on survival of C. fragile. At low densities, urchin fronts were more likely to bypass the invasive alga, though urchins following behind the front eventually consumed most individuals. Urchins' preferred food, laminarian kelps, affected the survival time of C. fragile by slowing the forward propagation of the front, but did not divert urchins from consuming C. fragile. The presence of dense stands of the unpalatable macroalgae Desmarestia viridis and periods of high water temperature and wave action appeared to facilitate the survival of C. fragile by affecting urchin foraging behaviour. Our results suggest that, although urchins have the potential to exert strong control over populations of C. fragile, the outcome of interactions between the 2 species is likely to depend on their biotic and abiotic context. Web of Science Codium fragile ssp. tomentosoides Canada Novia Scotia St. Margaret’s Ba 44.35 -64.03 Field - Experimental marine Intertidal/Near Shore Invasion Hyp. Enemy Release primary 340 MacKay, James; Kotanen, Peter M. 2008 Local escape of an invasive plant, common ragweed (Ambrosia artemisiifolia L.), from above-ground and below-ground enemies in its native area journal JOURNAL OF ECOLOGY 96 6 1152 1161 1. The Enemy Release Hypothesis proposes that exotic species gain an advantage in new regions because their natural enemies are lost during invasion; however, enemy release could also occur as a result of much smaller scale movements within an invasive plant's native range, i.e. if it escapes enemies while colonizing new sites. Few studies have considered this possibility, and none has compared escape from multiple guilds of enemies. 2. We studied an invasive North American weed, Ambrosia artemisiifolia (common ragweed), to determine whether it escapes above-ground or below-ground enemies at a local scale in its native range. Exotic populations of this plant are known to have escaped above-ground enemies in Europe. 3. Experimental populations of ragweed isolated from existing populations by just 100 m experienced reduced levels of damage by invertebrate folivores and seed predators; however, there was no clear evidence that this escape led to improved performance. 4. Plants inoculated with unsterilized soil grew better than plants in sterile soil, likely reflecting a need for mycorrhizal colonization. Inoculum from ragweed populations was as beneficial as inoculum from nearby ragweed-free sites, suggesting only a small initial role for site-specific pathogens. 5. Performance declined over time when plants were serially inoculated with non-sterile soil, indicating negative feedback with the soil biota. This feedback was stronger for inocula derived from ragweed populations vs. those from nearby ragweed-free sites. 6. Seeds buried in ragweed populations were less likely to germinate subsequently than seeds buried in nearby ragweed-free sites. This difference was not reduced by treatment with fungicide; consequently, the mechanism is unclear. 7. Synthesis. These results indicate that ragweed can escape both above-ground and below-ground enemies by dispersing to new sites, resulting in reduced levels of folivory, seed predation, soil feedback and perhaps losses to seed pathogens. Although consequences often may be small, this demonstrates that enemy release can occur for native as well as exotic populations of this species, linking possible mechanisms of local spread with long-distance invasion. Web of Science Ambrosia artemisiifolia l. Canada Ontario Koffler Scientific Reserve at Jokers Hill 44.03 -79.29 Field - Experimental;Lab terrestrial Old Field Invasion Hyp. Enemy Release primary 350 Maron, John L.; Marler, Marilyn 2008 Field-based competitive impacts between invaders and natives at varying resource supply journal JOURNAL OF ECOLOGY 96 6 1187 1197 1. One line of thinking is that highly successful plant invaders achieve dominance in recipient communities via competitive superiority over natives. In contrast, it has been proposed that exotic species attain dominance not by competitive prowess but due to their colonizing abilities after disturbance. Interestingly, there have been relatively few attempts to quantify competitive effects of invaders on natives (and vice versa) in field settings. 2. We created monocultures of ten native perennial species and after two seasons of establishment we either left assemblages uninvaded or invaded them with seeds from one of three potent exotics; spotted knapweed (Centaurea maculosa), Dalmatian toadflax (Lineria dalmatica) and sulfur cinquefoil (Potentilla recta). Invasion was crossed with a supplemental water treatment to determine how increased resource supply might alter competitive outcomes. We also compared traits of exotics and natives to determine whether differences in height, lateral spread, shoot : root ratio and specific leaf area might shed light on competitive effects. 3. Exotics suppressed native biomass by an average of 51%. Water addition had no effect on invasibility or the competitive impact of exotics on natives. Although exotics decreased native biomass, invasion increased total above-ground biomass. Spotted knapweed was the most successful invader, and because of its greater abundance, it had the largest competitive impacts on natives. Spotted knapweed invasion also reduced plant-available soil nitrogen, water and light. 4. The majority of native species did not differ in their resistance to weed invasion, although Achillea millefolium and Festuca idahoensis monocultures were more resistant to invasion than monocultures of Antennaria rosea. Exotic biomass was either unaffected by competition with natives (knapweed) or was moderately suppressed by natives (cinquefoil and toadflax). Native species did not differ significantly in their competitive impacts on exotics and resource supply only influenced the competitive impacts of natives on spotted knapweed. Knapweed and toadflax, in particular, differed from all the natives in combined growth and leaf traits. 5. Synthesis. Our results show that exotics exert strong competitive dominance over individual native species with competitive effects relatively unaltered by increased resource supply. These effects occurred in undisturbed assemblages, suggesting that invader-native competitive outcomes can drive invasion dynamics for the species studied. Web of Science Centaurea maculosa; Lineria dalmatica; Potentilla recta United States Montana Garden terrestrial Grassland Impacts;Invasion Hyp. Inherent Superiority;Fluctuating Resources Superior Competitor primary 352 Martone, Rebecca Goldman; Wasson, Kerstin 2008 Impacts and interactions of multiple human perturbations in a California salt marsh journal OECOLOGIA 158 1 151 163 Multiple disturbances to ecosystems can influence community structure by modifying resistance to and recovery from invasion by non-native species. Predicting how invasibility responds to multiple anthropogenic impacts is particularly challenging due to the variety of potential stressors and complex responses. Using manipulative field experiments, we examined the relative impact of perturbations that primarily change abiotic or biotic factors to promote invasion in coastal salt marsh plant communities. Specifically we test the hypotheses that nitrogen enrichment and human trampling facilitate invasion of upland weeds into salt marsh, and that the ability of salt marsh communities to resist and/or recover from invasion is modified by hydrological conditions. Nitrogen enrichment affected invasion of non-native upland plants at only one of six sites, and increased aboveground native marsh biomass at only two sites. Percent cover of native marsh plants declined with trampling at all sites, but recovered earlier at tidally flushed sites than at tidally restricted sites. Synergistic interactions between trampling and restricting tidal flow resulted in significantly higher cover of non-native upland plants in trampled plots at tidally restricted sites. Percent cover of non-native plants recovered to pre-trampling levels in fully tidal sites, but remained higher in tidally restricted sites after 22 months. Thus, perturbations that reduce biotic resistance interact with perturbations that alter abiotic conditions to promote invasion. This suggests that to effectively conserve or restore native biodiversity in altered systems, one must consider impacts of multiple human disturbances, and the interactions between them. Web of Science Many United States California Elkhorn Slough 36.8167 -121.75 Field - Experimental terrestrial Wetland Invasion Hyp. Disturbance primary 358 McCay, Timothy S.; McCay, Deanna H. 2009 Processes regulating the invasion of European buckthorn (Rhamnus cathartica) in three habitats of the northeastern United States journal BIOLOGICAL INVASIONS 11 8 1835 1844 Web of Science Rhamnus cathartica United States New York Multiple Sites, Colgate University, Madison County, New York Field - Observational;Lab terrestrial Deciduous Forest;Coniferous Forest;Old Field Invasion Hyp. Mutualism Facilitation primary 359 McCay, Timothy S.; McCay, Deanna H.; Caragiulo, Anthony V.; Mandel, Toby L. 2009 Demography and distribution of the invasive Rhamnus cathartica in habitats of a fragmented landscape journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 136 1 110 121 MCCAY, T. S. (Department of Biology, Colgate University, Hamilton, NY 13346), D. H. MCCAY (Department of Geography, Colgate University, Hamilton NY 13346), A. V. CARAGIULO (Department of Biology, Colgate University, Hamilton, NY 13346), AND T. L. MANDEL (Department of Geography, Colgate University, Hamilton, NY 13346). Demography and distribution of the invasive Rhamnus cathartica in habitats of a fragmented landscape. J. Torrey Bot. Soc. 136: 110-121. 2009.-Forest fragmentation and abandonment of lands managed for agriculture are widespread processes in eastern North America that might promote the expansion of exotic pests. We studied populations of Rhamnus cathartica L. (European buckthorn), an invasive alien plant in North America, in maple-beech forests, abandoned agricultural fields, and unmanaged conifer plantations in central New York State. Surveys and neighborhood functions were used to examine demography and spatial distribution. Populations of R. cathartica in maple-beech forests were sparse (112 ha(-1)), dominated by seedlings and saplings, and strongly aggregated in space. Populations of R cathartica in plantations, by contrast, were dense (7,717 ha(-1)), not strongly concentrated at the low end of the diameter distribution, and less strongly aggregated than those in other habitats. Old fields included a high density of R. cathartica plants (5,912 ha(-1)), which were predominantly seedlings and strongly aggregated. Seedling density was positively related to availability of light at our forested plots, and plants were clustered near walking trails at three of four maple-beech plots. At all old field and two of four plantations, seedlings were spatially associated with fruiting R. cathartica, suggesting that they served as recruitment foci. Further, seedlings also were associated with non-fruiting adult R cathartica at 2 of 3 old-field and 2 of 4 plantation plots. Unmanaged conifer plantations with numerous canopy openings may permit colonization and population growth of R cathartica. Management for closed-canopy forest and the elimination of plants, particularly fruiting conspecifics, serving as recruitment foci are potentially successful approaches toward control of R. cathartica. Web of Science Rhamnus cathartica USA New York Field - Observational terrestrial Deciduous Forest;Coniferous Forest;Old Field Invasion Hyp. Disturbance primary 360 McCay, Timothy S.; McCay, Deanna H.; Czajka, Jessica L. 2009 Deposition of exotic bird-dispersed seeds into three habitats of a fragmented landscape in the northeastern United States journal PLANT ECOLOGY 203 1 59 67 Web of Science Many USA New York Colgate University, Madison County, New York 47.65 -75.58333 Field - Observational terrestrial Deciduous Forest;Coniferous Forest;Old Field Invasion Hyp. Mutualism Facilitation;Disturbance primary;omnivore 361 McDonald, Robert I.; Motzkin, Glenn; Foster, David R. 2008 Assessing the influence of historical factors, contemporary processes, and environmental conditions on the distribution of invasive species journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 135 2 260 271 Despite concern over potential detrimental effects of non-native invasive species on human and natural systems, the factors controlling regional distributions of invasive species remain unresolved. Few studies have evaluated the influence of both environmental factors and disturbance history on invasive species distributions, or assessed synthetically the importance of landscape-level disturbances like historical land-use, forest harvesting, and contemporary forest fragmentation. We analyzed vegetation, soils, and recent and historical land-use and landscape context for forests across central and western Massachusetts to identify controls on invasive species distributions. Almost half (49.3%) of 148 randomly selected sites had at least one non-native invasive plant present, and invasive species occurred more frequently on former agricultural sites than in continuous woodlands. We used logistic regression to model the probability of finding the four most common species: Japanese barberry (Berberis thunbergii DC), glossy buckthorn (Rhamnus frangula L.), multiflora rose (Rosa multiflora Thunb. ex Murr.), and oriental bittersweet (Celastrus orbiculata Thunb.). Soil richness was the most important predictor of invasive presence, with rich soils (i.e., lower C:N) being more likely to have these species. The structure of the current forested landscape (i.e., the amount of forest within a 10 km buffer around a site) is also important, with sites that are surrounded by more forest being less likely to have invasives. After accounting for variation in C:N ratios and the structure of the current forested landscape, historical land-use was not a significant predictor of non-native species occurrence; however, C:N ratios may be influenced by historical land-use and by current vegetation, thus complicating interpretations of this edaphic variable. Recent forest harvesting increased the likelihood of invasive occurrence for some but not all species. Overall, our results suggest that regional patterns of invasive plant distributions result from a complex function of edaphic conditions, and present and historical land-uses. Web of Science Berberis thunbergii;Rhamnus frangula;Rosa multiflora;Celastrus orbiculata U.S.A. Massachusetts Central and Western Region Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 363 McEwan, Ryan W.; Birchfield, M. Keith; Schoergendorfer, Angela; Arthur, Mary A. 2009 Leaf phenology and freeze tolerance of the invasive shrub Amur honeysuckle and potential native competitors journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 136 2 212 220 Web of Science Lonicera maackii USA Kentucky Field - Observational terrestrial Old Field Invasion Hyp. Inherent Superiority Superior Competitor;Broad Tolerances primary 364 McEwan, Ryan W.; Rieske, Lynne K.; Arthur, Mary A. 2009 Potential interactions between invasive woody shrubs and the gypsy moth (Lymantria dispar), an invasive insect herbivore journal BIOLOGICAL INVASIONS 11 4 1053 1058 As the range of the invasive and highly polyphagous gypsy moth (Lymantria dispar) expands, it increasingly overlaps with forest areas that have been subject to invasion by non-native shrubs. We explored the potential for interactions between these co-occurring invasions through a gypsy moth feeding trial using the following three highly invasive, exotic shrubs: honeysuckle (Lonicera maackii), privet (Ligustrum sinense) and burning bush (Euonymus alatus). We compared these with two native shrubs: spicebush (Lindera benzoin) and pawpaw (Asimina triloba). We fed gypsy moth caterpillars foliage exclusively from one of the five shrubs and measured their relative consumptive rate (RCR), relative growth rate (RGR), and development time (DT). The RCR of gypsy moth was strongly influenced by the species of foliage (F = 31.9; P < 0.0001) with little or no consumption of honeysuckle and privet. Caterpillar RGR was influenced by the shrub species (F = 66.2; P < 0.0001), and those caterpillars fed spicebush, honeysuckle or privet lost weight over the course of the assay. Caterpillar DT was also significantly (F = 11.79, P < 0.0001) influenced by the shrub species and those fed honeysuckle, privet and spicebush died prior to molting. Overall, our data suggest that honeysuckle, privet, and spicebush could benefit (indirectly) from the invasion of gypsy moth, while burning bush and pawpaw could be negatively impacted due to direct effects (herbivory). Similarly, invading gypsy moth populations could be sustained on a shrub layer of burning bush and pawpaw in the event of canopy defoliation. Further field and laboratory analysis is needed to clarify herbivore resistance of invasive shrubs, and to investigate the potential interactions among co-occurring insect and plant invasions. Web of Science Lymantria dispar; Lonicera maackii; Ligustrum sinense; Euonymus alatus USA Kentucky University of Kentucky Arboretum 38.0333 -84.5 Lab terrestrial Deciduous Forest Impacts;Invasion Hyp. Mutualism Facilitation primary;herbivore 367 McNatty, Alice; Abbott, Kirsti L.; Lester, Philip J. 2009 Invasive ants compete with and modify the trophic ecology of hermit crabs on tropical islands journal OECOLOGIA 160 1 187 194 Invasive species can dramatically alter trophic interactions. Predation is the predominant trophic interaction generally considered to be responsible for ecological change after invasion. In contrast, how frequently competition from invasive species contributes to the decline of native species remains controversial. Here, we demonstrate how the trophic ecology of the remote atoll nation of Tokelau is changing due to competition between invasive ants (Anoplolepis gracilipes) and native terrestrial hermit crabs (Coenobita spp.) for carrion. A significant negative correlation was observed between A. gracilipes and hermit crab abundance. On islands with A. gracilipes, crabs were generally restricted to the periphery of invaded islands. Very few hermit crabs were found in central areas of these islands where A. gracilipes abundances were highest. Ant exclusion experiments demonstrated that changes in the abundance and distribution of hermit crabs on Tokelau are a result of competition. The ants did not kill the hermit crabs. Rather, when highly abundant, A. gracilipes attacked crabs by spraying acid and drove crabs away from carrion resources. Analysis of naturally occurring N and C isotopes suggests that the ants are effectively lowering the trophic level of crabs. According to delta(15) N values, hermit crabs have a relatively high trophic level on islands where A. gracilipes have not invaded. In contrast, where these ants have invaded we observed a significant decrease in delta(15) N for all crab species. This result concurs with our experiment in suggesting long-term exclusion from carrion resources, driving co-occurring crabs towards a more herbivorous diet. Changes in hermit crab abundance or distribution may have major ramifications for the stability of plant communities. Because A. gracilipes have invaded many tropical islands where the predominant scavengers are hermit crabs, we consider that their competitive effects are likely to be more prominent in structuring communities than predation. Web of Science Anoplolepis gracilipes New Zealand Tokelau Nukunonu atoll -9.75 -171.58333 Field - Experimental;Field - Observational Intertidal/Near Shore Impacts;Invasion Hyp. Inherent Superiority Superior Competitor omnivore;predator;decomposer 373 Milne, Marc A.; Grefe, Norman A., III; Waller, Deborah A. 2008 Colonization and development of the Asian tiger mosquito (Aedes albopictus) in the purple pitcher plant (Sarracenia purpurea) journal AMERICAN MIDLAND NATURALIST 160 1 110 116 We report the expansion of the invasive container mosquito, Aedes alboapictus, into pitchers of the carnivorous pitcher plant, Sarracenia purpurea, in southeastern Virginia. The community of aquatic Dipteran larvae commonly associated within S. purpurea pitchers was not present at our research site, creating an unoccupied rearing habitat. We monitored mosquito presence and development within pitchers through two growing seasons. Oviposition traps placed near pitchers confirmed the abundance of gravid A. albopictus in the study area. Females oviposited in both newly opened and in senescing pitchers and larvae matured to adulthood in S. purpurea. Successful development of an exotic mosquito species within unoccupied pitchers of S. purpurea reinforces the hypothesis that invasive species may invade natural communities and occupy vacant niches. Web of Science Aedes alboapictus United States Virginia Blackwater Ecologic Preserve (BEP) 36.87 -76.83 Field - Observational Invasion Hyp. Empty Niche parasite 375 Minor, Emily S.; Tessel, Samantha M.; Engelhardt, Katharina A. M.; Lookingbill, Todd R. 2009 The role of landscape connectivity in assembling exotic plant communities: a network analysis journal ECOLOGY 90 7 1802 1809 Web of Science Many United States Maryland Antietam National Battlefield 39.47 -77.74 Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority;Disturbance Superior Competitor;Effective Disperser primary 376 Mitchell, Alison L.; Knouft, Jason H. 2009 Non-native fishes and native species diversity in freshwater fish assemblages across the United States journal BIOLOGICAL INVASIONS 11 6 1441 1450 The proliferation of non-native species in North American freshwater ecosystems is considered a primary threat to the integrity of native community structure. However, a general understanding of consistent and predictable impacts of non-native species on native freshwater diversity is limited, in part, because of a lack of broad-scale studies including data from numerous localities across multiple drainages. This study uses data from 751 localities collected during the United States Geological Survey (USGS) National Water Quality Assessment (NAWQA) program to examine the influence of non-native fish species on native freshwater fish assemblages across the United States. In general, no significant differences in native fish richness and diversity measures were detected between sites with only native species and sites containing non-native species. However, at sites with non-native species, the number of non-native species present was negatively correlated with native species richness and Shannon diversity and positively correlated with native evenness. Non-native piscivores were negatively correlated with native species richness and Shannon diversity and positively correlated with native evenness. Native piscivores were positively correlated with native richness and diversity and negatively correlated with native evenness at sites with only native species. Our results suggest that from a superficial perspective, native species richness and diversity are not different among sites with and without non-native species. However, when patterns of native species richness and diversity are examined at sites containing non-native species, correlations between non-native and native species richness and diversity imply the expected negative effect of invasive taxa. Additionally, non-native piscivores appear to have a significant negative effect on native taxa and possibly represent a novel selective force on naive native prey. Web of Science Many United States United States Field - Observational lotic Impacts;Invasion Hyp. Community Species Richness omnivore 378 Molina-Montenegro, Marco A.; Badano, Ernesto I.; Cavieres, Lohengrin A. 2008 Positive interactions among plant species for pollinator service: assessing the 'magnet species' concept with invasive species journal OIKOS 117 12 1833 1839 Plants with poorly attractive flowers or with little floral rewards may have inadequate pollinator service, which in turn reduces seed output. However, pollinator service of less attractive species could be enhanced when they are associated with species with highly attractive flowers (so called 'magnet-species'). Although several studies have reported the magnet species effect, few of them have evaluated whether this positive interaction result in an enhancement of the seed output for the beneficiary species. Here, we compared pollinator visitation rates and seed output of the invasive annual species Carduus pycnocephalus when grow associated with shrubs of the invasive Lupinus arboreus and when grow alone, and hypothesized that L. arboreus acts as a magnet species for C. pycnocephalus. Results showed that C. pycnocephalus individuals associated with L. arboreus had higher pollinator visitation rates and higher seed output than individuals growing alone. The higher visitation rates of C. pycnocephalus associated to L. arboreus were maintained after accounting for flower density, which consistently supports our hypothesis on the magnet species effect of L. arboreus. Given that both species are invasives, the facilitated pollination and reproduction of C. pycnocephalus by L. arboreus could promote its naturalization in the community, suggesting a synergistic invasional process contributing to an 'invasional meltdown'. The magnet effect of Lupinus on Carduus found in this study seems to be one the first examples of indirect facilitative interactions via increased pollination among invasive species. Web of Science Carduus pycnocephalus; Lupinus arboreus Chile Concepcion Peninsula Hualpen -36.75 -73.2167 Field - Observational terrestrial Grassland Invasion Hyp. Mutualism Facilitation primary 382 Monty, Arnaud; Stainier, Charles; Lebeau, Frederic; Pieret, Nora; Mahy, Gregory 2008 Seed rain pattern of the invasive weed Senecio inaequidens (Asteraceae) journal BELGIAN JOURNAL OF BOTANY 141 1 51 63 Dispersion capacity of alien invasive plants is a key feature for understanding invasion processes and risks. Here, we present an experimental study focussing on the seed rain pattern of Senecio inaequidens, an African plant widespread throughout Europe, under common favourable dispersal conditions. One hundred achenes from two Belgian populations underwent a drop time in still air experiment in order to assess linear correlation between several morphological traits and terminal velocity. Variation in morphological traits was measured for 250 additional achenes per population. The trait best correlated to terminal velocity was the square root of the plume loading. We then used this trait to model terminal velocity using a linear regression (r(2) of 79.7%). With this regression and imposing ecological parameters such as wind speed, turbulences and height of release to be representative of favourable dispersal conditions, we established a Gaussian tilted plume model to predict the seed rain pattern of the species. A wind tunnel experiment consequently permitted to validate the model. Under a wind speed of 5 m s(-1) with 2% turbulences along the vertical axis, and height of release of 0.40 m, 99.8% of achenes were dispersed within 100 meters, with a maximum deposition rate at 5.2 m from the parent plant. Uplifted achenes, not forecasted by the model, represent 6.25% of all achenes. Web of Science Senecio inaequidens Belgium Seraing; Antwerpen 50.36; 51.14 5.29; 4.23 Theoretical/Modeling terrestrial Invasion Hyp. Propagule Pressure primary 392 Murren, Courtney J.; Chang, Cynthia C.; Dudash, Michele R. 2009 Patterns of selection of two North American native and nonnative populations of monkeyflower (Phrymaceae) journal NEW PHYTOLOGIST 183 3 691 701 Web of Science Mimulus guttatu United States Maryland University of Maryland 38.989336 -76.943736 Field - Observational;Greenhouse;Garden terrestrial Invasion Hyp. Evolution in General 403 Nunez, Martin A.; Horton, Thomas R.; Simberloff, Daniel 2009 Lack of belowground mutualisms hinders Pinaceae invasions journal ECOLOGY 90 9 2352 2359 Web of Science Pseudotsuga menziesii; Pinus contorta; Pinus ponderosa Argentina Isla Victoria in Nahuel Huapi National Park -40.57 -71.33 Field - Experimental;Greenhouse terrestrial Coniferous Forest Invasion Hyp. Mutualism Facilitation primary 405 Nuzzo, Victoria A.; Maerz, John C.; Blossey, Bernd 2009 Earthworm Invasion as the Driving Force Behind Plant Invasion and Community Change in Northeastern North American Forests journal CONSERVATION BIOLOGY 23 4 966 974 Web of Science Alliaria petiolata; Berberis thunbergii; Microstegium vimineum United States New York; Pennsylvania Field - Observational terrestrial Deciduous Forest Invasion Hyp. Mutualism Facilitation primary 408 Oguz, Temel; Fach, Bettina; Salihoglu, Baris 2008 Invasion dynamics of the alien ctenophore Mnemiopsis leidyi and its impact on anchovy collapse in the Black Sea journal JOURNAL OF PLANKTON RESEARCH 30 12 1385 1397 The mechanisms governing the unprecedented 1989-90 anchovy-Mnemiopsis shift event in the Black Sea were evaluated with a coupled model of bioenergetic-based anchovy population dynamics and lower trophic food web structure. Simulations showed that a combination of direct and density-dependent effects of overfishing, eutrophication-induced nutrient enrichment, climate-induced over-enrichment and temperature-controlled Mnemiopsis spring production were involved in the shift. Eutrophication made the system vulnerable to further enrichment through the change of regional climate to a severe winter regime during 1985-87. While Mnemiopsis was acclimating to its new environment, increasing nitrate flux into the euphotic layer enhanced the carrying capacity of the system, but a disproportionate Mnemiopsis biomass increase was delayed until spring temperature conditions returned to normal in 1988-89. Enhanced carrying capacity provided a competitive advantage of food consumption to Mnemiopsis compared with anchovy, and warm spring temperature conditions promoted their spring-summer production. Prevalent high fishery pressure and increasing impact of Mnemiopsis on the food web further induced the anchovy stock collapse. However, the shift event did not result in alternation of the system to a new totally Mnemiopsis-invaded quasi-stable regime. Instead, anchovy started recovering when the subsequent strong 1991-93 cooling regime limited the Mnemiopsis population growth. Our analysis indicated that the switch of a large marine ecosystem to a totally gelatinous invader-dominated state requires extremely strong environmental perturbations. More often, environmental disturbances create a suitable niche for an alien gelatinous invader to become a member of the food web structure, and to share food resources with the native small pelagic fish community. Web of Science Mnemiopsis leidyi Black Sea Theoretical/Modeling marine Pelagic/Open Ocean Impacts;Invasion Hyp. Inherent Superiority;Empty Niche Superior Competitor filter 409 Okada, Miki; Grewell, Brenda J.; Jasieniuk, Marie 2009 Clonal spread of invasive Ludwigia hexapetala and L. grandiflora in freshwater wetlands of California journal AQUATIC BOTANY 91 3 123 129 Web of Science Ludwigia hexapetala; L. grandiflora United States California North Coast Watershed (Russian River Basin); Sacramento River Watershed; San Joaquin River Watershed Lab wetland Intertidal/Near Shore Invasion Hyp. Inherent Superiority;Propagule Pressure Clonal Reproduction primary 411 Oliver, Thomas H.; Pettitt, Tim; Leather, Simon R.; Cook, James M. 2008 Numerical abundance of invasive ants and monopolisation of exudate-producing resources - a chicken and egg situation journal INSECT CONSERVATION AND DIVERSITY 1 4 208 214 1. Invasive ants commonly reach abnormally high abundances and have severe impacts on the ecosystems they invade. Current invasion theory recognises that not only negative interactions, such as natural enemy release, but positive interactions, such as facilitation, are important in causing this increased abundance. 2. For invasive ants, facilitation can occur through mutualism with exudate-producing plants and insects. To obtain such partnerships, however, invaders must first displace native ants, whose communities are highly structured around such resources. 3. By manipulating the abundance of an invasive ant relative to a native, we show that a minimum threshold abundance exists for invasive ants to monopolise exudate-producing resources. In addition, we show that behavioural dominance is context dependent and varies with spatial location and numerical abundance. 4. Thus, we suggest a 'facilitation-threshold' hypothesis of ant invasion, whereby a minimum abundance of invasive ants is required before facilitation and behavioural dominance can drive abundance rapidly upwards through positive feedback. Web of Science Technomyrmex albipes United Kingdom Cornwall e Tropical Biome of the Eden Project, Cornwall Lab Invasion Hyp. Inherent Superiority;Propagule Pressure Superior Competitor herbivore 414 Otfinowski, R.; Kenkel, N. C. 2008 Clonal integration facilitates the proliferation of smooth brome clones invading northern fescue prairies journal PLANT ECOLOGY 199 2 235 242 Predicting exotic invaders and reducing their impacts on the biodiversity and function of native ecosystems require understanding of the mechanisms that facilitate their success during key stages of invasion. We determined whether clonal growth, characteristic of the majority of successful invaders of natural areas, facilitates the proliferation of Bromus inermis (smooth brome), an exotic grass invading prairie ecosystems across the Great Plains. By manipulating the below-ground connections of proliferating rhizomes as well as the levels of soil nitrogen along the margins of clones invading northern fescue prairies in Manitoba, Canada, we hypothesized that physiological integration would most benefit ramets invading low resource environments. Severing clonal connections reduced the mass of smooth brome shoots invading native prairies and was exacerbated by the immobilization of soil nutrients with glucose. Clonal connections were equally important in the maintenance of smooth brome density and the horizontal proliferation of ramets. Our results demonstrate the role of physiological integration in the proliferation of a clonal exotic invader and may help explain the success of clonal invaders in other regions. Although integration among invading ramets suggests several possibilities for successful management, future research must continue to elucidate differences in the invasiveness of native versus exotic species as well as the persistence of clonal connections among exotic invaders. Web of Science Bromus inermis Canada Manitoba Riding Mountain National Park 50.771208 -100.228271 Field - Experimental terrestrial Grassland Invasion Hyp. Inherent Superiority Clonal Reproduction primary 424 Pena, Eduardo; Hidalgo, Marisol; Langdon, Barbara; Pauchard, Anibal 2008 Patterns of spread of Pinus contorta Dougl. ex Loud. invasion in a Natural Reserve in southern South America journal FOREST ECOLOGY AND MANAGEMENT 256 5 1049 1054 Pinus species, which have formed the foundation of commercial forestry industry in many countries, are known to be invasive in natural ecosystems, especially in the Southern Hemisphere. Pinus contorta is considered one of the most aggressively invasive plantation species. In this paper we aim to: (a) determine patterns of P. contorta invasion in relation to its size and age structure and spatial distribution and (b) determine the effect of vegetation cover on its regeneration. For this purpose, we have chosen the Malalcahuello National Reserve in south-central Chile, which is dominated by Araucaria araucana forests. In the three A contorta trial plots, attributes were measured in order to describe its current structure. We selected one of the three P. contorta trial plots and set eight 50 m wide and 125 m centrifugal transects starting at the North Azimuth (0 degrees) orientation and then one each 45 degrees. In each transect 25 circular plots of 2.5 m radius were established every 25 m. In each plot, we measured collar diameter (CD) for each P. contorta individual and adjusted a diameter-age function. We recorded the presence of cones for each individual P. contorta within the plots and the total number of P. contorta individuals. In each plot, we measured percent vegetation cover (grass, understory and canopy). The selected parent stand showed a decrease in density from the original plantation spacing, from 2500 to 150 plants ha(-1). Of all sampled individuals, only a 38% had cones. We found reproductive structures in trees as young as 5-year-old. Regeneration was found in all transects. Mean density for the area was 1600 plants ha-1, and the greater plant number was found in the West transect, reaching an average of 6600 plants ha(-1). Through the interpolation performed with the kriging method, a map of the area with the spatial gradient of plant density was obtained. Naturally regenerated individuals of A contorta occupied an area of 78 ha where the most distant individual is located in the southeast direction at an average distance of 1200 m from the three study plots. We determined that a positive association exists between P. contorta and the species A. araucana and Nothofagus antarctica. The capacity for early and consistent reproduction and the establishment of individuals dispersed at great distances from the original plots allow us to conclude that P. contorta has great potential as an invasive species in forests of this area of the Andes of southern South America. Invasion of P. contorta has many important implications for the conservation of native forests in our region including diminished regeneration of A. araucana. (c) 2008 Elsevier B.V. All rights reserved. Web of Science Pinus contorta Chile Malalcahuello National Reserve -38.41 -71.55 Field - Observational terrestrial Coniferous Forest Invasion Hyp. Inherent Superiority High Reprod. Output primary 429 Petit, Jerome N.; Hoddle, Mark S.; Grandgirard, Julie; Roderick, George K.; Davies, Neil 2009 Successful spread of a biocontrol agent reveals a biosecurity failure: elucidating long distance invasion pathways for Gonatocerus ashmeadi in French Polynesia journal BIOCONTROL 54 4 485 495 Web of Science Gonatocerus ashmeadi French Polynesia Field - Observational terrestrial Urban Invasion Hyp. Other predator 431 Phartyal, Shyam S.; Godefroid, Sandrine; Koedam, Nico 2009 Seed development and germination ecophysiology of the invasive tree Prunus serotina (Rosaceae) in a temperate forest in Western Europe journal PLANT ECOLOGY 204 2 285 294 Web of Science Prunus serotina Belgium Sonian Forest Field - Observational terrestrial Deciduous Forest Fundamentals primary 436 Poll, Myriam; Naylor, Bridgett J.; Alexander, Jake M.; Edwards, Peter J.; Dietz, Hansjoerg 2009 Seedling establishment of Asteraceae forbs along altitudinal gradients: a comparison of transplant experiments in the native and introduced ranges journal DIVERSITY AND DISTRIBUTIONS 15 2 254 265 Since ecological and evolutionary context changes when a plant species is introduced to a new area, it can be assumed that responses of alien plants to changing conditions along environmental gradients differ from those in their native range. Even if seed availability is not limited, the distribution of alien plants along such a gradient might still be restricted by their ability to germinate and establish as seedlings. In the present study, we aim at testing what factors promote or limit plant invasions during early establishment by using altitude as a model gradient. Altitudinal gradients in the Wallowa Mountains (Oregon, USA) and the Swiss Alps (Valais, Switzerland). In transplant experiments along altitudinal gradients, we investigated the early establishment success of eight invasive alien Asteraceae species in their native and introduced ranges in the Wallowa Mountains and the Swiss Alps. Seedling recruitment was not restricted to relatively lower altitudes in the introduced range. In addition, we found no evidence for genetic adaptation along the altitudinal gradient in the introduced range, highlighting the importance of phenotypic flexibility for invasions. Furthermore, seedling recruitment was only enhanced by disturbance in the native range where vegetation was comparably dense but not in the introduced range. However, plant development was strongly delayed in the introduced range, probably due to low seasonal water availability. We conclude that introduced plants, due to their ability to tolerate a wide range of environmental conditions, are not necessarily more restricted in their altitudinal limits than they are in their native range. Furthermore, due to other interacting factors (e.g. different competition situations among ranges), attempts to predict distributions of alien plants in the introduced range that are based on their distributions in the native range may be misleading. Web of Science Conyza canadensis;Cichorium intybus;Cirsium arvense;Cirsium vulgare;Lactuca serriola;Erigeron annuus;Matricaria discoidea;Solidago canadensis USA;Switzerland Oregon;Valais 46;45 7;-117 Field - Experimental terrestrial Mountain Invasion Hyp. Evolution of Increased Competitive Ability;Disturbance primary 437 Pollock, Jarrod L.; Seastedt, Timothy R.; Callaway, Ragan M.; Kaur, Jasleen 2008 Allelopathy and plant invasions: traditional, congeneric, and bio-geographical approaches journal BIOLOGICAL INVASIONS 10 6 875 890 A relatively small subset of exotic plant species competitively exclude their neighbors in invaded 'recipient' communities but coexist with neighbors in their native habitat. Allelopathy has been argued as one of the mechanisms by which such exotics may become successful invaders. Three approaches have been used to examine allelopathy as a mechanism for invasion. The traditional approach examines exotic invasives in the same way that other native plants also suspected of allelopathic activities are studied. In this approach dose, fate, and replenishment of chemicals can provide powerful evidence for allelopathic processes. The bio-geographical approach often does not provide as much mechanistic evidence for allelopathy, but comparing the allelopathic effects of exotic invasives on species from their native and invaded communities yields stronger evidence than the traditional approach for whether or not allelopathy actually contributes to invasive success. The congeneric, or phylogenetic, approach involves comparative studies of exotic species with natives in the same genus or that are as closely related as possible. Congeneric approaches are limited in inference and have been used to study the role of natural enemies in exotic invasion, but this approach has not been widely used to study allelopathy and invasion. We discuss these three approaches and present a data set for congeneric Lantana and Prosopis to illustrate how the congeneric approach can be used, and use Centaurea maculosa and (+/-)-catechin to demonstrate experimentally how traditional and bio-geographic approaches can be integrated to shed light on allelopathy in exotic plant invasions. Web of Science Centaurea maculosa USA Montana 46.8603 -113.9781 Field - Experimental;Lab terrestrial Grassland Invasion Hyp. Novel Weapons primary 438 Polo-Cavia, Nuria; Lopez, Pilar; Martin, Jose 2009 Interspecific differences in heat exchange rates may affect competition between introduced and native freshwater turtles journal BIOLOGICAL INVASIONS 11 8 1755 1765 Web of Science Trachemys scripta elegans Spain Badajoz Guadiana river 38.93 -5.99 Lab lentic;lotic Invasion Hyp. Inherent Superiority Superior Competitor predator 439 Polo-Cavia, Nuria; Lopez, Pilar; Martin, Jose 2009 Interspecific differences in chemosensory responses of freshwater turtles: consequences for competition between native and invasive species journal BIOLOGICAL INVASIONS 11 2 431 440 The red-eared slider (Trachemys scripta elegans) is an introduced invasive species in many Mediterranean countries that is displacing the populations of native endangered Spanish terrapins (Mauremys leprosa). However, it is relatively unknown how potential competitive interactions could be taking place. In many freshwater turtles, semiochemicals from different glands might facilitate species and sex recognition. We hypothesized that chemosensory detection of competitor species might affect space use and habitat selection by freshwater turtles. We analyzed whether T. scripta and M. leprosa turtles recognized chemical cues from male and female conspecifics and heterospecifics in water. We compared time spent by turtles in clean water pools vs. water pools containing the different chemical stimuli. Introduced T. scripta did not avoid nor prefer water pools with chemical stimuli of native M. leprosa terrapins, which might favor the expansion of the invasive species. In contrast, M. leprosa preferred water with chemical stimuli of conspecifics and avoided water with chemical cues of T. scripta, which suggests that chemical cues could be used by native M. leprosa to avoid water pools occupied by introduced T. scripta. We suggest that this avoidance behavior of native M. leprosa may be one of the causes that contribute to the observed displacement of their populations by invasive T. scripta. Web of Science Trachemys scripta elegans Spain Iberian Peninsula 40 -4.99 Garden lentic;lotic Invasion Hyp. Inherent Superiority Superior Competitor predator 443 Poulet, Nicolas; Balaresque, Patricia; Aho, Teija; Bjorklund, Mats 2009 Genetic structure and dynamics of a small introduced population: the pikeperch, Sander lucioperca, in the Rhone delta journal GENETICA 135 1 77 86 Genetic data on introduced populations may help us to understand how these species succeed in colonising new territories. The pikeperch is a predatory fish widely introduced in Europe and has at times been considered as an invasive species. However, little is known about the genetics of both native and introduced populations. In the present study, we surveyed an introduced pikeperch population from the Rhone River delta, a habitat that has been highly modified for agricultural purposes. Using six microsatellites, we genotyped 93 individuals distributed among four hydraulically connected water bodies: the Rhone River, an irrigation canal, a drainage canal and a brackish lagoon. Population isolation were revealed by significant genetic distances and bottleneck highlighted by population monitoring. However, values of allelic richness and unbiased expected heterozygosity observed in these populations were similar, or even higher, compare to 18 native populations from the Baltic Sea drainage. It may be explained by multiple introductions in the Rhonee drainage but also by demographic strategy that would have facilitated population persistence in this fragmented habitat. Similarly, heterozygote deficits (revealed by F-IS values) have been detected, but were also found in native populations suggesting that mating among relatives could also result from a mating behavior of the species, maybe reinforce here by the reduced carrying capacity of the artificial canals and their respective isolation. Despite harsh environmental conditions and suspected inbreeding, the pikeperch has successfully maintained viable populations in the Rhone delta. Our study suggests that one of the factors in this invasive success, apart from its ecology, could be the maintenance of a good level of genetic diversity in introduced pikeperch populations. This genetic diversity probably stem from both its popularity as game fish and food resource which led to numerous stocking and an increasing propagule pressure and the reproductive strategy of the species. Web of Science Sander lucioperca France Rhone River 43.0011 4.0011 Field - Observational lotic Invasion Hyp. Propagule Pressure predator 447 Preisser, Evan L.; Elkinton, Joseph S.; Abell, Kristopher 2008 Evolution of increased cold tolerance during range expansion of the elongate hemlock scale Fiorinia externa Ferris (Hemiptera: Diaspididae) journal ECOLOGICAL ENTOMOLOGY 33 6 709 715 1. Alien species often face novel challenges to their spread and population growth. One critical hurdle often involves an organism's ability to tolerate environmental extremes characteristic of their invaded range. Although abiotic factors often determine range limits, there is less evidence for local adaptation in invasive organisms whose initial arrival and rapid population growth is separated by a lengthy lag period. 2. The invasive elongate hemlock scale Fiorinia externa feeds on Eastern hemlock, Tsuga canadensis, on the east coast of North America. Following its 1908 arrival, it remained localised until entering a period of rapid northward range expansion in the 1970s. 3. The present study tested the survival of overwintering F. externa populations from four sites in the north and south of the invaded range (n = 8 sites total) when exposed to -15 degrees C for 0-36 h. 4. This experiment was repeated on F. externa offspring that had been reared in a common-garden environment in order to control for parental effects. 5. Northern populations were more tolerant of exposure to cold temperatures than were southern populations. This held true in both the source-population experiment and common-garden experiment. The common-garden experiment demonstrates that this difference has a genetic basis and may be the consequence of local adaptation to lower winter temperatures. 6. The results provide evidence for local adaptation to extreme temperatures in F. externa. This provides one possible explanation for the lag period between the arrival of this species and its eventual northward range expansion. Web of Science Fiorinia externa USA Maryland;Connecticut Garden;Lab terrestrial Coniferous Forest Invasion Hyp. Evolution in General herbivore 448 Price, Andrew J.; Runion, G. Brett; Prior, Stephen A.; Rogers, Hugo H.; Torbert, H. Allen 2009 Tropical Spiderwort (Commelina benghalensis L.) Increases Growth under Elevated Atmospheric Carbon Dioxide journal JOURNAL OF ENVIRONMENTAL QUALITY 38 2 729 733 Although considerable effort is being spent studying exotic plant pests, little consideration his been given as to how invasive plants might react to the increasing concentration of CO2 in the atmosphere. Tropical spiderwort (Commelina benghalensis L) is considered one the world's worst weeds and is becoming more of it problem in agricultural settings of tire Southeastern USA, Growth responses of tropical spiderwort were evaluated using plants grown in containers with a soilless potting medium under ambient and elevated (ambient + 200 mu mol mol(1)) levels of CO2 in open-top field chambers. Although plant height was unaffected by CO2 leaf and flower number tended to increase (approximately 23%) when exposed to elevated CO2 Aboveground plant parts exhibited significant increases in dry weight when exposed to high CO2; leaf, flower, stein, and total shoot (try weights were increased by 36, 30, 48 and 44%, respectively. Total plant dry weight was increased by 41% for plants grown under high CO2. Root dry weight and root length were unaffected by CO2 concentration, Tropical spiderwort allocated more biomass to stems and tended to allocate less to roots when plants were exposed to high CO2. Plant carbon concentration and content tended to be higher in CO2-enriched plants, whereas plant nitrogen concentration tended to be lower; thus, elevated CO2-grown plants had higher C/N ratios. Also, the amount of biomass produced per unit nitrogen was higher for plants exposed to elevated CO2. The growth response of this plant is in the upper range typical for C3 plants. Web of Science Commelina benghalensis United States Alabama USDA-ARS National Soil Dynamics Laboratory 32.61 -85.49 Greenhouse terrestrial Invasion Hyp. Climate Change primary 451 Proches, Serban; Wilson, John R. U.; Richardson, David M.; Chown, Steven L. 2008 Herbivores, but not other insects, are scarce on alien plants journal AUSTRAL ECOLOGY 33 5 691 700 Understanding how the landscape-scale replacement of indigenous plants with alien plants influences ecosystem structure and functioning is critical in a world characterized by increasing biotic homogenization. An important step in this process is to assess the impact on invertebrate communities. Here we analyse insect species richness and abundance in sweep collections from indigenous and alien (Australasian) woody plant species in South Africa's Western Cape. We use phylogenetically relevant comparisons and compare one indigenous with three Australasian alien trees within each of Fabaceae: Mimosoideae, Myrtaceae, and Proteaceae: Grevilleoideae. Although some of the alien species analysed had remarkably high abundances of herbivores, even when intentionally introduced biological control agents are discounted, overall, herbivorous insect assemblages from alien plants were slightly less abundant and less diverse compared with those from indigenous plants - in accordance with predictions from the enemy release hypothesis. However, there were no clear differences in other insect feeding guilds. We conclude that insect assemblages from alien plants are generally quite diverse, and significant differences between these and assemblages from indigenous plants are only evident for herbivorous insects. Web of Science Many South Africa Western Cape Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Enemy Release primary 453 Puliafico, K. P.; Schwarzlaender, M.; Harmon, B. L.; Hinz, H. L. 2008 Effect of generalist insect herbivores on introduced Lepidium draba (Brassicaceae): implications for the enemy release hypothesis journal JOURNAL OF APPLIED ENTOMOLOGY 132 7 519 529 The enemy release hypothesis (ERH) states that decreased regulation by natural enemies allows plants to increase in distribution, abundance and vigour following their introduction into an exotic range. Invasive plants rarely escape herbivory entirely, and for hoary cress [Lepidium draba L. (Brassicaceae)] it has been demonstrated that generalist insect abundance is greater in its introduced North American range than in the native European range. We assessed the role of increased generalist herbivory on hoary cress using representatives of four important herbivore niches commonly found in the introduced range. We experimentally examined the density dependent impact of these herbivores individually and in combination on hoary cress in a series of greenhouse experiments. We found that defoliation of the oligophagous diamondback moth Plutella xylostella (L.) (Lep., Plutellidae) had the strongest and most consistent impact, while damage by the stem-mining weevil Ceutorhynchus americanus Buchanan (Col., Curculionidae) tended to have the highest per capita effect. Plant response to feeding by the oligophagous crucifer flea beetle Phyllotreta cruciferae (Goeze) (Col., Chrysomelidae) was minor despite obvious feeding damage, and the impact of the polyphagous tarnished plant bug Lygus hesperus Knight (Het., Miridae) was negligible. In multiple-species experiments, herbivore impacts were usually additive. In general, we found that hoary cress can tolerate high densities of oligophagous insect herbivory and effectively resisted attack by the polyphagous L. hesperus, but also the oligophagous C. americanus. Our results indicate that a combination of plant resistance and tolerance allows hoary cress to withstand increased generalist herbivore load in its introduced range, consistent with the predictions of the ERH. Web of Science Lepidium draba USA Greenhouse terrestrial Grassland;Deciduous Forest;Urban;Old Field Invasion Hyp. Enemy Release primary 454 Qaderi, M. M.; Reid, D. M. 2008 COMBINED EFFECTS OF TEMPERATURE AND CARBON DIOXIDE ON PLANT GROWTH AND SUBSEQUENT SEED GERMINABILITY OF SILENE NOCTIFLORA journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 169 9 1200 1209 Effects of global climate change on invasive alien species of plants and on the resulting progeny have received little attention. We examined the combined effects of temperature and carbon dioxide (CO2) on plant growth and physiological characteristics, reproductive yield components, and subsequent germination patterns of fresh- and dry-stored seeds of night-flowering catchfly (Silene noctiflora). Plants were grown under two temperature regimes (22 degrees/18 degrees C and 28 degrees/24 degrees C) at ambient (370 mu mol mol(-1)) and elevated (740 mu mol mol(-1)) CO2 concentrations in controlled-environment growth chambers. Higher temperature reduced plant height; average individual leaf area; capsule length, width, and mass; sound seed number; and mass per capsule but increased specific leaf mass. Elevated CO2 increased single sound seed mass. Higher temperature decreased both percentage and rate of germination, whereas elevated CO2 decreased germination percentage but increased germination rate. Seed germination increased with storage duration. Higher temperature increased transpiration. However, elevated CO2 decreased transpiration but increased net CO2 assimilation and water use efficiency. Elevated CO2 increased chlorophyll b but decreased chlorophyll a : b ratio. Ethylene production was enhanced by increased temperature. We conclude that despite the negative effects of higher temperature on some plant characteristics, S. noctiflora has the potential to thrive under conditions of climate change. Web of Science Silene noctiflora Canada Alberta University of Calgary 51.06 -115.16 Lab terrestrial Invasion Hyp. Climate Change primary 457 Quiroz, Constanza L.; Choler, Philippe; Baptist, Florence; Gonzalez-Teuber, Marcia; Molina-Montenegro, Marco A.; Cavieres, Lohengrin A. 2009 Alpine dandelions originated in the native and introduced range differ in their responses to environmental constraints journal ECOLOGICAL RESEARCH 24 1 175 183 Few studies have compared the response of native and invasive populations under stressful conditions. Furthermore, there is little consensus as to whether a plastic response is related to invasiveness in stressful environments. Exotic species have recently been reported in the high Andes of central Chile, where individuals have to cope with drought and poor soils, in addition to extreme temperatures. We explored if the exotic species Taraxacum officinale (dandelion) has plastic responses to soil moisture and nutrient availability, and whether two sets of alpine populations derived from native and introduced populations can converge to similar plastic responses to environmental constraints. Using a common garden approach, we compared plants grown from seeds collected in alpine populations of its native range (Alps, France) and in alpine populations of its introduced range (Andes, Chile) under a drought experiment, a potassium gradient, and a nitrogen gradient. Plasticity was only found as a response to drought. Moreover, different responses were found between both origins. Andean individuals are drought-resistant, while individuals from the Alps were drought-sensitive. According to the nutrient experiments, Andean dandelions behave as a nitrogen demanding-potassium avoiding species, whereas individuals from the Alps did not show any particular dependency or repulsion tendency to either of these two nutrients. Results suggest that differences in life history traits of both derived sets of populations may have an important role in determining the response of dandelions under the evaluated conditions. However, the relative importance of genetic adaptation in these responses is still unclear. Although T. officinale is a cosmopolite weed, this is the first study that compares individuals coming from its native and invaded range under stressful conditions. Web of Science Taraxacum officinale Chile Andes Field - Experimental terrestrial Mountain Invasion Hyp. Evolution of Increased Competitive Ability;Plasticity primary 468 Richards, Christina L.; Walls, Ramona L.; Bailey, John P.; Parameswaran, Radha; George, Tara; Pigliucci, Massimo 2008 Plasticity in salt tolerance traits allows for invasion of novel habitat by Japanese knotweed s. l. (Fallopia japonica and F-bohemica, Polygonaceae) journal AMERICAN JOURNAL OF BOTANY 95 8 931 942 Japanese knotweeds are among the most invasive organisms in the world. Their recent expansion into salt marsh habitat provides a unique opportunity to investigate how invasives establish in Dew environments. We used morphology. cytology, and AFLP genotyping to identify taxa and clonal diversity in roadside and salt marsh populations. We conducted a greenhouse study to determine the ability to tolerate salt and whether salt marsh populations are more salt tolerant than roadside populations as measured by the efficiency of PSII, leaf area, succulence, height, root-to-shoot ratio. and total biomass. Clonal diversity was extremely low with one F. japonica clone and five F. xbohemica genotypes. The two taxa were significantly different in several traits, but did not vary in biomass or plasticity of any trait. All traits were highly plastic in response to salinity, but differed significantly among genets. Despite this variation, plants from the salt marsh habitats did not perform better in the salt treatment, suggesting that they are not better adapted to tolerate salt. Instead, our data support the hypothesis that plasticity in salt tolerance traits may allow these taxa to live in saline habitats without specific adaptation to tolerate salt. Web of Science Fallopia japonica United States New York Long Island 40.7993 -72.7735 Greenhouse;Lab terrestrial Wetland;Urban Invasion Hyp. Plasticity primary 469 Ridenour, Wendy M.; Vivanco, Jorge M.; Feng, Yulong; Horiuchi, Jun-ichiro; Callaway, Ragan M. 2008 No evidence for trade-offs: Centaurea plants from America are better competitors and defenders journal ECOLOGICAL MONOGRAPHS 78 3 369 386 The natural enemies hypothesis has led to a number of ideas by which invaders might evolve superior competitive ability. In this context, we compared growth, reproduction, competitive effect, competitive response, and defense capabilities between invasive North American populations of Centaurea maculosa and populations in Europe, where the species is native. We found that Centaurea from North America were larger than plants from European populations. North American Centaurea also demonstrated stronger competitive effects and responses than European Centaurea. However, competitive superiority did not come at a cost to herbivore defense. North American plants were much better defended against generalist insect herbivores and slightly better defended against specialists. North Americans showed a stronger inhibitory effect on the consumers ( resistance) and a better ability to regrow after attack by herbivores ( tolerance). Better defense by North Americans corresponded with higher constitutive levels of a biochemical defense compound precursor, tougher leaves, and more leaf trichomes than Europeans. North American F1 progeny of. eld collected lines retained the traits of larger size and greater leaf toughness suggesting that genetic differences, rather than maternal effects, may be the cause of intercontinental differences, but these sample sizes were small. Our results suggest that the evolution of increased competitive ability may not always be driven by physiological trade- offs between the allocation of energy or resources to growth or to defense. Instead, we hypothesize that Centaurea maculosa experiences strong directional selection on novel competitive and defense traits in its new range. Web of Science Centaurea maculosa North America Greenhouse terrestrial Invasion Hyp. Evolution of Increased Competitive Ability;Evolution in General primary 472 Rius, Marc; Pascual, Marta; Turon, Xavier 2008 Phylogeography of the widespread marine invader Microcosmus squamiger (Ascidiacea) reveals high genetic diversity of introduced populations and non-independent colonizations journal DIVERSITY AND DISTRIBUTIONS 14 5 818 828 The spread of non-indigenous species into new marine habitats represents an increasing threat to global diversity. Genetic techniques provide basic understanding of the invasion processes. The ascidian Microcosmus squamiger is considered to be native to Australia, having been spread worldwide via transoceanic vessels. It has successfully invaded artificial and natural habitats where it has become a pest. We studied phylogeography and genetic structure of 12 M. squamiger populations, including samples from its native range (Australia) and introduced populations from the Indian, Pacific, and Atlantic oceans, as well as the Mediterranean Sea. We amplified 574 bp of the mitochondrial COI gene in 258 individuals and found a total of 52 haplotypes. A haplotype tree revealed two main groups of haplotypes. The relative frequency of each group of haplotypes, multidimensional scaling, and analysis of molecular variance showed important differences between the western Australia localities and the remaining ones (eastern Australia and introduced populations). Furthermore, we found that the colonization of the different areas by M. squamiger has not occurred independently, as many introduced populations shared some low frequency alleles. A nested clade analysis showed a global pattern of restricted gene flow with isolation by distance, although we found episodes of long-distance dispersal in some clades. A contiguous range expansion was detected between Australian populations. We conclude that M. squamiger is native to Australia and has most likely expanded its range of distribution sequentially through worldwide shipping, especially from the harbours of the more populated eastern Australia. In introduced populations, we found a high genetic diversity which suggests enhanced invasive potential. Consequently, there is a need to control this species, as it outcompetes local biota and is an economic threat. Web of Science Microcosmus squamiger Field - Observational marine Intertidal/Near Shore Invasion Hyp. Other filter 478 Rodriguez-Buritica, Susana; Miriti, Maria N. 2009 Biting the hand that feeds: the invasive grass Schismus barbatus (Poaceae) is facilitated by, but reduces establishment of, the native shrub Ambrosia dumosa (Asteraceae) journal JOURNAL OF VEGETATION SCIENCE 20 2 241 250 We present a study of positive and negative interactions between the invasive grass Schismus barbatus (Poaceae) and Ambrosia dumosa (Asteraceae). Ambrosia facilitates seedling establishment, and such facilitation may accelerate invasion of exotic species, which, in turn, may reduce establishment of native plants. Joshua Tree National Park, California, USA. During 2003-2004, we used field surveys to characterize the natural spatial distribution of Schismus in relation to native shrubs, and experimentally manipulated seed rain of Ambrosia and Schismus at three distances from adult Ambrosia canopies. We measured percentage germination and individual performance of both species. Field data were complemented by a greenhouse experiment that measured competition between Ambrosia seedlings and Schismus planted at three densities and five relative abundances under controlled conditions. Field surveys showed that the density of Schismus is independent of Ambrosia shrubs, but growth is enhanced near shrub canopies. In our field experiment Schismus is facilitated by adult Ambrosia. Under controlled conditions, Schismus does not respond to the density of Ambrosia seedlings, but changes in density of Schismus decreased performance of Ambrosia seedlings. Schismus invasion may be detrimental to native perennial plant populations. Although a reduction of seedling establishment is not usually expected to slow population growth of long-lived perennials, recent unprecedented adult mortality in this community, and the well-documented facilitative role of Ambrosia, suggest that Schismus invasion may be of high ecological significance. Web of Science Schismus barbatus USA California Joshua Tree Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Mutualism Facilitation primary 480 Rodriguez-Echeverria, Susana; Crisostomo, Joao A.; Nabais, Cristina; Freitas, Helena 2009 Belowground mutualists and the invasive ability of Acacia longifolia in coastal dunes of Portugal journal BIOLOGICAL INVASIONS 11 3 651 661 The ability to form symbiotic associations with soil microorganisms and the consequences for plant growth were studied for three woody legumes grown in five different soils of a Portuguese coastal dune system. Seedlings of the invasive Acacia longifolia and the natives Ulex europaeus and Cytisus grandiflorus were planted in the five soil types in which at least one of these species appear in the studied coastal dune system. We found significant differences between the three woody legumes in the number of nodules produced, final plant biomass and shoot N-15 content. The number of nodules produced by A. longifolia was more than five times higher than the number of nodules produced by the native legumes. The obtained N-15 values suggest that both A. longifolia and U. europaeus incorporated more biologically-fixed nitrogen than C. grandiflorus which is also the species with the smallest distribution. Finally, differences were also found between the three species in the allocation of biomass in the different studied soils. Acacia longifolia displayed a lower phenotypic plasticity than the two native legumes which resulted in a greater allocation to aboveground biomass in the soils with lower nutrient content. We conclude that the invasive success of A. longifolia in the studied coastal sand dune system is correlated to its capacity to nodulate profusely and to use the biologically-fixed nitrogen to enhance aboveground growth in soils with low N content. Web of Science Acacia longifolia Portugal Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority Rapid Growth primary 483 Roscher, Christiane; Bessler, Holger; Oelmann, Yvonne; Engels, Christof; Wilcke, Wolfgang; Schulze, Ernst-Detlef 2009 Resources, recruitment limitation and invader species identity determine pattern of spontaneous invasion in experimental grasslands journal JOURNAL OF ECOLOGY 97 1 32 47 1. A number of experimental studies have supported the hypothesis that diversity increases invasion resistance, but several mechanisms were proposed to explain this relationship. We studied spontaneous invasion in experimental grasslands varying in species richness (1-16 (60)) and plant functional group richness and identity (1-4; grasses, legumes, tall herbs small herbs) during the first 3 years after establishment on large-area plots of 20 x 20 m size. 2. Invader species number, biomass and density decreased with increasing community species richness. The identity of successful invaders changed through time as the relative importance of external invaders (= species not belonging to the experimental species pool) decreased, while internal invaders (= species belonging to the experimental species pool) became more important. The presence of legumes increased, while the presence of grasses in the plant communities decreased density, biomass and species number of external invaders and biomass of internal invaders in the second and third year after establishment. 3. Analyses of viable seeds in the topsoil, a higher invasion in communities with more potential invaders in adjacent plots and an edge effect with a higher invader density and species number at the margin of the plots suggested recruitment limitation of internal invader species in contrast to external invader species that were more strongly limited by community characteristics. 4. Resource availability, in particular percentage cover of resident species, root length density and soil nitrate, and propagule availability had significant effects on invasibility. However, statistical analyses revealed that these variables did not completely control for effects of community species richness and the presence of grasses and legumes respectively on invasion resistance. 5. Separate analyses of frequent invader species showed that the invasion success of individual species varied in response to biodiversity and resource niches. 6. Synthesis. Our results confirm that a more complete use of available resources in plant communities of increasing species richness generally decreases invasibility. However, the overall positive effects of biodiversity on invasion resistance are dependent on species identity of the invader species. Thus, mechanisms at species level are important to understand community invasion resistance. Web of Science Many Germany Jena River Sale 50.0833 11.5833 Field - Experimental terrestrial Grassland Invasion Hyp. Community Species Richness primary 484 Ross, Christel A.; Auge, Harald 2008 Invasive Mahonia plants outgrow their native relatives journal PLANT ECOLOGY 199 1 21 31 Invasive populations often grow more vigorously than conspecific populations in the native range. This has frequently been attributed to evolutionary changes resulting either from founder effects, or from natural selection owing to enemy release. Another mechanism contributing to evolutionary change has largely been neglected in the past: Many invasive plant species do actually descend from cultivated plants and were therefore subject to breeding, including hybridization and artificial selection. In a common garden experiment, we compared invasive Central European populations of the ornamental shrub, Mahonia, with native populations of its putative parental species, Mahonia aquifolium and M. repens, from North America. We hypothesized that plants of invasive populations show increased growth and retained high levels of heritable variation in phenotypic traits. Indeed, invasive Mahonia plants grew larger in terms of stem length, number of leaves and above-ground biomass than either of the two native species, which did not differ significantly from each other. Since there are no hints on release of invasive Mahonia populations from natural enemies, it is likely that hybridization and subsequent selection by breeders have lead to an evolutionary increase of plant vigour in the introduced range. Further on, heritable variation was not consistently reduced in invasive populations compared with populations of the two native species. We suggest that interspecific hybridization among the Mahonia species has counteracted the harmful effects of genetic bottlenecks often associated with species introductions. Based on this case study, we conclude that, more attention has to be paid on the role of plant breeding when assessing the mechanisms behind successful plant invasions in future. Web of Science Mahonia aquifolium Germany Bad Lauchstädt 51.37 11.83 Field - Experimental terrestrial Deciduous Forest;Old Field Invasion Hyp. Hybridization primary 486 Ross, Christel A.; Faust, Daniela; Auge, Harald 2009 Mahonia invasions in different habitats: local adaptation or general-purpose genotypes? journal BIOLOGICAL INVASIONS 11 2 441 452 Rapid evolutionary adaptations and phenotypic plasticity have been suggested to be two important, but not mutually exclusive, mechanisms contributing to the spread of invasive species. Adaptive evolution in invasive plants has been shown to occur at large spatial scales to different climatic regions, but local adaptation at a smaller scale, e.g. to different habitats within a region, has rarely been studied. Therefore, we performed a case study on invasive Mahonia populations to investigate whether local adaptation may have contributed to their spread. We hypothesized that the invasion success of these populations is promoted by adaptive differentiation in response to local environmental conditions, in particular to the different soils in these habitats. To test this hypothesis, we carried out a reciprocal transplantation experiment in the field using seedlings from five Mahonia populations in Germany that are representative for the range of habitats invaded, and a greenhouse experiment that specifically compared the responses to the different soils of these habitats. We found no evidence for local adaptation of invasive Mahonia populations because seedlings from all populations responded similarly to different habitats and soils. In a second greenhouse experiment we examined genetic variation within populations, but seedlings from different maternal families did not vary in their responses to soil conditions. We therefore suggest that local adaptation of seedlings does not play a major role for the invasion success of Mahonia populations and that phenotypic plasticity, instead, could be an important trait in this stage of the life cycle. Web of Science Mahonia aquifolium; Mahonia repens Germany Bad Lauchstädt 51.37 11.83 Field - Experimental terrestrial Deciduous Forest;Old Field Invasion Hyp. Plasticity primary 487 Ross, Kenneth G.; Shoemaker, D. DeWayne 2008 Estimation of the number of founders of an invasive pest insect population: the fire ant Solenopsis invicta in the USA journal PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES 275 127 2231 2240 Determination of the number of founders responsible for the establishment of invasive populations is important for developing biologically based management practices, predicting the invasive potential of species, and making inferences about ecological and evolutionary processes. The fire ant Solenopsis invicta is a major invasive pest insect first introduced into the USA from its native South American range in the mid-1930s. We use data from diverse genetic markers surveyed in the source population and the USA to estimate the number of founders of this introduced population. Data from different classes of nuclear markers (microsatellites, allozymes, sex-determination locus) and mitochondrial DNA are largely congruent in suggesting that 9-20 unrelated mated queens comprised the initial founder group to colonize the USA at Mobile, Alabama. Estimates of founder group size based on expanded samples from throughout the southern USA were marginally higher than this, consistent with the hypothesis of one or more secondary introductions of the ant into the USA. The rapid spread and massive population build-up of introduced S. invicta occurred despite the loss of substantial genetic variation associated with the relatively small invasive propagule size, a pattern especially surprising in light of the substantial genetic load imposed by the loss of variation at the sex-determination locus. Web of Science Solenopsis invicta USA Field - Observational terrestrial Fundamentals omnivore 488 Ross, Louise C.; Lambdon, Philip W.; Hulme, Philip E. 2008 Disentangling the roles of climate, propagule pressure and land use on the current and potential elevational distribution of the invasive weed Oxalis pes-caprae L. on Crete journal PERSPECTIVES IN PLANT ECOLOGY EVOLUTION AND SYSTEMATICS 10 4 251 258 Climatic warming and land use change are likely to facilitate range expansions in invasive plant species, although the ability to predict such changes requires a better mechanistic understanding of the biological limits of populations. The introduced weed Oxalis pes-caprae, a significant pest of cultivation in many Mediterranean-type ecosystems, presents a suitable case study. The species distribution in the Mediterranean Basin closely follows that of olive Cultivation, limited to below 600 m; yet its potential to colonise Vulnerable areas at higher elevations has yet to be adequately assessed. To investigate the possibility, plant performance was assessed by experimentally sowing O. pes-caprae bulbils along an altitudinal gradient in the Lefka Ori mountains, Crete. The survivorship and bulbil biomass of the resulting plants all declined significantly with elevation, irrespective of soil type, initial bulbil size or seasonal variation. Whilst plants survived vegetatively up to 1400 in, seasonal bulbil productivity, likely to be critical to population viability, exceeded that of the sown bulbil biomass only below 750 in. These data indicate that the current elevation of O. pes-caprae is close to, but not at, its current climatic limit, and that low propagule pressure and scarcity of suitable habitat probably also act to limit the altitudinal distribution. Plant performance was correlated strongly with the duration of spring snow cover. Despite a 2 degrees C difference in mean spring temperatures in the 2 years of study, the predicted elevational change was only 37 m higher in the milder conditions. Overall, our results suggest that while O. pes-caprae performance is strongly linked to climate and is Currently close to its climatic limit on Crete, there is limited scope for further spread unless land use and/or propagule pressure change at higher elevations. For this species, these elements are likely to be more significant drivers of invasion risk than the predicted changes of future climates. (C) 2008 Rubell Foundation, ETH Zurich. Published by Elsevier GmbH. All rights reserved. Web of Science Oxalis pes-caprae Crete Lefka Ori (White Mountains) 35.26 24.07 Field - Experimental terrestrial Mountain Invasion Hyp. Inherent Superiority;Preadaptation to Climate Broad Tolerances primary 490 Rossiter-Rachor, N. A.; Setterfield, S. A.; Douglas, M. M.; Hutley, L. B.; Cook, G. D.; Schmidt, S. 2009 Invasive Andropogon gayanus (gamba grass) is an ecosystem transformer of nitrogen relations in Australian savanna journal ECOLOGICAL APPLICATIONS 19 6 1546 1560 Web of Science Andropogon gayanus Australia at Wildman Reserve, Northern Territory -12.43 131.49 Field - Observational terrestrial Grassland Impacts;Invasion Hyp. Other primary 500 Sakano, Hiroyuki; Iguchi, Kei'ichiro 2009 Food Web Structure Composed of Alien Fishes in Okinawa Island, Japan: A Stable Isotope Approach journal JOURNAL OF FRESHWATER ECOLOGY 24 3 357 365 Web of Science Many Japan Hija River and the Haebaru Reservoir 26.22 127.45 Field - Observational lotic Invasion Hyp. Empty Niche 510 Schumacher, Eva; Kueffer, Christoph; Edwards, Peter J.; Dietz, Hansjoerg 2009 Influence of light and nutrient conditions on seedling growth of native and invasive trees in the Seychelles journal BIOLOGICAL INVASIONS 11 8 1941 1954 Web of Science Alstonia macrophylla;Cinnamomum verum;Psidium cattleianum;Sandoricum koetjape;Syzygium jambos;Tabebuia pallida Seychelles Mahe Sans Souci forestry station -4.75 55.45 Garden terrestrial Tropical Forest Invasion Hyp. Fluctuating Resources primary 511 Schumacher, Eva; Kueffer, Christoph; Tobler, Monika; Gmuer, Veronika; Edwards, Peter J.; Dietz, Hansjoerg 2008 Influence of drought and shade on seedling growth of native and invasive trees in the Seychelles journal BIOTROPICA 40 5 543 549 We studied the growth of seedlings of native and invasive tree species from secondary tropical forests on Mahe (Seychelles). We were interested in whether native or invasive species are more drought-tolerant, and therefore conducted a garden (pot) experiment comparing the growth of seedlings of five native and five invasive tree species under different light (7% and 60% transmittance) and water (natural and repeated drought stress) conditions. Differences in the responses of native and invasive species to these treatments were small. In both groups, mean relative growth rates were reduced only slightly by intermittent drought that caused wilting of leaves. However, invasive species produced clearly thinner leaves (high specific leaf area, SLA) and more root biomass than native species under high light, while these differences were small under low light. Native species performed better than invasive species under low light with low water availability. It appears that high phenotypic plasticity allows some fast-growing invasive species to cope with water stress by adjusting the relative allocation of resources to aboveground and belowground structures under high light, while this strategy is not effective when both light and water resources are limiting. We conclude that water stress may reduce the invasibility of shaded habitats by fast-growing invasive species, while water stress in unshaded habitats may have less effect on invasive species than previously recognized. Web of Science Alstonia macrophylla; Cinnamomum verum; Psidium cattleianum; Syzygium jambos (L.); Tabebuia pallida (Lindl.) Seychelles Mahe Sans Souci forestry station -4.38 55.27 Garden terrestrial Tropical Forest Invasion Hyp. Inherent Superiority Broad Tolerances primary 512 Schutzenhofer, Michele R.; Valone, Thomas J.; Knight, Tiffany M. 2009 Herbivory and population dynamics of invasive and native Lespedeza journal OECOLOGIA 161 1 57 66 Web of Science Lespedeza cuneata United States Missouri Washington University’s Tyson Research Center 38.531113 -90.560303 Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Enemy Release primary 514 Seabloom, Eric W.; Borer, Elizabeth T.; Martin, Burl A.; Orrock, John L. 2009 Effects of long-term consumer manipulations on invasion in oak savanna communities journal ECOLOGY 90 5 1356 1365 Consumer-plant interactions can alter the outcome of biological invasions when native and exotic plants differ systematically in their resistance to and/or tolerance of consumer impacts. Given evidence for indirect interactions and shifts in plant communities from the few existing long-term studies, it is clear that long-term studies are a critical component for understanding the role of consumers in plant invasions. Moreover, studies of the role of consumers in mediating invasions have focused on the effects of exotic consumers, while the effects of native consumers on invasion have received little attention. Here we examine the long-term impact of a largely native vertebrate consumer community on native and exotic understory plants and recruitment of native oaks in a California oak savanna. We sampled plant community composition, oak recruitment, and soils inside and outside of 10 exclosures (mean area 1000 m(2)) that had been in place for an average of 32 years. Plots with consumers present had 41% more exotic species, 31% higher cover of exotic species, and 33% lower richness of native herbaceous perennials, suggesting that native consumers may play an important role in mediating invasion in this system. The presence of oak canopies had a strong impact on the plant community independent of consumer effects, with greater recruitment of oaks, higher cover of native shrubs, and lower cover of exotic species cover under oak canopies. The concordant variation of native tree canopy and native woody plants suggests that adult oaks provide a refuge for their seedlings and other native woody plants. Thus, the widespread loss of native oaks has likely increased exotic invasion into an important refuge for native species in the California oak savanna ecosystem. Web of Science Many USA California Field - Observational terrestrial Deciduous Forest Invasion Hyp. Community Species Richness primary 516 Seifert, Elizabeth K.; Bever, James D.; Maron, John L. 2009 Evidence for the evolution of reduced mycorrhizal dependence during plant invasion journal ECOLOGY 90 4 1055 1062 Introduced species inevitably experience novel selection pressures in their new environments as a result of changes in mutualist and antagonist relationships. While most previous work has examined how escape from specialist enemies has influenced herbivore or pathogen resistance of exotic species, post-introduction shifts in exotic dependence on mutualists have not been considered. In a common environment, we compared dependence on AM fungi of North American and European populations of Hypericum perforatum (St. John's Wort), a forb native to Europe. Introduced North American populations responded less to inoculation with AM fungi than did European populations. Root architecture was strongly correlated with mycorrhizal response, and introduced populations had finer root architecture than native populations. Finally, introduced populations exhibited decreased root and increased reproductive allocation relative to European populations, consistent with a transition to a weedier life history; however, biomass allocation patterns were uncorrelated with mycorrhizal response. These findings are the first demonstration of a genetically based reduction of mycorrhizal dependence and shift in root architecture in an introduced species. Web of Science Hypericum perforatum United States Greenhouse terrestrial Invasion Hyp. Evolution in General primary 520 Shahid, Amirah; Garneau, Danielle E.; McCay, Timothy S. 2009 Selection of Seeds of Common Native and Non-native Plants by Granivorous Rodents in the Northeastern United States journal AMERICAN MIDLAND NATURALIST 162 1 207 212 Web of Science Lonicera morrowii;Rhamnus cathartica;Rosa multiflora USA New York Madison County 42.84 -75.61 Field - Experimental terrestrial Deciduous Forest;Old Field Invasion Hyp. Other primary 522 Sharma, G. P.; Esler, K. J. 2008 Phenotypic plasticity among Echium plantagineum populations in different habitats of Western Cape, South Africa journal SOUTH AFRICAN JOURNAL OF BOTANY 74 4 746 749 This paper addresses phenotypic variation among Paterson's Curse (Echium plantagineum L.) populations in four different habitat types (tar road verges, dirt road verges, abandoned fields and natural areas) in the Western Cape region of South Africa. The species showed significant differences in plant height, seed size and seed weight with varying habitats. The reproductive index (Ri), comprising a ratio of total number of seeds to the height of the plant, demonstrated the plastic behavior of E. plantagineum in the various habitats. Results indicate that plastic responses to different habitat types contribute to E. plantagineum invasiveness, allowing range expansion and establishment through production of lighter and heavier seeds, respectively. (C) 2008 SAAB. Published by Elsevier B.V. All rights reserved. Web of Science Echium plantagineum South Africa Western Cape Region Field - Observational terrestrial Old Field Invasion Hyp. Plasticity primary 523 Sharma, Gyan P.; Raghubanshi, A. S. 2009 Plant invasions along roads: a case study from central highlands, India journal ENVIRONMENTAL MONITORING AND ASSESSMENT 157 4 191 198 Web of Science Many India Vindhyan plateau in the Sonebhadra district of Uttar Pradesh 24.13 83.59 Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 525 Sharma, Sapna; Jackson, Donald A.; Minns, Charles K. 2009 Quantifying the potential effects of climate change and the invasion of smallmouth bass on native lake trout populations across Canadian lakes journal ECOGRAPHY 32 3 517 525 Web of Science Micropterus dolomieu Canada Statistical/Meta-analysis lentic Pelagic/Open Ocean Impacts;Invasion Hyp. Climate Change predator 527 Shipunov, Alexey; Newcombe, George; Raghavendra, Anil K. H.; Anderson, Cort L. 2008 Hidden diversity of endophytic fungi in an invasive plant journal AMERICAN JOURNAL OF BOTANY 95 9 1096 1108 Fungal endophytes are important in plant ecology and common in plants. We attempted to test cointroduction and host-jumping hypotheses on a community basis by comparing endophytes isolated from invasive spotted knapweed (Centaurea stoebe, Asteraceae) in its native and invaded ranges. Of 92 combined, sequence-based haplotypes representing eight classes of Fungi, 78 occurred in only one of the two ranges. In the native range of C. stoebe, one haplotype of Alternaria altenata was clearly dominant, whereas in the invaded range, no haplotype was dominant. Many haplotypes were closely related to one another and novel. For example, six putative, new species of Botrytis were discovered as endophytes of C. stoebe, which has never been reported to have Botrytis spp.. Apparent differences between the two communities of endophytes were significant according to an analysis of similarity, but phylogenetic community structure did not differ significantly between the ranges. Both host-jumping and cointroduction of fungal endophytes likely took place during the spotted knapweed invasion. Web of Science Centaurea stoebe Lab terrestrial Grassland Invasion Hyp. Mutualism Facilitation primary 530 Sloop, Christina M.; Ayres, Debra R.; Strong, Donald R. 2009 The rapid evolution of self-fertility in Spartina hybrids (Spartina alterniflora x foliosa) invading San Francisco Bay, CA journal BIOLOGICAL INVASIONS 11 5 1131 1144 Plant hybridization can lead to the evolution of invasiveness. We wished to determine whether hybrids between the largely self-sterile Atlantic Spartina alterniflora and California native S. foliosa had evolved self-fertility during their ca 30 year existence in San Francisco Bay, CA. In pollination experiments we found that neither of the parental species was self-fertile, nor were early generation hybrids. A large fraction of later generation hybrids were profusely self-fertile. Inbreeding depression was high in the parental species and early generation hybrids, but was much reduced in later generation hybrids-some even showed outbreeding depression. We found that populations of later generation hybrids and their seedling progeny were almost two-fold more homozygous than early generation hybrids, consistent with the evidence of increased selfing shown by our parentage analyses based upon 17 microsatellite markers. We posit that evolved self-fertility has contributed substantially to the rapid spread of hybrid Spartina in San Francisco Bay. Web of Science Spartina alterniflora x foliosa United States California Elsie Roemer Marsh;Robert’s Landing;Hayward Landing;Cogswell Marsh 37.7597 -122.48 Lab terrestrial Wetland Invasion Hyp. Inherent Superiority;Hybridization Self Compatible primary 534 Song, Liying; Wu, Jinrong; Li, Changhan; Li, Furong; Peng, Shaolin; Chen, Baoming 2009 Different responses of invasive and native species to elevated CO2 concentration journal ACTA OECOLOGICA-INTERNATIONAL JOURNAL OF ECOLOGY 35 1 128 135 Increasing atmospheric CO2 concentration is regarded as an important factor facilitating invasion. However, the mechanisms by which invasive plants spread at the expense of existing native plants are poorly understood. In this study, three invasive species (Mikania micrantha, Wedelia trilobata and lpomoea cairica) and their indigenous co-occurring species or congeners (Paederia scandens, Wedelia chinensis and lpomoea pescaprae) in South China were exposed to elevated CO2 concentration (700 mu mol mol(-1)), The invasive species showed an average increase of 67.1% in photosynthetic rate, significantly different from the native species (24.8%). On average the increase of total biomass at elevated CO2 was greater for invasive species (70.3%) than for the natives (30.5%). Elevated CO2 also resulted in significant changes in biomass allocation and morphology of invasive M. micrantha and W. trilobata. These results indicate a substantial variation in response to elevated CO2 between these invasive and native plant species, which might be a potential mechanism partially explaining the success of invasion with ongoing increase in atmospheric CO2. (C) 2008 Elsevier Masson SAS. All rights reserved. Web of Science Mikania micrantha;Wedelia trilobata;lpomoea cairica Greenhouse terrestrial Invasion Hyp. Climate Change primary 537 Stevens, Jens T.; Beckage, Brian 2009 Fire feedbacks facilitate invasion of pine savannas by Brazilian pepper (Schinus terebinthifolius) journal NEW PHYTOLOGIST 184 2 365 375 Web of Science Brazilian pepper (S. terebinthifolius Raddi.) United States Florida Long Pine Key 25.414129 -80.686684 Field - Observational terrestrial Subtropical Forest Invasion Hyp. Disturbance primary 541 Stroh, Esther D.; Struckhoff, Matthew A. 2009 Exotic Plant Species Associations with Horse Trails, Old Roads, and Intact Native Communities in the Missouri Ozarks journal NATURAL AREAS JOURNAL 29 1 50 56 We compared the extent to which exotic species are associated with horse trails, old roads, and intact communities within three native vegetation types in Ozark National Scenic Riverways, Missouri. We used a general linear model procedure and a Bonferroni multiple comparison test to compare exotic species richness, exotic to native species ratios, and exotic species percent cover across three usage types (horse trails, old roads, and intact communities) and three community types (river bottoms, upland waterways, and glades). We found that both exotic species richness and the ratio of exotic species to native species were greater in plots located along horse trails than in plots located either in intact native communities or along old roads. Native community types did not differ in the number of exotic species present, but river bottoms had a significantly higher exotic to native species ratio than glades. Continued introduction of exotic plant propagules may explain why horse trails contain more exotic species than other areas in a highly disturbed landscape. Web of Science Many United States Missouri Ozark National Scenic Riverways Field - Observational terrestrial Coniferous Forest;Riparian;Old Field Invasion Hyp. Other primary 542 Strong, James A.; Maggs, Christine A.; Johnson, Mark P. 2009 The extent of grazing release from epiphytism for Sargassum muticum (Phaeophyceae) within the invaded range journal JOURNAL OF THE MARINE BIOLOGICAL ASSOCIATION OF THE UNITED KINGDOM 89 2 303 314 The overall biotic pressure on a newly introduced species may be less than that experienced within its native range, facilitating invasion. The brown alga Sargassum muticum (Yendo) Fensholt is a conspicuous and successful invasive species originally from Japan and China. We compared S. muticum and native macroalgae with respect to the biotic pressures of mesoherbivore grazing and ectocarpoid fouling. In Strangford Lough, Northern Ireland, S. muticum thalli were as heavily overgrown with seasonal blooms of epiphytic algae as native macroalgal species were. The herbivorous amphipod Dexamine spinosa was much more abundant on S. muticum than on any native macroalga. When cultured with this amphipod, S. muticum lost more tissue than three native macroalgae, Saccharina latissima (Linnaeus) Lane et al., Halidrys siliquosa (Linnaeus) Lyngbye and Fucus serratus Linnaeus. Sargassum muticum cultured with both ectocarpoid fouling and amphipods showed a severe impact, consistent with our previous findings of large declines in the density of S. muticum observed in the field during the peak of fouling. Despite being a recent introduction into the macroalgal community in Strangford Lough, S. muticum appears to be under biotic pressure at least equal to that on native species, suggesting that release from grazing and epiphytism does not contribute to the invasiveness of this species in Strangford Lough. Web of Science Sargassum muticum United Kingdom Northern Ireland Strangford Lough, Dorn 54.4351 -5.5413 Field - Experimental marine Intertidal/Near Shore Invasion Hyp. Enemy Release primary 546 Sun, Yan; Ding, Jianqing; Rena, Mingxun 2009 Effects of simulated herbivory and resource availability on the invasive plant, Alternanthera philoxeroides in different habitats journal BIOLOGICAL CONTROL 48 3 287 293 In biological control programs, the insect natural enemy's ability to suppress the plant invader may be affected by abiotic factors, such as resource availability, that can influence plant growth and reproduction. Understanding plant tolerance to herbivory under different environmental conditions will help to improve biocontrol efficacy. The invasive alligator weed (Alternanthera philoxeroides) has been successfully controlled by natural enemies in many aquatic habitats but not in terrestrial environments worldwide. This study examined the effects of different levels of simulated leaf herbivory on the growth of alligator weed at two levels of fertilization and three levels of soil moisture (aquatic, semi-aquatic, and terrestrial habitats). Increasing levels of simulated (manual) defoliation generally caused decreases in total biomass in all habitats. However, the plant appeared to respond differently to high levels of herbivory in the three habitats. Terrestrial plants showed the highest below-above ground mass ratio (R/S), indicating the plant is more tolerant to herbivory in terrestrial habitats than in aquatic habitats. The unfertilized treatment exhibited greater tolerance than the fertilized treatment in the terrestrial habitat at the first stage of this experiment (day 15), but fertilizer appears not to have influenced tolerance at the middle and last stages of the experiment. No such difference was found in semi-aquatic and aquatic habitats. These findings suggest that plant tolerance is affected by habitats and soil nutrients and this relationship could influence the biological control outcome. Plant compensatory response to herbivory under different environmental conditions should, therefore, be carefully considered when planning to use biological control in management programs against invasive plants. (C) 2008 Elsevier Inc. All rights reserved. Web of Science Alternanthera philoxeroides China Wuhan Wuhan Botanical Institute 30.544965 114.420333 Greenhouse terrestrial;lotic Wetland;Riparian Fundamentals primary 557 Thorpe, Andrea S.; Thelen, Giles C.; Diaconu, Alecu; Callaway, Ragan M. 2009 Root exudate is allelopathic in invaded community but not in native community: field evidence for the novel weapons hypothesis journal JOURNAL OF ECOLOGY 97 4 641 645 Web of Science Centaurea stoebe United States Montana Moccasin Ridge 46.75 -113.75 Field - Experimental terrestrial Grassland Invasion Hyp. Novel Weapons primary 561 Traveset, Anna; Brundu, Giuseppe; Carta, Luisa; Mprezetou, Irene; Lambdon, Philip; Manca, Manuela; Medail, Frederic; Moragues, Eva; Rodriguez-Perez, Javier; Siamantziouras, Akis-Stavros D.; Suehs, Carey M.; Troumbis, Andreas Y.; Vila, Montserrat; Hulme, Philip E. 2008 Consistent performance of invasive plant species within and among islands of the Mediterranean basin journal BIOLOGICAL INVASIONS 10 6 847 858 Since the success of an invasive species depends not only upon its intrinsic traits but also on particular characteristics of the recipient habitat, assessing the performance of an invader across habitats provides a more realistic analysis of risk. Such an analysis will not only provide insights into the traits related to invasiveness, but also the habitat characteristics that underpin vulnerability to invasion that, taken together, will facilitate the selection of management strategies to mitigate the invader's effect. In the present study, we considered the Mediterranean basin islands as an excellent study region to test how the same invasive species perform in different habitats within a single island, and to scale up differences among islands with similar climate. We tested how the performance of three widespread plant invaders with clonal growth but contrasting life-history traits, a deciduous tree Ailanthus altissima, a succulent subshrub Carpobrotus spp., and an annual geophyte Oxalis pes-caprae, varied depending upon the species identity, habitat, and invaded island. The environmental parameters considered were habitat type, elevation, species diversity in the invaded plot, and several soil traits (% C, % N, C/N, pH, and relative humidity). The study documents that the performance of these three important and widespread plant invaders is dependent mainly on species identity, and less upon the invaded island's general features. Likewise, differences in performance among habitats were only significant in the case of Ailanthus, whereas Carpobrotus and Oxalis appear to perform equally well in different environments. Ailanthus thus appears to have a broader spectrum of invasiveness, being able to invade a larger number of habitat types. On the contrary, Carpobrotus spp. have not yet invaded habitats different from those where the species have been originally introduced and where they are still commonly spread by humans. Oxalis distribution is mainly related to agricultural activities and disturbed sites, and the total area infested by this geophyte may be more reflection of the extent of suitable habitats than of invasiveness or ecological impact. Our results confirm the potential for these species to significantly alter the functioning of ecosystems in the Mediterranean islands and highlight the risk to other islands not yet invaded. Web of Science Ailanthus altissima; Carpobrotus spp.; Oxalis pes-caprae Greece; Italy; France; Spain Crete and Lesbos in the Aegean archipelago of Greece, Sardinia in Italy, Corsica and the Hye`res Archipelago (i.e., Bagaud and Porquerolles) in France, as well as Mallorca and Menorca in Spain Field - Observational terrestrial Invasion Hyp. Other primary 562 Treier, Urs A.; Broennimann, Olivier; Normand, Signe; Guisan, Antoine; Schaffner, Urs; Steinger, Thomas; Mueller-Schaerer, Heinz 2009 Shift in cytotype frequency and niche space in the invasive plant Centaurea maculosa journal ECOLOGY 90 5 1366 1377 Polyploidy is often assumed to increase the spread and thus the success of alien plant species, but few empirical studies exist. We tested this hypothesis with Centaurea maculosa Lam., a species native to Europe and introduced into North America approximately 120 years ago where it became highly invasive. We analyzed the ploidy level of more than 2000 plants from 93 native and 48 invasive C. maculosa populations and found a pronounced shift in the relative frequency of diploid and tetraploid cytotypes. In Europe diploid populations occur in higher frequencies than tetraploids and only four populations had both cytotypes, while in North America diploid plants were found in only one mixed population and thus tetraploids clearly dominated. Our results showed a pronounced shift in the climatic niche between tetraploid populations in the native and introduced range toward drier climate in North America and a similar albeit smaller shift between diploids and tetraploids in the native range. The field data indicate that diploids have a predominately monocarpic life cycle, while tetraploids are often polycarpic. Additionally, the polycarpic life-form seems to be more prevalent among tetraploids in the introduced range than among tetraploids in the native range. Our study suggests that both ploidy types of C. maculosa were introduced into North America, but tetraploids became the dominant cytotype with invasion. We suggest that the invasive success of C. maculosa is partly due to preadaptation of the tetraploid cytotype in Europe to drier climate and possibly further adaptation to these conditions in the introduced range. The potential for earlier and longer seed production associated with the polycarpic life cycle constitutes an additional factor that may have led to the dominance of tetraploids over diploids in the introduced range. Web of Science Centaurea stoebe Lab terrestrial Invasion Hyp. Evolution in General;Preadaptation to Climate;Other primary 572 Van Grunsven, R. H. A.; Bos, F.; Ripley, B. S.; Suehs, C. M.; Veenendaal, E. M. 2009 Release from soil pathogens plays an important role in the success of invasive Carpobrotus in the Mediterranean journal SOUTH AFRICAN JOURNAL OF BOTANY 75 1 172 175 Introduced plant species can become locally dominant and threaten native flora and fauna. This dominance is often thought to be a result of release from specialist enemies in the invaded range, or the evolution of increased competitive ability. Soil borne microorganisms have often been overlooked as enemies in this context, but a less deleterious plant soil interaction in the invaded range could explain local dominance. Two plant species, Carpobrotus edulis and the hybrid Carpobrotus X cf. acinaciformis, are considered major pests in the Mediterranean basin. We tested if release from soil-borne enemies and/or evolution of increased competitive ability could explain this dominance. Comparing biomass production in non-sterile soil with that in sterilized soil, we found that inoculation with rhizosphere soil from the native range reduced biomass production by 32% while inoculation with rhizosphere soil from the invaded range did not have a significant effect on plant biomass. Genotypes from the invaded range, including a hybrid, did not perform better than plants from the native range in sterile soil. Hence evolution of increased competitive ability and hybridization do not seem to play a major role. We conclude that the reduced negative net impact of the soil community in the invaded range may contribute to the success of Carpobrotus species in the Mediterranean basin. (C) 2008 SAAB. Published by Elsevier B.V. All rights reserved. Web of Science Carpobrotus eduli Spain Cadiz; Malaga Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Evolution of Increased Competitive Ability;Hybridization primary 576 Vanparys, Valerie; Meerts, Pierre; Jacquemart, Anne-Laure 2008 Plant-pollinator interactions: comparison between an invasive and a native congeneric species journal ACTA OECOLOGICA-INTERNATIONAL JOURNAL OF ECOLOGY 34 3 361 369 Plant-pollinator interactions determine reproductive success for animal-pollinated species and, in the case of invasive plants, they are supposed to play an important role in invasive success. We compared the invasive Senecio inaequidens to its native congener S. jacobaea in terms of interactions with pollinators. Visitor guild, visitation rate, and seed set were compared over 3 years in three sites in Belgium. Floral display (capitula number and arrangement) and phenology were quantified, and visiting insects were individually censused, i.e. number of visited capitula and time per visited capitulum. As expected from capitula resemblance, visitor guilds of both species were very similar (proportional similarity = 0.94). Senecio inaequidens was visited by 33 species, versus 36 for S. jacobaea. For both species, main visitors were Diptera, especially Syrphidae, and Hymenoptera. Visitation rate averaged 0.13 visitor per capitulum per 10 min for S. inaequidens against 0.08 for S. jacobaea. However, insects visited more capitula per plant on S. jacobaea, due to high capitula density (886 m(-2) versus 206 m (2) for S. inaequidens), which is likely to increase self-pollen deposition considerably. Seed set of S. jacobaea was lower than that of S. inacquidens. We suggest that floral display is the major factor explaining the differences in insect visitation and seed set between the two Senecio species. (C) 2008 Elsevier Masson SAS. All rights reserved. Web of Science Senecio inaequidens Belgium Nossegem 50.8717;51.2433 4.5108;4.3875 Field - Observational terrestrial Invasion Hyp. Mutualism Facilitation primary 580 Vermeij, M. J. A.; Smith, T. B.; Dailer, M. L.; Smith, C. M. 2009 Release from native herbivores facilitates the persistence of invasive marine algae: a biogeographical comparison of the relative contribution of nutrients and herbivory to invasion success journal BIOLOGICAL INVASIONS 11 6 1463 1474 The effect of herbivory and nutrient enrichment on the growth of invasive and native macroalgal species was simultaneously studied in two biogeographic regions: the Caribbean and Hawaii. Herbivores suppressed growth of invasive algae in their native (Caribbean) and invaded range (Hawaii), but despite similar levels of herbivore biomass, the intensity of herbivory was lower in Hawaii. Algal species with a circumtropical distribution did not show a similar effect of herbivores on their growth. Nutrient enrichment did not enhance growth of any algal species in either region. The reduction in herbivore intensity experienced by invasive algae in Hawaii rather than an escape from (native) herbivores provided invasive macroalgae with 'enemy release' sensu the Enemy Release Hypothesis (ERH). Since native, Hawaiian herbivores still feed and even prefer invasive algae over native species, invasion scenario's that involve predation (e.g. the ERH) could be falsely dismissed when invasive species are only studied in their invasive range. We therefore argue that escape from herbivores (i.e. enemy release) can only effectively be determined with additional information on the intensity of predation experienced by an invasive species in its native range. Web of Science Acanthophora spicifera; Hypnea musciformis United States; Netherlands Antilles Hawaii; St. Thomas; Curacao n St. Thomas (United States Virgin Islands); Curacao (Netherlands Antilles); Hawaii Field - Experimental marine Coral Reef Invasion Hyp. Enemy Release;Fluctuating Resources primary 581 Vila, Montserrat; Bartomeus, Ignasi; Dietzsch, Anke C.; Petanidou, Theodora; Steffan-Dewenter, Ingolf; Stout, Jane C.; Tscheulin, Thomas 2009 Invasive plant integration into native plant-pollinator networks across Europe journal PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES 276 127 3887 3893 Web of Science Rhododendron ponticum L. (Ericaceae); , Himalayan Impatiens glandulifera Royle (Balsaminaceae); Carpobrotus affine acinaciformis (Aizoaceae); Opuntia stricta (Haw.) Haw. (Cactaceae); ; Solanum elaeagnifolium Cav. (Solanaceae) Ireland; Germany; Greece; Spain Field - Observational terrestrial Impacts;Invasion Hyp. Mutualism Facilitation primary 582 Vila, Montserrat; Siamantziouras, Akis-Stavros D.; Brundu, Giuseppe; Camarda, Ignazio; Lambdon, Philip; Medail, Frederic; Moragues, Eva; Suehs, Carey M.; Traveset, Anna; Troumbis, Andreas Y.; Hulme, Philip E. 2008 Widespread resistance of Mediterranean island ecosystems to the establishment of three alien species journal DIVERSITY AND DISTRIBUTIONS 14 5 839 851 Although some invasive plants are cosmopolitan, not all ecosystems are invaded to the same degree. Yet there is little experimental work on how ecosystem resistance to invasion at the establishment phase differs among ecosystems. We conducted two field sowing experiments in two consecutive years to examine establishment of the deciduous tree Ailanthus altissima, the succulent subshrub Carpobrotus spp. and the annual geophyte Oxalis pes-caprae in coastal dunes, shrublands and oldfields in more than 200 sites across six Mediterranean Basin islands differing in climatic conditions and local species richness. Establishment success (i.e. percentage of plots with at least one seedling) and rates (i.e. seedling to sown seed ratio) were low, especially for Ailanthus even when accounting for differences in seed viability. Oxalis was capable of producing a new cohort of seedlings the year following planting. By contrast, all Ailanthus seedlings and half the Carpobrotus seedlings died following the first summer. Differences in establishment success and rates among ecosystems were species-, island- and year-dependent. Differences in precipitation and mean temperature were associated with differences in establishment rates across sites. Establishment rates tended to be positively correlated with cumulative precipitation and negatively with mean T-a. Unexpectedly, native species richness was not a good predictor of seedling establishment, except for higher Oxalis establishment success in species rich habitats. By conducting field sowing tests at multiple sites across a region we found that except for Oxalis, Mediterranean island ecosystems are quite resistant to invader establishment. These results suggest that differences in the degree of invasion between ecosystems and islands might be more dependent upon the influence of invasion event factors (e.g. propagule pressure) or factors acting at a later life-history stages rather than differences in the resistance imposed by ecosystems to invader recruitment. Moreover, our results support the notion that in Mediterranean ecosystems invasions are highly idiosyncratic events and strongly dependent on water availability conditions. Web of Science Ailanthus altissima (P. Mill.); Carpobrotus acinaciformis (L.) Bol.; C. edulis (L.). Greece; Italy; France; Spain Crete and Lesbos in Greece; Sardinia in Italy; Porquerolles in France; Mallorca and Menorca in Spain Field - Experimental terrestrial Chaparral/Shrublands;Old Field Invasion Hyp. Community Species Richness;Propagule Pressure;Preadaptation to Climate primary 584 Walker, N. F.; Hulme, P. E.; Hoelzel, A. R. 2009 Population genetics of an invasive riparian species, Impatiens glandulifera journal PLANT ECOLOGY 203 2 243 252 Web of Science Impatiens glandulifera Royle England Field - Observational terrestrial Invasion Hyp. Propagule Pressure;Disturbance primary 585 Wang, N.; Yu, F. -H.; Li, P. -X.; He, W. -M.; Liu, J.; Yu, G. -L.; Song, Y. -B.; Dong, M. 2009 Clonal integration supports the expansion from terrestrial to aquatic environments of the amphibious stoloniferous herb Alternanthera philoxeroides journal PLANT BIOLOGY 11 3 483 489 Effects of clonal integration on land plants have been extensively studied, but little is known about the role in amphibious plants that expand from terrestrial to aquatic conditions. We simulated expansion from terrestrial to aquatic habitats in the amphibious stoloniferous alien invasive alligator weed (Alternanthera philoxeroides) by growing basal ramets of clonal fragments in soils connected (allowing integration) or disconnected (preventing integration) to the apical ramets of the same fragments submerged in water to a depth of 0, 5, 10 or 15 cm. Clonal integration significantly increased growth and clonal reproduction of the apical ramets, but decreased both of these characteristics in basal ramets. Consequently, integration did not affect the performance of whole clonal fragments. We propose that alligator weed possesses a double-edged mechanism during population expansion: apical ramets in aquatic habitats can increase growth through connected basal parts in terrestrial habitats; however, once stolon connections with apical ramets are lost by external disturbance, the basal ramets in terrestrial habitats increase stolon and ramet production for rapid spreading. This may contribute greatly to the invasiveness of alligator weed and also make it very adaptable to habitats with heavy disturbance and/or highly heterogeneous resource supply. Web of Science Alternanthera philoxeroides China Beijing Institute of Botany, Chinese Academy of Sciences in Beijing 30.522787 114.391537 Greenhouse Riparian Invasion Hyp. Inherent Superiority Clonal Reproduction primary 589 Webster, Christopher R.; Rock, Janet H.; Froese, Robert E.; Jenkins, Michael A. 2008 Drought-herbivory interaction disrupts competitive displacement of native plants by Microstegium vimineum, 10-year results journal OECOLOGIA 157 3 497 508 Biological invasions are often exacerbated by disturbance or deviations from historic disturbance regimes. Dense understory layers of invasive exotic plants can alter successional trajectories, resulting in consequences that cascade through the biota. However, it is unclear if such layers are self-sustaining or maintained by chronic disturbances that asymmetrically depress native competitors. We examined the role of white-tailed deer (Odocoileus virginianus Zimm.) herbivory and drought on the permeability of recalcitrant understory layers dominated by the invasive exotic Microstegium vimineum (Trin.) A. Camus in 15 exclosures and 15 control plots from 1997 to 2006. This study was conducted in Cades Cove, Great Smoky Mountains National Park, Tennessee, USA. M. vimineum cover exhibited high inter- and intra-annual variation in both exclosures and controls, but displayed a significant correspondence to drought severity. Native species richness and the abundance of woody plants increased within exclosures, but not controls, following a drought-induced nadir in M. vimineum cover that occurred in 2000. By 2003, all height classes of native tree seedlings were present in exclosures and seedlings were advancing into the sapling layer (>= 50 cm tall). After 10 years, no tree seedling on a control plot had been able to attain and maintain a height >= 20 cm. Our results suggest that chronic herbivory inhibits state transitions that could occur in response to intermittent disturbances, which reduce the abundance of the invader. Consequently, recalcitrance is likely reinforced by chronic herbivory. Web of Science Microstegium vimineum USA Tennessee Cades Cove, Great Smoky Mountains National Park 35.5942 -83.8419 Field - Experimental;Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 592 West, Elizabeth J.; Davis, Andrew R.; Barnes, Peter B.; Wright, Jeffrey T. 2009 The role of recreational activities in creating fragments of invasive Caulerpa taxifolia journal JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 376 1 17 25 Web of Science Caulerpa taxifolia Australia Port Hacking; Lake Conjola 34.05; 34.16 151.08; 151.30 Field - Observational estuarine Invasion Hyp. Inherent Superiority Effective Disperser primary 595 White, Eve; Vivian-Smith, Gabrielle; Barnes, Anna 2009 Variation in exotic and native seed arrival and recruitment of bird dispersed species in subtropical forest restoration and regrowth journal PLANT ECOLOGY 204 2 231 246 Web of Science Many Australia New South Wales -28.68 153.32 Field - Observational terrestrial Subtropical Forest Invasion Hyp. Inherent Superiority;Propagule Pressure Effective Disperser primary 596 Whitney, Kenneth D.; Ahern, Jeffrey R.; Campbell, Lesley G. 2009 Hybridization-prone plant families do not generate more invasive species journal BIOLOGICAL INVASIONS 11 5 1205 1215 Many plant taxa are both hybrid-derived and invasive, suggesting a causal connection. However, given that hybridization is not rare in plants, we should expect some fraction of invasive taxa to be hybrids, even in the absence of an underlying causal relationship. Here, we test the hypothesis that hybridization leads to invasiveness by asking whether the number of hybrids and the numbers of naturalized, weedy, and invasive taxa are correlated across 256 vascular plant families. Data were derived from six regional floras and three global databases listing weeds and invasives. To account for phylogenetic nonindependence, we combined a supertree analysis with phylogenetically independent contrasts. After correcting for family size and phylogeny, we conclude that vascular plant families with a higher propensity for hybridization are not more likely to produce more naturalized, weedy, or invasive species than families less prone to hybridization. Instead, hybridization-prone families were in some cases associated with fewer naturalized species and invaders. We present two hypotheses for these patterns, one based on Levin's (Syst Bot 31:8-12, 2006) ideas on reproductive interference and another based on Darwin's naturalization hypothesis. While these results do not preclude the possibility that hybridization generates weedy and invasive taxa with some frequency, they do suggest that the signal from the hybridization-invasion process may be relatively weak and easily obscured by other processes governing plant invasions. Web of Science Many Theoretical/Modeling terrestrial Invasion Hyp. Hybridization primary 603 Wilson, Julie C.; Nibbelink, Nathan P.; Peterson, Douglas L. 2009 Thermal tolerance experiments help establish survival probabilities for tilapia, a group of potentially invasive aquatic species journal FRESHWATER BIOLOGY 54 8 1642 1650 Web of Science Oreochromis nilotica USA Georgia Lab lentic Invasion Hyp. Inherent Superiority Broad Tolerances herbivore 608 Woods, Teresa M.; Hartnett, David C.; Ferguson, Carolyn J. 2009 High propagule production and reproductive fitness homeostasis contribute to the invasiveness of Lespedeza cuneata (Fabaceae) journal BIOLOGICAL INVASIONS 11 8 1913 1927 Web of Science Lespedeza cuneata United States Kansas 39.10; 39.06; 39.04; 39.14; 39.08; 39.21; 39.16; 39.16 -96.41; -96.34; -96.34; -96.31; -96.30; -96.46; -96.28; -96.29 Field - Observational terrestrial Grassland Invasion Hyp. Inherent Superiority;Plasticity High Reprod. Output primary 610 Wu, Shan-Huah; Tsai, J. K.; Sun, H. T.; Chen, C. F.; Chiou, Chyi-Rong 2009 Patterns of plant invasions in the preserves and recreation areas of Shei-Pa National Park in Taiwan journal BOTANICAL STUDIES 50 2 217 227 Web of Science Many China Taiwan Wuling district of Shei-Pa National Park 24.23 121.18 Field - Observational terrestrial Grassland;Coniferous Forest;Riparian;Mountain Invasion Hyp. Preadaptation to Climate;Disturbance primary 612 Xiao, Derong; Zhang, Liquan; Zhu, Zhenchang 2009 A study on seed characteristics and seed bank of Spartina alterniflora at saltmarshes in the Yangtze Estuary, China journal ESTUARINE COASTAL AND SHELF SCIENCE 83 1 105 110 Web of Science Spartina alterniflora China Chongming Dongtan Nature Reserve 31.25 121.5 Field - Observational;Lab terrestrial Wetland Invasion Hyp. Inherent Superiority Effective Disperser primary 614 Xiong, Wen; Yu, Dan; Wang, Qiang; Liu, Chunhua; Wang, Ligong 2008 A snail prefers native over exotic freshwater plants: implications for the enemy release hypotheses journal FRESHWATER BIOLOGY 53 11 2256 2263 1. One of the most popular single-factor hypotheses that have been proposed to explain the naturalization and spread of introduced species is the enemy release hypothesis (ERH). Most studies have considered how specialist consumers might affect the success of exotics, but the importance of generalist herbivores has received little attention 2. In this study, we compared the palatability of native and exotic freshwater plants in both phylogenetic pairings and in region-wide assays, using a generalist consumer (the pond snail Radix swinhoei). 3. Our study indicated that, when plants were paired by taxonomic relatedness, the snail preferred native over exotic freshwater plants by a 2 : 1 ratio. The snail also preferred native over exotic plants when tested across 20 native and seven exotic species found growing in Liangzi Lake. 4. Snails consumed more biomass of native than exotic plants, providing support for the ERH and suggesting that exotic species have a potential advantage in most lakes of the middle and lower reaches of the Yangtze River in China, thus helping their invasion. Web of Science Many China Hubei Province Freshwater Ecological Station on Liangzi Lake 30.16 114.33 Lab lentic Invasion Hyp. Enemy Release primary 619 Zhang, Qian; Yang, Ruyi; Tang, Jianjun; Chen, Xin 2008 Competitive interaction between the invasive Solidago canadensis and native Kummerowia striata in lead contaminated soil journal BOTANICAL STUDIES 49 4 385 391 Higher tolerance to stressful environments may result in exotic plants being more competitive than native ones, thus promoting plant invasion. We conducted a greenhouse experiment to test this hypothesis by using invasive Solidago canadensis and native Kummerowia striata as model plant species under lead contamination. Lead was applied as Pb(AC)(2).3H(2)O in solution at three levels (0, 300 mg kg(-1) and 600 mg kg(-1) soil) to simulate control and two pollution sites on which S. canadensis was found. Invasive Solidago canadensis, native Kummerowia striata, and their combination were grown Linder each Pb treatment. Under monoculture no differences of biomass, nitrogen (N) or phosphorus (P) contents in S. canadensis were found among treatments, but the growth of native K. striata was significantly depressed at higher soil Pb concentration. When both species were mixed, elevated soil Pb concentrations significantly increased shoot biomass ratio of S. canadensis to K. striata, implying that Pb enhanced the competition of S. canadensis over K. striata. Compared to monoculture, biomass and N and P contents of S. canadensis significantly increased under mixture with K. striata in each Pb treatment. Under both monoculture and mixed culture, Pb concentrations in shoots, roots, and rhizomes of S. canadensis increased with soil Pb content, but Pb concentrations in both above- and below-ground tissues of S. canadensis were significantly lower in Mixture than that in monoculture under each Pb treatment. Both Pb treatments and mixture with native K. striata did not change biomass allocation to shoot, root and rhizome of S. canadensis. Evidence from our experiment supported the hypothesis that higher tolerance to Pb stress enabled the invasive S. canadensis to outperform the native K. striata and may have promoted its rapid invasion in Pb contaminated soil. Web of Science Solidago canadensis China Zhejiang Province 28.54 118.3 Greenhouse terrestrial Invasion Hyp. Inherent Superiority Broad Tolerances primary 620 Zhang, Shanshan; Jin, Yili; Tang, Jianjun; Chen, Xin 2009 The invasive plant Solidago canadensis L. suppresses local soil pathogens through allelopathy journal APPLIED SOIL ECOLOGY 41 2 215 222 Recent studies suggest that invasive plants pose a significant effect on local soil pathogens, which in turn affects on the plant invasion. However, the mechanisms by which invasive plants affect soil pathogens were less well known. We conducted four experiments to test the hypothesis that the invasive plant species Solidago canadensis L. may affect soilborne pathogens through exudation of allelochemicals. Two common soilborne pathogens Pythium ultimum and Rhizoctonia solani were used in the study. Tomato (Lycopersicon esculentum Mill) variety Qianhong No. 1 which is sensitive to soil pathogens P. ultimum and R. solani was used to indicate pathogenic activity (in terms of seedling mortality and damping-off). Extracts from root and rhizome of S. canadensis significantly suppressed the growth and pathogenic activity of both pathogens under Petri dish culture and sand culture (experiments 1 and 2), providing direct evidence that S. canadensis exerts allelopathic effects on these pathogens. Subsequently, a pathogen inoculation experiment under sand culture showed that pathogenic activity of both P. ultimum and R. solani was lower under the soil with S. canadensis compared to that under the soil with a common native plant Kummerowia striata (Thunb.) Schindl (experiment 3), implying that invasive S. canadensis had but native K. striata did not have allelopathic effects on soil pathogens through root and rhizome exudation. Finally, results from field soil tests showed that mortality and damping-off rate of tomato seedlings were significantly lower under the soils collected from the fields dominated by S. canadensis than that dominated by native plants at both sampling sites, suggesting that suppression of pathogens also occurs in the field. From the present experimental results we suggest that invasive S. conadensis may acquire spreading advantage in non-native habitat by using 'novel weapons' to inhibit not only local plants but also soilborne pathogens. (C) 2008 Elsevier B.V. All rights reserved. Web of Science Solidago canadensis L. China Zhejiang Field - Experimental;Greenhouse;Lab terrestrial Old Field Invasion Hyp. Novel Weapons primary 622 Zou, Jianwen; Siemann, Evan; Rogers, William E.; DeWalt, Saara J. 2008 Decreased resistance and increased tolerance to native herbivores of the invasive plant Sapium sebiferum journal ECOGRAPHY 31 5 663 671 Release from natural enemies may favor invasive plants evolving traits associated with reduced herbivore-resistance and faster-growth in introduced ranges. Given a genetic trade-off between resistance and tolerance, invasive plants could also become more tolerant to herbivory than conspecifics in the native range. We conducted a field common garden study in the native range of Sapium sebiferum using seeds from native Chinese populations and invasive North American populations to compare their growth and herbivory resistance. We also performed a cage-pot experiment to compare their resistance and tolerance to Bikasha collaris beetles that are specialist feeders on S. sebiferum trees in China. Results of the common garden study showed that Sapium seedlings of invasive populations relative to native populations were more frequently attacked by native herbivores. Growth and leaf damage were significantly higher for invasive populations than for native populations. Growth of invasive populations was not significantly affected by insecticide spray, but insecticide spray benefited that of native populations. In the bioassay trial, beetles preferentially consumed leaf tissue of invasive populations compared to native populations when beetles had a choice between them. Regression of percent leaf damage on biomass showed that invasive populations tolerated herbivory more effectively than native populations. Our results suggest that S. sebiferum from the introduced range had lower resistance but higher tolerance to specialist herbivores. Both defense strategies could have evolved as a response to the escape from natural enemies in the introduced range. Web of Science Sapium sebiferum China Nanjing, Jiangsu Nanjing Agricultural Uni 32.2 118.5 Greenhouse;Garden terrestrial Invasion Hyp. Enemy Release;Evolution of Increased Competitive Ability primary 626 Thompson, Ken; McCarthy, Michael A. 2008 Traits of British alien and native urban plants journal JOURNAL OF ECOLOGY 96 5 853 859 1. As urbanization accelerates, interest is growing in the traits of urban plants. We classified 822 UK vascular plants on the basis of their occurrence along an urban-rural gradient in 26 710 samples of vegetation from 2508 UK 1-km grid squares, including a wide range of rural habitats and Sheffield and Birmingham, two of the UK's largest cities. 2. Both alien and native species were classified with respect to mean proportion of urban land cover in the 1-km grid squares in which the species occurs (urbanity), and absolute frequency in highly urban grid squares (urban frequency). Bayesian regression models were then developed for both measures, with a wide range of plant traits as explanatory variables. 3. Results for aliens and natives and for both urban measures were remarkably similar: the single, coherent picture of 'successful urban species' that emerges from our analysis is of robust plants of relatively fertile, dry, unshaded, base-rich habitats. Only seed mass behaved very differently for natives and aliens; seed mass was related positively to success of urban natives, and negatively to success of urban aliens. Neither clonality, seed dispersal nor seed persistence in the soil were strongly linked to success in urban habitats. 4. Synthesis. Cities can provide opportunities for surprisingly rich floras, but the traits of species that can persist in cities are quite narrowly circumscribed. More generally, it is clear that analysis of traits reveals important patterns in floristic data that would be far from obvious from a purely floristic analysis. Web of Science Many England Statistical/Meta-analysis terrestrial Urban Invasion Hyp. Inherent Superiority;Other Effective Disperser;Clonal Reproduction primary 647 Ramula, Satu; Knight, Tiffany M.; Burns, Jean H.; Buckley, Yvonne M. 2008 General guidelines for invasive plant management based on comparative demography of invasive and native plant populations journal JOURNAL OF APPLIED ECOLOGY 45 4 1124 1133 1. General guidelines for invasive plant management are currently lacking. Population declines may be achieved by focusing control on demographic processes (survival, growth, fecundity) with the greatest impact on population growth rate. However, we often have little demographic information on populations in the early stages of an invasion when control can be most effective. Here we determine whether synthesis of existing demographic data on invasive and native plant populations can address this knowledge problem. 2. We compared population dynamics between invasive and native species using published matrix population models for 21 invasive and 179 native plant species. We examined whether the population growth rate responsiveness to survival, growth and fecundity perturbations varied between invasive and native species, and determined which demographic processes of invaders to target for reductions in population growth rate. 3. Invaders had higher population growth rates (lambda) than natives, resulting in differences in demographic processes. Perturbations of growth and fecundity transitions (elasticities) were more important for population growth of invaders, whereas perturbations of survival had greater importance for population growth of natives. 4. For both invasive and native species, elasticities of lambda to survival increased with life span and decreased with lambda; while elasticities to growth and fecundity decreased with life span and increased with lambda. 5. For long-lived invaders, simulated reductions in either survival, growth or fecundity transitions were generally insufficient to produce population declines, whereas multiple reductions in either survival + growth or survival + fecundity were more effective. For short-lived invaders, simulated reductions in growth or fecundity and all pairwise multiple reductions produced population declines. 6. Synthesis and applications. Life history and population growth rate of invasive species are important in the selection of control targets. For rapidly growing populations of short-lived invaders, growth and fecundity transitions should be prioritized as control targets over survival transitions. For long-lived invaders, simultaneous reductions in more than one demographic process, preferably survival and growth, are usually required to ensure population decline. These general guidelines can be applied to rapidly growing new plant invasions and at the invasion front where detailed demographic data on invasive species are lacking. Web of Science Many Statistical/Meta-analysis terrestrial Invasion Hyp. Inherent Superiority High Reprod. Output primary 655 Hussain, Anwar; Sun, Changyou; Zhou, Xiaoping; Munn, Ian A. 2008 Ecological and economic determinants of invasive tree species on Alabama forestland journal FOREST SCIENCE 54 3 339 348 The spread of invasive tree species has caused increasing harm to the environment. This study was motivated by the considerations that earlier studies generally ignored the role of economic factors related to the occurrence and abundance of invasive species, and empirical analyses of invasive trees on forestland have been inadequate. We assessed the impact of ecological and economic factors on the occurrence and number of invasive tree species on Alabama forestland since 1990. Count data models were used to analyze the 2004 Alabama Forest Inventory Analysis (FIA) data. The proportion of FIA plots with invasive species was 1.06% in 1990, 1.24% in 2000, and 1.35% in 2004. Occurrence of invasive trees on a plot depended on forest type (e.g., natural pines, planted pines, or oak-pines). Plots with planted pine were 171% less likely to be infested with invasive trees than otherwise similar plots. Number of invasive trees per plot was determined by a wide variety of factors, including site productivity, growing stock, stand age, ecoregion, plot proximity to metropolitan centers, ownership type, and forest management activity. The magnitude of the impact was especially large for the ownership type, with more invasive trees on private forestlands than on public lands. These findings suggest that both ecological and economic factors need to be considered in the prevention and control of invasive species invasion. Web of Science Many USA Alabama Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 656 Yang Ruyi; Yu Guodong; Tang Jianjun; Chen Xin 2008 Effects of metal lead on growth and mycorrhizae of an invasive plant species (Solidago canadensis L.) journal JOURNAL OF ENVIRONMENTAL SCIENCES-CHINA 20 6 739 744 It is less known whether and how soil metal lead (Pb) impacts the invasion of exotic plants. A greenhouse experiment was conducted to estimate the effects of lead on the growth and mycorrhizae of an invasive species (Solidago canadensis L.) in a microcosm system. Each microcosm unit was separated into HOST and TEST compartments by a replaceable mesh screen that allowed arbuscular mycorrhizal (AM) fungal hyphae rather than plant roots to grow into the TEST compartments. Three Pb levels (control, 300, and 600 mg/kg soil) were used in this study to simulate ambient soil and two pollution sites where S. canadensis grows. Mycorrhizal inoculum, comprised five indigenous arbuscular mycorrhizal fungal species (Glomus mosseae, Glomus versiform, Glomus diaphanum, Glomus geosporum, and Glomus etunicatum). The N-15 isotope tracer was used to quantify the mycorrhizally mediated nitrogen acquisition of plants. The results showed that S. canadensis was highly dependent on mycorrhizae. The Pb additions significantly decreased biomass and arbuscular mycorrhizal colonization (root length colonized, RLC%) but did not affect spore numbers, N (including total N and N-15) and P uptake. The facilitating efficiency of mycorrhizae on nutrient acquisition was promoted by Pb treatments. The Pb was mostly sequestered in belowground of plant (root and rhizome). The results suggest that the high efficiency of mycorrhizae on nutrient uptake might give S. canadensis a great advantage over native species in Pb polluted soils. Web of Science Solidago canadensis L. China Zhejiang Province 28.54 118.3 Greenhouse terrestrial Invasion Hyp. Mutualism Facilitation primary 657 Maron, John L.; Marler, Marilyn 2008 Effects of native species diversity and resource additions on invader impact journal AMERICAN NATURALIST 172 0 S18 S33 Theory and empirical work have demonstrated that diverse communities can inhibit invasion. Yet, it is unclear how diversity influences invader impact, how impact varies among exotics, and what the relative importance of diversity is versus extrinsic factors that themselves can influence invasion. To address these issues, we established plant assemblages that varied in native species and functional richness and crossed this gradient in diversity with resource (water) addition. Identical assemblages were either uninvaded or invaded with one of three exotic forbs: spotted knapweed (Centaurea maculosa), dalmatian toadflax (Linaria dalmatica), or sulfur cinquefoil (Potentilla recta). To determine impacts, we measured the effects of exotics on native biomass and, for spotted knapweed, on soil moisture and nitrogen levels. Assemblages with high species richness were less invaded and less impacted than less diverse assemblages. Impact scaled with exotic biomass; spotted knapweed had the largest impact on native biomass compared with the other exotics. Although invasion depressed native biomass, the net result was to increase total community yield. Water addition increased invasibility (for knapweed only) but had no effect on invader impact. Together, these results suggest that diversity inhibits invasion and reduces impact more than resource additions facilitate invasion or impact. Web of Science Centaurea maculosa; Linaria dalmatica; Potentilla recta United States Montana Fort Missoula 46.846691 -114.062119 Field - Experimental terrestrial Coral Reef Impacts;Invasion Hyp. Community Species Richness;Fluctuating Resources primary 658 van Kleunen, Mark; Fischer, Markus 2008 Adaptive rather than non-adaptive evolution of Mimulus guttatus in its invasive range journal BASIC AND APPLIED ECOLOGY 9 3 213 223 Adaptive and non-adaptive evolutionary processes are likely to play important roles in biological invasions but their relative importance has hardly ever been quantified. Moreover, although genetic differences between populations in their native versus invasive ranges may simply reflect different positions along a genetic latitudinal cline, this has rarely been controlled for. To study non-adaptive evolutionary processes in invasion of Mimulus guttatus, we used allozyme analyses on offspring of seven native populations from western North America, and three and four invasive populations from Scotland and New Zealand, respectively. To study quantitative genetic differentiation, we grew 2474 plants representing 17 native populations and the seven invasive populations in a common greenhouse environment under temporarily and permanently wet soil conditions. The absence of allozyme differentiation between the invasive and native range indicates that multiple genotypes had been introduced to Scotland and New Zealand, and suggests that founder effects and genetic drift played small, if any, roles in shaping genetic structure of invasive M. guttatus populations. Plants from the invasive and native range did not differ in phenology, floral traits and sexual and vegetative reproduction, and also not in plastic responses to the watering treatments. However, plants from the invasive range produced twice as many flower-bearing upright side branches than the ones from the native populations. Further, with increasing latitude of collection, vegetative reproduction of our experimental plants increased while sexual reproduction decreased. Plants from the invasive and native range shared these latitudinal clines. Because allozymes showed that the relatedness between native and invasive populations did not depend on latitude, this suggests that plants in the invasive regions have adapted to the local latitude. Overall, our study indicates that quantitative genetic variation of M. guttatus in its two invasive regions is shaped by adaptive evolutionary processes rather than by non-adaptive ones. (C) 2007 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved. Web of Science Mimulus guttatus Germany Potsdam 52.24 13.01 Greenhouse terrestrial Invasion Hyp. Evolution in General primary 659 Lopez-Darias, Marta; Lobo, Jorge M. 2008 Factors affecting invasive species abundance: the Barbary ground squirrel on Fuerteventura Island, Spain journal ZOOLOGICAL STUDIES 47 3 268 281 We assessed the determinants of habitat selection by the Barbary ground squirrel (Atlantoxerus getulus) at Fuerteventura (Canary Is., Spain). We implemented general linear model (GLM) procedures to analyze the relationships between squirrel abundances and 4 kinds of variables related to the biological requirements of the species (environment, food resources, biotic interactions, and refuge/shelter). We performed a variance partitioning analysis between the most explicative categories to explore correlation patterns. The time of year and weather conditions of the census clearly influenced the number of individuals observed. Shelter variables were the best correlates of both the abundance of squirrels and the number of their scat. Although food resources were less important, the presence of certain plant species was correlated with squirrel abundance, while general environmental variables and interactions with other mammals did not affect its distribution. These results improve our understanding of the ecology and the establishment of this highly successful introduced species, providing basic knowledge for use with future management strategies in the Canarian Archipelago. Web of Science Atlantoxerus getulus Spain Fuerteventura Island Canarian Archipelago 27 -13 Field - Observational terrestrial Urban Invasion Hyp. Empty Niche;Fluctuating Resources herbivore 660 Cushman, J. Hall; Meentemeyer, Ross K. 2008 Multi-scale patterns of human activity and the incidence of an exotic forest pathogen journal JOURNAL OF ECOLOGY 96 4 766 776 1. Plant pathogens can have major impacts on diverse taxa and ecological systems world-wide, and some of the most conspicuous of these are invasive non-native species. Although many factors are known to influence the distribution and abundance of plant pathogens, the extent to which humans play a role is less well-known but still critical for understanding the dynamics of invasive pathogens in natural systems. 2. One invasive pathogen of great concern world-wide is Phytophthora ramorum, which causes Sudden Oak Death, an emerging forest disease. Here, we examined the influence of humans and a range of environmental factors on the distribution of P. ramorum at three distinct spatial scales in northern and central California. 3. At the local scale, P. ramorum more commonly occurred in soil on hiking trails used heavily by humans than in soil from adjacent areas off trails. These results support the hypothesis that humans dispersed the pathogen within already infected areas and into areas lacking local sources of inoculum. 4. At the landscape scale, using a network of 202 randomly located plots across a 275 km(2) area, we found that forests on public land open to recreation exhibited higher prevalence of disease in a critical infectious host tree (bay laurel, Umbellularia californica), than forests on private lands. Infection levels were also higher in plots surrounded by large amounts of forest with warm climatic conditions and greater potential soil moisture. Although prevalence of diseased canker hosts (Quercus agrifolia, Q. kelloggii and Lithocarpus densiflora) was positively associated with dominance of bay laurel and rainy season temperatures, it was not significantly related to public access, and we hypothesize that this occurred because our study area was in the early stages of infection. 5. At the regional scale, the probability of disease occurrence at 165 sites distributed across the geographic range of P. ramorum in California increased significantly as human population density increased in the surrounding area. Chances of infection also increased significantly with precipitation and presence of bay laurel. 6. Synthesis. Our results suggest that human activity - along with temperature, moisture and host composition - is associated with increased prevalence of an influential exotic forest pathogen. These results indicate that there may be conflicts between humans and disease, and that efforts to address this issue may require aggressive management of human activity. Web of Science Phytophthora ramorum United States California Field - Observational terrestrial Grassland;Deciduous Forest Invasion Hyp. Enemy Release;Disturbance pathogen 661 Jongejans, Eelke; Shea, Katriona; Skarpaas, Olav; Kelly, Dave; Sheppard, Andy W.; Woodburn, Tim L. 2008 Dispersal and demography contributions to population spread of Carduus nutans in its native and invaded ranges journal JOURNAL OF ECOLOGY 96 4 687 697 1. Invasive species usually exhibit different spatial population dynamics in their native and invaded range. This is often attributed to demographic differences, but may be due to differences in dispersal as well. 2. Regardless of how these dispersal and demographic differences from the native range arose, studying how they contributed to increases in population spread rates will increase our understanding of what has made these species invasive. Here we investigate which vital rates and dispersal parameters of the invasive thistle Carduus nutans drive the increases in spread rate in different invaded ranges compared to that in the native range in Eurasia. 3. We construct and analyse spatial integrodifference models that combine structured, local population models with mechanistic (WALD) models of seed dispersal by wind across a homogeneous landscape. Published and new demographic and dispersal data for single populations from the native (France) and invaded (Australia, New Zealand, Kansas and Pennsylvania) ranges were used for the parameterization. 4. We developed a variance decomposition method (c*-LTRE) to analyse the contributions of the changes in the vital rates and dispersal parameters to the increases in the invasion wave speed (c*) estimates for the different invaded ranges compared to that for the native range. 5. The c*-LTRE analysis showed that the net contribution of the dispersal parameters to c* increases varied among the populations from 51% (Australia), to 79% (Kansas), to 80% (New Zealand) and to 85% (Pennsylvanian experiment). Escape from natural enemies that reduce seed set by floral herbivory was important in all invaded ranges. Large positive contributions were also made by increases in rapid growth of seedlings and small rosettes, increases in flowering probabilities and potential seed production, as well as by increased plant height and lower falling velocities of the plumed seeds. 6. Synthesis. By incorporating a mechanistic dispersal model with a structured population model, and by linking this joint model to field data from several continents, we demonstrate the relative importance of dispersal and demography to invasion success. This approach can be used to analyse which aspects of an invader's life history have changed most importantly from the native range. Web of Science Carduus nutans Australia;New Zealand;USA Kybeyan; Midland; Kansas Theoretical/Modeling terrestrial Invasion Hyp. Enemy Release primary 663 Bossdorf, Oliver; Lipowsky, Annett; Prati, Daniel 2008 Selection of preadapted populations allowed Senecio inaequidens to invade Central Europe journal DIVERSITY AND DISTRIBUTIONS 14 4 676 685 Invasive species often evolve rapidly in response to the novel biotic and abiotic conditions in their introduced range. Such adaptive evolutionary changes might play an important role in the success of some invasive species. Here, we investigated whether introduced European populations of the South African ragwort Senecio inaequidens (Asteraceae) have genetically diverged from native populations. We carried out a greenhouse experiment where 12 South African and 11 European populations were for several months grown at two levels of nutrient availability, as well as in the presence or absence of a generalist insect herbivore. We found that, in contrast to a current hypothesis, plants from introduced populations had a significantly lower reproductive output, but higher allocation to root biomass, and they were more tolerant to insect herbivory. Moreover, introduced populations were less genetically variable, but displayed greater plasticity in response to fertilization. Finally, introduced populations were phenotypically most similar to a subset of native populations from mountainous regions in southern Africa. Taking into account the species' likely history of introduction, our data support the idea that the invasion success of Senecio inaequidens in Central Europe is based on selective introduction of specific preadapted and plastic genotypes rather than on adaptive evolution in the introduced range. Web of Science Senecio inaequidens (Asteraceae) Greenhouse terrestrial Invasion Hyp. Evolution in General primary 664 Knight, Kathleen S.; Oleksyn, Jacek; Jagodzinski, Andrzej M.; Reich, Peter B.; Kasprowicz, Marek 2008 Overstorey tree species regulate colonization by native and exotic plants: a source of positive relationships between understorey diversity and invasibility journal DIVERSITY AND DISTRIBUTIONS 14 4 666 675 The North American woody species, Prunus serotina Ehrh., is an aggressive invader of forest understories in Europe. To better understand the plant invasion process, we assessed understorey plants and Prunus serotina seedlings that have colonized a 35-year-old replicated common-garden experiment of 14 tree species in south-western Poland. The density and size of established (> 1 year old) P. serotina seedlings varied among overstorey species and were related to variation in light availability and attributes of the understorey layer. In a multiple regression analysis, the density of established P. serotina seedlings was positively correlated with light availability and understorey species richness and negatively correlated with understorey species cover. These results suggest that woody invader success is adversely affected by overstorey shading and understorey competition for resources. Simultaneously, however, invader success may generally be positively associated with understorey species richness because both native and invasive plant colonization respond similarly to environmental conditions, including those influenced by overstorey tree species. Identification of characteristics of forests that increase their susceptibility to invasion may allow managers to target efforts to detect invasives and to restore forests to states that may be less invasible. Web of Science Prunus serotina Ehrh. Poland Biadaszki Siemianice Experimental Forest 51.14 18.06 Field - Observational terrestrial Coniferous Forest Invasion Hyp. Community Species Richness;Fluctuating Resources primary 665 Baret, Stphane; Cournac, Laurent; Thebaud, Christophe; Edwards, Peter; Strasberg, Dominique 2008 Effects of canopy gap size on recruitment and invasion of the non-indigenous Rubus alceifolius in lowland tropical rain forest on Reunion journal JOURNAL OF TROPICAL ECOLOGY 24 0 337 345 An important challenge of invasion biology is to understand how interactions between species traits and ecosystem properties enable alien species to become invasive at particular locations. We investigated how gap dynamics in a tropical rain forest on the island of Reunion affected the invasiveness of alien plants. In the 12 000-m(2) study area, alien plants occupied 24.9% of the area of gaps, which represented 5.62% of the forest area, but only 0.8% of the understorey area. The most abundant invasive species was Rubus alceifolius, which formed dense, monospecific stands in the largest gaps (>25 m(2)). Although plants could persist in the shade, a germination experiment revealed that canopy openings were essential for seedling establishment. A cyclone that struck the study area in 2002 caused a temporary thinning of the canopy, increasing light levels to above the threshold needed for germination of R. alceifolius and also stimulating the growth of established plants. We conclude that the ability of this and other alien species to colonize intact lowland tropical rain forest is strongly influenced by the prevailing gap dynamics. Because gaps are also essential for the regeneration of many native trees in our study area, there is a real danger of the forest being progressively degraded by alien plants. There are no simple solutions to controlling species such as Rubus alceifolius, but efforts should be focused mainly upon the larger gaps where the species are most invasive. Web of Science Many Mauritius Reunion Mare Longue natural reserve -20 57 Field - Observational terrestrial Tropical Forest Invasion Hyp. Fluctuating Resources;Disturbance primary 669 Chytry, Milan; Jarosik, Vojtech; Pysek, Petr; Hajek, Ondrej; Knollova, Ilona; Tichy, Lubomir; Danihelka, Jiri 2008 Separating habitat invasibility by alien plants from the actual level of invasion journal ECOLOGY 89 6 1541 1553 Habitats vary considerably in the level of invasion (number or proportion of alien plant species they contain), which depends on local habitat properties, propagule pressure, and climate. To determine the invasibility (susceptibility to invasions) of different habitats, it is necessary to factor out the effects of any confounding variables such as propagule pressure and climate on the level of invasion. We used 20 468 vegetation plots from 32 habitats in the Czech Republic to compare the invasibility of different habitats. Using regression trees, the proportion of alien plants, including archaeophytes (prehistoric to medieval invaders) and neophytes (recent invaders), was related to variables representing habitat properties, propagule pressure, and climate. The propagule pressure was expressed as the proportion of surrounding urban and industrial or agricultural land, human population density, distance from a river, and history of human colonization in the region. Urban and industrial land use had a positive effect on the proportion of both archaeophytes and neophytes. Agricultural land use, higher population density, and longer history of human impact positively affected the proportion of archaeophytes. Disturbed human-made habitats with herbaceous vegetation were most invaded by both groups of aliens. Neophytes were also relatively common in disturbed woody vegetation, such as broad-leaved plantations, forest clearings, and riverine scrub. These habitats also had the highest proportion of aliens after removing the effect of propagule pressure and climate, indicating that they are not only the most invaded, but also most invasible. These habitats experience recurrent disturbances and are rich, at least temporarily, in available nutrients, which supports the hypothesis that fluctuating resources are the major cause of habitat invasibility. The least invaded habitats were mires and alpine-subalpine grasslands and scrub. After removing the effect of propagule pressure and climate, some habitats actually invaded at an intermediate level had very low proportions of aliens. This indicates that these habitats (e. g., dry, wet, and saline grasslands, base-rich fens, and broad-leaved deciduous woodlands) are resistant to invasion. Web of Science Many Czech Republic Field - Observational terrestrial Invasion Hyp. Propagule Pressure;Disturbance primary 675 Dlugosch, Katrina M.; Parker, Ingrid M. 2008 Invading populations of an ornamental shrub show rapid life history evolution despite genetic bottlenecks journal ECOLOGY LETTERS 11 7 701 709 Human-mediated species introductions offer opportunities to investigate when and how non-native species to adapt to novel environments, and whether evolution has the potential to contribute to colonization success. Many long-established introductions harbour high genetic diversity, raising the possibility that multiple introductions of genetic material catalyze adaptation and/or the evolution of invasiveness. Studies of nascent invasions are rare but crucial for understanding whether genetic diversity facilitates population expansion. We explore variation and evolution in founder populations of the invasive shrub Hypericum canariense. We find that these introductions have experienced large reductions in genetic diversity, but that increased growth and a latitudinal cline in flowering phenology have nevertheless evolved. These life history changes are consistent with predictions for invasive plants. Our results highlight the potential for even genetically depauperate founding populations to adapt and evolve invasive patters of spread. Web of Science Hypericum canariense U.S.A. California University of California - Santa Cruz 36.99286 -122.058306 Garden terrestrial Chaparral/Shrublands Invasion Hyp. Evolution of Increased Competitive Ability primary 676 Diez, Jeffrey M.; Sullivan, Jon J.; Hulme, Philip E.; Edwards, Grant; Duncan, Richard P. 2008 Darwin's naturalization conundrum: dissecting taxonomic patterns of species invasions journal ECOLOGY LETTERS 11 7 674 681 Darwin acknowledged contrasting, plausible arguments for how species invasions are influenced by phylogenetic relatedness to the native community. These contrasting arguments persist today without clear resolution. Using data on the naturalization and abundance of exotic plants in the Auckland region, we show how different expectations can be accommodated through attention to scale, assumptions about niche overlap, and stage of invasion. Probability of naturalization was positively related to the number of native species in a genus but negatively related to native congener abundance, suggesting the importance of both niche availability and biotic resistance. Once naturalized, however, exotic abundance was not related to the number of native congeners, but positively related to native congener abundance. Changing the scale of analysis altered this outcome: within habitats exotic abundance was negatively related to native congener abundance, implying that native and exotic species respond similarly to broad scale environmental variation across habitats, with biotic resistance occurring within habitats. Web of Science Many New Zealand Auckland Field - Observational terrestrial Invasion Hyp. Other primary 677 Liu, J.; He, W. M.; Zhang, S. M.; Liu, F. H.; Dong, M.; Wang, R. Q. 2008 Effects of clonal integration on photosynthesis of the invasive clonal plant Alternanthera philoxeroides journal PHOTOSYNTHETICA 46 2 299 302 A greenhouse experiment examined whether clonal integration improves photosynthesis of ramets of alligator weed [Alternanthera philoxeroides (Mart.) Griseb.], a widespread invasive clonal plant in China, in heterogeneous (He) nutrient habitats. The connected pairs of ramets experienced different nutrient levels [high homogeneous (Ho) nutrient, low Ho nutrient, and two He nutrient treatments]. Clonal integration significantly improved the net photosynthetic rate, stomatal conductance, transpiration rate, and minimal and maximal chlorophyll fluorescence of ramets of alligator weed in low nutrient condition. These characteristics may contribute to the success of the ramets of alligator weed in invading contrasting habitats. The clonal integration of the invasive clonal plants may contribute significantly to their invasiveness. Web of Science Alternanthera philoxeroides China Greenhouse lentic;lotic Riparian Invasion Hyp. Inherent Superiority Rapid Growth primary 679 Gyenge, Javier; Fernandez, Maria Elena; Sarasola, Mauro; Schlichter, Tomas 2008 Testing a hypothesis of the relationship between productivity and water use efficiency in Patagonian forests with native and exotic species journal FOREST ECOLOGY AND MANAGEMENT 255 9 3281 3287 The resource use efficiency, the relationship between productivity and the amount of used resources, have been proposed to increase as forests increase their productivity and rate of resource use (Binkley, D., Stape, J.L, Ryan, M.G., 2004. Thinking about efficiency of resource use in forests. For. Ecol. Manage. 1-2, 5-16). To test the generality of this hypothesis, we estimated annual productivity and water use efficiency (WUE) of an exotic Douglas-fir (Pseudotsuga menziesii (Mirb) Franco) plantation and a multi-species native forest in N.W. Patagonia, both growing on the same site. We hypothetized that, within a site, the more productive system (a priori the Douglas-fir plantation) has a higher WUE than the less productive system (the native forest), and that within the native forest, the more productive species have higher WUE than the less productive ones. Five taxa were the most conspicuous woody species in the native forest, which was codominated by Nothofagus antarctica and Lomatia hirsuta. Both studied systems had reached their maximum leaf area index (approximately, 5 and 11 for the native and exotic forests, respectively). Annual productivity was 2.3 times higher in the Douglas-fir plantation than in the native forest, however two native! species showed similar values of biomass productivity than the exotic species. The amount of water used by the native system was lower than that used by the Douglas-fir plantation, but not as low as the observed differences in productivity, thus resulting in a higher WUE in the Douglas-fir plantation than in the native forest (1.8 times higher). In addition, WUE was also different among the native species. The lower WUE at the stand level in the case of the native forest probably is due to the presence of retamos and lauras. We concluded that: (1) the more productive system (the Douglas-fir plantation) had a higher WUE than the less productive system (the native mixed forest); (2) within the native mixed forest, the most productive species (L. hirsuta and N. antarctica) had the highest WUE of all native species. Future research is needed to explain the physiological causes (daily patterns of transpiration and carbon fixation and allocation) of the observed differences in WUE between species and whole systems. (C) 2008 Elsevier B.V. All rights reserved. Web of Science Pseudotsuga menziesii Argentina Patagonia Field - Observational terrestrial Mountain Invasion Hyp. Inherent Superiority Rapid Growth primary 680 Stokes, Kate E. 2008 Exotic invasive black willow (Salix nigra) in Australia: influence of hydrological regimes on population dynamics journal PLANT ECOLOGY 197 1 91 105 Floodplain vegetation occupies disturbance prone habitats vulnerable to exotic plant invasion. Black willow (Salix nigra Marshall) is a flood-tolerant tree native to the southeastern United States and recently invasive in Australia, where it is considered detrimental to riparian environments. Effective management of S. nigra requires understanding the impacts of hydrological conditions on population dynamics at each stage of the plant's life cycle. The influence of inundation events (timing, duration, and recession rates) on S. nigra stand dynamics and relative growth rate (RGR) was quantified across a hydrological gradient on the shorelines of Blowering Dam reservoir (NSW, Australia). Successful recruitment (sexual and asexual) and establishment is highly dependent on the position of S. nigra recruits above reservoir water levels and exposure to flooding during the first few years of establishment. Recruitment was ubiquitous along the hydrological gradient but a greater number of asexual recruits were found at higher elevations where inundation events are less frequent. Juvenile mortality was highest at lower elevations, which experienced greater depth and duration of inundation. Mean RGR was greatest in S. nigra stands experiencing no inundation over the study period and declined as inundation duration increased. Flooding events inhibit adult growth, but create suitable conditions for seedling recruits, provided the depth and duration of the flood does not exceed complete submersion for more than 30 days. To investigate relative tolerance to water table decline rooted S. nigra cuttings were grown in rhizopods, controlled growth devices that allow water-table manipulation. Water-table decline rates of 0, 1, 2, 4, and 8 cm day(-1) were applied and the response of leaf abscission measured. S. nigra cuttings were not significantly impacted at water-table decline rates of between 1 and 4 cm day(-1). Spatial location of S. nigra recruits in Australian floodplains represents a trade-off among hydrological conditions that promote recruitment without inducing mortality, resulting in a narrow spatial and temporal regeneration window critical to successful establishment. Future distribution and abundance of S. nigra in Australia will be determined by propagule availability and the degree to which current and future flow regimes create suitable hydrological conditions for successful establishment. Web of Science Salix nigra Australia New South Wales Blowering Dam reservoir -35.4167 148.2333 Field - Observational;Greenhouse terrestrial Riparian Invasion Hyp. Fluctuating Resources primary 682 Geller, Jonathan; Sotka, Erik E.; Kado, Ryusuke; Palumbi, Stephen R.; Schwindt, Evangelina 2008 Sources of invasions of a northeastern Pacific acorn barnacle, Balanus glandula, in Japan and Argentina journal MARINE ECOLOGY-PROGRESS SERIES 358 0 211 218 Within years of its introduction, the North American barnacle Balanus glandula Darwin, 1854 became an abundant member of rocky intertidal communities in Japan and Argentina. To determine the regional sources of these invasions, we compared mitochondrial cytochrome c oxidase subunit 1 (COI) and nuclear elongation factor 1 alpha (EF1) genotypes of native and introduced populations. Previously described population structure at these loci in North America conferred geographic information to genotypes. B. glandula from Argentina and southern to central California shared genotypes not found in other native populations. B. glandula from Japan and the northeastern Pacific (Puget Sound and Alaska) were differentiated from other populations by the presence of a nearly fixed nucleotide in EF1 and contained all 3 major haplotype groups of COI. These patterns indicate that sources of B, glandula in Japan and Argentina are largely from Alaska/Puget Sound and California, respectively. The broad similarity of mean seawater temperatures among introduced and native regions may have facilitated these invasions. The presence of greater variation in air temperatures in the invaded than native regions raises the possibility that temperature-related selection may play an important role in the evolution of these invasive populations. We found no evidence of multiple geographic sources of B, glandula in Japan and Argentina, nor of genetic bottlenecks in either invaded region. Web of Science balanus glandula Japan; Argentina Field - Observational marine Invasion Hyp. Preadaptation to Climate filter 683 Madsen, John D.; Wersal, Ryan M. 2008 Growth regulation of Salvinia molesta by pH and available water column nutrients journal JOURNAL OF FRESHWATER ECOLOGY 23 2 305 313 Giant salvinia (Salvinia molesta D.S. Mitchell), a native of South America, is an invasive floating aquatic fern. Previous studies have reported that growth of S. molesta is dependent on dissolved nutrients in the water and that the plant achieves maximum biomass in circumneutral to slightly acidic water. We examined giant salvinia growth in a three-by-three factorial experiment, with pH levels of 5, 6.5, and 8 and low (no addition), medium (9.0 mg L-1 N and 4.5 mg L-1 P), and high (13.5 mg L-1 N and 6.7 mg L-1 P) concentrations of added nutrients. Results indicate that pH was not a significant factor affecting S. molesta biomass (p = 0.10) after 84 days, while nutrient level significantly affected growth (p < 0.01). Water pH was a significant (p = 0.04) factor influencing S. molesta growth after 14 days. While pH may not be a factor controlling the long-term growth of S. molesta, it is important during the early stages of colonization and growth in providing an optimal growing environment. Salvinia molesta will likely succeed best in waters with high nutrient loading rates, and it may not survive or compete in waters that are limited in nutrients. Web of Science Salvinia molesta USA Mississippi Field - Experimental lentic;lotic Riparian Invasion Hyp. Inherent Superiority Superior Competitor primary 684 Campos, Claudia M.; Peco, Begona; Campos, Valeria E.; Malo, Juan E.; Giannoni, Stella M.; Suarez, Francisco 2008 Endozoochory by native and exotic herbivores in dry areas: consequences for germination and survival of Prosopis seeds journal SEED SCIENCE RESEARCH 18 2 91 100 Mammalian herbivores can play a role in the endozoochorous dispersal of Prosopis seeds in the arid zones of Argentina, and the introduction of exotic mammals can change relevant parameters of the plant's reproductive ecology. Our specific goals were to quantify the seeds of Prosopis flexuosa, P. chilensis and P. torquata contained in the faeces of native [mara (Dolichotis patagonum), guanaco (Lama guanicoe)] and exotic [donkey (Equus asinus) and hare (Lepus europaeus)] mammals, and to determine the mortality, germination percentage and germination speed of seeds borne in faeces, compared with those collected from trees. In 2006, seeds were collected directly from trees or removed from mammal faeces. Seeds were counted and classified as apparently healthy or damaged. P. torquata and P flexuosa seeds were found in the dung of guanaco, hare and mara, whereas only P flexuosa seeds appeared in donkey faeces. P chilensis seeds were only found in guanaco faeces. There was a notable relative abundance of seeds contained in small herbivore faeces in comparison to the large herbivores. The passage through the digestive tract of animals modified seed germination capacity and speed, with great variability between animal species. Guanacos had greater effects than donkeys on mortality, germination percentage and germination speed. Differences between the effects of both smaller-sized herbivores on seeds were much smaller. Web of Science Prosopis flexuosa; Prosopis chilensis; Prosopis torquata Argentina Field - Experimental terrestrial Savanna Invasion Hyp. Mutualism Facilitation primary 690 Lohrer, Andrew M.; Chiaroni, Luca D.; Hewitt, Judi E.; Thrush, Simon F. 2008 Biogenic disturbance determines invasion success in a subtidal soft-sediment system journal ECOLOGY 89 5 1299 1307 Theoretically, disturbance and diversity can influence the success of invasive colonists if (1) resource limitation is a prime determinant of invasion success and (2) disturbance and diversity affect the availability of required resources. However, resource limitation is not of overriding importance in all systems, as exemplified by marine soft sediments, one of Earth's most widespread habitat types. Here, we tested the disturbance-invasion hypothesis in a marine soft-sediment system by altering rates of biogenic disturbance and tracking the natural colonization of plots by invasive species. Levels of sediment disturbance were controlled by manipulating densities of burrowing spatangoid urchins, the dominant biogenic sediment mixers in the system. Colonization success by two invasive species (a gobiid fish and a semelid bivalve) was greatest in plots with sediment disturbance rates <500 cm(3).m(-2).d(-1), at the low end of the experimental disturbance gradient (0 to >9000 cm(3).m(-2).d(-1)). Invasive colonization declined with increasing levels of sediment disturbance, counter to the disturbance-invasion hypothesis. Increased sediment disturbance by the urchins also reduced the richness and diversity of native macrofauna, (particularly small, sedentary, surface feeders), though there was no evidence of increased availability of resources with increased disturbance that would have facilitated invasive colonization: sediment food resources (chlorophyll a and organic matter content) did not increase, and space and access to overlying water were not limited (low invertebrate abundance). Thus, our study revealed the importance of biogenic disturbance in promoting invasion resistance in a marine soft-sediment community, providing further evidence of the valuable role of bioturbation in soft-sediment systems (bioturbation also affects carbon processing, nutrient recycling, oxygen dynamics, benthic community structure, and so on.). Bioturbation rates are influenced by the presence and abundance of large burrowing species (like spatangoid urchins). Therefore, mass mortalities of large bioturbators could inflate invasion risk and alter other aspects of ecosystem performance in marine soft-sediment habitats. Web of Science Acentrogobius pflaumi New Zealand Field - Experimental marine Benthic Invasion Hyp. Disturbance herbivore 691 Lankau, Richard 2008 A chemical trait creates a genetic trade-off between intra- and interspecific competitive ability journal ECOLOGY 89 5 1181 1187 The importance of non-resource-based mechanisms of competition between plant species has been increasingly recognized, but little is known about how genetic variation and evolutionary changes in the underlying competitive traits might affect species coexistence. I found that genetic variation in sinigrin concentration, a putative allelopathic agent in Brassica nigra, affected the fitness of three heterospecific neighbor species but did not affect neighboring B. nigra individuals. Investment in sinigrin led to a negative genetic correlation between intra- and interspecific competitive ability, which over many generations could provide a strong stabilizing force maintaining both species and genetic diversity in this system. Web of Science Brassica nigra USA California Field - Experimental terrestrial Grassland Invasion Hyp. Novel Weapons primary 692 Hwang, Bernice C.; Lauenroth, William K. 2008 Effect of nitrogen, water and neighbor density on the growth of Hesperis matronalis and two native perennials journal BIOLOGICAL INVASIONS 10 5 771 779 Disturbance is a well-recognized catalyst of exotic species invasion, depriving or releasing resources into communities and favoring the spread of some invaders. Hesperis matronalis (dame's rocket) is widespread in North America and has potential to become a major problem in natural communities due to anthropogenic influences. We used a target-neighbor design in a greenhouse to grow H. matronalis and native seedlings (Campanula rotundifolia and Muhlenbergia montana) at various levels of neighbor density, nitrogen and water. H. matronalis clearly reduced C. rotundifolia and M. montana aboveground growth and maintained its competitive advantage across all treatments. We expected H. matronalis to maximize its growth and have the greatest negative effect on native species under high resource conditions because ruderal species are able to take advantage of excess resources. H. matronalis demonstrated a clearly negative effect on native species, but a particular ability to outcompete native species at high resource levels depended on resource and native species identity. We also expected that the native species would not exploit excess resources as well as H. matronalis, instead growing better under ambient or low resource conditions because of local adaptation. Rather, M. montana benefited from high water inputs, inconsistent with plant strategies characteristic of stress tolerators. Information on the effects of H. matronalis on native plants in a controlled setting may aid land managers to understand its potential effects in natural communities. Web of Science Hesperis matronalis United States Colorado Front Range 40.38 -105.51 Greenhouse terrestrial Grassland Invasion Hyp. Inherent Superiority Superior Competitor;Rapid Growth primary 693 Cheplick, Gregory Paul 2008 Growth trajectories and size-dependent reproduction in the highly invasive grass Microstegium vimineum journal BIOLOGICAL INVASIONS 10 5 761 770 To better understand the ecological and evolutionary processes that underlie the ability of invasive plants to colonize and spread in a region, basic data on quantitative genetic variation in growth and reproduction of plants from contrasting microsites are desirable. The annual grass Microstegium vimineum is an invasive colonizer of the herbaceous layer in forests of the eastern United States. This greenhouse study utilized seeds collected from maternal plants in a shady forest or sunny edge microsite in central New Jersey, USA, to examine variation in growth trajectories and size-dependent reproduction. Questions addressed were (1) do growth trajectories vary significantly among families and between microsites? and (2) does reproductive mass scale with vegetative size? The trajectory for shoot dry mass over time was significantly related to microsite, due apparently to greater growth over the final 8 weeks of plants from the interior compared to those from the edge. It is suggested that a growth increase late in the season enables plants to maximize reproduction when light conditions improve following canopy leaf senescence. Number of tillers exhibited significant variation among families within microsites, but growth trajectories did not. Positive phenotypic and genetic correlations were detected between reproductive and vegetative mass per tiller; thus selection may favor large tillers to increase seed output, a critical life history trait for an invasive weed. Web of Science Microstegium vimineum USA New Jersey Millstone Township, Monmouth County 40.2094 -74.4375 Field - Observational;Greenhouse terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority;Plasticity Superior Competitor;High Reprod. Output primary 695 Deckers, Bart; Verheyen, Kris; Vanhellemont, Margot; Maddens, Eva; Muys, Bart; Hermy, Martin 2008 Impact of avian frugivores on dispersal and recruitment of the invasive Prunus serotina in an agricultural landscape journal BIOLOGICAL INVASIONS 10 5 717 727 Although seed dispersal is considered to be a key process determining the spatial structure and spread of non-native plant populations, few studies have explicitly addressed the link between dispersal vector behaviour, seed distribution and seedling recruitment to gain insight into the process of exotic species invasion within a fragmented landscape context. The present study analyses the relationship between avian frugivory and spatial patterns of seed deposition and seedling recruitment for an expanding population of the invasive Prunus serotina in a hedgerow network landscape in Flanders, Belgium. We quantified fruit production, observed frugivores, and determined the spatial distribution of bird droppings and P. serotina seedlings. A relatively diverse assemblage of frugivores visited P. serotina seed trees, with Columba palumbus and Turdus merula being by far the most important dispersers. Landscape structure strongly affected dispersal vector behaviour and the spatial distribution of perching birds, droppings and seedlings. Frugivorous birds non-randomly dispersed seeds to perching sites and an association between perching birds, seed deposition and seedling recruitment was found. Results indicate that landscape structure contributes to non-random seed deposition of P. serotina by common local frugivores. Cutting the larger seed trees is proposed as the most feasible measure to slow down the invasion rate. Web of Science Prunus serotina Belgium Flander Antwerp 51.7 5.2 Field - Observational terrestrial Coniferous Forest Invasion Hyp. Inherent Superiority Effective Disperser primary 696 Lambdon, Philip W.; Lloret, Francisco; Hulme, Philip E. 2008 Do alien plants on Mediterranean islands tend to invade different niches from native species? journal BIOLOGICAL INVASIONS 10 5 703 716 In order to understand invasions, it is important to know how alien species exploit opportunities in unfamiliar ecosystems. For example, are aliens concentrated in niches under-exploited by native communities, or widely distributed across the ecological spectrum? To explore this question, we compared the niches occupied by 394 naturalized alien plants with a representative sample from the native flora of Mediterranean islands. When niche structure was described by a functional group categorization, the distribution of native and alien species was remarkably similar, although 'succulent shrubs' and 'trees with specialized animal pollination mechanisms' were under-represented in the native species pool. When niche structure was described by Grime's CSR strategy, the positioning of aliens and natives differed more strongly. Stress-tolerance was much rarer amongst the aliens, and a competitive strategy was more prevalent at the habitat level. This pattern is similar to previous findings in temperate Europe, although in those regions it closely reflects patterns of native diversity. Stressed environments are much more dominant in the Mediterranean. We discuss a number of factors which may contribute to this difference, e.g., competitive and ruderal niches are often associated with anthropogenic habitats, and their high invasibility may be due partly to introduction patterns rather than to a greater efficiency of aliens at exploiting them. Thus far, the reasons for invasion success amongst introduced species have proved difficult to unravel. Despite some differences, our evidence suggests that alien species naturalize across a wide range of niches. Given that their ecologies therefore vary greatly, one may ask why such species should be expected to share predictable traits at all?. Web of Science Many Spain Mediterranean Islands Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Community Species Richness primary 700 Quinn, Lauren D.; Holt, Jodie S. 2008 Ecological correlates of invasion by Arundo donax in three southern California riparian habitats journal BIOLOGICAL INVASIONS 10 5 591 601 Arundo donax L. (Poaceae) is an aggressive invader in California's riparian habitats. Field experiments were conducted to examine invader and site attributes important in early invasion. One hundred A. donax rhizomes were planted along five transects into each of three southern California riparian habitats. Pre-planting rhizome weight was recorded, along with site variables including percent bare ground, litter depth, PAR, soil moisture, soil temperature, incidence of herbivory, native canopy cover, and plant community richness and diversity. A. donax shoot emergence, survival time, and shoot height were recorded for approximately 10 months. The experiment was repeated over three years in different locations within each site. When years and sites were pooled to reveal large-scale patterns, A. donax performance was explained by rhizome weight, soil moisture, bare ground, soil temperature, and herbivory. When each site was considered singly, A. donax was positively correlated with different variables in each location. Species richness was correlated with A. donax performance in only one site. Our results indicate that A. donax establishment in riparian habitats is promoted by both vegetative reproduction and favorable abiotic environmental factors and relatively unaffected by the composition of the native community. The positive response of A. donax to disturbance (bare ground) and high resource availability (soil moisture), combined with a competitive perennial habit suggest that this species takes advantage of a competitive-ruderal life history. The ability of A. donax to respond to different conditions in each site combined with low genetic and phenotypic variation seen in other studies also suggests that a high degree of environmental tolerance contributes to invasion success. Web of Science Arundo donax L. (Poaceae) United States California Santa Ana River in Riverside; San Luis Rey River in Oceanside; Aliso Creek in Aliso Viejo, in Orange County 33.58; 33.15; 33.33 -117.26; -117.43; -117.43 Field - Experimental terrestrial Riparian Invasion Hyp. Inherent Superiority;Community Species Richness Broad Tolerances;Rapid Growth primary 703 Cummings, D. O.; Williamson, J. E. 2008 The role of herbivory and fouling on the invasive green alga Caulerpa filiformis in temperate Australian waters journal MARINE AND FRESHWATER RESEARCH 59 4 279 290 The green macroalga Caulerpa filiformis is rapidly dominating algal assemblages in shallow subtidal regions along the New South Wales (NSW) coast. Given that invasive species are known for their competitive superiority, the interactions between C. filiformis and herbivores and fouling species was investigated and were compared with those co-occurring native species. Extensive field surveys were carried out to assess purported damage from herbivores, and co-occurrence of C. filiformis with herbivorous fish and invertebrate species. Signs of herbivory on C. filiformis were visible, and several common herbivorous invertebrates and fish co-occurred with the alga. Laboratory and field feeding assays with fresh algae indicated that generalist invertebrate herbivores such as Turbo torquatus did not consume C. filiformis, whereas herbivorous fish did consume C. filiformis but not in preference to other palatable algae. C. filiformis was fouled at similar concentrations and with similar epiphytic species to other co-occurring algae. Thus the ability of C. filiformis to deter herbivory and fouling by using biotic deterrents (both chemical and structural) is limited and unlikely to be the major factor driving its successful invasion into NSW habitats. Web of Science Caulerpa filiformis Australia New South Wales Terrigal; Maroubra -33.26; -33.95 151.27; 151.27 Field - Observational;Lab marine Intertidal/Near Shore;Benthic Invasion Hyp. Enemy Release;Novel Weapons primary 708 Bartuszevige, Anne M.; Endress, Bryan A. 2008 Do ungulates facilitate native and exotic plant spread? Seed dispersal by cattle, elk and deer in northeastern Oregon journal JOURNAL OF ARID ENVIRONMENTS 72 6 904 913 Large domestic and native ungulates have the potential to disperse large quantities of seeds throughout the landscape. Many studies have found that ungulates are capable of dispersing seeds but few quantify the relative importance of ungulate dispersal across the landscape. We investigated the potential for cattle, elk, and deer to disperse native and exotic plants in two different western North American ecosystems in northeast Oregon. We collected fecal samples of cattle, elk and deer that had been deposited during the current growing season. In the greenhouse we monitored the density and species richness of seedlings that germinated from the fecal samples. All three species act as seed dispersers for native and exotic plants. Cattle fecal pats had a higher species richness and density of exotic grasses germinating compared to the other ungulates; elk had a higher species richness and density of native and exotic forbs compared to the other ungulates. We then projected the number of seeds that each animal could disperse during a growing season. We predict that cattle disperse more than an order of magnitude more seeds than elk and deer per animal. Cattle, elk and deer interact with the landscape in different ways and this can have important ramifications for plant communities at local and regional scales. (C) 2007 Elsevier Ltd. All rights reserved. Web of Science Many USA Oregon Field - Observational terrestrial Invasion Hyp. Mutualism Facilitation primary 710 Owens, Chetta S.; Smarts, R. M.; Dick, G. O. 2008 Resistance of Vallisneria to invasion from hydrilla fragments journal JOURNAL OF AQUATIC PLANT MANAGEMENT 46 0 113 116 Weighted hydrilla fragments were introduced to containers of wild celery (Vallisneria americana Michx.) grown at four water depths (18, 46, 91, 122 cm) in a research pond at the Lewisville Aquatic Ecosystem Research Facility, Lewisville, Texas. Established wild celery effectively reduced invasion by hydrilla fragments, while hydrilla fragments readily established in control containers filled with sediment alone. Hydrilla biomass harvested from controls, representing the 'empty niche,' was significantly greater (40 times) than hydrilla biomass harvested from containers planted with wild celery for all water depth treatments. This study addresses the concept that preemptive establishment of wild celery can slow or prevent invasion from hydrilla fragments at different water treatment depths. Web of Science Hydrilla verticillata United States Texas Lewisville Aquatic Ecosystem Research Facility 33.061047 -96.994171 Field - Observational lentic Invasion Hyp. Empty Niche primary 713 van der Wal, Rene; Truscott, Anne-Marie; Pearce, Imogen S. K.; Cole, Lisa; Harris, Mike P.; Wanless, Sarah 2008 Multiple anthropogenic changes cause biodiversity loss through plant invasion journal GLOBAL CHANGE BIOLOGY 14 6 1428 1436 Non-native invasive plants are a widely acknowledged threat to global biodiversity. However, our understanding of the mechanisms underlying plant invasion, and the relative importance of multiple rather than single drivers, remains poor. Here, we provide a case study using time-series data to reconstruct patterns of change, and field experiments to test for causality. We show how, over a 50-year period, a series of unrelated human-induced changes created highly favorable conditions for the non-native tree mallow (Lavatera arborea) to turn invasive, causing loss of native vegetation and seabird breeding habitat. The combination of three drivers: human-introduced disease, climate warming and a fisheries-mediated increase in seabird populations, removed major constraints on plant population growth, (i.e. grazer control, climatic control, germination opportunity and nutrient limitation). Collectively, these changes created optimal conditions for the rapid expansion of tree mallow. The resulting dramatic impact on both the native vegetation and breeding seabirds, notably puffins (Fratercula arctica), exemplifies how non-native invasive plant species can transform terrestrial ecosystems. While climate change is regarded as a key factor behind plant invasion, we highlight that multiple rather than single factors may be critical to biodiversity loss. Web of Science Lavatera arborea Scotland Craigleith 56 -2 Field - Experimental terrestrial Grassland Invasion Hyp. Disturbance;Climate Change;Other primary 719 Murphy, H. T.; Metcalfe, D. J.; Bradford, M. G.; Ford, A. F.; Galway, K. E.; Sydes, T. A.; Westcott, D. J. 2008 Recruitment dynamics of invasive species in rainforest habitats following Cyclone Larry journal AUSTRAL ECOLOGY 33 4 495 502 In tropical forests, natural disturbance creates opportunities for species to claim previously utilized space and resources and is considered an important mechanism in the maintenance of species diversity. However, ecologists have long recognized that disturbance also promotes exotic plant invasions. Cyclones cause extensive defoliation, loss of major branches and multiple tree falls, resulting in a significantly more open canopy and increased light and heat levels in the understorey. The widespread and massive disturbance caused by cyclones provides ideal conditions for rapid recruitment and spread of invasive species. The ecological roles of invasive species in rainforest habitats following such a severe disturbance are poorly understood. Severe category 4 Cyclone Larry crossed the North Queensland coast in March 2006 causing massive disturbance to rainforest habitats from Tully to Cairns and west to the Atherton Tablelands. We established 10 plots in an area extensively damaged by this cyclone near El Arish in North Queensland. On each plot nine 2 x 2 m quadrats were established with three quadrats per plot in each of the following treatments: (i) complete debris removal down to the soil layer, (ii) removal of coarse woody debris only, and (iii) uncleared. We monitored recruitment, growth and mortality of all native and invasive species in the 90 quadrats every 3 months since the cyclone. Here we present the recruitment dynamics of invasive species across the study area in relation to the level of disturbance, the type of quadrat treatment, and the diversity and abundance of the native recruiting flora over the first 12 months post-cyclone. Our results suggest that invasive species will mostly comprise a transient component of the flora in the early stages of the successional response. However, some species may have longer-term effects on the successional trajectory of the rainforest and future forest composition and structure. Web of Science Many Australia Queensland Field - Observational terrestrial Subtropical Forest Invasion Hyp. Disturbance primary 721 Callaway, Ragan M.; Cipollini, Don; Barto, Kathryn; Thelen, Giles C.; Hallett, Steven G.; Prati, Daniel; Stinson, Kristina; Klironomos, John 2008 Novel weapons: Invasive plant suppresses fungal mutualists in America but not in its native Europe journal ECOLOGY 89 4 1043 1055 Why some invasive plant species transmogrify from weak competitors at home to strong competitors abroad remains one of the most elusive questions in ecology. Some evidence suggests that disproportionately high densities of some invaders are due to the release of biochemicals that are novel, and therefore harmful, to naive organisms in their new range. So far, such evidence has been restricted to the direct phytotoxic effects of plants on other plants. Here we found that one of North America's most aggressive invaders of undisturbed forest understories, Alliaria petiolata (garlic mustard) and a plant that inhibits mycorrhizal fungal mutualists of North American native plants, has far stronger inhibitory effects on mycorrhizas in invaded North American soils than on mycorrhizas in European soils where A. petiolata is native. This antifungal effect appears to be due to specific flavonoid fractions in A. petiolata extracts. Furthermore, we found that suppression of North American mycorrhizal fungi by A. petiolata corresponds with severe inhibition of North American plant species that rely on these fungi, whereas congeneric European plants are weakly affected. These results indicate that phytochemicals, benign to resistant mycorrhizal symbionts in the home range, may be lethal to naive native mutualists in the introduced range and indirectly suppress the plants that rely on them. Web of Science Alliaria petiolata United States; Germany; Spain Vermont; Oregon; Massachusetts; Montana 42.8717;45.505;42.5233;46.8833 -73.1883;-122.69;-72.185;-113.9717 Greenhouse terrestrial Deciduous Forest Invasion Hyp. Novel Weapons primary 723 Gravuer, Kelly; Sullivan, Jon J.; Williams, Peter A.; Duncan, Richard P. 2008 Strong human association with plant invasion success for Trifolium introductions to New Zealand journal PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 105 17 6344 6349 It has proven difficult, when focused only on biological determinants, to explain why some plant species become naturalized in or invade new locations, whereas others fail. We analyzed the invasion of Trifolium (true clover) species into New Zealand, assessing a range of human, biogeographic, and biological influences at three key invasion stages: introduction, naturalization, and spread. We used sparse principal component analysis (SPCA) to define suites of related attributes and aggregated boosted trees to model relationships with invasion outcomes. Human and biogeographic attributes were strongly associated with success at all stages. Whereas biogeographic attributes, notably large native range, were consistently associated with success, different human factors appeared to favor success at different stages, such as presence in early trade/immigration hotspots (introduction), intentional large-scale planting (naturalization), and frequent presence as a seed contaminant (relative spread rate). Biological traits were less strongly associated with success for introduction and spread and little if at all for naturalization; we found that tall perennials with long flowering periods were more frequently selected for introduction, whereas species With extended flowering in New Zealand spread more rapidly. In addition to causal relationships, the importance of human factors may reflect indirect associations, including ecological traits associated with both human use and invasion. Nevertheless, our results highlight key roles that humans can play in facilitating plant invasion via two pathways: (i) commercial introduction leading to widespread planting and concomitant naturalization and spread and (h) unintentional introduction and spread of species associated with human activities, such as seed contaminants. Web of Science Trifolium New Zealand Field - Observational terrestrial Urban;Old Field Invasion Hyp. Other primary 724 Morris, Kay; Boon, Paul I.; Raulings, Elisa J.; White, Sean D. 2008 Floristic shifts in wetlands: the effects of environmental variables on the interaction between Phragmites australis (Common Reed) and Melaleuca ericifolia (Swamp Paperbark) journal MARINE AND FRESHWATER RESEARCH 59 3 187 204 Over the past 40-50 years, the woody shrub Melaleuca ericifolia has progressively invaded large areas of Phragmites australis in Dowd Morass, a Ramsar-listed, brackish wetland in south-eastern Australia. To understand the processes underlying this shift we grew Phragmites and Melaleuca alone and together under contrasting sediment organic-matter loadings and salinities. To examine if the capacity of Phragmites to aerate the sediment influenced plant interactions, we also dissipated convective gas flow in some Phragmites plants by perforating their stems. Although Phragmites suppressed the growth of Melaleuca under all conditions, Melaleuca persisted. We did not find Phragmites ramets to be more sensitive to salinity than Melaleuca seedlings. Surprisingly Phragmites did not increase sediment redox and was more sensitive to increased organic-matter loading than Melaleuca. These results do not support the notion that colonisation by Melaleuca was facilitated by a decline in Phragmites at higher salinities or through aeration of the sediments by Phragmites. Seedlings of Melaleuca, however, were easily blown over by wind and it is likely that Phragmites stands shelter Melaleuca during establishment. Although our short-term experiment did not show that Melaleuca was a better competitor, differences in seasonal growth patterns may contribute to a shift in competitive abilities over a longer time scale. Web of Science Melaleuca ericifoli Australia Dowd Morass Garden wetland Wetland Invasion Hyp. Inherent Superiority Superior Competitor primary 725 Farji-Brener, Alejandro G.; Ghermandi, Luciana 2008 Leaf-cutting ant nests near roads increase fitness of exotic plant species in natural protected areas journal PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES 275 127 1431 1440 Understanding the mechanisms that promote the invasion of natural protected areas by exotic plants is a central concern for ecology. We demonstrated that nests of the leaf-cutting ant, Acromyrmex lobicornis, near roadsides promote the abundance, growth and reproduction of two exotic plant species, Carduus nutans and Onopordum acanthium, in a national park in northern Patagonia, Argentina and determine the mechanisms that produce these effects. Refuse dumps (RDs) from ant nests have a higher nutrient content than nearby non-nest soils (NNSs); foliar nutrient content and their N-15 isotopic signature strongly suggest that plants reach and use these nutrients. Both species of exotic plants in RDs were 50-600% more abundant; seedlings had 100-1000% more foliar area and root and leaf biomass; and adult plants produced 100-300% more seeds than nearby NNS plants. Plants can thus gain access to and benefit from the nutrient content of ant RD, supporting the hypotheses that enhanced resource availability promotes exotic plant performance that could increase the likelihood of biological invasions. The two exotics produce an estimated of 8 385 000 more seeds ha(-1) in areas with ant nests compared with areas without; this exceptional increase in seed production represents a potential threat to nearby non-invaded communities. We propose several management strategies to mitigate this threat. Removal efforts of exotics should be focused on ant RDs, where plants are denser and represent a higher source of propagules. Web of Science Carduus nutans; Onopordum acanthium Argentina Patagonia Field - Observational terrestrial Mountain Invasion Hyp. Mutualism Facilitation primary 728 Burns, Jean H. 2008 Demographic performance predicts invasiveness of species in the Commelinaceae under high-nutrient conditions journal ECOLOGICAL APPLICATIONS 18 2 335 346 Demographic models are powerful tools for making predictions about the relative importance of transitions from one life stage (e. g., seeds) to another (e. g., nonreproductives); however, they have never been used to compare the relative performance of invasive and noninvasive taxa. I use demographic models parameterized from common garden experiments to develop hypotheses about the role of different life stage transitions in determining differences in performance in invasive and noninvasive congeners in the Commelinaceae. I also extended nested life table response experiment (LTRE) analyses to accommodate interactions between nested and unnested factors. Invasive species outperformed their noninvasive congeners, especially under high-nutrient conditions. This difference in performance did not appear to be due to differences in elasticities of vital rates, but rather to differences in the magnitude of stage transitions. Self-compatible invasive species had greater fecundity in high-nutrient environments and a shorter time to first reproduction, and all invasive species had greater vegetative reproduction than their noninvasive congeners. Thus greater opportunism in sexual and asexual reproduction explained the greater performance of invasive species under high-nutrient conditions. Similar common garden experiments could become a useful tool to predict potential invaders from pools of potential introductions. I show that short-term and controlled experiments considering multiple nutrient environments may accurately predict invasiveness of nonnative plant species. Web of Science Commelina benghalensis;Murdannia nudiflora;Tradescantia fluminensis;Tradescantia zebrina Greenhouse terrestrial Invasion Hyp. Inherent Superiority High Reprod. Output;Self Compatible;Clonal Reproduction primary 730 Meats, A.; Fay, H. A. C.; Drew, R. A. I. 2008 Distribution and eradication of an exotic tephritid fruit fly in Australia: relevance of invasion theory journal JOURNAL OF APPLIED ENTOMOLOGY 132 5 406 411 Data from the eradication of the incursion of Bactrocera papayae Drew and Hancock (Dipt.: Tephritidae) in Australia (1995-1998) are used to assess the significance of various aspects of invasion theory, including the influence of towns on establishment, influence of propagule pressure on the pattern of establishment, and the existence of source-sink dynamics. Because there were no sentinel traps in place, considerable spread had occurred before the eradication campaign started. The distribution of fly density around the epicentre in the town of Cairns and a transect along the main traffic routes to the north and south fitted a Cauchy model with a tail having the same slope as a power model with an exponent of -2.4 extending to 160 km. The Cauchy model indicated that 50% of the flies on the transect would have occurred within 3.2 km of the epicentre, 90% within 13.2 km, and 99% within 60 km. The two major satellites at Mareeba (35 km from the epicentre in Cairns) and Mossman (65 km) were not used for the transect data and had respectively 15 and 30 times the density predicted by the model. The proportion of traps that caught flies (a measure of site occupancy) fell with distance from the epicentre. B. papayae was trapped consistently on only three of the 16 rainforest transects that were surveyed and these were relatively close to urban areas where eradication efforts were intense. Despite there being no eradication effort in the rainforest, the trends to extinction were similar to those in adjacent areas. The strategy of initially concentrating eradication efforts on the core and major satellites while maintaining a quarantine barrier at the airport and the boundaries of the infested area appears to be the key to the containment and rapid eradication of the incursion. Web of Science Bactrocera papayae Australia Cairns Field - Observational terrestrial Subtropical Forest Invasion Hyp. Propagule Pressure herbivore 731 Surrette, Sherry B.; Brewer, J. Stephen 2008 Inferring relationships between native plant diversity and Lonicera japonica in upland forests in north Mississippi, USA journal APPLIED VEGETATION SCIENCE 11 2 205 U14 Question: Do anthropogenic disturbances interact with local environmental factors to increase the abundance and frequency of invasive species, which in turn exerts a negative effect on native biodiversity? Location: Mature Quercus-Carya and Quercus-Carya-Pinus (oak-hickory-pine) forests in north Mississippi, USA. Methods: We used partial correlation and factor analysis to investigate relationships between native ground cover plant species richness and composition, percent cover of Lonicera japonica, and local and landscape-level environmental variables and disturbance patterns in mature upland forests. We directly measured vegetation and environmental variables within 34 sampling subplots and quantified the amount of tree cover surrounding our plots using digital color aerial photography. Results: Simple bivariate correlations revealed that high species richness and a high proportion of herbs were associated with low Lonicera japonica cover, moist and sandy uncompacted soils, low disturbance in the surrounding landscape, and periodic prescribed burning. Partial correlations and factor analysis showed that once we accounted for the environmental factors, L. japonica cover was the least important predictor of composition and among the least important predictors of species richness. Hence, much of the negative correlation between native species diversity and this invasive species was explained by soil texture and local and landscape-level land-use practices. Conclusions: We conclude that negative correlations between the abundance of invasive species and native plant diversity can occur in landscapes with a gradient of human disturbance, regardless of whether there is any negative effect of invasive species on native species. Web of Science Lonicera japonica USA Mississippi Field - Observational terrestrial Deciduous Forest Invasion Hyp. Community Species Richness;Disturbance primary 732 Franks, Steven J.; Pratt, Paul D.; Dray, F. Allen; Simms, Ellen L. 2008 Selection on herbivory resistance and growth rate in an invasive plant journal AMERICAN NATURALIST 171 5 678 691 The evolution of increased competitive ability (EICA) hypothesis proposes that invasive species evolve decreased defense and increased competitive ability following natural enemy release. Previous tests of EICA examined the result of evolution by comparing individuals from home and introduced ranges, but no previous study of this hypothesis has examined the process of evolution by analyzing patterns of selection. On the basis of EICA, there should be selection for competitive ability without herbivores and selection for defense with herbivores. Selection on competitive ability should be stronger for genotypes accustomed to herbivores (home range genotypes), and selection on defense should be stronger for genotypes unaccustomed to herbivores (introduced range genotypes). Using a field experiment, we tested these hypotheses for the invasive plant Melaleuca quinquenervia. There was a negative genetic correlation between resistance and growth, indicating a trade-off. However, selection for stem elongation (an indicator of competitive ability) was always positive, and selection on resistance was always negative and did not depend on genotype source or the presence of herbivores. The patterns of selection found in this study contrast with predictions from EICA and accurately predict the lack of evolutionary change in growth and resistance following the introduction of this species from Australia to Florida. Web of Science Melaleuca quinquenervia USA Florida Field - Experimental terrestrial Savanna Invasion Hyp. Evolution of Increased Competitive Ability primary 735 Iponga, D. M.; Milton, S. J.; Richardson, D. M. 2008 Superiority in competition for light: A crucial attribute defining the impact of the invasive alien tree Schinus molle (Anacardiaceae) in South African savanna journal JOURNAL OF ARID ENVIRONMENTS 72 5 612 623 Invasion of ecosystems by woody alien plant species is a widespread phenomenon. Interspecific competition has often been suggested as a mechanism for replacement of one species by another, but this is rarely tested. We investigated the potential of an invasive alien tree to transform vegetation by quantifying the relative abilities of the alien tree Schinus molle and dominant native trees Acacia tortilis and Rhus lancea to compete for light when growing in association within a South African semi-arid savanna. Due to dispersal of its fruits by birds, seedlings of S. molle establish under tree canopies. Using canopy symmetry as an index of ability to compete for light, we found that the alien S. molle consistently out-competes the dominant native tree species. The results also show that pod, production of A. tortilis was higher when it grew alone compared to when it grew with S. molle or R. lancea. The percentage of dead branches was higher on A. tortilis trees growing in association with the S. molle. The outcome is that the alien tree will gradually increase in abundance, changing woodland structure and ecosystem processes. Our findings provide evidence for the role of competition in the process of alien plant invasions. We suggest that S. molle, previously considered a benign naturalized species in South Africa, should be declared a noxious weed in some parts of that country. (c) 2007 Elsevier Ltd. All rights reserved. Web of Science Schinus molle South Africa Northern Cape Province -28.8 24.7667 Field - Observational terrestrial Savanna Invasion Hyp. Inherent Superiority Superior Competitor primary 736 Etterson, Julie R.; Delf, Daniel E.; Craig, Timothy P.; Ando, Yoshino; Ohgushi, Takayuki 2008 Parallel patterns of clinal variation in Solidago altissima in its native range in central USA and its invasive range in Japan journal BOTANY-BOTANIQUE 86 1 91 97 The ability of exotic species to proliferate and expand their range may hinge critically upon their potential for adaptive evolution. The finding of parallel patterns of genetically based clinal variation in native and non-native ranges across similar environmental gradients supports the hypothesis that adaptive evolution has played a role in establishment and spread. In this common garden study, we compared patterns of phenotypic variation among 12 populations of Solidago altissima L. that were sampled across similar latitudes in the native range in central USA (25 degrees N-43 degrees N) and across its invasive range in Japan (26 degrees N-43 degrees N). Significant clinal variation in phenotype corresponding to latitude was found among US and Japanese populations for height, leaf number, leaf length, leaf width, stem diameter, and stomatal guard-cell size. Only the slope of leaf width differed significantly between the native and invasive range, and the slope was significantly steeper in Japan. These results indicate that patterns of selection across latitude are similar in these two countries. We suggest that populations of S. altissima have rapidly differentiated in response to the cline in selection in Japan, possibly by the sorting of lineages from multiple introductions, and this has contributed to their success as an exotic invader. Web of Science Solidago altissima USA Field - Observational terrestrial Grassland Invasion Hyp. Evolution in General primary 738 Rice, A. M.; Pfennig, D. W. 2008 Analysis of range expansion in two species undergoing character displacement: why might invaders generally 'win' during character displacement? journal JOURNAL OF EVOLUTIONARY BIOLOGY 21 3 696 704 Ecological character displacement occurs when interacting species diverge in resource use and associated traits in response to selection to minimize resource competition between them. Yet, when resource quality is asymmetric, the species that monopolizes the more profitable resource following character displacement may have higher fitness and therefore be deemed the 'winner'. Here, we ask: does the winner tend to be the resident species (i.e. the earlier inhabitant of the geographic region where character displacement occurred) or the invader (i.e. the subsequent inhabitant of the region)? We focus on two spadefoot toad species that have undergone character displacement. Previous studies revealed that Spea bombifrons gains the higher quality resource following character displacement; consequently, Spea multiplicata must use the lower quality resource, and as a result, experiences negative fitness consequences. Where the two species have undergone character displacement, three lines of evidence implicate S. bombifrons as the invader: S. bombifrons possess lower haplotype and nucleotide diversity; they do not exhibit isolation by distance (in contrast to S. multiplicata); and they display much higher population growth rates. We hypothesize that historical patterns of selection in its ancestral range pre-adapted S. bombifrons to evolve phenotypes capable of monopolizing the superior resource. Generally, because superior competitive abilities may facilitate successful invasions, invaders may be well positioned to win during character displacement. Web of Science Spea bombifrons USA Arizona San Simon Valley Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority Superior Competitor predator 742 Wilson, John R. U.; Richardson, David M.; Rouget, Mathieu; Proches, Serban; Amis, Mao A.; Henderson, Lesley; Thuiller, Wilfried 2007 Residence time and potential range: crucial considerations in modelling plant invasions journal DIVERSITY AND DISTRIBUTIONS 13 1 11 22 A prime aim of invasion biology is to predict which species will become invasive, but retrospective analyses have so far failed to develop robust generalizations. This is because many biological, environmental, and anthropogenic factors interact to determine the distribution of invasive species. However, in this paper we also argue that many analyses of invasiveness have been flawed by not considering several fundamental issues: (1) the range size of an invasive species depends on how much time it has had to spread (its residence time); (2) the range size and spread rate are mediated by the total extent of suitable (i.e. potentially invasible) habitat; and (3) the range size and spread rate depend on the frequency and intensity of introductions (propagule pressure), the position of founder populations in relation to the potential range, and the spatial distribution of the potential range. We explored these considerations using a large set of invasive alien plant species in South Africa for which accurate distribution data and other relevant information were available. Species introduced earlier and those with larger potential ranges had larger current range sizes, but we found no significant effect of the spatial distribution of potential ranges on current range sizes, and data on propagule pressure were largely unavailable. However, crucially, we showed that: (1) including residence time and potential range always significantly increases the explanatory power of the models; and (2) residence time and potential range can affect which factors emerge as significant determinants of invasiveness. Therefore, analyses not including potential range and residence time can come to misleading conclusions. When these factors were taken into account, we found that nitrogen-fixing plants and plants invading arid regions have spread faster than other species, but these results were phylogenetically constrained. We also show that, when analysed in the context of residence time and potential range, variation in range size among invasive species is implicitly due to variation in spread rates, and, that by explicitly assuming a particular model of spread, it is possible to estimate changes in the rates of plant invasions through time. We believe that invasion biology can develop generalizations that are useful for management, but only in the context of a suitable null model. Web of Science Many South Africa Statistical/Meta-analysis terrestrial Invasion Hyp. Other primary 743 Brooks, M. L.; Matchett, J. R.; Berry, K. H. 2006 Effects of livestock watering sites on alien and native plants in the Mojave Desert, USA journal JOURNAL OF ARID ENVIRONMENTS 67 0 125 147 Increased livestock densities near artificial watering sites create disturbance gradients called piospheres. We studied responses of alien and native annual plants and native perennial plants within 9 piospheres in the Mojave Desert of North America. Absolute and proportional cover of alien annual plants increased with proximity to watering sites, whereas cover and species richness of native annual plants decreased. Not all alien species responded the same, as the alien forb Erodium cicutarium and the alien grass Schismus spp. increased with proximity to watering sites, and the alien annual grass Bromus madritensis ssp. rubens decreased. Perennial plant cover and species richness also declined with proximity to watering sites, as did the structural diversity of perennial plant cover classes. Significant effects were focused within 200m of the watering sites, suggesting that control efforts for alien annual plants and restoration efforts for native plants should optimally be focused within this central part of the piosphere gradient. Published by Elsevier Ltd. Web of Science Bromus madritensis; Schismus arabicus; Schismus barbatus; Erodium cicutarium USA Nevada Mojave Desert Field - Experimental terrestrial Chaparral/Shrublands Impacts;Invasion Hyp. Disturbance primary 744 Brooks, M. L.; Berry, K. H. 2006 Dominance and environmental correlates of alien annual plants in the Mojave Desert, USA journal JOURNAL OF ARID ENVIRONMENTS 67 0 100 124 Land managers are concerned about the negative effects of alien annual plants on native plants, threatened and endangered species such as the desert tortoise (Gopherus agassizii), and ecosystem integrity in the Mojave Desert. Management of alien plants is hampered by a lack of information regarding the dominance and environmental correlates of these species. The results of this study indicate that alien plant species comprised a small fraction of the total annual plant flora, but most of the annual plant community biomass. When rainfall was high in 1995, aliens comprised 6% of the flora and 66% of the biomass. When rainfall was low in 1999, aliens comprised 27% of the flora and 91% of the biomass. Bromus rubens, Schismus spp. (S. arabicus and S. barbatus), and Erodium cicutarium were the predominant alien species during both years, comprising 99% of the alien biomass. B. rubens was more abundant in relatively mesic microhabitats beneath shrub canopies and at higher elevations above 800-1000m, whereas Schismus spp. and E cicutarium were more abundant in the relatively and interspaces between shrubs, and, for Schismus spp., at lower elevations as well. Disturbance variables were more reliable indicators of alien dominance than were productivity or native plant diversity variables, although relationships often varied between years of contrasting rainfall. The strongest environmental correlates occurred between dirt road density and alien species richness and biomass of E. cicutarium, and between frequency and size of fires and biomass of B. rubens. Published by Elsevier Ltd. Web of Science Bromus rubens; Schismus arabicus; Schismus barbatus; Erodium cicutarium USA Nevada Mojave Desert Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Community Species Richness;Disturbance primary 747 Kao-Kniffin, Jenny; Balser, Teri C. 2007 Elevated CO2 differentially alters belowground plant and soil microbial community structure in reed canary grass-invaded experimental wetlands journal SOIL BIOLOGY & BIOCHEMISTRY 39 2 517 525 Several recent studies have indicated that an enriched atmosphere of carbon dioxide (CO2) could exacerbate the intensity of plant invasions within natural ecosystems, but little is known of how rising CO, impacts the belowground characteristics of these invaded systems. In this study, we examined the effects of elevated CO2 and nitrogen (N) inputs on plant and soil microbial community characteristics of plant communities invaded by reed canary grass, Phalaris arundinacea L. We grew the invasive grass under two levels of invasion: the invader was either dominant (high invasion) at > 90% plant cover or sub-dominant (low invasion) at < 50% plant cover. Experimental wetland communities were grown for four months in greenhouses that received either 600 or 365 mu l l(-1) (ambient) CO2. Within each of three replicate rooms per CO2 treatment, the plant communities were grown under high (30 mg l(-1)) or low (5 mg l(-1)) N. In contrast to what is often predicted under N limitation, we found that elevated CO-, increased native graminoid biomass at low N, but not at high N. The aboveground biomass of reed canary grass did not respond to elevated CO2, despite it being a fast-growing C3 species. Although elevated CO2 had no impact on the plant biomass of heavily invaded communities, the relative abundance of several soil microbial indicators increased. In contrast, the moderately invaded plant communities displayed increased total root biomass under elevated CO2, while little impact occurred on the relative abundance of soil microbial indicators. Principal components analysis indicated that overall soil microbial community structure was distinct by CO2 level for the varying N and invasion treatments. This study demonstrates that even when elevated CO2 does not have visible effects on aboveground plant biomass, it can have large impacts belowground. (c) 2006 Elsevier Ltd. All rights reserved. Web of Science Phalaris arundinacea USA Wisconsin Dickeyville Greenhouse wetland Wetland Invasion Hyp. Climate Change primary 750 Thiebaut, Gabrielle 2007 Invasion success of non-indigenous aquatic and semi-aquatic plants in their native and introduced ranges. A comparison between their invasiveness in North America and in France journal BIOLOGICAL INVASIONS 9 1 1 12 Aquatic and semi-aquatic plants comprise few species worldwide, yet the introduction of non-indigenous plants represents one of the most severe examples of biological invasions. My goal is to compare the distribution and the biology of aquatic and semi-aquatic plants in their introduced ranges and in their native ranges. The primary objective of this study is to test the hypothesis that invasive species have evolved traits likely to increase their success in the new range. I made two reciprocal comparisons, i.e. I compared European species in France and in North America, and North American species in France and in North America. Twenty-seven species were classified according to their invasiveness in their introduced area. I found six invasive macrophyte species in France native to North America and 17 invasive species in North America native to Europe. Four species are invasive in both areas. There is no general tendency for macrophytes to be more vigorous in their introduced ranges. Most non-indigenous aquatic and semi-aquatic species are potentially invasive or widespread and well-established in their introduced country, while few species seem to be restricted in their distribution. Web of Science Many USA; France Field - Observational lentic;lotic Invasion Hyp. Inherent Superiority Broad Tolerances primary 760 Jedlicka, Jan; Prach, Karel 2006 A comparison of two North-American asters invading in central Europe journal FLORA 201 8 652 657 Perennial North-American asters have become common in central Europe since the 17th century when they started to be cultivated as ornamental plants. Today, they are widely spreading especially in alluvial sites in lowlands. Two of the most common aster species, Aster lanceolatus and Aster novi-belgii, were investigated for their generative reproduction, including seed production and germination, and vegetative propagation (growth of rhizomes). Experimental sites with and without competition from the surrounding vegetation were used to test for differences between the species. Germination experiments showed that the asters produced a relatively high number of viable and easily dispersed seeds, which often germinated immediately after ripening and usually did not require any special treatment. Some aster clones produced more than 100 new rosettes from one initial rosette within a year. Apparently, asters are able to form large polycorms in a relatively short time. However, their rapid vegetative spread can be reduced by competition from established vegetation. (c) 2006 Elsevier GmbH. All rights reserved. Web of Science Aster lanceolatus;Aster novi-belgii Czech republic 48.9736 14.4536 Field - Experimental terrestrial Old Field Invasion Hyp. Inherent Superiority High Reprod. Output;Clonal Reproduction primary 761 Poeckl, Manfred 2007 Strategies of a successful new invader in European fresh waters: fecundity and reproductive potential of the Ponto-Caspian amphipod Dikerogammarus villosus in the Austrian Danube, compared with the indigenous Gammarus fossarum and G-roeseli journal FRESHWATER BIOLOGY 52 1 50 63 1. Fecundity of a Dikerogammarus villosus population at Spitz was studied in the Austrian Danube during the 3-year period 2002-2004. Ovigerous females were absent in October and November, and extremely scarce in December when the reproductive season started again slowly. From January to September pre-copulatory pairs and egg-carrying females were present. The reproductive cycle lasted for 9-10 months. 2. Various pigmentation phenotypes of D. villosus have been described in the literature. However, no significant differences were found between the reproductive variables studied here and several colour morphs. Mating was size-assortative; mean body length of males was about 1.3 times greater than that of their potential mates, and the wet weight was approximately twice as heavy. 3. The relationship between the number of embryos per clutch and the wet weight of females was described by a 3-parameter power equation. The population mean was 43 eggs with a range of five to 194 eggs. Eighty-two specimens from 1359 D. villosus females had more than 100 eggs: the smallest of these females was 12 mm long (30 mg) wet weight, and the largest, which was 18 mm long (91 mg), had 194 eggs in embryonic development stage 4. 4. Numbers of embryos in developmental stages 2 (early egg stage) and 7 (newly hatched neonates) differed significantly with body wet weight of ovigerous females (P < 0.05). For an average female in the range 10-12 mm (20-30 mg) the number of juveniles in the brood pouch was 74% of the number of stage 2 eggs. This value can be interpreted as the survival rate of eggs. 5. The overall mean egg volume (EV, +/- 95% CL) of stage 2 eggs of D. villosus was 0.05 +/- 0.001 mm(3), and EV increased significantly at each stage of development. At stage 6, egg volume had increased by a factor of 2.6, and averaged 0.13 +/- 0.001 mm(3). In comparison, G. fossarum and G. roeseli had significantly larger eggs in all developmental stages. 6. Mean egg size of D. villosus (0.063 mm(3)) was maximal in January. For D. villosus (and G. roeseli) the minimum mean egg size occurred in September. In contrast to G. fossarum and G. roeseli, a second peak in egg size was not observed for D. villosus, and egg size fell more or less successively from January to September. 7. A simple index of fecundity was calculated from the number of stage 2 eggs divided by the female's wet weight. The highest values were observed in April and May, when females from the overwintering generation grew to their maximum body size. Thus the release of a large number of neonates corresponds with the availability of plentiful food and rising water temperatures for juvenile growth in the spring. The lowest value occurred in December. In June the small females of a summer generation appeared, with a naturally low fecundity. 8. The relationship between brood development time and water temperature was studied in the laboratory at a series of constant temperatures. At 16 degrees C, mean brood development time was 14 days for D. villosus, compared with about 3 weeks for the indigenous species. At 10 degrees C, mean brood development time was 24 days in D. villosus, compared with 40 days in G. fossarum and 44 days in G. roeseli. At 4 degrees C it was 1.8 and 3.5 times longer in G. fossarum and G. roeseli. 9. The number of offspring produced by a single clutch from a large female D. villosus is considerably higher than the total numbers produced by the indigenous freshwater gammarids, such as G. fossarum, G. roeseli and G. pulex, during their life-spans of 1.5-2 years in seven to nine successive broods. Only one or two large ovigerous D. villosus would probably be enough to start a new population. A potentially high reproductive capacity, comparatively small eggs, optimal timing to release the maximum number of neonates per female in April/May, and a long reproductive cycle, together with rapid development of eggs, rapid growth to sexual maturation, short life span, tolerance to a wide range of environmental conditions, and exceptional predatory capabilities, all give the invasive Ponto-Caspian gammarid an opportunity to become globally distributed in freshwater ecosystems of the temperate climate zone. Web of Science Dikerogammarus villosus Austria Danube Field - Observational lotic Invasion Hyp. Inherent Superiority Broad Tolerances;High Reprod. Output omnivore 763 Peacor, Scott D.; Allesina, Stefano; Riolo, Rick L.; Pascual, Mercedes 2006 Phenotypic plasticity opposes species invasions by altering fitness surface journal PLOS BIOLOGY 4 11 2112 2120 Understanding species invasion is a central problem in ecology because invasions of exotic species severely impact ecosystems, and because invasions underlie fundamental ecological processes. However, the influence on invasions of phenotypic plasticity, a key component of many species interactions, is unknown. We present a model in which phenotypic plasticity of a resident species increases its ability to oppose invaders, and plasticity of an invader increases its ability to displace residents. Whereas these effects are expected due to increased fitness associated with phenotypic plasticity, the model additionally reveals a new and unforeseen mechanism by which plasticity affects invasions: phenotypic plasticity increases the steepness of the fitness surface, thereby making invasion more difficult, even by phenotypically plastic invaders. Our results should apply to phenotypically plastic responses to any fluctuating environmental factors including predation risk, and to other factors that affect the fitness surface such as the generalism of predators. We extend the results to competition, and argue that phenotypic plasticity's effect on the fitness surface will destabilize coexistence at local scales, but stabilize coexistence at regional scales. Our study emphasizes the need to incorporate variable interaction strengths due to phenotypic plasticity into invasion biology and ecological theory on competition and coexistence in fragmented landscapes. Web of Science Theoretical/Modeling Invasion Hyp. Plasticity 766 Daehler, Curtis C. 2006 Invasibility of tropical islands by introduced plants: partitioning the influence of isolation and propagule pressure journal PRESLIA 78 4 389 404 All else being equal, more isolated islands should be more susceptible to invasion because their native species are derived from a smaller pool of colonists, and isolated islands may be missing key functional groups. Although some analyses seem to support this hypothesis, previous studies have not taken into account differences in the number of plant introductions made to different islands, which will affect invasibility estimates. Furthermore, previous studies have not assessed invasibility in terms of the rates at which introduced plant species attain different degrees invasion or naturalization. I compared the naturalization status of introduced plants on two pairs of Pacific island groups that are similar in most respects but that differ in their distances from a mainland. Then, to factor out differences in propagule pressure due to differing numbers of introductions, I compared the naturalization status only among shared introductions. In the first comparison, Hawai'i (3700 km from a mainland) had three times more casual/weakly naturalized, naturalized and pest species than Taiwan (160 km from a mainland); however, roughly half (54%) of this difference can be attributed to a larger number of plant introductions to Hawai'i. In the second comparison, Fiji (2500 km from a mainland) did not differ in susceptibility to invasion in comparison to New Caledonia (1000 km from a mainland); the latter two island groups appear to have experienced roughly similar propagule pressure, and they have similar invasibility. The rate at which naturalized species have become pests is similar for Hawai'i and other island groups. The higher susceptibility of Hawai'i to invasion is related to more species entering the earliest stages in the invasion process (more casual and weakly naturalized species), and these higher numbers are then maintained in the naturalized and pest pools. The number of indigenous (not endemic) species was significantly correlated with susceptibility to invasion across all four island groups. When islands share similar climates and habitat diversity, the number of indigenous species may be a better predictor of invasibility than indices of physical isolation because it is a composite measure of biological isolation. Web of Science Many Taiwan; New Caledonia; USA Hawaii Statistical/Meta-analysis terrestrial Tropical Forest;Subtropical Forest;Chaparral/Shrublands Invasion Hyp. Community Species Richness primary 767 Cruz, Maria J.; Rebelo, Rui 2007 Colonization of freshwater habitats by an introduced crayfish, Procambarus clarkii, in Southwest Iberian Peninsula journal HYDROBIOLOGIA 575 0 191 201 The introduction of some crustacean species has produced alterations of freshwater environments and declines of native species worldwide. The red swamp crayfish, Procambarus clarkii Girard, was introduced in the Southwest Iberian Peninsula in the 1970's, producing severe impacts on rice agriculture and on native biota such as macrophytes, gastropods, native crayfish and amphibians. We studied the distribution of P. clarkii in two areas of SW Iberian Peninsula: the Sado River basin (SW Portugal), an area colonized by this species around 1990, and the Parque Natural del Entorno de Donana (SW Spain), colonized soon after its introduction in the Iberian Peninsula, in the 1970's. Our main goal was to determine which factors limit crayfish distribution, which could help to identify the most effective management practices to contain its spread. Procambarus clarkii was found in most types of water bodies, including small and shallow ones. Distance to a crayfish source was the single predictor variable explaining crayfish occurrence in most types of habitats and in both areas. The only exception was for the Sado permanent stream points, where crayfish presence was negatively affected by an interaction between elevation and flow velocity. Other habitat characteristics have apparently little or no importance for its successful colonization. Moreover, this study indicated that overland dispersal is apparently a frequent phenomenon in this species. Our findings can be used to determine which habitats are most likely to be colonized by the crayfish and to develop practical measures which may limit its spread and minimize its impacts. Web of Science Procambarus clarkii Portugal Sado River Field - Observational lotic Invasion Hyp. Inherent Superiority Effective Disperser omnivore 768 Mandryk, Adele M.; Wein, Ross W. 2006 Exotic vascular plant invasiveness and forest invasibility in urban boreal forest types journal BIOLOGICAL INVASIONS 8 8 1651 1662 The riverine forests of the northern city of Edmonton, Alberta, Canada display strong resilience to disturbance and are similar in species composition to southern boreal mixedwood forest types. This study addressed questions such as, how easily do exotic species become established in urban boreal forests (species invasiveness) and do urban boreal forest structural characteristics such as, native species richness, abundance, and vertical vegetation layers, confer resistance to exotic species establishment and spread (community invasibility)? Eighty-four forest stands were sampled and species composition and mean percent cover analyzed using ordination methods. Results showed that exotic tree/shrub types were of the most concern for invasion to urban boreal forests and that exotic species type, native habitat and propagule supply may be good indicators of invasive potential. Native forest structure appeared to confer a level of resistance to exotic species and medium to high disturbance intensity was associated with exotic species growth and spread without a corresponding loss in native species richness. Results provided large-scale evidence that diverse communities are less vulnerable to exotic species invasion, and that intermediate disturbance intensity supports species coexistence. From a management perspective, the retention of native species and native forest structure in urban forests is favored to minimize the impact of exotic species introductions, protect natural succession patterns, and minimize the spread of exotic species. Web of Science Many Canada Alberta Edmonton Field - Observational terrestrial Coniferous Forest;Urban Invasion Hyp. Community Species Richness;Propagule Pressure primary 769 Belote, R. Travis; Weltzin, Jake F. 2006 Interactions between two co-dominant, invasive plants in the understory of a temperate deciduous forest journal BIOLOGICAL INVASIONS 8 8 1629 1641 Negative interactions between non-indigenous and native species has been an important research topic of invasion biology. However, interactions between two or more invasive species may be as important in understanding biological invasions, but they have rarely been studied. In this paper, we describe three field experiments that investigated interactions between two non-indigenous plant species invasive in the eastern United States, Lonicera japonica (a perennial vine) and Microstegium vimineum (an annual grass). A press removal experiment conducted within a deciduous forest understory community indicated that M. vimineum was a superior competitor to L. japonica. We tested the hypothesis that the competitive success of M. vimineum was because it overgrew, and reduced light available to, L. japonica, by conducting a separate light gradient experiment within the same community. Shade cloth that simulated the M. vimineum canopy reduced the performance of L. japonica. In a third complementary experiment, we added experimental support hosts to test the hypothesis that the competitive ability of L. japonica is limited by support hosts, onto which L. japonica climbs to access light. We found that the abundance of climbing branches increased with the number of support hosts. Results of this experiment indicate that these two invasive species compete asymmetrically for resources, particularly light. Web of Science Lonicera japonica; Microstegium vimineum USA Tennessee Oak Ridge National Environmental Research Park 35.9 -84.3333 Field - Experimental terrestrial Deciduous Forest Fundamentals;Invasion Hyp. Mutualism Facilitation;Empty Niche primary 771 Domenech, Roser; Vila, Montserrat 2006 The role of successional stage, vegetation type and soil disturbance in the invasion of the alien grass Cortaderia selloana journal JOURNAL OF VEGETATION SCIENCE 17 5 591 598 Question: This paper studies the establishment and performance of Cortaderia selloana (Pampas grass), an alien South American ornamental species that is invading many parts of the world. We asked whether (1) early successional stages were the most susceptible to C. selloana invasion; (2) soil microdisturbances increased invasion at any point of succession, and (3) C. selloana invasion of later successional stages was modulated by vegetation type Location: Delta del Llobregat (Catalonia, NE Spain). Methods: We monitored survival and growth of transplanted C. selloana seedlings in disturbed and non-disturbed plots throughout a successional gradient with an age range of < 1 to > 10 years in different vegetation types and within the area of influence of coexisting species with similar growth form. Results: Although seedling survival was extremely low in all treatments, our results revealed that early successional stages were not the most easily invaded since we found no significant differences in the percentage survival of C. selloana along the successional gradient. However, survival and seedling biomass were enhanced by soil disturbance at any seral stage. This result suggested that inhibition ruled C. selloana invasion. Invasibility neither depended on the invaded vegetation type nor on the co-existing species with similar growth form. Finally, C. selloana invasion was not enhanced by decreasing competition with Phragntites australis, a native coexisting species because survival rates after a year were not significantly different. However, Phragmites increased C. selloana leaf length probably due to shading. Conclusions: C. selloana recruitment appears to be positively affected by soil disturbance but it is independent of successional stage or vegetation type. Web of Science Cortaderia selloana Spain Catalonia Delta del Llobregat Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Community Species Richness;Disturbance primary 774 Asner, Gregory P.; Martin, Roberta E.; Carlson, Kimberly M.; Rascher, Uwe; Vitousek, Peter M. 2006 Vegetation-climate interactions among native and invasive species in Hawaiian rainforest journal ECOSYSTEMS 9 7 1106 1117 We compiled a time series of Earth Observing-1 Hyperion satellite observations with field measurements to compare the structural, biochemical, and physiological characteristics of an invasive nitrogen-fixing tree Myrica faya and native Metrosideros polymorpha in montane rainforests in Hawai'i. Satellite-based canopy water measurements closely tracked variations in leaf area index, and the remotely sensed photochemical and carotenoid reflectance indices (PRI, CRI) indicated variations in upper-canopy leaf chlorophyll and carotenoid content during a climatological transition. The PRI and CRI were related to differences in light-use efficiency of each species, as indicated by field measurements of leaf electron transport rate. The suite of hyperspectral metrics indicated maximum differences in the structure, biochemistry, and physiology of Myrica and Metrosideros when canopy vapor pressure deficit was high during hotter and drier periods. These satellite data, combined with the Carnegue-Ames-Stanford Approach (CASA) carbon cycle model, suggested that Myrica growth rates were 16-44% higher than Metrosideros, with relative differences between species closely linked to climate conditions. The satellite hyperspectral data identified the basic biological mechanisms favoring the spread of an introduced tree, and provided a more detailed understanding of how vegetation-climate interactions affect the time course of plant growth with respect to the invasion process. Web of Science Myrica faya USA Hawaii Field - Observational terrestrial Mountain Invasion Hyp. Preadaptation to Climate primary 780 Brown, Gregory P.; Phillips, Benjamin L.; Webb, Jonathan K.; Shine, Richard 2006 Toad on the road: Use of roads as dispersal corridors by cane toads (Bufo marinus) at an invasion front in tropical Australia journal BIOLOGICAL CONSERVATION 133 1 88 94 Determining the factors that influence the rate of spread of invasive species is an important goal for conservation biology. if invasive species utilize specific landscape features as dispersal corridors, control programs can target such corridors. Radio-telemetry was used to determine landscape level factors that influence dispersal of an introduced anuran species (the cane toad) at an invasion front in tropical Australia. Most radio-tracked toads moved along roads and cleared fencelines, avoiding heavily vegetated habitat; they typically sheltered overnight close to these open corridors, returning to the road each evening to recommence dispersal. Surveys of the compass orientation of dispersing toads on roads showed that most animals were oriented along the main axis of the road (and thus, travelling along the road) rather than moving across it. To test the hypothesis that use of roads enables toads to disperse more rapidly than would be possible across more thickly vegetated sites, locomotor performance of toads was quantified under field conditions. As predicted, toads rapidly slowed down in dense roadside vegetation but continued to move rapidly through open areas. These results suggest that simple habitat manipulations of roadside verges might help to reduce the rate of dispersal of cane toads across tropical Australia. (c) 2006 Elsevier Ltd. All rights reserved. Web of Science Bufo marinus Australia Northern Territory Darwin Field - Observational terrestrial Tropical Forest Invasion Hyp. Inherent Superiority Effective Disperser omnivore 781 Siemann, Evan; Rogers, William E.; Dewalt, Saara J. 2006 Rapid adaptation of insect herbivores to an invasive plant journal PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES 273 127 2763 2769 Introduced plant success often is attributed to release from natural enemies in their new ranges. However, herbivores may accumulate over time and reduce invasiveness but evidence for this process to date is weak. We report here that enemy release is indeed limited to the early stages of introduction of the Chinese tallow tree (Sapium sebiferum). In bioassays and gardens along a geographical gradient of time since tallow tree introduction, herbivory was highest and tree performance was poorest where tallow tree has been present longer (i.e. introduced earlier). Additionally, Asian ecotypes (grown from seeds collected in Asia) had lower survival than North American ecotypes (seeds collected in North America), which is consistent with genetic responses to low herbivory in the introduced range (EICA Hypothesis). Release from insect herbivores appears to contribute to early success of the tallow tree, but accumulation of insect herbivores has apparently reduced this benefit over time. Web of Science Sapium sebiferum USA Texas; Louisiana; Florida; Georgia Garden terrestrial Deciduous Forest Invasion Hyp. Enemy Release;Evolution of Increased Competitive Ability primary 783 Wang, Q.; Wang, C. H.; Zhao, B.; Ma, Z. J.; Luo, Y. Q.; Chen, J. K.; Li, B. 2006 Effects of growing conditions on the growth of and interactions between salt marsh plants: Implications for invasibility of habitats journal BIOLOGICAL INVASIONS 8 7 1547 1560 A common but often less tested explanation for the successful invasion of alien species is that invasive alien species outcompete their co-occurring natives, which may not always be the case. In this study, we established artificial environmental gradients in a series of pot experiments with controlled environments to investigate the effects of salinity, sediment type and waterlogging on the performance of and interactions between Phragmites australis (native) and Spartina alterniflora (alien), which generally co-exist in the saline intertidal zones of Chinese and American coasts. Significant effects of salinity and waterlogging were detected on biomass production and morphological characteristics of S. alterniflora and P. australis, and the competitive interactions between the two species were found to vary with all three environmental factors in our experiments. Relative Neighbor Effect (RNE) analyses indicate that competitive dominance of S. alterniflora occurred under the conditions of high salinity, sandy sediment and full immersion, whereas P. australis showed competitive dominance under the conditions of low salinity and non-immersion. Our results suggest that S. alterniflora might outcompete P. australis under conditions present in early salt marsh succession, which support the viewpoint that the outcomes of competition between co-occurring native and invasive alien plants depend on the growing conditions. The implication of this study is that in response to the environmental changes expected from seawater intrusion and sea-level rise, the range of S. alterniflora is expected to expand further in the Yangtze River estuary in the future. Web of Science Spartina alterniflora China Yangtze River Greenhouse estuarine Invasion Hyp. Inherent Superiority Superior Competitor primary 784 Kitajima, Kaoru; Fox, Alison M.; Sato, Tamotsu; Nagamatsu, Dai 2006 Cultivar selection prior to introduction may increase invasiveness: evidence from Ardisia crenata journal BIOLOGICAL INVASIONS 8 7 1471 1482 Ardisia crenata (Myrsinaceae), an evergreen shrub with attractive red fruits introduced from Japan to the USA for ornamental purpose, invades the understory of mesic hardwood forests, forming dense patches (up to 300 stems per m2), and competitively displaces native understory plants by creating dense local shade. Comparison of the wild genotype that grows in mature evergreen broadleaf forests in central Kyushu, Japan, with the ecotype invading north central Florida revealed how selection for desirable cultivars might have inadvertently selected for traits that enhance the invasive potential of the species. In Japanese wild populations in deeply shaded evergreen forests, natural selection apparently maintained efficient architecture with a low degree of self-shading and large seed mass to enhance seedling shade tolerance. Cultivar selection for showy appearance can explain the greater fecundity but smaller seed size observed in the Florida populations compared to the Japanese population. Artificial selection for densely foliated appearance can also explain the greater degree of self-shading and less-efficient light use in the Florida genotype compared to the Japanese wild type grown under a common environment. Furthermore, the Florida ecotype allocated more biomass to root carbohydrate storage. These trait modifications resulted in slower growth rates, but greater competitive ability to cast shade upon neighbors and higher resprouting potential in the Florida populations. How traits are modified through the processes of artificial selection and cultivation must be taken into consideration in the evolutionary ecology of many other invasive plants introduced as ornamental plants. Web of Science Ardisia crenata USA Florida Gainesville Garden terrestrial Deciduous Forest Invasion Hyp. Evolution in General primary 785 Liu, Jian; Dong, Ming; Miao, Shi Li; Li, ZhenYu; Song, Ming Hua; Wang, Ren Qing 2006 Invasive alien plants in China: role of clonality and geographical origin journal BIOLOGICAL INVASIONS 8 7 1461 1470 Biological invasions have become a significant threat to the global environment. Unfortunately, to date there is no consensus on invasion mechanisms and predictive models. Controversies range from whether we can reliably predict which species may become invasive to which species characteristics (e.g., life history, taxonomic groups, or geographic origin) contribute to the invasion processes. We examined 126 invasive alien plant species in China to understand the role of clonality and geographical origin in their invasion success. These species were categorized into three groups (I, II, III) based on their invasiveness in terms of current spatial occupation and the degree of damage to invaded habitats. Clonal plants consisted of almost half (44%) of the 126 invasive species studied, and consisted of 66% of 32 the most invasive alien plant species (Group I). There was a significant positive relationship between clonality and species invasiveness. A 68% of the 126 species studied originated in the continent of America (North and/or South America). These preliminary findings support that America is the primary geographical origin of invasive alien plant species in China and that clonality of the invasive plant species contributed significantly to the their invasiveness. The results suggest an urgent need at the global scale to investigate the mechanisms whereby plant clonal growth influences plant invasions, and the need for a focus at regional scale to examine factors affecting the exchange of invasive plant species between America and China. Web of Science Many China Field - Observational terrestrial Invasion Hyp. Inherent Superiority Clonal Reproduction primary 786 Chmura, Damian; Sierka, Edyta 2006 Relation between invasive plant and species richness of forest floor vegetation: A study of Impatiens parviflora DC. journal POLISH JOURNAL OF ECOLOGY 54 3 417 428 In 13 forest reserves situated in southern Poland, 68 study plots were established in two regions: the Jurrasic Upland and the Silesian Upland. In these plots, size 10 in x 10 in divided into 100 subplots 1m(2) each and randomly placed in various forest communities, percentage cover of all species in ground layer was recorded. Relationships between highly invasive alien plant species, Asiatic small balsam Impatiens parviflora DC., and indigenous species, was estimated using various indexes of species richness and diversity. They were: Hill's numbers (N-0, N-1, N-2),Shannon Wiener's index at the level of a subplot, alpha diversity (species richness within sites), and beta diversity (species richness among sites) at level of a study plot. The subplots with a presence of L parviflora were compared with those where only native resident species occurred. The study has shown that subplots with the occurrence of L parviflora are characterized by higher species richness and diversity of native plants independently on vegetation type. The frequency of L parviflora was negatively correlated with beta diversity of study plots but there was no association with values of alpha diversity. In oak forest, alder carrs and floodplain forests the negative correlation between percent cover of L parviflora and species richness, as well as cover of the herb layer was observed. The percent cover of L parviflora was positively correlated with number of native species in beech forest and with their total cover in mixed coniferous forests. However, in natural well-preserved forest phytocoenoses L parviflora avoids patches characterized by high cover of ground layer species and colonizes empty sites as an additional element of a community. Web of Science Impatiens parviflora Poland Silesian-Kraków Upland Field - Observational terrestrial Deciduous Forest Invasion Hyp. Community Species Richness primary 788 Pairon, Marie; Chabrerie, Olivier; Casado, Carolina Mainer; Jacquemart, Anne-Laure 2006 Sexual regeneration traits linked to black cherry (Prunus serotina Ehrh.) invasiveness journal ACTA OECOLOGICA-INTERNATIONAL JOURNAL OF ECOLOGY 30 2 238 247 In order to better understand the invasive capacity of black cherry (Prunus serotina Ehrh.), the regeneration dynamics of the species was studied during two consecutive years in a Belgian Pine plantation. Flower and fruit production, seed rain, dispersal and viability as well as the survival of seedlings of different ages were assessed. Despite the low fruit/flower ratio, fruit production was high (up to 8940 fruits per tree) as trees produced huge quantities of flowers. Both flower and fruit productions were highly variable between years and among individuals. The production variability between individuals was not correlated with plant size variables. Fruits were ripe in early September and a majority fell in the vicinity of the parent tree. A wide range of bird species dispersed 18% of the fruits at the end of October. Sixty-two percent of the fruits were viable and mean densities of 611 fruits m(-2) were recorded on the forest floor. High mortality among young seedlings was observed and 95.3% of the fruits failed to give 4-year-old saplings. Nevertheless, the few saplings older than 4 years (1.32 m(-2)) presented a high survival rate (86%). All these regeneration traits are discussed in order to determine the main factors explaining the black cherry invasive success in Europe. (c) 2006 Elsevier Masson SAS. All rights reserved. Web of Science Prunus serotina Belgium 51.3167 5.1833 Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority High Reprod. Output primary 791 Callaway, Ragan M.; Kim, Judy; Mahall, Bruce E. 2006 Defoliation of Centaurea solstitialis stimulates compensatory growth and intensifies negative effects on neighbors journal BIOLOGICAL INVASIONS 8 6 1389 1397 Efforts to arrest the spread of invasive weeds with herbivory may be hindered by weak effects of the herbivores or strong compensatory responses of the invaders. We conducted a greenhouse experiment to study the effects of defoliation and soil fungi on competition between the invasive weed Centaurea solstitialis and C. solstitialis and Avena barbata, a naturalized Eurasian annual grass, and Nassella pulchra, a native California bunchgrass. Surprisingly, considering the explosive invasion of grasslands by C. solstitialis, Avena and Nassella were strong competitors and reduced the invader's biomass by 80.2% and 80.1% over all defoliation and soil fungicide treatments, respectively. However, our experiments were conducted in artificial environments where competition was probably accentuated. When fungicide was applied to the soil, the biomass of C. solstitialis was reduced in all treatment combinations, but reduction in the biomass of the invader had no corollary impact on the grasses. There was no overall effect of defoliation on the final biomass of C. solstitialis as the invader compensated fully for severe clipping. In fact, the directional trend of the clipping effect was +6.4% over all treatments after eight weeks. A significant neighbor x soil fungicide x clipping effect suggested that the compensatory response was the strongest without soil fungicide and when C. solstitialis was alone (+ 19%). Our key finding was that the compensatory response of C. solstitialis in all treatments was associated with an increase in the weed's negative effects on Nassella and Avena - there was a significant decrease in the total biomass of both grasses and the reproductive biomass of Avena in pots with clipped C. solstitialis. Our results were obtained in controlled conditions that may have been conducive to compensatory growth, but they suggest the existence of mechanisms that may allow C. solstitialis, like other Centaurea species, to resist herbivory. Web of Science Centaurea solstitialis Greenhouse Invasion Hyp. Inherent Superiority Superior Competitor primary 795 Pino, Joan; Segui, Josep Maria; Alvarez, Nora 2006 Invasibility of four plant communities in the Llobregat delta (Catalonia, NE of Spain) in relation to their historical stability journal HYDROBIOLOGIA 570 0 257 263 Presence and cover of alien plants were analysed in relation to recent naturalness changes (1956-1999) in the Llobregat delta by means of GIS techniques and field surveys. Two land cover maps of 1956 and 1999 were generated by photo-interpretation of orthoimages and they were then reclassified into naturalness classes, defined as the degree of preservation of the pristine state. The resulting naturalness maps were combined in order to obtain a naturalness change map, which was used to design field sampling in four pristine communities: reedbeds, rushbeds, halophilous scrubs and fixed dune communities. Two study areas were selected for each community and three stability regimes (stable, semi-stable and nonstable) obtained from the naturalness change map. Five vegetation inventories were performed on average in each of these areas using the classical sigmatist method. Results showed a negative relationship between stability and invasibility, with several variations between communities. No alien species were found in stable areas of all communities. Alien species number, species percentage and relative cover increased from semi-stable to non-stable regimes in reedbeds and dune communities, indicating that reversion towards the climax reduces opportunities for alien establishment in these communities. In contrast, halophilous habitats such as rushbeds and scrubs did not exhibit significant differences between semi-stable and non-stable plots, probably because saline stress makes their invasion by alien plants difficult, even under disturbance. Web of Science Many Spain Catalonia Field - Observational terrestrial Riparian;Chaparral/Shrublands Invasion Hyp. Disturbance primary 798 Moravcova, Lenka; Pysek, Petr; Pergl, Jan; Perglova, Irena; Jarosik, Vojtech 2006 Seasonal pattern of germination and seed longevity in the invasive species Heracleum mantegazzianum journal PRESLIA 78 3 287 301 We investigated the effects of different temperature regimes and dry storage on germination of H. mantegazzianum (Apiaceae, native to Caucasus) seeds in the laboratory and linked the results with studies of seasonal seed bank depletion in a common garden experiment and under field conditions. Seeds were collected at seven sites in the Slavkovsky les region, Czech Republic, cold-stratified for 2 months and germinated at seven temperature regimes. Under all temperature regimes, fresh seeds germinated to significantly higher percentages than older (1, 2, 3 years) seeds. For all storage lengths, seeds germinated best at alternating day/night temperatures of 20/5 degrees C. The length of the germination period had a significant effect only at low constant temperatures of 2 and 6 degrees C, where germination percentage increased between 2 and 6 months. Seasonal germination exhibited a distinct pattern, with rapid depletion of seed bank by the first spring after seed burial. Non-dormant seeds were present in the soil early in spring and late in autumn. The higher summer temperatures prevented dormancy breaking and another cold period of at least two months below 10 degrees C was needed to bring non-germinated seeds out of dormancy. The results suggest that (1) seed dormancy of H. mantegazzianum was not completely broken until the first spring, but that some seeds re-enter or retain dormancy during high summer temperatures and that (2) the threshold needed for breaking the dormancy was achieved gradually during the cold autumn and winter months. However, in a small fraction of seeds the dormancy breaking process took several years. Of seeds buried in 10 different regions of the Czech Republic, on average 8.8% survived 1 year, 2.7% 2 years and 1.2% remained viable and dormant after 3 years of burial. The ability of even small fraction of H. mantegazzianum seeds to survive for at least 3 years can result in re-invasion of this species into controlled sites. Web of Science Heracleum mantegazzianum Czech Republic Slavkovsky les region Field - Experimental terrestrial Deciduous Forest;Coniferous Forest Invasion Hyp. Inherent Superiority Broad Tolerances primary 799 Perglova, Irena; Pergl, Jan; Pysek, Petr 2006 Flowering phenology and reproductive effort of the invasive alien plant Heracleum mantegazzianum journal PRESLIA 78 3 265 285 Heracleum mantegazzianum is one of the most invasive species in the Czech flora. The present study describes its flowering phenology and assess the effectiveness of protandry in preventing selfing in this self-compatible species, describes the timing of flowering in a heavily invaded area of Slavkovsky les (Czech Republic) and estimates fruit set in a large sample of plants, which provides reliable data on the often exaggerated fecundity of this species, The study of flowering phenology revealed that protandry is always effective only within individual flowers, where male and female flowering phases are completely separated. In contrast, anther dehiscence in some flowers can occasionally overlap With stigma receptivity in other flowers in the same umbel, providing an opportunity for geitono-gamous (i.e. between-flower) selfing. Nevertheless, the potential for selfing in H. mantegazzianum is determined mainly by an overlap in the male and female flowering phases between umbels on the same plant; at least a short overlap between some umbels was observed in 99% of the plants at the Slavkovsky les. Although the degree of protandry in H. mantegazzianum favours outcrossing, the opportunity to self may be of crucial importance for an invasive plant, especially if a single plant colonizes a new location. At Slavkovsky les, flowering started within one week (from 20 to 27 June 2002) at all 10 sites. The duration of flowering of an individual plant was on average 36 days, with maximum of 60 days, and increased significantly with the number of umbels on a plant. In the second half of August, the majority of the fruits were ripe and had started to be shed. The beginning of flowering of a plant was significantly negatively correlated With the number of umbels it had - the earlier a plant started to flower the more umbels it had produced. A significant negative relationship was also found between basal diameter and beginning of flowering; plants with large basal diameters started to flower earlier. An average plant at Slavkovsky les produced 20,671 fruits. Of these, 44.6% were produced by the terminal umbel, 29.3% by secondary umbels on satellites, 22.6% by secondary umbels on branches and only 3.5% by tertiary umbels. The estimated fruit number of the most fecund plant was 46,470 - compared to an average plant, the proportional contribution of tertiary umbels increased relative to the primary umbel. This study revealed a significant positive relationship. between fecundity and plant basal diameter. Although the results of this study indicate that the fecundity of this species is often overestimated in the literature, the number of fruits produced by H. mantegazzianum provides this invasive species with an enormous reproductive capacity. Web of Science Heracleum mantegazzianum Czech Republic Slavkovsky les region Field - Experimental;Field - Observational terrestrial Grassland;Deciduous Forest;Coniferous Forest Invasion Hyp. Evolution in General;Inherent Superiority High Reprod. Output primary 800 Krivanek, Martin; Pysek, Petr; Jarosik, Vojtech 2006 Planting history and propagule pressure as predictors of invasion by woody species in a temperate region journal CONSERVATION BIOLOGY 20 5 1487 1498 We studied 28 alien tree species currently Planted for forestry purposes in the Czech Republic to determine the probability of their escape from cultivation and naturalization. Indicators of propagule pressure (number of administrative units in which a species is planted and total planting area) and time of introduction into cultivation were used as explanatory variables in multiple regression models. Fourteen species escaped from cultivation, and 39% of the variance was explained by the number of planting units and the time of introduction, the latter being more important. Species introduced early bad a higher probability of escape than those introduced later, with more than 95% probability of escape for those introduced before 1801 and < 5% for those introduced after 1892. Probability of naturalization was more difficult to predict, and eight species were misclassified. A model omitting two species with the largest influence on the model yielded similar predictors of naturalization as did the probability of escape. Both phases of invasion therefore appear to be driven by Planting and introduction history in a similar way. Our results demonstrate the importance of forestry for recruitment of invasive trees. Six alien forestry trees, classified as invasive in the Czech Republic, are currently reported in nature reserves. In addition, forestry authorities want to increase the diversity of alien species and planting area in the country. Web of Science Many Czech Republic Statistical/Meta-analysis;Review terrestrial Deciduous Forest;Coniferous Forest Invasion Hyp. Propagule Pressure primary 801 Cadotte, Marc W.; Murray, Brad R.; Lovett-Doust, Jon 2006 Evolutionary and ecological influences of plant invader success in the flora of Ontario journal ECOSCIENCE 13 3 388 395 It is not clear why some species are able to naturalize and spread in a new region while so many other species are not. Several general properties have been reported for successful non-indigenous plant species (NIPS). These include presence of a lag time and population expansion following invasion, arrival from a similar climate, ability to self-fertilize, a short lifespan, clonal growth (if perennial), and production of small fruits. We examined these patterns in comparisons of all recorded abundant and rare NIPS in Ontario (n = 1153). We used cross-species and phylogenetic regressions to examine ecological patterns across present-day species and to determine whether evolutionary divergences in NIPS success have been correlated consistently with divergences in any of the life-history traits. We found a significant time lag in invader spread, with species arriving after 1952 being more likely to be rare. Successful invaders (i.e., abundant NIPS) were significantly over-represented among species originating in Europe and Eurasia. Successful invaders were significantly more likely to demonstrate clonal growth, to grow on variable soil moistures, and to have comparatively long flowering periods. While analyses such as this do not reveal causal mechanisms for the observed patterns, our correlative findings suggest important mechanisms for NIPS success that we discuss in light of the theoretical expectations of the attributes of successful plant invaders. Web of Science Many Canada Ontario Statistical/Meta-analysis;Review terrestrial Invasion Hyp. Inherent Superiority Broad Tolerances;Self Compatible;Clonal Reproduction primary 802 Truscott, A-M.; Soulsby, C.; Palmer, S. C. F.; Newell, L.; Hulme, P. E. 2006 The dispersal characteristics of the invasive plant Mimulus guttatus and the ecological significance of increased occurrence of high-flow events journal JOURNAL OF ECOLOGY 94 6 1080 1091 1 Increased occurrence of high-flow events as a result of climate change may affect the dispersal success of an invasive plant species Mimulus guttatus and may result in range expansion. Predicted changes in climate point to a continuation of the recent observed trends in increased precipitation and high-flow events in Northern Europe. 2 The study focused on the dispersal characteristics of M. guttatus, and especially the roles of vegetative fragmentation with increasing water velocities, subsequent fragment survival, regeneration and colonization, as well as the buoyancy, survival and germination success of seeds. 3 M. guttatus was found to fragment readily under velocities typical of high flow conditions and even small fragments had high survival, regeneration and colonization capacity. 4 Large numbers of small (< 0.02 mg) seeds are produced; however, seeds have a short buoyancy period so the timing and magnitude of high-flow events is crucial in determining potential dispersal distances. Seeds germinate readily both in water and on sand with an average 33% germination within 9 days. 5 The dual strategy of dispersal by vegetative fragments and seeds, together with the opportunity of dispersing the two types of propagules during different periods of the year, facilitates local dominance by M. guttatus as well as long-distance colonization. As a result, the rate of spread of M. guttatus into inundation communities along rivers is likely to increase with more frequent high-flow events, especially if these coincide with the growing season. Thus, predicting the response of riparian invasive species to environmental change requires not only an understanding of the role of climate in plant demography but also the impact of changes in hydrology on rates of spread. Web of Science Mimulus guttatus Scotland Tarland Burn 57.1167 -2.85 Greenhouse;Lab terrestrial Riparian Invasion Hyp. Inherent Superiority Clonal Reproduction primary 803 Martin, Patrick H.; Marks, Peter L. 2006 Intact forests provide only weak resistance to a shade-tolerant invasive Norway maple (Acer platanoides L.) journal JOURNAL OF ECOLOGY 94 6 1070 1079 1 Intact, closed canopied forests appear highly resistant to exotic plant invasions, but there are few experimental studies of this observation. To test this issue and explore the conditions that foster resistance, we experimentally added Norway maple (Acer platanoides L.) seeds to intact forests for 3 years and monitored emergence, survivorship and height growth for 5 years. 2 Seed additions (250 seeds(-1) m(2)) were replicated in situ in combinations of light (deep shade vs. small gaps), soil fertility (NO3 and pH), and variation in soil moisture as influenced by topography (hill slopes vs. flat areas at slope bases) in five eastern deciduous forests in central New York and southern Connecticut. We then parameterized a model with this data to project long-term rates of sapling recruitment. 3 Seedlings had high survival and low growth rates in the deep shade, suggesting that this species readily forms a seedling bank in intact forests. By age 5, annual survivorship reached 93% in deep shade and 98% in small gaps. Median seedling heights were <= 10 cm in all treatments after 5 years, though the largest seedlings were markedly taller in gaps. Mean year 5 densities of all experimental seedlings (ages 3-5 years) were 14 seedlings(-1) m(2) (+/- 2.4 SE) in the shade and 19 seedlings(-1) m(2) (+/- 3.5 SE) in small gaps. 4 While seedlings colonized in all conditions, resistance to invasion varied markedly; resistance was highest in deeply shaded, acidic conditions (pH < 4.5). Small gaps initially promoted invasion, but by age 4 shade survivorship rates were equivalent to gaps. Higher soil pH (especially > 6) also significantly increased survivorship, particularly in deep shade. Shading's main effect was to suppress height growth. Overall, the model predicted impressive sapling recruitment; even in deeply shaded, acidic conditions, approximately 1% of seeds emerge and survive to become saplings. 5 Intact forests only weakly resisted A. platanoides colonization, but strongly suppressed its rate of invasion. As such, the frequency of disturbance, though ultimately unnecessary for A. platanoides invasions, will strongly influence its near-term invasiveness. Dispersal limitation and slow stand dynamics appear to be the primary constraints on its current distribution. Web of Science Acer platinoides USA Northeast Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Other primary 808 Bollache, Loic; Kaldonski, Nicolas; Troussard, Jean-Philippe; Lagrue, Clement; Rigaud, Thierry 2006 Spines and behaviour as defences against fish predators in an invasive freshwater amphipod journal ANIMAL BEHAVIOUR 72 0 627 633 Selective predation may be an important proximate cause of the success or failure of invader species. Gammarus roeseli is an invasive amphipod, for which the causes of establishment in rivers where the native species, Gammarus pulex, predominates remain unstudied. Freshwater amphipods are important prey for numerous fish predators, but empirical evidence of lower predation rates on exotic prey is scarce. In laboratory experiments, we compared the susceptibility of G. pulex and G. roeseli to fish predation, determined the mechanisms influencing prey selection, and studied the interaction between behavioural and morphological defences. Fish predators (brown trout, Salmo trutta fario) preyed selectively on G. pulex, but not because of differences in attack or capture probability. The presence of spines in G. roeseli appeared to contribute to its underpredation. Differential prey selection in this case might therefore have resulted from the trout's reaction to an adverse stimulus. We found no significant difference in antipredator behaviour between G. pulex and G. roeseli. General behavioural differences were nevertheless found between species, with G. roeseli spending more time under shelters than G. pulex. However, microcosm experiments suggested that this difference was not important for differential predation. Antipredator behaviour may nevertheless be important for G. roeseli against other predators less sensitive to spines. (c) 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. Web of Science Gammarus roeseli France Burgundy Field - Experimental;Lab lentic Invasion Hyp. Inherent Superiority Superior Competitor decomposer 809 Hata, Kenji; Suzuki, Jun-Ichirou; Kachi, Naoki; Yamamura, Yasuo 2006 A 19-year study of the dynamics of an invasive alien tree, Bischofia javanica, on a subtropical oceanic island journal PACIFIC SCIENCE 60 4 455 470 A 19-yr study of the dynamics of an invasive alien species, Bischofia javanica Blume, in a secondary forest was conducted in the Bonin Islands, Japan. The study was begun in 1984 when another alien species, Pinus luchuensis Mayer, had begun to die because of infection by a pine nematode as well as typhoon damage in 1983. Diameters at breast height (DBHs) of all trees in a 20 by 20 in plot and heights of all saplings (< 1.3 m, >= 03 m in height) were measured almost every 3 yr. The total basal area of P. luchuensis decreased over time, and all trees had fallen over by 1998. The total basal area of B. javanica increased more than 10-fold over 19 yr without changes in tree or sapling density. Up to 1990, growth rates of trees of B. javanica were higher than those of two native canopy trees (Pouteria obovata and Machilus kobu), but a third native canopy tree (Schima mertensiana) had growth rates comparable with those of B. javanica. After 1990, there were few differences between growth rates of B. javanica and native species. However, mortality and recruitment of B. javanica were lower than those of native species of canopy trees during the survey period. The higher growth rate, lower mortality, and lower recruitment led to a shift from a skewed size distribution of the individuals of B. javanica toward a more bell-shaped size distribution. Our results suggest that regeneration and maintenance of B. javanica populations in the secondary forests depend on canopy gaps occasionally created by disturbances. Web of Science Bischofia javanica Japan Bonin Islands Chichijima Island 27.04 142.12 Field - Observational terrestrial Deciduous Forest;Coniferous Forest Invasion Hyp. Mutualism Facilitation;Disturbance primary;parasite 812 Alston, Karen P.; Richardson, David M. 2006 The roles of habitat features, disturbance, and distance from putative source populations in structuring alien plant invasions at the urban/wildland interface on the Cape Peninsula, South Africa journal BIOLOGICAL CONSERVATION 132 2 183 198 Natural areas are becoming increasingly fragmented and embedded in an urban matrix. Natural and semi-natural areas at the urban/wildland interface are threatened by a variety of 'edge effects', and are especially vulnerable to invasion by introduced plants, with suburban gardens acting as significant sources of alien propagules. Urban/wildland interfaces also provide access for humans, leading to various types of disturbance. Alien plant invasions are one of the biggest threats facing remaining natural areas on the Cape Peninsula, South Africa. The area provides an ideal opportunity to study the dynamics of invasions at the urban/wildland interface, since the largest natural area, the Table Mountain National Park (TMNP), is surrounded by the city of Cape Town. We explored invasion patterns in Newlands Forest (a small section of the TMNP) and detailed the roles of habitat features and distance from putative source populations in three main habitat types: natural Afromontane forest, riverine woodland habitats, and plantations of exotic pines (Pinus radiata and P. pinaster). We also examined the role of disturbance in driving invasions in two of these habitat types (Afromontane forest and pine plantations). We hypothesized that alien richness and alien stem density would decrease with distance from the urban/wildland interface, and that alien richness and alien stem density would increase with increasing levels of human disturbance. Distance from putative source populations and levels of anthropogenic disturbance influenced alien richness in Newlands Forest but not alien stem density. Alien richness decreased significantly with distance from presumed sources in the pine habitat, and increased significantly with disturbance in the forest habitat. Percentage overstorey cover and soil pH were important environmental variables associated with alien plant species. A socio-economic approach is discussed as being the most effective approach to the management and prevention of alien plant species in Newlands Forest. (c) 2006 Elsevier Ltd. All rights reserved. Web of Science Many South Africa Cape Floristic Region Table Mountain National Park -33.9667 18.4333 Field - Observational terrestrial Deciduous Forest;Chaparral/Shrublands Invasion Hyp. Disturbance;Other primary 816 Liu, Hong; Pemberton, Robert W.; Stiling, Peter 2006 Native and introduced pollinators promote a self-incompatible invasive woody vine (Paederia foetida L) in Florida journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 133 2 304 311 Liu, H. (Department of Biology, University of South Florida, 4202 East Fowler Ave., SCA 110, Tampa, FL 33620), R. W. PEMBERTON (U.S. Department of Agriculture, Agricultural Research Service, Invasive Plant Research Laboratory, 3225 College Ave., Ft. Lauderdale, Florida 33314), AND P. STILING (Department of Biology, University of South Florida, 4202 East Fowler Ave., SCA 110, Tampa, FL 33620). Native and introduced pollinators promote an invasive woody vine (Paederia foetida L) in Florida. J. Torrey Bot. Soc. 133(2): 303-311. 2006-Little is known about the role of mutualistic relationships with local species in promoting or limiting introduced invasive plant species. In this study we carried out controlled pollination treatments and floral visitor watches at three sites varying in degree of human disturbance in central Florida to determine the breeding system and potential pollinators of Paederia foetida L (skunk vine). A native of eastern Asia, P. foetida is invasive in natural and human created habitats in the southern United States and Hawaii. Our data suggested that populations of P. foetida in Florida were self-incompatible and relied on both small-bodied halictid bees native to Florida and the introduced European honey bee for pollination. Visitation by native bees was more frequent in less disturbed sites, while the opposite was true for the honey bees. Pollinator limitation was evident at the relatively undisturbed and the highly disturbed sites, but not at the intermediate disturbed site. Mutualistic relationships with native pollinators as well as the introduced honey bee probably contributed to the establishment and spread of skunk vine in Florida. Web of Science Paederia foetida USA Florida Hillsborough County; Pasco County Field - Experimental terrestrial Broadleaf Evergreen Forest;Old Field Invasion Hyp. Mutualism Facilitation primary;omnivore 820 Newingham, Beth A.; Callaway, Ragan M. 2006 Shoot herbivory on the invasive plant, Centaurea maculosa, does not reduce its competitive effects on conspecifics and natives journal OIKOS 114 3 397 406 Herbivory can have negative, positive, or no effect on plants. However, insect biological control assumes that herbivory will negatively affect the weed and release natives from competition. Centaurea maculosa, an invader in North America, is tolerant to herbivory, and under some conditions, herbivory may increase its competitive effects on natives. Therefore, we investigated two hypotheses: 1) herbivory stimulates compensatory growth by C. maculosa, which increases its competitive effects, and 2) herbivory stimulates the allelopathic effect of C. maculosa. In the greenhouse, Trichoplusia ni shoot herbivory reduced C. maculosa biomass when shoot damage exceeded 40% of the total original leaf area. Conspecific neighbors had no effect on C. maculosa biomass, and the presence of the natives Festuca idahoensis and F. scabrella had a positive effect on C. maculosa. Neighbors did not alter the effects of shoot herbivory. More importantly, even intense shoot herbivory on C. maculosa did not benefit neighboring plants. In a field experiment, clipping 50% of C. maculosa aboveground biomass in the early summer and again in the late summer reduced final biomass by 40% at the end of the season; however, this clipping did not affect total biomass production or reproductive output. Festuca idahoensis neighbors did not increase the effects of clipping, and aboveground damage to C. maculosa did not release F. idahoensis from competition. In the greenhouse we used activated carbon to adsorb allelochemicals, which reduced the competitive effects of C. maculosa on F. idahoensis but not on F. scabrella or other C. maculosa. However, we found no increase in the allelopathic effects of C. maculosa after shoot herbivory. In summary, our results correspond with others indicating that exceptionally high intensities of herbivory are required to suppress C. maculosa growth and reproduction; however, even intense herbivory on C. maculosa does not insure that native bunchgrasses will benefit. Web of Science Centaurea maculosa USA Montana 46.8435 -113.9742 Field - Experimental;Greenhouse terrestrial Grassland Invasion Hyp. Inherent Superiority Superior Competitor primary 822 Levine, Jonathan M.; Pachepsky, Elizaveta; Kendall, Bruce E.; Yelenik, Stephanie G.; Hille Ris Lambers, Janneke 2006 Plant-soil feedbacks and invasive spread journal ECOLOGY LETTERS 9 9 1005 1014 Plant invaders have been suggested to change soil microbial communities and biogeochemical cycling in ways that can feedback to benefit themselves. In this paper, we ask when do these feedbacks influence the spread of exotic plants. Because answering this question is empirically challenging, we show how ecological theory on 'pushed' and 'pulled' invasions can be used to examine the problem. We incorporate soil feedbacks into annual plant invasion models, derive the conditions under which such feedbacks affect spread, and support our approach with simulations. We show that in homogeneous landscapes, strong positive feedbacks can influence spreading velocity for annual invaders, but that empirically documented feedbacks are not strong enough to do so. Moreover, to influence spread, invaders must modify the soil environment over a spatial scale larger than is biologically realistic. Though unimportant for annual invader spread in our models, feedbacks do affect invader density and potential impact. We discuss how future research might consider the way landscape structure, dispersal patterns, and the time scales over which plant-soil feedbacks develop regulate the effects of such feedbacks on invader spread. Web of Science Many Theoretical/Modeling Invasion Hyp. Other primary 823 Hierro, Jose L.; Villarreal, Diego; Eren, Ozkan; Graham, Jon M.; Callaway, Ragan M. 2006 Disturbance facilitates invasion: The effects are stronger abroad than at home journal AMERICAN NATURALIST 168 2 144 156 Disturbance is one of the most important factors promoting exotic invasion. However, if disturbance per se is sufficient to explain exotic success, then *invasion* abroad should not differ from *colonization* at home. Comparisons of the effects of disturbance on organisms in their native and introduced ranges are crucial to elucidate whether this is the case; however, such comparisons have not been conducted. We investigated the effects of disturbance on the success of Eurasian native Centaurea solstitialis in two invaded regions, California and Argentina, and one native region, Turkey, by conducting field experiments consisting of simulating different disturbances and adding locally collected C. solstitialis seeds. We also tested differences among C. solstitialis genotypes in these three regions and the effects of local soil microbes on C. solstitialis performance in greenhouse experiments. Disturbance increased C. solstitialis abundance and performance far more in nonnative ranges than in the native range, but C. solstitialis biomass and fecundity were similar among populations from all regions grown under common conditions. Eurasian soil microbes suppressed growth of C. solstitialis plants, while Californian and Argentinean soil biota did not. We suggest that escape from soil pathogens may contribute to the disproportionately powerful effect of disturbance in introduced regions. Web of Science Centaurea solstitialis USA; Argentina; Turkey California; Argentina Northern CA; Central Argentina 39.2667;-36.6667 -121.3;-64.8 Field - Experimental;Greenhouse terrestrial Grassland Invasion Hyp. Disturbance primary 824 Stokes, Kate E.; Buckley, Yvonne M.; Sheppard, Andrew W. 2006 A modelling approach to estimate the effect of exotic pollinators on exotic weed population dynamics: bumblebees and broom in Australia journal DIVERSITY AND DISTRIBUTIONS 12 5 593 600 The role of mutualisms in contributing to species invasions is rarely considered, inhibiting effective risk analysis and management options. Potential ecological consequences of invasion of non-native pollinators include increased pollination and seed set of invasive plants, with subsequent impacts on population growth rates and rates of spread. We outline a quantitative approach for evaluating the impact of a proposed introduction of an invasive pollinator on existing weed population dynamics and demonstrate the use of this approach on a relatively data-rich case study: the impacts on Cytisus scoparius (Scotch broom) from proposed introduction of Bombus terrestris. Three models have been used to assess population growth (matrix model), spread speed (integrodifference equation), and equilibrium occupancy (lattice model) for C. scoparius. We use available demographic data for an Australian population to parameterize two of these models. Increased seed set due to more efficient pollination resulted in a higher population growth rate in the density-independent matrix model, whereas simulations of enhanced pollination scenarios had a negligible effect on equilibrium weed occupancy in the lattice model. This is attributed to strong microsite limitation of recruitment in invasive C. scoparius populations observed in Australia and incorporated in the lattice model. A lack of information regarding secondary ant dispersal of C. scoparius prevents us from parameterizing the integrodifference equation model for Australia, but studies of invasive populations in California suggest that spread speed will also increase with higher seed set. For microsite-limited C. scoparius populations, increased seed set has minimal effects on equilibrium site occupancy. However, for density-independent rapidly invading populations, increased seed set is likely to lead to higher growth rates and spread speeds. The impacts of introduced pollinators on native flora and fauna and the potential for promoting range expansion in pollinator-limited 'sleeper weeds' also remain substantial risks. Web of Science Cytisus scoparius, Bombus terrestris Theoretical/Modeling terrestrial Invasion Hyp. Mutualism Facilitation primary;herbivore 826 Fleishman, Erica; Murphy, Dennis D.; Sada, Donald W. 2006 Effects of environmental heterogeneity and disturbance on the native and non-native flora of desert springs journal BIOLOGICAL INVASIONS 8 5 1091 1101 Vegetation often is used as a decision variable for conservation and resource management. Because time and money are limited, it is useful to identify predictable relationships between measures of vegetation diversity or status, the physical environment, and disturbance; native and non-native plants may have different functional responses. Working towards development of effective, practical strategies for management and ecological restoration in the Spring Mountains, an isolated mountain range in the eastern Mojave Desert (Nevada, USA) that is a focus of regional conservation planning, we examined whether native and non-native assemblages of spring-associated perennial plants have predictable relationships with elevation, springbrook length, and various land uses. We also tested whether elevation, springbrook length, and overall disturbance were associated with the degree of predictability of local species presence and absence. Consistent with work in other systems, species richness and cover of native plants tended to decrease as intensity of disturbance increased, whereas species richness (but not cover) of non-native plants tended to peak with intermediate disturbance. Our results may suggest that invasions of non-native plants at springs in the Spring Mountains are relatively recent, and that rapid restoration and management actions may help protect ecological processes and viability of native plants. Ability to predict the order in which individual species are likely to be extirpated from or colonize springs was limited, perhaps reflecting considerable environmental heterogeneity among springs. Web of Science Many USA Nevada Mojave Desert Field - Observational terrestrial Riparian Invasion Hyp. Disturbance primary 827 Thum, Ryan. A.; Lennon, Jay T. 2006 Is hybridization responsible for invasive growth of non-indigenous water-milfoils? journal BIOLOGICAL INVASIONS 8 5 1061 1066 Heterosis, or hybrid vigor, has recently been proposed as a factor promoting invasive growth of some non-indigenous aquatic plant species, particularly those capable of spreading rapidly within and among lakes through clonal reproduction. We tested this hypothesis for variable-leaf water milfoil (Myriophyllum heterophyllum), a non-indigenous aquatic plant that has become a major management and conservation concern in New England. Using nuclear ribosomal DNA, we looked for F-1 hybrid populations of invasive M. heterophyllum in 25 New Hampshire (NH) lakes. In contrast to a previous study that found F-1 hybrid lineages of invasive M. heterophyllum in Connecticut, we did not find hybrids in our study lakes. This result has two implications: (1) pure lineages of M. heterophyllum are also capable of invasive growth, and (2) the distribution of invasive M. heterophyllum lineages (hybrid vs. pure) may be spatially structured across New England. We stress the importance of more detailed distributional and ecological studies for understanding the invasive potential of this species. Web of Science Myriophyllum heterophyllum USA New Hampshire Field - Observational lentic Invasion Hyp. Hybridization primary 828 McDonald, Robert I.; Urban, Dean L. 2006 Edge effects on species composition and exotic species abundance in the North Carolina Piedmont journal BIOLOGICAL INVASIONS 8 5 1049 1060 Edges between forest and non-forest habitats often have significant effects on forest microclimate and resource availability, with corresponding effects on species composition and abundance. Exotic species are often increased in abundance near forest edges. This increase in abundance could be either because of the increase in resource availability near edges, or because of increased dispersal into forest edges. We measured species composition and a set of geospatial variables on transects at 66 edges in the North Carolina Piedmont in an attempt to distinguish between these two factors. Mantel tests show that species composition is significantly different in forest edges than in the forest interior, but that this effect only penetrates about 5 m into the forest. Indicator species analysis finds several species that are indicative of edge communities, including trumpet vine (Campsis radicans), two drought-tolerant oak species (Quercus stellata and Q. falcata), a serviceberry (Amelanchier arboreum), and a common exotic species, tree-of-heaven (Ailanthus altissima). Poisson regression techniques showed that in both the seedling and tree strata of the forest, exotic species increased in abundance on flat sites with a high potential seed source. Mapping predicted exotic species abundance onto the landscape. We find that large-scale variation in exotic species abundance is due mostly to variation in potential seed sources, while small-scale variation relates more to edaphic factors. Our results stress that both dispersal and environmental filters are important for determining exotic species abundance, but potentially the filters operate at different spatial scales. Web of Science Many USA North Carolina Duke Forest 35 -78.15 Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority;Propagule Pressure;Disturbance Effective Disperser primary 829 Colautti, Robert I.; Grigorovich, Igor A.; MacIsaac, Hugh J. 2006 Propagule pressure: A null model for biological invasions journal BIOLOGICAL INVASIONS 8 5 1023 1037 Invasion ecology has been criticised for its lack of general principles. To explore this criticism, we conducted a meta-analysis that examined characteristics of invasiveness (i.e. the ability of species to establish in, spread to, or become abundant in novel communities) and invasibility (i.e. the susceptibility of habitats to the establishment or proliferation of invaders). There were few consistencies among invasiveness characteristics (3 of 13): established and abundant invaders generally occupy similar habitats as native species, while abundant species tend to be less affected by enemies; germination success and reproductive output were significantly positively associated with invasiveness when results from both stages (establishment/spread and abundance/impact) were combined. Two of six invasibility characteristics were also significant: communities experiencing more disturbance and with higher resource availability sustained greater establishment and proliferation of invaders. We also found that even though 'propagule pressure' was considered in only similar to 29% of studies, it was a significant predictor of both invasiveness and invasibility (55 of 64 total cases). Given that nonindigenous species are likely introduced non-randomly, we contend that 'propagule biases' may confound current paradigms in invasion ecology. Examples of patterns that could be confounded by propagule biases include characteristics of good invaders and susceptible habitats, release from enemies, evolution of 'invasiveness', and invasional meltdown. We conclude that propagule pressure should serve as the basis of a null model for studies of biological invasions when inferring process from patterns of invasion. Web of Science Many Review/Meta-analysis Invasion Hyp. Propagule Pressure primary;herbivore;omnivore;predator;decomposer;filter 830 Bartuszevige, Anne M.; Gorchov, David L. 2006 Avian seed dispersal of an invasive shrub journal BIOLOGICAL INVASIONS 8 5 1013 1022 The incorporation of an animal-dispersed exotic plant species into the diet of native frugivores can be an important step to that species becoming invasive. We investigated bird dispersal of Lonicera maackii, an Asian shrub invasive in eastern North America. We (i) determined which species of birds disperse viable L. maackii seeds, (ii) tested the effect of gut passage on L. maackii seeds, and (iii) projected the seed shadow based on habitat use by a major disperser. We found that four native and one exotic bird species dispersed viable L. maackii seeds. Gut passage through American robins did not inhibit germination, but gut passage through cedar waxwings did. American robins moved mostly along woodlot edges and fencerows, leading us to project that most viable seeds would be defecated in such habitats, which are very suitable for L. maackii. We conclude that L. maackii has been successfully incorporated into the diets of native and exotic birds and that American robins preferentially disperse seeds to suitable habitat. Web of Science Lonicera maackii USA Ohio Field - Experimental;Field - Observational terrestrial Deciduous Forest Invasion Hyp. Mutualism Facilitation primary 831 Siemann, Evan; Rogers, William E. 2006 Recruitment limitation, seedling performance and persistence of exotic tree monocultures journal BIOLOGICAL INVASIONS 8 5 979 991 Many native plant communities are replaced by exotic monocultures that may be successional stages or persistent community types. We surveyed a stand of Sapium sebiferum (Chinese Tallow Tree) that replaced tallgrass prairie in Texas and performed experiments with seeds and seedlings to determine the contributions of recruitment limitation and natural enemy release to allowing such a forest type to persist or to allowing native species to reduce Sapium dominance. The stand was dominated by Sapium, especially for mature trees (> 99) and annual seed input (97) but less so for saplings (80). Field sown Sapium seeds had lower germination and survival rates than Celtis seeds. Together with the extreme dominance of Sapium in seed rain this suggests that native species are currently recruitment limited in this stand by seed supply but not by germination, early growth or survival. To investigate whether Sapium may benefit from low herbivory or diseases, we transplanted Sapium and Celtis seedlings into the forest and manipulated foliar fungal diseases and insect herbivores with sprays. As predicted, insect herbivores caused greater damage to Celtis seedlings than to Sapiumseedlings. However, suppression of insect herbivores caused significantly greater increases in survivorship of Sapium seedlings compared to Celtis seedlings. This suggests that herbivores in the understory of this Sapiumforest may significantly reduce Sapiumseedling success. Such a pattern of strong herbivore impact on seedlings growing near adult conspecifics was unexpected for this invasive species. However, even with insects and fungi suppressed, Sapium seedling performance was poor in this forest. Our results point towards Sapium as a successional species in a forest that will eventually be dominated by native trees that are currently recruitment limited but outperform Sapium in the understory. Web of Science Sapium sebiferum USA Texas Field - Experimental;Field - Observational;Greenhouse terrestrial Deciduous Forest Invasion Hyp. Enemy Release primary 834 Burns, Jean H. 2006 Relatedness and environment affect traits associated with invasive and noninvasive introduced commelinaceae journal ECOLOGICAL APPLICATIONS 16 4 1367 1376 Understanding the traits of invasive species may improve the ability to predict, prevent, and manage invasions. I compared morphological and performance traits of five congeneric pairs of invasive and noninvasive Commelinaceae across a factorial experiment using a range of water and nutrient availabilities. Invasive species had greater fecundity and vegetative reproduction than their noninvasive relatives. The invasive species also had higher relative growth rates, greater specific leaf area, and more plastic root-to-shoot ratios than noninvasive species. However, whether a trait was associated with invasiveness often depended on both environment and relatedness. Invasives had greater sexual and vegetative reproduction, higher specific leaf area, and greater relative growth rates than noninvasive congeners, but only in some environments. Differences between invasive and noninvasive taxa were greatest at high nutrient availabilities. These results. suggest that studies of invasive species' traits must incorporate information on conditions under which the trait was measured. In addition, incorporating information on relatedness improved our ability to detect associations between species traits, such as specific leaf area and relative growth rate, and invasiveness, suggesting that such information may be required for a complete understanding of what makes a species invasive. Web of Science Many Greenhouse terrestrial Invasion Hyp. Inherent Superiority Broad Tolerances;High Reprod. Output;Clonal Reproduction primary 835 Peters, Debra P. C.; Yao, Jin; Gosz, James R. 2006 Woody plant invasion at a semi-arid/arid transition zone: importance of ecosystem type to colonization and patch expansion journal JOURNAL OF VEGETATION SCIENCE 17 3 389 396 Question: How do patterns in colonization and patch expansion of an invasive woody plant (Larrea tridentata, Zygophyllaceae) differ between two grassland ecosystems at a biome transition zone? Location: Semi-arid/arid transition zone in central New Mexico. Methods: Frequency of occurrence, height, and surface area of saplings (n = 134) and patches of adult plants (n = 247) of the invasive shrub, L. tridentata, were measured within a mosaic of ecosystems dominated either by the Chihuahuan Desert species, Bouteloua eriopoda (Poaceae),or the shortgrass steppe species, B. gracilis, located within I km of the L. tridentata-dominated ecosystem. Distances between L. tridentata patches and patch area were used to estimate connectivity as a measure of propagule pressure. Sapling age (estimated from height using previously established relationships) and distance to the L. tridentata-dominated ecosystem was used to evaluate patterns in dispersal. Cover by species or functional group inside each L. tridentata patch was compared with surrounding vegetation to estimate changes in species composition with patch expansion. Results: L. tridentata saplings (< 1%) and adult patches (15%) occurred less frequently in B. gracilis-dominated ecosystems than expected based on areal extent of this ecosystem type. Propagule pressure did not differ with distance from the core ecosystem dominated by L. tridentata. Evidence for both local and long-distance dispersal events was found. Similar relationships between number of plants and patch area in both grassland types indicate similar patterns in patch expansion. Cover of perennial forbs was higher and cover of dominant grasses was lower in L. tridentata patches compared with the surrounding vegetation for both ecosystem types. Conclusions: Spatial variation in L. tridentata saplings and patches at this biome transition zone is related to the different susceptibilities to invasion by two grassland ecosystems. The persistence of grasslands at this site despite region-wide expansion by L. tridentata may be related to the spatial distribution of B. gracilis-dominated ecosystems that resist or deter invasion by this woody plant. Web of Science Larrea tridentata USA New Mexico 34.0667 -106.1167 Field - Observational terrestrial Grassland Invasion Hyp. Inherent Superiority;Propagule Pressure;Other Effective Disperser primary 837 Eppinga, Maarten B.; Rietkerk, Max; Dekker, Stefan C.; De Ruiter, Peter C.; Van der Putten, Wim H. 2006 Accumulation of local pathogens: a new hypothesis to explain exotic plant invasions journal OIKOS 114 1 168 176 Recent studies have concluded that release from native soil pathogens may explain invasion of exotic plant species. However, release from soil enemies does not explain all plant invasions. The invasion of Anunophila arenaria (marram grass or European beach grass) in California provides an illustrative example for which the enemy release hypothesis has been refuted. To explore the possible role of plant-soil community interactions in this invasion, we developed a mathematical model. First, we analyzed the role of plant-soil community interactions in the succession of A. arenaria in its native range (north-western Europe). Then, we used our model to explore for California how alternative plant-soil community interactions may generate the same effect as if A. arenaria were released from soil enemies. This analysis was carried out by construction of a 'recovery plane' that discriminates between plant competition and plant-soil community interactions. Our model shows that in California, the accumulation of local pathogens by A. arenaria could result in exclusion of native plant species. Moreover, this mechanism could trigger the rate and spatial pattern of invasive spread generally observed in nature. We propose that our 'accumulation of local pathogens' hypothesis could serve as an alternative explanation for the enemy release hypothesis to be considered in further experimental studies on invasive plant species. Web of Science Anunophila arenaria USA California Theoretical/Modeling terrestrial Grassland Invasion Hyp. Mutualism Facilitation primary 839 Henderson, Darcy C.; Chapman, Ross 2006 Caragana arborescens invasion in Elk Island National Park, Canada journal NATURAL AREAS JOURNAL 26 3 261 266 Siberian pea shrub, or caragana, (Caragana arborescens Lam.), was intentionally introduced on the northern Great Plains of North America for erosion control and ornamental hedgerows, but has invaded the understory of native deciduous forests. Although this species is widespread, there is little information on the ecology of naturalized populations or impacts of invasion. Our objectives were to describe the demographic structure of an invasive population and changes in shrub community diversity along a gradient of caragana density in an upland aspen (Populus tremuloides Michx.) forest at Elk Island National Park, Alberta, Canada. This caragana population spread through the understory and increased from 50 to approximately 60,000 individuals over 75 years. More than 85% of individuals were immature (< 10 yrs, < 1 m tall, non-flowering), and the size class-frequency distribution best fit a negative power function curve. Several native shrub species, including the dominant beaked hazel (Corylus cornuta Marsh.), were negatively associated with caragana, and the relationship between diversity and caragana density was quadratic. Control efforts will require perseverance since immature pea shrubs are difficult to locate beneath the dense growth of beaked hazel and the immature phase can last a decade. Web of Science Caragana arborescens Canada Alberta Elk Island National Park 53.618987 -112.868042 Field - Observational terrestrial Deciduous Forest;Coniferous Forest Fundamentals primary 840 Thuiller, Wilfried; Richardson, David M.; Rouget, Mathieu; Proches, Serban; Wilson, John R. U. 2006 Interactions between environment, species traits, and human uses describe patterns of plant invasions journal ECOLOGY 87 7 1755 1769 Although invasive alien species (IAS) are a major threat to biodiversity, human health, and economy, our understanding of the factors controlling their distribution and abundance is limited. Here, we determine how environmental factors, land use, life-history traits of the invaders, residence time, origin, and human usage interact to shape the spatial pattern of invasive alien plant species in South Africa. Relationships between the environmental factors and the extrinsic and intrinsic attributes of species were investigated using RLQ analysis, a multivariate method for relating a species-attribute table to an environmental table by way of a species presence/absence table. We then clustered species according to their position on the RLQ axes, and tested these groups for phylogenetic independence. The first three axes of the RLQ explained 99% of the variation and were strongly related to the species attributes. The clustering showed that, after accounting for environmental factors, the spatial pattern of IAS in South Africa was driven by human uses, life forms, and reproductive traits. The seven clusters of species strongly reflected geographical distribution, but also intrinsic species attributes and patterns of human use. Two of the clusters, centered on the genera Acacia and Opuntia, were phylogenetically non-independent. The remaining clusters comprised species of diverse taxonomic affinities, but sharing traits facilitating invasion in particular habitats. This information is useful for assessing the extent to which the potential spread of recent introductions can be predicted by considering the interaction of their biological attributes, region of origin, and human use. Web of Science Many South Africa Statistical/Meta-analysis terrestrial Invasion Hyp. Inherent Superiority;Disturbance Effective Disperser;Clonal Reproduction primary 841 Hale, Cindy M.; Frelich, Lee E.; Reich, Peter B. 2006 Changes in hardwood forest understory plant communities in response to European earthworm invasions journal ECOLOGY 87 7 1637 1649 European earthworms are colonizing earthworm-free northern hardwood forests across North America. Leading edges of earthworm invasion provide an opportunity to investigate the response of understory plant communities to earthworm invasion and whether the species composition of the earthworm community influences that response. Four sugar maple-dominated forest sites with active earthworm invasions were identified in the Chippewa National Forest in north central Minnesota, USA. In each site, we established a 30 X 150 m sample grid that spanned a visible leading edge of earthworm invasion and sampled earthworm populations and understory vegetation over four years. Across leading edges of earthworm invasion, increasing total earthworm biomass was associated with decreasing diversity and abundance of herbaceous plants in two of four study sites, and the abundance and density of tree seedlings decreased in three of four study sites. Sample points with the most diverse earthworm species assemblage, independent of biomass, had the lowest plant diversity. Changes in understory plant community composition were most affected by increasing biomass of the earthworm species Lumbricus rubellus. Where L. rubellus was absent there was a diverse community of native herbaceous plants, but where L. rubellus biomass reached its maximum, the herbaceous-plant community was dominated by Carex pensylvanica and Arisaema triphyllum and, in some cases, was completely absent. Evidence from these forest sites suggests that earthworm invasion can lead to dramatic changes in the understory community and that the nature of these changes is influenced by the species composition of the invading earthworm community. Web of Science Lumbricus rubellus USA Minnesota Field - Observational terrestrial Deciduous Forest Impacts;Invasion Hyp. Community Species Richness decomposer 842 Tenorio, Ramona C.; Drezner, Taly Dawn 2006 Native and invasive vegetation of karst springs in Wisconsin's Driftless area journal HYDROBIOLOGIA 568 0 499 505 Little is known about the vegetation found in the karst springs of Wisconsin's unglaciated region, the Driftless Area. We sampled 26 of these springs, documenting all associated plant species and their status (native, non-native, invasive) and analyzed whether vegetation patterns are related to spring orientation or to spring area. Two-way ANOVA results show that non-native and invasive species, namely Nasturtium officinale (watercress, Brassicaceae), are significantly more abundant than natives in north-facing springs (p < 0.01), but not in south-facing springs. Generally, native species are restricted to, or more abundant in, south-facing springs, and may have a microtopographical preference for these sites, which may receive more direct solar radiation. Nasturtium officinale, the most abundant invasive species, has high cover values in both north and south orientations and is less restricted in its distribution. Correlation analysis shows that the larger the spring, the higher the percent of Nasturtium (p < 0.01) and invasive species cover (as a percent of spring area) (p < 0.005). Larger springs often had slower moving water and this may have contributed to the success of Nasturtium, which may outcompete shade-intolerant natives in the larger springs. Native species cover was negatively related to spring area, though this result was marginally insignificant (p = 0.08). Web of Science Many USA Wisconsin Field - Observational lotic Riparian Invasion Hyp. Inherent Superiority Superior Competitor primary 843 Vaughn, Caryn C.; Spooner, Daniel E. 2006 Scale-dependent associations between native freshwater mussels and invasive Corbicula journal HYDROBIOLOGIA 568 0 331 339 In North America there is conflicting evidence concerning whether the invasive Asian clam, Corbicula fluminea, and native mussels (Unionidae), can successfully co-exist. One reason underlying disparate conclusions may be the different spatial scales at which data have been collected. We compared the distribution and abundance of native unionid mussels and Corbicula at two spatial scales, stream reaches and 0.25 m(2) patches, within one biogeographic region, the Ouachita Highlands, of the south central U.S. We found that Corbicula abundance was negatively related to native mussel abundance at small spatial scales. While Corbicula densities varied widely in patches without native mussels, and in patches where mussels occurred at low abundance, Corbicula density was never high in patches where mussels were dense. We hypothesize that the likelihood of successful Corbicula invasion decreases with increasing abundance of adult native mussels. Several mechanisms may potentially drive this pattern including lack of space for Corbicula to colonize, physical displacement by actively burrowing mussels, and locally reduced food resources in patches where native mussels are feeding. In addition, Corbicula may be unable to withstand environmental bottlenecks as readily as unionids. When patch-scale density and biomass information were pooled to represent entire stream reaches, the negative relationship between native mussels and Corbicula was no longer as apparent, and there was not a significant relationship between native mussels and Corbicula. These results point to the importance of appropriate sample scale in examining potential associations between species. Web of Science Corbicula fluminea USA Arkansas; Oklahoma Ouachita Highlands 34.696461 -93.856201 Field - Observational lotic Riparian Fundamentals filter 845 Pergl, Jan; Perglova, Irena; Pysek, Petr; Dietz, Hansjoerg 2006 Population age structure and reproductive behavior of the monocarpic perennial Heracleum mantegazzianum (Apiaceae) in its native and invaded distribution ranges journal AMERICAN JOURNAL OF BOTANY 93 7 1018 1028 Many invasive species are benign in their native region-are there interactions between their key traits and the new habitats that explain invasion success? The giant perennial herb Heracleum mantegazzianum is a problematic invader in Europe and is also naturalized in North America. We compared its population structure and reproductive behavior in the native (W. Caucasus) and invaded (Czech Republic) areas in managed (pastures) and unmanaged sites. The age structure of the populations and age at flowering were analyzed using herb-chronology, a method based on counting annual rings in the secondary xylem of roots. The species was strictly monocarpic; most plants in unmanaged sites in the invaded range flowered in the third and fourth yr (maximum 12 yr). In unmanaged habitats, plants from the native range flowered later than those from the invaded range. In both ranges, flowering was delayed in managed sites where the population density was higher and most plants flowered around the fifth year. Reproductive output of individual plants was neither related to population density nor to age at flowering. More favorable climatic conditions in the invaded region, together with increased chances for dispersal in a densely colonized central Europe, seemed to allow the massive invasion. Web of Science Heracleum mantegazzianum Georgia, Czech Republic Field - Observational terrestrial Grassland;Old Field Invasion Hyp. Inherent Superiority;Preadaptation to Climate;Disturbance Rapid Growth;High Reprod. Output primary 846 Radford, Ian J.; Dickinson, Katharine J. M.; Lord, Janice M. 2006 Nutrient stress and performance of invasive Hieracium lepidulum and co-occurring species in New Zealand journal BASIC AND APPLIED ECOLOGY 7 4 320 333 Many studies have highlighted the relationship between nutrient fluctuations and enrichment in the process of plant invasion. However, invasion may be also associated with conditions of plant stress, either nutrient depletion or toxicity, in the environment. In this study, we investigate the possible role of nutrient stress in the invasion of Hieracium lepidulum (Stenstroem) Omang, in South Island, New Zealand. We do this by comparing several performance attributes, and their plasticity, for H. lepidulum and a number of co-occurring species, across a series of nutrient depletion and toxicity tests. H. lepidulum had intermediate yields, high root:shoot ratios and high tissue nutrient contents at control. nutrient concentrations. H. lepidulum differed in eclaphic tolerance from all but Chionochloa flovescens var. brevis, in being insensitive to nutrient dilutions other than nitrogen. The significance of performance in terms of eclaphic tolerance and adaptations are discussed. Intermediate yields at control nutrient levels suggest that H. lepidulum should not be competitive compared to high yielding species including Agrostis stolonifera and Poo cita, but should be competitive with lower yielding Coprosma rugosa and C. flavescens var. brevis. Conversely, significant yield decreases under nitrogen (imitation stress suggests that H. lepidulum will not likely occupy very nutrient poor sites. H. lepidulum, along with C. flavescens var. brevis, were found to be tolerant of ammonium as an alternative source of nitrogen, while other species were not. These data suggest that H. lepidulum and C. flavescens var. brevis would be relatively tolerant of the stresses associated with acidic soils compared to the other species, but not to stresses associated with absolute shortage of nitrogen. Combined results point to the likely occurrence of H. tepidutum at sites of intermediate fertility. The possible roles of ammonium stress. and disturbance reliance in further defining H. lepidulurn ecology is discussed. (c) 2005 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved. Web of Science Many New Zealand Greenhouse Invasion Hyp. Inherent Superiority;Fluctuating Resources Broad Tolerances primary 847 Suehs, Carey Meredith; Charpentier, Stephane; Affre, Laurence; Medail, Frederic 2006 The evolutionary potential of invasive Carpobrotus (Aizoaceae) taxa: are pollen-mediated gene flow potential and hybrid vigor levels connected? journal EVOLUTIONARY ECOLOGY 20 5 447 463 Few studies have addressed the importance of native pollinators in shaping the breeding systems and evolutionary potential of invasive plants. We examined the pollination and gamete production of Carpobrotus affine acinaciformis (L.) L. Bol. and C. edulis (L.) N. E. Br. invading the coasts of southeast France (Provence), and found preliminary evidence that the pollen-mediated gene flow potential (PMGFP) within the four studied populations is positively correlated with their Relative Performance in Hybridization indices (RPH), suggesting a link between pollinator services, gene flow, and Carpobrotus hybridization. Flower density (FD) may be a driver behind pollinator abundance and visitation patterns since it shows a significant, positive relationship with relative pollinator abundance (FR) and a significant negative relationship with per flower visit frequencies (FR/F). In the populations with the highest RPH indices, and therefore high hybrid vigor, both taxa produce similar quantities of ovules and pollen per flower, whose ratios further indicate (facultative) xenogamy. Pollen diameter distributions include similar to 25% micro-pollen, and overall viability is less than one half. Viable pollen profiles consist of 3.5% micro, 85.5% normal and 10.9% macro pollen (considered as diplogametes) on average per flower for C. affine acinaciformis, and 0.7% micro, 73.0% normal and 26.2% macro pollen for C. edulis. Given the co-occurrence of (1) (facultative) xenogamic breeding strategies, (2) a significant, positive relationship between RPH and PMGFP, and (3) frequent pollen abnormalities, it is probable that hybrid dysgenesis mediated by the local pollinators occurs in these populations. Furthermore, the unusually high frequency of potentially viable, diploid macro-pollen underlines the evolutionary/polyploid potential of these invasive, introgressed populations. Native pollinator interactions may greatly affect the taxonomic status and evolutionary potential of invasive plant complexes. Web of Science Carpobrotus affine acinaciformis; Carpobrotus edulis France Provence National Park of Port Cros 43 6.38 Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Other primary 853 Guesewell, S.; Jakobs, G.; Weber, E. 2006 Native and introduced populations of Solidago gigantea differ in shoot production but not in leaf traits or litter decomposition journal FUNCTIONAL ECOLOGY 20 4 575 584 1. Invasive alien plants tend to have a greater specific leaf area and more nutrient-rich tissues than the invaded native vegetation. To test whether these traits differ between introduced and native populations of the same species, we compared 20 European (introduced) and 22 American (native) populations of Solidago gigantea Aiton (Asteraceae) in a common-garden experiment. 2. Five plants per population were grown for 2 years in pots and for one summer outdoors in nutrient-rich soil. We recorded shoot number and biomass, leaf production and senescence, flowering, leaf morphology and nutrient concentrations of leaves and litter. In laboratory assays, we compared litter decomposition and nutrient mineralization. 3. Shoot growth and leaf traits varied three- to 10-fold among the 42 populations. European plants produced, on average, more shoots than American plants, but did not differ in shoot size, leaf traits or litter decomposition. 4. The shoot number and total shoot biomass per plant in the experiment correlated positively with the number of new rhizomes produced by shoots of the same populations at their original field sites. 5. We conclude that introduced S. gigantea populations tend to produce more shoots through clonal growth than native populations. This may increase their ability to compete against the established vegetation in dense stands or at nutrient-poor sites. Web of Science Solidago gigantea Switzerland Zuerich Field - Experimental;Garden terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 855 Sanchez, Inigo; Fernandez, Consolacion 2006 Resource availability and invasibility in an intertidal macroalgal assemblage journal MARINE ECOLOGY-PROGRESS SERIES 313 0 85 94 The invasibility of a low intertidal macroalgal assemblage was experimentally tested from March 2003 to April 2004 at 1 locality in northern Spain. It was hypothesised that a community becomes more susceptible to invasion when there is an increase in the amount of key resources. A bifactorial ('nutrient supply' and 'macroalgal biomass removed') orthogonal experiment was designed with 3 levels in each factor (high, medium and control). Fertile plants of Sargassum muticum (Yendo) Fensholt were transplanted to each plot to simulate the arrival of an invader. The invasibility of the assemblage was quantified in the pre- (density of recruits) and post-settlement (percentage cover, size and density of S. muticum at the end of the experiment) phases of S. muticum's life cycle. Results supported the initial hypothesis. Both space availability and nutrient enrichment facilitated the establishment and spread of S. muticum in the experimental plots. Established S. muticum plants grew faster in enriched plots than in controls. Furthermore, different successional assemblages played different roles in resisting invasion as S. muticum's life cycle progressed. In the initial stage of the invasion, the Bifurcaria bifurcata canopy inhibited recruitment by S. muticum, whereas understory species did not have a significant effect on invasion success. In contrast, an increased survivorship of S. muticum beneath the canopy of B. bifurcata was observed in those plots where S. muticum had successfully recruited. This study shows that the invasibility of this low intertidal assemblage is mediated by a complex interaction of several resources acting at different stages during S. muticum's invasion. Web of Science Sargassum muticum Spain Aramar 43.6 -5.7667 Field - Experimental marine Intertidal/Near Shore Invasion Hyp. Fluctuating Resources primary 857 Aguiar, Francisca C.; Ferreira, Maria Teresa; Albuquerque, Antonio 2006 Patterns of exotic and native plant species richness and cover along a semi-arid Iberian river and across its floodplain journal PLANT ECOLOGY 184 2 189 202 Patterns of native and exotic species richness and cover were examined together with the composition of species assemblages along a typical Mediterranean river and across its floodplain. Major goals were to characterize species distribution regarding diverse environmental and habitat features, and to explore floodplain landforms relations using plant assemblages and invasion responses as biological indicators of aquatic-terrestrial connectivity. A floristic survey was undertaken during May and early June 1998 in six sites of a southern Iberian basin. Vegetation data were gathered from three transects in three landforms: inundated and frequently flooded banks (FF), infrequently flooded valley floors (IF), and rarely flooded higher floodplains (RF). We used 2x2 m plots to record each species present and visual estimates of percentage cover of each species. Cover of native and exotic species assemblages were also estimated for each plots, for the transects, and for the landforms. The total number of vascular plant species found was 287 of which only 26 were exotic. Despite the high environmental and geomorphological variability, the hierarchical classification showed that species composition varied across the floodplain, rather than along the river. The IF and RF landforms were the most species-rich, both for native and exotic species group, whereas the cover trends of exotic and native plant species were opposed, with exotics being consistently more abundant in FF, and native cover increasing towards RF landforms. We found positive correlations between native and exotic species richness on the floodplain scale, and on a smaller scale in FF and IF landforms, thus supporting the hypothesis that in aquatic and riparian ecosystems of semi-arid landscapes, species-rich communities are preferentially colonized by exotic species. However, this pattern was not consistently coupled with a high cover of exotic species, and it was not sustained for the dry areas of the RF landforms. Web of Science Many Spain; Portugal Field - Observational lotic Riparian Invasion Hyp. Community Species Richness primary 860 Krakau, M.; Thieltges, D. W.; Reise, K. 2006 Native parasites adopt introduced bivalves of the North Sea journal BIOLOGICAL INVASIONS 8 4 919 925 Introduced species may have a competitive advantage over native species due to a lack of predators or pathogens. In the North Sea region, it has been assumed that no metazoan parasites are to be found in marine introduced species. In an attempt to test this assumption, we found native parasites in the introduced bivalves Crassostrea gigas and Ensis americanus with a prevalence of 35% and 80%, respectively, dominated by the trematode Renicola roscovita. When comparing these introduced species with native bivalves from the same localities, Mytilus edulis and Cerastoderma edule, trematode intensity was always lower in the introduced species. These findings have three major implications: (1) introduced bivalves are not free of detrimental parasites which raises the question whether introduced species have an advantage over native species after invasion, (2) introduced bivalves may divert parasite burdens providing a relief for native species and (3) they may affect parasite populations by influencing the fate of infectious stages, ending either in dead end hosts, not being consumed by potential final hosts or by adding new hosts. Future studies should consider these implications to arrive at a better understanding of the interplay between native parasites and introduced hosts. Web of Science Crassostrea gigas; Ensis americanus Germany North Sea Field - Observational marine Intertidal/Near Shore Invasion Hyp. Enemy Release filter 864 Von Holle, Betsy; Joseph, Katherine. A.; Largay, Erin F.; Lohnes, Rebecca G. 2006 Facilitations between the introduced nitrogen-fixing tree, Robinia pseudoacacia, and nonnative plant species in the glacial outwash upland ecosystem of cape cod, MA journal BIODIVERSITY AND CONSERVATION 15 7 2197 2215 Robinia pseudoacacia, a nitrogen-fixing, clonal tree species native to the central Appalachian and Ozark Mountains, is considered to be one of the top 100 worldwide woody plant invaders. We initiated this project to determine the impact of black locust (Robinia pseudoacacia) on an upland coastal ecosystem and to estimate the spread of this species within Cape Cod National Seashore (CCNS). We censused 20 x 20 m plots for vegetation cover and environmental characteristics in the center of twenty randomly-selected Robinia pseudoacacia stands. Additionally, paired plots were surveyed under native overstory stands, comprised largely of pitch pine (Pinus rigida) and mixed pitch pine-oak (Quercus velutina and Quercus alba) communities. These native stands were located 20 m from the edge of the sampled locust stand and had similar land use histories. To determine the historical distribution of black locust in CCNS, we digitized and georeferenced historical and current aerial photographs of randomly-selected stands. Ordination analyses revealed striking community-level differences between locust and pine-oak stands in their immediate vicinity. Understory nonnative species richness and abundance values were significantly higher under Robinia stands than under the paired native stands. Additionally, animal-dispersed plant species tended to occur in closer stands, suggesting their spread between locust stands. Robinia stand area significantly decreased from the 1970's to 2002, prompting us to recommend no management action of black locust and a monitoring program and possible removal of associated animal-dispersed species. The introduction of a novel functional type (nitrogen-fixing tree) into this xeric, nutrient-poor, upland forested ecosystem resulted in 'islands of invasion' within this resistant system. Web of Science Robinia pseudoacacia USA Massachusetts Cape Cod Field - Observational terrestrial Deciduous Forest Invasion Hyp. Mutualism Facilitation primary 865 Vila, Montserrat; Gimeno, Isabel 2006 Potential for higher invasiveness of the alien Oxalis pes-caprae on islands than on the mainland journal PLANT ECOLOGY 183 1 47 53 The higher vulnerability of islands to invasions compared to mainland areas has been partially attributed to a simplification of island communities, with lower levels of natural enemies and competitors on islands conferring vacant niches for invaders to establish and proliferate. However, differences in invader life-history traits between populations have received less attention. We conducted a broad geographical analysis (i.e. 1050 km wide transect) of plant traits comparing insular and mainland populations to test the hypothesis that alien plants from insular populations have the potential for higher invasiveness than their alien mainland counterparts. For this purpose plants of the annual geophyte Oxalis pes-caprae were grown from bulbs collected in the Balearic islands and the Spanish mainland under common greenhouse conditions. There were no significant differences in bulb emergence and plant survival between descendants from insular and mainland populations. However, Oxalis descendants from insular populations produced 20% more bulbs without reducing allocation to bulb size, above-ground biomass or flowering than descendants from mainland populations. Based on the lack of sexual reproduction in Oxalis and the dependence of invasion on bulb production, our study suggests that the higher occurrence of Oxalis in the Balearic islands than in the Spanish mainland can partially be explained by genetically based higher propagation potential of insular populations compared to mainland populations. Web of Science Oxalis pes-caprae Greenhouse terrestrial Invasion Hyp. Empty Niche;Community Species Richness primary 866 Flory, S. Luke; Clay, Keith 2006 Invasive shrub distribution varies with distance to roads and stand age in eastern deciduous forests in Indiana, USA journal PLANT ECOLOGY 184 1 131 141 We documented the relationship between densities of invasive exotic shrubs, distance to road, and successional age of the forest in 14 forested sites throughout central and southern Indiana. Roadways are increasingly abundant, human-made features that can be conduits for the spread of invasive exotic plants in a number of ecosystems. Little is known, however, about the role of roads in eastern deciduous forest ecosystems where road density is high. Further, it is not known whether the distribution of exotic plants along roads depends on the successional age of the forest. In this study, densities of four of seven exotic shrub species declined with increasing distance to the nearest road across all successional ages. Greater densities of exotic shrubs were found in young and mid-successional forests than mature forests. However, there was no interaction between distance to road and forest age, suggesting that the role of roads in the invasion process does not change across forest successional ages. We outline several potential mechanisms that may drive patterns of shrub distribution along roadside edges as a guide for future research. Web of Science Many USA Indiana Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 871 Novak, SJ; Welfley, AY 1997 Genetic diversity in the introduced clonal grass Poa bulbosa (Bulbous bluegrass) journal NORTHWEST SCIENCE 71 4 271 280 Bulbous bluegrass (Pea bulbosa) is a perennial bunchgrass with a widespread distribution throughout its native range in Europe and the Mediterranean. This grass has been introduced into North America and now occurs throughout much of the western United States. Within its native range, bulbous bluegrass reproduces mainly through sexual means; however, in North America clonal reproduction occurs primarily through the production of vegetative structures called bulblets. High chromosome counts are frequently reported for this species and suggest it is a polyploid. To assess the level and pattern of genetic diversity of bulbous bluegrass across a portion of its introduced range, a total of 10 populations from Idaho, Oregon, and Washington were analyzed by staining for 14 enzymes that were coded for by 19 genetic loci. Results indicate that bulbous bluegrass contains higher levels of genetic variation than expected for an introduced clonal plant species: 27.9% of loci are polymorphic per population, with an average of 1.54 alleles per locus, and a mean observed heterozygosity of 0.202. On average, 64% of all individuals within these populations possess three or four alleles at one or more loci; a value consistent with previous reports for autopolyploid species. A total of 84 multilocus genotypes were detected in these 10 populations, with an average of 9.6 genotypes per population. The number and complex distribution of multilocus genotypes observed in this study may be the result of multiple introductions of this species into its new range, and/or occasional sexual reproduction within introduced populations. Web of Science Pea bulbosa USA Idaho; Oregon; Washington Field - Observational terrestrial Grassland Invasion Hyp. Other primary 878 Metcalf, C; Pezold, F; Crump, BG 1997 Food habits of introduced rainbow trout (Oncorhynchus mykiss) in the upper Little Missouri River drainage of Arkansas journal SOUTHWESTERN NATURALIST 42 2 148 154 Food habits of introduced rainbow trout (Oncorhynchus mykiss) in the upper Little Missouri River system of Arkansas were studied by analyzing 18 stomach samples taken from Blaylock Creek between March and April, 1991, 41 stomach samples taken from the Little Missouri River proper and 38 stomach pumped samples obtained from Long Creek between March and May, 1993. Forty-two percent of stomachs from Long Creek contained food items. Stonefly (Plecoptera) larvae were the most frequently found food items, occurring in 44% of the stomachs and comprising 28% of all items recovered. Perlodid stoneflies represented 38% of all food items taken and were present in every stomach containing food. Leptophlebiid mayflies were the most abundant prey in stomachs collected from Blaylock Creek, having a relative abundance of 33%. Stomach samples indicated that introduced rainbow trout feed on a variety of invertebrates in the Little Missouri River system. The annual introduction of rainbow trout may increase feeding competition and disrupt spawning by native fish species in their natural habitat. Web of Science Oncorhynchus mykiss USA Arkansas Field - Observational lotic Riparian Fundamentals predator 882 OHanlon, RP; Bolger, T 1997 Aspects of the life history and reproductive biology of the introduced terrestrial amphipod Arcitalitrus dorrieni (Hunt) at two sites in Co Galway, Ireland journal JOURNAL OF NATURAL HISTORY 31 8 1175 1202 The reproductive biology of Arcitalitrus dorrieni (Hunt) was investigated over a period of 25 months at a deciduous and a coniferous forest site at Kylemore, Co. Galway, Ireland. The species has an annual, univoltine reproductive cycle with ovigerous females found throughout the year. Recruitment of juveniles begins in May-June with a peak of reproductive activity in August-September. The populations at each site show a bimodal size-distribution for most of the year, with a unimodal distribution in March, April and May. Mortality occurs exponentially, and the life-span is 20-22 months. Mean fecundity was 5.65 eggs per female and was dependent on female size, egg size and brood stage. Brood mortality was 37.5% at Addergoole and 29.8% at Tullywee Bridge. Web of Science Arcitalitrus dorrieni Ireland Galway 53.55; 53.5667 -9.9; -9.9 Field - Observational terrestrial Deciduous Forest;Coniferous Forest Fundamentals decomposer 883 Albert, ME; DAntonio, CM; Schierenbeck, KA 1997 Hybridization and introgression in Carpobrotus spp. (Aizoaceae) in California .1. Morphological evidence journal AMERICAN JOURNAL OF BOTANY 84 7 896 904 Individuals of the invasive non-native plant species Carpobrotus edulis, its native or naturalized congener C, chilensis, and putative hybrids are found throughout coastal California. This study characterized morphological variation within the genus and assessed the extent of hybridization and direction of introgression between C. edulis and C, chilensis. Twelve randomly selected Carpobrotus individuals from each of 49 sample locations were classified as ''C. edulis ''C. ''chilensis,'' or one of three intermediate morphotype classes, and compared for clonal, vegetative, and fruit characters. Univariate comparisons showed that C. edulis individuals had deeper mats with more cover within the mat boundary, longer, wider, more serrate leaves, and wider fruits with more carpels than intermediate and C. chilensis morphotype classes, Carpobrotus Edulis and intermediates had more lateral branches than did C. chilensis, suggesting that hybrids tend to vary toward C. edulis. Discriminant function analysis (DFA) identified the following characters as discriminating significantly among Carpobrotus groups: leaf length. leaf width. leaf length/width, number of lateral branches, number of carpels, and fruit diameter, Using these characters, DM correctly classified 98% of apparently pure C edulis and C, chilensis. but only 76% of all Carpobrotus individuals when putative hybrids were included. Principal components analysis showed that C. edulis and C. chilensis cluster into distinct morphotypes. but that hybrids overlap with both groups. particularly with C. edulis. The genus Carpobrotus in California resembles a large hybrid swarm, with putative hybrids forming a large portion of the overall population and tending to vary toward C, edulis. Web of Science Carpobrotus edulis USA California Field - Observational terrestrial Invasion Hyp. Hybridization primary 886 Parker, IM 1997 Pollinator limitation of Cytisus scoparius (Scotch broom), an invasive exotic shrub journal ECOLOGY 78 5 1457 1470 Introductions of exotic species provide unique opportunities to study the demographic significance of species interactions, but as yet there is little information on how mutualistic interactions affect the invasion process. A shortage of mutualists could potentially limit the rate of population growth for an invading species. The introduced shrub Cytisus scoparius (Scotch broom, Leguminosae) is a pest plant on the west coast of North America. It produces flowers that are ''tripped'' open when pollinated and has a nearly obligatory relationship with resident bumble bees and honey bees. Experiments in the state of Washington showed that <1% of untripped flowers produced fruits and that outcross-pollinated flowers yielded fourfold more fruit than self-pollinated flowers, revealing apparent inbreeding depression. Mean pollinator visitation rate, as determined by the proportion of flowers tripped, varied among three years and among four populations but was low (3-30%) in every case. Two urban populations (Magnuson Park and Discovery Park in Seattle) received higher numbers of visits than two native prairie populations (Johnson Prairie and 13th Division Prairie in southwestern Washington). Hand-pollination experiments revealed significant pollinator limitation in all populations in both 1993 and 1994, with the mean increase in fruit production ranging from 280 to 2620%. Prairie populations were more pollinator limited than urban populations. Resources available for per-flower fruit production appeared to be equally available in all populations in 1993 but more available in prairie populations than in urban populations in 1994. The relationship between natural visitation and proportion fruit set per branch was a saturating curve in 1993 but a linear function in 1994 and 1995. Significant correlations were found between pollinator visitation and variation in whole-plant fruit production in all 3 yr. No evidence was found for either (1) reallocation of resources between branches within a season, or (2) a cost of reproduction between seasons in plants receiving supplemental pollen. Demographic analysis showed that a very large cost of reproduction would be required to counterbalance the increase in fecundity achieved with full pollination. Simulations of new populations invading over a short time scale (10-30 yr) demonstrated little effect of pollen limitation in the slow-growing urban populations, but a potentially large effect of increasing pollinator visitation in the rapidly invading prairie populations. Web of Science Cytisus scoparius USA Washington 47.116869 -122.56073 Field - Experimental terrestrial Grassland;Urban Invasion Hyp. Mutualism Facilitation primary 887 Andrew, J; Ward, RD 1997 Allozyme variation in the marine fanworm Sabella spallanzanii: Comparison of native European and introduced Australian populations journal MARINE ECOLOGY-PROGRESS SERIES 152 3 131 143 Three Australian (Cockburn Sound, Western Australia; Adelaide, South Australia; Port Phillip Bay, Victoria) and four European (Roscoff, Atlantic; Alicante, Carteau, and Marseille, all from the Mediterranean Sea) populations of Sabella spallanzanii were examined for variation at 23 allozyme loci. Levels of genetic variation were high, with average heterozygosities per locus ranging from 0.20 to 0.21 for the Australian collections, and from 0.23 to 0,27 for the European collections. The 3 Australian collections were genetically very closely related to one another, with no statistically significant differences at any of the 15 variable loci. This suggests either an introduction to one port, with a subsequent spread to other areas, or separate introductions with subsequent extensive gene flow. The 4 European collections showed limited, but significant, differentiation among themselves at 10 of 18 variable loci. Much of the heterogeneity reflected differences between the Roscoff (Atlantic) collection and the 3 Mediterranean collections. The Roscoff collection was less variable, in terms of both heterozygosity and mean numbers of alleles, than the Mediterranean collections. The Australian collections were more closely related to the Mediterranean collections (mean Nei distance = 0.040) than to the Roscoff collection (mean Nei distance = 0.084). Ii a Mediterranean origin is assumed, then the introduction to Australia was accompanied by the loss of about 18% of the original variation. Finally, the high genetic similarity of the Australian to the European collections of S. spallanzanii, and the very clear genetic separation of S. pavonina (mean Nei distance = 0.996), reaffirms that the Australian collections are truly S. spallanzanii and not an undescribed native species. Web of Science Sabella spallanzanii France; Spain; Australia Field - Observational marine Intertidal/Near Shore Fundamentals filter 888 PlantyTabacchi, AM 1997 Invasions of riparian corridors in Southwestern France by exotic plant species. journal BULLETIN FRANCAIS DE LA PECHE ET DE LA PISCICULTURE 0 127 427 439 In Southwestern France, 245 sites were studied along eight rivers from their headwater to their mouth. On the whole, 420 exotic plant species were found in riparian corridors. The more invaded stream is the Adour River. These 420 exotic species show a large pattern of biogeographic, historical, morphological, ecological and biological attributes. Most of these exotics were not pre-adapted to riparian conditions. The structure of the corridor, the hydrological regime, the human impact, and the climate control the establishment and the development of exotic species in riparian zones. The percentage of exotics in the total species richness was studied in 32 sites along the Adour River. This percentage was not constant. It changed according to the environmental gradients identified along the river. The percentage of exotics reflects the vulnerability of riparian zones to plant invasions, and it can be used as an indicator of riparian system dysfunction. Web of Science Many France Field - Observational lotic Riparian Invasion Hyp. Disturbance;Other primary 893 Kotanen, PM 1997 Effects of experimental soil disturbance on revegetation by natives and exotics in coastal Californian meadows journal JOURNAL OF APPLIED ECOLOGY 34 3 631 644 1. Disturbance is widely believed to facilitate invasions by exotic plants, but is also important for the persistence of many native species. Here, I report the results of a series of field experiments designed to investigate the effects of soil disturbance on natives and aliens in Californian grassland vegetation. I also compare the effects of different types of soil disturbance to establish whether some favour aliens to a greater degree than others. 2. In two experiments, conducted at different locations, three types of soil disturbance (excavation, burial and simulated gopher mounds) were created, and their revegetation was compared with changes in undisturbed control plots over the next three years. A third experiment was used to provide data on the effects of soil disturbance on soil temperature, moisture and KCl-extractable nitrogen. 3. Disturbance affected both soil temperature and chemistry. Buried plots contained the most KCl-extractable nitrogen, and were also the warmest. Effects on soil moisture were relatively small. 4. Initially, most disturbances greatly reduced the numerical abundance both of groups dominated by natives (perennial graminoids and bulbs) and of groups dominated by aliens (annual graminoids). Disturbance also reduced maximal (summer) species richness, but in some cases increased the fraction of richness contributed by natives. 5. In subsequent years, richness rebounded as natives and exotics re-invaded. Native bulbs and perennial graminoids were slow to recover; instead, most disturbances sr increasingly became numerically dominated by exotic annual grasses, accentuating the effects of a multi-year drought. 6. The differing effects of experimental disturbances on aliens and natives can best be explained by considering relationships between sources of propagules, life histories and geographical origins. 7. Some types of disturbance were less damaging to native-dominated groups than others, but most ultimately favoured exotics. Consequently, it may be difficult to develop management strategies that preserve the diversity of disturbance-dependent natives while still excluding weedy aliens. Web of Science Many USA California 39.0014 -123.0019 Field - Experimental terrestrial Grassland Invasion Hyp. Propagule Pressure;Disturbance primary 894 Zampella, RA; Laidig, KJ 1997 Effect of watershed disturbance on Pinelands stream vegetation journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 124 1 52 66 We related stream channel and stream bank plant species composition to eighteen site specific and regional environmental variables in the New Jersey Pinelands (Pine Barrens). Canonical correspondence analysis (CCA) and detrended correspondence analysis (DCA) related major patterns in species composition to complex watershed disturbance gradients. There were significant correlations between the first axes of both the CCA and DCA stream site ordinations and agricultural and developed land cover in a drainage area, pH, specific conductance, and channel sediment. There was a clear contrast between stream stations found within relatively undeveloped watersheds and those in highly developed or farmed drainage areas. Surface waters of the undisturbed sites displayed lower pH and specific conductance values compared with waters in the more disturbed watersheds. The most heavily impacted sites supported a unique group of peripheral or exotic plant species that replaced characteristic Pine Barrens species. Overall species richness did not change in response to watershed disturbance. The presence of disturbance indicator species, or species found only at disturbed sites, provided a good measure of watershed disturbance. High between-site variability in the species present at relatively undisturbed stations and the persistence of some species at more recently disturbed sites complicated the identification of sensitive species, or species found only at undisturbed sites. A comparison of the number of species historically found within and outside the Pine Barrens, rather than the presence or absence of particular sensitive species, provided an additional measure of ecological integrity. Web of Science Many USA New Jersey Pine Barrens 39.74 -74.57 Field - Observational terrestrial Coniferous Forest Invasion Hyp. Disturbance primary 895 Kuhn, NL; Zedler, JB 1997 Differential effects of salinity and soil saturation on native and exotic plants of a coastal salt marsh journal ESTUARIES 20 2 391 403 In many southern California salt marshes, increased freshwater inflows have promoted the establishment of exotic plant species. A comparative study showed that a native, perennial, high marsh dominant, Salicornia subterminalis, and an invasive, exotic annual grass, Polypogon monspeliensis, responded differently to soil salinity and saturation. Salicornia subterminalis seeds and young plants were more salt tolerant, and the native grew best at high salinities (23 g l(-1) and 34 g l(-1)) in greenhouse experiments. In contrast, the exotic had reduced growth at high salinities relative to nonsaline controls. The native, S. subterminalis, grew poorly as the duration of soil saturation increased from 2 wk to 32 wk, but P. monspeliensis grew equally well for all durations tested. The response of S. subterminalis and P. monspeliensis to increased salinity indicated that salt applications might be used to protect native vegetation in salt marshes where salt-sensitive exotics are a problem. A field experiment verified that a salt application of 850 g m(-2) mo(-1) for 3 mo was sufficient to control the exotic, while not noticeably affecting the native. Thus, salt applications may be a practical method for controlling P. monspeliensis invasions in areas receiving urban runoff or other unwanted freshwater inflows. Web of Science Polypogon monspeliensis USA California Field - Experimental;Greenhouse estuarine Wetland Invasion Hyp. Disturbance primary 896 Cameron, DS; Leopold, DJ; Raynal, DJ 1997 Effect of landscape position on plant diversity and richness on electric transmission rights-of-way in New York State journal CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE 75 2 242 251 Rights-of-way are kept free of tall trees to insure reliability of electric service. Selective management techniques such as application of cut-stump herbicide and stem foliar herbicide are used on some rights-of-way to remove undesirable tree species while minimizing disturbance to shrub and herbaceous vegetation. Because rights-of-way typically traverse broad productivity and disturbance gradients over large geographic areas and harbor both native and non-native species, they offer unique opportunities to study plant species diversity patterns and their underlying causes at different scales. Plant cover on six managed rights-of-way in forested landscapes of New York State was sampled to determine the effect of landscape position (i.e., xeric, mesic, and hydric sites) on species composition, diversity, and richness and contribution of non-native species. Species composition among sites was compared using redundancy analysis in which the individual covers of the most common species were ordinated with treatment levels. Diversity, species richness, and contribution of non-native species were compared using analysis of variance. Redundancy analysis shows trends in the occurrence of common species based on landscape position. Analysis of variance indicates diversity, richness, and contribution of non-natives are greater on the rights-of-way versus the adjacent woods for xeric and mesic positions, whereas no differences were indicated between rights-of-way and adjacent woods for hydric positions. Web of Science Many USA New York Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Disturbance primary 897 Fleischmann, K 1997 Invasion of alien woody plants on the islands of Mahe and Silhouette, Seychelles journal JOURNAL OF VEGETATION SCIENCE 8 1 5 12 A method is presented for a quick and easily repeatable evaluation of the state of invasion of alien woody plants and the ecological status (prominence value, diversity, singularity and rejuvenation) of potentially important biodiversity sites in the Seychelles. The usefulness of this method has been tested in a survey on the islands of Mahe and Silhouette. The survey revealed 34 species as invasive alien species, the most prominent being Cinnamomum zeylanicum, Psidium littorale, Adenanthera pavonina and Tabebuia pallida. The greatest intensity of invasion was recorded in Intermediate Forests on moderate or gentle slopes and in stream ravines protected from desiccating winds and insolation. 'Mountain Mist Forests', 'Palm Forests' and 'Glacis' are the least invaded vegetation types. The difference in prominence values of alien and native plant species between leeward and windward sides is significant. Glacis habitats do not show a decline in protection values with decreasing altitude. Prominence values and percentage frequency of invaders are exceeded by the endemic palm Phoenicophorium borsigianum which is able to maintain itself in areas suffering from forest destruction and topsoil erosion. Web of Science Many Seychelles Field - Observational terrestrial Subtropical Forest Invasion Hyp. Disturbance primary 898 Perry, WL; Lodge, DM; Lamberti, GA 1997 Impact of crayfish predation on exotic zebra mussels and native invertebrates in a lake-outlet stream journal CANADIAN JOURNAL OF FISHERIES AND AQUATIC SCIENCES 54 1 120 125 To test the hypothesis that Orconectes spp. crayfishes could be a significant source of zebra mussel (Dreissena polymorpha) mortality in streams, we conducted a laboratory experiment and a field experiment. In the laboratory experiment, maximum zebra mussel size consumed increased with increasing crayfish size for Orconectes rusticus, Orconectes propinquus, and Orconectes virilis. Slopes differed among crayfish species but not between O. rusticus sexes. To quantify crayfish impacts on seminatural zebra mussel populations, we placed 16 enclosures (0.2 m(2)) lined with artificial cobble substrata in a midwestern lake-outlet stream (mean width 17 m). Zebra mussels were stocked in each cage (20 000 individuals/m(2)) 14 days before male O. rusticus (20 individuals/m(2)) were stocked in each of eight enclosures. Densities of all sizes of zebra mussels were reduced in enclosures, with a total density reduction of 31% over the 28 days of the experiment, relative to the exclosures. Crayfish also reduced gastropod densities by 54%, but did not significantly affect other invertebrates. Laboratory and field results suggest that predation by Orconectes crayfishes may significantly reduce zebra mussel populations in streams. Web of Science Dreissena polymorpha USA Michigan 41.804462 -86.024666 Field - Experimental;Lab lotic Riparian Fundamentals predator 902 Daehler, CC; Strong, DR 1997 Hybridization between introduced smooth cordgrass (Spartina alterniflora; Poaceae) and native California cordgrass (S-foliosa) in San Francisco Bay, California, USA journal AMERICAN JOURNAL OF BOTANY 84 5 607 611 Introduced Spartina alterniflora (smooth cordgrass) is rapidly invading intertidal mudflats in San Francisco Bay, California. At several sites, S. alterniflora co-occurs with native S. foliosa (California cordgrass), a species endemic to California salt marshes. In this study, random amplified polymorphic DNA markers (RAPDs) specific to each Spartina species were identified and used to test for hybridization between the native and introduced Spartina species in the greenhouse and in the field. Greenhouse crosses were made using S. alterniflora as the pollen donor and S. foliosa as the maternal plant, and these crosses produced viable seeds. The hybrid status of the crossed offspring was confirmed with the RAPD markers. Hybrids had low self-fertility but high fertility when back-crossed with S. foliosa pollen. Hybrids were also found established at two field sites in San Francisco Bay; these hybrids appeared vigorous and morphologically intermediate between the parental species. Field observations suggested that hybrids were recruiting more rapidly than the native S. foliosa. Previous work identified competition from introduced S. alterniflora as a threat to native S. foliosa. In this study, we identify introgression and the spread of hybrids as an additional, perhaps even more serious threat to conservation of S. foliosa in San Francisco Bay. Web of Science Spartina alterniflora USA California San Francisco 37.66806 -122.290878 Field - Observational;Greenhouse estuarine Wetland Invasion Hyp. Hybridization primary 903 Greenberg, CH; Crownover, SH; Gordon, DR 1997 Roadside soils: A corridor for invasion of xeric scrub by nonindigenous plants journal NATURAL AREAS JOURNAL 17 2 99 109 Invasion of ecosystems by nonindigenous species threatens native biodiversity by altering species composition and site characteristics, and by potentially impacting endangered species. We compared plant communities and soil characteristics along clay, limerock, and unmodified sand roadsides, and in adjacent clearcuts in xeric Florida sand pine scrub to test our hypothesis that modified soils used in constructing roadways provide a roadside corridor for invasion by nonindigenous species and species that are uncharacteristic of xeric scrub. Clay and limerock roadsides had more clay and less sand than sand roadsides or clearcuts. Soil pH and levels of several nutrients differed significantly in limerock roadsides relative to the other substrates. In general, sand roadsides and clearcuts had higher characteristic but lower uncharacteristic and nonindigenous plant cover and number of species than modified roadside substrates. This suggests that xeric scrub may be somewhat resistant to invasion where native soils are present, even if disturbed. However, presence of nonindigenous species suggests that roadways facilitate the transport of source propagules to otherwise remote sites. Especially where roadside and native soil characteristics differ markedly, conditions may be enhanced for invasion by nonindigenous and uncharacteristic plants. Web of Science Many USA Florida Ocala National Forest Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Disturbance primary 905 Lemee, R; Pesando, D; Issanchou, C; Amade, P 1997 Microalgae: A model to investigate the ecotoxicity of the green alga Caulerpa taxifolia from the Mediterranean Sea journal MARINE ENVIRONMENTAL RESEARCH 44 1 13 25 The spectacular development of the green alga Caulerpa taxifolia (Vahl) C. Agardh, introduced in the Mediterranean in 1984, represents a biological pollution which threatens the biodiversity of the marine ecosystem. The weak pressure from grazers and the presence of repulsive secondary metabolites make the problem worse. Whereas the anti-appetant effect of these metabolites is well known, their role in competition between algae has not been extensively studied. Using a microalgal model representing the initial stage of the marine food chain, we studied the effects of C. taxifolia metabolites. We showed that organic extracts of C. taxifolia and caulerpenyne inhibit or delay the proliferation of several phytoplanktonic strains to various degrees. Seasonal variations of the toxicity were observed with a maximal effect in the summer. Experiments with Dunaliella minuta showed that caulerpenyne did not affect the protein content but strongly reduced that of the cell chlorophyll A. (C) 1997 Elsevier Science Ltd. Web of Science Caulerpa taxifolia France Lab marine Invasion Hyp. Inherent Superiority Superior Competitor primary 908 Ohgushi, T; Sawada, H 1997 A shift toward early reproduction in an introduced herbivorous ladybird journal ECOLOGICAL ENTOMOLOGY 22 1 90 96 1. In May 1971, fifteen male and thirty female overwintering adults of a thistle-feeding ladybird Epilachna niponica were taken from the Asiu Experimental Forest of Kyoto University and introduced into the Botanical Garden of Kyoto University, 30 km south of Asiu and 10 km south of the southern limits of its distribution. The introduced population established successfully and thereafter maintained densities sufficiently high to defoliate their host plants. 2. Reproductive parameters (reproductive lifespan of females, overall fecundity, and oviposition schedules) of the introduced population were compared with those of the source population 10 years after the introduction. Comparisons were made in the laboratory under five temperature regimes. 3. The lifespan of females differed significantly with temperature, decreasing linearly with increasing temperature. Temperature also had a significant effect on overall fecundity for both populations; overall fecundity at 15 and 30 degrees C was significantly lower than that at the 20-25 degrees C regimes. 4. The oviposition activity of the introduced population was significantly higher than that of the source population at 23 and 25 degrees C. The lifespan of females of the introduced population was also significantly shorter than those of the source population at 20 and 25 degrees C. 5. The reduced lifespan and higher oviposition activity of introduced females indicate that they directed greater reproductive efforts early in their reproductive lifetime than those of the source population. Web of Science Epilachna niponica Japan Kyoto 35.049111 135.764923 Field - Experimental;Lab terrestrial Deciduous Forest Fundamentals herbivore 911 Tilman, D 1997 Community invasibility, recruitment limitation, and grassland biodiversity journal ECOLOGY 78 1 81 92 Plant species composition, species abundances, and species richness were strongly recruitment limited in a 4-yr experiment in which seeds of up to 54 species were added to patches of native grassland. Four field seasons after a one-time addition of seed, many added species were still present and reproducing, with plots seeded at the highest rate having species richness that was 83% greater and total plant cover that was 31% greater than controls. Total plant community cover increased significantly with the number of species added as seed, but total cover of pre-existing species was independent of the number of species added as seed, suggesting that the new species mainly filled previously ''empty'' sites. The proportion of added species that became established was negatively correlated with initial species richness of plots, suggesting that species-rich sites were more resistant to invasion. Plot invasibility also depended on the abundances and species richness of plant functional groups in the plots, but was independent of seed size and of total plant cover. The major functional groups of plants differed in their abilities to invade as seed, with perennial grasses being the poorest invaders and herbaceous legumes being the best. Thus, local biotic interactions and recruitment dynamics jointly determined diversity, species composition, and species abundances in these native grassland communities. This supports a metapopulation-like perspective over a purely interspecific-interaction perspective or a purely regional perspective, suggesting that recruitment limitation may be more important, even on a local scale, than often recognized. Web of Science Many USA Minnesota Cedar Creek Natural History Area 45.419419 -93.195992 Field - Experimental terrestrial Grassland Invasion Hyp. Community Species Richness primary 912 DeMoor, IJ 1996 Case studies of the invasion by four alien fish species (Cyprinus carpio, Micropterus salmoides, Oreochromis macrochir and O-mossambicus) of freshwater ecosystems in southern Africa journal TRANSACTIONS OF THE ROYAL SOCIETY OF SOUTH AFRICA 51 0 233 255 The history of the invasion of 42 catchment regions in southern Africa (excluding Mozambique) by an altricial species (Cyprinus carpio), a moderately precocial species (Micropterus salmoides) and two highly precocial species (Oreochromis macrochir and O. mossambicus) is examined. The abundance of these species in different catchments is discussed in relation to the diversity of indigenous species. Results suggest that: a. Depauperate catchments of the southern Cape are vulnerable to invasion irrespective of the Life-history style of the alien species, compared to catchments (in Zimbabwe and north eastern Transvaal) with a higher diversity of indigenous species. b. Precocial species are more successful than altricial species in establishing populations in natural waters in more diverse ecosystems. c. Degradation and modification of the environment (particularly the building of impoundments) has played an important role in increasing the susceptibility of freshwater ecosystems to invasion. Web of Science Cyprinus carpio; Micropterus salmoides; Oreochromis macrochir; O. mossambicus southern Africa Field - Observational lotic Invasion Hyp. Inherent Superiority;Community Species Richness;Disturbance Rapid Growth predator 914 Bezic, C; DallArmellina, A; Gajardo, O 1996 Studies on vegetative production of Potamogeton illinoensis Morong in southern Argentina journal HYDROBIOLOGIA 340 3 7 10 Potamogeton illinoensis Morong is a major submerged weed invading irrigation channels in the Lower Valley of the Rio Negro, near Viedma, Argentina. Studies on morphology and growth characteristics of this species were conducted in an outdoor tank from August 1993 to May 1994 with the objective of increasing the knowledge of its ecology order to adjust control measures. The maximum aboveground biomass was reached in April, with a subsequent decrease to May when the water supply was cut off. Belowground biomass comprised two kinds of rhizomes. The first group (Rhizomes I) was produced from the beginning of the annual cycle causing both lateral shoots and new rhizomes I production. The second group (Rhizomes II) was distinguished as an enlargement of the extremes of rhizomes I from mid-November, producing only short overwintering sprouts. Plant parts production (DW in g/plant) in the first cycle was: 27.2 g leaves; 11.9 g stems; 17.4 g rhizomes I and 8.1 g rhizomes II. Vegetative propagation appeared to be an important survival strategy in this species. During the 3-4 month period without water only rhizomes with underground overwintering sprouts survive in the dry sediment. Web of Science Potamogeton illinoensis Argentina Viedma Field - Observational lotic Riparian Fundamentals primary 918 Nystrom, P; Strand, JA 1996 Grazing by a native and an exotic crayfish on aquatic macrophytes journal FRESHWATER BIOLOGY 36 3 673 682 1. We compared grazing by native noble crayfish (Astacus astacus) and the exotic signal crayfish (Pacifastacus leniusculus) on seedling or well-established macrophytes. 2. In a pool experiment, seedlings of emergent Scirpus lacustris and floating-leaved Potamogeton natans were heavily grazed by adult signal crayfish, whereas established plants of the same species sustained only minor damage. 3. In a preference experiment two submerged macrophytes (Chara vulgaris and Elodea canadensis), and both seedlings and established plants of S. lacustris and P. natans, were presented pairwise to signal and noble crayfish. There was no significant difference in preference by the two crayfish species. Chara vulgaris was preferred to all other plants presented, established plants of S. lacustris and P. natans were never preferred, and seedlings of P. natans were preferred to established P. natans. 4. An aquarium experiment was conducted in which the consumption of Chara by signal and noble crayfish was measured in relation to water temperature. Signal crayfish consumed significantly more Chara than noble crayfish, especially at higher temperatures. 5. Our results indicate that the signal crayfish is the more voracious grazer especially at higher temperatures. There may be negative effects on vegetation (emergents and floating-leaved, as well as submerged species) when the signal crayfish is introduced. Chara species are particularly susceptible, since they are preferred by crayfish and the genus includes a large number of rare species. Stocking of crayfish therefore could lead to the decline or removal of submerged species in order of crayfish feeding preferences and could prevent the spread or cause a decline of emergent and floating-leaved vegetation. Web of Science Pacifastacus leniusculus Sweden Greenhouse lentic Fundamentals herbivore 922 Dietz, H; Steinlein, T; Winterhalter, P; Ullmann, I 1996 Role of allelopathy as a possible factor associated with the rising dominance of Bunias orientalis L (Brassicaceae) in some native plant assemblages journal JOURNAL OF CHEMICAL ECOLOGY 22 10 1797 1811 Leaf extracts of Bunias orientalis were shown to inhibit seed germination of a variety of cultivar plant species and of species cooccurring with B. orientalis in the field. Root exudate solutions and leaf litter leachates of B. orientalis were tested for their allelopathic activity using seedling growth assays. Additionally, in comparative seedling growth assays soil cores removed from dense B. orientalis stands were tested bimonthly for elevated allelopathic effects. The impact of root exudates on seedling growth was generally weak and varied between species. Similar results were obtained for the effect of B. orientalis leaf litter leachates on seedlings grown in sand culture relative to the effect of leaf litter leachates of a plant species mixture. When soil as a growth substrate was used, no consistent differences in seedling growth were obtained between the two litter leachate treatments. In the soil core experiment seedlings grown in soil cores collected from a dense B. orientalis stand unexpectedly showed better performance than seedlings grown in soil cores collected from a nearby mixed plant stand without B. orientalis, at least in early spring and late autumn. Predominating nutrient effects are, therefore, assumed to conceal a potentially increased allelopathic effect of soil beneath dense B. orientalis stands. It is concluded that other factors than allelopathy must be investigated to explain the rapid establishment of dense stands of this alien plant species. Web of Science Bunias orientalis Lab terrestrial Deciduous Forest Invasion Hyp. Novel Weapons primary 923 Groth, AT; LovettDoust, L; LovettDoust, J 1996 Population density and module demography in Trapa natans (Trapaceae), an annual, clonal aquatic macrophyte journal AMERICAN JOURNAL OF BOTANY 83 11 1406 1415 The effects of population density on module demography were studied in Trapa natans L., an annual aquatic macrophyte capable of extensive clonal propagation. At low density, the floating plants produced ten times as many ramets (clonal offshoots) as those at high density. Module mortality occurred at three levels: leaf, ramet (shoot), and genet (genetic individual). There was approximate to 100-fold variation in the size of nuts containing germinable seeds. In early summer there was a highly significant linear relationship between dry mass of nuts and the total mass of ramets that each had produced. In early summer most (73-83%) of the variation in total plant biomass was attributable to variation in initial nut size. However the significance of initial nut size was diminished later in the season. The great success of the exotic weed T. natans at colonizing and monopolizing an aquatic habitat is a function of its highly productive clonal growth response to low-density conditions, combined with greater proportional allocation of biomass to reproductive structures, resulting in greatly increased nut production at low initial density. The species appears able to develop and maintain a population at extremely high density: plant buoyancy and the production of large, well-protected nuts allow rapid early growth from the sediment each year and early pre-emption of the water surface. Web of Science Trapa natans USA Massachusetts Lower Lake 42.254442 -72.572465 Field - Observational lentic Invasion Hyp. Inherent Superiority Rapid Growth;High Reprod. Output;Clonal Reproduction primary 924 Blankespoor, GW; May, JK 1996 Alien smooth brome (Bromus inermis Leyss) in a tallgrass prairie remnant: Seed bank, seedling establishment, and growth dynamics journal NATURAL AREAS JOURNAL 16 4 289 294 The natural diversity of tallgrass prairie remnants in the northern Great Plains of North America is being threatened by alien smooth brome (Bromus inermis Leyss.). We report the results of two studies designed to increase our knowledge of the Invasion dynamics of this species. Smooth brome seedling establishment in unbroken native tallgrass vegetation did not occur even when conditions for establishment were optimal. The soil at a lowland smooth brome site had finer texture, greater percent water, lower pH, and lower potassium than did the soil at an upland site. Tiller, stem base, and root biomass were greater in smooth brome individuals transplanted into the lowland site than in individuals transplanted into the upland site. Although the total length of rhizomes of individuals was not different between the two sites, rhizome length per tiller was greater at the upland site. This result indicates that the rate of horizontal spread of smooth brome may be greater at upland sites than at lowland sites. Web of Science Bromus inermis USA Field - Experimental terrestrial Grassland Fundamentals primary 932 Shabana, YM; Charudattan, R 1996 Microorganisms associated with Hydrilla in ponds and lakes in north Florida journal JOURNAL OF AQUATIC PLANT MANAGEMENT 34 0 60 68 The diversity and frequency of microorganisms associated with hydrilla [Hydrilla verticillata (L.F.) Royle] were determined by dilution-plating of water, sediment (soil), and hydrilla plant samples from four man-made ponds and two lakes in north Florida. Aqueous dilutions were plated on six selective and nonselective culture media: Sneh & Stack selective medium (SS), Komada's (K), PART selective medium (PART), chitin agar (CA, selective for actinomycetes), nutrient agar and hydrilla extract plus half-strength potato dextrose agar (HPDA). Four hundred and fifty eight different organisms (211 bacteria, 202 fungi, 44 actinomycetes, and 1 cyanobacterium) were recovered from 48 samples taken from the four ponds using the six media. Two hundred and ten (101 bacteria and 109 fungal isolates) were recovered from 15 samples taken from Rowell Lake. Seventy seven (31 bacteria, 45 fungi, and 1 cyanobacterium) were recovered from 10 samples from Orange Lake. The most effective medium for isolating the greatest variety of fungi was K. Nutrient agar and HPDA were best for isolating the largest diversity of bacteria, and CA and HPDA were best for actinomycetes. Fungi belonging to several plant pathogenic genera including Botryosporium, Cercosporidium, Chaetophoma, Diplodia, and Pyrenochaeta were found mainly in hydrilla and soil samples. Very few actinomycetes were recovered, mostly from pond soils, with a few from pond hydrilla. The frequency and diversity of the microorganisms isolated confirmed the occurrence of a rich microbial flora associated with hydrilla and the efficacy of the media and the isolation technique used. Web of Science Hydrilla verticillata USA Florida University of Gainesville 29.654344 -82.33326 Field - Observational lentic Fundamentals 933 Tabacchi, E; PlantyTabacchi, AM; Salinas, MJ; Decamps, H 1996 Landscape structure and diversity in riparian plant communities: A longitudinal comparative study journal REGULATED RIVERS-RESEARCH & MANAGEMENT 12 5 367 390 Patterns of plant species richness and community composition were studied in diverse riparian zones. Eight rivers in south-western France, one river in north-western USA and four rivers in south-eastern Spain were compared. A brief review is presented of factors that have been singled out as controlling diversity along rivers. The proportions of plant group classified according to life-span, morphology, ruderality and location along the rivers were analysed. Both proportions of plant traits and total species richness differed considerably between rivers. Semi-arid rivers were more influenced by local patterns than the other rivers. The patterns exhibited by true riparian species and invading, essentially non-riparian species, showed the importance of the relationships between the river and its close surroundings. The mean proportion of ruderals remained roughly the same in all rivers, suggesting some regulatory mechanisms independent of the general environmental settings. The longitudinal patterns of species richness in riparian plant communities of the oceanic rivers could be related to the intermediate disturbance hypothesis, whereas semi-arid rivers showed very irregular patterns of species richness along their courses, as a consequence of the irregular water availability. Exotic and ruderal species were more sensitive than other groups to the longitudinal zonation of the rivers and to environmental factors influenced by humans. Also, the permanency of superficial water appeared as a major factor in the control of riparian community structure in semi-arid regions. Web of Science Many France; Unites States; Spain Field - Observational lotic Riparian Fundamentals primary 934 Steinlein, T; Dietz, H; Ullmann, I 1996 Growth patterns of the alien perennial Bunias orientalis L (Brassicaceae) underlying its rising dominance in some native plant assemblages journal VEGETATIO 125 1 73 82 The polycarpic perennial Bunias orientalis L. (Brassicaceae) introduced to Central Europe in the 18th century recently entered a phase of rapid spread accompanied by sudden establishments of extensive dominance stands mainly on roadside locations. We studied vegetation structure and expansion rate of B. orientalis stands and performed a series of experiments to investigate key factors that underlie the colonizing and establishment of B. orientalis. Reiterated observations exposed a high current expansion rate of B. orientalis populations and vegetation surveys of B. orientalis stands showed that these stands were mainly composed of Artemisietea and Arrhenateretea species. Regeneration experiments with root fragments revealed high regeneration capacities: root fragments of 3 cm length showed 93% regeneration, varying water content (10-50% water loss) and separation into root cortex and root stele yielded regeneration of 30 to 50%. In a field study high regrowth after mowing with varying mowing intensity indicates B. orientalis to be well adapted to disturbed sites as its preferential locations for development of dominance stands. Vegetative growth parameters were studied in two controlled growth experiments with elevated nutrient availabilities. B. orientalis exhibited a high sensitivity to nutrient addition and rosette sizes of maximal 90 cm were reached. Biomass was comparable or even higher than that of native ruderals grown in the same experiment. Measurements of reproductive parameters revealed a high reproductive effort (0.2 to 0.45 g g(-1)) even under intense mowing regimes, resulting in a dense seed bank with maximal values of about 400 fruits (congruent to 550 seeds) l(-1) soil. With respect to colonization and establishment of B. orientalis the results of our study enable the formulation of three hypotheses. Web of Science Bunias orientalis Germany Unterfranken 49.787388 9.935331 Field - Experimental;Field - Observational terrestrial Urban Invasion Hyp. Inherent Superiority Broad Tolerances;Rapid Growth;High Reprod. Output;Effective Disperser;Clonal Reproduction primary 936 Rejmanek, M; Richardson, DM 1996 What attributes make some plant species more invasive? journal ECOLOGY 77 6 1655 1661 Web of Science Pinus spp. Statistical/Meta-analysis;Review terrestrial Coniferous Forest Invasion Hyp. Inherent Superiority Rapid Growth;High Reprod. Output primary 941 Anderson, RC; Dhillion, SS; Kelley, TM 1996 Aspects of the ecology of an invasive plant, garlic mustard (Alliaria petiolata), in central Illinois journal RESTORATION ECOLOGY 4 2 181 191 Alliaria petiolata (garlic mustard), an exotic plant species, has invaded woodlands in several areas in mid-western and northeastern United States and adjacent Canada, and it is displacing the indigenous under-story flora. This study was conducted to provide information about the species' biology that might be useful in controlling its spread in native woodlands. The plant is a strict biennial in North America, spending the first year of growth as a basal rosette. This period of relatively slow growth is followed by a period of rapid shoot elongation (1.9 cm/day) during early spring of the second growing season. The plant is capable of cross- and self-pollination, although pollination and stigma receptivity occur before the flower is open, so autogamy is the most likely breeding system. Garlic mustard invests 20.4% of its biomass in reproductive effort, with an annual seed rain of 15,000 seeds/m(2). Seed dispersal from fruits begins in early July and continues into October. Most seeds germinate in the spring following the year in which they were produced. Seedling recruitment is high (8.3-18.0 seedlings/dm(2)), but only about 7.5% of the plants survive to maturity. The success of the plant in invading woodlands appears to be related to (1) its autogamous breeding system that allows a single individual, or a few individuals, to establish populations of genetically similar but interfertile individuals; (2) high seed production, permitting establishment of large numbers of individuals; and (3) rapid growth during the second growing season, which increases its competitive ability. Because of garlic mustard's ability to occupy understory habitats successfully, it may be unrealistic to expect to eliminate the plant from many habitats it has already invaded. Web of Science Alliaria petiolata USA Illinois Bloomington 40.497941 -88.968658 Field - Observational terrestrial Grassland Invasion Hyp. Inherent Superiority Rapid Growth;High Reprod. Output;Self Compatible primary 946 PlantyTabacchi, AM; Tabacchi, E; Naiman, RJ; Deferrari, C; Decamps, H 1996 Invasibility of species rich communities in riparian zones journal CONSERVATION BIOLOGY 10 2 598 607 Invasibility of riparian plant communities was estimated by the percentage of alien species found along the Adour River (Southwest France) and along Lookout Creek, McKenzie River, and Willamette River (Central Cascades, Oregon, U.S.A.). At the patch scale, the invasibilities of riparian plant communities were compared between one exceptionally rich site of the Adour River and patches selected in the Hob and Dungeness watersheds (Olympic Peninsula, Washington, U.S.A.). Alien species represented 24% of 1396 species for the Adour and 30% of 851 species for the McKenzie. They represented 24% of 148 species for the Hob drainage and 28% of 200 species for the Dungeness drainage. Similar trends were found along the Adour River and along the McKenzie River for changes in total number of species per site and in percentages of alien species per site. These trends may be related to the intermediate disturbance regimes and tot he physical structure of the riparian corridors. Climatic and human factors are also involved in these longitudinal changes. Positive linear relationships were found between the total number of species and the percentage of aliens observed in each site. At the patch scale, most of the sampled communities contained alien species. Although mature vegetative patches appeared to be invasible, young communities contained more alien species than older ones. For entire corridors, a positive linear relationship was found between total species richness and percentage of alien species in each patch type for the richest site of the Adour River. This may be partially explained by landscape features considered in a successional context. We suggest the use of empirical rules, and stress the importance of riparian systems for monitoring the conservation of local and regional species pools are suggested. Web of Science Many United States; France Oregon Field - Observational terrestrial;lotic Grassland;Deciduous Forest;Coniferous Forest;Riparian;Chaparral/Shrublands;Old Field Invasion Hyp. Community Species Richness primary 953 Thebaud, C; Finzi, AC; Affre, L; Debussche, M; Escarre, J 1996 Assessing why two introduced Conyza differ in their ability to invade Mediterranean old fields journal ECOLOGY 77 3 791 804 Researchers have suggested that species-community interactions determine invasion success. Therefore, it is likely that small biological differences between species interact with habitat characteristics to produce distinct patterns of distribution and abundance throughout a new range. In this study we test the hypothesis that differences in the distribution and abundance of species sharing an identical set of ''ideal weed characteristics'' are explicable in terms of species-specific responses to environmental variation within their new range. Using multifactor experiments, we investigated some of the ecological interactions influencing reproductive success in two very closely related species of annuals having invaded the French Mediterranean region for >150 yr and showing marked differences in their local distribution and abundance patterns. We transplanted seedlings of Conyza canadensis (a species restricted to recently disturbed areas) and C. sumatrensis (a species colonizing early- to mid-successional old fields) at equal densities in three contrasting old fields (6 mo, 4 yr, 17-yr abandonment, respectively) during 1991-1992, a growing season with average rainfall. Individual performances (measured as survivorship, reproductive timing, and reproductive output) were evaluated with respect to: (1) competition with plant neighbors (tested with a weeding treatment), (2) resource availability (tested with nutrient and water addition), and (3) herbivory (tested with chemical limitation). Manipulated factors interacted in a rather complex fashion to influence survivorship and reproduction in both species. However, patterns of relative performance were consistent with relative distribution patterns across Mediterranean landscapes: C. sumatrensis performed better than C. canadensis in all fields, including the youngest one (6 mo old). Herbivory only slightly affected transplant performances. In contrast, competition with plant neighbors had substantial effects on either Conyza species and may be the most important determinant of performance in Mediterranean old fields. The experiment showed unambiguously that the two species differ markedly in their competitive ability, with C. sumatrensis performing better than C. canadensis in the presence of neighboring vegetation. In addition, C. sumatrensis displayed a superior ability to take up and/or to use water and nutrient resources when they become available in competitive environments. We argue that potential physiological or anatomical species differences responsible for this differential susceptibility to local resource reduction by neighbors could involve differences in constructional organization, leaf morphology, and reproductive phenologies. Web of Science Conyza canadensis; Conyza sumatrensis France Montpelier 43.65 3.85 Field - Experimental terrestrial Old Field Invasion Hyp. Inherent Superiority primary 955 Strefeler, MS; Darmo, E; Becker, RL; Katovich, EJ 1996 Isozyme characterization of genetic diversity in Minnesota populations of purple loosestrife, Lythrum salicaria (Lythraceae) journal AMERICAN JOURNAL OF BOTANY 83 3 265 273 Starch gel electrophoresis of plant proteins was used to identify purple loosestrife (Lythrum spp.) cultivars and weedy populations. Preliminary determinations were made as to what degree weedy loosestrife populations were related (or genetically similar) to populations of L. alatum, L. virgatum, and horticultural cultivars. Cluster analysis of the data indicated that native L. alatum was genetically different from all populations of purple loosestrife and cultivars examined. The L. salicaria and L. virgatum cultivars, as groups, were not genetically distinguishable from the weedy populations analyzed. Seven cultivars of L. salicaria origin analyzed as a group were not distinguishable from the eight cultivars of L. virgatum origin, indicating that separation by cultivar origin may not be feasible. While the two ''goups'' were not distinguishable, most individual cultivars could be distinguished from one another by isozyme phenotype. Genetic variation was high within populations of weedy purple loosestrife but low among populations, which is characteristic of polyploid, perennial plant species that are widely distributed. Geographic location did not consistently correlate with genetic similarity. Web of Science Lythrum salicaria USA Minnesota 44.989084 -93.316498 Field - Observational estuarine Wetland Invasion Hyp. Hybridization primary 958 Maron, JL; Connors, PG 1996 A native nitrogen-fixing shrub facilitates weed invasion journal OECOLOGIA 105 3 302 312 Invasions by exotic weedy plants frequently occur in highly disturbed or otherwise anthropogenically altered habitats. Here we present evidence that, within California coastal prairie, invasion also can be facilitated by a native nitrogen-fixing shrub, bush lupine (Lupinus arboreus). Bush lupines fix nitrogen and grow rapidly, fertilizing the sandy soil with nitrogen-rich litter. The dense lupine canopy blocks light, restricting vegetative growth under bushes. Heavy insect herbivory kills lupines, opening exposed nitrogen-rich sites within the plant community. Eventual re-establishment of lupine occurs because of an abundant and long-lived seed bank. Lupine germination, rapid growth, shading and fertilization of sites, and then death after only a few years, results in a mosaic of nutrient-rich sites that are available to invading species. To determine the role of bush lupine death and nitrogen enrichment in community composition, we examined nutrient dynamics and plant community characteristics within a site only recently colonized by lupine, comparing patches where lupines had recently died or were experimentally killed with adjacent areas lacking lupine. In experimentally killed patches, instantaneous pool sizes of exchangeable ammonium and nitrate nitrogen were higher than in adjacent sites free of lupine. Seedlings of the introduced grass Bromus diandrus accumulated 48% greater root biomass and 93% more shoot biomass when grown in a greenhouse in soil collected under experimentally killed lupines compared to B. diandrus seedlings grown in soil collected at least 1 m away from lupines. At the end of the spring growing season, total above-ground live plant biomass was more than twice as great in dead lupine patches as in the adjacent lupine-free grassland, but dead lupine patches contained 47% fewer plant species and 57% fewer native species. Sites where lupines have repeatedly died and reestablished during recent decades support an interstitial grassland community high in productivity but low in diversity, composed of mostly weedy introduced annual plants. In contrast, at a site only recently colonized by bush lupines, the interstitial grassland consists of a less productive but more diverse set of native and introduced species. We suggest that repeated bouts of lupine germination, establishment, and death can convert a rich native plant community into a less diverse collection of introduced weeds. Web of Science Bromus diandrus 38.306979 -123.0655 Field - Experimental terrestrial Grassland Invasion Hyp. Mutualism Facilitation primary 961 Crooks, JA 1996 The population ecology of an exotic mussel, Musculista senhousia, in a Southern California Bay journal ESTUARIES 19 1 42 50 Musculista senhousia is a small, infaunal mussel native to Asia. Over the last 75 yrs, humans have unintentionally introduced it to various parts of the world, including the Mediterranean, Australasia, and North America. Recently, M. senhousia has become abundant in Mission Bay, San Diego, California. Here, the mussel exhibits many traits typical of opportunistic species. It is small, only attaining a maximum length of about 32 mm, and is capable of rapid growth, reaching up to 25 mm after 1 yr. In San Diego, there was a major peak of recruitment during the late fall of 1990, and low levels of background recruitment throughout much of the year. Although the maximum life span of M. senhousia is approximately 2 yr, mortality is high and most of the population are only annuals. Overall, M. senhousia appears to display similar life-history characteristics both in this invaded system and within its native range. Web of Science Musculista senhousia USA California Mission Bay 32.772842 -117.21983 Field - Observational marine Intertidal/Near Shore Invasion Hyp. Inherent Superiority Rapid Growth filter 973 PYSEK, P; PYSEK, A 1995 INVASION BY HERACLEUM-MANTEGAZZIANUM IN DIFFERENT HABITATS IN THE CZECH-REPUBLIC journal JOURNAL OF VEGETATION SCIENCE 6 5 711 718 Heracleum mantegazzianum, a tall forb from the western Caucasus invaded several different habitats in the Czech Republic. The relation between invasion success and type of recipient habitat was studied in the Slavkovsky les hilly ridge, Czech Republic. The vegetation of 14 habitat types a occurring in an area of ca. 25 km(2) was analysed using phytosociological releves, and the invasion success of Heracleum (in terms of number of localities, area covered and proportion of available area occupied) was recorded separately in each of them. Site conditions were expressed indirectly using Ellenberg indicator values. The hypothesis tested was that Heracleum spreads in the majority of vegetation types regardless of the properties of the recipient vegetation. Community invasibility appeared to be affected by site conditions and the composition of the recipient vegetation. The species is not found in acidic habitats. Disturbed habitats with good possibilities of dispersal for Heracleum seeds are more easily invaded. Communities with a higher proportion of phanerophytes and of species with CS (Competitive/Stress-tolerating) strategy were more resistant to invasion. The invasion success was bigger in sites with increased possibilities of spread for Heracleum diaspores. Communities invaded by Heracleum had a lower species diversity and a higher indicator value for nitrogen than not-invaded stands. It appears that species contributing to community resistance against invasion of Heracleum, or capable of persisting in Heracleum-invaded stands, have similar ecological requirements but a different life strategy to the invader. Web of Science Heracleum mantegazzianum Czech Republic Horni Slavkov 50.15 12.8 Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Superior Competitor;Rapid Growth;Effective Disperser primary 974 KITAYAMA, K; MUELLERDOMBOIS, D 1995 BIOLOGICAL INVASION ON AN OCEANIC ISLAND MOUNTAIN - DO ALIEN PLANT-SPECIES HAVE WIDER ECOLOGICAL RANGES THAN NATIVE SPECIES journal JOURNAL OF VEGETATION SCIENCE 6 5 667 674 Spatial distribution patterns of alien plant species were compared with those of native species on a windward slope of Mt. Haleakala (3055 m). Oceanic islands are considered susceptible to biological invasion, and this study numerically tested this circumstantial evidence with the following questions: Are all habitats equally susceptible; and, do successful invaders have wider realized niches than natives? The mountain slope consists of three distinct altitudinal bioclimatic zones (hot moist lowland, wet montane cloud, and cool arid high-altitude zones). Ordination indicated that alien species' ranges and population expansions were clustered in the lowland and high-altitude zones. The lowland zone had been subjected to natural canopy dieback, and the high-altitude zone to grazing by domestic and feral ungulates. By contrast, the montane cloud forest was relatively intact in terms of number and cover of native species. Thus, susceptibility to alien invasion clearly differed among zones, and the primary causes seemed to be the obvious disturbance factors. The mean ecological range along the altitude-rainfall gradient was significantly (P < 0.05) greater for native than for alien species in most life-form groups. The reasons for the greater number of climate generalists among the natives vs. the range-restricted aliens appear to be related to: (1) the pre-alien condition with a depauperate flora which allowed for 'ecological release' of successful native colonizers, and (2) the climatic pre-adaptation of alien invaders which restricts them from penetrating over a broader spectrum of climatic zones in a floristic matrix subjected to increasing interspecific competition. Web of Science Many USA Hawaii Mt. Haleakala 20.707308 -156.226273 Field - Observational terrestrial Mountain Invasion Hyp. Inherent Superiority Broad Tolerances primary 976 DICK, JTA; ELWOOD, RW; MONTGOMERY, WI 1995 THE BEHAVIORAL BASIS OF A SPECIES REPLACEMENT - DIFFERENTIAL AGGRESSION AND PREDATION BETWEEN THE INTRODUCED GAMMARUS-PULEX AND THE NATIVE G-DUEBENI CELTICUS (AMPHIPODA) journal BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY 37 6 393 398 Previous studies have shown that differential predation by males on moulted female congenerics may be largely responsible for the elimination and replacement of the native Irish freshwater amphipod Gammarus duebeni celticus by the introduced G. pulex. Predation of moulted females occurs both shortly after their release from precopulatory mate-guarding and whilst they are being guarded by their mates. In the present study, two hypotheses concerning the underlying cause(s) of the differential predation pattern are tested. Firstly, female G. d. celticus may be more vulnerable to predation than female G. pulex due to the former being released from precopula guarding with the new exoskeleton in a less hardened state. Secondly, G. pulex may be an inherently more aggressive species than G. d. celticus during predatory interactions over guarded females. The first experiment indicated that differential predation was not mediated by species differences in the state of the female exoskeleton at the time of release from precopula by guarding males. The second experiment, however, showed that male G. pulex were significantly more aggressive than male G. d. celticus in attacking both guarding male congenerics and guarded moulted female congenerics. In addition, in defence against predatory attacks, paired male and female G. pulex were significantly more aggressive than paired male and female G. d. celticus. These differences in aggressive behaviour led to a significantly higher frequency of predation on G. d. celticus females than on G. pulex females, and also explains this finding in previous studies. It is concluded that differential predation due to differences in aggressive behaviour may explain the pattern of replacement between these species. Web of Science Gammarus pulex Ireland County Down River Lagan Field - Experimental lotic Invasion Hyp. Inherent Superiority Superior Competitor omnivore 979 WILLIAMS, PA; BUXTON, RP 1995 ASPECTS OF THE ECOLOGY OF 2 SPECIES OF PASSIFLORA (PASSIFLORA-MOLLISSIMA (KUNTH) L-BAILEY AND PASSIFLORA-PINNATISTIPULA CAV) AS WEEDS IN SOUTH ISLAND, NEW-ZEALAND journal NEW ZEALAND JOURNAL OF BOTANY 33 3 315 323 Vegetation invaded by two species of passionfruit (Passiflora mollissima and P. pinnatis-tipula) was examined at several sites in South Island, mostly containing small forest remnants of angiosperm species such as Melicytus ramiflorus and Macropiper excelsum. Several aspects of the regeneration of these Passiflora species were examined and the results generally reflected those of intensive studies of the same species conducted in Hawaii. Seed germination in the laboratory was continuous over an 8 month period from sowing, and in the wild this allows seeds to accumulate in the soil seed bank. Germinable seeds and seedling numbers, however, were of a similar magnitude to those of native angiosperms at the sites, and they do not reach the very large numbers of some woody weeds. Seedling growth was c. 10 cm over a seven month period at two sites at 300 m a.s.l., which is towards the upper altitudinal limit of Passiflora species. Stem cuttings readily establish in both a glasshouse and a shadehouse. As stems frequently become buried and fragmented on steep slopes, their regeneration may assist in the localised spread of the plant, and also in the re-establishment of plants on a wide range of sites after mechanical control operations. Establishment of Passiflora species is restricted to areas of high light levels and soil disturbance such as forest clearings and road cuttings in the absence of dense herbaceous growth. Small forest and scrub remnants with high edge-to-area ratios are therefore particularly vulnerable. Passiflora species are relatively new weeds which are probably still expanding their range, and they can be expected to increase, assisted by human activity, particularly adjacent to highways. Web of Science Passiflora mollissima; P. pinnatis-tipula New Zealand South Island -42.2167 173.8667 Field - Observational;Lab terrestrial Subtropical Forest Invasion Hyp. Inherent Superiority;Disturbance High Reprod. Output primary 980 PYLE, LL 1995 EFFECTS OF DISTURBANCE ON HERBACEOUS EXOTIC PLANT-SPECIES ON THE FLOODPLAIN OF THE POTOMAC RIVER journal AMERICAN MIDLAND NATURALIST 134 2 244 253 The objective of this study was to investigate specific effects of disturbance on exotic species in floodplain environments and to provide baseline data on the abundance of exotic herbs in the Potomac River floodplain. Frequency of exotics generally increased with man-made disturbance (forest fragmentation and recreational use of land) and decreased with increasing flooding frequency. Species richness of exotics followed a similar pattern. Some variation was found in individual species' responses to disturbance. The spread of Alliaria officinalis and Glecoma hederacea, the most frequent exotic species, was inhibited by forest fragmentation. Web of Science Many USA Maryland Falls Church, Seneca; Rockville 39.036786 -77.260666 Field - Observational lotic Riparian Invasion Hyp. Disturbance primary 982 DECAMPS, H; PLANTYTABACCHI, AM; TABACCHI, E 1995 CHANGES IN THE HYDROLOGICAL REGIME AND INVASIONS BY PLANT-SPECIES ALONG RIPARIAN SYSTEMS OF THE ADOUR RIVER, FRANCE journal REGULATED RIVERS-RESEARCH & MANAGEMENT 11 1 23 33 Changes in the hydrological regime affect the phenomenon of invasion by plant species along riparian systems. The dynamics of exotic (non-native) and native species were examined at five sites that differed in exposure to hydrological disturbance (floods) during three consecutive years (medium, wet and dry years). When considering the disturbance gradient, exotic plants were favoured by direct exposure to floods (main channel) and by high flood frequencies. The response to year to year changes in hydrology was rapid for both native and exotic communities. However, the exotic plants responded more rapidly and were favoured by a dry year. A general framework including human and natural factors involved in invasions by exotic plants along rivers is presented. Web of Science Many France Adour River 43.70114 -0.245991 Field - Observational lotic Riparian Invasion Hyp. Disturbance primary 986 DUBE, M; MORISSET, P 1995 NEW CYTOLOGICAL OBSERVATIONS ON FESTUCA-RUBRA SENSU-LATO (POACEAE) IN EASTERN CANADA journal CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE 73 8 1289 1294 Sixty-one chromosome number determinations in Festuca rubra L. from eastern Canada show that hexaploids plants (n = 21) are found in both natural habitats and ruderal places, octoploids rhizomatous plants (n = 28) are mostly found in ruderal places, but also in disturbed natural habitats. Morever, one aneuploid (2n = ca. 48) is found from a natural habitat and intercytotype hybrids are found in ruderal places or disturbed natural habitats. Web of Science Festuca rubra Canada Field - Observational terrestrial Deciduous Forest;Old Field Invasion Hyp. Hybridization primary 991 SCHIERENBECK, KA; HAMRICK, JL; MACK, RN 1995 COMPARISON OF ALLOZYME VARIABILITY IN A NATIVE AND AN INTRODUCED SPECIES OF LONICERA journal HEREDITY 75 0 1 9 Levels of allozyme variation are compared between a diploid invasive plant species, Lonicera japonica Thunb. (2n=18) and its polyploid native congener, Lonicera sempevirens L. (2n=36). Both are woody perennials and were sampled within the native range of L. sempervirens in the south-eastern United States where L, japonica has been an invader since the late 19th century. Genetic structure and allozyme diversity were determined for nine and ten populations of L. sempervirens and L. japonica, respectively. Genetic variation within L. japonica is similar to that in other species with similar life history traits (per cent polymorphic loci, P-s=75 per cent, mean alleles per polymorphic locus, A(ps)=2.28, and total genetic diversity, H-t=0.216); L. sempervirens has even higher genetic variation than L. japonica (P-s=91 per cent, A(ps)=2.60 and H-t=0.283). Although both species have high levels of genetic diversity, this may be less important than their life history traits to their success in early successful habitats. However, establishment of a relationship between success in naturalization for woody perennials and levels of genetic diversity is hampered by the paucity of comparable records for other native:alien congeneric pairs. Web of Science Lonicera japonica USA South Carolina; Georgia Field - Observational terrestrial Deciduous Forest Invasion Hyp. Evolution in General;Inherent Superiority primary 993 WILLIAMS, DG; MACK, RN; BLACK, RA 1995 ECOPHYSIOLOGY OF INTRODUCED PENNISETUM-SETACEUM ON HAWAII - THE ROLE OF PHENOTYPIC PLASTICITY journal ECOLOGY 76 5 1569 1580 The C-4 African grass, Pennisetum setaceum (fountaingrass), has a greater altitudinal distribution than any other grass on the island of Hawaii. Clones of P. setaceum were reciprocally transplanted among coastal dry grassland, montane dry shrubland, and subalpine dry forest sites on the leeward side of Hawaii to evaluate the contribution of local adaptation and individual tolerance to the broad ecological amplitude of this grass. Physiological, growth, and reproductive responses differed among sites without evidence of local adaptation. Greatest tiller production and the highest photosynthetic rates were observed at the mid-altitude site, but plants at the coastal site attained greater basal areas, aboveground biomass, and number of inflorescences. Correlation among the responses of different plant characters was environmentally dependent, suggesting that the integrated expression of these characters is also plastic. Few differences in plant responses, however, were attributable to a population's origin or the site-by-population interaction; resident populations and introduced populations responded similarly at each site. Furthermore, few characters exhibited variation among clones, indicating that these populations likely possess little genetic variation. Limited clonal variation was, however, detected for net photosynthesis, the ratio of internal to ambient CO2 concentration (c(i)/c(a)), and specific leaf area, but only on two of five dates over a 1-yr period. Phenotypic plasticity for both individual characters and the integration of physiological and morphological characters have apparently been most important in allowing P. setaceum to become dominant across diverse habitats on Hawaii. Web of Science Pennisetum setaceum USA Hawaii 19.754183 -155.528126 Field - Experimental terrestrial Grassland;Subtropical Forest;Chaparral/Shrublands Invasion Hyp. Inherent Superiority;Plasticity Broad Tolerances primary 1000 ROBINSON, GR; QUINN, JF; STANTON, ML 1995 INVASIBILITY OF EXPERIMENTAL HABITAT ISLANDS IN A CALIFORNIA WINTER ANNUAL GRASSLAND journal ECOLOGY 76 3 786 794 In an experimental test of plant community invasibility, we introduced seeds of a native ruderal, California poppy (Eschscholzia californica), at fixed density into experimental plots in a California winter annual grassland. Each of the 42 plots, which ranged in size from 2 m(2) to 32 m(2), had been studied for 4 yr previous to the introduction, with the common observation that a subset of plots of each size consistently held more species than others. It was primarily in these more species-rich plots that establishment and reproduction by the experimental invader occurred. Success of the invader per plot. measured as the total number of plants germinating, producing seeds, or perennating, varied with plot size, but the statistical contribution of plot size was secondary to that of local species number. Contributing variables were the extent of small mammal disturbance (positive) and the degree to which a single resident plant species (in particular, Bromus diandrus) dominated a plot (negative). In contrast to theories of competitive exclusion via niche partitioning, species-rich plots were more invasible. Web of Science Many USA California 38.546554 -121.743965 Field - Experimental terrestrial Grassland Invasion Hyp. Community Species Richness primary 1005 TABACCHI, E 1995 STRUCTURAL VARIABILITY AND INVASIONS OF PIONEER PLANT-COMMUNITIES IN RIPARIAN HABITATS OF THE MIDDLE ADOUR RIVER (SW FRANCE) journal CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE 73 1 33 44 The pioneer vegetation of five distinct littoral zones along the middle Adour River (SW France) was investigated during three successive low water periods. There was a high year to year variability in the hydrology of the river during the period of study with a normal (1987), a wet (1988), and a dry year (1989). Changes in population and life forms density of both native and exotic species were analyzed. Communities were species rich when 45% of the 428 species present in the study area (2-km-long stretch) were found in the 10 x 10 m plots. Most of the species were annuals, but perennials were also abundant. The exotic component represented nearly 20% of the species and of the total number of individuals. There was high spatial variability in pioneer communities; sites of the main river channel differed from those along abandoned arms in species composition and population densities. The communities responded to changes in the hydrology of the preceding growing season. Sharp year to year differences were found in population and species density. The nature of the hydrological change drove those changes. Plots located in the oldest arms of the river showed a greater sensitivity to flooding conditions than those located in young littoral zones, with an increase in hygrophilous species. Alternatively, plots adjacent to active river channels showed greater sensitivity to drought conditions, as the density of short-lived and exotic species increased. Comparatively, exotics appeared to be more sensitive to the type of hydrological changes than natives. Warmer years also affected native plants, which reacted like invasive species. Relationships between the observed changes, the level of hydrological disturbance, and the recent history of each site are discussed in this paper with the possibility of using introduced species as descriptors of climatic and hydrologic changes. Web of Science Many France Adour River Field - Observational lotic Invasion Hyp. Fluctuating Resources primary 1016 FENSHAM, RJ; FAIRFAX, RJ; CANNELL, RJ 1994 THE INVASION OF LANTANA-CAMARA L IN FORTY-MILE-SCRUB-NATIONAL-PARK, NORTH QUEENSLAND journal AUSTRALIAN JOURNAL OF ECOLOGY 19 3 297 305 Seventy-three per cent of dry rainforest in Forty Mire Scrub National Park and large areas in adjacent savanna woodland have more than 5000 individuals per ha of lantana (Lantana camara L.). Transect studies in dry rainforest and savanna woodland across varying intensities of lantana infestation show a negative correlation between the density of lantana and tree cover in rainforest. The density of pig rooting is very high in areas of the dry rainforest on deep soil that was not heavily infested with lantana. It is suggested that the digging activities of these animals may cause tree death and subsequent increased light penetration, which favours lantana. The species richness of the dry rainforest declines as the density of lantana increases. However, the saplings and seedlings and the soil seed bank of dry rainforest and savanna woodland tree species have comparable densities in heavy and light lantana infestations. The proliferation of lantana results in the build up of heavy fuel loads across the boundary of dry rainforest and savanna woodland. Recent fires have killed the canopy trees in a large area of dry rainforest within the Park. Active management of Forty Mile Scrub National Park is urgent and some initiatives are suggested. Web of Science Lantana camara Australia Queensland Forty Mile Scrub NP -18.1 144.84 Field - Observational terrestrial Subtropical Forest;Savanna Invasion Hyp. Disturbance primary 1023 INDERJIT; DAKSHINI, KMM 1994 ALLELOPATHIC POTENTIAL OF THE PHENOLICS FROM THE ROOTS OF PLUCHEA-LANCEOLATA journal PHYSIOLOGIA PLANTARUM 92 4 571 576 Aqueous leachates of roots of the perennial weed Pluchea lanceolata (DC.) C.B. Clarke, its root-incorporated soil and rhizosphere soil, interfered with the seedling growth of certain plant species. The soils from the rhizosphere zone of this plant had significantly higher total phenolics and HPLC analysis revealed that phenolic fractions represented by retention times of 1.6, 1.9, 2.5 (simple phenol, chlorogenic acid and phloroglucinol respectively), 3.7 and 4.3 min were contributed by roots of the weed to the soil. The phenolic fraction represented by the retention time 3.3 (formononetin 7-O-glucoside) was detected in the weed's rhizosphere soils and not in the root-incorporated soils. UV spectral studies established the presence of phloroglucinol, simple phenol, chlorogenic acid, formononetin 7-O-glucoside, and methylated coumarins in the root leachate, which affect the seedling growth of mustard (Brassica juncea). Present research established the allelopathic potential of P. lanceolata roots, and the possible involvement of allelopathy in its interference success. Web of Science Pluchea lanceolata India Dehli Lab terrestrial Grassland Invasion Hyp. Novel Weapons primary 1027 FRENOT, Y; GLOAGUEN, JC 1994 REPRODUCTIVE-PERFORMANCE OF NATIVE AND ALIEN COLONIZING PHANEROGAMS ON A GLACIER FORELAND, ILES KERGUELEN journal POLAR BIOLOGY 14 7 473 481 The retreat of the Ampere Glacier, on Kerguelen, has left wide ice-free areas where five native and two alien vascular plant species are involved in primary colonization. The number of seeds produced by individual fertile plants has been determined for each species and germination capacity has been tested under different temperature and light conditions. Colobanthus kerguelensis and Cerastium fontanum produced the highest number of seeds per plant. No dormancy mechanism occurred in either species and they appeared to be the most successful colonizers during the early stages following the deglaciation. No seeds of Azorella selago and Agrostis magellanica had germinated after 2 months. Dormancy was demonstrated only in Poa kerguelensis. Festuca contracta was the only species which exhibited a negative photo-sensitivity. Germination of indigenous seeds required relatively high temperatures, whereas the optimum temperature for germination in the introduced Poa annua was 10-degrees-C. These results are compared with the few data available in the subantarctic literature and ecological implications are discussed. Web of Science Poa annua; Cerastium fontanum Antarctica Kerguelen -49.491323 69.139709 Greenhouse terrestrial Tundra Invasion Hyp. Plasticity primary 1029 SCHIFFMAN, PM 1994 PROMOTION OF EXOTIC WEED ESTABLISHMENT BY ENDANGERED GIANT KANGAROO RATS (DIPODOMYS-INGENS) IN A CALIFORNIA GRASSLAND journal BIODIVERSITY AND CONSERVATION 3 6 524 537 Giant kangaroo rats (Dipodomys ingens) continually modify their burrow precincts by digging tunnels, clipping plants, and other activities. In the valley grasslands of the Carrizo Plain Natural Area (San Luis Obispo County, California), this chronic disturbance to soil and vegetation promoted the establishment of exotic ruderal and early successional plant species. Erodium cicutarium, Bromus madritensis ssp. rubens, and other Mediterranean annuals were found to constitute a very large proportion of the vegetation on giant kangaroo rat precincts. When vegetation on precincts was compared with the vegetation in less disturbed intermediate areas located between precincts, species richness, cover and frequency of exotic plants were significantly greater on precincts. The reverse was found for native species. In addition, exotic species encountered in this study had significantly larger seeds than did native species, suggesting that these granivorous kangaroo rats preferentially cache large weed seeds on their precincts. Since the kangaroo rats depend on exotic plants for food and the exotic plants depend upon the kangaroo rats to disturb their habitat continually, the weed-kangaroo rat relationship is mutualistic. This strong relationship may also inhibit population growth of native grassland plants which occupy disturbed habitats but have difficulty competing with exotic weeds for resources. From a conservation perspective, this mutualism presents an intractable management dilemma. Restoration of valley grasslands where endangered giant kangaroo rats occur, to conditions where native species dominate, may be impossible. Web of Science Many USA California Field - Observational terrestrial Grassland Invasion Hyp. Mutualism Facilitation primary 1034 DEAN, WRJ; MILTON, SJ; RYAN, PG; MOLONEY, CL 1994 THE ROLE OF DISTURBANCE IN THE ESTABLISHMENT OF INDIGENOUS AND ALIEN PLANTS AT INACCESSIBLE AND NIGHTINGALE ISLANDS IN THE SOUTH-ATLANTIC OCEAN journal VEGETATIO 113 1 13 23 Disturbances play an important role in the establishment of vegetation at Inaccessible and Nightingale Islands in the South Atlantic Ocean. Type, altitude and age of disturbance all influenced the species richness, life-form and abundance of seedlings. A few indigenous species appear to be dependent on small disturbances, such as the clearings around albatross nests, for their perpetuation, e.g. Acaena sarmentosa and Gnaphalium thouarsii. Alien forbs and grasses, e.g. Conyza albida, Holcus lanatus, Pseudognaphalium luteo-album and Rumex obtusifolius, tended to dominate large recent disturbances such as soil-slips and depressions, and to colonize man-modified sites. Alien plants were less common on the plateau at Inaccessible Island than on the lowlands. Their success appears to be enhanced by large-scale disturbances. The highest density and diversity of seedlings occurred on large soil-slips where mineral soil was exposed and vegetation cover was minimal. Web of Science Many -37.2667;-37.4667 -12.8667;-12.5333 Field - Experimental;Field - Observational terrestrial Grassland Invasion Hyp. Disturbance primary 1037 DEFERRARI, CM; NAIMAN, RJ 1994 A MULTISCALE ASSESSMENT OF THE OCCURRENCE OF EXOTIC PLANTS ON THE OLYMPIC PENINSULA, WASHINGTON journal JOURNAL OF VEGETATION SCIENCE 5 2 247 258 Exotic plants were surveyed in 208 plots within the Dungeness and Hoh river watersheds on the Olympic Peninsula, Washington, USA. Landscape patch types included uplands (clearcuts, young and mature forests) and riparian zones (cobble bars, shrub patches, riparian forests. and alder flats). Patterns of exotic plant invasions were assessed between watersheds, between riparian and upland areas, among patch types, and within clearcuts. 52 exotic plant species were encountered, accounting for 23 % of the flora in each watershed. In both watersheds, exotic species richness was approximately 33 % greater in riparian zones than in uplands, and mean number and cover of exotic species were > 50 % greater in riparian zones than in uplands. Among landscape patch types, richness and mean number and cover of exotics was highest in young riparian patches, intermediate in clearcuts and riparian forests, and lowest in young and mature forests. The exception to this was Hoh alder flats, which had the highest mean cover of exotic plants. Cover of exotic plants peaked in uplands 3 to 7 yr after clearcutting, then decreased with increased canopy closure. Disturbance type and time since disturbance were major factors influencing invasibility. Landscape patch size, position within watershed (distance from patch to human population centers, major highway, or fiver mouth), and environmental variables (slope, aspect, and elevation) were not important indicators of landscape patch invasibility. Riparian zones facilitated movement of exotic plants through landscapes, but did not appear to act as sources of exotic plants for undisturbed upland areas. Web of Science Many United States Washington Field - Observational terrestrial Coniferous Forest;Riparian Invasion Hyp. Disturbance primary 1038 MCINTYRE, S; LAVOREL, S 1994 PREDICTING RICHNESS OF NATIVE, RARE, AND EXOTIC PLANTS IN RESPONSE TO HABITAT AND DISTURBANCE VARIABLES ACROSS A VARIEGATED LANDSCAPE journal CONSERVATION BIOLOGY 8 2 521 531 Species richness o native, rare native, and exotic understorey plants was recorded at 120 sites in temperate grassy vegetation in New South Wales. Linear models were used to predict the effects of environment and disturbance on the richness of each of these groups. Total native species and rare native species showed similar responses, with richness declining on sites of increasing natural fertility of parent material as well as declining under conditions of water enrichment (resulting from human-induced changes in drainage characteristics, leading to increased run-off), severe livestock grazing, and soil disturbance. The response of rare native species to water enrichment however, was significantly greater than that of all native species. Exotic species richness varied in reverse to that of native species with positive responses to water enrichment and soil disturbance, The contrasting behaviors are attributed to differences in the evolutionary history of native and exotic assemblages and their resulting preadaptations to a landscape recently subjected to agricultural settlement It would appear that for exogenous disturbances, the intermediate disturbance hypothesis is not supported by our data In the sampled region, pastures represent the major land-use in terms of area, but have relatively low densities of native and rare species compared with more lightly grazed areas. However, their management is considered to be essential to the maintenance of diversity on a regional scale. Web of Science Many Australia New South Wales Field - Observational terrestrial Grassland Invasion Hyp. Disturbance primary 1039 BRANDT, CA; RICKARD, WH 1994 ALIEN TAXA IN THE NORTH-AMERICAN SHRUB-STEPPE 4 DECADES AFTER CESSATION OF LIVESTOCK GRAZING AND CULTIVATION AGRICULTURE journal BIOLOGICAL CONSERVATION 68 2 95 105 Because of its use as a nuclear materials production area, the 800-km2 sagebrush steppe of the Columbia River Plain in Washington State has functioned as a quasi-natural area protected from livestock grazing and agricultural development since 1944. Alien vegetation and animals have invaded the eastern Washington region in the past century and are currently represented in the Columbia River Plain. Investigations were undertaken to evaluate the distribution of alien species, particularly vegetation, and their relationships to other flora and fauna in this region. Recently disturbed areas were dominated by the alien annuals Russian thistle Salsola kali, tumble mustard Sisymbrium altissimum, prickly lettuce Lactuca serriola, and bur ragweed Ambrosia acanthicarpa. Old-field habitats were composed almost entirely of the alien annual cheatgrass Bromus tectorum. Alien vegetation also comprised a portion of the flora in habitats that had not been disturbed or grazed by cattle in the past. Cheat-grass and spring whitlow-grass Draba verna were able to set seed in undisturbed habitats, whereas Russian thistle and tumble mustard seldom did. These two species continue as components of undisturbed habitat primarily through seed dispersal from disturbed sites. Old-field habitats support a depauperate fauna compared to undisturbed sagebrush steppe vegetation. Shrub-nesting birds such as the sage sparrow Amphispiza belli were absent from old fields, and even ground-nesting species were found in abnormally low densities. Old fields supported relatively few mammal species, in part as a result of poor food supplies. Alien birds, the rock do ve Columba livia and the European starling Sturnus vulgaris, visited undisturbed habitat, but did not nest there. No alien mammals were found in undisturbed sage-brush steppe vegetation; the only alien mammals found in the area, the house mouse Mus musculus and Norway rat Rattus norvegicus, being limited to riparian areas and the vicinity of buildings. Alien taxa are likely to remain a component of any quasi-natural area in the sagebrush steppe ecoregion. Human disturbance need not be spatially extensive to maintain alien plants within undisturbed communities. Successional patterns after land disturbance produce conditions unfavorable for native fauna, but have not enhanced the distribution of alien fauna. Web of Science Many USA Washington Columbia River Plain 46.443062 -119.345169 Field - Observational terrestrial Grassland;Old Field Invasion Hyp. Disturbance primary;herbivore;omnivore;predator 1051 JONES, JI; EATON, JW; HARDWICK, K 1993 PHYSIOLOGICAL PLASTICITY IN ELODEA-NUTTALLII (PLANCH) ST-JOHN journal JOURNAL OF AQUATIC PLANT MANAGEMENT 31 0 88 94 Elodea nuttallii, a problem weed in Britain, has been found to adapt rapidly to high pH and low CO2, conditions which are normally associated with low growth rates. This adaptation has consequences with respect to modelling plant growth and predicting weed problems in the field. Investigations indicate that E. nuttallii is able to utilize bicarbonate by active transport, pumping H+ to the lower leaf surface and OH- to the upper surface, as proposed by Prins et al. (1982). For much of the time this mechanism does not operate in the field, but laboratory experiments have shown that it is switched on within a few days, over a very small pH range, as carbon dioxide supply becomes limiting. Evidence is presented that bicarbonate uptake does occur in the field and its significance to the plant's growth is discussed, These results are compared with physiological plasticity in the closely related Elodea canadensis. Web of Science Elodea nuttallii England 53.4667 -2.95 Lab Invasion Hyp. Inherent Superiority;Plasticity Superior Competitor primary 1065 CORNELL, HV; HAWKINS, BA 1993 ACCUMULATION OF NATIVE PARASITOID SPECIES ON INTRODUCED HERBIVORES - A COMPARISON OF HOSTS AS NATIVES AND HOSTS AS INVADERS journal AMERICAN NATURALIST 141 6 847 865 Herbivore species newly introduced into foreign locations (hosts as invaders) are often attacked by native parasitoid species. Here we compare the structure and diversity of 87 such parasitoid complexes with those on the same herbivore species in their native regions (hosts as natives). Overall parasitoid attack rates are generally lower on hosts as invaders than on hosts as natives. Also, parasitoid complexes on hosts as invaders are generally less rich and contain a higher proportion of generalists than those on hosts as natives. Overall richness shows a weak tendency to increase with duration in the region of introduction over the first 150 yr, but the ratio of generalists-to specialists does not change over this time period. These results, in part, parallel those for herbivore complexes on introduced host plants and suggest that common theoretical principles may apply to both trophic levels. The herbivores were also categorized by level of concealment and taxon (order) to determine whether life-style or phylogeny influenced parasitoid richness in native or foreign locations. No strong influences emerged. Our most novel result is a vulnerability-to-parasitism regression; the numbers of parasitoids attacking host species in invaded regions are correlated with the numbers in native regions. The biological characteristics of the herbivore as well as extrinsic region-specific factors may play important roles in setting parasitoid richness levels on hosts as natives and on hosts as invaders. Web of Science Many Statistical/Meta-analysis;Review terrestrial Invasion Hyp. Enemy Release herbivore 1067 PARKER, IM; MERTENS, SK; SCHEMSKE, DW 1993 DISTRIBUTION OF 7 NATIVE AND 2 EXOTIC PLANTS IN A TALLGRASS PRAIRIE IN SOUTHEASTERN WISCONSIN - THE IMPORTANCE OF HUMAN DISTURBANCE journal AMERICAN MIDLAND NATURALIST 130 1 43 55 Invasion by exotic plant species is a serious threat to the integrity of natural communities. The distribution of an exotic species depends upon environmental conditions, the structure of the native community, patterns of disturbance and ecological features of the species itself. This study identifies (1) associations between two exotic and seven native species in a tallgrass prairie in southeastern Wisconsin and (2) factors underlying the distribution of these species, with special regard to the effects of human disturbance. The distribution of two exotic species, Melilotus alba (white sweetclover) and Daucus carota (Queen Anne's lace), and seven native species, Potentilla arguta (prairie cinquefoil), Pedicularis canadensis (Canada lousewort), Dodecatheon meadia (Mead's shooting star), Equisetum laevigatum (scouring rush), Pycnanthemum virginianum (Virginia mountain mint), Phlox glaberrima (smooth phlox) and Solidago graminifolia (bushy goldenrod), were studied in 100, 4 m2 quadrats on five transects. Plant densities and soil characteristics were recorded for each quadrat and analyzed using nonparametric comparison of means and Spearman correlation analysis. Densities of the two exotic species were positively correlated with each other and negatively correlated with those of five of the seven natives. Most species exhibited a clear segregation between disturbed and undisturbed transects; Melilotus and Daucus dominated the disturbed transects, and native species dominated the undisturbed transects. Edaphic conditions appear to be the most important factor driving this habitat segregation between exotics and natives. Our finding is instructive for prairie restoration, because it suggests that in some cases, soil restoration may be desirable even if it results in additional mechanical disturbance. Although the prairie in its undisturbed state seems to resist invasion of these two exotic species, Daucus is able to escape disturbed microhabitats more extensively than is Melilotus. Web of Science Melilotus alba; Daucus carota United States Wisconsin Chiwaukee Prairie 42.527152 -87.816811 Field - Observational terrestrial Grassland Invasion Hyp. Disturbance primary 1069 MONTALDO, NH 1993 AVIAN DISPERSAL AND REPRODUCTIVE SUCCESS OF 2 SPECIES OF LIGUSTRUM (OLEACEAE) IN A SUBTROPICAL FOREST RELICT IN ARGENTINA journal REVISTA CHILENA DE HISTORIA NATURAL 66 1 75 85 Flowering, fruit production, and seed dispersal by birds of two exotic plants (Ligustrum lucidum Ait. and Ligustrum sinense Lour.) were studied from 1986 to 1988 in a riparian forest relict located in central Argentina. L. lucidum has heavily invaded this forest whereas L. sinense has been less successful. This fact is not clearly explained either by L. sinense's lower fruit/flower ratio (14% vs. 21%) or by its lower seed production. Eleven native bird species living permanently in the ama eat fruits of both introduced plants. Of these, only three species are important for effective seed dispersal, while two others destroy the seeds. The population of the main seed predator increases considerably during the availability period of ripe Ligustrum fruits. Dispersal mode varies according to different species (isolated seeds or clumps of seeds). Migrant fruit-eating birds are not involved in seed dispersal of these plants. Ligustrum lucidum and L. sinense are perfectly naturalized in the area. Avian seed dispersal is apparently not essential for Ligustrum perpetuation although such dispersal was probably instrumental in colonization. There were no significant differences in germination between bird-dispersed seeds and those that had not passed through the birds' digestive tracts. Web of Science Ligustrum lucidum; Ligustrum sinense Argentina -32.1 -63.63 Field - Observational terrestrial Subtropical Forest Invasion Hyp. Mutualism Facilitation;Inherent Superiority High Reprod. Output primary 1073 BERGELSON, J; NEWMAN, JA; FLORESROUX, EM 1993 RATE OF WEED SPREAD IN SPATIALLY HETEROGENEOUS ENVIRONMENTS journal ECOLOGY 74 4 999 1011 Communities subject to disturbance are apparently vulnerable to invasion in that they contain a large fraction of the introduced plant species persisting in any given area. Still, ecologists have a poor understanding of how details of the disturbance regime influence the success with which invaders spread through a community. In this paper, we report results from an experiment that investigates how the spatial distribution of bare ground influences the rate at which offspring of an introduced invader spread through a perennial ryegrass community. Artificially created gaps of three sizes were positioned along linear transects according to one of two spatial distributions. These six transects (one for each treatment combination) were positioned as spokes on a wheel and Senecio vulgaris was introduced into the center. After controlling for the total amount of gap area, we monitored the number ard position of Senecio vulgaris establishing for two subsequent generations. Our results showed that the rate of spread of Senecio vulgaris was sensitive to both the gap size and the gap distribution; plants moved a greater distance when the gaps were large and underdispersed. Simulation models confirm that this pattern follows from the way in which gaps sample from seed shadows. We derive an analytical expression to explain why the mean seed dispersal distance does not predict the spread of Senecio vulgaris adults, and show how rates of spatial spread will change under different spatial patterns of disturbance. Finally, a model of spatial point processes confirms that the distribution of gaps mediates the rate of weed spread in two dimensions as well. Web of Science Senecio vulgaris England Berkshire Institute of Grassland and Environmental Research Field - Experimental terrestrial Grassland Invasion Hyp. Disturbance primary 1077 CALLEY, M; BRAITHWAITE, RW; LADD, PG 1993 REPRODUCTIVE-BIOLOGY OF RAVENALA-MADAGASCARIENSIS GMEL AS AN ALIEN SPECIES journal BIOTROPICA 25 1 61 72 The exotic arborescent monocot species from Madagascar, Ravenala madagascariensis, was studied in suburban gardens in Darwin, Australia. Inflorescences are long-lived branched spikes produced at right angles to a spectacular fan-like array of foliage. They are composed of a variable number of green boat-like bracts which contain a dilute liquid. Each bract subtends a series of individual, stiff, upright, large flowers which appear every 2.3 days, the total number of flowers being variable (up to 29). The slightly musty sweet smelling, creamy white hermaphrodite flowers, sometimes protogynous, opened at night (82.6% of flowers observed). Anthesis lasted, on average, 1.3 days and stigmas were receptive within the 24 hours of flower opening. Initially, nectar production was copious (1400 mul 12 hr-1) and concentration moderate (14.5% sucrose equivalents), but maximum production (1600 mul 12 hr-1) with slightly reduced concentration (12.5% sucrose) occurred at 2400 hr. Seed set occurs in Darwin plants, with the brown seed enveloped in a bright blue aril and displayed very obviously in the dehisced capsule. While autogamy treatments revealed that Ravenala is at least a facultative selfer, in Darwin the flowers were most frequently visited by the megachiropteran bat, Pteropus alecto gouldii, and only occasionally by the smaller bat, Macroglossur lagochilus, and honeyeater birds (Meliphagidae). Apart from reproducing vegetatively, the ability of Ravenala to set seed when grown outside its normal range in the absence of its co-evolved pollinator(s), either by selfing or by using a suitable indigenous pollinator, could allow the species to assume pest status in parts of the tropics where it is planted as an ornamental. Web of Science Ravenala madagascarensis Australia Northern Territory Darwin -12.458318 130.842161 Field - Observational terrestrial Urban Invasion Hyp. Mutualism Facilitation;Inherent Superiority Self Compatible primary 1082 DANTONIO, CM 1993 MECHANISMS CONTROLLING INVASION OF COASTAL PLANT-COMMUNITIES BY THE ALIEN SUCCULENT CARPOBROTUS-EDULIS journal ECOLOGY 74 1 83 95 The South African succulent Carpobrotus edulis has been invading native and non-native plant assemblages in California since its introduction in the early 1900s. This study was designed to determine mechanisms controlling invasion by this species into three different communities: coastal grassland, backdune, and coastal scrub. The communities differed in several factors that influenced invasion by Carpobrotus: soil disturbance, herbivory, and identity of competitors. Disturbance of the soil was required for establishment of Carpobrotus at the grassland site. Soil disturbance did not promote Carpobrotus establishment in the coastal scrub or backdune. Establishment in these sites was restricted by herbivory. The influence of neighboring vegetation on Carpobrotus establishment was site dependent. At the grassland site, Carpobrotus seedling survival was reduced by grasses, and the only surviving seedlings were on gopher mounds. Growth of larger Carpobrotus plants, however, was unaffected by grasses. Proximity to shrubs, the dominant plant type at the backdune and coastal scrub sites, did not affect Carpobrotus seedling survival. It did, however, decrease both root and shoot biomass of seedlings and cuttings. Invasion is expected to occur most rapidly at the grassland site. Although germination and early survival there depend on the occurrence of rodent disturbances, these occur frequently, and seedling recruitment in the grassland was observed during this study. Once established, clonal growth is great and is not affected by herbivory or competition. In contrast, at the coastal scrub site, intense herbivory prevented successful establishment during this study. Cage experiments suggested that herbivory counteracted the high growth potential of Carpobrotus at this site. At the dune site, even caged plants showed very poor growth. Thus, although seedling recruitment does occur there, invasion is expected to be slow due to harsh physical conditions that limit both survival and growth. These findings demonstrate strong community differences in the factors governing invasability by Carpobrotus edulis. Web of Science Carpobrotus edulis United States California 34.6833 -120.6 Field - Experimental;Field - Observational terrestrial Grassland;Chaparral/Shrublands Invasion Hyp. Inherent Superiority;Disturbance Clonal Reproduction primary 1087 DAMASCOS, MA; GALLOPIN, GG 1992 ECOLOGY OF AN INTRODUCED SHRUB (ROSA-RUBIGINOSA-L = ROSA-EGLANTERIA L) - INVASION RISKS AND EFFECTS ON THE PLANT-COMMUNITIES OF THE ANDEAN-PATAGONIC REGION OF ARGENTINA journal REVISTA CHILENA DE HISTORIA NATURAL 65 4 395 407 The relation between presence of Rosa eglanteria L. and environmental or antropic variables was studied in fifty nine plots, randomly established in ten areas representing different environments in or around the Nahuel Huapi National Park. Floristic differences between areas invaded by this shrub and areas without Rosa eglanteria were studied. The degree of disturbance, the openness of the shrub stratum and the average annual rainfall were the main factors influencing the invasion by Rosa eglanteria. Communities in early stages of invasion and with low disturbance, showed on the average, a higher species richness than those without Rosa. However, samples from communities dominated by Rosa eglanteria showed lower species richness. With the exception of two native species, neither the abundance of native species, nor that of other exotic invaders showed significant differences between early stage invaded sites or non invaded sites. Web of Science Rosa eglanteria Argentina Nahuel Huapi National Park -40.99995 -71.499968 Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Disturbance primary 1090 GEHRING, JL; LINHART, YB 1992 POPULATION-STRUCTURE AND GENETIC DIFFERENTIATION IN NATIVE AND INTRODUCED POPULATIONS OF DESCHAMPSIA-CAESPITOSA (POACEAE) IN THE COLORADO ALPINE journal AMERICAN JOURNAL OF BOTANY 79 12 1337 1343 Deschampsia caespitosa is a widespread grass common in moist areas of the alpine tundra of the Rocky Mountains. Enzyme electrophoresis was used to examine population genetic structure along two soil moisture gradients in Rocky Mountain National Park, Colorado. Introduced plants used in a revegetation project were also sampled at one of the sites. At both sites, there were significant differences among subpopulations in allele frequencies, but these differences were distributed in a patchy fashion and were not correlated with the apparent soil moisture gradients. The degree of genetic subdivision differed between the two sites. At one site, gene flow appeared to be high and differences in allele frequencies are attributed to selection in a mosaic environment. At the other site, gene flow appeared more restricted and differences in allele frequencies between subpopulations are attributed to selection and limited gene flow acting simultaneously. Overall, 15% of the genetic variability is between subpopulations and gene flow is high, even between subpopulations separated by up to 1.5 km, but local conditions can apparently limit gene flow and increase the degree of genetic subdivision. The mean genetic distance between introduced plants and the native subpopulations was significantly higher than the mean genetic distance between all other subpopulations. Despite the high gene flow apparent in alpine tundra subpopulations of Deschampsia caespitosa, significant genetic structuring of these subpopulations has developed. Web of Science Deschampsia caespitosa United States Colorado 40.4 -105.75 Lab terrestrial Tundra Fundamentals primary 1092 WACQUANT, JP; PICARD, JB 1992 NUTRITIONAL DIFFERENTIATION AMONG POPULATIONS OF THE MEDITERRANEAN SHRUB DITTRICHIA-VISCOSA (ASTERACEAE) IN SILICEOUS AND CALCAREOUS HABITATS journal OECOLOGIA 92 1 14 22 Dittrichia (ex Inula) viscosa is a ruderal species that has recently become an invading plant in the north-west Mediterranean basin. A previous study failed to demonstrate the occurrence of morphologically differentiated ecotypes among populations of the species but suggested the existence of nutritional ecotypes. This latter possibility is examined here by comparing the ability of plants from contrasting habitats to control cation accumulation balance. Dittrichia viscosa plants. from eight siliceous habitats and nine calcareous habitats of southern France and neighbouring Spain and Italy, were cloned and grown together hydroponically with a solution simulating an acid soil with an aluminium constraint. Two independent hydroponic units containing solution supplemented with two levels of Al were used (2 Al levels x 17 populations x 3 genotypes x 3 replicates). The growth and cation content (K, Ca, Mg and Na) of plant shoots and the chemical composition of the soil of each habitat were analysed. At the high Al level (1.1 mM), populations differed in K, Ca and Mg plant proportions. Two groups could be distinguished: one containing all but one siliceous populations and the other containing all but one calcareous populations. Plants of the siliceous group accumulated proportionally more K and less Ca. and had better growth, than plants of the calcareous group, in the same way as calcifuge and calcicole species when grown on acid soil. At the lowest Al level (0.37 mM), differences between siliceous and calcareous populations were less marked. The results suggest that differences in the ability of plants to control K and Ca balance, which appear to be of adaptive significance, could have arisen through selection, and that Dittrichia viscosa has evolved calcifuge and calcicole nutritional ecotypes in siliceous and calcareous habitats respectively. Various degrees of calcifugy, and to a lesser extent of calcicoly, can thus be suggested to occur among the studied populations, some in relation to the intensity of mineral stress in the natural habitats. So far, only functional traits have provided evidence of ecotypic differentiations within Dittrichia viscosa. Web of Science Dittrichia viscosa France; Spain; Italy Greenhouse terrestrial Old Field Invasion Hyp. Evolution in General primary 1093 BOCK, JH; BOCK, CE 1992 VEGETATION RESPONSES TO WILDFIRE IN NATIVE VERSUS EXOTIC ARIZONA GRASSLAND journal JOURNAL OF VEGETATION SCIENCE 3 4 439 446 Grass and herb cover, and woody plant densities were measured on 25 native and 25 exotic grassland plots in southeastern Arizona between 1984 and 1990. At least 40 yr previously, the exotic plots had been seeded with two species of lovegrasses (Eragrostis spp.) native to southern Africa. A 1987 wildfire burned 11 native and 11 exotic plots. The fire reduced cover of both native and African grasses for two post-fire growing seasons. Herb cover as a whole increased after the fire for 2 yr, although there were important differences among species. One of two dominant shrubs (Haplopappus tenuisectus) was killed by the fire, while the other (Baccharis pteronioides) was little affected. Mesquite trees (Prosopis juliflora) were killed to the ground by the fire, but 62 of 66 trees had re-sprouted to an average 48% of pre-bum height by 1990. Native and exotic grasses appeared equally tolerant of fire, probably because both evolved in fire-type ecosystems. There was no evidence that fire can be used to permanently restore the diverse native flora to species-poor plantations of the South African exotics. Web of Science Eragrostis spp. United States Arizona Field - Observational terrestrial Grassland Invasion Hyp. Preadaptation to Climate primary 1094 BERMAN, J; HARRIS, L; LAMBERT, W; BUTTRICK, M; DUFRESNE, M 1992 RECENT INVASIONS OF THE GULF OF MAINE - 3 CONTRASTING ECOLOGICAL HISTORIES journal CONSERVATION BIOLOGY 6 3 435 441 Introduced species are common members of estuarine communities where their role as competitors and predators is of concern. This paper examines the invasion of Gulf of Maine benthic habitats by the ecologically similar alien invertebrates Styela clava, Botrylloides diegensis, and Membranipora membranacea. Styela clava increased slowly in abundance at study sites in Beverly, Massachusetts and Portsmouth, New Hampshire We found no evidence of competitive dominance by S. clava, even though it is the competitive dominant in similar habitats elsewhere. Botrylloides diegensis rapidly became a dominant species after its arrival in the Great Bay Estuary, but this dominance was short-lived. B. diegensis persists in the estuary as an early colonist of primary space and as an epibiont on secondary substrates in established communities. Membranipora membranacea became the dominant epiphyte on laminarian kelps within two years. Although M. membranacea overgrew the native epiphytes Obelia geniculata and Electra pilosa in the overwhelming majority of encounters, these native species are more common on other algal hosts. Therefore, competitive dominance is not likely a factor in the successful invasion of the Gulf of Maine by M. membranacea. These species provide evidence for opposing views of the role of competition in mediating community invasion We show that ecological similarity among species is not an accurate criterion to predict either the mechanism of invasion or the means of persistence. In addition, these data indicate that biological invasions must be examined on broad spatial and temporal scales; short-term or narrowly focused studies can lead to incorrect conclusions. Web of Science Syela clava; Botrylloides diegensis; Membranipora membranacea United States Massachusetts; New Hampshire; Maine Gulf of Maine Field - Observational marine Benthic Invasion Hyp. Inherent Superiority Superior Competitor filter 1095 ABBOTT, I 1992 BIOGEOGRAPHY OF GRASSES (POACEAE) ON ISLANDS OF SOUTHWESTERN AUSTRALIA journal AUSTRALIAN JOURNAL OF ECOLOGY 17 3 289 296 The number of native grass species and exotic grass species present on 129 offshore islands of southwestern Australia is best predicted by island area and island disturbance, respectively. Isolation of islands and gull activity on islands only slightly improved these predictions. Species turnover on a subset of 30 islands indicated that exotic grass species were more prone to local extinction and more likely to immigrate than native grass species. The major conservation implication of this study is that habitat disturbance on these islands should be minimized to reduce establishment of exotic grass species. Web of Science Many Australia south western islands Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Disturbance primary 1099 BROTHERS, TS 1992 POSTSETTLEMENT PLANT MIGRATIONS IN NORTHEASTERN NORTH-AMERICA journal AMERICAN MIDLAND NATURALIST 128 1 72 82 European settlement of northeastern North America created opportunities for expansion of native species preadapted to the new human-created landscapes. I used Gleason's (1963) New Britton and Brown Illustrated Flora of the Northeastern United States and Adjacent Canada to test predictions about the broad geographic range expansions of native species since settlement. As expected, most of the migrants are herbaceous species from plant families that include many weeds. The migrants are more commonly from dry grasslands than from such well-known weed sources as riverbanks and sea beaches. Range expansion has been highly asymmetric: almost all migrants have moved east or north. Forest clearing and creation of continuous xeric migration routes along roads and railroads have been important causes of uneven range expansion. Such invasions of human-disturbed mesic environments by species of drier regions are probably a general phenomenon. Web of Science Many United States Statistical/Meta-analysis terrestrial Fundamentals primary 1102 CALLAWAY, JC; JOSSELYN, MN 1992 THE INTRODUCTION AND SPREAD OF SMOOTH CORDGRASS (SPARTINA-ALTERNIFLORA) IN SOUTH SAN-FRANCISCO BAY journal ESTUARIES 15 2 218 226 Spartina alterniflora was first introduced into south San Francisco Bay in the 1970's. Since that time it has spread to new areas within the south bay and is especially well established at four sites. The spread of this introduced species was evaluated by comparing its vegetative and reproductive characteristics to the native cordgrass, Spartina foliosa. The characters studied were intertidal distribution, phenology, aboveground and belowground biomass, growth rates, seed production, and germination rates. Spartina alterniflora has a wider intertidal distribution than S. foliosa and outproduced the native cordgrass in all aspects that were studied. These results indicate that the introduced species has a much better chance of becoming established in new areas than the native species, and once established, it spreads more rapidly vegetatively than the native species. Spartina alterniflora is likely to continue to spread to new areas in the bay and displace the native plant. In addition, this introduced species may affect sedimentation dynamics, available detritus, benthic algal production, wrack deposition and disturbance, habitat structure for native wetland animals, benthic invertebrate populations, and shorebird and wading bird foraging areas. Web of Science Spartina alterniflora United States California San Francisco Bay 37.758094; 37.640471 -122.260838; -122.395248 Field - Observational;Lab estuarine Wetland Invasion Hyp. Inherent Superiority;Disturbance primary 1103 HOGENBIRK, JC; WEIN, RW 1992 TEMPERATURE EFFECTS ON SEEDLING EMERGENCE FROM BOREAL WETLAND SOILS - IMPLICATIONS FOR CLIMATE CHANGE journal AQUATIC BOTANY 42 4 361 373 Temperature treatments simulated global warming effects on seedling emergence of wetland species from soil seed banks of the Peace-Athabasca Delta, Alberta. Canada. Introduced weedy species. such as Tanacetum vulgare L., bad up to a 10-fold greater emergence at high temperature (30-degrees-C for 18 h with light. 15-degrees-C for 6 h in the dark) than at low temperature (20/10-degrees-C). Seedling emergence of native weedy species, such as Calamagrostis canadensis (Michx.) Beauv., was 1.5-3 times greater at low temperature. Other native weedy species. such as Rubus idaeus L., emerged only from samples at low temperature. Emergence of native non-weedy species was greatest at high temperature, even though mature plants of species such as Ranunculus hyperboreus Rottb. and Carex eburnea Boott are normally found in cool and moist habitats. Of those species expected to persist in warm and dry habitats. only introduced weedy species showed consistent and significantly greater seedling emergence at high temperature. It is hypothesized, therefore. that the abundance of introduced weedy species would increase in disturbed or sparsely vegetated zones around water bodies as these zones become dry and warm with climate change. Web of Science Tanacetum vulgare Canada Alberta Field - Observational terrestrial Wetland Invasion Hyp. Climate Change primary 1113 HARMON, GD; STAMP, NE 1992 EFFECTS OF POSTDISPERSAL SEED PREDATION ON SPATIAL INEQUALITY AND SIZE VARIABILITY IN AN ANNUAL PLANT, ERODIUM-CICUTARIUM (GERANIACEAE) journal AMERICAN JOURNAL OF BOTANY 79 3 300 305 By decreasing seed density, ants introduced into flats of uniformly sown seeds of Erodium cicutarium (Geraniaceae) created differences in the neighbor-free area available to individual plants. The changes in spatial patterns brought about by the ants were greater when a higher proportion of seeds was removed but were independent of initial seed density. These spatial changes and differences in seed density were examined for their effects on plant size and reproduction. Gini values were calculated to determine inequalities. As the inequality in space among individual plants increased, the variation in final biomass increased. The number of individuals reproducing was constant among treatments, and yet seed production per plant was significantly greater for populations in which the spatial pattern was influenced by seed predation. The decrease in density and changed spatial pattern, due to previous seed predation, resulted in a few individuals having much more space than others and consequently producing many more seeds. The increase in reproductive effort per flat was much greater than could be explained by the changing density alone. Our experiment demonstrates that spatial inequality, such as that generated by seed predators, can be more important than density in generating size inequalities in plant populations. This result can profoundly alter the competitive interactions between plants and determine which plants produce seed for the next generation. Web of Science Erodium cicutarium United States Greenhouse terrestrial Grassland;Desert Fundamentals primary 1120 APLET, GH; ANDERSON, SJ; STONE, CP 1991 ASSOCIATION BETWEEN FERAL PIG DISTURBANCE AND THE COMPOSITION OF SOME ALIEN PLANT ASSEMBLAGES IN HAWAII-VOLCANOS-NATIONAL-PARK journal VEGETATIO 95 1 55 62 Association analysis was used to assess relationships among 25 important alien plant species and their association with feral pig rooting in Hawaii Volcanoes National Park, Hawaii, U.S.A. Results of the association analysis were summarized by means of a simplified, rank-based, polar ordination which yielded three subjective species assemblages. One group was characterized by an association with the endpoint species, Ehrharta stipoides. A second group consisted of species associated with the other endpoint species, Andropogon virginicus. The third group comprised a diverse assemblage of 14 species in the middle of the ordination. Comparison of ordination scores with each species's association with pig-induced soil disturbance revealed that members of the Ehrharta group were strongly positively associated with pig activity, whereas members of the Andropogon group were generally negatively associated. The third group showed no association with pig-induced soil disturbance. These results suggest a strong relationship between feral pig activity and the composition of the alien portion of the plant community. Analysis of the ecologies of both plants and pigs suggests that some species may both encourage pig activity and benefit from it. Likewise, other alien plants appear to neither require nor benefit from pig-induced soil disturbance. While pigs appear to play an important role in the organization of these communities, their removal may have a negligible impact on the success of many of the common weeds in the area. Web of Science Many United States Hawaii Hawaii Volcanoes National Park 19.3333 -155.25 Statistical/Meta-analysis terrestrial Tropical Forest Invasion Hyp. Mutualism Facilitation;Disturbance primary 1122 RICE, KJ; MACK, RN 1991 ECOLOGICAL GENETICS OF BROMUS-TECTORUM .3. THE DEMOGRAPHY OF RECIPROCALLY SOWN POPULATIONS journal OECOLOGIA 88 1 91 101 By incorporating demographic analyses of fitness components (e.g., survival and reproduction) within a reciprocal sowing design, we tested for 3 consecutive years whether local adaptation has occurred in the alien grass Bromus tectorum (cheatgrass) within 7 habitats along an environmental gradient from arid steppe to subalpine forest in the Intermontain Region of western North America. Patterns of emergence and survival were strongly influenced by the local environment. In terms of survival, expression of significant local adaptation in Tsuga heterophylla habitat varied among years. In contrast, relative differences in flowering time among seed sources were stable across sites and years. Populations from the arid steppe were the earliest to flower; flowering was latest in populations from the mesic Tsuga heterophylla habitat. In terms of net reproductive rate, evidence for local adaptation in B. tectorum was obtained in populations from habitats representing environmental extremes: an arid, saline site dominated by the shrub Sarcobatus vermiculatus and clearings within the cool, mesic Tsuga heterophylla forest habitat. Unlike the plants introduced from other sites, members of the resident population at the Sarcobatus site flowered and produced seeds before soil water became limiting. In contrast, net reproductive rates in other habitats were sometimes the lowest for populations in their home site. This lack of an advantage for local populations within more environmentally moderate sites suggests that limited dispersal may restrict the rate at which superior genotypes are introduced into a particular site. Web of Science Bromus tectorum USA Washington Field - Experimental terrestrial Mountain;Chaparral/Shrublands Invasion Hyp. Evolution in General primary 1123 RICE, KJ; MACK, RN 1991 ECOLOGICAL GENETICS OF BROMUS-TECTORUM .2. INTRASPECIFIC VARIATION IN PHENOTYPIC PLASTICITY journal OECOLOGIA 88 1 84 90 For Bromus tectorum, an alien annual grass now widespread in western North America, we assessed the sensitivity of the phenotypic expression of populational differences in phenology and demography to variation in plant density. Plants were grown in an unheated glasshouse from seeds collected from six habitat types located along a moisture-temperature gradient. Survival to flowering was high with a mean overall survival of 91%. Survival was highest among plants from the coolest, most mesic site. Time to first flowering decreased at the higher sowing density and was dependent on seed source. Plant dry weight and average seed production was lowest within high density plots; the magnitude of this reduction was significantly dependent on seed source. Individual seed weight was also dependent on the interaction of seed source and sowing density. Seed weight did not vary as much as seed number or plant weight in response to density. Differences among sources in hierarchies of plant size and seed production were detected at low sowing densities. The degree of inequality in the distributions of plant size and seed number increased at high density. Web of Science Bromus tectorum USA Wasington Greenhouse terrestrial Mountain;Chaparral/Shrublands Invasion Hyp. Plasticity primary 1127 BERMAN, J; CARLTON, JT 1991 MARINE INVASION PROCESSES - INTERACTIONS BETWEEN NATIVE AND INTRODUCED MARSH SNAILS journal JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 150 2 267 281 We test two hypotheses to explain the success of a biological invader in marshes on the Pacific coast of North America. The first hypothesis focuses on the competitive superiority of an invading species over native species; the second hypothesis focuses on the absence of ecological equivalents in the aboriginal biota, such that no competitive interactions are necessary to facilitate successful invasion. As a model system we experimentally manipulated the introduced pulmonate snail Ovatella myosotis and the native prosobranch snails Assiminea californica and Littorina subrotundata. Manipulations included pair-wise enclosures to determine if Ovatella depressed the growth of the native species; pair-wise associations to determine whether or not snails demonstrated negative or positive clustering; removal experiments to see if native snails invaded regions occupied by Ovatella, and reciprocal transplants on a vertical gradient to determine the physiological breadth of the target species. In addition to monitoring population abundances of all three species seasonally, dietary overlap of these three gastropods was also examined. No evidence of competitive superiority by Ovatella was found. Ovatella possesses the physiological capacities to exist in a semiterrestrial environment and is therefore able to take advantage of resources unavailable to native gastropods. We conclude that the successful establishment of this Atlantic snail in the Pacific Northwest did not arise at the expense of native species. Web of Science Ovatella myosotis USA Oregon Field - Experimental marine Intertidal/Near Shore Invasion Hyp. Inherent Superiority;Empty Niche Superior Competitor herbivore 1132 RICHARDSON, DM; BOND, WJ 1991 DETERMINANTS OF PLANT-DISTRIBUTION - EVIDENCE FROM PINE INVASIONS journal AMERICAN NATURALIST 137 5 639 668 The question of which factors limit the occurrence of a plant species to a particular site is addressed by considering 53 cases in which the distribution of pines (Pinus species; Pinaceae) has changed in the last century. We consider expansions of pines in and adjacent to their natural ranges in the Northern Hemisphere and the spread from sites of introduction in the Southern Hemisphere well outside the contemporary range of pines. We first consider a neutral hypothesis (with respect to climate or biological interactions as determinants of invasion): invasion simply requires that a species is present in sufficient numbers, with sufficient propagules over sufficient time to invade. We then explore the relative importance of climatic changes. disturbance, competition (including competition between seedlings and herbaceous plants during early establishment), herbivory, pathogens, and other agents that might influence pine membership in communities. Determinants of susceptibility to invasion often interact in a complex fashion. Environmental stresses created by moisture and temperature appear to exercise primary control on invasibility at xeric and high-elevation sites, respectively, but play a smaller role at intermediate locations. At these sites, range limits are determined principally by interactions between pine seedlings and the resident biota in adjacent communities. This suggests that the effects of predicted global warming on the distribution of pines are unlikely to be simple functions of temperature or precipitation. except at climatic extremes. Pine invasions are most prevalent where there is limited competition in the regeneration niche and occur more easily in habitats where the dominant growth form is most different from that of pines, namely, in grasslands. The disturbance regime in the receiving habitat is important and interacts directly and indirectly with the *inherent* susceptibility to invasion. Severe disturbances may initiate pine invasions at any latitude, but are essential for reducing the cover of vigorous plant growth (and hence competition in the regeneration niche) in tropical and near-tropical regions. Contemporary practices such as deforestation and increased grazing pressure and those practices leading to accelerated erosion, modified fire regimes, and climate amelioration essentially duplicate ice-age stresses and disturbances that shaped plant communities in the Holocene. The fundamental role of biotic factors (either direct or indirect) in regulating the distribution of pines is discussed with reference to aspects of land husbandry including the management of biological invasions. Web of Science Many Statistical/Meta-analysis terrestrial Coniferous Forest Fundamentals primary 1136 STANIFORTH, RJ; SCOTT, PA 1991 DYNAMICS OF WEED POPULATIONS IN A NORTHERN SUB-ARCTIC COMMUNITY journal CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE 69 4 814 821 The introduced flora of Churchill, northern Manitoba, was studied to draw some conclusions about the dynamics of weeds in northern subarctic communities in general. One hundred and six introduced species have been recorded at Churchill. Fiftyfive percent of these were *temporary,* dying out when original colonizers senesced (e.g., Avena spp., Setaria viridis). Seventeen percent were *established,* i.e., able to set viable seed and maintain their populations (e.g., Thlaspi arvense, Crepis tectorum). Twenty-eight percent *persisted* locally by vegetative propagation or repeated seed input (e.g., Linaria vulgaris, Chenopodium album s.l.). The findings were compared with those of an earlier study. The number of species and their local distributions around Churchill have increased in the last 30 years. This may be due to an increase and diversification in the traffic with southern regions or to an amelioration in the climate. Although one in five species in the vicinity of Churchill are introduced, usually fewer than 12 weed species were established at any one site. Abandoned sites exhibited a rapid disappearance of weeds. Depauperate individuals of a few species were found away from inhabited areas, with none occurring in natural communities. Organic material in refuse tips provided a mild environment with a long growing season. Refuse tips may act as refuges for weeds and as potential sources of their seeds. Aliens that were successful at seed product on were either perennials, winter annuals, or biennials. These plants flowered early and hence are able to ripen their seeds. Years with long growing seasons may allow seed production in otherwise temporary species. Dynamics of weedy species around Churchill will likely reflect current and (or) future events in other, more isolated northern communities. Web of Science Many Canada Manitoba Field - Observational terrestrial Fundamentals primary 1145 CHAPMAN, HM; BANNISTER, P 1990 THE SPREAD OF HEATHER, CALLUNA-VULGARIS (L) HULL, INTO INDIGENOUS PLANT-COMMUNITIES OF TONGARIRO NATIONAL-PARK journal NEW ZEALAND JOURNAL OF ECOLOGY 14 0 7 16 The vegetation of 10 quadrats from each of 26 sites, in and around the Tongariro National Park, which contained the introduced dwarf shrub, Calluna vulgaris (L.) Hull, was analysed using Reciprocal Averaging and Indicator Species Analysis. Six major plant communities were recognised and related to previous mapping units: tussockland with shrubs and herbs (red tussock tussockland); heathland with tussock and Dracophyllum subulatum (monoao-red tussock tussock-shrubland); communities of herbfield and scoria slopes ([mountain inaka] gravelfield); Calluna-dominated tussock or heathland (heather-red tussock tussock shrubland and heathland shrubland); Gleichenia/Empodisma bog (red tussock/wire rush-gleichenia rushland); and weed/scrub communities of disturbed ground (unmapped). An ordination of the sites showed that the major directions of variation in the vegetation were associated with altitude and soil moisture. Calluna had increased in extent since the area was mapped in 1960, and has been observed to have increased further since this survey was completed in 1984. Calluna has a potential to spread in all the recognised communities, although increases have been greatest in tussock grassland and on disturbed ground at lower altitudes and least in boggy areas. Calluna thus remains a threat to the natural vegetation of the Park, although some areas may be equally liable to succeed to taller vegetation. It is suggested that future research should be directed towards the effective control of heather within the Park. Web of Science Calluna vulgaris New Zealand Tongariro National Park Field - Observational;Statistical/Meta-analysis terrestrial Chaparral/Shrublands Invasion Hyp. Disturbance primary 1146 MORIN, MP; CONANT, S 1990 NEST SUBSTRATE VARIATION BETWEEN NATIVE AND INTRODUCED POPULATIONS OF LAYSAN FINCHES journal WILSON BULLETIN 102 4 591 604 On Laysan Island, the endangered, endemic Laysan Finch (Telespiza cantans) nests almost exclusively in the native bunchgrass Eragrostis variabilis. Experimental nest boxes provided were never used for nesting. Marine debris was not used as nest substrate on Laysan Island. In contrast, the introduced Laysan Finch populations on four islands at Pearl and Hermes Reef used a wide variety of native and alien plants as nest substrates, as well as various kinds of human-made debris. However, nest boxes provided at Pearl and Hermes Reef were not used as nest substrates by finches. Eragrostis variabilis is uncommon on Pearl and Hermes Reef, except on Seal-Kittery Island, but is common on Laysan where it is the preferred nest substrate. Eragrostis is a dense bunchgrass which probably provides the nest with good protection from sun, rain, wind, disturbance, and predators. On Pearl and Hermes Reef, where Eragrostis variabilis is uncommon, other plants that provide dense cover are used as nest substrates, and human-made debris that provides some cover is also utilized. It is unclear why nest boxes were never used as nest substrates at either site. We suggest that the conservation of Laysan Finches on Laysan Island will require the maintenance of a native ecosystem where Eragrostis variabilis is a major vegetation component. Otherwise, changes in behavior, morphology, and energy expenditure associated with environmental differences are likely to occur, and may have already occurred in the introduced populations on Pearl and Hermes Reef. Web of Science Telespiza cantans United States Hawaii Field - Experimental;Field - Observational terrestrial Grassland Fundamentals omnivore 1155 POTVIN, C; SIMON, JP 1989 THE EVOLUTION OF COLD TEMPERATURE ADAPTATION AMONG POPULATIONS OF A WIDELY DISTRIBUTED C-4 WEED - BARNYARD GRASS journal EVOLUTIONARY TRENDS IN PLANTS 3 2 98 105 Web of Science Echinochloa crus-galli Lab terrestrial Fundamentals primary 1160 MCINTYRE, S; LADIGES, PY; ADAMS, G 1988 PLANT SPECIES-RICHNESS AND INVASION BY EXOTICS IN RELATION TO DISTURBANCE OF WETLAND COMMUNITIES ON THE RIVERINE PLAIN, NSW journal AUSTRALIAN JOURNAL OF ECOLOGY 13 4 361 373 Web of Science Many Australia New South Wales Riverine plain -34.64 145.86 Field - Observational terrestrial Wetland Invasion Hyp. Community Species Richness;Disturbance primary 1162 HOBBS, RJ; ATKINS, L 1988 EFFECT OF DISTURBANCE AND NUTRIENT ADDITION ON NATIVE AND INTRODUCED ANNUALS IN PLANT-COMMUNITIES IN THE WESTERN AUSTRALIAN WHEAT-BELT journal AUSTRALIAN JOURNAL OF ECOLOGY 13 2 171 179 Web of Science Many Australia Western Australia Durokoppin Reserve -31.4084 117.75845 Field - Experimental;Field - Observational terrestrial Broadleaf Evergreen Forest;Chaparral/Shrublands;Old Field Invasion Hyp. Fluctuating Resources;Disturbance primary 1171 KLOOT, PM 1987 THE INVASION OF KANGAROO ISLAND BY ALIEN PLANTS journal AUSTRALIAN JOURNAL OF ECOLOGY 12 3 263 266 Web of Science Many Australia Kangaroo Island Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Other primary 1175 LANDA, V; SOLDAN, T 1986 INVASIVE BEHAVIORAL-PATTERNS OF MAYFLIES (INSECTA, EPHEMEROPTERA) IN SOME MAN-INFLUENCED AQUATIC BIOTOPES IN CZECHOSLOVAKIA journal EKOLOGIA CSFR 5 3 239 246 Web of Science Many Czechoslovakia Field - Observational lentic;lotic Invasion Hyp. Inherent Superiority;Disturbance Broad Tolerances herbivore;decomposer;filter 1181 PARKIN, DT; COLE, SR 1985 GENETIC DIFFERENTIATION AND RATES OF EVOLUTION IN SOME INTRODUCED POPULATIONS OF THE HOUSE SPARROW, PASSER-DOMESTICUS IN AUSTRALIA AND NEW-ZEALAND journal HEREDITY 54 0 15 23 Web of Science Passer domesticus Australia; New Zealand Field - Observational;Lab terrestrial Fundamentals omnivore 1206 OSMOND, CB; NOTT, DL; FIRTH, PM 1979 CARBON ASSIMILATION PATTERNS AND GROWTH OF THE INTRODUCED CAM PLANT OPUNTIA-INERMIS IN EASTERN AUSTRALIA journal OECOLOGIA 40 3 331 350 Web of Science Opuntia inermis Australia New South Wales; Queensland Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Preadaptation to Climate primary 1210 NAYAR, BK; SWORUPANANDAN, K 1978 MORPHOLOGY OF FRUIT AND MECHANISM OF SEED DISPERSAL OF FRESHWATER WEED LIMNOCHARIS-FLAVA journal PROCEEDINGS OF THE INDIAN ACADEMY OF SCIENCES SECTION B 87 2 49 53 Web of Science Limnocharis flava India Kerala Field - Observational lentic;lotic Invasion Hyp. Inherent Superiority Effective Disperser primary 1212 BASKIN, JM; BASKIN, CC 1977 ROLE OF TEMPERATURE IN GERMINATION ECOLOGY OF 3 SUMMER ANNUAL WEEDS journal OECOLOGIA 30 4 377 382 Web of Science Ambrosia artemisiifolia; Chenopodium album; Amaranthus retroflexus USA Kentucky Greenhouse terrestrial Old Field Fundamentals primary 1215 GAUDET, JJ 1973 GROWTH OF A FLOATING AQUATIC WEED, SALVINIA UNDER STANDARD CONDITIONS journal HYDROBIOLOGIA 41 1 77 106 Web of Science Salvinia molesta Uganda Kampala Lab lentic;lotic Invasion Hyp. Inherent Superiority Rapid Growth primary 1220 SCARISBR.DH; HARVEY, HJ; IVINS, JD 1970 EFFECT OF CUTTING ON SUBSEQUENT GROWTH OF INTRODUCED RIBGRASS (PLANTAGO-LANCEOLATA) SEEDLINGS journal JOURNAL OF THE BRITISH GRASSLAND SOCIETY 25 3 207 & Web of Science Plantago lanceolata England Greenhouse terrestrial Grassland Invasion Hyp. Disturbance primary 1226 PIMENTEL, D 1966 POPULATION ECOLOGY OF INSECT INVADERS OF MARITIME PROVINCES journal CANADIAN ENTOMOLOGIST 98 8 887 & Web of Science Many Canada Ontario; Quebec Field - Observational terrestrial;marine Urban;Old Field Invasion Hyp. Community Species Richness;Disturbance herbivore 1229 Rosas, HL; Moreno-Casasola, P; Mendelssohn, IA 2006 Effects of experimental disturbances on a tropical freshwater marsh invaded by the African grass Echinochloa pyramidalis journal WETLANDS 26 2 593 604 Perennial African C4 grasses are highly successful invaders in tropical and subtropical environments. One of these species, Echinochloa pyramidalis, has been introduced in the freshwater wetlands of the Mexican tropics. This alien species reduces biodiversity by replacing native species. The removal of non-indigenous species from invaded communities often requires different techniques such as physical, chemical, or biological controls. We evaluated the effects of mechanical (cutting or soil-disking) and chemical (spraying Round Up (TM) herbicide) disturbance treatments on the plant community of a freshwater marsh invaded by E. pyramidalis. We predicted that intense disturbance would eliminate this African grass from the experimental plots. Over a nine-month period, we analyzed species cover, richness, and diversity in experimental plots that received different disturbance treatments. Also, we measured the aerial biomass at the end of the experiment. The treatment that best reduced the dominance of E. pyramidalis and increased the diversity of native species was soil disking, but this was not enough to eliminate the grass. After nine months, E. pyramidalis recovered in all the treatments and again became the dominant species. To eliminate this species completely, it is necessary to recreate the natural topography and hydrology of the wetland and to select control mechanisms that disrupt those growth characteristics (e.g., rapid propagation from rhizomes and horizontal expansion via tillers) that make this grass more competitive than native species. Web of Science Echinochloa pyramidalis Mexico 19.6 -96.3778 Field - Experimental terrestrial Wetland Invasion Hyp. Disturbance primary 1231 Acosta, A; Izzi, CF; Stanisci, A 2006 Comparison of native and alien plant traits in Mediterranean coastal dunes journal COMMUNITY ECOLOGY 7 1 35 41 This study is part of a general project to analyse the biological and ecological mechanisms that influence the invasion of Mediterranean sand dune ecosystems by alien plants. In this paper we analyse the morphological and functional traits of coastal dune wild species (natives and aliens) based mainly on information from the literature. The most common 130 wild species occurring on the recent (Holocenic) coastal dunes were included considering the invasive status of alien plants. A comparative analysis of functional groups was performed through ordination techniques (PCoA using the Gower index). This reveals four functional groups related to the most important plant communities in coastal vegetation zonation. Alien plants were found in all functional groups and no trait or set of traits was specifically related to them. This indicates that aliens show similar traits to those natives growing in different communities of the coastal dune zonation, from the small beach annuals to the evergreen taller shrubs of the Mediterranean macchia. When the invasive status of alien species was taken into account, however, some differences emerged: a) casual aliens were found in almost all groups but their traits were not interpreted as being due to any particular adaptive strategy; b) naturalised aliens were only found in the less fluctuating habitats of the inner coastal zones; c) invasive alien species were connected with two major plant strategies: annual invasive aliens (quick-to-mature low grasses and herbs) and perennial invasive aliens (taller and often strongly clonal). Web of Science Many Italy Lazio; Molise 41.43 13.3 Statistical/Meta-analysis;Review terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority Rapid Growth;Clonal Reproduction primary 1232 Govindarajulu, P; Price, WS; Anholt, BR 2006 Introduced bullfrogs (Rana catesbeiana) in western Canada: Has their ecology diverged? journal JOURNAL OF HERPETOLOGY 40 2 249 260 Organisms can diverge in life history when introduced outside their native range due to release from predators, competitors, and parasites, and also due to genetic drift and local adaptation. We studied the ecology of the American Bullfrog (Rana catesbeiana) in its introduced range in British Columbia (BC). To assess differences between introduced and native populations, we compared the population ecology of BC bullfrogs to published life-history parameters from the bullfrog's extensive native range in eastern North America. In BC, bullfrogs emerged from hibernation in late April and early May. Breeding choruses developed fully when air temperatures exceeded 20 degrees C. Eggs were laid from mid-June to mid-July when the mean water temperature was 20 degrees C. Mean egg mass size was 13,014 +/- 7,296 eggs (mean standard deviation). Tadpoles hatched in 3 to 5 days and overwintered the first year as tadpoles. Approximately 68% of the tadpoles metamorphosed at the end of the following summer, but the remaining spent a second winter in the pond. Bullfrogs were large enough to attain sexual maturity 2 yr after metamorphosis. Bullfrog population density among ponds varied from 4.1 to 530 frogs/ha. Terrestrial insects were the primary prey item of bullfrogs < 150 g, whereas frogs were the primary prey item of larger bullfrogs. The life-history parameter values estimated for BC bullfrogs were within the range observed for bullfrogs in their native habitats. Due to milder weather conditions in southwestern BC, the seasonal pattern and growth rate of bullfrogs were similar to lower latitude populations in Kentucky and Missouri. We found no evidence to support the hypothesis that when released from native predators and parasites bullfrogs build up to unusually high population densities or attain significantly larger sizes in their introduced range. Web of Science Rana catesbeiana Canada British Columbia Victoria 48 -123 Field - Observational lentic Pelagic/Open Ocean Invasion Hyp. Enemy Release predator 1236 Drake, JM; Drury, KLS; Lodge, DM; Blukacz, A; Yan, ND; Dwyer, G 2006 Demographic stochasticity, environmental variability, and windows of invasion risk for Bythotrephes longimanus in North America journal BIOLOGICAL INVASIONS 8 4 843 861 Biological invasions are a leading threat to freshwater biodiversity worldwide. A central unanswered question of invasion ecology is why some introduced populations establish while most fail. Answering this question will allow resource managers to increase the specificity and effectiveness of control efforts and policy. We studied the establishment of spiny water flea (Bythotrephes longimanus) in the United States and Canada by modeling introduction failure caused by demographic stochasticity, environmental variation, and seasonal environmental forcing. We compared predicted establishment rates with observed invasions of inland lakes in Ontario, Canada. Our findings suggest that environmental forcing can cause *windows* of invasion opportunity so that timing of introductions might be a greater determinant of population establishment than demographic stochasticity and random environmental variation. We expect this phenomenon to be exhibited by species representing a wide range of life histories. For spiny water flea in North America, a large window of invasion opportunity opens around the fourth week of May, persists through the summer, and closes with decreasing water temperatures in autumn. These results show how timing of introductions with respect to seasonally forced environmental drivers can be a key determinant of establishment success. By focusing on introductions during windows of invasion opportunity, resource managers can more effectively control invasion rates. Web of Science Bythotrephes longimanus United States; Canada Theoretical/Modeling lentic Pelagic/Open Ocean Invasion Hyp. Fluctuating Resources;Disturbance predator 1238 Labrie, G; Lucas, E; Coderre, D 2006 Can developmental and behavioral characteristics of the multicolored Asian lady beetle Harmonia axyridis explain its invasive success? journal BIOLOGICAL INVASIONS 8 4 743 754 Major impacts of biological invasions are widely recognized and underscore the need to understand the relation between life-history traits of invasive species and the invasion process. Growth of juveniles and adult survival of invasive species are key factors in invasion process. Life-history traits that increase juvenile fitness including increased rates of development and behavioral characteristics that facilitate competitive success such as increased predator efficiency and foraging ability may explain invasiveness of a species. Invasion of Harmonia axyridis Pallas (Coleoptera: Coccinellidae) in North America provides an opportunity to investigate life-history traits of juveniles of an invasive species. Here, we evaluate both developmental and behavioral traits that may explain the success of H. axyridis by comparing it to an ecologically similar indigenous species Coleomegilla maculata lengi Timberlake (Coleoptera: Coccinellidae). Three points may contribute to the invasiveness of H. axyridis. First, development of H. axyridis was faster during the 2nd larval instar than C. maculata, a characteristic that may reduce vulnerability at young instars. Second, H. axyridis reached the 4th instar more rapidly than C. maculata. The 4th instar of H. axyridis was also characterized by higher predation efficiency with increased voracity, lethal contact and search efficiency of pea aphids Acyrthosiphon pisum. Finally, surprisingly, a 5th larval instar occured in 33% of the individuals of H. axyridis and was characterized by the same developmental time, but with increased voracity and weight gain compared to 4th larval instars, suggesting an increased fitness of these individuals. These developmental characteristics coupled with increased predation efficiency and behavioral characteristics enhanced the juvenile growth and predatory abilities of this species and may contribute to the invasive ability of H. axyridis. Web of Science Harmonia axyridis Canada Quebec Montreal 45.35 -74 Lab terrestrial Invasion Hyp. Inherent Superiority Rapid Growth herbivore 1241 Marushia, RG; Holt, JS 2006 The effects of habitat on dispersal patterns of an invasive thistle, Cynara cardunculus journal BIOLOGICAL INVASIONS 8 4 577 593 Dispersal of offspring is a critical step in the spread of invasive species, yet dispersal patterns are seldom well studied, inhibiting effective management and ecological understanding of invasions. Dispersal patterns can be affected by characteristics of the parent plant and by climatic or site characteristics, including community vegetation structure, but these factors have not been studied in the context of plant invasion processes. Cynara cardunculus (L.) is a polycarpic perennial thistle invasive in coastal grasslands in California that produces large numbers of wind-dispersed seeds. This study quantified and compared C. cardunculus dispersal patterns in an exotic grassland (vegetated site) and an agricultural field (non-vegetated site). Seed size variation in C. cardunculus was also quantified within inflorescences, between inflorescences, and between years of production, and compared across dispersal distances. Results indicate that dispersal distance increased dramatically from less than 20 m in the vegetated site to more than 40 m in the non-vegetated site. Plants producing fewer seeds produced heavier seeds and dispersal distance decreased over time, but seed size was not related to dispersal distance, which may serve to spread the risk to seeds or seedlings across the environment. C. cardunculus has great potential for dispersal in open areas such as agricultural fields or disturbed sites, but may be limited in highly structured natural communities. Management of C. cardunculus and other wind-dispersed plant invasions may be improved by prioritizing populations with open or disturbed areas downwind and minimizing the removal of vegetation during dispersal. Web of Science Cynara cardunculus United States California Crystal Cove State Park 33.585351 -117.802134 Field - Experimental;Garden terrestrial Grassland Fundamentals primary 1242 Johnson, VS; Litvaitis, JA; Lee, TD; Frey, SD 2006 The role of spatial and temporal scale in colonization and spread of invasive shrubs in early successional habitats journal FOREST ECOLOGY AND MANAGEMENT 228 3 124 134 Early successional habitats are becoming increasingly scarce in the northeastern United States and may require additional management to support the diverse groups of plants and animals that are dependent on them. Because these habitats require some form of disturbance to maintain them, they may be especially vulnerable to exotic plant invasions. We examined the vulnerability to invasion of 44 early successional sites in southeastern New Hampshire using a two-tiered approach. Colonization (Tier 1, based on presence/absence) and establishment and spread (Tier 2, based on percent coverage of an occupied site) of invasive shrubs among patches of early successional habitat were related to landscape and local habitat features. Landscape elements (e.g., amount of disturbed lands within I km of the invaded patch) and features described at a local scale (e.g., soil pH and clay content) were associated with colonization, whereas spread of invasive shrubs at a patch of early successional habitat was described exclusively by local features. Prevalence of agricultural fields (historic and present day) was the most influential feature affecting both colonization and spread of invasive shrubs. Results of this study provided an approach for identifying early successional habitats that may be especially prone to exotic shrub invasions. Although our models explained only a portion of the vulnerability of a site to invasion, we suggest that an evaluation of factors that operate at different spatial scales provided new insight on the habitat characteristics that influence the range expansion of invasive plants. (c) 2006 Elsevier B.V. All rights reserved. Web of Science Many United States New Hampshire Field - Observational terrestrial Deciduous Forest;Coniferous Forest Invasion Hyp. Disturbance primary 1244 Birken, AS; Cooper, DJ 2006 Processes of Tamarix invasion and floodplain development along the lower Green River, Utah journal ECOLOGICAL APPLICATIONS 16 3 1103 1120 Significant ecological, hydrologic, and geomorphic changes have occurred during the 20th century along many large floodplain rivers in the American Southwest. Native Populus forests have declined, while the exotic Eurasian shrub, Tamarix, has proliferated and now dominates most floodplain ecosystems. Photographs from late 19th and early 20th centuries illustrate wide river channels with largely bare in-channel landforms and shrubby higher channel margin floodplains. However, by the mid-20th century, floodplains supporting dense Tamarix stands had expanded, and river channels had narrowed. Along the lower Green River in eastern Utah, the causal mechanism of channel and floodplain changes remains ambiguous due to the confounding effects of climatically driven reductions in flood magnitude, river regulation by Flaming Gorge Dam, and Tamanix invasion. This study addressed whether Tamarix establishment and spread followed climate- or dam-induced reductions in annual peak flows or whether Tamarix was potentially a driver of floodplain changes. We aged 235 Tamarix and 57 Populus individuals, determined the hydrologic and geomorphic processes that controlled recruitment, identified the spatial relationships of germination sites within floodplain stratigraphic transects, and mapped woody riparian vegetation cohorts along three segments of the lower Green River. The oldest Tamarix established along several sampling reaches in 1938, and 1.50-2.25 in of alluvium has accreted above their germination surfaces. Nearly 90% of the Tamarix and Populus samples established during flood years that exceeded the 2.5-year recurrence interval. Recruitment was most common when large floods were followed by years with smaller peak flows. The majority of Tamarix establishment and Green River channel narrowing occurred long before river regulation by Flaming Gorge Dam. Tamarix initially colonized bare instream sand deposits (e.g., islands and bars), and most channel and floodplain changes followed the establishment of Tamarix. Our results suggest that Tamarix recruitment was triggered by large annual floods that were followed by years with lower peak flows, not by periods of low flow alone. Tamarix appears to have actively invaded floodplains, while Populus colonization has been limited. Thus, Tamarix invasion may have greatly influenced floodplain development and riparian vegetation composition along the lower Green River since the early 20th century. Web of Science Tamarix sp. United States Utah 40.8811 -109.4208 Field - Observational terrestrial Riparian Impacts;Invasion Hyp. Climate Change primary 1247 Guo, QF; Qian, H; Ricklefs, RE; Xi, WM 2006 Distributions of exotic plants in eastern Asia and North America journal ECOLOGY LETTERS 9 7 827 834 Although some plant traits have been linked to invasion success, the possible effects of regional factors, such as diversity, habitat suitability, and human activity are not well understood. Each of these mechanisms predicts a different pattern of distribution at the regional scale. Thus, where climate and soils are similar, predictions based on regional hypotheses for invasion success can be tested by comparisons of distributions in the source and receiving regions. Here, we analyse the native and alien geographic ranges of all 1567 plant species that have been introduced between eastern Asia and North America or have been introduced to both regions from elsewhere. The results reveal correlations between the spread of exotics and both the native species richness and transportation networks of recipient regions. This suggests that both species interactions and human-aided dispersal influence exotic distributions, although further work on the relative importance of these processes is needed. Web of Science Many Eastern Asia; North America Statistical/Meta-analysis terrestrial Invasion Hyp. Enemy Release;Community Species Richness;Disturbance;Other primary 1251 Florentine, SK; Westbrooke, ME; Gosney, K; Ambrose, G; O'Keefe, M 2006 The and land invasive weed Nicotiana glauca R. Graham (Solanaceae): Population and soil seed bank dynamics, seed germination patterns and seedling response to flood and drought journal JOURNAL OF ARID ENVIRONMENTS 66 2 218 230 Disturbances in plant communities provide opportunities for weed germination, propagation, spread, and invasion. When the population density of a weed increases, fast-tracked and appropriate control management strategies are required. The objectives of this study were to: (i) examine the population and soil seed bank dynamics of Nicotiana glauca; (ii) compare the germination patterns of invasive N. glauca seeds collected from two states in Australia, and (iii) investigate the impact of a flood in September 1997 and subsequent drought on N. glauca seedlings. The density of N. glauca followed a steep positive increment during the sampling time (September 1999 to October 2004). The increment pattern was similar in flooded fenced and unfenced plots. Plant density increased over much of the observation period, but had declined to 80 and 432 stems ha(-1), respectively, by October 2004. Stem density recorded in October 2004 along two transects radiating from the central point of the newly created lake demonstrated that a significant number of stems appeared to be dead. A soil seed bank study revealed that seed density varied significantly (p = 0.0001) between flooded fenced (598.75 +/- 71) and flooded unfenced (327.5 +/- 66) plots. In contrast, no N. glauca seedlings were recruited from-the soil collected from the control plots. Germination trials were undertaken on N. glauca seed collected from New South Wales. There was no significance difference detected between treatments light and temperature. Similarly, no interaction was found between light and temperature. A comparative study on seed germination patterns of N. glauca seeds collected from Ivanhoe, New South Wales, and the Flinders Ranges, South Australia, showed that temperature had a significant effect on N. glauca seed germination. The effect varied significantly with main variables (state, length and time) and also with different interactions, except state x light (P = 0.3840). N. glauca seedlings exposed to flood were found to withstand partial flooding for at least 58 days. Under waterlogged conditions, the seedlings showed stem hypertrophy and produced adventitious roots. Only one seedling was found dead in the drought treatment. In conclusion, it is clear that N. glauca invaded the area after a rare flood event and began to function as a casual weed. Established seedlings in the field can withstand extreme ecological events such as flood and drought. Understanding the plants' ecological characteristics through a study such as this at an early rather than late stage in the invasion will help us to take appropriate control measures for this species. (c) 2005 Elsevier Ltd. All rights reserved. Web of Science Nicotiana glauca Australia New South Wales; South Australia -33.15;-30.35 144.1167;139.3667 Lab terrestrial Riparian Invasion Hyp. Disturbance primary 1254 Lewis, KC; Bazzaz, FA; Liao, Q; Orians, CM 2006 Geographic patterns of herbivory and resource allocation to defense, growth, and reproduction in an invasive biennial, Alliaria petiolata journal OECOLOGIA 148 3 384 395 We investigated geographic patterns of herbivory and resource allocation to defense, growth, and reproduction in an invasive biennial, Alliaria petiolata, to test the hypothesis that escape from herbivory in invasive species permits enhanced growth and lower production of defensive chemicals. We quantified herbivore damage, concentrations of sinigrin, and growth and reproduction inside and outside herbivore exclusion treatments, in field populations in the native and invasive ranges. As predicted, unmanipulated plants in the native range (Hungary, Europe) experienced greater herbivore damage than plants in the introduced range (Massachusetts and Connecticut, USA), providing evidence for enemy release, particularly in the first year of growth. Nevertheless, European populations had consistently larger individuals than US populations (rosettes were, for example, eightfold larger) and also had greater reproductive output, but US plants produced larger seeds at a given plant height. Moreover, flowering plants showed significant differences in concentrations of sinigrin in the invasive versus native range, although the direction of the difference was variable, suggesting the influence of environmental effects. Overall, we observed less herbivory, but not increased growth or decreased defense in the invasive range. Geographical differences in performance and leaf chemistry appear to be due to variation in the environment, which could have masked evolved differences in allocation. Web of Science Alliaria petiolata United States; Hungary Massachusetts; Connecticut 47; 42 19; -72 Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Enemy Release primary 1255 Klinger, T; Padilla, DK; Britton-Simmons, K 2006 Two invaders achieve higher densities in reserves journal AQUATIC CONSERVATION-MARINE AND FRESHWATER ECOSYSTEMS 16 3 301 311 1. Invasive species threaten marine biodiversity on a global scale. 2. To test whether marine reserves provide resistance to invading species, the abundance of two conspicuous invaders, a seaweed and an oyster, were measured inside marine reserves and in comparable areas outside reserves in north-western Washington State. 3. Densities of both invaders were significantly higher in marine reserves than in comparable unprotected areas outside reserves. Although the causal mechanisms have not yet been identified, differential rates of human harvest do not appear to be responsible for the patterns observed. 4. It is provisionally suggested that physical or biological aspects of the reserves themselves may directly or indirectly facilitate biological invasion. Copyright (c) 2006 John Wiley & Sons, Ltd. Web of Science Sargassum muticum; Crassostrea gigas United States Washington Field - Observational marine Intertidal/Near Shore;Benthic Invasion Hyp. Other primary;filter 1261 Leport, L; Baudry, J; Radureau, A; Bouchereau, A 2006 Sodium, potassium and nitrogenous osmolyte accumulation in relation to the adaptation to salinity of Elytrigia pycnantha, an invasive plant of the Mont Saint-Michel Bay journal CAHIERS DE BIOLOGIE MARINE 47 1 31 37 Elytrigia pycnantha (Godr.) Love (also named E. aetherica or Elymus athericus) is a monocot species native of salt marshes of the Mont Saint-Michel Bay. Usually found at the landward edge of the bay, this grass plant is now spraying in the middle of the marsh and even at the tidal hat boundaries. In this study, we have outlined some biochemical traits that may be linked to the spread of this invasive native clonal grass. Plants were collected at the west part of the bay (Le Vivier sur mer) along the salt marsh zonation, some of them were grown further in a glasshouse under different NaCl concentrations and nitrogen sources while others were analysed immediately without treatment. The plants collected from the bay and those treated under controlled conditions were sampled according to different vegetative organs, frozen dried, and water soluble compounds extracted. Potassium and sodium contents were measured by flam photometry and amino acids and betaine through HPLC procedure analysis. It is shown that sodium accumulation and amino acid profiles depend both on the location of the plant on the salt marsh and on the plant organ. We have also highlighted an effect of the nitrogen source (no N, N-NO3- or N-NH4+) on plant response to salt treatment. It is suggested that recent ability of this species to spray is related to its ability to perform nitrogenous metabolic adjustment under new nitrogen source availability. Web of Science Elytrigia pycnantha France Mont Saint-Michel Bay 48.641337 -1.516142 Field - Observational;Greenhouse marine Wetland Invasion Hyp. Fluctuating Resources primary 1268 Hill, JP; Germino, MJ 2005 Coordinated variation in ecophysiological properties among life stages and tissue types in an invasive perennial forb of semiarid shrub steppe journal CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE 83 11 1488 1495 Semiarid lands of North America are vulnerable to invasion by exotic forbs that frequently have an extended phenology compared with native herbaceous species. We hypothesized that photosynthetic steins, rosette leaves, and cauline leaves of Centaurea maculosa Lam. (knapweed) would differ in ecophysiological specialization and that these differences would enhance plant carbon uptake across seasonal variations in microclimate. Photosynthesis, water relations, and morphological features of C. maculosa were measured under natural variations in temperature and soil water, and under manipulated light environments, in adults compared with seedlings having only rosette leaves. Carbon gain was greater in adults than in seedlings owing to high photosynthesis in cauline and rosette leaves when water was abundant. Otherwise, photosynthesis was relatively lower but persistent through drought in all tissues and ages until senescence. Photosynthesis decreased with water stress in all tissues except stems. Steins comprised up to 36% of photosynthetic area following senescence of rosette leaves during seasonal drought. Seedlings expressed shade acclimation compared with rosette and especially cauline leaves of adults, although adult rosette leaves had flexible photosynthetic light responses. Contrasting ecophysiological specializations of photosynthetic tissues enhance carbon gain of adult C. maculosa as light, water, and temperature vary during its relatively long growth season. Web of Science Centaurea maculosa United States Montana 45.593297; 46.597704 -111.026659; -111.830635 Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority primary 1269 Jactel, H; Menassieu, P; Vetillard, F; Gaulier, A; Samalens, JC; Brockerhoff, EG 2006 Tree species diversity reduces the invasibility of maritime pine stands by the bast scale, Matsucoccus feytaudi (Homoptera : Margarodidae) journal CANADIAN JOURNAL OF FOREST RESEARCH-REVUE CANADIENNE DE RECHERCHE FORESTIERE 36 2 314 323 Species-rich plant communities may be more resistant to invasive herbivores because of reduced host-plant accessibility and increased natural enemy diversity and abundance. We tested these hypotheses in Corsica, a Mediterranean island recently invaded by the maritime pine bast scale, Matsucoccus feytaudi Duc., which causes widespread tree mortality in Pinus pinaster Ait. The endemic Matsucoccus pini Green infests Corsican pine, Pinus nigra laricio Poiret, where it is controlled by the native predatory bug, Elatophilus nigricornis Zetterstedt. As revealed by kairomone trapping, E. nigricornis was most abundant in pure Corsican pine in areas not yet colonized by M. feytaudi, and in pure maritime pine its density decreased with the distance from the nearest Corsican pine forest. The abundance of M. feytaudi was compared in five pairs of Pure maritime pine and mixed maritime and Corsican pine stands. It was consistently higher in pure than in mixed maritime pine stands, whereas E. nigricornis showed the opposite pattern, and relative differences were correlated with the proportion of Corsican pine in the Mixture. The predation by E. nigricornis was manipulated in pure maritime pine stands using synthetic attractants of the predator. Matsucoccus feytaudi density was significantly reduced in maritime pines baited with kairomone dispensers. Web of Science Matsucoccus feytaudi France Corsica Field - Observational terrestrial Coniferous Forest Invasion Hyp. Community Species Richness herbivore 1273 Thorpe, AS; Archer, V; DeLuca, TH 2006 The invasive forb, Centaurea maculosa, increases phosphorus availability in Montana grasslands journal APPLIED SOIL ECOLOGY 32 1 118 122 Centaurea maculosa Lam. (Asteraceae, spotted knapweed) was introduced to the United States from Eurasia in the late 1800s and now covers over 3 million ha in Washington, Idaho, Montana, and Wyoming. Several recent studies have suggested that the success of C. maculosa may be partly due to its ability to outcompete native species for phosphorus (P), through high root mass and/ or association with arbuscular mycorrhizal fungi. We used a combination of field and greenhouse studies to explore the P efficiency of C maculosa and its effects on soil P levels. C maculosa was P efficient in both the field study and greenhouse experiment. In the field, P concentration in C maculosa was more than twice that of three native species (Pseudorogneria spicata, Festuca idahoensis, and Lupinus sericeous). In the greenhouse experiment, even at extremely low levels of soil P availability, uptake of P by C maculosa was six times greater than that by the native, Lupinus argenteus. However, soil P levels were elevated in sites invaded by C. maculosa, which is the opposite of what would be expected if root or mycorrhizal uptake were responsible for the higher P efficiency. These results indicate that the success of C maculosa may be due to its greater ability to acquire P than native species, but do not indicate that C maculosa is actually outcompeting natives for the P that it acquires. In contrast, C. maculosa appears to have the ability to increase the availability of P in some soils. (c) 2005 Elsevier B.V. All rights reserved. Web of Science Centaurea maculosa United States Montana Field - Experimental;Statistical/Meta-analysis terrestrial Grassland Impacts;Invasion Hyp. Inherent Superiority Superior Competitor primary 1274 Walling, SZ; Zabinski, CA 2006 Defoliation effects on arbuscular mycorrhizae and plant growth of two native bunchgrasses and an invasive forb journal APPLIED SOIL ECOLOGY 32 1 111 117 Centaurea maculosa, an invasive forb in western North American grasslands, dominates more than 4 million ha of rangeland in the Rocky Mountain region. Our research examined the effects of herbivory and arbuscular mycorrhizae (AM) on the growth of C maculosa, and two native grasses, Festuca idahoensis and Pseudoroegneria spicata. Plants were grown for I I weeks, with or without AM, prior to simulated herbivory. We removed 75% of aboveground biomass from half of the plants, and harvested all plants 4 weeks later. All species increased their growth rate after clipping, but clipped plants were smaller than unclipped plants. The difference in biomass between clipped and unclipped plants was smaller for C maculosa (clipped: unclipped = 0.62) than for the native grasses (0.42 and 0.52). Plants with AM were smaller than non-AM plants across all species, with the greatest reduction in F idahoensis (77% versus 18% in C maculosa and P. spicata). Levels of AM colonization were minimal in F idahoensis (< 1% of root length colonized), intermediate in P. spicata (13% colonization) and highest in C maculosa (20%). Extra radical hyphae (ERH) lengths were highest for C. maculosa, and equal between the two grasses. Because of the lower biomass, plant tissue N concentrations were higher in AM plants, but P concentrations increased in AM plants for only C. maculosa and P. spicata. The superior competitive ability of C. maculosa may be the result of greater compensatory growth after herbivory and higher amounts of ERH, both of which result in greater resource capture. (c) 2005 Elsevier B.V. All rights reserved. Web of Science Centaurea maculosa United States Greenhouse terrestrial Invasion Hyp. Enemy Release primary 1276 Meiman, PJ; Redente, EF; Paschke, MW 2006 The role of the native soil community in the invasion ecology of spotted (Centaurea maculosa auct. non Lam.) and diffuse (Centaurea diffusa Lam.) knapweed journal APPLIED SOIL ECOLOGY 32 1 77 88 Diffuse (Centaurea diffusa Lam.) and spotted knapweed (Centaurea maculosa auct. non Lam.) are damaging exotic plant invaders of North American rangelands. Although existing weed management techniques can successfully reduce negative impacts of knapweeds, these plants continue to spread in an unpredictable manner. The successful spread of knapweeds into native plant communities may be driven, in part, by interactions between these plants and native soil communities. This study was conducted to evaluate the relative benefit of native soil communities to two native plants and two knapweeds and to investigate the growth of these plants in soil from knapweed infestations and from adjacent native rangelands. Individual plants of bluebunch wheatgrass (Pseudoroegneria spicata (Pursh) A. Love), yarrow (Achillea millefolium L.), spotted and diffuse knapweed were grown in a greenhouse in field collected soil. The relative benefit of the native soil community was determined by comparing emergence and production of native plants and exotic knapweeds in autoclaved versus unautoclaved native rangeland soil. Emergence and production were also determined in the greenhouse for native plants and exotic knapweeds grown in soil collected from the core and perimeter of knapweed infestations and in soil from the adjacent, uninvaded native rangeland. The native soil community had a negative effect on the growth of bluebunch wheatgrass (P spicata (Pursh) A. Love) and diffuse knapweed, but a positive effect on spotted knapweed emergence. The interactions between yarrow (A. millefolium L.) and the native soil community were variable. The native soil community appears to be more beneficial to spotted knapweed than to the other plants studied, including diffuse knapweed. Therefore, it appears that two closely related knapweeds have very different interactions with soil biota and perhaps different strategies for invasion. Soil from diffuse and spotted knapweed infestations did not prevent growth of two native plants. Diffuse knapweed growth was not promoted by soil from within a diffuse knapweed infestation, but soil from the core of a spotted knapweed infestation did increase emergence of spotted knapweed. (c) 2005 Elsevier B.V. All rights reserved. Web of Science Centaurea diffusa; Centaurea maculosa United States Greenhouse terrestrial Grassland Invasion Hyp. Mutualism Facilitation primary 1286 Jensen, JM; Six, DL 2006 Myrmecochory of the exotic plant, Centaurea maculosa: A potential mechanism enhancing invasiveness journal ENVIRONMENTAL ENTOMOLOGY 35 2 326 331 We hypothesized that the elaiosomes of seeds of the invasive plant, Centaurea maculosa (spotted knapweed), elicit seed-dispersing behavior by native ants (myrmecochory), potentially providing a mechanism enhancing its invasiveness into native plant communities. Elaiosomes are small nutrient-rich nodes produced on seeds of some plants. Ants collect and disperse elaiosome-bearing seeds, later consuming the elaiosome, but usually discarding the seed intact away from the parent plant. The seeds of C. maculosa possess elaiosomes, suggesting that the dispersal of its seeds and its ability to rapidly spread into native habitats may be enhanced by myrmecochory. We tested for myrmecochory at two Palouse prairie sites in Montana by presenting seeds of C. maculosa and two native dominants, Balsamor-hiza sagittata (a forb) and Psuedoroegneria spicata (a bunchgrass). Seeds were presented in choice (seeds of all three plants) and no choice (seeds of only one plant) treatments. At both study sites, ants readily dispersed the seeds of the invasive plant, C. maculosa, while ignoring seeds of the native plants, B. sagittata and P. spicata. In addition, myrmecochory was not influenced when all three seed types were presented together. Different ant species were observed removing seeds from stations at each site, indicating that myrmecochory of C. maculosa seeds is not restricted to one ant species but rather may be a generalized response across ant communities. Our results indicate that myrmecochory may enhance dispersal of C. maculosa and facilitate its invasion into native plant communities. Web of Science Centaurea maculosa United States Montana 46.9262;46.9233 -114.0067;-114.0247 Field - Experimental terrestrial Grassland Invasion Hyp. Mutualism Facilitation primary 1287 Bartuszevige, AM; Gorchov, DL; Raab, L 2006 The relative importance of landscape and community features in the invasion of an exotic shrub in a fragmented landscape journal ECOGRAPHY 29 2 213 222 Although invasive plants are recognized as a major ecological problem, little is known of the relative importance of plant community characteristics versus landscape context in determining invasibility of communities. We determined the relative importance of community and landscape features of 30 woodlots in influencing the invasion of Lonicera maackii. We sampled woodlots using the point-quarter method and calculated canopy openness and basal areas and densities of shrub, sapling and tree species, as well as woody species richness. We used aerial photos and ArcView GIS to calculate landscape parameters from the same woodlots using a buffer distance of 1500 m. We used logistic and linear regression analyses to determine the community and landscape factors that best explain L. maackii presence and density. We also tested whether woodlot invasion by L. maackii begins at woodlot edges. Presence of L. maackii was significantly explained only by distance from the nearest town (logistic regression, p=0.017); woodlots nearer town were more likely to be invaded. Among invaded woodlots, density of L. maackii was positively related to the amount of edge in the landscape (partial R-2=0.592) and negatively related to total tree basal area (partial R-2=0.134), number of native woody species (partial R-2=0.054), and sapling shade tolerance index (partial R-2=0.054). Lonicera maackii in woodlot interiors were not younger than those on the perimeters, leading us to reject the edge-first colonization model of invasion. Our findings reveal that landscape structure is of primary importance and community features of secondary importance in the invasion of L. maackii. This shrub is invading from multiple foci (towns) rather than an advancing front. Connectivity in the landscape (i.e. the number of corridors) did not promote invasion. However, edge habitat was important for invasion, probably due to increased propagule pressure. The community features associated with L. maackii invasion may be indicators of past disturbance. Web of Science Many United States Ohio Darke County 40.099911 -84.628744 Field - Observational terrestrial Deciduous Forest Invasion Hyp. Community Species Richness;Propagule Pressure;Disturbance;Other primary 1290 James, CS; Eaton, JW; Hardwick, K 2006 Responses of three invasive aquatic macrophytes to nutrient enrichment do not explain their observed field displacements journal AQUATIC BOTANY 84 4 347 353 In some eutrophic inland waters the invasive aquatic macrophyte Elodea canadensis has been displaced by the morphologically similar species Elodea nuttallii and Subsequently E. nuttallii by Lagarosiphon major. We investigated whether differences in the responses of these species and their associated epiphytic floras to five nutrient loadings in the range 30-480 mu g L-1 P and 0.21-3.36 mg L-1 N could explain their observed field displacements. The mean relative growth rate (RGR) of E. nuttallii (RGR 0.086 d(-1)) was significantly higher than that of either E. canadensis (RGR 0.066 d(-1)) or L major (RGR 0.063 d(-1)). All three species exhibited a plastic morphological response to increasing nutrient loadings with mean root weights reduced at the highest nutrient loading compared with the lowest loading by 33, 75 and 56% for E. canandensis, E. nuttallii and L. major, respectively. Mean tissue nitrogen concentrations increased significantly with increasing nutrient loading, with concentrations in E. canadensis (1.83-2.10% dry wt.) significantly higher than either E. nuttallii (1.56-2.10% dry wt.) or L. major (1.50-1.90% dry wt.). Tissue phosphorus concentrations likewise increased with increasing nutrient loadings although this trend was not as pronounced. Epiphyte biomass per unit photosynthetic surface area (PSA) was significantly higher on E. canadensis than on either E. nuttallii or L. major, but did not increase significantly with increasing nutrient loadings. We suggest that differences in species responses to nutrient enrichment do not explain the species displacements observed in the field. E. nuttallii's higher RGR may, regardless of nutrient supply, enable this species to shade out neighbouring species and outpace the establishment of algae on its leaves. (c) 2006 Elsevier B.V. All rights reserved. Web of Science Elodea canadensis; Elodea nuttallii; Lagarosiphon major 52.7833;53.5 -3.1;-2.9333 Lab lentic;lotic Invasion Hyp. Fluctuating Resources primary 1291 Crall, AW; Newman, GJ; Stohlgren, TJ; Jarnevich, CS; Evangelista, P; Geuenther, D 2006 Evaluating dominance as a component of non-native species invasions journal DIVERSITY AND DISTRIBUTIONS 12 2 195 204 Many studies have quantified plant invasions by determining patterns of non-native species establishment (i.e. richness and absolute cover). Until recently, dominance has been largely overlooked as a significant component of invasion. Therefore, we re-examined a 6-year data set of 323 0.1 ha plots within 18 vegetation types collected in the Grand Staircase-Escalante National Monument from 1998 to 2003, including dominance (i.e. relative cover) in our analyses. We specifically focused on the non-native species Bromus tectorum, a notable dominant annual grass in this system. We found that non-native species establishment and dominance are both occurring in species-rich, mesic vegetation types. Therefore, non-native species dominance may result despite many equally abundant native species rather than a dominant few, and competitive exclusion does not seem to be a primary control on either non-native species establishment or dominance in this study. Unlike patterns observed for non-native species establishment, relative non-native species cover could not be predicted by native species richness across vegetation types (R-2 < 0.001; P = 0.45). However, non-native species richness was found to be positively correlated with relative non-native species cover and relative B. tectorum cover (R-2 = 0.46, P < 0.01; R-2 = 0.17, P < 0.01). Analyses within vegetation types revealed predominantly positive relationships among these variables for the correlations that were significant. Regression tree analyses across vegetation types that included additional biotic and abiotic variables were a little better at predicting non-native species dominance (PRE = 0.49) and B. tectorum dominance (PRE = 0.39) than at predicting establishment. Land managers will need to set priorities for control efforts on the more productive, species-rich vegetation types that appear to be susceptible to both components of invasion. Web of Science Bromus tectorum United States Utah Grand Staircase-Escalante National Monument 37.4 -111.6833 Field - Observational terrestrial Grassland;Coniferous Forest;Riparian;Mountain;Chaparral/Shrublands Invasion Hyp. Inherent Superiority;Community Species Richness Superior Competitor primary 1292 Klinger, R; Underwood, EC; Moore, PE 2006 The role of environmental gradients in non-native plant invasion into burnt areas of Yosemite National Park, California journal DIVERSITY AND DISTRIBUTIONS 12 2 139 156 Fire is known to facilitate the invasion of many non-native plant species, but how invasion into burnt areas varies along environmental gradients is not well-understood. We used two pre-existing data sets to analyse patterns of invasion by non-native plant species into burnt areas along gradients of topography, soil and vegetation structure in Yosemite National Park, California, USA. A total of 46 non-native species (all herbaceous) were recorded in the two data sets. They occurred in all seven of the major plant formations in the park, but were least common in subalpine and upper montane conifer forests. There was no significant difference in species richness or cover of non-natives between burnt and unburnt areas for either data set, and environmental gradients had a stronger effect on patterns of non-native species distribution, abundance and species composition than burning. Cover and species richness of non-natives had significant positive correlations with slope (steepness) and herbaceous cover, while species richness had significant negative correlations with elevation, the number of years post-burn, and cover of woody vegetation. Non-native species comprised a relatively minor component of the vegetation in both burnt and unburnt areas in Yosemite (percentage species = 4%, mean cover < 6.0%), and those species that did occur in burnt areas tended not to persist over time. The results indicate that in many western montane ecosystems, fire alone will not necessarily result in increased rates of invasion into burnt areas. However, it would be premature to conclude that non-native species could not affect post-fire succession patterns in these systems. Short fire-return intervals and high fire severity coupled with increased propagule pressure from areas used heavily by humans could still lead to high rates of invasion, establishment and spread even in highly protected areas such as Yosemite. Web of Science Many United States California 37.4833 -119.2167 Statistical/Meta-analysis terrestrial Deciduous Forest;Coniferous Forest;Chaparral/Shrublands Invasion Hyp. Other primary 1293 Wangen, SR; Webster, CR 2006 Potential for multiple lag phases during biotic invasions: reconstructing an invasion of the exotic tree Acer platanoides journal JOURNAL OF APPLIED ECOLOGY 43 2 258 268 1. Perennial woody invaders often form persistent patches that significantly alter the structure and composition of native plant communities. Given their long generation times compared with ruderal invaders, these species may experience prolonged establishment phases between successful introduction and spread. Gap dynamics of shade-tolerant invaders could lead to multiple lag phases during the invasion process. 2. In order to investigate the potential for long or multiple lag phases, we reconstructed the invasion of Acer platanoides (a shade-tolerant, invasive, exotic tree) on an 1130-ha temperate forested island in Lake Huron, USA. We measured and mapped the spatial location of every A. platanoides >= 0.5 m in height that had successfully established within a 728-ha forested park on the island. A simple age-diameter relationship, developed from a randomly selected subsample of the population, was used to assign an establishment date to each individual. 3. Following a 34-year establishment phase, the area occupied by >= 1 A. platanoides ha(-1) increased linearly at a rate of 5.6 ha year(-1) for 35 years, after which range expansion slowed. Population growth lagged behind range expansion, with rapid population growth associated with infill between parents. During the expansion phase, numerous satellite populations established but contributed little to population growth and spatial expansion because of the long time required for them to become reproductive. These satellite populations will most probably accelerate population growth and spread once they reach reproductive age. 4. Roads and trails provided important corridors for propagule movement away from developed areas over the course of the invasion. They also appeared to facilitate longer distance dispersals than would be expected given the biology of the species. 6. Synthesis and application. Our results suggest that shade-tolerant invaders with long generation times may undergo long establishment phases as well as periodic lags during the expansion phase. These lags may provide windows of opportunity for control but could easily be misinterpreted as signs that the population has reached an equilibrium density or the geographical extent of its spread. Additionally, roads and trails may provide important corridors for movement of propagules via non-standard means of dispersal. Web of Science Acer platanoides United States Michigan Mackinac Island 45.85 -84.6167 Field - Observational terrestrial Deciduous Forest;Coniferous Forest Invasion Hyp. Disturbance primary 1294 Braby, CE; Somero, GN 2006 Ecological gradients and relative abundance of native (Mytilus trossulus) and invasive (Mytilus galloprovincialis) blue mussels in the California hybrid zone journal MARINE BIOLOGY 148 6 1249 1262 Marine communities are experiencing unprecedented rates of species homogenization due to the increasing success of invasive species, but little is known about the mechanisms that allow a species to invade and persist in a new habitat. In central California, native (Mytilus trossulus Gould 1850) and invasive (Mytilus galloprovincialis Lamarck 1819) blue mussels and their hybrids co-exist, providing an opportunity to analyze the mechanisms that determine the distributions of these taxa. Spatial and temporal variation in temperature and salinity and the relative frequencies of these mussel taxa were examined between 2000 and 2004 at four sites in San Francisco Bay and four in Monterey Bay, which were chosen for their different positions along inferred estuarine/oceanic gradients in the hybrid zone. Mussels were genetically identified as the parent species or hybrids by amplifying regions of two species-specific loci: the adhesive byssal thread protein (Glu-5') and the internal transcribed spacer region of ribosomal DNA (ITS 1). The proportion of M. trossulus at the eight hybrid zone sites correlated negatively with average salinity (R-2=0.60) and positively with maximal temperature (R-2 >= 0.72), a somewhat unexpected result given what is known about the phylogeography of this species. The proportion of M. galloprovincialis showed the opposite pattern. The proportion of hybrids was correlated neither with habitat temperature nor salinity. Genotypes of mussel populations at an additional 13 sites from Coos Bay, Oregon (latitude 43.35 degrees N) to Long Beach, California (latitude 33.72 degrees N), sampled at various intervals between 2000 and 2004, were also determined. This survey confirmed previous reports that the hybrid zone lies between Monterey and the Cape Mendocino region (latitudes 36.63 degrees N-40.5 degrees N). Within Monterey and San Francisco Bays, however, the temporal comparisons (1990s vs. 2000s) revealed abrupt changes in the proportions of the two parent species and their hybrids on annual and decadal time scales. These changes indicate that the blue mussel populations are in a highly dynamic state. The survey also showed that, regardless of habitat, M. trossulus is consistently of smaller average size than either M. galloprovincialis or hybrids. Web of Science Mytilus galloprovincialis United States California Field - Observational marine Benthic Invasion Hyp. Other filter 1295 Dong, M; Lu, BR; Zhang, HB; Chen, JK; Li, B 2006 Role of sexual reproduction in the spread of an invasive clonal plant Solidago canadensis revealed using intersimple sequence repeat markers journal PLANT SPECIES BIOLOGY 21 1 13 18 Invasive species, second only to habitat loss as a cause of biodiversity loss, pose serious threats to native biodiversity and ecosystems. Little is known about the mechanisms that some exotic plants use to become invasive in their non-native ranges. Solidago canadensis, native to North America, was intentionally introduced to many countries where it has become an invasive plant. To understand the roles that reproductive mode plays in successful invasion of exotic plants, and the relative importance of sexual reproduction and clonal growth, the genetic diversity and clonal structure of two S. canadensis populations from Shanghai, China were investigated using intersimple sequence repeats. Samples were collected in a grid pattern with intervals of 2 m among adjacent individuals within the studied area (approximately 30 m x 30 m) for each population. Results showed that the percentages of polymorphic loci for the two populations were 97.9% and 96.5% and clonal diversity measured using the Simpson Diversity Index was 1.00 for both populations. No identical genotypes were found among the analyzed samples. It is suggested from this study that sexual reproduction facilitates the establishment of new S. canadensis populations, whereas clonal expansion maintains and enlarges the established populations. Thus, limiting sexual reproduction of S. canadensis may effectively control the invasion of this species. Web of Science Solidago canadensis China 31.3508 121.279 Field - Observational;Lab terrestrial Old Field Invasion Hyp. Other primary 1297 Sun, BY; Tan, JZ; Wan, ZG; Gu, FG; Zhu, MD 2006 Allelopathic effects of extracts from Solidago canadensis L. against seed germination and seedling growth of some plants journal JOURNAL OF ENVIRONMENTAL SCIENCES-CHINA 18 2 304 309 To investigate the potential role of allelopathy in plant interference and in the successful invasion of alien species Solidago canadensis, aqueous and ethanolic extracts from rhizomes, steins and leaves of S. canadensis were prepared and used as treatment solutions to assess their effects on seed germination and seedling growth in four target species, mulberry (Morus alba); morning glory (Pharbitis nil), wheat (Triticum aestivum) and rape (Brassica campestris). Reduction and/or growth in germination and growth of the target plant species in the presence of both aqueous and ethanolic extracts at different concentrations indicated that the responses were species-specific and concentration-dependent. Generally, ethanolic extracts (especially from leaves) imposed stronger effects on both seed germination and seedling growth. Extracts with lower concentration at 0.001 g/ml dw could stimulate the seedling growth of rape and morning glory, whereas extracts at any given concentrations have inhibitory effects on wheat and mulberry. It is suggested that the aqueous and ethanolic extracts of all the three parts of S. canaderisis have significant allelopathic effects. Although both inhibition and stimulation occurred in the germination and growth of the target species, extracts with higher concentrations definitely inhibit seed germination and seedling growth of all target plants. We suggest that allelopathy plays a more important role than other mechanisms do in the out-competition of S. canadensis over other plants, and make it invasive in new habitats. Web of Science Solidago canadensis China Lab Invasion Hyp. Inherent Superiority;Novel Weapons Superior Competitor primary 1299 Christen, D; Matlack, G 2006 The role of roadsides in plant invasions: a demographic approach journal CONSERVATION BIOLOGY 20 2 385 391 Non-native plant species are common along roadsides, but presence does not necessarily indicate spread along the road axis. Roadsides may serve merely as habitat for a species spreading independently of roads. The potential conduit function of roads depends on the habitat specificity of the spreading species, its dispersal range relative to the spacing of roads in the landscape, and the relative importance of long- and short-range dispersal. We describe a demographic model of the roadxspecies interaction and suggest methods of assessing conduit function in the field based on the model results. A species limited to roadside habitat will be constrained to spread along the road axis unless its long-range dispersal is sufficient to carry it across the intervening unfavorable area to another road. It will propagate along a road corridor at a rate determined by the scale of short-range dispersal. Effective management of an invasion requires distinguishing between the habitat and conduit functions, a distinction difficult to make with only snapshot data. Invasions can be reconstructed by several methods, but none is totally satisfactory. We suggest comparing stem distributions on transects parallel and perpendicular to the road axis, and beside the road, and away from it, with an idealized Gaussian curve. Such comparisons would allow discrimination between pattern determined by habitat suitability and pattern reflecting random and facilitated dispersal. Web of Science Many Theoretical/Modeling terrestrial Invasion Hyp. Other primary 1300 Fields, PA; Rudomin, EL; Somero, GN 2006 Temperature sensitivities of cytosolic malate dehydrogenases from native and invasive species of marine mussels (genus Mytilus): sequence-function linkages and correlations with biogeographic distribution journal JOURNAL OF EXPERIMENTAL BIOLOGY 209 4 656 667 The blue mussel Mytilus galloprovincialis, a native of the Mediterranean Sea, has invaded the west coast of North America in the past century, displacing the native blue mussel, Mytilus trossulus, from most of its former habitats in central and southern California. The invasive success of M. galloprovincialis is conjectured to be due, in part, to physiological adaptations that enable it to outperform M. trossulus at high temperatures. We have examined the structure and function of the enzyme cytosolic malate dehydrogenase (cNMH) from these species, as well as from the more distantly related ribbed mussel, Mytilus californianus, to characterize the effects of temperature on kinetic properties thought to exhibit thermal adaptation. The M. trossulus cMDH ortholog differs from the other cMDHs in a direction consistent with cold adaptation, as evidenced by a higher and more temperature-sensitive Michaelis-Menten constant for the cofactor NADH (K-m(NADH)). This difference results from minor changes in sequence: the M. trossulus ortholog differs from the M. galloprovincialis ortholog by only two substitutions in the 334 amino acid monomer, and the M. californianus and M. trossulus orthologs differ by five substitutions. In each case, only one of these substitutions is non-conservative. To test the effects of individual substitutions on kinetic properties, we used site-directed mutagenesis to create recombinant cMDHs. Recombinant wild-type M. trossulus cMDH (rWT) has high K-m(NADH) compared with mutants incorporating the non-conservative substitutions found in M. californianus and M. galloprovincialis - V114H and V114N, respectively - demonstrating that these mutations are responsible for the differences found in substrate affinity. Turnover number (k(cat)) is also higher in rWT compared with the two mutants, consistent with cold adaptation in the M. trossulus ortholog. Conversely, rWT and V114H appear more thermostable than V114N. Based on a comparison of K-m(NADH) and k(cat) values among the orthologs, we propose that immersion temperatures are of greater selective importance in adapting kinetic properties than the more extreme temperatures that occur during emersion. The relative warm adaptation of M. galloprovincialis cMDH may be one of a suite of physiological characters that enhance the competitive ability of this invasive species in warm habitats. Web of Science Mytilus galloprovincialis Lab marine Benthic Invasion Hyp. Preadaptation to Climate filter 1301 Parker, JD; Burkepile, DE; Hay, ME 2006 Opposing effects of native and exotic herbivores on plant invasions journal SCIENCE 311 127 1459 1461 Web of Science Many Statistical/Meta-analysis terrestrial Invasion Hyp. Enemy Release primary 1305 Hill, JP; Germino, MJ; Wraith, JM; Olson, BE; Swan, MB 2006 Advantages in water relations contribute to greater photosynthesis in Centaurea maculosa compared with established grasses journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 167 2 269 277 Semiarid steppe communities in North America appear particularly vulnerable to persistent infestations by exotic, taprooted forbs, such as European spotted knapweed (Centaurea maculosa). We determined whether species differences in ecophysiological response to water availability could help link traits of Centaurea with invasibility of steppe communities. Plant-soil water relations and photosynthesis were measured under three water levels in a greenhouse and at two sites over two years in the field for Centaurea and dominant rangeland species of southwestern Montana: Pseudoregneria spicata, Pascopyron smithii, and Bromus inermis. Centaurea had greater and more seasonally persistent photosynthesis than the other species under field conditions but not in the greenhouse, where water availability was similar for the species. Centaurea had no greater water use efficiency, except under unusually dry conditions, but maintained greater water potentials despite greater transpiration than the grasses. Changes in soil water indicated uptake from deeper and wetter soils in Centaurea than in grasses. Greater photosynthesis in Centaurea compared with grasses may result from uptake of deeper soil water and corresponding drought avoidance. Interspecific differences in resource use may therefore contribute to the success of Centaurea, and Centaurea's ecological requirement for water matches an available resource niche in the communities we examined. Web of Science Centaurea maculosa United States Montana 45.677437;46.585907 -111.209135;-111.77639 Garden terrestrial Grassland Invasion Hyp. Empty Niche primary 1308 Buddenhagen, C; Jewell, KJ 2006 Invasive plant seed viability after processing by some endemic Galapagos birds journal ORNITOLOGIA NEOTROPICAL 17 1 73 80 In the Galapagos Islands, Ecuador, we investigated how the seed viability of important invasive plant species was affected by processing and digestion by endemic birds, namely, Galapagos Mockingbirds (Nesomimus parpulus), and Medium (Geospiza fontis) and Small (G. fuliginosa) ground finches. Multiple feeding trials were carried out on five captive birds of each species. They were fed amaranthus (Amaranthus dubius), passion fruit (Passiflora edulis), blackberry (Rubus niveus), guava (Psidium guajava), sauco (Cestrum auriculatum), and lantana (Lantana camara). The Galapagos Mockingbird is likely to be an effective disperser of invasive plants, as it defecated seeds of all species except amaranthus, without lowering their viability. Seeds were retained in the gut for an average of 87 min. Mockingbirds ate fruit in more of the trials than did the finches. Finches are confirmed as seed predators as they generally crushed seeds before ingesting them. Only one intact viable blackberry seed was defecated by a Small Ground Finch. All three bird species were observed moving fruit (and seeds) around their cages while feeding. Seed dispersal over short distances could happen in this way. Web of Science Many Ecuador Galapagos Islands Lab terrestrial Invasion Hyp. Mutualism Facilitation primary 1309 Pauchard, A; Alaback, PB 2006 Edge type defines alien plant species invasions along Pinus contorta burned, highway and clearcut forest edges journal FOREST ECOLOGY AND MANAGEMENT 223 3 327 335 Forest edges have been long recognized as the first landscape elements to be invaded by alien plant species in forest ecosystems. However, little is known about the role of forest edge type in invasive species patterns. In the Northern Rocky Mountains of the United States, disturbance-caused forest edges are a common feature in the landscape with anthropogenic (e.g. roadside, clearcut) and natural (e.g. burned, windthrown) edge types. In this paper we examine patterns of alien species invasion and native community structure across three forest edge types in Pinus contorta forests including contrasts between undeveloped landscapes in Yellowstone National Park (YNP), and developed (roaded and logged) portions of the adjacent Gallatin National Forest (GNF). Six sets of transects were located in each of five study sites, including clearcut, burn and highway edge types. When burn and highways edges were compared between GNF and YNP, landscape matrix did not have a significant effect on either alien species richness or cover. In both landscapes, highway edges had higher alien species richness and cover than burn edges. For burn and highway edges, alien species richness and cover were significantly related to edge type, distance from edge and the interaction between both variables. In Gallatin NF, alien species were concentrated along highway edges, while burn and clearcut edges are significantly less invaded. Overall, alien species richness was negatively correlated with native species richness in plots with at least one alien species (R-2 = 0.30, p < 0.001). We were able to explain from 23 to 68% of the variation in alien species richness from simple measures of vegetation structure within each of the edge types. Our study suggests that at least for high elevation conifer ecosystems such as West Yellowstone, alien plant invasion into interior forest is significantly enhanced by disturbance edges only along roadsides. Further studies are needed to determine causal mechanisms that explain the high degree of invisibility of roadside edges. Our results highlight the need for careful planning and management of roads, as they may become a primary conduit of alien plant invasions. (c) 2005 Elsevier B.V. All rights reserved. Web of Science Many United States Montana Yellowstone National Park; Gallatin National Forest 44.8;44.6167 -111.2;-111 Field - Observational terrestrial Coniferous Forest Invasion Hyp. Disturbance primary 1310 Kissling, WD; Lord, JM; Schnittler, M 2006 Agamospermous seed production of the invasive tussock grass Nardus stricta L. (Poaceae) in New Zealand - evidence from pollination experiments journal FLORA 201 2 144 151 The breeding system of the European tussock grass Nardus stricta L. (Poaccae) was investigated with pollination experiments. Plants were sampled from two populations at Lake Pukaki, Canterbury, New Zealand, where the species is recognised as an alien invader. Bagging of flowers with king-sized cigarette paper and hand-pollination were used to test for three modes of reproduction in the greenhouse: (1) agamospermy (apomixis), (2) autogamy and self-compatibility, and (3) allogamy (outcrossing). Two control groups without experimental treatments were further tested for seed set under (1) greenhouse and (2) field conditions. The success or failure of all experimental treatments was assessed with seed set and germination trials. All agamospermy treatments showed high seed set and germination proportions arguing for an apomictic mode of reproduction in Nardus stricta. Cross-pollination treatments were also successful making it difficult to estimate the degree of outcrossing, selfing, and agamospermous seed production in Nardus stricta. Fecundity in field populations was considerably reduced, possibly due to environmental factors acting upon seed development during maturation. The reproductive strategy of Nardus stricta might be particularly beneficial during invasion because single tussocks can form reproducing colonies and high reproductive output is ensured even in the absence of pollination. Genetic studies in combination with pollination experiments would be necessary to gain deeper insights into the breeding strategy of Nardus stricta. (c) 2005 Elsevier GmbH. All rights reserved. Web of Science Nardus stricta New Zealand Lake Pukaki -44.050781 170.105209 Greenhouse terrestrial Grassland Invasion Hyp. Inherent Superiority High Reprod. Output;Self Compatible;Clonal Reproduction primary 1311 MacDougall, AS; Boucher, J; Turkington, R; Bradfield, GE 2006 Patterns of plant invasion along an environmental stress gradient journal JOURNAL OF VEGETATION SCIENCE 17 1 47 56 Question: Do stressful environments facilitate plant invasion by providing refuges from intense above-ground competition associated with productive areas, or prevent it by favouring locally adapted native species? Location: An invaded and fragmented oak savanna ecosystem structured along a landscape-level stress gradient associated with soil depth, elevation, and canopy openness. Methods: Vegetation and environmental data were collected from 184 plots in seven savanna remnants along the gradient. Using multivariate (CCA) and post-hoc regression analyses, we determined the relationship between environment and the richness and abundance of invasives. Results: 46 of 119 species were naturalized exotics. CCA indicated the importance of environmental variation (mostly soil depth) for community structure but not for invasion; invasive species richness was similar in all areas. However, the abundance of invasives and their impacts on native diversity appear to increase significantly in less stressful habitats. Deeper soils had lower evenness and significantly fewer native species. This result was associated with dominance by exotic perennial grasses and large increases in vegetation height, suggesting strong above-ground competition. Conclusions: Low-stress environments were not more invasible per se but appear to be more susceptible to invasion by species with strong competitive impacts. The causes of decreasing exotic impact with decreasing soil depth may reflect shifts in competitive intensity or an increased importance of stress tolerance, both of which may favour natives. Alternatively, this ecosystem may simply lack high-impact invaders capable of dominating shallow soils. Conservation challenges are twofold for this endangered plant community: controlling invasives that currently dominate deeper-soils and accounting for a diverse pool of invaders that proliferate when the current dominants are removed. Web of Science Many Canada British Columbia Vancouver Island 48.538432 -123.673096 Field - Observational terrestrial Grassland Invasion Hyp. Other primary 1312 Piola, RF; Johnston, EL 2006 Differential tolerance to metals among populations of the introduced bryozoan Bugula neritina journal MARINE BIOLOGY 148 5 997 1010 Resistance to heavy metals is a potentially important trait for introduced marine organisms, facilitating their successful invasion into disturbed natural communities. We conducted laboratory and field experiments to examine differential resistance to copper (Cu) between two source populations of the introduced bryozoan Bugula neritina, originating from a polluted (Port Kembla Harbour, NSW, Australia) and an unpolluted (Botany Bay, NSW, Australia) environment. A laboratory toxicity test was conducted to test the relative resistance of B. neritina recruits from the two sources, by measuring the attachment success, survival and growth of individuals exposed to a range of Cu concentrations (0, 25, 50 and 100 mu g l(-1) Cu). Upon completion, reciprocal transplantation of the colonies to the original polluted and unpolluted locations was carried out to assess ongoing survival and growth of colonies in the field. B. neritina colonies originating from the polluted Port Kembla Harbour had increased resistance to Cu relative to populations from an unpolluted part of Botany Bay. There appeared to be a cost associated with increased metal tolerance. In the laboratory, Botany Bay recruits displayed significantly higher growth in control treatments and significantly poorer growth at 100 mu g l(-1) Cu with respect to Port Kembla Harbour individuals, which showed unusually uniform and low growth irrespective of Cu concentration. No difference in attachment success or post-metamorphic survival was observed between populations. Field transplantation showed copper resistance in Port Kembla Harbour colonies constituted an advantage in polluted but not benign environments. The findings of this study provide evidence of the benefits to invasive species of pollution tolerance and suggest that human disturbance can facilitate the establishment and spread of invasive species in marine systems. Web of Science Bugula neritina Australia New South Wales Port Kembla Harbour; Botany Bay Field - Experimental;Lab marine Benthic Invasion Hyp. Disturbance filter 1314 Stout, JC; Parnell, JAN; Arroyo, J; Crowe, TP 2006 Pollination ecology and seed production of Rhododendron ponticum in native and exotic habitats journal BIODIVERSITY AND CONSERVATION 15 2 755 777 Alien plants may be reproductively limited in exotic habitats because of a lack of mutualistic pollinators. However, if plants are adequately served by generalist pollinators, successful reproduction, naturalisation and expansion into exotic habitats may occur. Rhododendron ponticum is very successful, ecologically damaging invasive plant in Britain and Ireland, but is in decline in its native Iberian habitat. It spreads locally by sending out lateral branches, but for longer distance dispersal it relies on sexually produced seeds. Little is known about R. ponticum's pollination ecology and breeding biology in invaded habitats. We examined the flower-visiting communities and maternal reproductive success of R. ponticum in native populations in southern Spain and in exotic ones in Ireland. R. ponticum in flowers are visited by various generalist (polylectic) pollinator species in both native and exotic habitats. Although different species visited flowers in Ireland and Spain, the flower visitation rate was not significantly different. Insects foraging on R. ponticum in Spain carried less R. ponticum pollen than their Irish counterparts, and carried fewer pollen types. Fruit production per inflorescence varied greatly within all populations but was significantly correlated with visitation at the population level. Nectar was significantly depleted by insects in some exotic populations, suggesting that this invasive species is providing a floral resource for native insects in some parts of Ireland. The generality of the pollination system may be factor contributing to R.ponticum's success in exotic habitats. Web of Science Rhododendron ponticum Spain; Ireland Field - Observational terrestrial Invasion Hyp. Mutualism Facilitation primary 1315 Gosper, CR; Vivian-Smith, G; Hoad, K 2006 Reproductive ecology of invasive Ochna serrulata (Ochnaceae) in south-eastern Queensland journal AUSTRALIAN JOURNAL OF BOTANY 54 1 43 52 We investigated aspects of the reproductive ecology of Ochna serrulata (Hochst.) Walp., an invasive plant in eastern Australia. O. serrulata drupes were similar in size to fleshy fruits of other local invasive plants, but showed some distinct differences in quality, with a very high pulp lipid content ( 32.8% of dry weight), and little sugar and water. Seeds were dispersed by figbirds, Sphecotheres viridis Vieillot, a locally abundant frugivore, and comprised between 10 and 50% of all non-Ficus spp. fruit consumed during October and November. The rate of removal of O. serrulata drupes was greater in bushland than suburban habitats, indicating that control in bushland habitats should be a priority, but also that suburban habitats are likely to act as significant seed sources for reinvasion of bushland. Germination occurred under all seed-processing treatments ( with and without pulp, and figbird gut passage), suggesting that although frugivores are important for dispersal, they are not essential for germination. Recruitment of buried and surface-sown seed differed between greenhouse and field experiments, with minimal recruitment of surface-sown seed in the field. Seed persistence was low, particularly under field conditions, with 0.75% seed viability after 6 months and 0% at 12 months. This provides an opportunity to target control efforts in south-eastern Queensland in spring before fruit set, when there is predicted to be few viable seeds in the soil. Web of Science Ochna serrulata Australia Queensland -27.5715;-27.4875 153.0767;153.1138 Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Mutualism Facilitation primary 1316 Pausas, JG; Lloret, F; Vila, M 2006 Simulating the effects of different disturbance regimes on Cortaderia selloana invasion journal BIOLOGICAL CONSERVATION 128 1 128 135 Disturbances favour plant invasions because they provide a pulse of resources for seedling establishment and growth. However, little attention has been paid to the importance of the different disturbance regimes in the extent of invasion. In this paper we asked to what extent invasion depends on spatial and temporal patterns of disturbance. By using the spatially explicit model FATELAND, we simulated how Cortaderia selloana, a large-wind dispersed perennial grass invading Mediterranean grasslands, responds to different medium-term (up to 55 years) disturbance regimes. The different scenarios combine disturbance frequency, extent of disturbance and temporal and spatial disturbance variability, and they roughly mimic real situations of habitat management and disturbances in cultural landscapes. The model predicted that the proportion of invaded area would increase with disturbance frequency. The extent of the disturbance overcame the importance of frequency. Aggregated disturbances randomly distributed in space had a more positive effect on invasion than scattered disturbances at repeatedly fixed locations. Whether the disturbances regularly occurred in time or were irregularly distributed did not influence the percentage of invaded landscape. Our simulation analysis unambiguously supports the hypothesis that disturbances are essential for the persistence and expansion of Cortaderia sellona. The high amount of seed rain from a few individuals (e.g., gardens) make this species very sensitive to landscape changes produced by different disturbance patterns (e.g., land abandonment, habitat management or rubbish dumping). Our results can contribute to redirect land management options. (c) 2005 Elsevier Ltd. All rights reserved. Web of Science Cortaderia selloana Theoretical/Modeling terrestrial Grassland Invasion Hyp. Disturbance primary 1319 McKinney, ML 2006 Correlated non-native species richness of birds, mammals, herptiles and plants: scale effects of area, human population and native plants journal BIOLOGICAL INVASIONS 8 3 415 425 Several extrinsic factors (area, native species diversity, human population size and latitude) significantly influence the non-native species richness of plants, over several orders of magnitude. Using several data sets, I examine the role of these factors in non-native species richness of several animal groups: birds, mammals and herptiles (amphibians, reptiles). I also examine if non-native species richness is correlated among these groups. I find, in agreement with Sax [2001, Journal of Biogeography 28: 139-150], that latitude is inversely correlated with non-native species richness of many groups. Once latitude is accounted for, area, human population size and native plant species richness are shown to be important extrinsic factors influencing non-native animal species. Of these extrinsic factors, human population size and native plant species richness are the best predictors of non-native animal species richness. Area, human population size and native plant species richness are highly intercorrelated, along with non-native species richness of all taxa. Indeed a factor analysis shows that a single multivariate axis explains over half of the variation for all variables among the groups. One reason for this covariation is that humans tend to most densely occupy the most productive and diverse habitats where native plant species richness is very high. It is thus difficult to disentangle the effects of human population size and native species richness on non-native species richness. However, it seems likely that these two factors may combine to increase non-native species richness in a synergistic way: high native species richness reflects greater habitat variety available for non-native species, and dense human populations (that preferentially occupy areas rich in native species) increase non-native species importation and disturbance of local habitats. Web of Science Many Statistical/Meta-analysis Invasion Hyp. Community Species Richness;Disturbance;Other 1320 Muth, NZ; Pigliucci, M 2006 Traits of invasives reconsidered: Phenotypic comparisons of introduced invasive and introduced noninvasive plant species within two closely related clades journal AMERICAN JOURNAL OF BOTANY 93 2 188 196 In attempting to determine the traits associated with invasive plant species, ecologists have often used species native to the invaded range as *control species.* Because many native species themselves are aggressive colonizers, comparisons using this type of control do not necessarily yield information relevant to distinctions between invasive and noninvasive species. Here we implement an alternative study design that compares phenological, architectural, size, and fitness traits of several introduced invasive species to introduced noninvasive species within two genera of Asteraceae (Crepis and Centaurea). While there were many significant differences between the genera, there were few shared attributes among invasive or noninvasive congeners, even for traits as seemingly important as the number of inflorescences produced and the size of seed heads. Instead, the results suggest that differences in invasiveness between closely related species is better explained as the result of complex trait interactions and specific introduction histories. Web of Science Many United States Greenhouse terrestrial Invasion Hyp. Other primary 1322 Lambrinos, JG 2006 Spatially variable propagule pressure and herbivory influence invasion of chaparral shrubland by an exotic grass journal OECOLOGIA 147 2 327 334 Although numerous studies have identified mechanisms that either resist or facilitate biological invasions, few studies have explicitly tested how resisting and facilitating mechanisms interact to drive invasion success. In California, USA, undisturbed Mediterranean-type shrublands have resisted invasion by the perennial tussock grass Cortaderia jubata. In some cases, however, this resistance has been spectacularly breached even in the absence of large-scale disturbance. I tested the hypothesis that these invasions are facilitated by local reductions in the strength of biotic resistance. I evaluated invasive success using C. jubata seed and seedling additions at different microhabitats: the edge of a chaparral stand, under shrub canopy at different distances from the stand edge, and in canopy gaps within the stand. When left exposed to mammalian herbivores, seedling survivorship decreased sharply from nearly 40% on the stand edge to zero just 10 m into the stand. When transplants were protected from herbivory, however, distance from the edge had no significant influence on transplant survivorship. Seedling emergence was also greater on the edge and in canopy gaps than under the canopy, but these differences were not caused by differences in herbivory. The flux of invasive propagules reaching the soil surface was immense and greater along the edge and within gaps than under the stand canopy. Mirroring these patterns, naturally occurring seedling abundance declined dramatically with distance from the stand edge, and seedlings were far more common within stand gaps than would be expected given gap frequency within the stand. Despite strong biotic resistance to invasion within the stand, the cover of C. jubata has increased 20% over the last 9 years. These results suggest that the relative amount of susceptible edge habitat and the supply of invasive propagules can facilitate invasion even in the face of strong local biotic resistance. Web of Science Cortaderia jubata United States California 34.6833 -120.6 Field - Experimental;Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Other primary 1326 Baret, S; Strasberg, D 2005 The effects of opening trails on exotic plant invasion in protected areas on La Reunion Island (Mascarene Archipelago, Indian Ocean) journal REVUE D ECOLOGIE-LA TERRE ET LA VIE 60 4 325 332 Exotic species have become a major problem in protected areas. A better knowledge of ecosystem functioning is necessary to improve management practice that facilitates habitat conservation. We suggest that small-scale disturbances such as trail opening and the effects on exotic plants invasions are underestimated. We have, therefore, quantitatively measured the effect of forest trail building on invasive plant colonization, a phenomenon in constant progression but never studied before. Our study shows that Rubus alceifolius, the widespread exotic invasive plant on La Reunion, is able to germinate on both narrow and wide trails, but persists only on the wider ones. Our results show moreover that wide forest trails favored establishment of exotics and significantly decreases species richness. We suggest to forest managers that building narrow forest trails is preferable as it will stop the persistence and propagation of R. alceifolius and other non-indigenous plants. Web of Science Rubus alceifolius France La Reunion -21.130237 55.526047 Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 1331 Dwire, KA; Parks, CG; McInnis, ML; Naylor, BJ 2006 Seed production and dispersal of sulfur cinquefoil in Northeast Oregon journal RANGELAND ECOLOGY & MANAGEMENT 59 1 63 72 Sulfur cinquefoil (family Rosaceae) is an invasive, herbaceous perennial, native to Eurasia. It has wide ecological amplitude and has become established throughout North America in numerous habitat types. Sulfur cinquefoil reproduces only by seed (achenes); however, little is known about its regenerative strategy or reproductive biology. To improve understanding of the mechanisms of expansion for sulfur cinquefoil, we quantified seed production and measured seed dispersal at sites infested with sulfur cinquefoil in different habitats in northeast Oregon. Seed dispersal was measured by using sticky traps (30 X 100 cm, replaced every 2 weeks) radiating in 4 cardinal directions from individual source plants. Estimated seed production for 2 years (2001 and 2002) was nearly 4 times higher than previously reported (approximate to 6000 seeds per plant; range approximate to 2620-15150 seeds per plant). For most sites, seed production was similar in both years. However, site, year, and their interaction (site X year) had significant influence on flower and stem production. Seeds were dispersed from July through mid-October 2001, although almost 40% of the seeds were captured between mid-July and mid-August. Dispersal followed a classic decay function; approximately 83% of the seeds were captured within 60 cm of the source plants. Once sulfur cinquefoil reaches a site, it appears to spread and persist by releasing numerous seeds near the parent plants, thereby forming increasingly dense stands. Web of Science Potentilla recta USA Oregon Blue Mountain Province 45.2967 -118.1336 Field - Observational terrestrial Old Field Invasion Hyp. Inherent Superiority High Reprod. Output primary 1333 Jurado, E; Garcia, JF; Flores, J; Estrada, E 2006 Leguminous seedling establishment in Tamaulipan thornscrub of northeastern Mexico journal FOREST ECOLOGY AND MANAGEMENT 221 3 133 139 Due to extensive land clearing in northeastern Mexico, there is an increasing need for restoration for which knowledge on plant establishment biology becomes a priority, for restoration practices. In here we tested the influence of current environmental variation on the establishment biology of common woody species from Tamaulipan thornscrub. Seedling establishment was monitored; four native species (Acacia berlandieri Benth., Ebenopsis ebano (Benth.) Coult, Havardia pallens (Benth.) Brintton and Rose, Prosopis laevigata (Humb & Bonpl. ex. Wild.) M.C. Johston), and one exotic species (Leucaena leucocephala (Lam.) de Wit). Seedling emergence, seedling survivorship, length of stems and number of leaves were evaluated over 1 year in environments with different light regimes: (i) dense thornscrub; (ii) thornscrub edge; (iii) cleared thornscrub (direct sunlight). Ten plots of 4m(2) (2 m x 2 m) were sampled in each environment. Seedling emergence occurred on spring and late summer and was greater on dense thornscrub for all species. Native species had higher survivorship and growth and had more leaves in dense thornscrub than in other environments. Exotic L. leucocephala had similar survivorship, shoot length and number of leaves across environments. All seedlings from all species died by late spring, possibly due to environmental stress. Seedling survival was longer for all native plants, as there were surviving seedlings in early spring for all species but not of exotic L. leucocephala. Perhaps mainly as a result of high temperature and low humidity. Additional watering, shading and moisture retaining gels should thus be considered when rehabilitation programs are made with seeds and seedlings in the region. (c) 2005 Elsevier B.V All rights reserved. Web of Science Leucaena leucocephala Mexico Tamaulipas Ciudad Victoria 23.6667 -99.0833 Field - Experimental terrestrial Savanna Fundamentals primary 1334 Ohlemuller, R; Walker, S; Wilson, JB 2006 Local vs regional factors as determinants of the invasibility of indigenous forest fragments by alien plant species journal OIKOS 112 3 493 501 Both local and regional filters can determine the invasion of alien species into native plant communities. However, their relative importance is essentially unknown. We used plot data from fragments of indigenous forests in southeastern New Zealand to infer which factors are important in explaining invasibility, measured as alien species richness. Twenty-eight predictor variables comprising both local factors (stand structure and soil) and regional ones (climate and land cover) were assessed. Reduction or increase in deviance in linear models was assessed, both individually and with a forward and backward stepwise variable selection procedure using the Akaike information criterion (AIC). We found that higher alien species richness was mainly associated with forest fragments of small area in warm and dry climates and where there were only small areas of surrounding indigenous forest. Local soil and stand structure variables had considerably smaller effects on alien species richness than the regional land cover and climate variables. Alien species richness showed no relationship with native species richness. We conclude that in the forest fragments investigated here, of the variables included in the analyses, regional land cover and climate variables are potentially important drivers for alien species richness at plot level. This has implications for projections of alien species spread in the future under different climate change and land use scenarios. Web of Science Many New Zealand Theoretical/Modeling;Statistical/Meta-analysis terrestrial Invasion Hyp. Other 1335 Thomsen, MA; D'Antonio, CM; Suttle, KB; Sousa, WP 2006 Ecological resistance, seed density and their interactions determine patterns of invasion in a California coastal grassland journal ECOLOGY LETTERS 9 2 160 170 Relatively little experimental evidence is available regarding how ecological resistance and propagule density interact in their effects on the establishment of invasive exotic species. We examined the independent and interactive effects of neighbour cover (biotic resistance), winter vs. spring water addition (abiotic resistance) and seed density on the invasion of the European perennial grass Holcus lanatus into a California coastal grassland dominated by exotic annual grasses. We found that decreased competition from resident exotic grasses had no effect. In contrast, increased late-season water availability eroded the abiotic resistance offered by naturally dry conditions, facilitating invasion. Finally, watering treatment and seed density interacted strongly in determining seedling survival: while seedling mortality was close to 100% in ambient and winter water addition plots, survivor numbers increased with seed density in spring-watered plots. Thus, decreased abiotic resistance can amplify the effect of increased propagule density on seedling establishment, thereby increasing the likelihood of invasion. Web of Science Holcus lanatus USA California Mendocino 39.7292 -123.6444 Field - Experimental terrestrial Grassland Invasion Hyp. Propagule Pressure;Other primary 1336 Stark, SC; Bunker, DE; Carson, WP 2006 A null model of exotic plant diversity tested with exotic and native species-area relationships journal ECOLOGY LETTERS 9 2 136 141 At large spatial scales, exotic and native plant diversity exhibit a strong positive relationship. This may occur because exotic and native species respond similarly to processes that influence diversity over large geographical areas. To test this hypothesis, we compared exotic and native species-area relationships within six North American ecoregions. We predicted and found that within ecoregions the ratio of exotic to native species richness remains constant with increasing area. Furthermore, we predicted that areas with more native species than predicted by the species-area relationship would have proportionally more exotics as well. We did find that these exotic and native deviations were highly correlated, but areas that were good (or bad) for native plants were even better (or worse) for exotics. Similar processes appear to influence exotic and native plant diversity but the degree of this influence may differ with site quality. Web of Science North America Statistical/Meta-analysis terrestrial Fundamentals primary 1337 Chytry, M; Pysek, P; Tichy, L; Knollova, I; Danihelka, J 2005 Invasions by alien plants in the Czech Republic: a quantitative assessment across habitats journal PRESLIA 77 4 339 354 Occurrence of alien plant species in all the major habitats in the Czech Republic was analysed using a data set of 20,468 vegetation plots, classified into 32 habitats according to the EUNIS classification. The plots contain on average 9.0% archaeophytes and 2.3% neophytes; for neophytes, this proportion is much smaller than 26.8% reported for the total flora of the country. Most neophytes are found in a few habitats: only 5.6% of them were recorded in more than ten habitats. By contrast, archaeophytes, and especially native species, tend to occur in a broader range of habitats. Highest numbers of aliens were found on arable land, in annual synantropic vegetation, trampled habitats and anthropogenic tall-forb stands. These habitats contain on average 22-56% archaeophytes and 4.4-9.6% neophytes. Neophytes are also common in artificial broadleaved forestry plantations; they also tend to make up a high percentage of the cover in wet tall-forb stands, but are represented by fewer species there. Entirely or nearly free of aliens are plots located in raised bogs, alpine grasslands, alpine and subalpine scrub and natural coniferous woodlands. Correlations between the number of archaeophytes or neophytes and the number of native species, calculated with habitat mean values, were non-significant, but there was a positive correlation between the numbers of archaeophytes and neophytes. The ratio of archaeophytes to neophytes was high in semi-natural dry and mesic grasslands and low in disturbed habitats with woody vegetation, such as artificial broadleaved forestry plantations, forest clearings and riverine willow stands. When individual plots were compared separately within habitats, the relationships between the number of archaeophytes, neophytes and native species were mostly positive. This result does not support the hypothesis that species-rich communities are less invasible, at least at the scale of vegetation plots, i.e. 10(0)-10(2) m(2). Web of Science Many Czech republic 49.733001 15.197753 Statistical/Meta-analysis terrestrial Invasion Hyp. Community Species Richness primary 1338 Jewett, EB; Hines, AH; Ruiz, GM 2005 Epifaunal disturbance by periodic low levels of dissolved oxygen: native vs. invasive species response journal MARINE ECOLOGY-PROGRESS SERIES 304 0 31 44 Hypoxia is increasing in marine and estuarine systems worldwide, primarily due to anthropogenic causes. Periodic hypoxia represents a pulse disturbance, with the potential to restructure estuarine biotic communities. We chose the shallow, epifaunal community in the lower Chesapeake Bay, Virginia, USA, to test the hypothesis that low dissolved oxygen (DO) (< 4 mg l(-1)) affects community dynamics by reducing the cover of spatial dominants, creating space both for less dominant native species and for invasive species, Settling panels were deployed at shallow depths in spring 2000 and 2001. at Gloucester Point, Virginia, and were manipulated every 2 wk from late June to mid-August. Manipulation involved exposing epifaunal communities to varying levels of DO for up to 24 h followed by redeployment in the York River. Exposure to low DO affected both species composition (presence or absence) and the abundance of the organisms present. Community dominance shifted away from barnacles as level of hypoxia increased. Barnacles were important spatial dominants which reduced species diversity when locally abundant. The cover of Hydroides dianthus, a native serpulid polychaete, doubled when exposed to periodic hypoxia. Increased H. dianthus cover may indicate whether a local region has experienced periodic, local DO depletion and thus provide an indicator of poor water-quality conditions. In 2001, the combined cover of the invasive and cryptogenic species in this community, Botryllus schlosseri (tunicate), Molgula manhattensis (tunicate), Ficopomatus enigmaticus (polychaete) and Diadumene lineata (anemone), was highest on the plates exposed to moderately low DO (2 mg l(-1) < DO < 4 mg l(-1)). All 4 of these species are now found worldwide and exhibit life histories well adapted for establishment in foreign habitats. Low DO events may enhance success of invasive species, which further stress marine and estuarine ecosystems. Web of Science Botryllus schlosseri; Molgula manhattensis; Ficopomatus enigmaticus; Diadumene lineata USA Virginia Chesapeake Bay 37.25009 -76.50816 Field - Experimental marine Intertidal/Near Shore Invasion Hyp. Inherent Superiority filter 1349 Aquiloni, L; Ilheu, M; Gherardi, F 2005 Habitat use and dispersal of the invasive crayfish Procambarus clarkii in ephemeral water bodies of Portugal journal MARINE AND FRESHWATER BEHAVIOUR AND PHYSIOLOGY 38 4 225 236 We used radio-telemetry to analyze habitat use and dispersal of the invasive crayfish Procambarus clarkii in the extreme environmental conditions of a temporary river in southern Portugal. The rationale of this study was that an understanding of the properties that make this species a successful invader can be of help for the conservation of freshwater biodiversity. The results showed that: (1) crayfish displaced at a similar rate (ranging 2.5-38?m?d -1 ) as other European populations; (2) movement was faster at night; (3) crayfish movement had no clear environmental correlates, except for water temperature; (4) peaks of more intense locomotion were intercalated with longer periods of slow or null speed; and (5) P. clarkii did not excavate burrows in the study habitat, but took refuge under boulders and most often occupied complex microhabitats (e.g., vegetated sections of the river). The conclusion was that, notwithstanding their extreme conditions, ephemeral water bodies in southern Europe are highly susceptible to invasion by P. clarkii. Web of Science Procambarus clarkii Portugal Guadiana River 37.650339 -7.510071 Field - Observational lotic Invasion Hyp. Inherent Superiority omnivore 1351 Gurvich, DE; Tecco, PA; Diaz, S 2005 Plant invasions in undisturbed ecosystems: The triggering attribute approach journal JOURNAL OF VEGETATION SCIENCE 16 6 723 728 The invasion of a target community by a non-indigenous plant species includes the stages of arrival, establishment and spread, which tend to depend on different characteristics of the invasive species and its context. While the mechanisms behind the invasion of highly disturbed ecosystems are well known, our understanding of the invasion process in undisturbed or weakly disturbed ecosystems is much more limited. Here we propose that, once a non-indigenous species has arrived to a new ecosystem and become established, the likelihood that it spreads, and thus becomes invasive, may depend on just one or very few characteristics, called 'triggering attributes' (TA). We propose that a TA is a vegetative or regenerative attribute discontinuously distributed in comparison to the resident community. This attribute allows the species to benefit from a resource that is permanently or temporarily unused by the resident community. We present an original study case and examples from the literature to illustrate our approach, and we also propose some ways to test it in different ecosystems. Web of Science Ligustrum lucidum; Pyracantha angustifolia Argentina -33.556044 -63.735353 Field - Observational terrestrial Deciduous Forest;Mountain Invasion Hyp. Other primary 1352 Bellingham, PJ; Tanner, EVJ; Healey, JR 2005 Hurricane disturbance accelerates invasion by the alien tree Pittosporum undulatum in Jamaican montane rain forests journal JOURNAL OF VEGETATION SCIENCE 16 6 675 684 Questions: Do past disturbance, soil nutrients, or species diversity predict the invasion success of the alien tree Pitto-sporum undulatum in an island montane rain forest? What are the consequences of its invasion for forest composition and species diversity? Location: Blue Mountains, Jamaica. Methods: Censuses of trees >= 3 cm DBH in permanent plots in four sites within ca. 7 ha; 1974-2004 (intensive sites) and in 16 plots within 250 ha; 1990-2004 (extensive plots). Results: Pittosporum was unrecorded in the intensive sites before a severe hurricane in 1988: by 2004 all four sites were invaded. Pittosporum had invaded 25% of the extensive plots in 1990 and 69% in 2004, where its basal area increased from 0.5 +/- 0.4 (SEM) m(2).ha(-1) in 1990 to 2.8 +/- 1.3 m(2).ha(-1) in 2004. It had zero stem mortality and diameter growth rate exceeded that of native species fourfold. Pittosporum's basal area in the extensive plots in 2004 was positively related to the stand basal area damaged in the 1988 hurricane and negatively related to soil N concentrations. Pittosporum invasion was unrelated to stand-level tree species diversity in the extensive plots but as its basal area increased over time the basal area of native species and stand-level diversity declined. Conclusions: There are no obvious functional attributes of Pittosporum unrepresented in the native tree flora although it has high photosynthetic efficiency compared with native trees. More widespread invasion of these forests by Pittosporum seems inevitable since hurricanes, which accelerated the invasion, affect these forests frequently. Web of Science Pittosporum undulatum Jamaica Blue Mountains 18.117335 -76.667519 Field - Observational terrestrial Tropical Forest Invasion Hyp. Community Species Richness;Disturbance primary 1355 Drake, JM; Lodge, DM 2006 Allee effects, propagule pressure and the probability of establishment: Risk analysis for biological invasions journal BIOLOGICAL INVASIONS 8 2 365 375 Colonization is of longstanding interest in theoretical ecology and biogeography, and in the management of weeds and other invasive species, including insect pests and emerging infectious diseases. Due to accelerating invasion rates and widespread economic costs and environmental damages caused by invasive species, colonization theory has lately become a matter of considerable interest. Here we review the concept of propagule pressure to inquire if colonization theory might provide quantitative tools for risk assessment of biological invasions. By formalizing the concept of propagule pressure in terms of stochastic differential equation models of population growth, we seek a synthesis of invasion biology and theoretical population biology. We focus on two components of propagule pressure that affect the chance of invasion: (1) the number of individuals initially introduced, and (2) the rate of subsequent immigration. We also examine how Allee effects, which are expected to be common in newly introduced populations, may inhibit establishment of introduced propagules. We find that the establishment curve (i.e., the chance of invasion as a function of initial population size), can take a variety of shapes depending on immigration rate, carrying capacity, and the severity of Allee effects. Additionally, Allee effects can cause the stationary distribution of population sizes to be bimodal, which we suggest is a possible explanation for time lags commonly observed between the detection of an introduced population and widespread invasion of the landscape. Web of Science Theoretical/Modeling Invasion Hyp. Propagule Pressure 1359 De Barro, PJ; Bourne, A; Khan, SA; Brancatini, VAL 2006 Host plant and biotype density interactions - their role in the establishment of the invasive B biotype of Bemisia tabaci journal BIOLOGICAL INVASIONS 8 2 287 294 Bemisia tabaciis a complex of closely related genetic types of whiteflies, few of which are invasive. One of these, B biotype, has proven to be particularly adapted to invading new areas, but the underlying reasons as to why it has a well-developed capacity to invade is not known. To develop an understanding of factors that may be contributing to B's invasive capacity, inter-biotype mating interactions and host plant suitability for the exotic B (B. tabaci Mediterranean/Asia Minor/Africa) and the indigenous Australian (AN) biotype (B. tabaci Australia) were examined. The results suggest that when confined to a mutually acceptable host, B cannot establish when the ratio of AN : B exceeds 20 : 1. However, when simultaneously provided with a host that only it prefers, B is able to establish even at 50 : 1 (AN : B). Further, when both biotypes occur together the number of progeny per female increases (relative to the number produced when only one biotype is present). The response is observed for both biotypes, but is considerably greater in the case of B. In addition, B performs better in the presence of the AN biotype B. tabaci Australia while AN perform worse in coexistence with B, but only if the demographics allow B to mate without significant interference. This leads to the prediction that B will invade in circumstances where its unique hosts are of sufficient number to escape the full negative impact of inter-biotype mating interactions and reduced competitiveness in terms of reproductive rate, while exposing the indigenous biotype to the full effects of the interaction. Web of Science Bemisia tabaciis Australia Queensland Indooroopilly -27.493761 152.973948 Lab terrestrial Grassland Fundamentals herbivore 1361 Hyatt, LA; Araki, S 2006 Comparative population dynamics of an invading species in its native and novel ranges journal BIOLOGICAL INVASIONS 8 2 261 275 Although the ecology of many exotic invaders has been intensively examined in the novel range, few studies have comparatively explored how population dynamics differ in native and novel parts of an invading plants' range. The population dynamics of mile-a-minute weed, Polygonum perfoliatum L., was explored in both the native (Japan) and novel (northeastern USA) portions of its range and evaluated using periodic matrix models. Projected per capita population growth rate (lambda) varied within and between native and novel range populations. Surprisingly, five of the six populations in the novel range were projected to fail to replace themselves (lambda<1) while only two of the four native range populations were projected to decline, although these projections had wider confidence intervals than in the novel habitat. While changes in germination, survivorship, fecundity and seed banking would have equivalent effects on population growth in the invasive habitat, small increases in plant survivorship would greatly increase lambda in native populations. The differences between native and novel population growth rates were driven by lower adult survival in the native range caused by annual flooding and higher fecundity. Simulation analyses indicated that a 50% reduction in plant survival would be required to control growing populations in the novel range. Further comparative studies of other invading species in both their native and novel ranges are needed to examine whether the high per capita population growth and strong regulatory effects of adult survival in the native habitat are generally predictive of invasive behavior in novel habitats. Web of Science Polygonum perfoliatum USA Pennsylvania Ridley Creek State Park 39.943871 -75.444174 Field - Observational terrestrial Old Field Invasion Hyp. Inherent Superiority primary 1362 Spector, T; Putz, FE 2006 Biomechanical plasticity facilitates invasion of maritime forests in the southern USA by Brazilian pepper (Schinus terebinthifolius) journal BIOLOGICAL INVASIONS 8 2 255 260 Biomechanical plasticity and within-species growth form diversity are traits that can facilitate invasion by non-native plant species. We support this argument with evidence from the invasion of coastal habitats in northern Florida, USA, by Schinus terebinthifolius and describe some of the consequences of this invasion for overtopped saltmarsh plants. In crowded stands, Schinus grows more like a vine than a tree, with stem height : diameter ratios nearly twice than those observed in open-grown individuals but with no changes in wood density or the modulus of elasticity of stem material. When extracted from the surrounding vegetation, the formerly crowded Schinus stems buckle under their own weight. Schinus crowns also extend much further over adjacent saltmarsh than crowns of Juniperus virginiana, the only other tree species abundant in the study site. Along forest edges, the above-ground biomass of saltmarsh plants overtopped by Schinus crowns was reduced by more than an order of magnitude. The biomechanical plasticity of Schinus allows it to adapt its growth form to suit habitat conditions and can dominate the edges of salt marshes as a sprawling shrub and maritime forests as either a free-standing tree or a woody vine, depending on stand crowding. Web of Science Schinus terebinthifolius USA Florida Flager Beach 29.440988 -81.113462 Field - Observational terrestrial Wetland Invasion Hyp. Plasticity primary 1364 Reinhart, KO; Maestre, FT; Callaway, RM 2006 Facilitation and inhibition of seedlings of an invasive tree (Acer platanoides) by different tree species in a mountain ecosystem journal BIOLOGICAL INVASIONS 8 2 231 240 Facilitation is known to be an important process structuring natural plant communities. However, much less is known about its role in facilitating the invasion of ecosystems by non-native plant species. In this study we evaluated the effects of invasive (Acer platanoides) and native (Pseudotsuga menziesii) forest types on the performance of A. platanoides seedlings, and related these effects to structural and functional properties associated with the two forest types, in a native P. menziesii forest that is being invaded by A. platanoides. Acer platanoidesseedlings had higher densities, recruitment, and survival, and experienced less photoinhibition and water stress when beneath conspecific canopies than in the adjacent P. menziesii forest. Soil moisture and canopy cover were greater in the invaded patch than the native forest. There was no difference in soil fertility or understory light levels between locations. These demographic (i.e. seedling survival), physiological, and environmental differences appeared to be due to the effects of A. platanoides and P. menziesii trees. Thus, Acer trees appear to produce a more mesic environment by modifying the structure and phenology of the forest canopy and by altering the timing of transpirational water loss relative to P. menziesii. Environmental modification by invaders that lead to positive effects on conspecifics may help us to understand the dramatic success and lag periods of some invasive species Web of Science Acer platanoides USA Montana Bonner 46.875055 -113.857169 Field - Observational terrestrial Deciduous Forest;Coniferous Forest Invasion Hyp. Ecosystem Engineers primary 1365 Batten, KM; Scow, KM; Davies, KF; Harrison, SP 2006 Two invasive plants alter soil microbial community composition in serpentine grasslands journal BIOLOGICAL INVASIONS 8 2 217 230 Plant invasions pose a serious threat to native ecosystem structure and function. However, little is known about the potential role that rhizosphere soil microbial communities play in facilitating or resisting the spread of invasive species into native plant communities. The objective of this study was to compare the microbial communities of invasive and native plant rhizospheres in serpentine soils. We compared rhizosphere microbial communities, of two invasive species, Centaurea solstitialis (yellow starthistle) and Aegilops triuncialis (barb goatgrass), with those of five native species that may be competitively affected by these invasive species in the field (Lotus wrangelianus, Hemizonia congesta, Holocarpha virgata, Plantago erecta, and Lasthenia californica). Phospholipid fatty acid analysis (PLFA) was used to compare the rhizosphere microbial communities of invasive and native plants. Correspondence analyses (CA) of PLFA data indicated that despite yearly variation, both starthistle and goatgrass appear to change microbial communities in areas they invade, and that invaded and native microbial communities significantly differ. Additionally, rhizosphere microbial communities in newly invaded areas are more similar to the original native soil communities than are microbial communities in areas that have been invaded for several years. Compared to native plant rhizospheres, starthistle and goatgrass rhizospheres have higher levels of PLFA biomarkers for sulfate reducing bacteria, and goatgrass rhizospheres have higher fatty acid diversity and higher levels of biomarkers for sulfur-oxidizing bacteria, and arbuscular mycorrhizal fungi. Changes in soil microbial community composition induced by plant invasion may affect native plant fitness and/or ecosystem function. Web of Science Centaurea solstitialis; Aegilops triuncialis USA California McLaughlin Natural Reserve 38.873554 -122.429695 Impacts;Invasion Hyp. Mutualism Facilitation primary 1369 Morgan, JW 2006 Bryophyte mats inhibit germination of non-native species in burnt temperate native grassland remnants journal BIOLOGICAL INVASIONS 8 2 159 168 Species-rich native grasslands in western Victoria, Australia, are often small, have a high perimeter to area ratio and are surrounded by non-native species. Few non-native species, however, have invaded them. A feature of species-rich grasslands is the presence of a bryophyte mat (composed of mosses and liverworts) that carpets the intertussock spaces. I assessed the role of these mats in plant invasions by sowing three non-native species (Briza maxima, Hypochoeris radicata, Plantago lanceolata) in replicated disturbed (mats removed) and undisturbed (mats intact) microsites at three grassland remnants (two recently burnt, one unburnt for 3 years) and followed seedling emergence, survival and growth for 5 months. Three native species were also sown for comparison. The rate of germination and total percent germination of non-native species were significantly enhanced at both burnt sites when the mat was disturbed. The large-seeded Briza maxima failed to germinate at both burnt sites in the absence of soil disturbance. The native species generally did not show a strong germination or growth response to soil disturbance in burnt areas. At the unburnt site, where monthly percent soil moisture was highest, final percent germination of the non-native and native species was greatest of any site in both microsites, and germination was not significantly affected by soil disturbance. Differences in the seed morphology of native and non-native species may play an important role in their ability to establish on bryophyte mats in moisture-limiting environments. Any activity that disrupts the mats in the frequently burnt, species-rich grassland remnants is likely to significantly enhance the germination and subsequent growth by non-natives. However, where burning is infrequent, germination of some non-native species may be expected, regardless of disturbance, although growth will likely be favoured in disturbed areas. Web of Science Briza maxima; Hypochoeris radicata; Plantago lanceolata Australia Victoria Melbourne -37.994729 144.48801 Field - Experimental terrestrial Grassland Invasion Hyp. Disturbance primary 1373 Von Holle, B; Simberloff, D 2005 Ecological resistance to biological invasion overwhelmed by propagule pressure journal ECOLOGY 86 12 3212 3218 Models and observational studies have sought patterns of predictability for invasion of natural areas by nonindigenous species, but with limited success. In a field experiment using forest understory plants, we jointly manipulated three hypothesized determinants of biological invasion outcome: resident diversity, physical disturbance and abiotic conditions, and propagule pressure. The foremost constraints on net habitat invasibility were the number of propagules that arrived at a site and naturally varying resident plant density. The physical environment (flooding regime) and the number of established resident species had negligible impact on habitat invasibility as compared to propagule pressure, despite manipulations that forced a significant reduction in resident richness, and a gradient in flooding from no flooding to annual flooding. This is the first experimental study to demonstrate the primacy of propagule pressure as a determinant of habitat invasibility in comparison with other candidate controlling factors. Web of Science Many USA Virginia Big Stony Creek 37.410692 -80.590324 Field - Experimental terrestrial Riparian Invasion Hyp. Community Species Richness;Propagule Pressure primary 1374 Morales, CL; Aizen, MA 2006 Invasive mutualisms and the structure of plant-pollinator interactions in the temperate forests of north-west Patagonia, Argentina journal JOURNAL OF ECOLOGY 94 1 171 180 1 Alien species may form plant-animal mutualistic complexes that contribute to their invasive potential. Using multivariate techniques, we examined the structure of a plant-pollinator web comprising both alien and native plants and flower visitors in the temperate forests of north-west Patagonia, Argentina. Our main objective was to assess whether plant species origin (alien or native) influences the composition of flower visitor assemblages. We also examined the influence of other potential confounding intrinsic factors such as flower symmetry and colour, and extrinsic factors such as flowering time, site and habitat disturbance. 2 Flowers of alien and native plant species were visited by a similar number of species and proportion of insects from different orders, but the composition of the assemblages of flower-visiting species differed between alien and native plants. 3 The influence of plant species origin on the composition of flower visitor assemblages persisted after accounting for other significant factors such as flowering time, bearing red corollas, and habitat disturbance. This influence was at least in part determined by the fact that alien flower visitors were more closely associated with alien plants than with native plants. The main native flower visitors were, on average, equally associated with native and alien plant species. 4 In spite of representing a minor fraction of total species richness (3.6% of all species), alien flower visitors accounted for > 20% of all individuals recorded on flowers. Thus, their high abundance could have a significant impact in terms of pollination. 5 The mutualistic web of alien plants and flower-visiting insects is well integrated into the overall community-wide pollination web. However, in addition to their use of the native biota, invasive plants and flower visitors may benefit from differential interactions with their alien partners. The existence of these invader complexes could contribute to the spread of aliens into novel environments. Web of Science Many Argentina Patagonia Nahuel Huapi National Park -40.791771 -71.532898 Field - Observational terrestrial Deciduous Forest;Coniferous Forest Invasion Hyp. Mutualism Facilitation primary;herbivore 1376 Cavieres, LA; Quiroz, CL; Molina-Montenegro, MA; Munoz, AA; Pauchard, A 2005 Nurse effect of the native cushion plant Azorella monantha on the invasive non-native Taraxacum officinale in the high-Andes of central Chile journal PERSPECTIVES IN PLANT ECOLOGY EVOLUTION AND SYSTEMATICS 7 3 217 226 Positive interactions among native plant species are common in alpine habitats, particularly those where one species (nurse plant) generates microclimatic conditions that are more benign than the surrounding environment, facilitating the establishment of other species. Nonetheless, these microclimatic conditions could facilitate the establishment of non-native species as well. A conspicuous component of the alien alpine flora of the central Chilean Andes is the perennial herb Taraxacum officinale agg. (dandelion). In contrast to other alien species that are restricted to human-disturbed sites, T officinale is frequently observed growing within native plant communities dominated by cushion plants. In this study we evaluated if T officinale is positively associated with the cushion plant Azorella monantha. Via seedling survival experiments and gas-exchange measurements we also assessed the patterns of facilitation between cushions and dandelions, and explore the potential mechanisms of invasion by dandelions. T officinale grows spatially positively associated with cushions of A. monantha. Survival of seedlings, as well as their net-photo synthetic rates and stomatal conductance., were higher within cushions than in open areas away from them, suggesting that the microclimatic modifications generated by this native cushion facilitates the establishment and performance of a non-native invasive species. Our results, as well as other recent studies, highlight the role of native communities in facilitating rather than constraining non-native plant invasions, particularly in stressful habitats such as alpine environments. (c) 2005 Rubel Foundation, ETH Zurich. Published by Elsevier GmbH. All rights reserved. Web of Science Taraxacum officinale Chile Santiago Andes -33.337068 -69.899368 Field - Observational;Greenhouse terrestrial Mountain Invasion Hyp. Mutualism Facilitation primary 1378 Arevalo, JR; Delgado, JD; Otto, R; Naranjo, A; Salas, M; Fernandez-Palacios, JM 2005 Distribution of alien vs. native plant species in roadside communities along an altitudinal gradient in Tenerife and Gran Canaria (Canary Islands) journal PERSPECTIVES IN PLANT ECOLOGY EVOLUTION AND SYSTEMATICS 7 3 185 202 Roadside plant communities were studied along two roads following an altitudinal gradient in Gran Canaria and Tenerife (Canary Islands). Our aim was to investigate variation in plant species richness, particularly of the alien flora, along a gradient from coastal shrubland to summit vegetation (1950 m a.s.l. in Gran Canaria, 2300 m in Tenerife) in relation to variation in habitat factors (altitude, habitat structure, roadside disturbance, distance to urban nuclei). We compared different species groups that were classified in terms of their biogeographical status, origin and life form. Altitude was the most important factor determining species richness and composition along both roadside transects. Alien plants showed a unimodal distribution pattern along the altitudinal gradient, with less species and lower abundance at low and high altitudes, and highest abundance at intermediate altitude. Alien plant species were also relatively more frequent near urban centres. The number of native and alien species was significantly positively correlated along the altitudinal gradient. Both alien and native, non-endemic species showed differences in their distribution along the altitudinal gradient according to their biogeographical affinities and climatic tolerances. Despite considerable differences in species pools these patterns were consistent among the two islands. Environmental (abiotic) stress is proposed as a primary, altitude-related factor acting as a filter against most alien plants at coastal and high-mountain altitudes. A higher frequency or intensity of disturbance at intermediate altitudes may be a further causal factor promoting alien plants in this zone. Future management efforts to control alien plants along roads should, therefore, concentrate on intermediate altitudinal zones of the higher Canary Islands. (c) 2005 Rubel Foundation, ETH Zurich. Published by Elsevier Gmbh. All rights reserved. Web of Science Many Spain Canary Islands Gran Canaria; Tenerife 28.266408 -16.636505 Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Community Species Richness primary 1379 Becker, T; Dietz, H; Billeter, R; Buschmann, H; Edwards, PJ 2005 Altitudinal distribution of alien plant species in the Swiss Alps journal PERSPECTIVES IN PLANT ECOLOGY EVOLUTION AND SYSTEMATICS 7 3 173 183 In summer 2003 we recorded the presence and abundance of alien plant species at 232 sites (107 railway stations and 125 road sites) along mountain passes in the Swiss Alps. The altitudinal distribution of species was related to the current abundance of the species in Switzerland and time since introduction. A total of 155 alien taxa were recorded. Numbers of species per site declined exponentially with altitude, and only a few species were found in the alpine zone (> 2000 m). In contrast, species richness among comparable native taxa appeared to be nearly independent of altitude over the range investigated. Maximum altitude reached by alien species was related positively to both total area occupied in Switzerland and to time since introduction. A comparison of the results with earlier records suggests that many species, particularly those previously restricted to low or intermediate altitudes, have advanced their altitudinal limits over the past few decades. Various hypotheses are presented to explain the declining abundance of alien species with altitude: low-altitude filter effects, low propagule pressure, and genetic swamping of peripheral populations at higher altitudes. However, at present we do not have sufficient evidence to determine the relative importance of these effects. We conclude that invasion into mountain areas such as the Swiss Alps tends to proceed rather slowly, though the process may be accelerated by climatic warming. For this reason, further research to investigate the processes determining how plants invade mountain areas is urgently needed. And more generally, investigations into the distribution of alien species along strong altitudinal gradients may provide valuable insights into the mechanisms driving the spread of alien organisms. (c) 2005 Rubel Foundation, ETH Zurich. Published by Elsevier GmbH. All rights reserved. Web of Science Many Switzerland 47.16843 7.909241 Field - Observational terrestrial Mountain Fundamentals primary 1380 McDougall, KL; Morgan, JW; Walsh, NG; Williams, RJ 2005 Plant invasions in treeless vegetation of the Australian Alps journal PERSPECTIVES IN PLANT ECOLOGY EVOLUTION AND SYSTEMATICS 7 3 159 171 A total of 128 invasive plant species have been recorded in treeless vegetation in the Australian Alps. Most of these are forbs and most are uncommon. Cover of invasive species is generally minimal unless there has been gross disturbance to natural vegetation and soils. Although there is a significantly positive correlation between invasive and native species diversity, suggesting that conditions that allow numerous native species to co-exist also permit more plant invasions, altitude is the most important determinant of invasive species diversity. Only 22 of the 128 species have been recorded above 1800 in. Some plant communities (e.g. those with high pH or relatively nutrient-rich soils), however, seem to be vulnerable to invasions regardless of altitude. Most invasive species appear to have been introduced unintentionally (e.g. as seed attached to vehicles, animals and humans) but a few were introduced to assist with revegetation of disturbed soils and for amenity plantings in ski resorts, and have subsequently established in native vegetation. Treeless communities in the Australian Alps are likely to face increasing pressure from invasive species as a result of global warming and continued introduction of non-native plants to ski resort gardens. Whilst it may be difficult to prevent invasive species of low elevations migrating to higher elevations as temperatures rise, the risk of invasion from garden plants could be minimised through regulation. Non-native plants in ski resort gardens pose a far greater risk than most invasive species currently present in the Alps because they have been chosen for their capacity to survive at high altitudes. Crown Copyright (c) 2005 Published by Elsevier GmbH on behalf of Rubel Foundation, ETH Zurich. All rights reserved. Web of Science Many Australia Victoria Australian Alps -37.3033 146.864319 Field - Observational;Review terrestrial Mountain Fundamentals primary 1384 Riley, SPD; Busteed, GT; Kats, LB; Vandergon, TL; Lee, LFS; Dagit, RG; Kerby, JL; Fisher, RN; Sauvajot, RM 2005 Effects of urbanization on the distribution and abundance of amphibians and invasive species in southern California streams journal CONSERVATION BIOLOGY 19 6 1894 1907 Urbanization negatively affects natural ecosystems in many ways, and aquatic systems in particular Urbanization is also cited as one of the potential contributors to recent dramatic declines in amphibian populations. 1,From 2000 to 2002 we determined the distribution and abundance of native amphibians and exotic predators and characterized stream habitat and invertebrate communities in 35 streams in an urbanized landscape north of Los Angeles (U.S.A.). We measured watershed development as the percentage of area within each watershed occupied by urban land uses. Streams in more developed watersheds often bad exotic crayfish (Procambarus clarkii) and fish, and had fewer native species such as California newts (Taricha torosa) and California treefrogs (Hyla cadaverina). These effects seemed particularly evident above 8% development a result coincident with other urban stream studies that show negative impacts beginning at 10-15% urbanization. For Pacific treefrogs (H. regilla), the most widespread native amphibian, abundance was lower in the presence of exotic crayfish, although direct urbanization effects were not found. Benthic macroinvertebrate communities were also less diverse in. urban streams, especially for sensitive species. Faunal community changes in urban streams may be related to changes in physical stream habitat, such as fewer pool and more run habitats and increased water depth and flow, leading to more permanent streams. Variation in stream permanence was particularly evident in 2002 a dry year when many natural streams were dry but urban streams were relatively unchanged. Urbanization has significantly altered stream habitat in this region and may. enhance invasion by axotic species and negatively affect diversity and abundance of native amphibians. Web of Science Procambarus clarkii; Rana catesbeiana USA California Malibu 34.073592 -118.81897 Field - Observational lotic Invasion Hyp. Other herbivore;omnivore 1385 Genton, BJ; Kotanen, PM; Cheptou, PO; Adolphe, C; Shykoff, JA 2005 Enemy release but no evolutionary loss of defence in a plant invasion: an inter-continental reciprocal transplant experiment journal OECOLOGIA 146 3 404 414 When invading new regions exotic species may escape from some of their natural enemies. Reduced top-down control (*enemy release*) following this escape is often invoked to explain demographic expansion of invasive species and also may alter the selective regime for invasive species: reduced damage can allow resources previously allocated to defence to be reallocated to other functions like growth and reproduction. This reallocation may provide invaders with an *evolution of increased competitive ability* over natives that defend themselves against specialist enemies. We tested for enemy release and the evolution of increased competitive ability in the North American native ragweed (Ambrosia artemisiifblia: Asteraceae), which currently is invading France. We found evidence of enemy release in natural field populations from the invaded and native ranges. Further we carried out a reciprocal transplant experiment, comparing several life history traits of plants from two North American (Ontario and South Carolina) and one French population in four common gardens on both continents. French and Canadian plants had similar flowering phenologies, flowering earlier than plants from further south in the native range. This may suggest that invasive French plants originated from similar latitudes to the Canadian population sampled. As with natural populations, experimental plants suffered far less herbivore damage in France than in Ontario. This difference in herbivory translated into increased growth but not into increased size or vigour. Moreover, we found that native genotypes were as damaged as invading ones in all experimental sites, suggesting no evolutionary loss of defence against herbivores. Web of Science Ambrosia artemisiifblia France Lyon 45.576754 5.250549 Field - Experimental terrestrial Grassland Invasion Hyp. Enemy Release primary 1387 Keeley, JE; Baer-Keeley, M; Fotheringham, CJ 2005 Alien plant dynamics following fire in Mediterranean-climate California shrublands journal ECOLOGICAL APPLICATIONS 15 6 2109 2125 Over 75 species of alien plants Were recorded during the first five years alter fire in. southern California shrublands, most of which were European annuals. Both cover and richness of aliens varied between years and plant association. Alien cover was lowest in the first postfire year in all plant associations and remained low during succession in chaparral but increased in sage scrub. Alien cover and richness were significantly correlated with year (time since disturbance) and with precipitation in both coastal and interior sage scrub associations. Hypothesized. factors determining alien dominance were tested with structural equation modeling. Models that included nitrogen deposition and distance from the coast were not significant, but with those variables removed we obtained a significant model that gave an R-2 = 0.60 for the response variable of fifth year alien dominance. Factors directly affecting alien dominance were (1) woody canopy closure and (2) alien seed banks. Significant indirect effects were (3) fire intensity, (4) fire history, (5) prefire stand structure, (6) aridity, and (7) community type. According to this model the most critical factor influencing aliens is the rapid return of the shrub and subshrub canopy. Thus, in these communities a single functional type (woody plants) appears to the most critical element controlling alien invasion and persistence. Fire history is an important indirect factor because it affects both prefire stand structure and postfire alien seed banks. Despite being fire-prone ecosystems, these shrublands are not adapted to fire per se, but rather to a particular fire regime. Alterations in the fire regime produce a very different selective environment, and high fire frequency changes the selective regime to favor aliens. This study does not support the widely held belief that prescription burning is a viable management practice for controlling alien species on semiarid landscapes. Web of Science Many USA California Southern California 34.457654 -118.084717 Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Disturbance primary 1388 Jacquemyn, H; Brys, R; Neubert, MG 2005 Fire increases invasive spread of Molinia caerulea mainly through changes in demographic parameters journal ECOLOGICAL APPLICATIONS 15 6 2097 2108 We investigated the effects of fire on population growth rate and invasive spread-of the perennial tussock grass Molinia caerulea. During the last decades, this species has invaded heathland communities in Western Europe, replacing typical heathland species such as Calluna vulgaris and Erica tetralix. M. caerulea is considered a major threat to heathland conservation. In 1996, a large and unintended fire destroyed almost one-third of the Kalmthoutse Heide, a large heathland area in northern Belgium. To study the impact of this fire on the population dynamics and invasive spread of M. caerulea, permanent monitoring plots were established both in burned and unburned heathland. The fate of each M. caerulea individual in these plots was monitored over four years (1997-2000). Patterns of seed dispersal were inferred from a seed germination experiment using soil cores sampled one month after seed rain at different distances from seed-producing plants. Based on these measures, we calculated projected rates of spread for M. caerulea in burned and unburned heathland. Elasticity and sensitivity analyses were used to determine vital rates that contributed most to population growth rate, and invasion speed. Invasion speed was, on average, three times larger in burned compared to unburned plots. Dispersal distances on the other hand, were not significantly different between burned and unburned plots indicating If at differences in invasive spread, were mainly due to differences in demography. Elasticities for fecundity and growth of seedlings and juveniles were higher for burned than for unburned plots, whereas elasticities for survival were higher in unburned plots: Finally, a life table response experiment (LTRE) analysis revealed that the effect of fire was mainly contributed by increases in sexual reproduction (seed production and germination) and growth of seedlings and juveniles. Our results clearly showed, increased invasive spread of M. caerulea after fire, and call for active management guidelines to prevent further encroachment of the species and to reduce the probability of large, accidental fires in the future. Mowing of resprouted plants before flowering is the obvious management tactic to halt massive invasive spread of the species after fire. Web of Science Molinia caerulea Belgium Kalmthoutse Heide 51.416595 4.395676 Field - Experimental terrestrial Grassland Invasion Hyp. Disturbance primary 1392 Wolfson, BAS; Kolb, TE; Sieg, CH; Clancy, KM 2005 Effects of post-fire conditions on germination and seedling success of diffuse knapweed in northern Arizona journal FOREST ECOLOGY AND MANAGEMENT 216 3 342 358 Introduction of exotic plant species is confounding treatments designed to reduce unnaturally high tree densities in ponderosa pine (Pinus ponderosa P. & C. Lawson) forests of the western United States. Also, the recent increase in large, stand-replacing wildfires may promote introduction and spread of species, such as diffuse knapweed (Centaurea diffusa Lam.), which may lead to reduced forage and land values and major ecosystem changes. We hypothesized that diffuse knapweed germination and seedling growth would respond positively to burned conditions in northern Arizona ponderosa pine forests. Our first field study was based on a May 2002 wildfire near Flagstaff, Arizona (Site I). For the field study at Site I, we buried diffuse knapweed seeds in sealed mesh packets in four forest floor conditions: severely burned, moderately burned, unburned bare soil and unburned. We removed packets monthly and measured percent germination. Germination under severely burned conditions at Site I (overall average 76%) was higher than in unburned conditions (59%) (P = 0.017). Our second field study was based on a fuel reduction treatment with slash piles burned in February 2003 (Site H). Germination in seed packets was higher (P = 0.003) in pile burn scars (67%) than in adjacent unburned locations (38%) at Site II. In fall 2002, we planted knapweed seeds in pots containing intact 'oil cores from Site I from unburned and severely burned conditions. We allowed competition to grow in half the pots, and removed competition in the other half. Diffuse knapweed biomass/pot was greater (P = 0.035) in soil from the severely burned (2.6 g) compared to the unburned condition (0.6 g) from Site I. Knapweed biornass/pot also appeared greater when grown in soil from pile burn scars (3.3 g) compared with unburned locations (2.5 g) from Site II, although the difference was not significant (P = 0.317). We conclude that severe wildfire or pile burning can promote germination and seedling growth of diffuse knapwecd in northern Arizona pine forests. Moreover, diffuse knapweed may also threaten unburned forests, as average germination was 48% in unburned locations. Failure to consider exotic invasive species in fuel reduction and wildfire rehabilitation may result in trading one undesirable condition for another. (c) 2005 Elsevier B.V. All rights reserved. Web of Science Centaurea diffusa USA Arizona Flagstaff 35.339942 -111.752357 Field - Experimental terrestrial Coniferous Forest Invasion Hyp. Disturbance primary 1394 Bulleri, F; Airoldi, L 2005 Artificial marine structures facilitate the spread of a non-indigenous green alga, Codium fragile ssp tomentosoides, in the north Adriatic Sea journal JOURNAL OF APPLIED ECOLOGY 42 6 1063 1072 1. Artificial structures have become ubiquitous features of coastal landscapes. Although they provide novel habitats for the colonization of marine organisms, their role in facilitating biological invasions has been largely unexplored. 2. We investigated the distribution and dynamics of the introduced green alga, Codium fragile ssp. tomentosoides, at a variety of spatial scales on breakwaters in the north Adriatic Sea, and analysed experimentally the mechanisms underlying its establishment. We assessed the provision of sheltered habitats by breakwaters, the role of disturbance (e.g. from recreational harvesting and storms) acting at different times of the year, and the interactions between Codium and the dominant native space-occupier, the mussel Mytilus galloprovincialis. 3. Codium fragile ssp. tomentosoides has established viable populations on artificial structures along the shores investigated. The density, cover and size (length, branching and weight) of annual erect thalli of Codium was enhanced in sheltered conditions, resulting in the monopolization of landward low-shore habitats of breakwaters. 4. On the landward sides of breakwaters, disturbance enhanced recruitment of Codium. The time when bare space was provided within mussels beds was crucial. Removal of mussels in April or January did not affect the recruitment of Codium, whereas harvest in August, shortly before Codium gamete release, doubled its success. On the seaward sides of breakwaters, the effects of disturbance were more complex because mussels both inhibited recruitment of Codium and provided shelter from wave action to adult thalli. 5. Synthesis and applications. Artificial structures can provide suitable habitats for non-indigenous marine species and function as corridors for their expansion. Physical (wave exposure) and biotic (resident assemblages) features of artificial habitats can be important determinants of their susceptibility to biological invasions. Alternative options in the design of artificial structures and effective management of native assemblages could minimize their role in biological invasions. In particular, increased water motion and retention of space by mussels in spring-summer would be effective in reducing the ability of C. fragile ssp. tomentosoides to persist on the breakwaters investigated in this study. Web of Science Codium fragile ssp. tomentosoides Italy Trieste Adriatic Sea 45.67673 13.756027 Field - Experimental marine Intertidal/Near Shore Invasion Hyp. Disturbance primary 1395 Henry, PY; Bousset, L; Sourrouille, P; Jarne, P 2005 Partial selfing, ecological disturbance and reproductive assurance in an invasive freshwater snail journal HEREDITY 95 6 428 436 Although reproductive assurance ( RA) might play a central role in the evolution of the selfing rate, this hypothesis has never been seriously investigated in an hermaphroditic animal. We studied the mating system of the freshwater snail Physa acuta in which the availability of mating partners might be highly variable, because this species is an efficient colonizer occupying unstable habitats. A total of 11 populations differing in ecological disturbance regime ( water level, openness) and snail densities were monitored over 2 years. The outcrossing rate was estimated in ca 10 families per population using microsatellite markers and the progeny-array approach. Components of fecundity and survival were recorded for each progeny. Predominant outcrossing ( t(m) = 0.94) was detected, with a few individuals ( 4%) purely The outcrossing rate did not explain among- family variation in fitness components. None of the predictions formulated under the RA hypothesis were verified: ( i) selfing was related neither to disturbed habitats, nor to temporal density fluctuations, ( ii) it was positively related to population density, ( iii) it co- occurred with multiple paternity, and ( iv) it did not induce delayed reproduction. Explanations for these negative results are discussed in light of other arguments supporting the RA hypothesis in P. acuta, as well as alternative theories explaining the occurrence of partial selfing, as either a genetically fixed or plastic trait. Web of Science Physa acuta France Montpellier 43.600582 3.891678 Field - Observational lotic Invasion Hyp. Inherent Superiority Self Compatible herbivore 1397 Agrawal, AA; Kotanen, PM; Mitchell, CE; Power, AG; Godsoe, W; Klironomos, J 2005 Enemy release? An experiment with congeneric plant pairs and diverse above- and belowground enemies journal ECOLOGY 86 11 2979 2989 Several hypotheses. proposed to explain the success of introduced species focus on altered interspecific interactions. One of the most prominent, the Enemy Release Hypothesis, posits that invading species benefit compared to their native counterparts if they lose their herbivores and pathogens during the invasion process. We previously reported on a common garden experiment (from 2002) in which we compared levels of herbivory between 30 taxonomically paired native and introduced old-field plants. In this phylogenetically controlled comparison, herbivore damage tended to be higher on introduced than on native plants. This striking pattern, the opposite of current theory, prompted us to further investigate herbivory and several other interspecific interactions in a series of linked experiments with the same set of species. Here we show that, in these new experiments, introduced plants, on average, received less insect herbivory and were subject to half the negative soil microbial feedback compared to natives; attack by fungal and viral pathogens also tended to be reduced on introduced plants compared to natives. Although plant traits (foliar C:N, toughness, and water content) suggested that introduced species should be less resistant to generalist consumers, they were not consistently more heavily attacked. Finally, we used meta-analysis to combine data from this study with results from our previous work to show that escape generally was inconsistent among guilds of enemies: there were few instances in which escape from multiple guilds occurred for a taxonomic pair, and more cases in which the patterns of escape from different enemies canceled out. Our examination of multiple interspecific interactions demonstrates that escape from one guild of enemies does not necessarily imply escape from other guilds. Because the effects of each guild are likely to vary through space and time, the net effect of all enemies is also likely to be variable. The net effect of these interactions may create *invasion opportunity windows*: times when introduced species make advances in native communities. Web of Science Many United States New York 44.05 -79.4833 Garden;Review terrestrial Old Field Invasion Hyp. Enemy Release;Other primary 1398 Rogers, WE; Siemann, E 2005 Herbivory tolerance and compensatory differences in native and invasive ecotypes of Chinese tallow tree (Sapium sebiferum) journal PLANT ECOLOGY 181 1 57 68 The Evolution of Increased Competitive Ability (EICA) hypothesis proposes that exotic plants may become superior competitors in their introduced ranges because they have evolved reduced defense allocation and increased growth in response to low herbivory. Long-term common garden studies with Chinese tallow tree (Sapium sebiferum), a problematic invader in the southeastern United States, support EICA predictions of invasive ecotypes displaying rapid growth with poorly defended leaves, whereas native ecotypes are slower growing and have nitrogen rich, highly defended leaves. We conducted two full-factorial experiments designed to assess the effects of leaf herbivory and soil fertility on growth of Sapium seedlings derived from seeds obtained in the species' native Chinese range and introduced range along the Texas Gulf Coast. The first was a field study employing simulated defoliation to examine herbivory tolerance, while the second was a pot study using grasshopper bioassays to measure the compensatory regrowth of native and introduced Sapium ecotypes. In accordance with EICA predictions, introduced Texas ecotypes compensated for mechanical and natural defoliation regardless of resource conditions while growth of native Chinese ecotypes was significantly reduced as a result of both simulated and natural herbivory damage. These results demonstrate that invasive Sapium ecotypes have a greater capacity to compensate for herbivory damage than native Sapium ecotypes. The differences between Sapium ecotypes are consistent with the mechanisms of EICA and other findings demonstrating that invasive ecotypes have become herbivory tolerant due to post-introduction changes in tissue quality. Web of Science Sapium sebiferum USA Texas Galveston 29.332083 -95.042152 Field - Experimental terrestrial Grassland Invasion Hyp. Evolution of Increased Competitive Ability primary 1402 Bubb, DH; Thom, TJ; Lucas, MC 2005 The within-catchment invasion of the non-indigenous signal crayfish Pacifastacus leniusculus (Dana), in upland rivers journal BULLETIN FRANCAIS DE LA PECHE ET DE LA PISCICULTURE 0 127 665 673 The American signal crayfish, Pacifastacus leniusculus, is an invasive species from North America that has been widely introduced through Europe, where it is a major threat to native European crayfish species and causing increasing concern because of its impact on the wider aquatic ecosystem. Although widely considered invasive, little is known of the rates of invasion and colonisation. The temporal and spatial pattern of spread of signal crayfish populations in two upland rivers in Northern England is described. Range expansion of up to 2.4 km year(-1) were recorded from an established population, but rates over an order of magnitude less were recorded in the initial stages of establishment. Range expansion of both populations was strongly biased in a downstream direction, which has implications for directing possible management efforts and determining the timescale of threat which expanding signal crayfish populations pose. Web of Science Pacifastacus leniusculus England Yorkshire River Warfe 54.063579 -1.714783 Field - Observational lotic Impacts;Fundamentals omnivore 1403 Murren, CJ; Denning, W; Pigliucci, M 2005 Relationships between vegetative and life history traits and fitness in a novel field environment: Impacts of herbivores journal EVOLUTIONARY ECOLOGY 19 6 583 601 At the edge of a species range, plants may experience myriad microenvironmental gradients, which may differ and impose strong yet complex selective regimes. We explore these issues using the model organism Arabidopsis thaliana, a native of Europe that has naturalized in North America, which we planted in a common garden field plot in Knoxville, Tennessee and observed across two biotic gradients. We found evidence that directional selection favors increased plant size, consistent with hypotheses of plant responses to novel environments. However, selection differed among plants with fungus gnat larvae damage, aphid damage, and plants that escaped herbivory, evidence that the selective landscape is variable and complex even for quasi-natural field plots. We did not uncover evidence for resistance; however, our results suggest that tolerance of A. thaliana may play an important role for population establishment and persistence in the presence of herbivores in a novel environment. Our findings highlight the variation in one segment of the biotic selective landscape of field environments, as well as the importance of biotic interactions in shaping the success of recently established populations that may be a critical component of post-invasion evolution. Web of Science Arabidopsis thaliana USA Tennessee Knoxville 35.983785 -83.980408 Field - Experimental terrestrial Old Field Invasion Hyp. Evolution in General primary 1404 Muller, C; Martens, N 2005 Testing predictions of the 'evolution of increased competitive ability' hypothesis for an invasive crucifer journal EVOLUTIONARY ECOLOGY 19 6 533 550 The successful spread of invasive plants may result from an evolutionary shift in resource allocation from defence to growth due to release from enemies, as proposed by the 'evolution of increased competitive ability' hypothesis (EICA). The crucifer Lepidium draba was used to test this hypothesis, measuring growth and levels of glucosinolates and myrosinase of leaves as constitutive defence parameters. Individuals from 21 populations of the native (Europe) and the invasive range (North-America) were grown under common greenhouse conditions. According to the EICA hypothesis it was predicted that plants from the invasive range might show stronger growth and have lower levels of defence as a result of selection favouring such genotypes. There was significant variation between populations in shoot, root, total biomass, and number of ramets of 3-month-old plants but no difference due to origin from both continents. The main glucosinolate p-hydroxybenzyl glucosinolate was significantly higher in seedlings of the invasive range while myrosinase activity was higher in old plants of the invasive range. Therefore, the EICA hypothesis does not hold, however, alternatively there is evidence for selection favouring stronger defence in the invasive range. The binary defence system of this crucifer is discussed with respect to the degree of specialisation of potential herbivores. Web of Science Lepidium draba USA Idaho 43.6487 -116.4936 Garden terrestrial Grassland Invasion Hyp. Evolution of Increased Competitive Ability primary 1406 Wasson, K; Fenn, K; Pearse, JS 2005 Habitat differences in marine invasions of central california journal BIOLOGICAL INVASIONS 7 6 935 948 We carried out a two-part investigation that revealed habitat differences in marine invertebrate invasions. First, we compared invasion levels of hard vs soft substrata in Elkhorn Slough, an estuary in Central California, by comparing abundance and richness of native vs exotic species in quantitative samples from each habitat type. Our results revealed that the hard substrata were much more heavily invaded than the soft substrata. Nearly all the hard substrata in Elkhorn Slough, as in most estuaries along the Pacific coast of North America, are artificial (jetties, rip-rap, docks). Some exotic species may by chance be better adapted to this novel habitat type than are natives. Two major vectors responsible for marine introductions, oyster culturing and ship-hull fouling, are also more likely to transport species associated with hard vs soft substrata. Secondly, we compared estuarine and open coast invasion rates. We examined species richness in Elkhorn Slough and adjacent rocky intertidal habitats along the Central California coast. The absolute number of exotic species in the estuary was an order of magnitude higher than along the open coast (58 vs 8 species), as was the percentage of the invertebrate fauna that was exotic (11% vs 1%). Estuaries on this coast are geologically young, heavily altered by humans, and subject to numerous transport vectors bringing invasive propagules: all these factors may explain why they are strikingly more invaded than the open coast. The finding that the more species rich habitat - the open coast - is less invaded is in contrast to many terrestrial examples, where native and exotic species richness appear to be positively correlated at a broad geographic scale. Web of Science Many USA California Elkhorn Slough 36.814411 -121.754122 Field - Observational estuarine Benthic Fundamentals primary;decomposer;filter 1407 Torchin, ME; Byers, JE; Huspeni, TC 2005 Differential parasitism of native and introduced snails: Replacement of a parasite fauna journal BIOLOGICAL INVASIONS 7 6 885 894 The role of parasites in a marine invasion was assessed by first examining regional patterns of trematode parasitism in the introduced Japanese mud snail, Batillaria cumingi (= B. attramentaria), in nearly all of its introduced range along the Pacific Coast of North America. Only one parasite species, which was itself a non-native species, Cercaria batillariae was recovered. Its prevalence ranged from 3 to 86%. Trematode diversity and prevalence in B. cumingi and a native sympatric mud snail, Cerithidea californica, were also compared in Bolinas Lagoon, California. Prevalence of larval trematodes infecting snails as first intermediate hosts was not significantly different (14% in B. cumingi vs 15% in C. californica). However, while the non-native snail was parasitized only by one introduced trematode species, the native snail was parasitized by 10 native trematode species. Furthermore, only the native, C. californica, was infected as a second intermediate host, by Acanthoparyphium spinulosum(78% prevalence). Given the high host specificity of trematodes for first intermediate hosts, in marshes where B. cumingi is competitively excluding C. californica, 10 or more native trematodes will also become locally extinct. Web of Science Batillaria cumingi USA California Bolinas Lagoon 37.920818 -122.680428 Field - Observational estuarine Benthic Invasion Hyp. Enemy Of My Enemy herbivore 1408 Uowolo, AL; Binkley, D; Adair, EC 2005 Plant diversity in riparian forests in northwest Colorado: Effects of time and river regulation journal FOREST ECOLOGY AND MANAGEMENT 218 3 107 114 During the 20th Century the flow of most rivers in the United States was regulated by diversions and dams, with major impacts on riparian forests. Few unregulated rivers remain to provide baseline information for assessing these impacts. We characterized patterns in riparian plant communities along chronosequences on the unregulated Yampa River and the regulated Green River in northwestern Colorado, examining patterns in plant species diversity in relation to the ages of floodplain terraces. On both rivers, mean plant species richness in cottonwood (Populus deltoides Marshall subsp. wislizenzii (Watson) Eckenwalder) dominated riparian forests declined by more than 50% from young sites ( < 20 years) to old upland terraces ( > 250 years). Mean species richness (number of plant species/1000 m(2)) was 40% higher on the unregulated Yampa River than on the regulated Green River, and 84% of the variance in total species richness related to age class, river, and tree cover. One-third of the plant species in all plots were exotic and 63% of the variance in exotic species richness was explained by a positive correlation with the richness of native species. On the Yampa and Green Rivers, ecosystem development and river regulation both reduce species richness, and these effects appear to be additive. The methods and insights from this study can be applied to other river systems to investigate the processes that change species diversity over time, and vegetation responses to the major changes in environmental conditions that follow river regulation. (c) 2005 Elsevier B.V. All rights reserved. Web of Science Many USA Colorado Yampa and Green Rivers 40.231734 -106.898804 Field - Observational terrestrial Riparian Invasion Hyp. Disturbance primary 1411 Galli, P; Stefani, F; Benzoni, F; Zullini, A 2005 Introduction of alien host-parasite complexes in a natural environment and the symbiota concept journal HYDROBIOLOGIA 548 0 293 299 When a species is introduced in a new territory its parasites may also follow, thus forming a sort of biotic unit. We propose the term symbiota to indicate this host-parasite complex. This concept is at the basis of the present research in which 11 species of alien and native freshwater fish were collected by electrofishing in the Po river area (Northern Italy). The alien host fish Ictalurus melas and Silurus glanis were parasitized by only one monogenean species each. Lepomis gibbosus, of North American origin, hosted four monogeneans and Carassius carassius three. All these parasites should be considered as alien species, except those collected from C. carassius that should be considered in part natives and in part aliens. Web of Science Ictalurus melas; Silurus glanis; Lepomis gibbosus; Carassius carassius Italy Po Valley Po River 44.94264 10.452576 Field - Observational lentic Invasion Hyp. Mutualism Facilitation herbivore;omnivore;predator;parasite 1412 Kissling, WD; Schnittler, M; Seddon, PJ; Dickinson, KJM; Lord, JM 2005 Invasion ecology of the alien tussock grass Nardus stricta (Poaceae) at Lake Pukaki, Canterbury, New Zealand journal NEW ZEALAND JOURNAL OF BOTANY 43 3 601 612 The European matgrass Nardus stricta has naturalised in New Zealand, often on damp soils within wetlands and grasslands. In this paper, we present for the first time field data on the ecology of this alien invader in New Zealand, from eight kettle-hole wetlands on lateral moraine along the western side of Lake Pukaki, South Canterbury. The invaded wetland sites were all acidic but varied in other soil characteristics. Nardus stricta was the most dominant species within these wetland communities with 40% of all plots showing more than 50% coverage, and 21% having more than 90% cover. Species richness (including vascular plants and mosses) at some sites was relatively high (c. 40 species), but species richness and abundance were significantly reduced in quadrats with high Nardus stricta density. Seedling densities of Nardus stricta were high but variable (overall mean of 38.6 116 seedlings per m(2)), and establishment mainly occurred on the cushion-forming sedge Oreobolus pectinatus. Most reproductive tussocks (90%) produced up to 1000 florets, but single tussocks were able to produce up to 10 000 and more florets. Our results suggest that Nardus stricta is still expanding its local range and, therefore, is likely to increase in abundance and dominance, resulting in further negative effects on native species diversity. Web of Science Nardus stricta New Zealand South Canterbury Lake Pukaki -44.169104 170.112076 Field - Observational terrestrial Wetland Impacts;Fundamentals primary 1414 Barrat-Segretain, MH 2005 Competition between invasive and indigenous species: impact of spatial pattern and developmental stage journal PLANT ECOLOGY 180 2 153 160 Elodea canadensis (indigenous) and Elodea nuttallii (invasive) were grown in experimental tanks in monocultures and mixtures in two spatial patterns (aggregated or mixed) and two developmental stages (small or large plants of E. canadensis, and small plants of E. nuttallii). Competitive interactions between the two species were assessed by monitoring the area colonised by each species, the number of rootings and biomass after 10 weeks. In monocultures the growth of E. canadensis was significantly lower than that of E. nuttallii. In mixtures the number of rootings and biomass of E. canadensis were always significantly less than those of E. nuttallii. The tank surface area colonised by E. canadensis was always significantly less than that occupied by E. nuttallii, but it was higher in the aggregated treatment, where the colonisation of E. nuttallii was lower. Therefore both spatial pattern and developmental stage of an indigenous species (E. canadensis) may influence the outcome of competition with potential invaders (E. nuttallii). Web of Science Elodea nuttallii France Rhône-Alpes Lyon 45.60174 4.819334 Lab lotic Invasion Hyp. Inherent Superiority Rapid Growth primary 1416 Williamson, M; Pysek, P; Jarosik, V; Prach, K 2005 On the rates and patterns of spread of alien plants in the Czech Republic, Britain, and Ireland journal ECOSCIENCE 12 3 424 433 The rates and patterns of spread of 63 species in the Czech Republic and seven in Britain and Ireland were determined from quadrat records, mapovaci pole (11- x 12-km mapping zones in the Czech Republic), and 10- x 10-km hectads in Britain and Ireland. Species that have straight sections on logarithmic, square root, and arithmetic plots were found; the last group (10 of them) are generally casuals. Straight square root plots (52 found) are expected from Fisher-Skellam reaction diffusion models, logarithmic equivalents (36 found) where the dispersal kernel has a thicker tail or where spread involves scattered colonies. The greater frequency of the straight square root plots is unexpected. The straightness of so many plots shows that there is no significant variation in recorder bias. About a third of the species showed lags, and many species showed a later slowing of the rate of spread, called here bends. Lags may indicate an initial casual phase as well as slower growth; bends, a lack of further areas to spread to. Typically, with much variation, areas of occupancy double in about 10 y (logarithmic mode) or spread at about 2 km (.) y(-1) (square root mode). Both speeds indicate that most spread is from human activity. The reasons for the major phenomena (the occurrence of the two types of spread predicted by models, their distinctness, and the distribution in rates) may reflect economic and landscape features as well as biological ones. The straightness, speed, and patterns found are all new results for invasion biology. Keywords: Britain, Czech Republic, data transformations, Ireland, patterns of spread, rates of spread. Web of Science Many Britain; Czech Republic 53.136226; 50.024682 -2.651369; 15.190428 Theoretical/Modeling Fundamentals 1417 Tabacchi, E; Planty-Tabacchi, AM 2005 Exotic and native plant community distributions within complex riparian landscapes: A positive correlation journal ECOSCIENCE 12 3 412 423 We studied the riparian vegetation on the agricultural floodplain of the Middle Garonne River (SW France) in order to compare native and exotic plant community patterns. In total, we investigated the vegetation of 1,824 plots during four seasons along 50-m-long transects delineated transversely from the banks of five types of water bodies (subsystems) differing by their exposure to natural and to human-induced disturbance. Exotic species accounted for 21% of the total of 726 species identified. We characterized native and exotic plant communities of each subsystem on the basis of Grime's ecological strategies, species lifespan, species richness, and species cover. The communities of each subsystem were compared with respect to the landscape structure (35 patch types) and to their distribution according to the distance to the bank of each water body, the distance to the main channel of the river, the annual duration of inundation, the total plant cover, the total species richness, and the proportion of exotics. Although significant contrasts exist between the community structures of each water body, we found a strong correlation between the attributes of native and exotic species pools. Native and exotic species covers were negatively correlated, while native species richness was positively correlated to exotic species richness, both at local and large scale. This positive correlation remained significant when comparing plots within each patch type. Few or no differences were detected between the distribution of native and exotic species according to the six variables of interest, the effect of the origin (exotic or native) of the plants being negligible as a discriminant attribute. The possible role of landscape complexity and the role of combined natural and human-induced disturbances are discussed to explain these patterns. Web of Science Many France Aquitane Toulouse 44.161125 0.892181 Field - Observational terrestrial Riparian Invasion Hyp. Community Species Richness primary 1418 Richardson, DM; Rouget, M; Ralston, SJ; Cowling, RM; Van Rensburg, BJ; Thuiller, W 2005 Species richness of alien plants in South Africa: Environmental correlates and the relationship with indigenous plant species richness journal ECOSCIENCE 12 3 391 402 This study explores the correlates of alien plant species richness in South Africa at the scale of quarter-degree squares (QDS; similar or equal to 25 x 27 km; 675 km(2)). We considered all alien plant species for which we had records and a subset of these - those that invade natural and semi-natural vegetation. The main source of data for species richness of indigenous and alien plant species was a national database based on herbarium specimens. For invasive alien species, data were from a national atlassing project. First, we explored the importance of energy availability and habitat heterogeneity as correlates of indigenous, alien, and invasive alien plant species richness. Linear regression models showed that species richness in the three groups of plants was explained by the same variables: a principal component of climatic factors and topographic roughness were the top-ranking variables for all groups. Next, we examined the role of indigenous species richness together with a range of environmental and human-activity variables in explaining species richness of alien and invasive alien plants. Results reveal an interplay of natural features and variables that quantify the dimension of human activities. If indigenous species richness is ignored, human-activity variables are more strongly correlated with alien species richness than with invasive alien species richness. Numbers of alien and invasive species in QDSs are significantly correlated with indigenous plant species richness in the 1,597 QDSs selected for analysis, a pattern consistent with findings from other parts of the world. Analysis of residuals between observed and predicted values showed that patterns differed between biomes. The results are useful for planning long-term intervention policy at the national scale; they suggest that areas with rich native biodiversity will face a sustained onslaught from invasive alien species and that ongoing management actions will be required to reduce and mitigate impacts from biological invasions in these areas. Web of Science Many South Africa -29.523758 24.997558 Statistical/Meta-analysis Invasion Hyp. Community Species Richness primary 1419 Lavoie, C; Dufresne, C; Delisle, F 2005 The spread of reed canarygrass (Phalaris arundinacea) in Quebec: A spatio-temporal perspective journal ECOSCIENCE 12 3 366 375 Reed canarygrass (Phalaris arundinacea) is one of the most invasive plant species in North American wetlands, but there are few historical data regarding the spread of this species, particularly at its northeastern distribution limit. We reconstructed the spread of reed canarygrass in Quebec using herbarium specimens and a method that accounts for some of the biases associated with this type of historical record. We hypothesized that the beginning of the spread of the species coincided with the introduction in Canada of reed canarygrass cultivars for forage. Reed canarygrass specimens collected during the 19(th) century in places as remote as Lake Mistassini and Anticosti Island provide strong evidence that this species is native to northeastern North America. The spatial distribution of specimens collected before 1925 suggests that reed canarygrass probably occupied most of its present-day area at that time. There is no strong evidence that reed canarygrass expanded its distribution limits in Quebec during the 20(th) century. However, the species colonized several new sites within its distribution limits in recent decades, especially from 1963 to 1978. The spread was probably associated with nitrate pollution and road construction in southern Quebec, and with water level fluctuations of the St. Lawrence River. Although herbarium specimens suffer from sampling biases, their use may provide new spatio-temporal insights into the spread of invasive species and facilitate the identification of probable causes of invasiveness. Web of Science phalaris arundinacea Canada quebec 47.058148 -71.7334 Statistical/Meta-analysis terrestrial Wetland Fundamentals primary 1420 Civille, JC; Sayce, K; Smith, SD; Strong, DR 2005 Reconstructing a century of Spartina alterniflora invasion with historical records and contemporary remote sensing journal ECOSCIENCE 12 3 330 338 Remote sensing is becoming a vital tool for understanding the changing vegetation patterns that are associated with broad-scale plant invasions. The establishment of North American east coast native Spartina alterniflora (smooth cordgrass) in Willapa Bay, Washington is a specific example of broad-scale invasion following local introduction. In this study, we examined a 120-y historical record of aerial photographs, oral histories, museum records, and publications to reconstruct the spatial, temporal, and historical elements of this invasion. We conclude that the most likely means for S. alterniflora to have reached Willapa Bay was the transport and translocation of oysters from New York harbour. Our data and analysis suggest that multiple areas were colonized between 1894 and 1920 coincident with sustained import of oysters from the Atlantic seaboard. We have evidence that S. alterniflora had been long established and growing in multiple widely spread locations by 1945, which is in contrast to a widely reported single introduction. Multiple foci would not only explain the colonization patterns we have observed, but could also increase the heterogeneity of the founding populations, helping to overcome barriers to reproduction that may have initially slowed the colonization in isolated populations during the first 50-70 y. Web of Science Spartina alterniflora USA Washington Willapa Bay 46.478206 -123.958168 Statistical/Meta-analysis estuarine Intertidal/Near Shore Fundamentals primary 1423 Lavi, A; Perevolotsky, A; Kigel, J; Noy-Meir, I 2005 Invasion of Pinus halepensis from plantations into adjacent natural habitats journal APPLIED VEGETATION SCIENCE 8 1 85 92 Questions: Do invasions of P. halepensis (Aleppo pine) from plantations into adjacent natural communities occur in the Mediterranean region, where the species is native? What are the spatio-temporal processes involved in pine invasions in contrasting Mediterranean and semi-arid climatic regions? Location: Mediterranean and semi-arid regions of Israel. Methods: The density of invading Pinus was measured in relation to the distance from the plantation edge. Plants were categorized by age, height, basal stem girth and developmental stage, their spatial distribution was also recorded. Results: Analysis of plant age distribution indicates that the invasion process started when the plantations were 20-25 years old. Most invading plants were found within 20 m from the plantation edge, but a few individuals reached distances up to 100 m and became new invasion foci. Plant density declined sharply with distance from adult trees, data showing a better fit to a power model than to a negative exponential model. Invading Pinus began to produce cones earlier in the semi-arid than in the Mediterranean region (9 vs 12 years to 50% reproductive plants). In both regions, higher densities of invading plants were found on the west side of the plantation, the opposite direction to the hot winds that prevail during seed release. Conclusion: The frontal advance of P. halepensis from plantations is relatively slow, but the populations also expand by a saltation process, creating spreading 'islands' of pine trees in the natural vegetation. Spatial pattern of recruits with distance from the source population was remarkably similar to the pattern of seed dispersal in the same region (Nathan et al. 1999). This implies that the probability of a dispersed seed developing into a plant is independent of the distance from the forest edge. Web of Science Pinus halepensis Israel Galilee; Judean moutnains Ya’ar-Hasolelim; Gvaot-Gad 33.1667;31.4833 35.3333;34.8833 Field - Observational terrestrial Coniferous Forest Fundamentals primary 1424 Herrick, BM; Wolf, AT 2005 Invasive plant species in diked vs. undiked Great Lakes wetlands journal JOURNAL OF GREAT LAKES RESEARCH 31 3 277 287 We compared the standing vegetation, seed banks, and substrate conditions in seven pairs of diked and undiked wetlands near the shores of Lake Michigan and Lake Huron, North America. Our analysis tested the null hypothesis that construction of artificial dikes has no effect on the vulnerability of Great Lakes coastal wetlands to non-native and native invasive species. Both the standing vegetation and seed banks in diked wetlands contained significantly more species and individuals of invasive plants. In addition, diked wetlands exhibited significantly higher levels of organic matter and nutrient levels, and significantly higher average pH. Two pervasive non-native invasive species in the Great Lakes region, Lythrum salicaria (purple loosestrife) and Phalaris arundinacea (reed canary grass) were significantly more abundant in diked wetlands. Typha spp. (cattail) also formed a much higher percent vegetation cover in the diked wetlands. Our results support the view that diking of shoreline wetlands modifies natural hydrologic regimes, leading to nutrient-rich aquatic environments that are vulnerable to invasion. The shallower, more variable water levels in non-diked wetlands, on the other hand, appear to favor another undesirable invasive species, Phragmites australis (common reed grass). Web of Science Lythrum salicaria; Phalaris arundinacea; Phragmites australis USA Michigan Lake Michigan; Lake Huron 44.6667;43.8333 -87.9167;-83.6667 Field - Experimental estuarine Wetland Invasion Hyp. Disturbance primary 1426 Hill, SJ; Tung, PJ; Leishman, MR 2005 Relationships between anthropogenic disturbance, soil properties and plant invasion in endangered Cumberland Plain Woodland, Australia journal AUSTRAL ECOLOGY 30 7 775 788 Invasive exotic plants are a significant threat to areas of conservation value, with endangered ecological communities being especially vulnerable. We assessed the role of different anthropogenic disturbances in determining the success of exotic plants in the endangered Cumberland Plain Woodland community of western Sydney and examined the impact of these disturbances on soil characteristics that are likely to impact on vegetation, including total P, pH, water retention capacity, organic matter content and electrical conductivity. The disturbance types were: (i) land use incorporating clearing, agriculture and grazing by stock; (ii) creeks draining a developed catchment; and (iii) roads. Remnants that had been cleared and grazed had higher exotic and lower native species richness and cover than all other disturbance types. Areas that had been grazed but not cleared did not have more exotic species richness or cover than uncleared/ungrazed areas, thus retaining high conservation value. Areas within 2 m of a creek edge had higher exotic species richness and cover than areas further from the creek edge. Areas downslope of sealed roads had significantly higher exotic species richness and cover than areas below unsealed roads. No single soil attribute or combination of soil attributes was consistently able to account for variation in exotic species cover under the different disturbance types. Thus it appears that other factors such as site history and propagule pressure may be more important in determining exotic species success than soil characteristics alone, in this vegetation community. Web of Science Paspalum dilatatum; Axonopus affinis; Paspalum dilatatum; Axonopus affinis; Setaria gracilis; Sporobolus indicus; Australia New South Wales Cumberland Plain -34.001898 150.803375 Field - Observational terrestrial Savanna Invasion Hyp. Propagule Pressure;Disturbance primary 1428 Totland, O; Nyeko, P; Bjerknes, AL; Hegland, SJ; Nielsen, A 2005 Does forest gap size affects population size, plant size, reproductive success and pollinator visitation in Lantana camara, a tropical invasive shrub? journal FOREST ECOLOGY AND MANAGEMENT 215 3 329 338 Invasive species are regarded as one of the largest global threats to biodiversity, but little is still known about the invasion of exotic plants into tropical forests. In this paper, we examine how the size and canopy openness of human-created gaps inside the Mabira forest-reserve in Uganda, affect the invasion of one of the world's most noxious weeds, Lantana camara L. Subpopulation size inside gaps was positively related to gap size, and components of individual plant size increased with increasing gap size and canopy openness. Moreover, the reproductive effort of L. camara increased with gap size and canopy openness, whereas the fruit production of individual plants was unrelated to gap size and canopy openness. Finally, there was no relationship between gap size and pollinator visitation to inflorescence, but a marginally significant relationship occurred between canopy openness and pollinator visitation. Overall, our results suggest that the size of human-created gaps inside Mabira forest-reserve positively affect aspects of the population dynamics of L. camara. We propose strategies for a campaign aimed at removing L. camara from this forest-reserve, with minimal disturbance to intact forest habitats. (c) 2005 Elsevier B.V. All rights reserved. Web of Science Lantana camara Uganda Mukono district Mabira forest-reserve 0.386784 33.000069 Field - Observational terrestrial Tropical Forest Invasion Hyp. Disturbance primary 1430 Gelbard, JL; Harrison, S 2005 Invasibility of roadless grasslands: An experimental study of yellow starthistle journal ECOLOGICAL APPLICATIONS 15 5 1570 1580 Roadless habitats are commonly found to be less invaded than habitats near roads, but few studies have tested whether this pattern is due to propagule limitation or to greater invasion resistance of roadless sites. We examined reasons for the lower frequency and cover of yellow starthistle (Centaurea solstitialis) in grassland sites > 1000 m vs. 10 m from roads in an inland California, USA, foothill landscape. During winter 2001 and 2002, we planted 100 Centaurea seeds in 64 pairs of 30 x 30 cm plots (uncleared and cleared of aboveground plant material) at sites stratified by distance from roads (10 m and > 1000 m), soil type (nonserpentine and serpentine), and aspect (cool, warm, and neutral slopes). In nonserpentine grasslands, Centaurea survival was greater in uncleared (but not cleared) near (10 m) plots than in distant (> 1000 m) plots. These findings suggest that the effect of distance from roads on survival corresponds with higher aboveground biotic resistance in distant sites than in near sites. Centaurea biomass was greater in near than in distant plots (both uncleared and cleared) on nonserpentine soil, suggesting that either abiotic resistance or below ground biotic resistance could limit its growth in distant sites. These distance effects were no longer significant in models that included two biotic covariates: native grass cover (which was higher in distant sites and negatively correlated with Centaurea performance) and bare ground (which was lower in distant sites and positively correlated with Centaurea performance). On serpentine soil, there was no effect of road proximity on the performance of planted Centaurea. Our results suggest that Centaurea seeds can germinate in nonserpentine and serpentine grasslands regardless of distance from roads. Beyond the seedling stage, however, biotic resistance associated with higher native grass cover and lower levels of disturbance may inhibit Centaurea invasion of nonserpentine grassland sites-that are distant from roads. Web of Science Centaurea solstitialis USA California Middletown 38.75 -122.25 Field - Experimental terrestrial Grassland Invasion Hyp. Disturbance primary 1431 Reed, HE; Seastedt, TR; Blair, JM 2005 Ecological consequences of C-4 grass invasion of a C-4 grassland: A dilemma for management journal ECOLOGICAL APPLICATIONS 15 5 1560 1569 Many successful exotic invasive species are functionally distinct from the dominant native species they displace. Occasionally invasion occurs where the exotic species possesses functional traits relatively similar to those of the dominant native. We examined the ecological consequences of such an invasion within a mesic, temperate grassland at the Konza Prairie Long-Term Ecological Research site. We assessed potential changes in carbon (C) and nitrogen (N) cycling and plant diversity following the invasion of a C-4 bunch grass species, Andropogon bladhii, into a tallgrass prairie dominated by the native C-4 grass species, A. gerardii. In these prairies burning is an important management tool used to maintain native-species dominance. We determined how frequent spring fires affected the impacts of A. bladhii in this system. Over a two-year study our results show that burning regulated the effects that the invasive species has on the native prairie. Compared to the native species, A. bladhii exhibited significantly greater plant biomass, significantly lower pools of soil N, significantly lower rates of decay and C cycling, and higher foliar and root tissue C:N ratio in response to burning. Notable spatial heterogeneity in C and N cycling was evident in areas dominated by the invasive bunch grass. In addition to altered ecosystem processes, areas dominated by the invasive, A. bladhii, had significantly lower plant species diversity. In a grassland ecosystem where burning is an important management tool for controlling exotic-species establishment, maintaining native-species dominance, and increasing productivity, A. bladhii may be able to successfully out-compete the native C-4 grass species by using traits typically used to explain the dominance of the native species. With frequent fire, the invasive species has the potential to decrease long-term fertility by lowering N inputs in litter and increasing erosion in non-vegetated soil between bunches, while also having a negative effect on plant diversity. By using fire to promote native C-4 grasses and maintain these tallgrass prairies, the threat of invasion by normative C-4 species may raise a dilemma for future management of these C-4 grasslands. Web of Science Andropogon bladhii USA Kansas Konza Prairie 39.090261 -96.572685 Field - Experimental terrestrial Grassland Invasion Hyp. Inherent Superiority;Disturbance Superior Competitor primary 1433 Lee, KA; Martin, LB; Wikelski, MC 2005 Responding to inflammatory challenges is less costly for a successful avian invader, the house sparrow (Passer domesticus), than its less-invasive congener journal OECOLOGIA 145 2 244 251 When introduced into new regions, invading organisms leave many native pathogens behind and also encounter evolutionarily novel disease threats. In the presence of predominantly novel pathogens that have not co-evolved to avoid inducing a strong host immune response, costly and potentially dangerous defenses such as the systemic inflammatory response could become more harmful than protective to the host. We therefore hypothesized that introduced-populations exhibiting dampened inflammatory responses will tend to be more invasive. To provide initial data to assess this hypothesis, we measured metabolic, locomotor, and reproductive responses to inflammatory challenges in North American populations of the highly invasive house sparrow (Passer domesticus) and its less-invasive relative, the tree sparrow (Passer montanus). In the house sparrow, there was no effect of phytohemagglutimn (PHA) challenge on metabolic rate, and there were no detectable differences in locomotor activity between lipopolysaccharide (LPS)-injected birds and saline-injected controls. In contrast, tree sparrows injected with PHA had metabolic rates 20-25% lower than controls, and LPS injection resulted in a 35% drop in locomotor activity. In a common garden captive breeding experiment, there was no effect of killed-bacteria injections on reproduction in the house sparrow, while tree sparrows challenged with bacteria decreased egg production by 40% compared to saline-injected controls. These results provide some of the first data correlating variation in immune defenses with invasion success in introduced-vertebrate populations. Web of Science Passer domesticus USA Missouri; Illinois St. Louis; Meredosia 36; 40 -90; -90 Lab terrestrial Invasion Hyp. Inherent Superiority Superior Competitor omnivore 1434 Krinke, L; Moravcova, L; Pysek, P; Jarosik, V; Pergl, J; Perglova, I 2005 Seed bank of an invasive alien, Heracleum mantegazzianum, and its seasonal dynamics journal SEED SCIENCE RESEARCH 15 3 239 248 The seed bank of Heracleum mantegazzianum, native to the western Caucasus and invasive in Europe, was studied in the Slavkovsky les Protected Landscape Area, the Czech Republic, during the course of two growing seasons. In each of seven study sites with dominating stands of the species, soil samples were taken in October (after the fruit release), April (before germination) and June-July (before the fruit release). Ten samples were taken from each site using a soil hand bore, 4.6 cm in diameter. Seeds elutriated from the samples were immediately germinated in laboratory conditions (10 degrees C, 12 h light/12 h dark); those that germinated during 1 month were considered as non-dormant. Non-germinated but viable seeds, tested for viability by tetrazolium, were considered as dormant. The number of dead seeds was also recorded. The total number of seeds significantly increased with mean density of flowering plants at a site. Of the total variation in seed-bank size, about four-fifths were attributed to that among sites, and one-fifth to that within sites. The number and proportion of living seeds differed significantly between years in summer, but not in autumn and spring. Total number and the numbers of dormant, non-dormant, living and dead seeds significantly differed among the autumn, spring and summer samples. The percentage of living seeds in the total seed bank decreased from 56% in autumn to 42% in spring to 15% in summer. The percentage of non-dormant seeds among those living was 0.3% in autumn, it increased to 87.5% in the spring sample, and decreased to 3% in summer. Pooled across all sites, the average seed numbers (expressed per m(2)) were 6719 +/- 4119 (mean +/- SD) in autumn, 4907 +/- 2278 in spring and 1301 +/- 1036 in summer for the total number of seeds, and 3759 +/- 2906, 2044 +/- 1198 and 192 +/- 165, respectively, for living seeds. The majority of seeds (95%) were concentrated in the upper 5 cm soil layer. However, some seeds were present in lower soil layers, which indicates a short-term persistent seed bank. The present data are the first quantitative estimate of the seed bank in H. mantegazzianum, and show that the reproductive potential of the species is enormous, which seems to be a crucial feature of its invasion success. Web of Science Heracleum mantegazzianum Czech republic Slavkovsky les protected 50.052201 12.797241 Field - Observational terrestrial Grassland Invasion Hyp. Propagule Pressure primary 1435 Dickens, SJM; Gerhardt, F; Collinge, SK 2005 Recreational portage trails as corridors facilitating non-native plant invasions of the Boundary Waters Canoe Area Wilderness (USA) journal CONSERVATION BIOLOGY 19 5 1653 1657 Wilderness areas are protected and valued in part for recreation; recreational use, however, can negatively impact these areas. In particular, recreational use can facilitate transport of non-native propagules and create open sites for establishment of non-native species. We examined the role of recreational portage trails in the introduction and establishment of non-native plants into the Boundary Waters Canoe Area Wilderness of northern Minnesota (US.A.). On 20 portages, we sampled non-native plant richness and cover at four distances (0, 10, 25, and 50 m) from trails. Non-native richness and cover were not related to distance from wilderness entry point. Non-native richness and cover were, however, negatively related to distance from trails. All six non-native species we observed were either directly on or within I m of trails. These results suggest that recreational trails act as corridors facilitating invasions of non-native plants into wilderness areas. It remains unclear, however, whether these effects are caused by dispersal of propagules, creation of bare ground, or changes in the native plant community. Web of Science Plantago major; Trifolium pratense USA Minnesota Boundary waters 47.95 -91.8 Field - Observational terrestrial Deciduous Forest;Coniferous Forest Invasion Hyp. Disturbance primary 1438 Clark, GF; Johnston, EL 2005 Manipulating larval supply in the field: a controlled study of marine invasibility journal MARINE ECOLOGY-PROGRESS SERIES 298 0 9 19 In order to gather experimental data to test theories of invasion biology, ecologists have recently adopted a rigorous experimental approach in which community traits and propagule supply are manipulated independently. However, these studies have been limited to terrestrial systems and their generality is not well understood. We conducted a manipulative field experiment to test the relationship between common human disturbances and invasibility in hard-substrate marine epifaunal communities. A larval dosing technique was developed to allow marine experimental units to be dosed with a controlled supply of propagules under field conditions. Six month old assemblages were exposed to 3 fully crossed factors of (1) physical disturbance, (2) chemical disturbance, and (3) timing of larval dose relative to the disturbances. Physical disturbance was shown to increase the invasion success of the introduced species, Bugula neritina, up to 30 d following the disturbance. This was mainly through an increase of recruitment onto primary space, however physical impacts with an antifoulant surface also led to increased recruitment on secondary space. After 15 d, B. neritina recruits on primary space were found to be larger than recruits on secondary space, suggesting an elevated threat of invasion through primary recruitment. Natural recruitment of barnacles, ascidians, and sedentary polychaetes was also increased by physical disturbance, although these effects were weaker and varied between taxa and sampling times. This study supports the theory that disturbance facilitates invasions in marine epifaunal communities, and contributes a new technique of manipulating propagule supply in the marine environment. Web of Science Bugula neritina Australia New South Wales Botany Bay -33.975168 151.182804 Field - Experimental marine Intertidal/Near Shore Invasion Hyp. Disturbance filter 1439 Davis, HG 2005 r-Selected traits in an invasive population journal EVOLUTIONARY ECOLOGY 19 3 255 274 I compared life-history traits and self-fertilization rates in greenhouse culture of native Spartina alterniflora with an invasive population from a low-density Pacific estuary to see whether plants in the novel r-selective regime exhibit early reproduction, greater self-compatibility and high reproductive effort putting individuals at greater risk of death. Plants were grown from seed collected from the Atlantic and Gulf coasts of North America and a population introduced approximately 100 years ago to Willapa Bay, Washington, USA that has expanded to cover over ca. 6000 hectares. Pacific marshes have almost no native emergent vascular plants in the intertidal habitat, offering a virtually empty niche for invasive S. alterniflora. The low-density plants at the leading edge of this rapidly expanding population suffer a severe Allee effect of greatly reduced fecundity, caused by pollen limitation, compared to high-density areas. I found 99% of the invasive plants initiated reproduction in the first year of this study, while only 52% of the native range plants did so in the first year, followed by 34% in the second and 14% of native plants had not initiated reproduction after three years. The invasive plants had more than twice the reproductive effort of the native plants. Plants with the highest reproductive effort in the first year of growth died regardless of coastal site of origin, although nearly all of those that died over two years were invasive Pacific plants (27%). The invaders set two times the seed as the natives under forced selfing, suggesting greater self-compatibility or reproductive effort. These results suggest either a founding and bottleneck event and/or the invasive population has evolved from the long-lived, predominantly self-incompatible, K-selected state of the probable invasive propagules originating in dense, competitive native marshes. Web of Science Spartina alterniflora USA Washington Willapia Bay 46.549086 -123.90049 Greenhouse estuarine Invasion Hyp. Evolution in General primary 1442 van der Putten, WH; Yeates, GW; Duyts, H; Reis, CS; Karssen, G 2005 Invasive plants and their escape from root herbivory: a worldwide comparison of the root-feeding nematode communities of the dune grass Ammophila arenaria in natural and introduced ranges journal BIOLOGICAL INVASIONS 7 4 733 746 Invasive plants generally have fewer aboveground pathogens and viruses in their introduced range than in their natural range, and they also have fewer pathogens than do similar plant species native to the introduced range. However, although plant abundance is strongly controlled by root herbivores and soil pathogens, there is very little knowledge on how invasive plants escape from belowground enemies. We therefore investigated if the general pattern for aboveground pathogens also applies to root-feeding nematodes and used the natural foredune grass Ammophila arenaria as a model. In the late 1800s, the European A. arenaria was introduced into southeast Australia (Tasmania), New Zealand, South Africa, and the west coast of the USA to be used for sand stabilization. In most of these regions, it has become a threat to native vegetation, because its excessive capacity to stabilize windblown sand has changed the geomorphology of coastal dunes. In stable dunes of most introduced regions, A. arenaria is more abundant and persists longer than in stabilized dunes of the natural range. We collected soil and root samples and used additional literature data to quantify the taxon richness of root-feeding nematodes on A. arenaria in its natural range and collected samples from the four major regions where it has been introduced. In most introduced regions A. arenaria did not have fewer root-feeding nematode taxa than the average number in its natural range, and native plant species did not have more nematode taxa than the introduced species. However, in the introduced range native plants had more feeding-specialist nematode taxa than A. arenaria and major feeding specialists (the sedentary endoparasitic cyst and root knot nematodes) were not found on A. arenaria in the southern hemisphere. We conclude that invasiveness of A. arenaria correlates with escape from feeding specialist nematodes, so that the pattern of escape from root-feeding nematodes is more alike escape from aboveground insect herbivores than escape from aboveground pathogens and viruses. In the natural range of A. arenaria, the number of specialist-feeding nematode taxa declines towards the margins. Growth experiments are needed to determine the relationship between nematode taxon diversity, abundance, and invasiveness of A. arenaria. Web of Science Ammophila arenaria USA; New Zealand; Australia 46.099968; -40.378773; -41.144949 -123.937118; 175.225525; 146.628571 Field - Observational terrestrial Grassland Invasion Hyp. Enemy Release primary 1443 Colautti, RI; Muirhead, JR; Biswas, RN; MacIsaac, HJ 2005 Realized vs apparent reduction in enemies of the European starling journal BIOLOGICAL INVASIONS 7 4 723 732 Release from parasites, pathogens or predators (i.e. enemies) is a widely cited 'rule of thumb' to explain the proliferation of nonindigenous species in their introduced regions (i.e. the 'enemy release hypothesis', or ERH). Indeed, profound. effects of some parasites and predators on host populations are well documented. However, some support for the ERH comes from studies that find a reduction in the species richness of enemies in the introduced range, relative to the native range, of particular hosts. For example, data on helminth parasites of the European starling in both its native Eurasia and in North America support a reduction of parasites in the latter. However, North American 'founder' starlings were likely not chosen randomly from across Eurasia. This could result in an overestimation of enemy release since enemies affect their hosts on a population level. We control for the effects of subsampling colonists and find, contrary to previous reports, no evidence that introduced populations of starlings experienced a reduction in the species richness of helminth parasites after colonization of North America. These results highlight the importance of choosing appropriate contrast groups in biogeographical analyses of biological invasions to minimize the confounding effects of 'propagule biases'. Web of Science Sturnus vulgaris USA 41.849924 -74.238288 Field - Observational terrestrial Urban Invasion Hyp. Enemy Release omnivore 1444 Constible, JM; Sweitzer, RA; Van Vuren, DH; Schuyler, PT; Knapp, DA 2005 Dispersal of non-native plants by introduced bison in an island ecosystem journal BIOLOGICAL INVASIONS 7 4 699 709 An understanding of the mechanisms of seed dispersal is critical to effectively managing populations of non-native plants. We investigated whether introduced bison on Santa Catalina Island, California, have the potential to spread non-native plants through the shedding of clumps of seed-laden hair and/or ingesting and later excreting seeds. We collected clumps of hair shaved from bison during a roundup and dislodged by wallowing activity. Greenhouse and field trials were used to test for seed viability and persistence of hair clumps in wallows. In addition to trials with bison hair, we collected samples of bison dung and tested for seed germination in a greenhouse. The majority of seeds extracted from bison hair clumps were of non-native forbs. There was a significant positive relationship between the size of hair clumps and the number of seeds extracted from the clumps, suggesting that managing the introduced bison population at a lower level will help minimize the spread of non-native plants by the species. Seeds of non-native plants were capable of germinating under conditions similar to those on Santa Catalina Island. Clumps of bison hair persisted in wallows, but did not remain intact and lost nearly 40% of their original mass. The number of germinable seeds contained in bison dung was low: 18 seeds germinated from 6 of 18 dung samples. Introduced bison appear to facilitate the dispersal of non-native plants over native plants on Santa Catalina Island. Our study suggests that a comprehensive strategy to control non-native plants must involve the management of the animal agents of plant dispersal. Web of Science Many USA California Santa Catalina Island 33.376756 -118.41362 Field - Observational terrestrial Grassland Invasion Hyp. Mutualism Facilitation primary 1447 Pysek, P 2005 Survival rates in the Czech Republic of introduced plants known as wool aliens journal BIOLOGICAL INVASIONS 7 4 567 576 The paper analyses an unintentional experiment conducted 40 years ago with species termed wool aliens which were observed in employee garden allotments of a wool-processing factory in Brno, Czech Republic. The waste from processing was used as a garden fertilizer, and alien species were recorded by Dvorak and Kuhn (1966) Zavlecene rostliny na pozemcich pradelny vlny 'Mosilana' n.p. v Brne. Preslia 38: 327-332. The survival of these species was assessed by their occurrence in the current alien flora of the Czech Republic. Of the 56 species introduced in the 1960s and classified as wool aliens, 18 are still present in the Czech alien flora. The remaining 38 species are considered extinct, i.e. alien plants not capable of long-term survival in the country. The resulting survival rate of wool aliens is 22.1%. Three species on the list (5.4%) were clearly capable of naturalization. Compared to the other alien flora of the Czech Republic, wool aliens were disproportionally introduced from Australia, Africa and South and Central America. Species from Europe and Africa tended to survive the best. Grasses were. most strongly represented, contributing 62.5% to wool alien species but only 7.9% to the total Czech neophyte flora. All surviving species were annuals, whereas none of the perennials survived; the survival rate in annuals was 37.5%. Survival of species introduced with wool was significantly comparable to their performance in the UK and in Central Europe, indicating that survival is not determined by mere chance and that the same species tend to be successful elsewhere in Europe. Maximum height and the month of first flowering were not significantly related to the species survival. The role of specific events in the enrichment of alien floras is discussed. Web of Science Many Czech republic Moravia Brno 49.192766 16.610584 Field - Observational terrestrial Invasion Hyp. Preadaptation to Climate primary 1448 Schaffelke, B; Deane, D 2005 Desiccation tolerance of the introduced marine green alga Codium fragile ssp tomentosoides - clues for likely transport vectors? journal BIOLOGICAL INVASIONS 7 4 557 565 The invasive marine green macroalga Codium fragile ssp. tomentosoides is now considered to be an introduced marine pest along the northwest Atlantic and southern Australian coasts. International or domestic translocation of C. fragile ssp. tomentosoides is usually attributed to the fouling of ship hulls or shellfish, particularly oysters. A likely domestic vector is shipboard transport, involving the translocation of whole thalli or fragments entangled in fishing nets, ropes, etc. that are then released in a previously unaffected area. Here we investigated the survival of C. fragile ssp. tomentosoides under emersed conditions, simulating shipboard transport. C. fragile ssp. tomentosoides was able to survive periods of emersion of up to 90 days in high relative air humidity. Net photosynthesis remained positive at about 50% of the rates of submersed control thalli. After 2 days of emersion and 4 days of rehydration under submersed conditions thalli recover to their initial net photosynthesis rates. Hence, C. fragile ssp. tomentosoides is likely to survive long shipboard journeys entrapped in fishing nets, anchor wells. or other protected, high-humidity areas of a vessel. Furthermore, C. fragile ssp. tomentosoides may survive emersion on an exposed deck during short trips, especially in cooler conditions such as at night. The incursion sites of C. fragile ssp. tomentosoides in Australia are generally in modified environments, often associated with shipping-related infrastructure such as wharves, jetties, rip rap, and moorings. Web of Science Codium fragile ssp. tomentosoides Australia New South Wales Sydney -33.854002 151.213145 Lab marine Intertidal/Near Shore Invasion Hyp. Inherent Superiority Effective Disperser primary 1449 Malmstrom, CM; McCullough, AJ; Johnson, HA; Newton, LA; Borer, ET 2005 Invasive annual grasses indirectly increase virus incidence in California native perennial bunchgrasses journal OECOLOGIA 145 1 153 164 In California valley grasslands, Avenafatua L. and other exotic annual grasses have largely displaced native perennial bunchgrasses such as Elymus glaucus Buckley and Nassella pulchra (A. Hitchc.) Barkworth. The invasion success and continued dominance of the exotics has been generally attributed to changes in disturbance regimes and the outcome of direct competition between species. Here, we report that exotic grasses can also indirectly increase disease incidence in nearby native grasses. We found that the presence of A. fatua more than doubled incidence of infection by barley and cereal yellow dwarf viruses (B/CYDVs) in E. glaucus. Because B/CYDV infection can stunt E. glaucus and other native bunchgrasses, the indirect effects of A. fatua on virus incidence in natives suggests that apparent competition may be an additional mechanism influencing interactions among exotic and native grasses in California. A. fatua's influence on virus incidence is likely mediated by its effects on populations of aphids that vector B/CYDVs. In our study, aphids consistently preferred exotic annuals as hosts and experienced higher fecundity on them, suggesting that the exotics can attract and amplify vector populations. To the best of our knowledge, these findings are the first demonstration that exotic plants can indirectly influence virus incidence in natives. We suggest that invasion success may be influenced by the capacity of exotic plant species to increase the pathogen loads of native species with which they compete. Web of Science Avena fatua USA California Yolo County 38.559227 -122.006149 Greenhouse terrestrial Grassland Invasion Hyp. Mutualism Facilitation primary 1451 Thiebaut, G 2005 Does competition for phosphate supply explain the invasion pattern of Elodea species? journal WATER RESEARCH 39 14 3385 3393 Two invasive aquatic plants, Elodea canadensis and Elodea nuttallii, occurred in north-eastern France. In this study, we examine the influence of phosphorus availability in soft water streams to explain the invasion pattern of exotic species (E. nuttallii and E. canadensis) compared to native plants (Callitriche platycarpa, Ranunculus peltatus). Total phosphorus was measured in these four aquatic macrophytes. Sediment total phosphorus and water-soluble reactive phosphorus were also analysed each season in 2001. Phosphorus content in the two invasive species and in R. peltatus was higher than in C platycarpa. Elodea species are adapted to the seasonal phosphorus fluctuations as well as R. peltatus and exhibited high phosphorus storage ability. The high fluctuation availability of resources in space or/and time favoured the spread of the invasive plants and confirms the theory of invasibility of Davis et at. [2000. Fluctuating resources in plant communities: a general theory of invasibility. J. Ecol. 88, 528-534]. The eutrophication process increases the invasibility of E. nuttallii's, while inducing competition between E. nuttallii and native macrophyte species. (c) 2005 Elsevier Ltd. All rights reserved. Web of Science Elodea canadensis; Elodea nuttallii France Alsace Biosphere Reserve of the Northern Vosges 48.04008 7.132416 Field - Observational lotic Invasion Hyp. Fluctuating Resources primary 1452 Hamilton, MA; Murray, BR; Cadotte, MW; Hose, GC; Baker, AC; Harris, CJ; Licari, D 2005 Life-history correlates of plant invasiveness at regional and continental scales journal ECOLOGY LETTERS 8 10 1066 1074 We implemented cross-species and independent-contrasts multiple regression models to compare life-history correlates of invasion success between regional and continental spatial scales among non-native plants of eastern Australia. We focussed on three life-history traits that represent major axes of variation in plant life history: specific leaf area (SLA), plant height and seed mass. After controlling for residence time and cross-correlation with other life-history traits, small seed mass was significantly and uniquely correlated with invasion success at continental and regional scales. High SLA was significantly and uniquely correlated with invasion success at the continental scale only. Plant height could not explain unique variation in invasion success at either spatial scale. Variation among spatial scales in the significance and strength of life-history relationships with invasion success suggests that the search for predictive tools of invasion need not be fruitless, as long as predictive investigations are targeted at appropriate spatial scales. Web of Science Many Australia Queensland; New South Wales -27.113901 149.663084 Statistical/Meta-analysis terrestrial Invasion Hyp. Inherent Superiority primary 1453 Yu, XJ; Yu, D; Lu, ZJ; Ma, KP 2005 A new mechanism of invader success: Exotic plant inhibits natural vegetation restoration by changing soil microbe community journal CHINESE SCIENCE BULLETIN 50 11 1105 1112 Since the 1950s of the last century, the exotic plant, Eupatorium adenophorum, has spread rapidly across southwest China, damaging native ecosystems and causing great economic losses. We examined the pH, N, P, K, and organic matter concentrations, and the bacterial community character (by Biolog EcoPlate (TM)) in soils from sites heavily and lightly invaded by this exotic species. Also, soil from the lightly invaded site was treated with a water extract of E. adenophorum roots to examine the effect of the plant on soil properties. We grew three plant species, one native and two exotic, in pot experiment using soil from heavily invaded site to examine the effects of the soil on these plants growth. The soil analysis demonstrated that the pH, organic matter, total N, total P and total K in soils from the heavily invaded site were only slightly different from those of the lightly invaded site, but concentrations of NH4+, NO3- and available P and K in the heavily invaded site were greater than those in the lightly invaded site. The catabolic activity of soil bacterial community in the heavily invaded site was different from that in the lightly invaded site. The catabolic activity of bacterial community in soils treated by the water extract of E. adenophorum roots changed and became similar to that in soils from the heavily invaded site. The pot experiment showed that the exotic plants growth in heavily invaded soil were not different from in lightly invaded soil; however, the native plant biomass decreased dramatically when grown in soil from the heavily invaded site as compared to soil from the lightly invaded site; and the same phenomenon was found when any potential allelopathic effects by E. adenophorum were eliminated by added activated carbon to those soils. Difference in soil nutrient availability and allelopathy could not explain this phenomenon of the native plant in the soils from the heavily and lightly invaded sites. Changes observed in the soil bacterial community were obviously related to native plant growth in those tow soils. Those results suggest that changing soil microbial community may be an important part of E. adenophorum invasion process. Since the soil microbial community serves as bridge in connection of exotic and natural plants, the exotic plant could inhibit the natural plant growth and reproduction by changing the soil microbial community in invaded site. Web of Science Eupatorium adenophorum China Sichuan Panzhihua 26.6 101.6 Field - Observational;Garden terrestrial Subtropical Forest Invasion Hyp. Mutualism Facilitation primary 1454 Pokorny, ML; Sheley, RL; Zabinski, CA; Engel, RE; Svejcar, TJ; Borkowski, JJ 2005 Plant functional group diversity as a mechanism for invasion resistance journal RESTORATION ECOLOGY 13 3 448 459 A commonly cited mechanism for invasion resistance is more complete resource use by diverse plant assemblages with maximum niche complementarity. We investigated the invasion resistance of several plant functional groups against the nonindigenous forb Spotted knapweed (Centaurea maculosa). The study consisted of a factorial combination of seven functional group removals (groups singularly or in combination) and two C. maculosa treatments (addition vs. no addition) applied in a randomized complete block design replicated four times at each of two sites. We quantified aboveground plant material nutrient concentration and uptake (concentration X biomass) by indigenous functional groups: grasses, shallow-rooted forbs, deep-rooted forbs, spikemoss, and the nonindigenous invader C. maculosa. In 2001, C. maculosa density depended upon which functional groups were removed. The highest C. maculosa densities occurred where all vegetation or all forbs were removed. Centaurea maculosa densities were the lowest in plots where nothing, shallow-rooted forbs, deep-rooted forbs, grasses, or spikemoss were removed. Functional group biomass was also collected and analyzed for nitrogen, phosphorus, potassium, and sulphur. Based on covariate analyses, postremoval indigenous plot biomass did not relate to invasion by C. maculosa. Analysis of variance indicated that C. maculosa tissue nutrient percentage and net nutrient uptake were most similar to indigenous forb functional groups. Our study suggests that establishing and maintaining a diversity of plant functional groups within the plant community enhances resistance to invasion. Indigenous plants of functionally similar groups as an invader may be particularly important in invasion resistance. Web of Science Centaurea maculosa USA Montana Bozeman 45.0011 -111.0011 Field - Experimental terrestrial Grassland Invasion Hyp. Community Species Richness primary 1462 Abbott, KL 2005 Supercolonies of the invasive yellow crazy ant, Anoplolepis gracilipes, on an oceanic island: Forager activity patterns, density and biomass journal INSECTES SOCIAUX 52 3 266 273 Ants have the capacity to reach unusually high densities, mostly in their introduced ranges. Numerical dominance is often cited as key to the ability of exotic ants to displace native ant species, reduce the abundance of invertebrates and negatively impact upon bird, land crab and other vertebrate populations. On Christmas Island, Indian Ocean, the yellow crazy ant, Anoplolepis gracilipes (Jerdon), forms supercolonies, where extremely high densities of foraging ants have contributed to 'invasional meltdown' in rainforest areas. Densities of up to 2254 foraging ants per m(2) and a biomass of 1.85 g per m(2) were recorded, and nest densities reached 10.5 nest entrances per m(2). Populations of A. gracilipes can overcome and kill red endemic land crabs (Gecarcoidea natalis) over 100 times their own biomass. This is the highest recorded density of foraging ants, and adds another element to the definition of 'supercolony' of unicolonial ants. This paper documents one extreme in a continuum of densities of unicolonial, invasive ant species and highlights the need to incorporate forager densities into invasive ant research. Web of Science Anoplolepis gracilipes Australia Christmas Island -10.484706 105.641556 Field - Observational terrestrial Tropical Forest Invasion Hyp. Inherent Superiority High Reprod. Output omnivore 1463 Lach, L 2005 Interference and exploitation competition of three nectar-thieving invasive ant species journal INSECTES SOCIAUX 52 3 257 262 Plant and insect exudates are known to play a key role in structuring tropical ant communities, but less is known about the utilization of these resources in communities dominated by invasive ants. Invasive ants are thought to require large amounts of carbohydrates such as honeydew or nectar to maintain their high abundances. Invasive ants that consume floral nectar may compete with legitimate floral visitors through interference or exploitation competition. I compared the nectar-thieving behavior of three widespread invasive ant species: long-legged ants (Anoplolepis gracilipes), Argentine ants (Linepithema humile), and big-headed ants (Pheidole megacephala) in inflorescences of the native Hawaiian 'ohi'a tree, an important food source for native fauna. A. gracilipes was least likely to leave inflorescences unvisited and visited inflorescences in higher numbers than both L. humile and P megacephala. A. gracilipes and L. humile visited more flowers in an inflorescence and were less likely to retreat from a flower with a competitor than P megacephala. A. gracilipes was able to take 5.5 and 11.3 times the amount of nectar than L. humile and P megacephala, respectively. Thus, A. gracilipes may be effective at both interference and exploitation competition against other nectarivores, L. humile may be effective at interference competition, and P megacephala may be relatively weak at both types of competition against other nectarivores. Ascertaining the competitive abilities of invasive ants against legitimate floral visitors will be especially important in agricultural and other systems that are nectar or pollinator limited. Web of Science Anoplolepis gracilipes; Linepithema humile; Pheidole megacephala USA Hawaii Volcanoes National Park 19.488861 -155.440979 Field - Observational terrestrial Tropical Forest Invasion Hyp. Inherent Superiority Superior Competitor herbivore 1464 Ducey, PK; West, LJ; Shaw, G; De Lisle, J 2005 Reproductive ecology and evolution in the invasive terrestrial planarian Bipalium adventitium across North America journal PEDOBIOLOGIA 49 4 367 377 Comparisons between invasive species and their relatives can help in identifying traits that facilitate dispersal and colonization, and comparisons among populations within invasive species may highlight the rotes of plasticity and evolutionary adaptation. Bipalium adventitium Hyman 1943 is an exotic, earthworm-eating soil flatworm that has become widespread and abundant in North America. As a first step in better understanding the ecology and evolution of this invasive planarian, we studied its reproductive traits in populations across its extensive geographic range and conducted an experiment on the effects of food availability. Colonization by B. adventitium is facilitated by hermaphroditism, sperm storage, and tough egg capsules containing multiple offspring, traits present in most Terricola. The egg capsules produced by B. adventitium were large (22.5 mg), hatched in 7-37 days (mean = 23 days), contained 1-8 offspring (mean = 3.4), and represented about 21% of a parent's predeposition mass. Many individuals produced multiple egg capsules. Although considerable intraspecific variation was detected for most reproductive parameters, significant differences among geographic populations were noted for egg capsule mass, mean offspring mass, and measures of total reproductive output. Intraspecific correlations between parent mass and the masses of egg capsules and offspring, and the results of our experiment showing that food availability affected egg capsule production, together suggest that thus far intra-population variation and plasticity have been more important than local evolutionary adaptation in the invasion of this species. (c) 2005 Elsevier GmbH. All rights reserved. Web of Science Bipalium adventitium USA California; Michigan; New York; Ohio; West Virginia 37.36; 42.66; 40.72; 43.207; 38.37; 41.56 -121.97; -73.77; -73.71; -76.74; -82.44; -81.38 Field - Observational;Lab terrestrial Invasion Hyp. Plasticity predator 1465 Rudgers, JA; Mattingly, WB; Koslow, JM 2005 Mutualistic fungus promotes plant invasion into diverse communities journal OECOLOGIA 144 3 463 471 Reducing the biological diversity of a community may decrease its resistance to invasion by exotic species. Manipulative experiments typically support this hypothesis but have focused mainly on one trophic level (i.e., primary producers). To date, we know little about how positive interactions among species may influence the relationship between diversity and invasibility, which suggests a need for research that addresses the question: under what conditions does diversity affect resistance to invasion? We used experimental manipulations of both plant diversity and the presence of an endophytic fungus to test whether a fungal mutualist of an invasive grass species (Lolium arundinaceum) switches the relationship between plant community diversity and resistance to invasion. Association with the fungal endophyte (Neotyphodium coenophialum) increased the ability of L. arundinaceum to invade communities with greater species diversity. In the absence of the endophyte, the initial diversity of the community significantly reduced the establishment of L. arundinaceum. However, establishment was independent of initial diversity in the presence of the endophyte. Fungal symbionts, like other key species, are often overlooked in studies of plant diversity, yet their presence may explain variation among studies in the effect of diversity on resistance to invasion. Web of Science Lolium arundinaceum; Neotyphodium coenophialum USA Indiana Bloomington Greenhouse terrestrial Grassland Invasion Hyp. Mutualism Facilitation primary 1466 Hawkes, CV; Wren, IF; Herman, DJ; Firestone, MK 2005 Plant invasion alters nitrogen cycling by modifying the soil nitrifying community journal ECOLOGY LETTERS 8 9 976 985 Plant invasions have dramatic aboveground effects on plant community composition, but their belowground effects remain largely uncharacterized. Soil microorganisms directly interact with plants and mediate many nutrient transformations in soil. We hypothesized that belowground changes to the soil microbial community provide a mechanistic link between exotic plant invasion and changes to ecosystem nutrient cycling. To examine this possible link, monocultures and mixtures of exotic and native species were maintained for 4 years in a California grassland. Gross rates of nitrogen (N) mineralization and nitrification were quantified with N-15 pool dilution and soil microbial communities were characterized with DNA-based methods. Exotic grasses doubled gross nitrification rates, in part by increasing the abundance and changing the composition of ammonia-oxidizing bacteria in soil. These changes may translate into altered ecosystem N budgets after invasion. Altered soil microbial communities and their resulting effects on ecosystem processes may be an invisible legacy of exotic plant invasions. Web of Science USA California Hopland 38.999602 -123.066216 Field - Experimental terrestrial Grassland Invasion Hyp. Ecosystem Engineers primary 1467 Parker, JD; Hay, ME 2005 Biotic resistance to plant invasions? Native herbivores prefer non-native plants journal ECOLOGY LETTERS 8 9 959 967 In contrast to expectations of the enemy release hypothesis, but consistent with the notion of biotic resistance, we found that native generalist crayfishes preferred exotic over native freshwater plants by a 3 : 1 ratio when plants were paired by taxonomic relatedness. Native crayfishes also preferred exotic over native plants when tested across 57 native and 15 exotic plants found growing sympatrically at 11 sites throughout the southeastern USA. Exotic grass carp that share little evolutionary history with most of these plants exhibited no preference for native vs. exotic species. Analyses of three terrestrial data sets showed similar patterns, with native herbivores generally preferring exotic plants, while exotic herbivores rarely exhibited a preference. Thus, exotic plants may escape their coevolved herbivores only to be preferentially consumed by the native generalist herbivores in their new ranges, suggesting that native herbivores may provide biotic resistance to plant invasions. Web of Science Egeria densa; Hydrilla verticillata; Myriophyllum spicatum; Eichhornia crassipes; Ludwigia hexapetala; Myriophyllum aquaticum; Colocasia esculenta; Pistia stratiotes; Panicum repens; Murdannia keisak USA Florida; Georgia Lake Griffin; Lake Juliette 33.074; 28.855 -83.815; -81.850 Lab lentic Invasion Hyp. Enemy Release;Other primary 1477 Weber, E 2005 Lonicera henryi Hemsl. - a potential exotic forest weed in Switzerland journal BOTANICA HELVETICA 115 1 77 81 Lonicera henryi is an introduced climbing woody perennial that has become naturalized in scattered localities in Switzerland. Growth-related traits of this vine were measured at one forest site near Zurich to assess its invasion potential. Current-year shoots were 47-150 cm long, indicating fast growth. There were 128-366 shoots or stems and 0-96 rooted nodes per m(-2) of forest floor, indicating considerable competition for other species. Species richness was significantly lower in plots covered by L. henryi mats compared to adjacent control plots. The results suggest that L. henryi has a considerable ability to cover forest floors with a carpet of intertwining stems, and to climb rapidly on shrubs and trees. Further spread of this vine may impede forest tree establishment and crowd out native species. Web of Science Lonicera henryi Switzerland Zurich 47.332 8.402 Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Rapid Growth primary 1481 Leger, EA; Forister, ML 2005 Increased resistance to generalist herbivores in invasive populations of the California poppy (Eschscholzia californica) journal DIVERSITY AND DISTRIBUTIONS 11 4 311 317 Escape from enemies in the native range is often assumed to contribute to the successful invasion of exotic species. Following optimal defence theory, which assumes a trade-off between herbivore resistance and plant growth, some have predicted that the success of invasive species could be the result of the evolution of lower resistance to herbivores and increased allocation of resources to growth and reproduction. Lack of evidence for ubiquitous costs of producing plant toxins, and the recognition that invasive species may escape specialist, but not generalist enemies, has led to a new prediction: invasive species may escape ecological trade-offs associated with specialist herbivores, and evolve increased, rather than decreased, production of defensive compounds that are effective at deterring generalist herbivores in the introduced range. We tested the performance of two generalist lepidopteran herbivores, Trichoplusia ni and Orgyia vetusta, when raised on diets of native and invasive populations of the California poppy, Eschscholzia californica. Pupae of T ni were significantly larger when reared on native populations. Similarly, caterpillars of O. vetusta performed significantly better when raised on native populations, indicating that invasive populations of the California poppy are more resistant to herbivores than native populations. The chance of successful establishment of some non-indigenous plant species may be increased by retaining resistance to generalist herbivores, and in some cases, invasive species may be able to escape ecological trade-offs in their new range and evolve, as we observed, even greater resistance to generalist herbivores than native plants. Web of Science Eschscholzia californica Chile La Aquada -31.6333 -71.1833 Garden terrestrial Chaparral/Shrublands Invasion Hyp. Evolution in General primary 1486 Hendrickson, C; Bell, T; Butler, K; Hermanutz, L 2005 Disturbance-enabled invasion of Tussilago farfara (L.) in Gros Morne National Park, Newfoundland: Management implications journal NATURAL AREAS JOURNAL 25 3 263 274 The recent invasion of the exotic weed Tussilago farfara L. (coltsfoot) in Gros Morne National Park (GMNP) Newfoundland, Canada, was examined to determine which resource changes accompanying disturbance enabled population expansion. Resource levels reflecting environmental variables are defined here as the abiotic components of the environment used by plants. The environmental variables of pH, soil moisture, soil type, duff cover and photosynthetically active radiation were measured in 17 disturbance types of natural and anthropogenic origin - notably hiking trails, roads, gravel quarries, shorelines, slopes, hydro corridors, and forests killed by spruce budworm - and across a gradient from disturbed to undisturbed in 12 vegetation types. Balsam fir forest comprises 36% of the park and has the highest number of disturbance types. Disturbances favoring Tussilago were characterized by a pH of 6.8-8.3, high light intensity, increased bare ground, absence of duff cover, and moist, gravelly substrates. These levels were typical of both natural and anthropogenic disturbances in which the canopy and duff cover were absent, and the pH of acidic native soils had been raised by the addition of quarried limestone or granitic gravel. The difference in resource levels across the disturbance gradient indicates that Tussilago is unable to colonize undisturbed native vegetation. Likewise, a change in resource levels over time, which favors other species and is unsuitable for Tussilago, appears to be the mechanism of Tussilago's recession. Not all disturbance types present resource levels favorable for Tussilago establishment. However, resource levels associated with some disturbance types of anthropogenic origin indicate that aggregate quarry management practices have unintentionally enabled the invasion of Tussilago in GMNP Control of invasive vegetation can be addressed by identifying disturbance-related plant resource shifts that may have been caused by policies and procedures under local control. Web of Science Tussilago farfara Canada Newfoundland Gros Morne National Park 49.59 -57.75 Field - Observational terrestrial Coniferous Forest Invasion Hyp. Disturbance primary 1487 Gordon, DR; Greenberg, CH; Crownover, SH; Slapcinsky, OL 2005 Effects of unpaved road soils on persistence of three non-native grass species journal NATURAL AREAS JOURNAL 25 3 257 262 Amended roadsides, with their modified fertility, soil structure, and disturbance regimes, may provide invading plant species access into adjacent natural communities. We experimentally tested whether soil amendments alone or in combination with the environmental conditions of roadsides facilitate invasion by non-native grass species into xeric sand pine scrub in Ocala National Forest, Florida. In 1995 we planted seeds of three non-native grasses (bahiagrass [Paspalum notatum] Flugge, centipede grass [Eremochloa ophiuroides] [Munro] Hack., and natal grass [Ryncheletrum repens] [Willd.] C.E. Hubb.) in plots of three road-soil types (two amended road-soils: clay and limerock-clay, and one unamended natural soil: sand). Factorial combinations of seeds and soil were reciprocally placed both along clay roadsides and in interior sites that were parallel to the roads in adjacent clearcuts of xeric sand pine scrub (n = 4 blocks). Initial establishment was higher than was persistence in the plots four years later. In 1995, species frequency was similar in roadside and interior plots. By 1999 only centipede grass persisted in the interior plots, while all species were present in the roadside plots. In both years, non-native species frequency was greater on clay than on limerock-clay or sand soils. In 1999, natal grass was found only, and centipede grass was more frequent on amended than on unamended roadside plots. No non-native grasses were found in sand soils in interior sites in 1999. Our results indicate that the xeric, sandy soil of interior sand pine scrub is relatively inhospitable to the non-native grasses tested, and that both clay soils and other roadside conditions facilitate their persistence. Web of Science Paspalum notatum; Eremochloa ophiuroides; Ryncheletrum repens USA Florida Ocala National Forest 29.2 -81.73 Field - Experimental terrestrial Subtropical Forest Invasion Hyp. Disturbance primary 1490 Cipollini, D; Mbagwu, J; Barto, K; Hillstrom, C; Enright, S 2005 Expression of constitutive and inducible chemical defenses in native and invasive populations of Alliaria petiolata journal JOURNAL OF CHEMICAL ECOLOGY 31 6 1255 1267 The Evolution of Increased Competitive Ability (EICA) hypothesis posits that invasive plants in introduced habitats with reduced herbivore pressure will evolve reduced levels of costly resistance traits. In light of this hypothesis, we examined the constitutive and inducible expression of five chemical defense traits in Alliaria petiolata from four invasive North American and seven native European populations. When grown under common conditions, significant variation among populations within continents was found for trypsin inhibitors and peroxidase activity, and glucosinolates and trypsim inhibitors were significantly jasmonate-inducible across populations. Across populations, constitutive levels of glucosinolates and trypsin inhibitors were negatively correlated with their degree of induction, with three North American populations tending to have lower constitutive levels and higher inducibility of glucosinolates than the seven European populations. Alliarinoside and isovitexin 6*-O-beta-D-glueopyranoside levels were both higher in North American plants than in European plants, but levels of these compounds were generally increased by jasmonate in European plants and decreased by the same treatment in North American plants. Aside from the tendency for invasive populations to have reduced constitutive glucosinolate levels coupled with increased inducibility, little support for the predictions of EICA was evident in the chemical defenses that we studied. Web of Science Alliaria petiolata USA Pennsylvania; Ohio Ligonier; Waterman; Cedarville; Fairborn 40.2333;40.6167;39.5667;39.6333 79.2333;79.15;83.8;84.0167 Garden terrestrial Deciduous Forest Invasion Hyp. Evolution of Increased Competitive Ability primary 1491 Meyer, G; Clare, R; Weber, E 2005 An experimental test of the evolution of increased competitive ability hypothesis in goldenrod, Solidago gigantea journal OECOLOGIA 144 2 299 307 The mechanisms that allow introduced plants to become invasive are poorly understood. Here, we present a test of the evolution of increased competitive ability hypothesis, which holds that because specialized natural enemies may be absent from the introduced range, exotic plants may evolve to invest less in anti-herbivore defenses and thereby gain a competitive advantage over native plants. We grew Solidago gigantea plants derived from both the native range (North America) and the invasive range (Europe) in a common garden in the native range for 2 years. Half the plants were treated with insecticide to protect them from insect herbivores and the other half were exposed to insects that colonized the garden from nearby fields. Insect herbivore biomass was significantly higher on European plants than US plants in the first year but not the second. European plants were more heavily attacked by pathogens in both years of the study. When exposed to insect herbivores, US plants produced more seed than European plants, but when plants were protected from herbivores, seed production was equivalent between US plants and European plants. The presence of insect herbivores suppressed seed production of European plants much more than that of US plants, even though the level of herbivory experienced by European and US plants was similar in the second year, suggesting that the ability to tolerate herbivory was diminished in European plants. These results partially support the EICA hypothesis: plants from the introduced range were more susceptible to some natural enemies and benefited more from insect removal than plants from the native range. The prediction that European plants would perform better than US plants in the absence of insect herbivores was not supported. Web of Science Solidago gigantea Europe Garden terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 1492 Hansen, MJ; Clevenger, AP 2005 The influence of disturbance and habitat on the presence of non-native plant species along transport corridors journal BIOLOGICAL CONSERVATION 125 2 249 259 The impact from transportation corridors on surrounding habitat often reaches far beyond the edge of the corridor. The altered disturbance regime in plant communities along corridor edges and vehicle traffic facilitate the spread and establishment of invasive non-native plant species. We compared the frequency of non-native plant species along highways and railways and the ability of these species to invade grasslands and dense forests along these corridors. We measured the frequency of several non-native plant species along transects 0-150 In from the edge of highways and railways in grasslands and forests, as well as at control sites away from corridors. Both transportation corridors had higher frequency of non-native species than respective control sites. Grasslands had higher frequency of non-native species than forested habitats, but the frequency did not differ between the highways and the railways. The frequency of non-native species in grasslands along highways and railways was higher than at grassland control sites up to 150 In from the corridor edge, whereas the frequency in forested habitats along corridors was higher than at forested control sites up to only 10 In from the corridor edge. There was a significant decrease in the frequency of non-native species with increasing distance from both corridors in the forest, while grasslands showed no significant change in non-native species frequency with distance from corridors. This suggests that corridor edges and grassland habitats act as microhabitats for non-native species and are more prone to invasion than forests, especially if disturbed. Our results emphasize the importance of minimizing the disturbance of adjacent plant communities along highways and railways during construction and maintenance, particularly in grassland habitats and in areas sensitive to additional fragmentation and habitat loss. (c) 2005 Elsevier Ltd. All rights reserved. Web of Science Agropyron cristatum; Bromus inermis; Cirsium arvense; Festuca rubra; Leucanthemum vulgare; Linaria vulgaris; Medicago sativa; Melilotus officinalis; Phleum pratense; Poa pratensis; Poa communis; Sonchus arvensis; Tanecetum vulgare; Taraxacum officinale; Trifolium hybridum; Trifolium repens Canada Alberta Banff National Park 51.16 -115.6 Field - Observational terrestrial Grassland;Coniferous Forest Invasion Hyp. Disturbance primary 1494 Domenech, R; Vila, M; Pino, J; Gesti, J 2005 Historical land-use legacy and Cortaderia selloana invasion in the Mediterranean region journal GLOBAL CHANGE BIOLOGY 11 7 1054 1064 Two major components of global change: land-use changes and intentional or accidental species introduction are threatening the conservation of native species worldwide. In particular, Mediterranean coastal areas are highly susceptible to the invasion of alien species and they also have experienced major changes in land use such as agricultural abandonment and urbanization. However, there has been little research done which quantitatively links biological invasions and the components of land-use changes (i.e. number, trajectory and direction of the changes). We analysed the current distribution and abundance of Cortaderia selloana (Schultes et Schultes fil.) Asch. et Graebner, an alien ornamental species, in 332 fields in Aiguamolls de l'Emporda (Catalonia, NE Spain) and related the patterns of invasion to spatiotemporal data on land-use changes from 1956 to 2003. Our aim was to determine which land uses had been more susceptible to C. selloana invasion during the last 5 years and to find out which components of land-use changes triggered invasion. We found that 22.30% of the fields are currently invaded. In the last 5 years, fields have triplicated the total density of C. selloana. The presence of C. selloana decreases with the distance from urban areas. Invasion is over-represented in pastures and old-fields, and it has increased with time since abandonment. The presence of C. selloana was also associated to fields that had experienced many changes in land use in the last 46 years. The most heavily invaded fields were those that were pastures in 1956 and are now old fields in 2003. On average, the largest plants are found in agricultural field margins and in fields that had a disturbed land use both in 1956 and in 2003. Furthermore, pastures had the lowest proportion of reproductive plants. Overall, current C. selloana patterns of invasion can be explained by the historical legacy of land-use changes. Web of Science Cortaderia selloana Spain Catalonia Aiguamolls de l'Emporda 42.23 3.07 Field - Observational terrestrial Old Field Invasion Hyp. Other primary 1496 Glasby, TM; Gibson, PT; Kay, S 2005 Tolerance of the invasive marine alga Caulerpa taxifolia to burial by sediment journal AQUATIC BOTANY 82 2 71 81 Beds of the invasive alga Caulerpa taxifolia were observed to be buried with sediment after heavy rainfall, and it was proposed that burial and subsequent uncovering could help explain rapid changes in the sizes of beds of C. taxifolia. Responses of C. taxifolia fragments to the different extents of burial and for different durations (2, 6, 17 days) were investigated in the laboratory. Once uncovered, fragments in all treatments began to grow, and by 92 days partially buried fragments were not significantly different from controls in terms of the numbers of stolon meristems or total stolon length. Fragments buried totally were severely affected, but nevertheless, 35% of the fragments survived total burial for 17 days, and began to recover slowly when the sediment was removed. C. taxifolia can, therefore, persist for long periods under sediments, meaning that, in areas where burial is likely, the actual distribution of the species may be underestimated. Moreover, any potential control technique needs to penetrate sediments to be totally effective. Crown Copyright (c) 2005 Published by Elsevier B.V. All rights reserved. Web of Science Caulerpa taxifolia Australia New South Wales Botany Bay -34 151.19 Lab marine Intertidal/Near Shore Fundamentals primary 1497 Van Kleunen, M; Johnson, SD 2005 Testing for ecological and genetic allee effects in the invasive shrub Senna didymobotrya (Fabaceae) journal AMERICAN JOURNAL OF BOTANY 92 7 1124 1130 For an introduced plant species to become invasive, it must be able to reproduce even in initially small populations We tested for Aliee effects (reduced reproductive performance of individuals in small populations) in the nonclonal, NW-pollinated shrub Senna didymobotrya in its invasive range in South Africa. The species is self-compatible. but we found that in its invasive range in South Africa it requires pollinators to set seed. Nearly all stigmas (90%) received pollen. but natural fruit set has very low (3-20%), Pollen receipt and fruit set were not significantly correlated with population size. We thus found no evidence for an ecological Alice effect arising from pollen limitation in small populations. Offspring seedling performance, measured in terms of stern volume and leaf area, was also not significantly correlated with the number of plants in the source population. indicating that genetic Alice effects, such as inbreeding depression, are either absent or of such a small magnitude that they would be unlikely to limit further spread of S. didymobotrya in South Africa. Web of Science Senna didymobotrya South Africa KwaZulu-Natal Pietermaritzburg -29.6 30.32 Field - Experimental terrestrial Grassland;Chaparral/Shrublands Fundamentals primary 1499 Gilbert, B; Lechowicz, MJ 2005 Invasibility and abiotic gradients: The positive correlation between native and exotic plant diversity journal ECOLOGY 86 7 1848 1855 We sampled the understory community in an old-growth, temperate forest to test alternative hypotheses explaining the establishment of exotic plants. We quantified the individual and net importance of distance from areas of human disturbance, native plant diversity, and environmental gradients in determining exotic plant establishment. Distance from disturbed areas, both within and around the reserve, was not correlated to exotic species richness. Numbers of native and exotic species were positively correlated at large (50 m(2)) and small (10 m(2)) plot sizes, a trend that persisted when relationships to environmental gradients were controlled statistically. Both native and exotic species richness increased with soil pH and decreased along a gradient of increasing nitrate availability. Exotic species were restricted to the upper portion of the pH gradient and had individualistic responses to the availability of soil resources. These results are inconsistent with both the diversity-resistance and resource-enrichment hypotheses for invasibility. Environmental conditions favoring native species richness also favor exotic species richness, and competitive interactions with the native flora do not appear to limit the entry of additional species into the understory community at this site. It appears that exotic species with niche requirements poorly represented in the regional flora of native species may establish with relatively little resistance or consequence for native species richness. Web of Science Many Canada Quebec Montreal 45.5167 73.1333 Field - Observational terrestrial Deciduous Forest Invasion Hyp. Community Species Richness primary 1500 Bourgeois, K; Suehs, CM; Vidal, E; Medail, F 2005 Invasional meltdown potential: Facilitation between introduced plants and mammals on French Mediterranean islands journal ECOSCIENCE 12 2 248 256 In the increasingly important domain of insular invasion ecology, the role of facilitation between different introduced taxa has been mentioned, but rarely studied. This paper outlines facilitation between introduced mammals and the invasive succulents Carpobrotus edulis and C. aff. acinaciformis on offshore islands in southeast France. Rats and rabbits are the primary seed dispersers of Carpobrotus sp. on the islands studied. No such dispersal activity was detected on the adjacent mainland. Seed digestion by rats and rabbits also enhanced percent seed germination and speed, in spite of an associated reduction in seed size. In return, Carpobrotus provides a water/energy-rich food source during the dry summer season, thus demonstrating a clear case of mutualism between invaders. Web of Science Carpobrotus edulis; Carpobrotus acinaciformis France ProParc National de Port Crosvence-Alpes-Côte d'Azur Port Cros National Park 43 6.4 Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Mutualism Facilitation primary 1506 Taylor, B; Ganf, GG 2005 Comparative ecology of two co-occurring floodplain plants: the native Sporobolus mitchellii and the exotic Phyla canescens journal MARINE AND FRESHWATER RESEARCH 56 4 431 440 In the northern Murray - Darling Basin (MDB), Australia, the displacement of native floodplain grasses by Phyla canescens ( Lippia), an exotic herb, coincided with a reduced frequency of floodplain inundation owing to river regulation. Although river regulation and P. canescens occur in the southern MDB, P. canescens abundance has not increased significantly since 1988. This work reports on the current distribution of P. canescens and the native grass Sporobolus mitchellii on the lower River Murray. It demonstrates that there are significant differences in the edaphic characteristics of sites occupied by the two species and co-occurrence is rare. To explain this observation, two factors were investigated: the resilience of S. mitchellii to invasion by P. canescens and the response of both species to artificial spring floods. At initial densities of> 25%, S. mitchellii exhibited strong resilience to invasion by P. canescens. The growth response of both species to spring floods was similar. However, P. canescens reproduced asexually when inundated and, on exposure, exhibited a root distribution that would enhance its capacity to survive future droughts. In contrast, S. mitchellii was more tolerant of low soil moisture than P. canescens. The re-introduction of spring floods could favour the expansion of P. canescens. Web of Science Phyla canescens Australia New South Wales Darling Basin -35.16 148.88 Field - Observational terrestrial Riparian Invasion Hyp. Disturbance primary 1512 Abrahamson, WG; Dobley, KB; Houseknecht, HR; Pecone, CA 2005 Ecological divergence among five co-occurring species of old-field goldenrods journal PLANT ECOLOGY 177 1 43 56 Approximately 130 species of goldenrods are native to North America and many occur sympatrically. Such cooccurrence among closely related species raises the question of whether differences among the species in smallscale distribution and growth forms facilitate their co-occurrence. We investigated five goldenrods that frequently co-occur within their native ranges in Pennsylvania USA old fields. We measured goldenrod abundances, soil textures, nutrients, pH, and moisture within 30 old fields, and determined biomass allocation and flower and seed traits for each goldenrod species at a common site. Ordination revealed that Solidago altissima and S. gigantea were associated with fields having circum-neutral soils, whereas Euthamia graminifolia and S. rugosa achieved their highest abundances on acidic soils. Soil clay content and moisture may be associated with a further separation of species as the abundance of S. altissima tended to be higher on well-drained soils while S. gigantea had a tendency to attain its highest abundances on moist soils that had relatively stable moisture levels over time. Euthamia was more likely to be abundant on clay-rich soils while S. rugosa was often associated with soils containing little clay. Solidago juncea tended to associate with droughty soils that underwent marked soil-moisture changes over time. The latter goldenrod had the greatest absolute and relative root mass, the least absolute and relative leaf mass, highest seed-reproductive allocation, and heaviest achenes. In contrast, S. gigantea and Euthamia, which were often associated with more mesic and stable soil moisture conditions, allocated the least to roots and relatively high amounts of mass to leaves. Solidago gigantea, S. altissima, and Euthamia are invasive species across Europe. The species with the highest colonization rate across Europe, S. gigantea, allocated the most to reproduction in our study, while S. altissima, with the second highest colonization rate, was highly clonal producing the most rhizome mass. Life-history trait variation among goldenrods appears to be linked to differences in small-scale distributions and rates of colonization. Web of Science Solidago altissima; Solidago gigantea; Euthamia graminifolia Europe Field - Observational terrestrial Old Field Invasion Hyp. Inherent Superiority High Reprod. Output primary 1513 Broncano, MJ; Vila, M; Boada, M 2005 Evidence of Pseudotsuga menziesii naturalization in montane Mediterranean forests journal FOREST ECOLOGY AND MANAGEMENT 211 3 257 263 Invasion of natural habitats by conifer species is a well-known phenomenon worldwide. Here, we describe naturalization by the American Pseudotsuga menziesii (Douglas fir) in Montseny Natural Park (Catalonia, NE Spain). Establishment of seedlings started 15 years after plantation. Seedling density was positively associated to low tree density, small plantation area, grazing and the presence of a shrubland understorey of intermediate cover. Seedling recruitment outside the plantations occurred at high altitudes (> 1000 m). In less than 30 years after plantation, P. menziesii invaded adjacent areas 100 m far from the plantation. We conclude that at high altitudes, under disturbance, seedling establishment can take place as soon as planted trees produce cones. Therefore, the time-lag appears to be primarily related to propagule availability. (c) 2005 Elsevier B.V. All rights reserved. Web of Science Pseudotsuga menziesii Spain Catalonia Montseny Natural Park 41.75 2.355 Field - Observational terrestrial Coniferous Forest Invasion Hyp. Disturbance primary 1514 Williams, MC; Wardle, GM 2005 The invasion of two native Eucalypt forests by Pinus radiata in the Blue Mountains, New South Wales, Australia journal BIOLOGICAL CONSERVATION 125 1 55 64 Invasions of Pinus species are a major environmental concern in South Africa and New Zealand where pines are beginning to dominate native grasslands and shrublands. Pines are widely cultivated in Australia with almost a million hectares growing in large plantations. Plantations are commonly bordered by native Eucalypt vegetation resulting in a high potential for invasion and providing an opportunity to study pine invasion processes within forest environments. In order to determine if Pinus radiata equally invades different dry Eucalypt woodland vegetation types, two areas in the upper Blue Mountains in New South Wales, Australia were surveyed. Similar levels of invasion were observed in both Eucalypt forest types. An average pine abundance of 55 individuals for the Eucalyptus oreades and Eucalyptus sieheri vegetation type and 49 individuals for the Eucalyptus mannifera and Eucalyptus dives vegetation type was recorded in 20 m by 20 m plots located 50 In from the plantation boundary. To characterise the spatial distribution of the pines, transects were placed perpendicular to the plantation edge. As expected pine numbers diminished with distance from the plantation, however, large reproductive pine trees were found up to 4 km from the seed source signifying long distance dispersal. Investigation of wildling pine response to fire suggests that it may not always be an appropriate management tool. Fire stimulated seed release from cones and resulted in high recruitment of seedlings around reproductive pines which were large enough to survive the burn. Infrequent fires at intervals greater than time to maturity will lead to increased pine densities and further spread into the native vegetation. (c) 2005 Elsevier Ltd. All rights reserved. Web of Science Pinus radiata Australia New South Wales Blue Mountains -33.4 150.2 Field - Experimental terrestrial Grassland;Deciduous Forest Invasion Hyp. Disturbance;Other primary 1518 Dybdahl, MF; Kane, SL 2005 Adaptation vs. phenotypic plasticity in the success of a clonal invader journal ECOLOGY 86 6 1592 1601 The relative importance of plasticity vs.. adaptation for the spread of invasive species has rarely been studied. We examined this question in a clonal population of invasive freshwater snails (Potamopyrgus antipodarum) from the western United States by testing whether observed plasticity in life history traits conferred higher fitness across a range of temperatures. We raised isofemale lines from three populations from different climate regimes (high- and low-elevation rivers and an estuary) in a split-brood, common-garden design in three temperatures. We measured life history and growth traits and calculated population growth rate (as a measure of fitness) using an age-structured projection matrix model. We found a strong effect of temperature on all traits, but no evidence for divergence in the average level of traits among populations. Levels of genetic variation and significant reaction norm divergence for life history traits suggested some role for adaptation. Plasticity varied among traits and was lowest for size and reproductive traits compared to age-related traits and fitness. Plasticity in fitness was intermediate, suggesting that invasive populations are not general-purpose genotypes with respect to the range of temperatures studied. Thus, by considering plasticity in fitness and its component traits, we have shown that trait plasticity alone does not yield the same fitness across a relevant set of temperature conditions. Web of Science Potamopyrgus antipodarum USA Idaho; Wyoming; Oregon Snake, Madison; and Colombia Rivers 43.72; 44.64; 46.16 -116.85; -110.86; -123.92 Garden lotic;estuarine Invasion Hyp. Evolution of Increased Competitive Ability;Plasticity herbivore 1521 Walters, AC; Mackay, DA 2005 Importance of large colony size for successful invasion by Argentine ants (Hymenoptera : Formicidae): Evidence for biotic resistance by native ants journal AUSTRAL ECOLOGY 30 4 395 406 The Argentine ant, Linepithema humile (Mayr), is a widespread invasive ant species that has been associated with losses of native ant species and other invertebrates from its introduced range. To date, various abiotic conditions have been associated with limitations to the spread of Argentine ants, however, competitive interactions with native ant fauna may also affect the spread of Argentine ants. Here, we experimentally manipulated colony sizes of Argentine ants in the laboratory to assess whether Argentine ants were able to survive and compete for resources with a widespread, dominant native ant, Iridomyrmex'rufoniger'. The results showed that over 24 h, the proportions of Argentine ants that were alive, at baits, and at sugar water decreased significantly in the presence of Iridomyrmex. In addition, Argentine ant mortality increased over time, however, the proportion of the colony that was dead decreased with the largest colony size. Argentine ants were only able to overcome Iridomyrmex when their colony sizes were 5-10 times greater than those of the native ants. We also conducted trials in which colonies of Argentine ants of varying sizes were introduced to artificial baits occupied by Iridomyrmex in the field. The results showed that larger Argentine ant colonies significantly affected the foraging success of Iridomyrmex after the initial introduction (5 min). However, over the first 20 min, when the Argentine ants were present at the baits, and over the entire 50 min experimental period, the numbers of Iridomyrmex at baits did not differ significantly with the size of the Argentine ant colony. This is the first experimental study to investigate the role of colony size in the invasion biology of Argentine ants in Australia, and the results suggest that Iridomyrmex may reduce the spread of Argentine ants, and that Argentine ants may need to attain large colony sizes in order to survive in the presence of Iridomyrmex. We address the implications of these findings for the invasion success of Argentine ants in Australia, and discuss the ability of Argentine ants to attain large colony sizes in introduced areas. Web of Science Linepithema humile Australia South Australia Adelaide -34.9294 138.5992 Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Other omnivore 1522 Lindsay, EA; French, K 2005 Litterfall and nitrogen cycling following invasion by Chrysanthemoides monilifera ssp rotundata in coastal Australia journal JOURNAL OF APPLIED ECOLOGY 42 3 556 566 1. On the south-east coast of Australia there are extensive infestations of the environmental weed bitou bush Chrysanthemoides monilifera ssp. rotundata. This exotic weed is highly invasive and persistent, yet little is known about its impacts and how it dominates coastal vegetation. 2. A field study was carried out with sites selected for having an area heavily invaded by C. monilifera and an uninvaded native shrubland area. The mass and components of the litterfall and ground litter layer were monitored and compared over 12 months. Nutrient analysis was performed on the abscised leaves and mature green leaves. Soil properties and nitrogen content were also examined. 3. There was a greater input of litter to the native areas (4800 &PLUSMN; 450 kg ha(-1)), which was highly seasonal, compared with the C. monilifera areas (1690 &PLUSMN; 150 kg ha(-1)). There was also a greater mass of litter on the ground in the native areas (9600 &PLUSMN; 560 kg ha(-1)) than C. monilifera areas (3750 &PLUSMN; 170 kg ha(-1)), probably as a result of the higher leaf fall rate and slow decomposition rate. 4. A large proportion of nutrients was withdrawn from the native (48-80%) and C. monilifera leaves (38-60%) before abscission. The litterfall was estimated to contain more than twice the amount of nitrogen and phosphorous within the native areas, because of the high leaf fall rate rather than a high nutrient content. 5. The total soil nitrogen was two to five times higher in the invaded areas (average 2570 &PLUSMN; 620 kg ha(-1)) than within the native areas (730 &PLUSMN; 90 kg ha(-1)). This was accompanied by an increase in ammonia content. The bulk density was lower in invaded areas, but there was no clear trend in the change in soil pH. 6. Synthesis and applications. The higher soil nitrogen beneath the weed infestations could increase the competitive superiority of C. monilifera directly by increasing growth rate, or indirectly by impairing the establishment of native species that are adapted to growing in nutrient-poor soils. The control technique of spraying C. monilifera with herbicide, then burning and spraying seedlings again, could lead to greater regeneration success for natives species than spraying C. monilifera with herbicide only. Web of Science Chrysanthemoides monilifera Australia New South Wales Culburra 34.9667 150.7833 Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Ecosystem Engineers primary 1529 Carey, EV; Marler, MJ; Callaway, RM 2004 Mycorrhizae transfer carbon from a native grass to an invasive weed: evidence from stable isotopes and physiology journal PLANT ECOLOGY 172 1 133 141 Invasive exotic weeds pose one of the earth's most pressing environmental problems. Although many invaders completely eliminate native plant species from some communities, ecologists know little about the mechanisms by which these exotics competitively exclude other species. Mycorrhizal fungi radically alter competitive interactions between plants within natural communities, and a recent study has shown that arbuscular mycorrhizal (AM) fungi provide a substantial competitive advantage to spotted knapweed, Centaurea maculosa, a noxious perennial plant that has spread throughout much of the native prairie in the northwestern U. S. Here we present evidence that this advantage is potentially due to mycorrhizally mediated transfer of carbon from a native bunch-grass, Festuca idahoensis, to Centaurea. Centaurea maculosa, Festuca idahoensis (Idaho fescue, C-3), and Bouteloua gracilis (blue gramma, C-4) were grown in the greenhouse either alone or with Centaurea in an incomplete factorial design with and without AM fungi. Centaurea biomass was 87-168% greater in all treatments when mycorrhizae were present in the soil (P < 0.0001). However, Centaurea biomass was significantly higher in the treatment with both mycorrhizae and Festuca present together than in any other treatment combination (P < 0.0001). This high biomass was attained even though Centaurea photosynthetic rates were 14% lower when grown with Festuca and mycorrhizae together than when grown with Festuca without mycorrhizae. Neither biomass nor photosynthetic rates of Centaurea were affected by competition with the C-4 grass Bouteloua either with or without mycorrhizae. The stable isotope signature of Centaurea leaves grown with Festuca and mycorrhizae was more similar to that of Festuca, than when Centaurea was grown alone with mycorrhizae (P = 0.06), or with Festuca but without mycorrhizae (P = 0.09). This suggests that carbon was transferred from Festuca to the invasive weed. We estimated that carbon transferred from Festuca by mycorrhizae contributed up to 15% of the aboveground carbon in Centaurea plants. Our results indicate that carbon parasitism via AM soil fungi may be an important mechanism by which invasive plants out compete their neighbors, but that this interaction is highly species-specific. Web of Science Centaurea maculosa USA Montana Garden terrestrial Grassland Invasion Hyp. Mutualism Facilitation primary 1537 Rose, M; Hermanutz, L 2004 Are boreal ecosystems susceptible to alien plant invasion? Evidence from protected areas journal OECOLOGIA 139 3 467 477 Although biological invasion by alien species is a major contributor to loss of indigenous biological diversity, few studies have examined the susceptibility of the boreal biome to invasion. Based on studies of other ecosystems, we hypothesized that alien plants will be restricted to disturbed areas near human activity and will not be found in natural areas of boreal ecosystems in Gros Morne National Park (Canada), a protected area experiencing a wide range of disturbance regimes. The distribution of alien plants in the region was evaluated using surveys, and study sites were established in naturally and anthropogenically disturbed habitats that had been invaded. Within study sites, randomization tests evaluated the importance of disturbance to alien plant invasion by examining changes in environmental conditions and species abundance within various disturbance regimes, while the importance of site characteristics limiting the distribution of alien plants were examined using Canonical Correspondence Analysis. Consistent with studies in a variety of biomes, areas of high disturbance and human activity had the greatest abundance of resources and the highest percentage of alien species. However, contrary to our hypothesis, natural areas of boreal ecosystems were found susceptible to alien plant invasion. Vegetation types vulnerable to invasion include forests, riparian areas, fens, and alpine meadows. Natural disturbance occurring in these vegetation types caused increases in bare ground and/or light availability facilitating alien plant invasion. Although high soil pH was associated with alien plants in these areas, disturbance was not found to cause changes in soil pH, suggesting susceptibility to invasion is pre-determined by bedrock geology or other factors influencing soil pH. Moose (Alces alces), a non-native herbivore, acts as the primary conduit for alien plant invasion in GMNP by dispersing propagules and creating or prolonging disturbance by trampling and browsing vegetation. The recurrent nature of disturbance within the boreal biome and its interaction with site conditions and herbivores enables alien plants to persist away from areas of high human activity. Managers of natural lands should monitor such interactions to decrease the invasion potential of alien plants. Web of Science Many Canada Newfoundland Gros Morne National Park 49.61 -57.72 Field - Observational terrestrial Invasion Hyp. Disturbance primary 1538 Miller, KE; Gorchov, DL 2004 The invasive shrub, Lonicera maackii, reduces growth and fecundity of perennial forest herbs journal OECOLOGIA 139 3 359 375 Effects of invasive plant species on native plant species are frequently assumed or inferred from comparisons, but rarely quantified experimentally. Such quantification is important to assessing risks and impacts of invasives. We quantified the effects of Lonicera maackii, an exotic shrub invasive in many eastern North American forests, on survival, growth, and reproduction of three perennial herbs: Allium burdickii, Thalictrum thalictroides , and Viola pubescens. We predicted that the spring ephemeral, A. burdickii , would be most impacted, due to early leaf expansion of L. maackii. Field experiments were carried out in two deciduous forest stands, one (Gregg's Woodlot, GW) disturbed and the other (Western Woods, WW) relatively undisturbed. In each stand, individual herbs were transplanted into a blocked design of 60 plots where L. maackii was present, absent, or removed, and monitored for 5 growing seasons. Lonicera maackii did not affect survival of transplants, but reduced growth and final size of individuals of all three species. For two of the species, A. burdickii and V. pubescens, L. maackii reduced the proportion of live plants flowering in both stands, and reduced the seed or fruit number per flowering individual in GW. For T. thalictroides the proportion flowering was not affected, but seed number per flowering plant was reduced by L. maackii in both stands. For all three species, cumulative seed production over the course of the study was reduced by L. maackii. Overall, effects on the spring ephemeral, A. burdickii, were similar to effects on the other herbs. Because mortality of these established individuals was not affected, short-term studies might conclude forest herbs are unaffected by invasive shrubs. However, the growth and reproduction impacts documented here suggest that populations are impacted in the long-term. Web of Science Lonicera maackii USA Ohio Oxford 39.5 84.75 Field - Experimental terrestrial Deciduous Forest Impacts;Invasion Hyp. Disturbance primary 1540 Maron, JL; Vila, M; Bommarco, R; Elmendorf, S; Beardsley, P 2004 Rapid evolution of an invasive plant journal ECOLOGICAL MONOGRAPHS 74 2 261 280 Exotic plants often face different conditions from those experienced where they are native. The general issue of how exotics respond to unfamiliar environments within their new range is not well understood. Phenotypic plasticity has historically been seen as the primary. mechanism enabling exotics to colonize large, environmentally diverse areas. However, new work indicates that exotics can evolve quickly, suggesting that contemporary evolution may be more important in invasion ecology than previously appreciated. To determine the influence of contemporary evolution; phenotypic plasticity, and founder effects in affecting phenotypic variation among introduced plants, we compared the size, fecundity, and leaf area of St. John's wort (Hypericum perforatum) collected from native European and introduced western and central North American populations in common gardens in Washington, California, Spain, and Sweden. We also determined genetic relationships among these plants by examining variation in amplified fragment length polymorphism (AFLP) markers. There was substantial genetic variation among introduced populations and evidence for multiple introductions of H. perforatum into North America. Across common gardens introduced plants were neither universally larger nor more fecund than natives. However, within common gardens, both introduced and native populations exhibited significant latitudinally based clines in size and fecundity. Clines among introduced populations broadly converged with those among native populations. Introduced and native plants originating from northern latitudes generally outperformed those originating from southern latitudes when grown in northern latitude gardens of Washington and Sweden. Conversely, plants from southern latitudes performed best in southern gardens in Spain and California. Clinal patterns in leaf area, however, did not change between gardens; European and central North American plants from northern latitudes had larger leaves than plants from southern latitudes within these regions in both Washington and California, the two gardens where this trait was measured. Introduced plants did not always occur at similar latitudes as their most closely related native progenitor, indicating that pre-adaptation (i.e., climate matching) is unlikely to be the sole explanation for clinal patterns among introduced populations. Instead, results suggest that introduced plants are evolving adaptations to broad-scale environmental conditions in their introduced range. Web of Science Hypericum perforatum USA California; Washington 41.43; 46.63 -122.25; -122.95 Garden terrestrial Old Field Invasion Hyp. Evolution in General primary 1542 Cassidy, TM; Fownes, JH; Harrington, RA 2004 Nitrogen limits an invasive perennial shrub in forest understory journal BIOLOGICAL INVASIONS 6 1 113 121 Plant invasions can harm communities by domination of one or more vegetation layers. We Studied whether Japanese barberry (Berberis thunbergii DC.) is limited by soil acidity or nitrogen availability in its domination of relatively undisturbed forest understories. In two sites, one more acid than the other, we applied lime, urea, or a sawdust-sugar mix to replicate plots in established barberry populations. We predicted that the acid site would be pH or cation limited. while the less acid site was N limited, unless N availability was inherently higher before treatment. Barberry above-ground net primary production (NPP) was estimated by a combination of harvest and allometric analysis. Foliar N increased in the urea treatment and was proportional to incubation estimates of net N mineralization and nitrification. Foliar Ca and P were unaffected by the treatments. Foliar K was proportional to foliar N. The more acid site had higher foliar Mn, but otherwise the sites differed little. Barberry NPP was proportional to pre-treatment biomass. The ratio of net production to pre-treatment woody biomass (relative production rate) increased with foliar N and soil N availability and decreased when soil N was immobilized by sawdust and sugar. There was no effect of soil pH or cation status on barberry growth, although a correlation with foliar K was reflected by the maintenance of a constant K : N ratio. Although more severely acid sites may be less invasible than those studied here, N availability is the primary limitation to invasive dominance in this landscape. Web of Science Berberis thunbergi USA Massachusetts Quabbin Reservoir 42.48 -72.26 Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Ecosystem Engineers primary 1544 Green, PT; Lake, PS; O'Dowd, DJ 2004 Resistance of island rainforest to invasion by alien plants: influence of microhabitat and herbivory on seedling performance journal BIOLOGICAL INVASIONS 6 1 1 9 Experiments have promise in determining mechanisms by which communities resist invasion. Growth and survivorship of transplanted seedlings of introduced tree species (Leucaena leucocephala, Muntingia calabura, Adenanthera pavonia, and Clausena excavata) were used to assess abiotic (light regime) and biotic resistance (herbivory) to invasion of rainforest on Christmas Island (Indian Ocean). At four sites, seedlings were transplanted into the forest edge along roadside verges and into adjacent intact forest; half were caged to prevent access by the dominant seedling consumer, the red land crab (Gecarcoidea natalis). Red crab densities did not differ between roadside and forest plots. Red crabs initially reduced survivorship of Leucaena in both edge and interior plots but virtually all seedlings in the forest interior were dead after 41 weeks. Survivorship of Muntingia was also initially reduced by crabs in the forest edge, but again, all but one seedling died by the end of the experiment. Seedlings of Adenanthera and Clausena fared much better overall, surviving well in both locations. Red crabs had no overall effect on Adenanthera survival but significantly reduced survival of Clausena in forest plots. For both species, seedling performance was greater in the forest edge than in the forest interior. Red crabs had no effect on height increment for either species; however. for Clausena, red crabs reduced seedling mass in the forest interior. Both Adenanthera and Clausena were able to persist in the intact forest. Clausena is now actively invading intact rainforest, but Adenanthera appears dispersal-limited. Resistance factors in intact forest appear hierarchical: biotic resistance afforded by land crabs can impede establishment of some plant invaders but seedling responses to abiotic factors (e.g., the light regime) largely overwhelm its effect. Together, these two community attributes are likely to restrict the range of plant invaders to a small suite of species that can successfully establish in intact rainforest on the island. However, increased propagule pressure from a variety of shade-tolerant species and further declines in the abundance of the dominant seedling consumer may lead to increasing invasion success in this island rainforest. Web of Science Leucaena leucocephala; Muntingia calabura; Adenanthera pavonia; Clausena excavata Australia Christmas Island -10.478 105.629 Field - Experimental terrestrial Tropical Forest Invasion Hyp. Other primary 1545 St Denis, M; Cappuccino, N 2004 Reproductive biology of Vincetoxicum rossicum (Kleo.) Barb. (Asclepiadaceae), an invasive alien in Ontario journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 131 1 8 15 We investigated the reproductive biology of the alien invasive vine Vincetoxicum rossicum (Asclepiadaceae) and evaluated pollinator visitation rate in the field, evidenced by missing pollinaria, to flowers of isolated plants and those of plants in dense monocultures. Flowers in dense monocultures were visited less frequently than those on isolated plants surrounded by old-field grasses. Visited flowers were more likely to produce fruit and those fruits contained more polyembryonic seeds. However, a greenhouse experiment in which we cross- or self-pollinated flowers revealed no difference in fruit set, seed production, seed weight or embryony. This suggests that the higher fruit set and greater polyembryony of visited flowers in the field was not the consequence of visitation, but may have been the result of floral visitors having chosen the most vigorous flowers. Day-old flowers emasculated in the greenhouse experiment occasionally produced a fruit, indicating that the germination of self-pollen begins the day a flower opens. The ability to produce large numbers of selfed seeds is no doubt advantageous to this highly invasive asclepiad. Web of Science Vincetoxicum rossicum Canada Ontario Ottawa 45.4167 75.7167 Field - Observational;Greenhouse Old Field Invasion Hyp. Inherent Superiority High Reprod. Output;Self Compatible primary 1547 Smith, DH; Smart, RM 2004 Influence of water level on torpedograss establishment in Lake Okeechobee, Florida journal LAKE AND RESERVOIR MANAGEMENT 20 1 1 13 Lake Okeechobee, a 173,200 ha shallow subtropical lake located in south Florida, has been invaded recently by torpedograss (Panicum repens), an exotic, terrestrial species, that was intentionally introduced to Florida in the early 1900s. Since the 1970s, more than 6,000 ha of native plants, including spikerush (Eleocharis cellulosa) and beakrush (Rhynchospora spp.) and open water habitat have been displaced by torpedograss in areas of the marsh where inundation depths often are less than 50 cm. The ability of torpedograss to disperse and become established at different water depths was evaluated in a series of experimental pond studies. These studies revealed that fragments remain buoyant for extended periods and so facilitate the dispersal of torpedograss within the lake. If fragments become anchored to sediment that is either exposed or in shallow water, they can readily root and establish mature plants; Once established, torpedograss can thrive in depths of 75 cm or less and can survive prolonged exposure to flooding depths greater than I m. In this manner, low water periods can contribute to the dispersal and colonization pattern of torpedograss in the lake. When coupled with lake elevation data, these findings suggest that low water levels or drawdowns would increase the marsh area susceptible to torpedograss invasion. Web of Science Panicum repens USA florida lake okeechobee 26.935 -80.79 Field - Experimental lentic Invasion Hyp. Inherent Superiority Effective Disperser primary 1549 Callaway, RM; Thelen, GC; Barth, S; Ramsey, PW; Gannon, JE 2004 Soil fungi alter interactions between the invader Centaurea maculosa and North American natives journal ECOLOGY 85 4 1062 1071 Soil microbes may affect the way exotic invasive plants interact with native neighbors. We investigated the effects of soil fungi on interactions between the invasive weed Centaurea maculosa (spotted knapweed) and six species native to the intermountain prairies of the northwestern United States. We also compared the effect of C. maculosa on the composition of the soil microbial community to that of the native species. In the field, fungicide (Benomyl) reduced AM mycorrhizal colonization of C. maculosa roots by >80%. Fungicide did not significantly reduce non-AM fungi. When grown alone, the biomass of C. maculosa was not affected by the fungicide application. However, depending on the combination of native competitor and fungicide, C. maculosa biomass varied from 10-fold decreases to 1.9-fold increases. In untreated soils, C. maculosa grew larger in the presence of Festuca idahoensis or Koeleria cristata than when alone. When fungicide was applied these positive effects of Festuca and Koeleria on C. maculosa did not occur. A third native grass, Pseudoroegneria spicata, had much stronger competitive effects on C. maculosa than Festuca or Koeleria, and fungicide reduced the competitive effects of Pseudoroegneria. Fungicide increased Centaurea biomass when competing with the forb Gallardia aristata. However, fungicide did not affect the way two other forbs; Achillea millefolium and Linum lewisii, interacted with C. maculosa. Rhizosphere microbial communities in the root zones of the three native bunchgrass species differed from that of C. maculosa. However, despite the strong effects of soil fungi in field interactions and differences in microbial community composition, soil biota from different plant rhizospheres did not affect the growth of C. maculosa in the absence of native competitors in greenhouse experiments. Our results suggest that successful invasions by exotic plant species can be affected by complex and often beneficial effects of local soil microbial communities. These effects were not manifest as simple direct effects, but become apparent only when native plants, invasive plants, and soil microbial communities were interacting at the same time. Web of Science Centaurea stoebe USA Montana Missoula 46.861 -113.948 Garden terrestrial Grassland Invasion Hyp. Community Species Richness primary 1550 Thornber, CS; Kinlan, BP; Graham, MH; Stachowicz, JJ 2004 Population ecology of the invasive kelp Undaria pinnatifida in California: environmental and biological controls on demography journal MARINE ECOLOGY-PROGRESS SERIES 268 0 69 80 We combined field monitoring and laboratory experiments to examine the population ecology of both the microscopic and macroscopic stages of a new invasion of Undaria pinnatifida in California. Over the course of 1 yr, we observed 2 distinct recruitment pulses of individuals in the Santa Barbara harbor; the appearance of these pulses was strongly correlated with a 4degreesC drop in ocean temperature approximately 2 mo prior to recruitment, Cultures of zoospores and successive microscopic stages revealed thermal tolerances consistent with field recruitment data; individuals grown at 13degreesC had significantly higher survivorship than individuals grown at higher temperatures (harbor temperatures annually ranged from 12 to 21degreesC). The 2 cohorts also differed greatly in individual size, growth rate, and survival to maturity. Grazing by herbivores, predominately the native kelp crab Pugettia producta, effectively prevented nearly all individuals in the second cohort from reaching reproductive maturity. Grazer control was effective despite far higher rates of recruitment during the second recruitment pulse. Our results highlight the potential for extreme variability in U. pinnatifida demography mediated by local oceanographic and biotic factors. Understanding controls on U. pinnatifida demography helps to explain variation in the spread and impact of this invader worldwide, and allows better prediction of when and where U. pinnatifida may continue its invasion along the west coast of North America. Web of Science Undaria pinnatifida USA California Santa Barbara 34.408 -119.685 Field - Observational;Lab marine Intertidal/Near Shore Fundamentals primary 1552 Gosper, CR 2004 Fruit characteristics of invasive bitou bush, Chrysanthemoides monilifera (Asteraceae), and a comparison with co-occurring native plant species journal AUSTRALIAN JOURNAL OF BOTANY 52 2 223 230 Bitou bush, Chrysanthemoides monilifera (L.) Norlindh ssp. rotundata (DC.) Norlindh, is an invasive weed of coastal vegetation types in eastern Australia. It produces fleshy fruits, which are dispersed by birds and mammals. Compared with a range of vertebrate-dispersed fruits of native plant species that co-occur with naturalised C. monilifera, or occur elsewhere in south-eastern Australia, C. monilifera fruits and endocarps are intermediate in all dimensions and in the ratio of endocarp to pulp. C. monilifera fruits contain moderate quantities of sugars, but low quantities of protein and fat relative to many native fruits. Phenology, however, substantially distinguishes C. monilifera from co-occurring native plant species. C. monilifera produces fruits throughout the year, with the peak of production occurring in autumn to winter, a time when few native species in coastal vegetation produce fruits. Additionally, 9 of the 12 native species that do fruit, at least partly, over this period, differ substantially from C. monilifera in fruit morphology. C. monilifera, along with other invasive species, has substantially altered the temporal pattern of fruit availability in coastal vegetation. These fruiting characteristics have rendered C. monilifera fruits attractive to frugivores and have contributed to its successful spread. Web of Science Chrysanthemoides monilifera Australia New South Wales Myall Lakes National Park -32.509 152.345 Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Mutualism Facilitation primary 1553 Mandak, B; Pysek, P; Bimova, K 2004 History of the invasion and distribution of Reynoutria taxa in the Czech Republic: a hybrid spreading faster than its parents journal PRESLIA 76 1 15 64 The distribution of four alien Reynoutria taxa (R. japonica var. japonica, R. japonica var. compacta, R. sachalinensis and R. x bohemica), native to East Asia, and history of their introduction to and spread in the Czech Republic was studied. The most widely distributed representative of the genus, R. japonica var. japonica, was first recorded in 1883 by A. Weidmann in cultivation in S Bohemia. The first record outside cultivation is from N Bohemia in 1902. Up to 2000, it has been recorded in 1335 localities, most frequently in riparian and human-made habitats. The dwarf variety R. japonica var. compacta is of a limited distribution that depends on rare cultivation and subsequent escape. The first herbarium specimen was collected in 1948 and the first record out of cultivation is from 1995. R. sachalinensis was recorded in 261 localities. It was first collected in 1921 in Central Bohemia. A herbarium specimen of a plant cultivated in the Botanical Garden of the Charles University in Prague, collected in 1950, has been re-determined as R. x bohemica, the hybrid between R. japonica var. japonica and R. sachalinensis, and represents the earliest record of the hybrid in the Czech Republic. Since then, this taxon was observed in 381 localities. Herbarium records were used to compare the rate of spread among the three common taxa in 1952-1995, i.e. since when the hybrid started to appear in herbaria. R. japonica var. japonica has been spreading significantly faster than R. sachalinensis and the hybrid exhibits twice the rate of invasion of its parents. Web of Science Reynoutria japonica; Reynoutria sachalinensis; Reynoutria bohemica Czech Republic Bohemia 49.85 13.61 Field - Observational terrestrial Riparian;Old Field Invasion Hyp. Hybridization primary 1555 Ellsworth, JW; Harrington, RA; Fownes, JH 2004 Seedling emergence, growth, and allocation of Oriental bittersweet: effects of seed input, seed bank, and forest floor litter journal FOREST ECOLOGY AND MANAGEMENT 190 3 255 264 The establishment of invasive plant populations is controlled by seed input, survival in the soil seed bank, and effects of soil surface disturbance on emergence, growth, and survival. We studied the invasive vine Celastrus orbiculatus Thunb. (Oriental bittersweet) to determine if seedlings in forest understory germinate from the seed bank or from seed rain. We also conducted a greenhouse experiment to investigate the role of leaf litter mass and physical texture on seedling survival, growth, and allocation. In the understory of an invaded mixed hardwood forest, we measured seed input, seedling emergence with seed rain, and seedling emergence without seed rain. Mean seed rain was 168 seeds m(-2): mean seedling emergence was 107 m(-2), and there was a strong correlation between seed rain and seedling emergence. The ratio of seedlings to seed input (0.61) was close to the seed viability (0.66) leaving very few seeds to enter the seed bank. Seed bank germination under field conditions was low (1 seedling m(-2)). Soil cores were incubated in a greenhouse to determine seed bank viability, and germination from these soil cores did not occur. To determine how litter affects seedling establishment and growth, we measured seedling emergence and biomass allocation in a greenhouse experiment. Seeds were placed below intact and fragmented deciduous leaf litter in amounts ranging from zero to the equivalent of 16 Mg ha(-1). Seedling emergence was not affected by fragmented litter, but decreased to <20% as intact litter increased to 16 Mg ha(-1). Increasing litter resulted in greater allocation to hypocotyl and less to cotyledon and radicle, and this effect was greater in intact litter. C orbiculatus seedlings achieve emergence through forest floor litter through plasticity in allocation to hypocotyl growth. The low survival of C. orbiculatus in the seed bank suggests that eradication of seedling advance regeneration and adult plants prior to seed rain may be an effective control strategy. However, the intact forest floor litter of an undisturbed forest will not prevent seedling establishment. (C) 2003 Elsevier B.V. All rights reserved. Web of Science Celastrus orbiculatus USA Massachusetts Amherst 42.395 -72.507 Field - Experimental;Greenhouse terrestrial Deciduous Forest Fundamentals primary 1556 Yates, ED; Levia, DF; Williams, CL 2004 Recruitment of three non-native invasive plants into a fragmented forest in southern Illinois journal FOREST ECOLOGY AND MANAGEMENT 190 3 119 130 Plant invasions are a current threat to biodiversity conservation, second only to habitat loss and fragmentation. Density and heights of three invasive plants, Rosa multiflora, Lonicera japonica, and Elaeagnus umbellata, were examined between edges and adjacent interiors of forest sites in southern Illinois. Density (stems m(-2)) and heights (cm) of invasive plants were obtained in plots along transects at edge and interior sampling locations within forest sites. The effect of species, sampling location, and site shape index on invasive plant density was investigated, as well as differences in heights of invasive plants in edge vs. interior sampling locations. Species, sampling location, and fragment shape index were significant factors influencing invasive plant density at study sites. Density for all three species ranged from 0 to 18 stems m(-2). All three species invaded interiors of sites, however, R. multiflora and L. japonica had significantly greater densities in edge as opposed to interior transects. These two species also had significant differences in density among site shape indices. Density of E. umbellata was not significantly different between edge and interior sampling locations or among site shape indices. Mean heights of all three invasive plants were higher in edge transects, however, this relationship was only significant for L. japonica. These findings suggest that (1) preservation of tracts of forest with less edge can minimize invasion by these three plants in this area. Interiors of forest sites can be protected from invasion by having less edge habitat for invasive species to enter and become established; and (2) E. umbellata, unlike the other two species, is established in both interior and edges of study sites. Therefore, E. umbellata may pose the most ecological damage because it is well established throughout sites, and should be given a high priority when implementing management and control efforts in southern Illinois forest ecosystems. (C) 2003 Elsevier B.V. All rights reserved. Web of Science Rosa multiflora; Lonicera japonica; Elaeagnus umbellata USA Illinois Shawnee National Forest 37.47 -89.15 Field - Observational terrestrial Deciduous Forest Fundamentals primary 1558 Vila, M; Weiner, J 2004 Are invasive plant species better competitors than native plant species? evidence from pair-wise experiments journal OIKOS 105 2 229 238 Invasive plants often appear to be more competitive than native species, but there have been few tests of this hypothesis. We reviewed published pair-wise experiments between invading and native plant species. Although the designs that have been used allow only limited inferences, the available data suggest that the effect of invasive species on native species is usually stronger than vice versa. Furthermore, mixtures of invasive and native species are generally less productive than monocultures of the native species, but not less than monocultures of the invasive species. However, the selection of invaders and natives for study has not been random, and the data could be biased towards highly competitive invaders and natives that are weaker than average competitors. We attempt to clarify confusion surrounding the concept of competitive superiority in the context of plant invasions, and we discuss the limitations of the methods that have been used to investigate competition between invasive and native species. To rigorously test the generality of the hypothesis that invaders are better competitors than natives we need to compare the effects of closely related native and invasive species on each other. We suggest that the influence of an invading species on total plant community biomass is an important clue in understanding the role of competition in a plant invasion. The role of competition in the establishment and naturalization stages of the invasion process may be very different from its role in the *outbreak* stage. Web of Science Many Statistical/Meta-analysis;Review terrestrial Invasion Hyp. Inherent Superiority Superior Competitor primary 1559 DeWalt, SJ; Denslow, JS; Hamrick, JL 2004 Biomass allocation, growth, and photosynthesis of genotypes from native and introduced ranges of the tropical shrub Clidemia hirta journal OECOLOGIA 138 4 521 531 We tested the hypothesis that the tropical shrub Clidemia hirta appears more shade tolerant and is more abundant in its introduced than native range because of genetic differences in resource acquisition, allocation, and phenotypic plasticity between native and introduced genotypes. We examined growth, biomass allocation, and photosynthetic parameters of C. hirta grown in a greenhouse from seed collected from four populations in part of its native range (Costa Rica) and four populations in part of its introduced range (Hawaiian Islands). Six-month-old seedlings were placed in high (10.3-13.9 mol m(-2) day(-1)) or low (1.4-4.5 mol m(-2) day(-1)) light treatments and grown for an additional 6 months. Our study provided little evidence that Hawaiian genotypes of C. hirta differed genetically from Costa Rican genotypes in ways that would contribute to differences in habitat distribution or abundance. Some of the genetic differences that were apparent, such as greater allocation to stems and leaf area relative to whole plant biomass in Costa Rican genotypes and greater allocation to roots in Hawaiian genotypes, were contrary to predictions that genotypes from the introduced range would allocate more biomass to growth and less to storage than those from the native range. Hawaiian and Costa Rican genotypes displayed no significant differences in relative growth rates, maximal photosynthetic rates, or specific leaf areas in either light treatment. In the high light environment, however, Hawaiian genotypes allocated more biomass to reproductive parts than Costa Rican genotypes. Phenotypic plasticity for only 1 of 12 morphological and photosynthetic variables was greater for Hawaiian than Costa Rican genotypes. We conclude that genetic shifts in resource use, resource allocation, or plasticity do not contribute to differences in habitat distribution and abundance between the native and introduced ranges of C. hirta. Web of Science Clidemia hirta USA Hawaii Waiakea Forest Reserve 19.6833 -155.1333 Greenhouse terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 1560 Bossdorf, O; Prati, D; Auge, H; Schmid, B 2004 Reduced competitive ability in an invasive plant journal ECOLOGY LETTERS 7 4 346 353 One explanation for successful plant invaders is that they evolved to be more competitive. An intuitive prediction of this Evolution of Increased Competitive Ability (EICA) hypothesis never previously tested is that invasive populations should outcompete their native 'ancestors' in a common environment. We tested this idea in a diallel competition experiment with Alliaria petiolata where offspring from native and invasive populations were grown alone or in all pairwise combinations. While without competition, there were no differences between native and invasive populations, native populations outperformed invasive ones when competing against each other. Our results contradict the EICA hypothesis and we conclude that it does not not hold for Alliaria petiolata. Instead, we formulate a new ERCA (Evolutionary Reduced Competitive Ability) hypothesis: if there is less competition in the invasive range and competitive ability involves traits that have a fitness cost, then selection might act against it, thereby reducing intraspecific interactions too. Web of Science Alliaria petiolata Greenhouse terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 1561 Vivanco, JM; Bais, HP; Stermitz, FR; Thelen, GC; Callaway, RM 2004 Biogeographical variation in community response to root allelochemistry: novel weapons and exotic invasion journal ECOLOGY LETTERS 7 4 285 292 Centaurea diffusa is one of the most destructive invasive weeds in the western USA and allelopathy appears to contribute to its invasiveness (Callaway & Aschehoug 2000). Here we identify a chemical from the root exudates of C. diffusa, 8-hydroxyquinoline, not previously reported as a natural product, and find that it varies biogeographically in its natural concentration and its effect as an allelochemical. 8-Hydroxyquinoline is at least three times more concentrated in C. diffusa-invaded North American soils than in this weed's native Eurasian soils and has stronger phytotoxic effects on grass species from North America than on grass species from Eurasia. Furthermore, experimental communities built from North American plant species are far more susceptible to invasion by C. diffusa than communities built from Eurasian species, regardless of the biogeographical origin of the soil biota. Sterilization of North American soils suppressed C. diffusa more than sterilization of Eurasian soils, indicating that North American soil biota may also promote invasion by C. diffusa. Eurasian plants and soil microbes may have evolved natural resistance to 8-hydroxyquinoline while North American plants have not, suggesting a remarkable potential for evolutionary compatibility and homeostasis among plants within natural communities and a mechanism by which exotic weeds destroy these communities. Web of Science Centaurea diffusa USA Lab terrestrial Grassland Invasion Hyp. Novel Weapons primary 1566 DeWalt, SJ; Denslow, JS; Ickes, K 2004 Natural-enemy release facilitates habitat expansion of the invasive tropical shrub Clidemia hirta journal ECOLOGY 85 2 471 483 Normative, invasive plant species often increase in growth, abundance, or habitat distribution in their introduced ranges. The enemy-release hypothesis, proposed to account for these changes, posits that herbivores and pathogens (natural enemies) limit growth or survival of plants in native areas, that natural enemies have less impact in the introduced than in the native range, and that the release from natural-enemy regulation in areas of introduction accounts in part for observed changes in plant abundance. We tested experimentally the enemy-release hypothesis with the invasive neotropical shrub Clidemia hirta (L.) D. Don (Melastomataceae). Clidentia hirta does not occur in forest in its native range but is a vigorous invader of tropical forest in its introduced range. Therefore, we tested the specific prediction that release from natural enemies has contributed to its expanded habitat distribution. We planted C. hirta into understory and open habitats where it is native (Costa Rica) and where it has been introduced (Hawaii) and applied pesticides to examine the effects of fungal pathogen and insect herbivore exclusion. In understory sites in Costa Rica, C. hirta survival increased by 12% if sprayed with insecticide, 19% with fungicide, and 41% with both insecticide and fungicide compared to control plants sprayed only with water. Exclusion of natural enemies had no effect on survival in open sites in Costa Rica or in either habitat in Hawaii. Fungicide application promoted relative growth rates of plants that survived to the end of the experiment in both habitats of Costa Rica but not in Hawaii, suggesting that fungal pathogens only limit growth of C. hirta where it is native. Galls, stem borers, weevils, and leaf rollers were prevalent in Costa Rica but absent in Hawaii. In addition, the standing percentage of leaf area missing on plants in the control (water only) treatment was five times greater on plants in Costa Rica than in Hawaii and did not differ between habitats. The results from this study suggest that significant effects of herbivores and fungal pathogens may be limited to particular habitats. For Clidemia hirta, its absence from forest understory in its native range likely results in part from the strong pressures of natural enemies. Its invasion into Hawaiian forests is apparently aided by a release from these herbivores and pathogens. Web of Science Clidemia hirta United States; Costa Rica Hawaii 9.646093; 10.455258; 10.200461; 19.620987; 19.697676; 19.453094 -82.749091; -84.001994; -83.607559; -155.135422; -155.141144; -154.894581 Field - Experimental terrestrial Tropical Forest Invasion Hyp. Enemy Release primary 1567 Hager, HA 2004 Competitive effect versus competitive response of invasive and native wetland plant species journal OECOLOGIA 139 1 140 149 Non-native plants can have adverse effects on ecosystem structure and processes by invading and out-competing native plants. I examined the hypothesis that mature plants of non-native and native species exert differential effects on the growth of conspecific and heterospecific seedlings by testing predictions that (1) invasive vegetation has a stronger suppressive effect on seedlings than does native vegetation, (2) seedlings of invasive species are better able to grow in established vegetation than are native seedlings, and (3) invasive species facilitate conspecific and inhibit heterospecific seedling growth. I measured growth rates and interaction intensities for seedlings of four species that were transplanted into five wetland monoculture types: invasive Lythrum salicaria; native L. alatum, Typha angustifolia, T. latifolia; unvegetated control. Invasive L. salicaria had the strongest suppressive effect on actual and per-individual bases, but not on a per-gram basis. Seedlings of T. latifolia were better able to grow in established vegetation than were those of L. salicaria and T. angustifolia. These results suggest that L. salicaria is not a good invader of established vegetation, but once established, it is fairly resistant to invasion. Thus, it is likely that disturbance of established vegetation facilitates invasion by L. salicaria, allowing it to compete with other species in even-aged stands where its high growth rate and consequent production of aboveground biomass confer a competitive advantage. Web of Science Lythrum salicaria USA Minnesota Carlos Avery Wildlife Management Area 45.3167 -93.086 Field - Experimental lotic Invasion Hyp. Inherent Superiority Superior Competitor primary 1572 Liu, CH; Wu, G; Yu, D; Wang, D; Xia, SL 2004 Seasonal changes in height, biomass and biomass allocation of two exotic aquatic plants in a shallow eutrophic lake journal JOURNAL OF FRESHWATER ECOLOGY 19 1 41 45 The two exotic species, Eichhornia crassipes (Mart.) Solms and Alternanthera philoxeroides (Mart.) Griseb., are floating aquatic plants that cause serious problems throughout the world. The community establishment of these two aquatic plants and seasonal variations in Lake Donghu were studied during 1996 and 1998. The peak plant height and the maximum biomass of E. crassipes occurred in October and November respectively, whereas these peaks occurred respectively in September and November for A. philoxeroides. The variation of mat thickness of A. philoxeroides was not as intense as plant height. The biomass allocation of these species was also evaluated in 1997. Web of Science Eichhornia crassipes; Alternanthera philoxeroides China Hubei Lake Donghu 30.58 114.4 Field - Observational lentic Fundamentals primary 1573 Kalisz, PJ; Powell, JE 2004 Exotic isopods (Crustacea : Isopoda) in disturbed and undisturbed forest soils on the Cumberland Plateau of Kentucky, USA journal NATURAL AREAS JOURNAL 24 1 54 56 This three-year study used pitfall trapping to examine the pattern of occurrence of exotic isopods (Crustacea: Isopoda) on dry ridge tops in an extensive forest area with relatively low levels of use and disturbance by humans. Native species of isopods were not found on the study area. Exotic isopods did not occur on undisturbed forest sites, but occurred on 33% of the roadsides and on 25% of the campsites. The pH on undisturbed sites (pH 4.3) and campsites (pH 4.4) did not differ, whereas the pH along roadsides (pH 6.9) was elevated due to input of calcareous dust from the limestone road-surfacing material. Armadillidium nasatum Budde-Lund, which is native to limestone areas in Europe, was the only species found on roadsides; Porcellio scaber Latreille, which is native to acid heaths and sand dunes in Europe, accounted for 75% of the specimens on campsites. The long-term effects of the exotic species on the ecology of these dry ridge tops remain to be determined. Web of Science Armadillidium nasatum; Porcellio scaber USA Kentucky Cumberland Plateau 36.89 -84.25 Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance omnivore 1574 Fowler, SP; Larson, KC 2004 Seed germination and seedling, recruitment of Japanese honeysuckle in a Central Arkansas natural area journal NATURAL AREAS JOURNAL 24 1 49 53 Nonindigenous plant species are an increasingly common problem in natural areas and effective management of invasive plants depends in part on accurate information about the life history of the invading species. The negative impact of Lonicera japonica, Japanese honeysuckle, on native plant communities is well known, as is this species capacity for prolific vegetative spreading by trailing stems. Surprisingly, despite being known for impressive floral displays, the capacity of L. japonica for establishment by seed is not known. We found that natural seedling recruitment rate in a L. japonica invaded state park in central Arkansas was only 0.002 seedlings per m(2) germinating and surviving one year. Results from experimental seed sowings indicated that germination of L. japonica seeds was patchy, but not significantly different in a shady forest interior and a sunnier forest edge, or impacted by predation or ground cover. Overall, 13.8% of the 2400 seeds sowed germinated from early spring to summer during the first year; no seeds germinated from the experimental plots the following spring, indicating no evidence of a seed bank in our study. Of the seeds that germinated, 14.4% survived one year in the forest interior, while no seedlings survived one year at the forest edge. Web of Science Lonicera japonica USA Arkansas 34.84 -92.48 Field - Observational terrestrial Deciduous Forest Fundamentals primary 1575 Lesica, P; Miles, S 2004 Beavers indirectly enhance the growth of Russian olive and tamarisk along eastern Montana Rivers journal WESTERN NORTH AMERICAN NATURALIST 64 1 93 100 Russian olive and tamarisk are introduced woody plants invading western North American riparian communities. Beavers can play an important role in structuring these communities by removing the dominant cottonwood trees. Our study explored the way in which beavers interact with cottonwood, Russian olive, and tamarisk along 4 rivers on the Great Plains of eastern Montana. We sampled cottonwood stands that supported populations of 1 or both exotic species, recording beaver damage and density in addition to size and age of cottonwood, Russian olive, and tamarisk. In stands where beaver had been present, they felled an average of 80% of cottonwood trees while rarely using Russian olive or tamarisk. Beaver foraging was apparent in nearly 90% of stands within 50 m of the river channel but only 21% of stands farther away, creating a sunny corridor along the river channel that may increase the invasive potential of Russian olive and tamarisk. Growth rates of both Russian olive and tamarisk were substantially higher where beavers had reduced the cottonwood canopy cover. Managers wishing to reintroduce beavers should consider the potential effect on invasive exotic plants. Web of Science Elaeagnus angustifolia; Tamarix spp. USA Montana Marias River 47.93 -110.47 Field - Observational terrestrial Riparian Invasion Hyp. Mutualism Facilitation primary 1580 Piscart, C; Devin, S; Beisel, JN; Moreteau, JC 2003 Growth-related life-history traits of an invasive gammarid species: evaluation with a Laird-Gompertz model journal CANADIAN JOURNAL OF ZOOLOGY-REVUE CANADIENNE DE ZOOLOGIE 81 12 2006 2014 Although the invasive gammarid Dikerogammarus villosus (Crustacea, Amphipoda) is a recent successful invader of Western Europe's lakes and rivers and a threat to North American aquatic ecosystems, its biology is scarcely known. Different growth models for each sex were established for the first time for a natural population of a freshwater gammarid. The Laird-Gompertz growth curve was used because it best fit our data, and it was associated with an environmental forcing function to adjust the growth rate according to seasonal variations in environmental conditions. The growth curve was applied to a length decomposition obtained using the Bhattacharya method, realised on data obtained from a 1-year population dynamics study. The models allowed an assessment of biological traits such as lifespan, the age of sexual maturity, the potential number of generations per year, and the growth rate as a function of environmental conditions. Differences in growth rate between males and females were consistent with biological processes such as allocation of energy for reproduction. Dikerogammarus villosus had higher rates of growth and earlier sexual maturity than all other taxa studied, which may explain its invasive tendencies and its ability to colonize numerous new ecosystems, thus becoming a cosmopolitan freshwater species. Web of Science Dikerogammarus villosus France Argancy Moselle River 49.2 6.2 Field - Observational lotic Invasion Hyp. Inherent Superiority Rapid Growth omnivore 1581 Callaway, RM; Thelen, GC; Rodriguez, A; Holben, WE 2004 Soil biota and exotic plant invasion journal NATURE 427 127 731 733 Invasive plants are an economic problem and a threat to the conservation of natural systems. Escape from natural enemies might contribute to successful invasion(1), with most work emphasizing the role of insect herbivores(2-4); however, microbial pathogens are attracting increased attention(5). Soil biota in some invaded ecosystems may promote 'exotic' invasion(6-9), and plant-soil feedback processes are also important. Thus, relatively rare species native to North America consistently demonstrate negative feedbacks with soil microbes that promote biological diversity(10), whereas abundant exotic and native species demonstrate positive feedbacks that reduce biological diversity(10). Here we report that soil microbes from the home range of the invasive exotic plant Centaurea maculosa L. have stronger inhibitory effects on its growth than soil microbes from where the weed has invaded in North America. Centaurea and soil microbes participate in different plant-soil feedback processes at home compared with outside Centaurea's home range. In native European soils, Centaurea cultivates soil biota with increasingly negative effects on the weed's growth, possibly leading to its control. But in soils from North America, Centaurea cultivates soil biota with increasingly positive effects on itself, which may contribute to the success of this exotic species in North America. Web of Science Centaurea maculosa USA Montana Missoula 46.8731 -113.9958 Lab terrestrial Grassland Invasion Hyp. Mutualism Facilitation primary 1583 Bubb, DH; Thom, TJ; Lucas, MC 2004 Movement and dispersal of the invasive signal crayfish Pacifastacus leniusculus in upland rivers journal FRESHWATER BIOLOGY 49 3 357 368 1. The American signal crayfish Pacifastacus leniusculus, an invasive species widely introduced throughout Europe, is a major threat to native European crayfish species and is causing increasing concern because of its wide impact on aquatic ecosystems. 2. Whilst various control and management methods have been proposed, very little is known about the factors influencing dispersal and movements of signal crayfish. 3. Sixty-four adult signal crayfish (carapace length 31.9-63.8 mm) were radiotagged in upland rivers in northern England, during four periods. Tracking was carried out at two sites, a low-density establishing population and a high-density established population. Tracking was carried out at both sites concurrently during midsummer (June to August 2002), during late summer (August to September 2001) at the low-density population site and during autumn to winter (October to February 2000/01) at the high-density population site. 4. Maximum movement occurred during midsummer. Temperature appeared to be a major factor influencing the timing and extent of movements between tracking periods. 5. The frequency distribution of the maximum distance moved upstream and downstream by radiotagged crayfish showed an inverse power relationship. The median maximal upstream and downstream distances moved were 13.5 m (range 0-283 m) and 15 m (range 0-417 m), respectively. There was a significant difference between the distributions of upstream and downstream ranges, with greater distances moved downstream. 6. All downstream movements made by crayfish appeared to be active movements and not the result of passive movement during periods of high discharge. There was no apparent influence of size, sex or density on the amount of movement recorded. 7. The study provides important information on the spatial and temporal behaviour of introduced crayfish in upland lotic systems. In contrast to lowland rivers, our results suggest that flow or gradient may influence the invasive potential of signal crayfish in an upstream direction in upland rivers. Web of Science Pacifastacus leniusculus UK England York 54.09 -1.3 Field - Observational lotic Fundamentals omnivore 1585 Lankau, RA; Rogers, WE; Siemann, E 2004 Constraints on the utilisation of the invasive Chinese tallow tree Sapium sebiferum by generalist native herbivores in coastal prairies journal ECOLOGICAL ENTOMOLOGY 29 1 66 75 1. Introduced plants generally have lower generalist herbivore loads than native plants. Herbivores may be avoiding a potentially edible food source (Behavioural Constraint Hypothesis) or defences of introduced plants may be unusually toxic (Novel Defence Hypothesis). 2. To examine these hypotheses, acridid grasshoppers (Melanoplus angustipennis and Orphullela pelidna) were enclosed in a Texas grassland. Each enclosure contained native prairie vegetation and a seedling of either introduced Sapium sebiferum (Chinese tallow tree) or native Celtis laevigata (hackberry). Sapium invades many ecosystems in the south-east U.S.A. Celtis seedlings also establish in these ecosystems. 3. Although grasshoppers usually feed sparingly on Sapium, in field enclosures they fed heavily on this introduced tree species, supporting a role for behavioural avoidance. In laboratory feeding trials, M. angustipennis grasshoppers preferred Sapium foliage over the foliage of three native tree species. In a greenhouse experiment, M. angustipennis individuals fed more on Sapium in prairie mesocosms if they were conditioned on Sapium. 4. In another field experiment with single seedlings in enclosures, grasshoppers consumed similar amounts of Sapium from its introduced (Texas, U.S.A.) and native (China) ranges, suggesting that Sapium may have been a suitable host plant since it was introduced. Behavioural avoidance by generalist herbivores may contribute to Sapium's low herbivore load in its introduced range. Web of Science Sapium sebiferum USA Texas La Marque 29.362 -95.034 Field - Observational;Greenhouse;Garden terrestrial Grassland Invasion Hyp. Novel Weapons;Other primary 1586 Belote, RT; Weltzin, JF; Norby, RJ 2004 Response of an understory plant community to elevated [CO2] depends on differential responses of dominant invasive species and is mediated by soil water availability journal NEW PHYTOLOGIST 161 3 827 835 Rising atmospheric CO2 concentrations are likely to have direct effects on terrestrial ecosystems. Here, we describe effects of elevated concentrations of CO2 on an understory plant community in terms of production and community composition. In 2001 and 2002 total and species-specific above-ground net primary productivity (ANPP) were estimated by harvesting above-ground biomass within an understory community receiving ambient [CO2] and elevated [CO2] at Oak Ridge National Laboratory's free-air carbon dioxide enrichment (FACE) facility. During a wet year, community composition differed between plots receiving ambient [CO2] and elevated [CO2], but total ANPP did not differ. By contrast, during a drier year, community composition did not differ, but total ANPP was greater in elevated than ambient [CO2] plots. These patterns were driven by the response of two codominant species, Lonicera japonica and Microstegium vimineum, both considered invasive species in the south-eastern United States. The ANPP of L. japonica was consistently greater under elevated [CO2], whereas the response of M. vimineum to CO2 enrichment differed between years and mediated total community response. These data suggest that community and species responses to a future, CO2-enriched atmosphere may be mediated by other environmental factors and will depend on individual species responses. Web of Science Lonicera japonica; Microstegium vimineum USA Tennessee Oak Ridge National Laboratory 35.925 -84.315 Garden terrestrial Coniferous Forest Invasion Hyp. Climate Change primary 1589 Govedich, FR; Bain, BA; Burd, M; Davies, RW 2003 Reproductive biology of the invasive Asian freshwater leech Barbronia weberi (Blanchard, 1897) journal HYDROBIOLOGIA 510 3 125 129 Barbronia weberi were collected from Hydrilla verticillata purchased from aquarium suppliers in Melbourne, Australia and additional B. weberi were obtained from aquatic plants in Canberra, ACT, Australia. Adult leeches fed Tubifex sp. ad libitum successfully reproduced under laboratory conditions (21 +/- 5 degreesC). Reproductively mature B. weberi produced cocoons every week for up to three months at which time the adults began to senesce. Cocoons contained one to five ((x) over bar = 2.41 +/- 0.78 SD, N = 58) eggs with juveniles leaving the cocoon within 27 +/- 3.4 SD days (N = 13) of cocoon production. Juvenile B. weberi reached reproductive maturity within four months (N = 7) of hatching and had a maximum growth rate of 1.10 mm(2) d(-1) once they left the cocoon at around 30 days. Individual egg volume (r = 0.63, scaling exponent = 1.21) and cocoon volume (r = 0.65, scaling exponent = 1.24) showed a significant (P < 0.001) and nearly isometric relationship when scaled with maternal body size. Because this species can grow rapidly and produce a large number of eggs over a short period of time and can piggyback with plant species and travel through the aquarium trade, there is potential for B. weberi to rapidly invade new localities. Web of Science Barbronia weberi Australia Australian Capital Territory Canberra -35.28 149.11 Field - Observational;Lab lotic Invasion Hyp. Inherent Superiority Rapid Growth;High Reprod. Output predator 1592 Kercher, SM; Zedler, JB 2004 Multiple disturbances accelerate invasion of reed canary grass (Phalaris arundinacea L.) in a mesocosm study journal OECOLOGIA 138 3 455 464 Disturbances that intensify with agriculture and/or urban development are thought to promote the spread of invasive plants, such as the clonal perennial reed canary grass ( Phalaris arundinacea L). To test this relationship and interactions among disturbances, we subjected wet prairie assemblages within 1.1 m(2) mesocosms to invasion by Phalaris and addition of nutrients, sediments, and flooding. Species richness decreased with the application of sediments and/or flooding of 4 consecutive weeks or longer. Losses of up to six dominant and subdominant species in these treatments increased light transmission through the plant canopy by as much as 400% over the control. Light availability in July and September was a strong predictor of end-of-season aboveground biomass of Phalaris. Phalaris was also 35% and 195% more productive when nutrients were added at low and high levels, respectively. Multiple factors in combination were usually additive in their effects on invasion, but sediments and nutrients interacted with flood regime to synergistically increase invasion in some cases. A separate experiment likewise revealed a synergistic interaction between added nutrients and simulated grazing. We suggest that multiple factors be mitigated simultaneously to reduce invasion of Phalaris. Web of Science Phalaris arundinacea USA Wisconsin Madison Garden lentic Riparian Invasion Hyp. Disturbance primary 1595 Lee, CE; Remfert, JL; Gelembiuk, GW 2003 Evolution of physiological tolerance and performance during freshwater invasions journal INTEGRATIVE AND COMPARATIVE BIOLOGY 43 3 439 449 Invasive species that penetrate habitat boundaries are likely to experience strong selection and rapid evolution. This study documents evolutionary shifts in tolerance and performance following the invasion of fresh water by the predominantly estuarine and salt marsh copepod Eurytemora affinis. Common-garden experiments were performed on freshwater-invading (Lake Michigan) and ancestral saline (St. Lawrence marsh) populations to measure shifts in adult survival (at 0, 5, and 25 PSU), and survival during development and development time (both using full-sib clutches split across 0, 5, 15, and 25 PSU). Results showed clear evidence of heritable shifts in tolerance and performance associated with freshwater invasions. The freshwater population exhibited a gain in low-salinity tolerance and a reduction in high-salinity tolerance relative to the saline population, suggesting tradeoffs. These tradeoffs were supported by negative genetic correlations between survival at fresh (0 PSU) versus higher salinities. Mortality in response to salinity occurred primarily before metamorphosis, suggesting that selection in response to salinity had acted primarily on the early life-history stages. The freshwater population exhibited curious patterns of life-history evolution across salinities, relative to the saline population, of retarded development to metamorphosis but accelerated development from metamorphosis to adulthood. This pattern might reflect tradeoffs between development rate and survival in fresh water at the early life-history stages, but some other selective force acting on later life-history stages. Significant effects of clutch (genotype) and clutch-by-salinity interaction (G X E) on survival and development time in both populations indicated ample genetic variation as substrate for natural selection. Variation for high-salinity tolerance was present in the freshwater population despite negative genetic correlations between high- and low-salinity tolerance. Results implicate the importance of natural selection and document the evolution of reaction norms during freshwater invasions. Web of Science Eurytemora affinis USA Wisconsin Racine 42.81 -87.75 Garden lentic Invasion Hyp. Evolution of Increased Competitive Ability herbivore 1600 Frenzel, M; Brandl, R 2003 Diversity and abundance patterns of phytophagous insect communities on alien and native host plants in the Brassicaceae journal ECOGRAPHY 26 6 723 730 The herbivore load (abundance and species richness of herbivores) on alien plants is supposed to be one of the keys to understand the invasiveness of species. We investigate the phytophagous insect communities on cabbage plants (Brassicaceae) in Europe. We compare the communities of endophagous and ectophagous insects as well as of Coleoptera and Lepidoptera on native and alien cabbage plant species. Contrary to many other reports, we found no differences in the herbivore load between native and alien hosts. The majority of insect species attacked alien as well as native hosts. Across insect species, there was no difference in the patterns of host range on native and on alien hosts. Likewise the similarity of insect communities across pairs of host species was not different between natives and aliens. We conclude that the general similarity in the community patterns between native and alien cabbage plant species are due to the chemical characteristics of this plant family. All cabbage plants share glucosinolates. This may facilitate host switches from natives to aliens. Hence the presence of native congeners may influence invasiveness of alien plants. Web of Science Many Poland Garden terrestrial Invasion Hyp. Enemy Release primary 1601 Rouget, M; Richardson, DM 2003 Inferring process from pattern in plant invasions: A semimechanistic model incorporating propagule pressure and environmental factors journal AMERICAN NATURALIST 162 6 713 724 Propagule pressure is intuitively a key factor in biological invasions: increased availability of propagules increases the chances of establishment, persistence, naturalization, and invasion. The role of propagule pressure relative to disturbance and various environmental factors is, however, difficult to quantify. We explored the relative importance of factors driving invasions using detailed data on the distribution and percentage cover of alien tree species on South Africa's Agulhas Plain (2,160 km(2)). Classification trees based on geology, climate, land use, and topography adequately explained distribution but not abundance (canopy cover) of three widespread invasive species (Acacia cyclops, Acacia saligna, and Pinus pinaster). A semimechanistic model was then developed to quantify the roles of propagule pressure and environmental heterogeneity in structuring invasion patterns. The intensity of propagule pressure (approximated by the distance from putative invasion foci) was a much better predictor of canopy cover than any environmental factor that was considered. The influence of environmental factors was then assessed on the residuals of the first model to determine how propagule pressure interacts with environmental factors. The mediating effect of environmental factors was species specific. Models combining propagule pressure and environmental factors successfully predicted more than 70% of the variation in canopy cover for each species. Web of Science Acacia cyclops;Acacia saligna;Pinus pinaster South Africa Cape Florisitc Region -34.732735 19.794502 Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Propagule Pressure primary 1603 Siemann, E; Rogers, WE 2003 Increased competitive ability of an invasive tree may be limited by an invasive beetle journal ECOLOGICAL APPLICATIONS 13 6 1503 1507 Invasive plants are often more vigorous in novel habitats than in their native ranges. Sapium sebiferum (Chinese tallow tree) is a major invader of habitats in the southern United States. Long-term common garden experiments in Texas and Hawaii (USA) with S. sebiferant genotypes from its native range (Asia) and from areas in North America where it is invasive suggest that post-introduction evolutionary changes may contribute to its invasiveness in Texas. In Texas, where there was uniformly low herbivory, fast-growing, poorly defended invasive North American genotypes outperformed slower growing, better defended native Asian genotypes in common garden plots. In Hawaii, in contrast, an Asian herbivore, Adoretus sinicus (Chinese rose beetle) is abundant, and S. sebiferum is not invasive. In Hawaiian common garden plots, A. sinicus caused greater damage to North American genotypes, and Asian genotypes were competitively superior. Our results suggest that exotic plants freed from herbivory can evolve greater competitive ability, allowing them to become much more abundant than in their native ranges. This did not seem to occur, though, if herbivores from the native range were abundant. Web of Science Sapium sebiferum U.S.A. Texas;Hawaii Galveston Co.;Honolul Co. 29.399804;21.41327 -94.94545;-158.050804 Garden terrestrial Deciduous Forest Invasion Hyp. Evolution of Increased Competitive Ability primary 1604 Ingram, KK; Gordon, DM 2003 Genetic analysis of dispersal dynamics in an invading population of Argentine ants journal ECOLOGY 84 11 2832 2842 The ecology and dispersal dynamics of unicolonial ant invaders are poorly understood. In this study, we investigated the genetic structure of a well-documented, invading population of Argentine ants in the Jasper Ridge Biological Preserve in northern California to examine the dispersal distances of reproductives, the direction and mode of population expansion, and changes in the genetic differentiation among nests over time. Using microsatellite data, we measure both traditional F-ST statistics and multi-locus genotype assignment distances to determine the patterns of genetic structure at three spatial scales: population-wide gene flow, population substructure, and mixing between neigh-boring nests. At the population level, there was little viscosity across the Jasper Ridge population, suggesting recent rapid expansion and/or considerable long-distance gene flow, presumably mediated by winged males. The pattern of genetic structure across distance indicates that the scale of queen dispersal was limited to less than 100 m. At the level of population substructure, hierarchical F statistics measures were low across subpopulations, locations within subpopulations, and nests. However, multi-locus genotype assignment tests revealed significant structure between subpopulations and between locations. Genetic distances between nests were lower within locations than between locations, indicating that nests are most closely related to neighboring nests and that the expansion of subpopulations is primarily due to the local budding of new nests from existing nests at the invasion front. At the level of nest connectivity, the genetic differentiation among neighboring nests was associated with the time since invasion. As the invasion proceeds, nearby nests tend to be less closely related, indicating that extensive local mixing does not occur among more established nests. Our results show that the genetic structure of nests was not homogenous across unicolonial populations. Instead, the patterns of genetic structure reflect the limitations of and barriers to the dispersal of Argentine ant reproductives, the demographic history of the Jasper Ridge invasion, and changes in the genetic and ecological environment during the course of the invasion. Web of Science Linepithema humile U.S.A. California Jasper Ridge Biological Preserve 37.408805 -122.224288 Field - Observational terrestrial Fundamentals herbivore 1605 van Kleunen, M; Schmid, B 2003 No evidence for an evolutionary increased competitive ability in an invasive plant journal ECOLOGY 84 11 2816 2823 We tested whether Solidago canadensis, which was introduced from North America into Europe from the 17th century onward, has evolved an increased competitive ability (EICA) at the cost of tolerance against herbivory in its new ranged We grew plants from nine introduced European and 10 native American populations in a common garden in Europe. In half of the plants, we simulated herbivory by removing 50% of the leaf area and by spraying them with jasmonic acid. Although plants from Europe had 30.5% larger leaves, they had 27.4% smaller inflorescences and tended to grow less tall (-7.0%) and produce fewer vegetative offspring (-5.0%) than plants from North America. The simulated herbivory treatment did not result in any significant differences in height, inflorescence biomass, or number of vegetative offspring between treatment and control plants. Moreover, there were no significant differences in the response of European and American plants to simulated herbivory, indicating that they did not differ in their tolerance against herbivory. We conclude that the EICA-hypothesis does not hold in the case of the S. canadensis complex, and the worldwide invasion success. of this species must be based on other mechanisms. Web of Science Solidago canadensis Switzerland Zurich University of Zurich 47.55 8.5833 Garden terrestrial Urban;Old Field Invasion Hyp. Evolution of Increased Competitive Ability primary 1606 Pauchard, A; Alaback, PB; Edlund, EG 2003 Plant invasions in protected areas at multiple scales: Linaria vulgaris (Scrophulariaceae) in the west Yellowstone area journal WESTERN NORTH AMERICAN NATURALIST 63 4 416 428 Invasive alien plants have long been recognized as a threat to low-elevation, disturbed environments, but the case of Linaria vulgaris Mill. in Yellowstone National Park and Gallatin National Forest shows that invasions can also spread to high-elevation natural reserves. Because invasions in protected areas are a product of complex processes occurring over a broad range of scales, we argue that a multi-scale research approach is needed to capture both patterns and potential mechanisms of the invasion process. Mapping L. vulgaris at the landscape scale, we found the species occupying a broad range of sites, apparently originating from just 2 historical sources, colonizing both human-caused and natural disturbances. Analyzed at the stand scale, patches tend to aggregate in newly invaded areas and disperse in heavily infested areas. The data suggest that patches grow in size by clonal growth and in number by creation of new satellite patches. Radial patch growth rates are related to site characteristics. Clonal patch scale analysis shows that ramet densities and Linaria's effects on native plants are highest in patch centers. Both mean ramet height and reproductive vs. vegetative ramet height ratio are higher in patch cores. These results suggest that L. vulgaris may displace natural vegetation by maintaining vigor even in large and old clonal patches. Our results confirm that L. vulgaris is a significant threat to native biodiversity in open, human- or naturally disturbed environments in protected areas of the Rocky Mountains. A multi-scale method can allow managers to better understand patterns of invasion and prioritize managemerit activities to control invasive alien plants, especially in heterogeneous protected area landscapes. Web of Science Linaria vulgaris U.S.A. Montana West Yellowstone 44.8;44.6167 -111.2;-111 Field - Observational terrestrial Chaparral/Shrublands;Old Field Impacts;Invasion Hyp. Inherent Superiority;Disturbance Superior Competitor;Rapid Growth;Effective Disperser;Clonal Reproduction primary 1607 Novotny, V; Miller, SE; Cizek, L; Leps, J; Janda, M; Basset, Y; Weiblen, GD; Darrow, K 2003 Colonising aliens: caterpillars (Lepidoptera) feeding on Piper aduncum and P-umbellatum in rainforests of Papua New Guinea journal ECOLOGICAL ENTOMOLOGY 28 6 704 716 1. Caterpillar assemblages feeding on two alien plants, Piper aduncum and P. umbellatum, were studied in lowland rainforest in Papua New Guinea and compared with assemblages from 69 species of native woody hosts, including congeneric P. macropiper. 2. Species richness of caterpillars feeding on P. aduncum (29 species per 1500 m(2) of foliage) and P. umbellatum (36 species) was higher than the median richness for the 69 native hosts (23 species). 3. The probability that a caterpillar species colonised alien Piper increased with its host range from 3% for the species feeding on a single plant family to 92% for the species with host range >10 plant families. 4. The assemblage on P. aduncum was dominated by a single species (Herpetogramma sp. near licarsisalis, Crambidae), which represented 48% of individuals, and also had a high proportion (34%) of rare species, collected as single individuals. This community structure was indistinguishable from that of a typical native host. In contrast, the P. umbellatum assemblage was unusual as no species represented >10% of individuals. 5. The aggressive invasion by P. aduncum of early successional vegetation is not explained by a competitive advantage due to low herbivore load, as the abundance of caterpillars feeding on it was comparable to that of native pioneer plants. 6. The caterpillar assemblage on P. aduncum demonstrated that an assemblage indistinguishable from native assemblages in density, species richness, and dominance structure (but not in host specificity) can originate from the existing species pool in lowland rainforests on a recently established tree species in <50 years. Web of Science Piper aduncum;Piper umbellatum Papua New Guinea Madang Province Baitabag;Ohu;Mis -5.1333;-5.2333 145.6833;145.8 Field - Observational terrestrial Tropical Forest Fundamentals;Invasion Hyp. Enemy Release primary;herbivore 1609 Walters, AC; Mackay, DA 2003 An experimental study of the relative humidity preference and survival of the Argentine ant, Linepithema humile (Hymenoptera, Formicidae): comparisons with a native Iridomyrmex species in South Australia journal INSECTES SOCIAUX 50 4 355 360 The Argentine ant, Linepithema humile (Mayr), is a widespread invasive ant species that commonly displaces native ants and other ground-dwelling invertebrates in its introduced range. Previous studies have documented a relationship between the spread of Argentine ants and abiotic conditions (particularly water availability) in invaded areas, suggesting that the invasion success of Argentine ants may be related to specific abiotic factors. This study describes the relative humidity preferences and survival of Argentine ants and a dominant native ant, Iridomyrmex 'rufoniger' sp. group, in the laboratory. In a preference experiment, Argentine ant workers showed a significantly greater propensity than Iridomyrmex to locate themselves in containers with the highest relative humidity. A series of survival trials revealed that the survival of both species was related to the relative humidities within experimental containers. The survival of Argentine ant colonies was reduced in comparison with those of Iridomyrmex sp. after 4 h, however by 24 h both species displayed similar levels of survival in all relative humidity conditions. These findings confirm a relationship between the level of available moisture and the distribution and survival of Argentine ants, and may help to account for the current distribution and invasion success of Argentine ants in Australia. Web of Science Linepithema humile Australia South Australia Adelaide -35.017504 138.573117 Lab terrestrial Urban Invasion Hyp. Preadaptation to Climate;Other herbivore 1611 Reinhart, KO; Packer, A; Van der Putten, WH; Clay, K 2003 Plant-soil biota interactions and spatial distribution of black cherry in its native and invasive ranges journal ECOLOGY LETTERS 6 12 1046 1050 One explanation for the higher abundance of invasive species in their non-native than native ranges is the escape from natural enemies. But there are few experimental studies comparing the parallel impact of enemies (or competitors and mutualists) on a plant species in its native and invaded ranges, and release from soil pathogens has been rarely investigated. Here we present evidence showing that the invasion of black cherry (Prunus serotina) into north-western Europe is facilitated by the soil community. In the native range in the USA, the soil community that develops near black cherry inhibits the establishment of neighbouring conspecifics and reduces seedling performance in the greenhouse. In contrast, in the non-native range, black cherry readily establishes in close proximity to conspecifics, and the soil community enhances the growth of its seedlings. Understanding the effects of soil organisms on plant abundance will improve our ability to predict and counteract plant invasions. Web of Science Prunus serotina U.S.A.;Netherlands Indiana; Indiana Research and Training Preserve;Griffy Lake Nature Preserve;The Leeren Doedel;The Ossenbos 39.1968;39.1986;52.0087;52.1337 -86.5147;-86.5127;5.8385;5.8001 Field - Observational;Greenhouse terrestrial Deciduous Forest Invasion Hyp. Enemy Release primary 1612 Siemann, E; Rogers, WE 2003 Changes in light and nitrogen availability under pioneer trees may indirectly facilitate tree invasions of grasslands journal JOURNAL OF ECOLOGY 91 6 923 931 1 The first trees establishing in grasslands may indirectly favour their seedlings in competition with neighbouring herbaceous vegetation by increasing soil fertility with nitrogen-rich litter and by reducing light levels under their canopies. It is predicted that increasing soil nitrogen availability will accelerate invasion of trees by stimulating their growth more than that of herbaceous species. Decreasing light availability is predicted to increase tree invasion by limiting the growth of herbaceous vegetation more than that of trees (competitive release). 2 We tested these predictions using Chinese tallow tree (Sapium sebiferum), which is an aggressive alien invader of grasslands in the southern USA, and Hackberry (Celtis laevigata), which is a native tree common in these grasslands. 3 Nitrogen and light were manipulated in two factorial field experiments in grasslands in Texas, USA. In the first, nitrogen was increased and light was decreased in plots with planted Celtis or Sapium seedlings. In the second experiment, light availability to planted Celtis or Sapium seedlings was increased by holding back prairie vegetation. 4 In the first experiment, growth of Celtis and Sapium seedlings increased with nitrogen fertilization while the above-ground biomass of prairie vegetation did not change. Prairie vegetation biomass decreased and tree seedling growth increased under shading. Sapium's growth increased dramatically in the treatment with combined nitrogen and shade. Sapium survival decreased when shade was applied. 5 In the second experiment, Sapium growth increased with increased light. Thus, increased Sapium growth at low light levels in the shade experiment was probably a consequence of decreased competitive interference from prairie vegetation, rather than better absolute performance of Sapium in low light levels. 6 These results provide evidence for facilitation as a mechanism involved in tree invasions of grasslands. Changes in resource levels, perhaps in combination with other factors, may explain rapid conversion of grassland communities to woodlands after the first pioneer trees are established. The marked response of Sapium to the combination of nitrogen and shade suggests that these positive feedbacks may be particularly strong for this alien plant species. Web of Science Sapium sebiferum U.S.A. Texas The University of Houston Coastal Centre 29.3833 -95.0408 Field - Experimental terrestrial Grassland Invasion Hyp. Mutualism Facilitation;Disturbance primary 1613 MacNeil, C; Fielding, NJ; Dick, JTA; Briffa, M; Prenter, J; Hatcher, MJ; Dunn, AM 2003 An acanthocephalan parasite mediates intraguild predation between invasive and native freshwater amphipods (Crustacea) journal FRESHWATER BIOLOGY 48 12 2085 2093 1. The balance of predation between closely related invasive and native species can be an important determinant of the success or failure of biological invasions. In Irish freshwaters, the introduced amphipod Gammarus pulex has replaced the native G. duebeni celticus, possibly through differential mutual intraguild predation (IGP). Theoretically, parasitism could mediate such predation and hence the invasion outcome. However, this idea remains poorly studied. 2. In a field survey, we show that the acanthocephalan parasite Echinorynchus truttae is present in more G. pulex populations than G. d. celticus populations. In addition, within parasitised populations, E. truttae is more prevalent in the invader than in the native. 3. We show for the first time that an acanthocephalan parasite mediates predation between its intermediate macroinvertebrate hosts. In a field experiment, E. truttae parasitism of the invader lowered IGP upon the unparasitised native. In laboratory experiments, parasitism of G. pulex significantly reduced their predatory impact on recently moulted female G. d. celticus. Parasitism also appeared to cause reduction in predatory behaviour, such as attacks per contact on precopula guarded female natives. 4. We conclude that higher parasite prevalence in invaders as compared with natives, by mediation of interspecific interactions, could promote species coexistence, or at least slow species replacements, in this particular biological invasion. Web of Science Gammarus pulex Northern Ireland Antrim;Down 54.38 -5.91 Field - Experimental;Field - Observational;Lab lotic Invasion Hyp. Inherent Superiority Superior Competitor filter 1616 McCauley, DE; Smith, RA; Lisenby, JD; Hsieh, C 2003 The hierarchical spatial distribution of chloroplast DNA polymorphism across the introduced range of Silene vulgaris journal MOLECULAR ECOLOGY 12 12 3227 3235 Silene vulgaris was introduced into North America sometime prior to 1800. In order to document the population structure that has developed since that time, collections were made from 56 local populations distributed among 9 geographical regions in eastern North America. Individual plants were characterized for chloroplast DNA (cpDNA) haplotype by restriction fragment size analysis of four noncoding regions of cpDNA amplified by polymerase chain reaction. A total of 19 cpDNA haplotypes were detected using this method. The overall gene diversity of 0.85 is quite similar to the diversity detected in these same regions of cpDNA in a previously published sample of S. vulgaris taken from across much of Europe. The spatial distribution of the North American cpDNA diversity was quantified by hierarchical F-statistics that partitioned the genetic variance into variation among local populations within regions, and variation among regions. The average F-ST among populations within regions was 0.66 and the F-ST among regions was 0.09. The among-region variation was due to both differences among regions in the frequency of two most common haplotypes, and to the presence of a number of region-specific haplotypes. In order to test for isolation by distance at the regional level, F-ST values were calculated for all possible pairs of regions, and regressed against the geographical distance between those regions. There was no evidence for isolation by distance. It is suggested that the local population structure is generated by recent extinction/colonization dynamics, and that the among-region structure reflects demographic events associated with range expansion following introduction to North America. Web of Science Silene vulgaris U.S.A. Lab terrestrial Urban Fundamentals primary 1619 Scherber, C; Crawley, MJ; Porembski, S 2003 The effects of herbivory and competition on the invasive alien plant Senecio inaequidens (Asteraceae) journal DIVERSITY AND DISTRIBUTIONS 9 6 415 426 Senecio inaequidens DC. (Asteraceae) is an invasive alien plant introduced to Europe from South Africa in around 1896. It contains pyrrolizidine alkaloids that are toxic to livestock and humans. S. inaequidens would therefore be an economic and ecological problem if it became established and abundant in natural or farmed grassland ecosystems. We conducted field experiments using a split-plot design to determine the effects of rabbit grazing, interspecific plant competition, mollusc and insect herbivory on growth, survival and reproduction of S. inaequidens. Plants were grown from seeds of three different ecotypes under standardized greenhouse conditions and transplanted into field plots. Rabbits (Oryctolagus cuniculus L.) were excluded from experimental plots using rabbit fences. Competition was manipulated by either creating subplots with bare ground or leaving the vegetation cover intact. Data were recorded between June and August 2002. Ecotypes differed significantly in morphological parameters, and in their responses to invertebrate herbivory. Interspecific plant competition and rabbit grazing significantly reduced growth and reproduction of S. inaequidens. Regrowth shoots of S. inaequidens produced after rabbit grazing were not subsequently eaten by rabbits. Unpalatability of regrowth shoots may be attributable to changes in pyrrolizidine alkaloid composition with plant age. Mollusc herbivory significantly reduced the number of capitulae produced. We found adults of Longitarsus jacobaeae Waterhouse (Coleoptera: Chrysomelidae), a specialist herbivore of European Senecio jacobaea L. (Asteraceae), feeding on 79% of S. inaequidens plants. 320 larvae of Tyria jacobaeae L. (Lepidoptera: Arctiidae) did not feed on S. inaequidens under free-choice field conditions. We conclude that S. inaequidens is able to survive and reproduce in disturbed grassland ecosystems. L. jacobaeae might be a suitable agent for biological control of S. inaequidens in European introduced populations in the future. Web of Science Senecio inaequidens England Silwood Park 51.4167 -0.5833 Field - Experimental terrestrial Grassland Invasion Hyp. Enemy Release;Inherent Superiority;Disturbance Superior Competitor primary 1621 Pysek, P; Brock, JH; Bimova, K; Mandak, B; Jarosik, V; Koukolikova, I; Pergl, J; Stepanek, J 2003 Vegetative regeneration in invasive Reynoutria (Polygonaceae) taxa: The determinant of invasibility at the genotype level journal AMERICAN JOURNAL OF BOTANY 90 10 1487 1495 Vegetative regeneration of individual genotypes of Asian Reynoutria taxa. which are invasive in the Czech Republic, was studied in R. sachalinensis (five genotypes), R. japonica (a single genotype present in the country), and their hybrid R. X bohemica (nine genotypes). Identity of genotypes was confirmed by isozyme analysis. Ten rhizome segments of each genotype were planted in a randomized block design. After 30 d, the regeneration rate of each genotype was measured as the proportion of rhizomes that produced shoots. Emergence time and final mass of each shoot were recorded. The regeneration rate and final shoot mass were significantly affected by genotype in R. X bohemica but not in R. sachalinensis. In R. X bohemica, easily regenerating genotypes grew faster. Regeneration characteristics that crucially contribute to the fitness of these vegetatively spreading plants are closely related to each other. In genotypes with a low regeneration rate, early-emerging shoots produced more biomass, while in those with a high regeneration rate. shoot mass was independent of emergence time. Mean clone size recorded in the field was marginally significantly related to emergence time during regeneration; regeneration characteristics might thus affect the extent of R. X bohemica invasion at a regional scale. Hybrids genetically intermediate between the parents regenerated better than those closely related to parents. Novel hybrid invasive genotypes may be produced by rare sexual reproduction, fixed by clonal growth, and present a previously unknown threat to native vegetation. Web of Science Reynoutria sachalinensis;Reynoutria japonica Czech Republic Pruhonice Academy of Sciences of the Czech Republic 49.9947 14.5656 Garden terrestrial Riparian Invasion Hyp. Inherent Superiority;Hybridization Rapid Growth;Clonal Reproduction primary 1623 Smith, GR; Dingfelder, HA; Vaala, DA 2003 Effect of plant size and density on garlic mustard reproduction journal NORTHEASTERN NATURALIST 10 3 269 276 Garlic mustard (Alliaria petiolata) is a non-native invasive herb that has the potential to alter the understory plant community. We investigated the reproductive output of garlic mustard as a function of plant size and conspecific and heterospecific density in a central Ohio population. In general, taller plants produced more reproductive units (seeds, siliques). Density of conspecifics and heterospecifics had no effect on plant height or reproductive output. Reproductive output in our population of garlic mustard is lower and mean seed size is larger than most other populations for which data have been published, possibly because of the dry upland habitat of our population. Web of Science Alliaria petiolata USA Ohio Denison University Biological Reserve 40.094882 -82.529297 Field - Observational terrestrial Deciduous Forest;Coniferous Forest;Old Field Invasion Hyp. Inherent Superiority Superior Competitor primary 1624 Larson, DL 2003 Native weeds and exotic plants: relationships to disturbance in mixed-grass prairie journal PLANT ECOLOGY 169 2 317 333 Disturbance frequently is implicated in the spread of invasive exotic plants. Disturbances may be broadly categorized as endogenous (e.g., digging by fossorial animals) or exogenous ( e. g., construction and maintenance of roads and trails), just as weedy species may be native or exotic in origin. The objective of this study was to characterize and compare exotic and native weedy plant occurrence in and near three classes of disturbance digging by prairie dogs ( an endogenous disturbance to which native plants have had the opportunity to adapt), paved or gravel roads ( an exogenous disturbance without natural precedent), and constructed trails ( an exogenous disturbance with a natural precedent in trails created by movement of large mammals) - in three geographically separate national park units. I used plant survey data from the North and South Units of Theodore Roosevelt National Park and Wind Cave National Park in the northern mixed-grass prairie of western North and South Dakota, USA, to characterize the distribution of weedy native and exotic plants with respect to the three disturbance classes as well as areas adjacent to them. There were differences both in the susceptibility of the disturbance classes to invasion and in the distributions of native weeds and exotic species among the disturbance classes. Both exotic and native weedy species richness were greatest in prairie dog towns and community composition there differed most from undisturbed areas. Exotic species were more likely to thrive near roadways, where native weedy species were infrequently encountered. Exotic species were more likely to have spread beyond the disturbed areas into native prairie than were weedy native species. The response of individual exotic plant species to the three types of disturbance was less consistent than that of native weedy species across the three park units. Web of Science Many USA North Dakota;South Dakota Theodore Roosevelt National Park;Wind Cave National Park 46.919317;43.591582 -103.526230;-103.474045 Field - Observational terrestrial Grassland Invasion Hyp. Disturbance primary 1626 Myers, CV; Anderson, RC 2003 Seasonal variation in photosynthetic rates influences success of an invasive plant, garlic mustard (Alliaria petiolata) journal AMERICAN MIDLAND NATURALIST 150 2 231 245 Alliaria petiolata, an invasive biennial plant, actively grows and achieves high maximum rates of photosynthesis in early spring during its second growing season, when many indigenous ground layer species are still dormant and high levels of irradiance reach the forest floor. Alliaria petiolata also extends its growing season into the summer through stem elongation and production of new leaves that are adapted to ambient irradiance levels, unlike native deciduous forest spring ephemeral species or summer forbs. Photosynthetic rates for two populations of A. petiolata in a forest ground layer were measured in Summer and fall of the plant's first growing season (1998) and in spring of the second growing season (1999). During the second growing season, estimates of native ground layer cover were made at 3-4 wk intervals from early April to late May. Maximum photosynthetic rates (A(Max)) were positively correlated (r(2) = 0.791, df = 3, P = 0.0436) with mid-day irradiance reaching the forest ground layer and were negatively correlated (r(2) - 0.911, df = 3, P = 0.0116) with percent ground layer cover. The highest A(Max) (mean +/- SE) occurred on 6 April (17.8 +/- 0.6 mumol CO2 m(-2) s(-1)) and then declined during May, being 8.8 +/- 0.3 mumol CO2 m(-2) s(-1) and 4.7 +/- 0.4 mumol CO2 m(-2) s(-1) on 2 and 24 May, respectively. Alliaria petiolata's pre-adaptation to achieve maximum rates of photosynthesis before the active growth of many native ground layer species when irradiance reaching the ground layer is high, and temperature and moisture conditions are favorable for the species, contributes to its successful spread and eventual domination of forest ground layers. Web of Science Alliaria petiolata USA Illinois ParkLands Foundation Merwin Nature Preserve Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Superior Competitor primary 1627 Piazzi, L; Cinelli, F 2003 Evaluation of benthic macroalgal invasion in a harbour area of the western Mediterranean Sea journal EUROPEAN JOURNAL OF PHYCOLOGY 38 3 223 231 Many studies have been performed to investigate invasions in marine habitats, but little is known about the consequences of the simultaneous presence of more alien organisms in the same area. The aims of this work were to quantify the colonization of alien macroalgal species co-occurring in a harbour area of the northwestern Mediterranean Sea and to compare the structure of native phytobenthic communities in invaded and control areas. To achieve these objectives, invasions of four introduced macroalgae (Acrothamnion preissii, Womersleyella setacea, Caulerpa tax folia and C. racemosa) have been quantified in three different habitats (rocks, matte and Posidonia oceanica meadows) throughout one year. A combination of multivariate and univariate analyses was used to detect differences among macroalgal assemblages in control and invaded areas. Results showed that introduced species represented a very high percentage of macroalgal abundance in all the habitats studied. In Posidonia oceanica meadows, the macroalgal assemblage was almost completely represented by introduced turf-forming Rhodophyta. On rocks and matte, invasive species constituted about 50% of the cover of the macroalgal assemblage throughout the year. Both univariate and multivariate analysis showed that, in the study area, the structure of macroalgal assemblages was very different in invaded and control areas. Total percentage cover and diversity were lower in invaded areas than in control areas in all three habitats investigated and temporal modifications in macroalgal assemblages appeared to be linked to the growth cycle of invaders. The results of this study show that the co-occurrence of more alien algae does not seem to limit the total cover of invaders, which reached similar values independently of the dominant species. Web of Science Acrothamnion preissii; Womersleyella setacea; Caulerpa taxfolia; Caulerpa racemosa Italy Tuscany Field - Observational marine Intertidal/Near Shore Invasion Hyp. Community Species Richness primary 1629 Lenz, TI; Facelli, JM 2003 Shade facilitates an invasive stem succulent in a chenopod shrubland in South Australia journal AUSTRAL ECOLOGY 28 5 480 490 The invasive stem succulent Orbea variegata (L) Haw. (Asclepiadaceae) tends to be more abundant underneath shrubs than in open areas in chenopod shrublands near Whyalla, South Australia. To assess the role of facilitation in the life cycle of O. variegata, we investigated the effect of chenopod shrubs on different life stages of the species by experimentally manipulating temperature, light, soil moisture and nutrient levels. Experimental results suggest that the reduction in light and temperature under shrubs, but not increased nutrient levels, are the main facilitative mechanisms for O. variegata. Temperatures above 30degreesC, which are more likely to occur on the soil surface of open areas than under shrubs, inhibited seed germination. Seedling survival at low watering frequency and the growth of established ramets were increased by 75-80% shade cloth. Ramets growing in full light contained a high concentration of anthocyanin pigments. One of the functions of these pigments is to absorb excess radiation, suggesting that O. variegata experiences radiation stress in full light. In the field O. variegata performed considerably better under Atriplex vesicaria Heward ex Benth. (Chenopodiaceae) or under 75-80% shade cloth than in full light. Monthly irrigation of 20 mm did not reduce this positive effect of the A. vesicaria canopy on O. variegata, suggesting that O. variegata is inhibited by high light intensities or temperatures, independent of water availability. In conclusion, whereas shrub canopies do not seem to be required for the establishment or survival of O. variegata, shrubs improve adult growth and can improve establishment. The possibility of exotic plants being facilitated by other plants has to be taken into account when assessing the probability and rate of invasion. Web of Science Orbea variegata Australia South australia Whyalla Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Mutualism Facilitation primary 1632 Vila, M; Gomez, A; Maron, JL 2003 Are alien plants more competitive than their native conspecifics? A test using Hypericum perforatum L. journal OECOLOGIA 137 2 211 215 The evolution of increased competitive ability hypothesis predicts that introduced plants that are long liberated from their natural enemies may lose costly herbivore defense, enabling them to reallocate resources previously spent on defense to traits that increase competitive superiority. We tested this prediction by comparing the competitive ability of native St John's wort (Hypericum perforatum) from Europe with introduced St John's wort from central North America where plants have long grown free of specialist herbivores, and introduced plants from western North America where plants have been subjected to over 57 years of biological control. Plants were grown in a greenhouse with and without competition with Italian ryegrass (Lolium multiflorum). St John's wort from the introduced range were not better interspecific competitors than plants from the native range. The magnitude of the effect of ryegrass on St John's wort was similar for introduced and native genotypes. Furthermore, introduced plants were not uniformly larger than natives; rather, within each region of origin there was a high variability in size between populations. Competition with ryegrass reduced the growth of St John's wort by >90%. In contrast, St John's wort reduced ryegrass growth <10%. These results do not support the contention that plants from the introduced range evolve greater competitive ability in the absence of natural enemies. Web of Science Hypericum perforatum USA Greenhouse terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 1633 Tassin, J; Riviere, JN 2003 Species richness altitudinal gradient of invasive plants on Reunion Island (Mascareigne archipelago, Indian Ocean) journal REVUE D ECOLOGIE-LA TERRE ET LA VIE 58 3 257 270 The variation of the specific richness of plant invaders with elevation is poorly documented. During March and April 1998, floristic data were collected along three altitudinal transects on the leeward side of La Reunion Island (Mascarene archipelago, Indian Ocean). The variation of the specific richness of plant invaders with altitude is hump-shaped, with a maximum on the band 1300-1400 m, nearby the medium altitude of the gradient. Richness and altitude are strongly negatively correlated (r = -0.934; p < 0.001) in the upper part of the gradient. On the whole gradient, elevation amplitude and maximal altitude are positively correlated (r = 0.758; p < 0.001). The elevation amplitude of about 25% of the plant invaders ranks between 500 m and 1000 m. The shape of the altitudinal variation of the specific richness of plant invaders is determined by at least three mean factors : (1) physic permanent factors (thermic gradient, occurrence of frost), (2) historic factors (decreasing introduction and cultivation pressure from low to high altitude), and (3) geometric effects which maximize the probability of occurrence of plants in the centre of the gradient. Web of Science Many France La Reunion Island Field - Observational terrestrial Subtropical Forest Invasion Hyp. Disturbance primary 1635 van Ruijven, J; De Deyn, GB; Berendse, F 2003 Diversity reduces invasibility in experimental plant communities: the role of plant species journal ECOLOGY LETTERS 6 10 910 918 Several studies have presented experimental evidence that diversity reduces invasibility in grassland communities. The interpretation of these results has been disputed recently and it was proposed that sampling effects were responsible for the observed decrease of invasibility with diversity. The experiments performed to date were not designed to adequately separate sampling from diversity effects. Using the establishment of native plant species in experimental plant communities as a model of invasibility, we show that the number of invaders decreased with increasing diversity. When the presence of particular species is included, their effects are dominant. Centaurea jacea showed a strong effect at low diversity, whereas Leucanthemum vulgare showed a very strong negative impact at each diversity level. The negative effect of the latter might be related to root-feeding nematodes that showed far higher abundance in plots with Leucanthemum. However, diversity remained a significant factor in determining the number of invading species and the numbers of an abundant invader. Web of Science Centaurea jacea; Leucanthemum vulgare; Plantago lanceolata; Rumex acetosa; Agrostis capillaris; Anthoxanthum odoratum; Festuca rubra; Holcus lanatus Garden terrestrial Grassland Invasion Hyp. Community Species Richness primary 1637 Sanford, NL; Harrington, RA; Fownes, JH 2003 Survival and growth of native and alien woody seedlings in open and understory environments journal FOREST ECOLOGY AND MANAGEMENT 183 3 377 385 Although plant invasion is often facilitated by disturbance, several non-native trees and shrubs have successfully invaded intact forest habitats in northeastern North America. To better understand invasive plant performance in intact versus disturbed forest habitats, we compared survival, relative height growth rate, aboveground biomass allocation, and leaf area of alien and native woody seedlings. In replicated understory versus open treatment plots at two sites we planted three pairs of native and alien species that appear ecologically similar: sugar maple (Acer saccharum) and Norway maple (Acer platanoides), arrowwood (Viburnum dentatum) and glossy buckthorn (Rhamnus frangula), and silky dogwood (Corpus amomum) and autumn olive (Eleagnus umbellata). Seedlings were protected from deer browsing by open-topped cages made of chicken wire. Norway maple survival in open and understory environments was greater than that of sugar maple, and autumn olive survival in understory environments was greater than that of silky dogwood. The species differed in their responses to open versus understory environments in height growth, aboveground biomass and leaf area. The four shrub species grew faster in the open, with glossy buckthorn growing faster than the others, while the two tree species did not differ in growth between the environments. Leaf mass per unit leaf area was greater in the open than in the understory for all six species, but the difference did not vary among species. Arrow-wood, silky dogwood, and autumn olive decreased leaf area per unit biomass in the understory, but variation in survival among species was not related to maintenance of leaf area ratio. Among the six species, the increase in biomass from understory to open environments was negatively correlated with growing season survival in the understory. This apparent trade-off relationship applied equally to native and alien species, indicating that release from physiological constraints does not explain the success of the invasive species. (C) 2003 Elsevier Science B.V. All rights reserved. Web of Science Acer platanoides;Rhamnus frangula;Rhamnus frangula U.S.A. Massachusetts Sunderland 42.503 -72.517 Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Superior Competitor;Broad Tolerances primary 1639 Bais, HP; Vepachedu, R; Gilroy, S; Callaway, RM; Vivanco, JM 2003 Allelopathy and exotic plant invasion: From molecules and genes to species interactions journal SCIENCE 301 127 1377 1380 Here we present evidence that Centaurea maculosa (spotted knapweed), an invasive species in the western United States, displaces native plant species by exuding the phytotoxin (-)-catechin from its roots. Our results show inhibition of native species' growth and germination in field soils at natural concentrations of (-)- catechin. In susceptible species such as Arabidopsis thaliana, the allelo-chemical triggers a wave of reactive oxygen species (ROS) initiated at the root meristem, which leads to a Ca2+ signaling cascade triggering genome-wide changes in gene expression and, ultimately, death of the root system. Our results support a *novel weapons hypothesis* for invasive success. Web of Science Centaurea maculosa USA Lab terrestrial Grassland Invasion Hyp. Novel Weapons primary 1640 Rodgers, JC; Parker, KC 2003 Distribution of alien plant species in relation to human disturbance on the Georgia Sea Islands journal DIVERSITY AND DISTRIBUTIONS 9 5 385 398 This study investigates the effects of human disturbance and environmental factors on the distribution of alien plant species on the Georgia Sea Islands (GSI), USA. We sampled the absolute cover of native and alien plant species on two tourist islands (St. Simons Island and Jekyll Island) and on two protected National Wildlife Refuge Islands (Blackbeard Island and Wassaw Island). On each island, vegetation composition and environmental variables (soil properties and salt spray) were measured in two habitats that differed substantially in their degree of environmental stress, the more exposed primary dune and the more sheltered and inland maritime forest. Sites were further stratified within each habitat into areas that had different levels of human disturbance. Many alien species were present on all islands and the absolute cover of alien species was not significantly different among islands even though they varied substantially in their degree of accessibility and overall land use. Alien plant cover was appreciably greater in severely disturbed sites than in less disturbed sites on all islands and within both habitats. However, the difference between disturbance categories was much less pronounced in the primary dunes where human disturbance agents do not mitigate the harsh environmental conditions of this habitat (salt spray and saline soils). Alien plant abundance on the GSI is evidently more dependent upon the availability of disturbed ground than the degree of accessibility or overall island development. It appears that human disturbance increases alien cover in general, but in environments where the stress levels are not mitigated, human disturbance does little to foster alien invasions. Web of Science Many USA Georgia Sea Islands Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 1641 Dzialowski, AR; Lennon, JT; O'Brien, WJ; Smith, VH 2003 Predator-induced phenotypic plasticity in the exotic cladoceran Daphnia lumholtzi journal FRESHWATER BIOLOGY 48 9 1593 1602 1. The exotic cladoceran Daphnia lumholtzi has recently invaded freshwater systems throughout the United States. Daphnia lumholtzi possesses extravagant head spines that are longer than those found on any other North American Daphnia. These spines are effective at reducing predation from many of the predators that are native to newly invaded habitats; however, they are plastic both in nature and in laboratory cultures. The purpose of this experiment was to better understand what environmental cues induce and maintain these effective predator-deterrent spines. We conducted life-table experiments on individual D. lumholtzi grown in water conditioned with an invertebrate insect predator, Chaoborus punctipennis, and water conditioned with a vertebrate fish predator, Lepomis macrochirus. 2. Daphnia lumholtzi exhibited morphological plasticity in response to kairomones released by both predators. However, direct exposure to predator kairomones during postembryonic development did not induce long spines in D. lumholtzi. In contrast, neonates produced from individuals exposed to Lepomis kairomones had significantly longer head and tail spines than neonates produced from control and Chaoborus individuals. These results suggest that there may be a maternal, or pre-embryonic, effect of kairomone exposure on spine development in D. lumholtzi. 3. Independent of these morphological shifts, D. lumholtzi also exhibited plasticity in life history characteristics in response to predator kairomones. For example, D. lumholtzi exhibited delayed reproduction in response to Chaoborus kairomones, and significantly more individuals produced resting eggs, or ephippia, in the presence of Lepomis kairomones. Web of Science Daphnia lumholtzi Lab lotic Invasion Hyp. Plasticity herbivore 1645 Duda, JJ; Freeman, DC; Emlen, JM; Belnap, J; Kitchen, SG; Zak, JC; Sobek, E; Tracy, M; Montante, J 2003 Differences in native soil ecology associated with invasion of the exotic annual chenopod, Halogeton glomeratus journal BIOLOGY AND FERTILITY OF SOILS 38 2 72 77 Various biotic and abiotic components of soil ecology differed significantly across an area where Halogeton glomeratus is invading a native winterfat, [Krascheninnikovia (=Ceratoides) lanata] community. Nutrient levels were significantly different among the native, ecotone, and exotic-derived soils. NO3, P, K, and Na all increased as the cover of halogeton increased. Only Ca was highest in the winterfat area. A principal components analysis, conducted separately for water-soluble and exchangeable cations, revealed clear separation between halogeton- and winterfat-derived soils. The diversity of soil bacteria was highest in the exotic, intermediate in the ecotone, and lowest in the native community. Although further studies are necessary, our results offer evidence that invasion by halogeton alters soil chemistry and soil ecology, possibly creating conditions that favor halogeton over native plants. Web of Science Halogeton glomeratus United States Utah Desert Experimental Range Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Ecosystem Engineers primary 1647 Brooks, ML; Matchett, JR 2003 Plant community patterns in unburned and burned blackbrush (Coleogyne ramosissima Torr.) shrublands in the Mojave Desert journal WESTERN NORTH AMERICAN NATURALIST 63 3 283 298 The blackbrush vegetation type is dominated by Coleogyne ramossisima, which is thought to preclude the coexistence of many other plant species. Fire can remove blackbrush cover and possibly increase plant species richness and evenness. Fire also may increase the frequency and cover of alien annual grasses, thereby intensifying landscape flammability. We tested these predictions in unburned and burned (6-14 years postfire) blackbrush at 3 sites spanning the range of this vegetation type in the Mojave Desert. Species richness in unburned blackbrush was similar to published values for other vegetation types in western North America, but richness varied significantly among the 3 sites and 4 spatial scales (1, 10, 100, and 1000 m(2)). Richness values declined in order from annual forbs, woody perennials, herbaceous perennials, annual grasses, cacti, to perennial grasses. Fire reduced Coleogyne cover, thus boosting species evenness. In contrast, species richness decreased after burning, although the results varied among spatial scales. Total cover was unaffected by fire because cover of woody perennials decreased, while cover of annual forbs, annual grasses, herbaceous perennials, and perennial grasses increased. Native species richness and cover decreased, whereas alien richness and cover increased after burning, especially where the alien forb Erodium cicutarium was present. Fire had no effect on frequency and variable effects on cover of alien annual grasses. These results indicate that in blackbrush species richness can vary among sites and local spatial scales, and effects of fire can vary among plant life-forms and between natives and aliens. Web of Science Erodium cicutarium USA California Mojave Desert Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Disturbance primary 1648 Lounibos, LP; Escher, RL; Lourenco-de-Oliveria, R 2003 Asymmetric evolution of photoperiodic diapause in temperate and tropical invasive populations of Aedes albopictus (Diptera : Culicidae) journal ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA 96 4 512 518 Aedes albopictus became established in Brazil and the USA during the same approximate period of the mid-1980s and spread rapidly in both countries in succeeding years. Early populations in the USA, believed derived from temperate Japan, all possessed a photoperiodically inducible egg diapause, but a population from Brazil, of probable tropical origins, did not. Based on responses of geographic populations to a common short (10L:14D) day length, we demonstrate that the spread of A. albopictus in Florida from more temperate USA has been associated with a gradual loss of diapause, such that diapause incidence is now positively correlated with latitude in the southern USA. In Brazil, most populations tested 15 yr after the initial invasion show no evidence of diapause, except for three from the two southernmost states (>26degreesS), in which a small, but significant percentage of eggs from mothers exposed to short day lengths were dormant. Diapause reduction in the southern USA and diapause acquisition by A. albopictus in southern Brazil have not resulted in similar response levels at comparable latitudes in the two countries, in part because of genetic constraints of different founder populations from temperate and tropical origins and different selective regimes in the two invaded countries. Web of Science Aedes albopictus USA; Brazil Florida Field - Observational terrestrial Invasion Hyp. Evolution in General predator 1650 Agrawal, AA; Kotanen, PM 2003 Herbivores and the success of exotic plants: a phylogenetically controlled experiment journal ECOLOGY LETTERS 6 8 712 715 ln a field experiment with 30 locally occurring old-field plant species grown in a common garden, we found that non-native plants suffer levels of attack (leaf herbivory) equal to or greater than levels suffered by congeneric native plants. This phylogenetically controlled analysis is in striking contrast to the recent findings from surveys of exotic organisms, and suggests that even if 'enemy release' does accompany the invasion this may not be an important mechanism of invasion, particularly for plants with process, close relatives in the recipient flora. Web of Science Many Canada Ontario Jokers Hil Field - Experimental terrestrial Old Field Invasion Hyp. Enemy Release primary 1652 Milbau, A; Nijs, I; Van Peer, L; Reheul, D; De Cauwer, B 2003 Disentangling invasiveness and invasibility during invasion in synthesized grassland communities journal NEW PHYTOLOGIST 159 3 657 667 An experiment with synthesized grassland communities was performed to identify plant traits that contribute to invasiveness and community traits that promote invasibility, and to study the relationship between, and the relative importance of, invasiveness and invasibility. Eight perennial grass species were used both as invasible monocultures and as potential invaders in gaps in these monocultures. Invasion success in the establishment phase, and invader and monoculture traits were assessed. Invasion success expressed as germination correlated significantly with germination time (invader trait), light penetration in the gaps and N acquisition by the edge plants (monoculture traits). Success expressed as leaf length correlated with seed mass, germination time (invader traits) and light penetration. Forty-six per cent of the variation in germination was explained by invader identity and 8% by monoculture identity, whereas, for leaf length, they explained 15% and 18%, respectively. Regenerative traits (seed mass and germination time) correlated with invasiveness, and resource availability (light and nitrogen) with invasibility. The results suggest that species characteristics would largely determine the extent of an invasion event (number of seedlings), while the success of individual invaders (growth and survival) is determined by both species and ecosystem characteristics. Web of Science Many Belgium Garden terrestrial Grassland Invasion Hyp. Inherent Superiority Superior Competitor primary 1653 Annapurna, C; Singh, JS 2003 Phenotypic plasticity and plant invasiveness: Case study of congress grass journal CURRENT SCIENCE 85 2 197 201 This paper highlights the phenotypic variation of congress grass (Parthenium hysterophorus) to varying soil texture. Plants demonstrated significant differences in some traits among the different soil types and these phenotypically plastic traits, in combination, contribute to invasiveness of the species, allowing for the range expansion observed in different habitats. Web of Science Parthenium hysterophorus India Varanasi Greenhouse terrestrial Invasion Hyp. Plasticity primary 1654 Bray, SR; Kitajima, K; Sylvia, DM 2003 Mycorrhizae differentially alter growth, physiology, and competitive ability of an invasive shrub journal ECOLOGICAL APPLICATIONS 13 3 565 574 Mycorrhizae improve phosphorus availability to host plants and alter their morphology, physiology, and competitive ability. We examined how different isolates of arbuscular mycorrhizal fungi, soil-P, light, and competition affect the growth, physiology, and biomass allocation of seedlings of an exotic invasive shrub of the southeastern United States, Ardisia crenata, in two greenhouse experiments. When Ardisia seedlings were grown singly in pots without competition, soil phosphorus concentration and light had no effect on seedling growth. Relative growth rates (RGR) and leaf area ratio (LAR), however, were higher for seedlings inoculated with mycorrhizal fungi isolated from Ardisia roots than those inoculated with single-spore isolates and nonmycorrhizal controls. In the second experiment, an Ardisia seedling was grown in each pot in competition with another conspecific seedling or with a seedling of Prunus caroliniana, a native subcanopy tree. The identity of the competitor had little effect on seedling RGR of Ardisia, but LAR was significantly higher for seedlings in conspecific competition. Overall, Prunus seedlings had higher RGR than Ardisia, but RGR and survival of Prunus seedlings were significantly reduced in competition with Ardisia when mycorrhizal fungi were suppressed by benomyl. These results suggest that competitive interactions of exotic invasive plants with native plants are dependent on the isolates of mycorrhizae present. Web of Science Ardisia crenata USA Greenhouse terrestrial Deciduous Forest Invasion Hyp. Mutualism Facilitation primary 1656 Cully, AC; Cully, JF; Hiebert, RD 2003 Invasion of exotic plant species in tallgrass prairie fragments journal CONSERVATION BIOLOGY 17 4 990 998 The tallgrass prairie is one of the most severely affected ecosystems in North America. As a result of extensive conversion to agriculture during the last century, as little as 1% of the original tallgrass prairie remains. The remaining fragments of tallgrass prairie communities have conservation significance, but questions remain about their viability and importance to conservation. We investigated the effects of fragment size, native plant species diversity, and location on invasion by exotic plant species at 25 tallgrass prairie sites in central North America at various geographic scales. We used exotic species richness and relative cover as measures of invasion. Exotic species richness and cover were not related to area for all sites considered together. There were no significant relationships between native species richness and exotic species richness at the cluster and regional scale or for all sites considered together. At the local scale, exotic species richness was positively related to native species richness at four sites and negatively related at one. The 10 most frequently occurring and abundant exotic plant species in the prairie fragments were cool-season, or C-3, species, in contrast to the native plant community, which was dominated by warm-season, or C-4, species. This suggests that timing is important to the success of exotic species in the tallgrass prairie. Our study indicates that some small fragments of tallgrass prairie are relatively intact and should not be overlooked as long-term refuges for prairie species, sources of genetic variability, and material for restoration. Web of Science Many USA Iowa; Missouri; Minnesota; Nebraska Field - Observational terrestrial Grassland Invasion Hyp. Community Species Richness primary 1657 Siemann, E; Rogers, WE 2003 Herbivory, disease, recruitment limitation, and success of alien and native tree species journal ECOLOGY 84 6 1489 1505 The Enemies Hypothesis predicts that alien plants have a competitive advantage over native plants because they are often introduced with few herbivores or diseases. To investigate this hypothesis, we transplanted seedlings of the invasive alien tree, Sapitan sebiferum (Chinese tallow tree) and an ecologically similar native tree, Celtis laevigata (hackberry), into mesic forest, floodplain forest, and coastal prairie sites in east Texas and manipulated foliar fungal diseases and insect herbivores with fungicidal and insecticidal sprays. As predicted by the Enemies Hypothesis, insect herbivores caused significantly greater damage to untreated Celtis seedlings than to untreated Sapium seedlings. However, contrary to predictions, suppression of insect herbivores caused significantly greater increases in survivorship and growth of Sapium seedlings compared to Celtis seedlings. Regressions suggested that Sapium seedlings compensate for damage in the first year but that this greatly increases the risk of mortality in subsequent years. Fungal diseases had no effects on seedling survival or growth. The Recruitment Limitation Hypothesis predicts that the local abundance of a species will depend more on local seed input than on competitive ability at that location. To investigate this hypothesis, we added seeds of Celtis and Sapitan on and off of artificial soil disturbances at all three sites. Adding seeds increased the density of Celtis seedlings and sometimes Sapitan seedlings, with soil disturbance only affecting density of Celtis. Together the results of these experiments suggest that the success of Sapium may depend on high rates of seed input into these ecosystems and high growth potential. as well as performance advantages of seedlings caused by low rates of herbivory. Web of Science Sapitan sebiferum USA Texas Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Enemy Release primary 1658 Buckley, YM; Downey, P; Fowler, SV; Hill, R; Memmot, J; Norambuena, H; Pitcairn, M; Shaw, R; Sheppard, AW; Winks, C; Wittenberg, R; Rees, M 2003 Are invasives bigger? A global study of seed size variation in two invasive shrubs journal ECOLOGY 84 6 1434 1440 We explored the spatial structure of seed size variation and tested whether seed size differed between native and exotic populations in two invasive species. Seed of Cytisus scoparius (Scotch broom) is significantly heavier in its exotic range, whereas seed of Ulex europaeus (European gorse) is no different between ranges. This result suggests that seed size in C. scoparius is either adaptively or phenotypically responsive to conditions in its exotic range or that plants with large seeds were preferentially introduced. We found that modern ornamental broom seed was no bigger than seed from natural or naturalized populations, suggesting that large seed size in the exotic range is not due to preferential introduction of ornamental varieties with large seeds. Most previous studies of trait differences between native and exotic ranges in invasive species have not taken variation throughout the ranges into account. This is the most comprehensive survey of seed size variation in any species, and the first time that variation in a trait of an invasive species has been studied from individual plant level up to global ranges. Demographic rates can be affected by seed attributes making this study an important first step in understanding how population processes may differ between native and exotic ranges. Web of Science Cytisus scoparius; Ulex europaeus Field - Observational terrestrial Deciduous Forest Invasion Hyp. Evolution in General primary 1659 Fargione, J; Brown, CS; Tilman, D 2003 Community assembly and invasion: An experimental test of neutral versus niche processes journal PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 100 15 8916 8920 A species-addition experiment showed that prairie grasslands have a structured, nonneutral assembly process in which resident species inhibit, via resource consumption, the establishment and growth of species with similar resource use patterns and in which the success of invaders decreases as diversity increases. In our experiment, species in each of four functional guilds were introduced, as seed, into 147 prairie-grassland plots that previously had been established and maintained to have different compositions and diversities. Established species most strongly inhibited introduced species from their own functional guild. introduced species attained lower abundances when functionally similar species were abundant and when established species left lower levels of resources unconsumed, which occurred at lower species richness. Residents of the C4 grass functional guild, the dominant guild in nearby native grasslands, reduced the major limiting resource, soil nitrate, to the lowest levels in midsummer and exhibited the greatest inhibitory effect on introduced species. This simple mechanism of greater competitive inhibition of invaders that are similar to established abundant species could, in theory, explain many of the patterns observed in plant communities. Web of Science Agropyron repens; Oenothera biennis; Penstemon grandiflorus;Trifolium pratense; Desmodium canadense USA Minnesota Cedar Creek Field - Experimental terrestrial Grassland Invasion Hyp. Community Species Richness primary 1660 DeFalco, LA; Bryla, DR; Smith-Longozo, V; Nowak, RS 2003 Are Mojave Desert annual species equal? Resource acquisition and allocation for the invasive grass Bromus madritensis subsp rubens (Poaceae) and two native species journal AMERICAN JOURNAL OF BOTANY 90 7 1045 1053 Abundance of invasive plants is often attributed to their ability of outcompete native species. We compared resource acquisition and allocation of the invasive annual grass Bromus madritensis subsp. rubens with that of two native Mojave Desert annuals, Vulpia octoflora and Descurainia pinnata, in a glasshouse experiment. Each species was grown in monoculture at two densities and two levels of N availability to compare how these annuals capture resources and to understand their relative sensitivities to environmental change. During >4 mo of growth, Bromus used water more rapidly and had greater biomass and N content than the natives, partly because of its greater root-surface area and its exploitation of deep soils. Bromus also had greater N uptake, net assimilation and transpiration rates. and canopy area than Vulpia. Resource use by Bromus was less sensitive to changes in N availability or density than were the natives. The two native species in this study produced numerous small seeds that tended to remain dormant, thus ensuring escape of offspring from unfavorable germination conditions; Bromus produced fewer but larger seeds that readily germinated. Collectively. these traits give Bromus the potential to rapidly establish in diverse habitats of the Mojave Desert, thereby gaining an advantage over coexisting native species. Web of Science Bromus madritensis USA Nevada Mojave Desert Greenhouse terrestrial Grassland Invasion Hyp. Inherent Superiority Effective Disperser primary 1663 MacNeil, C; Bigsby, E; Dick, JTA; Hynes, HBN; Hatcher, MJ; Dunn, AM 2003 Temporal changes in the distribution of native and introduced freshwater amphipods in Lough Neagh, Northern Ireland journal ARCHIV FUR HYDROBIOLOGIE 157 3 379 395 Studies of invasion scenarios over long time periods are important to refine explanations and predictions of invasion success and impact. We used data from surveys in 1958 and 1999 of the macroinvertebrates of Lough Neagh, Northern Ireland, to assess changes in the distribution of native and introduced amphipods in relation to the wider assemblage. In 1958, the invader G. tigrinus dominated the shoreline fauna, with the native G. d. celticus present in very low numbers, whereas in 1999 the reverse was evident. In both surveys, G. tigrinus was the only amphipod present in the mid-Lough. G. tigrinus thus seems to have become established within L. Neagh, perhaps overshot and then senesced, with the native species re-establishing on the shoreline, with the invader mostly restricted to the deep mid-Lough. The non-amphipod macroinvertebrate assemblage was similar between the two surveys, in terms of Bray-Curtis community similarity, assemblage diversity, dominance and the taxa based ASPT water quality index. However, the mean density of macroinvertebrates (all taxa combined) was lower in 1999 compared to 1958, largely accounted for by a decline in oligochaete numbers. Since Gammarus species may be predators of other macroinvertebrates and influence their distribution and abundance, we investigated this trophic link in staged laboratory encounters. Both G. tigrinus and G. d. celticus preyed on isopods, alderflies, mayflies, chironomids and mysids, however, the native G. d. celticus had a significantly greater predatory impact on isopods and chironomids than did the invader G. tigrinus. While we cannot definitively ascribe cause and effect in the present scenario, we discuss how replacement of one amphipod species by another may have impacts on the wider macroinvertebrate assemblage. Web of Science Gammarus tigrinus Ireland Lough Neagh Field - Observational marine Intertidal/Near Shore Fundamentals omnivore 1671 Pearce, CM; Smith, DG 2003 Saltcedar: Distribution, abundance, and dispersal mechanisms, northern Montana, USA journal WETLANDS 23 2 215 228 Introduced saltcedar (Tamarix ramosissima, T. chinensis, and their hybrids) reaches its northward distribution in the Great Plains in Montana, USA. We mapped the locations, patterns of abundance, and ages of saltcedar along the Musselshell River and Fort Peck Reservoir in northeastern Montana to identify concentrations of plants that could be used to infer introduction location, establishment year, and mechanisms of dispersal. We estimated the presence of 24,500 plants on the Musselshell River over a river distance of 240 km, with concentrations at three nodes close to Roundup (2,000 plants, seedlings to 24 years), Melstone' (6,000 plants, seedlings to 23 years), and the mouth of the river at Fort Peck Reservoir (10,000 plants, seedlings to at least 11 years). Concentrations at Roundup and Melstone probably originated from urban plantings in the 1960s. The third concentration may have established from seeds and plant pieces washed downriver during floods and deposited in the hydraulic backwater of the Musselshell River delta at Fort Peck Reservoir. We believe there may be one-half to one million plants on Fort Peck Reservoir, with concentration nodes at recreation areas on the south shore. We estimated 3,500 mature saltcedar to be present at the Devils Creek Recreation Area, more than 11,000 plants at Hell Creek Recreation Area, and more than 40,000 plants at 6 sites at the south end of Dry Arm close to the Nelson Creek Recreation Area and mouth of Big Dry Creek. The oldest plants on the reservoir were 21 to 33 years old in 2001. Based on these ages, we suggest that saltcedar arrived at the south shore of Fort Peck Reservoir in the mid- to late 1960s, which means that it must have dispersed from the Bighorn/Yellowstone River system soon after it became established in southern Montana. Although wind dispersal and ornamental plantings cannot be ruled out as primary transport mechanisms to the reservoir, the concentrations and ages of saltcedar at recreation areas suggest that seeds and other plant propagules were also transported to the reservoir by earth-moving equipment during site construction between 1966 and the mid-1980s and later by boats and their towing vehicles. Saltcedar was dispersed away from these nodes by wind and water. As Tamarix ramosissima and T. chinensis originated in the cold dry deserts of northeastern Asia, saltcedar may not be limited in its northward expansion by the cold winters, short growing seasons, and periodic droughts characteristic of the northern Great Plains in Canada. Web of Science Tamarix ramosissima; Tamarix chinensis USA Montana Musselshell River Field - Observational terrestrial Riparian Invasion Hyp. Other primary 1672 Call, LJ; Nilsen, ET 2003 Analysis of spatial patterns and spatial association between the invasive tree-of-heaven (Ailanthus altissima) and the native black locust (Robinia pseudoacacia) journal AMERICAN MIDLAND NATURALIST 150 1 1 14 Invasive exotic plants can persist and successfully spread within ecosystems and negatively affect the recruitment of native species. The exotic invasive Ailanthus altissima and the native Robinia pseudoacacia are frequently found in disturbed sites and exhibit similar growth and reproductive characteristics, yet each has distinct functional roles such as allelopathy and nitrogen fixation, respectively. Spatial point pattern analysis of trees in a silvicultural experiment was used to analyze the potential intraspecific and interspecific interference between these two species by looking at their individual spatial distribution and their spatial association. Analysis of spatial point patterns in the field with Ripley's K indicated that A. altissima and R. pseudoacacia were positively associated with each other along the highly disturbed skid trails in the majority of the field sites. Robinia pseudoacacia was clumped in the majority of the sites, whereas A. altissima was randomly distributed in most sites. Locally, increased disturbances could lead to more opportunities for A. altissima to invade, interact with R pseudoacacia and other native species and potentially have an effect on the native plant community. Web of Science Ailanthus altissima USA Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 1678 MacNeil, C; Dick, JTA; Hatcher, MJ; Terry, RS; Smith, JE; Dunn, AM 2003 Parasite-mediated predation between native and invasive amphipods journal PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON SERIES B-BIOLOGICAL SCIENCES 270 127 1309 1314 Parasites can structure biological communities directly through population regulation and indirectly by processes such as apparent competition. However, the role of parasites in the process of biological invasion is less well understood and mechanisms of parasite mediation of predation among hosts are unclear. Mutual predation between native and invading species is an important factor in determining the outcome of invasions in freshwater amphipod communities. Here, we show that parasites mediate mutual intraguild predation among native and invading species and may thereby facilitate the invasion process. We find that the native amphipod Gammarus duebeni celticus is host to a microsporidian parasite, Pleistophora sp. (new species), with a frequency of infection of 0-90%. However, the parasite does not infect three invading species, G. tigrinus, G. pulex and Crangonyx pseudogracilis. In field and laboratory manipulations, we show that the parasite exhibits cryptic virulence: the parasite does not affect host fitness in single-species populations, but virulence becomes apparent when the native and invading species interact. That is, infection has no direct effect on G. d. celticus survivorship, size or fecundity; however, in mixed-species experiments, parasitized natives show a reduced capacity to prey on the smaller invading species and are more likely to be preyed upon by the largest invading species. Thus, by altering dominance relationships and hierarchies of mutual predation, parasitism strongly influences, and has the potential to change, the outcome of biological invasions. Web of Science Gammarus tigrinus; Gammarus pulex; Crangonyx pseudogracilis Great Britain Field - Experimental lotic Invasion Hyp. Mutualism Facilitation omnivore 1681 Bleeker, W 2003 Hybridization and Rorippa austriaca (Brassicaceae) invasion in Germany journal MOLECULAR ECOLOGY 12 7 1831 1841 Introgressive hybridization between the invasive Rorippa austriaca and the native R. sylvestris in Germany has been studied using chloroplast DNA (trn L intron) and amplified fragment length polymorphism. Three hybrid zones between the invasive and native species were located in the Ruhr Valley (Mulheim) and at the River Main near Wurzburg (Randersacker, Winterhausen). In each hybrid zone hybridization was indicated by additivity of region-specific amplified fragment length polymorphism markers proving independent hybridization events. The hybrids were either morphologically intermediate (R. x armoracioides) or were close to R. sylvestris. The trn L intron of R. austriaca is characterized by a species-specific deletion. This diagnostic chloroplast marker of R. austriaca was detected in three individuals of R. sylvestris providing evidence for introgression of the invasive chloroplast into the native species. Bidirectional introgression of R. austriaca markers into R. sylvestris and of R. sylvestris markers into R. austriaca was detected in the amplified fragment length polymorphism analysis. Some of the invasive R. austriaca populations showed high within-population variation. A possible association among introgression, within-population variation and invasion success is discussed. The morphologically intermediate hybrid R. x armoracioides is currently spreading in northern Germany. It forms large populations without its parent species R. austriaca and R. sylvestris. It is concluded that hybridization between invasive R. austriaca and native R. sylvestris may lead to the evolution of a new invasive species R. x armoracioides. Web of Science Rorippa austriaca Germany Mulheim; Wurzburg River Main; Ruhr Valley Field - Observational terrestrial Invasion Hyp. Hybridization primary 1682 Walker, NF; Hulme, PE; Hoelzel, AR 2003 Population genetics of an invasive species, Heracleum mantegazzianum: implications for the role of life history, demographics and independent introductions journal MOLECULAR ECOLOGY 12 7 1747 1756 The population genetic structure of an invasive, nonindigenous riparian weed (Heracleum mantegazzianum) in the northeast of England was investigated using microsatellite DNA markers. Data were used to assess the size and frequency of introductions into three catchments and the subsequent spread. We sampled 13 populations, including a remote population (Perivale, London) for comparison. Five loci were screened and considerable variation was found. Results revealed greater overall variation between populations from different catchments than those in the same catchment, and suggested the generation of population structure in the relatively short time since the initial introduction. Between-catchment variation may reflect population structure generated by local founders as the species spread and may indicate a large initial founder population at the time of the introduction into Britain, or multiple introductions. Within-catchment variation was consistent with expectations based on the water-borne dispersal of seeds in this species, and the relatively small dispersal range of likely pollinators. Independent introductions stand out in some cases as exceptions to the general pattern. Taken together the results are consistent with a relatively large initial founder population, and the subsequent spread of the species in local founder populations, followed by some level of inbreeding within local populations and novel introductions in some localities. Web of Science Heracleum mantegazzianum) England London; NE England Field - Observational terrestrial Riparian Fundamentals primary 1683 Dupont, L; Jollivet, D; Viard, F 2003 High genetic diversity and ephemeral drift effects in a successful introduced mollusc (Crepidula fornicata : Gastropoda) journal MARINE ECOLOGY-PROGRESS SERIES 253 0 183 195 Human-mediated biological invasions are known to threaten biodiversity and are often the cause of economic problems, mainly via interspecific interactions with commercially valuable indigenous species. The hermaphroditic gastropod Crepidula fornicata (L.) is a successful marine invader of European coasts. In France, it was first recorded in the 1940s and now proliferates, competing with cultured and fished bivalves. To analyze the patterns of spread and the genetic architecture of the Populations of this invader, 13 p0opulations, 12 French and 1 native (American) (N = 660) were sexed and analyzed using 8 polymorphic enzyme loci. The majority of the Populations showed balanced sex ratios. A high level of genetic diversity was detected in the French populations, contrary to the usual pattern of founder effect frequently reported for invaders. Moreover, most of the introduced populations were shown to be in migration-drift equilibrium. Thus, our results suggest that, in its introduced range, C. fornicata has stable populations and behaves genetically and demographically in the same way that it does over its native range. The pattern among French populations suggests that the introduction process was complex, and that C. fornicata from France derives from several genetically diverse, but poorly differentiated, source populations. Finally, this dataset also showed that the effects of shell-farmer-mediated transport between bays are only detectable at some specific localities. On the other hand, there was a good fit between patterns of genetic differentiation and the Major hydrodynamic features along the French coasts, strongly suggesting that larval dispersal plays an important role in the spread of C. fornicata in Europe. Web of Science Crepidula fornicata France Field - Observational marine Intertidal/Near Shore Invasion Hyp. Inherent Superiority Effective Disperser herbivore 1684 Woitke, M; Dietz, H 2002 Shifts in dominance of native and invasive plants in experimental patches of vegetation journal PERSPECTIVES IN PLANT ECOLOGY EVOLUTION AND SYSTEMATICS 5 3 165 184 While it is widely accepted that disturbance often promotes the process of plant invasion, few data are available on specific relationships between different types of disturbance and success of plant invaders. Nor is much known about variation in invader behaviour in response to changing composition of the dominant native species in the recipient habitats. In the middle Main valley near Wurzburg (Germany), two invasive Brassicaceae forbs, Bunias orientalis and Rorippa austriaca, are frequently associated with a small number of dominant native species in the herbaceous vegetation of productive, disturbed sites. Variation in the relative dominance of these species suggests high variability between sites in the factors influencing the local invasion process. In our study, we examined variation in regeneration mode, type and frequency of disturbance, and native species composition, and considered life history differences between the two invasive species as factors contributing to the distinct dominance patterns. These factors were tested in a controlled field experiment in which individuals of the two invasive species and four native species were grown in mixed stands for almost 3 years. The development of the plants was monitored by cover values and all plants were harvested at the end of the study. All factors investigated contributed considerably to the development of distinct dominance patterns in the species mixtures. Relative to the natives, both invasive species were promoted by regeneration from vegetative fragments as compared to development from sexual offspring. While both invasive species were generally promoted by disturbance relative to the natives, they differed in their response to distinct types of disturbance, and these differences were strongly affected by species composition. Our results indicate that invasion success of R. austriaca may depend more on soil disturbance, soil transport and deposition, while B. orientalis is expected to particularly expand at mown sites that do not have dense cover by meadow grasses. Whether the native resident vegetation is mainly composed of successional competitors that suffer from disturbance or of ruderal competitors that compete early and strongly with the invasive species may be of critical importance for invasion by the two species. Web of Science Bunias orientalis; Rorippa austriaca Germany Wurzburg Field - Experimental terrestrial Old Field Invasion Hyp. Disturbance primary 1687 Lowe, PN; Lauenroth, WK; Burke, IC 2003 Effects of nitrogen availability on competition between Bromus tectorum and Bouteloua gracilis journal PLANT ECOLOGY 167 2 247 254 Exotic plant invasions are a serious concern for land managers and conservationists. There is evidence that increased nitrogen availability favors exotic species and decreased nitrogen availability favors non-weedy native species. This study was conducted to test the effect of nitrogen availability on competition between two grass species with contrasting life histories, cheatgrass (Bromus tectorum), a North American exotic, and blue grama (Bouteloua gracilis), a North American native. We investigated the effects of nitrogen availability and competition on aboveground biomass, belowground biomass, height, and % nitrogen tissue concentrations by growing the two species in the greenhouse under five levels of nitrogen and six levels of competition. Nitrogen availability affected competition between Bromus tectorum and Bouteloua gracilis. At the lowest level of N availability, neither species was affected by competition. As N availability increased, aboveground biomass gain of Bromus was more negatively affected by intraspecific competition relative to interspecific competition while the opposite occurred for Bouteloua. At the competition level at which each species gained the most aboveground biomass, Bromus had a linear response to increasing N availability while the response of Bouteloua was asymptotic. Our results do provide some support for the theory that fast growing exotic species have a rapid response to nutrient enrichment while native non-weedy species do not, and that low N levels can reduce competitive pressure from the exotic on the native. Web of Science Bromus tectorum USA Greenhouse terrestrial Grassland Invasion Hyp. Inherent Superiority Rapid Growth primary 1688 Miller, RC; Zedler, JB 2003 Responses of native and invasive wetland plants to hydroperiod and water depth journal PLANT ECOLOGY 167 1 57 69 Monotypic stands of reed canary grass, Phalaris arundinacea, replace native wetland vegetation where storm-water runoff alters hydrologic conditions, nutrient inflows, and sedimentation rates. We asked if different hydrologic conditions could explain the dominance of Phalaris and/or loss of the native grass, Spartina pectinata, and we compared the growth of each species alone and together under four hydroperiods (varying inundation frequency and duration) each at two water depths (surface saturation and flooding to 15 cm). When grown alone, aboveground biomass was similar for the two species, but Phalaris produced twice the stem length of Spartina via its low tissue density. Per unit biomass, Phalaris distributed its leaves over a larger canopy volume. Flooding reduced belowground biomass and increased total shoot length and shoot: root biomass of each species. Phalaris produced the most biomass, shoots, and total shoot length when wetter and drier conditions alternated weekly, while Spartina grew best with prolonged (4-week) inundation. When grown with Spartina, Phalaris changed its morphology by increasing its total shoot length: biomass ratio by 50%. However, ratios of Spartina: Phalaris aboveground biomass, shoot number, and total shoot length in two-species pots were not significantly affected by water depth or hydroperiod. We conclude that two plant attributes facilitate Phalaris' dominance of wetlands: its high ratio of total shoot length: biomass and its adaptable morphology ( characterized herein as increased total shoot length: biomass when grown with Spartina). Web of Science Phalaris arundinacea USA Wisconsin Garden lentic;lotic Wetland Invasion Hyp. Inherent Superiority Superior Competitor;Broad Tolerances primary 1689 Harris, MR; Facelli, JM 2003 Competition and resource availability in an annual plant community dominated by an invasive species, Carrichtera annua (L. Aschers.), in South Australia journal PLANT ECOLOGY 167 1 19 29 The last decade has seen spirited debates about how resource availability affect the intensity of competition. This paper examines the effect that a dominant introduced species, Carrichtera annua, has upon the winter annual community in the arid chenopod shrublands of South Australia. Manipulative field experiments were conducted to assess plant community response to changing below-ground resource levels and to the manipulation of the density of C. annua. Changes in the density of C. annua had little effect on the abundance of all other species in the guild. Nutrient addition produced an increase in the biomass of the most abundant native species, Crassula colorata. An analysis of the root distribution of the main species suggested that the areas of soil resource capture of C. annua and C. colorata are largely segregated. Our results suggest that intraspecific competition may be stronger than interspecific competition, controlling the species responses to increased resource availability. The results are consistent with a two-phase resource dynamics systems, with pulses of high resource availability triggering growth, followed by pulses of stress. Smaller plants were nutrient limited under natural field conditions, suggesting that stress experienced during long interpulse phases may override competitive effects after short pulse phases. The observed differences in root system structure will determine when plants of a different species are experiencing a pulse or an interpulse phase. We suggest that the limitations to plant recruitment and growth are the product of a complex interplay between the length and intensity of the pulse of resource availability, the duration and severity of the interpulse periods, and biological characters of the species. Web of Science Carrichtera annua Australia South australia Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Fluctuating Resources primary 1691 Forman, J; Kesseli, RV 2003 Sexual reproduction in the invasive species Fallopia japonica (Polygonaceae) journal AMERICAN JOURNAL OF BOTANY 90 4 586 592 Fallopia japonica (Polygonaceae) is an invasive perennial plant, well known in North America for its ability to spread aggressively via vegetative reproduction. The contribution of sexual reproduction to the distribution of this species is not well documented, and as a result. F. Japonica is treated solely as a clonal species. To investigate the role of sexual reproduction in this species, germination experiments were conducted using seed collected from 29 parents from field sites in Massachusetts and from four greenhouse-grown cultivars. Results showed that wild F. japonica produce large quantities of seed that typically have high germinability. This seed is viable whether sown immediately after collection or subjected to various conditions during the winter season and germinated the following spring. Cultivars of F. japonica also produce viable seed and can thus contribute to the invasiveness of this species. In addition, wild F. Japonica seedlings were observed at several field sites, with several of these seedlings Surviving the winter and resprouting the following spring. That Sexual reproduction and seedling Survival occur in the wild has strong implications for the development of management strategies for this species. Web of Science Fallopia japonica USA Massachusetts Field - Observational terrestrial Old Field Invasion Hyp. Inherent Superiority High Reprod. Output primary 1692 Rogers, WE; Siemann, E 2003 Effects of simulated herbivory and resources on Chinese tallow tree (Sapium sebiferum, Euphorbiaceae) invasion of native coastal prairie journal AMERICAN JOURNAL OF BOTANY 90 2 243 249 Trade-offs associated with maintaining herbivory resistance and herbivory tolerance are frequently inferred in plant life histories. Invasive success for many non-native plants is often attributed to novel resistance that repels native herbivores. Chinese tallow tree (Sapium sebiferum, Euphorbiaceae) is a non-native invader that threatens ecosystems throughout the southeastern United States, including imperiled coastal prairie regions. Low herbivore loads due to costly resistance are generally assumed to give Sapium a competitive advantage over native plants. We predicted that if Sapium experienced higher damage levels it would show significant decreases in growth and reduced ability to compete with native prairie vegetation. We conducted full-factorial, paired greenhouse and field experiments designed to assess the effects of simulated leaf herbivory on Sapium growth in the presence of prairie vegetation at different levels of light and nitrogen. Contrary to our expectations, neither low-intensity, chronic defoliation nor high-intensity, acute defoliation negatively affected Sapium seedlings in any resource combination in either experiment. These studies reveal that Sapium possesses considerable phenotypic plasticity, and herbivory tolerance is a newly appreciated trait that likely contributes to its invasive potential. Web of Science Sapium sebiferum United States Texas Field - Experimental;Greenhouse terrestrial Savanna Invasion Hyp. Enemy Release;Plasticity primary 1693 Wijnhoven, S; van Riel, MC; van der Velde, G 2003 Exotic and indigenous freshwater gammarid species: physiological tolerance to water temperature in relation to ionic content of the water journal AQUATIC ECOLOGY 37 2 151 158 Bioinvasions by closely related species often lead to niche competition between exotic and indigenous species. The outcome of this competition is partly determined by differences in physiological tolerance of the competing species to the environmental conditions of the colonised habitat. Physiological tolerance of the invading gammarid species Gammarus tigrinus, Echinogammarus ischnus and Dikerogammarus villosus and the indigenous gammarid species Gammarus pulex, Gammarus roeseli and Gammarus fossarum from Dutch waters was studied in the laboratory by comparing their pleopod beats at rest at different water temperatures, which reflect the gammarid's oxygen consumption. Pleopod beat frequencies increased from a minimum ventilatory activity of 0 beats per minute at 1degreesC to maximum activity of up to 300 beats per minute at temperatures between 25degreesC and 35degreesC. At the state of maximum activity, a further increase in temperature was followed by a strong decrease in pleopod beat frequency, indicating acute stress, and subsequently mortality. Frequency response patterns of invading and indigenous gammarids were found to be highly similar, indicating a wide tolerance to temperature for all species. The tolerance of D. villosus, however, was reduced in brook water, indicating a lower competitive ability in relatively ion-poor water. G. tigrinus survived at higher temperatures in the more ion-rich, polluted waters than the indigenous gammarids, indicating a wider physiological tolerance and thus a higher competitive ability in these waters. Web of Science Gammarus tigrinus; Echinogammarus ischnus; Dikerogammarus villosus Netherlands 51.69 6.04 Field - Experimental lotic Invasion Hyp. Inherent Superiority Broad Tolerances omnivore 1694 Stoffels, RJ; Humphries, P 2003 Ontogenetic variation in the diurnal food and habitat associations of an endemic and an exotic fish in floodplain ponds: consequences for niche partitioning journal ENVIRONMENTAL BIOLOGY OF FISHES 66 3 293 305 In floodplain ponds with low piscivore abundance, both endemic Midgley's gudgeons, Hypseleotris sp. 5, and exotic mosquitofish, Gambusia holbrooki, showed significant ontogenetic variation in the use of food and space. Small gudgeons were generally associated with surface and benthic habitats, then restricted their distribution to benthic habitats at a size of approximately 24 mm ( standard length). The ontogenetic variation in mosquitofish habitat use was less discrete, and could be described as a tendency for larger individuals to be associated with the bottom of the littoral macrophyte beds than with the surface of the macrophyte beds or surface of the limnetic zone. Small gudgeons exhibited high spatial overlap with mosquitofish within the surface habitats of the ponds. All size-class/species comparisons showed significant partitioning of food resources, however, the diets of small gudgeons and mosquitofish were very similar. Therefore, juv enile gudgeons may have to pass through a similar spatial and trophic niche to introduced mosquitofish before recruiting to the adult stage. Possible mechanisms driving the ontogenetic variation in gudgeon and mosquitofish habitat use are discussed. This paper demonstrates that ontogenetic niche shifts at fine spatial scales can affect our interpretation of interactions between native and introduced fishes. Web of Science Gambusia holbrooki Australia Victoria Killawarra State Forest Field - Observational lotic Fundamentals herbivore 1698 Schreiber, ESG; Quinn, GP; Lake, PS 2003 Distribution of an alien aquatic snail in relation to flow variability, human activities and water quality journal FRESHWATER BIOLOGY 48 6 951 961 1. Disturbance and anthropogenic land use changes are usually considered to be key factors facilitating biological invasions. However, specific comparisons of invasion success between sites affected to different degrees by these factors are rare. 2. In this study we related the large-scale distribution of the invading New Zealand mud snail (Potamopyrgus antipodarum ) in southern Victorian streams, Australia, to anthropogenic land use, flow variability, water quality and distance from the site to the sea along the stream channel. 3. The presence of P. antipodarum was positively related to an index of flow-driven disturbance, the coefficient of variability of mean daily flows for the year prior to the study. 4. Furthermore, we found that the invader was more likely to occur at sites with multiple land uses in the catchment, in the forms of grazing, forestry and anthropogenic developments (e.g. towns and dams), compared with sites with low-impact activities in the catchment. However, this relationship was confounded by a higher likelihood of finding this snail in lowland sites close to the sea. 5. We conclude that P. antipodarum could potentially be found worldwide at sites with similar ecological characteristics. We hypothesise that its success as an invader may be related to an ability to quickly re-colonise denuded areas and that population abundances may respond to increased food resources. Disturbances could facilitate this invader by creating spaces for colonisation (e.g. a possible consequence of floods) or changing resource levels (e.g. increased nutrient levels in streams with intense human land use in their catchments). Web of Science Potamopyrgus antipodarum Australia Victoria Field - Observational lotic Invasion Hyp. Disturbance herbivore 1699 Cantero, JJ; Liira, J; Cisneros, JM; Gonzalez, J; Nunez, C; Petryna, L; Cholaky, C; Zobel, M 2003 Species richness, alien species and plant traits in Central Argentine mountain grasslands journal JOURNAL OF VEGETATION SCIENCE 14 1 129 136 Pattern of native vegetation, distribution of alien species and variation of environmental parameters were studied in mountain grasslands in a lithologically homogeneous Cordoba mountain range in Central Argentina. CCA showed that altitude was the most important factor determining the compositional variation of the vegetation, with soil nutrient status and stoniness as additional factors. Short-grass communities, associated with the driest habitats on plateaus, showed higher small-scale native species richness than wet-turf communities in valleys and tall-grass communities on slopes. Species richness was negatively correlated with soil parameters that indicate nutrient status and water availability. Also, there was a negative correlation between soil Ca- and Mg-content and richness. High native species richness coincided with high alien species richness. When smaller units - community types - were considered, it became evident that within short-grass vegetation, the three most species-rich community types contained significant numbers of alien species, while the other two did not. Even within one community type, the same quadrats that contained the highest number of native species, were also characterized by the highest numbers of alien species. Evidently, the same mechanism was responsible for high richness of both native and alien species. Alien species were distinguished by a greater proportion of annuals and prostrate stoloniferous plants, by lower palatability and by smaller proportion of zoochory. DCA ordination of quadrats on the basis of plant traits as attributes resulted in a clear distinction of three main vegetation types. Short-grass vegetation was distinguished by a predomination of late flowering species, tall-grass vegetation by the presence of high herbaceous plants and bushes, and wet-turf vegetation by the presence of plants with storage organs, the lack of hairy leaves, and by a high proportion of cryptophytes. Quadrats with and without alien species were distinguished as well, indicating that the occurrence of aliens may be dependent on plant traits in a particular patch of a community. Web of Science Many Argentina Cordoba mountain range Field - Observational terrestrial Mountain Invasion Hyp. Community Species Richness primary 1704 Kley, A; Maier, G 2003 Life history characteristics of the invasive freshwater gammarids Dikerogammarus villosus and Echinogammarus ischnus in the river Main and the Main-Donau canal journal ARCHIV FUR HYDROBIOLOGIE 156 4 457 469 The life history characteristics of two invasive gammarids, Dikerogammarus villosus and Echinogammarus ischnus, from 2 sites in the river Main and one in the Main-Donau canal were studied monthly from May to October 2000 and one additional time in April 2002. The species coexisted, but D. villosus was much more abundant at upstream sites whereas E. ischnus prevailed at the downstream site. Females of D. villosus produced big clutches; mean clutch size during the period of reproduction ranged between 29 and 136 and maximum clutch size was 188 eggs per ovigerous female. Volume of stage 2 eggs was between 0.07 and 0.08 mm(3). Echinogammarus ischnus females produced smaller clutches than D. villosus females but larger eggs. Mean clutch size in this species varied between 14 and 27 and maximum clutch size was 51 eggs per ovigerous female. Volume of stage 2 eggs varied between 0.1 and 0.2 mm(3). The calculated fecundity index (weight-specific number of eggs per clutch) was higher in D. villosus than in E. ischnus (0.62-1.37 vs. 0.44-0.60, respectively) while the reproductive effort (egg volume times fecundity index) was fairly the same in both species (0.05-0.12). Ovigerous females and precopula pairs were absent in September/October indicating the reproductive diapause. The results point to different reproductive strategies in these species. Large eggs (probably supplied with reserves) suggest advantage of E. ischnus when food is scarce while big clutches with small eggs suggest reproductive superiority of D. villosus under conditions of abundant food. Web of Science Dikerogammarus villosus; Echinogammarus ischnus Germany Bavaria River Main Field - Observational lotic Invasion Hyp. Inherent Superiority High Reprod. Output omnivore 1710 Gorchov, DL; Trisel, DE 2003 Competitive effects of the invasive shrub, Lonicera maackii (Rupr.) Herder (Caprifoliaceae), on the growth and survival of native tree seedlings journal PLANT ECOLOGY 166 1 13 24 Invasive plants are often associated with reduced cover of native plants, but rarely has competition between invasives and natives been assessed experimentally. The shrub Lonicera maackii, native to northeastern Asia, has invaded forests and old fields in numerous parts of eastern North America, and is associated with reduced tree seedling density in Ohio forests. A field experiment was conducted to test the effects of established L. maackii on the survival and growth of transplanted native tree species. The experiment examined above-ground competition (by removing L. maackii shoots) and below-ground competition (by trenching around transplanted seedlings). The effects of above-ground competition with L. maackii were generally more important than below-ground competition, though both were detected. Shoot treatment was the key determinant for the survival of all species except P. serotina, whereas trenching only enhanced survival for A. saccharum caged and P. serotina, and only in the shoot removal treatment. For the surviving seedlings, L. maackii shoot removal increased growth of A. saccharum seedlings protected with cages, but actually reduced the growth of unprotected Q. rubra and A. saccharum seedlings, indicating that L. maackii shoots confer some protection from deer browsing. Significant interactions between root and shoot treatment on Q. rubra growth parameters, specifically greatest growth in the shoot present & trenched treatment, is attributed to protection from deer browsing combined with release from below-ground competition. Despite this protective function of L. maackii shoots, the overall effect of this invasive shrub is increased mortality of native tree seedlings, suggesting it impacts the natural regeneration of secondary forests. Web of Science Lonicera maackii USA Ohio Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Superior Competitor primary 1711 Bimova, K; Mandak, B; Pysek, P 2003 Experimental study of vegetative regeneration in four invasive Reynoutria taxa (Polygonaceae) journal PLANT ECOLOGY 166 1 1 11 Garden experiments focused on vegetative regeneration were carried out with four invasive taxa of the genus Reynoutria (R. japonica var. japonica, R. japonica var. compacta, R. sachalinensis and a hybrid between R. sachalinensis and R. japonica var. japonica, R. x bohemica). Regeneration ability of stems and rhizomes, timing of shoot emergence and biomass production were studied under the following treatments: laid horizontally on the soil surface; placed upright; buried in the soil; floating in water. Two different soils (sand and garden loam) representing contrasting nutrient levels were applied. Differences were found in the capability and speed of regeneration, as well as in the quality of shoots produced. Regeneration from stems was less efficient than that from rhizomes in all taxa except R. sachalinensis. R. x bohemica exhibits higher regeneration potential (61%) than all other taxa and can be considered as the most successful taxon of the Czech representatives of the genus Reynoutria in terms of regeneration and establishment of new shoots. High regeneration capacity was also exhibited by R. japonica var. compacta (52%). Other taxa showed generally lower regeneration rates (R. japonica var. japonica 39% and R. sachalinensis 21%), but under some treatments the percentage of regenerated segments was high, too. R. japonica var. japonica rhizomes regenerated successfully in all three soil treatments but not in the water. An opposite pattern was found for its stems: they regenerated well if exposed to water treatment but in the soil, they did not regenerate at all. Particular taxa responded to the soil type in a contrasting way. R. sachalinensis and R. x bohemica regenerated better in loam while the opposite was true in R. japonica var. japonica. R. japonica var. compacta produced the tallest and R. x bohemica the heaviest and most robust shoots. It is concluded that rhizomes are more crucial than stems for the spread of knotweeds through fragmentation and clonal growth, suggesting the importance of soil disturbance. Web of Science Reynoutria japonica; Reynoutria sachalinensis Czech Republic Central Bohemia Garden terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Clonal Reproduction primary 1712 Brooks, ML 2003 Effects of increased soil nitrogen on the dominance of alien annual plants in the Mojave Desert journal JOURNAL OF APPLIED ECOLOGY 40 2 344 353 1. Deserts are one of the least invaded ecosystems by plants, possibly due to naturally low levels of soil nitrogen. Increased levels of soil nitrogen caused by atmospheric nitrogen deposition may increase the dominance of invasive alien plants and decrease the diversity of plant communities in desert regions, as it has in other ecosystems. Deserts should be particularly susceptible to even small increases in soil nitrogen levels because the ratio of increased nitrogen to plant biomass is higher compared with most other ecosystems. 2. The hypothesis that increased soil nitrogen will lead to increased dominance by alien plants and decreased plant species diversity was tested in field experiments using nitrogen additions at three sites in the in the Mojave Desert of western North America. 3. Responses of alien and native annual plants to soil nitrogen additions were measured in terms of density, biomass and species richness. Effects of nitrogen additions were evaluated during 2 years of contrasting rainfall and annual plant productivity. The rate of nitrogen addition was similar to published rates of atmospheric nitrogen deposition in urban areas adjacent to the Mojave Desert (3.2 g N m(-2) year(-1)). The dominant alien species included the grasses Bromus madritensis ssp. rubens and Schismus spp. (S. arabicus and S. barbatus) and the forb Erodium cicutarium . 4. Soil nitrogen addition increased the density and biomass of alien annual plants during both years, but decreased density, biomass and species richness of native species only during the year of highest annual plant productivity. The negative response of natives may have been due to increased competitive stress for soil water and other nutrients caused by the increased productivity of aliens. 5. The effects of nitrogen additions were significant at both ends of a natural nutrient gradient, beneath creosote bush Larrea tridentata canopies and in the interspaces between them, although responses varied among individual alien species. The positive effects of nitrogen addition were highest in the beneath-canopy for B. rubens and in interspaces for Schismus spp. and E. cicutarium. 6. The results indicated that increased levels of soil nitrogen from atmospheric nitrogen deposition or from other sources could increase the dominance of alien annual plants and possibly promote the invasion of new species in desert regions. Increased dominance by alien annuals may decrease the diversity of native annual plants, and increased biomass of alien annual grasses may also increase the frequency of fire. 7. Although nitrogen deposition cannot be controlled by local land managers, the managers need to understand its potential effects on plant communities and ecosystem properties, in particular how these effects may interact with land-use activities that can be managed at the local scale. These interactions are currently unknown, and hinder the ability of managers to make appropriate land-use decisions related to nitrogen deposition in desert ecosystems. 8. Synthesis and applications. The effects of nitrogen deposition on invasive alien plants should be considered when deciding where to locate new conservation areas, and in evaluating the full scope of ecological effects of new projects that would increase nitrogen deposition rates. Web of Science Bromus madritensis; Schismus arabicus; Schismus barbatus USA Nevada Mojave Desert Field - Experimental terrestrial Invasion Hyp. Inherent Superiority Superior Competitor primary 1715 Fornwalt, PJ; Kaufmann, MR; Huckaby, LS; Stoker, JA; Stohlgren, TJ 2003 Non-native plant invasions in managed and protected ponderosa pine Douglas-fir forests of the Colorado Front Range journal FOREST ECOLOGY AND MANAGEMENT 177 3 515 527 We examined patterns of non-native plant diversity in protected and managed ponderosa pine/Douglas-fir forests of the Colorado Front Range. Cheesman Lake, a protected landscape, and Turkey Creek, a managed landscape, appear to have had similar natural disturbance histories prior to European settlement and fire protection during the last century. However, Turkey Creek has experienced logging, grazing, prescribed burning, and recreation since the late 1800s, while Cheesman Lake has not. Using the modified-Whittaker plot design to sample understory species richness and cover, we collected data for 30 0.1 ha plots in each landscape. Topographic position greatly influenced results, while management history did not. At both Cheesman Lake and Turkey Creek, low/riparian plots had highest native and non-native species richness and cover; upland plots (especially east/west-facing, south-facing and flat, high plots) had the lowest. However, there were no significant differences between Cheesman Lake and Turkey Creek for native species richness, native species cover, non-native species richness' or non-native species cover for any topographic category. In general, non-native species richness and cover Were highly positively correlated with native species richness and/or cover (among other variables). In total, 16 non-native species were recorded at Cheesman Lake and Turkey Creek; none of the 16 non-native species were more common at one site than another. These findings suggest that: (1) areas that are high in native species diversity also contain more non-native species; (2) both protected and managed areas can be invaded by non-native plant species, and at similar intensities; and (3) logging, grazing, and other similar disturbances may have less of an impact on non-native species establishment and growth than topographic position (i.e., in lowland and riparian zones versus upland zones). Published by Elsevier Science B.V. Web of Science Many USA Colorado Cheesman Lake; Turkey Creek Field - Observational terrestrial Coniferous Forest Invasion Hyp. Community Species Richness primary 1718 Stampe, ED; Daehler, CC 2003 Mycorrhizal species identity affects plant community structure and invasion: a microcosm study journal OIKOS 100 2 362 372 Previous studies have shown that arbuscular mycorrhizal fungi (AMF) can mediate plant interactions, thereby affecting plant community structure. Little is known, however, about whether the presence of different AMF species leads to differences in plant community structure or invasion success by introduced species. To investigate the effects of AMF species on community structure and invasion, we created replicate microcosms containing soil inoculated with one of three different AMF species (Glomus spurcum Pfeiffer, Walker & Bloss, Scutellospora erythropa (Koske & Walker) Walker & Sanders, or Scutellospora verrucosa (Koske & Walker) Walker & Sanders) or a mixture of all three AMF species. Seeds of seven naturally co-occurring plant species (Ageratum conyzoides L., Cyperus compressus L., Chamaecrista nictitans (L.), Crotalaria incana L., Hyptis pectinata (L.) Poit., Sida rhombifolia L., Melinis repens (Willd.) Zizka) in Hawai'i were sown equally into these microcosms, which were placed on outdoor benches. Plant community development was monitored over a season. Mid-way through the experiment, an invader (Bidens pilosa L.) was added to the established communities to determine whether mycorrhizal species identity affected invasion success. Final aboveground and belowground phytomass were used to assess plant community differences among treatments. Although the identity of the dominant plant species (Melinis repens) remained the same in all treatments, community dominance, community productivity, plant species richness, Shannon index of diversity, and invasion success all varied with AMF species identity. Invasion success was not inversely related to species richness or diversity. Instead, increased richness, diversity, and invasion success all appeared to be related to decreased dominance by M. repens in the presence of certain AMF species. These results indicate that the composition of the AMF community belowground can influence the structure of the plant community aboveground, and may play a role in facilitating or repelling invasion. Web of Science Bidens pilosa United States Hawaii Lab terrestrial Chaparral/Shrublands Invasion Hyp. Mutualism Facilitation primary 1719 Gerlach, JD; Rice, KJ 2003 Testing life history correlates of invasiveness using congeneric plant species journal ECOLOGICAL APPLICATIONS 13 1 167 179 We used three congeneric annual thistles, which vary in their ability to invade California (USA) annual grasslands, to test whether, invasiveness is related to differences in life history traits. We hypothesized that populations of these summer-flowering Centaurea species must pass through a demographic gauntlet of survival and reproduction in order to persist and that the most invasive species (C. solstitialis) might possess unique life history characteristics. Using the idea of a demographic gauntlet as a conceptual framework, we compared each congener in terms of (1) seed germination and seedling establishment, (2) survival of rosettes subjected to competition from annual grasses, (3). subsequent growth and flowering in adult plants, and (4) variation in breeding system. Grazing and soil disturbance is thought to affect Centaurea establishment, growth, and reproduction, so we also explored differences among congeners in their response to clipping and to different sizes of soil disturbance. We found minimal differences among congeners,in either seed germination responses or seedling establishment and survival. In contrast,. differential growth responses of congeners to different sizes of canopy gaps led to large differences in adult size and fecundity. Canopy-gap size and clipping affected the fecundity of each species, but the most invasive species (C solstitialis) was unique in its strong positive response to combinations of clipping and canopy gaps. In addition, the phenology of C solstitialis allows this species to extend its growing season into the summer-a time when competition from winter annual vegetation for soil water is minimal. Surprisingly, C. solstitialis Was highly self-incompatible while the less invasive species were highly self-compatible. Our results suggest that the invasiveness of C. solstitialis. arises, in part, from its combined ability to persist in competition, with annual grasses and,its plastic growth and reproductive responses to open, disturbed habitat patches. Web of Science Centaurea solstitialis; Centaurea melitensis; Centaurea sulphurea USA California Davis Garden terrestrial Old Field Invasion Hyp. Inherent Superiority Superior Competitor;High Reprod. Output;Self Compatible primary 1721 Adams, MJ; Pearl, CA; Bury, RB 2003 Indirect facilitation of an anuran invasion by non-native fishes journal ECOLOGY LETTERS 6 4 343 351 Positive interactions among non-native species could greatly exacerbate the problem of invasions, but are poorly studied and our knowledge of their occurrence is mostly limited to plant-pollinator and dispersal interactions. We found that invasion of bullfrogs is facilitated by the presence of co-evolved non-native fish, which increase tadpole survival by reducing predatory macroinvertebrate densities. Native dragonfly nymphs in Oregon, USA caused zero survival of bullfrog tadpoles in a replicated field experiment unless a non-native sunfish was present to reduce dragonfly density. This pattern was also evident in pond surveys where the best predictors of bullfrog abundance were the presence of non-native fish and bathymetry. This is the first experimental evidence of facilitation between two non-native vertebrates and supports the invasional meltdown hypothesis. Such positive interactions among non-native species have the potential to disrupt ecosystems by amplifying invasions, and our study shows they can occur via indirect mechanisms. Web of Science Rana catesbeiana USA Oregon Field - Experimental lentic Invasion Hyp. Mutualism Facilitation omnivore 1724 Vincent, T; Brancotte, V 2002 Present distribution and spreading modes of Corbicula spp. in France journal BULLETIN DE LA SOCIETE ZOOLOGIQUE DE FRANCE 127 3 241 252 Corbicula is a bivalve mollusc genus with a wide distribution in Asia, Africa and Australia. Corbiculidae have been accidentally introduced, during the first half of the twentieth century, in USA. They have since dispersed widely in the whole American continent. The introduction of Corbicula spp. to Europe dates from the 1980s. Some specimens were encountered in the mouth of the river Tage (in Portugal) and in the lower course of the river Dordogne (in France). During the 1990s, this species has been observed in Spain, Belgium, the Netherlands and Germany. The taxonomic status of Corbicula species still remains uncertain in Europe. The polymorphism of Corbicula spp. has induced some researchers to see in the specimens collected from various rivers, different species or sub-species. In the present study, the authors describe and illustrate two different types, based on the morphology of the shell, which are assigned to the species C. fluminalis and C. fluminea. The historical background of this settlement in France shows that the spread of Corbicula spp. is extremely fast. After a first observation in 1980 in the lower Dordogne, this species has been successively discovered in 1985 in the river Garonne, then in the *canal du Midi* in 1989, in the river Loire in 1990, in the lateral canal to the river Garonne in 1993, in the river Rhin and in the river Moselle in 1994, and finally in the river Seine in 1997. The different steps of the invasion of the French hydrological network are analysed. In 1999, the colonization in progress in the river Seine prompted the authors to examine the spread of this bivalve mollusc through the hydrological bassin of the river Seine. The importance of navigation canals, linking up several rivers, in the mode of progression of this species could thus be revealed, particularly as the authors were also surveying the spread of the species in the river Loire at the same time. The rapid spread of Corbicula implies effective colonizing strategies in this invasive species which are discussed in a specific chapter. The impact of such an alien species on a weakened freshwater environment is also emphasised, since a fast expansion has ecological consequences for the physical environment and the local malacofauna. Web of Science Corbicula fluminalis; Corbicula fluminea France Field - Observational lotic Impacts;Invasion Hyp. Inherent Superiority Effective Disperser filter 1727 Leger, EA; Rice, KJ 2003 Invasive California poppies (Eschscholzia californica Cham.) grow larger than native individuals under reduced competition journal ECOLOGY LETTERS 6 3 257 264 Invasive plants can be larger and more fecund in their invasive range than in their native range, although it is unknown how often this is a result of a genetically controlled shift in traits, a plastic response to a favourable environment, or a combination thereof. Here we present data from common garden experiments that compare the size and fecundity of native and invasive California poppies, Eschscholzia californica Cham. Individuals from 20 populations, half from California (native) and half from Chile (invasive), were grown both with and without competition from other plants in a container experiment and at two field locations. There were no differences in survival between native and invasive plants at any location. We found significant increases in size and fecundity in invasive populations at two of three locations when poppies were grown without competition from other plants. Our results indicate that genetic shifts in traits have occurred in invasive populations, and that the invasive plants are better at maximizing growth and reproduction in open environments. Web of Science Eschscholzia californica Chile Garden terrestrial Grassland Invasion Hyp. Evolution of Increased Competitive Ability primary 1730 MacNeil, C; Bigsby, E; Dick, JTA; Hatcher, MJ; Dunn, AM 2003 Differential physico-chemical tolerances and intraguild predation among native and invasive amphipods (Crustacea); a field study journal ARCHIV FUR HYDROBIOLOGIE 156 2 165 179 We used field surveys and transplant experiments to elucidate the relative roles of physico-chemical regime and intraguild predation in determining the generally mutually exclusive distributions of native and invader freshwater amphipod species. Field surveys showed that the native Gammarus duebeni celticus dominates the shoreline of Lough Neagh, N. Ireland, with some co-occurrence with the N. American invader G. tigrinus. However, the latter species dominates the deeper areas of the mid-Lough. Transplant experiments showed no difference in survival of the native and invader in single species 'bioassay tubes' placed along the shoreline. However, there was significantly higher survival of the invader compared with the native in single species tubes placed in the mid-Lough. In mixed species tubes on the shoreline, the native killed and ate the invader, with no reciprocal interaction, leading to significant reductions of the invader. However, the invader had significantly higher survival than the native in mixed species tubes in the mid-Lough, with no evidence. of predation between the two species. These results indicate that, whereas differential intraguild predation may determine domination of the shoreline by the native, differential physico-chemical tolerances may be major determinants of the domination of the mid-Lough by the invader. This study emphasises the need to consider the habitat template in conjunction with biotic interactions before attempting to draw conclusions about mechanisms determining relative distribution patterns of native and invasive species. Web of Science Gammarus tigrinus Ireland Lough Neagh Field - Observational lotic Invasion Hyp. Inherent Superiority Broad Tolerances omnivore 1731 Leps, J; Novovotny, V; Cizek, L; Molem, K; Isua, B; Boen, W; Kutil, R; Auga, J; Kasbal, M; Manumbor, M; Hiuk, S 2002 Successful invasion of the neotropical species Piper aduncum in rain forests in Papua New Guinea journal APPLIED VEGETATION SCIENCE 5 2 255 262 Piper aduncum is a neotropical invasive species which has spread throughout Papua New Guinea over the past three decades. It has become a most successful alien woody plant in New Guinea, occurring from sea level up to 2000 in a.s.l. The species prefers initial stages of forest succession and is particularly common in recently abandoned gardens representative of a system of swidden agriculture. It often attains high cover, suppresses other pioneer species and becomes the absolute dominant species in these habitats. The species is now also spreading into naturally disturbed habitats far from direct human influence, such as natural tree-fall gaps, landslides and frequently flooded stream banks. It has, however, never been found in a closed primary forest. The species germinates from faeces of mammal and bird species, and we conclude that dispersal through endozoochory contributes to this species' extraordinary success in Papua New Guinea. A similar invasion behaviour has been documented over a large geographic area, from Malaysia to Fiji. Piper aduncum has attributes which are common amongst successful invasive species: (1) a large native geographic range; (2) aggressively colonizing disturbed habitats in its native area; (3) relatively small seeds; (4) a short juvenile period; (5) a large seed production every year. Web of Science Piper aduncum Papua New Guinea Field - Observational terrestrial Tropical Forest Invasion Hyp. Mutualism Facilitation primary 1740 Parker, IM; Rodriguez, J; Loik, ME 2003 An evolutionary approach to understanding the biology of invasions: Local adaptation and general-purpose genotypes in the weed Verbascum thapsus journal CONSERVATION BIOLOGY 17 1 59 72 The role of evolution in the invasion of non-native species has important implications for conservation, weed science, risk assessment, and policy. In this paper we first discuss why an evolutionary perspective can be helpful and outline a range of potentially useful approaches from population biology and ecological genetics. As a case study, we then ask how adaptation and genetic structure may promote or constrain the expansion of an invasive weed, Verbascum thapsus , into high elevations in the Sierra Nevada of California. We used growth-chamber and common-garden experiments to assay a range of morphological and physiological traits that could influence plant fitness at high elevation. There was a significant relationship between elevation and leaf size and reflectance above 800 m, although we found no relationship between elevation and most other traits ( growth rate in warm or cool temperatures, freezing tolerance when grown in warm or cool temperatures, leaf number, rosette morphology, plant height ). We did see marked genetic differentiation among populations, possibly reflecting founder effects and a history of genetic drift. When we partitioned the phenotypic variance, there was almost no variation among maternal families within populations, limiting the potential for selection to act. The majority of the variance for all traits was among individuals within families, suggesting that environmental conditions strongly influenced the phenotype. Overall, the increasing success of V. thapsus at high elevations appears to conform more to Baker's concept of a general-purpose genotype than to invasion by rapid adaptation. Web of Science Verbascum thapsus USA California Sierra Nevada Garden;Lab terrestrial Mountain Invasion Hyp. Inherent Superiority Broad Tolerances primary 1741 Mitchell, CE; Power, AG 2003 Release of invasive plants from fungal and viral pathogens journal NATURE 421 127 625 627 Invasive plant species both threaten native biodiversity and are economically costly(1-5), but only a few naturalized species become pests(2,4). Here we report broad, quantitative support for two long-standing hypotheses that explain why only some naturalized species have large impacts. The enemy release hypothesis argues that invaders' impacts result from reduced natural enemy attack(2,4,6-10). The biotic resistance hypothesis argues that interactions with native species, including natural enemies, limit invaders' impacts(6-8). We tested these hypotheses for viruses and for rust, smut and powdery mildew fungi that infect 473 plant species naturalized to the United States from Europe. On average, 84% fewer fungi and 24% fewer virus species infect each plant species in its naturalized range than in its native range. In addition, invasive plant species that are more completely released from pathogens are more widely reported as harmful invaders of both agricultural and natural ecosystems. Together, these results strongly support the enemy release hypothesis. Among noxious agricultural weeds, species accumulating more pathogens in their naturalized range are less widely noxious, supporting the biotic resistance hypothesis. Our results indicate that invasive plants' impacts may be a function of both release from and accumulation of natural enemies, including pathogens. Web of Science Many USA Statistical/Meta-analysis terrestrial Invasion Hyp. Enemy Release primary 1743 Callaway, RM; Mahall, BE; Wicks, C; Pankey, J; Zabinski, C 2003 Soil fungi and the effects of an invasive forb on grasses: Neighbor identity matters journal ECOLOGY 84 1 129 135 We studied the effects of soil fungi on interactions between Centaurea melitensis, an exotic invasive weed in central California, and two co-occurring grasses, Nassella pulchra and Avena barbata, The fungicide benomyl reduced the abundance of arbuscular mycorrhizal (AM) fungi in plant roots but did not affect non-AM fungi. Centaurea plants grown alone were >50% smaller with the resident microbial community intact than when benomyl was applied. When grown with Nassella, the effect of benomyl was reversed. Centaurea grew almost five times larger with the resident microbial community intact. Fungicide had no effect on the biomass of Centaurea grown with Avena, but biomass of Centaurea was significantly lower when grown with Avena than when grown with Nassella or alone. Photosynthetically fixed carbon may have been transferred from Nassella via soil fungi to Centaurea, constituting a form of soil fungi-mediated parasitism, but such a transfer did not occur from Avena to Centaurea. Second. Nassella may have been more inhibited by soil pathogens in the presence of Centaurea than when alone. and the inhibition of Nassella may have released Centaurea from competition. A third possibility is that Nassella has strong positive effects on the growth of Soil fungi. but the positive feedback of beneficial soil fungi to Nassella is less than the positive feedback to Centaurea. Regardless of the mechanism, the difference in soil fungicide treatment effects on competition between Centaurea and Nassella vs. Centaurea and Avena has important implications for the invasion of California grasslands. Web of Science Centaurea melitensis USA California Santa Barbara Greenhouse terrestrial Grassland Invasion Hyp. Mutualism Facilitation primary 1744 Eviner, VT; Chapin, FS 2003 Gopher-plant-fungal interactions affect establishment of an invasive grass journal ECOLOGY 84 1 120 128 Many attempts have been made to link invasions of exotic plants to specific plant traits and key attributes of invaded ecosystems. While these factors play a role in determining the potential for invasion. they are often inadequate in predicting the Success of a specific invasion. We show that interactions of an invasive grass with other members of the community determine the local pattern of invasion. A fungus, Ulocladium atrum, aids the establishment of barbed goatgrass (Aegilops triuncialis) by weakening the grass's tough seed head. thereby accelerating germination and seedling establishment. In contrast, gophers. Thomomys bottae, decrease establishment of this invader by selectively burying patches of goatgrass seedlings under mounds. Plants that survive these gopher disturbance produce seeds that are uninfected by Ulocladium atrum, which may further decrease the establishment of the next generation of goatgrass. A field survey indicated that goatgrass achieves dominance in areas with minimal gopher disturbance. but has limited establishment in pastures with high gopher activity, indicating that the landscape pattern of gopher activity influences patterns of goatgrass invasion by manipulating gopher-plant-fungal interactions. Web of Science Aegilops triuncialis USA California Mendocino Field - Observational terrestrial Grassland Invasion Hyp. Mutualism Facilitation primary 1745 Brown, RL; Peet, RK 2003 Diversity and invasibility of southern Appalachian plant communities journal ECOLOGY 84 1 32 39 We propose that the relationship between diversity and community invasibility depends on the degree to which community composition is driven by immigration processes. When immigration is enhanced by high propagule pressure or low-intensity disturbance, the relationship between diversity and exotic species invasion should be positive. Only when such immigration processes are limited should competitive interactions lead to a negative correlation between diversity and invasibility. Moreover, competition should be more apparent at smaller scales where individual plants compete directly for space; thus, diversity and invasibility are more likely to be negatively correlated at small spatial scales. We tested these predictions by comparing exotic and native species diversity of vascular plants across five spatial scales in riparian and upland plant communities in the southern Appalachians, We found a positive relationship between species diversity and exotic invasion in riparian areas at large scales (100 m(2)). Which graded into a negative relationship at small scales (0.01 m(2)). In uplands, there was a slight positive relationship between native and exotic species diversity at both scales of observation. Overall, riparian areas had more exotic and native species than upland areas, and both native and exotic species diversity increased with flood frequency within the riparian zone. Web of Science Many United States North Carolina southern Appalachians Field - Observational terrestrial Deciduous Forest;Riparian Invasion Hyp. Community Species Richness primary 1748 Verlaque, R; Aboucaya, A; Fridlender, A 2002 Invasive alien flora of France: Ecology, life-forms and polyploidy journal BOTANICA HELVETICA 112 2 121 136 The expanding alien flora of France (221 taxa) have been classified in 3 groups: (1) the *patent or transformer invaders* (i.e. the most damaging taxa which change the character of natural ecosystems); (2) the *colonizers or potential invaders* of natural ecosystems, which have been hitherto non-proliferating; (3) the *pests or weeds* that essentially grow in man-made habitats. The geographical origin, habitats and regions colonized in France, the mode of introduction (intentional or not), the life-forms sensu Raunkiaer and the chromosome numbers have been sought for each taxon. Chromosome numbers of 53 exotic species (previously little or not at all studied) have been counted in populations in France: except for some hybrids, naturalization occurs without any change of chromosome number. All the studied traits have been analysed with regard to the 3 cytological categories (sensu Hodgson): diploids, recent polyploids, and relictual polyploids (i.e. without extant diploid relatives). The Mediterranean area, zones at low altitudes, wetlands and coastal habitats are the most strongly affected by the invasions in France. The human role is essential, not only through the increasing disturbances of the environment, but also because of the constant and often massive deliberate introductions (3/4 of invaders). Comparison of the life-forms and cytological types shows very wide differences between the native and the alien floras, but also between the 3 groups of invaders. Polyploidy constitutes a very favourable attribute for the success of alien plants, above all for the patent invaders (P = 77%) and those that are widespread in France (P = 86%). The polyploid percentage increases with the difficulties of the colonization, overall and irrespective of the life-form, but specially in the groups that are naturally the most vulnerable (Thero- and Cryptophytes). In conclusion, woody species, hydrophytes and polyploid aliens constitute the most serious threats for the conservation of natural ecosystems. Web of Science Many France Statistical/Meta-analysis terrestrial Wetland;Chaparral/Shrublands Invasion Hyp. Other primary 1749 Tallent-Halsell, NG; Walker, LR 2002 Responses of Salix gooddingii and Tamarix ramosissima to flooding journal WETLANDS 22 4 776 785 Impoundments create unnatural shorelines that differ from lake shorelines in patterns of waterlevel fluctuations, flow, sediment transport, and shoreline vegetation dynamics. Shoreline plant communities of impoundments in the American Southwest often become dominated by mature, senescent Populus and Salix, with few if any seedlings. The failure of native plant community replacement is exacerbated by the fact that Tamarix, a prolific invader, is abundant on regulated rivers and occupies extensive areas along the shores of impoundments. Efforts to replant natives within the drawdown zone surrounding Lake Mohave, a lower Colorado River impoundment bordering Nevada and Arizona, have not been successful. A greenhouse experiment was designed to examine the responses of cuttings of a native species, Salix gooddingii (Goodding willow), and the invasive species, Tarnarix romosissinia (salt cedar), to different hydroperiods comparable to those influencing Lake Mohave riparian plant communities. Higher survival and greater biomass under saturated but not flooded soil conditions demonstrated that both Salix and Tarnarix cuttings can prosper in soils within the exposed drawdown zone, provided that the shoots are not submerged. However, greater biomass of Tamarix under conditions favorable to the native Salix also indicates that Tainarix colonization will have to be controlled. This research substantiates that the physiological tolerances of native and invasive riparian plant species and the prevailing hydrodynamics of a waterway must be considered when attempting to restore native vegetation. Web of Science Tarnarix romosissinia; Salix gooddingii USA Nevada Lake Mojave Greenhouse lentic Invasion Hyp. Inherent Superiority Broad Tolerances primary 1752 Blaney, CS; Kotanen, PM 2002 Persistence in the seed bank: The effects of fungi and invertebrates on seeds of native and exotic plants journal ECOSCIENCE 9 4 509 517 Fungal pathogens and invertebrate seed predators both may limit the establishment of persistent seed banks. Exotic plants may be less subject to attack by these natural enemies than are native species; if so, this may provide exotics with an important advantage by reducing seed mortality and enhancing the persistence of colonizing populations. We investigated this idea with a field experiment in which we used fungicides and screening to protect seeds of 39 native and exotic old field plants. The recovery of germinable seeds was improved by fungicide additions, but not by the exclusion of macroinvertebrates. The effects of fungicide varied among species and sampling dates, but the recovery of natives was not consistently improved more than the recovery of exotics. These results suggest that soil fungi have important impacts on the seed banks of many species, but that exotics are not consistently more resistant than natives to attacks by either fungal pathogens or invertebrates. Consequently, it is unlikely that the majority of invaders benefit from reduced pest loads at the seed bank stage. Web of Science Many Canada Ontario Field - Experimental terrestrial Old Field Invasion Hyp. Enemy Release primary 1754 Sexton, JP; McKay, JK; Sala, A 2002 Plasticity and genetic diversity may allow saltcedar to invade cold climates in North America journal ECOLOGICAL APPLICATIONS 12 6 1652 1660 Two major mechanisms have been proposed to explain the ability of introduced populations to colonize over large habitat gradients, despite significant population bottlenecks during introduction: (1) Broad environmental tolerance-successful invaders possess life history traits that confer superior colonizing ability and/or phenotypic plasticity, allowing acclimation to a wide range of habitats. (2) Local adaptation-successful invaders rapidly adapt to local selective pressures. However, even with bottlenecks, many introduced species exhibit surprisingly high levels of genetic variation and thus the potential for evolutionary increases in invasive traits and plasticity. Here we assess the invasive potential of Tamarix ramosissima, by examining the degree of genetic differentiation within and among populations from the latitudinal extremes of its introduced range. Using growth chamber experiments we examined ecologically important variation in seedlings, both in trait means and their reaction norms across temperature environments. Although we found no genetic variation for gas exchange traits, within or among populations, we did find significant genetic variation for growth traits, both in the trait means and in the degree of plasticity in these traits. Northern ecotypes invested more in roots relative to southern ecotypes but only under low temperatures. Both ecotypes increased shoot investment in warm temperatures. Increased root investment in cold temperatures by northern ecotypes may increase their first winter survival. Genetic differences in seedling root investment may contribute to the ability of this species to successfully tolerate and invade a broader latitudinal range. Our data support a model in which both plasticity and adaptive evolution can contribute to the invasive potential of introduced species. Web of Science Tamarix ramosissima USA Arizona; Montana Gila River; Yellowstone River Lab terrestrial Riparian Invasion Hyp. Inherent Superiority;Plasticity Broad Tolerances primary 1757 Bellingham, PJ; Coomes, DA 2003 Grazing and community structure as determinants of invasion success by Scotch broom in a New Zealand montane shrubland journal DIVERSITY AND DISTRIBUTIONS 9 1 19 28 Scotch broom (Cytisus scoparius (L.) Link; Fabaceae) is a problematic invasive plant in many countries, and while attention has been paid to traits that make it a successful invader, there has been less focus on the properties of ecosystems that it invades. We conducted an experiment in a New Zealand montane shrubland with tussock grasses that has been invaded by Scotch broom to determine features that rendered it susceptible to invasion. We planted broom seedlings into the shrubland (control) and into three treatments: (1) resident shrubs removed, (2) tussocks removed and (3) shrubs and tussocks removed. We measured broom seedling mortality and growth over two growing seasons. The site was grazed by sheep in the first season, and scarcely grazed in the second, wetter season. Survivorship across all treatments after 19 months was 42%, and was lowest where shrubs were retained but tussocks removed. Broom seedlings grew taller and had greater leaf areas in treatments that retained shrubs. Neighbouring (within 49 cm) shrubs had no effects on survivorship or growth of broom seedlings. Neighbouring tussocks increased survivorship of broom seedlings but depressed their growth. Grazing by sheep was the most important determinant of survivorship and growth of broom seedlings, and effects were uniform regardless of experimental treatments. Initial high mortality of seedlings (48% in the first 3 months) was due to grazing, and height growth was often negative during periods of grazing. In the second growing season when the site was less grazed and there was greater rainfall, there was a rapid increase in height across all treatments. Continued grazing of the site by sheep is likely to be the chief means of retarding the invasion. Web of Science Cytisus scoparius New Zealand Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Community Species Richness primary 1759 Bashkin, M; Stohlgren, TJ; Otsuki, Y; Lee, M; Evangelista, P; Belnap, J 2003 Soil characteristics and plant exotic species invasions in the Grand Staircase - Escalante National Monument, Utah, USA journal APPLIED SOIL ECOLOGY 22 1 67 77 The Grand Staircase-Escalante National Monument (GSENM) contains a rich diversity of native plant communities. However, many exotic plant species have become established, potentially threatening native plant diversity. We sought to quantify patterns of native and exotic plant species and cryptobiotic crusts (mats of lichens, algae, and mosses on the soil surface), and to examine soil characteristics that may indicate or predict exotic species establishment and success. We established 97 modified-Whittaker vegetation plots in I I vegetation types over a 29,000 ha area in the Monument. Canonical correspondence analysis (CCA) and multiple linear regressions were used to quantify relationships between soil characteristics and associated native and exotic plant species richness and cover. CCA showed that exotic species richness was significantly (P < 0.05) associated with soil P (r = 0.84), percentage bare ground (r = 0.71), and elevation (r = 0.67). Soil characteristics alone were able to predict 41 and 46% of the variation in exotic species richness and cover, respectively. In general, exotic species invasions tend to occur in fertile soils relatively high in C, N and P. These areas are represented by rare mesic high-elevation habitats that are rich in native plant diversity. This suggests that management should focus on the protection of the rare but important vegetation types with fertile soils. Published by Elsevier Science B.V. Web of Science Many USA Utah Escalante Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Community Species Richness primary 1761 Stachowicz, JJ; Terwin, JR; Whitlatch, RB; Osman, RW 2002 Linking climate change and biological invasions: Ocean warming facilitates nonindigenous species invasions journal PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 99 24 15497 15500 The spread of exotic species and climate change are among the most serious global environmental threats. Each independently causes considerable ecological damage, yet few data are available to assess whether changing climate might facilitate invasions by favoring introduced over native species. Here, we compare our long-term record of weekly sessile marine invertebrate recruitment with interannual variation in water temperature to assess the likely effect of climate change on the success and spread of introduced species. For the three most abundant introduced species of ascidian (sea squirt), the timing of the initiation of recruitment was strongly negatively correlated with winter water temperature, indicating that invaders arrived earlier in the season in years with warmer winters. Total recruitment of introduced species during the following summer also was positively correlated with winter water temperature. In contrast, the magnitude of native ascidian recruitment was negatively correlated with winter temperature (more recruitment in colder years) and the timing of native recruitment was unaffected. In manipulative laboratory experiments, two introduced compound ascidians grew faster than a native species, but only at temperatures near the maximum observed in summer. These data suggest that the greatest effects of climate change on biotic communities may be due to changing maximum and minimum temperatures rather than annual means. By giving introduced species an earlier start, and increasing the magnitude of their growth and recruitment relative to natives, global warming may facilitate a shift to dominance by nonnative species, accelerating the homogenization of the global biota. Web of Science Ascidiella aspersa; Botrylloides violaceous; Diplosoma listerianum USA Connecticut Field - Observational marine Intertidal/Near Shore Invasion Hyp. Inherent Superiority Superior Competitor filter 1765 Barrat-Segretain, MH; Elger, A; Sagnes, P; Puijalon, S 2002 Comparison of three life-history traits of invasive Elodea canadensis Michx. and Elodea nuttallii (Planch.) H. St. John journal AQUATIC BOTANY 74 4 299 313 Three life-history traits, regeneration and colonisation of vegetative plant fragments, resistance to water current and palatability to a generalist herbivore were compared in two invasive macrophyte species, Elodea canadensis Michx. and Elodea nuttallii (Planch.) H. St. John. Few differences in traits were found between these species. Both species showed similar resistance to water current, whilst fragment regeneration and colonisation and palatability were only slightly higher in E. nuttaffli than in E. canadensis. These small differences do not explain the displacement of E. canadensis by E. nuttallii as observed in the field. (C) 2002 Elsevier Science B.V. All rights reserved. Web of Science Elodea canadensis; Elodea nuttallii France Rhône River Greenhouse lotic Invasion Hyp. Inherent Superiority Effective Disperser;Clonal Reproduction primary 1767 Moody, ML; Les, DH 2002 Evidence of hybridity in invasive watermilfoil (Myriophyllum) populations journal PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 99 23 14867 14871 Invasions of nonindigenous species have caused ecological devastation to natural communities worldwide, yet the biological bases for invasiveness remain poorly understood. Our studies of invasive watermilfoil (Myriophyllum) populations revealed widespread polymorphisms in biparentally inherited nuclear ribosomal DNA sequences, which were not detected in populations of native North American species. Subclones of the polymorphic regions revealed the occurrence of distinct sequences matching those acquired from both nonindigenous and native North American species. Molecular data demonstrate clearly that invasive watermilfoil populations in North America have resulted from hybridization between nonindigenous and native species. These observations suggest that invasiveness in these aggressive aquatic weeds may be linked to heterosis maintained by vegetative propagation. Web of Science Myriophyllum aquaticum USA Field - Observational lotic Invasion Hyp. Inherent Superiority;Hybridization Clonal Reproduction primary 1769 Seghieri, J; Simier, M 2002 Variations in phenology of a residual invasive shrub species in Sahelian fallow savannas, south-west Niger journal JOURNAL OF TROPICAL ECOLOGY 18 0 897 912 The aim of this work was to analyse the phenological variation of a residual invasive semi-evergreen shrub in Sahelian fallows in Niger. This species, Guiera senegalensis (Combretaccae), has benefited from the elimination of other species thanks to its high resistance to the increasing cutting pressure for cultivation. We sought to identify traits of its life cycle that could contribute to its persistence and widespread dominance under such a disturbance regime. Leafing, flowering and fruiting were monitored on seven fallows differing in topographic location, age, shrub density and degradation state, during two rainy seasons and one dry season. Phenological spectra showed similar timing of the three phenophases of the seven populations. Differences were observed mainly in magnitude of the phases. However, there were both a high intra-fallow variability (64.6% of the whole variability) and a statistically significant inter-fallow variability, despite only 35.4% of the total variability being due to differences between fallows. A statistical classification of the fallows was proposed based on shrub phenological course over the two cycles monitored. This classification corresponds to a gradient of life-cycle achievement primarily linked to the topographic situation of the stations, and then to a combination of other factors. The flexibility of the phenology at the individual, population and metapopulation scales, inherent to its specific semi-evergreenness property, appeared as an essential phenological attribute contributing to successful widespread persistence of G. senegalensis in the study area. Web of Science Guiera senegalensis Niger Sahelian fallow Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Plasticity primary 1771 Cappuccino, N; Mackay, R; Eisner, C 2002 Spread of the invasive alien vine Vincetoxicum rossicum: Tradeoffs between seed dispersability and seed quality journal AMERICAN MIDLAND NATURALIST 148 2 263 270 The relationship between seed weight, dispersal ability and seed *quality* was tested for the seeds of pale swallow-wort Vincetoxicum rossicum (Kleo.) Barb., an invasive alien vine. In a field release, small seeds traveled significantly farther than large seeds. In one of two greenhouse experiments, large seeds were significantly more likely to germinate than small seeds. Seed weight also had a significant effect on seedling size at the time of harvest, but only when the seeds were grown in competition with a mixture of grasses. Seeds containing more than one embryo produced greater total seedling weight in the absence of competition, but polyembryony was not advantageous when seedlings were grown with grasses. We argue that if long-distance dispersers are less likely to germinate or survive, measured seed dispersal curves could lead to overestimation of the rate of spread of invasive plants. Web of Science Vincetoxicum rossicum Canada Ontario Greenhouse terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Effective Disperser primary 1773 Morris, LL; Walck, JL; Hidayati, SN 2002 Growth and reproduction of the invasive Ligustrum sinense and native Forestiera ligustrina (Oleaceae): Implications for the invasion and persistence of a nonnative shrub journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 163 6 1001 1010 Ligustrum sinense (Oleaceae) is an invasive shrub in the southeastern United States that was introduced from China. In middle Tennessee, the species grows with Forestiera ligustrina (Oleaceae), a shrub native to the southeastern United States, in the redcedar and/or hardwood forests surrounding cedar (limestone) glades. Here we compare the growth and reproduction of the two species and identify attributes that might influence the invasiveness and persistence of L. sinense. Plants of both species were sampled along the woodland edges of cedar glades and in the (primarily) redcedar forest at Stones River National Battlefield, Rutherford County, Tennessee, between March 2000 and February 2001. MANOVAs (Pless than or equal to0.05) indicated significant differences between species and habitats for several of the 23 traits measured in the study. Regardless of the habitat, L. sinense had a more treelike growth form-higher leaf area ratio (leafiness), leaf mass ratio (investment in leaf biomass), stem elongation rate, and number of fruits per ramet- and a lower percentage of insect-damaged leaves and leaf abscission rate than F. ligustrina. Height and leaf areas of L. sinense plants growing in the woods were greater than those of L. sinense plants growing along the glade and greater than those of F. ligustrina plants growing in both habitats. Branch architecture did not differ appreciably between the species. Ligustrum sinense appears to possess a competitive advantage over F. ligustrina because of its greater ability to spatially and temporally capture light, a phenomenon that may lead to higher photosynthetic capacity and resource-use efficiency, and because of the higher fruit production we observed. Web of Science Ligustrum sinense USA Tennessee 35.8764 -86.4328 Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Superior Competitor primary 1774 Charbonnel, N; Angers, B; Rasatavonjizay, R; Bremond, P; Debain, C; Jarne, P 2002 The influence of mating system, demography, parasites and colonization on the population structure of Biomphalaria pfeifferi in Madagascar journal MOLECULAR ECOLOGY 11 11 2213 2228 Current evolutionary forces and historical processes interact to shape the distribution of neutral genetic variability within and among populations. Focusing on the genetics of recently introduced organisms offers a good opportunity to understand the relative importance of these factors. This study concerns variation at 8 polymorphic microsatellite loci in 30 populations of Biomphalaria pfeifferi. The sampling area spans most of the species' range in Madagascar where it was probably introduced recently. Extremely low variation was found within all populations studied, which may partly result from high selfing rates. However, this cannot account for the variance of variation across populations, which is better explained by habitat openness (that reflects environmental stochasticity), the prevalence of the parasitic trematode Schistosoma mansoni and historical demography (colonization and subsequent bottlenecks). Large global differentiation was also observed, suggesting that current gene flow among populations is limited to small distances, within watersheds and to few individuals. Our data set also allowed us to test several hypotheses regarding colonization, based on bottleneck and admixture tests. The observed pattern requires at least two independent introductions from slightly differentiated genetic sources in the western part of Madagascar. Another introduction, from a very different genetic origin, should also be postulated to explain the genetic composition of eastern populations. That this introduction occurred recently suggests that the colonization of Madagascar by B. pfeifferi is an ongoing process. Web of Science Biomphalaria pfeifferi Madagascar Andilamena 17.1333 48.55 Field - Observational;Lab lentic Fundamentals herbivore 1775 Sobrino, E; Sanz-Elorza, M; Dana, ED; Gonzalez-Moreno, A 2002 Invasibility of a coastal strip in NE Spain by alien plants journal JOURNAL OF VEGETATION SCIENCE 13 4 585 594 The alien plant species and the ecological factors that facilitate their invasion to a coastal strip in the Baix Camp region (Tarragona, NE Spain) were studied. A detailed inventory of the area showed that 20% of the plant species, most of them from the American Continent, were aliens, many of which were strongly invasive. At the habitat level, the relationships between the invasive behaviour and a number of autecological, ecological and habitat variables were analysed by means of logistic analyses. In the best model five variables were related to alien plant invasions: climatic affinity, disturbance of the invaded habitat, route of introduction, soil moisture during summer, and life form. To elucidate the environmental factors that could be responsible for alien plant invasions at a regional scale, the number of alien taxa and the environmental features at 13 localities of the western Mediterranean area were analysed. The warm lowlands, subjected to low annual rainfall and high population density, exhibited the greatest reception capacity for alien plants. It is concluded that various specific environmental features - high mean temperatures, the abundance of riparian systems, the existence of biotopes with favourable water balance which harbour a great richness of alien species and the high human pressure to which the enclave is subjected, combined with the ecological requirements of the alien species and certain species attributes (biotype) can interact at different scales and have caused the over-representation of alien plants. Web of Science Many Spain Tarragona Field - Observational terrestrial Riparian Invasion Hyp. Inherent Superiority;Disturbance primary 1776 McKinney, ML 2002 Influence of settlement time, human population, park shape and age, visitation and roads on the number of alien plant species in protected areas in the USA journal DIVERSITY AND DISTRIBUTIONS 8 6 311 318 I examined a data set of 77 protected areas in the USA (including national and state parks) to determine which of the following variables most strongly influence alien plant species richness: park area, climate (temperature and precipitation), native species richness, visitation rate, local human population size, total road length, park shape and duration of European settlement. Many of these predictor variables are intercorrelated, so I used multiple regression to help separate their effects. In support of previous studies, native species richness was the best single predictor of alien species richness, probably because it was a good estimator of both park area and habitat diversity available for establishment of alien species. Other significant predictors of alien species richness were years of occupation of the area by European settlers and the human population size of adjacent counties. Climate, visitation rate, road length and park shape did not influence alien species richness. The proportion of alien species (alien richness/native richness) is inversely related to park area, in agreement with a previous study. By identifying which variables are most important in determining alien species richness, such findings suggest ways to reduce alien species establishment. Web of Science Many USA National Parks Statistical/Meta-analysis terrestrial Invasion Hyp. Community Species Richness;Disturbance primary 1777 Woo, I; Zedler, JB 2002 Can nutrients alone shift a sedge meadow towards dominance by the invasive Typha x glauca? journal WETLANDS 22 3 509 521 Where wetlands receive urban runoff, Typha spp. and other invasive plants often displace the native vegetation. We tested the ability of nutrients (N and P) to increase vegetative growth of T. X glauca (a hybrid of T. latifolia and T. angustifolia). In the greenhouse, 17 treatments revealed that T. X glauca required both N and P for growth, and total leaf length was most stimulated where a higher proportion of P was added (7N:1P vs. 14N:1P, with N constant and P changed), regardless of concentration (the High treatment was 4X the Low treatment). In Gardner Marsh (Madison, Wisconsin, USA), we set up 28 plots (I X 6 m) that bisected the boundary between sedge meadow (graminoids) and T. X glauca, and we added a common lawn fertilizer (9N: 1P:4K) at high (62.5 g/m(2)), medium (31.3 g/m(2)), low (15.6 g/m(2)), and control (0 g/m(2)) rates on five dates, with n=7 plots/treatment. After one growing season, fertilizer addition increased T. X glauca ramet density, height, and biomass, especially where the sedge meadow graminoids were initially dominant. Aboveground biomass of T. X glauca in the high nutrient addition treatment (1029 +/- 256.1 g/m(2)) was more than double that for control plots (431 +/- 80.52 g/m(2)) overall, with the greatest percent increase in sedge meadow subplots. In contrast, native graminoids (mostly Carex spp.) did not respond to treatment, either in biomass or percent cover. Typha X glauca allocated nutrients to both growth and storage, as indicated by higher N and P concentrations in leaves, shoot bases, and rhizomes in plots with high nutrient addition. Because fertilizing the marsh enhanced the shoot growth of T. X glauca but not native graminoids, and because the 7N:1P treatment stimulated growth in the greenhouse, we suggest that wetland managers focus on reducing P inflows to urban wetlands. Fertilizer additions below those recommended by the manufacturer for new lawns (5X that of our highest treatment) should be more economical and have fewer impacts on receiving wetlands. Web of Science Typha x glauca USA Wisconsin Gardner Marsh 43.1 -89.7 Field - Experimental;Greenhouse estuarine Wetland Invasion Hyp. Empty Niche primary 1778 Sheppard, AW; Hodge, P; Paynter, Q; Rees, M 2002 Factors affecting invasion and persistence of broom Cytisus scoparius in Australia journal JOURNAL OF APPLIED ECOLOGY 39 5 721 734 1. The effective management of invasive plants requires an understanding of their invasiveness in contrasting environments. The effects of disturbance on recruitment of broom Cytisus scoparius, a European shrub invading parts of Australasia, was assessed in a 7-year experiment carried out in two countries, respectively, in its native and exotic ranges. This paper presents the results for Australia and their implications for the biological control of this weed. 2. Disturbance treatments involved removal (cut or cut plus cultivation) and grazing effects on broom seed banks and recruitment, in mature and immature stands and in three habitats, ranging from improved, largely exotic pasture to unimproved native grassland. 3. The time between recruitment and flowering varied between 5 and 7 years depending on habitat, the slowest being in native unimproved grassland. In cultivated plots, regeneration was faster in immature compared with mature broom stands. 4. Following broom removal, whether the ground was cultivated or not had little effect on the speed of regeneration, indicating weak suppression from the ground flora in uncultivated plots. In contrast, grazing tended to increase the rate of regeneration. 5. The timing of seedling establishment had little effect on survival to reproduction, in marked contrast to European populations. The overall rates of seedling mortality were greater in Australia compared with Europe. 6. A simulation model, parameterized from the field data, was used to explore the likely impact of biological control from pre-dispersal seed predation. 7. The simulation studies demonstrated large habitat-specific differences in seed rain requirement for broom persistence and the potential impact of seed predators. Seed rain requirements were fivefold less in improved exotic pasture vs. native grassland. Seed loss of 62% was theoretically sufficient to suppress broom in native grassland, whereas > 97% was required in exotic pasture. 8. This study suggests that successful broom control in Australia is likely to be site dependent, because while broom seed has greater opportunities for recruitment in Australia than in Europe, immature plant mortality can be very high, particularly in native grassland. Web of Science Cytisus scoparius Australia New South Wales -35.8;-35.2833 149.6667;149.8 Field - Experimental terrestrial Grassland Invasion Hyp. Disturbance primary 1780 Bastlova, D; Kvet, J 2002 Differences in dry weight partitioning and flowering phenology between native and non-native plants of purple loosestrife (Lythrum salicaria L.) journal FLORA 197 5 332 340 Invasive plants of Lythrum salicaria (purple loosestrife). a species native to Eurasia. exhibit different ecological strategies to indigenous plants by growing more vigorously. The hypothesis is tested that the more vigorous growth of invasive L. salicaria plants is a result of differences in dry weight partitioning between native and non-native plants. Plants of three native Central European and three non-native North American populations of L. salicaria were exposed to the same experimental conditions for 4 months. Size and growth related plant characteristics were measured in ten-day internals in both native and non-native plants. From these characteristics, relative growth rate, reproductive effort and leaf weight ratio were calculated. The dependence of net photosynthesis on photon flux density in both native and non-native plants of L. salicaria was measured. plants of the non-native populations grew taller than the native plants and produced, on average, twice as much dry weight of stems, leaves and primary lateral branches as plants of native populations but no significant differences in net photosynthesis time courses was found between the native and non-native plants. The native and non-native plant,, exhibited different dry weight partitioning patterns, connected with differences in flowering phenology. These differences probably affect competitive ability of the native and non-native plants and are also responsible for more vigorous growth of the non-native plants. Web of Science Lythrum salicaria USA Wisconsin Madison Greenhouse estuarine Wetland Invasion Hyp. Inherent Superiority Superior Competitor;Rapid Growth primary 1783 Kolb, A; Alpert, P; Enters, D; Holzapfel, C 2002 Patterns of invasion within a grassland community journal JOURNAL OF ECOLOGY 90 5 871 881 1 Relatively few studies have looked for patterns of invasion by non-native species within communities. We tested the hypotheses that: (i) some types of microhabitats within a community are more invasible than others; (ii) microhabitat types that differ in invasion also differ in resource availability; and (iii) invasibility is mediated by effects of these resources on competition between native and non-native species. 2 To test the first two hypotheses, we measured plant cover and soils in a coastal grassland in northern California. Consistent with these hypotheses, cover of non-native plants was consistently high where nitrogen-fixing shrubs had recently grown, in the bottoms and sides of gullies and on deep soils, and these microhabitats tended to have relatively high nitrogen or water availability. 3 Cover and number of native species tended to be lower where cover of non-native species was higher, indicating that non-native species as a group negatively affected native species. However, the number of non-native species also tended to be lower where the total cover of non-natives was higher. This suggests that a few non-native species excluded natives and other non-natives alike. 4 To test the third hypothesis, we grew a common non-native, the annual grass Lolium multiflorum , and a common native, the perennial grass Hordeum brachyantherum , at different levels of water and nitrogen. The relative competitive ability of the native was higher at lower nitrogen availability but not at lower water availability. When 10-week-old native plants were grown with non-native seedlings and nitrogen was relatively low, the native out-competed the non-native. However, the non-native out-competed the native at all resource levels when species were both grown as seedlings. Competition between native and non-native grasses in this system may thus help prevent invasion by non-natives in microhabitats where nitrogen availability is low, but invasion may be relatively irreversible. Web of Science Lolium multiflorum USA California Field - Experimental terrestrial Grassland Invasion Hyp. Inherent Superiority Superior Competitor primary 1784 Arenas, F; Viejo, RM; Fernandez, C 2002 Density-dependent regulation in an invasive seaweed: responses at plant and modular levels journal JOURNAL OF ECOLOGY 90 5 820 829 1 The effects of density on the vital rates, growth form and population size structure of the invasive seaweed Sargassum muticum (Yendo) Fensholt were evaluated experimentally. 2 The initial difference in plant number between the highest and the lowest density (200 and 6400 plants m(-2) ) was considerably reduced by the end of the experiment. Surprisingly, this was mostly due to numbers increasing at lower densities, probably because microscopic forms were not removed during the experimental thinning. 3 The allometric length-dry mass relationship fitted a simple linear model on log-log scale for both the highest and the lowest densities, but had different slopes. At higher densities plants became taller and thinner as a consequence of variations in the production and growth of modules. 4 Mean size (dry mass) and the development of size hierarchies of plants were affected by both the addition of further (microscopic) recruits and asymmetrical competition among plants. Plant length distributions were also influenced by changes in the growth form of plants. The length hierarchies of main branches also suggested the presence of asymmetrical competition at this modular level. 5 Density influenced both mean size and morphology of the plants and thus induced changes in reproduction. The negative effect of density on individual plant size reduced the percentage of fertile plants and possibly their annual reproductive allocation, but these effects may be attenuated by morphological responses. 6 The responses of S. muticum to crowding are closely linked to its ability to colonize bare space. The massive reproductive output and very limited dispersal range account for local and dense recruitment patterns. Our results suggest that the responses of S. muticum to crowding allow the establishment of dense populations with high persistence and resistance to colonization by other species. Web of Science Sargassum muticum Spain 43.6114 5.7747 Field - Observational marine Intertidal/Near Shore Invasion Hyp. Inherent Superiority Rapid Growth;High Reprod. Output primary 1789 Wilsey, BJ; Polley, HW 2002 Reductions in grassland species evenness increase dicot seedling invasion and spittle bug infestation journal ECOLOGY LETTERS 5 5 676 684 Previous experiments that tested whether diverse plant communities have lower invasibility have all varied species richness. We experimentally varied evenness of four grassland species (three grasses and one forb) by planting a field experiment in Texas, and monitored the number of unplanted dicot and monocot species that invaded plots for two growing seasons. By varying evenness, we eliminated any sampling effect in our diversity treatment, because all plots contained the same plant species. Experimentally reducing evenness led to a greater number of dicot invaders, which emerged in plots throughout the growing season, but had less of an effect on monocot invaders, which emerged in flushes when experimental plants were semi-dormant. Frequency of Solidago canadensis (altissima ) stems with spittle bugs significantly increased with reductions in evenness during the first year, apparently because the greater number of Solidago stems in high evenness plots diluted the spittle-bug effect. These results support the view that higher diversity plant communities are more resistant to dicot invaders and insect herbivores. Web of Science Many United States Texas 31.054754 -97.347965 Field - Experimental terrestrial Grassland Invasion Hyp. Community Species Richness;Other primary 1794 Dick, JTA; Platvoet, D; Kelly, DW 2002 Predatory impact of the freshwater invader Dikerogammarus villosus (Crustacea : Amphipoda) journal CANADIAN JOURNAL OF FISHERIES AND AQUATIC SCIENCES 59 6 1078 1084 To assess the increasing threats to aquatic ecosystems from invasive species, we need to elucidate the mechanisms of impacts of current and predicted future invaders. Dikerogammarus villosus, a Ponto-Caspian amphipod crustacean, is invading throughout Europe and predicted to invade the North American Great Lakes. European field studies show that populations of macroinvertebrates decline after D. villosus invasion. The mechanism of such impacts has not been addressed empirically; however, D. villosus is known to prey upon and replace other amphipods. Therefore, in this study, we used microcosm and mesocosm laboratory experiments, with both single and mixed prey species scenarios, to assess any predatory impact of D. villosus on a range of macro invertebrate taxa, trophic groups, and body sizes. Dikerogammarus villosus predatory behaviour included shredding of prey and infliction of *bite* injuries on multiple victims. Dikerogammarus villosus killed significantly greater numbers of macroinvertebrates than did the native Gammarus duebeni, which is currently being replaced by D. villosus. This invader thus appears to impact on freshwater ecosystems through its exceptional predatory capabilities. We predict that future invasions by D. villosus will have serious direct and indirect effects on freshwaters, with its invasion facilitated in a larger *invasional meltdown* in regions like the North American Great Lakes. Web of Science Dikerogammarus villosus Lab lentic Benthic Invasion Hyp. Inherent Superiority Superior Competitor predator 1795 Gibson, DJ; Spyreas, G; Benedict, J 2002 Life history of Microstegium vimineum (Poaceae), an invasive grass in southern Illinois journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 129 3 207 219 The ecological life history of Microstegium vimineum, an invasive grass, was compared among four populations throughout southern Illinois. A detailed investigation of seed production was conducted at one of these populations in a secondary oak-hickory forest in Dixon Springs State Park, Illinois. In this park, M. vimineum occurs as a central, main population with several disjunct subpopulations. Size of flowering and non-flowering individuals was determined as the plants set seed. Seed dispersal was assessed using seed traps. A severe late summer drought impacted the Dixon Springs population in 1999 and few plants flowered. Plants that did flower were significantly larger than those not flowering and were limited to one small area at the edge of the core population. At Dixon Springs, the germinable seed bank was estimated from soil samples collected in Fall 1999 before flowering, and in the subsequent spring. Seedlings emerged from soils placed in a greenhouse from samples collected in the spring. No seedlings emerged from samples collected in the fall. Germinable seed had a 10 times higher density in samples collected near the soil surface than from samples collected at 5-10 cm depth. Seed dispersal occurred within the main population only. Despite the lack of seed dispersal in 1999, seedlings emerged from six of seven subpopulations in spring 2000, with the highest densities where plants had flowered in 1999. These data indicate the presence of a persistent soil seed bank for M. vimineum. Even following summer drought and discounting spring seedling emergence, the size of the seed bank increased by similar to25% in 1999. Reestablishment of the Dixon Springs population following the 1999 drought was vigorous, but the location of the largest, most fecund plants in 2000 was not the same as in 1999. In 2000, end of season survivorship of M. vimineum among all populations was 40-50%, with 90% of surviving individuals flowering. Performance of M. vimineum varied significantly within and among populations and was related to soil texture and chemistry, and overhead canopy cover. The findings of our study reflect the invasive nature of this plant. A sufficiently large seed bank and a highly plastic morphological response to local microhabitat conditions likely ensures its persistence in invaded sites. Web of Science Microstegium vimineum USA Illinois Dixon Springs State Park; Bell Smith Springs; Lusk Creek; Cove Hollow 37.3833; 37.6167; 38.0667; 37.6167 -88.6667; -88.6667; -89.4667; -88.8 Field - Observational;Greenhouse terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority;Plasticity High Reprod. Output primary 1797 Renne, IJ; Barrow, WC; Randall, LAJ; Bridges, WC 2002 Generalized avian dispersal syndrome contributes to Chinese tallow tree (Sapium sebiferum, Euphorbiaceae) invasiveness journal DIVERSITY AND DISTRIBUTIONS 8 5 285 295 Plants possessing generalized dispersal syndromes are likely to be more invasive than those relying on specialist dispersal agents. To address this issue on a local and regional scale, avian seed dispersal of the invasive alien Chinese tallow tree (Sapium sebiferum (L.) Roxb.) was assessed in forests and spoil areas of South Carolina and along forest edges in Louisiana during the 1997-99 fruiting seasons. Tallow trees in these floristically distinct habitats had a few common and many casual visitors, and considerable species overlap among habitats was found. However, bird species differed in the importance of dispersing and dropping seeds among habitats. Important dispersal agents common to forests and spoil areas of South Carolina included Northern Flicker, American Robin and Red-winged Blackbird, whereas Red-bellied Woodpecker and European Starling were important in the former and latter habitat, respectively. In Louisiana, Red-bellied Woodpecker, American Robin, Northern Cardinal and Eastern Bluebird dispersed many seeds. Nearly all species foraging on seeds were winter residents. Estimated numbers of seeds dispersed and dropped were higher in spoil areas of South Carolina than in Louisiana because of higher numbers of individuals per visit, higher seed consumption and seed dropping rates, and longer foraging durations. Within South Carolina, more seeds were dispersed and dropped in spoil areas than in forests because of higher numbers of birds per visit. These findings show that among habitats, tallow tree attracts diverse but variable coteries of dispersal agents that are qualitatively similar in seed usage patterns. We suggest that its generalized dispersal syndrome contributes to effective seed dispersal by many bird species throughout its range. Effects of differential avian use among locales may include changes in local bird communities, and differing tallow tree demographics and invasion patterns. Web of Science Sapium sebiferum USA South Carolina; Louisiana Field - Observational terrestrial Deciduous Forest Invasion Hyp. Mutualism Facilitation primary 1799 Sax, DF 2002 Native and naturalized plant diversity are positively correlated in scrub communities of California and Chile journal DIVERSITY AND DISTRIBUTIONS 8 4 193 210 An emerging body of literature suggests that the richness of native and naturalized plant species are often positively correlated. It is unclear, however, whether this relationship is robust across spatial scales, and how a disturbance regime may affect it. Here, I examine the relationships of both richness and abundance between native and naturalized species of plants in two mediterranean scrub communities: coastal sage scrub (CSS) in California and xeric-sloped matorral (XSM) in Chile. In each vegetation type I surveyed multiple sites, where I identified vascular plant species and estimated their relative cover. Herbaceous species richness was higher in XSM, while cover of woody species was higher in CSS, where woody species have a strong impact upon herbaceous species. As there were few naturalized species with a woody growth form, the analyses performed here relate primarily to herbaceous species. Relationships between the herbaceous cover of native and naturalized species were not significant in CSS, but were nearly significant in XSM. The herbaceous species richness of native and naturalized plants were not significantly correlated on sites that had burned less than one year prior to sampling in CSS, and too few sites were available to examine this relationship in XSM. In post 1-year burn sites, however, herbaceous richness of native and naturalized species were positively correlated in both CSS and XSM. This relationship occurred at all spatial scales, from 400 m(2) to 1 m(2) plots. The consistency of this relationship in this study, together with its reported occurrence in the literature, suggests that this relationship may be general. Finally, the residuals from the correlations between native and naturalized species richness and cover, when plotted against site age (i.e. time since the last fire), show that richness and cover of naturalized species are strongly favoured on recently burned sites in XSM; this suggests that herbaceous species native to Chile are relatively poorly adapted to fire. Web of Science Many United States; Chile California 34.05;-33.0167 -118.2333;-71.6333 Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Community Species Richness primary 1802 Gaskin, JF; Schaal, BA 2002 Hybrid Tamarix widespread in US invasion and undetected in native Asian range journal PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 99 17 11256 11259 Biological invasions are drastically altering natural habitats and threatening biodiversity on both local and global levels. In one of the United States' worst invasions, Eurasian Tamarix plant species have spread rapidly to dominate over 600,000 riparian and wetland hectares. The largest Tamarix invasion consists of Tamarix chinensis and Tamarix ramosissima, two morphologically similar species. To clarify the identity, origins, and population structuring of this invasion, we analyzed DNA sequence data from an intron of a nuclear gene, phosphoenolpyruvate carboxylase (PepC). This intron proved to be highly variable at the population level, and the 269 native and invasive specimens yielded 58 haplotypes, from which we constructed a gene genealogy. Only four of these haplotypes were common to both the U.S. and Eurasia. Surprisingly, we found that the most common plant in this U.S. invasion is a hybrid combination of two species-specific genotypes that were geographically isolated in their native Eurasian range. Less extensive hybrids exist in the invasion, involving combinations of T. ramosissima and T. chinensis with Tamarix parviflora and Tamarix gallica. The presence of potentially novel hybrids in the U.S. illustrates how importation of exotics can alter population structures of species and contribute to invasions. Web of Science Tamarix chinensis; Tamarix ramosissima United States; Iran; Republic of Georgia; Turkmenistan; Kazakstan Lab terrestrial Invasion Hyp. Hybridization primary 1803 Blank, RR; Qualls, RG; Young, JA 2002 Lepidium latifolium: plant nutrient competition-soil interactions journal BIOLOGY AND FERTILITY OF SOILS 35 6 458 464 Exotic weeds are invading rangelands of the western United States at unprecedented rates. Understanding plant-soil relationships and competitive interactions of invasive weeds is crucial in long-term control strategies. In a greenhouse experiment, we investigated the influence of soil nutrient depletion on plant growth and plant competition between the exotic invasive weeds, Lepidium latifolium (invading wetlands) and Bromus tectorum (invading a multitude of habitats). Plants were grown individually and in combination until L. latifolium flowered, then roots and aboveground mass were harvested. Soil in individual pots was homogenized, subsamples collected for nutrient analyses, and the soil was re-planted to the same species, grown, and harvested twice more for a total of three growth cycles. As nutrient supplying capacity of the soil declined through growth cycles, aboveground mass of L. latifolium decreased significantly (Pless than or equal to0.05) and growth potential of B. tectorum surpassed that of L. latifolium. Only bicarbonate-extractable soil ortho-P positively correlated with plant mass of L. latifolium. A separate experiment demonstrated that L. latifolium has a narrow window of soil water potentials for optimal growth; greatest growth at -20 kPa with significantly declining growth at saturation and -400 kPa. Our data suggest that L. latifolium primarily invades wetlands because the high soil water content reduces tortuosity and allows efficient transport of nutrients to this sparsely rooted species. When soil moisture and/or the nutrient supplying capacity of the soil declines, plants with greater root density can out-compete L. latifolium. Monocultural stands of L. latifolium may be self-limiting in time as available nutrients, particularly P, are biocycled to drier upper soil layers. Web of Science Lepidium latifolium; Bromus tectorum United States Nevada University of Nevada, Reno, Experiment Statio 39.605688 -119.816895 Greenhouse terrestrial Invasion Hyp. Inherent Superiority;Fluctuating Resources Superior Competitor primary 1804 Brown, BJ; Mitchell, RJ; Graham, SA 2002 Competition for pollination between an invasive species (purple loosestrife) and a native congener journal ECOLOGY 83 8 2328 2336 Invasive species are frequently regarded as Superlative competitors that can vegetatively crowd Out natives, but little is known about whether invasives call compete for pollination services with native plants. We hypothesized that, when the showy invasive species Lythrum salicaria (purple loosestrife) was present, pollinator visitation and seed set would be reduced in a native congener, L. alatum (winged loosestrife). To test this hypothesis, we constructed mixed and monospecific plots of the two species. Over two years of study, we found that L. salicaria significantly reduced both pollinator visitation and seed set in L. alatum. Furthermore, pollinators moved frequently between the two plant species, which may cause heterospecific pollen transfer. Thus, reductions in both pollen quantity and pollen quality may reduce L. alatum seed set. If similar patterns occur in the field, invasive plants may be an even greater threat to natives than previously thought. Web of Science Lythrum salicaria United States Ohio Kent State University 41.211722 -81.334534 Field - Experimental terrestrial Wetland Impacts;Invasion Hyp. Mutualism Facilitation primary 1813 Vellend, M 2002 A pest and an invader: White-tailed deer (Odocoileus virginianus Zimm.) as a seed dispersal agent for honeysuckle shrubs (Lonicera L.) journal NATURAL AREAS JOURNAL 22 3 230 234 Predicting and managing the spread of invasive plant species require a Sound and detailed knowledge of dispersal mechanisms. I examined white-tailed deer (Odocoileus virginianus Zimm.) feces in Five mature forest stands in central New York, USA, and found seeds of alien invasive bush honeysuckles (Lonicera tatarica L., L. morrowii A. Gray, L. x bella Zabel) in feces from all five stands. Lonicera seeds were found in 66 of 72 pellet groups examined, and the overall mean number of seeds per pellet group was 62 +/- 19 SE; within-stand means ranged from 0.6 +/- 0.3 SE to 334 +/- 165 SE. Percent germination of seeds collected in feces from one site was 70%, compared to 81% for fresh-collected seeds, and Lonicera seedlings were observed growing out of feces in the field. Prior to this study, the only important dispersers recognized for invasive Lonicera spp. have been birds. Using data from the literature on the feeding, digestive, and movement behaviors of deer vs. birds, I show that white-tailed deer have tremendous potential for contributing to the spread of invasive honeysuckles and perhaps other plant species. Web of Science invasive bush honeysuckles (Lonicera tatarica L., L. morrowii A. Gray, L. x bella Zabel) Field - Observational terrestrial Invasion Hyp. Inherent Superiority Effective Disperser primary 1817 Forys, EA; Allen, CR 2002 Functional group change within and across scales following invasions and extinctions in the everglades ecosystem journal ECOSYSTEMS 5 4 339 347 Cross-scale resilience theory predicts that the combination of functional diversity within scales and functional redundancy across scales is an important attribute of ecosystems because it helps these systems resist minor ecological disruptions and regenerate after major disturbances such as hurricanes and fire. Using the vertebrate fauna of south Florida, we quantified how the loss of native species and invasion by normatives may alter functional group richness within and across scales. We found that despite large changes in species composition due to potential extinctions and successful invasions by normative species, functional group richness will not change significantly within scales, there will not be any significant loss of overall redundancy of ecology function across scales, and overall body mass pattern will not undergo substantial change. However, the types of functions performed will change, and this change may have profound effects on not only the Everglades ecosystem but On the entire landscape of south Florida. Web of Science Many USA Florida Everglades Impacts;Fundamentals herbivore;omnivore;predator 1819 Dukes, JS 2002 Comparison of the effect of elevated CO2 on an invasive species (Centaurea solstitialis) in monoculture and community settings journal PLANT ECOLOGY 160 2 225 234 The ongoing increase in atmospheric CO2 concentration ([CO2]) is likely to change the species composition of plant communities. To investigate whether growth of a highly invasive plant species, Centaurea solstitialis (yellow starthistle), was affected by elevated [CO2], and whether the success of this species would increase under CO2 enrichment, I grew the species in serpentine soil microcosms, both as a monoculture and as a component of a grassland community. Centaurea grown in monoculture responded strongly to [CO2] enrichment of 350 mumol mol(-)1, increasing aboveground biomass production by 70%, inflorescence production by 74%, and midday photosynthesis by an average of 132%. When grown in competition with common serpentine grassland species, Centaurea responded to CO2 enrichment with similar but nonsignificant increases (+69% aboveground biomass, +71% inflorescence production), while total aboveground biomass of the polyculture increased by 28%. Centaurea's positive CO2 response in monoculture and parallel (but non-significant) response in polyculture provoke questions about possible consequences of increasing CO2 for more typical California grasslands, where the invader already causes major problems. Web of Science Centaurea solstitialis USA California Woodside 37.4 -122.2333 Field - Experimental terrestrial Grassland Invasion Hyp. Climate Change primary 1820 Morgan, A; Carthew, SM; Sedgley, M 2002 Breeding system, reproductive efficiency and weed potential of Acacia baileyana journal AUSTRALIAN JOURNAL OF BOTANY 50 3 357 364 Acacia baileyana F. Muell. is a native environmental weed which has invaded bush areas of south-eastern Australia from ornamental plantings. There are two main colour forms, the typical green-leaf form and the variety 'purpurea', which has purple new growth. Only the green form appears to have invaded natural bush. The weed potential of A. baileyana was investigated in terms of its breeding system and seed production. It was found that the purple form is as reproductively efficient as the green form. Both forms were outcrossing, highly self-incompatible, grew very rapidly and flowered by two years of age. For open, natural pollination, final pod set was low-less than 0.41%. However, seed production was high due to the high number of flowers present. Maximum flower production for a 2-year-old plant was over 300 000, resulting in more than 8000 seeds. Precocity and high flower numbers appear to be the reasons for the weed status of A. baileyana. Given the similarity in reproductive efficiency between both forms, it is postulated that the absence of the purple form as a weed could be due to it being a relatively new horticultural variety, or to the purple colour being a recessive trait. Web of Science Acacia baileyana F. Muell. Australia The University of Adelaide -34.854383 138.614502 Field - Experimental terrestrial Invasion Hyp. Inherent Superiority Rapid Growth;High Reprod. Output primary 1822 Kennedy, TA; Naeem, S; Howe, KM; Knops, JMH; Tilman, D; Reich, P 2002 Biodiversity as a barrier to ecological invasion journal NATURE 417 127 636 638 Biological invasions are a pervasive and costly environmental problem(1,2) that has been the focus of intense management and research activities over the past half century. Yet accurate predictions of community susceptibility to invasion remain elusive. The diversity resistance hypothesis, which argues that diverse communities are highly competitive and readily resist invasion(3-5), is supported by both theory(6) and experimental studies(7-14) conducted at small spatial scales. However, there is also convincing evidence that the relationship between the diversity of native and invading species is positive when measured at regional scales(3,11,15,16). Although this latter relationship may arise from extrinsic factors, such as resource heterogeneity, that covary with diversity of native and invading species at large scales, the mechanisms conferring greater invasion resistance to diverse communities at local scales remain unknown. Using neighbourhood analyses, a technique from plant competition studies(17-19), we show here that species diversity in small experimental grassland plots enhances invasion resistance by increasing crowding and species richness in localized plant neighbourhoods. Both the establishment (number of invaders) and success (proportion of invaders that are large) of invading plants are reduced. These results suggest that local biodiversity represents an important line of defence against the spread of invaders. Web of Science Many United States Minnesota Cedar Creek Natural History Area 45.422432 -93.194103 Theoretical/Modeling terrestrial Grassland Invasion Hyp. Other primary 1827 Sher, AA; Marshall, DL; Taylor, JP 2002 Establishment patterns of native Populus and Salix in the presence of invasive nonnative Tamarix journal ECOLOGICAL APPLICATIONS 12 3 760 772 Despite growing concern and research interest in plant invasions, we know very little about ecological processes involved during invasion episodes. Understanding these dynamics is especially important for habitats subject to reestablishment of historical disturbance regimes; because many invasive species respond positively to disturbance, interactions between colonizing natives and nonnatives at the seedling stage may determine success of invasions. In the American Southwest, reduced flood disturbance in this century has been associated with the invasion of nonnative Tamarix ramosissima, with Tamarix appearing to displace native flood-dependent species of Populus and Salix. We studied two riparian communities of these woody species that had established after over-bunk flooding was allowed to occur in two protected areas in New Mexico. Growth and mortality were monitored for each individual within 1-m(2) plots of seedling communities within these sites for 2-4 yr. Abiotic conditions measured for each plot included soil salinity, texture, and nitrogen and phosphorus concentration. Although Tamarix seedling densities were an order of magnitude greater than those of the native species at initial establishment, mortality of Tamarix was also much greater than for Populus or Salix and occurred primarily in plot where native species were the most dense. Both natives were taller and grew faster above ground than Tamarix in the first 4 yr, and growth of Tamarix was negatively correlated with neighbor densities. In contrast, Populus and Salix growth and survival were never correlated with Tamarix densities. For all species, none of the abiotic variables measured was as important as neighbor density for explaining growth and survival patterns. These results have positive implications for managers who wish to reestablish the native dominants of riparian forests through reinstatement of flooding. Although Tamarix can respond positively to flooding, a range of conditions clearly exists in which Populus and Salix establishment can be stimulated by flooding, even when Tamarix seedlings are present. Furthermore, the presence of such natives even at the seedling stage may help to reduce densities of invasive Tamarix seedlings. Web of Science Tamarix ramosissima United States New Mexico Middle Rio Grande 33.48 -106.53 Field - Observational terrestrial Riparian Invasion Hyp. Disturbance primary 1829 Dietz, H; Kohler, A; Ullmann, I 2002 Regeneration growth of the invasive clonal forb Rorippa austriaca (Brassicaceae) in relation to fertilization and interspecific competition journal PLANT ECOLOGY 158 2 171 182 A special type of clonal growth, spread by lateral roots, is hypothesized to be a favourable trait of invasive, opportunistic plant species of disturbed habitats. We tested this hypothesis for the invasive forb Rorippa austriaca (Brassicaceae). Regeneration from root fragments, subsequent vegetative spread and allocation patterns in relation to varied nutrient supply and intensity and pattern of interspecific competition were analyzed in container experiments. Regeneration success from root fragments was 100% and clonal spread was rapid but vegetative performance was strongly reduced under unfertilized conditions and, particularly, when interspecific competition was present. While the ratio of above- to belowground bio-mass did not differ considerably between treatments, R. austriaca allocated a high amount of resources to belowground growth resulting in low aboveground but high belowground biomass at harvest time relative to the matrix vegetation. Differences in shoot number or biomass between simulated gaps and densely vegetated quadrants in the containers were (relatively) weak. Reproductive effort was less reduced under low resource levels, and the clones did not set seed at all, irrespective of the treatment. Our results show that clonal growth by lateral roots and plasticity in clonal growth patterns in R. austriaca promote both exploitation of gaps and nutrient-rich microsites and resistance to competitors. Such plasticity, combined with its ability to regenerate from widely-dispersed root fragments, contribute to the ability of the species to invade and persist within disturbed and spatially heterogeneous habitats. Web of Science Rorippa austriaca Germany Würzburg Field - Experimental lotic Invasion Hyp. Inherent Superiority Clonal Reproduction primary 1838 Roy, K; Jablonski, D; Valentine, JW 2002 Body size and invasion success in marine bivalves journal ECOLOGY LETTERS 5 2 163 167 The role of body size in marine bivalve invasions has been the subject of debate. Roy et al. found that large-bodied species of marine bivalves were more likely to be successful invaders, consistent with patterns seen during Pleistocene climatic change, but Miller et al. argued that such selectivity was largely driven by the inclusion of mariculture species in the analysis and that size-selectivity was absent outside of mariculture introductions. Here we use data on non-mariculture species from the north-eastern Pacific coast and from a global species pool to test the original hypothesis of Roy et al. that range limits of larger bivalves are more fluid than those of smaller species. First, we test the hypothesis that larger bivalve species are more successful than small species in expanding their geographical ranges following introduction into new regions. Second, we compare body sizes of indigenous and non-indigenous species for 299 of the 303 known intertidal and shelf species within the marine bivalve clade that contains the greater number of non-mariculture invaders, the Mytilidae. The results from both tests provide additional support for the view that body size plays an important role in mediating invasion success in marine bivalves, in contrast to Miller et al. Thus range expansions in Recent bivalves are consistent with patterns seen in Pleistocene faunas despite the many differences in the mechanisms. Web of Science Many Statistical/Meta-analysis marine Intertidal/Near Shore Invasion Hyp. filter 1840 Meiners, SJ; Pickett, STA; Cadenasso, ML 2002 Exotic plant invasions over 40 years of old field successions: community patterns and associations journal ECOGRAPHY 25 2 215 223 While exotic plant species often come to dominate disturbed communities, long-term patterns of invasion are poorly known. Here we present data from 40 yr of continuous vegetation sampling, documenting the temporal distribution of exotic plant species in old field succession. The relative cover of exotic species decreased with time since abandonment, with significant declines occurring greater than or equal to 20 yr post-abandonment. The number of exotic species per plot also declined with time since abandonment while field-scale richness of exotics did not change. This suggests displacement occurring at small spatial scales. Life history types changed from short-lived herbaceous species to long-lived woody species for both native and exotic plant species. However, shrubs and lianas dominated woody cover of exotic plants while trees dominated native woody cover. The species richness of exotic and native species was positively correlated at most times. In abandoned hay fields, however, the proportion of exotic plant cover per plot was inversely related to total species richness. This relationship suggests that it is not the presence, but the abundance of exotic species that may cause a reduction in community diversity. While the development of closed-canopy forest appears to limit most introduced plant species, several shade-adapted exotic species are increasing within the fields. These invasions may cause a reversal of the patterns seen in the first 40 yr of succession and may result in further impacts on community structure. Web of Science Many United States New Jersey Hutcheson Memorial Forest Center 40.498202 -74.565754 Field - Observational terrestrial Old Field Invasion Hyp. Other primary 1841 Neira, FJ; Sporcic, MI 2002 Use of ichthyoplankton ecology to evaluate ecosystem changes: a case study in a large, semi-enclosed Australian bay journal MARINE AND FRESHWATER RESEARCH 53 2 339 354 Intensive night sampling was conducted fortnightly in 1995/96 to investigate the ichthyoplankton assemblage of Port Phillip Bay. Results are compared with those from a similar survey in 1983/84, and are used to ascertain whether major changes have occurred in the composition and abundance of fish eggs and larvae, and whether these are related to ecosystem changes in the bay between 1969 and 1995. The 17 157 larvae caught during this study belonged to 60 taxa from 32 teleost fish families, with Gobiidae (54.2%), Engraulidae (16.7%), Clinidae (10.0%) and Odacidae (5.9%) dominating the catches. Larval concentrations peaked only in summer, in contrast to summer and winter in 1983/84. Larvae from 13 families recorded in 1995/96 did not occur in 1983/84, including Gobiesocidae (9 spp.) and Odacidae (3 spp.). Larvae absent in 1995/96 but present in 1983/84 included Acanthopegasus lancifer (Pegasidae) and taxa from another seven families. Neoodax balteatus larvae ranked fourth in 1995/96 but were absent in 1983/84, while Engraulis australis eggs and Gymnapistes marmoratus larvae were comparatively fewer in 1995/96. We suggest that some of the main differences between the two surveys may be attributable to major ecosystem changes in the bay, particularly the introduction and establishment of exotic marine species. Web of Science Many Australia Canberra Port Phillip Bay -38 145 Field - Observational marine Intertidal/Near Shore Invasion Hyp. Ecosystem Engineers primary;herbivore;omnivore;predator;filter 1848 Cabin, RJ; Weller, SG; Lorence, DH; Cordell, S; Hadway, LJ 2002 Effects of microsite, water, weeding, and direct seeding on the regeneration of native and alien species within a Hawaiian dry forest preserve journal BIOLOGICAL CONSERVATION 104 2 181 190 Tropical dry forests are among the most endangered ecosystems in the world in general and in Hawaii in particular. To investigate the regeneration ecology of native and alien dry forest species on the island of Hawaii, we used a factorial experiment with microsite (sub-canopy vs. inter-canopy), water (supplemental vs. ambient), and weeding (alien species removed vs, not removed) treatments, and also seeded six native woody species into each plot at the start of the experiment. At the end of the 21-month study, the biomass of the volunteer native and alien species (i.e. unplanted species consisting mainly of relatively fast-growing shrubs) was nearly three and 13 times that of the seeded species, respectively. The biomass of the native volunteers was greater in the inter-canopy plots, greater for the seeded species in the sub-canopy plots, and did not differ significantly within this treatment for the alien species. Few species survived in the ambient water plots, resulting in greater biomass in the watered plots for all species, There were no significant differences in the biomass of the native species within the weeded vs. non-weeded plots; on the contrary, we found consistently positive correlations between the abundance of the seeded species and the volunteer native and alien species. Thus it may be possible to restore Hawaii's degraded dry forests by manipulating these naturally recruiting species to create microsites favorable for the eventual re-establishment of the endangered native canopy tree flora. (C) 2002 Elsevier Science Ltd. All rights reserved. Web of Science Many United States Hawaii Kaupulehu preserve 19.872643 -155.986633 Field - Experimental terrestrial Tropical Forest Invasion Hyp. Propagule Pressure;Fluctuating Resources primary 1849 Stohlgren, TJ; Chong, GW; Schell, LD; Rimar, KA; Otsuki, Y; Lee, M; Kalkhan, MA; Villa, CA 2002 Assessing vulnerability to invasion by nonnative plant species at multiple spatial scales journal ENVIRONMENTAL MANAGEMENT 29 4 566 577 Basic information on where nonnative plant species have successfully invaded is lacking. We assessed the vulnerability of 22 vegetation types (25 sets of four plots in nine study areas) to nonnative plant invasions in the north-central United States. In general, habitats with high native species richness were more heavily invaded than species-poor habitats, low-elevation areas were more invaded than high-elevation areas, and riparian zones were more invaded than nearby upland sites. For the 100 1000-m(2) plots (across all vegetation types), 50% of the variation in nonnative species richness was explained by longitude, latitude, native plant species richness, soil total percentage nitrogen, and mean maximum July temperature (n = 100 plots; P < 0.001). At the vegetation-type scale (n = 25 sets of four 1000-m(2) plots/ type), 64% of the variation in nonnative species richness was explained by native plant species richness, elevation, and October to June precipitation (P < 0,001). The foliar cover of nonnative species (log) was strongly positively correlated with the nonnative species richness at the plot scale (r = 0.77, P < 0.001) and vegetation-type scale (r = 0.83, P < 0.001). We concluded that, at the vegetation-type and regional scales in the north-central United States, (1) vegetation types rich in native species are often highly vulnerable to invasion by nonnative plant species; (2) where several nonnative species become established, nonnative species cover can substantially increase; (3) the attributes that maintain high native plant species richness (high light, water, nitrogen, and temperatures) also help maintain nonnative plant species richness; and (4) more care must be taken to preserve native species diversity in highly vulnerable habitats. Web of Science Many United States Colorado; Wyoming; Montana; South Dakota; Minnesota shortgrass steppe at the Central Plains Experimental Range (Pawnee National Grassland, Nunn, Colorado), mixed grass prairie at the High Plains Experiment Station (Cheyenne, Wyoming), northern mixed prairie at Wind Cave National Park (Hot Springs, South Dakota), and tallgrass prairie at Pipestone National Monument (Pipestone, Minnesota). Field - Observational terrestrial Grassland Invasion Hyp. Community Species Richness;Disturbance primary 1850 Miller, TE; Kneitel, JM; Burns, JH 2002 Effect of community structure on invasion success and rate journal ECOLOGY 83 4 898 905 Although invasion has long been recognized as an important ecological process, there are very few experimental studies of invasion in natural communities and virtually no studies that determine how trophic structure affects the probability of invasion, We introduced novel protozoans and rotifers into the natural communities found in the water-filled leaves of the pitcher plant Sarracenia purpurea. The communities were manipulated in a factorial design of removal of predators (larvae of the mosquito Wyeomyia smithii) and addition of resources (dead insects). Three of the six protozoan species successfully established populations when introduced into pitchers, suggesting that these species are migration limited. The other three protozoans and a rotifer did not successfully invade established communities, although all four are naturally found in these inquiline communities. Of the three successfully invading protozoans, two were more likely to invade when resources were added and one of those even more frequently when predators were removed. Invasion by the third was unaffected by these experimental manipulations. Similar effects of predators and resources were found on population sizes of these three species. This study is one of very few that have addressed invasion experimentally; its results suggest that a variety of factors, including migration, predation, and resource availability, can have different influences on invasion by fairly similar protozoans. Web of Science Many United States Florida Sumatra 30.021023 -84.978862 Field - Experimental lentic Savanna Invasion Hyp. Enemy Release;Inherent Superiority;Propagule Pressure;Fluctuating Resources Effective Disperser predator;filter 1851 Pysek, P; Jarosik, V; Kucera, T 2002 Patterns of invasion in temperate nature reserves journal BIOLOGICAL CONSERVATION 104 1 13 24 The extent of plant invasions was studied in 302 nature reserves located in the Czech Republic, central Europe. Lists of vascular plant species were obtained for each reserve, alien species were divided into archaeophytes and neophytes (introduced before and after 1500, respectively). The statistical analysis using general linear models made it possible to identify the effects of particular variables. Flora representation by neophytes decreased with altitude (explained 23.8% of variance) while, with archaeophytes, the effect of altitude depended on their interaction with native species in particular vegetation types. The proportion of neophytes increased with increasing density of human population. Both the number and proportion of aliens plants significantly increased with increasing number of native species in a reserve. This relationship was affected by altitude, and after filtering out this variable, the effect remained positive for neophytes but became negative for archaeophytes in humid grasslands. The positive relationship between neophytes and native species is not a mere side effect of species-area relationship of native flora, but indicates that the two groups do not directly compete. Vegetation type alone explained 14.2 and 55.5% of variation in proportion of aliens in regions of mesophilous and mountain flora, respectively. Humid grasslands were the least invaded vegetation type. Positioning the reserve within large protected sections of landscape significantly decreases probability of it being invaded by potentially invasive alien species. Within the context of SLOSS debate, a new model - several small inside single large (SSISL) - is suggested as an appropriate solution from the viewpoint of plant invasions to nature reserves. (C) 2002 Elsevier Science Ltd. All rights reserved. Web of Science Many Czech Republic 302 nature reserves 49.89 15.06 Statistical/Meta-analysis terrestrial Grassland;Deciduous Forest;Coniferous Forest;Broadleaf Evergreen Forest;Savanna;Wetland;Riparian Invasion Hyp. Inherent Superiority;Community Species Richness;Disturbance Superior Competitor primary 1852 Green, EK; Galatowitsch, SM 2002 Effects of Phalaris arundinacea and nitrate-N addition on the establishment of wetland plant communities journal JOURNAL OF APPLIED ECOLOGY 39 1 134 144 1. Nutrient enrichment may adversely impact plant species richness in wetlands and enhance their susceptibility to colonization and dominance by invasive species. For North American prairie wetlands. enrichment by nitrate-N (NO3-N) from agricultural runoff is thought to contribute to the increasing colonization and dominance of Phalaris arundinacea (reed canary grass), especially during restoration. If true, P arundinacea might compromise the re-establishment of sedge meadow vegetation on sites reflooded with agricultural drainage water. 2. We tested this hypothesis using a fertilization experiment in wetlands with controlled hydrology. A community mixture comprising 11 species from native sedge meadow was seeded in mesocosms and grown under one of three NO3-N levels (0 g m(-2) year(-1), 12 g m(-2) year(-1), 48 g m(-2) year(-1)) with or without P arundinacea. Above- and below-ground biomass were measured after two growing seasons to assess the response of vegetation to NO3-N and P arundinacea treatments. 3. The total shoot biomass of the native community was suppressed in the presence of P arundinacea at all NO3-N levels, but shoot suppression was significantly greater at the highest NO3-N dose level (48 g m(-2)). Shoot growth of the native community was reduced by nearly one-half under these conditions. 4. The total root biomass of the community was also suppressed by P arundinacea when no NO3-N was added. 5. As NO3-N increased. the relative abundance (shoot biomass) of native graminoids declined while native forbs increased in communities with and without Phalaris. The most common graminoid. Glyceria grandis, was suppressed by P arundinacea at all levels, with suppression enhanced at the 48 g m(-2) NO3-N level. Three other species were suppressed at the highest NO3-N level, in the presence of Phalaris. The two most common forbs, Asclepias incarnata and Sium suave. exhibited a continual increase in growth with NO3-N additions along with overall suppression by P. arundinacea. 6. Community diversity and evenness declined with increasing NO3-N levels, whether or not P arundinacea was present. 7. Our results demonstrate that if P arundinacea is present. the restored sedge meadow community will not achieve levels of abundance that are possible when this species is absent. regardless of NO3-N enrichment conditions. 8. At the same time, the increased suppression by P arundinacea at the 48 g m(-2) NO3-N dose level supports the hypothesis that the dominance of this species over the native sedge meadow community is enhanced by NO3-N inputs at levels that are common in agricultural landscapes. 9. Our results carry two implications for achieving biodiversity conservation in agricultural landscapes. First. reducing nitrate loads to wetland reserves is essential for minimizing declines in community diversity. Secondly, the use of P arundinacea for soil conservation and other agri-environmental purposes should be curtailed because of the likelihood of off-site impacts to wetland biodiversity. Web of Science Phalaris arundinacea (reed canary grass) United States Minnesota Minnesota Horticultural Research Center 44.51 -93.36 Field - Experimental terrestrial Wetland Invasion Hyp. Disturbance primary 1855 Eldridge, DJ; Simpson, R 2002 Rabbit (Oryctolagus cuniculus L.) impacts on vegetation and soils, and implications for management of wooded rangelands journal BASIC AND APPLIED ECOLOGY 3 1 19 29 Rabbit warrens are a distinctive landscape feature in the semi-arid woodlands of eastern Australia. We examined the Surface morphology and vegetation composition of ten rabbit warrens in central-western NSW in order to assess their roles as a harbor for weedy plants. In general, mounds were characterised by a degraded soil surface dominated by bare soil and coarse gravel, whilst adjacent non-mound (control) surfaces were characterised by an extensive cover of cryptogams (lichens and mosses). Mounds supported significantly more exotic plants than non-mounds, and there was a clear separation between the two microsites in terms of the cover-abundances of vascular plants. Mound microsites contained significantly more tall (> 50 cm) species, and species with burrs compared with non-mound microsites. Germination studies indicated enhanced germination of two common, weedy, mound species (Marrubium vulgare and Brassica tournefortii) on the eroded mound surface, arid greater germination of the perennial grass Austrodanthonia caespitosa on the cryptogam-dominated non-mound surface. The work suggests that the higher cover-abundance of weedy species is a result of alterations to the soil surface caused by rabbit disturbances, and that destruction of the warren complex, in order to prevent re-invasion and hence re-working of the mound, is required to enable native perennials to colonise. Web of Science Many Australia New South Wales Yathong Nature Reserve -32.35 145.35 Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Disturbance;Ecosystem Engineers primary 1856 Sessions, L; Kelly, D 2002 Predator-mediated apparent competition between an introduced grass, Agrostis capillaris, and a native fern, Botrychium australe (Ophioglossaceae), in New Zealand journal OIKOS 96 1 102 109 This study provides an example of how invasive plant species may indirectly affect native species through apparent competition by altering the local invertebrate community. The native New Zealand fern Botrychium australe (Ophioglossaceae) is thought to benefit from disturbances such as fire, because this species is generally found in disturbed habitats with low shade and increasing competition. However, in this study we show that a mapped population of B. australe experienced a marked decrease in survival and reproduction after an accidental fire in May 1995. Mortality was not due to the direct effects of fire; in the year following the fire, survival was normal and reproduction was higher than in previous years. however, after 1996 an introduced grass (Agrostis capillaris) spread across the area and B. australe survival in the second to fourth years after the fire (1996 1999, 59.63%) was significantly lower than survival before the fire, and plants did not produce spores at all during this 3-yr period. B. australe survival was not lower in plots with dense. A. capillaris growth. From 1997 onwards, B. australe plants suffered very extensive defoliation by a herbivore, and insecticide and molluscicide experiments in 1999 and 2000 showed that the introduced slug Deroceras reticulation was responsible for the damage. The slug increased after the fire in association with the spread of Agrostis capillaris, probably because this plant created a suitable habitat for slugs. Web of Science Agrostis capillaris; slug Deroceras reticulation New Zealand Canterbury Cass -43.0317 171.7317 Field - Observational terrestrial Chaparral/Shrublands Impacts;Fundamentals primary;herbivore 1860 Levine, JM 2001 Local interactions, dispersal, and native and exotic plant diversity along a California stream journal OIKOS 95 3 397 408 Although the species pool, dispersal, and local interactions all influence species diversity, their relative importance is debated. I examined their importance in controlling the number of native and exotic plant species occupying tussocks formed by the sedge Carex nudata along a California stream. Of particular interest were the factors underlying a downstream increase in plant diversity and biological invasions. I conducted seed addition experiments and manipulated local diversity and cover to evaluate the degree to which tussocks saturate with species, and to examine the roles of local competitive processes, abiotic factors, and seed supply in controlling the system-wide patterns. Seeds of three native and three exotic plants sown onto experimentally assembled tussock communities less successfully established on tussocks with a greater richness of resident plants. Nonetheless, even the most diverse tussocks were somewhat colonized, suggesting that tussocks are not completely saturated with species. Similarly, in an experiment where I sowed seeds onto natural tussocks along the river, colonization increased two- to three-fold when I removed the resident species. Even on intact tussocks, however, seed addition increased diversity, indicating that the tussock assemblages are seed limited. Colonization success on cleared and uncleared tussocks increased downstream from km 0 to km 3 of the study site, but showed no trends from km 3 to km 8. This suggests that while abiotic and biotic features of the tussocks may control the increase in diversity and invasions from km 0 to km 3, similar increases from km 3 to km 8 are more likely explained by potential downstream increases in seed supply. The effective water dispersal of seed mimics and prevailingly downstream winds indicated that dispersal most likely occurs in a downstream direction. These results suggest that resident species diversity, competitive interactions, and seed supply similarly influence the colonization of native and exotic species. Web of Science Cirsium arvense; Plantago major; Agrostis stolonifera United States California South Fork Eel river 39.712997 -123.712921 Field - Experimental terrestrial Riparian Fundamentals;Invasion Hyp. Community Species Richness primary 1861 Williamson, J; Harrison, S 2002 Biotic and abiotic limits to the spread of exotic revegetation species journal ECOLOGICAL APPLICATIONS 12 1 40 51 Natural habitats vary in the degree to which they are invaded by exotic species, but it is unclear whether they differ in the mechanisms underlying the spatial spread of a given exotic species. To compare the dynamics of invasion in highly invaded nonserpentine oak woodlands and less-invaded serpentine habitats, we used an historical *experiment* consisting of the introduction of several normative species for post-mining revegetation, supplemented by a pot experiment and a factorial field experiment. Three species showed significant declines in abundance on transects from revegetated zones into natural habitats, indicating that these species had spread into the natural habitats from revegetated zones. Dactylis glomerata and Trifolium hirtum were found up to 95 m into oak woodland, 35 m into serpentine meadows, and 0-25 m into serpentine seeps and chaparral, while Elytrigia pontica was found up to 45 m into serpentine seeps. The pot experiment showed that this pattern of distribution for Dactylis was not caused or limited by variation in soil properties. The field experiment showed that Dactylis invasion in both oak woodland and serpentine meadow habitats was limited by disturbance and seed supply. Dactylis success was negatively correlated with species richness in oak woodlands, but positively correlated with richness in serpentine meadows, suggesting that the relationships between diversity, invasion, and underlying habitat suitability differed between these habitats. Our results show that in harsh serpentine soils, the spread of recently introduced exotic species is slower than in more fertile and more invaded oak woodlands. However, disturbance and propagule addition are equally important in promoting the spread of invaders in both environments. Web of Science Dactylis glomerata (orchard grass), Trifolium hirtum (rose clover), and Elytrigia pontica (wheatgrass), Bromus madritensis ssp. madritensis, Bromus hordeaceus, and Lolium multiflorum United States California Homestake Mine/ Donald and Sylvia McLaughlin UC Natural Reserve 38.88 -122.44 Field - Experimental;Field - Observational terrestrial Grassland;Deciduous Forest Impacts;Fundamentals;Invasion Hyp. Empty Niche;Propagule Pressure;Disturbance primary 1863 Lambrinos, JG 2002 The variable invasive success of Cortaderia species in a complex landscape journal ECOLOGY 83 2 518 529 It is likely that plant invasions result from complex interactions between species traits, community traits, and abiotic conditions. Despite this, there have been few experimental studies that directly examine these interactions. Two morphologically similar perennial grass species in the genus Cortaderia are currently invasive pest's in California, but their patterns of invasion differ. In this study I experimentally compared the performance of the two species across four vegetation types in central California. I examined how the different invasive patterns of the species result from differential responses to environmental factors that vary over relatively small spatial and temporal scales. Cortaderia selloana had consistently higher seed germination than C. jubata, but germination rates interacted significantly with soil disturbance and habitat type, and these interactions varied between experimental years. When mammalian herbivores were excluded, the principal cause of transplant mortality was physiological stress, and C. selloana transplants had greater survivorship than C. jubata transplants in all habitats except maritime chaparral. In the presence of mammalian herbivores, however, herbivory became the dominant source of transplant mortality, and the survivorship of both species was indistinguishable in all habitats. At the seasonal wetland site, patterns of transplant survivorship varied significantly between years, probably as a result of increased competition for water during the second experimental year. Transplants of the two species did not differ significantly in growth except at the seasonal wetland site where C. selloana transplants added significantly more leaf area than C. jubata transplants. These results indicate that the relative invasive potential of C. selloana and C. jubata is strongly moderated by the presence of generalist herbivores. The influence of herbivory is in turn dependent on the community type. In addition, plant competitors can modify the invasive success of the two species, but the effect of competitors varies with seasonal differences in resource supply. Although important mechanisms that influence the invasion process can be identified, the complex invasion dynamics exhibited by these morphologically similar species across relatively small spatial and temporal scales suggest that overly broad invasion rules will be of little practical utility in the regional management of invasive species. Web of Science Cortaderia selloana and Cortaderia jubata United States California Vandenberg Air Force Base (VAFB), Santa Barbara County 34.73 -120.53 Field - Experimental terrestrial Grassland;Chaparral/Shrublands Fundamentals;Invasion Hyp. Fluctuating Resources;Disturbance primary 1870 Ogle, SM; Reiners, WA 2002 A phytosociological study of exotic annual brome grasses in a mixed grass prairie/ponderosa pine forest ecotone journal AMERICAN MIDLAND NATURALIST 147 1 25 31 The annual brome grasses, Bromus japonicus and B. tectorum, are common invaders of the Northern Great Plains. Our objective was to determine if these exotic plants were positively or negatively associated with particular plant species or functional types in a prairie/pine ecotone at Wind Cave National Park, South Dakota. We addressed this issue by sampling at two spatial scales-the landscape scale and the site scale. For the landscape we evaluated species associations across a 3800 ha ecotone using 90 transects. Annual bromes were positively associated with C-3 grasses, particularly Agropyron smithii and Stipa viridula, in addition to the shrub Symphoricarpos occidentalis. Annual bromes were negatively associated with trees, C-4 grasses, particularly A. gerardii, Bouteloua curtipendula and Schizachyrium scoparium, as well as the shrub Rhus aromatica. For the bite scale we assessed relationships at a finer resolution within two 1 ha stands of grassland vegetation. Annual bromes were negatively associated with Poa pratensis in both stands, Results indicate that the bromes often dominate in portions of the landscape with C-3 grasses and Symphoricarpos occidentalis. Within individual sites, the bromes appear most limited by a competitive interaction with R pratensis, resulting from phenological overlap. Web of Science annual brome grasses, Bromus japonicus and B. tectorum United States South Dakota Wind Cave National Park 43.591333 -103.476105 Field - Observational terrestrial Grassland;Coniferous Forest Fundamentals primary 1871 Nowierski, RM; Zeng, Z; Schroeder, D; Gassmann, A; Fitzgerald, BC; Cristofaro, M 2002 Habitat associations of Euphorbia and Aphthona species from Europe: Development of predictive models for natural enemy release with ordination analysis journal BIOLOGICAL CONTROL 23 1 1 17 Biotic and abiotic factors can have a profound influence on the occurrence, species composition, structure, distribution, relative abundance, and dynamics of plant species and their associated natural enemies. Elucidation of some of the more relevant habitat characteristics for a pestiferous plant or phytophage species in its place of origin may enable better prediction of its rates of colonization and spread should it accidentally be introduced into new areas. A similar analysis of the habitat requisites for the associated natural enemies of the plant/phytophage should enable the development of predictive models that identify habitat factors conducive to the establishment and impact on the particular plant or phytophage species. In this study, habitat associations were characterized for four different Euphorbia species and their associated flea beetle species in the Aphthona complex from 17 field sites in Europe, representing xeric, mesic, and hydric habitats. Micro- and macronutrient analyses were conducted on soil and spurge foliage and roots; physical properties of the soil were analyzed; plant cover of grasses, forbs (a broad-leaved herbaceous plant), and Euphorbia species (and total plant productivity) were estimated at each of the sites, and relative abundance counts were made for each of the flea beetle species at each of the 17 sites during spring, early summer, and mid-summer 1991. Spurge species included Euphorbia cyparissias, E. lucida, E. seguieriana, and E. virgata. Flea beetles species included Aphthona cyparissiae, A. czwalinae, A. lacertosa, A. nigriscutis, A. pygmaea, A. venustula, and A. violacea. Ordination models generated for the spurge species suggested that E. virgata and E. lucida were associated with higher levels of soil matric potential, clay, organic matter, Ca, Fe, K, Mg, N, P, Zn (soil layer B), and plant productivity. In contrast, E. cyparissias and E. seguieriana were associated with relatively lower levels of plant productivity and higher levels of sand, CaCO3, and Zn (soil layer A). Ordination models developed for the Aphthona species suggested that A czwalinae and A lacertosa were associated with sites containing higher levels of clay and plant productivity and higher levels of Mn in the Euphorbia roots; A. violacea was associated with sites with intermediate levels of sand, clay, and plant productivity, in addition to spurge roots with higher levels of Cu, Fe, K, N, P, and Zn. A nigriscutis was associated with sandier soils with lower levels of plant productivity and higher levels of Ca, K, and N in the Euphorbia roots. A. cyparissiae, A. pygmaea, and A venustula were associated with moderately sandy soils with relatively lower levels of plant productivity and Euphorbia species with higher levels of Ca and N in the roots. The ordination models generated from this study provide the diagnostic framework for the identification of appropriate habitats and key site requisites that might be conducive to the establishment and impact of the Aphthona species on leafy spurge in North America. (C) 2001 Elsevier Science. Web of Science Spurge species included Euphorbia cyparissias, E. lucida, E. seguieriana, and E. virgata. Flea beetles species included Aphthona cyparissiae, A. czwalinae, A. lacertosa, A. nigriscutis, A. pygmaea, A. venustula, and A. violacea Austria, Germany, Hungary, Italy, and Switzerland Field - Observational;Theoretical/Modeling terrestrial Invasion Hyp. Preadaptation to Climate primary;herbivore 1872 Brewer, JS 2002 Disturbances increase seedling emergence of an invasive native shrub in pitcher-plant bogs journal NATURAL AREAS JOURNAL 22 1 4 10 Hex glabra (L,) Gray is an invasive, low-growing shrub that increases in frequency in pitcher-plant (Sarracenia alata [Wood] Wood) bogs in the southeastern United States following conversion to pine plantations. To evaluate one potential cause of such increases, I simulated, at a small scale. the effects of some types of chemical site preparation (i.e., herbicide application) on seedling establishment of L. glabra by removing ground-cover plant canopies in pitcher-plant bogs and pine flatwoods communities in southeastern Mississippi. Disturbances that removed standing dead vegetation and litter increased seedling emergence in open areas of two different bogs. The inhibitory effect of standing dead vegetation on seedling emergence diminished by the third year as this dead biomass decomposed. Successful recruitment of adults (shoots >0.25 m tall) from seedlings, however, did not occur within cleared plots during a three-year period. Seedling emergence was relatively high near trees in bogs but was not increased by removing shrubs. Tall shrubs and trees were the preferred perches of avian dispersers and probably shaded the disturbed plots in these areas. Hence, the effects of anthropogenic disturbances on seedling emergence of this invasive shrub can be overridden by increased seed deposition and shade from adjacent trees and tall shrubs. Furthermore, other variables (e.g., drainage, nutrient limitation, and fire suppression) probably are more important in the establishment of adults. Web of Science Hex glabra (L,) Gray is an invasive, low-growing shrub United States Mississippi pitcher-plant bogs and pine flatwoods communities Field - Experimental terrestrial Coniferous Forest;Savanna Invasion Hyp. Disturbance primary 1873 Prieur-Richard, AH; Lavorel, S; Linhart, YB; Dos Santos, A 2002 Plant diversity, herbivory and resistance of a plant community to invasion in Mediterranean annual communities journal OECOLOGIA 130 1 96 104 Several components of the diversity of plant communities, such as species richness, species composition, number of functional groups and functional composition, have been shown to directly affect the performance of exotic species. Exotics can also be affected by herbivores of the native plant community. However, these two possible mechanisms limiting invasion have never been investigated together. The aim of this study was to investigate the relationships between plant diversity, herbivory and performance of two annual exotics, Conyza bonariensis and C. canadensis, in Mediterranean annual communities. We wanted to test whether herbivory of these exotics was influenced either by species richness, functional-group richness or functional-group composition. We also studied the relationship between herbivory on the exotic species and their performance. Herbivory increased with increasing species and functional-group richness for both Conyza species. These patterns are interpreted as reflecting a greater number of available herbivore niches in a richer, more complex, plant community. The identities of functional groups also affected Conyza herbivory, which decreased in the presence of Asteraceae or Fabaceae and increased in the presence of Poaceae. Increasing herbivory had consequences for vegetative and demographic parameters of both invasive species: survival, final biomass and net fecundity decreased with increasing herbivory, leading to a loss of reproductive capacity. We conclude that communities characterised by a high number of grass species instead of Asteraceae or Fabaceae may be more resistant to invasion by the two Conyza species, in part due to predation by native herbivores. Web of Science C. bonariensis; C. canadensis France Montpellier Camp Redon 43.606748 3.873217 Field - Experimental terrestrial Invasion Hyp. Enemy Release;Community Species Richness primary 1876 Thompson, K; Hodgson, JG; Grime, JP; Burke, MJW 2001 Plant traits and temporal scale: evidence from a 5-year invasion experiment using native species journal JOURNAL OF ECOLOGY 89 6 1054 1060 1 A long-term experiment was established in 1990 in which seeds of 54 native species, not originally present at the site, were sown into a fertility x disturbance matrix established in unproductive limestone grassland at the Buxton Climate Change Impacts Laboratory (BCCIL). The objective was to examine the roles of productivity and disturbance as major factors controlling the invasibility of plant communities, and to identify the functional characteristics of successful invaders in response to different types of invasion opportunity. The results of the first 2 years of the study have already been published. 2 After 2 years, invasion was strongly promoted by disturbance and less so by increased fertility. Three years later the cover of invaders had declined over most of the matrix, and the greatest cover of sown species was where the highest levels of fertility and disturbance coincided. However, no part of the fertility-disturbance matrix was immune to invasion and the area of the matrix occupied by each of the sown species that successfully established was unique. Abundance of invaders was reduced by low soil pH. 3 The identity and distribution of the successful invaders changed as the early stages of invasion gave way to a later stage of consolidation. After 2 years regenerative traits (seed mass and germination characteristics) were the best predictors of success. After 5 years these traits were unrelated to success of the invaders, the most successful invaders were perennial grasses, and no single trait was a good predictor of invasiveness. 4 Our results are consistent with the hypothesis that invasions are promoted by an increase in the availability of resources, either through addition of extra resources or a reduction in their use by the resident vegetation. Web of Science Many United Kingdom Derbyshire Buxton Climate Change Impacts Laboratory 53.852527 -2.06543 Field - Experimental terrestrial Grassland Invasion Hyp. Inherent Superiority;Climate Change High Reprod. Output primary 1881 Amsellem, L; Noyer, JL; Hossaert-McKey, M 2001 Evidence for a switch in the reproductive biology of Rubus alceifolius (Rosaceae) towards apomixis, between its native range and its area of introduction journal AMERICAN JOURNAL OF BOTANY 88 12 2243 2251 We compared the reproductive system of Rubus alceifolius in its native range in Southeast Asia, in Madagascar, where the plant was introduced apparently some centuries ago, and in La Reunion, an Indian Ocean island onto which R. alceifolius was introduced (from Madagascan source populations) around 1850. While tetraploidy makes it impossible to analyze variation in R. alceifolius using classical methods of population genetics, both the patterns of genetic diversity (as revealed by AFLP [amplified fragment length polymorphism] markers) and differences between half-sib progeny and their maternal parents (revealed by microsatellite markers) show that in the plant's native range in southeast Asia. seeds are produced sexually, In contrast, in Madagascar sexual reproduction cannot alone account for the genetic patterns observed with microsatellite markers. Over 85% of the half-sib progeny resulting from open pollination gave multilocus genotypes identical to those of their respective maternal parents, despite the fact that the latter had alleles that were rare in the population. The other progeny differed in having an allele with one motif more or less than that of the maternal parent. Seeds thus appear to be produced mostly or exclusively by apomixis in Madagascar. We present findings suggesting that Madagascan populations result from hybridization of introduced R. alceifolius and native populations of R. roridus, a closely related species of Rubus subgenus Malachobatus, and suggest that apomixis was a consequence of this hybridization. In Reunionese populations of R. alceifolius (derived from Madagascan populations), seeds obtained in controlled pollination experiments were all genetically identical to maternal parents. While genetic variation (microsatellite markers) in Reunionese populations was low, it was sufficient to allow us to demonstrate that seeds could not have resulted from fertilization by the pollen donors chosen for controlled pollinations. or from autogamy, and were produced exclusively by apomixis. Web of Science Rubus alceifolius Vietnam; Madagascar Lang Son; La Reunion 22.05;-21.04 106.38;55.4 Greenhouse terrestrial Invasion Hyp. Hybridization primary 1887 Barthell, JF; Randall, JM; Thorp, RW; Wenner, AM 2001 Promotion of seed set in yellow star-thistle by honey bees: Evidence of an invasive mutualism journal ECOLOGICAL APPLICATIONS 11 6 1870 1883 We examined the role of nonnative honey bees (Apis mellifera) as pollinators of the invasive, nonnative plant species yellow star-thistle (Centaurea solstitialis), both introduced to the western United States in the early to middle 1800s. Using four different treatments (three exclosure types) at flower heads, we observed visitation rates of different pollinators. Honey bees were the most common visitors at each of three transects established at three study locales in California: University of California at Davis, Cosumnes River Preserve. and Santa Cruz Island. A significant correlation existed between honey bee visitation levels monitored in all these transects and the average number of viable seeds per seed head for the same transects. Selective exclusion of honey bees at flower heads using a 3 mm diameter mesh significantly reduced seed set per seed head at all locales. Seed set depression was less dramatic at the island locale because of high visitation rates by generalist halictid bees Augochlorella pomoniella and Agapostemon texanus that penetrated the 3-mm mesh. The introduced megachilid bee Megachile apicalis occurred at all three locales as well (though in much lower numbers) and may contribute to pollination. In an ancillary study, seed set of plants with bagged heads was compared with that of plants without any bagged heads to test for resource shunting effects. These results showed that seed set differences observed between treatments within a single plant were not exaggerated due to resource shunting induced by the bagging technique. Yellow star-thistle may have low or variable levels of self-compatibility (as reflected by low seed set levels in small-mesh bags), increasing the importance of pollination in its breeding system. These results suggest that honey bees and yellow star-thistle may act as invasive mutualists, an association that may extend to other normative plant and pollinator species from Eurasia. Web of Science honey bees (Apis mellifera); yellow star-thistle (Centaurea solstitialis) United States California University of California at Davis, Cosumnes River Preserve. and Santa Cruz Island Field - Experimental terrestrial Old Field Impacts;Invasion Hyp. Mutualism Facilitation primary 1890 Talman, SG; Keough, MJ 2001 Impact of an exotic clam, Corbula gibba, on the commercial scallop Pecten fumatus in Port Phillip Bay, south-east Australia: evidence of resource-restricted growth in a subtidal environment journal MARINE ECOLOGY-PROGRESS SERIES 221 0 135 143 Corbula gibba (Olivi, 1792) a small exotic bivalve from the eastern Atlantic and the Mediterranean has been present in Port Phillip Bay, Victoria, Australia, from as early as 1987. C. gibba is widespread, abundant, and possesses characteristics such as fast growth which may confer a competitive advantage over endemic species like the commercial scallop Pecten fumatus Reeve, 1855. Experimental manipulations in the field showed that ambient densities of C. gibba significantly affected the size and growth of juvenile P. fumatus. This effect was greater than the effect of an equivalent number of conspecific scallops. C. gibba did not, however, affect scallop condition or survival in the short term, although the power of the test to detect a 50% decrease in survival was low. The percentage of experimental scallops lost to different sources of mortality was also unaffected by the presence of C. gibba, as was the density of predators found in experimental enclosures. This study is the first to experimentally demonstrate the impact of an introduced marine mollusc on an endemic species in Australia, A possible mechanism underlying this impact is competition for food, as both species are suspension feeders which live in an environment where resource limitation may occur. Web of Science Corbula gibba Australia Port Phillip Bay -38.080528 144.740067 Field - Experimental estuarine Intertidal/Near Shore Impacts;Invasion Hyp. Inherent Superiority Superior Competitor filter 1891 Siemann, E; Rogers, WE 2001 Genetic differences in growth of an invasive tree species journal ECOLOGY LETTERS 4 6 514 518 Invasive plants are often more vigorous in their introduced ranges than in their native ranges. This may reflect an innate superiority of plants from some habitats or an escape from their enemies. Another hypothesis proposes that invasive plants evolve increased competitive ability in their introduced range. We present the results of a 14-year common garden experiment with the Chinese Tallow Tree (Sapium sebiferum) from its native range (Asia), place of introduction to North America (Georgia) and areas colonized a century later (Louisiana and Texas). Invasive genotypes, especially those from recently colonized areas, were larger than native genotypes and more likely to produce seeds but had lower quality, poorly defended leaves. Our results demonstrate significant post-invasion genetic differences in an invasive plant species. Post-introduction adaptation by introduced plants may contribute to their invasive success and make it difficult to predict problem species. Web of Science Chinese Tallow Tree (Sapium sebiferum) United States Greenhouse;Garden terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 1893 King, SA; Buckney, RT 2001 Exotic plants in the soil-stored seed bank of urban bushland journal AUSTRALIAN JOURNAL OF BOTANY 49 6 717 720 Native vegetation reserves in urban areas have been invaded by exotic plants, particularly along edges. However, it is not known whether the seeds of exotic plants in the soil-stored seed bank are also largely restricted to edges. Ten urban bushland sites in northern Sydney were randomly selected and the readily germinable, soil-stored seed bank examined to assess whether the number of exotic and native species varied with distance from an urban edge. The similarity of the contents of the seed bank and the composition of the above-ground vegetation was also examined. Soil samples were collected from quadrats 0-10, 20-30 and 50-60 m from the edge at each site, then spread on germination trays in a glasshouse and germinated seedlings identified. Soil samples were collected every 3 months for a year. The number of exotic species in the seed bank was found to be highest near urban edges, as was the total number of species. The above-ground vegetation was found to be a poor indicator of the contents of the seed bank, for both native and exotic species. Most of the exotic species found in the seed bank were not found in the immediately surrounding vegetation. Furthermore, some exotic species were found in the seed bank at sites where no exotic species were present in the vegetation. The results suggest that it is the lack of suitable conditions that is largely restricting invasion of exotic species to edges of bushland. The results also highlight the need for seedbank studies to assess the contents of the soil seed bank in urban bushland in order to prevent further invasions of exotic plants. Web of Science Many New South Wales Sydney 10 urban bushland sites -33.865356 151.207323 Field - Observational terrestrial Urban Invasion Hyp. Disturbance primary 1894 Callaway, RM; Newingham, B; Zabinski, CA; Mahall, BE 2001 Compensatory growth and competitive ability of an invasive weed are enhanced by soil fungi and native neighbours journal ECOLOGY LETTERS 4 5 429 433 Compensatory responses to herbivory by invasive weeds may foil attempts to arrest their spread with biological controls. We conducted an experiment to study the effects of defoliation and soil fungi on interactions between Centaurea melitensis, an invasive annual from Eurasia, and Nassella pulchra, a native Californian bunchgrass. Defoliation of C. melitensis reduced its final biomass in all species-fungicide treatments, except when C. melitensis was grown with both Nassella and non-treated soil fungi at the same time. In this treatment, the biomass of clipped C. melitensis plants was equal to that of unclipped plants, indicating that soil fungi and Nassella promoted a compensatory response in the weed. Overall, the biomass of C melitensis was 44% lower when soil fungi were reduced. However, in soil not treated with fungicide, the total biomass of C melitensis increased in the presence of Nassella, but decreased when it was grown alone. When stressed by defoliation, C. melitensis may benefit from a form of mycorrhizae-mediated parasitism through a common mycorrhizal network, or Nassella may alter the fungal community in a way that enhances the positive direct effects of soil fungi on Centaurea. Web of Science Centaurea melitensis United States California University of California, Santa Barbara 34.419655 -119.848309 Greenhouse terrestrial Invasion Hyp. Mutualism Facilitation;Disturbance primary 1895 Davis, MA; Pelsor, M 2001 Experimental support for a resource-based mechanistic model of invasibility journal ECOLOGY LETTERS 4 5 421 428 Recent theory has suggested a mechanistic relationship between resource availability, competition and invasibility. In a field experiment, in which we manipulated resources and competition, we confirmed that changes in resource availability affected competition intensity, which in turn affected invasibility. We found that fluctuations in resource availability of as short as a few weeks had a large impact on plant invasion success (survival and percentage cover), including up to 1 year following the fluctuations. If resource availability is a primary mechanism controlling invasibility, it may serve as a unifying concept that can integrate earlier ideas regarding invasibility. The results emphasize the important role of history in the invasion process, particularly the occurrence of stochastic, short-lived events that temporarily reduce or suspend competition and increase invasibility. Therefore, it may be very difficult, or even impossible, to reconstruct the ecology of particular invasions after the fact. Web of Science Many United States Minnesota Cedar Creek Natural History Area 45.406887 -93.200111 Field - Experimental terrestrial Old Field Invasion Hyp. Fluctuating Resources primary 1896 Amsellem, L; Chevallier, MH; Hossaert-McKey, M 2001 Ploidy level of the invasive weed Rubus alceifolius (Rosaceae) in its native range and in areas of introduction journal PLANT SYSTEMATICS AND EVOLUTION 228 4 171 179 A change in ploidy level could increase invasiveness of introduced plants in insular plant communities. To examine this question for R. alceifolius, we compared its ploidy level in its Asian native range and in the Indian Ocean islands where it has been introduced. We first counted chromosomes on root tips from a Vietnamese individual, which proved to be tetraploid (2n = 4x = 28). The nuclear DNA content of other individuals from the native range and areas of introduction was estimated using the flow cytometry method. The Vietnamese individual on which chromosomes Were counted was added to the sample, to enable deduction of the ploidy level of all individuals from their nuclear DNA content. All individuals were found to be tetraploid, except 10 individuals from a single clone collected in a Vietnamese population, estimated to be triploid, and morphologically different of other individuals of this study. We showed that while polyploidy of the source population may have predisposed this plant to become a successful invader, its introduction into Indian Ocean islands was not associated with any change in ploidy level. Web of Science R. alceifolius France Montpellier 43.614205 3.882294 Greenhouse terrestrial Invasion Hyp. Evolution in General primary 1897 Gabriel, AGA; Chown, SL; Barendse, J; Marshall, DJ; Mercer, RD; Pugh, PJA; Smith, VR 2001 Biological invasions of Southern Ocean islands: the Collembola of Marion Island as a test of generalities journal ECOGRAPHY 24 4 421 430 It has been suggested previously that the presence and abundance of indigenous species have a marked influence on the likelihood of invasion of a community. It has also been suggested that such biotic resistance has a negligible influence on the outcome of an invasion, but that the abiotic characteristics of the environment being invaded are more important. The latter has been claimed to be especially important on the islands of the Southern Ocean. In order to test these competing hypotheses we examined the distribution and abundance of indigenous and introduced springtails across 13 habitats, which differ considerably in the properties of their soils, and soil temperature, on the eastern quarter of sub-Antarctic Marion Island. There was no evidence of negative abundance covariation or species associations within habitats, nor were there significant relationships between species richness or abundance of the indigenous as opposed to the introduced collembolans across habitats. Interspecific interactions thus seem to have played no readily identifiable role in the outcome of invasions by Collembola on Marion Island. In contrast, the indigenous and introduced species responded very differently to abiotic variables. The indigenous Collembola prefer drier, more mineral soils with a low organic carbon content, and species richness tends to be highest in cold, fellfield areas. On the other hand, the introduced springtails prefer moist, warm sites, with organically enriched soils. Introduced species richness was negligible in cold, fellfield areas. Disturbance also appeared to influence positively the species richness and abundance of introduced species at a site. These results provide independent support for the idea that abiotic factors, especially temperature, significantly influence the likelihood of biological invasions on Southern Ocean islands. They also suggest that predicting the outcome of climate change on community structure in this region is likely to be problematic, especially in the case of the Collembola. Web of Science Many Prince Edward Islands Marion Island -46.92 37.82 Field - Observational terrestrial Grassland;Tundra Invasion Hyp. Community Species Richness;Preadaptation to Climate;Disturbance primary 1898 Restrepo, C; Vitousek, P 2001 Landslides, alien species, and the diversity of a Hawaiian montane mesic ecosystem journal BIOTROPICA 33 3 409 420 In the Ninole ridges of Hawai'i, we evaluated changes in plant species diversity and composition and the effect of alien species on the growth and recruitment of native species after disturbance by landsliding. We chose nine landslides representing three age categories (young, 4-17 yr; intermediate, 18-42 yr; and old, ca 130 yr) plus three undisturbed forest sites (325-525 yr) to sample and manipulate the vegetation; the undisturbed forest developed on tephra-derived soils underlain by basalt. The ordination of sites and species using detrended correspondence analysis (DCA) showed that species establishing on landslides were different than those found in the undisturbed forest; moreover, a large fraction of the species establishing on young landslides were represented by aliens, mostly grasses and orchids. The manipulation of alien species (clipping of aboveground parts and removal of above- and belowground parts, including soil) on young landslides (< 17 yr) significantly affected seedling growth of the native tree species Metrosideros polymorpha and the recruitment of native species. In addition, the manipulation of grasses and orchids favored the recruitment of a second group of alien species that were uncommon in, or absent from, our study sites. The removal of tephra-derived soils by landslides, in combination with an increased presence of alien species, may greatly alter successional trajectories in the Ninole ridges of Hawai'i. Web of Science Many United States Hawaii Ninole ridges, Kau District 19 -155 Field - Observational terrestrial Subtropical Forest Impacts;Invasion Hyp. Disturbance primary 1899 Blaney, CS; Kotanen, PM 2001 Effects of fungal pathogens on seeds of native and exotic plants: a test using congeneric pairs journal JOURNAL OF APPLIED ECOLOGY 38 5 1104 1113 1. It has previously been hypothesized that low rates of attack by natural enemies may contribute to the invasiveness of exotic plants. 2. We tested this hypothesis by investigating the influence of pathogens on survival during a critical life-history stage: the seed bank. We used fungicide treatments to estimate the impacts of soil fungi on buried seeds of a taxonomically broad suite of congeneric natives and exotics, in both upland and wetland meadows. 3. Seeds of both natives and exotics were recovered at lower rates in wetlands than in uplands. Fungicide addition reduced this difference by improving recovery in wetlands, indicating that the lower recovery was largely attributable to a higher level of fungal mortality. This suggests that fungal pathogens may contribute to the exclusion of upland species from wetlands. 4. The effects of fungicide on the recovery of buried seeds did not differ between natives and exotics. Seeds of exotics were recovered at a higher rate than seeds of natives in uplands, but this effect was not attributable to fungal pathogens. 5. Fungal seed pathogens may offer poor prospects for the management of most exotic species. The lack of consistent differences in the responses of natives vs. exotics to fungicide suggests few aliens owe their success to low seed pathogen loads, while impacts of seed-pathogenic biocontrol agents on non-target species would be frequent. Web of Science Many Canada Ontario University of Toronto Joker’s Hill field station, Regional Municipality of York 44 79 Field - Experimental;Greenhouse terrestrial Wetland Invasion Hyp. Enemy Release primary;pathogen 1900 Aguiar, FC; Ferreira, MT; Moreira, I 2001 Exotic and native vegetation establishment following channelization of a western Iberian river journal REGULATED RIVERS-RESEARCH & MANAGEMENT 17 5 509 526 Channelization is often a major cause of human impacts on river systems. It affects both hydrogeomorphic features and habitat characteristics and potentially impacts riverine flora and fauna. Human-disturbed fluvial ecosystems also appear to be particularly vulnerable to exotic plant establishment. Following a 12-year recovery period, the distribution, composition and cover of both exotic and native plant species were studied along a Portuguese lowland river segment, which had been subjected to resectioning, straightening and two-stage bank reinforcement, and were compared with those of a nearby, less impacted segment. The species distribution was also related to environmental data. Species richness and floristic composition in the channelized river segment were found to be similar to those at the more 'natural' river sites. Floral differences were primarily consistent with the dominance of cover by certain species. However, there were significant differences in exotic and native species richness and cover between the 'natural' corridor and the channelized segment, which was more susceptible to invasion by exotic perennial taxa, such as Eryngium pandanifolium, Paspalum paspalodes, Tradescantia fluminensis and Acacia dealbata. Factorial and canonical correspondence analyses revealed considerable patchiness in the distribution of species assemblages. The latter were associated with small differences in substrate composition and their own relative position across the banks and along the river segments in question. Data was also subjected to an unweighted pair-group arithmetic average clustering, and the Indicator Value methodology was applied to selected cluster noda in order to obtain significant indicator species. Copyright (C) 2001 John Wiley & Sons, Ltd. Web of Science Many Portugal River Mondego Field - Observational terrestrial Riparian Invasion Hyp. Disturbance primary 1902 Meekins, JF; McCarthy, BC 2001 Effect of environmental variation on the invasive success of a nonindigenous forest herb journal ECOLOGICAL APPLICATIONS 11 5 1336 1348 With the ever-burgeoning spread of nonindigenous plants, often facilitated by human activities, it is imperative to conduct case studies of particular invasive plants and the sites they invade in order to develop effective and efficient habitat management strategies, Alliaria petiolata is a native European biennial mustard that has become a serious invasive pest in many North American forests. In order to better characterize habitat vulnerability to invasion by A. petiolata, we conducted an experiment to test the effects of environmental heterogeneity in the form of habitat, microenvironment, and small-scale litter disturbance on A. petiolata germination, survival, growth, and reproduction. Treatments consisted of two habitats (upland and lowland), two microenvironments (forest edge and forest interior), and three small-scale litter disturbance treatments (control, litter completely removed, and litter partially removed). Seeds were sown into plots in November, and plots were monitored for two years. Lowland plots had greater soil moisture and less litter per unit area than upland plots. In general, forest edge plots had greater understory cover and light availability and lower overstory cover than forest interior plots. Rosette survival, mature plant survival, plant biomass, height, and fruit and seed production were significantly greater for plants in the lowland compared with plants in the upland. Germination, rosette survival, mature plant survival, and reproduction were significantly greater in the forest edge plots when compared with interior plots. Litter disturbance had no significant effect on germination, growth, or reproduction. It is apparent that site colonization by A. petiolata was not dependent on the creation of patches of bare soil by disturbance, since plants were capable of invading sites with an intact litter layer. Alliaria petiolata growth and reproduction was greatest in plots with adequate soil moisture and increased light availability. Therefore, mesic forests with a more open canopy structure and forest trails or edges may be the most vulnerable to invasion and the most difficult sites to manage. Drier upland forest interiors, which were more resistant to invasion, may be more responsive to management techniques. Web of Science Alliaria petiolata United States Ohio Ridges Land Laboratory 39 82 Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 1904 Scott, NA; Saggar, S; McIntosh, PD 2001 Biogeochemical impact of Hieracium invasion in New Zealand's grazed tussock grasslands: Sustainability implications journal ECOLOGICAL APPLICATIONS 11 5 1311 1322 The establishment and spread of invasive plants could be enhanced by plant-soil feedbacks that alter the cycling of biologically important elements. In New Zealand. overgrazing of tussock grasslands in the South Island has led to land degradation and simultaneous invasion of exotic weeds (primarily Hieracium spp.) over large areas. While Hieracium continues to spread rapidly, little is known about variation in the impact of Hieracium across landscapes characterized by a range of environmental conditions. We examined the impact of Hieracium invasion on soil and ecosystem processes first at the scale of individual patches under one disturbance regime and uniform *environment* (i.e.. one aspect and elevation), and then under different environmental conditions (aspects) and disturbance regimes (long-term grazing, no grazing since 1978). Around individual plants on heavily grazed north-facing slopes with significant bare ground, Hieracium invasion increased total soil C and N and lowered soil pH and mineral N relative to the adjacent herb-field vegetation. Soil C mineralization was higher, and net N mineralization was lower under Hieracium than under the adjacent herb-field vegetation. Litter quality differences did not explain differences in net N mineralization. However, results from C-13 NMR spectroscopy suggest qualitative differences in organic-matter inputs under Hieracium compared to native vegetation. These results suggest that Hieracium may lower N availability by outcompeting native plants for mineral N, making it difficult for native species to reestablish and promoting the spread of Hieracium. Our results differed on cooler, wetter, less heavily grazed south-facing slopes, where soil C and N pools and cycling rates were lower under Hieracium than under the native herb-field vegetation (which differed across aspects). Whether the (longer term) impact of Hieracium on the south aspect resembles that on the north aspect may depend on management. Our results suggest that Hieracium invasion can alter ecosystem processes, but the impact of invasion may depend on the ecological context (aspect and disturbance) prior to invasion. Web of Science Hieracium spp. New Zealand South Island Glencairn Station, upper Waitaki Valley, South Island, -44 170.771484 Field - Experimental;Field - Observational terrestrial Grassland Impacts;Invasion Hyp. Disturbance primary 1905 Ehrenfeld, JG; Kourtev, P; Huang, WZ 2001 Changes in soil functions following invasions of exotic understory plants in deciduous forests journal ECOLOGICAL APPLICATIONS 11 5 1287 1300 Eastern deciduous forests have been invaded by two exotic species that often dominate the understory vegetation. Berberis thunbergii, a woody shrub. forms dense thickets, while Microstegium vimineum, a C-4 grass, forms continuous lawns; the two species often co-occur. We hypothesized that a variety of characteristics of the exotic species may cause soil-based ecosystem processes to change following invasion, and that such changes could establish positive feedback processes that enhance the spread of the exotic. We examined changes in soil pH, nitrogen cycling, and litter dynamics in stands infested with both species in three locations in northern New Jersey (USA). Soils directly beneath each of the two exotics had higher pH values and higher nitrification rates and often had higher net N mineralization rates than did soils beneath adjacent patches of the most common native understory shrub, Vaccinium pallidum. These differences could be replicated in the greenhouse by growing the exotics in previously uninvaded soils. Berberis litter was much higher in N concentration than was litter of the native species; it decomposed more rapidly than litter of native dominant tree species, with little or no immobilization of N. In contrast, Microstegium litter decomposed more slowly than the native species' litters, and it immobilized N. We suggest that the same change in soil-increased pH and nitrification-result from different combinations of mechanisms in the two exotic species. Both species evidently favor uptake of nitrate. which may elevate pH. However, Berberis combines large biomasses of N-rich roots with N-rich leaf litter, while Microstegium populations combines small biomasses of N-rich roots with small biomasses of N-poor litter that leave much of the surface soil with few roots. The ability to change soil functions may be an important and previously unrecognized characteristic that renders species capable of invading intact communities, while the likelihood that changes in soil functions can alter the growth of the exotics may be an important component of invasibility. Web of Science Berberis thunbergii; Microstegium vimineum United States New Jersey Morristown National Historical Park; Allamuchy State Park; Worthington State Forest; Field - Observational;Greenhouse terrestrial Deciduous Forest Impacts;Invasion Hyp. Ecosystem Engineers primary 1909 Radho-Toly, S; Majer, JD; Yates, C 2001 Impact of fire on leaf nutrients, arthropod fauna and herbivory of native and exotic eucalypts in Kings Park, Perth, Western Australia journal AUSTRAL ECOLOGY 26 5 500 506 The vegetation of Kings Park, near the centre of Perth, Western Australia, once had an overstorey of Eucalyptus marginata (jarrah) or Eucalyptus gomphocephala (tuart), and many trees still remain in the bushland parts of the Park. Avenues and roadsides have been planted with eastern Australian species, including Eucalyptus cladocalyx (sugar gum) and Eucalyptus botryoides (southern mahogany), both of which have become invasive. The present study examined the effect of a recent burn on the level of herbivory on these native and exotic eucalypts. Leaf damage, shoot extension and number of new leaves were measured on tagged shoots of saplings of each tree species in unburnt and burnt areas over an 8-month period. Leaf macronutrient levels were quantified and the number of arthropods on saplings was measured at the end of the recording period by chemical knockdown. Leaf macronutrients were mostly higher in all four species in the burnt area, and this was associated with generally higher numbers of canopy arthropods and greater levels of leaf damage. It is suggested that the pulse of soil nutrients after the fire resulted in more nutrient-rich foliage, which in turn was more palatable to arthropods. The resulting high levels of herbivory possibly led to reduced shoot extension of E. gomphocephala, E. botryoides and, to a lesser extent, E. cladocalyx. This acts as a negative feedback mechanism that lessens the tendency for lush, post-fire regrowth to outcompete other species of plants. There was no consistent difference in the levels of the various types of leaf damage or of arthropods on the native and the exotic eucalypts, suggesting that freedom from herbivory is not contributing to the invasiveness of the two exotic species. Web of Science Eucalyptus cladocalyx; Eucalyptus botryoides Australia Western Australia Kings Park Field - Observational terrestrial Deciduous Forest Invasion Hyp. Enemy Release primary 1910 Clark, SE; Van Driesche, RG; Sturdevant, N; Elkinton, J; Buonaccorsi, JP 2001 Effects of site characteristics and release history on establishment of Agapeta zoegana (Lepidoptera : Cochylidae) and Cyphocleonus achates (Coleoptera : Curculionidae), root-feeding herbivores of spotted knapweed, Centaurea maculosa journal BIOLOGICAL CONTROL 22 2 122 130 We evaluated several factors to identify features or practices that might increase the probability of establishment following the release of two root-feeding insects (the cochylid moth Agapeta zoegana L. and the weevil Cyphocleonus achates Fahraeus) that attack the invasive plant, spotted knapweed (Cen. taurea maculosa Lamarck). At each of 99 sites where releases had been made in previous years, we assessed (1) the number of insects of each species released, (2) the number of years in which releases were made, (3) the number of years since the first release, (4) the size of the knapweed infestation, (5) its shape (linear, large single patch, many small patches), (6) the knapweed plant density, and (7-18) 12 physical site characteristics: habitat type, elevation, percentage slope, aspect, topographic type, forest structure at or by the site, disturbance factors, land use category, percentage forest canopy at or near site, percentage bare soil, annual precipitation, and soil type. We found that continuous, nonlinear patches of spotted knapweed on loamy soil that were surrounded by even-age forest stands had the highest rates of establishment for A. zoegana, but likelihood of establishment was not greater for larger releases (>200 adults). This suggests that roadside strips of knapweed should not be selected as release sites and that many, smaller releases (100-200 adults) are better than fewer, larger releases (300-500 adults or greater). For the weevil C. achates, we found that the probability of establishment was also greatest in continuous knapweed patches, rather than in strips, and that larger infestations (>2 ha) were better than smaller infestations. Establishment was also highest at mid-elevations (750-1500 m), compared to higher or lower locations. (C) 2001 Academic Press. Web of Science the cochylid moth Agapeta zoegana L.; the weevil Cyphocleonus achates Fahraeus; Centaurea maculosa Lamarck United States Montana; Washington; Idaho Field - Experimental terrestrial Invasion Hyp. Preadaptation to Climate;Disturbance;Other parasite 1911 Grosholz, E 2001 Small spatial-scale differentiation among populations of an introduced colonial invertebrate journal OECOLOGIA 129 1 58 64 Introduced species frequently undergo rapid evolutionary change in ecologically important traits that may strongly influence their performance in their introduced range. But for many introduced species, and particularly those in marine systems, the spatial and temporal dimensions of this evolutionary change are largely unknown. In this study, I conducted a common garden transplant experiment using replicate clones of an introduced tunicate, Botrylloides sp., collected from three sites in the southern Gulf of Maine to test for differential growth and survival in response to local thermal regimes. This species has a restricted larval development period, which may permit significant population differentiation over relatively small spatial scales. I found dramatic among-site differences in survival rates: tunicates collected from both the transplant site and from a distant northern site had high survival, while those collected from a southern site experienced 100% mortality. The most likely cause of this differential mortality was an anomalous upwelling event that produced some of the coldest mid-summer temperatures in the last 10 years based on NOAA weather buoy data. I also found significant differences in growth rates among sites as well as among clones within a site in comparison with growth-rate differences within clones. An estimate of broad-sense heritability based on these data was consistent with a genetic basis for among-site differences in growth rates, which were strongly predictive of subsequent mortality. I conclude that this species has undergone significant evolutionary change that has resulted in population differentiation with respect to temperature tolerances among sites separated by < 60 km. Web of Science tunicate, Botrylloides sp. United States Maine Cape Neddick; Isles of Shoals; near Gloucester, Massachusetts 43.1833;42.9667;42.6833 -70.6;-70.6167;-70.6167 Garden marine Intertidal/Near Shore Invasion Hyp. Evolution in General filter 1915 Levine, CM; Stromberg, JC 2001 Effects of flooding on native and exotic plant seedlings: implications for restoring south-western riparian forests by manipulating water and sediment flows journal JOURNAL OF ARID ENVIRONMENTS 49 1 111 131 Unregulated streams of the U.S. South-west typically carry large sediment loads during high flow. Seedlings can be injured or killed by floods that deposit sediment, but as seedlings grow larger they develop greater resistance to damage from flood flows. On dam-regulate streams, natural sedimentation processes are interrupted, possibly altering competitive dynamics among seedlings. In this suite of experiments, seeds of three native woody species, Baccharis salicifolia, Populus fremontii, Salix gooddingii, and an exotic, Tamarix ramosissima, were sawn in greenhouse pots. Seedlings were experimentally buried by sediment at progressive age intervals up to ninety days. Sediment treatments varied in terms of depth (1 and 2 cm) and method of application (undisturbed sifting or forceful burial). Our studies indicated that at an early age, P. fremontii had significantly greater ability than T ramosissima, S. gooddingii and B. salicifolia to survive 1 cm sifted sediment deposition. However, as the seedlings became taller, survivorship of S. gooddingii and T. ramosissima approached or equalled that of P. fremontii. Tamarix ramosissima had greater survivorship than native species only when it also was taller; in some cases, natives had greater survivorship when they were shorter than T. ramosissima. Populus fremontii survived I cm of sediment deposition in large numbers by the time it reached 2 cm tall; a size that it reached at a very young age (< 2 weeks). Salix gooddingii showed high survivorship at 3-4 cm, but required five weeks to achieve this threshold height. Tamarix ramosissima survived in large numbers when it reached a height range of 4-6 cm, a value it did not attain until it also was nearly 5 weeks of age. These results suggest that P. fremontii may be more competitive than T. ramosissima under natural sediment flow regimes. One approach to managing for native species involves restoring the physical conditions under which they are more competitive. Based on the results of our experiments and those of others, we suggest ways in which discharges of water and sediment in degraded reaches could be managed to favor the establishment of desired native species. (C) 2001 Academic Press. Web of Science Tamarix ramosissima United States Arizona Greenhouse terrestrial Riparian Invasion Hyp. Inherent Superiority Broad Tolerances primary 1916 Moen, J; Meurk, CD 2001 Competitive abilities of three indigenous New Zealand plant species in relation to the introduced plant Hieracium pilosella journal BASIC AND APPLIED ECOLOGY 2 3 243 250 The competitive abilities of three montane indigenous New Zealand plant species (Acaena buchananii, Festuca novae-zelandiae, and Raoulia australis) when growing with the locally invasive, introduced Hieracium pilosella were compared in an outdoor pot experiment. Competitive ability was divided into the competitive effect, or the ability to deplete resources, and the competitive response, or the ability to tolerate low resource levels. The plants were grown in pots with or without Hieracium, in shade or full sunlight, and with high or low soil fertility. The competitive response rankings showed consistent hierarchies in the different treatments with Festuca being less suppressed than Acaena and Raoulia. Festuca performed especially well in low soil fertility and in shaded treatments, while the other two species were strongly suppressed by Hieracium even in those conditions. However, all three species did relatively better (less badly) in the low fertility and shaded treatments than in the more resource-rich treatments when interacting with Hieracium. The effect on Hieracium biomass of the indigenous species was generally small and the rankings of competitive effect showed no agreement between the species in the different environmental treatments. We suggest that competitive rankings based on the competitive response component is likely to be a more sensitive measure of competitive ability for these indigenous, slow-growing plants. The results also indicates that these two components of a plant's competitive ability were negatively correlated and thus reflect trade-offs in dealing with competitive situations. Finally, in competition with Hieracium, low-growing indigenous species are likely to perform best when nutrients and light are maintained at low levels. Web of Science Hieracium pilosella New Zealand South Island Mackenzie Basin -43.977005 170.090332 Garden terrestrial Impacts;Fundamentals;Invasion Hyp. Inherent Superiority Superior Competitor primary 1917 Leiss, KA; Muller-Scharer, H 2001 Population dynamics of the annual plant Senecio vulgaris in ruderal and agricultural habitats journal BASIC AND APPLIED ECOLOGY 2 1 53 64 The annual plant Senecio vulgaris has migrated from ruderal to agricultural habitats resulting in weed populations. The population dynamics of S. vulgaris and its naturally associated rust fungus Puccinia lagenophorae were investigated as a basis for the biological control of S. vulgaris with the rust. A detailed basic study at a single ruderal site and a parallel investigation at each five ruderal and five agricultural sites were conducted from April to November 1997. During the whole period of study the spatial distribution of plants was aggregated and plants showed a relatively large size hierarchy as indicated by mean values of the Gini coefficient higher than 0.5. Seedling establishment appeared to be a major factor influencing the dynamics of S. Vulgaris. The importance of seedling establishment, together with the observed short generation time of 5 weeks and the broad range of plant sizes at reproduction classifies S. vulgaris as a ruderal strategist. The population dynamics of S. vulgaris differed between the ruderal and the agricultural habitat. Plants of S. vulgaris at the ruderal habitat survived over winter, resulting in greater population sizes (0.1 to 1 of the maximum) and a majority of plants in flower and seed set (31.9%) in spring. At the agricultural habitat, where only a few S. vulgaris winter due to weed control measures, population sizes in spring were smaller (0 to 0.16 of the maximum) with mainly vegetative plants (66.7%). The limited number of suitable hosts at the agricultural habitat in spring lead to a delay of rust infection until August, in contrast to the ruderal habitat where the rust was already present in April. In both habitats mature plant stages were more susceptible to rust infection than vegetative stages. Manipulating the dynamics of the host over winter may enhance rust epidemics in spring serving as biological control of S. vulgaris. Web of Science Senecio vulgaris Switzerland Arconciel; Sensine; Praz; Chesopelloz; Corjolens; Coussiberle; Sion; Müntschemier; Hauterive; Courtepin 46.748801 7.121372 Field - Observational terrestrial Urban Invasion Hyp. Enemy Release primary 1920 Lindenmayer, DB; McCarthy, MA 2001 The spatial distribution of non-native plant invaders in a pine-eucalypt landscape mosaic in south-eastern Australia journal BIOLOGICAL CONSERVATION 102 1 77 87 Factors influencing the spatial distribution of two major species of non-native plants, blackberry (Rubus fruticosus) and radiata pine (Pinus radiata) wildlings in a fragmented forest landscape in south-eastern Australia were quantified. A total of 1067 plots within three broad groups of sites was surveyed for these two non-native plant species. The sites were in large continuous areas of native eucalypt forest, an extensive plantation of P. radiata, and sites in patches of remnant eucalypt forest embedded within the pine plantation. In the case of the 507 plots located within patches of remnant eucalypt forest, an array of variables (e.g. distance to surrounding pine plantation, and floristic and structural attributes) was measured and used in statistical analyses of non-native plant occurrence. P. radiata wildlings were totally absent from plots in large continuous areas of native eucalypt forest, but present at 5% of plots within patches of eucalypt remnants embedded within the pine plantation. Logistic regression showed that the occurrence of P. radiata wildlings in the eucalypt remnants was significantly higher in plots where the neighbouring pine plantation had been established for a long time, plots that were dominated by dry eucalypt forest types, and plots with a limited cover of ground vegetation. The occurrence of R. fruticosus differed significantly (P<0.001) between the groups of sites; 59% of plots in the pine plantation, 41% in the eucalypt remnants, and 7% in continuous areas of native forest were invaded. For the eucalypt remnants, the occurrence of this species was significantly greater in plots close to the surrounding pine plantation, with fewer species of native shrubs, in wet eucalypt forest types, and with low values for both eucalypt basal area and rock cover. The results of this study indicate that even though non-native plant invasion is already relatively extensive in the study area, it is likely to further increase. The array of factors influencing the spread and establishment of P. radiata wildlings and R. fruticosus indicate that the control of these non-native plants will be extremely difficult in the existing plantation estate. However, the adoption of some simple protocols could make it feasible to limit their spread to newly established areas of the pine plantation estate. (C) 2001 Elsevier Science Ltd. All rights reserved. Web of Science blackberry (Rubus fruticosus); radiata pine (Pinus radiata) New South Wales Tumut region of southern New South Wales -35.272532 148.222046 Field - Observational terrestrial Coniferous Forest Invasion Hyp. Propagule Pressure;Disturbance primary 1923 Mazia, CN; Chaneton, EJ; Ghersa, CM; Leon, RJC 2001 Limits to tree species invasion in pampean grassland and forest plant communities journal OECOLOGIA 128 4 594 602 Factors limiting tree invasion in the Inland Pampas of Argentina were studied by monitoring the establishment of four alien tree species in remnant grassland and cultivated forest stands. We tested whether disturbances facilitated tree seedling recruitment and survival once seeds of invaders were made available by hand sowing. Seed addition to grassland failed to produce seedlings of two study species, Ligustrum lucidum and Ulmus pumila, but did result in abundant recruitment of Gleditsia triacanthos and Prosopis caldenia. While emergence was sparse in intact grassland, seedling densities were significantly increased by canopy and soil disturbances. Longer-term surveys showed that only Gleditsia became successfully established in disturbed grassland. These results support the hypothesis that interference from herbaceous vegetation may play a significant role in slowing down tree invasion, whereas disturbances create microsites that can be exploited by invasive woody plants. Seed sowing in a Ligustrum forest promoted the emergence of all four study species in understorey and treefall gap conditions. Litter removal had species-specific effects on emergence and early seedling growth, but had little impact on survivorship. Seedlings emerging under the closed forest canopy died within a few months. In the treefall gap, recruits of Gleditsia and Prosopis survived the first year, but did not survive in the longer term after natural gap closure. The forest community thus appeared less susceptible to colonization by alien trees than the grassland. We conclude that tree invasion in this system is strongly limited by the availability of recruitment microsites and biotic interactions, as well as by dispersal from existing propagule sources. Web of Science Gleditsia triacanthos L.; Ulmus pumila L.; Ligustrum lucidum Ait.; Prosopis caldenia Burk. Argentina Carlos Casares Inland Pampas; Estancia San Claudio -36 -61.0833 Field - Experimental terrestrial Grassland Fundamentals;Invasion Hyp. Disturbance primary 1924 Meng, L; Matern, SA 2001 Native and introduced larval fishes of Suisun Marsh, California: The effects of freshwater flow journal TRANSACTIONS OF THE AMERICAN FISHERIES SOCIETY 130 5 750 765 We sampled ichthyoplankton weekly in Suisun Marsh in the San Francisco Estuary front February to June cacti year from 1994 to 1999. We collected approximately 227,900 fish, predominantly shimofuri goby Tridentiger bifasciatus (60%) and prickly sculpin Cottus asper (33%). Principal components analysis and canonical correspondence analysis were used to explore relationships among several environmental variables and the 13 species that made up 99.96% of the catch. A group of native fishes (prickly sculpin. Sacramento sucker Catostomus occidentalis, threespine stickleback Gasterosteus aculeatus, longfin smelt Spirinchus thaleichthys, and Sacramento splittail [also known simply as splittail] Pogonichthys macrolepidotus) were associated with the cool temperatures and higher outflows characterizing early-season conditions in Suisun Marsh. In contrast, a group of introduced species (shimofuri goby, inland silverside Menidia beryllina, striped bass Morone saxatilis, and threadfin shad Dorosoma petenense) were associated with the warm temperatures and lower outflows that characterize late-season marsh conditions. Catch composition was similar among marsh waterways (called sloughs), except for Cordelia Slough in the western marsh, which had lower total catch, greater diversity, and most of the threespine stickleback, northern anchovy Engraulis mordax, and longfin smelt. Longfin smelt were captured mostly in February and March, whereas delta smelt Hypomesus transpacificus catches were later and more evenly distributed throughout the marsh. Delta smelt catches overlapped temporally and spatially with catches of the introduced wakasagi H. nipponensis. Sacramento splittail catches were confined mostly to 1995, a year when high flows peaked during their spawning season in March and April. Our results suggest that temperature and interannual variations in freshwater flow arc important for determining habitat quality for native and introduced larval fishes. We conclude that mimicking natural flow regimes in this highly regulated system is important for early life stages of native fishes. Web of Science shimofuri goby, inland silverside Menidia beryllina, striped bass Morone saxatilis, and threadfin shad Dorosoma petenense United States California Suisun Marsh, San Francisco Estuary 38.23818 -122.066345 Field - Observational estuarine Intertidal/Near Shore Invasion Hyp. Other omnivore 1928 Roy, K; Jablonski, D; Valentine, JW 2001 Climate change, species range limits and body size in marine bivalves journal ECOLOGY LETTERS 4 4 366 370 We use data on the Pleistocene and modern range limits of Californian marine bivalves to show that species that shifted their geographical ranges in response to Pleistocene climatic fluctuations were preferentially drawn from the large end of the regional body size-frequency distributions. This difference is not due to phylogenetic effects (i.e. dominance of extralimital species by a few large-bodied clades), differences among major ecological categories (burrowing versus surface-dwelling, or suspension feeding versus non-suspension feeding), or differences in modes of reproduction and larval development. In addition, we show that successful invasive species of bivalves in present-day marine habitats also tend to be large-bodied, despite the difference in mechanisms between present-day and Pleistocene range expansions. These results indicate that range limits of large-bodied bivalve species are more unstable than small-bodied ones, and that body size and its correlates need to be considered when attempting to predict the responses of marine communities to climate change, biotic interchanges and human-mediated invasions. Web of Science Many United States California Theoretical/Modeling marine Intertidal/Near Shore Invasion Hyp. Other filter 1929 Mitchell, RJ; Ankeny, DP 2001 Effects of local conspecific density on reproductive success in Penstemon digitalis and Hesperis matronalis journal OHIO JOURNAL OF SCIENCE 101 2 22 27 We investigated the effects of plant density on reproductive success for two insect-pollinated plant species-the native North American wildflower Penstemon digitalis (Foxglove-leaved Penstemon), and the showy introduced weed Hesperis matronalis (Dame's Rocket). We found no indication that local density (within 3.0 m) affected reproductive success (seeds per fruit, proportion fruit set, total seeds per plant) for either species. Penstemon digitalis suffered heavy fruit predation from micro-lepidopterans, and such damage tended non-significantly to increase with density. We discuss the reasons for our results, and suggest that an understanding of those causes is important for conservation. Web of Science Hesperis matronalis (Dame's Rocket) United States Ohio MetroParks 41.2597 81.5211 Field - Observational terrestrial Fundamentals primary 1932 Frenot, Y; Gloaguen, JC; Masse, L; Lebouvier, M 2001 Human activities, ecosystem disturbance and plant invasions in subantarctic Crozet, Kerguelen and Amsterdam Islands journal BIOLOGICAL CONSERVATION 101 1 33 50 Recent floristic surveys of the French islands of the southern Indian Ocean (Ile de la Possession, in the Crozet archipelago, Iles Kerguelen and Ile Amsterdam) allow a comparison of the status of the alien vascular plant species in contrasted environmental and historical situations. Four points are established: (1) the current numbers of alien plant species are almost the same on Amsterdam (56) and La Possession (58), slightly higher on Kerguelen (68); (2) some of these species are common to two or three islands but a high number of them are confined to only one island (18, 28 and 28 on La Possession, Kerguelen and Amsterdam, respectively); (3) all the alien plant species are very common species in the temperate regions of the northern hemisphere and belong to the European flora; and (4) a high proportion of the introduced species are present on the research stations or their surroundings (100, 72 and 84% on La Possession, Kerguelen and Amsterdam, respectively). These results are discussed in term of propagule pressure (mainly attributed to ships visiting these islands), invasibility of such ecosystems (in relation to climatic conditions and degree of disturbance by previous or current human activities such as sheep farming or waste deposits) and invasion potential of alien plant species. (C) 2001 Elsevier Science Ltd. All rights reserved. Web of Science Many French islands of the southern Indian Ocean Ile de la Possession, in the Crozet archipelago, Iles Kerguelen and Ile Amsterdam -46.411825 51.738052 Field - Observational terrestrial Invasion Hyp. Enemy Of My Enemy;Preadaptation to Climate;Disturbance primary 1933 French, K; Major, RE 2001 Effect of an exotic Acacia (Fabaceae) on ant assemblages in South African fynbos journal AUSTRAL ECOLOGY 26 4 303 310 Ant assemblages in South African fynbos invaded by Acacia saligna were compared with ant assemblages in undisturbed fynbos to determine whether ant assemblages change under exotic plants that produce ant-dispersed seeds. Overall, no differences in the species richness of ants were found between weed-infested and native sites but there were differences in both ant abundance and the composition of the ant assemblage. Ants were much less abundant in weed-infested sites. To investigate whether changes in ant assemblages in weed-infested areas could be due to a preference for native seeds over exotic seeds, seeds of a range of species were offered to ants and ants that handled seeds were identified. Thirteen species of ants handled A. saligna seeds and there was no evidence to suggest that the ant assemblage as a whole preferred native seeds to A. saligna seeds. Hypotheses that may account for this pattern are discussed. Web of Science Acacia saligna South Africa Cape Town -33.895497 18.428192 Field - Observational terrestrial Chaparral/Shrublands Impacts;Fundamentals primary 1934 Safford, HD; Harrison, SP 2001 Grazing and substrate interact to affect native vs. exotic diversity in roadside grasslands journal ECOLOGICAL APPLICATIONS 11 4 1112 1122 We compared the native and exotic species composition of ungrazed roadside verges with that of adjacent grazed interiors in the grasslands of California's inner northern coast range (Napa and Lake Counties). We sampled 72 pairs of verge and interior quadrats at five sites representative of the region's grasslands, on both fertile (loan]) and infertile (serpentine) soils, avoiding all obvious forms of roadside physical disturbance. We found that, on serpentine soils, ungrazed verges had a higher proportion of exotic species than grazed interiors; on nonserpentine soils, the reverse was true. Within serpentine soils, native species were more prevalent in quadrats with lower biomass within nonserpentine, natives were more prevalent in quadrats receiving less radiation. Overall, the total species diversity was higher in grazed interiors than on ungrazed verges, regardless of the fertility of the substrate. Our results indicate that the ecological role of roadside verges depends oil the interactive effects of community composition and history, environmental gradients, and land use practices that characterize a region. Web of Science Many United States California inner northern coast range (Napa and Lake Counties) 38.4 -122.25 Field - Observational terrestrial Grassland;Chaparral/Shrublands Invasion Hyp. Disturbance primary 1935 Duncan, RP; Bomford, M; Forsyth, DM; Conibear, L 2001 High predictability in introduction outcomes and the geographical range size of introduced Australian birds: A role for climate journal JOURNAL OF ANIMAL ECOLOGY 70 4 621 632 1. We investigated factors hypothesized to influence introduction success and subsequent geographical range size in 52 species of bird that have been introduced to mainland Australia. 2. The 19 successful species had been introduced more times, at more sites and in greater overall numbers. Relative to failed species, successfully introduced species also had a greater area of climatically suitable habitat available in Australia, a larger overseas range size and were more likely to have been introduced successfully outside Australia. After controlling for phylogeny these relationships held, except that with overseas range size and, in addition, larger-bodied species had a higher probability of introduction success. There was also a marked taxonomic bias: gamebirds had a much lower probability of success than other species. A model including five of these variables explained perfectly the patterns in introduction success across-species. 3. Of the successful species, those with larger geographical ranges in Australia had a greater area of climatically suitable habitat, traits associated with a faster population growth rate (small body size, short incubation period and more broods per season) and a larger overseas range size. The relationships between range size in Australia, the extent of climatically suitable habitat and overseas range size held after controlling for phylogeny. 4. We discuss the probable causes underlying these relationships and why, in retrospect, the outcome of bird introductions to Australia are highly predictable. Web of Science Many Australia Theoretical/Modeling Invasion Hyp. Inherent Superiority;Propagule Pressure;Preadaptation to Climate Rapid Growth herbivore;omnivore 1939 Wonham, MJ; Walton, WC; Ruiz, GM; Frese, AM; Galil, BS 2001 Going to the source: role of the invasion pathway in determining potential invaders journal MARINE ECOLOGY-PROGRESS SERIES 215 0 1 12 Biological invasions are an increasing agent of change in aquatic systems, and ballast-water transfer in ships is a leading pathway of these invasions. During sequential stages of ballast transfer (uptake, transport, and release), the density and diversity of the plankton assemblage is selectively filtered, determining the pool of potential invaders. Understanding taxon-specific patterns of mortality along the invasion pathway is key to understanding and predicting successful invasions. We quantified taxon-specific trends in plankton mortality during a 16 d trans-Atlantic ballast water voyage. In the ballast tanks, we collected a miminum of 50 live taxa. Over 50 % of taxa and > 98% of organisms collected in initial samples were not detected at the end of the voyage. No ballasted organisms survived experimental transfer to coastal harbor water. We suggest that the invasion success of a particular taxon may be predicted both by high density at the end of a voyage (which is comparatively easy to measure) and by low mortality during a voyage (which may indicate good body condition, but is harder to measure). These 2 predictors were not, however, correlated across taxa. Mid-ocean exchange, the most widely used method for reducing ballast-mediated invasion risk, alters the pool of potential invaders. In an experimental test of mid-ocean exchange, 93 to 100 % of the coastal water and 80 to 100 % of the coastal organisms were removed. However, the total density and diversity of plankton in the ballast tanks increased significantly following exchange and in laboratory experiments ocean water was not lethal to coastal organisms. Web of Science Many Israel; United States Hadera; Baltimore voyage across Atlantic Ocean, ballast water Field - Observational marine Pelagic/Open Ocean Invasion Hyp. Propagule Pressure;Other 1941 Li, Y; Norland, M 2001 The role of soil fertility in invasion of Brazilian pepper (Schinus terebinthifolius) in Everglades National Park, Florida journal SOIL SCIENCE 166 6 400 405 Brazilian pepper (Schinus terebinthifolius Raddi), an exotic invasive plant, is native to South America. In south Florida, this plant has invaded abandoned agricultural lands, poorly managed pastures, roadsides, and canal banks extensively. The *Hole-in-the Donut (HID)*, approximately 4000 ha within the Everglades National Park, is a major site of invasion of this exotic plant. This area was previously short hydroperiod prairie and pineland, but it is now a monospecific stand of Brazilian pepper. It has been hypothesized that this transformation is related to rock-plowing soil (crushing the limestone bedrock to increase soil depth) and to intensive vegetable production 25 to 70 years ago. The objectives of this study were to compare the chemical and physical differences of soils from four land uses (undisturbed land, rock-plowed farm land, non-rock-plowed farm land, and restored land) and the mineral nutrient contents of Brazilian pepper and sawgrass (Cladium jamaicense Crantz). Farming in the HID area changed the soil chemical properties significantly through rock-plowing and the application of agrichemicals necessary for commercial vegetable production. Rock-plowing increased the percenage of rock fragments and the soil pH. Total concentrations of nutrients (N, P, Zn, and Cu) in soils were elevated in both rock-plowed and non-rock-plowed farm lands. Plant-available nutrients in soil of rock-plowed farm land increased about 3 times for P, 6 times for Zn, and 10 times for Cu. As a result of the increased soil fertility, concentrations of P and Zn in Brazilian pepper leaves were 5 and 3 times higher, respectively, than those in sawgrass. High correlation coefficients between leaf P and total and plant-available P in soils indicate that P enrichment in farmed soils facilitated the invasion of Brazilian pepper in this area. Web of Science Brazilian pepper (Schinus terebinthifolius Raddi) United States Florida Everglades National Park 25.336579 -80.906067 Field - Observational terrestrial Wetland Invasion Hyp. Disturbance primary 1942 Renne, IJ; Spira, TP; Bridges, WC 2001 Effects of habitat, burial, age and passage through birds on germination and establishment of Chinese tallow tree in coastal South Carolina journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 128 2 109 119 RENNE, I. J., T. P SPIRA (Department of Biological Sciences, Clemson University, Clemson, South Carolina 29634) AND W C. BRIDGES, JR. (Department of Experimental Statistics, Clemson University, Clemson, South Carolina 29634). Effects of habitat, burial, age and passage through birds on germination and establishment of Chinese tallow toe in coastal South Carolina. J. Torrey Hot. Sec. 128:000-000. 2001. - Factors affecting germination and seedling establishment of the nonindigenous, invasive Chinese tallow tree (Sapium sebiferum (L.) Roxb.) were investigated under greenhouse and held conditions. In greenhouse experiments, buried seeds had higher germination rates and percentages than surface seeds, and simulated and actual seed passage through the avian gut enhanced germination. One year of aging reduced germination and seed viability, particularly for seeds unhandled by birds. In the field, seedling emergence and survival were greater in mixed pine-hardwood forest than in pine-turkey oak forest or spoil areas. Planting date did not affect overall seedling emergence or survival. Seeds sown in March 1998 and 1999 in five coastal forests that contained established tallow trees emerged throughout the growing season. While seedling emergence rates varied, final seedling numbers were similar across habitats in 1998, but were lower and differed across habitats in 1999. Recruitment was thus spatially and temporally variable. Viability of seeds buried for one and two years ranged from 16 to 69% in the five habitats, but did not differ among habitats or length of burial time. Because habitat type did not affect seed dormancy (both years) and final seedling number (1998 only), we conclude that other factors influence the differential success of tallow trees among coastal forests in South Carolina. Management strategies (e.g., fire) should consider the seedling phenology and seed bank capability of tallow tree. Web of Science Chinese tallow tree (Sapium sebiferum (L.) Roxb.) United States South Carolina Gulf Coast 32.99023 -79.94751 Field - Experimental;Field - Observational;Greenhouse terrestrial Subtropical Forest Invasion Hyp. Mutualism Facilitation;Inherent Superiority Effective Disperser primary 1945 Crawford, JS; Wahren, CHA; Kyle, S; Moir, WH 2001 Responses of exotic plant species to fires in Pinus ponderosa forests in northern Arizona journal JOURNAL OF VEGETATION SCIENCE 12 2 261 268 Changes in disturbance due to fire regime in southwestern Pinus ponderosa forests over the last century have led to dense forests that are threatened by widespread fire. It has been shown in other studies that a pulse of native, early-seral opportunistic species typically follow such disturbance events. With the growing importance of exotic plants in local flora, however, these exotics often fill this opportunistic role in recovery. We report the effects of fire severity on exotic plant species following three widespread fires of 1996 in northern Arizona P. ponderosa forests. Species richness and abundance of all vascular plant species, including exotics, were higher in burned than nearby unburned areas. Exotic species were far more important, in terms of cover, where fire severity was highest. Species present after wildfires include those of the predisturbed forest and new species that could not be predicted from above-ground flora of nearby unburned forests. Web of Science Many United States Arizona 36.022447 -112.203369 Field - Observational terrestrial Coniferous Forest Invasion Hyp. Disturbance primary 1947 Harrison, S; Rice, K; Maron, J 2001 Habitat patchiness promotes invasion by alien grasses on serpentine soil journal BIOLOGICAL CONSERVATION 100 1 45 53 Serpentine soils are considerably less invaded by alien species than nonserpentine soils in California's North Coast Ranges. However, alien species are significantly more prevalent on small patches of serpentine (< 5 ha) than in the interiors (> 100 m from edges) of very large ones (< 1 km(2)). We studied reasons for this pattern, focusing on the Mediterranean annual grasses Avena fatua L. and Bromus hordeaceus L. Using field transects, we found that both Avena and Bromus were more common at the edges of large patches than in large-patch interiors, even though soils from edges were not significantly different from soils in interiors. Using a growth experiment, we found that soils from small patches did not support better growth of either grass than soils from large-patch interiors. We conclude that the observed pattern is probably caused by small patches and large-patch edges receiving a higher flow of propagules from the nonserpentine matrix, and not by differences in habitat suitability. In both species, populations from small serpentine patches outperformed nonserpentine populations when grown on small-patch soil. This suggests that small serpentine patches may promote the evolution of serpentine-tolerant ecotypes of these alien grasses. (C) 2001 Elsevier Science Ltd. All rights reserved. Web of Science Avena fatua L.; Bromus hordeaceus L. United States California Lake; Napa; Sonoma Counties 36.36 -123.07 Field - Observational terrestrial Invasion Hyp. Propagule Pressure;Disturbance primary 1950 Farnsworth, EJ; Ellis, DR 2001 Is purple loosestrife (Lythrum salicaria) an invasive threat to freshwater wetlands? Conflicting evidence from several ecological metrics journal WETLANDS 21 2 199 209 Conflicting interpretations of the negative impacts of invasive species can result if inconsistent measures are used among studies or sites in defining the dominance of these species relative to the communities they invade. Such conflicts surround the case of Lythrum salicaria (purple loosestrife). a widespread exotic wetland perennial. We describe here a 1999 study in which we quantified stand characteristics of L. salicaria and associated vegetation in arrays of 30 1-m(2) plots in each of five wet meadows in Connecticut, USA. We explored linear and non-linear relationships of above-ground plant biomass. stem density, and indices of species richness, diversity, and composition to gradients of L. salicaria dominance, including stem density, percent cover, and biomass. Species richness, other diversity metrics, and stem density of other species were not significantly correlated with the density or percent cover of L. salicaria stems. The relative importance values (number of quadrats in which they were found) of co-occurring species in low-density L. salicaria quadrats were significantly correlated with their relative importance in high-density L. salicaria quadrats, indicating that only modest shifts in abundance occurred as L. salicaria increased in density. No individual species were consistently associated with or repelled by the presence of L. salicaria across sites. In contrast to density and diversity features, however, the total biomass of species other than L. salicaria was significantly, negatively correlated with the total biomass of L. salicaria at each site surveyed. Lythrum salicaria in pure, dense stands maintained a greater above-ground standing biomass on invaded sites than uninvaded vegetation of similar physiognomy. This study demonstrates that hypotheses about L. salicaria effects can vary depending upon the ecological metric that is examined. Where one-time, correlative studies are the most feasible option, data taken on a range of metrics-especially biomass-should be taken to inform us about mechanisms by which L. salicaria invades and predominates in wetlands. Web of Science Lythrum salicaria (purple loosestrife) United States Connecticut Wethersfield; Hamden; Rocky Hill; Bloomfield; Southbury 41.21 -72.55 Field - Observational terrestrial Wetland Invasion Hyp. Community Species Richness primary 1953 Smith, MD; Knapp, AK 2001 Physiological and morphological traits of exotic, invasive exotic, and native plant species in tallgrass prairie journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 162 4 785 792 We compared 13 traits of invasive exotic, noninvasive exotic, and ecologically similar native species to determine if there are generalizable differences among these groups that relate to persistence and spread of exotic species in tallgrass prairie plant communities. When species were grouped as invasive (two species), noninvasive (five species), and native (six species), no differences were found for the suite of traits examined, likely because of the high variability within and between groups. However, when exotic species, regardless of invasiveness, were compared with the native species, specific leaf area was ca. 40% higher for the exotic species, a result that is consistent with that of other studies. This pattern was also observed for five of seven pairwise comparisons of exotic and native species with similar life history traits. In contrast, total end-of-season biomass was as much as three times higher for the native species in five of seven of the native-exotic species pairs. For other traits, differences between exotic and native species were species-specific and were generally more numerous for noninvasive than for invasive exotic species pair-wise comparisons. Thus, contrary to predictions, exotic species capable of successfully invading tallgrass prairie did not differ considerably from native species in most traits related to resource utilization and carbon gain. Moreover, invasive exotic species, those capable of displacing native species and dominating a community, were not distinct for the observed traits from their native counterparts. These results indicate that other traits, such as the ability to respond to resource pulses or herbivory, may explain more effectively why certain invasive species are able to invade these communities aggressively. Web of Science Many United States Kansas Konza Prairie Biological Station 39.10369 -96.60862 Field - Observational terrestrial Grassland Invasion Hyp. Inherent Superiority;Other Rapid Growth primary 1954 Goergen, E; Daehler, CC 2001 Reproductive ecology of a native Hawaiian grass (Heteropogon contortus; poaceae) versus its invasive alien competitor (Pennisetum setaceum; poaceae) journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 162 2 317 326 We compared the reproductive biology of a declining native grass, Heteropogon contortus, and its invasive alien competitor, Pennisetum setaceum, in Hawaii to identify differences that could explain why the alien has spread so successfully while the native has declined. Both species are drought-tolerant, perennial, C-4 bunch-grasses that rely on apomictic seeds for reproduction. In a series of field observations and greenhouse experiments, we compared the phenology, ovule production, seed production, and seed germination in H. contortus and P. setaceum. In the field, the alien produced two to nine times more seeds per plant than the native. Furthermore, the germination rate for fresh seeds was significantly greater for P. setaceum (45%) than for H. contortus (13%), giving the alien the ability to quickly spread after setting seed. In greenhouse experiments, clipping, burning, and pollen addition did not affect final reproductive output or seed-set rate in either species. However, P. setaceum recovered from clipping and burning more rapidly both in terms of vegetative regrowth and flowering, which likely gives it an advantage in disturbed environments and in competition with H. contortus. When plants were grown under varying nutrient and water conditions, P. setaceum failed to produce seeds in low-water and low-nutrient treatments. In contrast, H. contortus flowered and produced seeds in all treatments, indicating better tolerance of low resources. These findings help explain the current distribution of remnant H. contortus populations in the driest, most nutrient-poor habitats of the Hawaiian Islands. Web of Science Pennisetum setaceum United States Hawaii O'ahu; Hawai' Field - Observational;Greenhouse terrestrial Invasion Hyp. Inherent Superiority;Disturbance Broad Tolerances;Rapid Growth;High Reprod. Output primary 1957 Goslee, SC; Peters, DPC; Beck, KG 2001 Modeling invasive weeds in grasslands: the role of allelopathy in Acroptilon repens invasion journal ECOLOGICAL MODELLING 139 1 31 45 We used an individual plant-based simulation model (ECOTONE) to evaluate the importance of allelopathy and soil texture to the invasion of semiarid grasslands by the non-native perennial C, forb Acroptilon repens. We also assessed the sensitivity of model results to the negative effects of allelochemicals on recruitment and growth of perennial grasses. ECOTONE simulates the recruitment, growth, and mortality of individual plants on a small plot (0.12 m(2)) through time at an annual time step. A daily time step, multi-layer model of soil water dynamics (SOILWAT) was incorporated into ECOTONE to represent competition for soil water on a finer temporal scale. The model was parameterized for a shortgrass community in eastern Colorado, USA, using data available from the literature. Experimental simulations examined the effects of four soil textures and a range of levels of plant sensitivity to allelochemicals on the aboveground biomass of A. repens and of native perennial grasses. Simulation results showed that A. repens dominated the aboveground biomass on a plot only if native species were affected by allelopathic interactions. At moderate levels of plant sensitivity, A. repens became dominant faster and reached a higher proportion of the total biomass on fine- than on coarse-textured soils. Community composition and rate of A. repens dominance were more affected by the sensitivity of plant growth to allelochemicals than the sensitivity of species recruitment. Allelopathic interactions were an important component of the invasion dynamics of this perennial invasive weed, and further field investigations are warranted. (C) 2001 Elsevier Science B.V. All rights reserved. Web of Science Acroptilon repens United States Colorado Central Plains Experimental Range 40.816667 -107.783333 Theoretical/Modeling terrestrial Grassland Fundamentals;Invasion Hyp. Novel Weapons;Other primary 1959 Buckland, SM; Thompson, K; Hodgson, JG; Grime, JP 2001 Grassland invasions: effects of manipulations of climate and management journal JOURNAL OF APPLIED ECOLOGY 38 2 301 309 1. Climate change, in combination with the impacts of land use, will give rise to new opportunities for grassland invasion. This paper reports on the repercussions of a field experiment. 2. Plant species, sown into experimental plots as part of a 6-year study investigating factors limiting the success of seedling invasions, were resurveyed in 1999, 3 years after terminating experimental manipulations of climate, soil fertility and disturbance. 3. The most dramatic observation was the protracted expansion in populations of Brachypodium pinnatum, despite being at the northern limit of its distribution in Britain. In contrast, all other sown species, including those of both southern and widespread distribution in Britain, had become extinct, declined or remained unchanged in abundance. 4. Patterns of establishment were strongly deterministic. Populations of the southern grass, B. pinnatum, were highest in areas of the experimental plots unamended by fertilizer and physical disturbance, but expansion was apparently promoted by cessation of management. Among invaders of widespread distribution, two were dependent upon fertilizer addition (Arrhenatherum elatius and Dactylis glomerata), one significantly increased its cover with a combination of fertilizer and disturbance (Holcus lanatus), and one benefited from disturbance (Plantago lanceolata). 5. Two southern perennials, Origanum vulgare and Senecio erucifolius, both remained present in 1999 in plots that were formerly heated and subject to drought (1991-96), whereas they had become extinct in control plots. 6. Although the most successful invader was a rhizomatous perennial grass, an alternative strategy for survival and expansion was revealed after the severe drought in 1995: gap recolonization by annuals with a persistent seed bank. 7. Most notably, this study revealed the hidden potential of a native species to establish beyond its current range of distribution and, contrary to many recognized weeds, the capacity to achieve dominance in the absence of eutrophication or disturbance. This highlights the potent effects of climate change when plant traits effective for establishment coincide with the removal of current barriers to dispersal. Web of Science Many United Kingdom Derbyshire 53.25 -2.2 Field - Experimental terrestrial Grassland Invasion Hyp. Fluctuating Resources;Disturbance;Climate Change primary 1960 Grigulis, K; Sheppard, AW; Ash, JE; Groves, RH 2001 The comparative demography of the pasture weed Echium plantagineum between its native and invaded ranges journal JOURNAL OF APPLIED ECOLOGY 38 2 281 290 1. Echium plantagineum is native to the western Mediterranean Basin, where it is a common, but not dominant, component of species-rich annual grasslands. Since its introduction into Australia, E. plantagineum has spread to infest vast areas of predominantly agricultural land in south-east and south-west Australia, where it can be the dominant pasture species. 2. To unravel the ecological factors responsible for the high population abundance of E. plantagineum in Australia, its demography was compared between sites in the invaded and native ranges. Demographic parameters of E. plantagineum populations were estimated at a site near Canberra in south-eastern Australia, and at a site near Evora in southern Portugal. Identical factorial experiments were set up at each site with treatment combinations of the presence or absence of grazing and pasture competition. 3. The recruitment, survival, fecundity and seed bank dynamics of E. plantagineum populations were measured for each of the treatment combinations over 2 years at each site. These data allowed the estimation of demographic parameters describing the proportion of E. plantagineum individuals moving from one life-cycle stage to the next. 4. Seedling establishment fractions were two to five times greater at Canberra than at Evora, and seed bank incorporation rates were three times greater at Canberra than Evora. These demographic differences were those most likely to play an important role in the greater abundance of E. plantagineum in Australia compared with Mediterranean Europe. Neither seed bank survival rates nor seed production differed between populations at Canberra and Evora, while seedling survival rates were always lower at Canberra than at Evora. 5. Neither grazing nor pasture competition limited the seed production or seedling survival of E. plantagineum populations at Evora more than at Canberra. 6. An effective approach for the control of E. plantagineum in Australia may thus be through the reduction of the seedling establishment fraction. This may be achieved by maintaining significant pasture vegetation cover and reducing the available space for E. plantagineum establishment during autumn. Web of Science Echium plantagineum Australia Canberra Australian Capital Territory -35.18 149.08 Field - Experimental terrestrial Invasion Hyp. Inherent Superiority;Disturbance Superior Competitor primary 1965 Rouget, M; Richardson, DM; Milton, SJ; Polakow, D 2001 Predicting invasion dynamics of four alien Pinus species in a highly fragmented semi-arid shrubland in South Africa journal PLANT ECOLOGY 152 1 79 92 This study explored the determinants of spread of four alien Pinus species and the ability of models to predict invasion dynamics in a complex fragmented landscape. The role of environmental factors, natural and anthropogenic disturbance in relation to invasion history was assessed for different stages in the invasion process using a Geographic Information System. Pines escaped from plantations over the past 30 years and spread into the natural semi-arid shrubland (renosterveld). The pattern of spread was compared with a simulated random distribution using two different techniques, a standard logistic regression, and a new recursive modelling approach (Formal Inference-based Recursive Modelling; FIRM). FIRM analysis improved the accuracy of predictions and revealed interactive effects of variables hidden by the logistic regression analysis. More than 80% of isolated pine individuals were found in 20% of the habitat classified as suitable by the models. Soil pH was the most important predictor for the distribution of isolated trees, whereas the establishment of dense pine stands was largely determined by fire history. Differences in invasive behaviour could be explained by species attributes such as limited dispersal for P. canariensis, and better drought-tolerance for P. halepensis. Sixty-five percent of the current pine distribution was accurately predicted by the spatial distribution of the first trees to have invaded. Such models could be used to predict potential spread of invasive plants and gain a better understanding of the main factors driving the invasion process. However, the spread of invasive species in fragmented landscapes, strongly modified by human activities, is very complicated, and the spread remains difficult to predict in the long term. The dynamics of invasion are discussed in relation to changes in land use and disturbance regime. Web of Science Pinus canariensis; P. radiata; P. pinaster; P. halepensis South Africa Western Cape Kango Valley 33.36 22.06 Theoretical/Modeling terrestrial Chaparral/Shrublands Invasion Hyp. Preadaptation to Climate;Disturbance;Other primary 1968 Lambrinos, JG 2001 The expansion history of a sexual and asexual species of Cortaderia in California, USA journal JOURNAL OF ECOLOGY 89 1 88 98 1 The expansion histories of two South American species of Cortaderia, similar in morphology but differing profoundly in their breeding systems, were compared in California, USA. 2 Both species were introduced to California in the mid-1800s, but herbarium records indicate that the sexual C. selloana has expanded spatially at twice the rate of the asexual C. jubata. 3 The invasiveness of C. selloana has increased over time, whereas that of C. jubata has remained relatively constant. Populations of C. selloana now occupy more vegetation types and more non-ruderal habitats than C. jubata. 4 Populations of C. selloanu have experienced directional morphological change, whereas the morphology of C. jubata has been constant over the 90 years for which preserved specimens are available. 5 The invasion of an alien species appears to be a malleable process, rather than a singular event. Species traits, such as inbreeding, can be advantageous at some stages but disadvantageous at others. Alien species also adjust over time to the novel and diverse selective regimes that they encounter as they expand spatially. Sexual species may have a greater ability to adjust to diverse selective landscapes relative to asexual species. Web of Science Cortaderia selloana; Cortaderia jubata USA California 35 -120.5 Field - Observational terrestrial Wetland;Chaparral/Shrublands Fundamentals;Invasion Hyp. Evolution in General;Inherent Superiority Self Compatible 1969 Philip, LJ; Posluszny, U; Klironomos, JN 2001 The influence of mycorrhizal colonization on the vegetative growth and sexual reproductive potential of Lythrum salicaria L. journal CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE 79 4 381 388 Lythrum salicaria L., purple loosestrife, is a heterostylous, perennial plant with prolific and at times invasive vegetative growth and sexual reproduction. Sexual reproduction occurs following pollination and fertilization between two different floral morphs. We investigated the influence of the arbuscular mycorrhizal fungus, Glomus aggregatum Schenck and Smith emend. Koske, on the vegetative growth and sexual reproductive potential of L. salicaria. Mycorrhiza decreased plant biomass both aboveground and belowground. Flower production, number of days to anthesis, numbers of flowers per inflorescence, and inflorescence lengths were not significantly different between mycorrhizal and non-mycorrhizal treatments. However, pollen production per anther and per flower increased with mycorrhizal colonization. Though ovule production was not affected, some aspects of purple loosestrife morphology did change. Plants with mycorrhizae produced inflorescence (in lateral positions) further up the stem. In addition, flower distribution within an inflorescence differed according to morph (short, mid, and long style) such that in the mid and long morphs flower number increased with inflorescence length and was unevenly distributed, while in the short morph this distribution appeared even. The relative biomass of stems, leaves, lateral branches, and reproductive structures were not significantly different in mycorrhizal plants, whereas in the absence of mycorrhizal colonization, stem biomass was higher relative to other structures. This study suggests some vegetative and reproductive characteristics in purple loosestrife change with an association with arbuscular mycorrhizal fungi. Web of Science Lythrum salicaria Canada Ontario Guelph 43.46 -80.11 Greenhouse estuarine Wetland Invasion Hyp. Mutualism Facilitation primary 1972 Blaney, CS; Kotanen, PM 2001 Post-dispersal losses to seed predators: an experimental comparison of native and exotic old field plants journal CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE 79 3 284 292 Invasions by exotic plants may be more likely if exotics have low rates of attack by natural enemies, including post-dispersal seed predators (granivores). We investigated this idea with a field experiment conducted near Newmarket, Ontario, in which we experimentally excluded vertebrate and terrestrial insect seed predators from seeds of 43 native and exotic old-field plants. Protection from vertebrates significantly increased recovery of seeds; vertebrate exclusion produced higher recovery than controls for 30 of the experimental species, increasing overall seed recovery from 38.2 to 45.6%. Losses to vertebrates varied among species, significantly increasing with seed mass. In contrast, insect exclusion did not significantly improve seed recovery. There was no evidence that aliens benefitted from a reduced rate of post-dispersal seed predation. The impacts of seed predators did not differ significantly between natives and exotics, which instead showed very similar responses to predator exclusion treatments. These results indicate that while vertebrate granivores had important impacts, especially on large-seeded species, exotics did not generally benefit from reduced rates of seed predation. Instead, differences between natives and exotics were small compared with interspecific variation within these groups. Web of Science Many Canada Ontario Newmarket 44.043007 -79.456 Field - Experimental terrestrial Old Field Invasion Hyp. Enemy Release primary 1973 Champion, PD; Tanner, CC 2000 Seasonality of macrophytes and interaction with flow in a New Zealand lowland stream journal HYDROBIOLOGIA 441 3 1 12 Introduced submerged macrophytes have come to dominate many shallow water bodies in New Zealand, and are a common component of many lowland streams. We investigated the seasonal variation of macrophyte abundance, its influence on flow and channel volume, and the implications of this on stream habitat and functioning in Whakapipi Stream, a typical lowland stream draining a predominantly agricultural catchment. Abundance of macrophytes over the summer was primarily controlled by the phenological cycles of the two dominant species. Mean minimum total macrophyte biomass (36 g m(-2)) and cover (7%) occurred in winter (June and August, respectively), and mean maximum biomass (324 g m(-2)), and cover (79%) occurred in late summer (March and February respectively). Egeria densa comprised the majority of both cover and biomass during the study period, except early summer (December) when Potamogeton crispus was prevalent in the shallow stream reaches. Macrophyte beds had a major impact on summer stream velocities, reducing average velocities by an estimated 41%. Stream cross-sectional area was maintained at relatively stable levels similar to that recorded over winter, when stream discharge was in the order of seven times greater. The mean velocity distribution coefficient (alpha), and Manning's roughness coefficient (n) were dependent on and displayed a positive linear relationship with macrophyte abundance. The velocity distribution coefficient is recommended as a better indicator of macrophyte effects on velocity in natural streams, as it does not assume uniform velocity, channel depth and slope within the stream reach. Our study shows that submerged macrophytes play an important structuring role within the stream during the summer period, where macrophyte beds act as semi-permeable dams, retarding flow velocities and increasing stream depth and cross-sectional area. This promotes habitat heterogeneity by creating a greater range of flow velocity variation, and also provides large stable low-flow areas. Other likely ecosystem effects resulting from macrophyte/velocity interactions include increased sedimentation, potential for nutrient processing and increased primary production, both by macrophytes and attached epiphyton. The complex architecture of submerged macrophytes and their influence on stream flow may also provide an increased diversity of habitat for other aquatic biota. We propose that management of degraded lowland streams such as the Whakapipi Stream to maintain stretches with moderate quantities of submerged macrophytes interspersed with shaded areas would optimise stream health during low summer flows. Web of Science Egeria densa;Potamogeton crispus New Zealand Aukland Whakapipi Stream -37.251 174.964 Field - Observational lotic Impacts;Fundamentals primary 1974 Spyreas, G; Gibson, DJ; Basinger, M 2001 Endophyte infection levels of native and naturalized fescues in Illinois and England journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 128 1 25 34 Fungal endophytes are thought to play a major role in the ecology of many cool-season grasses. However, the frequency of endophyte infection in the wild remains poorly known. populations of wild fescues were tested for systemic fungal endophyte infection by taking samples from four native or naturalized species throughout southern Illinois (Festuca arundinacea, F. rubra, F. obtusa, and F. paradoxa), and one of these species (F. arundinacea) from native populations in England. The two grasses native to southern Illinois (F. obtusa and F. paradoxa) were highly infected (mean infection of 91 % and 100 %, respectively). The introduced grass F. rubra was uninfected. Festuca arundinacea showed variable levels of infection among populations in both southern Illinois and England (71 % and 64 %, respectively). The role of endophytes in natural systems is contingent upon infection levels that appear to vary widely among these four species. Furthermore, the use of agricultural cultivars may differentially affect infection levels of naturalized plants. Web of Science Festuca arundinacea; Festuca rubra USA Illinois Jackson county -12.3833 89.1833 Field - Observational terrestrial Grassland Fundamentals primary 1980 Green, EK; Galatowitsch, SM 2001 Differences in wetland plant community establishment with additions of nitrate-N and invasive species (Phalaris arundinacea and Typha xglauca) journal CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE 79 2 170 178 Restored prairie pothole wetlands in North America are often enriched by nitrate-N (NO3-N) that has been lost from surrounding agricultural systems. In addition, these wetlands are increasingly colonized by invasive taxa including Phalaris arundinacea L. and Typha x glauca Godr. To explore the impacts of NO3-N enrichment, suppression by invasive species, and the interaction of these factors on restored communities, we grew native sedge meadow communities from seed in greenhouse mesocosms and subjected them to NO3-N and invasive species for 4 months. Typha x glauca did not reduce overall native community biomass and actually enhanced Aster spp. biomass. Phalaris arundinacea suppressed growth of the native community to an equal relative extent across all NO3-N levels. The shoot biomass of the entire native community in untreated plots was similar to the P. arundinacea fraction of the treated plots. Phalaris arundinacea demonstrated greater plasticity in root-shoot allocation than the native community over the range of NO3-N inputs. Proportional allocation to root biomass was greater for P. arundinacea than for the native community at all but the highest NO3-N level. Both factors may be important in explaining dominance of P. arundinacea over the native community in a range of fertility conditions. Regardless of NO3-N inputs, the restoration of diverse native wetlands requires strict control of P. arundinacea during community establishment, as evidenced by the relatively rapid rate of suppression of native community biomass by P. arundinacea compared with T. x glauca. Web of Science Phalaris arundinacea; Typha x glauca USA Minnesota St. Paul 44.93 -93.1 Greenhouse wetland Wetland Invasion Hyp. Hybridization;Plasticity primary 1984 Smith, MD; Knapp, AK 2001 Size of the local species pool determines invasibility of a C-4-dominated grassland journal OIKOS 92 1 55 61 The size of the local species pool (i.e., species surrounding a community capable of dispersal into that community) and other dispersal limitations strongly influence native plant community composition. However, the role that the local species pool plays in determining the invasibility of communities by exotic plants remains to be evaluated. We hypothesized that the richness and abundance of exotic species would be greater in C-4-dominated grassland communities if the local species pool included a larger proportion of exotic species. We also predicted that an increase in the exotic species pool would increase the invasibility of sites thought to be resistant to invasion (annually burned grassland). To test these hypotheses, study plots were established within two long-term (> 20 yr) fire experiments at a tallgrass prairie preserve in NE Kansas (USA). Study plots were surrounded by either a small pool of exotic species (small species pool (SSP) plots; six species) or a larger exotic species pool (large species pool (LSP) plots; 18 species). We found that richness and absolute cover of exotic species were significantly (P < 0.001) lower ( 70 and 90%, respectively) in annually burned compared to unburned plots, regardless of the size of the exotic species pool. As predicted, exotic species richness was higher (P < 0.001) for LSP plots (3.9 per 250 m(2)) than for SSP plots (0.7 per 250 m(2)); however, absolute cover was unaffected by the size of the exotic species pool. In the absence of fire, plots with a LSP had four times as many exotic species than SSP plots. An increase in the local exotic species pool also increased the invasibility of annually burned grassland. Indeed, richness of exotic plant species in annually burned LSP plots did not differ from unburned plots with a SSP, indicating that a larger pool of exotic species countered the negative effects of fire. These findings have important implications for predicting how the invasion of plant communities may respond to human-induced global changes, such as habitat fragmentation. Community characteristics or factors such as frequent fires in grasslands may impart resistance to invasions by exotic species in large, intact ecosystems. However, when a large pool of exotic species is present, frequent fire may not be sufficient to limit the invasions of exotic plants in fragmented landscapes. Web of Science Many USA Kansas Manhattan 39.0833 96.5833 Field - Experimental terrestrial Grassland Invasion Hyp. Disturbance;Other primary 1985 Ridenour, WM; Callaway, RM 2001 The relative importance of allelopathy in interference: the effects of an invasive weed on a native bunchgrass journal OECOLOGIA 126 3 444 450 The relative importance of allelopathy and resource competition in plant-plant interactions has been vigorously debated but seldom tested. We used activated carbon to manipulate the effects of root exudates of Centaurea maculosa, a noxious weed in much of western North America, on root elongation rates and growth of the native bunchgrass Festuca idahoensis in order to investigate the relative importance of allelopathy in the total interference of Centaurea. In root observation chambers, Festuca root elongation rates decreased to approximate to 50% of the control, beginning 4 days before contacting Centaurea roots in silica sand. However, when activated carbon, which has a high affinity for adsorbing to organic compounds, was added to the sand the effects of Centaurea roots on Festuca root elongation were reduced. In other experiments, Festuca plants were 50% smaller when grown with Centaurea than with conspecifics in pure silica sand. However, Festuca grown with Centaurea in mixtures of sand and activated carbon were 85% larger than Festuca grown with Centaurea in silica sand without carbon. These results suggest that allelopathy accounts for a substantial proportion of the total interference of Centaurea on Festuca, shifting the balance of competition in favor of Centaurea. However, Centaurea outperformed Festuca even in the presence of activated carbon, demonstrating the importance of the combined roles of resource competition and allelopathy. Web of Science Centaurea maculosa USA Washington Palouse Prarie 46.59 -117.07 Field - Observational;Greenhouse terrestrial Grassland Invasion Hyp. Inherent Superiority;Novel Weapons Rapid Growth primary 1986 Durand, LZ; Goldstein, G 2001 Photosynthesis, photoinhibition, and nitrogen use efficiency in native and invasive tree ferns in Hawaii journal OECOLOGIA 126 3 345 354 Photosynthetic gas exchange, chlorophyll fluorescence, nitrogen use efficiency, and related leaf traits of native Hawaiian tree ferns in the genus Cibotium were compared with those of the invasive Australian tree fern Sphaeropteris cooperi in an attempt to explain the higher growth rates of S. cooperi in Hawaii. Comparisons were made between mature sporophytes growing in the sun (gap or forest edge) and in shady understories at four sites at three different elevations. The invasive tree fern had 12-13 cm greater height increase per year and approximately 5 times larger total leaf surface area per plant compared to the native tree ferns. The maximum rates of photosynthesis of S. cooperi in the sun and shade were significantly higher than those of the native Cibotium spp (for example, 11.2 and 7.1 mu mol m(-2) s(-1), and 5.8 and 3.6 mu mol m(-2) s(-1) respectively for the invasive and natives at low elevation). The instantaneous photosynthetic nitrogen use efficiency of the invasive tree fern was significantly higher than that of the native tree ferns, but when integrated over the life span of the frond the differences were not significant. The fronds of the invasive tree fern species had a significantly shorter life span than the native tree ferns (approximately 6 months and 12 months, respectively), and significantly higher nitrogen content per unit leaf mass. The native tree ferns growing in both sun and shade exhibited greater photoinhibition than the invasive tree fern after being experimentally subjected to high light levels. The native tree ferns recovered only 78% of their dark-acclimated quantum yield (F-v/F-m), while the invasive tree fern recovered 90% and 86% of its dark-acclimated F-v/F-m when growing in sun and shade, respectively. Overall, the invasive tree ft nl appears to be more efficient at capturing and utilizing light than the native Cibotium species, particularly in high-light environments such as those associated with high levels of disturbance. Web of Science Sphaeropteris cooperi USA Hawaii 21.502 -158.149 Field - Experimental terrestrial Tropical Forest Invasion Hyp. Inherent Superiority Superior Competitor;Rapid Growth primary 1987 Thebaud, C; Simberloff, D 2001 Are plants really larger in their introduced ranges? journal AMERICAN NATURALIST 157 2 231 236 The *rule* that individuals of nonindigenous plant species are larger where they are introduced than where they are native is not borne out in detailed comparisons of European species introduced to California or the Carolinas and species from California and the Carolinas introduced to Europe. On average, individuals of California species are taller in California than in Europe, while individuals of species native to Europe do not differ between Europe and California. Similarly, individuals of species from the Carolinas are, on average, taller in the Carolinas than in Europe, while individuals of European species are the same height in Europe and the Carolinas or, depending on the nature of the statistical analysis, taller in Europe. Results for herbaceous species only are substantially the same. Although there is no general tendency for species to be taller in their introduced ranges, many species are, in fact, taller in some regions where they are introduced than in their native ranges. Absence of natural enemies in the introduced range is one hypothesis for such observations, but other hypotheses are possible, and the specific reasons for height differences must be sought case by case. The absence of a general tendency casts doubt on the biological control strategy of introducing sequences of phytophages, none of which delivers a knockout blow to a weed, with the expectation that each successive phytophage will force the plant to devote more resources to defense and fewer to traits such as increased size that make it more competitive. Web of Science Many USA; Europe CA Statistical/Meta-analysis terrestrial Invasion Hyp. Enemy Release;Evolution in General primary 1989 Kedzie-Webb, SA; Sheley, RL; Borkowski, JJ; Jacobs, JJ 2001 Relationships between Centaurea maculosa and indigenous plant assemblages journal WESTERN NORTH AMERICAN NATURALIST 61 1 43 49 Ecological impacts of invasive plants include displacement of indigenous species and declines in species richness and diversity. The objective of this study was to characterize the functional relationship between plant community composition and Centaurea maculosa Lam. (spotted knapweed) within a Festuca idahoensis / Pseudoroegneria spicatum habitat type in Montana. Density, cover, and biomass of all species were collected along a gradient of spotted knapweed cover ranging from 0% to about 100%. Step-down regression was used to determine the relationship among C. maculosa, indigenous species, species richness, and Shannon-Weaver's diversity index. Regressions showed that indigenous perennial grass cover, species richness, and species diversity were inversely related to C. maculosa cover. There was no relationship between C. maculosa and indigenous forbs. While this study does not imply a causal relationship, the literature suggests that C. maculosa displaces indigenous species and/or invades areas of reduced indigenous plant cover, low diversity, or low species richness. Knowing levels of indigenous perennial grass cover will help managers predict the outcome of weed management on rangelands that are vulnerable to weed infestation. Web of Science Centaurea maculosa USA Montana Bozeman 45.7 -111.0167 Field - Observational terrestrial Grassland Invasion Hyp. Community Species Richness primary 1990 Larson, DL; Anderson, PJ; Newton, W 2001 Alien plant invasion in mixed-grass prairie: Effects of vegetation type and anthropogenic disturbance journal ECOLOGICAL APPLICATIONS 11 1 128 141 The ability of alien plant species to invade a region depends not only on attributes of the plant, but on characteristics of the habitat being invaded. Here, we examine characteristics that may influence the success of alien plant invasion in mixed-grass prairie at Theodore Roosevelt National Park, in western North Dakota, USA. The park consists of two geographically separate units with similar vegetation types and management history, which allowed us to examine the effects of native vegetation type, anthropogenic disturbance, and the separate park units on the invasion of native plant communities by alien plant species common to counties surrounding both park units. If matters of chance related to availability of propagules and transient establishment opportunities determine the success of invasion, park unit and anthropogenic disturbance should better explain the variation in alien plant frequency. If invasibility is more strongly related to biotic or physical characteristics of the native plant communities, models of alien plant occurrence should include vegetation type as an explanatory variable. We examined >1300 transects across all vegetation types in both units of the park. Akaike's Information Criterion (AIC) indicated that the fully parameterized model, including the interaction among vegetation type, disturbance, and park unit, best described the distribution of both total number of alien plants per transect and frequency of alien plants on transects where they occurred. Although all vegetation types were invaded by alien plants, mesic communities had both greater numbers and higher frequencies of alien plants than did drier communities. A strong element of stochasticity, reflected in differences in frequencies of individual species between the two park units, suggests that prediction of risk of invasion will always involve uncertainty. In addition, despite well-documented associations between anthropogenic disturbance and alien plant invasion, five of the six most abundant alien species at Theodore Roosevelt National Park had distributions unrelated to disturbance. We recommend that vegetation type be explicitly taken into account when designing monitoring plans for alien species in natural areas. Web of Science Many USA North Dakota Theodore Roosevelt National Park 46.918 -103.528 Field - Observational terrestrial Grassland Invasion Hyp. Disturbance primary 1992 Specht, RL 2000 Savannah woodland vegetation in the South-East District of South Australia: the influence of evaporative aerodynamics on the foliage structure of the understorey invaded by introduced annuals journal AUSTRAL ECOLOGY 25 6 588 599 Evaporative aerodynamics determine the foliage projective cover of the understorey of perennial tussock grasses and associated perennial herbs in the savannah woodland dominated by Eucalyptus camaldulensis on gleyed podsolic soils in the Mediterranean climate of the South-East District of South Australia. By the mid 1940s, winter-spring evapotranspiration from the 'thin' leaves (with low leaf specific weight) of introduced annual plants was depleting surface soil water and thus reducing the annual growth of the summer-growing savannah understorey; perennial herbs between the tussock grasses were the first to succumb to this competition. During spring, the percentage of the ground covered by the savannah understorey was increased by 10% in the subhumid zone to 30% in the humid zone as the pre-European perennial herbs between the tussock grasses were replaced by introduced annuals. Application of phosphatic fertilizer to the understorey increased the growth of introduced annuals, which formed a dense stratum during their winter-spring growing season, increasing evapotranspiration and leading eventually to the extinction of the native perennial grasses. When the savannah understorey, invaded by introduced annuals in the mid-1940s, was converted to improved pasture, the percentage of ground covered by the seasonal foliage was increased by 20-30%; 100% coverage of overlapping foliage resulted in the humid zone. Web of Science Many Australia South Australia South-East District 36.3333 140.6667 Field - Experimental terrestrial Deciduous Forest;Savanna Invasion Hyp. Inherent Superiority Broad Tolerances primary 1993 Yoder, CK; Nowak, RS 2000 Phosphorus acquisition by Bromus madritensis ssp rubens from soil interspaces shared with Mojave Desert shrubs journal FUNCTIONAL ECOLOGY 14 6 685 692 1. Bromus madritensis ssp. rubens (L.) Husnot (Red Brome) is an invasive annual grass that is associated with increases in fire frequency and decreases in perennial plant diversity. The success of Red Brome in the Mojave Desert has been attributed to its competitive ability, but competition between Red Brome and native shrubs for below-ground resources has not been investigated previously. In this study we present a modification of previous dual-isotope methods that assesses competitive interactions and responses among plants under field conditions. We then use this method to (i) determine if direct competition for phosphorus (P) occurs between Red Brome and native shrubs, and (ii) evaluate the effectiveness of phosphate acquisition by Red Brome from soil interspaces shared with different Mojave Desert shrub species. 2. Clipping Red Brome to remove approximate to 85% of its foliage on the day prior to labelling soil interspaces with P isotopes did not have the desired effect of inhibiting phosphorus uptake by Red Brome. Therefore we were unable to verify that direct competition for P occurred between Red Brome and native shrubs. 3. Nonetheless, by sampling plant tissue from unclipped strips of Red Brome that were centred between two shrubs, we were able to evaluate the effectiveness of phosphate acquisition by Red Brome from interspaces shared with different shrubs. There were no differences in the amount of phosphorus acquired by Red Brome from soil interspaces shared with the evergreen shrub Larrea tridentata (D.C.) Cov. versus soil interspaces shared with the drought deciduous shrub Lycium pallidum Miers. However, Red Brome acquired more than six times as much P from soil interspaces shared with Larrea than from soil interspaces shared with the drought deciduous shrub Ambrosia dumosa Payne. Less P uptake by Red Brome from soil interspaces shared with Ambrosia suggests greater effectiveness of Ambrosia compared with Larrea to deplete soil P. Web of Science Bromus madritensis ssp. rubens USA Nevada Mojave Desert 36.5833;37.25 115.9167;116.5833 Field - Observational terrestrial Desert Invasion Hyp. Inherent Superiority Superior Competitor primary 1994 Linde, M; Diel, S; Neuffer, B 2001 Flowering ecotypes of Capsella bursa-pastoris (L.) Medik. (Brassicaceae) analysed by a cosegregation of phenotypic characters (QTL) and molecular markers journal ANNALS OF BOTANY 87 1 91 99 Capsella bursa-pastoris (Brassicaceae) is an annual to biennial predominantly autogamous species distributed worldwide. Using a linkage map with RAPDs and isozymes we studied quantitative trait loci (QTL) controlling phenotypic traits in this invasive species. To obtain a mapping population we crossed two plants occurring in different climatic regions in California, USA (Central Valley and Sierra Nevada) with the most diverse ecotypes (phenotypic parameters) and genotypes (isozyme multilocus genotypes). A hundred and thirteen F-2 individuals were raised and analysed for segregation at 107 RAPDs, six isozyme loci, and one locus determining leaf type. The number, location and magnitude of genes underlying 13 traits were determined by using both interval and composite interval mapping. Two to five QTL affecting one character have been detected. Altogether the 13 quantitative traits produced 48 QTL. The inheritance patterns of trails ranged from those controlled by one QTL with a major effect to those controlled by several QTL with only minor effects. Closely linked QTL, e.g. onset of flowering with rosette leaf number, were interpreted as pleiotropic. Three major QTL account for onset of flowering. These loci were linked to at least three isozyme loci and several other QTL responsible for developmental traits like rosette leaf number. Heritability of quantitative traits, segregation of the leaf type, and segregation of the allozymes was tested in the F-3 generation. We conclude that historical events alone are insufficient to explain the distribution pattern of isozyme multilocus genotypes during the colonization of new regions and habitats. The present evidence indicates that ecotypic adaptation and genetic linkage of isozyme loci with adaptive characters are involved. (C) 2000 Annals of Botany Company. Web of Science Capsella bursa-pastoris USA California Central Valley;Sierra Nevada 35.4167 119.05 Field - Observational terrestrial Grassland;Mountain Invasion Hyp. Evolution in General primary 1995 Dzialowski, AR; O'Brien, WJ; Swaffar, SM 2000 Range expansion and potential dispersal mechanisms of the exotic cladoceran Daphnia lumholtzi journal JOURNAL OF PLANKTON RESEARCH 22 12 2205 2223 Recently the exotic cladoceran Daphnia lumholtzi has invaded freshwater systems throughout the southern and midwestern United States. We conducted regional surveys of eastern Kansas reservoirs to document the range expansion of D.lumholtzi. Daphnia lumholtzi was found in five of 35 reservoirs sampled in 1994, and 11 of the 35 reservoirs when re-sampled in 1997. In addition, we sampled 40 small ponds inaccessible to recreational boats, within the watershed of an invaded reservoir. We did not find D.lumholtzi in any of these ponds, suggesting that non-human dispersal mechanisms play an insignificant role in the range expansion of D.lumholtzi throughout the United States. Further experimentation, however, is needed to determine if the absence of D.lumholtzi from these small ponds is due to insufficient dispersal mechanisms or the inability of this invader to successfully colonize following arrival. Daphnia lumholtzi has broad limnological tolerances. However, invaded reservoirs tend to be larger in area, have higher Secchi disk depths, and lower total phosphorus, total nitrogen and chlorophyll a levels relative to non-invaded reservoirs. Analyses of pre-invasion zooplankton communities indicate that D.lumholtzi may be invading reservoirs in which native Daphnia species are rare. While the long-term effects of the invasion of D.lumholtzi are unknown, it has the potential to dominate late summer zooplankton communities in eastern Kansas reservoirs. Therefore, we need to continue to survey and monitor invaded reservoirs to document the range expansion of D.lumholtzi and determine the long-term implications of the introduction of this invader. Web of Science Daphnia lumholtzi USA Kansas Council Grove City 38.68 -96.5 Field - Observational lentic Invasion Hyp. Community Species Richness herbivore 1996 Zotz, G; Franke, M; Woitke, M 2000 Leaf phenology and seasonal carbon gain in the invasive plant, Bunias orientalis L. journal PLANT BIOLOGY 2 6 653 658 In two potentially competing herbaceous plants, the invasive Bunias orientalis L. (Brassicaceae) and the native Picris hieracioides L. (Asteraceae), seasonal changes in leaf CO2 gas exchange and plant growth were studied over an entire growing season from February 1998 to December 1998 in two experimental fields. The study was motivated by the hypothesis that pre-adaptive phenological displacement of alien species relative to the native flora may be an important reason for the observed expansion of B. orientalis in central Europe. We quantified the importance of phenological differences for annual carbon gain in both species by estimating total leaf carbon gain from the results of leaf CO2 exchange and changes in plant leaf area. Bunias orientalis achieved almost half of its annual carbon gain in the time between early September and December, when competition for light by other species, like P. hieracioides, is low. Our quantitative approach corroborates the notion that the phenological shift of a relatively poor competitor, such as B. orientalis, could be of great importance for the success as an invasive species. Web of Science Bunias orientalis Europe Germany Wurzburg 49.788 9.915 Field - Experimental terrestrial Invasion Hyp. Plasticity primary 1997 Meekins, JF; Ballard, HE; McCarthy, BC 2001 Genetic variation and molecular biogeography of a North American invasive plant species (Alliaria petiolata, Brassicaceae) journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 162 1 161 169 A study was conducted using molecular-based population genetic data to interpret biogeographic relationships and survey genetic similarity within and among populations of Alliaria petiolata from its native and introduced ranges. Three of the populations examined were from Europe, the native range of A. petiolata, whereas eight populations were from North America, where A. petiolata was introduced over 125 yr ago and where it has since become an invasive pest. Inter-simple sequence repeat (ISSR) analysis using two different primers revealed 56 unique fragments. Genetic variation was greater in some native populations (Scottish and Dutch) compared with introduced populations. Estimates of the Shannon phenotypic diversity index among populations ranged from 0.917 to 0.996. Analysis of molecular variance indicated that there was strong population structuring, with the greatest variance among populations (61.0%) and with much less variance both between continents (16.3%) and within populations (22.7%). Significant differences were detected within and among populations and between ranges (native and introduced). Unweighted pair-group mean analysis and principal-coordinates analysis separated individuals into two large groups comprising two European populations (Belgium and The Netherlands), on the one hand, and the remaining nine populations, including Scotland, on the other. The data indicate that several North American populations, including those from Ohio, West Virginia, New York, and Kentucky, may have originated from plants from the British Isles, although it is possible that multiple introductions of A. petiolata from Europe have occurred. Web of Science Alliaria petiolata USA;Canada Ohio;West Virginia;New York;Kentucky;Indiana;Washington;Canada 37.6 -82.8 Field - Observational terrestrial Old Field Fundamentals primary 1998 Prieur-Richard, AH; Lavorel, S 2000 Do more diverse plant communities greater resistance to invasions? journal REVUE D ECOLOGIE-LA TERRE ET LA VIE 0 0 37 51 Early theoretical analyses and observations of community structure have led to the hypothesis that a high diversity of communities increases their resistance to invasions. However, to this date, observation and experimental data have shown positive or negative relationships between plant community diversity and invasibility. Studies of biological invasions proposed several others mechanisms explaining invasions: disturbances, presence of empty niches and interactions with others community trophic levels. The role of plant diversity can be decomposed in two factors: is specific richness per se and/or the diversity of functional groups that lead to invasion resistance of communities? A study carried out in old fields of Montpellier country showed a general picture of invasion and its complexity in this country. Our observations of these invasion patterns confirmed the difficulties to observe clear relationships with their diversity. We then resorted to semi-controlled field experiments. We sowed annual old field communities with different levels of diversity: variation in species richness, variation in functional richness and variation in functional identities for a fixed Functional richness. Demographic and vegetative parameters of two exotic probes transplanted into these communities, Conyza bonariensis and C.canadensis, were measured along their life cycle. Primary community functioning parameters of the model ecosystems were measured simultaneously. Species richness had little effect on performance of the two Conyza species. Functional composition appeared more relevant than functional richness per se to explain community invasibility. Mechanisms of functional composition effects are proposed. Web of Science Conyza bonariensis; C.canadensis France Montpellier country 43.610974 3.879204 Field - Experimental terrestrial Old Field Invasion Hyp. Community Species Richness primary 2000 Sher, AA; Marshall, DL; Gilbert, SA 2000 Competition between native Populus deltoids and invasive Tamarix ramosissima and the implications for reestablishing flooding disturbance journal CONSERVATION BIOLOGY 14 6 1744 1754 Changes in historical disturbance regimes have been shown to facilitate non-native invasions, but reinstatement of disturbance can be successful only if native colonizers are able to outcompete colonizing invasives. Reintroduction of flooding in the southwestern United States is being promoted as a means of reestablishing Populus deltoides subsp. wislizenii, but flooding can also promote establishment of an introduced, invasive species, Tamarix ramosissima. We investigated competition between Populus and Tamarix at the seedling stage to aid in characterizing the process by which Tamarix may invade and to determine the potential ability of Populus to establish itself with competitive pressure from Tamarix. We planted seedlings of Tamarix and Populus in five ratios at three densities for a total of 15 treatments. The growth response of each species was measured in terms of height, above-ground biomass, and tissue concentrations of nitrogen and phosphorous. These measurements across treatments were modeled as three-dimensional response surfaces. For both species, Populus density was more important than Tamarix density for determining growth response. Both species were negatively affected by increasing numbers of Populus seedlings. Due to the large size of the native Populus, we predict that its superior competitive ability can lead to its dominance when conditions allow native establishment. Our results suggest that even in the presence of an invader that positively responds to disturbance, reestablishment of historical flooding regimes and post-flood hydrology can restore this ecosystem by promoting its dominant plant species. Web of Science Tamarix ramosissima United States New Mexico Albuquerque, New Mexico, Bosque del Apache Wildlife Refuge (150 km south of Albuquerque), and Los Lunas (32 km south of Albuquerque) 35.094631 -106.65184 Garden terrestrial Invasion Hyp. Inherent Superiority Superior Competitor primary 2005 Walther, GR 2000 Climatic forcing on the dispersal of exotic species journal PHYTOCOENOLOGIA 30 4 409 430 Changes in vegetation composition and distribution are often paralleled to a changing climate. Especially at the boundaries of the distribution area of a given vegetation type, shifts due to changing environmental conditions as e.g. climatic change are expected to be detected first. In a recent study conspicuous changes in vegetation composition have been reported in climatically sensitive areas with particular boundary position as e. g. the Insubrian area in southern Switzerland. More than a dozen exotic species recently started to colonise and in some places even to dominate - forest understorey vegetation. All I:he exotic species share equal characteristics (evergreen broad-leaved or laurophyllous plant functional type) and a synchronous pattern of dispersal in time and space. This stresses the fact that external factors may determine the process. Climatic data from local meteorological stations are evaluated with special regard to limiting climatic parameters for laurophyllous species. With this background, climatic forcing must be considered as one of the major contributing factors for this increasing tendency of exotic species dispersal and their capability to establish in forests. The present case study for southern Switzerland gives insights on the rapid reorganisation of a forest community with shifting ranges of indigenous species and pre-adapted non-indigenous species invading possible vacant niches. Web of Science Many Switzerland Insubrian area Field - Observational terrestrial Broadleaf Evergreen Forest Invasion Hyp. Climate Change primary 2007 Naeem, S; Knops, JMH; Tilman, D; Howe, KM; Kennedy, T; Gale, S 2000 Plant diversity increases resistance to invasion in the absence of covarying extrinsic factors journal OIKOS 91 1 97 108 Biological invasion is a widespread, but poorly understood phenomenon. Elton's hypothesis. supported by theory, experiment, and anecdotal evidence, suggests that an important determinant of invasion success is resident biodiversity, arguing that high diversity increases the competitive environment of communities and makes them more difficult to invade. Observational studies of plant invasions, however, find little support for this hypothesis and argue strongly against it. Lack of control of extrinsic factors (e.g., disturbance. climate, or soil fertility) that covary with biodiversity and invasion in observational studies makes it difficult to determine if their findings truly refute Elton's hypothesis. We examined performance of Crepis tectorum (an invasive, annual composite weed) in experimental prairie grassland plots and greenhouse plant assemblages in which resident species richness was directly manipulated. Under these conditions, unlike observational studies, no covarying extrinsic factors could interfere with interpreting results. We found a strong inverse association between resident diversity and invader performance as predicted by Elton's hypothesis. Higher resident diversity increased crowding, decreased available light, and decreased available nutrients all of which increased the competitive environment of diverse plant assemblages and reduced C. tectorum success. Examination of individual resident species impacts on C. tectorum performance demonstrated that this diversity effect was not due to the sampling effect. These results suggest that both Elton's hypothesis and its competitive mechanism may operate in nature, but covarying extrinsic factors may obscure the negative impact of diversity on invader success. Web of Science Crepis tectorum United States Minnesota Cedar Creek Natural History Area 45.406646 -93.200798 Field - Observational;Greenhouse terrestrial Grassland Invasion Hyp. Community Species Richness primary 2009 Hirai, N; Sakashita, S; Sano, T; Inoue, T; Ohigashi, H; Premasthira, C; Asakawa, Y; Harada, J; Fujii, Y 2000 Allelochemicals of the tropical weed Sphenoclea zeylanica journal PHYTOCHEMISTRY 55 2 131 140 Nine plant growth inhibitors were isolated from the tropical weed Sphenoclea zeylanica, which shows allelopathic properties. Those compounds hitherto not reported from any plant source were the isomers of cyclic thiosulfinate, (1S,3R,4R)-(+)- and (1R,3R,4R)-(-)-4-hydroxy-3-hydroxymethyl-1,2-dithiolane-1-oxides, and (2R,3R,4R)-(-)- and (2S,3R,4R)-(+)-4-hydroxy-3hydroxmethyl-1,2-dithiolane-2- oxides. These were named zeylanoxide A, epi-zeylanoxide A, zeylanoxide B and epi-zeylanoxide B, respectively. The absolute configurations at C-3 and C-4 were elucidated by chemical synthesis of both enantiomers from L- and D-glucose. Two of the inhibitors were secologanic acid and secologanoside, and three other inhibitors were by known secoiridoid glucosides formed as artifacts during extraction with methanol. The cyclic thiosulfinates and secoiridoid glucosides completely inhibit the root growth of rice seedlings at 3.0 mM. While the specific activity of the inhibitors was not high, since they accumulated to circa 0.61% S. zeylanica by dry weight, this suggests that the inhibitors are nevertheless potent allelochemicals in this weed. (C) 2000 Elsevier Science Ltd. All rights reserved. Web of Science Sphenoclea zeylanic Thailand Ang Thong Lab terrestrial Invasion Hyp. Novel Weapons primary 2013 Callaway, RM; Aschehoug, ET 2000 Invasive plants versus their new and old neighbors: A mechanism for exotic invasion journal SCIENCE 290 127 521 523 Invading exotic plants are thought to succeed primarily because they have escaped their natural enemies, not because of novel interactions with their new neighbors. However, we find that Centaurea diffuse, a noxious weed in North America, has much stronger negative effects on grass species from North America than on closely related grass species from communities to which Centaurea is native. Centaurea's advantage against North American species appears to be due to differences in the effects of its root exudates and how these root exudates affect competition for resources. Our results may help to explain why some exotic species so successfully invade natural plant communities. Web of Science Centaurea diffuse United States Montana Greenhouse;Lab terrestrial Grassland Invasion Hyp. Novel Weapons primary 2020 King, SA; Buckney, RTG 2000 Urbanization and exotic plants in northern Sydney streams journal AUSTRAL ECOLOGY 25 5 455 461 The vegetation and sediment of urban and non-urban streams in the northern Sydney region were compared to examine the possible effects of urbanization on within-stream vegetation. Many sediment characteristics were significantly different in urban streams. At least one exotic plant species was found in each urban stream sampled, but none were found in the non-urban streams. The presence of exotic species led to the overall number and abundance of plant species being significantly higher in urban streams. Interestingly, the number and abundance of native species at the urban sites were the same as non-urban sites, but a different suite of species was usually present. This suggests that urban streams favour exotic plants and certain native plants that are adapted to the modified conditions. The differences between the plant communities in the urban and non-urban streams appeared to be associated with the increased level of nutrients in the urban stream sediment. Several multivariate techniques were used to assess the relative importance of individual nutrients, but no nutrients were directly associated with the observed differences. In particular, total phosphorus levels were less important in explaining the vegetation patterns than a combination of nutrients. It is therefore likely that the general increase of nutrients in stream sediment has enhanced exotic invasion and altered stream plant communities in Sydney streams. Web of Science Many Australia New South Wales Hornsby Plateau -33.8333 151.3333 Field - Observational lotic Invasion Hyp. Disturbance primary 2021 Jesson, L; Kelly, D; Sparrow, A 2000 The importance of dispersal, disturbance, and competition for exotic plant invasions in Arthur's Pass National Park, New Zealand journal NEW ZEALAND JOURNAL OF BOTANY 38 3 451 468 This study investigated the effects of disturbance, dispersal, and plant competition on exotic plant invasion. An assessment of the change in species distributions in the Mingha Valley, Arthur's Pass National Park, over five years showed that many species had increased in range, suggesting that dispersal had limited the distribution of these species. The dispersal barrier was removed experimentally by transplanting plants and seeds of Anthoxanthum odoratum, Holcus lanatus, Cerastium fontanum, and Hieracium pilosella into undisturbed areas. Although transplants of A. odoratum, H. lanatus, and H. pilosella could survive without disturbance, it was essential for the establishment from seed in all four species. These species were therefore limited by the absence of disturbance. A survey of the plant distribution in the Mingha and Edwards Valleys found many exotic species associated with hut, track, and river disturbance regimes. The association of exotic plants with disturbances may be due to the role of disturbance as a window through the barriers of competition, dispersal, and abiotic barriers. The success of these exotic plants in New Zealand seems largely due to success of seedlings of exotic species establishing in areas disturbed by human activity. Web of Science Anthoxanthum odoratum; Holcus lanatus; Cerastium fontanum; Hieracium pilosella New Zealand Arthur's Pass National Park -42.9333 171.55 Field - Experimental;Field - Observational terrestrial Grassland;Deciduous Forest Invasion Hyp. Disturbance primary 2022 Prieur-Richard, AH; Lavorel, S; Grigulis, K; Dos Santos, A 2000 Plant community diversity and invasibility by exotics: invasion of Mediterranean old fields by Conyza bonariensis and Conyza canadensis journal ECOLOGY LETTERS 3 5 412 422 A series of communities were established in situ to differentiate the effects of species richness, functional richness and functional group identity on invasibility of Mediterranean annual old fields. We monitored the demographic and vegetative parameters of two exotic annuals introduced as seedlings, Conyza bonariensis and C. canadensis. Community species richness and functional composition determined resistance to invasion by Conyza. Conyza bonariensis biomass decreased with increasing species richness. Legumes increased the biomass and consequently the net fecundity of both Conyza, while survival was favoured by Asteraceae. Communities with fewer Asteraceae and grasses increased the reproductive effort of C. bonariensis. A separate glasshouse experiment using the same species mises revealed chat establishment of Conyza decreased with increasing species richness or when grasses were present. Patterns of Conyza performance are interpreted in the light of measurements of ecosystem functional parameters, making it possible to formulate hypotheses about mechanisms limiting community invasibility. Web of Science Conzya bonariensis; Conzya canadensis France Montpellier 43.65 3.85 Field - Experimental terrestrial Old Field Invasion Hyp. Empty Niche;Community Species Richness primary 2023 Byers, JE 2000 Differential susceptibility to hypoxia aids estuarine invasion journal MARINE ECOLOGY-PROGRESS SERIES 203 0 123 132 I examined the resistance of 2 competing estuarine mudsnails, Cerithidea californica (native) and Batillaria attramentaria (exotic), to mortality from microbes and associated alteration of the abiotic environment (i.e., hypoxia). B, attramentaria is displacing C, californica from salt marshes of northern California where the 2 species overlap. I first examined the mortality and distribution of the snails during 2 natural experiments in Bolinas salt marsh (Marin Co., California, USA) that exposed the snails to high bacteria levels and low oxygen conditions for prolonged periods (>3 wk). Second, I conducted 2 laboratory experiments designed to quantify the rates and mechanisms of snail mortality related to bacterial activity. In both the field and the lab, B, attramentaria was significantly more resistant to death by low oxygen. Lab experiments demonstrated that indirect effects of bacteria, i.e., low oxygen levels las opposed to direct infection by bacteria), were responsible for the high mortality rate of C. californica. In the field, C, californica seemed able to mitigate effects of hypoxia by migrating away from sources of high stress, but only when the harmful bacterial activity was highly localized. Ultimately this study illustrates that stress from microbial action differentially affects the 2 competing species and thus contributes to the invader's documented displacement of the native in marshes where they co-occur. Given the growing incidence of eutrophication and associated anoxic conditions in near-shore aquatic environments worldwide, differential susceptibility to hypoxia/anoxia may increasingly contribute to the outcomes of biological invasions in these habitats. Web of Science Batillaria attramentaria United States California Bolinas Lagoon 37.909669 -122.677374 Field - Observational;Lab estuarine Invasion Hyp. Inherent Superiority Superior Competitor herbivore 2025 Dean, WRJ; Milton, SJ 2000 Directed dispersal of Opuntia species in the Karoo, South Africa: are crows the responsible agents? journal JOURNAL OF ARID ENVIRONMENTS 45 4 305 314 The densities of self-established non-indigenous prickly pears (Opuntia ficus-indica) in rangelands of the Karoo recorded on 3434 km of road transects, were on average 800 times greater below telegraph and transmission poles than away from poles, and 200 times greater next to wire fences along roads than in open rangelands. We suggest that this uneven establishment pattern is mainly due to the dispersal of Opuntia ficus-indica seeds by crows and other vertebrates (chiefly primates). Cape (Corvus capensis) and pied crows (C. albus) feed on fruits of Opuntia ficus-indica in the Karoo, and regurgitate pellets containing viable seeds of these plants below nest sites, roosts and occasional perch sites. Crows use man-made structures such as wire fences, telegraph and transmission poles and windmills for perching, roosting and nesting. Crow pellets, containing regurgitated bones and viable seeds of Opuntia spp., and other alien and indigenous plants, are most common around such perch sites. Crows are frequently associated with roads in the Karoo because they scavenge on road kills in the Karoo as well as feeding on fruits, insects and reptiles in road verges. We suggest that dispersal of seeds by crows is important for range extension and establishment of new Opuntia populations. (C) 2000 Academic Press. Web of Science Opuntia ficus-indica South Africa Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Mutualism Facilitation primary 2028 Quinn, TP; Unwin, MJ; Kinnison, MT 2000 Evolution of temporal isolation in the wild: Genetic divergence in timing of migration and breeding by introduced chinook salmon populations journal EVOLUTION 54 4 1372 1385 The timing of migration and breeding are key life-history traits; they are not only adaptations of populations to their environments, but can serve to increase reproductive isolation, facilitating further divergence among populations. As part of a study of divergence of chinook salmon, Oncorhynckus tshawytscha, populations, established in New Zealand from a common source in the early 1900s, we tested the hypotheses that the timing of migration and breeding are under genetic control and that the populations genetically differ in these traits despite phenotypic overlap in timing in the wild. Representatives of families from two populations were collected within a day or two of each other, reared in a common environment, and then released to sea from each of two different rivers, while other family representatives were retained in fresh water to maturity. The date of maturation of fish held in fresh water and the dates of return from the ocean and maturation of fish released to sea all showed significant differences between the two populations and among families within populations. The very high heritabilities and genetic correlations estimated for migration and maturation date indicated that these traits would respond rapidly to selection. Combined with the results of related studies on these chinook salmon populations, it appears that spawning time may not only evolve during the initial phases of divergence, but it may play an important role in accelerating divergence in other traits. Web of Science Oncorhynchus tshawytscha New Zealand Field - Experimental;Lab marine;lotic Pelagic/Open Ocean Fundamentals predator 2033 Willis, AJ; Memmott, J; Forrester, RI 2000 Is there evidence for the post-invasion evolution of increased size among invasive plant species? journal ECOLOGY LETTERS 3 4 275 283 Many plant species grow taller and have higher reproductive capacity where they are nonindigenous invaders than where they are native components of the flora. Traditionally, it has been accepted that this is a plastic response to a benign environment, though recently this assumption has been challenged and a genetic basis for increased plant size has been invoked. We tested the hypothesis that the increased size of certain weed species is genetically, rather than environmentally, based. A common environment growth experiment revealed no significant differences in the size of Carduus nutans, Digitalis purpurea, Echium vulgare or Senecio jacobaea sampled from alien (Australia and New Zealand) or native (Britain and continental Europe) habitats. We conclude that post-invasion genetic changes associated with increased size may be unusual and that the phenomenon, where it occurs, generally reflects a plastic response to a novel environment. Web of Science Carduus nutans; Digitalis purpurea; Echium vulgare; Senecio jacobaea Australia; New Zealand Garden terrestrial Invasion Hyp. Evolution of Increased Competitive Ability;Plasticity primary 2053 Eckert, CG; Massonnet, B; Thomas, JJ 2000 Variation in sexual and clonal reproduction among introduced populations of flowering rush, Butomus umbellatus (Butomaceae) journal CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE 78 4 437 446 Butomus umbellatus L. is an invasive emergent aquatic plant that exhibits wide variation in seed production. Native European populations are fertile and diploid or sterile and triploid. However, adventive North American populations are widely reported to be sexually sterile. We quantified sexual fertility and self-compatibility under greenhouse conditions for nine introduced populations from eastern Ontario, Canada. All populations were highly fertile and self-compatible. Each flower produced an average of 127 +/- 7 (mean +/- SE) filled seeds and 31.4 +/- 0.4% of seeds germinated. This level of fertility is much higher than previously reported, even for fertile native populations. We also quantified the production of seeds, flowers, and inflorescence-borne asexual bulbils in 19 natural populations from eastern Ontario; 17 populations were highly fertile (200 +/- 9 seeds/fruit) and 2 produced almost no seeds (0.0-0.3 seeds/fruit), because ovules were either not fertilized or were aborted soon after fertilization. We found no evidence of a trade-off between sexual reproduction and clonal reproduction via bulbils. The wide variation in reproductive strategy observed in these populations raises questions concerning the evolutionary loss of sex in clonal populations, and may have significant implications for the spread and management of this exotic species. Web of Science Butomus umbellatus Canada Ontario Greenhouse lentic Invasion Hyp. Inherent Superiority High Reprod. Output;Clonal Reproduction primary 2065 Milne, RI; Abbott, RJ 2000 Origin and evolution of invasive naturalized material of Rhododendron ponticum L. in the British Isles journal MOLECULAR ECOLOGY 9 5 541 556 Information concerning the area of origin, genetic diversity and possible acquisition of germplasm through hybridization is fundamental to understanding the evolution, ecology and possible control measures for an introduced invasive plant species. Rhododendron ponticum is extensively naturalized in the British Isles, but it is not known whether native material in Turkey, Spain or Portugal gave rise to the naturalized material, or to what extent introgression has affected this material. Chloroplast (cp) and nuclear ribosomal DNA (rDNA) restriction fragment length polymorphisms (RFLPs) were sought which could distinguish between native material of R. ponticum, and between 15 other Rhododendron species including R. ponticum's closest relatives. Thereafter, a total of 260 naturalized accessions of R. ponticum from throughout the British Isles was examined with respect to informative polymorphisms. It was found that 89% of these accessions possessed a cpDNA haplotype that occurred in native material of R. ponticum derived almost entirely from Spain, while 10% of accessions had a haplotype unique to Portuguese material. These results therefore indicated an Iberian origin for British material. rDNA or cpDNA evidence of introgression from R. catawbiense was found in 27 British accessions of R. ponticum, and such accessions were significantly more abundant in Britain's coldest region, eastern Scotland, than elsewhere. This could indicate that introgression from R. catawbiense confers improved cold tolerance. Introgression from R. maximum and an unidentified species was also detected. Web of Science Rhododendron ponticum Great Britain Field - Observational;Lab terrestrial Broadleaf Evergreen Forest;Intertidal/Near Shore Invasion Hyp. Hybridization primary 2066 Levine, JM 2000 Species diversity and biological invasions: Relating local process to community pattern journal SCIENCE 288 127 852 854 In a California riparian system, the most diverse natural assemblages are the most invaded by exotic plants. A direct in situ manipulation of local diversity and a seed addition experiment showed that these patterns emerge despite the intrinsic negative effects of diversity on invasions. The results suggest that species loss at small scales may reduce invasion resistance. At community-wide scales, the overwhelming effects of ecological factors spatially covarying with diversity, such as propagule supply, make the most diverse communities most likely to be invaded. Web of Science Cirsium arvense; Plantago major; Agrostis stolonifera USA California South Fork Eel river Field - Experimental terrestrial Invasion Hyp. Community Species Richness;Propagule Pressure primary 2067 Rogers, HM; Hartemink, AE 2000 Soil seed bank and growth rates of an invasive species, Piper aduncum, in the lowlands of Papua New Guinea journal JOURNAL OF TROPICAL ECOLOGY 16 0 243 251 Secondary fallow vegetation in parts of the Papua New Guinea lowlands is dominated by the shrub Piper aduncum L. that originates from South America. Here we report on its seed bank, growth rate and biomass accumulation. P. aduncum accounted for 69 % (408 m(-2)) of the seed bank in the forest and 53 % (1559 m(-2)) of the seed bank under fallow. About 90 % of the tree seed bank at the fallow site was dominated by P. aduncum whereas this was 78 % in the forest soil. Two-year-old P. aduncum had grown to 4.5 m height and had accumulated 48 Mg dry matter (DM) per ha of above ground biomass. The rate of biomass accumulation increased from 10 Mg DM ha(-1) y(-1) in the first year to 40 Mg DM ha(-1) y(-1) in the second year when 76 % of the biomass consisted of mainstems. The highest growth rate of 134 kg DM ha(-1) d(-1) occurred when P. aduncum was 17-mo-old. Aggressive invasion and monospecific stands of P. aduncum are explained by its dominance in the seed bank, fast growth, and high rates of biomass accumulation. P. aduncum is a major competitor to indigenous tree species and presents a threat to Papua New Guinea's rich biodiversity. Web of Science Piper aduncum Papua New Guinea -6.75;-6.5667 146.7833;147.0333 Field - Experimental;Field - Observational terrestrial Old Field Invasion Hyp. Inherent Superiority Rapid Growth;High Reprod. Output primary 2069 Marchetti, MP; Moyle, PB 2000 Spatial and temporal ecology of native and introduced fish larvae in lower Putah Creek, California journal ENVIRONMENTAL BIOLOGY OF FISHES 58 1 75 87 For two years we studied the distribution and abundance of native and introduced fish larvae in Putah Creek (Yolo County, CA), a low elevation regulated stream. We used light traps and conical drift nets to sample the fish larvae at two spatially separated sites from March through July 1997 and at four sites from February through August 1998. Native larvae occurred both earlier in the year and in higher abundance than those of introduced species. Both native larvae and overall numbers of larvae were more abundant at upstream sites in both years. Sampling of larvae appeared to be sensitive to the detection of rare species. Drift nets and light traps collected similar numbers of larvae, but each method tended to select for different taxa. There were significant trends in diel patterns of abundance, with more fish larvae being found during the hours of darkness. We suggest that differences between the sites were due to habitat changes resulting from an upstream dam that has created a refuge of diverse habitat and cool flowing water for native taxa. Web of Science Many USA California Yolo County 38.493302 -122.028451 Field - Observational lentic Riparian Invasion Hyp. Inherent Superiority Broad Tolerances predator 2075 Jarnagin, ST; Swan, BK; Kerfoot, WC 2000 Fish as vectors in the dispersal of Bythotrephes cederstroemi: diapausing eggs survive passage through the gut journal FRESHWATER BIOLOGY 43 4 579 589 1. Bythotrephes cederstroemi (Crustacea: Onychopoda: Cercopagidae) is an introduced invertebrate predator currently spreading through the Laurentian Great Lakes region of North America. We examined a previously unsuspected way in which B. cederstroemi may be dispersed by fish by their consumption of diapausing eggs. 2. Ninety-four percentage of the mature B. cederstroemi diapausing eggs consumed by fish were egested apparently intact. This proportion is considerably above previous estimates for the ephippial eggs of Daphnia. The hatching success of diapausing eggs was compared among four categories: (a) eggs released naturally by B. cederstroemi (control, 73% hatched) (b) eggs released during 'stressful confinement' (46% hatched) (c) eggs dissected from dead females (13% hatched) and (d) eggs recovered from faecal pellets following consumption by fish (viable gut passage experiment, 41% hatched). 3. Samples of small fish and B. cederstroemi were collected simultaneously. Examination of gut contents revealed that fish contained B. cederstroemi diapausing eggs and that B. cederstroemi bearing resting eggs were consumed selectively over those without eggs. Moreover, fish selected B. cederstroemi bearing mature rather than immature diapausing eggs. 4. The fact that diapausing eggs survive gut passage is important for the dispersal of B. cederstroemi. Fish often move between the pelagic and littoral zones of lakes and may thus disperse diapausing eggs widely. Fish may also move between lakes connected by river systems and can be caught and passively dispersed by anglers or piscivorous birds. Our results demonstrate the potential for fish to act as vectors in the spread of B. cederstroemi. Web of Science Bythotrephes cederstroemi (Crustacea: Onychopoda: Cercopagidae) United States Michigan Lake Michigamme 46.5 -88.1 Field - Observational;Lab lentic Invasion Hyp. Inherent Superiority Effective Disperser predator 2076 Schappert, PJ; Shore, JS 1999 Cyanogenesis, herbivory and plant defense in Turnera ulmifolia on Jamaica journal ECOSCIENCE 6 4 511 520 Field surveys of eight populations of Turnera ulmifolia L., a Jamaican weed exhibiting quantitative genetic variation for cyanogenesis, were undertaken to assess the effectiveness of cyanogenesis as a plant defense. Populations known to be characteristically acyanogenic, cyanogenic or to exhibit within-population variation were surveyed for cyanogenesis, plant size, and the presence and identity of invertebrate plant visitors. A developmental series of 10 leaves from a shoot of each surveyed plant was analyzed, using image analysis techniques, for the type and extent of damage present. We also surveyed two additional plant populations for the presence of plants with eggs or larvae of Euptoieta hegesia Cramer, a Nymphalid butterfly that is potentially the most damaging herbivore of T. ulmifolia, and a paired comparison analysis of cyanogenesis in plants with the herbivore versus plants without the herbivore was conducted. We found that T. ulmifolia are attacked by a reasonably diverse insect fauna, but a relatively small suite of specialist herbivores that are seemingly undeterred by cyanogenesis inflicts most of the leaf damage. Cyanogenesis does appear to play a role in determining the types, numbers, and presence of generalist herbivores found within and between populations. Tissue loss sustained by plants varies both within and between populations; however, the proportion of leaf tissue lost due to herbivory is low, ranging from only 1-9% on average, and does not appear to be correlated with cyanogenesis in a consistent way. An analysis of covariance did, however, reveal that cyanogenesis has a significant effect on both plant height and number of shoots per plant. These results suggest that cyanogenesis might afford protection against herbivory from generalizing herbivores. Web of Science Turnera ulmifolia L. Field - Observational terrestrial Invasion Hyp. Novel Weapons primary 2086 Baruch, Z; Pattison, RR; Goldstein, G 2000 Responses to light and water availability of four invasive Melastomataceae in the Hawaiian islands journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 161 1 107 118 Plant invasion by Neotropical Melastomataceae is prominent in Hawaii. To understand life history traits of four successful invasive Melastomataceae, two shade-intolerant herbs (Arthrostema ciliatum and Tibouchina herbacea) and two shade-tolerant woody species (Clidemia hirta, a shrub, and Miconia calvescens, a tree) were subjected to three light levels and two watering regimes in a greenhouse. Plant height, leaf number and area, biomass allocation, relative growth rate (RGR), carbon assimilation (A), leaf nutrient content, leaf construction costs (CC), specific leaf mass (SLM), and leaf spectral properties were determined at the end of the experimental period. Plant size, total biomass, RGR, A, CC, and SLM decreased, whereas leaf light transmittance and leaf N increased under low light in all species. The effects of water stress were weaker than light-stress effects. Relative growth rate of herbs grown in sun and partial shade (0.046 and 0.033 g g(-1) d(-1), respectively) was higher than in the woody species (0.027 and 0.020 g g(-1) d(-1)). Woody species allocated more biomass to leaf production than herbs, which allocated more biomass to stem production. Shade increased allocation of biomass to leaves, and water stress increased the root-shoot ratio in all species. Partial shade increased leaf area ratios more in the herbs (140%) than in woody species (68%). Miconia calvescens and C. hirta had higher leaf absorbance (92%) than both herbs (79%). Maximum A under all light treatments was similar in all species, and there was substantial acclimation to the different light levels. Leaf construction cost was higher-in the apparently long-lived leaves of the woody species. Relative growth rate, carbon allocation, and SLM showed larger changes to light and water stress than A and related photosynthetic parameters. All species showed responses qualitatively similar to those of other tropical species including the high acclimation potential to light, but the herbs exhibited the largest quantitative responses. When compared with a large group of native species, the four melastomes appear to be better suited to capture and use light, which is consistent with their rapid spread in mesic and disturbed Hawaiian environments. Web of Science Arthrostema ciliatum; Tibouchina herbacea; Clidemia hirta; Miconia calvescens United States Hawaii Maui; Ohau Greenhouse terrestrial Invasion Hyp. Inherent Superiority;Preadaptation to Climate Broad Tolerances primary 2089 Parendes, LA; Jones, JA 2000 Role of light availability and dispersal in exotic plant invasion along roads and streams in the H. J. Andrews Experimental Forest, Oregon journal CONSERVATION BIOLOGY 14 1 64 75 We examined the roles of dispersal mechanism, a biological barrier, light availability, an environmental barrier; and level of disturbance, a physical barrier, in explaining the spatial patterns of exotic plant species along road and stream segments in a forest landscape in the western Cascade Range of Oregon (U.S.A). The presence or absence of 21 selected exotic plant species and light levels were observed along 0.3- to 1.0-km transects within four habitat types. Each habitat represented a different level of disturbance: high-use roads, low-use roads, abandoned roads, and streams in the H.J. Andrews Experimental Forest. Nearly 300 50 X 2-m sampling units were surveyed along five transects in each habitat type. We used ordination (nonmetric multidimensional scaling) and logistic regression to analyze data. All of the nearly 200 sampling units along roads with high and low levels of vehicle traffic contained at least one exotic plant species, and some contained as many as 14. Streams that were most recently disturbed by floods 20-30 years ago and abandoned spur roads with no traffic for 20-40 years also had numerous exotic species. Roads and streams apparently serve multiple functions that enhance exotic species invasion in this landscape: they act as corridors or agents for dispersal, provide suitable habitat, and contain reservoirs of propagules for future episodes of invasion. Species-specific dispersal mechanisms, habitat characteristics, and disturbance history each explain some, but not all, of the patterns of exotic species invasion observed in this study. Web of Science Many United States Oregon h. j. andrews experimental forest 44.215925 -122.254829 Field - Observational terrestrial Invasion Hyp. Inherent Superiority;Disturbance;Other Effective Disperser primary 2091 Pate, JS; Bell, TL 2000 Host associations of the introduced annual root hemiparasite Parentucellia viscosa in agricultural and bushland settings in Western Australia journal ANNALS OF BOTANY 85 2 203 213 Populations of the introduced annual root hemiparasite, Parentucellia viscosa (L.) Caruel (Scrophulariaceae), were examined in habitats where introduced, mixed introduced plus native, or solely native species provided potential hosts. Presence of haustoria on host roots confirmed parasitism of 17 introduced and ten native taxa across the sites investigated. Paired plots, one with all hosts removed early in the season, the other left intact, showed overall increases in shoot dry matter of the parasites over 3 months of growth. Results indicated a substantial growth benefit to the parasite from continued access to introduced and indigenous plant species, although the parasite continued growing to a limited extent after removal of hosts. Carbon isotope discrimination values (delta(13)C) were consistently more negative for parasites than for associated hosts, and more negative for parasites in plots containing hosts than in plots from which hosts had been removed. Values for delta(15)N discrimination of shoot dry matter of parasites lay mostly within the range of those of hosts. The delta(13)C data suggested poorer water use efficiency of parasite than hosts, while corresponding delta(15)N data indicated particularly effective uptake of N-containing compounds from the N-2-fixing host, Lotus angustissimus. Where the parasite had access to only one or a few closely related hosts, the composition of the soluble amino fraction of its leaves generally matched that of foliage of host(s). However, in some instances the parasite accumulated certain amino compounds to a much greater or lesser relative extent than did its partner host(s). Where many hosts were being exploited, compositional features of the soluble amino fraction of the parasite suggested major access to nitrogenous solutes from specific hosts. Data are discussed in relation to previously published observations on haustorial-derived benefits indicated for other species of root hemiparasites. (C) 2000 Annals of Botany Company. Web of Science Parentucellia viscosa (L.) Caruel (Scrophulariaceae) Australia Perth Forrestdale Lake -31.57 115.52 Field - Observational;Lab terrestrial Invasion Hyp. Other parasite 2092 Willis, AJ; Blossey, B 1999 Benign environments do not explain the increased vigour of non-indigenous plants: a cross-continental transplant experiment journal BIOCONTROL SCIENCE AND TECHNOLOGY 9 4 567 577 Invasive plants tend to be taller and produce more biomass in their introduced range than conspecifics growing in their native range. Such observations are usually explained by more 'benign' environments, implying that plastic, phenotypic responses are responsible for increased vigour: We compared the growth of 10 Lythrum salicaria,populations from indigenous and non-indigenous distributions in two gardens. one located in Ern ope (indigenous range), the other in North America (non-indigenous range). Spearman rank correlations of different growth variables were generally significant, suggesting that certain genotypes show increased vigour regardless of growing location. More benign climates or the absence of natural enemies are not sufficient to explain this increased vigour. Plant performance tended to be higher in populations from the introduced range, though few differences were statistically significant. To test alternative hypotheses of 'increased vigour' larger sample sizes will be required which was not attempted in this study. Web of Science Lythrum salicaria North America Garden terrestrial Invasion Hyp. Plasticity primary 2093 Lonsdale, WM 1999 Global patterns of plant invasions and the concept of invasibility journal ECOLOGY 80 5 1522 1536 With a simple model, I show that comparisons of invasibility between legions are impossible to make unless one can control for all of the variables besides invasibility that influence exotic richness, including the rates of immigration of species and the characteristics of the invading species themselves. Using data from the literature for 184 sites around the world, I found that nature reserves had one-half of the exotic fraction of sites outside reserves, and island sites had nearly three: times the exotic fraction of mainland sites. However, the exotic fraction and the number of exotics were also dependent on site area, and this had to be taken into account to make valid comparisons between sites. The number of native species was used as a surrogate fur site area and habitat diversity. Nearly 70% of the variation in the number of exotic species was accounted for by a multiple regression containing the following predictors: the number of native species, whether the site was an island or on the mainland, and whether or not it was a nature reserve. After controlling for scale, there were significant differences among biomes, but not continents in their level of invasion. Multiple biome regions and temperate agricultural or urban sites were among the most invaded biomes, and deserts and savannas were among the least. However, there was considerable within-group variation in the mean degree of invasion. Scale-controlled analysis also showed that the New World is significantly more invaded than the Old World, but only when sire native richness (probably a surrogate fur habitat diversity) is factored our. Contrary to expectation, communities richer in native species had more, not fewer, exotics. For mainland sites, the degree of invasion increased with latitude, but there was no such relationship for islands. Although islands are more invaded than mainland sites, this is apparently not because of low native species richness, as the islands in this data set were no less rich in native species than were mainland sites of similar area. The number of exotic species in nature reserves increases with the number of visitors. However, it is difficult to draw conclusions about relative invasibility, invasion potential, or the roles of dispersal and disturbance from any of these results. Most of the observed patterns here and in the literature could potentially be explained by differences between regions in species properties, ecosystem properties, or propagule pressure. Web of Science Many Statistical/Meta-analysis;Review terrestrial Invasion Hyp. Community Species Richness;Other primary 2097 Morrison, SL; Molofsky, J 1999 Environmental and genetic effects on the early survival and growth of the invasive grass Phalaris arundinacea journal CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE 77 10 1447 1453 Both genetic and environmental factors can determine whether an invasive plant species will establish. To determine how these factors influence the establishment of the invasive grass Phalaris arundinacea L. (reed canary grass), we grew three genotypes in 10 artificial environments and asked how a genotype's growth and survivorship was affected by environmental conditions. We found that genotype strongly influenced survivorship, but there was no significant effect of environment on survivorship. However, environmental conditions did significantly affect growth. Individual plants produced more aboveground and belowground biomass when grown singly than they did when grown with competitors. The identity of neighboring competitors had no effect. Although genotype had no significant efffect, there was a significant genotype x environment interaction. Clone 1 produced more root biomass than either clone 2 or clone 3 when there was no or little competition, but in competitive neighborhoods, clone 3 allocated relatively more biomass to roots than to shoots. Under ideal conditions in the greenhouse, clone 2 produced more tillers than the other two clones. Based on these results, it appears that clone 1 may have an advantage under sparse vegetative cover, but clone 3 may have a competitive advantage in highly competitive neighborhoods because it could preferentially allocate more biomass to roots. The presence of three growth patterns from such a small, localized sample suggests that different growth strategies are probably common within populations of reed canary grass and may be important for allowing reed canary grass to successfully invade new habitats. Web of Science Phalaris arundinacea L. (reed canary grass) United States Vermont University of Vermont 44.478809 -73.194952 Greenhouse terrestrial Invasion Hyp. Evolution in General;Inherent Superiority Superior Competitor;Broad Tolerances primary 2103 Leege, LM; Murphy, PG 2000 Growth of the non-native Pinus nigra in four habitats on the sand dunes of Lake Michigan journal FOREST ECOLOGY AND MANAGEMENT 126 2 191 200 We examined the post-planting success of the non-native Pinus nigra Arnold (Austrian pine) in four habitats in a Lake Michigan sand dune system, into which approximately 26 000 seedlings had been introduced between 1956 and 1972. Growth (height, diameter, and stem volume) of P. nigra on the dunes was compared to that of individuals of similar age in managed plantations and in the native European range. Tree size differed more within than among dune habitats, indicating that the coarse-scale differences in environmental factors among habitats, such as distance from the lake, soil moisture, and wind exposure, account for only some of the variation in growth. Comparisons with native European populations indicate that P. nigra grows as well or better on the dunes of southern Lake Michigan than in its native range. The broad ecological tolerance of P. nigra appears to be a major attribute in its successful establishment in a variety of dune conditions. (C) 2000 Elsevier Science B.V. All rights reserved. Web of Science Pinus nigra Arnold (Austrian pine) United States Michigan Allegan County 42.41 -86.12 Field - Observational terrestrial Invasion Hyp. Inherent Superiority Broad Tolerances primary 2110 Baruch, Z; Goldstein, G 1999 Leaf construction cost, nutrient concentration, and net CO2 assimilation of native and invasive species in Hawaii journal OECOLOGIA 121 2 183 192 The effects of biological invasions are most evident in isolated oceanic islands such as the Hawaiian Archipelago, where invasive plant species are rapidly changing the composition and function of plant communities. In this study, we compared the specific leaf area (SLA), leaf tissue construction cost (CC), leaf nutrient concentration, and net CO2 assimilation (A) of 83 populations of 34 native and 30 invasive species spanning elevation and substrate age gradients on Mauna Loa volcano in the island of Hawaii. In this complex environmental matrix, where annual precipitation is higher than 1500 mm, we predicted that invasive species, as a group, will have leaf traits, such as higher SLA and A and lower leaf CC, which may result in more efficient capture of limiting resources (use more resources at a lower carbon cost) than native species. Overall, invasive species had higher SLA and A, and lower CC than native species, consistent with our prediction. SLA and foliar N and P were 22.5%, 30.5%, and 37.5% higher, respectively, in invasive species compared to native ones. Light-saturated photosynthesis was higher for invasive species (9.59 mu mol m(-2) s(-1)) than for native species (7.31 mu mol m(-2) s(-1)), and the difference was larger when A was expressed on a mass basis. Leaf construction costs, on the other hand, were lower for the invasive species (1.33 equivalents of glucose g(-1)) than for native species (1.37). This difference was larger when CC was expressed on an area basis. The trends in the above traits were maintained when groups of ecologically equivalent native and invasive species (i.e., sharing similar life history traits and growing in the same habitat) were compared.:Foliar N and P were significantly higher in invasive species across all growth forms. Higher N may partially explain the higher A of invasive species. Despite relatively high N, the photosynthetic nitrogen use efficiency of invasive species was 15% higher than that of native species. These results suggest that invasive species may not only use resources more efficiently than native species, but may potentially demonstrate higher growth rates, consistent with their rapid spread in isolated oceanic islands. Web of Science Many United States Hawaii Hawaii 19.55 -155.52 Field - Observational terrestrial Invasion Hyp. Inherent Superiority;Other Rapid Growth primary 2114 Ehrenfeld, JG 1999 A rhizomatous, perennial form of Microstegium vimineum (Trin.) A-Camus in New Jersey journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 126 4 352 358 Populations of Microstegium vimineum (Trin.) A. Camus have been found in New Jersey containing individuals that have clusters of large rhizomes, and which evidently exhibit the perennial growth habit. This species, a major invasive exotic pest throughout the east coast,has previously only been known as an annual, both in the US and in its native geographical range in temperate and tropical Asia and India. Rhizomatous plants were observed in 6 populations, in sites ranging over a 100 km distance, and accounted for 8-15% of the culms in each population. Lower nodes of decumbent culms have on average 4 rhizomes (maximum 13 per node and 23 per culm were observed), which are 0.1 to 7 cm long (mean 1 cm). Significant differences in the number of rhizomes per culm and the size distribution of rhizomes were found among three sampled populations. Rhizomatous specimens had open, exserted terminal panicles which flowered 2-3 weeks before the non-rhizomatous specimens, which have cleistogamous spikelets within the leaf sheaths and a variably exserted, closed terminal panicle. Rhizomes sprouted in the greenhouse, after cold treatment, demonstrating their perennial capacity. This is the first reported occurrence of rhizomes in the genus, and also is the first apparent example of a trade-off between annual/perennial life history and cleistogamous/chasmogamous reproduction. In addition to the implications for the evolution of plant life history characteristics and breeding systems,the finding has important implications for control strategies for this invasive plant species; current recommendations for its control will not be effective against perennial forms. Web of Science Microstegium vimineum USA New Jersey Field - Observational terrestrial Deciduous Forest Invasion Hyp. Evolution in General primary 2120 Knops, JMH; Tilman, D; Haddad, NM; Naeem, S; Mitchell, CE; Haarstad, J; Ritchie, ME; Howe, KM; Reich, PB; Siemann, E; Groth, J 1999 Effects of plant species richness on invasion dynamics, disease outbreaks, insect abundances and diversity journal ECOLOGY LETTERS 2 5 286 293 Declining biodiversity represents one of the most dramatic and irreversible aspects of anthropogenic global change, yet the ecological implications of this change are poorly understood. Recent studies have shown that biodiversity loss of basal species, such as autotrophs or plants, affects fundamental ecosystem processes such as nutrient dynamics and autotrophic production. Ecological theory predicts that changes induced by the loss of biodiversity at the base of an ecosystem should impact the entire system. Here we show that experimental reductions in grassland plant richness increase ecosystem vulnerability to invasions by plant species, enhance the spread of plant fungal diseases, acid alter the richness and structure of insect communities. These results suggest that the loss of basal species may have profound effects on the integrity and functioning of ecosystems. Web of Science Many United States Minnesota Cedar Creek 45.403633 -93.201656 Field - Experimental terrestrial Grassland Invasion Hyp. Community Species Richness primary 2122 Brown, JR; Archer, S 1999 Shrub invasion of grassland: Recruitment is continuous and not regulated by herbaceous biomass or density journal ECOLOGY 80 7 2385 2396 Proliferation of woody plants in grasslands and savannas since the 1800s has been widely documented. In the southwestern United States, increased abundance of honey mesquite (Prosopis glandulosa var. glandulosa) has been attributed to heavy grazing by livestock. Here, we test the hypothesis that P. glandulosa invasion of grasslands requires, first, reductions in herbaceous biomass and density such as those that accompany livestock grazing and, second, episodes of high soil moisture availability. No combination of grass density (nonmanipulated or reduced 50%) or defoliation (none, moderate, heavy) significantly affected P. glandulosa seedling emergence within a watering regime (natural and supplemented) at our field site in semiarid southern Texas. Seedling emergence on plots receiving only natural rainfall was high (42%), despite the fact that precipitation was substantially below normal. Supplemental watering, to generate moisture levels approximating years of unusually high annual rainfall, increased emergence to 59%. Seedling survival after 2 yr was high (62-77%) and statistically comparable across the density, defoliation, and watering treatments. Net photosynthesis (A(n)) of 1-yr-old seedlings was enhanced by supplemental watering, but reductions in grass density or biomass had little effect on seedling A(n) or xylem water potential. Height, aboveground biomass, and leaf area were comparable among 1- and 2-yr-old seedings across all density, defoliation, and watering combinations. High seedling emergence and survival on unwatered plots, even during a *drought year,* suggests that Prosopis recruitment is not contingent upon unusual or episodic rainfall. Reductions in biomass and density of herbaceous vegetation had no influence on seedling emergence, growth, or survival, suggesting that Prosopis invasion is minimally influenced by grass competition. Historic grazing at this site appears to have altered herbaceous composition and reduced above- and belowground biomass production below the threshold level required for competitive exclusion of woody vegetation. Such data suggest that rates and patterns of seed dispersal may be the primary determinants of P. glandulosa encroachment on present-day landscapes in semiarid regions. Minimizing livestock dispersal of seed (in the case of leguminous shrubs) and maintenance of an effective fire regime (through production of fine fuels) may be crucial for sustaining herbaceous composition and production in grazed systems prone to invasion by unpalatable woody plants. Web of Science Prosopis glandulosa var. glandulosa United States Texas Texas Agricultural Experiment Station 27.6667 -98.2 Field - Experimental terrestrial Savanna Invasion Hyp. Fluctuating Resources;Disturbance primary 2124 Anderson, R 1999 Disturbance as a factor in the distribution of sugar maple and the invasion of Norway maple into a modified woodland journal RHODORA 101 127 264 273 Disturbances have the potential to increase the success of biological invasions. Norway maple (Acer platanoides), a common street tree native to Europe, is a foreign invasive with greater tolerance and more efficient resource utilization than the native sugar maple (Acer saccharum). This study examined the role disturbances from a road and path played in the invasion of Norway maple and in the distribution of sugar maple. Disturbed areas on the path and nearby undisturbed areas were surveyed for both species along transects running perpendicular to a road. Norway maples were present in greater number closer to the road and on the path, while the number of sugar maples was not significantly associated with either the road or the path. These results suggest that human-caused disturbances have a role in facilitating the establishment of an invasive species. Web of Science Acer platanoides United States Massachusetts Middlesex Fells Reservation 42.454874 -71.090298 Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 2127 Willis, AJ; Thomas, MB; Lawton, JH 1999 Is the increased vigour of invasive weeds explained by a trade-off between growth and herbivore resistance? journal OECOLOGIA 120 4 632 640 Blossey and Notzold (1995) recently hypothesised that the increased vigour of certain invasive plant species has been at the expense of defences against natural enemies. A prediction of their evolution of increased competitive ability (EICA) hypothesis is that invasive genotypes are relatively poorly defended. We tested this prediction with herbivore bioassays and with direct quantification of plant secondary metabolites comparing non-indigenous genotypes of Lythrum salicaria L. (purple loosestrife) with indigenous forms. The herbivore bioassays revealed no significant intra-specific variation in herbivore resistance between indigenous and nonindigenous hosts. The phenolic content of L. salicaria leaves was significantly higher in indigenous genotypes, as predicted by the EICA hypothesis. The average phenolic content of leaves (regardless of their origin) was, however, low, implying that the role of plant phenolics in purple loosestrife anti-herbivore defence is probably limited. It is suggested that the ESCA hypothesis, as tested in the current study, does not explain the increased vigour of L. salicaria in non-indigenous habitats. Web of Science Lythrum salicaria United Kingdom Greenhouse;Lab terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 2128 Smith, MD; Knapp, AK 1999 Exotic plant species in a C-4-dominated grassland: invasibility, disturbance, and community structure journal OECOLOGIA 120 4 605 612 We used data from a 15-year experiment in a C-4-dominated grassland to address the effects of community structure (i.e., plant species richness, dominance) and disturbance on invasibility, as measured by abundance and richness of exotic species. Our specific objectives were to assess the temporal and spatial patterns of exotic plant species in a native grassland in Kansas (USA) and to determine the factors that control exotic species abundance and richness (i.e., invasibility). Exotic species (90% C-3 plants) comprised approximately 10% of the flora, and their turnover was relatively high (30%) over the 15-year period. We found that disturbances significantly affected the abundance and richness of exotic species. In particular, long-term annually burned watersheds had lower cover of exotic species than unburned watersheds, and fire reduced exotic species richness by 80-90%. Exotic and native species richness were positively correlated across sites subjected to different fire (r = 0.72) and grazing (r = 0.67) treatments, and the number of exotic species was lowest on sites with the highest productivity of C-4 grasses (i.e., high dominance). These results provide strong evidence for the role of community structure, as affected by disturbance, in determining invasibility of this grassland. Moreover, a significant positive relationship between exotic and native species richness was observed within a disturbance regime (annually burned sites, r = 0.51; unburned sites, r = 0.59). Thus, invasibility of this C-4-dominated grassland can also be directly related to community structure independent of disturbance. Web of Science Many United States Kansas Konza Prairie Research Natural Area 39.0833 -96.5833 Field - Experimental terrestrial Grassland Invasion Hyp. Community Species Richness;Disturbance primary 2130 Gido, KB; Brown, JH 1999 Invasion of North American drainages by alien fish species journal FRESHWATER BIOLOGY 42 2 387 399 1. Data from the literature were used to document colonization patterns by introduced freshwater fishes in 125 drainages across temperate North America. We analysed this data set to quantify susceptibility to invasion, success of the invaders and changes in species richness. 2. Drainages with a high number of impoundments, large basin area and low native species diversity had the greatest number of introduced species. Those drainages containing few native fishes exhibited great variation in the number of invaders, while waters with a rich native fauna contained few introduced species. However, this pattern did not differ significantly from random simulations because the pool of potential invaders is greater for drainages with low species richness. 3. In most drainages, there were more introduced than imperilled or extirpated species, suggesting that invaders tend to increase overall species richness. 4. These patterns suggest that North American fish communities are not saturated with species, but instead, are capable of supporting higher levels of diversity if the pool of potential colonists and the rate of colonization from that pool is increased. Web of Science Many North America Statistical/Meta-analysis lentic Invasion Hyp. Community Species Richness 2132 Marler, MJ; Zabinski, CA; Wojtowicz, T; Callaway, RM 1999 Mycorrhizae and fine root dynamics of Centaurea maculosa and native bunchgrasses in western Montana journal NORTHWEST SCIENCE 73 3 217 224 Centaurea maculosa is an invasive exotic pest plant of intermountain grasslands of the western United States. We investigated whether there were differences in fine root and mycorrhizal development between the exotic forb C. maculosa and two native grasses, since these are factors known to influence competitive ability of plants. We measured colonization by arbuscular mycorrhizal (AM) fungi of the native bunch grasses Pseudoroegnaria spicata and Festuca idahoensis, and C. inaculosa, and used root periscopes to investigate fine root patterns of P. spicata and C. maculosa. AM fungal colonization of the exotic was similar to F: idahoensis in 1995 (43.6% vs. 44.7%), and was higher than I? spicata in 1995 and 1996 (43.6% vs. 26.9%, and 55.4% vs. 15.6%). Colonization of the grasses was not affected by the presence of C. maculosa. Fine roots of C. maculosa developed earlier, with a higher proportion of deep roots than P. spicata. Thirty nine per cent of C. maculosa roots, but only 25% of P. spicata roots, were deeper than 30 cm. Early and deep root development and extensive mycorrhizal colonization in the field may contribute to competitive dominance of C. maculosa. Web of Science Centaurea maculosa United States Montana 46.857315 -113.969078 Field - Observational terrestrial Grassland Invasion Hyp. Inherent Superiority Superior Competitor primary 2135 Dietz, H; Fischer, M; Schmid, B 1999 Demographic and genetic invasion history of a 9-year-old roadside population of Bunias orientalis L. (Brassicaceae) journal OECOLOGIA 120 2 225 234 The population history of a 9-year-old roadside population of the invasive plant Bunias orientalis was reconstructed by demographic analysis including size, position, age (determined by herbchronology) and RAPD-PCR patterns of individual plants. We evaluated emerging patterns of population growth and genetic structure during a full period of population development under typical site conditions (anthropogenic disturbance) and their possible consequences for the invasion potential of the species. The population has grown rapidly and continuously (though with slowing geometric population increase) during the 9 years since its foundation, filling the space available in the study area. Genetic variation (RAPD markers) was already high in the founder cohorts and remained at the same level throughout population development (variance fluctuations < 15%). Both results may be related to the mowing management at the site which seems to promote population growth of B. orientalis relative to other co-occuring species and to prevent the genetic drift and the development of spatial genetic structure that would be expected under isolation-by-distance models. Large founder plants had comparatively low genetic variance and were more closely related to younger cohorts than were small founder plants, indicating that selection acted during population development. Overall, the current anthropogenic disturbance regimes may contribute to high genetic variability by artificially increasing gene flow and thereby promoting the adaptability of invasive species to the often unpredictable conditions at disturbed sites. Our approach using retrospective demographic investigation allows the detection of spatio-temporal microscale patterns in genetic and phenotypic variation. Thus it allows a thorough understanding of local invasions of perennial herbaceous plants. Web of Science Bunias orientalis Germany Unterfranken 49.85 9.85 Field - Observational terrestrial Grassland Invasion Hyp. Evolution in General;Disturbance primary 2140 Marler, MJ; Zabinski, CA; Callaway, RM 1999 Mycorrhizae indirectly enhance competitive effects of an invasive forb on a native bunchgrass journal ECOLOGY 80 4 1180 1186 Mycorrhizae are important mediators of plant competition, but little is known about the role of mycorrhizae in the intense competitive effects that exotic plants can have on native species. In the greenhouse, we tested the effect of arbuscular mycorrhizal (AM) fungi on interspecific competition between Centaurea maculosa and Festuca idahoensis, on intraspecific competition between individuals of both species, and the growth of C. maculosa with either inorganic or organic phosphorus. Mycorrhizae had no direct effect on either species, but mycorrhizae increased C. maculosa's negative effect on F. idahoensis. When competing with C. maculosa, nonmycorrhizal F. idahoensis were 171% larger than they were when mycorrhizae were present. In a second experiment, C. maculosa grown with larger F. idahoensis were 66% larger, in the presence of AM fungi, than when AM fungi were absent. Centaurea maculosa biomass was not affected by AM fungi, in either phosphorus treatment, in the absence of F. idahoensis. Root:shoot ratios differed between phosphorus treatments, but this difference seemed to be a result of slower growth in the organic phosphorus treatment. Our results were unusual in that the direct effects of mycorrhizae on both species were weak, but the indirect effect of AM fungi on the interactions between C. maculosa and F. idahoensis was strong. Our results suggest that AM fungi strongly enhance the ability of C. maculosa to invade native grasslands of western North America. Web of Science Centaurea maculosa United States Montana Greenhouse terrestrial Invasion Hyp. Inherent Superiority Superior Competitor primary 2143 Baruch, Z; Bilbao, B 1999 Effects of fire and defoliation on the life history of native and invader C-4 grasses in a Neotropical savanna journal OECOLOGIA 119 4 510 520 African grasses, introduced into Neotropical savannas to improve forage quality, have spread successfully and displaced native plants. To understand their competitive relationships, we compared biomass production and allocation, plant architecture and phenology, net photosynthesis (Pn), water relations, and nutrient content under fire and simulated herbivory between two C-4 grasses, the native Trachypogon plumosus and the introduced Hyparrhenia rufa from a seasonal savanna in Venezuela. All variables were strongly influenced by the rainfall regime. Huparrhenia,pan produced bigger plants (in mass and size) with a large proportion of mass (>75%) allocated to leaves and culms. Its biomass production was more affected by fire than by defoliation. In contrast, Trachypogon was more affected by defoliation than by fire which promoted a flush of leaf growth even in the dry season. Fire caused up to 85% mortality in Hyparrhenia but none in Trachypogon, where it increased inflorescence production. However, fire promoted abundant seed germination and fast seedling growth in Hyparrhenia, enabling it to colonize new areas. During the growing season Trachypogon,pogon had higher Pn and lower leaf water potential (Psi) than Hyparrhenia but differences among treatments were not significant for either grass. Pn of Trachypogon ceased at a lower Psi(-3.0 MPa) than in Hyparrhenia (-2.0 MPa), indicating its higher tolerance to water stress. During the dry season, Trachypogon,pogon leaves remained alive and retained low Pn. Leaf nutrient content was higher during the rainy season in both species. Differences in Pn could not explain the higher seasonal biomass production of Hyparrhenia. However, its water stress evasion strategy, larger biomass allocated to leaves, abundant germination and fast seedling growth appeared to be responsible for the success of Hyparrhenia as an invader of Neotropical savannas. Web of Science Hyparrhenia Venezuela Guarico State Research Station Biologica de los Llano 8.56 -67.25 Field - Experimental terrestrial Savanna Invasion Hyp. Inherent Superiority;Disturbance Superior Competitor primary 2151 Jacobs, JS; Sheley, RL 1999 Competition and niche partitioning among Pseudoroegneria spicata, Hedysarum boreale, and Centaurea maculosa journal GREAT BASIN NATURALIST 59 2 175 181 Maximizing desired plant diversity has been suggested as a means of minimizing non-indigenous plant invasion on rangeland by maximizing niche occupation. Competition between 2 desired indigenous species, Pseudoroegneria spicata (Pursh.) Love (bluebunch wheatgrass) and Hedysarum boreale Nutt. var. boreale (northern sweetvetch), and a non-indigenous invader, Centaurea maculosa Lam. (spotted knapweed), was quantified using growth of isolated individuals and 2 three-species addition series experiments. Seeding densities of P. spicata remained constant at 0, 200, 400, and 800 seeds m(-2) in both experiments. H. boreale and C. maculosa seeding densities were 0, 200, 400, and 800 seeds m(-2), respectively, in the Ist experiment and 0, 400, 800, and 1600 seeds m(-2), respectively, in the 2nd experiment. Densities were factorially arranged. Pots were placed in an environmental chamber (12 degrees C, 12-h day length, 200 mu mol photons m(-2) s(-1) spectral light) in a randomized-complete-block design. After 90 d the growth rate of P. spicata (92.1 mg d(-1) shoot growth) was greater than that of the 2 forts (1.6 and 5.5 mg d(-1) for H. boreale and C. maculosa, respectively), and growth rates of the 2 forts were similar to one another. Curvilinear regression indicated that intraspecific competition was more important in determining shoot weight than interspecific competition. In addition, the 2 forts competed more directly with each other than with Il spicata. Competition coefficient ratios (1.42 and 1.53 for II spicata with H. boreale and C, maculosa, respectively, and 1.03 for H. boreale with C. maculosa) indicated substantial partitioning of resources between Il spicata and each of the forts. Little or no resource partitioning occurred between forts. This study suggests that increasing desired. plant diversity may minimize weed invasion by increasing niche occupation. Web of Science Centaurea maculosa Lam. (spotted knapweed) Lab terrestrial Invasion Hyp. Community Species Richness primary 2155 Morrison, SL; Molofsky, J 1998 Effects of genotypes, soil moisture, and competition on the growth of an invasive grass, Phalaris arundinacea (reed canary grass) journal CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE 76 11 1939 1946 The successful establishment of an invasive plant species in a new environment depends upon the interplay between the plant's genetic diversity and morphological plasticity and the physical and biotic environment it encounters. To determine the relative importance of these factors in influencing the spread of the invasive grass, Phalaris arundinacea L. (reed canary grass), we transplanted three genotypes into a pasture that contained variable soil moisture, species composition, and vegetative cover. We found that P. arundinacea produced more above- and belowground biomass in sparsely vegetated plots than in densely vegetated plots, but biomass production was not affected by soil moisture. There was also a significant clone x vegetative cover interaction. Genotypes differed in how strongly their growth was inhibited by dense vegetative cover. Vegetative cover also influenced biomass allocation patterns. As vegetative cover increased, P. arundinacea allocated more biomass to roots, a strategy that gives transplants a competitive advantage during the following spring. Our results suggest that. because it grows poorly in high vegetative cover, P. arundinacea is most likely to become a pest in disturbed or low-density plant communities. Furthermore, differences among genotypes in their response to vegetative cover suggest that continual introductions of new genotypes of reed canary grass substantially increase the chance that a particular genotype will flourish and spread. Web of Science Phalaris arundinacea L. (reed canary grass) United States Vermont Jericho 44.504586 -72.997842 Field - Experimental terrestrial Invasion Hyp. Evolution in General;Inherent Superiority;Community Species Richness Broad Tolerances primary 2158 Hofstra, DE; Clayton, J; Green, JD; Auger, M 1999 Competitive performance of Hydrilla verticillata in New Zealand journal AQUATIC BOTANY 63 4 305 324 In outdoor tanks, Hydrilla verticillata was grown in equal start, and established, cultures with each of four other submerged adventive aquatic macrophytes Egeria densa, Lagarosiphon major, Ceratophyllum demersum and Elodea canadensis. Plant growth and performance were monitored for a year, then all the plants and H, verticillata tubers (subterranean turions) were harvested. There was a significant difference in H. verticillata biomass obtained when grown with each of the competitor species and the highest and lowest biomass values were obtained with C. demersum and E, densa, respectively. Planting time also affected H. verticillata biomass. In equal start experiments with any competitor species biomass was significantly greater than when the competitor species had between 2-8 weeks to establish. Similarly, H. verticillata tuber numbers were greater when H. verticillata was grown with C. demersum compared with other hydrocharitaceans. Although its growth varied significantly, depending on the species with which it was planted, and it encroached on the space occupied by its competitors, H. verticillata appeared to have little impact on the biomass of its potential competitors over the duration of this study. Nevertheless, the capacity of H. verticillata to grow and compete effectively with other adventive aquatic macrophyte species that already cause problems in lakes and waterways was evident and highlights the highly invasive nature and threat that H. verticillata poses to the New Zealand aquatic environment. (C) 1999 Elsevier Science B.V. All rights reserved. Web of Science Hydrilla verticillata New Zealand Hamilton -37.788081 175.275879 Garden lentic Invasion Hyp. Inherent Superiority Superior Competitor primary 2161 Treberg, MA; Husband, BC 1999 Relationship between the abundance of Lythrum salicaria (purple loosestrife) and plant species richness along the Bar River, Canada journal WETLANDS 19 1 118 125 Lythrum salicaria (purple loosestrife) is a perennial herbaceous plant that was introduced in the 1800s into North America. Its geographical expansion has generated much concern, in part because its spread may lead to a reduction in the diversity of plant species in wetlands. We tested this hypothesis by examining the association between the abundance of Lythrum salicaria and vascular plant species richness in forty-one 2m x 2m plots located along the Bar River, Ontario, Canada. No significant differences in mean species richness were found between plots with and without L. salicaria. For those plots containing L. salicaria, species richness was not related to the percentage cover of L. salicaria. Furthermore, there were no significant differences in the number of introduced plant species between plots with and without L. salicaria, nor were there differences with increasing percent cover of L. salicaria. Plant species such as Nuphar variegatum, Scirpus atrovirens, Scirpus cyperinus, and Scirpus microcarpus were more likely to be found in plots with Lythrum salicaria than without. However, no plant species were significantly mon likely to be found in plots without Lythrum salicaria than with it. Collectively, these results provide no support for the hypothesis that the number of species in wetlands is decreasing in association with the invasion of Lythrum salicaria in Ontario. Web of Science Lythrum salicaria (purple loosestrife) Canada Ontario Bar River 46.442115 -84.025841 Field - Observational terrestrial Riparian Invasion Hyp. Community Species Richness primary 2162 Maron, JL; Jefferies, RL 1999 Bush lupine mortality, altered resource availability, and alternative vegetation states journal ECOLOGY 80 2 443 454 Nitrogen-fixing plants, by altering the availability of soil N, potentially facilitate plant invasion. Here we describe how herbivore-driven mortality of a native N-fixing shrub, bush lupine (Lupinus arboreus), increases soil N and light availability, which promotes Invasion by introduced grasses to the detriment of a native plant community. Soils under live and dead lupine stands contained large amounts of total N, averaging 3.14 mg N/g dry mass of soil (398 g/m(2)) and 3.45 mg N/g dry mass of soil (438 g/m(2)), respectively, over four years. In contrast, similar lupine-free soil was low in N and averaged only 1.66 mg N/g dry mass of soil (211 g/m(2)) over three years. The addition of N fertilizer to lupine-free soil produced an 81% increase in aboveground plant biomass compared to plots unamended with N. Mean rates of net N mineralization were higher under live lupine and where mass die-off of lupine had occurred compared to soils free of bush lupine. At all sites, only 2.5-4.2% of the total soil N pool was mineralized annually. Soil enriched by lupine is not available to colonists while lupines are alive. The dense canopy of lupine shades soil under shrubs, reducing average photon-flux density in late spring from 1725 mu mol . m(-2) . s(-1) (full sunlight) to 13 mu mol . m(-2) . s(-1) (underneath shrubs). Stand die-off due to insect herbivory exposed this bare, enriched soil. In January, when annual plants are establishing, average photon-flux density under dead lupines killed by insect herbivores was 370 mu mol m(-2) . s(-1), compared to the photon-flux density under live lupines of the same age, which averaged 83 mu mol . m(-2) . s(-1). The availability of bare, N-rich patches of soil enabled nonnative annuals (primarily Lolium multiflorum and Bromus diandrus) to colonize sites, grow rapidly, and dominate the plant assemblage until lupines reestablished after several years. The N content of these grasses was significantly greater than the N content of the mostly native plants that occupied adjacent coastal prairie devoid of bush lupine. Between 57 and 70% of the net amount of N mineralized annually was taken up by introduced grasses and subsequently returned to the soil upon the death of these annuals. Even in the absence of further N inputs, we estimate that it would take at least 25 yr to reduce the soil N pool by 50%, indicating that the reestablishment of the native prairie flora is likely to be long term. Web of Science Many United States California University of California Bodega Marine Reserve 39.436193 -123.134766 Field - Observational terrestrial Grassland Invasion Hyp. Other primary 2166 Reusch, TBH; Williams, SL 1999 Macrophyte canopy structure and the success of an invasive marine bivalve journal OIKOS 84 3 398 416 In both terrestrial and aquatic environments introductions of non-indigenous species are continuing and represent one important component of global change. Negative biotic interactions by resident species may prevent successful invaders from becoming pests. Few experimental data are available on the presence and significance of such biotic resistance other than predation or competition. This study addresses the role of habitat structure provided by a native eelgrass (Zostera marina) canopy on growth and survival of the non-indigenous mussel Musculista senhousia, a habitat-modifying gregarious suspension feeder with strong effects on native infauna and eelgrass. In 2 southern California bays, a series of transplantation experiments using tagged mussels revealed that inside an eelgrass canopy, Musculista growth rates were reduced by more than half in 3 of 4 experiments compared to adjacent unvegetated areas. Musculista survival also decreased inside the vegetation in a 4-mo experiment. As one element of habitat structure, we tested the effects of eelgrass parch size, using natural (1 site) and planted (1 site) eelgrass patches of defined sizes. Growth rates of Musculista were highest outside the veneration and decreased as eelgrass patch size increased. As a potential mechanism for the canopy effects, we suggest that Musculista receives less food inside the vegetation. In the experimental plots, the presence and spatial extent of the macrophyte canopy strongly affected near bottom (10 cm) horizontal water flow assessed with a direct dye tracking method. Reduced mussel growth rates were linearly associated with lower water flow, and presumably, food flux. Over a period of 7 mo, food resources (particulate chlorophyll a) were consistently lower 1 and 5 cm above the sea floor inside eelgrass patches compared to the sand Aat. The reduction in food availability matched the growth reduction of Musculista. Also, mussel condition (dry flesh mass/shell mass) was worse in individuals growing in eelgrass than in the sand Aat. Previous experiments revealed that dense beds of Musculista impede the rhizome growth and vegetative propagation of eelgrass, yet mussels attain abundances sufficient for interference only if eelgrass beds are patchy. Thus, anthropogenic disturbances on eelgrass beds, which often result in meadow fragmentation, and the proliferation of Musculista may have synergistic negative effects on the persistence of eelgrass beds. Web of Science Musculista senhousia United States California Field - Experimental estuarine Intertidal/Near Shore Invasion Hyp. Empty Niche filter 2170 Stohlgren, TJ; Schell, LD; Vanden Heuvel, B 1999 How grazing and soil quality affect native and exotic plant diversity in rocky mountain grasslands journal ECOLOGICAL APPLICATIONS 9 1 45 64 We used multiscale plots to sample vascular plant diversity and soil characteristics in and adjacent to 26 long-term grazing exclosure sites in Colorado, Wyoming, Montana, and South Dakota, USA. The exclosures were 7-60 yr old (31.2 +/- 2.5 yr, mean +/- 1 SE). Plots were also randomly placed in the broader landscape in open rangeland in the same vegetation type at each site to assess spatial variation in grazed landscapes. Consistent sampling in the nine National Parks, Wildlife Refuges, and other management units yielded data from 78 1000-m(2) plots and 780 1-m(2) subplots. We hypothesized that native species richness would be lower in the exclosures than in grazed sites, due to competitive exclusion in the absence of grazing. We also hypothesized that grazed sites would have higher native and exotic species richness compared to ungrazed areas, due to disturbance (i.e., the intermediate-disturbance hypothesis) and the conventional wisdom that grazing may accelerate weed invasion. Both hypotheses were soundly rejected. Although native species richness in l-mz subplots was significantly higher (P < 0.05) in grazed sites, we found nearly identical native or exotic species richness in 1000-m(2) plots in exclosures (31.5 +/- 2.5 native and 3.1 +/- 0.5 exotic species), adjacent grazed plots (32.6 +/- 2.8 native and 3.2 +/- 0.6 exotic species), and randomly selected grazed plots (31.6 +/- 2.9 native and 3.2 +/- 0.6 exotic species). We found no significant differences in species diversity (Hill's diversity indices, N1 and N2), evenness (Hill's ratio of evenness, E5), cover of various life-forms (grasses, forbs, and shrubs), soil texture, or soil percentage of N and C between grazed and ungrazed sites at the 1000-m(2) plot scale. The species lists of the long-ungrazed and adjacent grazed plots overlapped just 57.9 +/- 2.8%. This difference in species composition is commonly attributed solely to the difference in grazing regimes. However, the species lists between pairs of grazed plots (adjacent and distant 1000-m(2) plots) in the same vegetation type overlapped just 48.6 +/- 3.6%, and the ungrazed plots and distant grazed plots overlapped 49.4 +/- 3.6%. Differences in vegetation and soils between grazed and ungrazed sites were minimal in most cases, but soil characteristics and elevation were strongly correlated with native and exotic plant diversity in the study region. For the 78 1000-m(2) plots, 59.4% of the variance in total species richness was explained by percentage of silt (coefficient = 0.647, t = 5.107, P < 0.001), elevation (coefficient = 0.012, t = 5.084, P < 0.001), and total foliar cover (coefficient = 0.110, t = 2.104, P < 0.039). Only 12.8% of the variance in exotic species cover (log(10)cover) was explained by percentage of clay (coefficient = -0.011, t = -2.878, P < 0.005), native species richness (coefficient = -0.011, t = -2.156, P < 0.034), and log(10)N (coefficient = 2.827, t = 1.860, P < 0.067). Native species cover and exotic species richness and frequency were also significantly positively correlated with percentage of soil N at the 1000-m(2) plot scale. Our research led to five broad generalizations about current levels of grazing in these Rocky Mountain grasslands: (1) grazing probably has little effect on native species richness at landscape scales; (2) grazing probably has little effect on the accelerated spread of most exotic plant species at landscape scales; (3) grazing affects local plant species and life-form composition and cover, but spatial variation is considerable; (4) soil characteristics, climate, and disturbances may have a greater effect on plant species diversity than do current levels of grazing; and (5) few plant species show consistent, directional responses to grazing or cessation of grazing. Web of Science Many United States Colorado; Wyoming; Montana; South Dakota Field - Experimental terrestrial Grassland Invasion Hyp. Disturbance primary 2175 Glenn, E; Tanner, R; Mendez, S; Kehret, T; Moore, D; Garcia, J; Valdes, C 1998 Growth rates, salt tolerance and water use characteristics of native and invasive riparian plants from the delta of the Colorado River, Mexico journal JOURNAL OF ARID ENVIRONMENTS 40 3 281 294 Six riparian plant species representing native and invasive species from the Colorado River delta in the Sonoran Desert of Mexico were tested for salt tolerance and water use characteristics in a greenhouse study in Tucson, Arizona. Negative linear regression equations relating relative growth rates (RGR, g g(-1) day(-1)) of each species to mean root zone salinity had high coefficients of determination (r(2) = 0.73-0.86, P < 0.001). Salt tolerance levels, expressed as % reduction in RGR per g l(-1) NaCl in soil solution, varied widely among species: Allenrolfea occidentalis, 0% reduction; Tamarix ramosissima, 1.8% reduction; Pluchea sericea, 3.5% reduction; and Baccharis salicifolia, Salix gooddingii and Populus fremontii, 7-9% reduction (p < 0.05). Transpiration was proportional to RGR for all species. Contrary to some previous reports, Tamarix did not have unusually high water use compared to the other species. Differences in salt tolerance among species determined in this study support field observations that soil salinity, which can reach high values along channelized and flow-regulated stretches of south-western United States rivers due to lack of overbank flooding, is a major factor in the replacement of native riparian species by invasive species. (C) 1998 Academic Press. Web of Science Tamarix ramosissima Mexico Ejido Oviedo Mota 32.2 -115.1 Greenhouse terrestrial Riparian Invasion Hyp. Inherent Superiority Broad Tolerances primary 2177 Meyer, JY 1998 Observations on the reproductive biology of Miconia calvescens DC (Melastomataceae), an alien invasive tree on the island of tahiti (South Pacific Ocean) journal BIOTROPICA 30 4 609 624 Miconia calvescens DC (Melastomataceae) is a dominant invasive species in the tropical oceanic island of Tahiti (French Polynesia, South Pacific Ocean), where it was introduced as an ornamental plant. Whereas this small tree is sparse in its native range of Central America, it has spread in Tahiti into a wide variety of habitats including native wet forests. The remarkable success of this invasion is due in great part to prolife reproduction: a mature tree can bear up to 220 inflorescences with an average of 1330 flowers/inflorescence, 208 fruits/infructescence and 195 seeds/fruit. Two and a half years of phenological observations in a highly invaded site indicated that three major peaks of flowering occur/year over brief periods: flower anthesis lasted a few days and pollen grain germination suggested a short stigmatic receptivity of only a few hours; no pollinators were observed foraging on flowers during our survey; the production of fruits containing viable seeds in bagged inflorescences showed that self-fertilization can occur; pollen-ovule ratio (log P/O = 2.68) suggested facultative xenogamy; bagged isolated flowers to test for autogamy and style cutting to learn whether apomixis occured or not were not conclusive. The flowering phenology and the breeding system of M. calvescens enable this plant to build up rapidly successful populations from even a single propagule on the island of Tahiti and on other sires of introduction The vegetation structure of Polynesian native forests compared to Neotropical rain forests probably plays an important role in determining the reproductive success of M, calvescens and could provide a complementary explanation of the biological invasion processes in tropical oceanic islands. Web of Science Miconia calvescens DC (Melastomataceae) French Polynesia Tahiti Belvedere -17.33 -149.25 Field - Observational terrestrial Invasion Hyp. Inherent Superiority;Propagule Pressure High Reprod. Output primary 2179 Paynter, Q; Fowler, SV; Memmott, J; Sheppard, AW 1998 Factors affecting the establishment of Cytisus scoparius in southern France: implications for managing both native and exotic populations journal JOURNAL OF APPLIED ECOLOGY 35 4 582 595 1. The ecology of the woody shrub Cytisus scoparius was studied for 4 years in its native range in southern France to investigate how it call become an invasive weed. 2. The proportion of the seed bank that germinated each year was highest in disturbed plots and was correlated with the March rainfall. The seed bank declined at a rate of c. 50% per year when fresh seed rain was excluded, 3. The fate of 2863 seedlings was followed for a variety of treatments. 4. Seedling survival depended on disturbance: none survived their first summer in undisturbed plots; more than 40% survived their first summer and c. 14% survived to flowering age in plots that were initially cultivated. 5. Seedlings flowered first in their fourth year, although only c, 10% set seed. 6. Neither inter- nor intraspecific competition was found to affect significantly seedling survival on cultivated plots. However, some seedlings grown in the absence of interspecific competitors flowered and set seed in their third year. 7. Applications of insecticide, molluscicide or fungicide did not affect significantly seedling survival, growth or minimum age of reproduction on cultivated plots. 8. It is concluded that management strategies should minimize disturbance to competing vegetation, which can inhibit germination and smother emerging seedlings. In many circumstances strategies that target the seed bank, such as burning, are not expected to work. 9. Herbivores and pathogens may prevent stand re-establishment indirectly, by reducing the size, vigour and density of broom plants so that competing vegetation can persist and smother emergent seedlings following the death of the parent stand. Web of Science Cytisus scoparius France Mandagout 44.01 3.38 Field - Experimental terrestrial Invasion Hyp. Disturbance primary 2181 Dunn, AM; Dick, JTA 1998 Parasitism and epibiosis in native and non-native gammarids in freshwater in Ireland journal ECOGRAPHY 21 6 593 598 The introduced amphipod crustaceans Gammarus pulex and G. tigrinus are displacing the native G. duebeni celticus in a number of freshwater sites in Northern Ireland. We investigated parasite and epibiont infection in populations in the River Lagan and Lough Neagh where both native and invading species occur. Prevalence of the four parasites and epibionts observed was higher in the native G. d, celticus than in the invading amphipods at both field sites. In Lough Neagh, G. d. celticus individuals suffered higher burdens of the rotifer Embata parasitica and the protozoan Epistylis in comparison with the invading species. These patterns may reflect host specificity by the parasites or may result from different susceptibilities of the native and invading host species. We consider the influence of parasitism on host invasions and resulting species distributions. Web of Science Gammarus pulex; G. tigrinus Ireland The River Lagan 54.081297 -6.779594 Field - Observational lotic Invasion Hyp. Other herbivore 2186 Rose, AB; Basher, LR; Wiser, SK; Platt, KH; Lynn, IH 1998 Factors predisposing short-tussock grasslands to Hieracium invasion in Marlborough, New Zealand journal NEW ZEALAND JOURNAL OF ECOLOGY 22 2 121 140 The effects of environment and management on the composition of short-tussock grasslands and the abundance of the invasive weed Hieracium pilosella were investigated in two small catchments. Species composition and site factors were recorded on a total of 182 plots and the management history of each catchment was reviewed. H. pilosella was present on >80% of all plots, but was at an early stage of invasion in one catchment (<5% cover) and dominant in the other (25% cover). Classification and ordination revealed strong between-catchment differences in community composition that reflected differences in environment (soil fertility and rainfall), disturbance history (animal populations and burning), and the stage of invasion by H. pilosella. In both catchments H. pilosella tended to be least abundant on the wettest, driest, and most fertile soils. However, such relationships were weak. Generalised additive models and regression showed that in the earlier stage of invasion individual site factors explained less than 20% of the variation in H. pilosella cover. Topographic position and slope (both indicative of soil moisture) were the most significant combined predictors, but together explained only 32% of the variation. In the later stage of invasion individual factors explained up to 33% of the variation. Topsoil sulphur, slope, and topsoil calcium were the most significant combined predictors, but together explained only 53% of the variation. Between-catchment comparisons highlighted the inter-related roles of environment, disturbance history, geographic location, availability of H. pilosella propagules, and stage of invasion in more fully explaining the abundance of H. pilosella. Of five models that have been proposed for Hieracium invasion, the: *grassland decline* model best incorporated the inter-related factors that influence spatial and temporal variation in H. pilosella abundance in the study area. This model concentrates on identifying predisposing and trigger factors that increase the likelihood of invasion and accounts for multiple causes and interactions by specifying five key factors that influence the ability of a plant species to invade existing vegetation: environment, disturbance, vegetation structure and composition, life history attributes of the invader, and the availability of invading propagules. The model potentially provides a comprehensive framework for evaluating the causes of Hieracium invasion, targeting research effort, and developing sustainable management strategies. Web of Science Hieracium pilosella New Zealand Andy’s Gully; Limestone Stream -42.02 173.26 Field - Observational;Statistical/Meta-analysis terrestrial Grassland Invasion Hyp. Inherent Superiority;Disturbance;Other Broad Tolerances primary 2191 Anttila, CK; Daehler, CC; Rank, NE; Strong, DR 1998 Greater male fitness of a rare invader (Spartina alterniflora, Poaceae) threatens a common native (Spartina foliosa) with hybridization journal AMERICAN JOURNAL OF BOTANY 85 11 1597 1601 Hybridization with abundant invaders is a well-known threat to rare native species. Our study addresses mechanisms of hybridization between a rare invader, smooth cordgrass (Spartina alterniflora) and the common native California cordgrass (S. foliosa) in the salt marshes of San Francisco Bay. These species are wind-pollinated and flower in summer. The invader produced 21-fold the viable pollen of the native, and 28% of invader pollen germinated on native stigmas (1.5-fold the rate of the native's own pollen). Invader pollen increased the seed set of native plants almost eightfold over that produced with native pollen, while native pollen failed to increase seed set of the invader. This pollen swamping and superior airing ability by the invader could lead to serial genetic assimilation of a very large native population. Unlike California cordgrass, smooth cordgrass can grow into low intertidal habitats and cover open mud necessary to foraging shorebirds, marine life, navigation, and flood control in channels. To the extent that intertidal range of the hybrids is more similar to the invader than to the native parent, introgression will lead to habitat ross for shore birds and marine life as well to genetic pollution of native California cordgrass. Web of Science Spartina alterniflora USA California San Francisco Bay Field - Observational estuarine Invasion Hyp. Hybridization primary 2193 Stapanian, MA; Sundberg, SD; Baumgardner, GA; Liston, A 1998 Alien plant species composition and associations with anthropogenic disturbance in North American forests journal PLANT ECOLOGY 139 1 49 62 A probability-based sampling scheme was used to survey plant species composition in forests of 16 states in seven geopolitical regions of the United States (California, Colorado, Minnesota, and parts of the Pacific Northwest, Southeast, Mid-Atlantic, and Northeast) in 1994. The proportion of alien species relative to the total species number and to canopy cover in the ground stratum (0-0.6 m height) was evaluated in 279 plots. Visually evident anthropogenic disturbances (e.g., artificial regeneration, logging, prescribed burning, and grazing by livestock), if any, were recorded on each plot. In each of the seven regions we quantified (1) the percentage of the number of species and total cover comprised of alien species, (2) the difference in these percentages for disturbed and undisturbed plots, and (3) the origin or native range for the alien species. The percentage of alien species ranged from approximately 4.5% (Colorado) to approximately 13.2% (California). The percentage of alien species cover ranged from approximately 1.5% in Colorado to 25% in California. In five regions, species introduced from temperate Eurasia comprised the largest proportion of alien species and cover. In the Southeast, species introduced from far eastern and subtropical Asia dominated the alien flora. In the Mid-Atlantic, the majority of alien species was Eurasian and the majority of alien species cover consisted of far eastern and subtropical Asian species. The proportion of plots in which at least one alien species was recorded was significantly higher in disturbed than undisturbed plots in the Southeast and marginally significantly higher (p = 0.053) in the Northeast. These results are consistent with other published studies that indicate that anthropogenic disturbance affects the structure and composition of both the ground stratum and upper canopy of forest habitats. In other regions, however, no significant differences were found. Web of Science Many United States California; Colorado; Minnesota; Maine; NH; VT; MA; CT; DE; MD; NJ; VA; AL; GA; OR; WA Field - Observational terrestrial Invasion Hyp. Disturbance primary 2196 Appleby, MWA 1998 The incidence of exotic species following clearfelling of Eucalyptus regnans forest in the Central Highlands, Victoria journal AUSTRALIAN JOURNAL OF ECOLOGY 23 5 457 465 Invasion by exotic species following clearfelling of Eucalyptus regnans F. Muell. (Mountain Ash) forest was examined in the Toolangi State Forest in the Central Highlands of Victoria. Coupes ranging in age from < 1- to 10-years-old and the spar-stage forests (1939 bushfire regrowth) adjacent to each of these coupes and a mature, 250-year-old forest were surveyed. The dispersal and establishment of weeds was facilitated by clearfelling. An influx of seeds of exotic species was detected in recently felled coupes but not in the adjacent, unlogged forests. Vehicles and frequently disturbed areas, such as roadside verges, are likely sources of the seeds of exotic species. The soil seed bank of younger coupes had a greater number and percentage of seeds of exotics than the 10-year-old coupes and the spar-stage and mature forests. Exotic species were a minor component (< 1% vegetation cover) in the more recently logged coupes and were not present in 10-year-old coupes and the spar-stage and mature forests. These particular exotic species did nor persist in the dense regeneration nor exist in the older forests because the weeds were ruderal species (light-demanding, short-lived and short-statured plants). The degree of influence that these particular exotic species have on the regeneration and survival of native species in E. regnans forests is almost negligible. However, the current management practices may need to be addressed to prevent a more threatening exotic species from establishing in these coupes and forests. Web of Science Many Australia Victoria Toolangi State Forest -37.555737 145.466881 Field - Observational terrestrial Invasion Hyp. Disturbance primary 2199 Stohlgren, TJ; Bull, KA; Otsuki, Y; Villa, CA; Lee, M 1998 Riparian zones as havens for exotic plant species in the central grasslands journal PLANT ECOLOGY 138 1 113 125 In the Central Grasslands of the United States, we hypothesized that riparian zones high in soil fertility would contain more exotic plant species than upland areas of low soil fertility. Our alternate hypothesis was that riparian zones high in native plant species richness and cover would monopolize available resources and resist invasion by exotic species. We gathered nested-scale vegetation data from 40 1 m(2)subplots (nested in four 1000 m(2) plots) in both riparian and upland sites at four study areas in Colorado, Wyoming, and South Dakota (a total of 320 1 m(2)subplots and 32 1000 m(2) plots). At the 1 m(2) scale, mean foliar cover of native species was significantly greater (P < 0.001) in riparian zones (36.3% +/- 1.7%) compared to upland sites (28.7% +/- 1.5%), but at this small scale there were no consistent patterns of native and exotic species richness among the four management areas. Mean exotic species cover was slightly higher in upland sites compared to riparian sites (9.0% +/- 3.8% versus 8.2% +/- 3.0% cover). However, mean exotic species richness and cover were greater in the riparian zones than upland sites in three of four management areas. At the 1000 m(2) scale, mean exotic species richness was also significantly greater (P < 0.05) in riparian zones (7.8 +/- 1.0 species) compared to upland sites (4.8 +/- 1.0 species) despite the heavy invasion of one upland site. For all 32 plots combined, 21% of the variance in exotic species richness was explained by positive relationships with soil % silt (t = 1.7, P = 0.09) and total foliar cover (t = 2.4, P = 0.02). Likewise, 26% of the variance in exotic species cover (log(10) cover) was explained by positive relationships with soil % silt (t = 2.3, P = 0.03) and total plant species richness (t = 2.5, P = 0.02). At landscape scales (four 1000 m(2) plots per type combined), total foliar cover was significantly and positively correlated with exotic species richness (r = 0.73, P < 0.05) and cover (r = 0.74, P < 0.05). Exotic species cover (log(10) cover) was positively correlated with log(10)% N in the soil (r = 0.61, P = 0.11) at landscape scales. On average, we found that 85% (+/-5%) of the total number of exotic species in the sampling plots of a given management area could be found in riparian zones, while only 50% (+/-8%) were found in upland plots. We conclude that: (1) species-rich and productive riparian zones are particularly invasible in grassland ecosystems; and (2) riparian zones may act as havens, corridors, and sources of exotic plant invasions for upland sites and pose a significant challenge to land managers and conservation biologists. Web of Science Many United States Colorado; South Dakota; Wyoming 40.777422;43.578401; 43.731414; 45.131196 -104.547272;-103.474731;-101.982651;-108.172073 Field - Observational terrestrial Grassland;Riparian Invasion Hyp. Empty Niche;Community Species Richness primary 2201 Ohgushi, T; Sawada, H 1998 What changed the demography of an introduced population of an herbivorous lady beetle? journal JOURNAL OF ANIMAL ECOLOGY 67 5 679 688 1. The population dynamics of an introduced population of Epilachna niponica (Lewis) (Coleoptera: Coccinellidae) was investigated for a 7-year period following its introduction to a site outside of its natural range. A population from Asiu Experimental Forest was introduced to Kyoto University Botanical Garden, 10 km south of its natural distribution. 2. Arthropod predation was much lower in the introduced than in the source population. As a result of the lower predation in the Botanical Garden, larvae reached densities five times higher than in the Asiu Forest and host plants were frequently defoliated. Food shortage caused larval deaths from starvation and increased dispersal. 3. The density of the introduced population was much more variable than that of the source population. The variation in population density in both the introduced and source populations is limited by density-dependent reduction in fecundity and female survival. However, variation in the introduced population's density was increased due to host plant defoliation that resulted in overcompensating density-dependent mortality. In years with high larval density plants were defoliated and this increased adult mortality during the prehibernation period. Besides, the density-dependent regulatory mechanisms that produce population stability were weaker in the introduced population than in the source population. Web of Science Epilachna niponica (Lewis) (Coleoptera: Coccinellidae) Japan Kyoto Botanical Garden of Kyoto University 35.027747 135.780716 Field - Observational terrestrial Invasion Hyp. Enemy Release herbivore 2203 Crossland, MR 1998 Ontogenetic variation in toxicity of tadpoles of the introduced toad Bufo marinus to native Australian aquatic invertebrate predators journal HERPETOLOGICA 54 3 364 369 This study investigated. ontogenetic variation in toxicity of tadpoles of the introduced tod Bufo marinus to three species of native Australian aquatic invertebrate predators. Crayfish (Cherax quadricarinatus) and dytiscid beetles (Hydaticus vittatus) consumed. early mid, and late developmental stages of larval Bufo without apparent ill effect. Belostomatids (Lethocerus insulanus) also preyed upon early developmental stages of Bufo without apparent ill effect, but they experienced significant mortality after preying upon mid and late developmental stages of these tadpoles. There was intraspecific variation in the toxic effects of mid and late developmental stages of tadpoles on L. insulanus: consumption of these stages was fatal to some individuals but not to others. The observed inter- and intraspecific variation in tonicity was not related to the number of tadpoles consumed. Such variability may reflect variation in toxicity among individual tadpoles, or variation in susceptibility to toxins of Bufo within and among predatory species. The results demonstrate that the toxicity of larval B, marinus increases ontogenetically However, not all native aquatic invertebrate predators are adversely affected by this increase in toxicity. Web of Science Bufo marinus Australia Lab lentic Wetland Invasion Hyp. Novel Weapons omnivore 2204 Chown, SL; Gremmen, NJM; Gaston, KJ 1998 Ecological biogeography of southern ocean islands: Species-area relationships, human impacts, and conservation journal AMERICAN NATURALIST 152 4 562 575 Previous studies have concluded that southern ocean islands are anomalous because past glacial extent and current temperature apparently explain most variance in their species richness. Here, the relationships between physical variables and species richness of vascular plants, insects, land and seabirds, and mammals were reexamined for these islands. Indigenous and introduced species were distinguished, and relationships between the latter and human occupancy variables were investigated Most variance in indigenous species richness was explained by combinations of area and temperature (56%)-vascular plants; distance (nearest continent) and vascular plant species richness (75%)-insects; area and chlorophyll concentration (65%)-seabirds; and indigenous insect species richness and age (73%)-land birds. Indigenous insects and plants, along with distance (closest continent), explained most variance (70%) in introduced land bird species richness. A combination of area and temperature explained most variance in species richness of introduced vascular plants (73%), insects (69%), and mammals (69%). However, there was a strong relationship between area and number of human occupants. This suggested that larger islands attract more human occupants, increasing the risk of propagule transfer, while temperature increases the chance of propagule establishment. Consequently, human activities on these islands should be regulated more tightly. Web of Science Many Southern Ocean Islands Statistical/Meta-analysis Invasion Hyp. Inherent Superiority;Other Broad Tolerances 2209 Kotanen, PM; Bergelson, J; Hazlett, DL 1998 Habitats of native and exotic plants in Colorado shortgrass steppe: a comparative approach journal CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE 76 4 664 672 Invading species often are close relatives, and therefore share many characteristics' as a consequence of their common ancestry. This tends to confound studies of invasions, since many irrelevant characteristics are likely to be correlated with a species' geographic origin (alien or native). We address this problem by using phylogenetically independent comparisons to investigate the habitat characteristics of plants of the Central Plains Experimental Range (Colorado, U.S.A.). We initially show that exotic species are more likely than natives to occur in riparian zones, roadsides, and disturbed sites, and less likely to occur in grassland. The relationship between exotic origins and disturbed sites disappears when phylogenetic dependence is removed from the analyses; in contrast, the other associations persist following phylogenetic detrending, indicating that aliens and their native relatives consistently differ in their ability to exploit riparian, roadside, and grassland habitats. Our results indicate that disturbed sites currently are dominated by only a few groups of related exotic ruderals, while the ability to exploit roadsides and riparian zones has been and may continue to be important for the success of many taxa of invaders. Web of Science Many United States Colorado Central Plains Experimental Range 40.49 107.47 Statistical/Meta-analysis terrestrial Grassland Invasion Hyp. Climate Change;Other primary 2217 Schneider, DW; Ellis, CD; Cummings, KS 1998 A transportation model assessment of the risk to native mussel communities from zebra mussel spread journal CONSERVATION BIOLOGY 12 4 788 800 When introduced species threaten native flora and fauna, protection requires an analysis of the risk that native species face from the spread of the introduced species. Models of invading species, however, often do not include a dynamic component of risk. North American freshwater mussels are at risk, of fouling by the introduced zebra mussel (Dreissena polymorpha). Predictions of the risk to native mussel communities of invasion by the zebra mussel can help prioritize conservation efforts. We present a model for the spatial analysis of zebra mussel spread that allows the characterization of relative risk of infestation to the high-quality mussel communities of Illinois streams. A gravity model, constrained at origin and destination, was parameterized with data on boat use at 120 boat landings in Illinois. The risk of spread of zebra mussels depends on the number of boat trips from infested waters, which in turn depends on distance from an infested water, boat use at a site, and the position of a lake within a river system. Habitats supporting a high diversity of native mussels and threatened and endangered species are at risk of infestation from reservoirs upstream. Invasion of inland lakes and reservoirs in Illinois is predicted to occur first at areas of high boat use close to currently, infested waters, including the Fox Chain of Lakes, followed by central Illinois reservoirs. These reservoirs will act as stepping stones, facilitating the invasion of lakes upstream of critical native mussel habitats. Efforts to protect waters that center on prevention of the initial invasion of stepping-stone lakes could significantly reduce the risk of infestation. Education and inspection efforts are predicted to be more effective than quarantine because quarantines would displace boat traffic to critical habitats. The class of models presented here is useful for predicting risk of invasion when complete data on vector movement are not available. Web of Science zebra mussel (Dreissena polymorpha) United States Illinois Theoretical/Modeling lentic Invasion Hyp. Inherent Superiority Effective Disperser filter 2218 Daehler, CC 1998 Variation in self-fertility and the reproductive advantage of self-fertility for an invading plant (Spartina alterniflora) journal EVOLUTIONARY ECOLOGY 12 5 553 568 The factors responsible for the reproductive success or failure of individuals in small, founding populations have received little attention. Previous work on a small population of smooth cordgrass (Spartina alterniflora) invading San Francisco Bay, California found that most clones flower prolifically but set little or no seed, while a few clones have high rates of viable seed sell producing most of the seeds in the population. This study first identifies recruitment from seeds as the main source of new smooth cordgrass plants during invasion and then tests the influence of growing conditions and pollination treatment on viable seed set among clones established in San Francisco Bay. Field transplants indicated that a clone's seed set rate was not strongly dependent on its site of establishment. Low and high nutrient greenhouse treatments also had little effect on viable seed set rates within most clones. In contrast, pollination treatment (self-pollination or outcrossing) had a major effect on viable seed set rates. Most clones had high seed set rates after outcross-pollination, but clones varied widely in their selfing capacity. Zero or low viable self-seed set rates were most common; however, a few clones had high viable self-seed set rates, comparable to outcross seed set rates. A clone's selfing capacity was significantly correlated across years (r = 0.89, P < 0.001), and capacity to set viable self-pollinated seeds in the greenhouse was significantly correlated with the clone's rate of viable seed set in the field (r(s) = 0.74, P < 0.005). In this growing population where cross-pollination is limited, only the clones with high selfing ability had high viable seed set rates in the field. Among primarily outcrossing plant invaders, variation in self-fertility among individuals may be a common phenomenon, with important implications for genetic differentiation, effective population size and patterns of spatial spread during an invasion. Web of Science smooth cordgrass (Spartina alterniflora) United States California San Francisco Bay 37.780484 -122.419968 Field - Experimental;Field - Observational;Greenhouse terrestrial Wetland Invasion Hyp. Inherent Superiority;Propagule Pressure;Other Self Compatible primary 2228 Holmquist, JG; Schmidt-Gengenbach, JM; Yoshioka, BB 1998 High dams and marine-freshwater linkages: Effects on native and introduced fauna in the Caribbean journal CONSERVATION BIOLOGY 12 3 621 630 Caribbean steams are dominated by a shrimp and a fish assemblage for which amphidromy (eggs or larvae carried to the ocean followed by migration of juveniles upriver) is suspected. Effects of of dams on this assemblage are likely to demonstrate complex interactions as a function of reproductive strategy and type of dam structure. Our goals were to determine (1) whether high dams reduce or eliminate steam corridor permeability with respect to migration, (2) the extent to which permeability is a function of spillway discharge, (3) the relative roles of native fauna and disturbance suppression (in this case, river regulation) as predictors of success by exotic fishes, and (4) the uniformity and extent of obligate amphidromy in this assemblage. We sampled adults and juveniles of shrimps and fishes in Puerto Rican streams via electrofishing and sampled shrimp larvae with drift nets. Replicate stream reaches were assigned to the following five categories: undammed, above or below dams, and with or without water released over spillways. Dams without such discharge were impermeable barriers that eliminated all native fish and shrimp fauna from upstream reaches. Though more permeable, dams with spillway discharge has smaller populations of native species above these structures than below the dams or on undammed streams. Our data on adult and larval distributions, combined with the absence of first-stage shrimp larvae, indicate that amphidromy is obligate for most of the native fauna. Disturbance regime appeared to be a poor predictor of successful invasion by exotics in this system, whereas exotic abundance was consistently inversely related to abundance and species richness of native fauna across all sampling categories. The prevalent amphidromy in these streams provides a tight marine-upland linkage that is disrupted by dams in several ways. We recommend adding shrimp and fishways to dams on these tropical streams. Web of Science Many Puerto Rico 18.229351 -66.950684 Field - Observational lotic Invasion Hyp. Community Species Richness;Disturbance herbivore;omnivore;predator;decomposer 2230 Morgan, JW 1998 Patterns of invasion of an urban remnant of a species-rich grassland in southeastern Australia by non-native plant species journal JOURNAL OF VEGETATION SCIENCE 9 2 181 190 The invasion by non-native plant species of an urban remnant of a species-rich Themeda triandra grassland in southeastern Australia was quantified and related to abiotic influences. Richness and cover of non-native species were highest at the edges of the remnant and declined to relatively uniform levels within the remnant. Native species richness and cover were lowest at the edge adjoining a roadside but then showed little relation to distance from edge. Roadside edge quadrats were floristically distinct from most other quadrats when ordinated by Detrended Correspondence Analysis. Soil phosphorus was significantly higher at the roadside edge but did not vary within the remnant itself. All other abiotic factors measured (NH4, NO3, S, pH and % organic carbon) showed little variation across the remnant. Non-native species richness and cover were strongly correlated with soil phosphorus levels. Native species were negatively correlated with soil phosphorus levels. Canonical Correspondence Analysis identified the perennial non-native grasses of high biomass as species most dependent on high soil nutrient levels. Such species may be resource-limited in undisturbed soils. Three classes of non-native plants have invaded this species-rich grassland. (1) generalist species (greater than or equal to 50 % frequency), mostly therophytes with non-specialized habitat or germination requirements; (2) resource-limited species comprising perennial species of high biomass that are dependent on nutrient increases and/or soil disturbances before they can invade the community and; (3) species of intermediate frequency (1-30 %), of low to high biomass potential, that appear to have non-specialized habitat requirements but are currently limited by seed dispersal, seedling establishment or the current site management. Native species richness and cover are most negatively affected by increases in non-native cover. Declines are largely evident once the non-native cover exceeds 40 %. Widespread, generalist non-native species are numerous in intact sites and will have to be considered a permanent part of the flora of remnant grasslands. Management must aim to minimize increases in cover of any non-native species or the disturbances that favour the establishment of competitive nonnative grasses if the native grassland flora is to be conserved in small, fragmented remnants. Web of Science Many Australia Victoria -37.35 144.44 Field - Observational terrestrial Grassland Impacts;Invasion Hyp. Empty Niche;Disturbance;Other primary 2231 Stover, ME; Marks, PL 1998 Successional vegetation on abandoned cultivated and pastured land in Tompkins County, New York journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 125 2 150 164 To investigate influences of land use on old field successional vegetation, we sampled twenty-one old fields with agricultural histories of either cultivation or pasturing in Tompkins County, New York. A TWINSPAN classification showed a major division corresponding to field history, with apple-dominated old pastures clustered together. Analyses of ground-layer vegetation did not show the same division. Common and important woody plants included Acer rubrum, Cornus racemosa, Crataegus spp., Fraxinus americana, Malus spp., Pinus strobus, Prunus serotina, Rhamnus cathartica, and Viburnum dentatum. Formerly pastured old fields more frequently contained apple, pear, buckthorn, and hawthorn, which were sometimes the dominant trees. These taxa were infrequent and never dominant in formerly cultivated old fields, which more commonly contained red maple and white pine. Exotic plants were a major pare of the successional vegetation, comprising over one quarter of the woody and one third of the herbaceous taxa identified. Most of the exotic woody taxa were early successional species, however. A number of herbaceous forest understory species appeared in formerly cultivated old fields. One formerly pastured site that had never been plowed contained 13 such taxa, which apparently persisted through fifty years of pasturing. Web of Science Many U.S.A. New York Tompkins County 42.442073 -76.554909 Field - Observational terrestrial Deciduous Forest;Old Field Invasion Hyp. Disturbance primary 2232 Ernst, WHO 1998 Invasion, dispersal and ecology of the South African neophyte Senecio inaequidens in The Netherlands: from wool alien to railway and road alien journal ACTA BOTANICA NEERLANDICA 47 1 131 151 Senecio inaequidens, a perennial pioneer plant, invaded The Netherlands at Tilburg with sheep's wool from South Africa in 1939, where it failed to establish a permanent population. In 1942 a new invasion from an expanding invader population at Liege occurred at Eijsden, establishing a new dispersal centre in southern Limburg, The Netherlands. In the 1980s a further dispersal throughout The Netherlands resulted in additional dispersal centres at the railway stations at Amsterdam and Hengelo.,The dispersal along new railway lines in the Amsterdam region confirmed the importance of trains for occasional long-distance dispersal events because in general the majority of the anemochorous achenes remained in the vicinity of the parent plants. Expansion dynamics and ecology was studied in a new established population at the railway station in Hoofddorp. The species has a high self-fertility. Adaptation to the Atlantic climate of The Netherlands was accompanied by the selection for flowering earliness from August to May and prolongation of the flowering period to end of December. Achene mass mostly declined from high values in July to 70%:lower ones in :December. Low dormancy of early summer achenes allowed establishment of a new generation in the same year; late autumn achenes had a high dormancy and germinated in next spring. Dormant achenes persisted for two winter periods and survived frost at -15 degrees C. Caterpillars of Tyria jacobaeae were recorded as leaf herbivores on S. inaequidens, but had nearly no impact on a plant's performance. The extinction or survival of the various founder populations as wool aliens in Europe is discussed in relation to founder effects, adaptation to winter temperature in western Europe, prolongation of the flowering period and the importance of modern traffic means and climatic changes for its rapid expansion after 1985. Web of Science Senecio inaequidens The Netherlands Limburg Field - Observational terrestrial Old Field Invasion Hyp. Inherent Superiority;Empty Niche Broad Tolerances primary 2240 Fensham, RJ 1998 The grassy vegetation of the Darling Downs, south-eastern Queensland, Australia. Floristics and grazing effects journal BIOLOGICAL CONSERVATION 84 3 301 310 An ordination of floristic data from the grassy vegetation of the Darling Downs in southern Queensland describes four broad vegetation types, red gum (Eucalyptus camaldulensis/E. tereticornis) woodland associated with the flood-plain of the major streams, grassland on alluvial clay, poplar box (E. populnea) on clay loam terraces and hill woodland dominated by any of E. albens, E. crebra, E. melliodora, E. orgadophila. Ten per cent of species proved sensitive to grazing intensity categories (derived largely from land tenure) in hill woodland compared to 3% of species in grassland or poplar box woodland. There were no clear trends in the relative response of native and exotic species, although overall, species richness was greatest in either the moderate or heavily grazed treatment for all broad vegetation types. It is suggested that the interaction between Themeda dominance and the inter-tussock flora may contribute to the importance of grazing as a determinant of floristic composition in hill woodland broad vegetation type. Mechanical disturbance is implicated as a means of effecting the spread of exotic plants. However, there are relatively few exotic species that appear to have the capacity to displace native species without mechanical disturbance, although a notable exception is Phyla canescens in the flood-prone habitat. Moderate domestic stock grazing is compatible with nature conservation on the Darling Downs, although it is demonstrated that a proportion of the flora is sensitive to grazing. Remnants will need to be managed under a range of grazing regimes, including light total grazing pressure that excludes domestic stock to ensure the survival of the full range of species. (C) 1998 Elsevier Science Ltd. All rights reserved. Web of Science Many Australia Queensland Darling Downs -27.420538 150.595093 Field - Observational terrestrial Grassland Invasion Hyp. Disturbance primary 2241 Vidal, E; Medail, F; Tatoni, T; Roche, P; Vidal, P 1998 Impact of gull colonies on the flora of the Riou archipelago (Mediterranean islands of south-east France) journal BIOLOGICAL CONSERVATION 84 3 235 243 The effects of an increasingly large yellow-legged gull Larus cachinnans colony on the flora of a Mediterranean limestone archipelago (south-east France) were studied through the analysis of floristical changes which have occurred in the past 36 years. Island plant lists can be distinguished first according to the island area, but all the islands show a common pattern of historical changes in flora. This floristical change appears to be correlated with the gull density and the percentage of ruderal plant species. Disturbance by gulls favours the massive establishment of non-native plant species which has led to the extinction of some endangered taxa through this plant species 'enrichment'. Small islets appear to be more affected than large islands. Some preliminary conservation measures are presented. (C) 1998 Elsevier Science Ltd. All rights reserved. Web of Science Many France Marseille Riou archipelago 43.12 5.2 Field - Observational;Review terrestrial Invasion Hyp. Disturbance primary 2243 Ullmann, I; Bannister, P; Wilson, JB 1998 Lateral differentiation and the role of exotic species in roadside vegetation in southern New Zealand journal FLORA 193 2 149 164 Roadside vegetation was surveyed across the southern part of the South Island, New Zealand. Samples were taken at 10 km intervals along 750 km of selected roads that provided a climatic gradient from semi-arid to hyperoceanic conditions and which crossed both, areas of farmland, where the native vegetation has been replaced by an anthropogenic plant cover consisting almost entirely of introduced species, and areas of managed native tussock grassland and native forest. Contiguous plots, placed in four zones parallel to the road, were used to examine any lateral differentiation of vegetation. Variation in floristic composition in all four zones was associated with variation in rainfall, continentality, altitude, and the presence of forest. In all sites there was a distinct change in species composition from the outer verge to the inner roadside. The vegetation of the zone nearest to the road showed weaker correlation with altitude and stronger correlation with continentality, a marked increase in short-lived exotic species, and a greater proportion of the more continental and weedy vegetation types than the vegetation of the outermost verge. This supports the hypothesis of anthropogenic continentality of road-shoulders. The most frequent species on the road-shoulders are those exotic species that transgress climatic barriers in their native continents. This suggests that, globally, the range of such species is liable to expand, particularly in the habitat-complex provided by roadsides. Web of Science Many New Zealand South Island Field - Observational terrestrial Invasion Hyp. Inherent Superiority;Disturbance Broad Tolerances primary 2245 Vila, M; D'Antonio, CM 1998 Fruit choice and seed dispersal of invasive vs. noninvasive Carpobrotus (Aizoaceae) in coastal California journal ECOLOGY 79 3 1053 1060 Natural hybridization between previously allopatric plant species can produce highly successful lineages. However, the ecological processes controlling the spread of hybrid genotypes have rarely been studied in the field. We compared fruit characteristics, fruit preference, and seed dispersal by native frugivores among the non-indigenous succulent Carpobrotus edulis, the putative native congener C. chilensis, and the hybrids resulting from introgressive hybridization. In this system, the non-native C. edulis and hybrids are known to be very successful invaders of California coastal plant communities. Carpobrotus edulis and hybrids produced more fruits per clone than C. chilensis, primarily as a consequence of larger clone size. Clone size and energy content of fruits were good predictors of fruit removal. Marked fruits of C. edulis and hybrids were removed faster than those of the other morphotypes, and C. edulis fruits were preferred over those of C. chilensis in a fruit transplant experiment. However, total fruit removal by the end of the growing season was very high for all morphotypes. Seats from black-tailed jackrabbit (Lepus californicus) and mule deer (Odocoileus hemionus), the most common frugivores in our sites, contained more seeds from C. edulis and hybrid morphotypes than from C. chilensis, and more than would be expected based on relative fruit abundance. Germination of seeds from C. edulis and hybrids was enhanced after gut passage, whereas germination of C. chilensis decreased after gut passage, compared to seed germination from intact fruits. The results suggest that patterns of fruit preference by native frugivores and seed survival after gut passage facilitate the successful spread of an aggressive introduced species and hybrids in contrast to the less aggressive, apparently native congener. Web of Science Carpobrotus spp. (Aizoaceae) United States California Bodega Bay Marine Reserve 38.19 -123.4 Field - Observational terrestrial Invasion Hyp. Inherent Superiority;Hybridization Effective Disperser primary 2247 Crossland, MR; Alford, RA 1998 Evaluation of the toxicity of eggs, hatchlings and tadpoles of the introduced toad Bufo marinus (Anura : Bufonidae) to native Australian aquatic predators journal AUSTRALIAN JOURNAL OF ECOLOGY 23 2 129 137 The early life history stages of anurans in the Family Bufonidae often possess chemicals that are noxious or toxic to predators. Predators with no evolutionary history of exposure to bufonids may be particularly susceptible to these toxins. We conducted a series of laboratory experiments to investigate the toxic effects of eggs, hatchlings and tadpoles of the introduced toad, Bufo marinus (Linnaeus), on native Australian aquatic predators. There was considerable interspecific and intraspecific variation in these effects. Bufo marinus were highly toxic to some predator species, but were readily consumed by other species without apparent in effect. Interspecific variation in toxic effects was not related to predator feeding mode or the number of B. marinus ingested by predators, and there was no clear pattern of distribution of vulnerability among species within higher taxa. Intraspecific variation in responses to toxins may result from individual variation in the resistance of predators to B. marinus toxins, or from individual variation in toxicity among B. marinus. Some native species adversely affected by B. marinus appeared unable to detect and avoid B. marinus toxins. This may result from a general inability to assess the toxicity of food items or from a lack of evolutionary exposure to B. marinus toxins. Web of Science Bufo marinus (Linnaeus) Australia Townsville James Cook University; Heathlands Reserve, Cape York Peninsula -19.20; -11.45 146.46; 142.35 Lab Invasion Hyp. Enemy Release;Novel Weapons omnivore 2249 Higgins, SI; Richardson, DM 1998 Pine invasions in the southern hemisphere: modelling interactions between organism, environment and disturbance journal PLANT ECOLOGY 135 1 79 93 Current theories of plant invasion have been criticized for their limited heuristic and predictive value. We explore the heuristic and predictive potential of a model which explicitly simulates the mechanisms of plant invasion. The model, a spatially-explicit individual-based simulation, is applied to the invasion of pine trees (Pinus spp.; Pinaceae) in three vegetation types in the southern hemisphere. The model simulates factors which have been invoked as major determinants of invasive success: plant traits, environmental features and disturbance level. Results show that interactions between these determinants of invasive success are at least as important as the main effects. The complexity of invasions has promoted the belief that many factors must be invoked to explain invasions. This study shows that by incorporating interactions and mechanisms into our models we can potentially reduce the number of factors needed to predict plant invasions. The importance of interactions, however, means that predictions about invasions must be context-specific. The search for all-encompassing rules for invasions is therefore futile. The model presented here is of heuristic value since it improves our understanding of invasions, and of management value since it defines the data and models needed for predicting invasions. Web of Science Pinus spp. Theoretical/Modeling terrestrial Invasion Hyp. Inherent Superiority;Disturbance Effective Disperser primary 2251 Gillespie, RD; Meinesz, A; Critchley, AT 1997 Growth responses of Caulerpa taxifolia (Ulvophyceae, Chlorophyta) from the South African aquarist trade. A potential invasive of South African coastal waters journal SOUTH AFRICAN JOURNAL OF BOTANY 63 6 480 483 Caulerpa taxifolia (Vahl) C. Agardh is an invasive marine alga in the northern Mediterranean Sea where it poses a serious threat to indigenous fauna and flora. Caulerpa taxifolia obtained through the aquarist trade in South Africa was grown under controlled temperature and irradiance conditions. Two separate univariate studies were performed: i) Temperature treatments of 15 degrees, 20 degrees, 25 degrees and 30 degrees C, all at 90 mu mol photons.m(-2).s(-1) irradiance and ii) irradiance treatments of 20, 75 and 130 mu mol photons.m(-2).s(-1), all at 25 degrees C. The optimum temperature for maximal stolen and assimilator extension was 25 degrees C; the alga showed growth as high as 30 degrees C with slight growth occurring as low as 15 degrees C. Growth of C. taxifolia was similar over the range of irradiance values studied. Maximum mean stolen and assimilator extension were recorded at an irradiance of 75 mu mol photons.m(-2).s(-1). Caulerpa taxifolia commonly available in the South African aquarist trade was shown to have a wide temperature tolerance range, well within the range experienced by the east coast of the country. Web of Science Caulerpa taxifolia South Africa Lab marine Intertidal/Near Shore Invasion Hyp. Inherent Superiority Broad Tolerances primary 2262 Kittelson, PM; Boyd, MJ 1997 Mechanisms of expansion for an introduced species of cordgrass, Spartina densiflora, in Humboldt Bay, California journal ESTUARIES 20 4 770 778 The dominant plant in Humboldt Bay salt marshes is Spartina densiflora, a species of cordgrass apparently introduced from South America. At several salt marshes and restoration sites around Humboldt Bay, distribution of this plant has increased significantly. We investigated the relative contributions of vegetative tiller production and seed germination to the establishment and expansion of S. densiflora. Lateral spread of plants surrounded by competitors were compared to areas without competing plant species. Plants growing in areas without competitors had significantly higher rates of vegetative expansion (p < 0.0001). Viable seed production, germination rates, seedling survivorship, and growth of adult plants were measured in six salinity treatments. Approximately 1,977 +/- 80 viable seeds are produced per plant (0.25-0.5 m(2)). The number of germinating seeds was inversely related to increases in salinity. Salinity treatments between 19 parts per thousand and 35 parts per thousand produced significantly lower germination rates than salinities of 0-18 parts per thousand (p < 0.0001). Seedling survivorship was 50% at less than or equal to 4 parts per thousand and 8-14% at greater than or equal to 11 parts per thousand. Lateral expansion of adult, greenhouse-grown plants occurred in all salinity treatments, with modest decreases in the highest salinity treatments (p < 0.05). Our findings indicate that S. densiflora expands primarily by vegetative expansion, and lateral tillers are produced by throughout the year. Spartina densiflora produces prolific amounts of seed, but recruitment in mature salt marshes may be limited by competitors and higher salinities. At restoration sites, planting of native species such as Salicorina virginica, Distichlis spicata, or Jaumea carnosa may prevent monospecific stands of S. densiflora from developing. Web of Science Spartina densiflora United States California Humboldt Bay 40.722283 -124.242496 Field - Observational;Greenhouse terrestrial Wetland Invasion Hyp. Inherent Superiority High Reprod. Output;Clonal Reproduction primary 2263 Panetta, FD; McKee, J 1997 Recruitment of the invasive ornamental, Schinus terebinthifolius, is dependent upon frugivores journal AUSTRALIAN JOURNAL OF ECOLOGY 22 4 432 438 Generalist avian frugivores often play an important role in the processes of naturalization and invasion for plants introduced for ornamental and landscaping purposes. We investigated the potential role of Australian birds in the current invasion of riparian habitats and coastal wetlands by the ornamental Schinus terebinthifolius Raddi. Feeding trials in captivity predicted silvereyes (Zosterops lateralis Latham) as dispersal vectors for this weed. There were no differences in either total germination or germination rate between seeds voided by caged silvereyes and those from which exocarps had been removed manually. Germination of seeds incubated within entire fruits was minimal, as was emergence from intact fruits in a held experiment. Seed banks of S. terebinthifolius were relatively transient under field conditions, with no seeds surviving for 9 months. Since fewer than 5% of the seeds in sown whole fruits gave rise to seedlings (cf. 20-42% for sown bare seeds), we conclude that recruitment potential of S. terebinthifolius is highly dependent upon the consumption of its fruits by frugivores. Web of Science Schinus terebinthifolius Australia Queensland -28.136107;-27.52616 153.488574;152.974663 Garden;Lab terrestrial Wetland;Riparian Invasion Hyp. Mutualism Facilitation primary 2265 Sharma, Gyan P.; Raghubanshi, Akhilesh S. 2010 How Lantana invades dry deciduous forest: a case study from Vindhyan highlands, India journal TROPICAL ECOLOGY 51 2 305 316 Invasion by exotic species is among the most important global-scale problems experienced by natural ecosystems. Studies document that floristic changes that emerge after habitat fragmentation may be due to invasion by exotic weeds. When either habitat modification or the introduction of foreign species results in changes in the community, then native species populations could undergo local decline or extinction. The present study provides a qualitative and quantitative overview of the effects of habitat fragmentation on the invasive success of Lantana camara is well as the subsequent effects of this invader on ecosystem structure and function in the Vindhyan dry deciduous forest of India. Web of Science Lantana camara India Uttar Pradesh Vindhyan highlands Field - Observational terrestrial Deciduous Forest Impacts;Invasion Hyp. Community Species Richness;Disturbance;Ecosystem Engineers primary 2267 Miranda, Nelson A. F.; Perissinotto, Renzo; Appleton, Christopher C. 2010 SALINITY AND TEMPERATURE TOLERANCE OF THE INVASIVE FRESHWATER GASTROPOD TAREBIA GRANIFERA journal SOUTH AFRICAN JOURNAL OF SCIENCE 106 4 55 61 Invasive aquatic species, such as the gastropod Tarebia granifera, can cause ecological disturbances and potentially reduce biodiversity by displacing indigenous invertebrates. In South Africa, T. granifera was first recorded in an estuarine environment in the St Lucia Estuary. Its tolerance to salinity and temperature was investigated through the experimental manipulation of these factors. T. granifera can tolerate temperatures between 0 degrees C and 47.5 degrees C, allowing it to survive high temperature extremes. The species may also survive cold snaps and invade higher altitude areas. More remarkably, this snail survives high salinity for a relatively long time, as LS50 (lethal salinity for 50% of the population) was reached at 30 psu over 65-75 days. However, higher salinity adversely affected the T. granifera population. Snails acclimated to freshwater conditions and suddenly transferred to 30 psu experienced 100% mortality within 48 h. Snail activity also declined with increasing salinity. T. granifera's environmental tolerance and parthenogenetic characteristics are the keys to successful introduction and establishment. Therefore, the management of T. granifera may prove difficult in the short to medium term. The present findings constitute a contribution to the knowledge of biological invasions in Africa and to the understanding of estuarine invasions by T. granifera. Web of Science Tarebia granifera South Africa Catalina Bay -26.273714 32.080078 Lab estuarine Invasion Hyp. Inherent Superiority Broad Tolerances herbivore 2268 Corbin, Jeffrey D.; D'Antonio, Carla M. 2010 Not novel, just better: competition between native and non-native plants in California grasslands that share species traits journal PLANT ECOLOGY 209 1 71 81 Invasive plants have often been shown to possess novel traits such as the ability to fix nitrogen, access unused resource pools, or the ability to exude allelopathic chemicals. We describe a case of a successful invasion where the native and non-native species are very similar in most life-history characteristics including their growth forms, lifespan, and degree of summertime activity. Data from permanent transects suggest that exotic perennial grass invaders can establish into intact native-dominated grasslands, achieving cover values from 6 to 71% over several years. We also established a 4-year competition experiment to test the effect of each group-the native and non-native perennial grasses-on the other. Competitive interactions were found to consistently favor the non-native grasses: native perennial grass productivity was significantly lower in plots with exotic perennial grasses as compared to plots without exotic perennial grasses. By contrast, productivity of the exotic perennial grasses was not reduced by the presence of the native perennial grasses. These results suggest that competitive ability, rather than a unique trait, has contributed to the success of the exotic perennial grasses in our system. Management tools to control exotic perennial grass invasions are likely to negatively influence native perennial grass populations, as strategies that succeed against the invasive species may kill or reduce the native species as well. Web of Science Festuca arundinacea Schreber; Holcus lanatus L.; Phalaris aquatica United States California Tom’s Point Preserve 38.13 -122.57 Field - Experimental;Field - Observational terrestrial Grassland Impacts;Invasion Hyp. Inherent Superiority Superior Competitor primary 2270 Cripps, Michael G.; Edwards, Grant R.; Bourdot, Graeme W.; Saville, David J.; Hinz, Hariet L.; Fowler, Simon V. 2010 Enemy release does not increase performance of Cirsium arvense in New Zealand journal PLANT ECOLOGY 209 1 123 134 Cirsium arvense (L.) Scop. (Californian, Canada, or creeping thistle) is an exotic perennial herb indigenous to Eurasia that successfully established in New Zealand (NZ) approximately 130 years ago. Presently, C. arvense is considered one of the worst invasive weeds in NZ arable and pastoral productions systems. A mechanism commonly invoked to explain the apparent increased vigour of introduced weeds is release from natural enemies. The enemy-release hypothesis (ERH) predicts that plants in an introduced range should experience reduced herbivory, particularly from specialists, and that release from this natural enemy pressure facilitates increased plant performance in the introduced range. In 2007, surveys were carried out in 13 populations in NZ (7 in the North Island and 6 in the South Island) and in 12 populations in central Europe to quantify and compare growth characteristics of C. arvense in its native versus introduced range. Altitude and mean annual precipitation for each population were used as covariates in an attempt to explain differences or similarities in plant traits among ranges. All plant traits varied significantly among populations within a range. Shoot dry weight was greater in the South Island compared to Europe, which is in line with the prediction of increased plant performance in the introduced range; however, this was explained by environmental conditions. Contrary to expectations, the North Island was not different from Europe for all plant traits measured, and after adjustment for covariates showed decreased shoot density and dry weight compared to the native range. Therefore, environmental factors appear to be more favourable for growth of C. arvense in both the North and South Islands. In accordance with the ERH, there was significantly greater endophagous herbivory in the capitula and stems of shoots in Europe compared to both NZ ranges. In NZ, capitulum attack from Rhinocyllus conicus was found only in the North Island, and no stem-mining attack was found anywhere in NZ. Thus, although C. arvense experiences significantly reduced natural enemy pressure in both the North and South Islands of NZ there is no evidence that it benefits from this enemy release. Web of Science Cirsium arvense (L.) Scop. New Zealand Field - Observational terrestrial Invasion Hyp. Enemy Release primary 2272 Pairon, Marie; Petitpierre, Blaise; Campbell, Michael; Guisan, Antoine; Broennimann, Olivier; Baret, Philippe V.; Jacquemart, Anne-Laure; Besnard, Guillaume 2010 Multiple introductions boosted genetic diversity in the invasive range of black cherry (Prunus serotina; Rosaceae) journal ANNALS OF BOTANY 105 6 881 890 Black cherry (Prunus serotina) is a North American tree that is rapidly invading European forests. This species was introduced first as an ornamental plant then it was massively planted by foresters in many countries but its origins and the process of invasion remain poorly documented. Based on a genetic survey of both native and invasive ranges, the invasion history of black cherry was investigated by identifying putative source populations and then assessing the importance of multiple introductions on the maintenance of gene diversity. Genetic variability and structure of 23 populations from the invasive range and 22 populations from the native range were analysed using eight nuclear microsatellite loci and five chloroplast DNA regions. Chloroplast DNA diversity suggests there were multiple introductions from a single geographic region (the north-eastern United States). A low reduction of genetic diversity was observed in the invasive range for both nuclear and plastid genomes. High propagule pressure including both the size and number of introductions shaped the genetic structure in Europe and boosted genetic diversity. Populations from Denmark, The Netherlands, Belgium and Germany showed high genetic diversity and low differentiation among populations, supporting the hypothesis that numerous introduction events, including multiple individuals and exchanges between sites, have taken place during two centuries of plantation. This study postulates that the invasive black cherry has originated from east of the Appalachian Mountains (mainly the Allegheny plateau) and its invasiveness in north-western Europe is mainly due to multiple introductions containing high numbers of individuals. Web of Science Black cherry (Prunus serotina) Lab terrestrial Invasion Hyp. Propagule Pressure primary 2273 Tojo, Koji; Tanaka, Yoshiki; Kuranishi, Ryoichi B.; Kanada, Shoji 2010 Reproductive Biology and Adaptability of the Invasive Alien Freshwater Amphipod Crangonyx floridanus (Crustacea: Amphipoda, Crangonyctidae) journal ZOOLOGICAL SCIENCE 27 6 522 527 We studied the reproductive biology and adaptability of the alien freshwater crangonyctid amphipod Crangonyx floridanus, currently inhabiting a large portion of Japan, both in the field and under controlled laboratory conditions. In the Chikuma River population of this alien amphipod, egg-bearing individuals were found throughout the year. In terms of egg maturation cycle, egg development (during embryogenesis), and egg count per ovipositional cycle, these amphipods display a very efficient reproductive system. This study also established their adaptability to a wide range of water temperatures (primarily 4-20 degrees C, however in some cases, these individuals are able to survive at up to 30 degrees C). C. floridanus's strong capacity to adapt to broad and variable environmental conditions is certainly contributing to its high rate of population increase, and rapid dispersion throughout Japan. Web of Science crangonyctid amphipod Crangonyx floridanus Japan Chikuma River Field - Observational;Lab lotic Invasion Hyp. Inherent Superiority Broad Tolerances;High Reprod. Output herbivore 2274 Turnbull, Lindsay A.; Levine, Jonathan M.; Fergus, Alexander J. F.; Petermann, Jana S. 2010 Species diversity reduces invasion success in pathogen-regulated communities journal OIKOS 119 6 1040 1046 The loss of natural enemies is thought to explain why certain invasive species are so spectacularly successful in their introduced range. However, if losing natural enemies leads to unregulated population growth, this implies that native species are themselves normally subject to natural enemy regulation. One possible widespread mechanism of natural enemy regulation is negative soil feedbacks, in which resident species growing on home soils are disadvantaged because of a build-up of species-specific soil pathogens. Here we construct simple models in which pathogens cause resident species to suffer reduced competitive ability on home soils and consider the consequences of such pathogen regulation for potential invading species. We show that the probability of successful invasion and its timescale depend strongly on the competitive ability of the invader on resident soils, but are unaffected by whether or not the invader also suffers reduced competitive ability on home soils (i.e. pathogen regulation). This is because, at the start of an invasion, the invader is rare and hence mostly encounters resident soils. However, the lack of pathogen regulation does allow the invader to achieve an unusually high population density. We also show that increasing resident species diversity in a pathogen-regulated community increases invasion resistance by reducing the frequency of home-site encounters. Diverse communities are more resistant to invasion than monocultures of the component species: they preclude a greater range of potential invaders, slow the timescale of invasion and reduce invader population size. Thus, widespread pathogen regulation of resident species is a potential explanation for the empirical observation that diverse communities are more invasion resistant. Web of Science Theoretical/Modeling terrestrial Invasion Hyp. Enemy Release;Community Species Richness primary 2275 Ashton, Gail V.; Burrows, Michael T.; Willis, Kate J.; Cook, Elizabeth J. 2010 Seasonal population dynamics of the non-native Caprella mutica (Crustacea, Amphipoda) on the west coast of Scotland journal MARINE AND FRESHWATER RESEARCH 61 5 549 559 Information on the life history and population dynamics of non-native species is essential to understand the process of invasion and impacts on invaded ecosystems. The non-native marine caprellid amphipod Caprella mutica has successfully established populations on coastlines throughout the temperate northern hemisphere and in New Zealand in the southern hemisphere. The introduction mechanism has been surpassed and it is now important to understand its ecology and biology in non-native habitats. The seasonal population dynamics of C. mutica were investigated over 18 months at four sites with different levels of anthropogenic disturbance on the west coast of Scotland. Abundance of C. mutica fluctuated seasonally at all sites, peaking during June to October. The highest abundance recorded on a single mesh collector was 319 000 individuals m(-2) in August 2004 at one of the fish farms. Both seasonal and site-specific factors influenced the population dynamics of C. mutica. Both males and females were significantly larger and more abundant at the fish farm sites. Individuals displayed reproductive characteristics at a smaller size at the fish farm sites, indicating earlier maturity. The results suggest that anthropogenic disturbance and artificial resource enhancement contribute to the global establishment success of non-native C. mutica. Web of Science Caprella mutica Scotland Lynne of Lorne; Dunstaffnage fish farm 56.27 -5.24 Field - Observational lentic Invasion Hyp. Disturbance herbivore 2276 Guan, Baohua; An, Shuqing; Schooler, Shon; Cai, Ying 2010 Influence of Substrate Phosphorus Concentration and Plant Density on Growth and Phosphorus Accumulation of Alternanthera philoxeroides journal JOURNAL OF FRESHWATER ECOLOGY 25 2 219 225 We investigated the effects of three substrate phosphorus concentration and three plant density on the phenotypic plasticities of the invasive plant, alligator weed (Alternanthera philoxeroide, Amaranthaceae). Phosphorus concentration affected mainly the plant tissue phosphorus accumulation, while plant density affected mainly growth traits, especially those of the stem. The greatest stem mass and stem basal diameter occurred with the combined treatment of medium substrate phosphorus concentration and high plant density (64 ind. m(-2)), while the greatest stem length and internode number occurred with medium phosphorus concentration and low plant density (16 ind. m(-2)). Alligator weed had highest leaf, stem, and root phosphorus concentrations with treatment of high phosphorus concentration and low plant density (16 ind. m(-2)). These results suggest that alligator weed has plasticity in response to substrate phosphorus and plant density and adapts to high phosphorus by accumulating more phosphorus into plant tissues and to high plant density by producing larger but less vegetative individuals, these are strategies that might facilitate invasiveness in eutrophic shallow waters. Web of Science Alternanthera philoxeroide, Amaranthaceae China Nanjing 32.04 118.78 Greenhouse lentic Invasion Hyp. Plasticity primary 2278 Molinari, Nicole; Knight, Charles 2010 Correlated evolution of defensive and nutritional traits in native and non-native plants journal BOTANICAL JOURNAL OF THE LINNEAN SOCIETY 163 1 1 13 We performed a comparative analysis of defensive and nutritional plant traits responsible for differential herbivory in a series of experimental feeding trials with generalist herbivores. We measured three defensive traits (leaf strength, leaf mass per unit area and endophytic fungal infection) and two nutritional traits (foliar nitrogen and water) for 26 native and eight non-native plant species from coastal California shrublands. Our feeding trials involved three species of generalist herbivore (beet armyworm, cabbage looper and the garden snail) in two types of laboratory feeding trial (single plant species and preference tests). All traits were significantly related to the amount of leaf area consumed, with foliar nitrogen followed by leaf strength explaining most of the variation in herbivore damage. Defensive and nutritional traits were tightly correlated with one another. These correlations were still apparent after incorporation of the phylogenetic relationships of species using independent contrasts, suggesting that there has been repeated selection for certain trait combinations. Non-native species had lower defensive traits and greater nutrient content and therefore experienced greater herbivory damage than natives. Poorly defended, nutrient-rich species (like most of the non-natives in our study) may be better suited for rapid growth and nutrient acquisition, thus reducing the cost of replenishing leaf material lost to herbivores. (c) 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 163, 1-13. Web of Science Many United States California San Luis Obispo County 35.286265 -120.659065 Lab terrestrial Invasion Hyp. Enemy Release;Inherent Superiority Rapid Growth primary 2279 Pisula, Nikki L.; Meiners, Scott J. 2010 Relative allelopathic potential of invasive plant species in a young disturbed woodland journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 137 1 81 87 PISULA, N. L. AND S. J. MEINERS. (Department of Biological Sciences, Eastern Illinois University, Charleston, IL 61920). Relative allelopathic potential of invasive plant species in a young disturbed woodland. J. Torrey Bot. Soc. 137: 81-87. 2010-Invasive plant species are often more successful within introduced areas when compared to their natural ranges. Allelopathy has been suggested as a potential mechanism for this success because invasive plants frequently establish monocultures and may produce allelochemicals evolutionarily novel to the recipient community. However, species are typically tested in isolation making the relative strength of allelopathy difficult to assess. We conducted laboratory bioassays for 10 co-occurring non-native species to determine the relative strength of their allelopathic potential. These species represented a suite of successful invaders within a young forest and were from a variety of plant life forms: trees, lianas, shrubs, and herbs. We determined the germination responses of a target species to a gradient of leaf extract concentrations to assess relative allelopathic potential. The relative strength of germination inhibition was quantified by the slope (beta) of the germination response to plant extract concentration. Ailanthus altissima extract had the greatest inhibitory effect on target species germination out of all 10 species (beta = -0.55) while the other tree species, Acer platanoides extract, had small effects on germination (beta = -0.14). For lianas, Celastrus orbiculatus extract inhibited the target species (beta = -0.28) more than Lonicera japonica extract (beta = -0.06). All invasive shrub extracts had very small effects on seed germination (beta value -0.03 to -0.19). Extracts of the two herbaceous species, Alliaria petiolata and Microstegium vimineum, had very large inhibitory effects (beta = -0.37 and -0.38, respectively). In this system, we screened a suite of invasive species for allelopathic potential and determined the relative strength of germination inhibition. Most species, particularly invasive shrubs, did not exhibit sufficient allelopathic potential to suggest allelopathy would occur in the field. Four species, Ailanthus altissima, Alliaria petiolata, C orbiculatus, and M. vimineum all exhibited strong germination inhibition and warrant additional study in the field. Web of Science Many USA Illinois Lab terrestrial Deciduous Forest Invasion Hyp. Novel Weapons primary 2280 Van De Meutter, F.; Trekels, H.; Green, A. J.; Stoks, R. 2010 Is salinity tolerance the key to success for the invasive water bug Trichocorixa verticalis? journal HYDROBIOLOGIA 649 1 231 238 Trichocorixa verticalis is a North American water bug (Heteroptera: Corixidae) that occurs in brackish and saline aquatic systems. Recently, it has been found invading three continents including Europe. Its invasive success has been attributed to the capacity of tolerating hypersalinity. We compared both the realized and standardized salinity niche of invasive T. verticalis and native Corixidae to verify if T. verticalis may fill in an unoccupied niche. We first established the field distribution of T. verticalis and native Corixidae along a salinity gradient. Second, we experimentally tested the salinity tolerance of T. verticalis and three common native Corixidae species. Of the seven Corixidae species found in the field study, three were positively related to the salinity gradient: S. selecta, S. stagnalis, and T. verticalis. T. verticalis showed the highest salinity optimum, however, after correcting for environmental background variation, salinity optima differed little among the three halophilic species. In the salinity tolerance experiment, S. selecta outperformed T. verticalis, which performed as well as S. stagnalis. Based on our experimental results, we cannot support the hypothesis that T. verticalis' invasion is mediated by a high salinity tolerance that allows this species to colonize habitats unoccupied by native Corixidae. Although these findings contrast with the field patterns in which T. verticalis showed the highest niche optimum and tolerance, these patterns may have been partly due to other environmental factors, particularly anthropogenic disturbance. Our comparative results are for adults only, and it remains possible that relative salinity tolerance patterns for juveniles differ from that for adults, which may add to the observed field pattern. Web of Science Trichocorixa verticalis Spain 37.04 -6.21 Field - Observational;Lab estuarine Wetland Invasion Hyp. Inherent Superiority;Empty Niche Broad Tolerances herbivore 2281 Williams, Jennifer L.; Auge, Harald; Maron, John L. 2010 Testing hypotheses for exotic plant success: parallel experiments in the native and introduced ranges journal ECOLOGY 91 5 1355 1366 A central question in ecology concerns how some exotic plants that occur at low densities in their native range are able to attain much higher densities where. they are introduced. This question has remained unresolved in part due to a lack of experiments that assess factors that affect the population growth or abundance of plants in both ranges. We tested two hypotheses for exotic plant success: escape from specialist insect herbivores and a greater response to disturbance in the introduced range. Within three introduced populations in Montana, USA, and three native populations in Germany, we experimentally manipulated insect herbivore pressure and created small-scale disturbances to determine how these factors affect the performance of houndstongue (Cynoglossum officinale), a widespread exotic in western North America. Herbivores reduced plant size and fecundity in the native range but had little effect on plant performance in the introduced range. Small-scale experimental disturbances enhanced seedling recruitment in both ranges, but subsequent seedling survival was more positively affected by disturbance in the introduced range. We combined these experimental results with demographic data from each population to parameterize integral projection population models to assess how enemy escape and disturbance might differentially influence C. officinale in each range. Model results suggest that escape from specialist insects would lead to only slight increases in the growth rate (lambda) of introduced populations. In contrast, the larger response to disturbance in the introduced vs. native range had much greater positive effects on lambda. These results together suggest that, at least in the regions where the experiments were performed, the differences in response to small disturbances by C. officinale contribute more to higher abundance in the introduced range compared to at home. Despite the challenges of conducting experiments on a wide biogeographic scale and the logistical constraints of adequately sampling populations within a range, this approach is a critical step forward to understanding the success of exotic plants. Web of Science Cynoglossum officinale United States; Germany Montana Field - Experimental terrestrial Grassland Invasion Hyp. Enemy Release;Disturbance primary 2283 Stanisci, A.; Acosta, A. T. R.; Di Iorio, A.; Vergalito, M. 2010 Leaf and root trait variability of alien and native species along Adriatic coastal dunes (Italy) journal PLANT BIOSYSTEMS 144 1 47 52 This study regards the analysis of leaf and root trait variability of the most invasive alien species and some common native species developing along central-southern Adriatic sand dunes in Italy. The results highlight that large leaf area, the reproductive period in late summer, a biennial/annual life cycle and thick, long roots are useful traits for the successful colonisation of the most invasive species Oenothera biennis, Erigeron canadensis and Xanthium orientale subsp. italicum along the mobile coastal dunes. These alien plants grow in spatial niches generated by eutrophication and human pressure, such as waste deposits on the beach and inter-dune gaps, flattened and altered by human trampling. We suggest that exotic species in the study area are currently occupying temporal and spatial niches that are not being exploited by native species and, therefore, they are not competing directly for the same resources. Web of Science Carpobrotus edulis;Oenothera biennis;Xanthium italicum;Erigeron canadensis Italy central-southern Adriatic sand dunes 41.91 14.73 Field - Observational terrestrial Intertidal/Near Shore Invasion Hyp. Empty Niche primary 2289 Yager, Lisa Y.; Miller, Deborah L.; Jones, Jeanne 2010 Susceptibility of Longleaf Pine Forest Associations in South Mississippi to Invasion by Cogongrass [Imperata cylindrica (L.) Beauv.] journal NATURAL AREAS JOURNAL 30 2 226 232 If fire affects spread of cogongrass (Imperata cylindrica), a non-native grass that displaces native plants, managers can determine best use of resources to restore and maintain the diverse herbaceous groundcovers of longleaf pine-bluestem (Pinus palustris - Andropogon spp. and Schizachyrium spp.) forests of the southeastern United States. In 2003 and 2004, we measured rates of vegetative encroachment of cogongrass into burned and unburned pine-bluestem and pine-shrub forests one and two years post-burning on Camp Shelby Training Site, Mississippi. Linear growth and tiller production were significantly greater in pi ne-bluestem forests compared to pine-shrub forests for both time periods. Cogongrass growth was not affected by burning in either forest type one-year post-burning, but was significantly greater in burned forests after two years of growth. Two-years post-burning, mean linear growth of cogongrass was 235 cm in burned pine-bluestem, 139 cm in unburned pine-bluestem, 177 cm in burned pine-shrub, and 92 cm in unburned pine- shrub. Tiller productionhn2 for 2004 was greatest in pine-bluestem burned plots and least in pine-shrub unburned plots. Linear growth of cogongrass was significantly and positively correlated to percent cover of adjacent herbaceous vegetation but tiller numbers were significantly and negatively correlated to percent cover of adjacent shrubs. Efforts to restore pine-shrub forests to pine-bluestem forest conditions should implement control of cogongrass before and after use of fire. Vigilant control efforts are needed as restoration shifts conditions to those of pine-bluestem forests and increases susceptibility to cogongrass invasion. Web of Science Imperata cylindrica USA Mississippi Camp Shelby Training Site 31.217499 -89.184265 Field - Observational terrestrial Coniferous Forest Invasion Hyp. Disturbance primary 2290 Lymbery, A. J.; Hassan, M.; Morgan, D. L.; Beatty, S. J.; Doupe, R. G. 2010 Parasites of native and exotic freshwater fishes in south-western Australia journal JOURNAL OF FISH BIOLOGY 76 7 1770 1785 In this study, 1429 fishes of 18 different species (12 native and six exotic) were sampled from 29 localities to compare the levels of parasitism between native and exotic fish species and to examine the relationship between environmental degradation and parasite diversity. Forty-four putative species of parasites were found and most of these appear to be native parasites, which have not previously been described. Two parasite species, Lernaea cyprinacea and Ligula intestinalis, are probably introduced. Both were found on or in a range of native fish species, where they may cause severe disease. Levels of parasitism and parasite diversity were significantly greater in native fishes than in exotic species, and this may contribute to an enhanced demographic performance and competitive ability in invading exotics. Levels of parasitism and parasite diversity in native fishes were negatively related to habitat disturbance, in particular to a suite of factors that indicate increased human use of the river and surrounding environment. This was due principally to the absence in more disturbed habitats of a number of species of endoparasites with complex life cycles, involving transmission between different host species. (C) 2010 The Authors Journal compilation (C) 2010 The Fisheries Society of the British Isles Web of Science Many Australia South-West Coast Drainage Divisio Field - Observational lentic;lotic Invasion Hyp. Enemy Release herbivore;omnivore;predator 2291 O'Donnell, Kelly L.; Pigliucci, Massimo 2010 SELECTION DYNAMICS IN NATIVE AND INTRODUCED PERSICARIA SPECIES journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 171 5 519 528 Plant invasions represent natural experiments that allow us to both explore the dynamics of natural selection in the wild and examine the evolution of an invader on contemporary timescales. We conducted a study of 10 natural populations of two invasive species (Persicaria lapathifolia and Persicaria cespitosa) and one native species ( Persicaria pensylvanica) to quantify the amount of natural selection acting on these species to compare the selection dynamics to which each is exposed. We also conducted a germination trial to compare the potential for invasion determined by germination rate. A Lande-Arnold-style multiple regression selection analysis was performed on five morphological traits ( height, stem diameter, leaf number, leaf shape, and leaf area) using flower number as our fitness proxy. Most selection was indirect and caused by correlations with other traits under selection. However, there was significant direct selection for increased leaf number in both natives and invasives and for thicker stems in just the invasives. The germination test showed that not only do the invasive plants have a significantly higher germination rate (>60% compared with 3% for the noninvasives) but they also germinate significantly faster; both findings have large implications for the ability of these two invasive species to spread. Web of Science Persicaria lapathifolia; Persicaria cespitosa United States New York Long Island; Stony Brook University 40.90521 -73.116417 Greenhouse terrestrial Invasion Hyp. Inherent Superiority High Reprod. Output primary 2292 Harner, Mary J.; Mummey, Daniel L.; Stanford, Jack A.; Rillig, Matthias C. 2010 Arbuscular mycorrhizal fungi enhance spotted knapweed growth across a riparian chronosequence journal BIOLOGICAL INVASIONS 12 6 1481 1490 Arbuscular mycorrhizal fungi (AMF) mediate nutrient uptake that accelerates plant growth and reproduction. Thus, AMF may promote plant invasions often observed along rivers. We assessed the importance of AMF in improving growth of the invasive species, spotted knapweed (Centaurea stoebe), during succession of riparian vegetation along a flood plain in Montana, USA. We grew spotted knapweed with and without AMF in soils collected from riparian sites ranging from 1 to 72 years old and measured the plant's growth response to AMF. We observed variability in relative effects of AMF, with greatest growth benefits in recently deposited alluvial sediments. We then separated effects of soil and inoculum source by growing spotted knapweed with soils and inocula collected from young or old sites and found that growth responses were greatest in young soils regardless of inoculum source. Our results demonstrate that AMF directly benefit growth of spotted knapweed, especially in soils that typify early successional sites on this alluvial flood plain. Web of Science Centaurea stoebe United States Montana Greenhouse terrestrial Riparian Invasion Hyp. Mutualism Facilitation primary 2293 Burnham, Katharine M.; Lee, Thomas D. 2010 Canopy gaps facilitate establishment, growth, and reproduction of invasive Frangula alnus in a Tsuga canadensis dominated forest journal BIOLOGICAL INVASIONS 12 6 1509 1520 The primary objective of this study was to determine whether the exotic, invasive shrub, glossy buckthorn (Frangula alnus), is more abundant in canopy gaps created by logging than in uncut forests. Secondary objectives were to determine whether buckthorn abundance in gaps is related to gap size, and whether or not buckthorn exhibits advanced regeneration. The abundance of glossy buckthorn was estimated in five patch cuts and three single-tree cuts in a 90 year old eastern hemlock-eastern white pine-sweet birch forest at the Woodman Horticultural Farm in Durham, NH, USA. Glossy buckthorn was 96 times more abundant in logged areas than in uncut control plots. The three largest but youngest gaps (> 0.08 ha; 5 years old) had the greatest proportion of tall (> 2 m), reproductively mature glossy buckthorn individuals, with 18.4% fruiting. The older, medium-sized gaps (ca. 0.03 ha; 10 years old) contained the highest overall densities of glossy buckthorn, but few stems were flowering (similar to 2%) and none were fruiting at the time of sampling. Small gaps (< 0.01 ha; 10 years old) appeared to be sinks for glossy buckthorn, as all individuals were < 0.5 m tall and none were > 4 years old. As age and size of gaps were correlated, it was difficult to determine which factor played a larger role in the establishment and persistence of glossy buckthorn. However, the greater proportion of individuals > 2 m tall and greater reproductive vigor of glossy buckthorn in large gaps relative to small gaps-despite fewer years available for growth-suggest that larger disturbances lead to more resources available for buckthorn growth, survival, and reproduction. Individuals < 0.5 m tall were observed in uncut control plots at low density (< 30 stems/ha) and 5% of stems in large gaps were older than the gaps themselves, suggesting that gap formation released previously established glossy buckthorn individuals (i.e., advanced regeneration). Web of Science frangula alnus U.S.A. New Hampshire Durham 43.144702 -70.947139 Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 2295 Kremer, Laura P.; Rocha, Rosana M.; Roper, James J. 2010 An experimental test of colonization ability in the potentially invasive Didemnum perlucidum (Tunicata, Ascidiacea) journal BIOLOGICAL INVASIONS 12 6 1581 1590 Exotic species invasions are one of the greatest threats to marine systems and ascidians have many characteristics that favor transport, colonization and establishment into new regions. Didemnum perlucidum is a widespread species that has been introduced into tropical ports around the world. Here we examine the colonizing ability of D. perlucidum by experimental use of artificial plates in a shellfish culture. The experiment comprised paired plates for colonization (bare and occupied) in 16 monthly replicates. Recruitment and space occupation were compared between bare and occupied plates and an estimation of reproductive effort was based on the number of larvae produced in each of ten colonies collected on the culture structures. D. perlucidum reproduced continuously but greatest reproduction occurred between December 2006 and May 2007. While recruitment was somewhat greater (number of new colonies) on bare plates, this species can colonize already occupied substrates and, surprisingly, colony area was always similar between treatments. Thus, while fewer colonies formed on occupied plates, once formed, colonies grew at rates similar to those on clean plates. Thus, D. perlucidum colonizes substrates very efficiently, especially when unoccupied space is available. Web of Science Didemnum perlucidum Brazil Santa Catarin Penh -26.463 -48.3634 Field - Experimental;Field - Observational marine Intertidal/Near Shore Invasion Hyp. Inherent Superiority Rapid Growth;High Reprod. Output 2298 Funk, Jennifer L.; Zachary, Virginia A. 2010 Physiological responses to short-term water and light stress in native and invasive plant species in southern California journal BIOLOGICAL INVASIONS 12 6 1685 1694 As climate variability increases in low-resource environments, the ability of native and invasive species to tolerate stress and respond to large, ephemeral resource pulses will strongly influence plant fitness and, consequently, competitive outcomes. We examined how native and invasive species occurring in arid coastal sage scrub communities in southern California responded to water and high-light stress. We also examined how plants responded to irrigation following short-term water stress. While species responded differently to water and light treatments, no general pattern emerged between native and invasive species. Photosynthetic function of Ricinus communis (invasive) and Salvia mellifera (native) was most robust to water stress and most responsive to irrigation following water stress. Leaf transpiration data suggested that Ricinus and Salvia maintained photosynthetic function by high water use efficiency rather than higher water status via large root biomass. Brassica nigra (invasive) and Encelia californica (native) were more resistant to photoinhibition in response to high-light stress than Ricinus, Salvia, Artemesia californica (native) or Nicotiana glauca (invasive). Our data suggest that native and invasive species in these arid systems display a range of physiological responses to stress and that strategies for invasive species control or native ecosystem restoration based on plant responses to stress may require species-specific approaches. Web of Science Many United States California Chapman University 37.300275 -117.773437 Greenhouse;Garden terrestrial Chaparral/Shrublands Invasion Hyp. Fluctuating Resources primary 2301 Roiloa, Sergio R.; Rodriguez-Echeverria, Susana; de la Pena, Eduardo; Freitas, Helena 2010 Physiological integration increases the survival and growth of the clonal invader Carpobrotus edulis journal BIOLOGICAL INVASIONS 12 6 1815 1823 Clonal growth seems to be a common trait for many of the most aggressive invasive plant species. However, little research has been conducted to determine the role of clonality in the successful invasion of new areas by exotic species. Carpobrotus edulis (L.) N.E. Br. is a mat-forming succulent plant, native to South Africa that is invasive in coastal dunes of Australia, New Zealand, USA and Southern Europe. Although Carpobrotus edulis is a clonal plant, there is no information on the role of clonality for the invasion by this species, therefore the objective of this study was to test whether or not physiological integration improves the performance of C. edulis invading coastal sand dunes. To do that, a 6-month field experiment was designed in which the stolon connections between the apical ramets and the C. edulis mats were severed to prevent physiological integration. This treatment was applied to ramets growing under high and low competition with the native species. Apical ramets with intact stolon connections were used as control. Integration improved the survivorship and growth of apical ramets, both in high and low competition. Connected ramets showed a more pronounced increase of clonal growth (estimated as stolon length) during the experimental period and a higher total biomass and number of ramets at the completion of the experiment. In terms of survivorship, the benefit of integration was greater under high competition. Physiological integration can therefore be considered an important factor in the invasiveness of C. edulis, both in open space and in direct competition with the native plants. Web of Science Carpobrotus edulis (L.) N.E. Br. Portugal Mata Nacional das Dunas de Quiaio 40.13 -8.53 Field - Experimental terrestrial Invasion Hyp. Inherent Superiority Clonal Reproduction primary 2302 Jesse, Laura C.; Nason, John D.; Obrycki, John J.; Moloney, Kirk A. 2010 Quantifying the levels of sexual reproduction and clonal spread in the invasive plant, Rosa multiflora journal BIOLOGICAL INVASIONS 12 6 1847 1854 Rosa multiflora Thunb., (Rosaceae), an invasive plant in the eastern U.S., was introduced into the U.S. in the early 1800s and was widely planted in the 1940s as a living fence, for wildlife cover, and to prevent soil erosion. This species spread rapidly from these original plantings via seed dispersal (sexual reproduction) and clonal spread, invading pasture and wooded areas. In this study we used allozyme markers to test for significant differences in the levels of asexual and sexual spread in large (> 9 m cirumference) verses small (< 2 m circumference) patches of R. multiflora and in pasture verses park settings. Although larger patches of R. multiflora tended to be dominated by one genotype, they exhibited significantly greater genetic diversity and inputs from sexual reproduction than did small patches; all large patches (N = 10) contained multiple unique genotypes. In contrast six of ten smaller patches of R. multiflora, consisted of a single genotype, though three patches had two genotypes and one had three unique genotypes. Similar analyses revealed clonal structure in R. multiflora populations both park and pasture habitats but with significantly greater genetic diversity and sexual inputs in the former than the latter. These results are consistent with a model of invasive spread involving clonal spread, sexual reproduction, and bird-mediated seed dispersal into established patches. Sexual inputs appear to be highest in larger patches and park habitats where perching sites for birds are most abundant. This flexible reproduction system likely contributes to the invasiveness of R. multiflora and to current management failures. Web of Science Rosa multiflora Thunb., (Rosaceae) United States Iowa Boone Co. and Story Co. 42.11 -93.11 Field - Observational terrestrial Invasion Hyp. Inherent Superiority High Reprod. Output;Effective Disperser;Clonal Reproduction 2303 Bradley, Bethany A.; Wilcove, David S.; Oppenheimer, Michael 2010 Climate change increases risk of plant invasion in the Eastern United States journal BIOLOGICAL INVASIONS 12 6 1855 1872 Invasive plant species threaten native ecosystems, natural resources, and managed lands worldwide. Climate change may increase risk from invasive plant species as favorable climate conditions allow invaders to expand into new ranges. Here, we use bioclimatic envelope modeling to assess current climatic habitat, or lands climatically suitable for invasion, for three of the most dominant and aggressive invasive plants in the southeast United States: kudzu (Pueraria lobata), privet (Ligustrum sinense; L. vulgare), and cogongrass (Imperata cylindrica). We define climatic habitat using both the Maxent and Mahalanobis distance methodologies, and we define the best climatic predictors based on variables that best 'constrain' species distributions and variables that 'release' the most land area if excluded. We then use an ensemble of 12 atmosphere-ocean general circulation models to project changes in climatic habitat for the three invasive species by 2100. The combined methodologies, predictors, and models produce a robust assessment of invasion risk inclusive of many of the approaches typically used individually to assess climate change impacts. Current invasion risk is widespread in southeastern states for all three species, although cogongrass invasion risk is more restricted to the Gulf Coast. Climate change is likely to enable all three species to greatly expand their ranges. Risk from privet and kudzu expands north into Ohio, Pennsylvania, New York, and New England states by 2100. Risk from cogongrass expands as far north as Kentucky and Virginia. Heightened surveillance and prompt eradication of small pockets of invasion in northern states should be a management priority. Web of Science kudzu (Pueraria lobata); privet (Ligustrum sinense; L. vulgare); cogongrass (Imperata cylindrica) United States Theoretical/Modeling terrestrial Invasion Hyp. Climate Change primary 2308 Radford, Ian J.; Dickinson, Katharine J. M.; Lord, Janice M. 2010 Does disturbance, competition or resource limitation underlie Hieracium lepidulum invasion in New Zealand? Mechanisms of establishment and persistence, and functional differentiation among invasive and native species journal AUSTRAL ECOLOGY 35 3 282 293 The processes underlying plant invasions have been the subject of much ecological research. Understanding mechanisms of plant invasions are difficult to elucidate from observations, yet are crucial for ecological management of invasions. Hieracium lepidulum, an asteraceous invader in New Zealand, is a species for which several explanatory mechanisms can be raised. Alternative mechanisms, including competitive dominance, disturbance of resident vegetation allowing competitive release or nutrient resource limitation reducing competition with the invader are raised to explain invasion. We tested these hypotheses in two field experiments which manipulated competitive, disturbance and nutrient environments in pre-invasion and post-invasion vegetation. H. lepidulum and resident responses to environmental treatments were measured to allow interpretation of underlying mechanisms of establishment and persistence. We found that H. lepidulum differed in functional response profile from native species. We also found that other exotic invaders at the sites were functionally different to H. lepidulum in their responses. These data support the hypothesis that different invaders use different invasion mechanisms from one another. These data also suggest that functional differentiation between invaders and native resident vegetation may be an important contributing factor allowing invasion. H. lepidulum appeared to have little direct competitive effect on post-invasion vegetation, suggesting that competition was not a dominant mechanism maintaining its persistence. There was weak support for disturbance allowing initial establishment of H. lepidulum in pre-invasion vegetation, but disturbance did not lead to invader dominance. Strong support for nutrient limitation of resident species was provided by the rapid competitive responses with added nutrients despite presence of H. lepidulum. Rapid competitive suppression of H. lepidulum once nutrient limitation was alleviated suggests that nutrient limitation may be an important process allowing the invader to dominate. Possible roles of historical site degradation and/or invader-induced soil chemical/microbial changes in nutrient availability are discussed. Web of Science Hieracium lepidulum New Zealand -44.26 168.39 Field - Experimental terrestrial Grassland Invasion Hyp. Inherent Superiority;Disturbance Superior Competitor primary 2311 Launey, Sophie; Brunet, Geraldine; Guyomard, Rene; Davaine, Patrick 2010 Role of Introduction History and Landscape in the Range Expansion of Brown Trout (Salmo trutta L.) in the Kerguelen Islands journal JOURNAL OF HEREDITY 101 3 270 283 Human-mediated biological invasions constitute interesting case studies to understand evolutionary processes, including the role of founder effects. Population expansion of newly introduced species can be highly dependant on barriers caused by landscape features, but identifying these barriers and their impact on genetic structure is a relatively recent concern in population genetics and ecology. Salmonid populations of the Kerguelen Islands archipelago are a favorable model system to address these questions as these populations are characterized by a simple history of introduction, little or no anthropogenic influence, and demographic monitoring since the first introductions. We analyzed genetic variation at 10 microsatellite loci in 19 populations of brown trout (Salmo trutta L.) in the Courbet Peninsula (Kerguelen Islands), where the species, introduced in 3 rivers only, has colonized the whole water system in 40 years. Despite a limited numbers of introductions, trout populations have maintained a genetic diversity comparable with what is found in hatchery or wild populations in Europe, but they are genetically structured. The main factor explaining the observed patterns of genetic diversity is the history of introductions, with each introduced population acting as a source for colonization of nearby rivers. Correlations between environmental and genetic parameters show that within each *source population* group, landscape characteristics (type of coast, accessibility of river mouth, distances between rivers, river length ...) play a role in shaping directions and rates of migration, and thus the genetic structure of the colonizing populations. Web of Science brown trout (Salmo trutta L.) French Southern and Antarctic Lands Kerguelen Archipelago -49.37 -69.5 Field - Observational;Lab lotic Invasion Hyp. Other omnivore 2312 Rodger, James G.; van Kleunen, Mark; Johnson, Steven D. 2010 DOES SPECIALIZED POLLINATION IMPEDE PLANT INVASIONS? journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 171 4 382 391 Generalized pollination systems and autonomous self-fertilization are traits that have been linked with plant invasiveness. However, whether specialized pollination requirements pose a significant barrier to plant invasions is not yet clear. Likewise, the contribution of pollinators to the fecundity of facultatively self-pollinating invasive plant species is poorly understood. We addressed these issues using the self-compatible and autonomously self-pollinating Lilium formosanum, which also has large, showy flowers that are adapted for pollination by hawk moths. We investigated the pollination of this lily-which is indigenous to Taiwan-in KwaZulu-Natal, South Africa, where it is invasive. The long-tongued hawk moth Agrius convolvuli was identified as the primary pollinator on the basis of field observations, pollen load analysis, presence of lepidopteran scales on stigmas, and higher seed production in emasculated flowers exposed at night than in those exposed during the day. Remarkably, this moth is native to much of the Old World, including Taiwan and South Africa. Autonomous self-pollination resulted in seed production, but at a reduced level relative to the seed production of open-and hand-pollinated flowers, which was significant in one out of two populations examined. Thus, pollinators potentially contribute to invasion by increasing seed production and genetic variability through cross-pollination, although contributions of pollinators to seed set versus that of autonomous self-pollination may vary between populations. We conclude that specialized pollination requirements do not present a barrier to invasions when plants are specialized to pollinators or pollinator functional groups with very wide distributions. Web of Science Lilium formosanum South Africa KwaZulu-Natal -30 30.5 Field - Observational terrestrial Grassland Invasion Hyp. Mutualism Facilitation primary 2313 Britton, J. R.; Cucherousset, J.; Davies, G. D.; Godard, M. J.; Copp, G. H. 2010 Non-native fishes and climate change: predicting species responses to warming temperatures in a temperate region journal FRESHWATER BIOLOGY 55 5 1130 1141 1. Temperate regions with fish communities dominated by cold-water species (physiological optima <20 degrees C) are vulnerable to the effects of warming temperatures caused by climate change, including displacement by non-native cool-water (physiological optima 20-28 degrees C) and warm-water fishes (physiological optima >28 degrees C) that are able to establish and invade as the thermal constraints on the expression of their life history traits diminish. 2. England and Wales is a temperate region into which at least 38 freshwater fishes have been introduced, although 14 of these are no longer present. Of the remaining 24 species, some have persisted but failed to establish, some have established populations without becoming invasive and some have become invasive. The aim of the study was to predict the responses of these 24 non-native fishes to the warming temperatures of England and Wales predicted under climate change in 2050. 3. The predictive use of climate-matching models and an air and water temperature regression model suggested that there are six non-native fishes currently persistent but not established in England and Wales whose establishment and subsequent invasion would benefit substantially from the predicted warming temperatures. These included the common carp Cyprinus carpio and European catfish Silurus glanis, fishes that also exert a relatively high propagule pressure through stocking to support angling and whose spatial distribution is currently increasing significantly, including in open systems. 4. The potential ecological impacts of the combined effects of warming temperatures, current spatial distribution and propagule pressure on the establishment and invasion of C. carpio and S. glanis were assessed. The ecological consequences of C. carpio invasion were assessed as potentially severe in England and Wales, with impacts likely to relate to habitat destruction, macrophyte loss and increased water turbidity. However, evidence of ecological impacts of S. glanis elsewhere in their introduced range was less clear and so their potential impacts in England and Wales remain uncertain. Web of Science Many England; Wales Statistical/Meta-analysis lentic Invasion Hyp. Climate Change 2314 Tucker, Andrew J.; Williamson, Craig E.; Rose, Kevin C.; Oris, James T.; Connelly, Sandra J.; Olson, Mark H.; Mitchell, David L. 2010 Ultraviolet radiation affects invasibility of lake ecosystems by warm-water fish journal ECOLOGY 91 3 882 890 Predicting where species invasions will occur remains a substantial challenge in ecology, but identifying factors that ultimately constrain the distribution of potential invaders could facilitate successful prediction. Whereas ultraviolet radiation (UVR) is recognized as an important factor controlling species distribution and community composition, the role of UVR in a habitat invasibility context has not been explored. Here we examine how underwater UVR can regulate warm-water fish invasion. In Lake Tahoe, California and Nevada. USA, established populations of exotic bluegill sunfish (Lepomis macrochirus) are currently limited to turbid, low-UVR embayments. An in situ incubation experiment that manipulated incident UVR exposure of larval bluegill, combined with an assessment of UVR exposure levels in nearshore habitats around Lake Tahoe, demonstrates that UVR can mediate habitat invasibility. Our findings suggest that the susceptibility to invasion by UVR sensitive species may increase in transparent aquatic systems threatened by declining water quality, and they highlight the importance of abiotic factors as regulators of invasion risk in ecosystems. Web of Science Lepomis macrochirus United States California; Nevada Lake Tahoe Lab lentic Invasion Hyp. Other predator 2317 Elena de Villalobos, Ana; Vazquez, Diego P.; Martin, Jean-Louis 2010 Soil disturbance, vegetation cover and the establishment of the exotic shrub Pyracantha coccinea in southern France journal BIOLOGICAL INVASIONS 12 5 1023 1029 We evaluate the mechanisms that determine the establishment of the non-indigenous shrub Pyracantha coccinea (Rosaceae) in the Montpellier region of southern France. P. coccinea establishes in abandoned agricultural fields in this region; yet, despite its high propagule pressure, it has not become a widespread invasive. We hypothesized that the disturbance conditions prevailing in abandoned agricultural fields right after abandonment may enhance the emergence, survival and growth of P. coccinea, but that shortly after abandonment colonizing vegetation prevents further establishment of this species. We conducted a field experiment to evaluate this hypothesis, studying the response of seedling emergence and growth of P. coccinea to soil and vegetation disturbance. Our results show that both lack of vegetation cover and soil disturbance promote the emergence of seedlings of P. coccinea. Thus, the disturbance conditions prevailing in abandoned agricultural fields seem crucial to allow establishment of this species. However, other factors such as lack of summer dormancy and seed predation might explain why this species has not become a widespread invasive. Web of Science Pyracantha coccinea France Montpellier 43.65 3.85 Field - Experimental terrestrial Old Field Invasion Hyp. Disturbance primary 2318 Davis, Naomi E.; Forsyth, David M.; Coulson, Graeme 2010 Facilitative interactions between an exotic mammal and native and exotic plants: hog deer (Axis porcinus) as seed dispersers in south-eastern Australia journal BIOLOGICAL INVASIONS 12 5 1079 1092 Endozoochory by exotic mammalian herbivores could modify vegetation composition by facilitating the dispersal and establishment of exotic and native plant species. We examined the potential for endozoochoric dispersal of native and exotic plants by exotic hog deer (Axis porcinus) in south-eastern Australia. We quantified the germinable seed content of hog deer faecal pellets collected in five vegetation types within a 10,500-ha study area that was representative of their Australian range. Twenty exotic and 22 native species germinated from hog deer faecal pellets and significantly more native species germinated compared to exotic species. Seedlings of the encroaching native shrub Acacia longifolia var. sophorae emerged, but no native trees emerged and the percentage of grasses that germinated was low (11%). The species composition of germinants was similar among the five vegetation types. We estimated that the hog deer population in our study area could potentially disperse > 130,000 viable seeds daily. Our study shows how an exotic mammal can disperse seeds from both native and invasive plants and highlights the need for endozoochory to be considered more widely in studies assessing the impacts of exotic mammals on plant communities. Web of Science Many Australia Victoria Wilsons Promontory National Park -38.8833;-39.0333 146.2333;146.3167 Field - Observational terrestrial Grassland;Deciduous Forest Invasion Hyp. Mutualism Facilitation primary;herbivore 2319 Kwong, King Lun; Dudgeon, David; Wong, Pak Ki; Qiu, Jian-Wen 2010 Secondary production and diet of an invasive snail in freshwater wetlands: implications for resource utilization and competition journal BIOLOGICAL INVASIONS 12 5 1153 1164 Invasive species can monopolize resources and thus dominate ecosystem production. In this study we estimated secondary production and diet of four populations of Pomacea canaliculata, a freshwater invasive snail, in wetlands (abandoned paddy, oxbow pond, drainage channel, and river meander) in monsoonal Hong Kong (lat. 22A degrees N). Apple snail secondary production (ash-free dry mass [AFDM]) ranged from 165.9 to 233.3 g m(-2) year(-1), and varied between seasons. Production was lower during the cool dry northeast monsoon, when water temperatures might have limited growth, but fast growth and recruitment of multiple cohorts were possible throughout much (7-10 months) of the year and especially during the warm, wet southwest monsoon. The diet, as revealed by stomach-content analysis, consisted mainly of detritus and macrophytes, and was broadly consistent among habitats despite considerable variation in the composition and cover of aquatic plants. Apple snail annual production was > 10 times greater than production estimates for other benthic macroinvertebrates in Hong Kong (range 0.004-15 g AFDM m(-2) year(-1), n = 29). Furthermore, annual production estimates for three apple snail populations (i.e. > 230 g AFDM m(-2) year(-1)) were greater than published estimates for any other freshwater snails (range 0.002-194 g AFDM m(-2) year(-1), n = 33), regardless of climatic regime or habitat type. High production by P. canaliculata in Hong Kong was attributable to the topical climate (annual mean similar to 24A degrees C), permitting rapid growth and repeated reproduction, together with dietary flexibility including an ability to consume a range of macrophytes. If invasive P. canaliculata can monopolize food resources, its high productivity indicates potential for competition with other macroinvertebrate primary consumers. Manipulative experiments will be needed to quantify these impacts on biodiversity and ecosystem function in wetlands, combined with management strategies to prevent further range extension by P. canaliculata. Web of Science Pomacea canaliculata China Hong Kong 22.5063;22.5151;22.4508;22.5056 114.0814;114.1226;114.1432;114.1112 Field - Observational Wetland Invasion Hyp. Inherent Superiority Rapid Growth;High Reprod. Output herbivore 2320 Song, Li-Ying; Li, Chang-Han; Peng, Shao-Lin 2010 Elevated CO2 increases energy-use efficiency of invasive Wedelia trilobata over its indigenous congener journal BIOLOGICAL INVASIONS 12 5 1221 1230 Increasing atmospheric CO2 concentration is regarded as an important factor facilitating plants invasions by stimulating invasive species growth. However, the physiological mechanisms by which invasive plants increase at the expense of existing native plants are poorly understood. Plant growth is always related to energy-use process including energy assimilation and expenditure, and thus examination of energetic properties could provide mechanistic insight into growth responses to increased CO2. The aims of this study were to examine the effect of rising CO2 on the growth and energetic properties of alien invasive species (Wedelia trilobata (L.) Hitchc.) and its native congener (Wedelia chinensis (Osbeck.) Merr.) in South China, and to determine if the specific energetic properties of invasive species at elevated CO2 favoring its growth. Elevated CO2 stimulated a greater increase in biomass production for invasive W. trilobata (58.9%) than for its indigenous congener (48.1%). Meanwhile, elevated CO2 altered the energetic properties differently upon species. For invasive W. trilobata, elevated CO2 significantly increased total energetic gain via photosynthetic activity (A (total)), but decreased energetic cost of biomass construction (CC), and thus enhanced photosynthetic energy-use efficiency (PEUE) by 85.3%. In contrast, the indigenous W. chinensis showed a slight increase in PEUE by 43.8%. Additionally, W. trilobata individuals grown in elevated CO2 increased energy allocation towards stems. Statistic analysis revealed significant associations between growth characteristics (relative growth rate and biomass) and energetic properties (CC and PEUE), suggesting the greater growth stimulation in invasive species could be partly explained by its specific energetic properties in elevated CO2 concentration. The invasive species showed a greater increase in energy-use efficiency under elevated CO2, which consequently facilitated its growth. It might be a physiological mechanism promoting success of invasion with ongoing increase in atmospheric CO2 concentration. Web of Science Wedelia trilobata China Guangzhou Lab terrestrial Invasion Hyp. Climate Change primary 2325 Otfinowski, Rafael; Kenkel, Norm C. 2010 Covariance between disturbance and soil resources dictates the invasibility of northern fescue prairies journal BIOLOGICAL INVASIONS 12 5 1349 1361 Increasing environmental impacts of exotic organisms have refocused attention on the ability of diverse communities to resist biological invaders. Although resource availability, often related to natural and anthropogenic disturbances, appears central to the invasibility of biological communities, understanding the links between resources, diversity and invasibility is often confounded by the covariance among key variables. To test the hypothesis that community invasibility remains contingent on the type and intensity of disturbance and their impacts on plant community diversity and resource availability, we designed an experiment testing the invasibility of northern fescue prairies by smooth brome (Bromus inermis Leyss.), a Eurasian perennial grass, threatening the structure and function of prairie remnants throughout the Great Plains. Using soil disturbances and herbicide, we imposed treatments manipulating the diversity and resource availability of native prairies. Our observations demonstrate that the vulnerability of native prairies to exotic plant invasions remains contingent on resources. While the establishment of smooth brome seedlings increased with increasing disturbance, its impact depended on the availability of soil nitrogen. As a result, soil burial treatments, simulating disturbance by northern pocket gophers, provided poor recruitment areas for smooth brome, and their low levels of soil moisture and nitrogen, combined with the rapid recovery of the prairie community, compromised seedling establishment. Emphasizing the covariance of diversity and key environmental variables following disturbance, our findings illustrate the importance of disturbance type and intensity on community invasibility. Such a consideration is critical in the conservation and restoration of native prairie remnants throughout the Great Plains. Web of Science Bromus inermis Canada Manitoba Riding Mountain National Park 50.771208 -100.228271 Field - Experimental terrestrial Grassland Invasion Hyp. Disturbance primary 2326 Williams, Peter A.; Kean, John M.; Buxton, Rowan P. 2010 Multiple factors determine the rate of increase of an invading non-native tree in New Zealand journal BIOLOGICAL INVASIONS 12 5 1377 1388 We reconstructed the invasion of a non-native tree (hawthorn, Crataegus monogyna) into fire-induced grassland in montane South Island, New Zealand. Using the relationship between height and age to reconstruct the rate of increase of the population, we identified three distinct invasion phases. We hypothesised that these related to the abundance of woody vegetation and therefore of non-native blackbirds (Turdus merula), the primary disperser of hawthorn in this environment. From the 1930s to 1959, increase was relatively slow, with hawthorn spread probably constrained due to browsing of seedlings by European rabbits (Oryctolagus cuniculus) and the low abundance of a native N-fixing shrub (matagouri, Discaria toumatou) providing few perches and nesting sites for blackbirds and safe sites for hawthorn establishment. Subsequently, from 1959 to 1976, hawthorn showed greater than six fold acceleration in its rate of population increase, resulting largely from intensive rabbit control, less frequent fires, and aerial topdressing of phosphate fertilizer promoting the growth of matagouri scrub. In addition, maturing hawthorn trees provided additional food and nesting sites for blackbirds. Hawthorn population increase slowed again from 1976, possibly because most suitable habitat in the immediate vicinity of the population neared saturation. From this case study we have constructed a general hypothesis for the factors determining the rate of invasion of matagouri-grassland habitats by bird-dispersed non-native woody plants in montane New Zealand. Web of Science Crataegus monogyna New Zealand South Island Field - Observational terrestrial Grassland;Chaparral/Shrublands Invasion Hyp. Mutualism Facilitation primary 2331 Elisa Ferreras, Ana; Galetto, Leonardo 2010 From seed production to seedling establishment: Important steps in an invasive process journal ACTA OECOLOGICA-INTERNATIONAL JOURNAL OF ECOLOGY 36 2 211 218 It is widely accepted that exotic invasive species are one of the most important ecological and economic problems. Reproductive and establishment traits are considered key features of a population expansion process, but few works have studied many of these simultaneously. This work examines how large the differences are in reproductive and establishment traits between two Fabaceae, the exotic invasive, Gleditsia triacanthos and the native, Acacia aroma. Gleditsia is a serious leguminous woody invader in various parts of the world and Acacia is a common native tree of Argentina. Both species have similar dispersal mechanisms and their reproductive phenology overlaps. We chose 17 plants of each species in a continuous forest of the Chaco Serrano Forest of Cordoba, Argentina. In each plant we measured fruit production, fruit removal (exclusion experiments), seed predation (pre- and post-dispersal), seed germination, seed bank (on each focal tree, three sampling periods during the year), and density of seedlings (around focal individuals and randomly in the study site). Gleditsia presented some traits that could favour the invasion process, such as a higher number of seeds per plant, percentage of scarified seed germination and density of seedlings around the focal individuals, than Acacia. On the other hand, Gleditsia presented a higher percentage of seed predation. The seed bank was persistent in both species and no differences were observed in fruit removal. This work highlights the importance of simultaneously studying reproductive and establishment variables involved in the spreading of an exotic invasive species. It also gives important insight into the variables to be considered when planning management strategies. The results are discussed from the perspective of some remarkable hypotheses on invasive species and may contribute to rethinking some aspects of the theory on invasive species. (C) 2010 Elsevier Masson SAS. All rights reserved. Web of Science Gleditsia triacanthos Argentina Cordoba Chaco Serrano Forest -31.7614 -64.4585 Field - Experimental;Field - Observational terrestrial Tropical Forest Invasion Hyp. Mutualism Facilitation;Inherent Superiority High Reprod. Output primary 2332 Ma Gonzalez-Rodriguez, Agueda; Baruch, Zdravko; Palomo, Debora; Cruz-Trujillo, Gilberto; Soledad Jimenez, Ma; Morales, Domingo 2010 Ecophysiology of the invader Pennisetum setaceum and three native grasses in the Canary Islands journal ACTA OECOLOGICA-INTERNATIONAL JOURNAL OF ECOLOGY 36 2 248 254 Pennisetum setaceum (fountain grass) is an aggressive invader in the arid and semi-arid habitats of the tropics and subtropics. In the last twenty years the spread of fountain grass in the Canary Islands has been very rapid. We compared its ecophysiological, architectural and reproductive traits with those of three native grasses (Hyparrhenia hirta, Cenchrus ciliaris and Aristida adscensionis) in two habitats of Tenerife Island which differ in rainfall. The detection of traits that differ between native and invader grasses may provide information for the improved control and eradication of the latter contributing to protect the native plant diversity. P. setaceum and the native grasses differed in all measured traits and in their response to water availability which is more restricted in the southern site. Specific leaf area was lower in P. setaceum than in the native grasses. Although this reduces carbon assimilation per unit area, it also reduces transpiration, increasing water use efficiency and contributes to the maintenance of high relative water content. Leaf N in P. setaceum was lower than in the native grasses indicating higher nitrogen use efficiency. The activity of photosystem II was higher and lasted longer in P. setaceum than in the native grasses. The ecophysiological traits of P. setaceum support its large size, extensive canopy and shorter leaf senescence period. They confer considerable competitive advantage to the invader and partially explain its success in the Canary Islands. The differences between the invader and the native grasses were maintained in both sites revealing a good adaptation of P. setaceum to the low resource local habitats in the Canary Islands and confirms its large plasticity. The large invasive potential of P. setaceum, in concert with the projected global changes, forecast eventual risks for the conservation of the endemic flora and remaining native communities in the Canary Islands. (C) 2010 Elsevier Masson SAS. All rights reserved. Web of Science Pennisetum setaceum Spain Canary Islands 28.3775;28.2431 16.8492;16.4053 Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority Superior Competitor primary 2334 Funk, Jennifer L.; Throop, Heather L. 2010 Enemy release and plant invasion: patterns of defensive traits and leaf damage in Hawaii journal OECOLOGIA 162 4 815 823 Invasive species may be released from consumption by their native herbivores in novel habitats and thereby experience higher fitness relative to native species. However, few studies have examined release from herbivory as a mechanism of invasion in oceanic island systems, which have experienced particularly high loss of native species due to the invasion of non-native animal and plant species. We surveyed putative defensive traits and leaf damage rates in 19 pairs of taxonomically related invasive and native species in Hawaii, representing a broad taxonomic diversity. Leaf damage by insects and pathogens was monitored in both wet and dry seasons. We found that native species had higher leaf damage rates than invasive species, but only during the dry season. However, damage rates across native and invasive species averaged only 2% of leaf area. Native species generally displayed high levels of structural defense (leaf toughness and leaf thickness, but not leaf trichome density) while native and invasive species displayed similar levels of chemical defenses (total phenolics). A defense index, which integrated all putative defense traits, was significantly higher for native species, suggesting that native species may allocate fewer resources to growth and reproduction than do invasive species. Thus, our data support the idea that invasive species allocate fewer resources to defense traits, allowing them to outperform native species through increased growth and reproduction. While strong impacts of herbivores on invasion are not supported by the low damage rates we observed on mature plants, population-level studies that monitor how herbivores influence recruitment, mortality, and competitive outcomes are needed to accurately address how herbivores influence invasion in Hawaii. Web of Science Many United States Hawaii Hawaii Field - Observational terrestrial Invasion Hyp. Enemy Release primary 2335 MacDonald, A. Andrew M.; Kotanen, Peter M. 2010 The effects of disturbance and enemy exclusion on performance of an invasive species, common ragweed, in its native range journal OECOLOGIA 162 4 977 986 Common ragweed (Ambrosia artemisiifolia) is an abundant weed in its native North America, despite supporting a wide range of natural enemies. Here, we tested whether these enemies have significant impacts on the performance of this plant in its native range. We excluded enemies from the three principal life-history stages (seed, seedling, and adult) of this annual in a series of field experiments; at the adult stage, we also manipulated soil disturbance and conspecific density. We then measured the consequences of these treatments for growth, survival, and reproduction. Excluding fungi and vertebrate granivores from seeds on the soil surface did not increase germination relative to control plots. Seedling survivorship was only slightly increased by the exclusion of molluscs and other herbivores. Insecticide reduced damage to leaves of adult plants, but did not improve growth or reproduction. Growth and survivorship of adults were strongly increased by disturbance, while higher conspecific density reduced performance in disturbed plots. These results indicate ragweed is insensitive to attack by many of its natural enemies, helping to explain its native-range success. In addition, they suggest that even though ragweed lost most of its insect folivores while invading Europe, escape from these enemies is unlikely to have provided a significant demographic advantage; instead, disturbance is likely to have been a much more important factor in its invasion. Escape from enemies should not be assumed to explain the success of exotic species unless improved performance also can be demonstrated; native-range studies can help achieve this goal. Web of Science Ambrosia artemisiifolia Canada Toronto Koffler Scientific Reserve Field - Experimental terrestrial Old Field Invasion Hyp. Enemy Release primary 2336 Schamp, Brandon S.; Aarssen, Lonnie W. 2010 The role of plant species size in invasibility: a field experiment journal OECOLOGIA 162 4 995 1004 Large plant species self-thin to disproportionately lower densities than smaller plant species, and therefore may leave more patches of unused space suitable for invasion. Using experimental monocultures of 11 old-field perennial plant species differing in maximum size, as well as mixtures composed of all monoculture species, we tested our primary hypothesis that monocultures of larger species will be more susceptible to natural invasion. After 3 years, monocultures of larger species were invaded by a significantly greater number of species, and more ramets, from the surrounding vegetation. Invading plant species were significantly smaller than the monoculture species being invaded, suggesting that smaller plant species may be better invaders. Thus, we quantified a trade-off between species size, which is frequently associated with increased competitive ability for light, and invasibility, suggesting one reason why large and small species coexist in virtually all plant communities. Although we expected that invasion would enhance biomass production by more fully capturing available resources, we found that the most highly invaded plots of each species produced significantly less biomass. This suggests that increased diversity resulting from invasion did not result in complementary resource use. Mixture plots containing all experimental species did not admit a significantly different number of invading ramets or species than most monocultures, indicating no obvious role for diversity in resistance to invasion, or complementary resource use. Our results suggest that relatively large species may be limited in their capacity to competitively exclude other, smaller species from communities because pure stands of the former are more susceptible to invasion by the latter. Web of Science Many Canada Ontario Queen's University Biology Station 44.5667 -76.3333 Field - Experimental terrestrial Old Field Invasion Hyp. Community Species Richness;Other primary 2337 Rao, Leela E.; Allen, Edith B. 2010 Combined effects of precipitation and nitrogen deposition on native and invasive winter annual production in California deserts journal OECOLOGIA 162 4 1035 1046 Primary production in deserts is limited by soil moisture and N availability, and thus is likely to be influenced by both anthropogenic N deposition and precipitation regimes altered as a consequence of climate change. Invasive annual grasses are particularly responsive to increases in N and water availabilities, which may result in competition with native forb communities. Additionally, conditions favoring increased invasive grass production in arid and semi-arid regions can increase fire risk, negatively impacting woody vegetation that is not adapted to fire. We conducted a seeded garden experiment and a 5-year field fertilization experiment to investigate how winter annual production is altered by increasing N supply under a range of water availabilities. The greatest production of invasive grasses and native forbs in the garden experiment occurred under the highest soil N (inorganic N after fertilization = 2.99 g m(-2)) and highest watering regime, indicating these species are limited by both water and N. A classification and regression tree (CART) analysis on the multi-year field fertilization study showed that winter annual biomass was primarily limited by November-December precipitation. Biomass exceeded the threshold capable of carrying fire when inorganic soil N availability was at least 3.2 g m(-2) in pion-juniper woodland. Due to water limitation in creosote bush scrub, biomass exceeded the fire threshold only under very wet conditions regardless of soil N status. The CART analyses also revealed that percent cover of invasive grasses and native forbs is primarily dependent on the timing and amount of precipitation and secondarily dependent on soil N and site-specific characteristics. In total, our results indicate that areas of high N deposition will be susceptible to grass invasion, particularly in wet years, potentially reducing native species cover and increasing the risk of fire. Web of Science Bromus madritensis United States California Mojave Desert; Sonoran Desert 34.89 -115.87 Field - Experimental terrestrial Invasion Hyp. Disturbance primary 2338 Allred, Brady W.; Fuhlendorf, Samuel D.; Monaco, Thomas A.; Will, Rodney E. 2010 Morphological and physiological traits in the success of the invasive plant Lespedeza cuneata journal BIOLOGICAL INVASIONS 12 4 739 749 To better understand the strategies and mechanisms of invading plants in tallgrass prairie, physiological and morphological characteristics of the invasive Lespedeza cuneata were compared to the dominant and abundant natives Ambrosia psilostachya and Andropogon gerardii. Gas exchange, chlorophyll fluorescence, plant water status, and total and specific leaf area were quantified in the field for each species both throughout daily sampling periods and across the growing season. Total and specific leaf area (cm(2) g(-1) of leaves) exceeded that of native species and may allow L. cuneata to successfully establish and dominate in tallgrass prairie, aiding in both resource acquisition and competitive exclusion. Gas exchange traits (e.g. net photosynthesis, stomatal conductance, and water use efficiency) of L. cuneata did not exceed other species, but remained constant throughout the daily sampling periods. The daily consistency of net photosynthesis and other gas exchange traits for L. cuneata reveal characteristics of stress tolerance. The combination of these characteristics and strategies may assist in the invasion of L. cuneata and also provide insight into general mechanisms responsible for successful invasions into tallgrass prairie. Web of Science Lespedeza cuneata United States Oklahoma Oklahoma State University Range Research Station 36.1168 -97.061462 Field - Observational terrestrial Grassland Invasion Hyp. Inherent Superiority Superior Competitor primary 2339 Marco, Audrey; Lavergne, Sebastien; Dutoit, Thierry; Bertaudiere-Montes, Valerie 2010 From the backyard to the backcountry: how ecological and biological traits explain the escape of garden plants into Mediterranean old fields journal BIOLOGICAL INVASIONS 12 4 761 779 To explain current ornamental plant invasions, or predict future ones, it is necessary to determine which factors increase the probability of an alien species becoming invasive. Here, we focused on the early phases of ornamental plant invasion in order to identify which plant features and cultivation practices may favor the escape of ornamental plants from domestic gardens to abandoned agricultural land sites in the Mediterranean Region. We used an original approach which consisted in visiting 120 private gardens in an urbanizing rural area of the French Mediterranean backcountry, and then visited surrounding old fields to determine which planted species had escaped out of the gardens. We built a database of 407 perennial ornamental alien species (most of which were animal-dispersed), and determined nineteen features that depicted the strength of species' propagule pressure within gardens, the match between species requirements and local physical environment, and each species' reproductive characteristics. Using standard and phylogenetic logistic regression, we found that ornamental alien plants were more likely to have escaped if they were planted in gardens' margins, if they had a preference for dry soil, were tolerant to high-pH or pH-indifferent, and if they showed a capacity for clonal growth. Focusing only on animal-dispersed plants, we found that alien plants were more likely to have escaped if they were abundant in gardens and showed preference for dry soil. This suggests that gardening practices have a primary impact on the probability of a species to escape from cultivation, along with species pre-adaptation to local soil conditions, and capacity of asexual reproduction. Our results may have important implications for the implementation of management practices and awareness campaigns in order to limit ornamental plants to becoming invasive species in Mediterranean landscapes. Web of Science Many France Mediterranean Region Field - Observational terrestrial Urban;Old Field Invasion Hyp. Inherent Superiority;Propagule Pressure Clonal Reproduction primary 2342 Mattingly, W. Brett; Swedo, Barbara L.; Reynolds, Heather L. 2010 Interactive effects of resource enrichment and resident diversity on invasion of native grassland by Lolium arundinaceum journal PLANT ECOLOGY 207 2 203 212 Resident diversity and resource enrichment are both recognized as potentially important determinants of community invasibility, but the effects of these biotic and abiotic factors on invasions are often investigated separately, and little work has been done to directly compare their relative effects or to examine their potential interactions. Here, we evaluate the individual and interactive effects of resident diversity and resource enrichment on plant community resistance to invasion. We factorially manipulated plant diversity and the enrichment of belowground (soil nitrogen) and aboveground (light) resources in low-fertility grassland communities invaded by Lolium arundinaceum, the most abundant invasive grass in eastern North America. Soil nitrogen enrichment enhanced L. arundinaceum performance, but increased resident diversity dampened this effect of nitrogen enrichment. Increased light availability (via clipping of aboveground vegetation) had a negligible effect on community invasibility. These results demonstrate that a community's susceptibility to invasion can be contingent upon the type of resource pulse and the diversity of resident species. In order to assess the generality of these results, future studies that test the effects of resident diversity and resource enrichment against a range of invasive species and in other environmental contexts (e.g., sites differing in soil fertility and light regimes) are needed. Such studies may help to resolve conflicting interpretations of the diversity-invasibility relationship and provide direction for management strategies. Web of Science Lolium arundinaceum United States Indiana Greenhouse terrestrial Grassland Invasion Hyp. Community Species Richness;Fluctuating Resources primary 2343 Droste, Tyler; Flory, S. Luke; Clay, Keith 2010 Variation for phenotypic plasticity among populations of an invasive exotic grass journal PLANT ECOLOGY 207 2 297 306 Phenotypic plasticity is a common feature of plant invaders, but little is known about variation in plasticity among invading populations. Variation in plasticity of ecologically important traits could facilitate the evolution of greater plasticity and invasiveness. We examined plasticity among invasive populations of Microstegium vimineum (Japanese stiltgrass), a widespread and often dominant grass of forests in the eastern U.S. with two separate experiments. First, we exposed seven Microstegium populations to a drought treatment in growth chambers and monitored growth and physiological responses. Then, we established a greenhouse experiment using a subset of the populations; two that exhibited the most divergent responses and one intermediate population. In the greenhouse, we manipulated drought and shade and evaluated biomass production and specific leaf area (SLA). Microstegium exhibited plasticity for biomass production and SLA in the greenhouse experiment, and populations significantly varied in the degree of plasticity under drought and shade treatments. Two populations significantly increased biomass production under favorable conditions, unlike the third population. The most productive populations also responded to shade stress via greater SLA, possibly allowing for greater utilization of available light, while the third population did not. These results show that Microstegium can exhibit plastic responses to environmental conditions. Moreover, variation for plasticity among populations provides the potential for further evolution of plasticity. Future studies should focus on the relative importance of plasticity for the success of Microstegium and other plant invaders and evaluate post-introduction evolution of plasticity. Web of Science Microstegium vimineum USA Indiana Many sites (see comments) Greenhouse;Lab terrestrial Deciduous Forest Invasion Hyp. Evolution of Increased Competitive Ability;Plasticity primary 2344 Jiang, Lin; Tan, Jiaqi; Pu, Zhichao 2010 An Experimental Test of Darwin's Naturalization Hypothesis journal AMERICAN NATURALIST 175 4 415 423 One of the oldest ideas in invasion biology, known as Darwin's naturalization hypothesis, suggests that introduced species are more successful in communities in which their close relatives are absent. We conducted the first experimental test of this hypothesis in laboratory bacterial communities varying in phylogenetic relatedness between resident and invading species with and without a protist bacterivore. As predicted, invasion success increased with phylogenetic distance between the invading and the resident bacterial species in both the presence and the absence of protistan bacterivory. The frequency of successful invader establishment was best explained by average phylogenetic distance between the invader and all resident species, possibly indicating limitation by the availability of the unexploited niche (i.e., organic substances in the medium capable of supporting the invader growth); invader abundance was best explained by phylogenetic distance between the invader and its nearest resident relative, possibly indicating limitation by the availability of the unexploited optimal niche (i.e., the subset of organic substances supporting the best invader growth). These results were largely driven by one resident bacterium ( a subspecies of Serratia marcescens) posting the strongest resistance to the alien bacterium ( another subspecies of S. marcescens). Overall, our findings support phylogenetic relatedness as a useful predictor of species invasion success. Web of Science Many United States New Jersey Lab Invasion Hyp. Empty Niche 2345 Thiele, Jan; Isermann, Maike; Otte, Annette; Kollmann, Johannes 2010 Competitive displacement or biotic resistance? Disentangling relationships between community diversity and invasion success of tall herbs and shrubs journal JOURNAL OF VEGETATION SCIENCE 21 2 213 220 Questions Are negative invasion-diversity relationships due to biotic resistance of the invaded plant community or to post-invasion displacement of less competitive species? Do invasion-diversity relationships change with habitat type or resident traits? Location/species Lowlands and uplands of western and southern Germany, Heracleum mantegazzianum; mountain range in central Germany, Lupinus polyphyllus; and coastal dunes of northwest Germany, Rosa rugosa. Methods We tested the significance and estimated regression slopes of invasion-diversity relationships using generalized linear (mixed effects) models relating invader cover and habitat type to species richness in different plant groups, stratified based on size, life cycle and community association. Results We found negative, positive and neutral relationships between invader cover and species richness. There were negative linear correlations of invader cover with small plant species throughout, but no negative linear correlation with tall species. Invasion-diversity relationships tended to be more negative in early-successional habitats, such as dunes or abandoned grasslands, than in late-successional habitats. Conclusions Invasion diversity-relationships are complex; they vary among habitat types and among different groups of resident species. Negative invasion-diversity relationships are due to asymmetric competitive displacement of inferior species and not due to biotic resistance. Small species are displaced in early-successional habitats, while there is little effect on persistence of tall species. Web of Science Heracleum mantegazzianum; Lupinus polyphyllus; Rosa rugosa Germany Field - Observational terrestrial Grassland Invasion Hyp. Inherent Superiority;Community Species Richness Superior Competitor primary 2349 Dyer, Andrew R.; Brown, Cynthia S.; Espeland, Erin K.; McKay, John K.; Meimberg, Harald; Rice, Kevin J. 2010 The role of adaptive trans-generational plasticity in biological invasions of plants journal EVOLUTIONARY APPLICATIONS 3 2 179 192 High-impact biological invasions often involve establishment and spread in disturbed, high-resource patches followed by establishment and spread in biotically or abiotically stressful areas. Evolutionary change may be required for the second phase of invasion (establishment and spread in stressful areas) to occur. When species have low genetic diversity and short selection history, within-generation phenotypic plasticity is often cited as the mechanism through which spread across multiple habitat types can occur. We show that trans-generational plasticity (TGP) can result in pre-adapted progeny that exhibit traits associated with increased fitness both in high-resource patches and in stressful conditions. In the invasive sedge, Cyperus esculentus, maternal plants growing in nutrient-poor patches can place disproportional number of propagules into nutrient-rich patches. Using the invasive annual grass, Aegilops triuncialis, we show that maternal response to soil conditions can confer greater stress tolerance in seedlings in the form of greater photosynthetic efficiency. We also show TGP for a phenological shift in a low resource environment that results in greater stress tolerance in progeny. These lines of evidence suggest that the maternal environment can have profound effects on offspring success and that TGP may play a significant role in some plant invasions. Web of Science Aegilops triuncialis United States California Davis Greenhouse;Garden terrestrial Chaparral/Shrublands Invasion Hyp. Plasticity primary 2355 Jacquemyn, Hans; Van Looy, Kris; Breyne, Peter; Honnay, Olivier 2010 The Meuse river as a corridor for range expansion of the exotic plant species Sisymbrium austriacum: evidence for long-distance seed dispersal journal BIOLOGICAL INVASIONS 12 3 553 561 Riparian habitats are particularly prone to invasion of non-indigenous plant species and several species have been shown to rapidly expand their range along river networks, possibly mediated by the occurrence of frequent long-distance seed dispersal events. However, there is still relatively little empirical evidence for long-distance seed dispersal along river networks and most studies to date are inconclusive with regards to the direction (upstream vs. downstream) of seed movement. Using assignment analyses based on dominant AFLP markers, we provide empirical evidence that downstream long-distance seed dispersal has facilitated range expansion of the exotic plant Sisymbrium austriacum along the Meuse River. Of 242 sampled individuals, 13 (5.4%) were allocated to a population other than the one from which it was sampled. Of these, nine (3.7%) individuals were assigned to a known population within the area, the furthest being more than 20 km away from the population from which it was sampled. All putative source populations were located upstream, thus providing strong evidence for downstream migration of propagules. These results support the general view that river systems may serve as efficient transport vectors of plant species and thus may play an important role in increasing the spatial spread and range expansion of exotic plant species. Web of Science Sisymbrium austriacum Belgium Meuse River 50.999119 5.766878 Field - Observational terrestrial Riparian Invasion Hyp. Other primary 2356 Masciocchi, Maite; Farji-Brener, Alejandro G.; Sackmann, Paula 2010 Competition for food between the exotic wasp Vespula germanica and the native ant assemblage of NW Patagonia: evidence of biotic resistance? journal BIOLOGICAL INVASIONS 12 3 625 631 The success of a biological invasion may depend on the interactions between the invader and the native biota. However, little experimental evidence demonstrates whether local species can successfully compete with exotics. We experimentally determined the existence of competition for food between the exotic wasp Vespula germanica, one of the most recent Patagonian invaders, and the native ant assemblage. Both wasps and ants are generalist predators and scavengers, sharing habitat and food resources. We selected 30 sites within scrubland habitats where both ants and wasps were present. At each site, we placed containers with protein baits under three treatments: wasp exclusion, ant exclusion, and control (i.e., free access for wasps and ants). Ant exclusion increased the number of wasps (with regard to a control), but wasp exclusion did not affect ant abundance. This result suggests that native ants affect the foraging activity of exotic wasps but not vice versa. Aggressive behaviors and worker aggregation may explain the competitive advantage of ants. Ants bite wasp legs and massively aggregate on food sources, physically limiting the landing of wasps on baits. If the outcome of interactions at baits reported here influence wasp population-level parameters, this competitive interaction could be one of the factors explaining the low abundance of this exotic wasp in NW Patagonia in comparison with other invaded regions. Web of Science Vespula germanica Argentina Patagonia Nahuel Huapi National Park -40.998298 -71.499023 Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Other omnivore 2357 Kleinbauer, I.; Dullinger, S.; Peterseil, J.; Essl, F. 2010 Climate change might drive the invasive tree Robinia pseudacacia into nature reserves and endangered habitats journal BIOLOGICAL CONSERVATION 143 2 382 390 Static networks of nature reserves disregard the dynamics of species ranges in changing environments. In fact, climate warming has been shown to potentially drive endangered species out of reserves. Less attention has been paid to the related problem that a warmer climate may also foster the invasion of alien species into reserve networks. Here, we use niche-based predictive modelling to assess to which extent the Austrian Natura 2000 network and a number of habitat types of conservation value outside this network might be prone to climate warming driven changes in invasion risk by Robinia pseudacacia L., one of the most problematic alien plants in Europe. Results suggest that the area potentially invaded by R. pseudacacia will increase considerably under a warmer climate. Interestingly, invasion risk will grow at a higher than average rate for most of the studied habitat types but less than the national average in Natura 2000 sites. This result points to a potential bias in legal protection towards high mountain areas which largely will remain too cold for R. pseudacacia. In contrast, the selected habitat types are more frequent in montane or lower lying regions, where R. pseudacacia invasion risk will increase most pronouncedly. We conclude that management plans of nature reserves should incorporate global warming driven changes in invasion risk in a more explicit manner. In case of R. pseudacacia, reducing propagule pressure by avoiding purposeful plantation in the neighbourhood of reserves and endangered habitats is a simple but crucial measure to prevent further invasion under a warmer climate. (C) 2009 Elsevier Ltd. All rights reserved. Web of Science Robinia pseudacacia Austria Theoretical/Modeling terrestrial Invasion Hyp. Climate Change primary 2358 Schlaepfer, Daniel R.; Glaettli, Melanie; Fischer, Markus; van Kleunen, Mark 2010 A multi-species experiment in their native range indicates pre-adaptation of invasive alien plant species journal NEW PHYTOLOGIST 185 4 1087 1099 P>To understand prerequisites of biological invasions, it is imperative to know whether species have traits that pre-adapt them to become invasive elsewhere. However, few experimental studies have explicitly tested this by comparing traits between invasive and noninvasive species in their native range instead of in the nonnative range. We used native plant material of 14 European congeneric pairs of herbaceous species that were all introduced to North America, and of which one species per pair is invasive. In our germination and common garden experiment with and without fertilizer addition, the invasive species germinated faster, produced more biomass and had a higher proportion of flowering plants than the noninvasive congeners. Our results indicate that species traits, which lead to a high plant performance in the native range, can confer pre-adaptation to become invasive. We suggest that such traits may be especially relevant for use in risk-assessment protocols before introduction elsewhere. Web of Science Many Switzerland Bern 46.9212 7.5024 Greenhouse terrestrial Invasion Hyp. Preadaptation to Climate primary 2359 Andrew, Margaret E.; Ustin, Susan L. 2009 Effects of microtopography and hydrology on phenology of an invasive herb journal ECOGRAPHY 32 5 860 870 Phenological traits may influence invasion success via effects on invasiveness of the colonizing species and invasibility of the receiving ecosystems. Many species exhibit substantial fine-scaled spatial variation in phenology and interannual differences in phenological timing in response to environmental variation. Yet describing and understanding this variation is limited by the availability of appropriate spatial and temporal datasets. Remote sensing provides such datasets, but has primarily been used to monitor broad-scale phenological patterns at coarse resolutions, necessarily missing fine spatial detail and intraspecies variation. We used hyperspectral remote sensing to characterize the spatial and temporal phenological variation of the invasive species Lepidium latifolium (perennial pepperweed) at two sites in California's San Francisco Bay/Sacramento-San Joaquin River Delta. Considerable phenological variation was detected: L. latifolium was simultaneously present in vegetative, early flowering, peak flowering, fruiting, and senescent stages in late June; the relative dominance and distribution of these stages varied interannually. Environmental determinants of phenology were investigated with variables derived from the hyperspectral image data, from a high resolution LiDAR (light detection and ranging) digital elevation model (DEM), and from local precipitation and streamflow data. Lepidium latifolium phenology was found to track water availability, and may also be influenced by intraspecific competition and edaphic stress. Lepidium latifolium has a unique phenology (summer flowering) relative to the communities it invades, which may allow invasion of an empty niche. Furthermore, many habitats are invaded by L. latifolium, which occurs in locally appropriate phenologies under the different environmental conditions. The environmental responsiveness of L. latifolium phenology may mediate the wide breadth of invasible habitats. Web of Science Lepidum latifolium United States California San Francisco Bay 38.208; 38.288 -122.028; 121.408 Field - Observational terrestrial Invasion Hyp. Empty Niche primary 2360 Garcia-de-Lomas, Juan; Cozar, Andres; Dana, Elias D.; Hernandez, Ignacio; Sanchez-Garcia, Inigo; Garcia, Carlos M. 2010 Invasiveness of Galenia pubescens (Aizoaceae): A new threat to Mediterranean-climate coastal ecosystems journal ACTA OECOLOGICA-INTERNATIONAL JOURNAL OF ECOLOGY 36 1 39 45 Blanket weed Galenia pubescens (Aizoaceae) is a prostrate perennial species native to South Africa. The naturalization in other Mediterranean-climate ecosystems has recently been noted in South-western Australia, California, and Southern Spain. In this paper, the invasiveness of C. pubescens was evaluated by testing a variety of stochastic and biological features and by studying the incipient impacts in two well-differentiated coastal ecosystems of Southern Spain- dunes and salty wetlands. Several features of G. pubescens were found as indicators of invasiveness: (i) the genus Galenia was not represented in native flora, and the majority of the species of the family (Aizoaceae) were alien or invasive; (ii) the growth type of G. pubescens (dense prostrate mats) was not found among the native species; (iii) resprouting ability, growth rates and seed production were within the range of well-known invaders Such as Carpobrotus spp and Mesembryanthemum crystallinum L; (iv) the overlapping in flowering periods (73-94%) with those of native flora and the effective shading (99%) of the G. pubescens mats were considerably high. A significant lower native richness and Shannon's diversity index was found in the invaded plant communities. These results demand the consideration of G. pubescens into the management plans of the Mediterranean-climate coastal ecosystems in order to prevent further dispersal and impacts. (C) 2009 Elsevier Masson SAS. All rights reserved. Web of Science Galenia pubescens Spain 36.45 -6.2333 Field - Observational terrestrial Wetland Invasion Hyp. Inherent Superiority;Community Species Richness High Reprod. Output primary 2362 Prevey, Janet S.; Germino, Matthew J.; Huntly, Nancy J.; Inouye, Richard S. 2010 Exotic plants increase and native plants decrease with loss of foundation species in sagebrush steppe journal PLANT ECOLOGY 207 1 39 51 Dominant plant species, or foundation species, are recognized to have a disproportionate control over resources in ecosystems, but few studies have evaluated their relationship to exotic invasions. Loss of foundation species could increase resource availability to the benefit of exotic plants, and could thereby facilitate invasion. The success of exotic plant invasions in sagebrush steppe was hypothesized to benefit from increased available soil water following removal of sagebrush (Artemisia tridentata), a foundation species. We examined the effects of sagebrush removal, with and without the extra soil water made available by exclusion of sagebrush, on abundance of exotic and native plants in the shrub steppe of southern Idaho, USA. We compared plant responses in three treatments: undisturbed sagebrush steppe; sagebrush removed; and sagebrush removed plus plots covered with *rainout* shelters that blocked winter-spring recharge of soil water. The third treatment allowed us to examine effects of sagebrush removal alone, without the associated increase in deep-soil water that is expected to accompany removal of sagebrush. Overall, exotic herbs (the grass Bromus tectorum and four forbs) were 3-4 times more abundant in shrub-removal and 2 times more abundant in shrub-removal + rainout-shelter treatments than in the control treatment, where sagebrush was undisturbed. Conversely, native forbs were only about half as abundant in shrub removal compared to control plots. These results indicate that removal of sagebrush facilitates invasion of exotic plants, and that increased soil water is one of the causes. Our findings suggest that sagebrush plays an important role in reducing invasions by exotic plants and maintaining native plant communities, in the cold desert we evaluated. Web of Science Many United States Idaho Barton Road Ecological Research Area 42.853 -112.402 Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Community Species Richness;Other primary 2364 Stevens, Jens T.; Beckage, Brian 2010 Fire Effects on Demography of the Invasive Shrub Brazilian Pepper (Schinus terebinthifolius) in Florida Pine Savannas journal NATURAL AREAS JOURNAL 30 1 53 63 Fire is a common disturbance in savanna ecosystems that may either facilitate or impede non-native plant invasions. Although fire can create recruitment opportunities for non-native plants, it can also prevent their invasion if it exerts strong negative effects on their demographic processes. Some savannas may, therefore, be able to resist invasion provided the natural, frequent-fire regime remains intact. We examined the effects of fire on the demography of the invasive shrub Brazilian pepper, Schinus terebinthifolius Raddi., which is invading fire-prone slash pine savannas of southern Florida. We studied survivorship, growth, and reproduction of low-density populations of Brazilian pepper in a pine savanna within Everglades National Park to investigate whether fire might suppress Brazilian pepper in the early stages of invasion. We found a significant decrease in Brazilian pepper survivorship following fire, particularly among small individuals. We further found that fire reduced fecundity of surviving Brazilian pepper individuals for at least two years. However, resprouting individuals that survived fire had high relative growth rates the following year, which could facilitate population recovery during inter-fire periods. We used a simple population simulation to show that a low-density cohort of Brazilian pepper may be rapidly eliminated from pine savannas with fire-return intervals of four years or less, but individuals may persist for > 50 years with fire-return intervals of eight years or more. Our study suggests the need to maintain the historical frequent-fire regime in pine savannas in order to prevent their invasion by fire-intolerant shrubs such as Brazilian pepper. Web of Science Schinus terebinthifolius United States Florida Everglades National Park 25.398 -80.644 Field - Observational terrestrial Savanna Invasion Hyp. Disturbance primary 2366 Panetta, F. Dane 2009 Seed persistence of the invasive aquatic plant, Gymnocoronis spilanthoides (Asteraceae) journal AUSTRALIAN JOURNAL OF BOTANY 57 8 670 674 Seed persistence of Gymnocoronis spilanthoides (D. Don) DC.; Asteraceae (Senegal tea), a serious weed of freshwater habitats, was examined in relation to burial status and different soil moisture regimes over a 3-year period. Seeds were found to be highly persistent, especially when buried. At the end of the experiment, 42.0%, 27.3% and 61.4% of buried seeds were viable following maintenance at field capacity, water logged and fluctuating (cycles of 1 week at field capacity followed by 3 weeks' drying down) soil moisture conditions, respectively. Comparable viability values for surface-situated seeds were similar to 3% over all soil moisture regimes. Predicted times to 1% viability are 16.2 years for buried seed and 3.8 years for surface-situated seed. Persistence was attributed primarily to the absence of light, a near-obligate requirement for germination in this species, although secondary dormancy was induced in some seeds. Previous work has demonstrated low fecundity in field populations of G. spilanthoides, which suggests that soil seed banks may not be particularly large. However, high levels of seed persistence, combined with ostensibly effective dispersal mechanisms, indicate that this weed may prove a difficult target for regional or state-wide eradication. Web of Science Gymnocoronis spilanthoides Australia Queensland -28.0022 152.0025 Garden lentic Invasion Hyp. Inherent Superiority High Reprod. Output primary 2367 Charles-Dominique, T.; Edelin, C.; Bouchard, A. 2010 Architectural strategies of Cornus sericea, a native but invasive shrub of Southern Quebec, Canada, under an open or a closed canopy journal ANNALS OF BOTANY 105 2 205 220 Qualitative and quantitative studies of the pattern of invasive plant development is considered a key aspect in understanding invasiveness. An architectural analysis was therefore performed in order to understand the relationship between shoot architecture and invasiveness in red-osier dogwood, Cornus sericea (Cornaceae). The structural and ontogenic characteristics of individuals in invading and non-invading populations in the native range of the species were compared to test the implication of developmental plasticity on invasiveness. The results show that the shrub has a modular architecture governed by strong developmental rules. Cornus sericea is made up of two levels of organization, each with its own intrinsic sequence of differentiation. These intrinsic mechanisms were used as a framework for comparison and it was found that, in response to the light environment, developmental plasticity was elevated, resulting in two architectural strategies. This developmental plasticity concerns the growth direction and the size of the modules, the speed of their time-course changes, their branching and flowering. Under an open canopy, C. sericea rapidly develops large vertical structures and abundant flowering. This strategy leads the plant to be invasive by excluding competitors and disseminating in the landscape. In the understorey, C. sericea slowly develops long horizontal structures which creep across the soil surface, while assimilating structures are poorly developed. This strategy does not lead to invasiveness but may allow the plant to survive in the understorey and reach sunny patches. Web of Science Cornus sericea Canada Quebec Montreal 45.0839;45.9844 -74.2525;-73.9858 Field - Observational terrestrial Invasion Hyp. Inherent Superiority;Plasticity Superior Competitor primary 2368 Blanchard, Megan L.; Barney, Jacob N.; Averill, Kristine M.; Mohler, Charles L.; DiTommaso, Antonio 2010 DOES POLYEMBRYONY CONFER A COMPETITIVE ADVANTAGE TO THE INVASIVE PERENNIAL VINE VINCETOXICUM ROSSICUM (APOCYNACEAE)? journal AMERICAN JOURNAL OF BOTANY 97 2 251 260 Determining which traits may allow some introduced plant species to become invasive in their new environment continues to be a key question in invasion biology. Vincetoxicum rossicum is an invasive, perennial vine colonizing natural and seminatural habitats primarily in the northeastern United States and southeastern Canada. More than half its seeds exhibit polyembryony, a relatively uncommon condition in which a single seed produces multiple seedlings. For evaluating the potential consequences of polyembryony on invasiveness, V. rossicum plants derived from seeds of three embryonic classes-singlets, doublets, and triplets (one, two, and three seedlings per seed, respectively)-were paired in all combinations intraspecifically and with the co-occurring native herbs Solidago canadensis and Asclepias syriaca in a greenhouse study. Vincetoxicum rossicum biomass was 25-55% greater and follicle production 55-100% greater under intraspecific competition compared with interspecific competition. However, within a competitive environment, follicle production varied little. Regardless of competitive environment, V. rossicum originating from seeds with a greater number of embryos typically performed no better than plants arising from seed with fewer embryos (singlets = doublets = triplets)-except intraspecifically where doublets outperformed singlets, and with S. canadensis where triplets outperformed singlets. Our findings suggest that overall performance and fitness of V. rossicum is higher in mono-cultures than in mixed stands and that its ability to invade new habitats may not be attributable to the production of polyembryonic seeds. Web of Science Vincetoxicum rossicum United States New York 42.7 -76.6 Greenhouse terrestrial Old Field Invasion Hyp. Inherent Superiority High Reprod. Output primary 2370 Mozdzer, Thomas J.; Zieman, Joseph C. 2010 Ecophysiological differences between genetic lineages facilitate the invasion of non-native Phragmites australis in North American Atlantic coast wetlands journal JOURNAL OF ECOLOGY 98 2 451 458 1. Over the last century, native Phragmites australis lineages have been almost completely replaced along the North American Atlantic coast by an aggressive lineage originating from Eurasia. Understanding the mechanisms that facilitate biological invasions is critical to better understand what makes an invasive species successful. 2. Our objective was to determine what makes the introduced lineage so successful in the study area by specifically investigating if morphological and ecophysiological differences exist between native and introduced genetic lineages of P. australis. We hypothesized a priori that due to phenotypic differences and differences in plant nitrogen (N) content between lineages, the introduced lineage would have a greater photosynthetic potential. 3. In situ ecophysiological and morphological data were collected for 2 years in a mid-Atlantic tidal marsh and in a glasshouse experiment. We measured photosynthetic parameters (A(max), water use efficiency, stomatal conductance) using infrared gas analysis, in conjunction with ecophysiological and morphological parameters [specific leaf area (SLA), leaf area, chlorophyll content, N content]. 4. Introduced P. australis maintained 51% greater rates of photosynthesis and up to 100% greater rates of stomatal conductance which are magnified by its 38-83% greater photosynthetic canopy compared to the native type. The introduced lineage also had a significantly greater SLA and N content. Glasshouse-grown plants and naturally occurring populations demonstrated similar trends in ecophysiological characteristics, verifying the heritability of these differences. These ecophysiological differences, when combined with an extended growing season, provide the mechanism to explain the success of introduced P. australis in North America. 5. Our findings suggest the native type is a low-nutrient specialist, with a more efficient photosynthetic mechanisms and lower N demand, whereas the introduced type requires nearly four times more N than the native type to be an effective competitor. 6. Synthesis. Our study is the first to combine field and laboratory data to explain a biological invasion attributed to ecophysiological differences between genetic lineages. Our data corroborates earlier work suggesting anthropogenic modification of wetland environments has provided the state change necessary for the success of introduced P. australis. Finally, our results suggest that genotypic differences within species merit further investigations, especially when related to biological invasions. Web of Science Phragmites australis United States Maryland; Virginia 38.0017;38.0011;37.0019 -75.0022;-75.0017;-75.0014 Field - Observational;Greenhouse terrestrial Wetland Invasion Hyp. Inherent Superiority;Disturbance Superior Competitor primary 2371 Willis, Charles G.; Ruhfel, Brad R.; Primack, Richard B.; Miller-Rushing, Abraham J.; Losos, Jonathan B.; Davis, Charles C. 2010 Favorable Climate Change Response Explains Non-Native Species' Success in Thoreau's Woods journal PLOS ONE 5 1 NA NA Invasive species have tremendous detrimental ecological and economic impacts. Climate change may exacerbate species invasions across communities if non-native species are better able to respond to climate changes than native species. Recent evidence indicates that species that respond to climate change by adjusting their phenology (i.e., the timing of seasonal activities, such as flowering) have historically increased in abundance. The extent to which non-native species success is similarly linked to a favorable climate change response, however, remains untested. We analyzed a dataset initiated by the conservationist Henry David Thoreau that documents the long-term phenological response of native and non-native plant species over the last 150 years from Concord, Massachusetts (USA). Our results demonstrate that non-native species, and invasive species in particular, have been far better able to respond to recent climate change by adjusting their flowering time. This demonstrates that climate change has likely played, and may continue to play, an important role in facilitating non-native species naturalization and invasion at the community level. Web of Science Many United States Massachusetts Concord 42.4606 -71.3483 Field - Observational terrestrial Invasion Hyp. Climate Change primary 2372 Vellend, Mark; Drummond, Emily B. M.; Tomimatsu, Hiroshi 2010 Effects of genotype identity and diversity on the invasiveness and invasibility of plant populations journal OECOLOGIA 162 2 371 381 Genetic diversity within species is a potentially important, but poorly studied, determinant of plant community dynamics. Here we report experiments testing the influence of genotype identity and genotypic diversity both on the invasibility of a foundation, matrix-forming species (Kentucky bluegrass, Poa pratensis), and on the invasiveness of a colonizing species (dandelion, Taraxacum officinale). Genotypes of Kentucky bluegrass in monoculture showed significant variation in productivity and resistance to dandelion invasion, but the productivity and invasion resistance of genotypic mixtures were not significantly different from those of genotypic monocultures. Indirect evidence suggested temporal shifts in the genotypic composition of mixtures. Dandelion genotypes in monoculture showed striking and significant variation in productivity and seed production, but there was no significant tendency for these variables in mixtures to deviate from null expectations based on monocultures. However, productivity and seed production of dandelion mixtures were consistently greater than those of the two least productive genotypes, and statistically indistinguishable from those of the three most productive genotypes, suggesting the possibility of greater invasiveness of genotypically diverse populations in the long run due to dominance by highly productive genotypes. In both experiments, the identity of genotypes was far more important than genetic diversity per se. Web of Science Taraxacum officinale Canada British Columbia Totem Field 49.256532 -123.250294 Garden terrestrial Grassland Invasion Hyp. Other primary 2373 Radford, Ian J.; Dickinson, Katharine J. M.; Lord, Janice M. 2009 Does the invader Hieracium lepidulum have a comparative growth advantage over co-occurring plants? High leaf area and low metabolic costs as invasive traits journal NEW ZEALAND JOURNAL OF BOTANY 47 4 395 403 High leaf area has been associated statistically with plant invasiveness, but few studies have quantified metabolic costs of this trait. We have little information on whether high leaf area provides a universal growth advantage or an advantage only under limited conditions. We ask, do invasive Hieracium lepidulum and co-occurring aliens in New Zealand have higher leaf area and lower metabolic tissue costs than co-occurring native species? Invasive and co-occurring plants were grown under standard conditions across a resource availability gradient and leaf area ratio (LAR) estimated. To quantify metabolic costs of above- and below-ground plant tissues, construction costs based on heat of combustion (W-G), plant ash, and nitrogen content (V-G) were measured. Leaf longevity was measured as an index of nutrient use and metabolic efficiency. Hieracium lepidulum and invaders overall did have higher LAR than co-occurring native plant species. Tissue construction costs overlapped among invaders and native species; however, unlike in native species, tissue construction costs in both invaders were reduced at lower nutrient resource levels. This suggests that there would not be a universal growth advantage for invaders, rather there would be more pronounced growth advantage at lower nutrient resource levels. This is discussed in terms of the ecological context within which H. lepidulum and its co-occurring species are found. Web of Science Hieracium lepidulum New Zealand Greenhouse terrestrial Grassland;Deciduous Forest;Old Field Invasion Hyp. Inherent Superiority Superior Competitor primary 2375 Catford, Jane A.; Downes, Barbara J. 2010 Using multi-scale species distribution data to infer drivers of biological invasion in riparian wetlands journal DIVERSITY AND DISTRIBUTIONS 16 1 20 32 Aim Biological invasion is a major conservation problem that is of interest to ecological science. Understanding mechanisms of invasion is a high priority, heightened by the management imperative of acting quickly after species introduction. While information about invading species' ecology is often unavailable, species distribution data can be collected near the onset of invasion. By examining distribution patterns of exotic and native plant species at multiple spatial scales, we aim to identify the scale (of those studied) that accounts for most variability in exotic species abundance, and infer likely drivers of invasion. Location River Murray wetlands, south-eastern Australia. Methods A nested, crossed survey design was used to determine the extent of variation in wetland plant abundance, grazing intensity and water depth at four spatial scales (reaches, wetland clumps, wetlands, wetland sections), and among three Depth-strata. We examined responses of exotic and native species groups (grouped into terrestrial and amphibious taxa), native weeds and 10 individual species using hierarchical ANOVA. Results As a group dominated by terrestrial taxa, exotic species cover varied at reach-, wetland- and section-scales. This likely reflects differences in abiotic characteristics and propagule pressure at these scales. Groups based on native species did not vary at any scale examined. Cover of 10 species mostly varied among and within wetlands (patterns unrelated to species' origin or functional group), but species' responses differed, despite individual plants being similar in size. While flora mostly varied among wetlands, exotic cover varied most among reaches (26%), which was attributed to hydrological modification and human activities. Main conclusions Multi-scale surveys can rapidly identify factors likely to affect species' distributions and can indicate where future research should be directed. By highlighting disproportionate variation in exotic cover among reaches, this study suggests that flow regulation and human-mediated dispersal facilitate exotic plant invasion in River Murray wetlands. Web of Science Many Australia New South Wales River Murray Field - Observational terrestrial Riparian Invasion Hyp. Propagule Pressure;Disturbance;Other primary 2377 Colautti, Robert I.; White, Neil A.; Barrett, Spencer C. H. 2010 VARIATION OF SELF-INCOMPATIBILITY WITHIN INVASIVE POPULATIONS OF PURPLE LOOSESTRIFE (LYTHRUM SALICARIA L.) FROM EASTERN NORTH AMERICA journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 171 2 158 166 Colonization may favor self-compatibility (SC) in invasive plants, a process consistent with Baker's law. We investigated this hypothesis in invasive eastern North American populations of tristylous Lythrum salicaria L. (purple loosestrife) by controlled self- and cross-pollinations of 124 plants sampled from 12 populations grown under uniform glasshouse conditions. We evaluated whether populations at the northern front of the invasion exhibited higher levels of SC than southern populations, which are closer to source populations for the North American invasion. We also sought evidence for morph-specific differences in the strength of trimorphic incompatibility. We used the ASTER statistical program to jointly model three measures of SC: (1) the probability of producing at least one seed following self- pollination, (2) the number of fruits produced by self-pollination, and (3) the average number of seeds per fruit resulting from self- pollination. Just over one-quarter of plants set at least one fruit after self- pollination, and there was a significant effect of style morph on variation in SC, with the mid-styled morph most compatible. Although variation for SC was detected in 11 of the 12 populations, there was no evidence that SC increased toward the northern range limit as a result of the invasion process. Web of Science Lythrum salicaria Canada Ontario Greenhouse terrestrial Invasion Hyp. Inherent Superiority Self Compatible primary 2378 Grosholz, E. 2010 Avoidance by grazers facilitates spread of an invasive hybrid plant journal ECOLOGY LETTERS 13 2 145 153 Biological invasions greatly increase the potential for hybridization among native and non-native species. Hybridization may influence the palatability of novel hybrids to consumers potentially influencing invasion success; however, the palatability of non-native hybrids relative to the parent species is poorly known. In contrast, studies of native-only hybrids find they are nearly always more palatable to consumers than the parent species. Here, I experimentally demonstrate that an invasive hybrid cordgrass (Spartina) is dramatically less palatable to grazing geese than the native parent species. Using field and aviary experiments, I show that grazing geese ignore the hybrid cordgrass and preferentially consume native Spartina. I also experimentally demonstrate that reduced herbivory of the invasive hybrid may contribute to faster spread in a California estuary. These results suggest that biological invasions may increase future opportunities for creating novel hybrids that may pose a greater risk to natural systems than the parent species. Web of Science Spartina alterniflora United States California San Francisco Bay 37.6708;37.6328;37.9065;37.9235 -122.0003;-122;-122.0026;-122.0004 Field - Observational estuarine Invasion Hyp. Enemy Release;Hybridization primary 2383 Nelis, Lisa Castillo; Wootton, J. Timothy 2010 Treatment-based Markov chain models clarify mechanisms of invasion in an invaded grassland community journal PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES 277 127 539 547 What are the relative roles of mechanisms underlying plant responses in grassland communities invaded by both plants and mammals? What type of community can we expect in the future given current or novel conditions? We address these questions by comparing Markov chain community models among treatments from a field experiment on invasive species on Robinson Crusoe Island, Chile. Because of seed dispersal, grazing and disturbance, we predicted that the exotic European rabbit (Oryctolagus cuniculus) facilitates epizoochorous exotic plants (plants with seeds that stick to the skin an animal) at the expense of native plants. To test our hypothesis, we crossed rabbit exclosure treatments with disturbance treatments, and sampled the plant community in permanent plots over 3 years. We then estimated Markov chain model transition probabilities and found significant differences among treatments. As hypothesized, this modelling revealed that exotic plants survive better in disturbed areas, while natives prefer no rabbits or disturbance. Surprisingly, rabbits negatively affect epizoochorous plants. Markov chain dynamics indicate that an overall replacement of native plants by exotic plants is underway. Using a treatment-based approach to multi-species Markov chain models allowed us to examine the changes in the importance of mechanisms in response to experimental impacts on communities. Web of Science Many Chile Robinson Crusoe Island -33.6167 -78.8833 Field - Experimental;Theoretical/Modeling terrestrial Grassland Invasion Hyp. Mutualism Facilitation primary;herbivore 2384 Peterson, A. Townsend; Stewart, Aimee; Mohamed, Kamal I.; Araujo, Miguel B. 2008 Shifting Global Invasive Potential of European Plants with Climate Change journal PLOS ONE 3 6 NA NA Global climate change and invasions by nonnative species rank among the top concerns for agents of biological loss in coming decades. Although each of these themes has seen considerable attention in the modeling and forecasting communities, their joint effects remain little explored and poorly understood. We developed ecological niche models for 1804 species from the European flora, which we projected globally to identify areas of potential distribution, both at present and across 4 scenarios of future (2055) climates. As expected from previous studies, projections based on the CGCM1 climate model were more extreme than those based on the HadCM3 model, and projections based on the a2 emissions scenario were more extreme than those based on the b2 emissions scenario. However, less expected were the highly nonlinear and contrasting projected changes in distributional areas among continents: increases in distributional potential in Europe often corresponded with decreases on other continents, and species seeing expanding potential on one continent often saw contracting potential on others. In conclusion, global climate change will have complex effects on invasive potential of plant species. The shifts and changes identified in this study suggest strongly that biological communities will see dramatic reorganizations in coming decades owing to shifting invasive potential by nonnative species. Web of Science Many Europe Theoretical/Modeling terrestrial Invasion Hyp. Climate Change primary 2386 Lortie, Christopher J.; Munshaw, Michael; Zikovitz, Andrea; Hierro, Jose 2009 Cage Matching: Head to Head Competition Experiments of an Invasive Plant Species from Different Regions as a Means to Test for Differentiation journal PLOS ONE 4 3 NA NA Many hypotheses are prevalent in the literature predicting why some plant species can become invasive. However, in some respects, we lack a standard approach to compare the breadth of various studies and differentiate between alternative explanations. Furthermore, most of these hypotheses rely on 'changes in density' of an introduced species to infer invasiveness. Here, we propose a simple method to screen invasive plant species for potential differences in density effects between novel regions. Studies of plant competition using density series are a fundamental tool applied to virtually every aspect of plant population ecology to better understand evolution. Hence, we use a simple density series with substitution contrasting the performance of Centaurea solstitialis in monoculture (from one region) to mixtures (seeds from two regions). All else being equal, if there is no difference between the introduced species in the two novel regions compared, Argentina and California, then there should be no competitive differences between intra and inter-regional competition series. Using a replicated regression design, seeds of each species were sown in the greenhouse at 5 densities in monoculture and mixed and grown till onset of flowering. Centaurea seeds from California had higher germination while seedlings had significantly greater survival than Argentina. There was no evidence for density dependence in any measure for the California region but negative density dependence was detected in the germination of seeds from Argentina. The relative differences in competition also differed between regions with no evidence of differential competitive effects of seeds from Argentina in mixture versus monoculture while seeds from California expressed a relative cost in germination and relative growth rate in mixtures with Argentina. In the former instance, lack of difference does not mean 'no ecological differences' but does suggest that local adaptation in competitive abilities has not occurred. Importantly, this method successfully detected differences in the response of an invasive species to changes in density between novel regions which suggests that it is a useful preliminary means to explore invasiveness. Web of Science Centaurea solstitialis Canada Ontario York University Greenhouse terrestrial Invasion Hyp. Evolution in General primary 2387 Naddafi, Rahmat; Eklov, Peter; Pettersson, Kurt 2009 Stoichiometric Constraints Do Not Limit Successful Invaders: Zebra Mussels in Swedish Lakes journal PLOS ONE 4 4 NA NA Background: Elemental imbalances of carbon (C): nitrogen (N): phosphorus (P) ratios in food resources can constrain the growth of grazers owning to tight coupling between growth rate, RNA allocation and biomass P content in animals. Testing for stoichiometric constraints among invasive species is a novel challenge in invasion ecology to unravel how a successful invader tackles ecological barriers in novel ecosystems. Methodology/Principal Findings: We examined the C:P and N:P ratios and the condition factor of a successful invader in lakes, the zebra mussel (Dreissena polymorpha), collected from two Swedish lakes. Concurrently, we analyzed the elemental composition of the food (seston) and tissue of the mussels in which nutrient composition of food and mussels varied over time. Zebra mussel condition factor was weakly related to the their own tissue N:P and C:P ratios, although the relation with the later ratio was not significant. Smaller mussels had relatively lower tissue N:P ratio and higher condition factor. There was no difference in C:P and N:P ratios between seston and mussels' tissues. Our results indicated that the variation in nutrient stoichiometry of zebra mussels can be explained by food quality and quantity. Conclusions/Significance: Our study suggests that fitness of invasive zebra mussels is not constrained by nutrient stoichiometry which is likely to be important for their proliferation in novel ecosystems. The lack of imbalance in C:P and N:P ratios between seston and mussels along with high tissue C:P ratio of the mussel allow them to tolerate potential P limitation and maintain high growth rate. Moreover, zebra mussels are able to change their tissue C:P and N:P ratios in response to the variation in elemental composition of their food. This can also help them to bypass potential nutrient stoichiometric constraints. Our finding is an important step towards understanding the mechanisms contributing to the success of exotic species from stoichiometric principles. Web of Science Dreissena polymorpha Sweden Field - Observational lentic Benthic Invasion Hyp. Inherent Superiority Broad Tolerances filter 2390 Hwang, Bernice C.; Lauenroth, William K. 2010 Effect of Nitrogen, Water and Neighbors on the Growth of Hesperis matronalis in a Natural Community journal AMERICAN MIDLAND NATURALIST 163 1 212 219 Disturbances may acid or remove resources from communities and can facilitate the spread of some invaders. Differential successes of exotic plants to spread into different communities suggest that some habitats are more invasible than others. Hesperis matronalis (dame's rocket) is widespread across the continent and has potential to become a major problem in natural communities owing to its ability to exploit excess resources and its negative effect on native species. We grew H. matronalis seedlings in a Colorado foothill community at various levels of nitrogen and water with and without neighbors. We expected H. matronalis to maximize its growth Under high resource conditions especially without. neighbors because ruderal species are able to take advantage of excess resources. Our results reveal that presence or absence of neighbors was the main decisive factor for H. matronalis (aboveground biomass and relative growth rate) success, though seedlings particularly suffered under low resource conditions. Early determination Of the potential invasiveness of a widespread exotic species such as H. matronalis in natural communities may promote effective management. Web of Science Hesperis matronalis United States Colorado 40.59 -105.35 Field - Experimental terrestrial Grassland Invasion Hyp. Fluctuating Resources;Disturbance primary 2391 Vaccaro, Lynn E.; Bedford, Barbara L.; Johnston, Carol A. 2009 LITTER ACCUMULATION PROMOTES DOMINANCE OF INVASIVE SPECIES OF CATTAILS (TYPHA SPP.) IN LAKE ONTARIO WETLANDS journal WETLANDS 29 3 1036 1048 Wetlands of the Great Lakes region are increasingly dominated by invasive cattails (Typha angustifolia and Typha X glauca) which form dense stands of live and dead biomass that may reduce plant diversity. We hypothesized that differences in plant litter accumulation explain cattail dominance under certain hydrologic regimes related to wetland hydrogeologic setting. We investigated cattail abundance, litter accumulation, and species density in three bayside wetlands hydrologically connected and three protected wetlands hydrologically isolated from Lake Ontario. Mean litter biomass was higher in bayside wetlands (1.7-2.6 vs. 0.4-1.2 kg/m(2)) and negatively related to species density (p = 0.004) in both settings. A litter addition experiment demonstrated that fallen litter negatively influenced seedling survival (p = 0.061) and species density (p = 0.024). Decomposition rates accounted only partially for higher overall litter accumulation in bayside wetlands. Growing season water levels in bayside wetlands tracked Lake Ontario levels and showed less variation than protected wetlands. More stable water levels and higher density of standing dead stems in bayside wetlands may limit litter fragmentation, resulting in greater litter accumulation. Thus, anthropogenic and natural factors affecting cattail litter production, fragmentation, and decomposition could influence species diversity in coastal wetlands. Web of Science Typha angustifolia; Typha x glauca United States New York Lake Ontario Field - Experimental;Field - Observational terrestrial Wetland Invasion Hyp. Other primary 2393 Werner, Christiane; Zumkier, Ulrich; Beyschlag, Wolfram; Maguas, Cristina 2010 High competitiveness of a resource demanding invasive acacia under low resource supply journal PLANT ECOLOGY 206 1 83 96 Mechanisms controlling the successful invasion of resource demanding species into low-resource environments are still poorly understood. Well-adapted native species are often considered superior competitors under stressful conditions. Here we investigate the competitive ability of the resource demanding alien Acacia longifolia, which invades nutrient-poor Mediterranean sand dunes such as in coastal areas of Portugal. We explore the hypothesis that drought may limit invasion in a factorial competition experiment of the alien invasive versus two native species of different functional groups (Halimium halimifolium, Pinus pinea), under well-watered and drought conditions. Changes in biomass, allocation pattern, and N-uptake-efficiency (via N-15-labeling) indicated a marked drought sensitivity of the invader. However, highly efficient drought adaptations of the native species did not provide a competitive advantage under water limiting conditions. The competitive strength of H. halimifolium towards the alien invader under well-watered conditions turned into a positive interaction between both species under drought. Further, low resource utilization by native species benefited A. longifolia by permitting continued high nitrogen uptake under drought. Hence, the N-fixing invader expresses low plasticity by continuous high resource utilization, even under low resource conditions. The introduction of novel traits into a community like N-fixation and high resource use may promote A. longifolia invasiveness through changes in the physical environment, i.e., the water and nutrient cycle of the invaded sand dune system, thereby potentially disrupting the co-evolved interactions within the native plant community. Web of Science Acacia longifolia Portugal University of Bielefeld 52.037709 8.494835 Greenhouse terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority;Fluctuating Resources Superior Competitor primary 2394 Lavergne, Sebastien; Muenke, Nikolas J.; Molofsky, Jane 2010 Genome size reduction can trigger rapid phenotypic evolution in invasive plants journal ANNALS OF BOTANY 105 1 109 116 The study of rapid evolution in invasive species has highlighted the fundamental role played by founder events, emergence of genetic novelties through recombination and rapid response to new selective pressures. However, whether rapid adaptation of introduced species can be driven by punctual changes in genome organization has received little attention. In plants, variation in genome size, i.e. variation in the amount of DNA per monoploid set of chromosomes through loss or gain of repeated DNA sequences, is known to influence a number of physiological, phenological and life-history features. The present study investigated whether change in genome size has contributed to the evolution of greater potential of vegetative growth in invasive populations of an introduced grass. The study was based on the recent demonstration that invasive genotypes of reed canarygrass (Phalaris arundinacea) occurring in North America have emerged from recombination between introduced European strains. The genome sizes of more than 200 invasive and native genotypes were measured and their genome size was related to their phenotypic traits measured in a common glasshouse environment. Population genetics data were used to infer phylogeographical relationships between study populations, and the evolutionary history of genome size within the study species was inferred. Invasive genotypes had a smaller genome than European native genotypes from which they are derived. This smaller genome size had phenotypic effects that increased the species' invasive potential, including a higher early growth rate, due to a negative relationship between genome size and rate of stem elongation. Based on inferred phylogeographical relationships of invasive and native populations, evolutionary models were consistent with a scenario of genome reduction by natural selection during the invasion process, rather than a scenario of stochastic change. Punctual reduction in genome size could cause rapid changes in key phenotypic traits that enhance invasive ability. Although the generality of genome size variation leading to phenotypic evolution and the specific genomic mechanisms involved are not known, change in genome size may constitute an important but previously under-appreciated mechanism of rapid evolutionary change that may promote evolutionary novelties over short time scales. Web of Science Phalaris arundinacea United States Vermont; North Carolina Greenhouse terrestrial Invasion Hyp. Evolution in General;Inherent Superiority Rapid Growth primary 2395 Tecco, Paula A.; Diaz, Sandra; Cabido, Marcelo; Urcelay, Carlos 2010 Functional traits of alien plants across contrasting climatic and land-use regimes: do aliens join the locals or try harder than them? journal JOURNAL OF ECOLOGY 98 1 17 27 P>1 Two main views have been put forward to explain whether coexisting alien and resident plant species should show converging or diverging functional attributes. According to the 'try-harder' hypothesis, successful aliens should differ from resident species with traits that allow them to deal better with the local conditions than resident species. On the other hand, the 'join-the-locals' hypothesis stresses the importance of filtering by environmental factors and predicts strong functional trait similarities between alien and native species, especially among the dominants. 2 On the basis of a functional trait comparison between native and alien species of central-western Argentina across five contrasting ecosystems and four land-use regimes, we tested these hypotheses over a broad range of habitats. We built a data set with common measurement methods and biogeographical factors but strongly varying environmental conditions, ranging from mesic to extremely dry, and from nearly pristine to heavily disturbed. 3 When considering all species together, the main trend of variation in trait syndromes was between acquisitive (tender, large leaves, with high specific area) and conservative (tough, small leaves, with low specific area and low nutrient content). Although both native and alien species appeared to be well spread across the whole range of trait variation, woody alien species showed a significantly more acquisitive set of attributes (higher specific leaf area, larger and thinner leaves, lower wood density) than native species. No significant difference was detected between herbaceous alien and native species. These general trends were maintained under contrasting climatic and land-use conditions. 4 Synthesis. The patterns detected for herbaceous species were in line with the 'join-the-locals' hypothesis. In contrast, those found for woody species, with woody alien species showing more acquisitive attributes than native species in more resource-rich habitats, provide partial support for the 'try-harder' hypothesis. Overall, our findings reinforce the idea that a universal suit of attributes is unlikely to explain alien plant distribution. They also stress the need for caution when mixing major life-forms in comparative plant trait analysis. Web of Science Many Argentina Field - Observational terrestrial Grassland;Deciduous Forest;Chaparral/Shrublands Invasion Hyp. Inherent Superiority;Other primary 2396 Blair, Amy C.; Hufbauer, Ruth A. 2010 Hybridization and invasion: one of North America's most devastating invasive plants shows evidence for a history of interspecific hybridization journal EVOLUTIONARY APPLICATIONS 3 1 40 51 Hybridization has been hypothesized to influence invasion through the generation of novel phenotypes and/or increased levels of genetic variance. Based on morphology, hybrids between diffuse knapweed and spotted knapweed, two invasive plants in North America, are present in the invaded range. Some individuals within most diffuse knapweed sites in North America exhibit intermediate diffuse x spotted floral morphology. We examined hybridization at the molecular level, using amplified fragment length polymorphisms. Approximately a quarter of the assayed North American diffuse knapweed individuals exhibited evidence of introgression from spotted knapweed. However, plants with intermediate morphology did not show evidence of mixed ancestry more often than the plants with typical diffuse knapweed morphology. The high proportion of hybrid individuals in North American diffuse knapweed sites found here, combined with evidence from recent studies, suggests that diffuse knapweed was likely introduced with admixed individuals, and the hybrids are not newly created postintroduction. A century of backcrossing with diffuse knapweed has likely decoupled the relationship between morphology and admixture at the molecular level. In contrast to the scenario encountered in North America, in the native range where diploid diffuse and spotted knapweed overlap, hybrid swarms are common. In such sites, the floral phenotype aligns more closely with the genotype. Web of Science Centaurea stoebe; Centaurea diffusa USA WA; OR; CO; WY 46.585;39.5047;45.9161;43.3853 -120.4592;-102.5503;-119.5586;-107.0625 Field - Observational terrestrial Invasion Hyp. Hybridization primary 2397 Ridley, Caroline E.; Ellstrand, Norman C. 2010 Rapid evolution of morphology and adaptive life history in the invasive California wild radish (Raphanus sativus) and the implications for management journal EVOLUTIONARY APPLICATIONS 3 1 64 76 Understanding the evolution and demography of invasive populations may be key for successful management. In this study, we test whether or not populations of the non-native, hybrid-derived California wild radish have regionally adapted to divergent climates over their 150-year history in California and determine if population demographic dynamics might warrant different region-specific strategies for control. Using a reciprocal transplant approach, we found evidence for genetically based differences both between and among northern, coastal and southern, inland populations of wild radish. Individual fitness was analyzed using a relatively new statistical method called 'aster modeling' which integrates temporally sequential fitness measurements. In their respective home environments, fitness differences strongly favored southern populations and only slightly favored northern populations. Demographic rates of transition and sensitivities also differed between regions of origin, suggesting that the most effective approach for reducing overall population growth rate would be to target different life-history stages in each region. Web of Science Raphanus sativus United States California 38.0367;33.9649 -122.963;-117.3454 Field - Experimental terrestrial Invasion Hyp. Evolution in General primary 2399 Hawkes, Christine V.; Douglas, Angela E.; Fitter, Alastair H. 2010 Origin, local experience, and the impact of biotic interactions on native and introduced Senecio species journal BIOLOGICAL INVASIONS 12 1 113 124 A key gap in understanding the long-term success of invasive species is how biotic interactions change with the duration of experience in the introduced range. We examined biotic interactions using a common garden experiment with native, hybrid, and exotic Senecio species representing a range of experience in the UK. Introduced species had fewer aphids and pathogens and more root colonization by mycorrhizal fungi compared to natives; hybrids generally had intermediate levels of interactions. The duration of experience in the introduced range was reflected by an increasing degree of variability in enemy release. These findings support the enemy release hypothesis and indicate the potential for changes in enemy release as time and experience in the new range increase. Web of Science Solidago vulgaris x squalidus; Solidago ciliocarpa; Solidago squalidus United Kingdom University of York Garden terrestrial Invasion Hyp. Enemy Release primary 2401 Lapointe, Brian E.; Bedford, Bradley J. 2010 Ecology and nutrition of invasive Caulerpa brachypus f. parvifolia blooms on coral reefs off southeast Florida, USA journal HARMFUL ALGAE 9 1 1 12 Coral reefs off southeast Florida have experienced an unprecedented succession of invasive chlorophyte blooms over the past two decades, most recently the non-native Caulerpa brachypus f. parvifolia. To better understand the ecology and nutrition of the C. brachypus invasion, we monitored benthic cover, water column dissolved inorganic nutrients, tissue C:N:P ratios and stable nitrogen isotopes (delta N-15) of C. brachypus and native chlorophytes (Caulerpa racemosa, Caulerpa verticillata, Caulerpa mexicana, Codium isthmocladum) quarterly at two reef sites - the Princess Anne (PA) and North Colonel's Ledge (NCL) - in 2003-2004. The PA site was influenced by stormwater discharges from the Lake Worth inlet whereas NCL was farther distant from these discharges. Between winter and spring of 2003, C. brachypus became the dominant benthic chlorophyte, expanding to >60% cover at both PA and NCL. Following cold temperatures (13 degrees C) associated with strong upwelling and high nitrate concentrations (21 mu M) at NCL in July 2003, C brachypus cover decreased, suggesting that upwelling can stress growth of this tropical alga. Mean ammonium (0.60 mu M), nitrate (2.7 mu M) and DIN (3.2 mu M) concentrations were high for coral reef environments. Low mean C:N ratios of similar to 13 in C. brachypus at both PA and NCL indicated little, if any, N-limitation compared to higher C:N ratios (up to 24) and greater N-limitation in native chlorophytes. Despite a relatively high mean SRP concentration (0.21 mu M), mean N:P ratios of similar to 39 in C. brachypus and other chlorophytes at PA and NCL suggested that these blooms were P-limited. Multiple lines of evidence support the hypothesis that land-based nutrient sources fueled the C. brachypus invasion. First, more persistent blooms of C brachypus at PA compared to NCL correlated with significantly lower tissue C:P and higher delta N-15 values (wet season) at PA, the site most directly influenced by land-based stormwater runoff. Second, C:N, C:P, and delta N-15 values of C. brachypus correlated with seasonal patterns of rainfall and stormwater runoff. Third, delta N-15 values of C. brachypus and other chlorophytes decreased at NCL following strong upwelling in July 2003, confirming that upwelled nitrate was not the cause of the elevated delta N-15 values observed in these blooms. Lastly, the mean delta N-15 values of C. brachypus and other chlorophytes off southeast Florida (+4.9 parts per thousand) were in the range of sewage nitrogen and significantly higher than values (+1.2 parts per thousand) for reference chlorophytes in the Abacos, Bahamas, an area that experiences relatively little sewage input. (C) 2009 Elsevier B.V. All rights reserved. Web of Science Caulerpa brachypus United States Florida Field - Observational marine Coral Reef Invasion Hyp. Disturbance primary 2402 Everard, Katherine; Seabloom, Eric W.; Harpole, W. Stanley; de Mazancourt, Claire 2010 Plant Water Use Affects Competition for Nitrogen: Why Drought Favors Invasive Species in California journal AMERICAN NATURALIST 175 1 85 97 Classic resource competition theory typically treats resource supply rates as independent; however, nutrient supplies can be affected by plants indirectly, with important consequences for model predictions. We demonstrate this general phenomenon by using a model in which competition for nitrogen is mediated by soil moisture, with competitive outcomes including coexistence and multiple stable states as well as competitive exclusion. In the model, soil moisture regulates nitrogen availability through soil moisture dependence of microbial processes, leaching, and plant uptake. By affecting water availability, plants also indirectly affect nitrogen availability and may therefore alter the competitive outcome. Exotic annual species from the Mediterranean have displaced much of the native perennial grasses in California. Nitrogen and water have been shown to be potentially limiting in this system. We parameterize the model for a Californian grassland and show that soil moisture-mediated competition for nitrogen can explain the annual species' dominance in drier areas, with coexistence expected in wetter regions. These results are concordant with larger biogeographic patterns of grassland invasion in the Pacific states of the United States, in which annual grasses have invaded most of the hot, dry grasslands in California but perennial grasses dominate the moister prairies of northern California, Oregon, and Washington. Web of Science Many United States California Theoretical/Modeling terrestrial Grassland Invasion Hyp. Preadaptation to Climate primary 2403 Cherwin, Karie L.; Seastedt, Timothy R.; Suding, Katharine N. 2009 Effects of Nutrient Manipulations and Grass Removal on Cover, Species Composition, and Invasibility of a Novel Grassland in Colorado journal RESTORATION ECOLOGY 17 6 818 826 Cover and richness of a 5-year revegetation effort were studied with ,respect to small-scale disturbance and nutrient manipulations. The site, originally a relict tallgrass prairie mined for gravel, was replanted to native grasses using a seed mixture of tall-, mixed-, and short-grass species. Following one wet and three relatively dry years, a community emerged, dominated by species common in saline soils not found along the Colorado Front Range. A single species, Alkali sacaton (Sporobolus airoides), composed nearly 50% of relative vegetation cover in control plots exhibiting a negative relationship between cover and richness. Seeded species composed approximately 92% of vegetation cover. The remaining 8% was composed of weeds from nearby areas, seed bank survivors, or mix contaminants. Three years of soil nutrient amendments, which lowered plant-available nitrogen and phosphorus, significantly increased relative cover of seeded species to 97.5%. Fertilizer additions of phosphate enhanced abundance of introduced annual grasses (Bromus spp.) but did not significantly alter cover in control plots. Unmanipulated 4-m2 plots contained an average of 4.7 planted species and 3.9 nonplanted species during the 5-year period, whereas plots that received grass herbicide averaged 5.4 nonplanted species. Species richness ranged from an average 6.9 species in low-nutrient, undisturbed plots to 10.9 species in the relatively high-nutrient, disturbed plots. The use of stockpiled soils, applied sparingly, in conjunction with a native seed mix containing species uncommon to the preexisting community generated a species-depauperate, novel plant community that appears resistant to invasion by ruderal species. Web of Science Bromus spp. United States Colorado 39.9167 -105.2 Field - Experimental terrestrial Grassland Invasion Hyp. Disturbance primary 2407 Fleming, Genie M.; Diffendorfer, James E.; Zedler, Paul H. 2009 The relative importance of disturbance and exotic-plant abundance in California coastal sage scrub journal ECOLOGICAL APPLICATIONS 19 8 2210 2227 Many ecosystems of conservation concern require some level of disturbance to sustain their species composition and ecological function. However, inappropriate disturbance regimes could favor invasion or expansion of exotic species. In southern California coastal sage scrub (CSS). re is a natural disturbance, but because of human influence, frequencies may now be unnaturally high. Other anthropogenic disturbances such as grazing also occur in reserve areas. Managers charged with imposing or tolerating. re or other disturbance within their reserves are concerned that habitat quality may be degraded by an increasing abundance of exotic plants. We used vegetation monitoring data from Camp Pendleton, California, USA, to assess the correlation between past disturbances (frequent. re, agriculture, or grazing and mechanical disturbances) and current exotic species abundance in CSS. We found that disturbance history was only modestly related to exotic abundance overall, but. re frequency showed the strongest association. We also examined whether cover and richness of various native plant life forms (woody species, perennial herbs, and annual herbs) were more strongly influenced by disturbance history or by exotic-plant abundance. Native plant responses varied among life forms, but woody species and annual herbs were generally more strongly and negatively associated with exotic abundance than with disturbance. Effective CSS conservation will require developing means to curb the negative impacts of exotic plants, which may abound with or without severe or recent disturbance. Additionally, more focus should be given to understory herbs showing sensitivity to invasion. Though understudied, native herbs comprise the greatest portion of plant diversity in CSS and are critical to preservation of the community as a whole. Web of Science Many United States California 33.308151 -117.315788 Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Disturbance primary 2408 Lonati, Michele; Gorlier, Alessandra; Ascoli, Davide; Marzano, Raffaella; Lombardi, Giampiero 2009 Response of the alien species Panicum acuminatum to disturbance in an Italian lowland heathland journal BOTANICA HELVETICA 119 2 105 111 The spread of exotic plants represents a new challenge for conservation management since practices commonly used to maintain semi-natural, open vegetation may promote the establishment of plant invaders. Panicum acuminatum Swartz is a perennial grass native to America that was naturalized in southern European heathlands. The effect of conservation management on the spread of this invasive species was studied in a heathland in NW Italy along an experimental disturbance gradient created by mowing, grazing, prescribed fire or various combinations of these treatments. Across treatments, the abundance of Panicum acuminatum was negatively correlated with the total abundance of the two dominant native species, Calluna vulgaris and Molinia arundinacea. The abundance of P. acuminatum differed significantly among treatments depending on the intensity and frequency of disturbance (phytomass removal). Thus, its abundance was highest in the repeated fire treatments as well as in the combined fire + grazing and fire + mowing treatments. Following these results, low-severity practices (grazing, mowing, occasional fire) seem most suitable to both reduce tree encroachment and control P. acuminatum spread. Web of Science Panicum acuminatum Italy Managed Nature Reserve Vauda 45.2203 7.6881 Field - Experimental terrestrial Grassland Invasion Hyp. Disturbance primary 2410 Yu, Fei-Hai; Wang, Ning; Alpert, Peter; He, Wei-Ming; Dong, Ming 2009 PHYSIOLOGICAL INTEGRATION IN AN INTRODUCED, INVASIVE PLANT INCREASES ITS SPREAD INTO EXPERIMENTAL COMMUNITIES AND MODIFIES THEIR STRUCTURE journal AMERICAN JOURNAL OF BOTANY 96 11 1983 1989 What determines the invasiveness of introduced plants is still poorly known. Many of the most invasive plant species are clonal, and physiological integration between connected individuals (ramets) of clonal plants may contribute to their ability to spread into communities and reduce performance of existing species. This contribution of integration to the invasiveness of clonal plants may be greater in denser communities. A greenhouse study was conducted to test these two hypotheses. High- and low-density communities were created by sowing seeds of eight grassland species. Each community was planted with three ramets of the stoloniferous, introduced plant Alternanthera philoxeroides that were disconnected from or left connected to ramets growing on bare soil. Connection increased the spread of Alternanthera within a community, but did not reduce community biomass. Alternanthera grew less in high-density communities, but connection did not improve its growth more than in low-density communities. Low-density Communities had higher evenness when Alternanthera was connected than when it was disconnected because shoot mass was lower in the more abundant species in the community and higher in the less abundant ones. These results partly supported the first hypothesis, but not the second. The effect of integration on community Structure could be due to higher resource import by the ramets of Alternanthera closer to the dominant species. Integration therefore can increase the initial spread of new clonal plant species into communities and modify the effects of this spread on Community structure. Web of Science Alternanthera philoxeroides Greenhouse terrestrial Grassland Invasion Hyp. Inherent Superiority Clonal Reproduction primary 2412 Densmore, Roseann V. 2008 Evidence for Higher Soil Temperature and Potassium Promoting Invasion of the Common Dandelion, Taraxacum officinale, in Denali National Park and Preserve, Alaska journal CANADIAN FIELD-NATURALIST 122 1 67 69 Common Dandelion, Taraxacum officinale ssp officinale (dandelion) is expanding its range in Alaska and is of particular Concern in National Park Service units This study investigated the influence of estimated soil temperature, available potassium (K) available phosphorous (P). and total nitrogen (N) on dandelion cover and density on a site near the elevational limit of dandelion. The study site in Denali National Park had been disturbed by construction and was revegetated with native plants 12 years before the study. Seed input to the study site was abundant. In a multiple regression analysis, higher levels of estimated soil temperature and available K accounted for 79% and 73% of the variation in dandelion cover and density. respectively. Practical control methods include not fertilizing disturbed areas with K and countering continued expansion of dandelion by monitoring human use areas and undisturbed habitats where soil temperatures are likely to be relatively warm. Web of Science Taraxacum officinale USA Alaska Denali National Park 63.636504 -150.611572 Field - Observational terrestrial Tundra Invasion Hyp. Empty Niche primary 2414 Bacigalupe, Leonardo D. 2009 Biological invasions and phenotypic evolution: a quantitative genetic perspective journal BIOLOGICAL INVASIONS 11 10 2243 2250 Among the many different components of global environmental change, biological invasions represent the one with the most long-term ecological and evolutionary consequences, as effects are irreversible. Although the ecological impact of invasive species has been under great scrutiny, its evolutionary aspects and consequences have remained less explored. Once established, an important part of the success of an invasive species will depend on the presence of genetic variation in populations at the geographic boundaries upon which natural selection can act. This information is integrated in G, the matrix of additive genetic variances and covariances for a suite of traits. The G-matrix shows the restrictions and potentialities of adaptive evolution and, together with natural selection determine the direction and rate of phenotypic evolution. Here I propose that a geographic analysis of G in populations of the introduced and native range becomes essential to understand critical evolutionary issues associated with invasion success. Web of Science Many Theoretical/Modeling Invasion Hyp. Evolution in General 2415 Mosher, Eric S.; Silander, John A., Jr.; Latimer, Andrew M. 2009 The role of land-use history in major invasions by woody plant species in the northeastern North American landscape journal BIOLOGICAL INVASIONS 11 10 2317 2328 Land-use history as a predictor of invasive alien plant distributions has received little study, especially across large spatial and temporal scales. Here we evaluate the importance of land-use history and other environmental characteristics as predictors of the distributions of a suite important invasive woody plant species in the northeastern United States. Using historical aerial photographs, we delineated 69 years (1934-2003) of land-use change across a typically heterogeneous 95 km(2) landscape. We randomly surveyed over 500 sites for six invasive plant species. We found that land use history patterns strongly affected presence and abundance of the invasive plants as a group, but affected some species more than others. Generally, past agricultural use favored invasive species, whereas intact forest blocks discouraged them. Current land-use trends toward residential/commercial development favor disturbance-adapted species like Celastrus orbiculatus (asiatic bittersweet) and will probably slow the spread of post-agricultural specialists such as Berberis thunbergii (Japanese barberry). Web of Science Celastrus orbiculatus;Berberis thunbergii;Elaeagnus umbellata;Euonymus alata;Lonicera morrowii;Rosa multiflora U.S.A. Connecticut Meshomasic State Forest 41.626461 -72.536087 Field - Observational terrestrial Deciduous Forest;Urban;Old Field Invasion Hyp. Disturbance primary 2419 Pysek, Petr; Jarosik, Vojtech; Pergl, Jan; Randall, Rod; Chytry, Milan; Kuehn, Ingolf; Tichy, Lubomir; Danihelka, Jiri; Chrtek, Jindrich Jun; Sadlo, Jiri 2009 The global invasion success of Central European plants is related to distribution characteristics in their native range and species traits journal DIVERSITY AND DISTRIBUTIONS 15 5 891 903 Aim Determining which traits predispose a species to become invasive is a fundamental question of invasion ecology, but traits affect invasiveness in concert with other factors that need to be controlled for. Here, we explore the relative effects of biological traits of plant species and their distributional characteristics in the native range on invasion success at two stages of invasion. Location Czech Republic (for native species); and the world (for alien species). Methods The source pool of 1218 species of seed plants native to Central Europe was derived from the flora of the Czech Republic, and their occurrence in 706 alien floras all over the world was recorded, distinguishing whether they were listed as an 'alien' or a 'weed' in the latest version of Randall's 'Global compendium of weeds' database. The latter type of occurrence was considered to indicate species ability to invade and cause economic impact, i.e. a more advanced stage of invasion. Using the statistical technique of regression trees, we tested whether 19 biological traits and five distributional characteristics of the species in their native range can be used to predict species success in two stages of invasion. Results The probability of a species becoming alien outside its native distribution range is determined by the size of its native range, and its tolerance of a wide range of climates acquired in the region of origin. Biological traits play only an indirect role at this stage of invasion via determining the size of the native range. However, the ability of species to become a weed is determined not only by the above characteristics of native distribution, but also directly by biological traits (life form and strategy, early flowering, tall stature, generative reproduction, number of ploidy levels and opportunistic dispersal by a number of vectors). Species phylogenetic relatedness plays only a minor role; it is more important at the lowest taxonomic levels and at the later stage of invasion. Main conclusion The global success of Central European species as 'weeds' is determined by their distributional characteristics in the native ranges and by biological traits, but the relative importance of these determinants depends on the stage of invasion. Species which have large native ranges and are common within these ranges should be paid increased attention upon introductions, and the above biological traits should be taken into account in screening systems applied to evaluate deliberate introductions of alien plants to new regions. Web of Science Many Global Statistical/Meta-analysis terrestrial Invasion Hyp. Inherent Superiority;Propagule Pressure;Other Superior Competitor;Broad Tolerances;Effective Disperser primary 2420 Sullivan, Jon J.; Williams, Peter A.; Timmins, Susan M.; Smale, Mark C. 2009 Distribution and spread of environmental weeds along New Zealand roadsides journal NEW ZEALAND JOURNAL OF ECOLOGY 33 2 190 204 Most non-native weeds and other naturalised plants are in the early stages of invasion into New Zealand landscapes. For this invasion to be controlled, even partially, it is important to understand the dominant routes, mechanisms, and rates of weed spread across landscapes. With their linear corridors of disturbed habitats, roadsides are thought to play a large role in the spread of some weeds. We used both new surveys and existing data to assess which of the 328 environmental weeds listed by the Department of Conservation are most frequently found on roadsides, where, and whether distribution patterns are consistent with linear dispersal. We also analysed historical survey data for relationships between reserve weediness and proximity to roads. We surveyed 340 plots of 100-m-long stretches of roadside across four regions and found between 2 and 19 environmental weeds per plot; 128 species in total (Chao estimate 148). Especially abundant were agricultural species (weeds and cultivated), species that have been naturalised for well over 50 years, and species that disperse externally attached to vertebrates. While we purposefully sampled within 10 km of town limits, we found no strong effect of distance from town on roadside weed richness, including richness of just ornamentally sourced weeds. Instead, number of houses within 250 m and presence of an adjacent house or other residential structure were both important, as was presence of woody vegetation on and adjacent to roadsides. Reserves adjacent to roads had significantly higher weed richness than reserves further from roads, although the causal mechanisms are unclear. Our results suggest that while roadsides include suitable habitats for most environmental weeds, distributions are patchy and roads show little sign of acting as linear dispersal corridors, instead largely reflecting neighbouring land uses. As such, roadside weeds should best be managed as part of the wider landscape. Web of Science Many Australia Field - Observational terrestrial Invasion Hyp. Disturbance primary 2421 Leger, Elizabeth A.; Espeland, Erin K.; Merrill, Keith R.; Meyer, Susan E. 2009 Genetic variation and local adaptation at a cheatgrass (Bromus tectorum) invasion edge in western Nevada journal MOLECULAR ECOLOGY 18 21 4366 4379 Cheatgrass (Bromus tectorum) is an invasive weed in western North America found primarily growing at elevations less than 2200 m. We asked whether cheatgrass is capable of becoming adapted to a marginal habitat, by investigating a population at a high elevation invasion edge. We used a combination of methods, including reciprocal field transplants, controlled environment studies and molecular analysis. High levels of SSR gene diversity (0.50 vs. 0.43) and comparable variation in phenotypic traits were observed at both the invasion edge and a low elevation, high-density population. Three heterozygotes were observed in the edge population, which is unusual in this predominantly self-pollinating plant. Plants from high elevations germinated more slowly in a growth chamber and had slower seedling growth rates. Survivorship was low at the edge (13%), compared with the low elevation site (55%), but surviving plants were of similar size and had equivalent reproductive output. Seed size positively affected survival and plant performance in the field and this trait was inherited. Emergence timing affected survival at the low elevation site and germination timing was also inherited. Local adaptation was seen in the low, rather than in the high elevation site, because of differential survival. While there was no evidence for local adaptation to the high elevation site observed in the field, family level and genotype-level differences in traits that affected field performance, high genetic diversity at the invasion edge, and evidence of outcrossing in this highly selfing species indicates that the potential for adaptation to a marginal habitat exists within this population. Web of Science Bromus tectorum USA Nevada 39.589286 -119.929504 Field - Experimental;Field - Observational terrestrial Grassland Invasion Hyp. Evolution in General primary 2422 Zukowski, Sylvia; Walker, Keith F. 2009 Freshwater snails in competition: alien Physa acuta (Physidae) and native Glyptophysa gibbosa (Planorbidae) in the River Murray, South Australia journal MARINE AND FRESHWATER RESEARCH 60 10 999 1005 Physa acuta (Draparnaud), an invasive species from Europe, is the most abundant freshwater snail in the Lower River Murray. Its ascendancy follows a general decline of native species, including the morphologically and ecologically similar Glyptophysa gibbosa (Gould). We began with two hypotheses. The first required comparisons of the salinity and temperature tolerances and other attributes of eggs, juveniles and adults to reveal differences that might account for the relative abundances of the species. As anticipated, P. acuta proved to have higher fecundity, shorter hatching time and higher salinity and temperature tolerances than G. gibbosa. The second hypothesis concerned a possible competitive interaction between the species. This was confirmed, as when juveniles were kept together, under laboratory conditions, the growth rate of P. acuta increased and that of G. gibbosa decreased (with some mortality). We suggest that the apparent decline of G. gibbosa in the Lower Murray may reflect its sensitivity to salinity and its vulnerability in interactions with P. acuta. This is a global concern as P. acuta has spread also to North America, Japan and South Africa, and there have been reports of impacts on local species. Web of Science Physa acuta Australia River Murray -34.1667 140.75 Lab lotic Riparian Invasion Hyp. Inherent Superiority Superior Competitor;Broad Tolerances;High Reprod. Output predator 2423 Marshall, Jordan M.; Buckley, David S.; Franklin, Jennifer A. 2009 Competitive interaction between Microstegium vimineum and first-year seedlings of three central hardwoods journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 136 3 342 349 MARSHALL, J. M., D. S. BUCKLEY, AND J. A. FRANKLIN (Department of Forestry, Wildlife and Fisheries, The University of Tennessee, Knoxville, TN 37996). Competitive interaction between Microstegium vimineum and first-year seedlings of three central hardwoods. J. Torrey Bot. Soc. 136: 342-349. 2009.-We established an experiment designed to compare effects of Microstegium vimineum (Japanese stiltgrass) on seedlings of three native hardwood species to investigate the hypothesis that competitive effects of M. vimineum Oil juvenile trees will vary across different tree species. Growth and survival of Acer rubrum, Liriodendron tulipifera, and Quercus rubra first-year seedlings were compared in plots with and without M. vimineum in three planting beds under 50 percent shade. The tree species studied are abundant and of particular interest in the Central Hardwood Region. A. rubrum and L. tulipifera seedlings experienced reduced growth in several foliar characteristics in the presence of M. vimineum. Q. rubra did not exhibit any differences in foliar characteristics between plots with and without M. vimineum, however there was a reduction in Q. rubra stern weight as a result of the presence of M. vimineum. The differential responses of A. rubrum, L. tulipifera, and Q. rubra to the presence of M. vimineum observed in this study support the hypothesis that effects of this exotic species will vary across tree species. As a result of reductions in the growth of A rubrum and L. tulipifera, the presence of M. vimineum in forest understories may reduce the rate at which seedlings of these species are recruited into larger size classes. Web of Science Microstegium vimineum USA Tennessee Knoxville Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Superior Competitor primary 2424 te Beest, Mariska; Stevens, Nicola; Olff, Han; van der Putten, Wim H. 2009 Plant-soil feedback induces shifts in biomass allocation in the invasive plant Chromolaena odorata journal JOURNAL OF ECOLOGY 97 6 1281 1290 P> Soil communities and their interactions with plants may play a major role in determining the success of invasive species. However, rigorous investigations of this idea using cross-continental comparisons, including native and invasive plant populations, are still scarce. We investigated if interactions with the soil community affect the growth and biomass allocation of the (sub)tropical invasive shrub Chromolaena odorata. We performed a cross-continental comparison with both native and non-native-range soil and native and non-native-range plant populations in two glasshouse experiments. Results are interpreted in the light of three prominent hypotheses that explain the dominance of invasive plants in the non-native range: the enemy release hypothesis, the evolution of increased competitive ability hypothesis and the accumulation of local pathogens hypothesis. Our results show that C. odorata performed significantly better when grown in soil pre-cultured by a plant species other than C. odorata. Soil communities from the native and non-native ranges did not differ in their effect on C. odorata performance. However, soil origin had a significant effect on plant allocation responses. Non-native C. odorata plants increased relative allocation to stem biomass and height growth when confronted with soil communities from the non-native range. This is a plastic response that may allow species to be more successful when competing for light. This response differed between native and non-native-range populations, suggesting that selection may have taken place during the process of invasion. Whether this plastic response to soil organisms will indeed select for increased competitive ability needs further study. The native grass Panicum maximum did not perform worse when grown in soil pre-cultured by C. odorata. Therefore, our results did not support the accumulation of local pathogens hypothesis. Synthesis. Non-native C. odorata did not show release from soil-borne enemies compared to its native range. However, non-native plants responded to soil biota from the non-native range by enhanced allocation in stem biomass and height growth. This response can affect the competitive balance between native and invasive species. The evolutionary potential of this soil biota-induced change in plant biomass allocation needs further study. Web of Science Chromolaena odorata Netherlands Greenhouse terrestrial Invasion Hyp. Enemy Release;Evolution of Increased Competitive Ability;Other primary 2425 Trtikova, Miluse 2009 Effects of competition and mowing on growth and reproduction of the invasive plant Erigeron annuus at two contrasting altitudes journal BOTANICA HELVETICA 119 1 1 6 Invasive plants are often abundant at frequently disturbed sites such as roadsides, because they benefit from reduced competition or increased nutrient availability. In Switzerland, roadsides are subjected to regular mowing, and to persist in these sites, plants must be able to compensate for the biomass removal. However, the ability to tolerate competition and mowing might decline under less favourable growth conditions, such as those at higher altitudes. I investigated how competition and mowing affect growth and reproduction of Erigeron annuus (L.) Pers., an invasive plant common on Swiss roadsides, and how these effects change with altitude. The experiment was replicated in common gardens at altitudes of 400 m and 1,000 m asl, representing growth conditions in the main distribution area of E. annuus and at its altitudinal limit, respectively. Vegetative growth was negatively affected by competition at both sites, but especially at 1,000 m. The number of capitula was not affected by competition at 400 m, but was reduced at 1,000 m. Plants regrew vigorously after mowing in both gardens. The effects of mowing on reproductive output were positive at 400 m, but negative at 1,000 m. These results imply that E. annuus is able to tolerate competition and mowing at low altitudes, but both of these factors hinder its reproduction at higher altitudes. Web of Science Erigeron annuus Switzerland Zug 47.207558 8.409948 Garden terrestrial Mountain Invasion Hyp. Disturbance primary 2426 Williams, Jennifer L. 2009 Flowering Life-History Strategies Differ between the Native and Introduced Ranges of a Monocarpic Perennial journal AMERICAN NATURALIST 174 5 660 672 Life-history theory makes several key predictions about reproductive strategies on the basis of demographic vital rates, particularly the relationship between juvenile and adult survival. Two such predictions concern the optimal time to begin reproducing and whether semelparity or iteroparity is favored. I tested these life-history predictions and explored how they might differ between the native and introduced ranges of the monocarpic perennial Cynoglossum officinale. I first compared vital rates between ranges. I then used these vital rates to parameterize integral projection models to calculate the population growth rate (lambda) and net reproductive rate (R-0) as surrogates for fitness to compare strategies within and between ranges. I found that both survival and growth were higher in the introduced range, where size at flowering was larger and iteroparity was much more common than in the native range. The observed and predicted strategies for size at flowering were similar in the native range. In the introduced range, however, even though plants flowered at a larger size, the observed size was not as large as the optimum predicted by lambda or the higher optimum predicted by R-0. Iteroparity conferred higher fitness in both ranges, as measured by both fitness metrics, suggesting that severe constraints, potentially specialist herbivores, prevent this strategy from becoming more common in the native range. Web of Science Cynoglossum officinale USA; Germany; Hungary Field - Observational terrestrial Grassland Invasion Hyp. Evolution in General primary 2427 Colautti, Robert I.; Maron, John L.; Barrett, Spencer C. H. 2009 Common garden comparisons of native and introduced plant populations: latitudinal clines can obscure evolutionary inferences journal EVOLUTIONARY APPLICATIONS 2 2 187 199 Common garden studies are increasingly used to identify differences in phenotypic traits between native and introduced genotypes, often ignoring sources of among-population variation within each range. We re-analyzed data from 32 common garden studies of 28 plant species that tested for rapid evolution associated with biological invasion. Our goals were: (i) to identify patterns of phenotypic trait variation among populations within native and introduced ranges, and (ii) to explore the consequences of this variation for how differences between the ranges are interpreted. We combined life history and physiologic traits into a single principal component (PCALL) and also compared subsets of traits related to size, reproduction, and defense (PCSIZE, PCREP, and PCDEF, respectively). On average, introduced populations exhibited increased growth and reproduction compared to native conspecifics when latitude was not included in statistical models. However, significant correlations between PC-scores and latitude were detected in both the native and introduced ranges, indicating population differentiation along latitudinal gradients. When latitude was explicitly incorporated into statistical models as a covariate, it reduced the magnitude and reversed the direction of the effect for PCALL and PCSIZE. These results indicate that unrecognized geographic clines in phenotypic traits can confound inferences about the causes of evolutionary change in invasive plants. Web of Science Many Statistical/Meta-analysis Invasion Hyp. Inherent Superiority Rapid Growth;High Reprod. Output primary 2428 Boulant, Nadine; Garnier, Aurelie; Curt, Thomas; Lepart, Jacques 2009 Disentangling the effects of land use, shrub cover and climate on the invasion speed of native and introduced pines in grasslands journal DIVERSITY AND DISTRIBUTIONS 15 6 1047 1059 Aims To determine how changes in land use, climate and shrub cover affect the invasion dynamics of native (Pinus sylvestris L.) and introduced (Pinus nigra Arn. subsp. nigra) pines in grasslands. To analyse how these factors interact and affect seedling recruitment, a bottleneck in the lifecycle of many trees. Such information is required to manage the dynamics of these species. Location Grands Causses, calcareous plateaus (Southern France). Methods We used both published and unpublished demographic and dispersal data to assess population growth and invasion speed of invading pines. A demographic and spatially explicit model, which included density dependence and stochasticity in dispersal, demography and environment, was run for different scenarios of sheep grazing pressure (nil, extensive or intensive), shrub cover (0, 10 or 20%) and drought frequency (past-to-present or future). For each scenario, population growth rate, invasion speed and elasticity of invasion speed to each demographic and dispersal parameter were computed. Results Grazing was the main factor for limiting invasion speed. Shrub cover reduced tree spread under nil or extensive grazing pressure, but increased it under intensive grazing pressure. Although dry years led to nil seedling establishment rates, an increase in their frequency had surprisingly few effects on pine invasion speed. This last result remained unchanged when very dry years, inducing seedling, but also sapling mortality were introduced. In most environmental conditions, population growth rate and invasion speed were higher for the introduced than for the native pine. Elasticity analysis highlighted the importance of demographic parameters on invasion speed, notably adult and sapling survival. Main conclusion Tree invasion speed may rely at least as much on human activities, like sheep grazing, tree cutting and non-native trees introduction, as on changes in climate factors. Therefore, human activities need to be explicitly taken into account in the prediction and management of tree dynamics. Web of Science Pinus nigra France Cevennes National Park 44 3.5 Theoretical/Modeling terrestrial Grassland;Coniferous Forest Invasion Hyp. Inherent Superiority;Disturbance Rapid Growth primary 2429 Karatayev, Alexander Y.; Burlakova, Lyubov E.; Padilla, Dianna K.; Mastitsky, Sergey E.; Olenin, Sergej 2009 Invaders are not a random selection of species journal BIOLOGICAL INVASIONS 11 9 2009 2019 We assembled information on 119 species of freshwater macroinvertebrate invaders in North America and Europe, and compared them to all native freshwater species in North America and Europe. We tested whether the invaders were a random or selected group among taxa (phylum or class), water quality requirements, and feeding habit. We found that freshwater macroinvertebrate invaders are not a random selection of species, and are over-represented by molluscs and crustaceans, while taxa richness of native communities are dominated by insects. Over 35% of native species of aquatic invertebrates in North America are only able to live in areas with excellent or very good water quality, and are intolerant of organic pollution. In contrast, all invaders are tolerant of at least moderate amounts of organic pollution. There was a significant difference in the distribution of feeding habits between native species and invaders: collector-filterers (including suspension feeders) were 2.5-3 times more abundant, and predators were 3-4 times less abundant among invaders than among native invertebrates. The ongoing spread of exotic species affects the biodiversity of selected taxa, shifts communities toward greater tolerance of organic pollution and increases the numbers of suspension feeders, thereby enhancing benthic pelagic coupling in waterbodies with high densities of invaders. Because these processes are very similar in Europe and North America, we suggest that the observed patterns may have a common global effect. Web of Science Many Global Statistical/Meta-analysis marine Invasion Hyp. Inherent Superiority Broad Tolerances herbivore;omnivore;predator;filter 2430 Poeckl, Manfred 2009 Success of the invasive Ponto-Caspian amphipod Dikerogammarus villosus by life history traits and reproductive capacity journal BIOLOGICAL INVASIONS 11 9 2021 2041 Dikerogammarus villosus originates from the Ponto-Caspian basin. In the Austrian stretch of the River Danube it was not found before 1989, and not before 1992 in the Bavarian Danube. It very quickly spread to Germany, the Netherlands, and France via the so called *Southern Corridor*. The invader also migrates via the *Central Corridor*, reaching as far west as the Vistula River. The species has been reported from a number of lakes. Reasons for the quick spread and high abundance are, beside others, its life history traits. A population of this invasive species was studied from 2002 to 2004 in the Austrian stretch of the Danube. The following life-history traits are important in the invasion success: long reproductive period, early sexual maturity, short generation time, a life span not exceeding 1 year (up to three generations and 14 cohorts being present at the same time), high growth rates resulting in large body size, short duration of embryonic development, large numbers of comparatively small eggs in the brood pouch, large reproductive capacity, and optimal timing to release the maximum number of neonates per female in May/June (maximising rapid growth at high summer temperatures and at times of plentiful food), increasing mating privilege for large specimens of both sexes with decreasing water temperatures during winter. These life cycle characteristics together with its predatory behaviour and its ability to cope with variation in oxygen, temperature and salinity, give this invader a potential to become distributed in freshwater ecosystems of the temperate climate zone all over the world. Additionally, several indications seem to prove the tendency that biological invasion and global warming have a positive feed-back on each other. This combined scenario is a huge threat to the indigenous aquatic fauna, and might contribute to bio-monotony. Web of Science Dikerogammarus villosus Austria 48.3544 15.4089 Field - Observational lotic Riparian Invasion Hyp. Inherent Superiority Broad Tolerances;Rapid Growth;High Reprod. Output decomposer 2431 Kestrup, Asa M.; Ricciardi, Anthony 2009 Environmental heterogeneity limits the local dominance of an invasive freshwater crustacean journal BIOLOGICAL INVASIONS 11 9 2095 2105 The impacts of an exotic species may vary along environmental gradients. We tested the hypothesis that site-specific heterogeneity in the physico-chemical environment alters the dominance of two competing amphipods: Gammarus fasciatus, the dominant native species in the upper St. Lawrence River, and Echinogammarus ischnus, a euryhaline Ponto-Caspian species that invaded the river in the late 1990s. E. ischnus has replaced G. fasciatus as the dominant amphipod at some sites, while remaining inferior at other sites-even several years after invasion. We tested the effect of water chemistry (conductivity) on the outcome of interactions between these two species in the laboratory and in the river in 2006 and 2007. Field experiments involved transplanting both species to different sites along a gradient of conductivity within the river, whereas the laboratory experiments examined interspecific predation in water collected from these sites. The laboratory experiments revealed that these species are mutual predators and their rate of predation on each other varies with conductivity; E. ischnus is the dominant predator at higher conductivity, while G. fasciatus dominates at lower conductivity. The field experiments showed interannual variation, but supported the lab results at high conductivity in 2006 and at low conductivity in 2007. E. ischnus was more sensitive than G. fasciatus to variation in conductivity, which apparently mediates this invader's ability to replace or dominate the native species in a heterogeneous environment. Web of Science Canada Quebec 45.369032 -73.852844 Field - Experimental;Field - Observational lentic Invasion Hyp. Fluctuating Resources decomposer 2433 Godoy, O.; Castro-Diez, P.; Valladares, F.; Costa-Tenorio, M. 2009 Different flowering phenology of alien invasive species in Spain: evidence for the use of an empty temporal niche? journal PLANT BIOLOGY 11 6 803 811 Flowering phenology is an important and poorly understood plant trait that may possibly be related to the invasiveness potential of alien species. The present work evaluates whether flowering time of invasive alien species is a key trait to overcome the climatic filters operating in continental Mediterranean ecosystems of Spain (characterised by summer drought and low temperatures in winter). We conducted comparisons between the flowering phenology of the invasive species in their native range and in Spain, and between flowering phenology of 91 coexisting invasive-native species pairs. For the alien species, geographical change from the native to the invaded region did not result in shifts in the start and the length of the flowering period. Overall, climatic conditions in the native range of species selected for a flowering pattern is maintained after translocation of the species to another region. Flowering of tropical and temperate invasive alien species peaked in summer, which contrasts with the spring flowering of native and invasive alien species of Mediterranean climate origin. By exploiting this new temporal niche, these invasive alien species native to tropical and temperate regions benefit from reduced competition with natives for abiotic and biotic resources. We suggest that human-mediated actions have reduced the strength of the summer drought filter in particular microhabitats, permitting the invasion of many summer-flowering aliens. Web of Science Many Spain Statistical/Meta-analysis terrestrial Invasion Hyp. Empty Niche primary 2434 Roscher, Christiane; Schmid, Bernhard; Schulze, Ernst-Detlef 2009 Non-random recruitment of invader species in experimental grasslands journal OIKOS 118 10 1524 1540 To assess potential effects of seed limitation, characteristics of invader species and characteristics of established plant communities on recruitment success, we conducted a split-plot experiment factorially combining three weeding treatments corresponding to increasing successional age (regular weeding < cessation of weeding after three years < never weeded since sowing) with two seed limitation treatments (control vs sowing a seed mixture of all experimental species=internal invaders) in experimental grasslands varying in species richness (1, 2, 4, 8, 16) and in functional group richness and composition (1, 2, 3, 4 functional groups: presence/absence of legumesxgrassesxtall herbsxsmall herbs). Seed addition increased internal invader seedling densities and the probability of successful colonization per species. Legumes, tall herbs and species with large and long-lived seeds or a requirement for specific vectors for pollination and dispersal benefited from seed addition most. The number of successfully established internal invader species was highest in plots with low initial species richness and in the regularly weeded treatments and lowest in plots with high initial species richness and in the never weeded treatments, indicating decreased recruitment with increased successional age. Resident plant communities with legumes had mostly negative (legume and small- and tall-herb internal invaders, external invaders) or neutral (grass invaders) effects on seedling density and colonization probability of invader species whereas resident communities with grasses had positive effects on the colonization probability of invader species except grasses themselves. These results show that seed limitation, invader characteristics, and community characteristics all can affect recruitment success in predictable ways, suggesting non-random community assembly during succession starting from different initial species pools. Web of Science Many Germany Thuringa 50.9167 11.5833 Field - Experimental terrestrial Grassland;Riparian Invasion Hyp. Inherent Superiority;Community Species Richness;Propagule Pressure High Reprod. Output primary 2435 Gomez-Aparicio, Lorena; Canham, Charles D. 2008 Neighbourhood analyses of the allelopathic effects of the invasive tree Ailanthus altissima in temperate forests journal JOURNAL OF ECOLOGY 96 3 447 458 1. Allelopathic interactions between invasive and native species have been suggested to be an important mechanism for the success of some of the most aggressive plant invaders. However, field experiments that test the effects of natural levels of allelopathic compounds on coexisting native species are exceptionally rare. 2. In this study, we analyzed the allelopathic effects of the invasive tree Ailanthus altissima on seedling emergence, survival and growth of three native tree species (Acer rubrum, A. saccharum and Quercus rubra) in temperate forests of the northeastern United States. We used activated carbon (AC) to reduce potential allelopathic interference, and developed neighbourhood models that explain the observed spatial variation in the effects of the AC treatments on seedling performance as a function of the size, abundance and distribution of Ailanthus trees in the neighbourhood. 3. Our results showed that the addition of AC to the soil did not affect seedling emergence or survival, but caused a significant increase in seedling growth of all three species. Moreover, the AC shifted the overall interaction between Ailanthus and maple seedlings from neutral or slightly positive to very positive for A. rubrum, and from negative to positive for A. saccharum, whereas the net interaction between Ailanthus and Q. rubra was always negative. As Ailanthus has the ability to increase soil fertility, these species-specific responses are presumably influenced by among-species differences in the net effects of both allelopathy and changes in resource availability caused by the presence of Ailanthus. 4. The cumulative allelopathic effects of Ailanthus were proportional to the density of Ailanthus in the neighbourhood, regardless of their size. In contrast, Ailanthus effects were strongly influenced by distance from a tree, generally dropping to zero within 5 m from the trunk. 5. Synthesis. Taken together, our results indicate that allelopathy is an important mechanism to take into account when trying to understand the causes and consequences of plant invasions. However, this study also strongly suggests that the real significance of the allelopathic effects of an invasive species cannot be assessed independently of its target community, or in isolation of other resource interactions involving the invader and the native community. Web of Science Ailanthus altissima United States Connecticut Amesville; Dark Entry Forest; New Milford Field - Observational;Statistical/Meta-analysis terrestrial Deciduous Forest Invasion Hyp. Novel Weapons primary 2437 Cano, L.; Escarre, J.; Fleck, I.; Blanco-Moreno, J. M.; Sans, F. X. 2008 Increased fitness and plasticity of an invasive species in its introduced range: a study using Senecio pterophorus journal JOURNAL OF ECOLOGY 96 3 468 476 1. When a plant species is introduced into a new range, it may differentiate genetically from the original populations in the home range. This genetic differentiation may influence the extent to which the invasion of the new range is successful. We tested this hypothesis by examining Senecio pterophorus, a South African shrub that was introduced into NE Spain about 40 years ago. We predicted that in the introduced range invasive populations would perform better and show greater plasticity than native populations. 2. Individuals of S. pterophorus from four Spanish (invasive) and four South African (native) populations were grown in Catalonia, Spain, in a common garden in which disturbance and water availability were manipulated. Fitness traits and several ecophysiological parameters were measured. 3. The invasive populations of S. pterophorus survived better throughout the summer drought in a disturbed (unvegetated) environment than native South African populations. This success may be attributable to the lower specific leaf area (SLA) and better water content regulation of the invasive populations in this treatment. 4. Invasive populations displayed up to three times higher relative growth rate than native populations under conditions of disturbance and non-limiting water availability. 5. The reproductive performance of the invasive populations was higher in all treatments except under the most stressful conditions (i.e. in non-watered undisturbed plots), where no plant from either population flowered. 6. The results for leaf parameters and chlorophyll fluorescence measurements suggested that the greater fitness of the invasive populations could be attributed to more favourable ecophysiological responses. 7. Synthesis. Spanish invasive populations of S. pterophorus performed better in the presence of high levels of disturbance, and displayed higher plasticity of fitness traits in response to resource availability than native South African populations. Our results suggest that genetic differentiation from source populations associated with founding may play a role in invasion success. Web of Science Senecio pterophorus Spain Catalonia Garden terrestrial Chaparral/Shrublands Invasion Hyp. Plasticity primary 2439 Nunez, Martin A.; Relva, Maria A.; Simberloff, Daniel 2008 Enemy release or invasional meltdown? Deer preference for exotic and native trees on Isla Victoria, Argentina journal AUSTRAL ECOLOGY 33 3 317 323 How interactions between exotic species affect invasion impact is a fundamental issue on both theoretical and applied grounds. Exotics can facilitate establishment and invasion of other exotics (invasional meltdown) or they can restrict them by re-establishing natural population control (as predicted by the enemy-release hypothesis). We studied forest invasion on an Argentinean island where 43 species of Pinaceae, including 60% of the world's recorded invasive Pinaceae, were introduced c. 1920 but where few species are colonizing pristine areas. In this area two species of Palearctic deer, natural enemies of most Pinaceae, were introduced 80 years ago. Expecting deer to help to control the exotics, we conducted a cafeteria experiment to assess deer preferences among the two dominant native species (a conifer, Austrocedrus chilensis, and a broadleaf, Nothofagus dombeyi) and two widely introduced exotic tree species (Pseudotsuga menziesii and Pinus ponderosa). Deer browsed much more intensively on native species than on exotic conifers, in terms of number of individuals attacked and degree of browsing. Deer preference for natives could potentially facilitate invasion by exotic pines. However, we hypothesize that the low rates of invasion currently observed can result at least partly from high densities of exotic deer, which, despite their preference for natives, can prevent establishment of both native and exotic trees. Other factors, not mutually exclusive, could produce the observed pattern. Our results underscore the difficulty of predicting how one introduced species will effect impact of another one. Web of Science Pinus ponderosa; Pseudotsuga menziesii Argentinia Isla Victoria -40.957086 -71.536102 Field - Experimental terrestrial Broadleaf Evergreen Forest Invasion Hyp. Mutualism Facilitation primary 2440 Mollo, Ernesto; Gavagnin, Margherita; Carbone, Marianna; Castelluccio, Francesco; Pozone, Ferdinando; Roussis, Vassilios; Templado, Jose; Ghiselin, Michael T.; Cimino, Guido 2008 Factors promoting marine invasions: A chemolecological approach journal PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 105 12 4582 4586 The Mediterranean Sea is losing its biological distinctiveness, and the same phenomenon is occurring in other seas. It gives urgency to a better understanding of the factors that affect marine biological invasions. A chemoecological approach is proposed here to define biotic conditions that promote biological invasions in terms of enemy escape and resource opportunities. Research has focused on the secondary metabolite composition of three exotic sea slugs found in Greece that have most probably entered the Mediterranean basin by Lessepsian migration, an exchange that contributes significantly to Mediterranean biodiversity. We have found toxic compounds with significant activity as feeding deterrents both in the cephalaspidean Haminoea cyanomarginata and in the nudibranch Melibe viridis. These findings led us to propose aposematism in the former and dietary autonomy in producing defensive metabolites in the latter case, as predisposing factors to the migration. In the third mollusk investigated, the anaspidean Syphonota geographica, the topic of marine invasions has been approached through a study of its feeding biology. The identification of the same compounds from both the viscera of each individual, separately analyzed, and their food, the seagrass Halophila stipulacea, implies a dietary dependency. The survival of S. geographica in the Mediterranean seems to be related to the presence of H. stipulacea. The initial invasion of this exotic pest would seem to have paved the way for the subsequent invasion of a trophic specialist that takes advantage of niche opportunities. Web of Science Haminoea cyanomarginata; Melibe viridis Greece Gulf of Corinth Field - Experimental;Field - Observational marine Benthic Invasion Hyp. Enemy Release;Empty Niche herbivore 2442 Donnelly, Melinda J.; Green, Danielle M.; Walters, Linda J. 2008 Allelopathic effects of fruits of the Brazilian pepper Schinus terebinthifolius on growth, leaf production and biomass of seedlings of the red mangrove Rhizophora mangle and the black mangrove Avicennia germinans journal JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 357 2 149 156 Exotic plant species can negatively affect native flora and fauna by changing the diversity and productivity of the system and altering successional processes. The novel weapons hypothesis has been suggested as one mechanism for invasion and spread of exotic plant species. It states that exotic species with *new weapons*, such as allelopathic chemicals, may have greater impacts on species in the invaded range without co-evolved defense strategies against the exotic chemicals. In Florida, one successful exotic species, Schinus terebinthifolius (Brazilian pepper), has invaded nearly every habitat throughout the state. Past studies have documented allelopathic properties of S. terebinthifolius negatively impacting the growth of native terrestrial flora. Here we document the effect of S. terebinthifolius for the first time on mangrove systems. We examined growth and survival of Rhizophora mangle (red mangrove) and Avicennia germinans (black mangrove) seedlings when exposed to a range of densities of intact and crushed S. terebinthifolius fruits (0, 25, 50) at two different salinities (15, 30 ppt). We also documented the natural density of S. terebinthifolius fruits beneath the tree canopy after fruit production in mangrove habitat. Growth and biomass were significantly reduced in A. germinans when exposed to the highest density of intact S. terebinthifolius fruits growing in 30 ppt saltwater. Trials with intact fruits had no significant effects on R. mangle; however, crushed fruits significantly decreased growth, and leaf production. The ecological importance of the different effects of crushed and intact fruits is supported by field observations which found equal or greater numbers of crushed fruits compared to intact fruits beneath the tree canopy of female S. terebinthifolius. In addition, abiotic factors, such as salinity, may interact with allelopathic chemicals in natural systems and needs to be addressed when planning future allelopathic studies. (C) 2008 Elsevier B.V. All rights reserved. Web of Science Schinus terebinthifolius United States Florida Field - Observational;Greenhouse wetland Wetland Invasion Hyp. Novel Weapons primary 2443 Milbau, Ann; Stout, Jane C. 2008 Factors associated with alien plants transitioning from casual, to naturalized, to invasive journal CONSERVATION BIOLOGY 22 2 308 317 To explain current plant invasions, or predict future ones, more knowledge on which factors increase the probability of alien species becoming naturalized and subsequently invasive is needed. We created a database of the alien plants in seminatural habitats in Ireland that included data on taxonomy, invasive status, invasion history, distribution, and biological and ecological plant characteristics. We used information from this database to determine the importance of these factors in increasing the ability of species to become naturalized and invasive. More specifically, we used two multiple logistic regressions toy factors that distinguish naturalized from casual alien plant species and invasive from noninvasive, identify naturalized alien species. Clonal growth, moisture-indicator value, nitrogen-indicator value, native range, and date of first record affected (in order of decreasing importance) the probability of naturalization. Factors that distinguished invasive from noninvasive species were ornamental introduction, hermaphrodite flowers, pollination mode, being invasive elsewhere, onset of flowering season, moisture-indicator value, native range, and date of first record. Incorporation of phylogenetic information had little influence on the results, suggesting that the capacity of alien species to naturalize and become invasive evolved largely independently in several phylogenetic lineages. Whereas some of the variables were important for both transitions, others were only important for naturalization or for invasion. This emphasizes the importance of studying different stages of the invasion process when looking for mechanisms of becoming a successful invasive plant, instead of simply comparing invasive with noninvasive alien species. Our results also suggest that a combination of species traits and other variables is likely to produce the most accurate prediction of invasions. Web of Science Many Ireland Statistical/Meta-analysis Invasion Hyp. Inherent Superiority Self Compatible;Clonal Reproduction primary 2444 Devin, Simon; Beisel, Jean-Nicolas 2008 Geographic patterns in freshwater gammarid invasions: an analysis at the pan-European scale journal AQUATIC SCIENCES 70 1 100 106 Biogeographic characteristics of freshwater gammarids at a pan-European scale were investigated to describe spatial gradients of richness and their relationships with the pattern of invasive species distribution. Species richness appeared to be linked to latitude and among the 25 European biogeographical areas, the Ponto-Caspian basin exhibited a particular position, being by far the most diverse area. A link between the species richness of an area and the number of invasive species coming from this area was observed, showing that rich areas are more prone to shelter potential invaders than others. The patterns of gammarid dispersals among European waterways suggest that, rather than a random distribution of invaders, a clump occurred in basins which served as refuge areas during the last glaciations. Several reasons explaining the pattern are discussed, including the possibility that among species evolving in a stimulating environment some of them have had the opportunity to develop special competitive attributes. Web of Science Many Europe Statistical/Meta-analysis lotic Invasion Hyp. Community Species Richness decomposer 2451 Hotchkiss, Emily E.; DiTommaso, Antonio; Brainard, Daniel C.; Mohler, Charles L. 2008 Survival and performance of the invasive vine Vincetoxicum rossicum(Apocynaceae) from seeds of different embryo number under two light environments journal AMERICAN JOURNAL OF BOTANY 95 4 447 453 The normative vine Vincetoxicum rossicum threatens several ecosystems in the Lower Great Lakes Basin of North America. One feature that may contribute to its invasiveness is the production of some seeds with multiple embryos (polyembryony), which may be beneficial as a bet-hedging strategy in variable environments. However, lower seed reserves per embryo in polyembryonic seeds may entail costs in low-light environments. The effect of seed from three embryonic classes (1, 2, or 3 embryos/seed) on V rossicum survival and growth was studied under two forest understory light environments: full canopy (shade) or canopy gaps (light) in New York state. Two seedling cohorts were planted, in May 2004 and in May 2005. The survival and growth of seedlings was monitored biweekly for two (2005 cohort) or three (2004 cohort) seasons. For both cohorts, plants grown in canopy shade had reduced survival and growth compared with those grown in gaps. Contrary to expectations, seed embryo number had no effect on the final height, survival, or dry mass of plants in either habitat. Our results suggest that any fitness advantage provided by polyembryony may be habitat (light) dependent and not a general trait that affords V rossicum a benefit in all habitats colonized. Web of Science Vincetoxicum rossicum United States New York Robert Musgrave Research Facility 43.2167 -77.0833 Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority High Reprod. Output primary 2456 Chadwell, Todd B.; Engelhardt, Katharina A. M. 2008 Effects of pre-existing submersed vegetation and propagule pressure on the invasion success of Hydrilla verticillata journal JOURNAL OF APPLIED ECOLOGY 45 2 515 523 1. With biological invasions causing widespread problems in ecosystems, methods to curb the colonization success of invasive species are needed. The effective management of invasive species will require an integrated approach that restores community structure and ecosystem processes while controlling propagule pressure of non-native species. 2. We tested the hypotheses that restoring native vegetation and minimizing propagule pressure of invasive species slows the establishment of an invader. In field and greenhouse experiments, we evaluated (i) the effects of a native submersed aquatic plant species, Vallisneria americana, on the colonization success of a non-native species, Hydrilla verticillata; and (ii) the effects of H. verticillata propagule density on its colonization success. 3. Results from the greenhouse experiment showed that V. americana decreased H. verticillata colonization through nutrient draw-down in the water column of closed mesocosms, although data from the field experiment, located in a tidal freshwater region of Chesapeake Bay that is open to nutrient fluxes, suggested that V. americana did not negatively impact H. verticillata colonization. However, H. verticillata colonization was greater in a treatment of plastic V. americana look-alikes, suggesting that the canopy of V. americana can physically capture H. verticillata fragments. Thus pre-emption effects may be less clear in the field experiment because of complex interactions between competitive and facilitative effects in combination with continuous nutrient inputs from tides and rivers that do not allow nutrient draw-down to levels experienced in the greenhouse. 4. Greenhouse and field tests differed in the timing, duration and density of propagule inputs. However, irrespective of these differences, propagule pressure of the invader affected colonization success except in situations when the native species could draw-down nutrients in closed greenhouse mesocosms. In that case, no propagules were able to colonize. 5. Synthesis and applications. We have shown that reducing propagule pressure through targeted management should be considered to slow the spread of invasive species. This, in combination with restoration of native species, may be the best defence against non-native species invasion. Thus a combined strategy of targeted control and promotion of native plant growth is likely to be the most sustainable and cost-effective form of invasive species management. Web of Science Hydrilla verticillata United States Maryland Otter Point Creek National Estuarine Research Reserve 39.45 -76.2667 Field - Experimental;Greenhouse terrestrial Invasion Hyp. Propagule Pressure primary 2459 Franks, Steven J.; Pratt, Paul D.; Dray, F. Allen; Simms, Ellen L. 2008 No evolution of increased competitive ability or decreased allocation to defense in Melaleuca quinquenervia since release from natural enemies journal BIOLOGICAL INVASIONS 10 4 455 466 If invasive plants are released from natural enemies in their introduced range, they may evolve decreased allocation to defense and increased growth, as predicted by the evolution of increased competitive ability (EICA) hypothesis. A field experiment using the invasive tree Melaleuca quinquenervia was conducted to test this hypothesis. Seeds were collected from 120 maternal trees: 60 in Florida (introduced range) and 60 in Australia (home range). Plants grown from these seeds were either subjected to herbivory by two insects from Australia that have recently been released as biological control agents or protected from herbivores using insecticides. Genotypes from the introduced range were initially more attractive to herbivores than genotypes from the home range, supporting EICA. However, genotypes from the introduced and home range did not differ in resistance to insects or in competitive ability, which does not support EICA. Plants from the introduced range had a lower leaf hair density, lower leaf: stem mass ratio, and a higher ratio of nerolidol: viridifloral chemotypes compared to plants from the native range. Plants with an intermediate density of leaf hairs and with high specific leaf area were more susceptible to herbivory damage, but there were no effects of leaf toughness or chemotype on presence of and damage by insects. Herbivory had a negative impact on performance of Melaleuca. Other than an initial preference by insects for introduced genotypes, there was no evidence for the evolution of decreased defense or increased competitive ability, as predicted by the EICA hypothesis. It does not appear from this study that the EICA hypothesis explains patterns of recent trait evolution in Melaleuca. Web of Science Melaleuca quinquenervia United States Florida 26.078988 -80.238669 Garden terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 2460 Marshall, Jordan M.; Buckley, David S. 2008 Influence of litter removal and mineral soil disturbance on the spread of an invasive grass in a Central Hardwood forest journal BIOLOGICAL INVASIONS 10 4 531 538 Soil and litter disturbances within Central Hardwood forests may facilitate exotic plant species invasion of interior forest areas. Microstegium vimineum is an annual exotic grass that has become common throughout the Southeastern United States. Three replicates of three different mineral soil and litter disturbance treatments, plus a control with no disturbance, were established on the leading edge of M. vimineum patches prior to seed fall. All patches were located in areas with similar forest canopy structure and slope in three Central Hardwood forest stands prior to seed fall. At the beginning of the following growing season, each individual M. vimineum seedling was mapped within the treatment plots. The mean number of M. vimineum individuals that established within each treatment did not differ significantly from the control. The distance at which 90% of the individuals had spread, and the overall mean distance spread were significantly farther for the litter removal treatment than the control. The farthest individual seedling from the boundary of existing patches in both the litter removal and the mineral soil disturbance and litter removal treatments were significantly farther than the control. The individuals that spread the farthest are of most concern due to the large number of viable seed that a single M. vimineum plant can produce. These results suggest that disturbance of the litter layer may increase the spread rate of M. vimineum and facilitate its invasion of new habitats, and that leaving litter layers intact may slow the spread of M. vimineum. Web of Science Microstegium vimineum United States Tennessee Oak Ridge 36 -84.2167 Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 2461 Pauchard, Anibal; Garcia, Rafael A.; Pena, Eduardo; Gonzalez, Cristian; Cavieres, Lohengrin A.; Bustamante, Ramiro O. 2008 Positive feedbacks between plant invasions and fire regimes: Teline monspessulana (L.) K. Koch (Fabaceae) in central Chile journal BIOLOGICAL INVASIONS 10 4 547 553 Invasive species can increase fire frequency and intensity, generating favorable conditions for their self-perpetuation. Mediterranean south-central Chile may be especially prone to the effects of invasive species on fire regimes because it is less adapted to fire and it contains a highly endemic flora. Teline monspessulana (L.) K. Koch (syn. Cytisus monspessulanus L.; Genista monspessulana (L.) L.A.S. Johnson) is an introduced shrub that forms monotypic stands or is present as an understory species in native forests as well as in forestry plantations. Dense T. monspessulana stands are completely destroyed by fire, generating the conditions for it seeds to germinate and establish an abundant regeneration, with up to 900 plants/m(2). We report key evidence on abundance and biomass in adult stands, and patterns of seed bank and regeneration after fire in stands of T. monspessulana around the city of Concepcion, Chile. We estimated living biomass in pure stands and underneath Eucalyptus plantations. In burned areas, we assessed T. monspessulana seed bank and studied regeneration patterns. We found that T. monspessulana densities reaches 52,778 plants/ha and 8.92 ton/ha in pure stands and 34,223 plants/ha and 2.31 ton/ha underneath Eucalyptus plantations. T. monspessulana generates small caliper fuel and acts as a ladder-fuel. Large soil seed banks allow for abundant regeneration after fire, with mean densities of 877,111 plants/ha, but an overall mortality of 37.2% in the first year after the fire. The high values of regeneration compared to final densities in adult stands suggest that density-dependent mortality. Our results indicate that T. monspessulana regeneration is not only favored by fires, but also that the species creates favorable conditions for intense and continuous fires, both under pure conditions, but also associated to exotic tree plantations. To understand the implications of positive feedbacks between invaders and fire, we recommend focusing in the mechanisms by which they increases fuel accumulation and fuel flammability, and how higher fire frequency and intensity favors invasive species recruitment over native species. Comprehension of this dynamics will allow for better management and control of these invasions which have major ecological, economical and social implications. Web of Science Teline monspessulana Chile Concepcion -36.8383 -73.0478 Field - Observational terrestrial Deciduous Forest;Coniferous Forest;Subtropical Forest Impacts;Invasion Hyp. Disturbance primary 2463 Belote, R. Travis; Jones, Robert H.; Hood, Sharon M.; Wender, Bryan W. 2008 Diversity-invasibility across an experimental disturbance gradient in Appalachian forests journal ECOLOGY 89 1 183 192 Research examining the relationship between community diversity and invasions by normative species has raised new questions about the theory and management of biological invasions. Ecological theory predicts, and small-scale experiments confirm, lower levels of nonnative species invasion into species-rich compared to species-poor communities, but observational studies across a wider range of scales often report positive relationships between native and nonnative species richness. This paradox has been attributed to the scale dependency of diversity-invasibility relationships and to differences between experimental and observational studies. Disturbance is widely recognized as an important factor determining invasibility of communities, but few studies have investigated the relative and interactive roles of diversity and disturbance on nonnative species invasion. Here, we report how the relationship between native and nonnative plant species richness responded to an experimentally applied disturbance gradient (from no disturbance up to clearcut) in oak-dominated forests. We consider whether results are consistent with various explanations of diversity-invasibility relationships including biotic resistance, resource availability, and the potential effects of scale (I m 2 to 2 ha). We found no correlation between native and normative species richness before disturbance except at the largest spatial scale, but a positive relationship after disturbance across scales and levels of disturbance. Post-disturbance richness of both native and normative species was positively correlated with disturbance intensity and with variability of residual basal area of trees. These results suggest that more nonnative plants may invade species-rich communities compared to species-poor communities following disturbance. Web of Science Many United States Virginia; West Virginia 36.791691; 37.509726; 38.694085 -82.705078; -80.15625; -79.93103 Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Community Species Richness;Disturbance primary 2464 Inoue, Maki N.; Yokoyama, Jun; Washitani, Izumi 2008 Displacement of Japanese native bumblebees by the recently introduced Bombus terrestris (L.) (Hymenoptera : Apidae) journal JOURNAL OF INSECT CONSERVATION 12 2 135 146 The introduced Bombus terrestris has recently been naturalized in Japan and become dominant in some local communities. We investigated potential niche overlaps between introduced and native bumblebees in terms of morphological characteristics, seasonal flight activity, foraging and nesting habitat use, and plant species visited. There were considerable niche overlaps in flower resource use between B. terrestris and B. hypocrita sapporoensis/B. pseudobaicalensis. Bombus terrestris also potentially competes for nest sites with B. hypocrita sapporoensis. During 3-year monitoring, B. pseudobaicalensis showed no noticeable change, but B. hypocrita sapporoensis decreased while B. terrestris increased. Abundant flower resources provided by exotic plants may buffer native bumblebees from competition for food with introduced species. By contrast, the number of nest usurpers found in B. terrestris nests increased between 2003 and 2005, indicating that availability of nest sites was limiting and queens strongly competed for nest sites. Our findings suggest that competition for nest sites rather than flower resources is the major ecological mechanism for displacement of native bees. The large reduction of B. hypocrita sapporoensis queen indicates that B. terrestris may cause local extinction of native bumblebees. Control of established B. terrestris populations and prevention of further range expansion are urgently needed. Web of Science Bombus terrestris Japan Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Superior Competitor herbivore 2466 Cipollini, Don; Stevenson, Randall; Cipollini, Kendra 2008 Contrasting effects of allelochemicals from two invasive plants on the performance of a nonmycorrhizal plant journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 169 3 371 375 In addition to resource competition, allelopathy is believed to contribute to the invasiveness and impact of several plant invaders of North America. In this study, we examined whether aqueous leaf extracts of Alliaria petiolata and Lonicera maackii, two invaders of deciduous forests in North America, affected growth and reproduction of a target nonmycorrhizal plant and whether effects varied across a soil fertility gradient. While nutrient addition substantially improved the performance of Arabidopsis thaliana grown in field soils in pots in a growth room, addition of A. petiolata extracts to these soils had no significant independent or interactive effects on growth or reproduction. In contrast, addition of L. maackii extracts both directly reduced growth and reproduction of A. thaliana and greatly constrained increases in growth and reproduction of A. thaliana in response to increasing nutrient availability. Use of a nonmycorrhizal target plant revealed that effects of L. maackii were independent of allelopathic effects on mycorrhizae, an effect attributed to A. petiolata in other studies. Web of Science Alliaria petiolata; Lonicera maackii United States Ohio Dayton 39.77 -84.02 Greenhouse terrestrial Deciduous Forest Invasion Hyp. Novel Weapons primary 2467 Pfeifer-Meister, Laurel; Cole, Esther M.; Roy, Bitty A.; Bridgham, Scott D. 2008 Abiotic constraints on the competitive ability of exotic and native grasses in a Pacific Northwest prairie journal OECOLOGIA 155 2 357 366 In prairie ecosystems, abiotic constraints on competition can structure plant communities; however, the extent to which competition between native and exotic plant species is constrained by environmental factors is still debated. The objective of our study was to use paired field and greenhouse experiments to evaluate the competitive dynamics between two native (Danthonia californica and Deschampsia cespitosa) and two exotic (Schedonorus arundinaceus and Lolium multiflorum) grass species under varying nutrient and moisture conditions in an upland prairie in the Willamette Valley, Oregon. We hypothesized the two invasive, exotic grasses would be more competitive under high-nutrient, moderate-moisture conditions, resulting in the displacement of native grasses from these environments. In the field, the experimental reduction of competition resulted in shorter, wider plants, but only the annual grass, Lolium multiflorum, produced more aboveground biomass when competition was reduced. In the greenhouse, the two exotic grasses produced more total biomass than the two native grasses. Competitive hierarchies were influenced by nutrient and/or moisture treatments for the two exotic grasses, but not for the two native grasses. L. multiflorum dominated competitive interactions with all other grasses across treatments. In general, S. arundinaceus dominated when in competition with native grasses, and D. cespitosa produced the most biomass in monoculture or under interspecific competition with the other native grass, D. californica. D. californica, D. cespitosa, and S. arundinaceus all produced more biomass in high-moisture, high-nutrient environments, and D. cespitosa, L. multiflorum, and S. arundinaceus allocated more biomass belowground in the low nutrient treatment. Taken together, these experiments suggest the competitive superiority of the exotic grasses, especially L. multiflorum, but, contrary to our hypothesis, the native grasses were not preferentially excluded from nutrient-rich, moderately wet environments. Web of Science Schedonorus arundinaceus; Lolium multiflorum United States Oregon Willamette Valley 44.007509 -122.979412 Field - Experimental;Greenhouse terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority;Other Superior Competitor primary 2468 Zou, Jianwen; Rogers, William E.; Siemann, Evan 2008 Increased competitive ability and herbivory tolerance in the invasive plant Sapium sebiferum journal BIOLOGICAL INVASIONS 10 3 291 302 The evolution of increased competitive ability (EICA) hypothesis predicts that release from natural enemies in the introduced range favors exotic plants evolving to have greater competitive ability and lower herbivore resistance than conspecifics from the native range. We tested the EICA hypothesis in a common garden experiment with Sapium sebiferum in which seedlings from native (China) and invasive (USA) populations were grown in all pairwise combinations in the native range (China) in the presence of herbivores. When paired seedlings were from the same continent, shoot mass and leaf damage per seedling were significantly greater for plants from invasive populations than those from native populations. Despite more damage from herbivores, plants from invasive populations still outperformed those from native populations when they were grown together. Increased competitive ability and higher herbivory damage of invasive populations relative to native populations of S. sebiferum support the EICA hypothesis. Regression of biomass against percent leaf damage showed that plants from invasive populations tolerated herbivory more effectively than those from native populations. The results of this study suggest that S. sebiferum has become a faster-growing, less herbivore-resistant, and more herbivore-tolerant plant in the introduced range. This implies that increased competitive ability of exotic plants may be associated with evolutionary changes in both resistance and tolerance to herbivory in the introduced range. Understanding these evolutionary changes has important implications for biological control strategies targeted at problematic invaders. Web of Science Sapium sebiferum United States; China Nanjing Agricultural University Garden terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 2469 Meyer, Gretchen A.; Hull-Sanders, Helen M. 2008 Altered patterns of growth, physiology and reproduction in invasive genotypes of Solidago gigantea (Asteraceae) journal BIOLOGICAL INVASIONS 10 3 303 317 Introduced plants may leave their specialized herbivores behind when they invade new ranges. The Evolution of Increased Competitive Ability (EICA) Hypothesis holds that this escape from herbivory could lead to reduced investment in defenses, thereby freeing resources for growth and reproduction. We tested the prediction that introduced genotypes of Solidago gigantea would outperform native genotypes when grown in the absence of herbivores, and examined whether tolerance to insect herbivory has changed in introduced genotypes. S. gigantea is native to North America and an exotic invasive in Europe. Insect damage reduced plant growth and biomass for both native and exotic genotypes. While there was no evidence that continent of origin influenced the degree to which plants compensated for herbivory, the mechanisms contributing to recovery differed for native and exotic plants. Damaged US plants showed enhanced photosynthetic rates to a greater extent than damaged European plants, while damaged European plants carried more leaves than damaged US plants. At the end of the season, leaf mass of European plants was significantly greater than that of US plants. Contrary to the predictions of the EICA hypothesis, US plants were more likely to flower than European plants. European plants invested significantly more of their total reproductive biomass into rhizomes rather than flowers than US plants. While other work with S. gigantea has supported some aspects of the EICA hypothesis, the results reported here generally do not. We conclude that multiple factors influence the success of introduced plants. Web of Science Solidago gigantea North America; Europe Greenhouse terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 2475 Ashton, Isabel W.; Lerdau, Manuel T. 2008 Tolerance to herbivory, and not resistance, may explain differential success of invasive, naturalized, and native North American temperate vines journal DIVERSITY AND DISTRIBUTIONS 14 2 169 178 Numerous hypotheses suggest that natural enemies can influence the dynamics of biological invasions. Here, we use a group of 12 related native, invasive, and naturalized vines to test the relative importance of resistance and tolerance to herbivory in promoting biological invasions. In a field experiment in Long Island, New York, we excluded mammal and insect herbivores and examined plant growth and foliar damage over two growing seasons. This novel approach allowed us to compare the relative damage from mammal and insect herbivores and whether damage rates were related to invasion. In a greenhouse experiment, we simulated herbivory through clipping and measured growth response. After two seasons of excluding herbivores, there was no difference in relative growth rates among invasive, naturalized, and native woody vines, and all vines were susceptible to damage from mammal and insect herbivores. Thus, differential attack by herbivores and plant resistance to herbivory did not explain invasion success of these species. In the field, where damage rates were high, none of the vines were able to fully compensate for damage from mammals. However, in the greenhouse, we found that invasive vines were more tolerant of simulated herbivory than native and naturalized relatives. Our results indicate that invasive vines are not escaping herbivory in the novel range, rather they are persisting despite high rates of herbivore damage in the field. While most studies of invasive plants and natural enemies have focused on resistance, this work suggests that tolerance may also play a large role in facilitating invasions. Web of Science Many United States New York Long Island 40.8683 -72.8617 Field - Experimental;Greenhouse terrestrial Old Field Invasion Hyp. Enemy Release primary 2476 Ayres, Debra R.; Zaremba, Katherine; Sloop, Christina M.; Strong, Donald R. 2008 Sexual reproduction of cordgrass hybrids (Spartina foliosa x alterniflora) invading tidal marshes in San Francisco Bay journal DIVERSITY AND DISTRIBUTIONS 14 2 187 195 We genetically analysed cordgrass plants and seedlings throughout the San Francisco, California, USA, estuary and found that hybrids between exotic Spartina alterniflora and native Spartina foliosa are the principal cordgrass invaders and colonizers. We hypothesized that this was due to higher seed set and siring ability by hybrids relative to the native species; too few alien parents remained in San Francisco Bay for our comparative studies. Hybrid seed comprised 91% to 98% of that set in the marsh study plants over the 2 years of the study. Total viable pollen production by hybrid plants was 400 times that of the native plants. Seed and pollen production were highly skewed towards a few hybrid genotypes. In addition to seed produced by hybrid plants, hybrid seed was produced by S. foliosa due to hybrid backcrossing. While the greatest advantage for hybrids was in pollen and seed production, hybrid seeds germinated, and seedlings survived and grew as well or better than the native species. As native S. foliosa becomes increasingly rare, hybrid seed floating on the tides will predominate, overwhelming recruitment sites and resulting in further colonization by hybrids. In an evolutionary context, hybrids with exceptional pollen and seed production will be initially favoured by natural selection, leading to the evolution of even more fertile hybrid genotypes. Web of Science Spartina alterniflora United States Calfornia San Francisco Bay 37.6467 -122.1433 Field - Observational;Greenhouse terrestrial Wetland Invasion Hyp. Hybridization primary 2477 Chabrerie, Olivier; Verheyen, Kris; Saguez, Robert; Decocq, Guillaume 2008 Disentangling relationships between habitat conditions, disturbance history, plant diversity, and American black cherry (Prunus serotina Ehrh.) invasion in a European temperate forest journal DIVERSITY AND DISTRIBUTIONS 14 2 204 212 Whether non-native plant invasions are causes, consequences, or independent of the low species diversity in recipient ecosystems remains a debated question. We tried to test these three hypotheses in the special case of the American black cherry (Prunus serotina Ehrh.), a gap-dependent tree species, which is invading European temperate forests. We compared plant communities, soil properties, and disturbance history between P. serotina-invaded and uninvaded paired-stands in a managed mixed forest. Relationships between invasion, disturbances, plant communities, and environmental conditions were investigated using redundancy analyses with variation partitioning. Several soil characteristics differed between paired stands, but were rather components of stand invasibility than invasion effects, except for topsoil available phosphorus. The disturbance history was similar among paired stands except for the amount of storm-induced tree falls, which correlated with the invader's density. Wild boar-disturbed soil areas were more important beneath P. serotina canopies, suggesting a positive feedback on its own establishment. Overall, species assemblages in invaded and uninvaded stands were similar; their ecological inconsistency suggested a management-sustained non-equilibrium. Habitat conditions and disturbances explained most of the variation in both plant diversity and P. serotina density, the last two factors exhibiting a weak direct association. We conclude that in managed forest ecosystems where plant communities are mainly driven by non-interactive factors and immigration processes, non-native plant species can naturalize without being directly influenced by measured features of the plant community in the receiving environment on the short term. Web of Science Prunus serotina France 49.3667 2.9 Field - Observational terrestrial Deciduous Forest Invasion Hyp. Community Species Richness;Preadaptation to Climate;Disturbance primary 2478 Ebeling, Susan Kathrin; Hensen, Isabell; Auge, Harald 2008 The invasive shrub Buddleja davidii performs better in its introduced range journal DIVERSITY AND DISTRIBUTIONS 14 2 225 233 It is commonly assumed that invasive plants grow more vigorously in their introduced than in their native range, which is then attributed to release from natural enemies or to microevolutionary changes, or both. However, few studies have tested this assumption by comparing the performance of invasive species in their native vs. introduced ranges. Here, we studied abundance, growth, reproduction, and herbivory in 10 native Chinese and 10 invasive German populations of the invasive shrub Buddleja davidii (Scrophulariaceae; butterfly bush). We found strong evidence for increased plant vigour in the introduced range: plants in invasive populations were significantly taller and had thicker stems, larger inflorescences, and heavier seeds than plants in native populations. These differences in plant performance could not be explained by a more benign climate in the introduced range. Since leaf herbivory was substantially reduced in invasive populations, our data rather suggest that escape from natural enemies, associated with increased plant growth and reproduction, contributes to the invasion success of B. davidii in Central Europe. Web of Science Buddleja davidii Germany Field - Observational terrestrial Invasion Hyp. Enemy Release primary 2480 Piola, Richard F.; Johnston, Emma L. 2008 Pollution reduces native diversity and increases invader dominance in marine hard-substrate communities journal DIVERSITY AND DISTRIBUTIONS 14 2 329 342 Anthropogenic disturbance is considered a risk factor in the establishment of non-indigenous species (NIS); however, few studies have investigated the role of anthropogenic disturbance in facilitating the establishment and spread of NIS in marine environments. A baseline survey of native and NIS was undertaken in conjunction with a manipulative experiment to determine the effect that heavy metal pollution had on the diversity and invasibility of marine hard-substrate assemblages. The study was repeated at two sites in each of two harbours in New South Wales, Australia. The survey sampled a total of 47 sessile invertebrate taxa, of which 15 (32%) were identified as native, 19 (40%) as NIS, and 13 (28%) as cryptogenic. Increasing pollution exposure decreased native species diversity at all study sites by between 33% and 50%. In contrast, there was no significant change in the numbers of NIS. Percentage cover was used as a measure of spatial dominance, with increased pollution exposure leading to increased NIS dominance across all sites. At three of the four study sites, assemblages that had previously been dominated by natives changed to become either extensively dominated by NIS or equally occupied by native and NIS alike. No single native or NIS was repeatedly responsible for the observed changes in native species diversity or NIS dominance at all sites. Rather, the observed effects of pollution were driven by a diverse range of taxa and species. These findings have important implications for both the way we assess pollution impacts, and for the management of NIS. When monitoring the response of assemblages to pollution, it is not sufficient to simply assess changes in community diversity. Rather, it is important to distinguish native from NIS components since both are expected to respond differently. In order to successfully manage current NIS, we first need to address levels of pollution within recipient systems in an effort to bolster the resilience of native communities to invasion. Web of Science Many Australia New South Wales -33.853025;-33.97383 151.222687;151.207581 Field - Experimental marine Benthic Invasion Hyp. Disturbance filter 2481 Pysek, Petr; Jarosik, Vojteck; Muellerova, Jana; Pergl, Jan; Wild, Jan 2008 Comparing the rate of invasion by Heracleum mantegazzianum at continental, regional, and local scales journal DIVERSITY AND DISTRIBUTIONS 14 2 355 363 This paper compares the rate of invasion of Heracleum mantegazzianum (Apiaceae), a Caucasian species invading Europe, at three spatial scales (continental, regional, and local). The rate of invasion was evaluated using inclusion curves, by plotting the cumulative number of invaded countries against time on the continental scale of Europe, number of occupied grid cells at the regional scale of the Czech Republic, and invaded area inferred from a series of aerial photographs taken at the local scale over a period of 49 years in the Slavkovky les region, Czech Republic. Time of 50% inclusion (with 95% confidence intervals, CI) of invaded countries, occupied grid cells, and invaded area was assessed. The invasion was slowest at the continental scale (62 years, CI = 53-70) and did not differ significantly between regional (16 years, CI = 10-20) and local (22 years, CI = 19-24) scales. Our results indicate that there are two different mechanisms of spread acting together in this system, namely human influences and natural spread, and the relative influence of these mechanisms appears to change in an inverse proportion from the largest to the smallest scale. At the local scale, under suitable habitat conditions, the process is driven by biological traits of the species related to dispersal. At the continental and regional scales, humans played a crucial role in the invasion of H. mantegazzianum by planting it as a garden ornamental. At these scales, human-mediated dispersal seems to have been the major driver of spread, responsible for creating dispersal foci in the initial phases of invasion. Species traits played an important role in local spread, resulting in the colonization of new sites. Web of Science Heracleum mantegazzianum Europe Statistical/Meta-analysis terrestrial Invasion Hyp. Inherent Superiority;Other Effective Disperser primary 2482 Ricklefs, Robert E.; Guo, Qinfeng; Qian, Hong 2008 Growth form and distribution of introduced plants in their native and non-native ranges in Eastern Asia and North America journal DIVERSITY AND DISTRIBUTIONS 14 2 381 386 There is a growing interest in understanding the influence of plant traits on their ability to spread in non-native regions. Many studies addressing this issue have been based on relatively small areas or restricted taxonomic groups. Here, we analyse a large data base involving 1567 plant species introduced between Eastern Asia and North America or from elsewhere to both regions. We related the extent of species distributions in each region to growth form and the distinction between upland and wetland habitats. We identified significant relationships between geographical distribution and plant traits in both native and exotic ranges as well as regional differences in the relationships. Range size was larger for herbaceous graminoids and forbs, especially annuals compared to perennials, than for woody species, and range size also was larger for plants of wetland compared to upland habitats. Distributions were more extensive in North America than in Eastern Asia, although native plants from both regions had broader distributions than non-natives, with exotics from elsewhere intermediate. Growth form and environment explained more of the variance in distribution of plants in North America than in Eastern Asia. The influence of growth form and habitat on distribution suggests that these traits might be related to tolerance of ecological conditions. In addition, the smaller extents of species in non-native compared to native areas suggest roles for dispersal limitation and adaptation to region-specific ecological conditions in determining distribution. Web of Science Many Eastern Asia; North America Statistical/Meta-analysis terrestrial Invasion Hyp. Inherent Superiority primary 2483 Truscott, A. -M.; Palmer, S. C. F.; Soulsby, C.; Hulme, P. E. 2008 Assessing the vulnerability of riparian vegetation to invasion by Mimulus guttatus: relative importance of biotic and abiotic variables in determining species occurrence and abundance journal DIVERSITY AND DISTRIBUTIONS 14 2 412 421 Riparian habitats are particularly susceptible to invasion by non-native plants. At present, attempts to build consensus as to what the primary drivers of plant invasion in riparian ecosystems might be is hindered by the absence of common standards for data collected on plant species (e.g. occurrence, or relative abundance). Mimulus guttatus L., a non-native riparian plant species, was used as a model to determine how environmental drivers influence two aspects of invasibility: species occurrence and abundance (assessed in relation to three variables number of patches, patch area and number of stems per patch). Mimulus occurrence and abundance, together with 20 environmental variables, were surveyed in almost 700 contiguous 50-m-long riverbank segments within a catchment in north-east Scotland. More than half of the segments had been colonized by Mimulus. Occurrence and number of patches responded to similar environmental gradients, particularly bare sediment, boulders, high soil moisture, short-statured ruderal communities, and open canopies, and tended to be highest downstream where the river was widest. In contrast to occurrence and patch number, patch area and stem number per patch were higher in the upper reaches of the catchment and were positively associated with low tree canopy and vegetation dominated by light-demanding species and smaller-statured species. Patch area and stem number per patch were also positively related to grazing. This study has highlighted the importance of assessing more than one measure of invasion success (occurrence or patch number and either patch area or stem number per patch), as they are each determined by a different suite of environmental variables. Abiotic factors, such as sediment availability and presence of boulders, appeared to be the major determinants of occurrence and patch number, whereas biotic factors, such as interspecific competition and grazing, were more important ecological determinants underlying area and stem number per patch. Web of Science Mimulus guttatus Scotland 57.1167 -2.85 Field - Observational terrestrial Riparian Invasion Hyp. Disturbance primary 2484 Walter, Hartmut S.; Levin, Geoffrey A. 2008 Feral sheep on Socorro Island: facilitators of alien plant colonization and ecosystem decay journal DIVERSITY AND DISTRIBUTIONS 14 2 422 431 The paper examines the role of feral sheep (Ovis aries) in facilitating the naturalization of alien plants and degrading a formerly robust and stable ecosystem of Socorro, an isolated oceanic island in the Mexican Pacific Ocean. Approximately half of the island is still sheep-free. The other half has been widely overgrazed and transformed into savannah and prairie-like open habitats that exhibit sheet and gully erosion and are covered by a mix of native and alien invasive vegetation today. Vegetation transects in this moderately sheep-impacted sector show that a significant number of native and endemic herb and shrub species exhibit sympatric distribution patterns with introduced plants. Only one alien plant species has been recorded from any undisturbed and sheep-free island sector so far. Socorro Island provides support for the hypothesis that disturbance of a pristine ecosystem is generally required for the colonization and naturalization of alien plants. Sheep are also indirectly responsible for the self-invasion of mainland bird species into novel island habitats and for the decline and range contraction of several endemic bird species. Web of Science Many Mexico Socorro Island 18.778916 -110.98732 Field - Experimental;Field - Observational terrestrial Grassland;Savanna Invasion Hyp. Disturbance primary 2485 Westcott, David A.; Setter, Melissa; Bradford, Matt G.; McKeown, Adam; Setter, Stephen 2008 Cassowary dispersal of the invasive pond apple in a tropical rainforest: the contribution of subordinate dispersal modes in invasion journal DIVERSITY AND DISTRIBUTIONS 14 2 432 439 Dispersal is a significant determinant of the pattern and process of invasions; however, weed dispersal distances are rarely described and descriptions of dispersal kernels are completely lacking for vertebrate-dispersed weeds. Here, we describe dispersal kernels generated by a native disperser, the endangered southern cassowary (Casuarius casuarius, L.) for an invasive, tropical rainforest plant, pond apple (Annona glabra, L.). Pond apple is primarily water-dispersed and is managed as such. We consider whether cassowary dispersal, as a numerically subordinate dispersal mode, provides an additional dispersal service that may modify the invasion process. In infested areas, pond apple seed was common in cassowary dung. Gut passage had no effect on the probability of single seed germination but deposition in clumps or as whole fruits reduced the probability of germination below that of single seeds. Gut passage times ranged from 65 to 1675 min. Combined with cassowary movement data, this resulted in estimated dispersal distances of 12.5-5212 m, with a median distance of 387 m (quartile range 112-787 m). Native frugivores can be effective dispersers of weeds in rainforest and even terrestrial dispersers can provide long-distance dispersal. Importantly, though pond apple might be expected to be almost entirely dispersed downstream and along the margins of aquatic and marine habitats, cassowaries provide dispersal upstream and between drainages, leading to novel dispersal outcomes. Even through the provision of small quantities of novel dispersal outcomes, subordinate dispersal modes can play a significant role in determining invasion pattern and influence the ultimate success of control programs by providing dispersal to locations unattainable via the primary mode. Web of Science Annona glabra Australia Queensland -17.5333 146.0333 Field - Observational terrestrial Tropical Forest Invasion Hyp. Mutualism Facilitation primary 2487 Batten, Katharine M.; Scow, Kate M.; Espeland, Erin K. 2008 Soil microbial community associated with an invasive grass differentially impacts native plant performance journal MICROBIAL ECOLOGY 55 2 220 228 This study is one of the first to show that invasive plant-induced changes in the soil microbial community can negatively impact native plant performance. This greenhouse experiment tested whether soil microbial communities specific to the rhizospheres of an invasive grass (Aegilops triuncialis) and two native plants (Lasthenia californica and Plantago erecta) affected invasive and/or native plant performance. Each of these species were grown in separate pots for 2 months to prime the soils with plant-specific rhizosphere microbial communities. Each plant species was then planted in native- and invasive-primed soil, and effects on plant performance were monitored. At 5 months, differences in microbial biomarker fatty acids between invaded and native soils mirrored previous differences found in field-collected soil. L. californica performance was significantly reduced when grown in invaded soil compared to native soil (flowering date was delayed, aboveground biomass decreased, specific root length increased, and root mass ratio increased). In contrast, P. erecta and A. triuncialis performance were unaffected when grown in invaded vs native soil. These results suggest that in some cases, invasion-induced changes in the soil microbial community may contribute to a positive feedback loop, leading to the increased dominance of invasive species in an ecosystem. Web of Science Aegilops triuncialis United States California University of California McLaughlin Reserve Greenhouse terrestrial Impacts;Invasion Hyp. Mutualism Facilitation primary 2488 Hazell, Steaphan P.; Vel, Terence; Fellowes, Mark D. E. 2008 The role of exotic plants in the invasion of Seychelles by the polyphagous insect Aleurodicus dispersus: a phylogenetically controlled analysis journal BIOLOGICAL INVASIONS 10 2 169 175 The accidental introduction of the spiralling whitefly, Aleurodicus dispersus Russell (Homoptera: Aleyrodidae) to Seychelles in late 2003 is exploited during early 2005 to study interactions between A. dispersus, native and exotic host plants and their associated arthropod fauna. The numbers of A. dispersus egg spirals and pupae, predator and herbivore taxa were recorded for eight related native/exotic pairs of host plants found on Mahe, the largest island in Seychelles. Our data revealed no significant difference in herbivore density (excluding A. dispersus) between related native and exotic plants, which suggests that the exotic plants do not benefit from 'enemy release'. There were also no differences in predator density, or combined species richness between native and exotic plants. Together these data suggest that 'biotic resistance' to invasion is also unlikely. Despite the apparent lack of differences in community structure significantly fewer A. dispersus egg spirals and pupae were found on the native plants than on the exotic plants. Additional data on A. dispersus density were collected on Cousin Island, a managed nature reserve in which exotic plants are carefully controlled. Significantly higher densities of A. dispersus were observed on Mahe, where exotic plants are abundant, than on Cousin. These data suggest that the rapid invasion of Seychelles by A. dispersus may largely be due to the high proportion of plant species that are both exotic and hosts of A. dispersus; no support was found for either the 'enemy release' or the 'biotic resistance' hypotheses. Web of Science Many Seychelles -4.75;-4.3333 55.5;55.6667 Field - Observational terrestrial Invasion Hyp. Enemy Release primary 2489 Jordan, Nicholas R.; Larson, Diane L.; Huerd, Sheri C. 2008 Soil modification by invasive plants: effects on native and invasive species of mixed-grass prairies journal BIOLOGICAL INVASIONS 10 2 177 190 Invasive plants are capable of modifying attributes of soil to facilitate further invasion by conspecifics and other invasive species. We assessed this capability in three important plant invaders of grasslands in the Great Plains region of North America: leafy spurge (Euphorbia esula), smooth brome (Bromus inermis) and crested wheatgrass (Agropyron cristatum). In a glasshouse, these three invasives or a group of native species were grown separately through three cycles of growth and soil conditioning in both steam-pasteurized and non-pasteurized soils, after which we assessed seedling growth in these soils. Two of the three invasive species, Bromus and Agropyron, exhibited significant self-facilitation via soil modification. Bromus and Agropyron also had significant facilitative effects on other invasives via soil modification, while Euphorbia had significant antagonistic effects on the other invasives. Both Agropyron and Euphorbia consistently suppressed growth of two of three native forbs, while three native grasses were generally less affected. Almost all intra- and interspecific effects of invasive soil conditioning were dependent upon presence of soil biota from field sites where these species were successful invaders. Overall, these results suggest that that invasive modification of soil microbiota can facilitate plant invasion directly or via 'cross-facilitation' of other invasive species, and moreover has potential to impede restoration of native communities after removal of an invasive species. However, certain native species that are relatively insensitive to altered soil biota (as we observed in the case of the forb Linum lewisii and the native grasses), may be valuable as 'nurse'species in restoration efforts. Web of Science Euphorbia esula; Bromus inermis; Agropyron cristatum United States Minnesota Greenhouse terrestrial Grassland Impacts;Invasion Hyp. Ecosystem Engineers primary 2490 Marko, Michelle D.; Gross, Elisabeth M.; Newman, Raymond M.; Gleason, Florence K. 2008 Chemical profile of the North American native Myriophyllum sibiricum compared to the invasive M. spicatum journal AQUATIC BOTANY 88 1 57 65 Myriophyllum spicatum L. is a nonindigenous invasive plant in North America that can displace the closely related native Myriophyllum sibiricum Komarov. We analyzed the chemical composition (including: C, N, P, polyphenols, lignin, nonpolar extractables, and sugars) of M. spicatum and M. sibiricum and determined how the chemistry of the two species varied by plant part with growing environment (lake versus tank), irradiance (full sun versus 50% shading), and season (July through September). M. spicatum had higher concentrations of carbon, polyphenols and lignin (C: 47%; polyphenols: 5.5%; lignin: 18%) than M. sibiricum (C: 42%; polyphenols: 3.7%; lignin: 9%) while M. sibiricum had a higher concentration of ash under all conditions (12% versus 8% for M. spicatum). Apical meristems of both species had the highest concentration of carbon, polyphenols, and tellimagrandin H, followed by leaves and stems. Tellimagrandin II was present in apical meristems of both M. spicatum (24.6 mg g(-1) dm) and M. sibiricum (11.1 mg g(-1) dm). Variation in irradiance from 490 (shade) to 940 (sun) mu mol of photons m(-2) s(-1) had no effect on C, N, and polyphenol concentrations, suggesting that light levels above 490 mu mol of photons m(-2) s(-1) do not alter chemical composition. The higher concentration of polyphenols and lignin in M. spicatum relative to M. sibiricum may provide advantages that facilitate invasion and displacement of native plants. (C) 2007 Elsevier B.V. All rights reserved. Web of Science Myriophyllum spicatum United States Minnesota Lab lentic Benthic Invasion Hyp. Inherent Superiority primary 2492 Trebitz, Anett S.; Taylor, Debra L. 2007 Exotic and invasive aquatic plants in great lakes coastal wetlands: Distribution and relation to watershed land use and plant richness and cover journal JOURNAL OF GREAT LAKES RESEARCH 33 4 705 721 We use data from inundated-area surveys of 58 coastal wetlands spanning a gradient of anthropogenic impacts across all five Laurentian Great Lakes to describe the distribution of nine exotic and invasive taxa of aquatic plants. We found plants that were exotic or have invasive strains to be substantially more prevalent in wetlands in Lakes Erie and Ontario than in Lakes Superior and Huron, with Lake Michigan wetlands intermediate. Najas minor (slender naiad), Butomus umbellatus (flowering rush), and Hydrocharis morsus-ranae (European frogbit) were restricted to the lower lakes and rarely dominant. Myriophyllum spicatum (Eurasian milfoil), Potamogeton crispus (curly pondweed), Lythrum salicaria (purple loosestrife), Phalaris arundinacea (reed canary grass), Phragmites australis (common reed), and Typha sp. (cattail) were more widespread and except for P. crispus, often among the dominant taxa. None of the submerged or floating-leaf exotic taxa were associated with altered total plant cover or richness, although M. spicatum, P. crispus, and native Stuckenia pectinatus (sago pondweed) were positively associated with agricultural intensity in the watershed (a surrogate for nutrient loading). Emergent P. australis, L. salicaria, and Typha were more likely to be present and dominant as agricultural intensity increased, and were associated with elevated emergent cover and decreased emergent genera richness. Effects of dominant taxa on plant cover and richness were readily detected using ordinal data from 100 m inundated segments but were harder to discern with data aggregated to the wetland scale. The sum of shoreline-wide abundance scores for four easily identified taxa (S. pectinata, P. australis, Typha, and L. salicaria) is proposed as a rapidly-measured indicator of anthropogenic disturbance across the Great Lakes. Web of Science Many United States Wisconsin; Michigan; New York; Ohio Great Lakes Field - Observational terrestrial;lentic Wetland Invasion Hyp. Community Species Richness primary 2494 Copp, G. H.; Templeton, M.; Gozlan, R. E. 2007 Propagule pressure and the invasion risks of non-native freshwater fishes: a case study in England journal JOURNAL OF FISH BIOLOGY 71 0 148 159 European countries in general, and England in particular, have a long history of introducing non-native fish species, but there exist no detailed studies of the introduction pathways and propagules pressure for any European country. Using the nine regions of England as a preliminary case study, the potential relationship between the occurrence in the wild of non-native freshwater fishes (from a recent audit of non-native species) and the intensity (i.e. propagule pressure) and diversity of fish imports was investigated. The main pathways of introduction were via imports of fishes for ornamental use (e.g. aquaria and garden ponds) and sport fishing, with no reported or suspected cases of ballast water or hull fouling introductions. The recorded occurrence of non-native fishes in the wild was found to be related to the time (number of years) since the decade of introduction. A shift in the establishment rate, however, was observed in the 1970s after which the ratio of established-to-introduced species declined. The number of established non-native fish species observed in the wild was found to increase significantly (P < 0-05) with increasing import intensity (log(10)x + 1 of the numbers of fish imported for the years 2000-2004) and with increasing consignment diversity (log(10)x + 1 of the numbers of consignment types imported for the years 2000-2004). The implications for policy and management are discussed. (c) 2007 Crown Copyright. Web of Science Many England Statistical/Meta-analysis lentic;lotic Invasion Hyp. Propagule Pressure omnivore 2495 Cavieres, L. A.; Quiroz, C. L.; Molina-Montenegro, M. A. 2008 Facilitation of the non-native Taraxacum officinale by native nurse cushion species in the high Andes of central Chile: are there differences between nurses? journal FUNCTIONAL ECOLOGY 22 1 148 156 Positive interactions between species are known to play an important role in the dynamics of native plant communities, particularly in stressful habitats. However, their role in plant invasions is less known, although recent studies have started to highlight the importance of positive interactions as a driver of invasion. It has been suggested that facilitative interactions during invasions are not expected to be species-specific. The perennial herb Taraxacum officinale (dandelion) is a conspicuous alien plant species invading the central Chilean Andes. In contrast to other alien species that are restricted to human-disturbed sites at high elevations, T. officinale is frequently observed growing within native plant communities dominated by cushion plants. We selected sites where two cushion species coexist (Laretia acaulis and Azorella monantha), and evaluated whether T. officinale is equally associated with the two cushion species or shows a preference for one of them. We assessed facilitative effects of the two cushion species on T. officinale via seedling survival experiments, measurements of photochemical efficiency of photosystem II (Fv/Fm and Phi PSII), reproductive output and recording the differences in soil temperature, humidity and nutrient contents between these cushion species and open areas. Taraxacum officinale was significantly and positively associated with only one of the two cushion species (A. monantha). Seedling survival was higher in A. monantha than on L. acaulis or the bare ground. Photochemical efficiency and reproductive output were higher within the two cushion species than outside them. However, performance of T. officinale was significantly better within the cushions of A. monantha than those of L. acaulis. Soil temperature, humidity and contents of nitrogen and phosphorous were similar within the two cushion species; however, potassium was two times higher in the soil beneath L. acaulis than beneath A. monantha. Results indicate that the native cushion species facilitates the establishment and performance of a non-native invasive species, and that this interaction is highly species-specific due to differences in soil nutrient content beneath different benefactor species. Our results indicate that native plants can have facilitative effects on invasive plants, particularly in stressful habitats such as alpine environments. Web of Science Taraxacum officinale Chile -33.3333 -70.2667 Field - Observational terrestrial Invasion Hyp. Mutualism Facilitation herbivore 2496 Polo-Cavia, Nuria; Lopez, Pilar; Martin, Jose 2008 Interspecific differences in responses to predation risk may confer competitive advantages to invasive freshwater turtle species journal ETHOLOGY 114 2 115 123 The nature of competitive interactions between native and introduced invasive species is unclear. In the Iberian Peninsula, the introduced red-eared slider (Trachemys scripta elegans) is an invasive species that is competing and displacing the endangered native Spanish terrapin (Mauremys leprosa). We hypothesized that interspecific differences in antipredatory behavior might confer competitive advantages to introduced T. scripta. We examined whether interspecific differences in responses to predation risk affect the time that turtles remained hidden in the shell before using an active escape to water. Both turtle species adjusted hiding times by balancing predation threat, microhabitat conditions and the costs of remaining hidden. However, introduced T. scripta showed longer hiding times before escaping than native M. Leprosa, which, in contrast, switched from waiting hidden in the shell to escape to deep water as soon as possible. These interspecific differences might result from the risk of facing different types of predators in different microhabitats (land vs. water) in their original habitats. However, in anthropogenically altered habitats where predators have been greatly reduced, T. scripta may avoid potential costs of unnecessary repeated escape responses to water (e.g. interruption of basking). These behavioral asymmetries could contribute to the greater competitive ability of introduced T. scripta within anthropogenically disturbed environments. Web of Science Trachemys scripta elegans Spain Madrid Garden lentic Invasion Hyp. Inherent Superiority Superior Competitor omnivore 2499 Ribeiro, Filipe; Elvira, Benigno; Collares-Pereira, Maria Joao; Moyle, Peter B. 2008 Life-history traits of non-native fishes in Iberian watersheds across several invasion stages: a first approach journal BIOLOGICAL INVASIONS 10 1 89 102 Freshwater ecosystems are seriously imperiled by the spread of non-native fishes thus establishing profiles of their life-history characteristics is an emerging tool for developing conservation and management strategies. We did a first approach to determine characteristics of successful and failed non-native fishes in a Mediterranean-climate area, the Iberian Peninsula, for three stages of the invasion process: establishment, spread and integration. Using general linear models, we established which characteristics are most important for success at each invasion stage. Prior invasion success was a good predictor for all the stages of the invasion process. Biological variables relevant for more than one invasion stage were maximum adult size and size of native range. Despite these common variables, all models produced a different set of variables important for a successful invasion, demonstrating that successful invaders have a combination of biological traits that may favor success at all invasion stages. However, some differences were found in relation to published studies on fish invasions in other Mediterranean-climate areas, suggesting that characteristics of the recipient ecosystem are as relevant as the characteristics of the invading species. Web of Science Many Spain; Portugal Statistical/Meta-analysis lotic Invasion Hyp. Inherent Superiority;Propagule Pressure Broad Tolerances;High Reprod. Output predator 2500 Van Kleunen, Mark; Manning, John C.; Pasqualetto, Vanessa; Johnson, Steven D. 2008 Phylogenetically independent associations between autonomous self-fertilization and plant invasiveness journal AMERICAN NATURALIST 171 2 195 201 Many plant species have been introduced from their native ranges to new continents, but few have become naturalized or, ultimately, invasive. It has been predicted that species that do not require the presence of compatible mates and the services of pollinators for reproduction will be favored in establishment after long-distance dispersal. We tested whether this hypothesis, generally referred to as Baker's law, holds for South African species of Iridaceae ( iris family) that have been introduced in other regions for horticultural purposes. Fruit and seed production of flowers from which pollinators had been experimentally excluded was assessed for 10 pairs of species from nine different genera or subgenera. Each species pair comprised one naturalized and one nonnaturalized species, all of which are used in international horticulture. On average, species of Iridaceae that have become naturalized outside their native ranges showed a higher capacity for autonomous fruit and seed production than congeneric species that have not become naturalized. This was especially true for the naturalized species that are considered to be invasive weeds. These results provide strong evidence for the role of autonomous seed production in increasing potential invasiveness in plants. Web of Science Many South Africa Nieuwoudtiville Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority Self Compatible primary 2503 White, Eve M.; Sims, Nichole M.; Clarke, Anthony R. 2008 Test of the enemy release hypothesis: The native magpie moth prefers a native fireweed (Senecio pinnatifolius) to its introduced congener (S madagascariensis) journal AUSTRAL ECOLOGY 33 1 110 116 The enemy release hypothesis predicts that native herbivores will either prefer or cause more damage to native than introduced plant species. We tested this using preference and performance experiments in the laboratory and surveys of leaf damage caused by the magpie moth Nyctemera amica on a co-occuring native and introduced species of fireweed (Senecio) in eastern Australia. In the laboratory, ovipositing females and feeding larvae preferred the native S. pinnatifolius over the introduced S. madagascariensis. Larvae performed equally well on foliage of S. pinnatifolius and S. madagascariensis: pupal weights did not differ between insects reared on the two species, but growth rates were significantly faster on S. pinnatifolius. In the field, foliage damage was significantly greater on native S. pinnatifolius than introduced S. madagascariensis. These results support the enemy release hypothesis, and suggest that the failure of native consumers to switch to introduced species contributes to their invasive success. Both plant species experienced reduced, rather than increased, levels of herbivory when growing in mixed populations, as opposed to pure stands in the field; thus, there was no evidence that apparent competition occurred. Web of Science Senecio madagascariensis Australia Queensland Lamington National Park -28.1333 153.1 Field - Observational;Lab terrestrial Grassland;Subtropical Forest Invasion Hyp. Enemy Release primary;herbivore 2507 Capers, Robert S.; Selsky, Roslyn; Bugbee, Gregory J.; White, Jason C. 2007 Aquatic plant community invasibility and scale-dependent patterns in native and invasive species richness journal ECOLOGY 88 12 3135 3143 Invasive species richness often is negatively correlated with native species richness at the small spatial scale of sampling plots, but positively correlated in larger areas. The pattern at small scales has been interpreted as evidence that native plants can competitively exclude invasive species. Large-scale patterns have been understood to result from environmental heterogeneity, among other causes. We investigated species richness patterns among submerged and floating-leaved aquatic plants (87 native species and eight invasives) in 103 temperate lakes in Connecticut (northeastern USA) and found neither a consistently negative relationship at small (3-m(2)) scales, nor a positive relationship at large scales. Native species richness at sampling locations was uncorrelated with invasive species richness in 37 of the 60 lakes where invasive plants occurred; richness was negatively correlated in 16 lakes and positively correlated in seven. No correlation between native and invasive species richness was found at larger spatial scales (whole lakes and counties). Increases in richness with area were uncorrelated with abiotic heterogeneity. Logistic regression showed that the probability of occurrence of five invasive species increased in sampling locations (3 m(2), n = 2980 samples) where native plants occurred, indicating that native plant species richness provided no resistance against invasion. However, the probability of three invasive species' occurrence declined as native plant density increased, indicating that density, if not species richness, provided some resistance with these species. Density had no effect on occurrence of three other invasive species. Based on these results, native species may resist invasion at small spatial scales only in communities where density is high (i.e., in communities where competition among individuals contributes to community structure). Most hydrophyte communities, however, appear to be maintained in a nonequilibrial condition by stress and/or disturbance. Therefore, most aquatic plant communities in temperate lakes are likely to be vulnerable to invasion. Web of Science Many USA Connecticut Field - Observational lentic Invasion Hyp. Community Species Richness primary 2509 Tillberg, Chadwick V.; Holway, David A.; LeBrun, Edward G.; Suarez, Andrew V. 2007 Trophic ecology of invasive Argentine ants in their native and introduced ranges journal PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 104 52 20856 20861 Although the ecological effects of invasions often become obvious soon after introduced species become established, more gradual effects may take years to manifest and can thus require long-term data for quantification. We analyzed an 8-year record of stable isotope data on Argentine ants (Linepithema humile) from southern California to infer how the trophic position of this widespread invasive species changes over time as native ant species are displaced. We couple this longitudinal analysis with a biregional comparison of stable isotope data (delta N-15) on ants from Argentina (native range) and California (introduced range) to quantify (i) how the trophic position of L. humile differs between native and introduced populations, and (h) how relative trophic position as estimated by delta N-15 values of Argentine ants compare with those of other ants at the same site. Both long-term and biregional comparisons indicate that the Argentine ant's relative trophic position is reduced at sites with a longer history of occupation. over the course of 8 years, the relative trophic position of L. humile remained high at the leading edge of an invasion front but declined, on average, behind the front as native ants disappeared. Relative to native populations, where L. humile is among the most carnivorous of ants, Argentine ants from California occupied lower trophic positions. These results support the hypothesis that Argentine ants shift their diet after establishment as a result of resource depletion and increasing reliance on plant-based resources, especially honeydew-producing Hemiptera. Our results demonstrate the value of long-term and biregional data in uncovering ecological effects of invasions. Web of Science Linepithema humile USA California 32.6431 -117.0208 Field - Observational terrestrial Chaparral/Shrublands Impacts;Invasion Hyp. Other herbivore;predator 2512 Kinnison, Michael T.; Unwin, Martin J.; Quinn, Thomas P. 2008 Eco-evolutionary vs. habitat contributions to invasion in salmon: experimental evaluation in the wild journal MOLECULAR ECOLOGY 17 1 405 414 Although trait evolution over contemporary timescales is well documented, its influence on ecological dynamics in the wild has received much less attention particularly compared to traditional ecological and environmental factors. For example, evolution over ecologically relevant timescales is expected in populations that colonize new habitats, where it should theoretically enhance fitness, associated vital rates of survival and reproduction, and population growth potential. Nonetheless, success of exotic species is much more commonly attributed to ecological aspects of habitat quality and 'escape from enemies' in the invaded range. Here, we consider contemporary evolution of vital rates in introduced Chinook salmon (Oncorhynchus tshawytscha) that quickly colonized New Zealand and diverged over c. 26 generations. By using experimental translocations, we partitioned the roles of evolution and habitat quality in modifying geographical patterns of vital rates. Variation in habitat quality within the new range had the greatest influence on broad geographical patterns of vital rates, but locally adapted salmon still exhibited more than double the vital rate performance, and hence fitness, of nonlocal counterparts. The scope of this fitness evolution far exceeds the scale of divergence in trait values for these populations, or even the expected fitness effects of particular traits. These results suggest that contemporary evolution can be an important part of the eco-evolutionary dynamics of invasions and highlight the need for studies of the emergent fitness and ecological consequences of such evolution, rather than just changes in trait values. Web of Science Oncorhynchus tshawytscha New Zealand -45.89861 169.988022 Field - Experimental lotic Riparian Invasion Hyp. Evolution in General predator 2514 Van Kleunen, Mark; Johnson, Steven D. 2007 Effects of self-compatibility on the distribution range of invasive European plants in North America journal CONSERVATION BIOLOGY 21 6 1537 1544 Many plant species have been introduced to new continents, but only a small subset of these have become invasive. It has been predicted that self-compatible species, particularly those that do not need the services of pollinators, are more likely to establish and spread after long-distance dispersal. We tested whether this hypothesis, commonly called Baker's law, applies to 361 species that have invaded the United States from Europe. Species capable of autonomous seed production occurred in significantly more states than species requiring a pollen vector. Moreover, of the species that are not capable of autonomous seed production, self-compatible species occurred in significantly more states than those that are not self-compatible. The positive effect of autonomous seed production on the range of invasion was larger for abiotically pollinated species than for biotically pollinated species and for monocarpic species than for polycarpic species. These results support Baker's law, and we recommend that screening protocols for predicting invasiveness of species considered for introduction should include assessment of their breeding system. Web of Science Many USA Statistical/Meta-analysis terrestrial Invasion Hyp. Inherent Superiority Self Compatible primary 2515 Kolbe, Jason J.; Glor, Richard E.; Schettino, Lourdes Rodriguez; Lara, Ada Chamizo; Larson, Allan; Losos, Jonathan B. 2007 Multiple sources, admixture, and genetic variation in introduced Anolis lizard populations journal CONSERVATION BIOLOGY 21 6 1612 1625 Invasive species are classically thought to suffer from reduced within-population genetic variation compared to their native-range sources due to founder effects and population bottlenecks during introduction. Reduction in genetic variation in introduced species may limit population growth, increase the risk of extinction, and constrain adaptation, hindering the successful establishment and spread of an alien species. Results of recent empirical studies, however, show higher than expected genetic variation, rapid evolution, and multiple native-range sources in introduced populations, which challenge the classical scenario of invasive-species genetics. With mitochondrial DNA (mtDNA) sequence data, we examined the molecular genetics of 10 replicate introductions of 8 species of Anolis lizards. Eighty percent of introductions to Florida and the Dominican Republic were from multiple native-range source populations. MtDNA haplotypes restricted to different geographically distinct populations in the native range of a species commonly occurred as intrapopulation polymorphisms in introduced populations. Two-thirds of introduced populations had two or more sources, and admixture elevated genetic variation in half of the introduced populations above levels typical of native-range populations. The mean pairwise sequence divergence among haplotypes sampled within introduced populations was nearly twice that within native-range populations (2.6% vs. 1.4%). The dynamics of introductions from multiple sources and admixture explained the observed genetic contrasts between native and introduced Anolis populations better than the classical scenario for most introduced populations. Elevated genetic variation through admixture occurred regardless of the mode or circumstances of an introduction. Little insight into the number of sources or amount of genetic variation in introduced populations was gained by knowing the number of physical introductions, the size of a species' non-native range, or whether it was a deliberate or accidental introduction. We hypothesize that elevated genetic variation through admixture of multiple sources is more common in biological invasions than previously thought. We propose that introductions follow a sequential, two-step process involving a reduction in genetic variation due to founder effects and population bottlenecks followed by an increase in genetic variation if admixture of individuals from multiple native-range sources occurs. Web of Science Many USA; Dominican Republic Florida Field - Observational terrestrial Subtropical Forest Invasion Hyp. Hybridization omnivore 2517 Leger, Elizabeth A.; Howe, Katherine M.; Gurevitch, Jessica; Woo, Eliza; Hickman, Jonathan; Ashton, Isabel W.; Lerdau, Manuel 2007 The interaction between soil nutrients and leaf loss during early 14 establishment in plant invasion journal FOREST SCIENCE 53 6 701 709 Nitrogen availability affects both plant growth and the preferences of herbivores. We hypothesized that an interaction between these two factors could affect the early establishment of native and exotic species differently, promoting invasion in natural systems. Taxonomically paired native and invasive species (Acer platanoides, Acer rubrum, Lonicera maackii, Diervilla lonicera, Celastrus orbiculata, Celastrus scandens, Elaeagnus umbellata, Ceanothus americanus, Ampelopsis brevipedunculata, and Vitis riparia) were grown in relatively high-resource (hardwood forests) and low-resource (pine barrens) communities on Long Island, New York, for a period of 3 months. Plants were grown in ambient and nitrogen-enhanced conditions in both communities. Nitrogen additions produced an average 12% initial increase in leaf number of all plants. By the end of the experiment, invasive species outperformed native species in nitrogen-enhanced plots in hardwood forests, where all plants experienced increased damage relative to control plots. Native species experienced higher overall amounts of damage in hardwood forests, losing, on average, 45% more leaves than exotic species, and only native species experienced a decline in growth rates (32% compared with controls). In contrast, in pine barrens, there were no differences in damage and no differences in performance between native and invasive plants. Our results suggest that unequal damage by natural enemies may play a role in determining community composition by shifting the competitive advantage to exotic species in nitrogen-enhanced environments. Web of Science Acer platanoides; Lonicera maacki; Celastrus orbiculata; Elaeagnus umbellata; Ampelopsis brevipedunculata USA New York Long Island Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Enemy Release primary 2518 Crutsinger, Gregory M.; Souza, Lara; Sanders, Nathan J. 2008 Intraspecific diversity and dominant genotypes resist plant invasions journal ECOLOGY LETTERS 11 1 16 23 Numerous studies have asked whether communities with many species deter invasions more so than do species-poor communities or whether dominant species deter invasion by colonizing species. However, little is known about whether high intraspecific diversity can deter biological invasions or whether particular genotypes might deter invasions. In this study, we present experimental evidence that intraspecific diversity and particular genotypes of tall goldenrod, Solidago altissima, can act as a barrier to colonization by new species. We found that biomass of colonizing species was negatively correlated with genotypic diversity, and particular genotypes affected the richness, cover, and biomass of colonizing species. Stem density of S. altissima increased with genotypic diversity and varied among genotypes, suggesting that stem density is a key mechanism in limiting colonization dynamics in this system. Our results indicate that the loss of intraspecific diversity within a dominant plant species can increase susceptibility to plant invasions. Web of Science USA Tennesee Knoxville Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Other primary 2519 Domenech, Roser; Vila, Montserrat 2007 Cortaderia selloana invasion across a Mediterranean coastal strip journal ACTA OECOLOGICA-INTERNATIONAL JOURNAL OF ECOLOGY 32 3 255 261 The invasive success of Cortaderia selloana, an alien perennial grass introduced from South America, was assessed by comparing plant and population performance in ruderal and non-ruderal habitats across a Mediterranean coastal strip. The main habitat differentiation criterion was the absence or presence of visible signs of recent disturbances. Plant functional group richness (i.e. number of plant groups classified as grasses, herbs, shrubs, vines and trees), total plant cover and percentage of bare ground was calculated in each habitat. in addition, soil samples were randomly taken in order to analyse total soil C, total N, CaCO3, pH and soil texture. Cortaderia selloana populations were characterized by calculating total density, proportion of juvenile plants, plant volume, number of panicles and reproductive effort (i.e. number of panicles/plant volume) and fecundity per unit area (number of panicles per ha). We compared whether population characteristics and plant performance were associated with biotic and abiotic habitat factors. We expected a better performance of C. selloana in ruderal habitats than in non-ruderal habitats. As expected, ruderal habitats had larger and denser C. selloana populations and recruitment was very high (the proportion of juvenile plants was more than 50%). In consequence, in ruderal habitats, on average, plants were smaller, produced fewer panicles, and had a lower reproductive effort. The high percentage of bare ground, low pH and low functional group richness were the best explanatory variables associated to C. selloana invasion success. (c) 2007 Elsevier Masson SAS. All rights reserved. Web of Science Cortaderia selloana Spain Field - Observational terrestrial Grassland;Old Field Invasion Hyp. Community Species Richness;Disturbance primary 2520 Johnson, Robert H.; Hull-Sanders, Helen M.; Meyer, Gretchen A. 2007 Comparison of foliar terpenes between native and invasive Solidago gigantea journal BIOCHEMICAL SYSTEMATICS AND ECOLOGY 35 12 821 830 To test a defensive chemistry prediction of the Evolution of Increased Competitive Ability (EICA) hypothesis, Solidago gigantea plants from North American and European (invasive) populations were grown in a screen-enclosed garden. Terpenes from 80 seed grown (dried leaves) and 320 rhizome propagated (moist leaves) individuals were confirmed by GC/MS and quantified by GC-FID. Native seed grown plants were found to have significantly greater diterpene concentrations than their European counterparts; foliar sesquiterpenes did not differ. The occurrence of specific sesquiterpenes and diterpenes was homogeneous across the two seed sources suggesting these biochemical pathways remain unchanged. Leaves from native rhizome propagated plants also had significantly greater monoterpene and diterpene concentrations; again sesquiterpene levels did not differ. Rhizome propagated plants exhibited significant population differences in monoterpene and diterpene concentrations. These data support the defensive chemistry predictions of the EICA hypotheses but cannot discount the role of possible founder effects in the invasive range. (C) 2007 Elsevier Ltd. All rights reserved. Web of Science Solidago gigantea United States Wisconsin 43.22 -88.01 Garden terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 2521 Nijjer, Somereet; Rogers, William E.; Lee, Cin-Ty A.; Siemann, Evan 2008 The effects of soil biota and fertilization on the success of Sapium sebiferum journal APPLIED SOIL ECOLOGY 38 1 1 11 Soil organisms can have important impacts on the structure, diversity, and invasion potential of plant communities. In particular, the short co-evolutionary history of non-native plants with soil biota could confer unusual benefits or costs to hosts in the introduced range with consequences for invasion success. We used parallel pot and field studies to examine how soil biota (active or sterilized soil) and fungicide (addition or control) affected the growth and survival of the invasive, non-native tree, Sapium sebiferum, and three co-occurring native tree species Liquidambar styraciflua, Nyssa sylvatica, and Quercus nigra in the Big Thicket National Preserve in east Texas, USA. In addition, because plant interactions with soil microbes vary with abiotic factors, we also included a fertilization treatment. The aboveground and belowground biomass of all species were higher in the presence of an active soil biotic community than in sterilized soil. Sapium alone showed more than additive growth increases under the combination of both field active and fertilized soils. It was also the only species to maintain high aboveground biomass and high aboveground nitrogen levels under those conditions. The high levels of arbuscular mycorrhizal colonization found on Sapium compared to natives suggest that arbuscular mycorrhizae may be involved in this phenomenon. These results indicate that belowground soil organisms provide unusual positive benefits to the invader that are not experienced by native species. This benefit may increase Sapium growth rates compared to natives in the forest understory and therefore facilitate Sapium invasion into mesic temperate forests currently experiencing high levels of anthropogenic nutrient inputs. (c) 2007 Elsevier B.V. All rights reserved. Web of Science Sapium sebiferum USA Texas Big Thicket National Preserve 30.25 -94.44 Field - Experimental;Greenhouse terrestrial Deciduous Forest Invasion Hyp. Mutualism Facilitation primary 2522 Essl, Franz 2007 From ornamental to detrimental? The incipient invasion of Central Europe by Paulownia tomentosa journal PRESLIA 79 4 377 389 The invasion of Paulownia tomentosa (Paulowniaceae), a new alien tree species in Central Europe, native to China, is analysed. By using its distribution in Austria, the invasion of this country is analysed in detail. The first reports of P. tomentosa in Austria were in the 1960s in Vienna. Since then, the number of sites has increased exponentially, with a total of 151 sites in 27 grid cells of the Floristic Mapping project of Austria. The number of sites per grid cell is strongly positively correlated with the minimum residence time in grid cell, which explains 86% of the deviance in the general linear model (GLM). The localities are confined to warm lowland areas (below 450 in altitude) and are concentrated in cities, with 90% of all localities recorded in cities with > 100,000 inhabitants. Paulownia tomentosa typically occurs in small populations of less then 10 individuals (83% of all records) and behaves as a pioneer species colonizing mainly disturbed urban habitats. Near-natural habitats, e.g. forest clearings and riparian shrubberies are rarely colonized. In extremely disturbed areas, the average number of vascular plant species is low (8.9 species), as is total plant cover (17%). As R tomentosa is currently mostly confined to synanthropic habitats in urban areas, the invasion is not yet a nature conservation issue. In the future, predicted climate change might allow P. tomentosa to spread beyond its current distribution. The habitat preference in the eastern USA indicates that further spread of P tomentosa in Central Europe might be accompanied by a switch to more natural habitats, e.g. forest clearings and forest margins. Thus, the future spread of this species should be closely monitored. Web of Science Paulownia tomentosa Austria Field - Observational terrestrial Deciduous Forest;Urban Invasion Hyp. Disturbance primary 2526 Lu, Min; Miller, Daniel R.; Sun, Jiang-Hua 2007 Cross-Attraction between an Exotic and a Native Pine Bark Beetle: A Novel Invasion Mechanism? journal PLOS ONE 2 12 NA NA Background. Aside from the ecological impacts, invasive species fascinate ecologists because of the unique opportunities that invasives offer in the study of community ecology. Some hypotheses have been proposed to illustrate the mechanisms that allow exotics to become invasive. However, positive interactions between exotic and native insects are rarely utilized to explain invasiveness of pests. Methodology/Principal Findings. Here, we present information on a recently formed association between a native and an exotic bark beetle on their shared host, Pinus tabuliformis, in China. In field examinations, we found that 35-40% of P. tabuliformis attacked by an exotic bark beetle, Dendroctonus valens, were also attacked by a native pine bark beetle, Hylastes parallelus. In the laboratory, we found that the antennal and walking responses of H. parallelus to host- and beetle-produced compounds were similar to those of the exotic D. valens in China. In addition, D. valens was attracted to volatiles produced by the native H. parallelus. Conclusions/Significance. We report, for the first time, facilitation between an exotic and a native bark beetle seems to involve overlap in the use of host attractants and pheromones, which is cross-attraction. The concept of this interspecific facilitation could be explored as a novel invasive mechanism which helps explain invasiveness of not only exotic bark beetles but also other introduced pests in principle. The results reported here also have particularly important implications for risk assessments and management strategies for invasive species. Web of Science Dendroctonus valens China Shanxi;Shaanxi Tunlanchuan Forest;Yaopin Forest 37.8;35.7667 111.7333;109.2667 Field - Observational terrestrial Coniferous Forest Invasion Hyp. Mutualism Facilitation herbivore 2527 Wattier, Remi A.; Haine, Eleanor R.; Beguet, Jeremie; Martin, Guenael; Bollache, Loic; Musko, Ilona B.; Platvoet, Dirk; Rigaud, Thierry 2007 No genetic bottleneck or associated microparasite loss in invasive populations of a freshwater amphipod journal OIKOS 116 11 1941 1953 Understanding what factors determine the success of an invasive species in its adopted range is crucial from an evolutionary ecology point of view, because it can provide insights into which biological characteristics are required for survival in varied environmental conditions. Successful establishment may depend on both maintaining genetic diversity, which will allow the species to evolve and/or adapt to new environments, and the presence or absence of natural enemies such as parasites. We tested these two hypotheses by studying populations of the amphipod crustacean Dikerogammarus villosus. This Ponto-Caspian invader has rapidly and successfully invaded western Europe and threatens macroinvertebrate biodiversity in its adopted ranges. It is a unique system to study since both its colonisation history and its geographic origins are well-known. Using samples from the whole geographic range of the invasion route, and using four molecular markers, we found no evidence for genetic bottlenecks during the invasion of D. villosus in western Europe, despite slight variations in allelic proportions according to spatio-temporal subdivisions of our dataset. In addition, we analysed the prevalence and diversity of parasites across its native and adopted range. We found no macro-parasites, and no significant parasite loss of microsporidian parasites during the invasive process. Our data suggest that D. villosus invasion was either massive, or recurrent, or both, allowing a parasitic cortege to follow the host. The maintenance of genetic diversity may have contributed to its success, including the variation in.resistance in the face of the natural enemies. Web of Science Dikerogammarus villosus Europe Field - Observational lotic Benthic Invasion Hyp. Evolution in General;Other predator 2528 Kang, Ming; Buckley, Yvonne M.; Lowe, Andrew J. 2007 Testing the role of genetic factors across multiple independent invasions of the shrub Scotch broom (Cytisus scoparius) journal MOLECULAR ECOLOGY 16 22 4662 4673 Knowledge of the introduction history of invasive plants informs on theories of invasiveness and assists in the invasives management. For the highly successful invasive shrub Scotch broom, Cytisus scoparius, we analysed a combination of nuclear and chloroplast microsatellites for eight native source regions and eight independent invasion events in four countries across three continents. We found that two exotic Australian populations came from different sources, one of which was derived from multiple native populations, as was an invasive sample from California. An invasive population from New Zealand appeared to be predominantly sourced from a single population, either from the native or exotic ranges. Four invasive populations from Chile were genetically differentiated from the native range samples analysed here and so their source of introduction could not be confirmed, but high levels of differentiation between the Chilean populations suggested a combination of different sources. This extensive global data set of replicated introductions also enabled tests of key theories of invasiveness in relation to genetic diversity. We conclude that invasive populations have similar levels of high genetic diversity to native ranges; levels of admixture may vary across invasive populations so admixture does not appear to have been an essential requirement for invasion; invasive and native populations exhibit similar level of genetic structure indicating similar gene flow dynamics for both types of populations. High levels of diversity and multiple source populations for invasive populations observed here discount founder effects or drift as likely explanations for previously observed seed size differences between ranges. The high levels of genetic diversity, differential and source admixture identified for most exotic populations are likely to limit the ability to source biocontrol agents from the native region of origin of invasive populations. Web of Science Cytisus scoparius Australia; New Zealand; USA; Chile Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Evolution in General primary 2529 Hussner, Andreas; Losch, Rainer 2007 Growth and photosynthesis of Hydrocotyle ranunculoides l. fil. in central Europe journal FLORA 202 8 653 660 Floating Pennywort (Hydrocotyle ranunculoides L. fil.) is a worldwide distributed aquatic plant. The species is native to North America and quite common also in Central and South America. In Europe, Japan and Australia it is known as an alien plant, sometimes causing serious problems for affected ecosystems and human use of water bodies. Starting from Western Europe with an eastwards directed spread, Floating Pennywort was recorded in Germany in 2004 for the first time. Since then, the species spread out and got established in western parts of Central Europe. For a definite prediction of the potential of a further spread, data about biology, in particular growth and photosynthesis are needed. Here, regeneration capacity, growth at different nutrient availabilities and photosynthesis of H. ranunculoides were investigated. In addition biomass samples were taken in the field. Results show an enormous regeneration capacity (e.g., by forming new shoots from small shoot fragments), increasing growth rates under increasing nutrient availability and a maximum increase of biomass reaching 0.132 +/- 0.008 gg(-1) dwd(-1). Dense populations of H. ranunculoides growing in ponds and oxbows were found at high nutrient content of the substrate, the biomass reaching there up to 532.4 +/- 14.2 g dw m(-2). Gas exchange analysis showed a physiological optimum of H. ranunculoides CO2 uptake at temperatures between 25 and 35 degrees C and high photon flux densities (PPFD) above similar to 800 mu mol photons m(-2) s(-1). In comparison, native Hydrocotyle vulyaris showed an optimum of net photosynthesis at 20-30 degrees C and a light saturation of CO2 gas exchange at similar to 350 mu mol photons m(-2) s(-1) (C) 2007 Elsevier GmbH. All rights reserved. Web of Science Hydrocotyle ranunculoide Germany Field - Observational lentic;lotic Invasion Hyp. Inherent Superiority Effective Disperser;Clonal Reproduction primary 2530 Blumenthal, Dana M.; Hufbauer, Ruth A. 2007 Increased plant size in exotic populations: A common-garden test with 14 invasive species journal ECOLOGY 88 11 2758 2765 The *evolution of increased competitive ability* (EICA) hypothesis predicts that exotic species will adapt to reduced herbivore pressure by losing costly defenses in favor of competitive ability. Previous studies often support the prediction that plants from exotic populations will be less well defended than plants from native populations. However, results are mixed with respect to the question of whether plants from exotic populations have become more competitive. In a common-garden experiment involving plants from two native and two exotic populations of 14 different invasive species, we tested whether exotic plants generally grow larger than conspecific native plants, and whether patterns of relative growth depend on the intensity of competition. We found a quite consistent pattern of larger exotic than native plants, but only in the absence of competition. These results suggest that invasive species may often evolve increased growth, and that increased growth may facilitate adaptation to noncompetitive environments. Web of Science Many United States Greenhouse terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 2531 Tiebre, Marie-S.; Bizoux, Jean-P.; Hardy, Olivier J.; Bailey, John P.; Mahy, Gregory 2007 Hybridization and morphogenetic variation in the invasive alien Fallopia (Polygonaceae) complex in Belgium journal AMERICAN JOURNAL OF BOTANY 94 11 1900 1910 The invasive alien knotweeds, Fallopia spp. (Polygonaceae), are some of the most troublesome invasive species in Europe and North America. Invasive success in Fallopia may be enhanced by multiple hybridization events. We examined the pattern of hybridization and its evolutionary consequences in Belgium with a concerted analysis of ploidy levels (chromosome counts and flow cytometry), morphological variation, and genetic variation (RAPDs). At least four taxa with different ploidy levels were part of the pattern of invasion in Belgium. Hybrid F. Xbohemica with various chromosome numbers restored the genotypic diversity that was lacking in the parental species. Hybrid genotypes were mainly assigned to a specific genetic pool and not to a mixture between the genetic pools of the putative parental species as would be expected for hybrids. Parental species and hexaploid hybrids differed significantly for a set of well-defined morphological characters, enabling future researchers to distinguish these taxa. On the basis of our results, the importance of hybridization has probably been underestimated in large parts of the adventive range of alien Fallopia species, pointing to the need for concerted molecular and morphological analyses in the study of the evolutionary consequences of hybridization. Web of Science Fallopia Belgium Field - Observational terrestrial Urban;Old Field Invasion Hyp. Hybridization primary 2532 Prentis, P. J.; White, E. M.; Radford, I. J.; Lowe, A. J.; Clarke, A. R. 2007 Can hybridization cause local extinction: a case for demographic swamping of the Australian native Senecio pinnatifolius by the invasive Senecio madagascariensis? journal NEW PHYTOLOGIST 176 4 902 912 center dot Hybridization between native and invasive species can have several outcomes, including enhanced weediness in hybrid progeny, evolution of new hybrid lineages and decline of hybridizing species. Whether there is a decline of hybridizing species largely depends on the relative frequencies of parental taxa and the viability of hybrid progeny. center dot Here, the individual- and population-level consequences of hybridization between the Australian native Senecio pinnatifolius and the exotic Senecio madagascariensis were investigated with amplified fragment length polymorphism (AFLP) markers, and this information was used to estimate the annual loss of viable seeds to hybridization. center dot A high frequency (range 8.3-75.6%) of hybrids was detected in open pollinated seeds of both species, but mature hybrids were absent from sympatric populations. A hybridization advantage was observed for S. madagascariensis, where significantly more progeny than expected were sired based on proportional representation of the two species in sympatric populations. Calculations indicated that S. pinnatifolius would produce less viable seed than S. madagascariensis, if hybridization was frequency dependent and S. madagascariensis reached a frequency of between 10 and 60%. center dot For this native-exotic species pair, prezygotic isolating barriers are weak, but low hybrid viability maintains a strong postzygotic barrier to introgression. As a result of asymmetric hybridization, S. pinnatifolius would appear to be under threat if S. madagascariensis increases numerically in areas of contact. Web of Science Senecio madagascariensis Australia Queensland/New South Wales Border Ranges Field - Observational;Greenhouse;Lab terrestrial Grassland;Subtropical Forest Invasion Hyp. Hybridization primary 2533 Collyer, Michael L.; Stockwell, Craig A.; Dean, C. Adams; Reiser, M. Hildegard 2007 Phenotypic plasticity and contemporary evolution in introduced populations: Evidence from translocated populations of white sands pupfish (Cyrpinodon tularosa) journal ECOLOGICAL RESEARCH 22 6 902 910 Contemporary evolution has been shown in a few studies to be an important component of colonization ability, but seldom have researchers considered whether phenotypic plasticity facilitates directional evolution from the invasion event. In the current study, we evaluated body shape divergence of the New Mexico State-threatened White Sands pupfish (Cyprinodon tularosa) that were introduced to brackish, lacustrine habitats at two different time in the recent past (approximately 30 years and 1 year previously) from the same source population (saline river environment). Pupfish body shape is correlated with environmental salinity: fish from saline habitats are characterized by slender body shapes, whereas fish from fresher, yet brackish springs are deep-bodied. In this study, lacustrine populations consisted of an approximately 30-year old population and several 1-year old populations, all introduced from the same source. The body shape divergence of the 30-year old population was significant and greater than any of the divergences of the 1-year old populations (which were for the most part not significant). Nonetheless, all body shape changes exhibited body deepening in less saline environments. We conclude that phenotypic plasticity potentially facilitates directional evolution of body deepening for introduced pupfish populations. Web of Science Cyprinodon tularosa United States New Mexico Field - Observational lentic;lotic Invasion Hyp. Evolution in General;Plasticity predator 2534 Bailey, John P.; Bimova, Katerina; Mandak, Bohumil 2007 The potential role of polyploidy and hybridisation in the further evolution of the highly invasive Fallopia taxa in Europe journal ECOLOGICAL RESEARCH 22 6 920 928 Japanese knotweed s.l. comprises Fallopia japonica, F. sachalinensis, F. x bohemica and any F2s or backcrosses. The parental taxa were introduced from the East to the West as garden ornamentals in the nineteenth century, and soon spread beyond the confines of the garden to become widespread and persistent weeds. Since only female F. japonica var. japonica was introduced, its impressive spread has occurred solely by vegetative means. However, the initial lack of genetic variability has been complemented by an extensive series of hybridisations in the adventive range. We examine the history, spread, reproductive biology and ecological impact of these species in the West. The role and importance of polyploidy and hybridisation in their invasion of the West is discussed, as are the implications of these factors for the potential further evolution of the group. Web of Science Fallopia japonica; Fallopia sachalinensis Europe Field - Observational terrestrial Riparian;Urban;Old Field Invasion Hyp. Inherent Superiority;Hybridization Clonal Reproduction primary 2536 Engelen A.H., Henriques N., Monteiro C., Santos R. 2011 Mesograzers prefer mostly native seaweeds over the invasive brown seaweed Sargassum muticum journal Hydrobiologia 669 1 157 165 Introduced algae form globally an increasing problem. Grazing on invaders could provide communities with resistance to algal invasions. In this study, we experimentally tested the food choice of mesoherbivores for native macroalgae versus the invader Sargassummuticum. We performed food choice experiments with common grazers (Gammarusinsensibilis, Hydrobia ulvae and Stenosoma nadejda) and both the brown algal invader Sargassummuticum and its native macroalgal competitors, from both the south (Cystoseirahumilis, Stypocaulonscoparium, Cladostephusspongiosus, Dictyotadichotoma, Dictyopterispolypodioides, Sargassumvulgare) and southwest (Cystoseirahumilis) coast of Portugal. We tested whether (i) the invader affects the growth rates of native macro algae, and (ii) the grazers have a food preference for S. muticum compared to native macroalgae. The presence of S. muticum did not affect the growth rates of any of the native species. Grazers affected the growth rate of all seaweeds, but S. muticum had the highest growth rates with and without grazers. For the south coast set of species, Stypocaulon scoparium was the most and S. muticum was the least or among the least preferred by grazers. The grazers from the southwest coast did not show a specific preference for C. humilis or S. muticum. Contrary to our expectations the food choice of mesoherbivores may provide S. muticum with some competitive advantage on the Portuguese south coast, but this may not be applicable to the Southwest communities. Âİ 2011 Springer Science+Business Media B.V. Web of Science Sargassum muticum Portugal Almograve; Evaristo 37.65 8.1333 Field - Experimental marine Intertidal/Near Shore Invasion Hyp. Enemy Of My Enemy primary 2537 Havel J.E. 2011 Survival of the exotic Chinese mystery snail (Cipangopaludina chinensis malleata) during air exposure and implications for overland dispersal by boats journal Hydrobiologia 668 1 195 202 The exotic Chinese mystery snail (Cipangopaludina chinensis malleata) has invaded lakes and rivers across North America and is particularly widespread in northern Wisconsin. Although deliberate introductions and aquarium releases have likely been important, recreational boats may speed the spread of this snail into lakes. Prior research indicated boater access to be a significant predictor of invasion by C. chinensis and other invasive species in Wisconsin. To mimic the process of boater transport between lakes, I examined the tolerance of juvenile C. chinensis to air exposure in a series of field and laboratory experiments. Field experiments under mesic conditions indicated that this snail can survive exposure to air for at least 4 weeks. Larger juveniles were more resistant than smaller juveniles, an effect that was also observed in the laboratory during short-term (3-14 days) experiments. Tolerance of small juveniles to air exposure appeared to be unaffected by temperature, but was affected by humidity, with higher survival at 64% than 34% relative humidity (RH). Results from the current study suggest that C. chinensis is highly resistant to air exposure and could be readily transported by boats moving between lakes, particularly in cool mesic environments. Since juvenile C. chinensis are common around the roots of emergent macrophytes, hitchhiking with boats should be particularly common with boats or trailers infested with aquatic plants. Âİ 2010 Springer Science+Business Media B.V. Web of Science Cipangopaludina chinensis malleata USA Wisconsin Field - Experimental lentic;lotic Invasion Hyp. Inherent Superiority Broad Tolerances herbivore 2539 Qiu J.-W., Chan M.T., Kwong K.L., Sun J. 2011 Consumption, survival and growth in the invasive freshwater snail Pomacea canaliculata: Does food freshness matter? journal Journal of Molluscan Studies 77 2 189 195 Understanding factors that determine the fitness of invasive species may help us predict their spread and impact. Previous studies of the survival, growth and reproduction of Pomacea canaliculata, a freshwater apple snail native to South America now widely spread in Asia, North America and Hawaii, have emphasized the use of fresh leaves as food. We compared the consumption and growth of P. canaliculata reared on fresh and decaying leaves of three species of macrophytes with contrasting content of phenolics (general plant defence chemicals) and nutrients. We conducted 1-day consumption assays using adult snails and a 1-month survival and growth experiment using snails of various sizes. Our results showed that the consumption, survival and growth of P. canaliculata were determined by plant nutrients and phenolics, rather than plant freshness. For Murdannia nudiflora, a species with low phenolic content, fresh leaves with high nitrogen content were more palatable and valuable for growth than decaying leaves with low nitrogen content. Survival was high and not different between the fresh and decaying leaf treatments. For Myriophyllum aquaticum, decaying leaves with moderate nitrogen and low phenolic contents were more palatable and valuable for snail survival and growth than fresh leaves with high nitrogen and high phenolic contents. For Polygonum barbatum, a species with low nitrogen and medium phenolic contents, both fresh and decaying leaves were unpalatable, resulted in low snail survivorship, and did not support snail growth. The results thus indicate that P. canaliculata can utilize both fresh and decaying leaves of adequate levels of nutrients and low levels of phenolics. This dietary flexibility may have contributed to its successful colonization of many types of freshwater wetlands in regions where high-quality fresh leaves are not available throughout the year. Âİ The Author 2011. Web of Science Pomacea canaliculata China Hong Kong Lab lentic;lotic Invasion Hyp. Inherent Superiority Broad Tolerances herbivore 2540 Northfield T.D., Paini D.R., Reitz S.R., Funderburk J.E. 2011 Within plant interspecific competition does not limit the highly invasive thrips, Frankliniella occidentalis in Florida journal Ecological Entomology 36 2 181 187 1. Species invasions are often linked to reductions in biodiversity, and competitive superiority is often cited as the main reason for the success of an invasive species. Although invaded ecosystems are often examined, few have studied areas in which an invasive species has failed to successfully invade. 2. The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is a damaging pest and tospovirus vector that has invaded most of the world, and competitive superiority is considered one of the main reasons for this species' success. 3. However, a recent study demonstrated that competition between larval F. occidentalis and a native thrips species may be limiting F. occidentalis abundance in much of the eastern United States. Frankliniella occidentalis also has a limited abundance in central and southern Florida, which is dominated by the endemic F. bispinosa (Morgan). The potential for interspecific competition to limit F. occidentalis abundance in Florida was assessed. 4. The effects of competition between F. occidentalis and F. bispinosa on adult reproduction on a common host (Capsicum annuum L.) were quantified, using a response surface experimental design and a combination of linear and non-linear competition models. 5. Evidence of symmetric competition between these thrips species was found, but contrary to expectations, F. occidentalis reproduced more in dense interspecific populations than F. bispinosa. These results suggest that, unlike most of the eastern US, interspecific competition is not important in limiting F. occidentalis abundance in central and southern Florida. Âİ 2011 The Authors. Ecological Entomology Âİ 2011 The Royal Entomological Society. Web of Science Frankliniella occidentalis USA Florida Lab terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Superior Competitor herbivore 2547 Erfmeier A., Bruelheide H. 2010 Invasibility or invasiveness? Effects of habitat, genotype, and their interaction on invasive Rhododendron ponticum populations journal Biological Invasions 12 3 657 676 The extent and nature of biological invasions are mainly influenced by either the genotype of the invading species, the suitability of the new habitat or by genotype-habitat interactions expressed in adaptations to the new environment. The relevance of these factors was assessed for the invasive evergreen shrub Rhododendron ponticum. Habitat characteristics of soil, climate and community properties were analysed in six native populations in both Georgia (Caucasus) and Spain and in six invasive ones in Ireland. Growth variables of rhododendron individuals and seedling occurrences in the field served as response variables. We performed a reciprocal transplant experiment with rhododendron cuttings and determined survival of transplants in all countries. Due to low survival rates in Georgia and Spain, vegetative increase was only analysed for Ireland. The Irish sites benefited from significantly higher nutrient supply than the Spanish and Georgian sites. We found both strong positive correlations of nutrient supply and negative correlations of seasonal temperature amplitude with growth variables of shoots and seedling density. Origin, target site and interaction effects were significant in the survival of transplanted rhododendron individuals. The Irish site was more favorable for all genotypes, but the invasive genotypes did not perform better than the native ones. The total increase in shoot length of transplants in Ireland was highest in the Irish genotypes, which might suggest adaptation of the Irish populations to their new area. In conclusion, we found evidence for invasiveness of Irish Rhododendron ponticum populations, but only in the invaded habitat. Nonetheless, habitats in the new range also seem to be well suited to native Spanish populations, supporting the idea that invasibility of these new sites also contributes to rhododendron invasion success. Âİ 2009 Springer Science+Business Media B.V. Web of Science Rhododendron ponticum Ireland Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Evolution in General primary 2562 Xiao Y., Tang J., Qing H., Zhou C., An S. 2011 Effects of salinity and clonal integration on growth and sexual reproduction of the invasive grass Spartina alterniflora journal Flora: Morphology, Distribution, Functional Ecology of Plants 206 8 736 741 The purpose of this study was to explore clonal integration of Spartina alterniflora under gradually changing substrate salinity conditions. We hypothesized that there might be a trade-off between growth and sexual reproduction influenced by soil salinity and, that clonal integration would change this trade-off. The experiment consisted of three levels of substrate salinity (5ƒ?ĝ, 20ƒ?ĝ and 35ƒ?ĝ), two clonal integration treatments (rhizomes severed or not), and three growth stages of daughter ramets (21, 40 and 60. cm tall). Both growth and sexual reproduction of S. alterniflora greatly decreased with increasing salinity. Clonal integration enhanced the survival, growth and sexual reproduction of daughter ramets experiencing salt stress, especially for young ramets, whereas the performance of mother ramets was reduced by clonal integration. Therefore, clonal integration did not affect performance of the whole clones. Contrary to expectations, there was no evidence for a trade-off between growth and sexual reproduction associated with salinity. In addition, clonal integration did not change the effect of salinity on the growth and sexual reproduction of mother and daughter ramets nor of the whole clones. ?? 2011 Elsevier GmbH. Web of Science Spartina alterniflora China Nanjing Greenhouse estuarine Fundamentals primary 2566 Geiger J.H., Pratt P.D., Wheeler G.S., Williams D.A. 2011 Hybrid vigor for the invasive exotic Brazilian peppertree (Schinus terebinthifolius Raddi., Anacardiaceae) in Florida journal International Journal of Plant Sciences 172 5 655 663 How can successful invaders overcome reduced genetic variation via small founder population sizes to persist, thrive, and successfully adapt to a new set of environmental conditions? An expanding body of literature posits hybridization, both interand intraspecific, as a driver of the evolution of invasiveness via genetic processes. We studied Brazilian peppertree (Schinus terebinthifolius), a tree species native to South America that is a successful invader throughout Florida. The tree was introduced separately to the east and west coasts of Florida more than 100 years ago from genetically distinct source populations. We conducted a common garden experiment to compare the early life-stage performance of hybrids versus their progenitors. We hypothesized that hybrids would outperform their progenitors due to the positive genetic effects of intraspecific hybridization (i.e., hybrid vigor). Hybrid seeds germinated at higher rates than eastern seeds. Over the 8-mo experiment, a greater proportion of hybrid seedlings survived than did western seedlings, and hybrids attained greater biomass than the western types. The cumulative hybrid advantage of both seed germination and seedling survival led to the establishment of nearly 45% more hybrid seedlings versus either progenitor. Documenting fitness advantages for hybrids over their progenitors is a requisite finding to consider hybridization as a factor in the success of invasive species. ?? 2011 by The University of Chicago. Web of Science Schinus terebinthifolius USA Florida Garden terrestrial Deciduous Forest Invasion Hyp. Hybridization primary 2568 Macneil C., Dick, Jaimie.T.A. 2011 Parasite-mediated intraguild predation as one of the drivers of co-existence and exclusion among invasive and native amphipods (Crustacea) journal Hydrobiologia 665 1 247 256 Parasitism is emerging as one of the forces determining the outcome of biological invasions. Using field survey and laboratory experiments, we investigate parasitism as one of the factors mediating the interactions among invasive and native amphipods. An extensive survey (100 sites) of a small British island, revealed the native Gammarus duebeni celticus to be parasitised by the muscle wasting microsporidian Pleistophora mulleri and the acanthocephalan duck parasite Polymorphus minutus, the introduced European Gammarus pulex only by P. minutus and the North American Crangonyx pseudogracilis by neither. While Gammarus spp. Were widespread in rivers (one or both species present in 64% of sites), C. pseudogracilis had a restricted distribution (7% of sites) and always co-occurred with Gammarus spp. In contrast, Gammarus spp. were absent from all pond/reservoir sites, with C. pseudogracilis present in over 90%. While the negative association of C. pseudogracilis with Gammarus spp. undoubtedly results from factors such as physico-chemical tolerance and predation as C. pseudogracilis can be heavily predated by Gammarus spp., it was notable that C. pseudogracilis cooccurred with Gammarus spp. more frequently when the latter were parasitised. Laboratory experiments clearly showed that predation on C. pseudogracilis was greatly diminished when G. d. celticus was parasitised by P. mulleri and G. pulex by P. minutus. Our study provides evidence that parasitism, by mediating a key interspecific interaction, is one of an array of interacting factors that may have a role in driving patterns of exclusion and co-existence in natives and invaders. ?? Springer Science+Business Media B.V. 2011. Web of Science Gammarus pulex;Crangonyx pseudogracilis Britain Lab lotic Invasion Hyp. Other omnivore 2570 Dostal P. 2011 Plant competitive interactions and invasiveness: Searching for the effects of phylogenetic relatedness and origin on competition intensity journal American Naturalist 177 5 655 667 The invasion success of introduced plants is frequently explained as a result of competitive interactions with native flora. Although previous theory and experiments have shown that plants are largely equivalent in their competitive effects on each other, competitive nonequivalence is hypothesized to occur in interactions between native and invasive species. Small overlap in resource use with unrelated native species, improved competitiveness, and production of novel allelochemicals are all believed to contribute to the invasiveness of introduced species. I tested all three assumptions in a common-garden experiment by examining the effect of plant origin and relatedness on competition intensity. Competitive interactions were explored within 12 triplets, each consisting of an invasive species, a native congeneric (or confamilial) species, and a native heterogeneric species that are likely to interact in the field. Plants were grown in pots alone or in pairs and in the absence or the presence of activated carbon to control for allelopathy. I found that competition intensity was not influenced by the relatedness or origin of competing neighbors. Although some exotic species may benefit from size advantages and species-specific effects in competitive interactions, none of the three mechanisms investigated is likely to be a principal driver of their invasiveness. ?? 2011 by The University of Chicago. Web of Science Many USA Illinois Garden terrestrial Invasion Hyp. Inherent Superiority Superior Competitor primary 2573 Kulmatiski A., Beard K.H., Meyerson L.A., Gibson J.R., Mock K.E. 2011 Nonnative phragmites australis invasion into Utah Wetlands journal Western North American Naturalist 70 4 541 552 Phragmites australis (Cav.) Trin. ex Steud. (common reed), already one of the world's most widespread plant species, has realized rapid range expansion in coastal wetlands of North America in the past century, but little is known about P. australis range expansion in inland wetland systems. We used genetic analyses, aerial photographs, field surveys, and a greenhouse experiment to study the extent and mechanism of nonnative P. australis invasion of Utah wetlands. We collected and genetically analyzed 39 herbarium samples across the state and 225 present-day samples from northern Utah's major wetland complexes. All samples collected before 1993 and all samples collected outside the major wetlands of northern Utah, including some as recent as 2001, were identified as native (haplotypes A, B, D, and H). Only 10 (4%) of the present-day samples were native, each from small, discrete, low-density stands; the remaining samples were nonnative (haplotype M). Our earliest nonnative sample was collected near the Great Salt Lake in 1993. Around the Great Salt Lake, which contains 40% of Utah's wetlands, P. australis cover has increased from 20% to 56% over the past 27 years - an increase that appears attributable to the nonnative strain. In a 3-month-long greenhouse experiment, the nonnative haplotype grew taller, had more aboveground biomass, and had a greater above- to below- ground biomass ratio than the native haplotypes regardless of nitrogen, phosphorus, or water availability. Nonnative P. australis is rapidly invading the wetlands of northern Utah. Areas in Utah where the native P. australis remains should be identified and protected. ?? 2010. Web of Science Phragmites australi USA Utah Field - Observational;Greenhouse wetland Wetland Invasion Hyp. Inherent Superiority Rapid Growth primary 2575 Trtikova M., Gusewell S., Baltisberger M., Edwards P.J. 2011 Distribution, growth performance and genetic variation of Erigeron annuus in the Swiss Alps journal Biological Invasions 13 2 413 422 We investigated whether local adaptation has been important in enabling the invasive apomictic species Erigeron annuus to extend its altitudinal range in the Swiss Alps. We first conducted a field survey along several major roads crossing the Swiss Alps to study the distribution and growth performance of E. annuus along an altitudinal gradient. We then used amplified fragment length polymorphism to assess genetic variation within and among populations originating from different altitudes. To complement the molecular analyses, we compared the performance of genotypes with different distributions (i. e. local, occasional, widespread genotypes) in two common gardens at 400 m and 1,000 m a. s. l. Although E. annuus was seldom found above 1,000 m, plant performance in field populations did not decrease with increasing altitude. However, there was a significant decline in genotypic diversity within populations, and highland (711-1,100 m) populations were more differentiated (Gst = 0.55) than lowland (200-530 m) populations (Gst = 0.33). In the common garden experiment, local genotypes (i.e. those restricted to a single population) grew less vigorously than widespread genotypes, and were less likely to reproduce. We found no evidence for on-going adaptive changes and conclude that any selection acting on particular genotypes at the altitudinal limit is weak. This leads us to propose that the patterns in the distribution of genotypic diversity in E. annuus are governed by processes of occasional sexual reproduction, dispersal and extinction that are to a large extent independent of altitude. ?? 2010 Springer Science+Business Media B.V. Web of Science Erigeron annuus Switzerland Alps Garden;Lab terrestrial Mountain Invasion Hyp. Evolution of Increased Competitive Ability primary 2578 Barbosa N.P.U., Fernandes G.W., Carneiro M.A.A., Junior L.A.C. 2010 Distribution of non-native invasive species and soil properties in proximity to paved roads and unpaved roads in a quartzitic mountainous grassland of southeastern Brazil (rupestrian fields) journal Biological Invasions 12 11 3745 3755 One of the most important disturbances of roads is the facilitation of the increase of non-native invasive species into adjacent plant communities. The rupestrian fields of Serra do Cip??, a montane grassland ecosystem in southeastern Brazil, are recognized for their enormous richness of species and endemism rates. The presence of non-native invasive species in this ecosystem could threaten the existence of the native flora and its associated organisms. The aim of this study is to understand how non-native invasive species and native species are distributed along paved and unpaved roads, in a montaneous grassland ecosystem such as the Brazilian rupestrian fields. The two road surfaces provide differing gradients from their edges with respect to nutrients, soil chemical aspects and plant species diversity. High content of calcium at the roadside in the paved road resulted from the paving process, in which limestone gravel is used in one of the several paving phases. In these newly created habitats the toxicity of aluminum is drastically reduced and nutrient enriched, hence representing favorable sites from where non-native invasive species are capable to colonize and grow for undetermined period waiting the chance to invade the adjacent pristine habitats. Disturbances provoked by any natural or human-caused event can provide the opportunity for the non-native invasive species to colonize new plant communities. ?? 2010 Springer Science+Business Media B.V. Web of Science Many Brazil Field - Observational terrestrial Grassland;Mountain Invasion Hyp. Disturbance primary 2596 Stiers, Iris; Njambuya, Josphine; Triest, Ludwig 2011 Competitive abilities of invasive Lagarosiphon major and native Ceratophyllum demersum in monocultures and mixed cultures in relation to experimental sediment dredging journal AQUATIC BOTANY 95 2 161 166 Competitive abilities of Lagarosiphon major (Ridley) Moss (invasive in Belgium) and native Ceratophyllum demersum L. were assessed experimentally in relation to sediment dredging. We mimicked these conditions by taking undisturbed sediment (*before dredging* treatment) and by using restored sediment where the uppermost nutrient rich top layer was removed (*after dredging* treatment). Both the species were allowed to grow for seven weeks in monocultures and mixed cultures at different planting densities. Overall, invasive L. major performed better than native C. demersum independent of the characteristics of the growth environment. L. major achieved a higher relative growth rate (RGR) in both treatments based on total length (0.17-0.21 week(-1)) and weight (0.10-0.19 week(-1)) compared to C. demersum (length: 0.04-0.07 week(-1); weight: 0.03-0.17 week(-1)). The better performance of L. major was due to a high plasticity under stressful conditions of low free CO(2) and high pH. Intraspecific competition and niche partitioning were observed between the two species indicating that species coexistence is favoured instead of competitive exclusion. L. major performed better in the *after dredging* treatment. Consequently, we deduce that sediment dredging will not lead to a decline of the invasive L. major. Web of Science Lagarosiphon major Belgium Field - Experimental lentic Invasion Hyp. Plasticity primary 2597 Eichhorn, Markus P.; Ratliffe, Louise C.; Pollard, Kathryn M. 2011 Attraction of ants by an invasive Acacia journal INSECT CONSERVATION AND DIVERSITY 4 3 235 238 1. Invasive plants are often released from the herbivores of their native range, but may also be deprived of their co-evolved mutualists. In southern Portugal Acacia dealbata has become naturalised in secondary woodland habitats and is apparently not damaged by local herbivores. It possesses inactive extra-floral nectaries (EFNs). 2. Artificial damage to leaves, mimicking herbivore attack, induced extra-floral nectar production on both adult trees and seedlings. This response was restricted to individual leaves rather than systemic. 3. Following EFN activation, trees were tended by the invasive Argentine ant Linepithema humile. Seedlings received a tenfold greater visitation rate from either L. humile or the native ant Plagiolepis pygmaea, which appears to displace the former. Eight days after the damage treatment the ants and nectar had largely gone. 4. There was no indication that either species of ant would defend the plant against potential herbivores. 5. This is the first recorded ant-plant interaction among two invasive species. Given the lack of natural herbivore damage and the absence of suitable ants in this novel community, nectar induction by A. dealbata is likely to be a dysfunctional response to damage in its invasive range, with little possibility of developing into a mutualism. Web of Science Acacia dealbata southern Portugal Field - Experimental terrestrial Savanna Invasion Hyp. Enemy Release primary 2598 Innis, Anne F.; Forseth, Irwin N.; Whigham, Dennis F.; McCormick, Melissa K. 2011 Genetic diversity in the invasive Rubus phoenicolasius as compared to the native Rubus argutus using inter-simple sequence repeat (ISSR) markers journal BIOLOGICAL INVASIONS 13 8 1735 1738 Invasive species are one of most significant factors in human-influenced global change. Management actions that prevent the spread and impacts of invasive species require knowledge of their ecological and genetic characteristics. The genetic characteristics of the invasive wine raspberry, Rubus phoenicolasius Maxim. (Rosaceae) and the native sawtooth blackberry, Rubus argutus Link, were examined in two forest habitats on the Maryland Coastal Plain. Using inter-simple sequence repeat (ISSR) markers we quantified the genetic diversity of both species. We analyzed genetic diversity using analysis of molecular variance (AMOVA) and found less genetic diversity in the invasive species, R. phoenicolasius, with variation between sites was 0.418 between sites and 0.075 within sites as compared to the native, R. argutus, where the variation between sites was 1.538 and 0.370 within sites. The lower genetic diversity in the invasive may be due to a history of limited introductions or frequent self-fertilization and clonal reproduction. Web of Science Rubus phoenicolasius USA Maryland Maryland Coastal Plain Field - Observational terrestrial Deciduous Forest Fundamentals primary 2599 Pickering, Catherine Marina; Mount, Ann; Wichmann, Matthias C.; Bullock, James M. 2011 Estimating human-mediated dispersal of seeds within an Australian protected area journal BIOLOGICAL INVASIONS 13 8 1869 1880 Dispersal is critical step in plant invasions but there is limited information about human-mediated long distance seed dispersal, including in protected areas. Seed dispersal by hikers was quantified for five invasive species (the native Acaena novae-zelandiae, and the non-native weeds Rumex acetosella Anthoxanthum odoratum, Dactylis glomerata and Festuca rubra) in part of Australia's Kosciuszko National Park. The proportion of seeds remaining attached to trousers and socks was quantified for replicated short (150 m) and long (5,000 m) distance walks. Functions were fitted for each dataset, and parameters compared among species and between trousers and socks. Dispersal data were combined with attachment rates and the number of people undertaking walks to estimate the total number of weed seeds that might be dispersed. The power exponential function gave the best fit for the majority of datasets, indicating that detachment probability decreased with distance. Seeds of all five species were more tightly attached to socks than trousers, with some seeds still present on socks at 5,000 m. Anthoxanthum and Acaena seeds were more tightly attached to clothing than the other species. Theoretically 1.9 million seeds could be dispersed on socks or 2.4 million seeds on trousers through a season but the actual numbers are likely to be much lower because of limited weed seed at the start of the walks. Because of differences in attachment and detachment rates, seeds from Acaena were more likely to be dispersed longer distances. Long distance human-mediated seed dispersal is potentially a major cause of spread of invasive weeds into protected areas that favours some invasive species over others. Web of Science Many Australia New South Wales Kosciuszko National Park Field - Observational terrestrial Mountain Invasion Hyp. Other primary 2600 Thomaz, Sidinei Magela; Michelan, Thaisa Sala 2011 Associations between a highly invasive species and native macrophytes differ across spatial scales journal BIOLOGICAL INVASIONS 13 8 1881 1891 The association between invasive and native species varies across spatial scales and is affected by phylogenetic relatedness, but these issues have rarely been addressed in aquatic ecosystems. In this study, we used a non-native, highly invasive species of Poaceae (tropical signalgrass) to test the hypotheses that (i) tropical signalgrass success correlates negatively with success of most native species of macrophytes at fine spatial scales, but its success correlates positively or at random with natives at coarse spatial scales, and that (ii) tropical signalgrass is less associated with native species belonging to the family Poaceae than with species belonging to other families (Darwin's naturalization hypothesis). We used a dataset obtained at fine (0.25 m(2)) and coarse (ca. 1,000 m(2)) scales. The presence/absence of all species was recorded at both scales, and their biomass was also measured at the fine scale. We tested the association between tropical signalgrass biomass and individual native species with logistic regressions at the fine scale, and using the T-score index between tropical signalgrass and each native species at both scales. The likelihood of the occurrence of six species (submersed and free-floating) was negatively affected by tropical signalgrass biomass at the fine scale. T-scores showed that three species were less associated with tropical signalgrass than expected by chance, but 22 species co-occurred more than expected by chance at the coarse scale. Associations between species of Poaceae and tropical signalgrass were null at the fine scale, but were positive or null at the coarse scale. In addition to showing that spatial scale affects the patterns of association among the non-native and individual native species, our results indicate that phylogeny did not explain associations between the invasive and native macrophytes, at both scales. Web of Science Urochloa subquadripara Brazil Field - Observational terrestrial;wetland Grassland Invasion Hyp. Other primary 2601 Jordaan, Lorinda A.; Johnson, Steven D.; Downs, Colleen T. 2011 The role of avian frugivores in germination of seeds of fleshy-fruited invasive alien plants journal BIOLOGICAL INVASIONS 13 8 1917 1930 Many highly invasive plant species have fleshy fruits which are eaten by native frugivorous animals. These frugivores play an important role in long-distance seed dispersal, and may also affect germination success. The aim of this study was to determine whether generalist frugivores enhance or decrease seed germination of invasive alien species through pulp removal or seed coat abrasion, besides serving as dispersal agents. Fruits of four fleshy-fruited invasive alien plant species, namely Solanum mauritianum, Cinnamomum camphora, Lantana camara and Psidium guajava, were fed to three generalist avian frugivorous species, which have been observed feeding on these fruits in the wild. Seed retention time was recorded as this affects dispersal distance and the duration that seeds are exposed to the effects of the gut. Seeds removed from excreta, seeds from manually de-pulped fruit, and whole fruit were planted in soil trays housed in a greenhouse. Daily germination counts were done. Seed retention times differed significantly between bird species for all fruits, except those of C. camphora. However, all frugivores had a similar effect on the germination success of seeds of S. mauritianum, L. camara and P. guajava, showing that gut retention time was not important. Germination of seeds from manually de-pulped fruits did not differ from that of ingested seeds of all plant species, suggesting that seed coat abrasion was also not important. Pulp removal resulted in significantly higher germination rates, both in the two species with larger, multi-seeded fruit (S. mauritianum and P. guajava), and in the two species having single-seeded fruit with waxy exocarps (C. camphora and L. camara). Pulp removal also resulted in significantly earlier germination of L. camara and P. guajava seeds. Therefore, frugivores not only accelerate dispersal, but also greatly enhance seed germination of all fleshy-fruited invasive alien species in this study. Web of Science Solanum mauritianum;Cinnamomum camphora;Lantana camara;Psidium guajava South Africa Greenhouse terrestrial Invasion Hyp. Mutualism Facilitation primary 2602 Aluja, M.; Guillen, L.; Rull, J.; Hoehn, H.; Frey, J.; Graf, B.; Samietz, J. 2011 Is the alpine divide becoming more permeable to biological invasions? - Insights on the invasion and establishment of the Walnut Husk Fly, Rhagoletis completa (Diptera: Tephritidae) in Switzerland journal BULLETIN OF ENTOMOLOGICAL RESEARCH 101 4 451 465 The Walnut Husk Fly, Rhagoletis completa Cresson (Diptera: Tephritidae), is native to North America (Midwestern US and north-eastern Mexico) and has invaded several European countries in the past decades by likely crossing the alpine divide separating most parts of Switzerland from Italy. Here, we determined its current distribution in Switzerland by sampling walnuts (Juglans regia L.) in ecologically and climatically distinct regions along potential invasion corridors. R. completa was found to be firmly established in most low altitude areas of Switzerland where walnuts thrive, but notably not a single parasitoid was recovered from any of the samples. Infested fruit was recovered in 42 of the 71 localities that were surveyed, with mean fruit infestation rate varying greatly among sites. The incidence of R. completa in Switzerland is closely related to meteorological mean spring temperature patterns influencing growing season length, but not to winter temperatures, reflecting survival potential during hibernation. Importantly, areas in which the fly is absent correspond with localities where the mean spring temperatures fall below 7 degrees C. Historical data records show that the natural cold barrier around the Alpine divide in the central Swiss Alps corresponding to such minimal temperatures has shrunk significantly from a width of more than 40 km before 1990 to around 20 km after 2000. We hypothesize on possible invasion/expansion routes along alpine valleys, dwell on distribution patterns in relation to climate, and outline future research needs as the incursion of R. completa into Switzerland; and, more recently, other European countries, such as Germany, Austria, France and Slovenia, represent an example of alien species that settle first in the Mediterranean Basin and from there become invasive by crossing the Alps. Web of Science Rhagoletis completa Switzerland terrestrial Fundamentals herbivore 2603 Chu, D.; Gao, C. S.; De Barro, P.; Wan, F. H.; Zhang, Y. J. 2011 Investigation of the genetic diversity of an invasive whitefly (Bemisia tabaci) in China using both mitochondrial and nuclear DNA markers journal BULLETIN OF ENTOMOLOGICAL RESEARCH 101 4 467 475 It is often considered that reduced genetic variation due to bottlenecks and founder effects limits the capacity for species to establish in new environments and subsequently spread. The recent invasion (during the past five years) of an alien whitefly, one member of Bemisia tabaci cryptic species complex, referred to as Mediterranean (herein referred to as Q-type) in Shandong Province, China, provides an ideal opportunity to study the changes in genetic variation between its home range in the Mediterranean region and its invasion range. Using both the mitochondrial cytochrome oxidase I (mtCOI) and nuclear (microsatellite) DNA, we show that Q in Shandong likely originated in the western Mediterranean. We also found that the haplotype diversity was low compared with its presumed geographic origin, whereas microsatellite allele diversity showed no such decline. A key factor in invasions is the establishment of females and so bottleneck and founder events can lead to a very rapid and considerable loss of mitochondrial diversity. The lack of haplotype diversity in Shandong supports the interpretation that, at one or more points between the western Mediterranean and China, the invading Q lost haplotype diversity, most probably through the serial process of establishment and redistribution through trade in ornamental plants. However, the loss in haplotype diversity does not necessarily mean that nuclear allelic diversity should also decline. Provided females can mate freely with whichever males are available, allelic diversity can be maintained or even increased relative to the origin of the invader. Our findings may offer some explanation to the apparent paradox between the concept of reduced genetic variation limiting adaptation to new environments and the observed low diversity in successful invaders. Web of Science Bemisia tabaci China Shandong Province Field - Observational terrestrial Deciduous Forest Invasion Hyp. Evolution in General herbivore 2604 Huebner, Cynthia D. 2011 Seed Mass, Viability, and Germination of Japanese Stiltgrass (Microstegium vimineum) under Variable Light and Moisture Conditions journal INVASIVE PLANT SCIENCE AND MANAGEMENT 4 3 274 283 The success of Japanese stiltgrass as an invader may be due to its ability to respond to stochastic events (e.g., by sexual reproduction via chasmogamous [CH] flowers) and to maintain a beneficial genetic make-up (e.g., by self-fertilizing via cleistogamous [CL] flowers) when conditions are stable. This paper evaluates the importance of Japanese stiltgrass seed type (chasmogamous seeds, cleistogamous seeds, and seeds originating from forest-interior [F-I] plants) in terms of seed mass, viability, and germination across variable moisture regimes (three regions in West Virginia) and at two light levels (roadside and forest interior). Seeds From nine populations were sampled in three site types in 2005 and 2008 and stored at 5 C until testing in April 2009. Seeds were tested for viability using a dye test. Seeds were germinated under both constant and fluctuating day/night temperatures. Additional samples of CH and CL seeds collected in 2008 were tested for viability again in September 2010 for a measure of seed longevity. CL and F-I seeds were smaller in mass than CH seeds. Seeds from the drier sites were smaller in mass than seeds from the more mesic sites. CL seeds, followed by F-I seeds, were less viable than CH seeds in 2005 and 2008. CL and F-I seeds had lower germination rates than CH seeds for each site type in 2005, but germination rates of the seed types did not differ in 2008. Differences in seed longevity for 2008 seeds were lower for CL compared to CH seeds, but only in the drier sites. Japanese stiltgrass' longer-lived and larger CH seeds from the roadsides may ensure population survival over the long term. Younger CL and F-I seeds differ less from CH seeds in terms of germination than older seeds, which may help Japanese stiltgrass to maintain populations under relatively stable conditions in the short term. Web of Science Microstegium vimineum USA West Virginia Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Broad Tolerances primary 2605 Spencer, David; Enloe, Stephen; Liow, Pul-Sze; Ksander, Greg; Carruthers, Raymond 2011 Does Superior Competitive Ability Explain Yellow Starthistle's (Centaurea solstitialis) Successful Invasion of Annual Grasslands in California? journal INVASIVE PLANT SCIENCE AND MANAGEMENT 4 3 284 295 Yellow starthistle represents one of the most spectacular examples of biological invasion in the western United States. However, the mechanisms leading to its success have not been clearly elucidated. Although its success has been attributed to superior competitive ability, few competition studies have been performed with yellow starthistle to test this assertion. Yellow starthistle and wild oat (a dominant component of California annual grasslands) were grown in monocultures and mixtures to assess the strength of competitive interactions between them. For either species, intraspecific competition exerted a greater influence over mean plant weight than did interspecific competition. A companion study revealed temporal separation in the phenology of these plants, explaining the weak role of interspecific competition. Additional measurements of growth and soil moisture dynamics in large 270-cm-tall by 50-cm-diam polyvinyl chloride columns also showed a lack of interspecific competition and confirmed that water use patterns differed between these species, indicating niche partitioning. Wild oat reduced soil moisture to 5% but only to a depth of approximately 150 cm. Yellow starthistle depleted soil moisture to less than 5% throughout the column to a depth of at least 270 cm. These patterns were present when wild oat and yellow starthistle were grown individually or together in the columns, indicating that yellow starthistle had a greater impact on soil moisture and to greater depths. Yellow starthistle's invasion of grasslands in California does not appear to be due to superior competitive ability, but may be due to its ability to access deeper soil moisture. These results support the empty niche hypothesis that implies that invasive species are successful in new habitats because they access resources not available to resident species. Web of Science Centaurea solstitialis USA California Field - Observational terrestrial Grassland Invasion Hyp. Inherent Superiority Superior Competitor primary 2606 Briski, Elizabeta; Ghabooli, Sara; Bailey, Sarah A.; MacIsaac, Hugh J. 2011 Assessing invasion risk across taxa and habitats: life stage as a determinant of invasion success journal DIVERSITY AND DISTRIBUTIONS 17 4 593 602 Aim Many aquatic invertebrates produce dormant life-history stages as a means to endure inhospitable environments and to facilitate natural long-distance dispersal, yet we have little understanding of the role of dormant stages as a mechanism for human-mediated introductions of non-indigenous species. We explore the survival of invertebrate dormant eggs in collected ships' ballast sediment over a 1-year period to determine relative invasion potential across taxa (i.e. rotifers, copepods, cladocerans and bryozoans) and different habitats (freshwater, marine). Location Canadian Atlantic and Pacific coasts and Laurentian Great Lakes. Methods During 2007 and 2008, 19 ballast samples were collected as a part of a larger study. The degradation rate of dormant eggs was assessed by enumerating dormant eggs and by conducting viability hatching experiments. Results Taxa examined included rotifers, copepods, anomopods, onychopods and bryozoans. Dormant eggs of rotifers degraded at the highest rate of all taxa examined, with no viable eggs remaining within 10 months. Copepods showed a less rapid degradation rate than rotifers. The degradation rate of anomopod dormant eggs was significantly slower than that of both rotifers and copepods. Onychopods and bryozoans did not visibly degrade at all over 12 months. Viability hatching experiments were successful for rotifers, copepods, and anomopods. Onychopods and bryozoans did not hatch during any of the three hatching trials. Main conclusions Dormancy is not equally beneficial to all invertebrate taxa. Our results indicate that dormant eggs of rotifers and copepods degrade at a rapid rate and may not pose high invasion risk. In contrast, the slow degradation rate of anomopod dormant eggs and the lack of degradation of onychopod and bryozoan dormant eggs could result in high invasion risk because of their accumulation in ballast tanks. Species having resistant dormant eggs mostly belong to freshwater taxa making freshwater habitats at higher invasion risk by dormant invertebrates than marine habitats. Web of Science Many USA Field - Observational marine;lentic Invasion Hyp. Inherent Superiority Effective Disperser primary;herbivore;predator 2607 Kumschick, Sabrina; Alba, Christina; Hufbauer, Ruth A.; Nentwig, Wolfgang 2011 Weak or strong invaders? A comparison of impact between the native and invaded ranges of mammals and birds alien to Europe journal DIVERSITY AND DISTRIBUTIONS 17 4 663 672 Aim Species introduced to an area outside of their native range are often thought to have higher impact in this new area. We examined whether this is really the case in mammals and birds and to what extent. In particular, we explored how impacts of alien species vary in relationship to invader identity and type of impact. Location Global. Methods We conducted a thorough review of the literature to compare the impact of alien European mammals and birds in their native and invaded ranges. Based on a series of environmental and economic impact scores, we ordered species along a continuum from weak invaders, which have lower impact in the invaded range, to strong invaders, which have higher impact in the invaded range. Results We found that nearly 80% of the mammals are strong invaders, but only half of the birds. Members of these two classes also affect their communities in different ways; birds more often have an impact via hybridization, whereas mammals have stronger impacts via herbivory, transmission of diseases to wildlife and their effects on agriculture, livestock and forestry. Main conclusions Generally, mammals and birds have different impacts when invading new regions. Although there are some bird species that are strong invaders, these remain the exception among birds, whereas most mammals increase their impact in the invaded range. This study provides a deeper insight into patterns of impact in the invaded range. Web of Science Many Statistical/Meta-analysis;Review terrestrial Impacts;Invasion Hyp. Other herbivore;omnivore;predator 2608 Pergl, Jan; Muellerova, Jana; Perglova, Irena; Herben, Tomas; Pysek, Petr 2011 The role of long-distance seed dispersal in the local population dynamics of an invasive plant species journal DIVERSITY AND DISTRIBUTIONS 17 4 725 738 Aim Long-distance dispersal is important for plant population dynamics at larger spatial scales, but our understanding of this phenomenon is mostly based on computer modelling rather than field data. This paper, by combining field data and a simulation model, quantifies the fraction of the seed of the alien species Heracleum mantegazzianum that needs to disperse over a long distance for successful invasion. Location Central Europe, Czech Republic. Methods To assess the role of random dispersal in long-term population dynamics of the studied species, we combined longitudinal data covering 50 years of the invasion of this plant from its very start, inferred from a series of aerial photographs of 60-ha plots, with data on population dynamics at a fine scale of 10-m(2) plots. Results A simulation model based on field data indicates that the fraction of seed that is dispersed from source plants not described by the short-distance dispersal kernel ranges from 0.1 to 7.5% of the total seed set. The fraction of long-distance dispersed seed that provides the best prediction of the observed spread was significantly negatively correlated with the percentage of habitats suitable for invasion. Main conclusions Our results indicate that the fraction of seeds that needed to be dispersed over long distances to account for the observed invasion dynamics decreased with increasing proportion of invasible habitats, indicating that the spatial pattern of propagule pressure differs in landscapes prone to invasion. Long-distance dispersal is an important component of the population dynamics of an invasive species even at relatively small scales. Web of Science Heracleum mantegazzianum Czech Republic Field - Observational terrestrial Deciduous Forest;Old Field Invasion Hyp. Propagule Pressure primary 2609 Hillstrom, Carl; Cipollini, Don 2011 VARIATION IN PHENOTYPIC PLASTICITY AMONG NATIVE AND INVASIVE POPULATIONS OF ALLIARIA PETIOLATA journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 172 6 763 772 Alliaria petiolata is a Eurasian biennial herb that is invasive in North America and for which phenotypic plasticity has been noted as a potentially important invasive trait. Using four European and four North American populations, we explored variation among populations in the response of a suite of antioxidant, antiherbivore, and morphological traits to the availability of water and nutrients and to jasmonic acid treatment. Multivariate analyses revealed substantial variation among populations in mean levels of these traits and in the response of this suite of traits to environmental variation, especially water availability. Univariate analyses revealed variation in plasticity among populations in the expression of all of the traits measured to at least one of these environmental factors, with the exception of leaf length. There was no evidence for continentally distinct plasticity patterns, but there was ample evidence for variation in phenotypic plasticity among the populations within continents. This implies that A. petiolata has the potential to evolve distinct phenotypic plasticity patterns within populations but that invasive populations are no more plastic than native populations. Web of Science Alliaria petiolata USA Field - Observational terrestrial Deciduous Forest Invasion Hyp. Plasticity primary 2610 Huttanus, Temsha D.; Mack, Richard N.; Novak, Stephen J. 2011 PROPAGULE PRESSURE AND INTRODUCTION PATHWAYS OF BROMUS TECTORUM (CHEATGRASS; POACEAE) IN THE CENTRAL UNITED STATES journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 172 6 783 794 An introduced species' propagule pressure strongly influences the genetic diversity and evolutionary potential of its descendants and even the likelihood of biological invasion. We examined population genetic consequences arising from introduction of the invasive annual grass Bromus tectorum into the central United States (U.S.). The origin and frequency of introductions were investigated by assembling allozyme diversity data from 60 widely spaced populations. At least five introduction events contributed to the grass's genetic diversity in the central U.S. Populations in this region have fewer alleles (30 vs. 43) and polymorphic loci (5 vs. 13) than native populations, evidence of a genetic bottleneck. However, the populations are, on average, more genetically diverse and less structured than native populations. Assembly within central U. S. populations of previously allopatric genotypes may have allowed the formation, via outcrossing, of a rare multilocus genotype. Genetic admixtures may have occurred through any combination of east-to-west spread coincident with nineteenth-century arrival of European settlers, dispersal from southern Ontario via Great Lakes shipping and commerce, and direct introduction from the native range. Our results illustrate the population genetic consequences of relatively high propagule pressure (i.e., repeated immigrations to a new range from multiple sources). Web of Science Bromus tectorum USA Field - Observational terrestrial Grassland Invasion Hyp. Propagule Pressure primary 2611 Erfmeier, Alexandra; Bruelheide, Helge 2011 MAINTENANCE OF HIGH GENETIC DIVERSITY DURING INVASION OF RHODODENDRON PONTICUM journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 172 6 795 806 Adaptive processes in invasive plant populations may explain exotic range expansions and ecotypic shifts between native and invasive populations of the same species. Sufficient genetic variation in invasive populations occurring within the new range is a precondition for selection. While genetic diversity can be considerably reduced during invasions following founder effects and genetic drift, it can also be maintained via mechanisms of effective gene flow. Rhododendron ponticum L., an aggressive invader in the British Isles, is an appropriate test species for investigating changes in genetic diversity and differentiation. Six native populations in Georgia and Spain each and six invasive populations in Ireland were analyzed with amplified fragment length polymorphism markers to calculate genetic distances, genetic diversity, and differentiation within and among populations. While the highest level of genetic diversity was found within native Georgian populations, thus indicating a refugium, native Spanish and invasive Irish populations showed reduced levels of genetic diversity but displayed no further reduction in the invasive range. Genetic differentiation within countries was weak. Spanish and Irish populations showed close relationships supporting a probable Spanish provenance for the invasive Rhododendron. We suggest that the preservation of sufficient genetic variation in invasive R. ponticum populations in Ireland has been vital to the species' adaptation to new environmental conditions. Web of Science Rhododendron ponticum Ireland Field - Observational terrestrial Deciduous Forest Invasion Hyp. Evolution in General primary 2612 Sadakiyo, Shou; Ishihara, Michihiro 2011 Rapid seasonal adaptation of an alien bruchid after introduction: geographic variation in life cycle synchronization and critical photoperiod for diapause induction journal ENTOMOLOGIA EXPERIMENTALIS ET APPLICATA 140 1 69 76 Whether alien insects that are introduced into temperate regions adapt to seasonally changing environmental conditions is an important question in evolutionary biology. If rapid evolution has occurred in a non-native environment, a latitudinal cline in critical photoperiod for diapause induction (i.e., the photoperiod at which half of the individuals enter diapause) and in life cycle synchronization with host plant phenology should be evident among locations. The alien bruchid Acanthoscelides pallidipennis (Motschulsky) (Coleoptera: Bruchidae) is native to North America and introduced into Japan with the host plant Amorpha fruticosa L. (Fabaceae) in the late 1940s. To examine whether seasonal adaptation has occurred in A. pallidipennis, we conducted a laboratory experiment and phenological observations using three latitudinally different populations. We bred F1 eggs at 22 degrees C and five photoperiodic regimens - L: D = 10: 14, 13: 11, 14: 10, 15: 9, or 16: 8 hours - and examined whether diapause was induced. The estimated critical photoperiod for diapause induction was longest in the most northern population and shortest in themost southern population. Life cycle was found to be synchronized with host phenology in each location. Also voltinism varied geographically, from univoltine in the northern population to bivoltine in the southern populations. These results showed that A. pallidipennis rapidly adapted to seasonal environmental conditions in Japan after its introduction. Web of Science Acanthoscelides pallidipennis Japan Field - Observational terrestrial Deciduous Forest Invasion Hyp. Evolution in General herbivore 2613 Bennett, Alison E.; Thomsen, Meredith; Strauss, Sharon Y. 2011 MULTIPLE MECHANISMS ENABLE INVASIVE SPECIES TO SUPPRESS NATIVE SPECIES journal AMERICAN JOURNAL OF BOTANY 98 7 1086 1094 Premise of the study : Invasive plants represent a significant threat to ecosystem biodiversity. To decrease the impacts of invasive species, a major scientific undertaking of the last few decades has been aimed at understanding the mechanisms that drive invasive plant success. Most studies and theories have focused on a single mechanism for predicting the success of invasive plants and therefore cannot provide insight as to the relative importance of multiple interactions in predicting invasive species' success. Methods : We examine four mechanisms that potentially contribute to the success of invasive velvetgrass Holcus lanatus : direct competition, indirect competition mediated by mammalian herbivores, interference competition via allelopathy, and indirect competition mediated by changes in the soil community. Using a combination of field and greenhouse approaches, we focus on the effects of H. lanatus on a common species in California coastal prairies, Erigeron glaucus, where the invasion is most intense. Key results : We found that H. lanatus had the strongest effects on E. glaucus via direct competition, but it also influenced the soil community in ways that feed back to negatively influence E. glaucus and other native species after H. lanatus removal. Conclusions : This approach provided evidence for multiple mechanisms contributing to negative effects of invasive species, and it identified when particular strategies were most likely to be important. These mechanisms can be applied to eradication of H. lanatus and conservation of California coastal prairie systems, and they illustrate the utility of an integrated set of experiments for determining the potential mechanisms of invasive species' success. Web of Science Holcus lanatus USA California Field - Experimental terrestrial Grassland Invasion Hyp. Mutualism Facilitation;Inherent Superiority;Novel Weapons;Ecosystem Engineers Superior Competitor primary 2614 DeWalt, Saara J.; Siemann, Evan; Rogers, William E. 2011 GEOGRAPHIC DISTRIBUTION OF GENETIC VARIATION AMONG NATIVE AND INTRODUCED POPULATIONS OF CHINESE TALLOW TREE, TRIADICA SEBIFERA (EUPHORBIACEAE) journal AMERICAN JOURNAL OF BOTANY 98 7 1128 1138 Premise of the study: Invasive plants often display genetically determined variation in patterns of growth and resource allocation between native and introduced genotypes, as well as among genotypes within different regions of the introduced range. We examined patterns of genetic variation within and among native and introduced populations of the tetraploid Chinese tallow tree (Triadica sebifera, Euphorbiaceae) to determine whether nonselective evolutionary processes or the introduction history could contribute to previously observed phenotypic differences between native and introduced populations as well as among introduced populations. Methods: We used six microsatellite markers to study 12 native populations in China, 51 introduced populations in the southeastern USA, and one introduced population in Australia. Key results: Genetic diversity was greater within and among native populations than introduced populations. Within the southeastern USA, populations in Georgia and South Carolina differed substantially in their genetic composition and had greater genetic diversity than the rest of the southeastern USA. Greater genetic similarity between some populations in the native range and introduced range indicate a common provenance for Georgia and South Carolina populations that could have come from any of several western or southern Chinese populations and a different provenance for other southeastern USA populations and the Australian population, which were most similar to more northeastern Chinese populations. Conclusions: Differences among introduced populations in potentially adaptive traits (e. g., herbivore tolerance, herbivore resistance, growth rates) may result in part from the introduction history, in particular from differences present among source populations in the native range. Web of Science Triadica sebifera USA ; Australia South Carolina;Georgia Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Rapid Growth primary 2615 Kirk, Heather; Paul, Jennifer; Straka, Jason; Freeland, Joanna R. 2011 LONG-DISTANCE DISPERSAL AND HIGH GENETIC DIVERSITY ARE IMPLICATED IN THE INVASIVE SPREAD OF THE COMMON REED, PHRAGMITES AUSTRALIS (POACEAE), IN NORTHEASTERN NORTH AMERICA journal AMERICAN JOURNAL OF BOTANY 98 7 1180 1190 Premise of the study : The Eurasian subspecies of the common reed (Phragmites australis subsp. australis, hereafter abbreviated as P. a. australis) was introduced to North America in the late 18(th) century and rapidly expanded its range, posing an ecological threat to wetlands. In this study, we aimed to determine whether admixture among multiple lineages, dispersal mechanisms, and high genetic diversity have contributed to the invasion of P. a. australis in the northeastern part of its range. Understanding mechanisms of the P. a. australis invasion will 1) contribute to a broader understanding of the factors that facilitate plant invasion, and 2) help us to develop effective management strategies for wetlands threatened by P. a. australis invasion. Methods : We used a population genetics approach incorporating nine microsatellite loci to study genetic diversity and population structure in relation to biogeography of introduced North American Phragmites a. australis stands in the northeastern continental region. Key Results : Phragmites a. australis is genetically diverse in the region studied here. Significant population structure exists, and population structure is likely influenced by both long-distance dispersal via major waterways, and short-distance dispersal overland. Different lineages sometimes colonize geographically proximate locations leading to opportunities for admixture. Clonal reproduction likely exaggerates geographical structure among some stands, although high genetic and clonal diversity within some stands implies that sexual reproduction occurs frequently in P. a. australis. Conclusions : A variety of factors, including admixture among multiple lineages, multiple modes of dispersal, and plasticity in reproductive strategy promote the invasion success of Phragmites a. australis. Wetland managers in the St. Lawrence River/Great Lakes region should focus monitoring efforts on the shores of conservation lands to prevent the establishment of propagules from novel lineages. Web of Science Phragmites australis USA Field - Observational wetland Wetland Invasion Hyp. Inherent Superiority;Plasticity Effective Disperser;Clonal Reproduction primary 2616 Gonthier, P.; Garbelotto, M. 2011 Amplified fragment length polymorphism and sequence analyses reveal massive gene introgression from the European fungal pathogen Heterobasidion annosum into its introduced congener H. irregulare journal MOLECULAR ECOLOGY 20 13 2756 2770 The paucity of fungal species known to be currently hybridizing has significantly hindered our understanding of the mechanisms driving gene introgression in these eukaryotic microbes. Here, we describe an area of hybridization and gene introgression between the invasive plant pathogen Heterobasidion irregulare (introduced from North America) and the native H. annosum in Italy. A STRUCTURE analysis of amplified fragment length polymorphism data for 267 individuals identified gene introgression in 8-42% of genotypes in the invasion area, depending on site. Data indicate that introgression is mostly occurring unilaterally from the native to the invasive species and is responsible for 5-45% of genomes in admixed individuals. Sequence analysis of 11 randomly selected and unlinked loci for 30 individuals identified introgression at every locus, thus confirming interspecific gene flow involves a large number of loci. In 37 cases, we documented movement of entire alleles between the two species, but in 7 cases, we also documented the creation of new alleles through intralocus recombination. Sequence analysis did not identify enrichment of either transcriptionally different nonsynonymous alleles or of transcriptionally identical synonymous alleles. These findings may suggest introgression is occurring randomly for extant alleles without an obvious enrichment process driven by selection. However, further studies are needed to ensure selection is not at work elsewhere in the genome. Web of Science Heterobasidion irregulare Italy Field - Observational terrestrial Coniferous Forest Invasion Hyp. Hybridization pathogen 2617 Merow, Cory; LaFleur, Nancy; Silander, John A., Jr.; Wilson, Adam M.; Rubega, Margaret 2011 Developing Dynamic Mechanistic Species Distribution Models: Predicting Bird-Mediated Spread of Invasive Plants across Northeastern North America journal AMERICAN NATURALIST 178 1 30 43 Species distribution models are a fundamental tool in ecology, conservation biology, and biogeography and typically identify potential species distributions using static phenomenological models. We demonstrate the importance of complementing these popular models with spatially explicit, dynamic mechanistic models that link potential and realized distributions. We develop general grid-based, pattern-oriented spread models incorporating three mechanisms-plant population growth, local dispersal, and long-distance dispersal-to predict broadscale spread patterns in heterogeneous landscapes. We use the model to examine the spread of the invasive Celastrus orbiculatus (Oriental bittersweet) by Sturnus vulgaris (European starling) across northeastern North America. We find excellent quantitative agreement with historical spread records over the last century that are critically linked to the geometry of heterogeneous landscapes and each of the explanatory mechanisms considered. Spread of bittersweet before 1960 was primarily driven by high growth rates in developed and agricultural landscapes, while subsequent spread was mediated by expansion into deciduous and coniferous forests. Large, continuous patches of coniferous forests may substantially impede invasion. The success of C. orbiculatus and its potential mutualism with S. vulgaris suggest troubling predictions for the spread of other invasive, fleshy-fruited plant species across northeastern North America. Web of Science Celastrus orbiculatus USA ; Canada Theoretical/Modeling;Statistical/Meta-analysis terrestrial Deciduous Forest Invasion Hyp. Mutualism Facilitation primary 2618 Dijkstra, Jennifer A.; Westerman, Erica L.; Harris, Larry G. 2011 The effects of climate change on species composition, succession and phenology: a case study journal GLOBAL CHANGE BIOLOGY 17 7 2360 2369 Climate change and its role in altering biological interactions and the likelihood of invasion by introduced species in marine systems have received increased attention in recent years. It is difficult to forecast how climate change will influence community function or the probability of invasion as it alters multiple marine environmental parameters including rising water temperature, lower salinity and pH. In the present study, we correlate changes in environmental parameters to shifts in species composition in a subtidal community in Newcastle, NH through comparison of two, 3-year periods separated by 23 years (1979-1981 and 2003-2005). We observed concurrent shifts in climate related factors and in groups of organisms that dominate the marine community when comparing 1979-1981 to 2003-2005. The 1979-1981 community was dominated by perennial species (mussels and barnacles). In contrast, the 2003-2005 community was dominated by annual native and invasive tunicates (sea-squirts). We also observed a shift in the environmental factors that characterized both communities. Dissolved inorganic nitrogen and phosphate characterized the 1979-1981 community while sea surface temperature, pH, and chlorophyll a characterized the 2003-2005 community. Elongated warmer water temperatures, through the fall and early winter months of the 2000s, extended the growing season of native organisms and facilitated local dominance of invasive species. Additionally, beta-diversity was greater between 2003-2005 than 1979-1981 and driven by larger numbers of annual species whose life-history characteristics (e.g., timing and magnitude of recruitment, growth and mortality) are driven by environmental parameters, particularly temperature. Web of Science Many USA New Hampshire Newcastle 43.06 -70.71 Field - Observational marine Invasion Hyp. Climate Change filter 2619 Erfmeier, Alexandra; Boehnke, Martin; Bruelheide, Helge 2011 Secondary invasion of Acer negundo: the role of phenotypic responses versus local adaptation journal BIOLOGICAL INVASIONS 13 7 1599 1614 During plant species invasions, the role of adaptive processes is particularly of interest in later stages of range expansion when populations start invading habitats that initially have not been disposed to invasions. The dioecious tree Acer negundo, primarily invasive in Europe in wet habitats along riversides and in floodplains, has increased its abundance in dry habitats of industrial wasteland and ruderal sites during the last decades in Eastern Germany. We chose 21 invasive populations from wet and from dry habitats in the region of Halle, Saxony-Anhalt, Germany, to test whether Acer negundo exhibits a shift in life-history strategy during expansion into more stressful habitats. We analyzed variables of habitat quality (pH, soil moisture, exchangeable cations, total C and N content) and determined density, sex ratio and regeneration of the populations. In addition, we conducted germination experiments and greenhouse studies with seedlings in four different soil moisture environments. Local adaptation was studied in a reciprocal transplant experiment. We found habitat type differentiation with lower nutrient and water supply at the dry sites than at the moist sites and significant differences in the number of seedlings in the field. In accordance, seeds from moist habitats responded significantly faster to germination treatments. In the transplant experiment, leaf life span was significantly larger for populations originating from dry habitat types than from moist habitats. This observed shift in life history strategy during secondary invasion of A. negundo from traits of establishment and rapid growth towards traits connected with persistence might be counteracted by high gene flow among populations of the different habitat types. However, prolonged leaf life span at dry sites contributed remarkably to the invasion of less favourable habitats, and, thus, is a first indication of ongoing adaptation. Web of Science Acer negundo Germany Eastern Germany Field - Experimental;Greenhouse terrestrial Riparian Invasion Hyp. Evolution in General primary 2620 Godoy, Oscar; Saldana, Alfredo; Fuentes, Nicol; Valladares, Fernando; Gianoli, Ernesto 2011 Forests are not immune to plant invasions: phenotypic plasticity and local adaptation allow Prunella vulgaris to colonize a temperate evergreen rainforest journal BIOLOGICAL INVASIONS 13 7 1615 1625 In the South American temperate evergreen rainforest (Valdivian forest), invasive plants are mainly restricted to open sites, being rare in the shaded understory. This is consistent with the notion of closed-canopy forests as communities relatively resistant to plant invasions. However, alien plants able to develop shade tolerance could be a threat to this unique forest. Phenotypic plasticity and local adaptation are two mechanisms enhancing invasiveness. Phenotypic plasticity can promote local adaptation by facilitating the establishment and persistence of invasive species in novel environments. We investigated the role of these processes in the recent colonization of Valdivian forest understory by the perennial alien herb Prunella vulgaris from nearby populations in open sites. Using reciprocal transplants, we found local adaptation between populations. Field data showed that the shade environment selected for taller plants and greater specific leaf areas. We found population differentiation and within-population genetic variation in both mean values and reaction norms to light variation of several ecophysiological traits in common gardens from seeds collected in sun and shade populations. The colonization of the forest resulted in a reduction of plastic responses to light variation, which is consistent with the occurrence of genetic assimilation and suggests that P. vulgaris individuals adapted to the shade have reduced probabilities to return to open sites. All results taken together confirm the potential for rapid evolution of shade tolerance in P. vulgaris and suggest that this alien species may pose a threat to the native understory flora of Valdivian forest. Web of Science Prunella vulgaris Chile Andes Puyehue National Park Theoretical/Modeling terrestrial Coniferous Forest Invasion Hyp. Plasticity primary 2622 Dybdahl, Mark F.; Drown, Devin M. 2011 The absence of genotypic diversity in a successful parthenogenetic invader journal BIOLOGICAL INVASIONS 13 7 1663 1672 Invasiveness might depend on the ability of genetically diverse populations of exotic species to adapt to novel environments, which suggests a paradox since exotic species are expected to lose genetic diversity when introduced. The apparent need for genetic diversity is particularly important for exotic species that lack bi-parental reproduction and genetic recombination. We used genetic marker studies to determine the genotypic diversity of invasive US populations of the clonal New Zealand mudsnail (Potamopyrgus antipodarum). We report here on a three-pronged survey of allozyme, microsatellite DNA, and mitochondrial DNA genetic markers of invasive populations with a focus on the western US. Combining the three types of genetic markers, we discovered four distinct genotypes of P. antipodarum. These results show that only one genotype (US 1) occupied the vast majority of the western US range, and a second occurred in the Great Lakes in the eastern US (US 2). Two other genotypes occurred in the western US (US 1a and US 3), but were restricted to populations near the presumed source of invasion in the middle Snake River, ID. These results suggest that P. antipodarum spread across a broad geographic range in the western US from a single introduced source population, and that the populations are comprised of a single clonal lineage. Web of Science Potamopyrgus antipodarum USA Idaho Snake River Field - Observational lentic;lotic Invasion Hyp. Inherent Superiority Clonal Reproduction omnivore 2626 Creese, Chris; Lee, Albert; Sack, Lawren 2011 DRIVERS OF MORPHOLOGICAL DIVERSITY AND DISTRIBUTION IN THE HAWAIIAN FERN FLORA: TRAIT ASSOCIATIONS WITH SIZE, GROWTH FORM, AND ENVIRONMENT journal AMERICAN JOURNAL OF BOTANY 98 6 956 966 Premise of the study: Hawaii is home to 238 native and 35 alien fern and lycophyte taxa distributed across steep gradients in elevation and resource availability. The fern flora spans a wide range of growth forms, with extraordinary diversity in morphology and plant size. Yet the potential factors underlying this diversity have remained enigmatic. Methods: We used a trait database generated from the most recent and comprehensive survey of Hawaiian ferns and lycophytes to test hypotheses of size-scaling and trait associations with environment and growth form as factors underlying this diversity. We also tested relationships among morphology, taxon abundance and distribution and identified key differences between native and alien taxa. Key results: Strong trait-trait relationships included geometric scaling of plant dimensions with a tendency for more divided fronds in larger ferns. Trait-environment relationships independent of size included more divided fronds at higher elevation, longer blades in shaded habitats, and fronds with shorter stipes and fewer pinnae in drier habitats. Growth forms differed in mean size with epiphytic and epipetric taxa smaller than terrestrial ferns. Plant size was independent of taxon abundance and distribution across islands, and native and alien ferns did not differ in mean size. Alien taxa were more abundant, especially at lower elevations, apparently due to human land use. Conclusions: These relationships point to linkages of fern form and demography with biogeography and highlight potential flora-scale physiological and morphological adaptations in ferns across contrasting environments. Web of Science Many USA Hawaii Field - Observational terrestrial Subtropical Forest Invasion Hyp. Disturbance primary 2627 Strong, James A.; Dring, Matthew J. 2011 Macroalgal competition and invasive success: testing competition in mixed canopies of Sargassum muticum and Saccharina latissima journal BOTANICA MARINA 54 3 223 229 The invasive fucoid Sargassum muticum is currently consolidating its occupation of subtidal fringe habitat in Strangford Lough, Northern Ireland. The native laminiarian Saccharina latissima is the dominant species historically associated with the invaded habitat. The competitive interaction between Sargassum and Saccharina and its ultimate outcome is therefore of considerable consequence for the subtidal communities in Strangford Lough. To examine competition between adult macroalgae, a replacement series methodology was used to quantify intra- and inter-specific competition for light in the process of canopy over-growth. Competitive effects were not apparent for Saccharina, whereas Sargassum grew better mixed with Saccharina and at low densities, suggesting intra-specific competition is strong in this species. These results suggest increases in Sargassum will not affect adult stands of Saccharina. Web of Science Sargassum muticum Ireland Northern Ireland Strangford Lough Lab marine Invasion Hyp. Inherent Superiority Superior Competitor primary 2629 Martinkova, Jana; Klimes, Leos; Klimesova, Jitka 2011 Multiple Regenerative Strategies of Short-Lived Species: An Effect on Geographical Distribution, Preference of Human-Made Habitats and Invasive Status journal FOLIA GEOBOTANICA 46 3 181 189 It is expected that plant species with multiple regenerative strategies have a wider ecological amplitude and geographical distribution. However there is still an anxious question why species with multiple regenerative strategies are not more frequent. In the presented work we asked whether short-lived plants with a potential bud bank i) have a wider geographical distribution, ii) occur more frequently in human-made habitats and iii) more frequently possess invasive status in comparison with the short-lived species without this additional regenerative strategy. Results show that short-lived plants with a potential bud bank are i) more widely geographically distributed, ii) under-represented in natural habitats and weakly over-represented in habitats disturbed by human activities and iii) contrary to expectation, less numerous among neophytes than species without a potential bud bank. This suggests that short-lived root-sprouters are more habitat-specialized when compared with such plants without adventitious bud-bank formation, but are more widely geographically distributed. A higher frequency of multiple regeneration strategies seems to be restricted by costs of having this ability in habitats or situations without a disturbance regime. Web of Science Many Czech Republic terrestrial Invasion Hyp. Plasticity;Disturbance primary 2630 Huotari, T.; Korpelainen, H.; Leskinen, E.; Kostamo, K. 2011 Population genetics of the invasive water weed Elodea canadensis in Finnish waterways journal PLANT SYSTEMATICS AND EVOLUTION 294 2 27 37 Invasions of exotic species often involve a rapid evolutionary change in the introduced populations. Elodea canadensis is an invasive aquatic weed native to North America. Our aims were to reveal the evolutionary consequences of invasion to the population genetic structure of the presumably clonal E. canadensis in Finland and to test the hypothesis that the whole Finnish population originates from the first introduction of the species. We used ten polymorphic microsatellite markers to analyze the genetic characteristics of seven introduced E. canadensis populations in Finland. Despite the species' totally asexual mode of reproduction in Finland, two to five alleles per locus were detected in Finnish populations, and the expected heterozygosities varied between 0.19 and 0.37. The majority of variation was found within populations. Except for one, all pairwise values of population differentiation (FST) were significant, indicating restricted gene flow among the Finnish populations. In addition, a Bayesian analysis of population structure revealed the presence of regional population structuring. Genetic analyses indicate that E. canadensis could have been introduced to Finland multiple times. However, the amount of genetic variation and regional clustering detected could also be explained by post-establishment evolution, and based on this study it is not possible to exclude one introduction event followed by rapid evolution. We also tested the usability of the micro-satellite markers for native North American samples in order to compare the within-population genetic characteristics of introduced and native populations. However, in native populations only four microsatellite markers amplified reliably, indicating sequence variation within primer-binding regions and, thus, genetic differentiation among populations of E. canadensis. Web of Science Elodea canadensis Finland Field - Observational lentic;lotic Fundamentals primary 2631 Haubensak, Karen A.; D'Antonio, Carla M. 2011 The importance of nitrogen-fixation for an invader of a coastal California grassland journal BIOLOGICAL INVASIONS 13 6 1275 1282 Whether a novel trait of an invader directly contributes to increased establishment of that invader is a relatively unstudied question in plant ecology. Nitrogen (N)-fixing shrubs comprise a significant subset of grassland invaders worldwide, which suggests the potential importance of the novel trait of N-fixation in the invasion process. We indirectly tested the importance of N-fixation in the invasion of Genista monspessulana (French broom) in a California grassland by alleviating N and phosphorus (P) limitation to the grassland matrix. Grassland productivity was co-limited by N and P; N alone did not release the resident vegetation, and did not affect Genista performance. Genista was strongly limited by P: seedlings had more nodules, greater leaf N concentration, and higher growth and survival with P additions. When N was added with P, however, growth of the resident vegetation was 50-70% greater than with N or P alone, accompanied by decreases in Genista performance. This suggests that the advantage conferred to Genista by N-fixation was dampened when the resident vegetation was released from nutrient limitation. Web of Science Genista monspessulana USA California Field - Experimental terrestrial Grassland Invasion Hyp. Inherent Superiority Superior Competitor primary 2632 Closset-Kopp, Deborah; Saguez, Robert; Decocq, Guillaume 2011 Differential growth patterns and fitness may explain contrasted performances of the invasive Prunus serotina in its exotic range journal BIOLOGICAL INVASIONS 13 6 1341 1355 This research investigates why the invasive American black cherry tends to dominate the forest canopy on well-drained, nutrient-poor soils, but usually hardly establishes on both waterlogged and calcareous soils in its exotic range. Prunus serotina was sampled from four soil types and two light conditions, to measure (1) radial growth; (2) height growth compared to the main native competitor, Fagus sylvatica; (3) leaf traits; (4) seed production; and (5) rate of fungal attack. We found that P. serotina invested a significant amount of energy in height growth and seed production on well-drained, nutrient-poor soils. These characteristics enabled it to rapidly capture canopy gaps and subsequently exert a mass effect on neighbouring stands. On moist soils, we found irregular growth patterns and high rates of fungal attack, while on calcareous soils, leaf traits suggested a low nitrogen assimilation rate, limiting the production of N-containing compounds. We conclude that P. serotina fails on waterlogged and calcareous soils because it is unable to allocate sufficient energy to fruiting and/or height growth. Conversely, it succeeds on well-drained, nutrient-poor soils because of high fitness which increases its invasiveness. Web of Science Prunus serotina France Compiègne Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Rapid Growth;High Reprod. Output primary 2633 Pintor, Lauren M.; Sih, Andrew 2011 Scale dependent effects of native prey diversity, prey biomass and natural disturbance on the invasion success of an exotic predator journal BIOLOGICAL INVASIONS 13 6 1357 1366 There is growing support for the general notion that the drivers of invasion success often shift from biotic to abiotic factors with increasing spatial scale. Most of this research, however, has been conducted on a single trophic level; i.e. it has primarily looked at how the diversity of native competitors may influence invasion success. Less attention has been paid to understanding how native prey diversity may influence the invasion success of exotic predators and whether such biotic factors are scale-dependent. We used a hierarchical spatial survey of 17 stream communities to test whether native prey diversity, along with native prey biomass, algal resource abundance and annual stream discharge, influenced the abundance of an exotic crayfish predator, and whether the importance of these factors were scale-dependent. We used a hierarchical generalized linear model to evaluate the influence of these community and stream characteristics on exotic crayfish abundance at both the transect scale (1 m(2)) and the stream scale (400 m(2)). Our results indicated that at the stream scale, high stream discharge significantly limited invader abundance. However, at the smaller transect scale, native prey biomass was a significant driver of invasion success and positively correlated with invader abundance. We suggest that our results add to the emerging pattern that abiotic processes are stronger determinants of invasion success at large spatial scales, whereas biotic processes become more important with decreasing spatial scale. However, for predator invasions, prey biomass, not prey diversity may be a more important for driver of invasion success at small spatial scales. Web of Science Pacifastacus leniusculus USA California northern California Field - Observational lotic Invasion Hyp. Empty Niche predator 2634 Cebrian, Emma; Ballesteros, Enric; Linares, Cristina; Tomas, Fiona 2011 Do native herbivores provide resistance to Mediterranean marine bioinvasions? A seaweed example journal BIOLOGICAL INVASIONS 13 6 1397 1408 Generalist herbivores in marine ecosystems are poorly examined for their potential to serve as a source of biotic resistance against algal invasion. We assessed how one of the main generalist herbivores in Mediterranean rocky reefs (the sea urchin Paracentrotus lividus) affects Lophocladia lallemandii and Caulerpa racemosa, two algal invaders with strong detrimental effects on native benthic communities. In a comparison of sea urchin gut contents to algal community composition, strong preferences were exhibited, leading to no relationship between consumption and availability. Both C. racemosa and L. lallemandi were abundant in algal assemblages (> 60% occurrence), but C. racemosa (20% of diet) was consumed more than L. lallemandi (3.5%). Experimental enclosures of sea urchins (12 sea urchins * m(-2)) were carried out in locations where L. lallemandii was already established and C. racemosa was rare (new invasion) or abundant (established invasion). C. racemosa was negatively affected by sea urchins only when it was rare, and no effect was detected when the alga was already abundant. Results for L. lallemandi were exactly opposite: urchins limited seasonal increases in L. lallemandi in highly-invaded areas. Because of the small amount of direct consumption of L. lallemandi, its decrease in abundance may be related to the grazing of native algae where L. lallemandii is attached. Overall, our results show that high densities of native herbivores may reduce invasive algae at low densities, due to a combination of direct and indirect effects, but it has no significant effect in highly-invaded areas. Web of Science Lophocladia lallemandii;Caulerpa racemosa Spain Balearic Islands Cabrera Archipelago Field - Observational marine Invasion Hyp. Other herbivore 2635 Lagrue, Clement; Kaldonski, Nicolas; Motreuil, Sebastien; Lefevre, Thierry; Blatter, Olivier; Giraud, Philippe; Bollache, Loic 2011 Interspecific differences in drift behaviour between the native Gammarus pulex and the exotic Gammarus roeseli and possible implications for the invader's success journal BIOLOGICAL INVASIONS 13 6 1409 1421 Drifting is known to subject aquatic invertebrates to intense predation by drift feeding fish. Consequently, interspecific variations in drifting behaviour could lead to differences in predation pressure between coexisting prey species. Predation being an important factor determining the success of invaders, differences in drift patterns could advantage either native or exotic invertebrates through differential predation by native fish predators. The exotic freshwater amphipod (Gammarus roeseli) has now largely colonized Western Europe where it is often found in sympatry with a native species (Gammarus pulex). Here we documented interspecific differences in drifting behaviour that might have favored the invader's success through differential predation. Benthic and drifting amphipods were sampled three times at the same site to compare the proportion of each species within and between sample types (benthos or drift) across time. Compared with the benthos, where the invader (G. roeseli) was significantly less abundant than the native (G. pulex), G. roeseli was proportionally overrepresented in the drift but displayed a very different drifting pattern. While G. pulex drift rates remained roughly constant over a 24 h period, G. roeseli showed a marked diel periodicity with low diurnal and high nocturnal drift rates. Such drifting behaviour could procure this species with a competitive advantage regarding predation as most drift feeding fish are diurnal. As a result, the native appears more disadvantaged with respect to drift. This may partly explain the ability of G. roeseli to coexist with G. pulex in a habitat more suitable to the native. Web of Science Gammarus roeseli France Burgundy lotic Invasion Hyp. Inherent Superiority Superior Competitor decomposer 2636 Giorgis, Melisa A.; Tecco, Paula A.; Cingolani, Ana M.; Renison, Daniel; Marcora, Paula; Paiaro, Valeria 2011 Factors associated with woody alien species distribution in a newly invaded mountain system of central Argentina journal BIOLOGICAL INVASIONS 13 6 1423 1434 To help determine the major factors associated with alien plant in a newly invaded mountain range; we analyzed the distribution patterns of woody alien species along the altitudinal gradient of the Crdoba mountains, in relation to biotic, abiotic and anthropogenic factors. We selected 303 plots using a Geographic Information System (GIS) covering all the variability of these factors. In the field we registered woody alien occurrence in these 303 and in 303 additional neighbor plots. We used 12 biotic, abiotic and anthropogenic variables from the GIS to predict the probability of presence of alien species through a logistic model. Then, we analyzed if neighbor alien occurrences could explain some additional variance. We created a probability map with 4 categories of alien occurrence which was then validated by new field sampling. Occurrence of woody aliens was highest in the eastern slope (with longer history of species introduction), at low altitudes, near sources of propagule pressure (human settlements, roads and neighbor sites with established alien plants), and associated to sheltered topographies. In the upper belt of the Crdoba Mountains woody invasion is incipient and thus in a transient stage. Accordingly, propagule pressure seems to be the major factor at play, while the relevance of disturbance and biotic interactions is less clear. Web of Science Many Argentina Cordoba Province Sierras Grandes Field - Observational terrestrial Mountain Invasion Hyp. Propagule Pressure primary 2637 Yamada, F. H.; Santos, L. N.; Takemoto, R. M. 2011 Gill ectoparasite assemblages of two non-native Cichla populations (Perciformes, Cichlidae) in Brazilian reservoirs journal JOURNAL OF HELMINTHOLOGY 85 2 185 191 The gills of 41 Cichla piquiti and 39 C. kelberi from Itaipu and Lajes reservoirs, respectively, Brazil, were examined to describe the ectoparasite assemblages of these two non-native peacock-bass populations. All ectoparasite species of the two studied hosts (C. piquiti and C. kelberi) were dominant, but Ascocotyle sp. (metacercariae) was the prevalent (58.53%) and most abundant helminth species in C. piquiti hosts, while Sciadicleithrum ergensi was the dominant species in C. kelberi hosts. Gill ectoparasites of C. piquiti and C. kelberi showed a typical pattern of overdispersion or aggregation, which is commonly reported for many other freshwater fishes. Ectoparasite prevalence and abundance did not vary between host sexes of the two Cichla populations. The prevalence and abundance of Ascocotyle sp. were positively correlated with C. piquiti standard length (SL), but only the abundance of S. ergensi showed a positive correlation with C. kelberi SL. Although environmental differences between reservoirs might also have influenced the results, we anticipated that the presence of a close congener in Itaipu reservoir and the lack of other Cichla species in Lajes reservoir were the key factors to explain the contrasts between C. piquiti and C. kelberi gill ectoparasites. Overall, our results suggest that the trend of parasite species loss through the invasion process may have contributed to the establishment of non-native C. piquiti and C. kelberi populations in Brazilian reservoirs. Web of Science Cichla piquiti ; Cichla kelberi Brazil Itaipu ; Lajes Field - Observational lotic Invasion Hyp. Enemy Release herbivore 2638 Karatayev, Alexander Y.; Mastitsky, Sergey E.; Padilla, Dianna K.; Burlakova, Lyubov E.; Hajduk, Marissa M. 2011 Differences in growth and survivorship of zebra and quagga mussels: size matters journal HYDROBIOLOGIA 668 1 183 194 The zebra mussel (Dreissena polymorpha) and its congener the quagga mussel (Dreissena rostriformis bugensis) are both invaders in freshwater, but have very different invasion histories, with zebra mussels attaining substantially faster rates of spread at virtually all spatial scales. However, in waterbodies where they co-occur, D. r. bugensis can displace D. polymorpha. To determine if the mechanisms for this displacement are associated with different survival and growth, we kept mussels in flow-through tanks for 289 days with two temperature regimes that mimicked the natural surface water (littoral zone) and hypolimnion conditions of Lake Erie. For the littoral zone regime, we used water directly from the surface of Lake Erie (range 4-25A degrees C, average 11.9 +/- A 0.6A degrees C). For the profundal zone treatment, Lake Erie surface water was chilled to about 6A degrees C (range 5-8A degrees C, average 6.2 +/- A 0.6A degrees C) for the full duration of the experiment. For each of these temperature regimes, we used three replicate tanks with only zebra mussels present and three replicate tanks with only quagga mussels (150 ind./tank each), and three replicate tanks with both species (75 ind./tank of each species). Quagga mussels had higher survivorship and grew more than zebra mussels in all treatments. For both species, the size of the mussel entering the winter was critical for survivorship. Larger mussels had a higher survival over the winter in all treatments. For both species, there was a survivorship and growth tradeoff. In the warmer littoral zone treatment both species had higher growth, but lower survival than in the colder profundal zone treatment. Surprisingly, although quagga mussels outperformed zebra mussels, zebra mussel survivorship was better when they were faced with competition by quagga mussels than with just intraspecific competition. In addition, quagga mussels suffered size-specific mortality during the growing season only when facing interspecific competition with zebra mussels. Further experiments are needed to determine the possible mechanisms for these interspecific effects. Web of Science Dreissena polymorpha;Dreissena rostriformis bugensis USA Lake Erie Lab lentic Fundamentals filter 2640 Chen, Yigen; Ciaramitaro, Tina; Poland, Therese M. 2011 Moisture content and nutrition as selection forces for emerald ash borer larval feeding behaviour journal ECOLOGICAL ENTOMOLOGY 36 3 344 354 1. The exotic phloem-feeding emerald ash borer (EAB), Agrilus planipennis, has killed tens of millions of North American ash trees (Fraxinus) since its first detection in the U. S. A. in 2002. Ash trees are killed by larval feeding in the cambial region, which disrupts translocation of photosynthates and nutrients. 2. We observed that EAB larvae feed predominantly downwards in naturally grown green ash trees, a behaviour confirmed in greenhouse-grown black ash seedlings. Furthermore, biomass of larvae feeding downwards was greater than that for larvae feeding upwards. 3. We sought to determine the relative importance of four selection forces (i.e. gravity, moisture content, plant defence, and nutrition) in driving this downward feeding behaviour in this study. The gravity and plant defence (i.e. polyphenols) hypotheses were ruled out because even when seedlings were grown upside down, more EAB larvae moved upwards (towards the root area), and phloem tissue below the feeding site contained higher concentrations of defensive compounds than that above the feeding site. 4. The moisture content hypothesis was supported as phloem moisture above the feeding site decreased to levels reducing survivorship and biomass but was unaffected below. The nutrition hypothesis was also supported as the levels of 11 amino acids (mostly essential amino acids) below the feeding site were greater than those above. Furthermore, growth of larvae reared on an artificial diet deficient in protein and amino acids was worse than larvae reared in diet with complete ingredient or diet deficient in either protein or amino acids. 5. We conclude that moisture content and nutrients are two selective forces for the downward feeding behaviour of EAB larvae. Web of Science Agrilus planipennis USA Michigan Ingham County Field - Observational terrestrial Deciduous Forest Fundamentals herbivore 2641 Godoy, Oscar; de Lemos-Filho, Jose Pires; Valladares, Fernando 2011 Invasive species can handle higher leaf temperature under water stress than Mediterranean natives journal ENVIRONMENTAL AND EXPERIMENTAL BOTANY 71 2 207 214 Thermal tolerance of Photosystem II (PSII) highly influences plant distribution worldwide because it allows for photosynthesis during periods of high temperatures and water stress, which are common in most terrestrial ecosystems and particularly in dry and semi-arid ones. However, there is a lack of information about how this tolerance influences invasiveness of exotic species in ecosystems with seasonal drought. To address this question for Mediterranean-type ecosystems (MTE) of the Iberian Peninsula, we carried out an experiment with fifteen phylogenetically related species (8 invasive and 7 native, Pinus pinaster Ait., Pinus radiata D. Don, Schinus molle Linn., Elaeagnus angustifolia L. Eucalyptus globulus Labill., Acacia melanoxylon R. Br., Gleditsia triacanthos L. Pistacia terebinthus L., Rhamnus alaternus L., Anagyris foetid L, Colutea arborescens L., Oenothera biennis L., Epilobium hirsutum L. Achille filipendulina Lam. and Achillea millefolium L). Seedlings were grown and maximal photochemical efficiency of PSII (F(v)/F(m)) was measured at two water availabilities (well-watered and with water stress). PSII thermal tolerance measurements were related to specific leaf area (SLA), which varied significantly across the study species, and to the mean potential evapotranspiration (PET) of the month with the lowest precipitation in the native areas of both groups and in the invaded area of the Iberian Peninsula. Additionally, PSII thermal tolerance measurements under water stress were phylogenetically explored. Invasive and native species neither differed in SLA nor in their thermal tolerance under well-watered conditions. For well-watered plants. SLA was significantly and positively related to PSII thermal tolerance when all species were explored together regardless of their invasive nature. However, this relationship did not persist under water stress and invasive species had higher plastic responses than Mediterranean natives resulting in higher leaf temperatures. Higher PSII thermal tolerance could explain invasiveness because it allows for longer periods of carbon acquisition under water stress. In fact, PSII thermal tolerance was positively related to the PET of the invaded and native areas of the Iberian Peninsula. PSII thermal tolerance was not related to PET at the native range of the invasive species, suggesting that successful invasive species were plastic enough to cope with novel dry conditions of the Iberian Peninsula. Moreover, our phylogenetic results indicate that future scenarios of increased aridity in MTE associated to climate change will filter invasion success by taxonomic identity. This study reveals the importance of studying ecophysiological traits to understand and better predict future biological invasions. (C) 2010 Elsevier B.V. All rights reserved. Web of Science Many Spain Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority Broad Tolerances primary 2642 Tantowijoyo, Warsito; Hoffmann, Ary A. 2011 Variation in morphological characters of two invasive leafminers, Liriomyza huidobrensis and L. sativae, across a tropical elevation gradient journal JOURNAL OF INSECT SCIENCE 11 0 Changes in morphological traits along elevation and latitudinal gradients in ectotherms are often interpreted in terms of the temperature-size rule, which states that the body size of organisms increases under low temperatures, and is therefore expected to increase with elevation and latitude. However other factors like host plant might contribute to spatial patterns in size as well, particularly for polyphagous insects. Here elevation patterns for trait size and shape in two leafminer species are examined, Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae) and L. sativae Blanchard, along a tropical elevation gradient in Java, Indonesia. Adult leafminers were trapped from different locations in the mountainous area of Dieng in the province of Central Java. To separate environmental versus genetic effects, L. huidobrensis originating from 1378 m and 2129 m ASL were reared in the laboratory for five generations. Size variation along the elevation gradient was only found in L. huidobrensis and this followed expectations based on the temperature-size rule. There were also complex changes in wing shape along the gradient. Morphological differences were influenced by genetic and environmental effects. Findings are discussed within the context of adaptation to different elevations in the two species. Web of Science Many Indonesia Java Dieng Field - Observational terrestrial Tropical Forest Fundamentals herbivore 2644 Lazzarotto, C. M.; Lazzari, S. M. N.; Penteado, S. R. C. 2011 Feeding Behavior of Two Exotic Aphid Species on their Original Hosts in a New Invaded Area journal NEOTROPICAL ENTOMOLOGY 40 3 316 321 Greenidea ficicola Takahashi and Greenidea psidii van der Goot (Aphididae: Greenideinae) are Asian aphid species newly introduced in Brazil associated with Moraceae and Myrtaceae. The feeding behavior of G. ficicola and G. psidii was investigated on their respective host plants, Ficus benjamina (Moraceae) and Psidium guajava (Myrtaceae), using the Electrical Penetration Graph (EPG). Fifteen females of each aphid species were monitored during 24h using a DC-EPG GIGA-4 monitor. The time spent in phloem phase (waveforms El and E2) was 13.6% of the total recording time for G. ficicola and 0.8% for G. psidii. The average time in the pathway phase (waveforms C and pd) represented 50% of the total time for both species. Aphids spent more time in non-penetration and stylet pathway activities than in the phloem phase or actual feeding. The principal component analysis (PCA) showed that the two species formed different groups in relation to EPG parameters, despite some overlapping. The probing patterns with multiple penetrations of short duration in the sieve elements for both species may indicate apparent unsuitability for sustained feeding on their respective host plants. These results suggest that these two exotic species are in the process of adaptation to their host plants in their new environment and/or the plants may present either chemical or physical barriers against these insects. Web of Science Greenidea ficicola Takahashi; Greenidea psidii van der Goot Brazil Field - Observational terrestrial Fundamentals herbivore 2645 Njambuya, Josphine; Stiers, Iris; Triest, Ludwig 2011 Competition between Lemna minuta and Lemna minor at different nutrient concentrations journal AQUATIC BOTANY 94 4 158 164 We investigated the differential responses of invasive alien Lemna minuta and native Lemna minor to nutrient loading as well as the mechanism of competition between the species. The role of nutrients, species identity, species influence in determining the outcome of competition between the species was estimated using the Relative Growth Rate Difference (RGRD) model. The two species differed in their response to nutrient loading. The native L minor responded indifferently to nutrient loading. The species Relative Growth Rate (RGR) was 0.10 d(-1), 0.11 d(-1) and 0.09 d(-1) in high, medium and low nutrients, respectively. On the other hand, the invasive L. minuta responded opportunistically to high nutrient availability and had an RGR of 0.13 d(-1), 0.10 d(-1) and 0.08 d(-1) in high, medium and low nutrients, respectively. As a result, the invasive species was dominant in high nutrient availability but lost to the native species at low nutrient availability. The invader formed approximately 60% and less than 50% of the stand final total dry biomass in high and low nutrient availability, respectively. Species RGR were reduced by both intra- and interspecific competition but intraspecific effects were stronger than interspecific effects. On the overall, the species significantly differed in their constant RGR. These differences in RGR between the species (species identity) and the differential response to nutrient loading were the main determinant of change in final biomass composition of these species in mixture. Species influence (competition) only had a small influence on the outcome of competition between the species. The observed species response to nutrient loading could be targeted in management of the invasive species. Lowering nutrients can be proposed to reduce the impact of the invasive L. minuta. (C) 2011 Elsevier B.V. All rights reserved. Web of Science Lemna minuta USA Florida Field - Experimental lentic Invasion Hyp. Plasticity primary 2646 Thierry, M.; Becker, N.; Hajri, A.; Reynaud, B.; Lett, J. -M.; Delatte, H. 2011 Symbiont diversity and non-random hybridization among indigenous (Ms) and invasive (B) biotypes of Bemisia tabaci journal MOLECULAR ECOLOGY 20 10 2172 2187 The whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) is a worldwide pest and a vector of numerous plant viruses. B. tabaci is composed of dozens of morphologically indistinguishable biotypes and its taxonomic status is still controversial. This phloem-feeder harbours the primary symbiont Portiera aleyrodidarum and potentially six secondary symbionts: Cardinium, Arsenophonus, Hamiltonella, Rickettsia, Wolbachia and Fritschea. In the southwest Indian Ocean, La Reunion hosts two biotypes of this species: B (invasive) and Ms (indigenous). A multiplex PCR was developed to study the symbiont community of B. tabaci on La Reunion. Symbiont community prevalence and composition, host mitochondrial and nuclear genetic diversity, as well as host plant and localization, were described on field populations of La Reunion for B and Ms B. tabaci biotypes and their hybrids. A clear association between symbiotypes and biotypes was shown. Cardinium, Arsenophonus and Rickettsia were found in the Ms biotype (73.6%, 64.2% and 3.3%, respectively). Hamiltonella (exclusively) and Rickettsia were found in the B biotype (78% and 91.2%, respectively). Hybrids harboured all symbiotypes found in Ms and B populations, but with a higher prevalence of Ms symbiotypes than expected under random hybridization. An unexpected majority was Cardinium mono-infected (65.6%), and a striking minority (9%) harboured Cardinium/Arsenophonus. In the hybrids only, genetic diversity was linked to symbiotype. Among the hybrids, significant links were found between symbiotypes and: (i) mitochondrial COI sequences, i.e. maternal origin; and (ii) alleles of nuclear microsatellite loci, specific to either Ms or B parental biotype. Taken together, our results suggest that Cardinium and/or Arsenophonus may manipulate the reproduction of indigenous (Ms) with invasive (B) biotypes of Bemisia tabaci. Web of Science Bemisia tabaci La Reunion Field - Observational terrestrial Invasion Hyp. Mutualism Facilitation herbivore 2647 Gerhold, Pille; Paertel, Meelis; Tackenberg, Oliver; Hennekens, Stephan M.; Bartish, Igor; Schaminee, Joop H. J.; Fergus, Alexander J. F.; Ozinga, Wim A.; Prinzing, Andreas 2011 Phylogenetically Poor Plant Communities Receive More Alien Species, Which More Easily Coexist with Natives journal AMERICAN NATURALIST 177 5 668 680 Alien species can be a major threat to ecological communities, but we do not know why some community types allow the entry of many more alien species than do others. Here, for the first time, we suggest that evolutionary diversity inherent to the constituent species of a community may determine its present receptiveness to alien species. Using recent large databases from observational studies, we find robust evidence that assemblage of plant community types from few phylogenetic lineages (in plots without aliens) corresponds to higher receptiveness to aliens. Establishment of aliens in phylogenetically poor communities corresponds to increased phylogenetic dispersion of recipient communities and to coexistence with rather than replacement of natives. This coexistence between natives and distantly related aliens in recipient communities of low phylogenetic dispersion may reflect patterns of trait assembly. In communities without aliens, low phylogenetic dispersion corresponds to increased dispersion of most traits, and establishment of aliens corresponds to increased trait concentration. We conclude that if quantified across the tree of life, high biodiversity correlates with decreasing receptiveness to aliens. Low phylogenetic biodiversity, in contrast, facilitates coexistence between natives and aliens even if they share similar trait states. Web of Science Many Netherlands Field - Observational;Statistical/Meta-analysis terrestrial Invasion Hyp. Community Species Richness primary 2648 Piscart, Christophe; Kefford, Ben J.; Beisel, Jean-Nicolas 2011 Are salinity tolerances of non-native macroinvertebrates in France an indicator of potential for their translocation in a new area? journal LIMNOLOGICA 41 2 107 112 Because of its geographic and economic position, the Western part of Europe and France is prone to biological invasions. Among the aquatic species non-native to France, a high proportion of these species are considered to be salt-tolerant. To verify this assumption, we compared the salinity tolerance of 18 native and non-native species in France in order to determine whether the introduced non-native species are more salt-tolerant than the native ones. Contrary to our expectations, our study shows that both native and non-native macroinvertebrate species from the same taxonomic group which had originated from within Eurasia had very similar salinity tolerance. Our results show that species originate from outside Eurasia (introduced by the ballast or drinking water on ships) were more salt tolerant than native from France and non-native species originated from Eurasia. Thus, derivation of the acute test of the salinity tolerance in native ranges may give good indications of their potential ability to survive during the translocation by shipping from the area of origin to another area. Our approach does provide empirical evidence for potential of non-native species to survive translocation in saline water using standard, quick and inexpensive protocols. (C) 2010 Elsevier GmbH. All rights reserved. Web of Science Many France Field - Observational lotic Invasion Hyp. Inherent Superiority Broad Tolerances omnivore 2649 Miranda, Rodrigo Q.; Oliveira, Marcela T. P.; Correia, Rafaela M.; Almeida-Cortez, Jarcilene S.; Pompelli, Marcelo F. 2011 Germination of Prosopis juliflora (Sw) DC seeds after scarification treatments journal PLANT SPECIES BIOLOGY 26 2 186 192 Invasive plant species are the second most important threat to global biodiversity loss after land-use change. Invasive species can modify native community composition, deplete species diversity and affect ecosystem processes. The Caatinga is one of the most human-affected Brazilian ecosystems owing to non-sustainable use of its natural resources. Prosopis juliflora is an important invasive plant species in the Caatinga ecosystem. Seed germination is a critical stage in plant life cycles and is a major factor in the establishment and success of invasive plant species. Among the factors that affect seed germination and dormancy, coat-imposed seems to be the most important for P. juliflora. In Prosopis species, the ingestion of fruits by wild and domestic animals may promote and accelerate germination, enhancing the dispersal of seeds and fruits of these species. We investigated the germination capacity of P. juliflora seeds after artificial mechanical and chemical scarification and analyzed the changes in seedling vigor caused by the scarification treatments. Germination rate, germination time (TMG) and germination synchrony (E) differed significantly with the length of the scarification treatments in H(2)SO(4) for both seeds with endocarps and seeds without endocarps (non-endocarp seeds). Sulfuric acid affected plant survival more strongly than germination rate, particularly in non-endocarp seeds. Web of Science Prosopis juliflora Brazil Field - Experimental terrestrial Chaparral/Shrublands Fundamentals primary 2650 Wada, Takashi; Matsukura, Keiichiro 2011 LINKAGE OF COLD HARDINESS WITH DESICCATION TOLERANCE IN THE INVASIVE FRESHWATER APPLE SNAIL, POMACEA CANALICULATA (CAENOGASTROPODA: AMPULLARIIDAE) journal JOURNAL OF MOLLUSCAN STUDIES 77 0 149 153 Linkage between cold hardiness and desiccation tolerance was examined in an invasive freshwater apple snail, Pomacea canaliculata, collected from locations in three different climatic zones. Snails collected from temperate Kyushu, Japan, showed enhanced cold hardiness after cold acclimation, and cold-tolerant snails survived longer after exposure to desiccation than cold-intolerant snails without cold acclimation. Progenies of tropical snails collected from Luzon and Mindanao, the Philippines, which had never experienced cold weather revealed the same response as Japanese snails to cold stress: enhancement of cold hardiness after cold acclimation. Cold-tolerant snails from tropical populations also attained better survivorship under desiccation conditions. Thus, linkage of tolerance between cold weather and desiccation appears to be a general feature of P. canaliculata. Cold hardiness of snails before and after cold acclimation, respectively, did not differ among the three populations from temperate and tropical regions. A trend was found for snails from Mindanao, in the tropical rainforest climatic zone (having a milder dry season), to be less desiccation-tolerant than snails from Kyushu and Luzon, having a colder or more severe dry season. Web of Science Pomacea canaliculata Japan; Philippines Field - Observational lentic;lotic Invasion Hyp. Inherent Superiority Broad Tolerances omnivore 2652 Lebouvier, M.; Laparie, M.; Hulle, M.; Marais, A.; Cozic, Y.; Lalouette, L.; Vernon, P.; Candresse, T.; Frenot, Y.; Renault, David 2011 The significance of the sub-Antarctic Kerguelen Islands for the assessment of the vulnerability of native communities to climate change, alien insect invasions and plant viruses journal BIOLOGICAL INVASIONS 13 5 1195 1208 The suite of environments and anthropogenic modifications of sub-Antarctic islands provide key opportunities to improve our understanding of the potential consequences of climate change and biological species invasions on terrestrial ecosystems. The profound impact of human introduced invasive species on indigenous biota, and the facilitation of establishment as a result of changing thermal conditions, has been well documented on the French sub-Antarctic Kerguelen Islands (South Indian Ocean). The present study provides an overview of the vulnerability of sub-Antarctic terrestrial communities with respect to two interacting factors, namely climate change and alien insects. We present datasets assimilated by our teams on the Kerguelen Islands since 1974, coupled with a review of the literature, to evaluate the mechanism and impact of biological invasions in this region. First, we consider recent climatic trends of the Antarctic region, and its potential influence on the establishment, distribution and abundance of alien insects, using as examples one fly and one beetle species. Second, we consider to what extent limited gene pools may restrict alien species' colonisations. Finally, we consider the vulnerability of native communities to aliens using the examples of one beetle, one fly, and five aphid species taking into consideration their additional impact as plant virus vectors. We conclude that the evidence assimilated from the sub-Antarctic islands can be applied to more complex temperate continental systems as well as further developing international guidelines to minimise the impact of alien species. Web of Science Many sub-antarctic Kerguelen Islands Field - Observational terrestrial Invasion Hyp. Climate Change predator 2653 Wintzer, Alpa P.; Meek, Mariah H.; Moyle, Peter B.; May, Bernie 2011 Ecological insights into the polyp stage of non-native hydrozoans in the San Francisco Estuary journal AQUATIC ECOLOGY 45 2 151 161 The populations of several invasive jellyfish appear to be increasing around the globe. While data on non-native hydromedusae in the San Francisco Estuary have been accumulating in recent years, little is known regarding their polyp phase. The goal of this study was to gather the first field-derived ecological data for polyp stages of Blackfordia virginica, Moerisia sp., and Cordylophora caspia in the estuary. Monthly fouling plates were deployed at five sites during 2007 and 2008. Settlement data indicate a seasonal presence of B. virginica and Moerisia sp., with both distribution and abundance correlated with a combination of water quality and physical parameters. Cordylophora caspia appeared to be present beyond the time period sampled and may be active in the system year-round. The ability of polyps to persist month to month was low, likely due to predation by other non-native species and competition for space. Web of Science Blackfordia virginica; Moerisia sp.; Cordylophora caspia USA San Francisco Field - Observational estuarine Fundamentals predator 2654 Bronnenhuber, Jennifer E.; Dufour, Brad A.; Higgs, Dennis M.; Heath, Daniel D. 2011 Dispersal strategies, secondary range expansion and invasion genetics of the nonindigenous round goby, Neogobius melanostomus, in Great Lakes tributaries journal MOLECULAR ECOLOGY 20 9 1845 1859 Dispersal strategies are important mechanisms underlying the spatial distribution and colonizing ability of all mobile species. In the current study, we use highly polymorphic microsatellite markers to evaluate local dispersal and colonization dynamics of the round goby (Neogobius melanostomus), an aquatic invader expanding its range from lake to river environments in its introduced North American range. Genetic structure, genotype assignment and genetic diversity were compared among 1262 round gobies from 20 river and four lake sites in three Great Lakes tributaries. Our results indicate that a combination of short-distance diffusion and long-distance dispersal, collectively referred to as 'stratified dispersal', is facilitating river colonization. Colonization proceeded upstream yearly (approximately 500 m/year; 2005-2009) in one of two temporal replicates while genetic structure was temporally stable. Contiguous dispersal from the lake was observed in all three rivers with a substantial portion of river fish (7.3%) identified as migrants. Genotype assignment indicated a separate introduction occurred upstream of the invasion front in one river. Genetic diversity was similar and relatively high among lake and recently colonized river populations, indicating that founder effects are mitigated through a dual-dispersal strategy. The remarkable success of round goby as an aquatic invader stresses the need for better diffusion models of secondary range expansion for presumably sessile invasive species. Web of Science Neogobius melanostromus USA; Canada Field - Observational lentic;lotic Invasion Hyp. Inherent Superiority Effective Disperser predator 2655 Speek, Tanja A. A.; Lotz, Lambertus A. P.; Ozinga, Wim A.; Tamis, Wil L. M.; Schaminee, Joop H. J.; van der Putten, Wim H. 2011 Factors relating to regional and local success of exotic plant species in their new range journal DIVERSITY AND DISTRIBUTIONS 17 3 542 551 Aim To estimate invasiveness of exotic plant species, many studies have used the frequency of occurrence within a defined region. This measure is informative on how widespread exotics are, however, it does not inform on their local dominance, which is crucial for conservation of biodiversity and ecosystem functioning. The aim of the present study is to determine if regional frequency of occurrence of exotic plant species indeed is indicative of their local dominance. We also determined which plant traits and other factors predict regional and local frequencies best. Location The Netherlands. Methods We used information on exotic plant species established in The Netherlands and compared traits relating to their frequency of occurrence regionally (the entire country) and their frequency of dominance locally (in 1-100 m2 quadrats). We created minimal adequate models with factors explaining regional frequency and frequency of local dominance of 111 exotic plant species in The Netherlands. Results The model that used plant traits to explain regional frequency of exotic plant species differed from the models that best explained their frequency of local dominance. Regionally, the factors that correlated with frequency were: life form, height, polyploidy, length of flowering season, residence time, human use and origin. The factors that correlated to frequency of local dominance were lateral vegetative spread and residence time. Main conclusions We conclude that plant traits relating to the regional frequency of exotic plant species differ from those that relate to their frequency of local dominance. The implication of our results is that predictive studies on plant invasiveness based on regional frequencies may not be indicative of the local impacts. Since the prediction of local impacts is crucial for conservation and risk assessment, our study emphasized the need for better information on the local abundance of exotic invaders. Web of Science Many The Netherlands Theoretical/Modeling terrestrial Invasion Hyp. Inherent Superiority;Other Clonal Reproduction primary 2656 Wang, Hsiao-Hsuan; Grant, William E.; Swannack, Todd M.; Gan, Jianbang; Rogers, William E.; Koralewski, Tomasz E.; Miller, James H.; Taylor, John W., Jr. 2011 Predicted range expansion of Chinese tallow tree (Triadica sebifera) in forestlands of the southern United States journal DIVERSITY AND DISTRIBUTIONS 17 3 552 565 Aim We present an integrated approach for predicting future range expansion of an invasive species (Chinese tallow tree) that incorporates statistical forecasting and analytical techniques within a spatially explicit, agent-based, simulation framework. Location East Texas and Louisiana, USA. Methods We drew upon extensive field data from the US Forest Service and the US Geological Survey to calculate spread rate from 2003 to 2008 and to parameterize logistic regression models estimating habitat quality for Chinese tallow within individual habitat cells. We applied the regression analyses to represent population spread rate as a function of habitat quality, integrated this function into a logistic model representing local spread, and coupled this model with a dispersal model based on a lognormal kernel within the simulation framework. We simulated invasions beginning in 2003 based on several different dispersal velocities and compared the resulting spatial patterns to those observed in 2008 using cross Mantel's tests. We then used the best dispersal velocity to predict range expansion to the year 2023. Results Chinese tallow invasion is more likely in low and flat areas adjacent to water bodies and roads, and less likely in mature forest stands and in pine plantations where artificial regeneration by planting seedlings is used. Forecasted invasions resulted in a distribution that extended from the Gulf Coast of Texas and Louisiana northward and westward as much as 300 km, representing approximately 1.58 million ha. Main conclusions Our new approach of calculating time series projections of annual range expansion should assist land managers and restoration practitioners plan proactive management strategies and treatments. Also, as field sampling continues on the national array of FIA plots, these new data can be incorporated easily into the present model, as well as being used to develop and/or improve models of other invasive plant species. Web of Science Triadica sebifera USA Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 2659 Wersal, Ryan M.; Madsen, John D. 2011 Influences of water column nutrient loading on growth characteristics of the invasive aquatic macrophyte Myriophyllum aquaticum (Vell.) Verdc. journal HYDROBIOLOGIA 665 1 93 105 Nuisance growth of Myriophyllum aquaticum has often been attributed to high amounts of nutrients. The uptake of nitrogen and phosphorus from sediments and their allocation have been documented in both natural and laboratory populations. However, nutrient loading to surface water is increasingly becoming an important issue for water quality standards. Aquatic macrophytes that develop adventitious roots may be able to survive through the uptake of water column nutrients. Our objectives for this study were to assess M. aquaticum growth when combinations of nitrogen and phosphorus were added to the water column. Mesocosm experiments were conducted where nitrogen (1.8, 0.8, and 0.4 mg l(-1); high, medium, and low) and phosphorus (0.09, 0.03, 0.01 mg l(-1); high, medium, and low) concentrations were paired and added to the water column. After 12 weeks, the combination of 1.80:0.01 N:P resulted in greater (P < 0.01) total biomass and greater biomass for all plant tissues. Total biomass at the 1.80:0.01 N:P combination was 53% greater than biomass at all other combinations. The yield response of M. aquaticum was a quadratic function of tissue nutrient content. Yield was positively (r (2) = 0.82) related to increasing nitrogen content, whereas a negative (r (2) = 0.89) relationship was determined for increasing phosphorus content. We propose the negative relationship is due to increased nutrient competition and shading by algae resulting in reduced M. aquaticum growth. Tissue nutrient content indicated that critical concentrations (1.8% nitrogen and 0.2% phosphorus) for growth were not attained except for nitrogen in plants grown in the 1.80:0.01 N:P combination. These data provide further evidence that M. aquaticum requires high levels of nitrogen to achieve nuisance growth. Survival through uptake of water column nutrients may be a mechanism for survival during adverse conditions, a means of long distance dispersal of fragments, or may offer a competitive advantage over species that rely on sediment nutrients. Web of Science Myriophyllum aquaticum USA Mississippi Field - Observational lentic;lotic Invasion Hyp. Inherent Superiority Effective Disperser;Clonal Reproduction primary 2660 Firth, Louise B.; Knights, Antony M.; Bell, Susan S. 2011 Air temperature and winter mortality: Implications for the persistence of the invasive mussel, Perna viridis in the intertidal zone of the south-eastern United States journal JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 400 2 250 256 Global climate change and invasive species represent two of the biggest threats to the environment. Biological communities are responding to global climate change through poleward shifts in distribution, and changes in abundance and phenology of both native and non-native species. An increase in the frequency and magnitude of extreme weather events is predicted with global climate change. Much is known about mortality events of marine organisms in relation to warm thermal stress with relatively little known about cold thermal stress, particularly in the tropics. Intertidal species are particularly susceptible to fluctuations in aerial conditions and many are considered indicators of climate change. Perna viridis is a recent invader to the United States where it fouls hard substrates and soft sediment habitats. During winter 2007/08, a mortality event was observed for P. viridis across Tampa Bay, Florida. This mortality event coincided with extreme weather conditions when air temperatures dropped below 2 degrees C for a period of 6 h during low water. The minimum air temperature recorded was 0.53 degrees C. During this period water temperature remained relatively constant (similar to 20 degrees C). We provide strong evidence supporting the hypothesis that thermal stress relating to exposure to cold air temperatures during emersion was the primary factor underpinning the mortality event. Similar mortality events occurred in 2009 and 2010, also coinciding with prolonged exposure to low air temperatures. In the short term, weather may be responsible for the temporary trimming back of populations at the edge of their geographic range but in the longer-term, it is expected that climate warming will trigger the poleward movement of both native and non-native species potentially facilitating biotic homogenisation of marine communities. The challenge now is to devise adaptive management strategies in order to mitigate any potential negative impacts to native biodiversity. (C) 2011 Elsevier B.V. All rights reserved. Web of Science Perna viridis USA Field - Observational marine Invasion Hyp. Climate Change filter 2661 Nemec, Kristine T.; Allen, Craig R.; Alai, Aaron; Clements, Greg; Kessler, Andrew C.; Kinsell, Travis; Major, Annabel; Stephen, Bruce J. 2011 Woody Invasions of Urban Trails and the Changing Face of Urban Forests in the Great Plains, USA journal AMERICAN MIDLAND NATURALIST 165 2 241 256 Corridors such as roads and trails can facilitate invasions by non-native plant species. The open, disturbed habitat associated with corridors provides favorable growing conditions for many non-native plant species. Bike trails are a corridor system common to many urban areas that have not been studied for their potential role in plant invasions. We sampled five linear segments of urban forest along bike trails in Lincoln, Nebraska to assess the invasion of woody non-native species relative to corridors and to assess the composition of these urban forests. The most abundant plant species were generally native species, but five non-native species were also present: white mulberry (Morus alba), common buckthorn (Rhamnus cathartica), tree-of-heaven (Ailanthus altissima), honeysuckle (Lonicera spp.) and elm (Ulmus spp.). The distribution of two of the woody species sampled, common buckthorn and honeysuckle, significantly decreased with increasing distance from a source patch of vegetation (P = 0.031 and 0.030). These linear habitats are being invaded by non-native tree and shrub species, which may change the structure of these urban forest corridors. If non-native woody plant species become abundant in the future, they may homogenize the plant community and reduce native biodiversity in these areas. Web of Science Many USA Field - Observational terrestrial Invasion Hyp. Disturbance primary 2662 Abraham, Shallin; Somers, Michael J.; Chown, Steven L. 2011 Seasonal, altitudinal and host plant-related variation in the abundance of aphids (Insecta, Hemiptera) on sub-Antarctic Marion Island journal POLAR BIOLOGY 34 4 513 520 Although aphids are the most species-rich group of invasive alien insects across the Southern Ocean Islands, their biology on the islands is poorly known. In this study, host plant-related, seasonal and altitudinal variation in the abundance of the three aphid species (Macrosiphum euphorbiae, Myzus ascalonicus, Rhopalosiphum padi) found on sub-Antarctic Marion Island is examined. Myzus ascalonicus is the most abundant of the species, reaching densities of c. 2,400 individuals per 1,200 cm(2) on the indigenous Acaena magellanica (Rosaceae) and 479 individuals per 1,200 cm(2) on the indigenous Cotula plumosa (Asteraceae), with lower numbers at elevations up to 300 m and a pronounced seasonal peak in December-February. Macrosiphum euphorbiae occurs on the same plant species in densities of between c. 11 individuals per 1,200 cm(2) on C. plumosa and c. 200 individuals per 1,200 cm(2) on A. magellanica, and with a pronounced summer peak in December. In both species, small numbers of winged forms are found (c. 1-5%), although they are permanently parthenogenetic on the island. Rhopalosiphum padi is also permanently parthenogenetic on the island and likewise shows a December peak in abundance. The current data suggest that low ambient temperatures, which are close to the lower development threshold of R. padi, and other temperate aphid species, limit development in winter, thus leading to a decline in abundance. Web of Science Macrosiphum euphorbiae; Myzus ascalonicus; Rhopalosiphum padi sub-antarctic marion island Field - Observational terrestrial Fundamentals herbivore 2663 Foxcroft, Llewellyn C.; Jarosik, Vojtech; Pysek, Petr; Richardson, David M.; Rouget, Mathieu 2011 Protected-Area Boundaries as Filters of Plant Invasions journal CONSERVATION BIOLOGY 25 2 400 405 Human land uses surrounding protected areas provide propagules for colonization of these areas by non-native species, and corridors between protected-area networks and drainage systems of rivers provide pathways for long-distance dispersal of non-native species. Nevertheless, the influence of protected-area boundaries on colonization of protected areas by invasive non-native species is unknown. We drew on a spatially explicit data set of more than 27,000 non-native plant presence records for South Africa's Kruger National Park to examine the role of boundaries in preventing colonization of protected areas by non-native species. The number of records of non-native invasive plants declined rapidly beyond 1500 m inside the park; thus, we believe that the park boundary limited the spread of non-native plants. The number of non-native invasive plants inside the park was a function of the amount of water runoff, density of major roads, and the presence of natural vegetation outside the park. Of the types of human-induced disturbance, only the density of major roads outside the protected area significantly increased the number of non-native plant records. Our findings suggest that the probability of incursion of invasive plants into protected areas can be quantified reliably. Web of Science Many South Africa Field - Observational terrestrial Invasion Hyp. Disturbance primary 2664 Chun, Young Jin; Le Corre, Valerie; Bretagnolle, Francois 2011 Adaptive divergence for a fitness-related trait among invasive Ambrosia artemisiifolia populations in France journal MOLECULAR ECOLOGY 20 7 1378 1388 The impact of natural selection on the adaptive divergence of invasive populations can be assessed by testing the null hypothesis that the extent of quantitative genetic differentiation (Q(ST)) would be similar to that of neutral molecular differentiation (F(ST)). Using eight microsatellite loci and a common garden approach, we compared Q(ST) and F(ST) among ten populations of an invasive species Ambrosia artemisiifolia (common ragweed) in France. In a common garden study with varying water and nutrient levels, we measured Q(ST) for five traits (height, total biomass, reproductive allocation, above- to belowground biomass ratio, and days to flowering). Although low F(ST) indicated weak genetic structure and strong gene flow among populations, we found significant diversifying selection (Q(ST) > F(ST)) for reproductive allocation that may be closely related to fitness. It suggests that abiotic conditions may have exerted selection pressure on A. artemisiifolia populations to differentiate adaptively, such that populations at higher altitude or latitude evolved greater reproductive allocation. As previous studies indicate multiple introductions from various source populations of A. artemisiifolia in North America, our results suggest that the admixture of introduced populations may have increased genetic diversity and additive genetic variance, and in turn, promoted the rapid evolution and adaptation of this invasive species. Web of Science Ambrosia artemisiifolia; France Garden terrestrial Invasion Hyp. Evolution in General primary 2665 Chang, Shu-Mei; Gonzales, Eva; Pardini, Eleanor; Hamrick, J. L. 2011 Encounters of old foes on a new battle ground for an invasive tree, Albizia julibrissin Durazz (Fabaceae) journal BIOLOGICAL INVASIONS 13 4 1043 1053 Studies of invasive species often demonstrate that exotic or invasive plants have reduced levels of predation when first introduced into novel geographic areas. In some systems, native predators may subsequently be introduced and the plant-predator association is re-established. In this study, we analyzed a recent reassociation between the introduced tree, Albizia julibrissin, and its native seed predator, Bruchidius terrenus, which has also been introduced, in the vicinity of Athens, GA, USA. We documented a rapid increase in the levels of bruchid beetle predation on seeds of A. julibrissin from 2001 to 2002 and substantial predation in the following 5 years. From a six-year survey, we found that relative susceptibility to beetle predation among individual trees remained consistent over time. Furthermore, we found that phenology had significant effects on beetle predation on fruits and seeds, with fruits developed from early flowers having higher levels of beetle attacks than ones developed from later flowers in the season. Finally, seeds and fruits attacked by beetles were more likely to be attacked by a Fusarium fungus, probably due to coinfestation of the two predators. Host-predator reassociation that causes substantial loss of fertility or shows a relationship with reproductive phenology may have population level demographic effects or evolutionary consequences and deserve further research attention. Web of Science Albizia julibrissin Greece; USA Field - Observational terrestrial Deciduous Forest Fundamentals primary 2666 Chun, Young Jin 2011 Phenotypic plasticity of introduced versus native purple loosestrife: univariate and multivariate reaction norm approaches journal BIOLOGICAL INVASIONS 13 4 819 829 The plastic responses to environmental change by Lythrum salicaria (purple loosestrife) were compared between native plants derived from seeds collected in Europe and those introduced into North America. Plants from nine populations each were grown under two levels of water and nutrient conditions. At the end of the growing season, samples were evaluated for eight traits related to their life history, plant size/architecture, and reproduction. Genetic (G), environmental (E), and G x E interactions were assessed by restricted maximum likelihood (REML) analysis of covariance (ANCOVA) and multivariate analysis of covariance (MANCOVA). Both univariate and multivariate reaction norm analyses were used to test for differences in the magnitude and direction of phenotypic plasticity between introduced and native plants. Under high-nutrient conditions, introduced plants were taller and had more branches and greater aboveground biomass. They also exhibited significantly greater amounts of phenotypic plasticity for aboveground biomass than did the natives in response to changing nutrient levels in standing water. This difference in univariate plasticity contributed to the general contrast in multivariate plasticity between introduced and native plants. These results support the idea that introduced plants may successfully invade a habitat and grow better than native plants in response to increased resources. Web of Science Lythrum salicaria North America Garden terrestrial Riparian Invasion Hyp. Plasticity primary 2667 Padron, Benigno; Nogales, Manuel; Traveset, Anna; Vila, Montserrat; Martinez-Abrain, Alejandro; Padilla, David P.; Marrero, Patricia 2011 Integration of invasive Opuntia spp. by native and alien seed dispersers in the Mediterranean area and the Canary Islands journal BIOLOGICAL INVASIONS 13 4 831 844 The success of many alien plant species depends on mutualistic relationships with other species. We describe the assemblage of seed dispersers on three species of alien Opuntia invading Mediterranean and Macaronesian habitats, and examine the quality of such plant-animal interactions. We identified vertebrates consuming O. maxima, O. dillenii and O. stricta fruits by direct observation and collecting droppings and pellets. Phenology of the alien species, as well as that of coexisting native species, was monitored for an entire year. Germination tests of ingested and non-ingested seeds were performed both in the greenhouse and in the field. Seed coat thickness and viability were also measured for all treatments. A great variety of taxa, including reptiles, birds and mammals actively participate in the seed dispersal of Opuntia. Phenology of Opuntia fruits in Menorca and Tenerife overlaps with only a few native fleshy-fruited plants present in the study areas, which suggests an advantage for the invader. Most seeds germinated during the second year of the experiment, independently of the effect produced by the dispersers' guts. We found great variation in the germination percentage of Opuntia after gut passage and in the effects of ingestion on seed coat thickness. Seed viability was somewhat reduced after gut passage compared to manually depulped seeds. Our results show how different Opuntia species are integrated into native communities by means of mutualistic interactions, with both native and alien dispersers. Although with heterogeneous effects, either type of disperser potentially contributes to the spread of these alien cacti in the recipient areas. Web of Science Opuntia maxima; Opuntia dillenii; Opuntia stricta Mediterranean; Macaronesia Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Mutualism Facilitation primary 2668 Shen, Xing-Yan; Peng, Shao-Lin; Chen, Bao-Ming; Pang, Jun-Xiao; Chen, Lei-Yi; Xu, Hao-Ming; Hou, Yu-Ping 2011 Do higher resource capture ability and utilization efficiency facilitate the successful invasion of native plants? journal BIOLOGICAL INVASIONS 13 4 869 881 The great damage caused by native invasive species on natural ecosystems is prompting increasing concern worldwide. Many studies have focused on exotic invasive species. In general, exotic invasive plants have higher resource capture ability and utilization capacity, and lower leaf construction cost (CC) compared to noninvasive plants. However, the physiological mechanisms that determine the invasiveness of native plants are poorly understood. We hypothesized that native invaders, like exotic invaders, may have higher resource capture ability and utilization efficiency compared to native noninvaders. To test this hypothesis, ecophysiological traits including light-saturated photosynthetic rate (A(max)), specific leaf area (SLA), photosynthetic nitrogen use-efficiency (PNUE), photosynthetic energy-use efficiency (PEUE), and mass-based and area-based leaf construction cost (CC(mass) and CC(area)) were measured. We compared the above traits between three pairs of native invasive and noninvasive native species, and between three pairs of exotic invasive and noninvasive species in Guangzhou, southern China. Our results showed that the native invaders had higher A(max), SLA, PNUE, PEUE and lower CC(mass), CC(area), compared to native noninvaders and that these traits were also found in the exotic invaders. PNUE and PEUE in the native invaders were 150.3 and 129.0% higher, respectively, than in noninvasive native species, while these same measures in exotic invaders were 43.0 and 94.2% higher, respectively, than in exotic noninvasive species. The results indicated that native invaders have higher resource capture ability and resource utilization efficiency, suggesting that these traits may be a common biological foundation underlying successful invasion by both native and exotic invasives. Web of Science Paederia scandens; Stephania longa; Pueraria phaseoloides; Ipomoea cairica; Lantana camara; Oxalis corymbosa China Guangzhou Field - Observational terrestrial Invasion Hyp. Inherent Superiority Superior Competitor primary 2669 Calvino-Cancela, Maria 2011 Seed dispersal of alien and native plants by vertebrate herbivores journal BIOLOGICAL INVASIONS 13 4 895 904 Seed dispersal is crucial for the success and spread of alien plants. Herbivores often establish a dual relationship with plants: antagonist, through herbivory, and mutualist, through seed dispersal. By consuming plants, herbivores may disperse large amounts of seeds, and can facilitate the spread of alien plants. However, seed dispersal of alien plants by herbivores has been largely uninvestigated. I studied factors associated with dispersal of alien and native seeds by the three most important vertebrate herbivores in SW Australia: emus (Dromaius novaehollandia), western grey kangaroos (Macropus fuliginosus) and European rabbits (Oryctolagus cuniculus). Overall frequencies of alien and native seeds dispersed by these herbivores were determined by differences among them in (1) the plant groups they predominantly disperse, that differed in frequencies of aliens versus natives, and (2) the predominant dispersal of aliens or natives within those plant groups. Emus and kangaroos (natives) tended to disperse predominantly alien seeds within plant groups (defined by life forms, dispersal syndromes, and diaspore size), whereas rabbits (alien) tended to disperse predominantly natives. This agrees with the hypothesis that herbivores will use predominantly plants that have evolved in different areas, because of less effective defences against new enemies. Overall frequencies were consistent with this pattern in kangaroos and rabbits, but not in emus. Kangaroos dispersed mostly plant groups that were mainly aliens (herbaceous species and small and medium sized dispersal units and seeds), which together with their predominant use of aliens over natives within groups resulted in the highest overall frequency of alien seeds (73%). Rabbits were similar to kangaroos in the type of plants dispersed, but their predominant use of natives over aliens within groups contributed to an overall predominance of native seeds in their pellets (88%). Emus dispersed mostly plant groups that were mainly natives (e.g. woody species with big diaspores), resulting in low overall frequency of alien seeds (11%), despite their predominant use of aliens over natives within plant groups. Thus, the within-groups trend pointed to a facilitative role of native herbivores of plant invasions through seed dispersal, but was obscured by the different use by herbivores of plant groups with different frequency of aliens. Web of Science Many Australia terrestrial Invasion Hyp. primary 2670 Powell, Kristin I.; Krakos, Kyra N.; Knight, Tiffany M. 2011 Comparing the reproductive success and pollination biology of an invasive plant to its rare and common native congeners: a case study in the genus Cirsium (Asteraceae) journal BIOLOGICAL INVASIONS 13 4 905 917 Previous studies have examined an association between reproductive success and pollination biology of rare versus widespread species through pair-wise comparisons of native and invasive congeners or rare and common congeners. To determine the importance of reproductive success and pollination biology for an invasive thistle, Cirsium vulgare, we compared it in its invaded range to five, co-occurring native Cirsium species that range from rare to common. Native study species include C. fontinale var. fontinale, C. andrewsii, C. brevistylum, C. occidentale, and C. quercetorum. We compared all species' reproductive success, insect visitation rate and composition, autonomous self-pollination, and level of pollen limitation in multiple populations. Species differed in their reproductive success; the invasive C. vulgare produced more flower heads per plant than most native species. C. vulgare attracted more visitors than its congeners. In addition, reproductive success and insect visitation significantly varied between populations within species, mainly due to aphid infestation in one population of C. occidentale. Unlike the rare species (C. fontinale and andrewsii), C. vulgare did not require a pollinator for high-levels of seed production. The remaining native species set fewer seeds than C. vulgare without a pollinator. However, differences in insect visitation and autonomous self-pollination did not lead to differences in pollen limitation across species or between populations. This result suggests that factors other than pollination biology determine the difference in reproductive success of these species. However, high levels of autonomous self-pollination and generalist insect visitation may allow the invasive C. vulgare to easily establish new populations from low numbers of propagules. Our study provides one contrast that should build towards a larger comparative analysis to examine general patterns in the relationship between reproductive success, pollination biology, rare and invasive species, and our ability to predict biological invasions in introduced species. Web of Science Cirsium vulgare USA California terrestrial Invasion Hyp. primary 2671 Abe, Tetsuto; Wada, Katsuyuki; Kato, Yuka; Makino, Shun'ichi; Okochi, Isamu 2011 Alien pollinator promotes invasive mutualism in an insular pollination system journal BIOLOGICAL INVASIONS 13 4 957 967 The alien predatory lizard, Anolis carolinensis, has reduced the insect fauna on the two main islands of the Ogasawara archipelago in Japan. As a result of this disturbance, introduced honeybees are now the dominant visitors to flowers instead of endemic bees on these islands. On the other hand, satellite islands not invaded by alien anoles have retained the native flower visitors. The effects of pollinator change on plant reproduction were surveyed on these contrasting island groups. The total visitation rates and the number of interacting visitor groups on main islands were 63% and 30% lower than that on satellite islands, respectively. On the main islands, the honeybees preferred to visit alien flowers, whereas the dominant endemic bees on satellite islands tended to visit native flowers more frequently than alien flowers. These results suggest that alien anoles destroy the endemic pollination system and caused shift to alien mutualism. On the main islands, the natural fruit set of alien plants was significantly higher than that of native plants. In addition, the natural fruit set was positively correlated with the visitation rate of honeybees. Pollen limitation was observed in 53.3% of endemic species but only 16.7% of alien species. These data suggest that reproduction of alien plants was facilitated by the floral preference of introduced honeybees. Web of Science Anolis carolinensis Japan Field - Observational terrestrial Subtropical Forest Invasion Hyp. Mutualism Facilitation predator 2673 Poulin, R.; Paterson, R. A.; Townsend, C. R.; Tompkins, D. M.; Kelly, D. W. 2011 Biological invasions and the dynamics of endemic diseases in freshwater ecosystems journal FRESHWATER BIOLOGY 56 4 676 688 P>1. Biological invasions, still occurring worldwide at an alarming rate, are widely acknowledged as threats to the integrity and functioning of ecosystems. In addition to introducing disease, biological invasions have also been linked to sudden increases in the incidence or severity of previously existing diseases. We review and illustrate the potential direct and indirect impacts of introduced species on the dynamics of endemic parasites in freshwater ecosystems. 2. Introduced species may trigger and sustain disease emergence by acting as competent hosts for endemic parasites in which infection is amplified and then 'spilled back' to native hosts. In contrast, if introduced species are not suitable hosts for endemic parasites but become infected anyway, they may act as sinks for parasites and thus dilute disease risk for native hosts. 3. Another mechanism by which introduced species can influence endemic parasitic diseases is by altering the relative abundance of one of the parasite's hosts in ways that could either enhance or reduce disease transmission to other native hosts in the parasite's life cycle. 4. Introduced species may also alter disease incidence and severity in native hosts through trait-mediated indirect effects. For example, the introduced species could change the exposure or susceptibility of native hosts to infection by causing alterations in their behaviour or immunocompetence. Also, by directly changing physicochemical conditions and modifying environmental stressors introduced species may indirectly affect native host exposure and/or resistance to disease. 5. A survey of parasites infecting introduced freshwater fish in four distinct geographical areas revealed that use of non-indigenous hosts by endemic parasites is widespread, mostly involving parasites transmitted via the food chain. 6. We conclude by presenting a framework, based on risk assessment, for the prediction and possible mitigation of the impact of introduced species on endemic diseases and by calling for greater recognition of the potential role of invasive species as triggers of endemic disease emergence. Web of Science Many Theoretical/Modeling;Statistical/Meta-analysis lentic;lotic Invasion Hyp. Enemy Release herbivore;predator 2674 Vervoort, Arnaud; Cawoy, Valerie; Jacquemart, Anne-Laure 2011 COMPARATIVE REPRODUCTIVE BIOLOGY IN CO-OCCURRING INVASIVE AND NATIVE IMPATIENS SPECIES journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 172 3 366 377 Two alien Impatiens species are spreading in Europe and share habitats with the native Impatiens noli-tangere. We studied their reproductive biology to estimate which traits facilitate invasiveness. Flower morphology was examined, insect observations were made, and hand pollination treatments were performed. Floral biology differed among species. Impatiens glandulifera and I. noli-tangere presented large quantities of sucrose-dominant nectar, contrary to Impatiens parviflora. The latter had high autonomous selfing ability (81.4% fruit set) linked to complete self-compatibility. No inbreeding depression was detected for this species. The second alien, I. glandulifera, showed lower autonomous selfing (9.3% fruit set), with high self-compatibility and low inbreeding depression (delta = 0.11). No evidence of autonomous selfing was found for the native, which presented the lowest self-compatibility and the highest inbreeding depression (delta = 0.42). However, all species can be considered self-compatible. Impatiens glandulifera flowers were visited by insects up to 250 times during their life span, whereas I. noli-tangere and I. parviflora flowers received fewer than seven visits. Both exotics present traits facilitating reproductive success. Impatiens parviflora exhibits autonomous self-pollination, whereas the other species possess attractive traits with respect to insect pollination. On the other hand, the native, unable to self-pollinate, is poorly attractive to pollinators. The high fecundity of the aliens seems to contribute to their invasiveness. Web of Science Many Field - Observational terrestrial Invasion Hyp. Inherent Superiority Self Compatible primary 2675 Mraz, Patrik; Bourchier, Robert S.; Treier, Urs A.; Schaffner, Urs; Mueller-Schaerer, Heinz 2011 POLYPLOIDY IN PHENOTYPIC SPACE AND INVASION CONTEXT: A MORPHOMETRIC STUDY OF CENTAUREA STOEBE SL journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 172 3 386 402 The taxonomy of the Centaurea stoebe complex is controversial. Diploid and tetraploid plants occur in its native European range, but to date only tetraploids have been recorded from its introduced range in North America. We examined morphological differentiation of C. stoebe using multivariate and univariate approaches to clarify the taxonomic status of the known cytotypes. We measured more than 40 morphological traits on plants originating from 78 populations, grown from seed under uniform glasshouse conditions. The ploidy of almost 300 plants from 2 native and 20 introduced populations from Canada was assessed to test for the absence of diploids from North America. Finally, we explored whether postintroduction processes have resulted in phenotypic changes in introduced plants which may have contributed to the invasion success of C. stoebe. Morphometric analyses showed a clear separation of 2x and 4x plants and thus supported recognition of both cytotypes as separate taxa. Differences in the life cycle, the number of florets, the shape of capitula, and the shape of young rosette leaves were the best discriminant characters. Only minor differences were found between native and introduced tetraploids. All plants from the introduced range except for one hexaploid were found to be tetraploid. Rare diploids from Canada were identified as Centaurea diffusa or Centaurea psamogenna. Web of Science Centaurea stoebe USA ; Canada Field - Observational terrestrial Grassland Invasion Hyp. Other primary 2679 Cushman, J. Hall; Lortie, Christopher J.; Christian, Caroline E. 2011 Native herbivores and plant facilitation mediate the performance and distribution of an invasive exotic grass journal JOURNAL OF ECOLOGY 99 2 524 531 1. Exotic plant species have become increasingly prominent features of ecological landscapes throughout the world, and their interactions with native and exotic taxa in these novel environments may play critical roles in mediating the dynamics of such invasions. 2. Here, we summarize results from comparative and experimental studies that explore the effects of two factors - herbivory and facilitation - on the performance and distribution of an invasive South African grass, Ehrharta calycina, in a coastal foredune system in northern California, USA. 3. Using a 2-year exclosure experiment, we show that a native herbivore, black-tailed jackrabbits (Lepus californicus), significantly reduced the height, shoot production, fecundity and above-ground biomass of this exotic grass. 4. Data from two comparative studies and a neighbour-removal experiment revealed that Ehrharta frequently escaped herbivores by associating with three neighbouring plant species an exotic perennial grass, Ammophila arenaria, an exotic perennial succulent, Carpobrotus edulis, and a native perennial shrub, Baccharis pilularis. Ehrharta growing in association with neighbours was taller, had fewer grazed shoots, produced greater numbers of spikelets and had greater above-ground biomass than unassociated individuals. Furthermore, removing neighbours generally eliminated these benefits in 7 months, although effects differed among neighbour species. 5. An additional neighbour-removal experiment conducted in the absence of jackrabbits indicated that neighbour removals did not have significant impacts on Ehrharta height, shoot production, spikelet production or above-ground dry biomass. These results suggest that the primary means by which Ehrharta benefits from neighbouring plants is protection from herbivores - either because they are less apparent to herbivores or less accessible and that Ehrharta likely incurred minimal costs from associating with neighbours. 6. Ehrharta was more frequently associated with neighbours than expected due to chance, and less frequently found in open dune habitat. These results are consistent with the hypothesis that the effects of herbivory and facilitation have been sufficiently strong to shape the local distribution of this invader in the landscape. 7. Synthesis. Our research has demonstrated that herbivory and facilitation have jointly influenced the dynamics of a biological invasion, and highlights the importance of evaluating the effects of multiple interactions on invasions in a single system. Web of Science Many USA California northern California Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Mutualism Facilitation primary;herbivore 2680 Fogarty, Sean; Cote, Julien; Sih, Andrew 2011 Social Personality Polymorphism and the Spread of Invasive Species: A Model journal AMERICAN NATURALIST 177 3 273 287 Ecological invasions are a major worldwide problem exacting tremendous economic and ecological costs. Efforts to explain variability in invasion speed and impact by searching for combinations of ecological conditions and species traits associated with invasions have met with mixed success. We use a simulation model that integrates insights from life-history theory, animal personalities, network theory, and spatial ecology to derive a new mechanism for explaining variation in animal invasion success. We show that spread occurs most rapidly when (1) a species includes a mix of life-history or personality types that differ in density-dependent performance and dispersal tendencies, (2) the differences between types are of intermediate magnitude, and (3) patch connections are intermediate in number and widely spread. Within-species polymorphism in phenotype (e.g., life-history strategies or personality), a feature not included in previous models, is important for overcoming the fact that different traits are associated with success in different stages of the invasion process. Polymorphism in sociability (a personality type) increases the speed of the invasion front, since asocial individuals colonize empty patches and facilitate the local growth of social types that, in turn, induce faster dispersal by asocials at the invasion edge. The results hold implications for the prediction of invasion impacts and the classification of traits associated with invasiveness. Web of Science Many Theoretical/Modeling Invasion Hyp. Other 2681 Tingley, Reid; Phillips, Benjamin L.; Shine, Richard 2011 Establishment Success of Introduced Amphibians Increases in the Presence of Congeneric Species journal AMERICAN NATURALIST 177 3 382 388 Darwin's naturalization hypothesis predicts that the success of alien invaders will decrease with increasing taxonomic similarity to the native community. Alternatively, shared traits between aliens and the native assemblage may preadapt aliens to their novel surroundings, thereby facilitating establishment (the preadaptation hypothesis). Here we examine successful and failed introductions of amphibian species across the globe and find that the probability of successful establishment is higher when congeneric species are present at introduction locations and increases with increasing congener species richness. After accounting for positive effects of congeners, residence time, and propagule pressure, we also find that invader establishment success is higher on islands than on mainland areas and is higher in areas with abiotic conditions similar to the native range. These findings represent the first example in which the preadaptation hypothesis is supported in organisms other than plants and suggest that preadaptation has played a critical role in enabling introduced species to succeed in novel environments. Web of Science Many Field - Observational terrestrial Invasion Hyp. Community Species Richness herbivore;predator 2682 Muirhead, Jim R.; Lewis, Mark A.; MacIsaac, Hugh J. 2011 Prediction and error in multi-stage models for spread of aquatic non-indigenous species journal DIVERSITY AND DISTRIBUTIONS 17 2 323 337 Aim Predictions of spread of non-indigenous species allow for greater efficiency in managing invasions by targeting areas for preventative measures. The invasion sequence is a useful concept in predictions of spread, as it allows us to test hypotheses about the transport and establishment of propagules in novel habitats. Our aims are twofold: (1) to develop and validate multi-stage invasion models for the introduced fishhook waterflea, Cercopagis pengoi, and (2) to assess how variability in the transport patterns of the propagules influences the accuracy and spatial extent for predictions of spread. Location New York State, USA. Methods We developed a two-stage model for the spread of C. pengoi. First, we developed a stochastic gravity model for dispersal based on surveys of recreational boat traffic in New York State as a proxy for propagule pressure. We then modelled the probability of establishment based on predicted levels of propagule pressure and measures of lakes' physicochemistry. In addition, we used Monte Carlo simulations based on the gravity model to propagate variability in boater traffic through the establishment model to assess how uncertainty in dispersal influenced predictions of spread. Results The amount recreationalists were willing to spend, lake area and population size of the city nearest to the destination lake were significant factors affecting boater traffic. In turn, boater traffic, lake area, specific conductance and turbidity were significant predictors of establishment. The inclusion of stochastic dispersal reduced the rate of false positives (i.e. incorrect prediction of an invasion) in detecting invasions at the upper 95% prediction interval for the probability of establishment. Main conclusions Combinations of measures of propagule pressure, habitat suitability and stochastic dispersal allow for the most accurate predictions of spread. Further, multi-stage spread models may overestimate the extent of spread if stochasticity in early stages of the models is not considered. Web of Science Cercopagis pengoi USA New York Field - Observational;Theoretical/Modeling lentic Invasion Hyp. Propagule Pressure herbivore 2683 Gosper, Carl R.; Yates, Colin J.; Prober, Suzanne M.; Williams, Matthew R. 2011 Fire does not facilitate invasion by alien annual grasses in an infertile Australian agricultural landscape journal BIOLOGICAL INVASIONS 13 3 533 544 Plant invasions are a significant threat to fragmented native plant communities in many agricultural regions. Fire potentially facilitates invasions, but in landscapes historically subject to recurrent fires, exclusion of fire is also likely to result in loss of biodiversity. We investigated the relationship between fire, fragmentation and alien plant invasion in mallee communities of the Western Australian wheatbelt. We hypothesized that invasion is limited by lack of propagules and the low soil nutrient levels of this old, infertile landscape, but that fire and/or fragmentation disrupt these limits. We tested the effects of three factors on establishment and abundance of alien annuals: +/- fire, +/- post-fire seeding with the locally invasive Avena barbata (propagule availability) and three landscape contexts. The three landscape contexts, exploring site limitations, were reserve interiors, perimeter edges adjacent to agricultural land and internal reserve roadside edges. Our first hypothesis was supported: Avena establishment was consistently greater in seeded plots, but away from perimeter edges, growth was poor. Our second hypothesis was supported only for perimeter edges: neither fire nor fragmentation by interior roads enhanced invasive plant establishment or biomass. At perimeter edges, invasive plant biomass was significantly greater. This was associated with higher propagule availability and elevated soil nutrient levels but was not enhanced by fire. We conclude that fire is unlikely to promote invasion by alien annuals in low-nutrient ecosystems such as mallee, hence is a viable disturbance strategy for biodiversity conservation away from nutrient-enriched edges. Web of Science Avena barbata Australia Field - Experimental terrestrial Old Field Invasion Hyp. Propagule Pressure;Disturbance primary 2686 Lejeusne, Christophe; Bock, Dan G.; Therriault, Thomas W.; MacIsaac, Hugh J.; Cristescu, Melania E. 2011 Comparative phylogeography of two colonial ascidians reveals contrasting invasion histories in North America journal BIOLOGICAL INVASIONS 13 3 635 650 Surveys of genetic structure of introduced populations of nonindigenous species may reveal the source(s) of introduction, the number of introduction events, and total inoculum size. Here we use the mitochondrial cytochrome c oxidase subunit 1 (COI) gene to explore genetic structure and contrast invasion histories of two ecologically similar and highly invasive colonial ascidians, the golden star tunicate Botryllus schlosseri and the violet tunicate Botrylloides violaceus, in their global and introduced North American ranges. Haplotype and nucleotide diversities for B. schlosseri were significantly higher than for B. violaceus both globally (h = 0.872; pi = 0.054 and h = 0.461; pi = 0.007, respectively) and in their overlapping North American ranges (h = 0.874; pi = 0.012 and h = 0.384; pi = 0.006, respectively). Comparative population genetics and phylogenetic analyses revealed clear differences in patterns of invasion for these two species. B. schlosseri populations on the west and east coasts of North America were seeded from the Pacific and Mediterranean regions, respectively, whereas all North American B. violaceus populations were founded by one or more introduction events from Japan. Differences in genetic structure of invasive populations for these species in North America are consistent with their contrasting probable introduction vectors. B. schlosseri invasions most likely resulted from vessel hull fouling, whereas B. violaceus was likely introduced as a 'fellow traveler' in the shellfish aquaculture trade. Web of Science Botryllus schlosseri;Botrylloides violaceus USA ; Canada Field - Observational marine Invasion Hyp. Other filter 2687 Funk, W. Chris; Garcia, Tiffany S.; Cortina, George A.; Hill, Rebbecca H. 2011 Population genetics of introduced bullfrogs, Rana (Lithobates) catesbeianus, in the Willamette Valley, Oregon, USA journal BIOLOGICAL INVASIONS 13 3 651 658 The American bullfrog, Rana (Lithobates) catesbeianus, is endemic to eastern North America, but has been introduced to approximately 40 countries on four continents and is considered one of the hundred worst invasive alien species in the world. Here, we investigated the genetics of invasive bullfrogs in the Willamette Valley, Oregon, USA, where bullfrogs are widespread and abundant to determine: (1) the minimum number of bullfrog introductions; (2) the native source population(s); and (3) whether genetic variation is reduced compared to source populations. To answer these questions, we analyzed partial sequences of the mitochondrial cytochrome b gene for 251 bullfrogs from the Willamette Valley and the native range. We found that bullfrogs from the Mississippi River basin and Great Lakes region were introduced at least once to the Willamette Valley. Genetic variation measured as haplotype diversity (h) and nucleotide diversity (pi (n) ) was not significantly different between Willamette Valley and source populations. Our results were in contrast to a recent genetic analysis of invasive bullfrog populations in Europe, which found that genetic variation in European bullfrog populations was much lower than in source populations. European bullfrogs also originated from different source populations than Willamette Valley bullfrogs. The difference in genetic composition between Willamette Valley and European bullfrogs is likely due to differences in their invasion histories and may have implications for the potential of bullfrogs in these different regions to adapt and expand. Web of Science Rana catesbeianus USA Oregon Willamette Valley Field - Observational lentic Fundamentals predator 2688 Ghabooli, Sara; Shiganova, Tamara A.; Zhan, Aibin; Cristescu, Melania E.; Eghtesadi-Araghi, Peyman; MacIsaac, Hugh J. 2011 Multiple introductions and invasion pathways for the invasive ctenophore Mnemiopsis leidyi in Eurasia journal BIOLOGICAL INVASIONS 13 3 679 690 The introduction and spread of non-indigenous species (NIS) in marine ecosystems accelerated during the twentieth century owing to human activities, notably international shipping. Genetic analysis has proven useful in understanding the invasion history and dynamics of colonizing NIS and identifying their source population(s). Here we investigated sequence variation in the nuclear ribosomal Internal Transcribed Spacer region of the ctenophore Mnemiopsis leidyi, a species considered one of the most invasive globally. We surveyed four populations from the native distribution range along the Atlantic coasts of the United States and South America, as well as six populations in the introduced range from the Black, Azov, Caspian and Baltic seas. Allelic and nucleotide diversity of introduced populations were comparable to those of native populations from which they were likely drawn. Introduced populations typically exhibited lower genetic differentiation (F (ST) = -0.014-0.421) than native populations (F (ST) = 0.324-0.688). Population genetic analyses supported the invasion of Eurasia from at least two different pathways, the first from the Gulf of Mexico (e.g., Tampa Bay) to the Black Sea and thence to the Caspian Sea, the second from the northern part of the native distribution range (e.g., Narragansett Bay) to the Baltic Sea. The relatively high genetic diversity observed in introduced populations is consistent with large inocula and/or multiple invasions, both of which are possible given ballast water transport and the extensive native distribution of the ctenophore in the Atlantic Ocean. Web of Science Mnemiopsis leidyi Many Field - Observational marine Fundamentals predator 2689 Culley, Theresa M.; Hardiman, Nicole A.; Hawks, Jennifer 2011 The role of horticulture in plant invasions: how grafting in cultivars of Callery pear (Pyrus calleryana) can facilitate spread into natural areas journal BIOLOGICAL INVASIONS 13 3 739 746 Although few plant species escape from cultivation, some horticultural practices used with woody ornamentals may enhance their invasion potential into natural areas. One such procedure is grafting, in which individuals are propagated for commercial sale by joining a clone of a desired cultivar (the scion) with rootstock obtained from a different individual. If the rootstock can sprout and flower, it can potentially cross-pollinate the scion, leading to fruit production in a self-incompatible species. The effect of grafting on invasion success was examined in the Callery pear, Pyrus calleryana, one of the most popular landscaping trees in the United States. Using nine microsatellite markers, scion and rootstock were genotyped for 57 cultivated trees to characterize rootstock genotypes and the rootstock gene pool. Invasive populations were then sampled to determine if rootstock genotypes have contributed to their formation. In no case were scion and rootstock genotypes identical for any given cultivated tree and rootstock genotypes were genetically variable, although some cloned rootstock genotypes were detected. Rootstock genotypes were also observed in invasive populations, with up to 17% of wild individuals having at least one rootstock parent. These results indicate that rootstock can contribute to the formation of invasive populations of the Callery pear through cross-pollination with other available genotypes. Future investigations of woody ornamentals propagated by grafting should consider this horticultural practice as a potential contributor to invasiveness. Furthermore, plant breeders are encouraged to assess the ability of rootstock to sprout as well as its cross-compatibility with the scion or other cultivar genotypes growing nearby. Web of Science Pyrus calleryana USA Field - Observational terrestrial Invasion Hyp. Other primary 2690 Kestrup, Asa M.; Thomas, Sara H.; van Rensburg, Karla; Ricciardi, Anthony; Duffy, Meghan A. 2011 Differential infection of exotic and native freshwater amphipods by a parasitic water mold in the St. Lawrence River journal BIOLOGICAL INVASIONS 13 3 769 779 A parasitic water mold (oomycete) of unknown origin was discovered infecting live native and exotic freshwater gammarid amphipods (Gammarus fasciatus and Echinogammarus ischnus, respectively) in the upper St. Lawrence River. Infections were associated with rapid die-offs of natural populations of amphipods, especially the exotic E. ischnus. Analysis of sequences of three different segments of the rRNA gene cluster indicated that the parasite was in the Saprolegniaceae family, and is related to other crustacean-associated Saprolegniaceae. Specific primers were designed based on the SSU rRNA gene and utilized for semi-quantitative analysis of parasite presence in live and dead amphipods. In laboratory experiments, infection prevalence was higher in E. ischnus individuals than in native amphipods. In addition, dead E. ischnus individuals exhibited more intense infections than G. fasciatus individuals. In contrast to the Great Lakes where E. ischnus has replaced G. fasciatus at many locations, the native species remains abundant in the St. Lawrence River more than a decade after invasion by E. ischnus in the late 1990s. We hypothesize that the parasite is facilitating the co-existence of the two amphipod species by reducing the abundance of E. ischnus in environments in which it might otherwise be dominant. Web of Science Echinogammarus ischnus USA St. Lawrence River Field - Observational lotic Invasion Hyp. Enemy Release omnivore;parasite 2691 Li, Weiguo; Wang, Jianbo 2011 Influence of light and nitrate assimilation on the growth strategy in clonal weed Eichhornia crassipes journal AQUATIC ECOLOGY 45 1 1 9 We studied as to how the inter-connected modular architecture of clonal Eichhornia crassipes allows nutrient to transfer from established ramets to developing ramets, and nitrate translocation within clonal system and how such a strategy may play an important role in successful establishment and expansion of this clonal plant. Using this stoloniferous E. crassipes as a model, we studied the effects of light and nitrate availability on growth and nitrate assimilation in inter-connected parent and offspring ramets. Our results showed that increase in light and nitrate availability significantly increased growth rate of the whole clonal fragments and reproduction of offspring ramets in E. crassipes. In addition, increases in nitrate reductase (NR) activity and glutamine synthetase (GS) activity were observed in both parent and offspring ramets with increase in light density and nitrate supply. We also found that nitrate translocation is greater in offspring ramets than in parent ramets under abundant light and nitrate environment in this fast-growing clonal plant. Consequently, majority of nitrate assimilation in offspring ramets is beneficial to the growth of whole clonal system, as indicated by a close correlation between nitrate assimilation in offspring ramets and RGR of whole clonal fragments. We strongly contend that nitrate translocation and assimilation within clone system is important for efficient utilization of nitrogen in alien clonal plant E. crassipes during establishment and expansion, and thus for increase in its invasiveness in natural water columns. Web of Science Eichhornia crassipes China Wuhan Nanhu Lake Field - Observational lentic;lotic Invasion Hyp. Inherent Superiority Clonal Reproduction primary 2692 LaRue, Elizabeth A.; Ruetz, Carl R., III; Stacey, Michael B.; Thum, Ryan A. 2011 Population genetic structure of the round goby in Lake Michigan: implications for dispersal of invasive species journal HYDROBIOLOGIA 663 1 71 82 Understanding subsequent dispersal of non-native species following introduction is important for predicting the extent and speed of range expansion and is critical for effective management and risk assessment. Post-introduction dispersal may occur naturally or via human transport, but assessing the relative contribution of each is difficult for many organisms. Here, we use data from seven microsatellite markers to study patterns of dispersal and gene flow among 12 pierhead populations of the round goby (Neogobius melanostomus) in Lake Michigan. We find significant population structure among sampling sites within this single Great Lake: (1) numerous populations exhibited significant pairwise F (ST) and (2) a Bayesian assignment analysis revealed three distinct genetic clusters, corresponding to different pierhead locations, and genetic admixture between these clusters in the remaining populations. Genetic differentiation (F (ST)) is generally related to geographic distance (i.e., isolation by distance), but is periodically interrupted at the scale of Lake Michigan due to gene flow among geographically distant sites. Moreover, average genetic differentiation among populations exhibit a significant, negative correlation with the amount of shipping cargo at ports. Our results, therefore, provide evidence that genetic structure of the round goby in Lake Michigan results from limited natural dispersal with frequent long-distance dispersal through anthropogenic activities such as commercial shipping. Our study suggests that while round gobies can undoubtedly disperse and found new populations through natural dispersal mechanisms, their spread within and among the Great Lakes is likely aided by transport via ships. We, therefore, recommend that ballast-water treatment and management may limit the spread of non-native species within the Great Lakes after the initial introduction in addition to preventing the introduction of non-native species to the Great Lakes. Web of Science Neogobius melanostomus USA Lake Michigan Field - Observational lentic Invasion Hyp. Other predator 2693 Dostal, Petr; Paleckova, Michaela 2011 Does relatedness of natives used for soil conditioning influence plant-soil feedback of exotics? journal BIOLOGICAL INVASIONS 13 2 331 340 The naturalisation hypothesis has been gaining attention recently as a possible mechanism to explain variations in invasion success. It predicts that exotic genera with native representatives should be less successful because of an overlap in resource use and of the existence of common specialised enemies. In this study, we tested whether native congenerics have more negative impact on exotic species than heterogenerics by increasing the effects of soil pathogens. We sampled soil in populations of three exotic species (Epilobium ciliatum, Impatiens parviflora and Stenactis annua) at sites with and without respective congeneric species. This soil was used as an inoculum for cultivating the first plant cohort, which included exotics, as well as native congenerics and heterogenerics. The conditioned soil was subsequently used for cultivating the second cohort of plants (exotics only). We found no consistent impact of relatedness of conditioning species on exotic growth. Although soil conditioned by congeneric E. hirsutum had the largest reduction on the performance of E. ciliatum, the final biomass of S. annua was lowest when grown in soil conditioned by itself. There was no effect of stimulating species on the biomass of I. parviflora. In both experimental phases, performance of exotics was improved when cultivated with sterilised inoculua, indicating the dominance of soil generalist pathogens. However, the biomass of S. annua was increased most by congeneric-stimulated inoculum from congeneric sites, suggesting a possible role for specialised symbionts. Our results suggest that variations in invasion success of at least some exotics may be affected by species-specific interactions mediated by the soil biota. Web of Science Many Czech Republic Field - Observational terrestrial Invasion Hyp. Empty Niche primary 2694 Hou, Yu-Ping; Peng, Shao-Lin; Chen, Bao-Ming; Ni, Guang-Yan 2011 Inhibition of an invasive plant (Mikania micrantha H.B.K.) by soils of three different forests in lower subtropical China journal BIOLOGICAL INVASIONS 13 2 381 391 Biological invasion represents one of the most serious threats to biodiversity, and invasion ecology research has become one of the central issues of contemporary environmental science. However, the relative role of soil development as correlated with succession in influencing variation in invasion resistance has seldom been examined. We hypothesized that the invasion potential of exotic plants depends on soil conditions. In this study, we explored variation among soils of three forest types in their resistance to invasion by Mikania micrantha H.B.K. in lower subtropical China; this species is one of the top ten most invasive weeds in the world. In model systems of soils from different forests, M. micrantha performed worst on undisturbed late-successional stage forest (monsoon evergreen broadleaf forest, MEBF) soils and did not appear to take advantage of abundant soil nutrients. These results could reflect that a potential inhibitory effect was driven by MEBF soil. Plant litter is an important component of soils, litter bioassay and addition experiments demonstrated native plant species from different forests differentially confer invasion resistance and affect the performance of exotic plants. Naturally, other factors such as the relative abundances of nutrients, microbial feedbacks, could have contributed to these results as well. Our results challenge the notion that forests are not immune to invasion and suggest that maintaining late-successional plant communities in lower subtropical China, which could be related to increased productivity and stability, should be a primary objective of land managers. Web of Science Mikania micrantha H.B.K. China lower subtropical Field - Observational terrestrial Deciduous Forest Invasion Hyp. Community Species Richness primary 2697 Kowalczyk, Rafa; Zalewski, Andrzej 2011 Adaptation to cold and predation-shelter use by invasive raccoon dogs Nyctereutes procyonoides in BiaowieA1/4a Primeval Forest (Poland) journal EUROPEAN JOURNAL OF WILDLIFE RESEARCH 57 1 133 142 Based on radio-tracking of raccoon dogs Nyctereutes procyonoides in BiaowieA1/4a Primeval Forest (E Poland) in 1997-2002, we addressed the hypothesis that pattern of shelter use by this invasive carnivore is an adaptation to both climatic conditions and predation. Raccoon dogs used various types of shelters but were invariably concealed in dense vegetation or in the shelters created by trunks, branches, or roots of fallen trees (58% of days). Burrows (mainly badger setts) and hollow trees (mainly fallen limes) were selected on 27% and 14% of days, respectively. The pattern of shelter use varied throughout the year. In crucial periods (breeding period and winter), raccoon dogs used shelter offering better protection: burrows and hollow trees (use of which increased with decreasing ambient temperature) in winter, and hollow trees and dense vegetation during breeding and raising pups. The pattern of shelter use by raccoon dogs was also strongly modified by forest structure. Raccoon dogs living in the pristine old-growth stands (with large amounts of dead wood) utilized mainly natural shelters created by fallen trees (trunks, branches, and roots) and sedge tussocks (38% and 37%, respectively). Individuals inhabiting the managed part of the Forest used mainly burrows (43%) and thicket (23%). We recorded very strong monogamous relationships between pair mates, manifested by shared resting on 84% of days per year. We conclude that hiding behavior and plasticity in shelter use is a response to high mortality due to predation and to unfavorable climatic conditions. High adaptability to various environmental conditions may be one of the factors underlying successful range expansion of raccoon dogs in Europe. Web of Science Nyctereutes procyonoides Poland Eastern Poland Field - Observational terrestrial Deciduous Forest Invasion Hyp. Plasticity predator 2698 Kleinteich, Anja; Schneider, Jutta M. 2011 Developmental strategies in an invasive spider: constraints and plasticity journal ECOLOGICAL ENTOMOLOGY 36 1 82 93 2. The present study investigated growth patterns under varying food conditions in the bridge spider, Larinioides sclopetarius, an extremely successful species in colonising urban habitats. 3. In L. sclopetarius growth ratios of successive instars were not constant but decreased over development. Instead, these spiders' growth is well described by a developmental growth rate (weight gain per moult) and a growth coefficient (weight gain per development time), both of which are based on a geometric progression. All developmental parameters, including developmental growth rate and growth coefficient as well as the intermoult duration and the number of instars, highly depend on food availability in L. sclopetarius and thus show plasticity. 4. Our study shows that geometric growth patterns do not necessarily preclude plasticity and that the parameters of geometric growth are affected by developmental plasticity. We suggest that their high developmental plasticity may facilitate bridge spiders' success in invading urban habitats. Web of Science Larinioides sclopetarius Germany Hafen City River Elbe Field - Observational terrestrial Urban Invasion Hyp. Plasticity predator 2699 Bock, D. G.; Zhan, A.; Lejeusne, C.; MacIsaac, H. J.; Cristescu, M. E. 2011 Looking at both sides of the invasion: patterns of colonization in the violet tunicate Botrylloides violaceus journal MOLECULAR ECOLOGY 20 3 503 516 Understanding the ecological and evolutionary forces that shape the genetic structure of invasive populations and facilitate their expansion across a large spectrum of environments is critical for the prediction of spread and management of ongoing invasions. Here, we study the dynamics of postestablishment colonization in the colonial ascidian Botrylloides violaceus, a notorious marine invader. After its initial introduction from the Northwest Pacific, B. violaceus spread rapidly along the Pacific and Atlantic coasts of North America, impacting both aquaculture facilities and natural ecosystems. We compare genetic diversity and patterns of gene flow among 25 populations (N = 679) from the West and East coasts, and evaluate the contribution of sexual vs. asexual reproduction to this species' invasion success using data from the mitochondrial cytochrome c oxidase subunit I (COI) gene and 13 nuclear polymorphic microsatellite loci. Our results reveal contrasting patterns of spread in the coastal waters of North America. While the West coast was colonized by noncontiguous (long-distance) dispersal, the East coast invasion appears to have occurred through contiguous (stepping-stone) spread. Molecular data further indicate that although dispersal in colonial ascidians is predominantly achieved through sexually produced propagules, aquaculture practices such as high-pressure washing can facilitate fragmentation and potentially exacerbate infestations and spread via asexual propagules. The results presented here suggest that caution should be used against the general assumption that all invasions, even within a single species, exhibit similar patterns of colonization, as highly contrasting dynamics may transpire in different invaded ranges. Web of Science Botrylloides violaceus USA Field - Observational marine Fundamentals filter 2700 McGlone, Christopher M.; Sieg, Carolyn Hull; Kolb, Thomas E. 2011 Invasion resistance and persistence: established plants win, even with disturbance and high propagule pressure journal BIOLOGICAL INVASIONS 13 2 291 304 Disturbances and propagule pressure are key mechanisms in plant community resistance to invasion, as well as persistence of invasions. Few studies, however, have experimentally tested the interaction of these two mechanisms. We initiated a study in a southwestern ponderosa pine (Pinus ponderosa Laws.)/bunch grass system to determine the susceptibility of remnant native plant communities to cheatgrass (Bromus tectorum L.) invasion, and persistence of cheatgrass in invaded areas. We used a 2 x 2 factorial design consisting of two levels of aboveground biomass removal and two levels of reciprocal seeding. We seeded cheatgrass seeds in native plots and a native seed mixture in cheatgrass plots. Two biomass removal disturbances and sowing seeds over 3 years did not reverse cheatgrass dominance in invaded plots or native grass dominance in non-invaded native plots. Our results suggest that two factors dictated the persistence of the resident communities. First, bottlebrush squirreltail (Elymus elymoides (Raf.) Swezey) was the dominant native herbaceous species on the study site. This species is typically a poor competitor with cheatgrass as a seedling, but is a strong competitor when mature. Second, differences in pretreatment levels of plant-available soil nitrogen and phosphorus may have favored the dominant species in each community. Annual species typically require higher levels of plant-available soil nutrients than perennial plants. This trend was observed in the annual cheatgrass community and perennial native community. Our study shows that established plants and soil properties can buffer the influences of disturbance and elevated propagule pressure on cheatgrass invasion. Web of Science Bromus tectorum USA Arizona Mt. Trumbull ; Uinkaret Mountains Field - Experimental terrestrial Grassland Invasion Hyp. Propagule Pressure;Disturbance primary 2701 Dennis, Brian; Civille, Janie C.; Strong, Donald R. 2011 Lateral spread of invasive Spartina alterniflora in uncrowded environments journal BIOLOGICAL INVASIONS 13 2 401 411 We present a stochastic model of clonal growth in uncrowded environments and use it to study data of 7,536 clones from the invasion of Willapa Bay, Washington by the Atlantic cordgrass Spartina alterniflora. The model incorporates effects on clone growth of covariates, spatial autocorrelation, and temporal trends. The deterministic component of the model assumes that growth rate of a clone's area is proportional to its perimeter, resulting in constant radial growth of the clone. The full stochastic model is built assuming that the fluctuations of radial growth increments (differences of square root-transformed areas) are normally distributed with constant variance. Graphical fit analysis with the density probability plot technique indicates that the stochastic model provides an excellent description of the S. alterniflora invasion. Variation in Spartina growth was significantly but weakly (5%) related to intertidal elevation, substrate type, year of survey, and the two-way interactions between these variables, suggesting that factors intrinsic to Spartina, along with localized high frequency noise, dominate the effects of larger scale abiotic factors on clone growth. Our model of clonal growth is potentially applicable to other systems with approximately circular plants or lichens. Web of Science Spartina alterniflora USA Washington Willapa Bay Theoretical/Modeling estuarine Invasion Hyp. Inherent Superiority Clonal Reproduction primary 2702 Holdredge, Christine; Bertness, Mark D. 2011 Litter legacy increases the competitive advantage of invasive Phragmites australis in New England wetlands journal BIOLOGICAL INVASIONS 13 2 423 433 Exotic plant invaders that form monocultures and exclude native plants are often the most detrimental to native diversity and the hardest to eradicate. To generate a monoculture, the invader must garner more resources than resident natives and, once established, persist despite high densities of conspecific neighbors. Coincident with expansion and long-term persistence, successful invaders typically accumulate senesced material, but the role of this litter in mediating the invader's ability to establish and maintain monospecific dominance has rarely been investigated. We used stands of the common reed, Phragmites australis, a prolific wetland invader in North America, to explore the impact of litter on interspecific competition with the native rush, Juncus gerardii, and intraspecific competition among live shoots. In 10 x 10 m areas positioned on Phragmites expansion fronts, we removed litter to isolate its effect from live Phragmites on light availability, aboveground biomass and community composition. Compared to adjacent, unmanipulated fronts, light availability nearly tripled and Juncus biomass increased > 170% in litter removal areas after 4 months. Although the positive response of Juncus and native forbs was most pronounced on the leading edge of Phragmites stands, litter removal triggered a 271% increase in native plant biomass even in the interior of stands where Phragmites' live stem density was highest. Litter treatment did not significantly affect Phragmites biomass, but more, shorter stems emerged in litter removals revealing Phragmites modifies stem phenotype in response to local litter and light conditions. These results suggest that litter plays a central role in Phragmites' invasion process, from initial establishment to subsequent monospecific dominance. Thus, prescribed litter removal may be an effective strategy to enhance coexistence of native plant populations in wetlands where eradication of invasive monocultures is not an ecologically or economically feasible option. Web of Science Phragmites australis USA New England Field - Experimental wetland Wetland Invasion Hyp. Ecosystem Engineers primary 2703 Jairus, Teele; Mpumba, Rebecca; Chinoya, Stephen; Tedersoo, Leho 2011 Invasion potential and host shifts of Australian and African ectomycorrhizal fungi in mixed eucalypt plantations journal NEW PHYTOLOGIST 192 1 179 187 Transportation of forestry materials results in unintended co-introduction of nonnative species that may cause enormous ecological or economic damage. While the invasion ecology of plants and animals is relatively well-known, that of microorganisms, except aboveground pathogens, remains poorly understood. This work addresses host shifts and invasion potential of root symbiotic ectomycorrhizal fungi that were co-introduced with Australian eucalypts and planted in clear-cut miombo woodlands in Zambia, south-central Africa. By use of rDNA and plastid intron sequence analysis for identification and phylogenetic techniques for inferring fungal origin, we demonstrated that host shifts were uncommon in the Australian fungi, but frequent in the African fungi, especially in mixed plantations where roots of different trees intermingle. There was evidence for naturalization, but not for invasion by Australian ectomycorrhizal fungi. Nevertheless, the fungi introduced may pose an invasion risk along with further adaptation to local soil environment and host trees. Inoculation of eucalypts with native edible fungi may ameliorate the potential invasion risks of introduced fungi and provide an alternative source of nutrition. Web of Science ectomycorrhizal fungi Zambia Field - Observational terrestrial Deciduous Forest Invasion Hyp. Mutualism Facilitation 2704 Katsanevakis, Stelios; Zenetos, Argyro; Macic, Vesna; Beqiraj, Sajmir; Poursanidis, Dimitrios; Kashta, Lefter 2011 Invading the Adriatic: spatial patterns of marine alien species across the Ionian-Adriatic boundary journal AQUATIC BIOLOGY 13 2 107 118 An important pathway of introduction of alien marine species in the Adriatic seems to be the northward expansion of species already established in the Ionian Sea, aided by the East Adriatic Current. We modelled the occupancy of alien marine species in the upper infralittoral zone of rocky bottoms across the Ionian-Adriatic border (Albanian and Montenegrin coastlines), based on underwater visual survey data. A method that took into account imperfect detection of the target species was applied to make unbiased occupancy estimations, based on a multi-model inference approach. A total of 6 alien species were found during the survey (in decreasing order of occupancy): Caulerpa racemosa, Percnon gibbesi, Ganonema farinosum, Lophocladia lallemandii, Asparagopsis taxiformis and Pinctada radiata. There was a general pattern of declining occupancy from northern Ionian Albanian coastal waters towards the southeastern Adriatic coastline. Possible reasons for this pattern are: (1) the invasion of some species from the northern Ionian Sea is still in progress and the limit of the current distributional range falls within or near the study area; (2) the lower temperatures in the Adriatic Sea restrict the northward expansion of thermophilic alien species; and (3) the part of Albania north of the Otranto Strait is characterized by sandy/muddy coasts, large estuarine areas and substantial freshwater input, creating a barrier for expansion of sessile species. There is a pool of 77 species established in the central Mediterranean but not yet observed in the Adriatic Sea. Among these, 14 species are present in the Greek Ionian Sea and may be considered as the most probable newcomers to the Adriatic Sea in the near future. Web of Science Caulerpa racemosa;Percnon gibbesi;Ganonema farinosum;Lophocladia lallemandii;Asparagopsis taxiformis;Pinctada radiata Albania Adriatic Sea marine Intertidal/Near Shore Fundamentals primary;herbivore;omnivore 2706 Darrigran, Gustavo; Damborenea, Cristina; Drago, Edmundo C.; Ezcurra de Drago, Ines; Paira, Aldo 2011 Environmental factors restrict the invasion process of Limnoperna fortunei (Mytilidae) in the Neotropical region: A case study from the Andean tributaries journal ANNALES DE LIMNOLOGIE-INTERNATIONAL JOURNAL OF LIMNOLOGY 47 3 221 229 The golden mussel Limnoperna fortunei was introduced into Argentina in 1991 and has since been spreading through the Plata and Guaiba basins at a rate of 240 km.year(-1). To assess their ability to invade the Andean tributaries of the Plata Basin (Pilcomayo, Bermejo and Salado del Norte rivers), their current range was assessed and related to the abiotic parameters of sites where they were present and absent. These data were then compared with their known tolerances to identify possible barriers to invasion. Outputs suggested that three environmental parameters are barriers to invasion: salinity and river flow intermittence in different sectors of the rivers Pilcomayo and Salado del Norte, and concentration of suspended sediments in the Bermejo River and in the upper reaches of the Salado del Norte and Pilcomayo rivers. The importance of these findings is discussed in relation to using environmental data to infer the invasion possibilities and the utility of environmental data to better understand invasion patterns and processes. Web of Science Limnoperna fortunei Argentina Plata Basin marine Fundamentals filter 2709 Wang, Rui; Wang, Jin-Feng; Qiu, Zhi-Jing; Meng, Bin; Wan, Fang-Hao; Wang, Yin-Zheng 2011 Multiple mechanisms underlie rapid expansion of an invasive alien plant journal NEW PHYTOLOGIST 191 3 828 839 With growing concerns over serious ecological problems, a particular challenge is to reveal the complex mechanisms underlying rapid expansion of invasive species. Ageratina adenophora is of particular interest in addressing this question. We used geographic information systems and logistic regression to identify the geographic and environmental factors contributing to the presence of A. adenophora. Join-count spatial statistics with reproduction mode examination were employed to elucidate the spatiotemporal dispersal mechanisms. Multiple factors have significantly contributed to the rapid expansion of A. adenophora. Its biological traits, favoring dispersal by water and wind coupled with local spatiotemporally heterogeneous geography and ecology, promote invasion downstream and upstream along river valleys, while other factors associated with human activities facilitate its invasion over high mountains and across river valleys, providing new scope for progressive invasions. We further identified an unusual invasion event of A. adenophora subsequent to a great flood that amplified its dispersal ability from vegetative propagules and seeds. These findings suggest that dynamic interactions of multiple factors in heterogeneous ecogeographical environments - a 'combinatorial' invasion mechanism would generate an unexpected invasion rate of an alien species or a seemingly stochastic invasion event. Web of Science Ageratina adenophora China Sichuan;Chongqing Field - Observational lotic Invasion Hyp. Inherent Superiority Effective Disperser primary 2710 Zhang, Zhi-Qiang; Zhang, Yong-Hong; Sun, Hang 2011 The reproductive biology of Stellera chamaejasme (Thymelaeaceae): A self-incompatible weed with specialized flowers journal FLORA 206 6 567 574 It has profound implications for species invasions and fitness, how weeds achieve reproductive success. We present the first study on the reproductive biology of Stellera chamaejasme, a toxic perennial weed which is abundant in the alpine meadows on the eastern Tibetan Plateau of China since the 1960s. S. chamaejasme has synchronogamy and herkogamous flowers, which last for about 11 days. Flowers can be yellow, white or reddish. Our results suggest that this species is self-incompatible and depends entirely on pollen vectors for seed production. All the pollinators observed were Lepidopteran species; however, the pollinator assemblage was significantly different among populations and likely independent on floral colour. Reproductive success and invasion of the weed might be a complex function of floral traits, breeding system and pollination ecology. Generally, plants with generalized pollination system are more invasive. However, our results suggest that specialized flowers and self-incompatibility in the present case may not prevent invasion of the weed. (C) 2011 Published by Elsevier GmbH. Web of Science Stellera chamaejasme China Tibetan Plateau terrestrial Mountain Invasion Hyp. Inherent Superiority Self Compatible primary 2711 Molina-Montenegro, Marco A.; Quiroz, Constanza L.; Torres-Diaz, Cristian; Atala, Cristian 2011 Functional differences in response to drought in the invasive Taraxacum officinale from native and introduced alpine habitat ranges journal PLANT ECOLOGY & DIVERSITY 4 1 37 44 Background: Phenotypic plasticity and ecotypic differentiation have been suggested as the main mechanisms by which widely distributed species can colonise broad geographic areas with variable and stressful conditions. Some invasive plant species are among the most widely distributed plants worldwide. Plasticity and local adaptation could be the mechanisms for colonising new areas. Aims: We addressed if Taraxacum officinale from native (Alps) and introduced (Andes) stock responded similarly to drought treatment, in terms of photosynthesis, foliar angle, and flowering time. We also evaluated if ontogeny affected fitness and physiological responses to drought. Methods: We carried out two common garden experiments with both seedlings and adults (F2) of T. officinale from its native and introduced ranges in order to evaluate their plasticity and ecotypic differentiation under a drought treatment. Results: Our data suggest that the functional response of T. officinale individuals from the introduced range to drought is the result of local adaptation rather than plasticity. In addition, the individuals from the native distribution range were more sensitive to drought than those from the introduced distribution ranges at both seedling and adult stages. Conclusions: These results suggest that local adaptation may be a possible mechanism underlying the successful invasion of T. officinale in high mountain environments of the Andes. Web of Science Taraxacum officinale Chile Andes Field - Observational terrestrial Mountain Invasion Hyp. Plasticity primary 2712 Davies, Kendi F.; Cavender-Bares, Jeannine; Deacon, Nicholas 2011 Native communities determine the identity of exotic invaders even at scales at which communities are unsaturated journal DIVERSITY AND DISTRIBUTIONS 17 1 35 42 Aim To determine why some communities are more invasible than others and how this depends on spatial scale. Our previous work in serpentine ecosystems showed that native and exotic diversity are negatively correlated at small scales, but became positively correlated at larger scales. We hypothesized that this pattern was the result of classic niche partitioning at small scales where the environment is homogeneous, and a shift to the dominance of coexistence mechanisms that depend on spatial heterogeneity in the environment at large scales. Location Serpentine ecosystem, Northern California. Methods We test the above hypotheses using the phylogenetic relatedness of natives and exotics. We hypothesized that (1) at small scales, native and exotic species should be more distantly related than expected from a random assemblage model because with biotic resistance, successful invaders should have niches that are different from those of the natives present and (2) at large scales, native and exotic species should not be more distantly related than expected. Result We find strong support for the first hypothesis providing further evidence of biotic resistance at small scales. However, at large scales, native and exotic species were also more distantly related than expected. Importantly, however, natives and exotics were more distantly related at small scales than they were at large scales, suggesting that in the transition from small to large scales, biotic resistance is relaxed but still present. Communities at large scales were not saturated in the sense that more species could enter the community, increasing species richness. However, species did not invade indiscriminately. Exotic species closely related to species already established the community were excluded. Main conclusions Native communities determine the identity of exotic invaders even at large spatial scales where communities are unsaturated. These results hold promise for predicting which species will invade a community given the species present. Web of Science Many USA California Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Community Species Richness primary 2713 Lubell, Jessica D.; Brand, Mark H. 2011 Germination, growth and survival of Berberis thunbergii DC. (Berberidaceae) and Berberis thunbergii var. atropurpurea in five natural environments journal BIOLOGICAL INVASIONS 13 1 135 141 Germination, growth and survival of green Berberis thunbergii and its purple ornamental form, Berberis thunbergii var. atropurpurea, were compared in five natural environments (full sun meadow, edge of woods, moist woods, dry woods, pine woods) to determine whether these two forms have a similar ability to naturalize. Berberis thunbergii and Berberis thunbergii var. atropurpurea had similar germination rates of about 25% at the end of 3 years. Most of the seed germination occurred in year one (89%), with a small amount of additional germination in year two (10%), and even less in year three (1%). Greatest germination occurred in the moist woods and full sun meadow sites and the least occurred at the pine woods site. Germination was reduced in the pine woods environment by the thick leaf litter layer present there. Barberry seedling survival during the first year was only 22% and survival dropped to 11.3% by the end of 2 years. Purple barberry seedlings had a lower 2 year survival rate than green barberry. There was no difference in seedling growth between purple and green barberry seedlings, but surviving seedling growth rates at the five environments were comparable. Seedlings achieved maximum growth in the edge of woods environment, but also grew well in the full sun meadow environment. At harvest, the full sun meadow had the greatest number of seedlings present, while no seedlings survived in the pine woods site. Web of Science Berberis thunbergii USA Connecticut Field - Experimental terrestrial Deciduous Forest;Coniferous Forest;Old Field Fundamentals primary 2714 Crooks, Jeffrey A.; Chang, Andrew L.; Ruiz, Gregory M. 2011 Aquatic pollution increases the relative success of invasive species journal BIOLOGICAL INVASIONS 13 1 165 176 Although individual ecosystems vary greatly in the degree to which they have been invaded by exotic species, it has remained difficult to isolate mechanisms influencing invader success. One largely anecdotal observation is that polluted or degraded areas will accumulate more invaders than less-impacted sites. However, the role of abiotic factors alone in influencing invisibility has been difficult to isolate, often because the supply of potential invaders is confounded with conditions thought to increase vulnerability to invasion. Here, we conducted a field experiment to test how the assemblages of exotic versus native marine invertebrates changed during community assembly under different exposure levels of a common pollutant, copper. The experiment was conducted by deploying fouling panels in a Randomized Block Design in San Francisco Bay. Panels were periodically removed, placed into buckets with differing copper concentrations, and returned to the field after 3 days. This design allowed propagule availability to the plates to be statistically independent of short-term copper exposure. The results demonstrate that copper caused significant differences in community structure. Average native species richness was significantly affected by copper exposure, but average exotic richness was not. The total native species pool within treatments exhibited a greater than 40% decline within increasing copper, while the exotic species pool did not change significantly. These results confirm that anthropogenic alteration of abiotic factors influences invader success, indicating that management strategies to reduce invader impacts should include both efforts to improve environmental conditions as well as reduce invader supply. Web of Science Many USA California San Francisco Estuary Field - Experimental estuarine Invasion Hyp. Disturbance primary;filter 2715 Robison, Ramona A.; Kyser, Guy B.; Rice, Kevin J.; DiTomaso, Joseph M. 2011 Light intensity is a limiting factor to the inland expansion of Cape ivy (Delairea odorata) journal BIOLOGICAL INVASIONS 13 1 35 44 Cape ivy (Delairea odorata) is a highly invasive climbing perennial vine that is primarily distributed in coastal communities of California and Oregon, with patchy infestations in some inland riparian areas. In this study, we evaluated light as a potential environmental limitation to the spread of Cape ivy into inland regions of the western United States. Cape ivy was collected from four locations representing the north to south range. Plants were grown for 9 to 11 weeks in full sunlight and under two shade regimes (20 and 6% of full sunlight). The experiment was conducted twice at two temperature regimes. Results show some within- and among-population variability, with the southernmost San Diego County population having the highest biomass under the warmer growing conditions and the three northern populations responding most favorably in the cooler growing conditions. Despite the minor differences within and between populations, Cape ivy grew very poorly in full sunlight in both experiments. Although plants growing under 6% light grew better than those in full sunlight, they were far less robust compared to plants growing at 20% light. Our results indicate that while Cape ivy will not persist in areas with prolonged high intensity sunlight, characterized by much of the interior regions of California and Oregon, it is expected to invade and spread in areas with reduced light, including coastal regions frequently exposed to fog or cloudy conditions, or sub-canopy layers of riparian forests or woodlands. These communities should be the target areas for early detection and rapid response programs to prevent further Cape ivy invasion. Web of Science Delairea odorata United States Greenhouse terrestrial Chaparral/Shrublands Fundamentals primary 2716 Pavlovic, Noel B.; Leicht-Young, Stacey A. 2011 Are temperate mature forests buffered from invasive lianas? journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 138 1 85 92 PAVLOVIC, N. B. AND S. A. LEICHT-YOUNG (U.S. Geological Survey, 1100 N. Mineral Springs Rd., Porter, IN 46304). Are temperate mature forests buffered from invasive lianas? J. Toekev Bur. Soc. 138: 85-92. 2011.-Mature and old-growth forests are often thought to be buffered against invasive species due to low levels of light and infrequent disturbance. Lianas (woody vines) and other climbing plants are also known to exhibit lower densities in older forests. As part of a larger survey of the lianas of the southern Lake Michigan region in mature and old-growth forests, the level of infestation by invasive lianas was evaluated. The only invasive liana detected in these surveys was Celastrus orbiculatus Thunb. (Celastraceae). Although this species had only attached to trees and reached the canopy in a few instances, it was present in 30% of transects surveyed, mostly as a component of the ground layer. Transects with C orbiculatus had higher levels of soil potassium and higher liana richness than transects without. In contrast, transects with the native scandens had higher pH, sand content, and soil magnesium and lower organic matter compared to transects where it was absent. Celastrus orbiculatus appears to be a generalist liana since it often occurs with native lianas. Celastrus orbiculatus poses a substantial threat to mature forests as it will persist in the understory until a canopy gap or other disturbance provides the light and supports necessary for it to ascend to the canopy and damage tree species. As a result, these forests should be monitored by land managers so that C orbiculatus eradication can occur while invasions are at low densities and restricted to the ground layer. Web of Science Celastrus orbiculatus USA Michigan Field - Observational terrestrial Deciduous Forest Invasion Hyp. Community Species Richness primary 2717 Saad, Layla; Tiebre, Marie-Solange; Hardy, Olivier J.; Mahy, Gregory; Vanderhoeven, Sonia 2011 Patterns of hybridization and hybrid survival in the invasive alien Fallopia complex (Polygonaceae) journal PLANT ECOLOGY AND EVOLUTION 144 1 12 18 Background Hybridization and polyploidization are considered important driving forces of invasive processes. In the invasive Fallopia spp. complex, hybridization between taxa of various ploidy levels has been experimentally demonstrated. Extensive genetic variation has also been observed among hybrids in the field. However, what makes a certain hybridization event of evolutionary importance is still the subject of speculation considering the invasive potential of hybrid Fallopia. Aims The present study examined landscape scale patterns of interspecific hybridization within the alien invasive Fallopia complex, and tested whether cold winter might act as selective agent for hybrid survival. Methods Eighty seeds per clone were collected from four taxa (F. japonica, F. sachalinensis, F aubertii, and F. x bohemica) and sown in greenhouse and outdoor conditions. Ploidy levels of the resulting seedlings were determined by flow cytometry at early stages of seedling growth and compared to those of mature clones present in the same landscapes. Key results The four studied taxa were involved in interspecific hybridization patterns. Seedlings resulting from hybridization had a large range of ploidy levels, including aneuploid and euploid progeny, and polyploid levels that were not observed in mature clones. Cold winter had a negative effect on germination success. However, a comparison of ploidy levels of seedlings that survived the cold winter with those grown under greenhouse conditions indicated that cold winter was not a significant selection agent for particular ploidy levels. Conclusions Our results stress the importance of interspecific hybridization and polyploidization events in generating invasive hybrids in the alien Fallopia spp. complex. Cold winter represents a selection agent for the survival of early stages of progeny but does not explain the discrepancies in ploidy levels between produced seedlings and currently occurring mature clones. Web of Science Fallopia spp Greenhouse terrestrial Invasion Hyp. Hybridization primary 2718 Siniscalco, C.; Barni, E.; Bacaro, G. 2011 Non-native species distribution along the elevation gradient in the western Italian Alps journal PLANT BIOSYSTEMS 145 1 150 158 In this work the occurrence of non-native species was recorded along the elevation gradient in the Alps, in order to establish their distribution pattern, their current altitudinal limits and to elucidate which species are presumably adapted to higher elevations. Plots were located along the course of rivers in five valleys from 100 to 2100m a.s.l. Sixty-eight non-natives were recorded in the study area. The proportion of invasives was found to be much higher in the study area then in the whole administrative region. The number of non-natives per plot decreased strongly with increasing elevation. The great majority (94%) of the non-native species grows at the lowest elevations, while only 6% survive up to 1500m and none was found above this limit. Results were interpreted considering the factors driving the invasion process (disturbance, the native communities' resistance to invasion, propagule pressure, climatic conditions) and plant traits with particular respect to pre-adaptation to the harsh climate, which increases progressively with elevation. Results confirm that the Alps are not immune from invasion, at least up to medium elevation. Web of Science Many Italy Alps Field - Observational terrestrial Mountain Invasion Hyp. Preadaptation to Climate primary 2720 Scharfy, Deborah; Funk, Andrea; Venterink, Harry Olde; Guesewell, Sabine 2011 Invasive forbs differ functionally from native graminoids, but are similar to native forbs journal NEW PHYTOLOGIST 189 3 818 828 P>Exotic plant invasions can alter ecosystem processes, particularly if the invasive species are functionally different from native species. We investigated whether such alterations can be explained by differences in functional traits between native and invasive plants of the same functional group or by differences in functional group affiliation. We compared six invasive forbs in Europe with six native forbs and six native graminoids in leaf and whole-plant traits, plasticity in response to nutrient supply and interspecific competition, litter decomposition rate, effects on soil nutrient availability, and allelopathy. All traits were measured in a series of pot experiments, and leaf traits additionally in the field. Invasive forbs differed from native forbs for only a few traits; they had less leaf chlorophyll and lower phosphorus (P) uptake from soil, but they tended to have a stronger allelopathic effect. The invasive forbs differed in many traits from the native graminoids, their leaves had lower tissue densities and a shorter life span, their litter decomposed faster and they had a lower nitrogen-use efficiency. Our results suggest that invasive forbs have the potential to alter ecosystem properties when invading graminoid-dominated and displacing native graminoids but not when displacing native forbs. Web of Science Many Europe Garden terrestrial Grassland Invasion Hyp. Novel Weapons;Plasticity;Ecosystem Engineers primary 2721 Xiao, Yan; Tang, Junbing; Qing, Hua; Zhou, Changfang; Kong, Weijing; An, Shuqing 2011 Trade-offs among growth, clonal, and sexual reproduction in an invasive plant Spartina alterniflora responding to inundation and clonal integration journal HYDROBIOLOGIA 658 1 353 363 The purpose of this article was to study the trade-offs among vegetative growth, clonal, and sexual reproduction in an aquatic invasive weed Spartina alterniflora that experienced different inundation depths and clonal integration. Here, the rhizome connections between mother and daughter ramets were either severed or left intact. Subsequently, these clones were flooded with water levels of 0, 9, and 18 cm above the soil surface. Severing rhizomes decreased growth and clonal reproduction of daughter ramets, and increased those of mother ramets grown in shallow and deep water. The daughter ramets disconnected from mother ramets did not flower, while sexual reproduction of mother ramets was not affected by severing. Clonal integration only benefited the total rhizome length, rhizome biomass, and number of rhizomes of the whole clones in non-inundation conditions. Furthermore, growth and clonal reproduction of mother, daughter ramets, and the whole clone decreased with inundation depth, whereas sexual reproduction of mother ramets and the whole clones increased. We concluded that the trade-offs among growth, clonal, and sexual reproduction of S. alterniflora would be affected by inundation depth, but not by clonal integration. Web of Science Spartina alterniflora China Greenhouse estuarine Invasion Hyp. Inherent Superiority Clonal Reproduction primary 2722 Drown, Devin M.; Levri, Edward P.; Dybdahl, Mark F. 2011 Invasive genotypes are opportunistic specialists not general purpose genotypes journal EVOLUTIONARY APPLICATIONS 4 1 132 143 It is not clear which forms of plasticity in fitness-related traits are associated with invasive species. On one hand, it may be better to have a robust performance across environments. On the other, it may be beneficial to take advantage of limited favorable conditions. We chose to study a worldwide invasive species, Potamopyrgus antipodarum, and compare the plasticity of life-history traits of a sample of invasive genotypes to a sample of ancestral-range genotypes. We examined the responses to salinity in this freshwater snail because it varies spatially and temporally in the introduced range and contributes to variation in fitness in our system. We used a recently developed statistical method that quantifies aspects of differences in the shape among reaction norms. We found that the invasive lineages survived and reproduced with an increased probability at the higher salinities, and were superior to ancestral-range lineages in only two traits related to reproduction. Moreover, we found that in terms of traits related to growth, the invasive lineages have a performance optimum that is shifted to higher salinities than the ancestral-range lineages as well as having a narrower niche breadth. Contrary to the prediction of the general purpose genotype hypothesis, we found that invasive lineages tended to be opportunistic specialists. Web of Science Potamopyrgus antipodarum Lab lentic;lotic Invasion Hyp. Plasticity herbivore 2723 Urian, Alyson G.; Hatle, John D.; Gilg, Matthew R. 2011 Thermal Constraints for Range Expansion of the Invasive Green Mussel, Perna viridis, in the Southeastern United States journal JOURNAL OF EXPERIMENTAL ZOOLOGY PART A-ECOLOGICAL GENETICS AND PHYSIOLOGY 315 1 12 21 Cold temperatures are thought to be among the most important determining factors of geographic distribution for tropical and sub-tropical marine invertebrates. The Asian green mussel, Perna viridis, has been introduced into coastal waters of Florida where its current distribution is hypothesized to be limited by low temperatures during winter. Lethal and sub-lethal effects (heat shock protein/Hsp70 expression) of cold water and air temperatures were analyzed in two size classes of P. viridis from Florida in an effort to determine the effects of current and forecasted temperatures on the potential for range expansion. Mussels were exposed to water temperatures of 14, 10, 7 and 3 degrees C for up to 30 days, or to air temperatures of 14, 7, 0 and -10 degrees C for periods of 2 hr. Mortality was significantly increased at all water and air temperaturesr <= 14 degrees C. No differences in mortality rates were observed between small (15-45 mm) and large (75-105 mm) size classes except after exposure to 7 degrees C air, in which small mussels had higher mortality. Significant increases in Hsp70 expression were observed after a 2-hour exposure to 10 degrees C water, but Hsp70 expression was not significantly increased at any temperatures in which mortality was not also significant. The temperature threshold for survival in this population appears to be between 10 and 14 degrees C, suggesting that under current conditions P. viridis may already be at the northern edge of its potential range in the United States. If water temperatures increase with global climate change, northerly flowing currents may permit range expansion as temperatures allow. J. Exp. Zool. 315: 12-21, 2011. (C) 2010 Wiley-Liss, Inc. Web of Science Perna viridis USA Florida Field - Observational marine Intertidal/Near Shore Invasion Hyp. Inherent Superiority Broad Tolerances filter 2724 Oduor, Ayub M. O.; Lankau, Richard A.; Strauss, Sharon Y.; Gomez, Jose M. 2011 Introduced Brassica nigra populations exhibit greater growth and herbivore resistance but less tolerance than native populations in the native range journal NEW PHYTOLOGIST 191 2 536 544 Rapid post-introduction evolution has been found in many invasive plant species, and includes changes in defence (resistance and tolerance) and competitive ability traits. Here, we explored the post-introduction evolution of a trade-off between resistance to and tolerance of herbivory, which has received little attention. In a common garden experiment in a native range, nine invasive and 16 native populations of Brassica nigra were compared for growth and defence traits. Invasive populations had higher resistance to, but lower tolerance of, herbivore damage than native populations. Invasive populations survived better and produced more seeds than native ones when released from herbivores; but fitness was equivalent between the regions under ambient herbivory. The invasive populations grew taller, and produced more biomass and lighter seeds than natives, irrespective of insecticide treatment. In addition to supporting the idea of post-introduction rapid evolution of plant traits, our results also contribute to an emerging pattern of both increasing resistance and growth in invasive populations, contrary to the predictions of earlier theories of resistance-growth trade-offs. Web of Science Brassica nigra USA Garden terrestrial Urban;Old Field Invasion Hyp. Evolution of Increased Competitive Ability primary 2725 Hulme, Philip E. 2011 Contrasting impacts of climate-driven flowering phenology on changes in alien and native plant species distributions journal NEW PHYTOLOGIST 189 1 272 281 P>Plant phenology is particularly sensitive to climate and a key indicator of environmental change. Globally, first flowering dates (FFDs) have advanced by several days per decade in response to recent climate warming, but, while earlier flowering should allow plant distributions to increase, a link between FFD and range changes has not been observed. Here I show for 347 species that the extent to which FFD has responded to climate warming is linked to the degree to which their relative distributions have changed over 30 yr across the British Isles. Native plant species whose phenology did not track climate change declined in distribution, whereas species that became more widespread all exhibited earlier flowering. In contrast, alien neophytes showed both a stronger phenological response to warming and a more marked increase in distribution, but no link between the two. These trends were consistent both for relative changes in the national distribution and for local abundance. At the national scale, the more recently an alien species became established in Britain, the more likely it was to increase in distribution irrespective of FFD, suggesting that recent changes in alien species distributions are decoupled from climate and driven by other factors. Web of Science Many Great Britain Statistical/Meta-analysis terrestrial Invasion Hyp. Climate Change primary 2726 Pachepsky, Elizaveta; Levine, Jonathan M. 2011 Density Dependence Slows Invader Spread in Fragmented Landscapes journal AMERICAN NATURALIST 177 1 18 28 Patchiness is a defining characteristic of most natural and anthropogenic habitats, yet much of our understanding of how invasions spread has come from models of spatially homogeneous environments. Except for populations with Allee effects, an invader's growth rate when rare and dispersal determine its spread velocity; intraspecific competition has little to no influence. How this result might change with landscape patchiness, however, is poorly understood. We used simulation models and their analytical approximations to explore the effect of density dependence on the spread of annual plant invaders moving through heterogeneous landscapes with gaps in suitable habitat. We found that landscape patchiness and discrete invader population size interacted to generate a strong role for density dependence. Intraspecific competition greatly slowed the spread of invasions through patchy landscapes by regulating how rapidly a population could produce enough seeds to surpass habitat gaps. Populations with continuously varying density showed no such effect of density dependence. We adapted a stochastic dispersal model to approximate spread when gap sizes were small relative to the mean dispersal distance and a Markov chain approximation for landscapes with large gaps. Our work suggests that ecologists must consider reproduction at both low and high densities when predicting invader spread. Web of Science Theoretical/Modeling terrestrial Invasion Hyp. Inherent Superiority Effective Disperser primary 2728 van Wilgen, Nicola J.; Richardson, David M. 2011 Is phylogenetic relatedness to native species important for the establishment of reptiles introduced to California and Florida? journal DIVERSITY AND DISTRIBUTIONS 17 1 172 181 Aim Charles Darwin posited that introduced species with close relatives were less likely to succeed because of fiercer competition resulting from their similarity to residents. There is much debate about the generality of this rule, and recent studies on plant and fish introductions have been inconclusive. Information on phylogenetic relatedness is potentially valuable for explaining invasion outcomes and could form part of screening protocols for minimizing future invasions. We provide the first test of this hypothesis for terrestrial vertebrates using two new molecular phylogenies for native and introduced reptiles for two regions with the best data on introduction histories. Location California and Florida, USA. Methods We performed an ordination of ecological traits to confirm that ecologically similar species are indeed closely related phylogenetically. We then inferred molecular phylogenies for introduced and native reptiles using sequence data for two nuclear and three mitochondrial genes. Using these phylogenies, we computed two distance metrics: the mean phylogenetic distance (MPD) between each introduced species and all native species in each region (which indicates the potential interactions between introduced species and all native species in the community) and the distance of each introduced species to its nearest native relative - NN (indicating the degree of similarity and associated likelihood of competition between each introduced species and its closest evolutionary analogue). These metrics were compared for introduced species that established and those that failed. Results We demonstrate that phylogenetically related species do share similar ecological functions. Furthermore, successfully introduced species are more distantly related to natives (for NN and MPD) than failed species, although variation is high. Main conclusions The evolutionary history of a region has value for explaining and predicting the outcome of human-driven introductions of reptiles. Phylogenetic metrics are thus useful inputs to multi-factor risk assessments, which are increasingly required for screening introduced species. Web of Science Many USA California;Florida Field - Observational terrestrial Invasion Hyp. Preadaptation to Climate herbivore;omnivore;predator 2729 Gomez-Gonzalez, Susana; Torres-Diaz, Cristian; Valencia, Graciela; Torres-Morales, Patricio; Cavieres, Lohengrin A.; Pausas, Juli G. 2011 Anthropogenic fires increase alien and native annual species in the Chilean coastal matorral journal DIVERSITY AND DISTRIBUTIONS 17 1 58 67 Aim We tested the hypothesis that anthropogenic fires favour the successful establishment of alien annual species to the detriment of natives in the Chilean coastal matorral. Location Valparaiso Region, central Chile Methods We sampled seed rain, seedbank emergence and establishment of species in four paired burned and unburned areas and compared (using GLMM) fire resistance and propagule arrival of alien and native species. To assess the relative importance of seed dispersal and seedbank survival in explaining plant establishment after fire, we compared seed rain and seedbank structure with post-fire vegetation using ordination analyses. Results Fire did not change the proportion of alien species in the coastal matorral. However, fire increased the number of annual species (natives and aliens) of which 87% were aliens. Fire reduced the alien seedbank and not the native seedbank, but alien species remained dominant in burned soil samples (66% of the total species richness). Seed rain was higher for alien annuals than for native annuals or perennials, thus contributing to their establishment after fire. Nevertheless, seed rain was less important than seedbank survival in explaining plant establishment in burned areas. Main conclusions Anthropogenic fires favoured alien and native annuals. Thus, fire did not increase the alien/native ratio but increased the richness of alien species. The successful establishment of alien annuals was attributable to their ability to maintain rich seedbanks in burned areas and to the greater propagule arrival compared to native species. The native seedbank also survived fire, indicating that the herbaceous community has become highly resilient after centuries of human disturbances. Our results demonstrate that fire is a relevant factor for the maintenance of alien-dominated grasslands in the matorral and highlight the importance of considering the interactive effect of seed rain and seedbank survival to understand plant invasion patterns in fire-prone ecosystems. Web of Science Many Chile Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Disturbance primary 2730 Jarnevich, Catherine S.; Reynolds, Lindsay V. 2011 Challenges of predicting the potential distribution of a slow-spreading invader: a habitat suitability map for an invasive riparian tree journal BIOLOGICAL INVASIONS 13 1 153 163 Understanding the potential spread of invasive species is essential for land managers to prevent their establishment and restore impacted habitat. Habitat suitability modeling provides a tool for researchers and managers to understand the potential extent of invasive species spread. Our goal was to use habitat suitability modeling to map potential habitat of the riparian plant invader, Russian olive (Elaeagnus angustifolia). Russian olive has invaded riparian habitat across North America and is continuing to expand its range. We compiled 11 disparate datasets for Russian olive presence locations (n = 1,051 points and 139 polygons) in the western US and used Maximum entropy (Maxent) modeling to develop two habitat suitability maps for Russian olive in the western United States: one with coarse-scale water data and one with fine-scale water data. Our models were able to accurately predict current suitable Russian olive habitat (Coarse model: training AUC = 0.938, test AUC = 0.907; Fine model: training AUC = 0.923, test AUC = 0.885). Distance to water was the most important predictor for Russian olive presence in our coarse-scale water model, but it was only the fifth most important variable in the fine-scale model, suggesting that when water bodies are considered on a fine scale, Russian olive does not necessarily rely on water. Our model predicted that Russian olive has suitable habitat further west from its current distribution, expanding into the west coast and central North America. Our methodology proves useful for identifying potential future areas of invasion. Model results may be influenced by locations of cultivated individuals and sampling bias. Further study is needed to examine the potential for Russian olive to invade beyond its current range. Habitat suitability modeling provides an essential tool for enhancing our understanding of invasive species spread. Web of Science Elaeagnus angustifolia United States Theoretical/Modeling terrestrial Riparian Fundamentals primary 2731 Souza, Lara; Bunn, Windy A.; Weltzin, Jake F.; Sanders, Nathan J. 2011 Similar biotic factors affect early establishment and abundance of an invasive plant species across spatial scales journal BIOLOGICAL INVASIONS 13 1 255 267 Research in community invasibiliy has focused on biotic and abiotic factors that influence the establishment of invasive species and whether such factors vary with spatial scale. Here, we investigate the role of both biotic and abiotic factors associated with the initial establishment of Lespedeza cuneata (L. cuneata) and its abundance at three spatial scales: neighborhoods (9-m(2) plots), communities (50-m(2) transect) and old fields (5,000-70,000 m(2)). We asked: (1) Do resource availability and community structure affect the establishment of L. cuneata?, and (2) Are resource availability and community structure associated with patterns of L. cuneata abundance from neighborhood scales to old-field scales? To investigate the first question, we manipulated soil nitrogen (N) availability at three levels in an existing old-field community and tracked emergence and persistence of L. cuneata seedlings, as well as total plant biomass of the community, availability of light, and soil moisture content. To address the second question, we performed surveys in which we estimated L. cuneata foliar cover at community scales (50-m(2) belt transects) and old-field scales (total area of 28 ha), and assessed the same biotic and abiotic variables as in the field experiment. The experiment revealed that establishment and persistence by L. cuneata seedlings were 15x and 5x lower in N-added plots than in N-reduced plots. Total plant community biomass was 30% greater in N-added plots than in N-reduced plots. Conversely, light and soil moisture were 60 and 20% lower in N-added plots than in N-reduced plots. Surveys of old fields indicated that community biomass was positively associated with L. cuneata cover at old-field scales likely resulting from greater soil N input from nitrogen fixation in fields with greater L. cuneata cover. In sum, these results indicate that biotic factors associated with establishment of a Rank 1 invasive plant species at the community scale are also related to its distribution at the old-field scale, but the direction of such associations changed across scales. Web of Science Lespedeza cuneata United States Field - Experimental;Field - Observational terrestrial Old Field Invasion Hyp. Empty Niche primary 2732 Helms, Ken R.; Hayden, Connor P.; Vinson, S. Bradleigh 2011 Plant-based food resources, trophic interactions among alien species, and the abundance of an invasive ant journal BIOLOGICAL INVASIONS 13 1 67 79 Recent research on invasive ants suggests that their success may be facilitated by increased resources at introduced locations stemming from the emergence of novel trophic interactions with abundant honeydew-producing Hemiptera. Moreover, those Hemiptera may themselves often be introduced or invasive. To test the importance of mutualisms for invasive species, we conducted a study in the southeastern United States of factors hypothesized to affect the abundance of an invasive ant native to South America, Solenopsis invicta. The study was conducted within grazing pastures, where S. invicta can be extremely abundant while also exhibiting substantial variability in abundance. A path analysis showed that the abundance of S. invicta was strongly and positively affected by the abundance of an invasive honeydew-producing mealybug native to Asia, Antonina graminis, and by the mealybugs' host grasses because of their strong positive effect on mealybug abundance. Abundance of the mealybug was primarily attributable to an invasive host grass native to Africa, Cynodon dactylon. The abundance of S. invicta was also positively affected by the abundance of other arthropods that they are likely to consume, and those arthropods were positively affected by the abundance of both the A. graminis host grasses and other plants. Thus the study shows that the distribution and abundance of different plant species could have important effects on the abundance of S. invicta through their effect on the ants' food resources. The results are also consistent with the hypothesis that the emergence of novel trophic interactions among invasive species can promote the abundance of invasive ants. Web of Science Solenopsis invicta United States Field - Observational terrestrial Invasion Hyp. Mutualism Facilitation omnivore 2733 Haider, Sylvia; Alexander, Jake; Dietz, Hansjoerg; Trepl, Ludwig; Edwards, Peter J.; Kueffer, Christoph 2010 The role of bioclimatic origin, residence time and habitat context in shaping non-native plant distributions along an altitudinal gradient journal BIOLOGICAL INVASIONS 12 12 4003 4018 An important factor influencing whether or not a non-native plant species becomes invasive is the climate in the area of introduction. To become naturalised in the new range, a species must either be climatically pre-adapted (climate matching), have a high phenotypic plasticity, or be able to adapt genetically, which in the latter case may take many generations. Furthermore, patterns of successful establishment across species might vary with habitat context. To address the interaction of these factors on non-native species richness, we recorded the presence of non-native annual plant species along an altitudinal gradient on Tenerife (Canary Islands, Spain). We compared the distributions of species differing in bioclimatic origin (Mediterranean and temperate) and time since introduction (old and recent introductions), and compared richness patterns of these groups in anthropogenic and natural habitats. Non-native species richness increased strongly from lowlands to midaltitudes, but dropped sharply at the transition from anthropogenic to natural habitats, and thereafter declined with altitude in the natural habitat. This pattern indicates that the altitude effects reflected changes in both climate and habitat context. Mediterranean and temperate species were distributed similarly along the altitudinal gradient, and we found no effect of bioclimatic origin on species distributions. As almost all species present at the highest sites also occurred in the lowlands, we conclude that most species were introduced to lowland sites and were therefore pre-adapted to those climatic conditions (lowland introduction filter). The altitudinal ranges of species tended to increase with time since introduction, and the species reaching the highest altitudes were mostly old introductions. This effect of time was more pronounced among Mediterranean than temperate species. Thus, while climatic pre-adaptation is important for establishment along this altitudinal gradient, species tend to extend their altitudinal range with time. Web of Science Many Spain Field - Observational terrestrial Invasion Hyp. Preadaptation to Climate primary 2734 Trueman, Mandy; Atkinson, Rachel; Guezou, Anne; Wurm, Penny 2010 Residence time and human-mediated propagule pressure at work in the alien flora of Galapagos journal BIOLOGICAL INVASIONS 12 12 3949 3960 Introduced species present the greatest threat to the unique terrestrial biodiversity of the Galapagos Islands. We assess the current status of plant invasion in Galapagos, predict the likelihood of future naturalizations and invasions from the existing introduced flora, and suggest measures to help limit future invasions. There has been a 1.46 fold increase in plant biodiversity in Galapagos due to alien plant naturalizations, reflecting a similar trend on islands elsewhere. There are 870 alien plant species recorded in the archipelago. Of evaluated species, 34% species have naturalized. Within this group are the invasive species (16% of evaluated) and the transformers (3.3% of evaluated). We show that, as expected, naturalized species have been present in the archipelago longer than non-naturalized species. We also find that a higher human-mediated propagule pressure is associated with a greater human population and with properties that have been settled longer. This, combined with the relatively recent introduction of most species, leads us to the conclusion that Galapagos is at an early stage of plant invasion. We predict that more species from the existing alien flora will find an opportunity to naturalize and invade as propagule pressure increases alongside rapid human population growth associated with immigration to serve the booming tourism industry. In order to reduce future invasion risk, we suggest reviewing inter-island quarantine measures and continuing community education efforts to reduce human-mediated propagule pressure. Web of Science Many Ecuador Galapagos Islands terrestrial Invasion Hyp. Propagule Pressure primary 2735 Fennell, Mark; Gallagher, Tommy; Osborne, Bruce 2010 Patterns of genetic variation in invasive populations of Gunnera tinctoria: an analysis at three spatial scales journal BIOLOGICAL INVASIONS 12 12 3973 3987 While there is evidence that the genetic structure of invasive populations may be distinct from native populations, it has proved difficult to establish the causes of any variation owing in part to the range of evolutionary processes involved. In order to assess differences in the genetic structure of invasive populations of Gunnera tinctoria, five native populations were compared to 23 geographically widely dispersed invasive populations using amplified fragment length polymorphic markers (AFLPs). In total, 221 individuals were sampled at three spatial scales: inter-regional, within-region, and at a high-resolution local scale. It was observed that there were high levels of genetic variation between most populations, that invasive populations were generally distinct from both native populations and from each other and that genetic variation away from founding populations can occur relatively quickly and within a small geographic area. Changes in the pattern of genetic variation observed in invasive populations strongly indicated that founder effects and genetic drift played a significant role in shaping their genetic structure. It was further concluded that gene flow had a homogenizing effect on the structure of invasive populations occurring in close proximity, increasing their allele content and potentially contributing to their successful establishment. Web of Science Gunnera tinctoria Chile; Portugal; Ireland; New Zealand The Azores Field - Observational terrestrial Invasion Hyp. Evolution in General primary 2736 Jakobs, Gabi; Kueffer, Christoph; Daehler, Curtis C. 2010 Introduced weed richness across altitudinal gradients in Hawai'i: humps, humans and water-energy dynamics journal BIOLOGICAL INVASIONS 12 12 4019 4031 Native species richness commonly declines with increasing altitude, but patterns of introduced species richness across altitudinal gradients have been less frequently studied. We surveyed introduced roadside weeds along altitudinal transects ranging from 30 to 4,100 min Hawai'i, with the objectives of (1) testing the hypothesis that a mass effect due to mixing of tropical and temperate species at mid-elevation promotes a hump-shaped pattern of introduced species richness with altitude, and (2) testing the potential roles of anthropogenic activity, energy (temperature) and water-energy dynamics (productivity-diversity hypothesis) in determining introduced weed richness. A total of 178 introduced weeds were recorded. Introduced weed richness does not decline monotonically with altitude. Rather, mixing of tropical and temperate species helps to maintain high mean richness up to 2,000 m, suggesting a mass effect, but without a distinct richness peak. Patchy occurrence of a transformer species, Pennisetum clandestinum, introduced high variance in richness at mid-elevations. General linear models considering estimated actual evapotranspiration (AET, a measure of energy-water dynamics) together with an index of human activity (distance from urban area or length of major roads) accounted for more variance in introduced weed richness than models with energy alone (temperature) and human activity. Native Hawaiian species richness along roadsides was also weakly correlated with AET but negatively associated with human activity. Our observed association between introduced species richness and AET mirrors patterns reported for native species richness around the world, indicating that AET-richness patterns can develop on a short time scale (on the order of 100 years). To test the generality of introduced weed richness patterns, we tried using the Hawai'i island model to predict weed richness on the neighboring island of Maui. Although weed richness on Maui was under-predicted, the same predictors (human activity and AET) were important on Maui. Scaling for differences in regional human population density or economic activity (both higher on Maui) may allow more accurate and transferable quantitative predictions of introduced weed richness patterns. Web of Science Many United States Hawaii Field - Observational terrestrial Invasion Hyp. Other primary 2737 Ansari, Shahin; Daehler, Curtis C. 2010 Life history variation in a temperate plant invader, Verbascum thapsus along a tropical elevational gradient in Hawaii journal BIOLOGICAL INVASIONS 12 12 4033 4047 Few studies have examined the life history of temperate plant invaders in the tropics. Temperate invaders that utilize seasonal cues to influence their life histories may be expected to behave differently in the tropics. This study examined variation in life history in an invading temperate weed, Verbascum thapsus, across an elevation gradient (1,690-2,720 m) along the montane and subalpine slopes of Mauna Kea, Hawaii. Over 7,000 seedlings were marked and monitored over a period of 3 years. Germination, survival, growth, and reproduction in V. thapsus varied among sites along the elevational gradient. Compared to plants at lower elevations, those at higher elevation sites (>2,000 m) had lower early seedling survival, higher established rosette survival, higher vegetative growth rates, higher threshold sizes for flowering, and commonly lived more than 3 years before flowering. The abundance of competing vegetation generally decreased with elevation, and this may drive variation in V. thapsus survival and growth. Size-dependent survival appears to play a major role in the selection for smaller size at first flowering and shorter generation time at lower elevations. This pattern is opposite to that reported in temperate mountains where high elevation plants flower sooner and at smaller size, but both patterns appear consistent with general life history theory for biennials. Due to novel biotic and climatic interactions in the tropics, predictions of growth patterns and invasion dynamics for temperate weeds in the tropics can be misleading when based on the plant's behavior in temperate systems. Web of Science Verbascum thapsus United States Hawaii Mauna Kea Field - Observational terrestrial Tropical Forest Invasion Hyp. Evolution in General primary 2738 Hartley, Maria K.; Rogers, William E.; Siemann, Evan 2010 Comparisons of arthropod assemblages on an invasive and native trees: abundance, diversity and damage journal ARTHROPOD-PLANT INTERACTIONS 4 4 237 245 The success of exotic plants may be due to lower herbivore loads than those on native plants (Enemies Release Hypothesis). Predictions of this hypothesis include lower herbivore abundances, diversity, and damage on introduced plant species compared to native ones. Greater density or diversity of predators and parasitoids on exotic versus native plants may also reduce regulation of exotic plants by herbivores. To test these predictions, we measured arthropod abundance, arthropod diversity, and foliar damage on invasive Chinese tallow tree (Triadica sebifera) and three native tree species: silver maple (Acer saccharinum), sycamore (Platanus occidentalis), and sweetgum (Liquidambar styraciflua). Arthropod samples were collected with canopy sweep nets from six 20 year old monoculture plots of each species at a southeast Texas site. A total of 2,700 individuals and 285 species of arthropods were caught. Overall, the species richness and abundance of arthropods on tallow tree were similar to the natives. But, ordination (NMS) showed community composition differed on tallow tree compared to all three native trees. It supported an arthropod community that had relatively lower herbivore abundance but relatively more predator species compared to the native species examined. Leaves were collected to determine damage. Tallow tree experienced less mining damage than native trees. The results of this study supported the Enemies Release Hypothesis predictions that tallow tree would have low herbivore loads which may contribute to its invasive success. Moreover, a shift in the arthropod community to fewer herbivores without a reduction in predators may further limit regulation of this exotic species by herbivores in its introduced range. Web of Science Triadica sebifera United States Texas Field - Observational terrestrial Deciduous Forest Invasion Hyp. Enemy Release primary 2739 Norf, Helge; Kniggendorf, Leif G.; Fischer, Albrecht; Arndt, Hartmut; Kureck, Armin 2010 Sexual and reproductive traits of Hypania invalida (Polychaeta, Ampharetidae): a remarkable invasive species in Central European waterways journal FRESHWATER BIOLOGY 55 12 2510 2520 1. The Ponto-Caspian polychaete Hypania invalida (Archiv fur Naturgeschichte, 1860, 26, 109) is undergoing rapid range expansion in the Rhine and other central European waterways. We examined its reproductive traits in an attempt to account for its remarkable invasive success. 2. For the first time in this species, we found males, dioecy (gonochorism) and an exclusively sexual mode of reproduction; no indication for hermaphroditism or (unisexual) parthenogenesis, that could explain the rapid range expansion of H. invalida, was found. 3. Our experimental evidence shows that H. invalida reproduces by males discharging their sperm into the water column while eggs are retained and fertilised in the female dwelling tubes. This mode of 'spermcast' reproduction is common in sessile benthic animals on wave-washed shores. 4. Fecundity of H. invalida ranged between 60 and 260 eggs per clutch and is increased by iteroparity (i.e. multiple cycles of oogenesis and egg-laying per specimen). Offspring are brooded for about 2 weeks before they leave the maternal dwelling tubes and disperse in the water column. 5. After connection to a supply of Rhine water, sediments in flumes were rapidly colonised up to a density of 12 000 ind. m(-2) via the settlement of small larvae (< 300 mu m) from the water column; these reached sexual maturity approximately 12 weeks after settlement. 6. The reproductive traits of H. invalida give the species a high rate of dispersal. The capacity of its larvae to survive passage through pumps before settlement enables them to travel in the ballast water of ships. This might explain the upstream expansion of H. invalida in rivers. We conclude that further range expansion, and especially intercontinental transport of this polychaete, can only be prevented by improved ballast water treatment. Web of Science Hypania invalida Lab lotic Invasion Hyp. Inherent Superiority High Reprod. Output omnivore 2741 Meimberg, Harald; Milan, Neil F.; Karatassiou, Maria; Espeland, Erin K.; McKay, John K.; Rice, Kevin J. 2010 Patterns of introduction and adaptation during the invasion of Aegilops triuncialis (Poaceae) into Californian serpentine soils journal MOLECULAR ECOLOGY 19 23 5308 5319 Multiple introductions can play a prominent role in explaining the success of biological invasions. One often cited mechanism is that multiple introductions of invasive species prevent genetic bottlenecks by parallel introductions of several distinct genotypes that, in turn, provide heritable variation necessary for local adaptation. Here, we show that the invasion of Aegilops triuncialis into California, USA, involved multiple introductions that may have facilitated invasion into serpentine habitats. Using microsatellite markers, we compared the polymorphism and genetic structure of populations of Ae. triuncialis invading serpentine soils in California to that of accessions from its native range. In a glasshouse study, we also compared phenotypic variation in phenological and fitness traits between invasive and native populations grown on loam soil and under serpentine edaphic conditions. Molecular analysis of invasive populations revealed that Californian populations cluster into three independent introductions (i.e. invasive lineages). Our glasshouse common garden experiment found that all Californian populations exhibited higher fitness under serpentine conditions. However, the three invasive lineages appear to represent independent pathways of adaptation to serpentine soil. Our results suggest that the rapid invasion of serpentine habitats in California may have been facilitated by the existence of colonizing Eurasian genotypes pre-adapted to serpentine soils. Web of Science Aegilops triuncialis United States California Field - Observational;Greenhouse terrestrial Chaparral/Shrublands Invasion Hyp. Preadaptation to Climate primary 2742 Kawamura, Kouichi; Yonekura, Ryuji; Ozaki, Yuiko; Katano, Osamu; Taniguchi, Yoshinori; Saitoh, Kenji 2010 The role of propagule pressure in the invasion success of bluegill sunfish, Lepomis macrochirus, in Japan journal MOLECULAR ECOLOGY 19 24 5371 5388 The bluegill sunfish, Lepomis macrochirus, is a widespread exotic species in Japan that is considered to have originated from 15 fish introduced from Guttenberg, Iowa, in 1960. Here, the genetic and phenotypic traits of Japanese populations were examined, together with 11 native populations of the USA using 10 microsatellite markers and six meristic traits. Phylogenetic analysis reconfirmed a single origin of Japanese populations, among which populations established in the 1960s were genetically close to Guttenberg population, keeping high genetic diversity comparable to the ancestral population. In contrast, genetic diversity of later-established populations significantly declined with genetic divergence from the ancestral population. Among the 1960s established populations, that from Lake Biwa showed a significant isolation-by-distance pattern with surrounding populations in which genetic bottlenecks increased with geographical distance from Lake Biwa. Although phenotypic divergence among populations was recognized in both neutral and adaptive traits, P(ST)-F(ST) comparisons showed that it is independent of neutral genetic divergence. Divergent selection was suggested in some populations from reservoirs with unstable habitats, while stabilizing selection was dominant. Accordingly, many Japanese populations of L. macrochirus appear to have derived from Lake Biwa population, expanding their distribution with population bottlenecks. Despite low propagule pressure, the invasion success of L. macrochirus is probably because of its drastic population growth in Lake Biwa shortly after its introduction, together with artificial transplantations. It not only enabled the avoidance of a loss in genetic diversity but also formed a major gene pool that supported local adaptation with high phenotypic plasticity. Web of Science Lepomis macrochirus Japan Field - Observational lentic Invasion Hyp. Propagule Pressure predator 2743 Nakano, Daisuke; Kobayashi, Takuya; Sakaguchi, Isamu 2010 Predation and depth effects on abundance and size distribution of an invasive bivalve, the golden mussel Limnoperna fortunei, in a dam reservoir journal LIMNOLOGY 11 3 259 266 We investigated the predation and depth effects on abundance and size distribution of an invasive freshwater bivalve, Limnoperna fortunei, post-larvae using screened (5-, 25-, and 50-mm mesh openings) and unscreened cages at three depths (6, 12, and 1 m above the bottom) in a dam reservoir, Lake Ohshio of Japan. The densities of L. fortunei on the unscreened cages were much lower than those of the 5-mm mesh screened cages at any depth. The predation rates estimated by dividing the density of the unscreened cage by that of the 5-mm mesh screened cage were 97.3% at 6 m depth, 96.6% at 12 m depth, and 95.8% at the bottom. Shell lengths of L. fortunei post-larvae were small on bottom cages, and their size distribution was significantly different from those at other depths. These results suggest that predation and depth affected the abundance and size distribution of L. fortunei in the lentic environment. The impact of L. fortunei invasion on the food web and the possibility of regulating their population by predation pressures are also discussed. Web of Science Limnoperna fortunei Japan Field - Experimental lentic Impacts;Fundamentals filter 2744 Yashiro, Toshihisa; Matsuura, Kenji; Guenard, Benoit; Terayama, Mamoru; Dunn, Robert R. 2010 On the evolution of the species complex Pachycondyla chinensis (Hymenoptera: Formicidae: Ponerinae), including the origin of its invasive form and description of a new species journal ZOOTAXA 0 2685 39 50 Ants are one of the most successful and widespread organisms in the world. Although ants of the genus Pachycondyla (Hymenoptera: Formicidae: Ponerinae) are predominantly tropical in distribution, Pachycondyla chinensis (Emery) is especially abundant in temperate zones in Asia. Recently, P. chinensis has also become an abundant invasive ant species in the United States. However, it was well-known that the Pachycondyla chinensis species complex remained unresolved. Our molecular and morphological results allow us to distinguish two species in the species complex: the species P. chinensis and the new cryptic species P. nakasujii sp. nov., and these two species are widely and sympatrically distributed and abundant in temperate forests in Japan. Moreover, phylogenetic analysis showed that P. chinensis has been introduced into the United States from Japan. In conclusion, our finding of the new species P. nakasujii suggests that much remains undiscovered even in biologically fascinating and well-studied organisms. Web of Science Pachycondyla chinensis; Pachycondyla nakasujii Japan; United States terrestrial Fundamentals predator 2745 Orrock, John L.; Baskett, Marissa L.; Holt, Robert D. 2010 Spatial interplay of plant competition and consumer foraging mediate plant coexistence and drive the invasion ratchet journal PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES 277 1698 3307 3315 Indirect effects may play an important role in structuring plant communities. Using a spatially explicit model of consumer foraging and plant competition, we demonstrate how the relationship between the spatial area over which plants compete and the spatial scale of consumer behaviour can determine the outcome of competition when one plant species provides a refuge for mobile consumers (i.e. refuge-mediated apparent competition). Once an initial population of the invader is established, complete invasion may be inevitable because of an ever-advancing invasion front ratchets forward driven by a feeding front of mobile consumers. Because the spatial extent of apparent competition determines the area available for colonization, consumers may also dictate the rate at which an invasion occurs. We find that, as long as refuge-mediated apparent competition is sufficiently localized, invasion is possible even in systems characterized by low overall levels of consumer pressure. Moreover, we show that a stable equilibrium can result in which both resident and invading plants coexist, suggesting that spatial heterogeneity created by refuge-mediated apparent competition may be important in mediating coexistence in plant communities. The spatial interplay of consumer behaviour and plant competition may be an under-appreciated mechanism affecting the composition, diversity and spatial pattern of plant communities. Web of Science Many Theoretical/Modeling terrestrial Invasion Hyp. Disturbance primary 2746 Meyer, Mary Hockenberry; Paul, Joe; Anderson, Neil O. 2010 Competive ability of invasive Miscanthus biotypes with aggressive switchgrass journal BIOLOGICAL INVASIONS 12 11 3809 3816 Miscanthus (Miscanthus sinensis Anderss. [Poaceae]) is an ornamental and invasive grass native to Asia that has naturalized in several areas of the Middle Atlantic United States. Predicting how likely miscanthus is to become invasive in other areas of the US is a concern of ecologists and horticulturists. The objective of this study was to measure the competitive ability of miscanthus with an aggressive native grass, switchgrass (Pancium virgatum L. [Poaceae]), in order to show which grass would be more likely to dominate when the two species were grown together. Although switchgrass is a smaller plant than miscanthus, in this greenhouse experiment it was significantly taller and had more vegetative and flowering culms than miscanthus. Miscanthus however, was a stable competitor and did not significantly change in shoot or root dry weight as 2 and 4 switchgrass plants replaced the respective number of miscanthus plants in each treatment. When miscanthus biotypes from four locations were compared, the Pennsylvania biotype was significantly larger and more competitive with switchgrass than was the Washington, DC biotype. As switchgrass plants were replaced with miscanthus, the shoot and root dry weights of the remaining switchgrass plants increased significantly, showing a higher competitive ability of switchgrass. Despite the fact that switchgrass was more competitive with itself than miscanthus, the highest overall dry weight per treatment contained eight switchgrass plants. Miscanthus showed stable, competitive growth when planted together with switchgrass and it is predicted to likely do the same in a field setting. Web of Science Miscanthus sinensis United States Greenhouse terrestrial Invasion Hyp. Inherent Superiority Superior Competitor primary 2747 Schoenfelder, Anna C.; Bishop, John G.; Martinson, Holly M.; Fagan, William F. 2010 RESOURCE USE EFFICIENCY AND COMMUNITY EFFECTS OF INVASIVE HYPOCHAERIS RADICATA (ASTERACEAE) DURING PRIMARY SUCCESSION journal AMERICAN JOURNAL OF BOTANY 97 11 1772 1779 Premise of the study: We sought to better understand the impacts and mechanisms underpinning a successful invasion of resource-poor sites by a nonnative plant on Mount St. Helens volcano (MSH). Methods: We investigated the short-term effects of the nonnative plant Hypochaeris radicata on growth of native species colonizing drought-prone primary successional surfaces under N-limited and N-augmented conditions. To understand the success of H. radicata, we compared its resource use efficiency to that of a closely related native colonist, Hieracium albiflorum, under the same conditions. Key results: Removing H. radicata did not affect growth of the most common colonists, but N addition demonstrated strong N limitation to growth in H. albiflorum, H. radicata, and Agrostis spp. Nonnative H. radicata exhibited lower water-use efficiency than H. albiflorum but did not differ in efficiency of N use. H. radicata biomass increased faster in response to an N pulse than did the native H. albiflorum, as did the pool of N held in H. radicata tissues. Conclusions: Our findings contrast with results from Hawaiian volcanic sites, where higher short-term resource use efficiency was reported for invasive species, including H. radicata. Our results suggest that at MSH, the success of H. radicata relies on rapid uptake and utilization of N rather than on higher efficiency. This strategy is especially advantageous at MSH because N pulses commonly occur as a consequence of herbivore-induced mortality of Lupinus lepidus (Fabaceae). Web of Science Hypochaeris radicata United States Field - Experimental terrestrial Mountain Invasion Hyp. Fluctuating Resources primary 2748 Chun, Young Jin; Kim, Chang-Gi; Moloney, Kirk A. 2010 Comparison of life history traits between invasive and native populations of purple loosestrife (Lythrum salicaria) using nonlinear mixed effects model journal AQUATIC BOTANY 93 4 221 226 We compared growth patterns of invasive and native populations of purple loosestrife (Lythrum salicaria) while varying water and nutrient levels. We examined three life-history traits (height, number of branches, and the size of largest leaf) during the growth period adopting a nonlinear mixed effects model. Invasive populations were found to be slower in shoot elongation but grew to be taller than native populations. Invasive populations produced more branches than natives only in the high water, high nutrient treatment. Invasive populations had a similar increase in the size of the largest leaf compared to natives, but ultimately produced a greater size of largest leaf than natives. Invasive populations were found to display a greater vegetative expansion, but this was not strongly affected by our treatments. (C) 2010 Elsevier B.V. All rights reserved. Web of Science Lythrum salicaria Germany; United States Garden wetland Invasion Hyp. Plasticity primary 2749 Hussner, Andreas 2010 Growth response and root system development of the invasive Ludwigia grandiflora and Ludwigia peploides to nutrient availability and water level journal FUNDAMENTAL AND APPLIED LIMNOLOGY 177 3 189 196 Ludwigia grandiflora and Ludwigia peploides, both native to South America, are aquatic plants, which favourably grow in stagnant or slow flowing waters. Due to their rapid growth both species are considered two of the most important aquatic weeds worldwide. The species have invaded several countries in SW Europe and often cause problems, e. g. in France, The Netherlands or Belgium. In the present study, growth and root system development of L. grandiflora and L. peploides was investigated under three different hydro regimes and three different substrates with different nutrient contents. Both species showed their strong abilities to grow on drained soils by an increase of the relative amount of root biomass and changes in the root system development. Relative growth rates (RGR) of L. grandiflora and L. peploides did not differ between the species, but were significantly different amongst the treatments for each species, i.e., RGR were significantly influenced by nutrients (both p < 0.001) and water level (L. grandiflora n.s., L. peploides p < 0.001). L. grandiflora and L. peploides showed a significant increase in the relative amount of roots with decreasing water level (both p < 0.001) and nutrients (both p < 0.001), when the relative amount of shoots decreased significantly (both: water level p < 0.001 and nutrients p < 0.001). In addition, both species responded to water level and nutrients with significant changes in the depth distribution of their root system. In conclusion, L. grandiflora and L. peploides showed a high tolerance to different water levels, which may be important for potential habitat distribution in the future. Web of Science Ludwigia grandiflora; Ludwigia peploides Germany Europe Greenhouse lentic Invasion Hyp. Inherent Superiority Broad Tolerances primary 2750 Colautti, Robert I.; Barrett, Spencer C. H. 2010 NATURAL SELECTION AND GENETIC CONSTRAINTS ON FLOWERING PHENOLOGY IN AN INVASIVE PLANT journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 171 9 960 971 Theory suggests that the contemporary evolution of local adaptation may increase the rate of biological invasion, yet natural selection has rarely been measured in invasive species. A recently published model predicted that latitudinal variation in the strength of stabilizing selection on two correlated traits-flowering time and size-can result in local adaptation during plant invasion but implicitly assumed that population 3 environment interactions are weak. We tested for stabilizing selection and the effect of growing environment on 13 populations of the invasive plant Lythrum salicaria sampled along a latitudinal gradient. Plants were grown under uniform glasshouse conditions and in a 3-year common garden field experiment at midlatitude. Consistent with model assumptions, the ranking of population means was highly correlated across the 3 years, and with glasshouse measurements, despite significant interannual differences in flowering time and vegetative size. As predicted, the first principal component (PC1) of flowering time and size was under stabilizing selection, and directional selection was detected on PC2, thus favoring plants that flowered earlier at a larger size. Our results demonstrate the value of using a priori models of natural selection to guide hypothesis testing and support the prediction that fitness trade-offs can constrain adaptive evolution in invasive species. Web of Science Lythrum salicaria United States; Canada Greenhouse;Garden terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 2751 Gilg, Matthew R.; Hoffman, Eric A.; Schneider, Kimberly R.; Ryabinov, Josiah; El-Khoury, Christine; Walters, Linda J. 2010 Recruitment preferences of non-native mussels: interaction between marine invasions and land-use changes journal JOURNAL OF MOLLUSCAN STUDIES 76 0 333 339 Preferential patterns of settlement of marine invertebrate larvae may significantly affect the expansion of introduced populations when coupled with anthropogenic changes to available substrates in marine environments. In the near-shore marine environments of the southeastern USA the addition of hard substrates into primarily salt marsh habitats may provide necessary settlement sites for recently introduced marine invertebrates such as the Asian green mussel, Perna viridis, and the South American charru mussel, Mytella charruana. Preliminary studies in Florida suggest that M. charruana adults are predominantly found on man-made substrates, especially docks. The present study investigated whether P. viridis and M. charruana preferentially settle on substrates commonly used in man-made structures such as plexiglass, wood and rock, or on natural substrates like the shells of oyster (Crassostrea virginica), green mussels or charru mussels. Frames containing a mixture of these six substrates were deployed at two locations in Florida and retrieved after 1, 2 and 3 months. Over 1-month deployments, both species preferentially recruited to natural substrates. While this pattern was repeated on substrates in the field for 2 months in M. charruana, there were no differences in P. viridis spat density among any of the substrates in the field for 2 or 3 months. These results suggest that man-made hard substrates will likely not affect expansion of these two species by providing preferred settlement sites. Man-made substrates may still, however, provide better locations for survival. Web of Science Perna viridia; Mytella charruana United States Florida Field - Experimental marine Invasion Hyp. Other filter 2752 McCormick, Melissa K.; Kettenring, Karin M.; Baron, Heather M.; Whigham, Dennis F. 2010 Spread of invasive Phragmites australis in estuaries with differing degrees of development: genetic patterns, Allee effects and interpretation journal JOURNAL OF ECOLOGY 98 6 1369 1378 1. The distribution of genetic variation can be interpreted to understand the timing and mechanisms of invasive species spread. Allee effects, positive relationships between fitness and density or number of conspecific individuals, can play a substantial role in determining the time lag between initial introduction and invasive spread and can produce genetic patterns in invading populations that can be interpreted to learn about factors affecting invasion mechanisms. 2. We examined the distribution of genetic variation in the invasive wetland grass Phragmites australis in the Chesapeake Bay, USA. We used microsatellite analysis to examine the reproductive mode (clonal vs. seed) by which the invasive haplotype of P. australis has spread and the distribution of genetic variation within and among brackish wetlands in nine subestuaries of the Chesapeake Bay. Watersheds associated with the subestuaries were dominated by forests, anthropogenic development or mixed forests and development. 3. Our results suggest that the invasive haplotype of P. australis has spread primarily sexually by seed, rather than clonally, and genetic diversity of patches within subestuaries increased while genetic similarity decreased with increasing development in the surrounding watershed. 4. This suggests a pattern whereby greater genetic diversity of patches may promote more rapid spread due to recruitment of multiple seedlings into a disturbed patch. 5. Synthesis. Evaluation of patterns of genetic distribution can help to identify factors affecting invasion in different environments and so inform management. Web of Science Phragmites australis United States Field - Observational;Lab wetland Invasion Hyp. Inherent Superiority Clonal Reproduction primary 2753 Shaltout, Kamal H.; Al-Sodany, Yassin M.; Eid, Ebrahem M. 2010 Growth behaviour of the invasive species Ipomoea carnea in the Nile Delta, Egypt journal HYDROBIOLOGIA 656 1 187 197 Ipomoea carnea Jacq., a native shrub of South America, grows in dense populations along river beds, river banks, canals and other waterlogged (wetland) areas. It has become naturalised along canals, drains, road sides and field edges in the Nile Delta, Egypt. The rapid growth rate, spread and adaptability from xeric to aquatic habitats indicates that this plant may potentially become a disastrous invasive species in Egyptian water bodies. Fifty established stands covering seven habitats (railway sides, waste lands, road sides, drain and canal banks, road dividers and field edges) in the Nile Delta were used in this experiment. In each stand, 20 ramets were permanently marked to estimate the monthly variations in such growth variables as phenology, height and diameter of the ramet canopy, number of flowers, leaves and fruits. The results showed a significant variation in growth variables relative to habitat types. Generally, I. carnea populations along the railway sides and field edges had the lowest values for most variables; while those of the road dividers, road sides and canal banks produced the highest values. The growth of I. carnea follows a seasonal pattern where the highest values for most growth variables were obtained during September and October and the lowest were recorded during June and July. The greatest flower and fruit production was observed between September and December. Similarly, it was shown that the flowering time varied in relation to habitat types; it began earlier on road sides and canal banks, but later on railway sides, road dividers and waste lands. Leaf areas of I. carnea populations in the wet habitats (e.g. drain and canal banks) were higher than those in other habitats. These results are discussed in relation to other related studies. Web of Science Ipomoea carnea Egypt Field - Observational wetland Wetland Invasion Hyp. Plasticity primary 2754 Kuhar, Urka; Germ, Mateja; Gaberscik, Alenka 2010 Habitat characteristics of an alien species Elodea canadensis in Slovenian watercourses journal HYDROBIOLOGIA 656 1 205 212 The distribution, abundance and habitat characteristics of an alien species, Elodea canadensis, were surveyed in watercourses in Slovenia. The accompanying plant community was also examined. Distribution and abundance of macrophytes were assessed in reaches of different length, and habitat assessment is based on 12 parameters of the Riparian, Channel, and Environmental (RCE) Inventory. E. canadensis thrived in 132 out of 1,227 reaches examined and in 12 of the 39 watercourses surveyed. It grew in the company of a variety of species, most frequently with different species of Potamogeton. It was rarely found as the prevailing, and never as the only species in any reach. Canonical correspondence analysis (CCA) of reaches with E. canadensis revealed that the presence of detritus, retention structures and properties of the riparian zone explained most of the variance in community composition. Habitat analysis of well-established stands of E. canadensis showed that its preferred habitats were watercourses flowing through agricultural landscape, with a narrow, more or less disturbed riparian zone, with moderate presence of retention structures, and with sediment that was a mixture of gravel, sand and silt with either coarse or fine organic matter. It was not found in the parts of streams with the most dynamic flow, and was absent from watercourses in the karst region, due to the frequent and extreme water level fluctuations. The alien species E. canadensis did not express its invasive character in heterogeneous watercourses with rich macrophyte communities. Web of Science Elodea canadensis Slovenia Field - Observational lotic Invasion Hyp. Fluctuating Resources primary 2755 Hofstra, D.; Champion, P.; Clayton, J. 2010 Predicting invasive success of Hydrilla verticillata (L.f.) Royle in flowing water journal HYDROBIOLOGIA 656 1 213 219 Alien aquatic plant species have had spectacular success in invading New Zealand's freshwaters. Their continued introduction has resulted in few water bodies retaining their natural or original indigenous aquatic vegetation, and associated adverse changes, such as reduced biodiversity and amenity values are well known. This highlights the need to accurately assess aquatic plant species that are already in the country and those outside for their potential to have a negative impact on New Zealand's lakes and waterways. The study presented in this paper describes an approach to evaluating the invasive weed potential of Hydrilla verticillata (L.f.) Royle compared with Elodea canadensis Michx. under flowing water conditions. The two species were planted in combination and alone, and in a sheltered or exposed position relative to the direction of the water flow. Over the 2-year study, two different waterflow rates were used (0.1 and 0.2 m/s) which represented the gauged flows from a stream of interest that contains E. canadensis and flows from a H. verticillata infested lake. H. verticillata was competitive compared with E. canadensis and able to persist and thrive in the presence of E. canadensis in both exposed and sheltered habitats. These results corroborate observations from other countries of H. verticillata growing in flowing waters and highlight the significant threat posed by H. verticillata to streams and waterways in New Zealand. Web of Science Hydrilla verticillata New Zealand Garden lotic Invasion Hyp. Inherent Superiority Superior Competitor primary 2757 Czarnecka, Magdalena; Kobak, Jaroslaw; Wisniewski, Ryszard 2010 Preferences of juveniles and adults of the invasive Ponto-Caspian amphipod Pontogammarus robustoides for various species of macrophytes and artificial substrata journal HYDROBIOLOGIA 655 1 79 88 We studied preferences of invasive Ponto-Caspian amphipod P. robustoides for various macrophyte species (Myriophyllum spicatum, Ceratophyllum demersum, Potamogeton perfoliatus, Elodea canadensis) and artificial plant-like objects (artificial Christmas tree branches) in laboratory pairwise-choice tests. Juvenile (< 7 mm) and adult gammarids exhibited different habitat preferences. Adults did not discriminate between artificial and natural substrata, or among most of the tested species of plants. In contrast, juveniles clearly preferred all tested macrophytes over artificial substrata. Moreover, they particularly preferred plants with the finest leaf elements: M. spicatum and C. demersum over the others and E. canadensis over P. perfoliatus. We found no influence of chironomid larvae, a potential food source for adult gammarids, on their distribution, nor any effect of adults on the habitat choice by juveniles. The habitat partitioning between juvenile and adult P. robustoides may help them survive in a new environment and increase their invasive potential by reducing the intraspecific competition and cannibalism. Web of Science Pontogammarus robustoides Poland Lab marine;lentic;lotic;estuarine Invasion Hyp. Plasticity predator 2758 Vermonden, Kim; Leuven, Rob S. E. W.; van der Velde, Gerard 2010 Environmental factors determining invasibility of urban waters for exotic macroinvertebrates journal DIVERSITY AND DISTRIBUTIONS 16 6 1009 1021 Aim Urbanization usually leads to biotic homogenization with a decrease in native species and increase in exotic species. We investigated whether local environmental factors in urban water bodies, such as water quality, habitat structure and biotic interactions, influenced the invasion of these systems by exotic macroinvertebrate species. Location Urban surface water systems in lowlands of the Rhine-Meuse delta. Methods Presence and abundance of native and exotic macroinvertebrate species were compared between different urban water types and related to environmental variables with multivariate analysis and spearman's correlations. Moreover, co-existence of related native and exotic species was studied. Results In total nine exotic species were found in the following taxa: Tricladida (1), Crustacea (5), Bivalvia (1) and Gastropoda (2). Taxonomically related native and exotic crustacean species did not seem to be influenced by competition in nutrient-rich urban waters; most species showed high abundances. Nevertheless, two exotic crustacean species were much more abundant in waters where other crustacean species were absent, possibly filling empty niches. Native species richness and abundance was positively related to environmental heterogeneity in the form of submerged vegetation. The occurrence and abundance of most exotic species were positively related to several eutrophication indicators, such as nitrate, sludge layer and lemnid vegetation. Main conclusions Exotic species in urban waters were mostly detritivorous or omnivorous and therefore dependent on leaf breakdown. In nutrient-rich water systems, where food availability was high, exotic crustacean species co-existed with native crustacean species, while in nutrient-poor, richly vegetated systems, native Asellidae dominated exotic Asellidae. In the turbid water bodies with very little vegetation, native species richness was low and two exotic crustacean species were relatively abundant in these water systems. Invasibility of urban water systems could be reduced by stimulating the development of submerged and nymphaeid vegetation and decreasing nutrient levels. Web of Science Many The Netherlands Field - Observational lentic;lotic Urban Invasion Hyp. Empty Niche 2759 Guo, Qinfeng; Ricklefs, Robert E. 2010 Domestic exotics and the perception of invasibility journal DIVERSITY AND DISTRIBUTIONS 16 6 1034 1039 Susceptibility of an area to invasion by exotic species is often judged by the fraction of introduced species in the local biota. However, the degree of invasion, particularly in mainland areas, has often been underestimated because of the exclusion of 'domestic exotics' (those introduced to internal units from within the national border) in calculations. Because all introduced species on islands are considered as exotics, this contributes to the perception that islands are more susceptible to invasion than are continental regions. Here, we determine the contribution of domestic exotic species to the degree of invasion (exotic fraction) in mainland areas. We quantify the relationships of exotic fraction to the area, human population density and land use within each of the 48 conterminous US states to identify mechanisms that potentially influence the degree of invasion. For each of the 48 conterminous US states, we compiled the number of species introduced from outside the United States ('foreign exotics') and the number of exotics introduced from other conterminous US states ('domestic exotics'). The status of each species as foreign or domestic was determined for each state by researching its precise origins through vouchered herbarium records, supplemented by literature (Kartesz, 2010). We found that (1) the exotic fraction inevitably decreases with increasing area as the pool of potential exotic species decreases; (2) exotic richness of areas within large mainland regions is underestimated to the extent that species introduced among areas within a region are considered as natives; and (3) human activities contribute disproportionately more exotics to smaller than to larger administrative areas. How we define 'exotic' influences how we count non-native species and perceive invasibility. Excluding domestic exotics in mainland regions leads to a biased perception of increased invasibility on islands, where all introduced species are considered exotic. Thus, future documentation and interpretation of invasion patterns and management of exotics should account for these biases in quantifying the exotic fraction. Web of Science Many United States Statistical/Meta-analysis Invasion Hyp. Other primary 2760 Essl, Franz; Moser, Dietmar; Dullinger, Stefan; Mang, Thomas; Hulme, Philip E. 2010 Selection for commercial forestry determines global patterns of alien conifer invasions journal DIVERSITY AND DISTRIBUTIONS 16 6 911 921 Question Are the patterns of alien conifer (Pinaceae, Cupressaceae) invasions different between continents, and how is invasion success influenced by commercial forestry practices? Location Temperate and subtropical countries and regions (n = 60) from five continents spanning both hemispheres. Methods We used generalized linear mixed models to test how continent identity, region area and use in commercial forestry affect probabilities of Pinaceae and Cupressaceae species to escape following introduction and cumulative logit regression models to assess how these predictors affect the likelihood that a species becomes naturalized or invasive. Results Sixty Pinaceae of a global total of 232 and 26 Cupressaceae of a total of 142 species have escaped from cultivation across the study regions examined. Average numbers of both alien Pinaceae and Cupressaceae species per region were highest in Oceania, followed by Africa. Moreover, the probability of alien Cupressaceae and Pinaceae becoming naturalized or invasive was particularly high in these two continents. For both families, species used in commercial forestry have a significantly higher probability of escape than those which are only introduced for ornamental or other purposes. In the case of Pinaceae, forestry species also become naturalized or invasive more frequently than non-forestry species, while no such effect was detectable for Cupressaceae. Conclusions We found that non-native conifers are more likely to escape from cultivation, naturalize and turn into invasive weeds on the continents of the Southern Hemisphere. In addition to this biogeographic signal, introduction effort strongly determines the behaviour of introduced Pinaceae, and less so, Cupressaceae. A clear conflict exists between the economic benefits of conifer forestry and the risks to the environment from invasions. Future expansion of commercial forestry should address spatial planning to ecosystems vulnerable to invasion and adopt comprehensive risk assessment procedures. Web of Science Many Statistical/Meta-analysis terrestrial Invasion Hyp. Other primary 2762 Ni, Guang-Yan; Schaffner, Urs; Peng, Shao-Lin; Callaway, Ragan M. 2010 Acroptilon repens, an Asian invader, has stronger competitive effects on species from America than species from its native range journal BIOLOGICAL INVASIONS 12 11 3653 3663 The ability to competitively suppress native species is key to successful invasion. Since invasions involve an increase in abundance or dominance of a species in its non-native range, competitive effects might be expected to be stronger in the non-native range of an invader; however, there have been few comparisons of the competitive effects of invasive plants on species from invaded ranges versus species from native ranges. We compared the competitive and allelopathic effects of Acroptilon repens on native North American species to effects on related species from the native range of Acroptilon in Uzbekistan. We also compared the competitive interactions among these North American and Eurasian species, in the absence of Acroptilon, examining the hypothesis that particular regional species pools may show differences in competitive ability. The results showed that Acroptilon had stronger competitive effects against native North American species than against species native to Uzbekistan. There was no difference in the competitive effects among Eurasians and North Americans. The effects of leachates collected from Acroptilon roots were weak but more negative on species from North America than on species from Uzbekistan. Our results suggest that inherently stronger competitive and allelopathic effects of Acroptilon on North American plants than on plants from its native range may contribute to its invasive success. Web of Science Acroptilon repens United States Field - Observational terrestrial Grassland Invasion Hyp. Inherent Superiority;Novel Weapons Superior Competitor primary 2765 West, Natalie M.; Gibson, David J.; Minchin, Peter R. 2010 Microhabitat analysis of the invasive exotic liana Lonicera japonica Thunb. journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 137 4 380 390 WEST, N. M., D. J. GIBSON (Department of Plant Biology, Center for Ecology, Southern Illinois University-Carbondale, Carbondale, Illinois 62901-6509) AND P.R. MINCHIN (Department of Biological Sciences, Southern Illinois University Edwardsville, Edwardsville, Illinois 62026). Microhabitat analysis of the invasive exotic liana Lonicera japonica Thunb. J.Torrey Bot. Soc. 137: 380-390. 2010.-We documented microhabitat occurrence and growth of Lonicera japonica to identify factors related to its invasion into a southern Illinois shale barren. The barren was surveyed for L. japonica in June 2003, and the microhabitats of established L. japonica plants were compared to random points that sampled the range of available microhabitats in the barren. Vine and leaf characters were used as measurements of plant growth. Lonicera japonica occurred preferentially in areas of high litter cover and species richness, comparatively small trees, low PAR, low soil moisture and temperature, steep slopes, and shallow soils. Plant growth varied among these microhabitats. Among plots where L. japonica occurred, growth was related to soil and light conditions, and aspects of surrounding cover. Overhead canopy cover was a common variable associated with nearly all measured growth traits. Plasticity of traits to improve invader success can only affect the likelihood of invasion once constraints to establishment and persistence have been surmounted. Therefore, understanding where L. japonica invasion occurs, and microhabitat interactions with plant growth are important for estimating invasion success. Web of Science Lonicera japonica United States Illinois Field - Observational terrestrial Invasion Hyp. Plasticity primary 2766 Meirmans, Patrick G.; Lamothe, Manuel; Gros-Louis, Marie-Claude; Khasa, Damase; Perinet, Pierre; Bousquet, Jean; Isabel, Nathalie 2010 COMPLEX PATTERNS OF HYBRIDIZATION BETWEEN EXOTIC AND NATIVE NORTH AMERICAN POPLAR SPECIES journal AMERICAN JOURNAL OF BOTANY 97 10 1688 1697 Premise of the study: Poplars and their hybrids are seen as important candidates for bioenergy initiatives. However, many concerns have been raised about large-scale plantations of new poplar cultivars. The deployment of such plants with novel traits brings the risk of potential spread of novel genome regions (including exotic genes, transgenes, or other heritable modifications) into natural populations of related species. The possibility of introgression is especially high in poplars because reproductive barriers between species are weak. Knowledge of the frequency of hybridization between cultivated trees and natural populations is one important step in the risk-assessment process. Methods: We studied the rate of spontaneous hybridization from two sexually mature poplar plantations into adjacent natural populations of Populus deltoides and P. balsamifera. The two plantations, both in eastern Canada, contain many different complex hybrid clones with components from exotic species, mostly P. nigra, P. trichocarpa, and P. maximowiczii. We analyzed 12 species-specific single nucleotide polymorphisms from six different genes in 5373 offspring sampled from the natural populations. Results: Contributions from all three exotics were found in the offspring, confirming low reproductive barriers among poplar species in these sections. The frequency of hybrid offspring varied among pollen donors, recipient populations, and years. Conclusions: The remarkably high rate of hybridization that was found in the smallest natural population sampled suggests that small peripheral populations carry a higher risk of introgression. These results could be used as a starting point for developing regulatory guidelines for the introduction of plants with novel traits. Web of Science Many Canada Field - Observational terrestrial Deciduous Forest Invasion Hyp. Hybridization primary 2767 Hardiman, Nicole A.; Culley, Theresa M. 2010 REPRODUCTIVE SUCCESS OF CULTIVATED PYRUS CALLERYANA (ROSACEAE) AND ESTABLISHMENT ABILITY OF INVASIVE, HYBRID PROGENY journal AMERICAN JOURNAL OF BOTANY 97 10 1698 1706 Premise of the study : Pyrus calleryana Decne., an ornamental tree species introduced from China, is a relatively new invasive that has only recently begun to spread across the United States after intraspecific hybridization between cultivars. The function of such hybridization in the evolution of invasiveness is still relatively understudied, especially with respect to the initial establishment and persistence of invasive genotypes. Multiple introductions of genetically divergent populations or cultivars may benefit from new genetic combinations created during hybridization events and/or release from Allee effects in founder populations. Methods : We quantified the outcome of intraspecific hybridization between cultivars of P. calleryana in a common garden. Measures of the reproductive success and establishment ability of their early-and advanced-generation hybrid offspring were collected to assess the likelihood of particular cultivar genotypes to establish in invasive populations. These traits also were compared between cultivated and invasive parents to identify any generational differences in invasive potential. Key results : Differences were detected in measures of reproductive ability, but no group emerged as consistently more fecund. Advanced-generation hybrids also had significantly less biomass, indicating a reduction in hybrid performance relative to that of the cultivated progeny. Conclusion : Ultimately, this study indicates that increased spread of P. calleryana has been initiated by introduction of multiple cultivar types and subsequent widespread planting and is not the result of an inherent fitness advantage of hybrid progeny. Web of Science Pyrus calleryana China Garden terrestrial Deciduous Forest Invasion Hyp. Hybridization primary 2768 Phillips, Megan L.; Murray, Brad R.; Pysek, Petr; Pergl, Jan; Jarosik, Vojtech; Chytry, Milan; Kuehn, Ingolf 2010 Plant species of the Central European flora as aliens in Australia journal PRESLIA 82 4 465 482 The Central European flora is an important source pool of plant species introduced to many regions throughout the world. In this study, we identified a total of 759 plant species of the Central European flora that are currently recognized as alien species in Australia. We explored temporal patterns of introduction of these species to Australia in relation to method of introduction, growth form, naturalization status and taxonomy. Across all species, substantially larger numbers of species were introduced between 1840 and 1880 as well as between 1980 and the present, with a small peak of introductions within the 1930s. These patterns reflect early immigration patterns to Australia, recent improvements in fast and efficient transportation around the globe, and emigration away from difficult conditions brought about by the lead up to the Second World War respectively. We found that the majority of species had deliberate (69%) rather than accidental (31%) introductions and most species have not naturalized (66% casual species, 34% naturalized species). A total of 86 plant families comprising 31 tree species, 91 shrub species, 533 herbaceous species and 61 grass species present in Central Europe have been introduced to Australia. Differential patterns of temporal introduction of species were found as a function of both plant family and growth form and these patterns appear linked to variation in human migration numbers to Australia. Web of Science Many Australia Statistical/Meta-analysis terrestrial Invasion Hyp. Other primary 2769 Harvey, Jeffrey A.; Bukovinszky, Tibor; van der Putten, Wim H. 2010 Interactions between invasive plants and insect herbivores: A plea for a multitrophic perspective journal BIOLOGICAL CONSERVATION 143 10 2251 2259 Invasive species represent one of the most important threats to biodiversity worldwide, with consequences for ecosystem functioning and the delivery of important ecological services to society. Several hypotheses have been generated to explain the success of exotic plants in their new ranges, with escape from their old natural enemies, such as pathogens and herbivores (the 'enemy release hypothesis') and novel defensive chemistry (the 'novel weapons hypothesis') receiving considerable attention. Thus far, virtually all studies of exotic plants and insects have been conducted in a strictly bi-trophic framework involving plants and herbivores. On the other hand, it has been argued that a better understanding of the forces regulating community structure and function should include natural enemies of the herbivores. Furthermore, indirect interactions between organisms in the plant roots (below-ground) and shoots (above-ground) are known to strongly effect the behaviour and performance of consumers in the opposite 'compartment'. Here, we discuss a range of physiological, evolutionary and ecological aspects of plant-herbivore-natural enemy interactions involving exotic plants. Further, interactions between soil and above-ground organisms are explored with respect to studies with exotic plants. We argue that it is important to link population and community ecology to individual-level variation in the physiology and behaviour of insects across several trophic levels in studies with invasive plants. Future research with invaders should also aim to integrate physically separated compartments (e.g, plant roots and shoots). This will facilitate a more complete understanding of the factors underlying the success (or failure) of exotic plants to spread and become dominant in their new ranges. Moreover, these data will also help to unravel the relative importance of top-down and bottom-up processes in regulating communities in which exotic plants have become established. Lastly, we discuss consequences for conservation. (C) 2010 Elsevier Ltd. All rights reserved. Web of Science Many Theoretical/Modeling terrestrial Invasion Hyp. Mutualism Facilitation primary 2770 Cavallero, Laura; Raffaele, Estela 2010 Fire enhances the 'competition-free' space of an invader shrub: Rosa rubiginosa in northwestern Patagonia journal BIOLOGICAL INVASIONS 12 10 3395 3404 Fire can influence reproductive phenology of plants, enhancing the reproductive rate of many species. Disturbances such as fire can promote the proliferation of exotic species in native plant communities. In this study we analyze the effect of fire on reproductive phenology in three native species (a shrub: Berberis buxifolia and two small trees: Maytenus boaria and Schinus patagonicus) and in an exotic shrub (Rosa rubiginosa). Flowering and fruiting phenology was monitored in neighbouring burned and unburned forests. The shrubs flowered and fruited in both sites, but the small trees did so only in the unburned site. There is no overlapping in the flowering and fruiting phenophases between the natives and the exotic species. Therefore, they do not compete in resource offering to pollinators and seed dispersers. Consequently, R. rubiginosa has a 'competition-free' space enhanced by fire, from the reproductive phenology perspective. Web of Science Rosa rubiginosa Argentina Patagonia Nahuel Huapi National Park Field - Observational terrestrial Coniferous Forest Invasion Hyp. Disturbance primary 2771 De Barro, Paul J.; Liu, Shu-Sheng; Bourne, Anne 2010 Age-based differential host acceptability and human mediated disturbance prevent establishment of an invasive species and displacement of a native competitor journal BIOLOGICAL INVASIONS 12 10 3429 3438 Establishment failure by immigrant species, while believed to be a common occurrence, is difficult to observe and so factors contributing to failure are poorly explored. Human mediated disturbance is a key element in facilitating biological invasions, but its role in preventing establishment is rarely considered. In Australia, the whitefly, Bemisia tabaci biotype B was first detected in 1994 and has since spread widely and displaced an indigenous competitor. However, in one location it has failed to establish permitting an indigenous competitor to persist. In this area, the dominant plant host is Euphorbia cyathophora. Through a combination of laboratory and field experimentation we show that while both can utilise the young, upper leaves only the indigenous competitor can use the older lower leaves. We then demonstrate that the removal of the upper leaves as part of foreshore vegetation management is the key factor in preventing the establishment of the invader and subsequent displacement of its competitor. While human mediated disturbance coupled with complex biological interactions may promote invasion they may equally well retard rather than facilitate invasion, a factor that appears to have been largely ignored. Complexities of this kind must be conceived in our thinking to achieve a comprehensive understanding of biological invasion. Web of Science Bemisia tabaci Australia Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Disturbance herbivore 2772 Barto, E. Kathryn; Powell, Jeff R.; Cipollini, Don 2010 How novel are the chemical weapons of garlic mustard in North American forest understories? journal BIOLOGICAL INVASIONS 12 10 3465 3471 The Novel Weapons Hypothesis predicts that invasive plants excel in their new ranges because they produce novel metabolites to which native species possess little resistance. We examined the novelty of the phytochemistry of the Eurasian invader, Alliaria petiolata, in North America by comparing its phytochemical profile with those of closely related Brassicaceae native to North America. We examined the profile and/or concentrations of glucosinolates, alliarinoside, flavonoids, cyanide, and trypsin inhibitors in cauline leaves of field-collected A. petiolata, Arabis laevigata, Cardamine concatenata, C. bulbosa, and C. douglassii. Cyanide and the glucosinolates and flavonoids produced by A. petiolata were detected only in A. petiolata. Trypsin inhibitor activity was highest in A. laevigata, intermediate in the Cardamine species, and lowest in A. petiolata. The phytochemical profile of A. petiolata was distinct from those of four closely related and/or abundant Brassicaceaeous species native to North America, providing support for the Novel Weapons Hypothesis. Web of Science Alliaria petiolata USA ; Canada Lab terrestrial Deciduous Forest Invasion Hyp. Novel Weapons primary 2773 Goodall, Jeremy; Witkowski, Ed T. F.; Ammann, Sigrun; Reinhardt, Carl 2010 Does allelopathy explain the invasiveness of Campuloclinium macrocephalum (pompom weed) in the South African grassland biome? journal BIOLOGICAL INVASIONS 12 10 3497 3512 Campuloclinium macrocephalum is an Asteraceous alien weed that invades roadside vegetation and grassland in South Africa. The role of allelopathy and competition in its invasiveness was investigated using Eragrostis curvula (weeping lovegrass, an indigenous grass), E. tef and Lactuca sativa (lettuce) as test species. Trials were conducted in Petri-dishes, pots and in the field. Root and shoot extracts of adult C. macrocephalum plants did not inhibit seed germination in any test species. The greatest effect was radicle stunting produced by leaf extracts at 10 and 25% w/v. Eragrostis curvula was less tolerant of the extracts than E. tef. Allelopathic effects could however not be confirmed in pot trials evaluating the interference potential of the weed or weed residue effects against E. curvula. E. curvula growth and biomass was not affected by plant densities of one or five C. macrocephalum per pot, whereas C. macrocephalum suffered a 17% mortality and density-dependant trade-offs of size and biomass for survival. Under field conditions C. macrocephalum had a broader ecological niche than E. curvula, invading hygrophilous and undisturbed grasslands not amenable for E. curvula establishment, this included well drained disturbed soils on which the latter proliferated. Evidence of competitive exclusion of E. curvula by C. macrocephalum or vice versa was not detected. The coexistence of both species irrespective of relative density suggested these species have different resource requirements. Allelopathy was not an adequate causal mechanism to explain invasiveness in Campuloclinium macrocephalum. A more traditional hypothesis such as the absence of natural enemies, at this stage, better justifies the weed's invasion success. Web of Science Campuloclinium macrocephalum South Africa Field - Experimental;Greenhouse;Lab terrestrial Grassland Invasion Hyp. Novel Weapons primary 2775 Witte, Sophia; Buschbaum, Christian; van Beusekom, Justus E. E.; Reise, Karsten 2010 Does climatic warming explain why an introduced barnacle finally takes over after a lag of more than 50 years? journal BIOLOGICAL INVASIONS 12 10 3579 3589 Invading alien species may have to await appropriate conditions before developing from a rare addition to the recipient community to a dominance over native species. Such a retarded invasion seems to have happened with the antipodean cirripede crustacean Austrominius modestus Darwin, formerly known as Elminius modestus, at its northern range in Europe due to climatic change. This barnacle was introduced to southern Britain almost seven decades ago, and from there spread north and south. At the island of Sylt in the North Sea, the first A. modestus were observed already in 1955 but this alien remained rare until recently, when in summer of 2007 it had overtaken the native barnacles Semibalanus balanoides and Balanus crenatus in abundance. At the sedimentary shores of Sylt, mollusc shells provide the main substrate for barnacles and highest abundances were attained on mixed oyster and mussel beds just above low tide level. A. modestus ranged from the upper intertidal down to the subtidal fringe. Its realized spatial niche was wider than that of the two natives. We suggest that at its current northern range in Europe a long series of mild winters and several warm summers in a row has led to an exponential population growth in A. modestus. Web of Science Elminius modestus;Austrominius modestus Germany Sylt Field - Observational marine Invasion Hyp. Climate Change filter 2776 He, Wei-Ming; Thelen, Giles C.; Ridenour, Wendy M.; Callaway, Ragan M. 2010 Is there a risk to living large? Large size correlates with reduced growth when stressed for knapweed populations journal BIOLOGICAL INVASIONS 12 10 3591 3598 A central hypothesis in ecology is that plant life history evolution is constrained by fundamental *compromises between the conflicting selection pressures resulting from particular combinations of competition, stress, and disturbance*, with stress being defined as abiotic conditions that restrict production. Biogeographic differences among native and non-native ranges of invasive plants may provide unique opportunities for tests of this theory. We conducted a greenhouse experiment with Centaurea stoebe plants from North American and European populations. We compared the total biomass and phenotypic plasticity indices for plants from the native and non-native ranges under stressed and non-stressed conditions. The average size of Centaurea stoebe plants from 13 North American populations was greater than that of plants from 18 European populations regardless of stress treatment. However, when plants from the same populations were exposed to lower resources the differences in biomass between plants from North American and European populations were significantly less, suggesting that large plants were poorer stress tolerators. For all 31 populations the regression slope for the relationship between mean mass for populations in non-stressful conditions and mean mass in stressful conditions was less than 1.0, indicating that populations that produced large plants in good conditions also produced plants that grew disproportionately less in stressful conditions. These findings suggest that Centaurea stoebe may be evolving towards being a good *competitor* (sensu Grime, 1977) in its invasive range, but at the cost of being a good *stress tolerator*. Web of Science Centaurea stoebe USA Greenhouse terrestrial Grassland Invasion Hyp. Evolution of Increased Competitive Ability primary 2777 de la Pena, Eduardo; de Clercq, Nikki; Bonte, Dries; Roiloa, Sergio; Rodriguez-Echeverria, Susana; Freitas, Helena 2010 Plant-soil feedback as a mechanism of invasion by Carpobrotus edulis journal BIOLOGICAL INVASIONS 12 10 3637 3648 Invasive plant species have been suggested to change the composition of the soil community in a way that results in a positive feedback for them and a negative feedback for the native plant community. Carpobrotus edulis, a species native to South Africa, is one of the most aggressive exotic species in Mediterranean Europe. Although several aspects of its invasion biology have been studied, the occurrence of plant-soil feedback has been scarcely investigated. We first checked for the existence of biotic resistance in soils from two invaded sites of Mediterranean Europe and one site in the native area. Secondly, we evaluated the effects of soil conditioning on the germination and plant growth of C. edulis and two key species of native dunes. Finally, we tested the effects of short- and long-term soil conditioning on the performance and reproductive effort of C. edulis. Our results show that at first there is a natural resistance to invasion by the soil biota. Later, biotic resistance in invaded soil is suppressed by the establishment of a soil community that enhances the growth of C. edulis and that negatively influences the growth and survival of the native plants. Long-term soil conditioning in the field resulted in shifts in the balance between vegetative growth and sexual reproduction. Long-term invasion was also reflected in high levels of endophyte colonization by chytrids in roots, although the physiological consequences of this colonization remain unknown. The results obtained illustrate a mechanism that explains how C. edulis breaks the initial biotic resistance of newly-invaded landscapes. Finally, this study highlights the importance of studying plant-soil interactions on different members of the plant community and temporal stages in order to fully understand invasion. Web of Science Carpobrotus edulis Portugal;Spain;South Africa Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Mutualism Facilitation;Ecosystem Engineers primary 2778 Hernandez-L, N.; Barragan, A. R.; Dupas, S.; Silvain, J. -F.; Dangles, O. 2010 Wing shape variations in an invasive moth are related to sexual dimorphism and altitude journal BULLETIN OF ENTOMOLOGICAL RESEARCH 100 5 529 541 Wing morphology has great importance in a wide variety of aspects of an insect's life. Here, we use a geometric morphometric approach to test the hypothesis that variation, in insect wing morphology patterns, occurs between sexes and along altitudinal gradients for invasive species, despite their recent association to this environment. We explored the variation in wing morphology between 12 invasive populations of the invasive potato pest, Tecia solanivora, at low and high altitude in the central highlands of Ecuador. After characterizing sexual dimorphism in wing shape, we investigated if moths at higher elevations differ in wing morphology from populations at lower altitudes. Results indicate wing shape and size differences between sexes and between altitudinal ranges. Females showed larger, wider wings than males, while high altitude moths showed larger, narrow-shaped wings by comparison to low-altitude moths. GLM analyses confirmed altitude was the only significant determinant of this gradient. Our study confirms a sexual dimorphism in size and wing shape for the potato moth. It also confirms and extends predictions of morphological changes with altitude to an invasive species, suggesting that wing morphology variation is an adapted response contributing to invasion success of the potato moth in mountainous landscapes. Ours is one of the first studies on the morphology of invasive insects and represents a valuable contribution to the study of insect invasions because it both offers empirical support to previous genetic studies on T. solanivora as well as proving broader insight into the mechanisms behind morphological evolution of a recently introduced pest. Web of Science Tecia solanivora Ecuador Field - Observational terrestrial Fundamentals primary;parasite 2779 Langston, Jacqueline N.; Schofield, Pamela J.; Hill, Jeffrey E.; Loftus, William F. 2010 Salinity Tolerance of the African Jewelfish Hemichromis letourneuxi, a Non-native Cichlid in South Florida (USA) journal COPEIA 0 3 475 480 The African Jewelfish (Cichlidae: Hemichromis letourneuxi) is a predatory, non-native fish that has recently (since 2000) begun to expand its geographic range across south Florida. The salinity tolerance of H. letourneuxi was unknown, and thus it was unclear whether the species could use estuarine or coastal environments. The response of H. letourneuxi to chronic change in salinity was evaluated here by exposing fish to progressively increasing salinities (0-80 ppt). Fish were held at target salinities for a minimum of 30 days. The species showed excellent survival from 0-50 ppt. At 60 ppt, only 25% of the fish survived, and mean estimated survival time was 12 days. Above 60 ppt, mortality was 100%. Fish grew equally well from 0-50 ppt. In another experiment, fish were transferred directly from freshwater to various salinities from 5-35 ppt (seawater) and held for seven days, after which survivors were returned to freshwater. All fish transferred directly from freshwater to salinities up to 20 ppt survived; only 56% survived when transferred from freshwater to 25 ppt, and none survived transfer above 25 ppt. Experimental results indicated that H. letourneuxi can persist easily in salinities prevalent in coastal environments, even during periods of hypersalinity common in south Florida estuaries. Salinity will not restrict its dispersal by coastal pathways. Web of Science Hemichromis letourneuxi USA Florida south Florida Lab lentic;lotic Invasion Hyp. Inherent Superiority Broad Tolerances predator 2780 Mineur, Frederic; Davies, Andrew J.; Maggs, Christine A.; Verlaque, Marc; Johnson, Mark P. 2010 Fronts, jumps and secondary introductions suggested as different invasion patterns in marine species, with an increase in spread rates over time journal PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES 277 1694 2693 2701 Not all introduced (invasive) species in a region will spread from a single point of introduction. Long-distance dispersal or further introductions can obscure the pattern of spread, but the regional importance of such processes is difficult to gauge. These difficulties are further compounded when information on the multiple scale process of invasive species range expansion is reduced to one-dimensional estimates of spread (e. g. km yr(-1)). We therefore compared the results of two different metrics of range expansion: maximum linear rate of spread and accumulation of occupied grid squares (50 x 50 km) over time. An analysis of records for 54 species of introduced marine macrophytes in the Mediterranean and northeast Atlantic revealed cases where the invasion process was probably missed (e. g. Atlantic Bonnemaisonia hamifera) and suggested cases of secondary introductions or erratic jump dispersal (Dasysiphonia sp. and Womersleyella setacea). A majority of species analysed showed evidence for an accumulation of invaded sites without a clear invasion front. Estimates of spread rate are increasing for more recent introductions. The increase is greater than can be accounted for by temporally varying search effort and implies a historical increase in vector efficiency and/or a decreased resistance of native communities to invasion. Web of Science Many Statistical/Meta-analysis marine Fundamentals 2781 HilleRisLambers, Janneke; Yelenik, Stephanie G.; Colman, Benjamin P.; Levine, Jonathan M. 2010 California annual grass invaders: the drivers or passengers of change? journal JOURNAL OF ECOLOGY 98 5 1147 1156 P>1. The dominance of invasive species is often assumed to reflect their competitive superiority over displaced native species. However, invasive species may be abundant because of their greater tolerance to anthropogenic impacts accompanying their introduction. Thus, invasive species can either be the drivers or passengers of change. 2. We distinguish between these two possibilities in California grasslands currently dominated by Mediterranean annuals (exotics) and subjected to livestock grazing since European settlement. We focused on native annual grasses and forbs, an understudied species-rich component of the California flora, and Mediterranean annual grasses, currently dominant and among the first non-native plants introduced to the area. 3. We established a field experiment with fenced and unfenced blocks in a cattle pasture. We measured concentrations of limiting resources (nitrogen, phosphorus, light and soil moisture) in monoculture plots as an index of competitive ability (i.e. R*). We then quantified grazing impacts on biomass and seed production in grazed vs. ungrazed monoculture plots. Finally, we measured biomass and seed production of each species competing in mixture plots, in the presence and absence of grazers. 4. We found that native and exotic species did not differ in R* indices of competitive ability, i.e. concentrations of limiting resources in ungrazed native monoculture plots did not differ from concentrations in ungrazed exotic monoculture plots. By contrast, exotic annuals suffered less from grazing than native annuals, perhaps reflecting their longer evolutionary history with cattle grazing. Consistent with these results, native and exotic annuals were equally abundant in ungrazed mixtures, but exotic species overwhelmingly dominated grazed mixtures. 5. Species able to draw down nitrogen and light to lower levels in monocultures (i.e. those with lower R* values) dominated biomass and seeds in mixed plots without grazers. However, R* did not predict the relative abundance of species in grazed plots. Moreover, the relative abundance of species in mixtures did not correlate with grazing impacts on their monocultures, implying that grazing alters inter-specific competitive dynamics. 6. Synthesis. We demonstrate that the displacement of native annuals by Mediterranean annual grasses in California may largely have been driven by cattle grazing. Web of Science Many USA California Field - Experimental terrestrial Grassland Invasion Hyp. Disturbance primary 2782 Huang, Wei; Siemann, Evan; Wheeler, Gregory S.; Zou, Jianwen; Carrillo, Juli; Ding, Jianqing 2010 Resource allocation to defence and growth are driven by different responses to generalist and specialist herbivory in an invasive plant journal JOURNAL OF ECOLOGY 98 5 1157 1167 P>1. Invasive plants often have novel biotic interactions in their introduced ranges. These interactions, including less frequent herbivore attacks, may convey a competitive advantage over native plants. Invasive plants may vary in defence strategies (resistance vs. tolerance) or in response to the type of herbivore (generalists vs. specialists), but no study to date has examined this broad set of traits simultaneously. 2. Here, we examined resistance and tolerance of Chinese tallow (Triadica sebifera) populations from the introduced and native ranges to generalist (Cnidocampa flavescens) and specialist herbivores (Gadirtha inexacta) in the native range. 3. In a field common-garden test of resistance, caterpillars of each species were raised on plants from native and invasive populations. We found the specialist grew larger on and consumed more mass of invasive plant populations than native populations, while the generalist showed the same performance between them. The results were consistent with our laboratory bioassay using excised leaves. Chemical analyses showed that the invasive plants had lower tannin content and higher ratio of carbohydrate to protein than those of their native counterparts, suggesting that plants from invasive populations have altered chemistry that has a larger impact on specialist than on generalist resistance. 4. To test for differences in herbivore tolerance, plants were first defoliated by specialist or generalist herbivory and then allowed to regrow for 100 days in a field common garden. We found that plants from invasive populations had greater herbivore tolerance than native populations, especially for tolerance to generalists. They also grew more rapidly than native counterparts in the absence of herbivory. 5. Synthesis. The results of these experiments indicate that differences in selective pressures between ranges have caused dramatic reductions in resistance to specialist herbivores and those changes in plant secondary chemistry likely underlie these differences. The greater tolerance of invasive populations to herbivory appears to at least partly reflect an increase in growth rate in the introduced range. The greater tolerance to generalist herbivores suggests the intriguing possibility of selection for traits that allow plants to tolerate generalist herbivores more than specialist herbivores. Web of Science Triadica sebifera China;USA Garden terrestrial Deciduous Forest Invasion Hyp. Enemy Release primary 2783 Hambright, K. David; Zamor, Richard M.; Easton, James D.; Glenn, Karen L.; Remmel, Emily J.; Easton, Anne C. 2010 Temporal and spatial variability of an invasive toxigenic protist in a North American subtropical reservoir journal HARMFUL ALGAE 9 6 568 577 The toxigenic marine flagellate Prymnesium parvum was first recorded in Lake Texoma, OK-TX, USA, an impoundment of the Red and Washita Rivers, following a massive fish kill in January 2004. Results of a 4.5-year monitoring program, spanning five bloom periods, revealed that Prymnesium abundances in the lake were temporally and spatially variable-densities were higher in winter, near-shore, and in Red River-associated sampling sites; the largest blooms were in Lebanon Pool, a large backwater basin often disconnected from the main reservoir. Prymnesium blooms appeared to have been fueled by high nutrient concentrations, and winter-spring densities were positively correlated with chlorophyll a, conductivity, total phosphorus, total nitrogen, and microzooplankton biomass, and negatively correlated with molar total nitrogen:total phosphorus and cladoceran and total crustacean zooplankton biomass. Comparison of Prymnesium densities with hydrological data suggested that Prymnesium blooms in Lebanon Pool were highest when the pool was disconnected from the main reservoir; no bloom occurred in the winter of 2004-2005, the only year since the 2003-2004 invasion in which Lebanon Pool and Lake Texoma were connected during the winter months. (c) 2010 Elsevier B.V. All rights reserved. Web of Science Prymnesium parvum USA Texas Field - Observational lentic;lotic Invasion Hyp. Plasticity primary 2784 Song, Liying; Chow, Wah Soon; Sun, Lanlan; Li, Changhan; Peng, Changlian 2010 Acclimation of photosystem II to high temperature in two Wedelia species from different geographical origins: implications for biological invasions upon global warming journal JOURNAL OF EXPERIMENTAL BOTANY 61 14 4087 4096 More intense, more frequent, and longer heat waves are expected in the future due to global warming, which could have dramatic ecological impacts. However, few studies have involved invasive species. The aims of this study were to examine the effect of extreme heating (40/35 degrees C for 30 d) on the growth and photosynthesis of an alien invasive species Wedelia trilobata and its indigenous congener (Wedelia chinensis) in South China, and to determine the development of this invasive species and its potential adaptive mechanism. In comparison with W. chinensis, W. trilobata suffered less inhibition of the relative growth rate (RGR) and biomass production due to high temperature, which was consistent with the changes of photosystem II (PSII) activity and net photosynthetic rate (P(n)). High temperature caused a partial inhibition of PSII, but the adverse effect was more severe in W. chinensis. Measurement of the minimum fluorescence (F(o)) versus temperature curves showed that W. trilobata had a higher inflexion temperature of F(o) (T(i)), indicating greater thermostability of the photosynthetic apparatus. Moreover, comparisons of absorbed light energy partitioning revealed that W. trilobata increased xanthophyll-dependent thermal dissipation (Phi(NPQ)) under high temperature, while retaining the higher fraction of absorbed light allocated to photochemistry (Phi(PSII)) relative to W. chinensis. The results suggest that the invasive W. trilobata has a high thermostability of its photosynthetic apparatus and an effective regulating mechanism in energy partitioning of PSII complexes to minimize potential damage and to retain greater capability for carbon assimilation. These factors confer greater heat stress tolerance compared with the native species. Therefore, the invasive W. trilobata may become more aggressive with the increasingly extreme heat climates. Web of Science Wedelia trilobata China South China Lab terrestrial Invasion Hyp. Climate Change primary 2785 Peter, Christopher Robert; Burdick, David M. 2010 Can Plant Competition and Diversity Reduce the Growth and Survival of Exotic Phragmites australis Invading a Tidal Marsh? journal ESTUARIES AND COASTS 33 5 1225 1236 The rapid proliferation of Phragmites australis in North America has challenged resource managers to curb its expansion and reduce the loss of functional tidal marsh. We investigated whether native plant competition could reduce the ability of Phragmites to invade a tidal marsh, and if plant diversity (species richness, evenness, and composition) altered the competitive outcome. Immature Phragmites shoots and four native halophytes were transplanted to small but dense field plots (similar to 1,200 shoots m(-2)) comprising three community structure types (Phragmites alone, Phragmites+1 native species, and Phragmites+4 native species). Interspecific competition significantly reduced Phragmites aboveground biomass, shoot length production, density, and survival by approximately 60%. Additionally, plots planted with greater native diversity contained Phragmites with the lowest growth and survival, potentially indicating diversity-enhanced resource competition. Competition consistently reduced the growth of Phragmites even under favorable conditions: lack of strong tidal flooding stresses as well as elevated nutrient pools. Web of Science Phragmites australis USA ; Canada Field - Experimental estuarine Invasion Hyp. Community Species Richness primary 2786 Todorovic, Sladana; Bozic, Dragana; Simonovic, Ana; Filipovic, Biljana; Dragicevic, Milan; Giba, Zlatko; Grubisic, Dragoljub 2010 Interaction of fire-related cues in seed germination of the potentially invasive species Paulownia tomentosa Steud journal PLANT SPECIES BIOLOGY 25 3 193 202 The Empress tree (Paulownia tomentosa Steud.) is a fast growing deciduous tree originating from East Asia. It is grown as an ornamental plant, but can also be used as industrial wood. However, in some parts of North America, this species is considered invasive, with high impact on autochthonous populations. We have investigated whether post-fire expansion of this species can be explained at the germination level by analyzing the interaction between physical (light and temperature) and chemical (smoke and nitrogenous compounds) fire-related cues in the regulation of P. tomentosa germination. Light is the key environmental signal in the induction of germination of positively photoblastic P. tomentosa seeds. Smoke, applied in the form of extract (liquid smoke [LS]), stimulates light-induced germination if applied during imbibition, or shortly after the inductive irradiation. This stimulatory effect of LS can be effectively prevented by far-red light, suggesting that the mechanism of smoke action is phytochrome related. The LS had no effect on the germination percentage when applied during the phase of radicle protrusion. However, LS reduced radicle elongation and slowed its protrusion. The LS had no effect on the optimal temperature range of germination (23-27 degrees C). The combined action of LS and KNO(3) in light-induced germination was more effective then when each chemical was applied separately. It can be concluded that all tested components of fire, except elevated temperature, operate to stimulate germination of P. tomentosa seeds, suggesting that the post-fire invasive potential of this species can, at least in part, be explained at the germination level. Web of Science Paulownia tomentosa USA ; Canada Greenhouse terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 2787 Crowder, David W.; Sitvarin, Michael I.; Carriere, Yves 2010 Mate Discrimination in Invasive Whitefly Species journal JOURNAL OF INSECT BEHAVIOR 23 5 364 380 Mate discrimination could be critical for invasive species that need to locate rare suitable mates and avoid costs associated with misdirected courtships to establish in new environments. Here, we tested whether individuals of two invasive whitefly species in the Bemisia tabaci species complex, commonly known as the B and Q biotypes, could discriminate between potential mates based on their species and sex. Behavioral observations showed that B females were more discriminating than Q females. Males of both species were able to discriminate between mates based on their species and sex, but in general B males discriminated more effectively than Q males. By incorporating these behavioral data into a conceptual model, we show that variation in mating behavior between females of different species was a more significant factor affecting mating than variation between males. These results indicate that mate discrimination could affect interactions between whitefly species and influence a species' ability to colonize novel environments. Web of Science Bemisia tabaci Arizona Yuma Field - Observational terrestrial Fundamentals herbivore 2788 Lachmuth, Susanne; Durka, Walter; Schurr, Frank M. 2010 The making of a rapid plant invader: genetic diversity and differentiation in the native and invaded range of Senecio inaequidens journal MOLECULAR ECOLOGY 19 18 3952 3967 To become invasive, exotic species have to succeed in the consecutive phases of introduction, naturalization, and invasion. Each of these phases leaves traces in genetic structure, which may affect the species' success in subsequent phases. We examined this interplay of genetic structure and invasion dynamics in the South African Ragwort (Senecio inaequidens), one of Europe's fastest plant invaders. We used AFLP and microsatellite markers to analyze 19 native African and 32 invasive European populations. In combination with historic data, we distinguished invasion routes and traced them back to the native source areas. This revealed that different introduction sites had markedly different success in the three invasion phases. Notably, an observed lag-phase in Northern Germany was evidently not terminated by factors increasing the invasiveness of the resident population but by invasive spread from another introduction centre. The lineage invading Central Europe was introduced to sites in which winters are more benign than in the native source region. Subsequently, this lineage spread into areas in which winter temperatures match the native climate more closely. Genetic diversity clearly increases with population age in Europe and less clearly decreases with spread rate up to population establishment. This indicates that gene flow along well-connected invasion routes counteracted losses of genetic diversity during rapid spread. In summary, this study suggests that multiple introductions, environmental preadaptation and high gene flow along invasion routes contributed to the success of this rapid invader. More generally, it demonstrates the benefit of combining genetic, historical, and climatic data for understanding biological invasions. Web of Science Senecio inaequidens South Africa ; Germany Field - Observational terrestrial Invasion Hyp. Evolution in General primary 2789 Chen, Hua; Qian, Hong; Spyreas, Greg; Crossland, Matthew 2010 Native-exotic species richness relationships across spatial scales and biotic homogenization in wetland plant communities of Illinois, USA journal DIVERSITY AND DISTRIBUTIONS 16 5 737 743 Aim To examine native-exotic species richness relationships across spatial scales and corresponding biotic homogenization in wetland plant communities. Location Illinois, USA. Methods We analysed the native-exotic species richness relationship for vascular plants at three spatial scales (small, 0.25 m2 of sample area; medium, 1 m2 of sample area; large, 5 m2 of sample area) in 103 wetlands across Illinois. At each scale, Spearman's correlation coefficient between native and exotic richness was calculated. We also investigated the potential for biotic homogenization by comparing all species surveyed in a wetland community (from the large sample area) with the species composition in all other wetlands using paired comparisons of their Jaccard's and Simpson's similarity indices. Results At large and medium scales, native richness was positively correlated with exotic richness, with the strength of the correlation decreasing from the large to the medium scale; at the smallest scale, the native-exotic richness correlation was negative. The average value for homogenization indices was 0.096 and 0.168, using Jaccard's and Simpson's indices, respectively, indicating that these wetland plant communities have been homogenized because of invasion by exotic species. Main Conclusions Our study demonstrated a clear shift from a positive to a negative native-exotic species richness relationship from larger to smaller spatial scales. The negative native-exotic richness relationship that we found is suggested to result from direct biotic interactions (competitive exclusion) between native and exotic species, whereas positive correlations likely reflect the more prominent influence of habitat heterogeneity on richness at larger scales. Our finding of homogenization at the community level extends conclusions from previous studies having found this pattern at much larger spatial scales. Furthermore, these results suggest that even while exhibiting a positive native-exotic richness relationship, community level biotas can/are still being homogenized because of exotic species invasion. Web of Science Many USA Illinois Field - Observational wetland Wetland Invasion Hyp. Community Species Richness primary 2790 Mastitsky, Sergey E.; Karatayev, Alexander Y.; Burlakova, Lyubov E.; Molloy, Daniel P. 2010 Parasites of exotic species in invaded areas: does lower diversity mean lower epizootic impact? journal DIVERSITY AND DISTRIBUTIONS 16 5 798 803 Aim Exotic species may serve as vectors for the introduction of parasites from their native range and may also become infected by parasites already present in invaded areas, but the total number of parasites infecting such exotic species in their invaded areas is typically less than that in their native range. We tested whether the diversity of parasites associated with exotic species in the native and invaded areas is related to the epizootic impact these parasites cause. Location Global. Methods We examined the diversity and epizootic impact of 384 parasite taxa associated with 22 exotic freshwater invertebrate species. The epizootic impact of each parasite was rated based on whether it had been documented to cause a major pathological impact on a large proportion of an infected host population (other than the invader under consideration). Results The total number of parasites associated with an exotic host in its native range was about twice that of all parasites associated with it in its entire invaded range. This was mainly because of the loss in the invaded areas of low impact parasites, whereas the average number of high impact parasites per host in these areas did not differ statistically from that in the native range. Main conclusions Our study suggests similar levels of adverse impact of parasites of exotic species in both their native and invaded areas. In addition to the introduction of highly pathogenic exotic parasites, other mechanisms that may be involved include (1) acquisition by the invaders of new high impact parasites in the invaded ranges, (2) high abundance of the invaders in their new ranges and (3) susceptibility of novel hosts to exotic parasites because of the 'naive host syndrome'. Web of Science Many Global Field - Observational lentic;lotic Invasion Hyp. Enemy Release parasite 2791 Paul, Jennifer; Vachon, Nicole; Garroway, Colin J.; Freeland, Joanna R. 2010 Molecular data provide strong evidence of natural hybridization between native and introduced lineages of Phragmites australis in North America journal BIOLOGICAL INVASIONS 12 9 2967 2973 Hybridization, both within and between taxa, can be an important evolutionary stimulus for bioinvasions. Novel intra-taxon hybridizations may arise either between formerly allopatric introduced lineages, or between native and introduced lineages. The latter can occur following a cryptic invasion of a non-native lineage, such as the nineteenth century introduction to North America of a European lineage of the common reed Phragmites australis. Previous studies found no evidence of natural hybridization between native and introduced lineages of P. australis, but produced some F(1) hybrids under experimental conditions when the seed parent was native and the pollen parent was introduced. In this study we used microsatellite data to compare genotypes of P. australis along a transect of approximately 2,000 km in eastern North America. Although hybridization appears uncommon, simulations and principle component analysis of genetic data provided strong evidence for natural hybridization at two sites adjacent to Lake Erie in which native and introduced lineages were sympatric. The seed parent was the native lineage in some cases, and the introduced lineage in other cases. There is now the potential for P. australis hybrids to become increasingly invasive, and managers should consider as a priority the removal of introduced stands from sites where they co-exist with native stands. Web of Science Phragmites australis USA;Canada Field - Observational wetland Wetland Invasion Hyp. Hybridization primary 2792 De Barro, Paul; Bourne, Anne 2010 Ovipositional host choice by an invader accelerates displacement of its indigenous competitor journal BIOLOGICAL INVASIONS 12 9 3013 3023 While competition for resources leading to invasion success is well recognized, avoidance of competition is much less so. Changes in behaviour that lead to avoidance are usually displayed by the weaker competitor. In our case though it was the stronger competitor that changed its behaviour by choosing a host for oviposition that was unacceptable to its competitor and avoiding one that was mutually acceptable; this accelerated the displacement of the competitor. We showed this by enclosing both invader (Middle East Asia Minor 1, B biotype) and indigenous (Australia, AN biotype) members of Bemisia tabaci species complex (sap sucking insects known as whiteflies) into field cages with either two plants that were a mutually acceptable oviposition host or one host that was acceptable to both and the other acceptable to the invader only. When only the mutually acceptable host was available, invader and indigenous females oviposited equally across the two plants. However, when given the choice, adult invaders still distributed themselves evenly across both hosts, but shifted their oviposition away from the mutually acceptable host and instead laid mostly on the host poorly utilized by the indigenous competitor. This indicates that the invader can change ovipositional choice to escape into competition free space. Web of Science Bemisia tabaci Turkey Field - Observational terrestrial Invasion Hyp. Plasticity herbivore 2794 Hoffmann, Benjamin D.; Saul, Wolf-Christian 2010 Yellow crazy ant (Anoplolepis gracilipes) invasions within undisturbed mainland Australian habitats: no support for biotic resistance hypothesis journal BIOLOGICAL INVASIONS 12 9 3093 3108 Ants are highly successful invaders, especially on islands, yet undisturbed mainland environments often do not contain invasive ants, and this observation is largely attributed to biotic resistance. An exception is the incursion of Yellow crazy ant Anoplolepis gracilipes within northeast Arnhem Land. The existence of A. gracilipes within this landscape's intact environments containing highly competitive ant communities indicates that biotic resistance is not a terminally inhibitory factor mediating this ant's distribution at the regional scale. We test whether biotic resistance may still operate at a more local scale by assessing whether ecological impacts are proportional to habitat suitability for A. gracilipes, as well as to the competitiveness of the invaded ant community. The abundance and species richness of native ants were consistently greater in uninfested than infested plots but the magnitude of the impacts did not differ between habitats. The abundance and ordinal richness of other macro-invertebrates were consistently lower in infested plots in all habitats. A significant negative relationship was found for native ant abundance and A. gracilipes abundance. No relationships were found between A. gracilipes abundance and any measure of other macro-invertebrates. The relative contribution of small ants (< 2.5 mm) to total abundance and relative species richness was always greater in infested sites coinciding with a reduction of the contribution of the larger size classes. Differences in the relative abundance of ant functional groups between infested and uninfested sites reflected impacts according to ant size classes and ecology. The widespread scale of these incursions and non-differential level of impacts among the habitats, irrespective of native ant community competitiveness and abiotic suitability to A. gracilipes, does not support the biotic resistance hypothesis. Web of Science Anoplolepis gracilipes Australia Northern Territory Arnhem Land Field - Observational terrestrial Tropical Forest Invasion Hyp. Other omnivore 2795 Noemi Mazia, C.; Chaneton, Enrique J.; Machera, Marina; Uchitel, Andrea; Victoria Feler, Maria; Ghersa, Claudio M. 2010 Antagonistic effects of large- and small-scale disturbances on exotic tree invasion in a native tussock grassland relict journal BIOLOGICAL INVASIONS 12 9 3109 3122 It is generally accepted that disturbances increase community invasibility. Yet the role of disturbance in plant invasions may be less predictable than often assumed, due to the influence of environmental stochasticity and interactions between disturbance regimes. We evaluated the single and interactive effects of prescribed burning (large-scale, infrequent event) and animal diggings (small-scale, frequent events) on the invasion success of Gleditsia triacanthos L. in a tussock grassland relict of the Inland Pampa, Argentina. Tree seedling emergence and survival were monitored over 4 years, after adjusting for propagule pressure through copious seed addition to all disturbance treatments. Burning altered community structure by suppressing tussock grasses and promoting exotic forbs, whereas simulated, armadillo-like diggings had little impact on herbaceous composition. Overall, seedling emergence rather than survival represented the main demographic bottleneck for tree invasion. Tree establishment success varied among seedling cohorts emerged in different climatic years. In a dry year, emergence was only slightly affected by disturbances. In contrast, for two consecutive wet years, initial burning and armadillo-like diggings exerted strong, antagonistic effects on tree recruitment. Whereas fire alone increased recruitment, the simulated burrowing regime prevented seedling emergence in both burned and unburned plots. The latter effect might be explained by reduced soil moisture, and increased seed burial and predation in excavated patches. Thus, the impact of a single, large-scale perturbation promoting woody plant invasion was overridden by a regime of small-scale, frequent disturbances. Our results show that grassland invasibility was contingent on inter-annual climatic variation as well as unexpected interactions between natural and anthropogenic disturbance agents. Web of Science Gleditsia triacanthos Argentina Inland Pampa Field - Observational terrestrial Grassland Invasion Hyp. Disturbance primary 2796 Ahern, Robert G.; Landis, Douglas A.; Reznicek, Anton A.; Schemske, Douglas W. 2010 Spread of exotic plants in the landscape: the role of time, growth habit, and history of invasiveness journal BIOLOGICAL INVASIONS 12 9 3157 3169 We investigated the relative contribution of minimum residence time, growth habit, and history of invasiveness to the spread of exotic plants in Michigan and California. Our data include minimum residence time as estimated by earliest herbarium collection records, growth habit, and history of invasiveness for over 2000 records from two herbaria (MI = 943, CA = 1131). Our data support the hypothesis that minimum residence time is highly associated with landscape spread, explaining 39-44% of variation in the number of counties invaded. In contrast, growth habit and history of invasiveness explained a small fraction of variation in spread in California but not Michigan. Over the past 30 years exotic plant species frequently became established in Michigan and California (a parts per thousand yen50 species per decade), suggesting that many more species will become invasive over time. There is an urgent need to develop effective policies for exotic plant management. In both states we found significant positive correlations between minimum residence time and species occurrence on state invasive plant lists. Further, we found historical information on the pest status of a plant species introduced into a similar environment to be relevant in determining landscape spread of exotic plants. We conclude that efforts to predict exotic species spread based on biological characteristics may have limited success, and instead endorse pest risk analysis for proposed new imports coupled with rapid detection and early response for unintended and unwanted introductions. Web of Science Many USA Michigan;California Field - Observational terrestrial Invasion Hyp. Other primary 2797 Rigal, Francois; Viard, Frederique; Ayata, Sakina-Dorothee; Comtet, Thierry 2010 Does larval supply explain the low proliferation of the invasive gastropod Crepidula fornicata in a tidal estuary? journal BIOLOGICAL INVASIONS 12 9 3171 3186 Human-mediated transport and aquaculture have promoted the establishment of non-indigenous species in many estuaries around the world over the last century. This phenomenon has been demonstrated as a major cause of biodiversity alterations, which has prompted scientists to provide explanations for the success or failure of biological invasions. Crepidula fornicata is a gastropod native from the East coast of North America which has successfully invaded many European bays and estuaries since the 19th century, with some noticeable exceptions. Its spread over Europe has been explained by a combination of human-mediated transport and natural dispersal through its long-lived planktonic larva. We here investigated whether larval supply may explain the failure in the proliferation of this species within a particular bay, the Bay of Morlaix (France). Patterns of larval distribution and larval size structure were analysed over ten sites sampled three times (20 July, 4 August and 21 August 2006), regarding characteristics of the adult population and environmental features. Our results evidenced a strong spatial structure in both larval abundance and size at the bay scale, even if larval abundances were low. In this scheme, the location of spawning adults played a critical role, with high numbers of early larvae above the main spawning location. The larval size structure further showed that settlement-stage larvae were rare, which suggested that released larvae might have been exported out of the bay. The use of an analytical model aimed to study the effect of tidal currents on the potential for larval exportation confirmed that larval retention within the bay might be low. The limitation in larval supply resulting from the interactions between spawning location and local hydrodynamics may thus impede the proliferation of this species which is well established for more than 50 years. This study provided an example of factors which may explain the failure of the transition between two major steps of biological invasions, i.e. sustainable establishment and proliferation. Web of Science Crepidula fornicata France Bay of Morlaix Field - Observational estuarine Invasion Hyp. Propagule Pressure herbivore 2798 Schramm, Jonathon W.; Ehrenfeld, Joan G. 2010 Leaf litter and understory canopy shade limit the establishment, growth and reproduction of Microstegium vimineum journal BIOLOGICAL INVASIONS 12 9 3195 3204 The invasive grass Microstegium vimineum is widely distributed in closed-canopy forests, but often is patchily distributed under uniform canopy conditions. We hypothesized that the occurrence of patches of invasion may be related to two interacting factors, the presence of dense understory shrub layers and the presence of thick litter layers on the forest floor. Seeds of M. vimineum were sown in plots located under or distant from Lindera benzoin (spicebush) shrubs, and with or without litter manipulations (none, half of natural amount, naturally occurring amount, double the natural amount) in a mature forest in central New Jersey, USA. Populations were monitored for germination and survivorship, as well as growth and fecundity of surviving plants. Neither shrub-associated shade nor litter depth affected seed germination, but both factors affected survivorship, growth and reproduction. The presence of shade from the shrubs reduced survivorship and seed set. Seeds germinating on top of the litter layer also experience higher mortality than seeds germinating under litter and in contact with soil. These results suggest that the interacting effects of shade from understory strata and deep litter layers may limit the spread of M. vimineum. The loss of shrub layers due to intense deer browse and other factors may thus accelerate the spread of this highly invasive species. Web of Science Microstegium vimineum USA New Jersey Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 2799 Lopez, Bernat C.; Pino, Joan; Lopez, Anna 2010 Explaining the successful introduction of the alpine marmot in the Pyrenees journal BIOLOGICAL INVASIONS 12 9 3205 3217 Alpine marmots were introduced into the northern Pyrenees between 1948 and 1988 from individuals captured in the French Alps, in order to bolster food sources for the golden eagle and brown bear. The marmot's subsequent occupation of the southern Pyrenees has been extremely fast. From an initial population of similar to 400 individuals, the present population in the southern Pyrenees is estimated to be of more than 10,000 individuals. The objective of this study was to assess what were the mechanisms that have enabled such a fast occupation of the territory. We studied habitat preferences and habitat selection of the alpine marmot in the southern Pyrenees both at the micro- and meso-scale, and compared our results with similar data in the bibliography on their native region. We also compared climatic data from both the native and introduction sites. Our results indicate relatively low climate (precipitation and temperature) matching between the two sites but a relatively high habitat matching. Marmots negatively select high woody cover and the presence of conifers in their home range, while they choose alpine and sub-alpine meadows close to rivers with boulders. Furthermore, the marmot population is independent of snow cover duration. We conclude that the successful establishment in the Pyrenees by the alpine marmot is explained both by the habitat- and climate-matching mechanisms. In both aspects, marmots show a generalist response. Meso-scale GIS-derived variables were non significant when analyzed together with local, micro-scale variables from field measurements. Web of Science Marmota marmota France Pyrenees Field - Observational terrestrial Mountain Invasion Hyp. Preadaptation to Climate herbivore 2800 Hill, Steven B.; Kotanen, Peter M. 2010 Phylogenetically structured damage to Asteraceae: susceptibility of native and exotic species to foliar herbivores journal BIOLOGICAL INVASIONS 12 9 3333 3342 Invasive plants often lose natural enemies while moving to new regions; however, once established in a new area, these invaders may be susceptible to attack by locally occurring enemies. Such damage may be more likely for exotics with close native relatives in the invaded area, since shifts of enemies should be more likely among closely related hosts. In this study, we evaluated whether exotics experience less herbivore damage than natives, and whether phylogenetically novel exotics experience less damage that those that are more closely related to locally occurring family members. Foliar damage was measured on 20 native and 15 exotic Asteraceae that co-occur locally in southern Ontario, Canada. The phylogenetic structure of this damage was quantified using an eigenvector decomposition method, and the relationship between damage and phylogenetic novelty of exotics was evaluated based on phylogenetic distances to other locally occurring Asteraceae. Our results show that 32% of the variation in damage was explained by phylogenetic relationship; similarity in damage tended to be associated with tribes. As predicted, exotics experienced lower damage than native species, even when the dataset was corrected for phylogenetic nonindependence. Contrary to our prediction, however, exotics that were more phylogenetically isolated from locally occurring relatives did not experience less damage. These results suggest that, though exotic Asteraceae may escape many of their natural enemies, this is not in general more likely for species phylogenetically distant from locally occurring native confamilials. Web of Science Many Canada Ontario Field - Observational terrestrial Deciduous Forest Invasion Hyp. Enemy Release primary 2801 Buczkowski, Grzegorz 2010 Extreme life history plasticity and the evolution of invasive characteristics in a native ant journal BIOLOGICAL INVASIONS 12 9 3343 3349 Disturbance resulting from urbanization is a leading cause of biotic homogenization worldwide. Native species are replaced with widespread non-native species and ants are among the world's most notorious invaders. To date, all documented cases of ant invasions involve exotic introduced species that are spread around the world by human-mediated dispersal. I investigated the effect of urbanization on the evolution of invasive characteristics in a native ant species, the odorous house ant, Tapinoma sessile (Say). Colony social structure, life history traits, and the spatial pattern of nest distribution were compared by sampling T. sessile across a gradient of three distinct habitats: natural, semi-natural, and urban. Results demonstrate a remarkable transition in colony social and spatial structure and life history traits between natural and urban environments. In natural habitats, T. sessile colonies are comprised of small, monogyne (single queen), and monodomous (single nest) colonies. In urban areas, T. sessile often exhibit extreme polygyny and polydomy, form large supercolonies, and become a dominant pest. Results also suggest that urban T. sessile colonies may have a negative impact on native ant abundance and diversity. In the natural environment T. sessile coexisted with a wide array of other ant species, while very few ant species were present in the urban environment invaded by T. sessile. Habitat degradation and urbanization can lead to extreme changes in social and spatial colony structure and life history traits in a native ant species and can promote the evolution of invasive characteristics such as polygyny, polydomy, and supercolonial colony structure. Web of Science Tapinoma sessile Europe Field - Observational terrestrial Urban Invasion Hyp. Plasticity omnivore 2802 Sharma, Gyan P.; Muhl, Sara A.; Esler, Karen J.; Milton, Suzanne J. 2010 Competitive interactions between the alien invasive annual grass Avena fatua and indigenous herbaceous plants in South African Renosterveld: the role of nitrogen enrichment journal BIOLOGICAL INVASIONS 12 9 3371 3378 Nitrogen enrichment may play a role in successful invasion of indigenous South African mediterranean shrublands by alien invasive annual grasses. To test the hypothesis that an increase in nitrogen would result in a greater increase in biomass for an alien annual grass than for various indigenous plant functional groups, we conducted a field study in Western Cape Renosterveld shrubland fragments, surrounded by wheat or vinyards, to assess alien grass abundance in relation to soil nitrogen availability. Significant decreases in invasive annual grass Avena fatua cover and soil nitrogen were observed from the edges to the interior of Renosterveld habitat fragments and there was a significant positive relationship between Avena fatua cover and soil nitrogen. In addition, Avena fatua was grown in competition with three indigenous species of different functional types, an annual forb (Dimorphotheca pluvialis), a geophyte (Oxalis purpurea) and an indigenous perennial grass (Tribolium uniolae) at three concentrations of soil nitrogen in a pot experiment. Results revealed that the alien grass Avena fatua had significant increases in biomass when nitrogen was added, whereas the indigenous species did not. Alien grass competition significantly influenced performance of the annual forb and the indigenous grass but did not affect the geophyte. Results suggest the prioritization of hierarchical management options for the different functional groups in Renosterveld in response to invasive grasses. Nutrient enrichment through run off must be restricted to conserve remnant Renosterveld fragments. Web of Science Avena fatu South Africa Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority Rapid Growth primary 2803 Fernandez-Zamudio, Rocio; Garcia-Murillo, Pablo; Cirujano, Santos 2010 Germination characteristics and sporeling success of Azolla filiculoides Lamarck, an aquatic invasive fern, in a Mediterranean temporary wetland journal AQUATIC BOTANY 93 2 89 92 Spore germination characteristics of Azolla filiculoides Lamarck, a recent invader of the Donana Mediterranean wetlands, have been quantified experimentally. Batches of spores were subjected to different storage conditions, salinity concentrations, phosphorus availability and drought effects. Cold pretreatment did not stimulate spore germination, whereas drought, a characteristic different from Azolla's native habitat, reduced it (40 +/- 7 vs 13 +/- 5). Germination declined with the increase of salinity (r = -0.50, notably above 5000 mu S cm(-1)), whereas phosphorus availability had no significant effect. (C) 2010 Elsevier B.V. All rights reserved. Web of Science Azolla filiculoides Spain Donana park Lab wetland Wetland Fundamentals primary 2804 Madden, A. A.; Davis, M. M.; Starks, P. T. 2010 First detailed report of brood parasitoidism in the invasive population of the paper wasp Polistes dominulus (Hymenoptera, Vespidae) in North America journal INSECTES SOCIAUX 57 3 257 260 The European paper wasp Polistes dominulus (Christ) is a model system in the fields of behavioral ecology, ecological immunology, and invasion biology. Since its introduction to the US in 1978, its invasion success has been attributed, in part, to a lack of parasites or parasitoids infecting this population. This is despite the number of parasites which infest the native population and the generalist polistine parasites and parasitoids documented in sympatric North American species. Multiple studies have cited low parasite pressure as evidence that the invasive population of P. dominulus is benefiting from a post-invasion release from enemies. Here, we present the first well documented case of parasitoidism of the invasive population of P. dominulus in North America. Web of Science Polistes dominulus USA Field - Observational terrestrial Invasion Hyp. Enemy Release parasite 2805 Larson, Eric R.; Olden, Julian D. 2010 Latent Extinction and Invasion Risk of Crayfishes in the Southeastern United States journal CONSERVATION BIOLOGY 24 4 1099 1110 Crayfishes are both a highly imperiled invertebrate group as well as one that has produced many invasive species, which have negatively affected freshwater ecosystems throughout the world. We performed a trait analysis for 77 crayfishes from the southeastern United States in an attempt to understand which biological and ecological traits make these species prone to imperilment or invasion, and to predict which species may face extinction or become invasive in the future. We evaluated biological and ecological traits with principal coordinate analysis and classification trees. Invasive and imperiled crayfishes occupied different positions in multivariate trait space, although crayfishes invasive at different scales (extraregional vs. extralimital) were also distinct. Extraregional crayfishes (large, high fecundity, habitat generalists) were most distinct from imperiled crayfishes (small, low fecundity, habitat specialists), thus supporting the *two sides of the same coin* hypothesis. Correct classification rates for assignment of crayfishes as invasive or imperiled were high (70-80%), even when excluding the highly predictive but potentially confounding trait of range size (75-90%). We identified a number of species that, although not currently listed as imperiled or found outside their native range, possess many of the life-history and ecological traits characteristic of currently invasive or imperiled taxa. Such species exhibit a high latent risk of extinction or invasion and consequently should be the focus of proactive conservation or management strategies. Our results illustrate the utility of trait-based approaches for taxonomic groups such as invertebrates, for which detailed species-specific data are rare and conservation resources are chronically limited. Web of Science Many USA Field - Observational lotic Invasion Hyp. Inherent Superiority Broad Tolerances;High Reprod. Output omnivore 2806 Shi, Juan; Luo, You-Qing; Zhou, Fan; He, Ping 2010 The relationship between invasive alien species and main climatic zones journal BIODIVERSITY AND CONSERVATION 19 9 2485 2500 Analysis of numbers of invasive species (insects, plants, plant diseases) in each of Chinese provinces and the world's climatic zones respectively, demonstrated positive correlations between diversity of bioinvasion and air temperature and precipitation (the two main criteria for classifying world climate types). When the air temperature is within the range of 1-25A degrees C, the degree of diversity of invasive alien species increases exponentially with air temperature. However, when the air temperature falls outside the range of 1-25A degrees C, the diversity of harmful invasive alien species changes with air temperature in a parabolic pattern, showing a *mid-latitude bulge*. Namely, when air temperatures are too high or too low, a lower average invasion frequency of harmful alien species is observed. Invasion by harmful invasive alien species is more weakly related to precipitation. Different climatic zones showed dramatic differences in resistance to the invasion of invasive alien species due to their different characteristic climatic factors, mainly including air temperature and precipitation. Web of Science Many China Field - Observational terrestrial Invasion Hyp. Other primary;herbivore;pathogen 2807 Penuelas, Josep; Sardans, Jordi; Llusia, Joan; Owen, Susan M.; Carnicer, Jofre; Giambelluca, Thomas W.; Rezende, Enrico L.; Waite, Mashuri; Niinemets, Uelo 2010 Faster returns on 'leaf economics' and different biogeochemical niche in invasive compared with native plant species journal GLOBAL CHANGE BIOLOGY 16 8 2171 2185 Plant-invasive success is one of the most important current global changes in the biosphere. To understand which factors explain such success, we compared the foliar traits of 41 native and 47 alien-invasive plant species in Oahu Island (Hawaii), a location with a highly endemic flora that has evolved in isolation and is currently vulnerable to invasions by exotic plant species. Foliar traits, which in most cases presented significant phylogenetic signal, i.e. closely related species tended to resemble each other due to shared ancestry, separated invasive from native species. Invasive species had lower leaf mass per area and enhanced capacities in terms of productivity (photosynthetic capacity) and nutrient capture both of macro- (N, P, K) and microelements (Fe, Ni, Cu and Zn). All these differences remain highly significant after removing the effects of phylogenetic history. Alien-invasive species did not show higher efficiency at using limiting nutrient resources, but they got faster leaf economics returns and occupied a different biogeochemical niche, which helps to explain the success of invasive plants and suggests that potential increases in soil nutrient availability might favor further invasive plant success. Web of Science Many USA Hawaii Oahu Island terrestrial Invasion Hyp. Inherent Superiority Superior Competitor primary 2808 Ando, Yoshino; Utsumi, Shunsuke; Ohgushi, Takayuki 2010 Community structure of insect herbivores on introduced and native Solidago plants in Japan journal ENTOMOLOGIA EXPERIMENTALIS ET APPLICATA 136 2 174 183 We compared community composition, density, and species richness of herbivorous insects on the introduced plant Solidago altissima L. (Asteraceae) and the related native species Solidago virgaurea L. in Japan. We found large differences in community composition on the two Solidago species. Five hemipteran sap feeders were found only on S. altissima. Two of them, the aphid Uroleucon nigrotuberculatum Olive (Hemiptera: Aphididae) and the scale insect Parasaissetia nigra Nietner (Hemiptera: Coccidae), were exotic species, accounting for 62% of the total individuals on S. altissima. These exotic sap feeders mostly determined the difference of community composition on the two plant species. In contrast, the herbivore community on S. virgaurea consisted predominately of five native insects: two lepidopteran leaf chewers and three dipteran leaf miners. Overall species richness did not differ between the plants because the increased species richness of sap feeders was offset by the decreased richness of leaf chewers and leaf miners on S. altissima. The overall density of herbivorous insects was higher on S. altissima than on S. virgaurea, because of the high density of the two exotic sap feeding species on S. altissima. We discuss the importance of analyzing community composition in terms of feeding guilds of insect herbivores for understanding how communities of insect herbivores are organized on introduced plants in novel habitats. Web of Science Solidago altissima Japan Field - Observational terrestrial Fundamentals primary 2809 Hillstrom, Michael L.; Vigue, Leanne M.; Coyle, David R.; Raffa, Kenneth F.; Lindroth, Richard L. 2010 Performance of the invasive weevil Polydrusus sericeus is influenced by atmospheric CO(2) and host species journal AGRICULTURAL AND FOREST ENTOMOLOGY 12 3 285 292 Natural forest systems constitute a major portion of the world's land area, and are subject to the potentially negative effects of both global climate change and invasion by exotic insects. A suite of invasive weevils has become established in the northern hardwood forests of North America. How these insects will respond to increasing CO(2) or O(3) is unknown. The present study examined the effects of elevated atmospheric CO(2) and O(3) on the invasive weevil Polydrusus sericeus Schaller at the Aspen Free Air CO(2) Enrichment (FACE) site near Rhinelander, Wisconsin. A performance assay was conducted in the laboratory during the summer of 2007 using mated pairs of P. sericeus fed a combination of aspen, birch and maple foliage. We recorded leaf area consumption, oviposition and adult longevity. We also conducted visual abundance surveys in the field from 2004 to 2007 on aspen and birch at Aspen FACE. Elevated CO(2), but not O(3), significantly affected P. sericeus performance. Female, but not male, longevity was reduced under elevated CO(2). Polydrusus sericeus also produced fewer eggs under elevated CO(2) conditions compared with ambient conditions. Adult P. sericeus strongly preferred birch over both aspen and maple, regardless of fumigation treatment. The effects of elevated CO(2) on P. sericeus populations at Aspen FACE were minimal, and varied among years and host tree species. Polydrusus sericeus abundance was significantly greater on birch than aspen. Over the long term, elevated CO(2) may reduce adult female longevity and fecundity of P. sericeus. Further studies are needed to evaluate how this information may scale to ecosystem impacts. Web of Science Many USA Wisconsin Rhinelander Garden terrestrial Deciduous Forest Invasion Hyp. Climate Change herbivore 2810 Roura-Pascual, Nuria; Bas, Josep M.; Hui, Cang 2010 The spread of the Argentine ant: environmental determinants and impacts on native ant communities journal BIOLOGICAL INVASIONS 12 8 2399 2412 The increasing numbers of invasive species have stimulated the study of the underlying causes promoting the establishment and spread of exotic species. We tracked the spread of the highly invasive Argentine ant (Linepithema humile) along an environmental and habitat gradient on the northeastern Iberian Peninsula to determine the role of climatic, habitat and biotic variables on the rate of spread, and examine impact on native ant communities. We found the species well-established within natural environments. The mean annual rate of spread of the invasion (7.94 +/- A 2.99 m/year) was relatively low compared to other studies, suggesting that resistance posed by native ants in natural environments with no or low human disturbance might delay (although not prevent) the spread of the invasion irrespectively of the land-use type. Factors related to the distance to urban areas and characteristics of native and introduced populations explained the rate of spread of the invasion, while habitat-related variables determined the distribution of native ants and the impact of the Argentine ant on them. Native ant communities became more homogeneous following the invasion due to the decline of species richness and abundance. Only few species (Plagiolepis pygmaea and Temnothorax spp.) were able to cope with the spread of the invasion, and were possibly favored by the local extinction of other ant species. Taken together, our results indicate that land uses per se do not directly affect the spread of L. humile, but influence its invasive success by molding the configuration of native ant communities and the abiotic suitability of the site. Web of Science Linepithema humile Spain Field - Observational terrestrial Invasion Hyp. Disturbance omnivore 2811 Albright, Thomas P.; Chen, Hao; Chen, Lijun; Guo, Qinfeng 2010 The ecological niche and reciprocal prediction of the disjunct distribution of an invasive species: the example of Ailanthus altissima journal BIOLOGICAL INVASIONS 12 8 2413 2427 Knowledge of the ecological niches of invasive species in native and introduced ranges can inform management as well as ecological and evolutionary theory. Here, we identified and compared factors associated with the distribution of an invasive tree, Ailanthus altissima, in both its native Chinese and introduced US ranges and predicted potential US distribution. For both ranges separately, we selected suites of the most parsimonious logistic regression models of occurrence based on environmental variables and evaluated these against independent data. We then incorporated information from both ranges in a simple Bayesian model to predict the potential US distribution. Occurrence of A. altissima in both ranges exhibited a unimodal response to temperature variables. In China, occurrence had negative relationships with topographic wetness and forest cover and positive relationships with precipitation and agricultural and urban land use. In the US, A. altissima was associated with intermediate levels of forest cover and precipitation. The Bayesian model identified 58-80% of 10-arc minute grid cells in the conterminous US as containing suitable areas for A. altissima. The best model developed from Chinese data applied to the US matched most areas of observed occurrence but under-predicted occurrence in lower probability areas. This discrepancy is suggestive of a broadening of the ecological niche of A. altissima and may be due to such factors as less intense competition, increased potency of allelopathy, and novel genotypes formed from multiple introductions. The Bayesian model suggests that A. altissima has the potential to substantially expand its distribution in the US. Web of Science Ailanthus altissima USA Field - Observational;Theoretical/Modeling terrestrial Deciduous Forest Invasion Hyp. Evolution in General;Novel Weapons primary 2812 Schofield, Pamela J.; Loftus, William F.; Kobza, Robert M.; Cook, Mark I.; Slone, Daniel H. 2010 Tolerance of nonindigenous cichlid fishes (Cichlasoma urophthalmus, Hemichromis letourneuxi) to low temperature: laboratory and field experiments in south Florida journal BIOLOGICAL INVASIONS 12 8 2441 2457 The cold tolerance of two non-native cichlids (Hemichromis letourneuxi and Cichlasoma urophthalmus) that are established in south Florida was tested in the field and laboratory. In the laboratory, fishes were acclimated to two temperatures (24 and 28A degrees C), and three salinities (0, 10, and 35 ppt). Two endpoints were identified: loss of equilibrium (11.5-13.7A degrees C for C. urophthalmus; 10.8-12.5A degrees C for H. letourneuxi), and death (9.5-11.1A degrees C for C. urophthalmus; 9.1-13.3A degrees C for H. letourneuxi). In the field, fishes were caged in several aquatic habitats during two winter cold snaps. Temperatures were lowest (4.0A degrees C) in the shallow marsh, where no fish survived, and warmest in canals and solution-holes. Canals and ditches as shallow as 50 cm provided thermal refuges for these tropical fishes. Because of the effect on survival of different habitat types, simple predictions of ultimate geographic expansion by non-native fishes using latitude and thermal isoclines are insufficient for freshwater fishes. Web of Science Hemichromis letourneuxi; Cichlasoma urophthalmus USA Florida Lab lotic Invasion Hyp. Inherent Superiority Broad Tolerances herbivore 2813 Fourqurean, James W.; Smith, Thomas J., III; Possley, Jennifer; Collins, Timothy M.; Lee, David; Namoff, Sandra 2010 Are mangroves in the tropical Atlantic ripe for invasion? Exotic mangrove trees in the forests of South Florida journal BIOLOGICAL INVASIONS 12 8 2509 2522 Two species of mangrove trees of Indo-Pacific origin have naturalized in tropical Atlantic mangrove forests in South Florida after they were planted and nurtured in botanic gardens. Two Bruguiera gymnorrhiza trees that were planted in the intertidal zone in 1940 have given rise to a population of at least 86 trees growing interspersed with native mangrove species Rhizophora mangle, Avicennia germinans and Laguncularia racemosa along 100 m of shoreline; the population is expanding at a rate of 5.6% year(-1). Molecular genetic analyses confirm very low genetic diversity, as expected from a population founded by two individuals. The maximum number of alleles at any locus was three, and we measured reduced heterozygosity compared to native-range populations. Lumnitzera racemosa was introduced multiple times during the 1960s and 1970s, it has spread rapidly into a forest composed of native R. mangle, A. germinans, Laguncularia racemosa and Conocarpus erectus and now occupies 60,500 m(2) of mangrove forest with stem densities of 24,735 ha(-1). We estimate the population growth rate of Lumnitzera racemosa to be between 17 and 23% year(-1). Populations of both species of naturalized mangroves are dominated by young individuals. Given the long life and water-dispersed nature of propagules of the two exotic species, it is likely that they have spread beyond our survey area. We argue that the species-depauperate nature of tropical Atlantic mangrove forests and close taxonomic relatives in the more species-rich Indo-Pacific region result in the susceptibility of tropical Atlantic mangrove forests to invasion by Indo-Pacific mangrove species. Web of Science Bruguiera gymnorrhiza USA Florida Field - Observational estuarine Invasion Hyp. Inherent Superiority;Community Species Richness Effective Disperser primary 2814 Affre, Laurence; Suehs, Carey M.; Charpentier, Stephane; Vila, Montserrat; Brundu, Giuseppe; Lambdon, Philip; Traveset, Anna; Hulme, Philip E. 2010 Consistency in the habitat degree of invasion for three invasive plant species across Mediterranean islands journal BIOLOGICAL INVASIONS 12 8 2537 2548 Habitats are known to vary in their vulnerability to invasion by alien plants and different species often colonise distinct habitats. To assess the consistency in the degree of invasion of particular habitats, this study examined the frequency of occurrence and local abundance of three invasive plant taxa: Ailanthus altissima, Carpobrotus spp., and Oxalis pes-caprae across different habitat types on four representative Mediterranean islands. We conducted systematic field surveys recording the presence-absence and cover of these taxa on the islands of Mallorca, Corsica, Sardinia and Crete. Drawing on the results of 5,285 sample points, the frequency of occurrence of the three invaders tends to be higher than expected in urban, ruderal and roadside habitats. In contrast, scrub habitats rarely contain any of the three invaders, indicating that they may be more resistant to invasion. The degree of invasion, determined by the local abundance of an invasive plant in any one habitat, varies according to the identity of the invader and the island. However, based on average abundance, Oxalis pes-caprae exhibits the highest degree of invasion, and Carpobrotus spp. the least. There is no indication that any one of the four islands is more prone to either higher frequencies or abundances of the three invaders. These patterns suggest that anthropogenic changes in Mediterranean islands will increase the vulnerability of certain habitats to invasion and increase the distribution of these three invasive taxa at any of the four islands. Web of Science Ailanthus altissima;Carpobrotus;Oxalis pes-caprae Mallorca;Corsica;Sardinia;Crete Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Disturbance primary 2816 Hewins, Daniel B.; Hyatt, Laura A. 2010 Flexible N uptake and assimilation mechanisms may assist biological invasion by Alliaria petiolata journal BIOLOGICAL INVASIONS 12 8 2639 2647 Although nitrogen has historically limited terrestrial plant productivity in the northern hemisphere, accelerated industrial activity is changing the availability of N, with consequences for ecosystem properties including altered susceptibility to biological invasion. Alliaria petiolata (Bieb.) Cavara & Grande is an increasingly problematic invader in forests of eastern North America. Population growth rate of this species is especially high in N-rich habitats, and it produces a variety of N-based compounds that have been shown to interfere with the growth and reproduction of native plants. To investigate how increases and shifts in forms of N will impact A. petiolata, seedlings were transplanted to the greenhouse from the field and grown in sand culture. We applied three concentrations of N (0.25, 1 and 2 mM) using five different ratios of NH(4) (+) and NO(3) (-) (100/0, 75/25, 50/50, 25/75, 0/100) in a crossed design to yield fifteen different treatments. Plants were measured throughout the growing season and a final harvest yielded measures of biomass and tissue quality. Plant growth increased significantly in response to increased concentration of total N. These increases were similar for all combinations of N. This flexibility in uptake ability may facilitate the invasion of this species, not only by increasing the range of habitats A. petiolata can occupy but also by enhancing N uptake that can lead to the production of secondary compounds disrupting other species' belowground mutualisms. We suggest that this species' ability to respond rapidly to changes in N availability, regardless of its form, may modify competitive interactions with natives and intensify its negative impacts. Web of Science Alliaria petiolata USA Greenhouse;Garden terrestrial Deciduous Forest Invasion Hyp. Plasticity primary 2817 Fornwalt, Paula J.; Kaufmann, Merrill R.; Stohlgren, Thomas J. 2010 Impacts of mixed severity wildfire on exotic plants in a Colorado ponderosa pine-Douglas-fir forest journal BIOLOGICAL INVASIONS 12 8 2683 2695 The 2002 Hayman Fire burned with mixed severity across 55,800 ha of montane Colorado forest, including pre-existing plots that were originally measured for understory plant composition and cover in 1997. We examined the influence of the Hayman Fire on exotic plants by remeasuring these plots annually from 2003 to 2007. We found that (1) exotic richness and cover generally increased as fire severity and time since fire increased; (2) the exotic species present in a plot before the fire were also largely present in the plot postfire, regardless of fire severity; (3) most of the new postfire species in a plot were present elsewhere in the study area before the fire, although some new species were truly new invaders that were not found in prefire surveys; (4) lightly burned riparian forests were not more susceptible to exotic invasion than surrounding uplands that burned with similar severity; and (5) native and exotic richness and cover were positively correlated or uncorrelated for all fire severities and years. Our findings indicate that exotics were stimulated by the Hayman Fire, especially in severely burned areas. However, exotic richness and cover remain low as of 2007, and correlations between native and exotic richness and cover suggest that exotics have not yet interfered with native understory development. Therefore, we conclude that exotic plants are not a major ecological threat at present, but recommend that monitoring be continued to evaluate if they will pose a threat in future years. Web of Science Many United States Colorado Field - Observational terrestrial Coniferous Forest Invasion Hyp. Disturbance primary 2818 Yue, Gen Hua; Li, Jiale; Bai, Zhiyi; Wang, Chun Ming; Feng, Felicia 2010 Genetic diversity and population structure of the invasive alien red swamp crayfish journal BIOLOGICAL INVASIONS 12 8 2697 2706 High genetic diversity is thought to characterize successful invasive species, as the potential to adapt to new environments is enhanced and inbreeding is reduced. The red swamp crayfish, Procambarus clarkii, native to northeastern Mexico and south-central USA was introduced to Nanjing, China from Japan in 1929. Little is known about the genetic diversity and population structure of this species in China. We examined the genetic diversity and population structure of six P. clarkii populations using nine polymorphic microsatellites. Among the six populations, Nanjing population showed the highest allele number, allele richness and gene diversity, which is consistent with records indicating Nanjing may be the first site of introduction. In all six populations, significant heterozygote deficit was observed, suggesting founder effects and non-random mating. Analysis of bottleneck under infinite allele model, stepwise mutation model and two-phased model of mutation revealed evidence of a recent bottleneck in all these populations. Pairwise genetic distance analysis, AMOVA and assignment tests demonstrated high genetic differentiation between populations. Pairwise genetic distance did not fit the pairwise geographic distance, suggesting that human mediated dispersal have played a role in the population expansion and genetic differentiation. Web of Science Procambarus clarkii China Nanjing wetland Wetland Invasion Hyp. Evolution in General omnivore 2819 Coffman, Gretchen C.; Ambrose, Richard F.; Rundel, Philip W. 2010 Wildfire promotes dominance of invasive giant reed (Arundo donax) in riparian ecosystems journal BIOLOGICAL INVASIONS 12 8 2723 2734 Widespread invasion of riparian ecosystems by the large bamboo-like grass Arundo donax L. has altered community structure and ecological function of streams in California. This study evaluated the influence of wildfire on A. donax invasion by investigating its relative rate of reestablishment versus native riparian species after wildfire burned 300 ha of riparian woodlands along the Santa Clara River in southern California in October 2003. Post-fire A. donax growth rates and productivity were compared to those of native woody riparian species in plots established before and after the fire. Arundo donax resprouted within days after the fire and exhibited higher growth rates and productivity compared to native riparian plants. Arundo donax grew 3-4 times faster than native woody riparian plants-up to a mean of 2.62 cm day(-1)-and reached up to 2.3 m in height less than 3 months after the fire. One year post-fire, A. donax density was nearly 20 times higher and productivity was 14-24 times higher than for native woody species. Three mechanisms-fire-adapted phenology, high growth rate, and growth response to nutrient enrichment-appear to promote the preemption of native woody riparian species by A. donax after fire. This greater dominance of A. donax after wildfire increased the susceptibility of riparian woodlands along the Santa Clara River to subsequent fire, potentially creating an invasive plant-fire regime cycle. Moreover, A. donax infestations appear to have allowed the wildfire to cross the broad bed of the Santa Clara River from the north, allowing thousands of acres of shrubland to the south to burn. Web of Science Arundo donax United States California Field - Observational terrestrial Riparian Invasion Hyp. Disturbance primary 2820 Blum, Michael J.; Walters, David M.; Burkhead, Noel M.; Freeman, Byron J.; Porter, Brady A. 2010 Reproductive isolation and the expansion of an invasive hybrid swarm journal BIOLOGICAL INVASIONS 12 8 2825 2836 Biological invasions involving hybridization proceed according to prezygotic and postzygotic reproductive isolating mechanisms. Yet few comparisons of reproductive isolation have been carried out to understand how different mechanisms prevent or promote invasions involving hybridization. Here we present a study of prezygotic and postzygotic isolation between non-native red shiner (Cyprinella lutrensis) and native blacktail shiner (C. venusta stigmatura) from the Coosa River basin (USA) to better understand the formation and expansion of invasive hybrid swarms. We conducted spawning trials to measure mating preferences and raised broods from crosses to assay hybrid viability through early juvenile development. Females of both species were more responsive to conspecific mates, although blacktail shiner females responded more often to heterospecific mates than did red shiner females. Fecundity of red shiner females was also higher than blacktail shiner females. Heterospecific crosses resulted in lower fertilization and egg hatching rates, but we found no other evidence of inviability. Rather, we found comparatively low larval mortality of F(1) hybrids, which is suggestive of heterosis. These findings support prior inferences of assortative mating from genetic descriptions of hybridization, and that the invasion in the Coosa River is likely proceeding due to interspecific competition and intrinsic hybrid viability. Web of Science Cyprinella lutrensis USA Coosa River Field - Observational lotic Invasion Hyp. Hybridization herbivore 2821 Martin, Patrick H.; Canham, Charles D.; Kobe, Richard K. 2010 Divergence from the growth-survival trade-off and extreme high growth rates drive patterns of exotic tree invasions in closed-canopy forests journal JOURNAL OF ECOLOGY 98 4 778 789 P>1. The study of invasiveness typically emphasizes early successional life-history traits in exotic plants, which enable the capture of high resources in disturbed environments and rapid growth. A key issue in invasion dynamics is whether such behaviours come at the expense of traits such as low-light survivorship, which allow species to become more dominant later in succession. 2. We used maximum-likelihood analysis to compare the growth and survivorship of two exotic trees, Ailanthus altissima and Acer platanoides, with nine dominant native tree species in closed-canopy forests in Connecticut, USA. Growth was modelled as a function of light and survivorship as a function of recent growth; combining models yielded estimates of light-dependent mortality. 3. The exotic species had strikingly high growth rates, exceeding all native species at light levels >= 10% full sun, and growing 2.6 times faster than the fastest-growing native species at 80% full sun. At low-light levels (< 3% full sun), however, growth rates of five native species exceeded both exotics. Exotic species survivorship (as a function of light-driven growth) was strongly dependent on the degree of shading: at 1% full sun, the annual mortality rate of A. platanoides was 10% and A. altissima was 17%; only two native species had higher mortalities. However, at 5% full sun, A. platanoides' mortality was < 1%, superior to all but three native species. Mortality of all species dropped to < 1% by 10% full sun, except A. altissima whose mortality remained high at c. 10%. 4. A life-history trade-off analysis (based on radial growth, height allometry and low-light survivorship) shows a nearly linear trade-off for most species. The native species and Ailanthus follow the common life-history trade-off of low-light survivorship vs. high-light growth. However, A. platanoides diverges from this trade-off pattern by combining very high growth rates with moderately high shade tolerance. 5. Simulations with SORTIE-ND (a forest dynamics model) indicate that poor survivorship of A. altissima will limit it to disturbed sites, whereas A. platanoides' unusual combination of traits makes it invasive in both disturbed and undisturbed forests. Overall, native shade-tolerant trees and slow stand dynamics make undisturbed forests highly resistant to invasion by exotic trees that are intolerant of shade. 6. Synthesis. This study showcases the importance of rapid growth in invasive plants, holding even for exotic tree species known to invade established forests. For A. altissima, high growth rates were accompanied by poor low-light survivorship. A. platanoides departs from the general trade-off pattern that exists among native species and A. altissima, and consequently it can be highly invasive in closed-canopy forests. Web of Science Ailanthus altissima;Acer platanoides USA Connecticut Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Rapid Growth primary 2822 Gallagher, Rachael V.; Beaumont, Linda J.; Hughes, Lesley; Leishman, Michelle R. 2010 Evidence for climatic niche and biome shifts between native and novel ranges in plant species introduced to Australia journal JOURNAL OF ECOLOGY 98 4 790 799 P>1. The potential invasive success of exotic plant species is thought to be associated with similarity in climate and biome between the original and novel range. We tested this assumption by quantifying the match between the realized climatic niches and biomes occupied in the exotic and native range of 26 plant species introduced to Australia. We then explored correlations between the propensity to shift climatic niche with residence time, invasion status, geographic range size, and species traits. 2. Occurrence data from the native and exotic range of 26 species introduced to Australia were obtained, and the overlap between native and exotic climate niches was calculated using between-class analysis. Shifts into novel biomes were assessed using a Geographic Information System (GIS). Correlations between introduction, distribution and species traits and the degree of climate matching were examined using nonparametric statistical tests. 3. Exotic species frequently occurred in climatic conditions outside those occupied in their native range (20 of 26 species). Nineteen species inhabited biomes in Australia not occupied in the native range and in some instances this shift represented the establishment of populations in novel biomes not present in the native range. No single-species trait, introduction or distributional characteristic was significantly associated with the degree of climatic niche shift. 4.Synthesis. Exotic species are able to occupy climate niches in the new range that differ substantially from those of the native range, and generally do not show biome conservatism between their native and introduced ranges. This implies that novel climatic conditions are not a major obstacle for exotic species establishing populations outside their native range. These results have important implications for the use and interpretation of ecological niche models used to predict the distribution of species in novel climates in time or space. The results also highlight the importance of alternate mechanisms, such as enemy release, phenotypic plasticity or rapid evolution, in the establishment of naturalized and invasive populations. Web of Science Many Australia Field - Observational;Theoretical/Modeling terrestrial Invasion Hyp. Evolution in General;Climate Change primary 2823 Henery, Martin L.; Bowman, Gillianne; Mraz, Patrik; Treier, Urs A.; Gex-Fabry, Emilie; Schaffner, Urs; Mueller-Schaerer, Heinz 2010 Evidence for a combination of pre-adapted traits and rapid adaptive change in the invasive plant Centaurea stoebe journal JOURNAL OF ECOLOGY 98 4 800 813 P>1. Introduced plants have the potential to rapidly evolve traits of ecological importance that may add to their innate potential to become invasive. During invasions, selection may favour genotypes that are already pre-adapted to conditions in the new habitat and, over time, alter the characteristics of subsequent generations. 2. Spotted knapweed (Centaurea stoebe) occurs in two predominantly spatially separated cytotypes in its native range (Europe-Western Asia), but currently only the tetraploid form has been confirmed in the introduced range (North America), where it is invasive. We used several common garden experiments to examine, across multiple populations, whether tetraploids and diploids from the native range differ in life cycle, leaf traits and reproductive capacity and if such differences would explain the predominance of tetraploids and their advance into new habitats in the introduced range. We also compared the same traits in tetraploids from the native and introduced range to determine whether any rapid adaptive changes had occurred since introduction that may have enhanced invasive potential of the species in North America. 3. We found tetraploids had lower specific leaf area, less lamina dissection and fewer, narrower leaves than diploids. Diploids exhibited a monocarpic life cycle and produced few if any accessory rosettes. Diploids produced significantly more seeds per capitulum and had more capitula per plant than tetraploids. In contrast, the vast majority of European tetraploids continued to flower in both seasons by regenerating from multiple secondary rosettes, demonstrating a predominantly polycarpic life cycle. 4. During early growth tetraploids from North America achieved greater biomass than both tetraploids and diploids from the native range but this did not manifest as larger above-ground biomass at maturity. In North American tetraploids there was also evidence of a shift towards a more strictly polycarpic life cycle, less leaf dissection, greater carbon investment per leaf, and greater seed production per capitulum. 5.Synthesis. Our results suggest that the characteristics of tetraploid C. stoebe pre-adapted them (compared to diploid conspecifics) for spread and persistence of the species into habitats in North America characterized by a more continental climate. After the species' introduction, small but potentially important shifts in tetraploid biology have occurred that may have contributed significantly to successful invasion. Web of Science Centaurea stoebe USA Garden terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 2824 Holzapfel, Claus; Shahrokh, Pouyan; Kafkewitz, David 2010 POLYPHENOL OXIDASE ACTIVITY IN THE ROOTS OF SEEDLINGS OF BROMUS (POACEAE) AND OTHER GRASS GENERA journal AMERICAN JOURNAL OF BOTANY 97 7 1195 1199 Premise of the study: Phenolic compounds exuded by roots have been implicated in allelopathic interactions among plants. Root enzymes that destroy phenolics may protect plants against allelopathic inhibition and thus may aid in invasiveness. Phenolic-degrading enzymes are chiefly found in aboveground plant parts, but have also been previously reported in root tissues where the enzyme's function is unknown. We explored phenolic oxidase activity in emerging roots of grasses in a survey across different grass genera; in particular, we aimed to test whether grasses of the genus Bromus, known for their large invasion potential, differ in this respect from other grass taxa. Methods: We assayed a range of grass genera commonly found in the United States for root enzyme activity with spectrophotometric assays of phenol oxidase activity using L-DOPA as the main substrate. Key results: In the survey of a grass genera, we discovered that roots of the genus Bromus contain large amounts of polyphenol oxidase (PPO) activity, while all other tested grass genera, even ones closely related to Bromus, did not. PPO was found to be present at germination and remained active throughout the life of the plant. Compared to other PPOs, the enzyme present in Bromus appears to have a narrow substrate range. Conclusions: The specific functions of the root PPO and the ecological ramifications of the special status of Bromus are not yet clear. The possibility that the enzyme plays a role in plant species interaction for bromes, a genus of grasses known to have high invasive potential, is raised. Web of Science Bromus USA terrestrial Grassland Invasion Hyp. Novel Weapons primary 2826 Walls, Ramona L. 2010 Hybridization and Plasticity Contribute to Divergence Among Coastal and Wetland Populations of Invasive Hybrid Japanese Knotweed s.l. (Fallopia spp.) journal ESTUARIES AND COASTS 33 4 902 918 Japanese knotweed s.l. (Fallopia spp.) is a highly invasive clonal plant, best known from roadside and riparian habitats. Its expansion into beaches on Long Island, NY, USA, represents a major habitat shift. I surveyed populations from beaches and wetlands and conducted a common garden experiment to test for variation in drought tolerance and phenotype among populations and habitats. All populations were composed mostly of first- and later-generation hybrids. I found significant variation among populations in growth, lamina size, specific leaf area (SLA), and biomass allocation, in both the field and the common garden. Lamina size, growth, and root-to-shoot responded plastically to drought treatment. Wetland populations tolerated drought as well as beach populations. Differentiation in SLA between habitats suggests that some selection for beach genotypes may have occurred. It appears that both hybridization and phenotypic plasticity are contributing to the expansion of Fallopia spp. into novel habitat. Web of Science Fallopia spp. United States New York Long Island Field - Observational terrestrial Invasion Hyp. Hybridization;Plasticity primary 2828 Eales, J.; Thorpe, R. S.; Malhotra, A. 2010 Colonization history and genetic diversity: adaptive potential in early stage invasions journal MOLECULAR ECOLOGY 19 14 2858 2869 The introduction of Anolis cristatellus from the multiple species anole community of Puerto Rico in the Greater Antilles to the island of Dominica in the Lesser Antilles, with its solitary endemic anole, provides an example of a very recent, timed, single colonization. We investigate the geographic origin and adaptive potential of the Dominican population using a range of methods including mtDNA phylogeography, nuclear microsatellite variation and multiple paternity studies, as well as heritability estimates, common garden experiments and comparative geographic studies of quantitative scalation traits. Phylogeographic analysis of NADH2 and microsatellite studies suggests that the Dominican population arose from a set of individuals from the central west area of Puerto Rico within their endemic range. The multiple-individual inoculation, together with sperm storage and evidence of multiple paternity indicate genetic variability and suggest the potential for adaptation by natural selection. Estimates of heritability, common garden experiments and broad sense Q(ST)/F(ST) ratios, linked to replicated comparisons along elevational transects go some way to suggesting that the invasive populations may be adapting by natural selection, in parallel with the endemic anole, in the brief period since their introduction. Web of Science Anolis cristatellus Dominican Republic Dominica Field - Observational terrestrial Tropical Forest Invasion Hyp. Evolution in General predator 2829 Carboni, Marta; Thuiller, Wilfried; Izzi, Francesca; Acosta, Alicia 2010 Disentangling the relative effects of environmental versus human factors on the abundance of native and alien plant species in Mediterranean sandy shores journal DIVERSITY AND DISTRIBUTIONS 16 4 537 546 Aim Mediterranean coastal sand dunes are characterized by both very stressful environmental conditions and intense human pressure. This work aims to separate the relative contributions of environmental and human factors in determining the presence/abundance of native and alien plant species in such an extreme environment at a regional scale. Location 250 km of the Italian Tyrrhenian coast (Region Lazio). Methods We analysed alien and native plant richness and fitted generalized additive models in a multimodel-inference framework with comprehensive randomizations to evaluate the relative contribution of environmental and human correlates in explaining the observed patterns. Results Native and alien richness are positively correlated, but different variables influence their spatial patterns. For natives, human population density is the most important factor and is negatively related to richness. Numbers of natives are unexpectedly lower in areas with a high proportion of natural land cover (probably attributable to local farming practices) and, to a lesser degree, affected by the movement of the coastline. On the other hand, alien species richness is strongly related to climatic factors, and more aliens are found in sectors with high rainfall. Secondarily, alien introductions appear to be related to recent urban sprawl and associated gardening. Main conclusions Well-adapted native species in a fragile equilibrium with their natural environment are extremely sensitive to human-driven modifications. On the contrary, for more generalist alien species, the availability of limited resources plays a predominant role. Web of Science Many Italy Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Disturbance primary 2830 Castillo, J. M.; Ayres, D. R.; Leira-Doce, P.; Bailey, J.; Blum, M.; Strong, D. R.; Luque, T.; Figueroa, E. 2010 The production of hybrids with high ecological amplitude between exotic Spartina densiflora and native S-maritima in the Iberian Peninsula journal DIVERSITY AND DISTRIBUTIONS 16 4 547 558 Aim Hybridization is a common and potent mechanism of plant evolution that has the potential to be evolutionary significant in its own right, and hybrids are common between invasive and native congeneric species. Our aims were to document the existence and nature of new Spartina hybrids arising between introduced Spartina densiflora and native S. maritima in tidal marshes of the Iberian Peninsula, to examine the actual and potential range of hybrids in the intertidal zone, and to analyse the seed set of hybrids. Location South-West Iberian Peninsula. Methods Hybrids were characterized using chloroplast and nuclear DNA, and ploidy assessments. The ecological tolerance of the hybrids was studied using vegetation surveys and transplant experiments. Results We found that both parental species have been seed parents to hybrids and that all hybrids had an additive pattern of species-specific nuclear markers consistent with F(1) hybrids. Hybrid chromosome numbers varied between 2n = ca. 65 and 2n = ca. 94-97, while S. maritima had 2n = ca. 60 and S. densiflora had 2n = ca. 70. Hybrids grew in three discrete locations along the intertidal zone but were capable of growing throughout the ranges of both parental species in transplanted gardens, and in most cases, grew better than the parental species. While the potential exists for the origination of another invasive Spartina hybrid species, thus far hybrid plants are not fertile, limiting their ability to invade and spread. Main conclusions We recommend the eradication of all of the currently quite limited hybrid cordgrass and to fight the S. densiflora invasion in the Iberian Peninsula to prevent the origination of a new invasive allopolyploid Spartina species. Web of Science Spartina densiflora Spain Field - Observational estuarine Invasion Hyp. Hybridization primary 2831 Ricotta, Carlo; Godefroid, Sandrine; Rocchini, Duccio 2010 Invasiveness of alien plants in Brussels is related to their phylogenetic similarity to native species journal DIVERSITY AND DISTRIBUTIONS 16 4 655 662 Aim Understanding the processes that drive invasion success of alien species has received considerable attention in current ecological research. From an evolutionary point of view, many studies have shown that the phylogenetic similarity between the invader species and the members of the native community may be an important aspect of invasiveness. In this study, using a coarse-scale systematic sampling grid of 1 km2, we explore whether the occupancy frequency of two groups of alien species, archaeophytes and neophytes, in the urban angiosperm flora of Brussels is influenced by their phylogenetic relatedness to native species. Location The city of Brussels (Belgium). Methods We used ordinary least-squares regressions and quantile regressions for analysing the relationship between the occupancy frequency of alien species in the sampled grid and their phylogenetic distance to the native species pool. Results Alien species with high occupancy frequency in the sampled grid are, on average, more phylogenetically related to native species than are less frequent aliens, although this relationship is significant only for archaeophytes. In addition, as shown by the quantile regressions, the relationship between phylogenetic relatedness to the native flora and occupancy frequency is much stronger for the most frequent aliens than for rare aliens. Main conclusions Our data suggest that it is unlikely that species with very low phylogenetic relatedness to natives will become successful invaders with very high distribution in the area studied. To the contrary, under future climate warming scenarios, present-day urban aliens of high occupancy frequency are likely to become successful invaders even outside urban areas. Web of Science Many Belgium terrestrial Urban Invasion Hyp. Preadaptation to Climate primary 2832 Fujisaki, Ikuko; Pearlstine, Elise V.; Mazzotti, Frank J. 2010 The rapid spread of invasive Eurasian Collared Doves Streptopelia decaocto in the continental USA follows human-altered habitats journal IBIS 152 3 622 632 Understanding factors related to the range expansion trajectory of a successful invasive species may provide insights into environmental variables that favour additional expansion or guide monitoring and survey efforts for this and other invasive species. We examined the relationship of presence and abundance of Eurasian Collared Doves Streptopelia decaocto to environmental factors using recent data from the North American Breeding Bird Survey to understand factors influencing its expansion into the continental USA. A zero-inflated Poisson (ZIP) model was used to account for excess zero observations because this species was not observed on the majority of survey routes, despite its large geographical range. Model fit was improved when we included environmental covariates as compared with the null model, which only included distance from the route where this species was first observed. Probability of zero count was positively related to the distance from the first route and road density and was inversely related to minimum temperature and distance to coast. Abundance of the species was positively related to road density and was inversely related to annual precipitation and distance to coast. Random intercept by land-cover type also improved model fit. Model fit was improved with the ZIP model over the standard Poisson model, suggesting that presence and abundance of this species are characterized by different environmental factors. However, overall low accuracy of model-predicted presence/absence and abundance with the independent validation dataset may indicate either that there are other explanatory factors or that there is great uncertainty in the species' colonization process. Our large-scale study provides additional evidence that the range expansion of this species tends to follow human-altered landscapes such as road and agricultural areas as well as responding to general geographical features such as coastlines or thermal clines. Such patterns may hold true for other invasive species and may provide guidelines for monitoring and assessment activities in other invasive taxa. Web of Science Streptopelia decaocto USA terrestrial Invasion Hyp. Other omnivore 2833 Martinez Dominguez, David; Cordoba Garcia, Francisco; Canalejo Raya, Antonio; Torronteras Santiago, Rafael 2010 Cadmium-induced oxidative stress and the response of the antioxidative defense system in Spartina densiflora journal PHYSIOLOGIA PLANTARUM 139 3 289 302 Spartina densiflora is an invasive cordgrass that is colonizing new habitats and ousting indigenous species in pro-oxidative environments like cadmium-polluted salt marshes in the Odiel estuary (Spain). The aim of our study was to characterize its antioxidative system in order to find out if the system underlies the tolerance of S. densiflora to cadmium toxicity. S. densiflora plants were firstly evaluated to ascertain its antioxidative status in the natural habitat and then they were cultured in the laboratory in unpolluted sand for 28 days. Throughout this period, plants acclimatized and oxidative stress markers reached stable low levels. Then, S. densiflora plants were exposed to cadmium concentrations (10, 100 and 1000 mu M Cd) for another 28 days. Higher Cd content in leaves was related to higher level of reactive oxygen species (ROS) causing important oxidative cell damage (lipid peroxidation and lower chlorophyll content). However, S. densiflora possesses a well-organized and appropriately modulated antioxidative defense system which comprises enzymatic activities of guaiacol peroxidase (EC 1.11.1.7), catalase (EC 1.11.1.6), ascorbate peroxidase (EC 1.11.1.11) and superoxide dismutase (EC 1.15.1.1) coupled with the activation of the ascorbate cycle, including enzymatic activities of glutathione reductase (EC 1.6.4.2), dehydroascorbate reductase (EC 1.8.5.1) and monodehydroascorbate reductase (EC 1.6.5.4). This activation was sufficient to reduce Cd-induced ROS accumulation and oxidative damage caused by the lowest Cd-concentrations, but not by the highest Cd-concentration (1000 mu M). Nevertheless, the antioxidant system seems to be efficient to achieve a tolerance to cadmium toxicity, allowing normal plant development, even at the presence of highest Cd concentration. Web of Science Spartina densiflora Spain Odiel estuary Lab estuarine Invasion Hyp. Inherent Superiority Broad Tolerances primary 2835 Har-Edom, Or-Leyl; Sternberg, Marcelo 2010 Invasive species and climate change: Conyza canadensis (L.) Cronquist as a tool for assessing the invasibility of natural plant communities along an aridity gradient journal BIOLOGICAL INVASIONS 12 7 1953 1960 The predicted reduction in precipitation in the eastern Mediterranean due to climate change may expose the natural plant communities to invasive species. We assessed whether natural plant communities along an aridity gradient in Israel were resistant to invasion by considering differences in abiotic conditions and community characteristics in these regions. We considered Conyza canadensis as a model plant as it is a common invader in the region. We examined the mechanisms and functional traits of both the plant communities and C. canadensis that promote or discourage invasion. Study sites represented a rainfall gradient with four ecosystem types: mesic Mediterranean, Mediterranean, semiarid and arid. Our results showed that the mechanisms of community invasion resistance varied along the aridity gradient. At the arid and semiarid sites, water deficiency impaired the establishment of C. canadensis. At the mesic Mediterranean site, plant competition had a negative effect on C. canadensis performance, thus greatly reducing the likelihood of its establishment. We conclude that a decrease in regional precipitation due to climate change may not affect intrinsic resistance characteristics of natural plant communities to invasion in the area. Web of Science Conyza canadensis Israel Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Community Species Richness;Climate Change primary 2836 Kuester, Eva C.; Durka, Walter; Kuehn, Ingolf; Klotz, Stefan 2010 Differences in the trait compositions of non-indigenous and native plants across Germany journal BIOLOGICAL INVASIONS 12 7 2001 2012 This paper explores the differences in the trait compositions of non-indigenous (neophytic) and native plant species for selected traits in Germany. Our set of functional traits addresses species' reproductive biology, life history, morphology and ecophysiology. To take account of broad-scale heterogeneity across the country we compared the relative frequencies of neophytes and natives with particular trait attributes at the scale of grid cells (c. 130 km(2) each). Subsequently, we compared the differences at the grid cell scale to the differences in the corresponding comparisons at the scale of the entire country. Finally, we explored how variation in the trait compositions of the non-indigenous species across the country relates to variation in the trait compositions of the natives. We found remarkable differences in the trait compositions of neophytes and natives at the grid cell scale. Neophytes were over-represented in insect- and self-pollinated species and in species with a later and longer flowering season. Furthermore, the proportions of species with mesomorphic or hygromorphic leaf anatomy, of annual herbs and of trees as well as of non-clonals and polyploids were significantly higher in neophytes than in natives. These differences at the grid cell scale could vary distinctly from the corresponding differences observed at the country scale. This result highlights the complexity of the invasion process and suggests an importance of spatial scale for the comparisons. Correlation analysis indicated, that for traits relating to plant morphology and ecophysiology, the relative frequencies of the non-indigenous species increased with those of the natives. This suggests that favourable environments for natives with particular attributes constitute an increased suitability for neophytes with these attributes as well. Our study provides a step forward towards an integrated understanding of traits in plant invasions across spatial scales and broad-scale heterogeneity and underlines the necessity to understand the role of functional traits in plant invasions with reference to spatial scale and in the context of the environment. Web of Science Many Germany Field - Observational terrestrial Invasion Hyp. Inherent Superiority Broad Tolerances;Self Compatible primary 2838 Liu Xuan; Li Yiming; McGarrity, Monica 2010 Geographical variation in body size and sexual size dimorphism of introduced American bullfrogs in southwestern China journal BIOLOGICAL INVASIONS 12 7 2037 2047 Invasive species often exhibit geographical variations in life history traits that may allow them to successfully invade different environments. We investigated geographical variation in body size and sexual size dimorphism (SSD) of invasive bullfrogs in southwestern China, by sampling two breeding populations (descendants of a single source population) inhabiting sites at low (1,412 m, Shiping) and high (2,692 m, Luguhu) altitudes. Both populations exhibited significant SSD, with females larger than males. At high altitude, mean body size of both sexes and the degree of SSD were significantly reduced; the reduction in mean body size with increasing altitude was more pronounced in females, although not significantly so. Female bullfrogs also showed a significant decrease in average age at high altitude that may be a major factor related to this pattern; average age of male bullfrogs did not vary significantly with altitude. Growth rate of both sexes was also lower at high altitude. Our results provide the first evidence that introduced bullfrog's exhibit geographical variation in morphology in invaded areas in response to different environments, likely due to changes in climate. Additional research is required to determine the mechanism of this variation (i.e., physiological or developmental plasticity, mortality rate, selective pressure) and most importantly, to evaluate the potential for variation in the impacts of introduced bullfrogs on native ecosystems in China. Web of Science Rana catesbeiana China Field - Observational terrestrial Invasion Hyp. Plasticity predator 2839 Lankau, Richard 2010 Soil microbial communities alter allelopathic competition between Alliaria petiolata and a native species journal BIOLOGICAL INVASIONS 12 7 2059 2068 Allelopathy has been increasingly invoked as a mechanism facilitating exotic plant invasions. However, studies even on the same target species often yield varying results concerning the strength and importance of allelopathic inhibition, suggesting that the process may depend on the specific environmental context. Here I studied how the allelopathic inhibition of sycamore (Platanus occidentalis) seedlings by garlic mustard (Alliaria petiolata) depended on the presence of a soil microbial community. Using three analytical approaches to quantifying allelopathy, I consistently found allelopathic inhibition only in sterilized soils, suggesting that certain microbial taxa inhibit the process, possibly by degrading the allelochemicals. Determining the environmental contexts that reduce or eliminate allelopathic inhibition could lead to a greater understanding of the spatial variation in invasion success and potentially lead to new avenues for management. Web of Science Alliaria petiolata USA Field - Observational terrestrial Invasion Hyp. Novel Weapons primary 2840 Huebner, Cynthia D. 2010 Establishment of an invasive grass in closed-canopy deciduous forests across local and regional environmental gradients journal BIOLOGICAL INVASIONS 12 7 2069 2080 Establishment of Microstegium vimineum, an invasive exotic grass, in closed-canopy U.S. eastern forests was evaluated across a local (roadside to forest interior) and regional (across two geographic provinces) environmental gradient in West Virginia. The two geographic provinces were the Allegheny Plateau (more mesic) and the Ridge and Valley Province (more xeric). Biotic, abiotic, and disturbance variables were measured in (1) systematically located plots, starting from the roadside and extending 50 m into the forests, and (2) randomly selected, forest interior plots, with equal numbers of plots containing or not containing M. vimineum. Associations between the variables and the presence of M. vimineum at both scales were evaluated using generalized linear models. Relative importance of the variables related to M. vimineum establishment in the forest interior plots at the regional scale was determined using logistic regression. Results confirmed Microstegium vimineum's reduced reproductive capacity in the forest interior compared to the roadside. Patches of M. vimineum in the forest interiors across the regional gradient were best defined by high native plant richness and diversity. Greater canopy opening, more moss, and shallower litter depths were also positively and significantly associated with M. vimineum presence, but only during the driest sample year. Web of Science Microstegium vimineum USA West Virginia Field - Observational terrestrial Deciduous Forest Invasion Hyp. Community Species Richness;Disturbance primary 2841 Huebner, Cynthia D. 2010 Spread of an invasive grass in closed-canopy deciduous forests across local and regional environmental gradients journal BIOLOGICAL INVASIONS 12 7 2081 2089 Spread of Microstegium vimineum, an invasive exotic grass, in closed-canopy forests of West Virginia, U.S. was evaluated across a local (roadside to forest interior) and regional (across two geographic provinces) environmental gradient. Seed dispersal distances from roadside populations into forest interiors based on seed rain and soil seed bank data were determined. Colonization and extinction of M. vimineum patches were followed over three years (2005-2007), and spread rate was estimated using a reaction-diffusion model. Direct seed dispersal from the roadside populations occurred primarily adjacent to the maternal plants, indicating that the disjunct M. vimineum patches within the forest interiors occurred via secondary seed dispersal over longer distances. Patches of M. vimineum were found as far as 45 m into the forest interior, but M. vimineum seed in the seed bank were only found within 10 m of the roadside population. Colonization rates of the forest interiors were significantly higher for the more mesic sites than the more xeric sites. The same trend was noted for the spread rate. Radial spread rates ranged between 0.16 and 0.50 m year(-1) and forest interiors were estimated to become saturated with M. vimineum in anywhere between 10 (more mesic sites) and 59 (more xeric sites) years. These results support the possibility of accelerating spread rates in forest interiors caused by more long-distance dispersal events, but slowed by a reduction in M. vimineum fitness in shaded or relatively dry environments. Web of Science Microstegium vimineum USA West Virginia Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 2842 Gosper, Carl R.; Vivian-Smith, Gabrielle 2010 Fruit traits of vertebrate-dispersed alien plants: smaller seeds and more pulp sugar than indigenous species journal BIOLOGICAL INVASIONS 12 7 2153 2163 Vertebrates play a major role in dispersing seeds of fleshy-fruited alien plants. However, we know little of how the traits of alien fleshy fruits compare with indigenous fleshy fruits, and how these differences might contribute to invasion success. In this study, we characterised up to 38 fruit morphology, pulp nutrient and phenology traits of an assemblage of 34 vertebrate-dispersed alien species in south-eastern Queensland, Australia. Most alien fruits were small (81% < 15 mm in mean width), and had watery fruit pulps that were high in sugars and low in nitrogen and lipids. When compared to indigenous species, alien fruits had significantly smaller seeds. Further, alien fruit pulps contained more sugar and more variable (and probably greater) nitrogen per pulp wet weight, and species tended to have longer fruiting seasons than indigenous species. Our analyses suggest that fruit traits could be important in determining invasiveness and could be used to improve pre- and post-border weed risk assessment. Web of Science Many Australia Queensland terrestrial Invasion Hyp. Mutualism Facilitation primary 2843 Belzile, Francois; Labbe, Julie; LeBlanc, Marie-Claire; Lavoie, Claude 2010 Seeds contribute strongly to the spread of the invasive genotype of the common reed (Phragmites australis) journal BIOLOGICAL INVASIONS 12 7 2243 2250 The introduced subspecies of the common reed (Phragmites australis (Cav.) Trin. ex Steud. subsp. australis; Poaceae) is considered one of the most invasive plants in North American wetlands. Given its relatively low seed set and its tremendous capacity to spread via stolons or rhizomes, it has generally been thought that the spread of vegetative diaspores was responsible for the establishment of new populations. To test this hypothesis, we sampled a single plant from each of 345 visually-distinct common reed stands located along the shores of Lake St. Fran double dagger ois (southern Quebec, Canada). With a set of six nuclear microsatellite markers, we distinguished 134 different genotypes. The number of individuals sharing the same genotype ranged from one to 16, and averaged 2.1. Most genotypes were encountered only once. We examined the spatial distribution of the most frequent genotypes and found little evidence of clusters along the lakeshore. These data contradict the hypothesis that a common reed invasion is initiated by the introduction of vegetative diaspores from a few clones. Rather, they clearly support the alternative hypothesis that seeds were the primary diaspores responsible for the establishment of common reed populations. Web of Science Phragmites australis Canada Quebec Field - Observational wetland Wetland Invasion Hyp. Inherent Superiority High Reprod. Output;Clonal Reproduction primary 2844 Le Roux, Johannes J.; Wieczorek, Ania M.; Tran, Carol T.; Vorsino, Adam E. 2010 Disentangling the dynamics of invasive fireweed (Senecio madagascariensis Poir. species complex) in the Hawaiian Islands journal BIOLOGICAL INVASIONS 12 7 2251 2264 Studies investigating the genetic variation of invasive species render opportunities to better understand the dynamics of biological invasions from an ecological and evolutionary perspective. In this study, we investigate fine-scale population genetic structure of invasive Senecio madagascariensis (fireweed) using microsatellite markers to determine levels of genetic diversity and how it pertains to introduction history of this species within and among the Hawaiian Islands. Dispersal patterns were interpreted and, together with a habitat suitability analysis, we aim to describe the potential range expansion of S. madgascariensis within the islands. Bayesian and frequency-based analyses revealed genetic structure with two major genetic demes corresponding to the two fireweed-infested islands of Maui and Hawaii. Both these demes showed further genetic sub-structure, each consisting of three genetically distinct subgroups. Overall, fireweed showed significant levels of inbreeding. Major genetic demes (Maui and Hawaii) differed in observed heterozygosities, inbreeding and genetic structure, each harbouring a large proportion of private alleles. In contrast to the current understanding of fireweed's introduction history between the Hawaiian Islands, fine-scale population genetic parameters suggest that this species has been introduced at least twice, possibly even more, to the archipelago. Spatial analyses also revealed high correlation between genetic similarity and geographical proximity (> 2 km apart) followed by a sharp decline. In addition, a single population was identified that likely resulted from a rare human- or animal-mediated extreme long-distance dispersal event from Maui to Hawaii. Bayesian and likelihood estimates of 'first generation migrants' also concurred that contemporary dispersal occurs more frequently over smaller spatial scales than larger scales. These findings indicate that spread in this species occurs primarily via a stratified strategy. Predictions from habitat suitability models indicate all Hawaiian Islands as highly suitable for fireweed invasion and the movement of propagules to currently uninfested islands and outlying suitable habitats should be avoided to circumvent further expansions of the invasion. Web of Science Senecio madagascariensis USA Hawaii terrestrial Invasion Hyp. Inherent Superiority Effective Disperser primary 2845 Molina-Montenegro, Marco A.; Atala, Cristian; Gianoli, Ernesto 2010 Phenotypic plasticity and performance of Taraxacum officinale (dandelion) in habitats of contrasting environmental heterogeneity journal BIOLOGICAL INVASIONS 12 7 2277 2284 Ecological theory predicts a positive association between environmental heterogeneity of a given habitat and the magnitude of phenotypic plasticity exhibited by resident plant populations. Taraxacum officinale (dandelion) is a perennial herb from Europe that has spread worldwide and can be found growing in a wide variety of habitats. We tested whether T. officinale plants from a heterogeneous environment in terms of water availability show greater phenotypic plasticity and better performance in response to experimental water shortage than plants from a less variable environment. This was tested at both low and moderate temperatures in plants from two sites (Corvallis, Oregon, USA, and El Blanco, Balmaceda, Chile) that differ in their pattern of monthly variation in rainfall during the growth season. We compared chlorophyll fluorescence (photosynthetic performance), flowering time, seed output, and total biomass. Plants subjected to drought showed delayed flowering and lower photosynthetic performance. Plants from USA, where rainfall variation during the growth season was greater, exhibited greater plasticity to water shortage in photosynthetic performance and flowering time than plants from Chile. This was true at both low and moderate temperatures, which were similar to early- and late-season conditions, respectively. However, phenotypic plasticity to decreased water availability was seemingly maladaptive because under both experimental temperatures USA plants consistently performed worse than Chile plants in the low water environment, showing lower total biomass and fewer seeds per flower head. We discuss the reliability of environmental clues for plasticity to be adaptive. Further research in the study species should include other plant traits involved in functional responses to drought or potentially associated with invasiveness. Web of Science Taraxacum officinale USA;Chile Oregon Field - Observational terrestrial Coniferous Forest Invasion Hyp. Plasticity primary 2846 Reiskind, Michael H.; Zarrabi, Ali A.; Lounibos, L. Philip 2010 Invasive leaf resources alleviate density dependence in the invasive mosquito, Aedes albopictus journal BIOLOGICAL INVASIONS 12 7 2319 2328 Interactions between invasive species can have important consequences for the speed and impact of biological invasions. Containers occupied by the invasive mosquito, Aedes albopictus Skuse, may be sensitive to invasive plants whose leaves fall into this larval habitat. To examine the potential for interactions between invasive leaf species and larval A. albopictus, we conducted a field survey of leaf material found with A. albopictus in containers in Palm Beach County, Florida and measured density dependent responses of A. albopictus larvae to two invasive and one native leaf species in laboratory experiments. We found increased diversity of leaf species, particularly invasive species, in areas further from the urbanized coast, and a significant positive association between the presence of Schinus terebinthifolious (Brazilian pepper) and the abundance of A. albopictus. In laboratory experiments, we determined that larval growth and survivorship were significantly affected by both larval density and leaf species which, in turn, resulted in higher population performance on the most abundant invasive species (Brazilian pepper) relative to the most abundant native species, Quercus virginiana (live oak). These results suggest invasive leaf species can alleviate density dependent reductions in population performance in A. albopictus, and may contribute to its invasion success and potential to spread infectious disease. Web of Science Aedes albopictus;Schinus terebinthifolious USA Florida terrestrial Invasion Hyp. Mutualism Facilitation predator 2849 Cameron, Guy N.; Spencer, Stephen R. 2010 ENTOMOFAUNA OF THE INTRODUCED CHINESE TALLOW TREE journal SOUTHWESTERN NATURALIST 55 2 179 192 Entomofauna in monospecific stands of the introduced Chinese tallow tree (Sapium sebiferum) and native mixed woodlands was sampled in 1982 along the Texas coast and compared to samples of arthropods from an earlier study of native coastal prairie and from a study of arthropods in S. sebilerum in 2004. Species diversity, richness, and abundance were highest in prairie, and were higher in mixed woodland than in S. sebiferum. Nonmetric multidimensional scaling distinguished orders and families of arthropods, and families of herbivores in S. sebiferum from mixed woodland and coastal prairie. Taxonomic similarity between S. sebiferum and mixed woodland was 51%. Fauna from S. sebiferum in 2001 was more similar to mixed woodland than to samples from S. sebiferun collected in 1982. These results indicate that the entomofauna in S. sebiferum originated from mixed prairie and that, with time, these faunas became more similar. Species richness and abundance of herbivores was lower in S. sebiferum, but proportion of total species in all trophic groups, except herbivores, was higher in S. sebifintm than mixed woodland. Low concentration of tannin in leaves of S. sebiferum did not explain low loss of leaves to herbivores. Lower abundance of herbivores on introduced species of plants fits the enemy release hypothesis, and low concentration of defense compounds in the face of low number of herbivores fits the evolution of increased competitive ability hypothesis. Web of Science Sapium sebiferum USA Texas Field - Observational terrestrial Deciduous Forest Invasion Hyp. Enemy Release primary 2851 Trtikova, Miluse; Edwards, Peter J.; Guesewell, Sabine 2010 No adaptation to altitude in the invasive plant Erigeron annuus in the Swiss Alps journal ECOGRAPHY 33 3 556 564 The altitudinal distribution of plants is restricted by various environmental factors, with climatic conditions being one of the primary constraints. Here, we investigate what limits the altitudinal range of the introduced species Erigeron annuus in the Swiss Alps. We planted offspring of E. annuus plants originating from different altitudes into two common gardens, one located at an altitude representing the main area of distribution (400 m) and the other close to the current altitudinal limit of E. annuus in Switzerland (1000 m). In both common gardens all established plants survived and grew vigorously during the growing season. However, there was high winter mortality of seedlings at 1000 m. Furthermore, plant phenology was delayed and reproductive output was reduced at 1000 m, although the seeds produced were larger. The general lack of adaptation to altitude and only moderate levels of plasticity suggest that there is little potential for E. annuus to persist beyond its current altitudinal limit in the Swiss Alps. However, climate warming might promote the upward range expansion of E. annuus by reducing winter mortality and by increasing the chance of producing seeds within the growing season. Web of Science Erigeron annuus Switzerland terrestrial Mountain Invasion Hyp. Evolution in General primary 2852 Carboni, M.; Santoro, R.; Acosta, A. T. R. 2010 Are some communities of the coastal dune zonation more susceptible to alien plant invasion? journal JOURNAL OF PLANT ECOLOGY-UK 3 2 139 147 Aims Coastal areas, and in particular coastal dunes, are ecosystems strongly affected by the invasion of alien plants. However, few attempts have ever been made to quantify alien species incidence in different communities along the coastal zonation. This work aims to analyze the distribution of alien plants along the coastal zonation of sandy shores on the Tyrrhenian coast, addressing specifically differences among plant communities in abundance of alien plants. Methods The study was performed on recent dunes (Holocene) of the central western coast of Italy. We selected dune landscapes where invasion processes were particularly evident. Vegetation plots were randomly sampled and through cluster analysis, we identified six plant communities corresponding to the typical zonation described for the Tyrrhenian sandy coast of Central Italy. We evaluated and compared frequency and abundance of invasion in these different communities. Further, we investigated how propagule pressure (measured using as proxy human structures) contributed to the observed invasion patterns. Important Findings We found a relatively low total number of aliens but also a differential distribution pattern and strong abundance of some of the aliens in specific sectors of the vegetation zonation. The perennial community of transition dunes appears most affected by invasion processes, related almost exclusively to the frequent and widespread Carpobrotus aff. acinaciformis. This alien species reaches high cover values, apparently lowering cover of native species of transition dune plant communities. Higher levels of invasion in the transition dune can be partially explained because of greater propagule pressure in this section of the dune profile. Our findings thus have important conservation and management implications since transition dune communities with Crucianella maritima are rare and protected (sensu Habitat 92/43/EEC Directive) along the entire Italian coast. Web of Science Many Italy Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Propagule Pressure primary 2853 Scherber, Christoph; Mwangi, Peter N.; Schmitz, Martin; Scherer-Lorenzen, Michael; Bessler, Holger; Engels, Christof; Eisenhauer, Nico; Migunova, Varvara D.; Scheu, Stefan; Weisser, Wolfgang W.; Schulze, Ernst-Detlef; Schmid, Bernhard 2010 Biodiversity and belowground interactions mediate community invasion resistance against a tall herb invader journal JOURNAL OF PLANT ECOLOGY-UK 3 2 99 108 Aims Species-rich plant communities are hypothesized to be more resistant against plant invasions because they use resources in a more efficient way. However, the relative contributions of aboveground competition and belowground interactions for invasion resistance are still poorly understood. Methods We compared the performance of Knautia arvensis transplants growing in plots differing in plant diversity both under full competition and with shoots of neighbors tied back to determine the relative strength of aboveground competition in suppressing this test invader without the confounding effect of shading. In addition, we assessed the effects of belowground competition and soil-borne pathogens on transplant performance. Important Findings Both aboveground competition and plant species richness strongly and independently affected invader performance. Aboveground biomass, height, leaf mass per area and flowering of transplanted individuals of K. arvensis decreased with increasing species richness of the host community. Species-rich and species-poor communities both imposed equally strong aboveground competition on K. arvensis. However, belowground interactions (especially belowground root competition) had strong negative effects on transplant performance. In addition, the presence of grasses in a plant community further reduced the performance of K. arvensis. Our results suggest that belowground competition can render species-rich host communities more suppressive to newly arriving species, thus enhancing community invasion resistance. Web of Science Knautia arvensis Germany terrestrial Invasion Hyp. Community Species Richness primary 2856 Netten, Jordie J. C.; Arts, Gertie H. P.; Gylstra, Ronald; van Nes, Egbert H.; Scheffer, Marten; Roijackers, Rudi M. M. 2010 Effect of temperature and nutrients on the competition between free-floating Salvinia natans and submerged Elodea nuttallii in mesocosms journal FUNDAMENTAL AND APPLIED LIMNOLOGY 177 2 125 132 In many aquatic ecosystems, free-floating plants compete with submerged plants for nutrients and light. Being on top of the water surface free-floating plants are superior competitors for light. Submerged plants can take up nutrients from the sediment and the water column, hereby reducing these levels for free-floating plants. Global warming may change chances of successful species invasion and can alter species dominance. We studied the combined effects of nutrient loading and increased temperature on the competition between the potentially invasive free-floating Salvinia natans (L.) All. and the naturalized submerged Elodea nuttallii Planch. St. John by an outdoor mesocosm experiment under temperate climate conditions (The Netherlands) over a period of 71 days. The free-floating S. natans benefited from increased temperature and increased nutrient loading and limited the chances for the submerged E. nuttallii to take advantage of these changed conditions. S. natans substantially increased temperature in the top layer, while limiting the temperature increase below the mat. Our results suggest that with global warming, invasive free-floating plants might become more successful at the expense of submerged plants. Web of Science Salvinia natans The Netherlands Garden lentic Invasion Hyp. Climate Change primary 2858 Kalogirou, S.; Corsini, M.; Kondilatos, G.; Wennhage, H. 2007 Diet of the invasive piscivorous fish Fistularia commersonii in a recently colonized area of the eastern Mediterranean journal BIOLOGICAL INVASIONS 9 8 887 896 The composition of the diet of the Indo-Pacific cornetfish Fistularia commersonii from the SE Aegean Sea is described. The stomach contents of 245 specimens collected between September 2004 and March 2005 were examined. Dietary comparisons were made reflecting the relationship between diet composition, time of year, and fish size. Correlation between predator length and prey length was significant. The diet of the blue cornetfish consists of 96% by number and 99.95% by weight of fish. Size classification and habitat of prey groups (benthic, supra-benthic, and pelagic) showed that with increased body length the blue cornetfish extended its diet to larger prey and more generalist feeding. Spicara smaris, Boops boops, and Mullidae spp. were the most abundant prey by weight whereas a variety of small benthic fish (especially gobiids) and newly hatched fish constituted the largest number of prey items. Length-weight relationships for the cornetfish were investigated. Web of Science Fistularia commersonii Aegean Sea Field - Observational marine Invasion Hyp. Plasticity predator 2859 Qin, Bo; Lau, Jennifer A.; Kopshever, Joseph; Callaway, Ragan M.; McGray, Heather; Perry, Laura G.; Weir, Tiffany L.; Paschke, Mark W.; Hierro, Jose L.; Yoder, John; Vivanco, Jorge M.; Strauss, Sharon 2007 No evidence for root-mediated allelopathy in Centaurea solstitialis, a species in a commonly allelopathic genus journal BIOLOGICAL INVASIONS 9 8 897 907 Phytotoxicity bioassays and pot experiments using activated carbon both suggest that Centaurea solstitialis (yellow star-thistle) does not rely on phytotoxic root exudates for invasion of California grasslands. Pot experiments in which five native species were grown in the presence/absence of C. solstitialis and in the presence/absence of activated carbon (fully crossed design) showed that C. solstitialis competitively suppressed native species, but did not inhibit them through allelochemicals. In separate experiments examining the role of root exudates in invasion success, treatment with crude root exudates and chloroform-extracted root exudates from C. solstitialis reduced growth of the model plant Arabidopsis thaliana. However, high concentrations of the exudates (50%, v/v or 500 mu g mL(-1)) were required to inhibit A. thaliana growth and did not result in A. thaliana mortality, suggesting the presence of only a weak growth inhibitor. Moreover, high concentrations of C. solstitialis crude root exudates did not affect the growth of five native grass species often displaced by C. solstitialis invasions in California grasslands. Finally, root exudates collected from C. solstitialis had weaker effects on a native California root parasite, Triphysaria versicolor, than root exudates collected from Zea mays, a species not renowned for its competitive or invasive capabilities. Our results suggest that, while C. solstitialis might possibly *be persuaded to yield a product that is toxic to one species or another* (Population biology of plants, Academic, 1977), we find no evidence that allelopathic root exudates play a role in the competitive success of this invasive. Web of Science Centaurea solstitialis USA California Field - Observational terrestrial Grassland Invasion Hyp. Novel Weapons primary 2863 Stringer, Lloyd D.; Haywood, John; Lester, Philip J. 2007 The influence of temperature and fine-scale resource distribution on resource sharing and domination in an ant community journal ECOLOGICAL ENTOMOLOGY 32 6 732 740 1. In order to coexist in sympatry, subordinate species must somehow obtain resources that dominant taxa may generally control. This study examines the response of an ant community to fine-scale variation in resource distribution, as a mechanism enabling resource acquisition by subordinates in the presence of dominant taxa. Food (6 g) was portioned as one, eight, or 64 items in a 0.4-m(2) area, centred on nests of Monomorium sydneyense Forel, considered the most dominant ant in the area. This ant is a newly established exotic species in our study site of Tauranga, New Zealand. 2. As the number of food items increased, a significant increase in the number of species utilising the food was observed, associated with an increase in the non-utilised proportion of food items. 3. The changing occupation rates of food items by M. sydneyense and three other species were modelled against soil surface temperature and the varying dispersion rates of the food resource. Significant main effects of food density, site, species, and temperature were observed on the probability of food being occupied by a species. However, there were also significant interaction effects, making it impossible to interpret the main effects in isolation. Monomorium sydneyense dominated a smaller proportion of resources in trials with increased resource distribution and cooler temperatures, allowing more species to access resources. 4. There was considerable variation between species in their responses to variation in temperature and food distribution. Although most species were able to respond to increasing resource dispersion, species that were in low abundance apparently could not. However, even species that could respond to increasing resource dispersion were limited in the number of resources they could secure. Web of Science Monomorium sydneyense New Zealand Tauranga Field - Observational;Theoretical/Modeling terrestrial Urban Fundamentals omnivore 2864 Ashley, Michael C.; Longland, William S. 2007 Microsatellite evidence of facultative outcrossing in cheatgrass (Bromus tectorum): Implications for the evolution of invasiveness journal PLANT SPECIES BIOLOGY 22 3 197 204 The presence or absence of heterozygous individuals and overall genetic variation were determined for the invasive exotic annual grass Bromus tectorum from four populations in northern Nevada using seven species-specific polymorphic di-nucleotide microsatellite markers. Allelic polymorphisms were found in all populations, but not at all loci within each population. Mean genetic diversity across loci within populations ranged from 0.009 +/- 0.006 to 0.551 +/- 0.073, across populations x = 0.234 +/- 0.043. Fifteen individuals from the total sample (8.24%) were heterozygous at 1-4 loci. Two populations exhibited no heterozygosity and the remaining two populations had relative heterozygote proportions of 22.5% and 12.1%. Facultative outcrossing is discussed as an aspect of reproductive plasticity in cheatgrass and as a mechanism promoting the evolution of invasive genotypes. Web of Science Bromus tectorum USA Nevada Field - Observational terrestrial Grassland Invasion Hyp. Evolution of Increased Competitive Ability primary 2866 Hawkes, Christine V. 2007 Are invaders moving targets? The generality and persistence of advantages in size, reproduction, and enemy release in invasive plant species with time since introduction journal AMERICAN NATURALIST 170 6 832 843 Successful plant invasions are often attributed to increased plant size, reproduction, or release from natural enemies, but the generality and persistence of these patterns remains widely debated. Meta-analysis was used to quantitatively assess invasive plant performance and release from enemy damage and how these change with residence time and geographic distribution. Invasive plants were compared either in their introduced and home ranges or with native congeners in the introduced range. Invasive plants in the introduced range were generally larger, allocated more to reproduction, and had lower levels of herbivore damage compared with conspecifics in the home range; pathogen attack, however, varied widely. In congener comparisons, invasive and native plants did not differ in size or herbivory, but invaders did allocate less to reproduction and had lower levels of pathogen damage. Time since introduction was a significant nonlinear predictor of enemy release for both herbivores and pathogens, with initial release in recently arrived species and little to no release after 50 to 200 years. Geographic distribution was also a significant nonlinear predictor of enemy release. The observed nonlinear relationships are consistent with dynamic invasions and may define targets for eradication efforts if these patterns hold up for individual species. Web of Science Many Field - Observational;Statistical/Meta-analysis;Review terrestrial Invasion Hyp. Enemy Release primary 2867 Lyons, Devin A.; Van Alstyne, Kathryn L.; Scheibling, Robert E. 2007 Anti-grazing activity and seasonal variation of dimethylsulfoniopropionate-associated compounds in the invasive alga Codium fragile ssp tomentosoides journal MARINE BIOLOGY 153 2 179 188 In this study, we present evidence that the invasive alga Codium fragile ssp. tomentosoides is chemically defended against grazing by a wound-activated chemical defense involving dimethylsulfoniopropionate (DMSP) and the products of its cleavage, dimethylsulfide (DMS), and acrylic acid (AA). DMSP in C. fragile ssp. tomentosoides was present throughout the year, but concentrations varied seasonally and were highest in the winter. Intra-thallus variation was neither large, nor consistent over time. High DMSP concentrations were uncommon among northwestern Atlantic macrophytes. Of 26 other species tested, only two, Ulva lactuca and Polysiphonia harveyi contained concentrations comparable to, or higher than, those of C. fragile ssp. tomentosoides. DMS and AA, both individually and together, deterred grazing by the green sea urchin Strongylocentrotus droebachiensis at *natural* concentrations. These results suggest that DMS and AA contribute to the avoidance of C. fragile ssp. tomentosoides by S. droebachiensis. As a result, the production of DMSP and its subsequent cleavage, upon injury, may reduce herbivory on C. fragile ssp. tomentosoides and contribute to its success. Web of Science Codium fragile marine Invasion Hyp. Novel Weapons primary 2868 Dejean, A.; Kenne, M.; Moreau, C. S. 2007 Predatory abilities favour the success of the invasive ant Pheidole megacephala in an introduced area journal JOURNAL OF APPLIED ENTOMOLOGY 131 10 625 629 The invasive African big-headed ant, Pheidole megacephala, is a dominant species in the many areas it has invaded. We examined whether one potential reason for its ecological success might be its predatory efficiency. We compared the density of termite nests in an area of Mexico invaded by P. megacephala with an adjacent area where P. megacephala is not present. We also compared the success of P. megacephala in preying on termites with that of 13 native ant species. We found that termite nest density was significantly lower in areas invaded by P. megacephala (0.33 vs. 1.05 nests per 30 m transect). In field trials, we established that P. megacephala workers were significantly more successful at capturing termite workers from termite nest fragments than even the most successful native ant species, Dorymyrmex pyramicus. For both P. megacephala and D. pyramicus, single scouts could trigger the mass recruitment of nestmates, but P. megacephala was able to recruit greater numbers of nestmates. Combined with their aggressiveness towards other ant species, their highly efficient predatory capacities help explain the ecological success of P. megacephala and demonstrate how it can be a major threat to invertebrate biodiversity in the areas it invades. Web of Science Pheidole megacephala Mexico terrestrial Invasion Hyp. Inherent Superiority Superior Competitor predator 2870 D'Amours, Olivier; Scheibling, Robert E. 2007 Effect of wave exposure on morphology, attachment strength and survival of the invasive green alga Codium fragile ssp tomentosoides journal JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 351 2 129 142 Hydrodynamic forces area key factor influencing morphology and survival of marine algae in intertidal and shallow subtidal habitats. Since 1989, the invasive green alga Codium fragile ssp. tomentosoides has spread rapidly in Atlantic Canada, forming dense stands in intertidal pools and shallow subtidal habitats. We measured the morphology and attachment strength of Codium over 4 seasons at 3 sites of differing wave exposure and water motion near Halifax, Nova Scotia. The bushiness index (circumference-to-length ratio) of Codium varied inversely with the degree of wave exposure and water motion. Attachment strength was weakly related to thallus morphology (circumference) and generally did not differ between sites and seasons. We examined the effect of morphology on survival of Codium by experimentally trimming the thallus (by cutting 33 or 66% of branches) in a field experiment over 1 year. Trimming, which simulated natural fragmentation, had a positive effect on survival relative to untrimmed controls, particularly at the most wave-exposed site and after a major storm event (Hurricane Juan), and the magnitude of this effect was related to the degree of trimming. We used a flume tank to measure drag forces at different flow velocities (0.3-0.5 m s(-1)) on experimentally trimmed plants (using the same levels of trimming as in the field experiment). Drag was positively related to plant circumference and water velocity, and negatively related to the degree of trimming. Attachment strength of these plants was 10 to 22 times greater than the drag force, suggesting that Codium is dislodged when flow velocities greatly exceed 0.5 m s(-1). The ratio of attachment strength to drag force decreased with circumference, indicating a greater risk of dislodgment with increasing plant size. (C) 2007 Elsevier B.V. All rights reserved. Web of Science Codium fragile Canada Nova Scotia marine Intertidal/Near Shore Invasion Hyp. Inherent Superiority primary 2872 Enright, Stephanie M.; Cipollini, Don 2007 Infection by powdery mildew Erysiphe cruciferarum (Erysiphaceae) strongly affects growth and fitness of Alliaria petiolata (Brassicaceae) journal AMERICAN JOURNAL OF BOTANY 94 11 1813 1820 Garlic mustard (Alliaria petiolata) is an invasive biennial that negatively impacts plant and animal communities throughout North America and lacks significant herbivory in its invasive range. Throughout Ohio, many garlic mustard populations support the powdery mildew fungus Erysiphe cruciferarum, although disease incidence varies among populations and environments. Effects of infection on plant growth, as well as both plant and fungal responses to drought and light conditions, were examined on greenhouse-grown, first-year garlic mustard plants. Also, the effects of the fungus on plant growth and fitness were studied in a naturally growing population of second-year plants in the field. Powdery mildew significantly reduced growth of first-year plants in the greenhouse, eventually causing complete mortality. Simulated drought slowed both plant growth and disease development, independent of light conditions. In the field, plants with little incidence of disease after their first year grew taller during their second year, producing significantly more siliques and twice as many seeds as heavily diseased plants did. Seed germination rates did not differ between plants with different levels of disease severity. Consistent reductions in survival, growth, and fitness caused by fungal infection may reduce populations of garlic mustard. These effects may be more evident in moist sites that favor fungal development. Web of Science Alliaria petiolata USA Ohio Field - Observational terrestrial Deciduous Forest Invasion Hyp. Enemy Release primary 2877 Stout, Jane C. 2007 Reproductive biology of the invasive exotic shrub, Rhododendron ponticum L. (Ericaceae) journal BOTANICAL JOURNAL OF THE LINNEAN SOCIETY 155 3 373 381 The reproductive biology of an exotic species will affect its ability to become naturalized and invasive in non-native habitats. Rhododendron ponticum is an ecologically damaging exotic weed in the British Isles, which spreads predominantly by seed. I investigated how inbreeding and outcrossing affect seed production and germination in a wild population of this species in Ireland. Experimental manipulations revealed low fruit and seed set when insects were excluded from flowers, suggesting that this species has limited capability for spontaneous autogamy. Hand-pollination treatments showed that, although flowers are self-compatible (with self and same plant pollen), higher levels of seed set occur following outcrossing (xenogamy). There was no significant difference in rate of germination of seeds from inbred or outcrossed treatments. The addition of xenogamous pollen to open flowers did not increase fruit or seed set, suggesting that flowers in this population are not pollen limited: native generalist pollinators, mainly bumblebees (Bombus spp.), are providing an adequate pollinator service. This work demonstrates that outcrossing increases seed set and pollinators are required to facilitate this. Hence, generalist native pollinators can promote invasion by exotic plants. Native pollinators can clearly play an important part in alien species invasion. (C) 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155, 373-381. Web of Science Rhododendron ponticum United Kingdom Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Mutualism Facilitation primary 2878 Garrett, Lucy J. H.; Jones, Carl G.; Cristinacce, Andrew; Bell, Diana J. 2007 Competition or co-existence of reintroduced, critically endangered Mauritius fodies and invasive Madagascar fodies in lowland Mauritius? journal BIOLOGICAL CONSERVATION 140 2 19 28 Habitat destruction and introductions of invasive species have been primary causes of endemic species loss on oceanic islands. This paper addresses the question of whether a reintroduced population of a critically endangered island endemic, the Mauritius fody (Foudia rubra) is competing or co-existing with an exotic congener, the Madagascar fody (F. madagascariensis). We investigated habitat use and feeding ecology of the Mauritius fody during two early phases of its reintroduction onto a restored islet, and compared these parameters with the sympatric population of Madagascar fodies. The number of Mauritius fody territories increased from 4 to 20 in a seven month period following release, and overall mean territory area (c. 1 ha) was significantly larger than that of the more abundant Madagascar fody (c. 0.07 ha). The initial four territories were located in mature coastal forest, whilst those of the Madagascar fody were characterised by open canopy, smaller trees and grass-dominated ground cover. Mauritius fodies foraged mainly in dead leaves for insects, whilst the Madagascar fody fed primarily on the seeds of a native grass species. Mauritius fody territories later expanded to include a range of habitats. Differing ecological requirements indicate that divergence between these congeners may be sufficient for them to coexist and exploit contrasting resources on restored islets. We discuss the implications of these findings for both the long-term restoration of the Mauritius fody and other avian recovery programmes and highlight the critical importance of long-term post-release monitoring to assess the success of reintroduction to offshore islets as a long-term conservation strategy. (C) 2007 Elsevier Ltd. All rights reserved. Web of Science Fodia madagascariensis Mauritius Field - Observational terrestrial Tropical Forest Fundamentals predator 2879 Dupont, L.; Viard, F.; David, P.; Bishop, J. D. D. 2007 Combined effects of bottlenecks and selfing in populations of Corella eumyota, a recently introduced sea squirt in the English Channel journal DIVERSITY AND DISTRIBUTIONS 13 6 808 817 The success of an exotic species depends notably on its capacity to initiate a new population from a few individuals, to survive genetic bottlenecks and to adapt locally. Species with multiple reproductive strategies (e.g. mixed-mating system with both self-and cross-fertilization) can be efficient colonizers. Herein we focus on Corella eumyota, an exotic ascidian that has rapidly invaded English Channel coasts in recent years. Interestingly, this brooding hermaphroditic ascidian is capable of self-fertilization in the laboratory. We developed 12 microsatellite markers from an enriched library of genomic DNA to investigate the level of inbreeding and selfing in two putatively native populations (South Africa, N = 34, and New Zealand, N = 28) and to examine if founder effects were possibly associated with its recent introduction in two French populations (Perros-Guirec, N = 22 and Brest; N = 25). Genetic polymorphism was very low in both native populations (i.e. less than 60% of the loci were polymorphic) and even lower in the introduced populations, one of which was monomorphic at all loci, suggesting a recent bottleneck. F is and a new method based on multi-locus heterozygosity were used to provide estimates of inbreeding. A high selfing rate was inferred in the South Africa population with both methods (s = 0.90), whereas in the other native population (New Zealand) a lower but significant estimate of selfing rate (s = 0.29) was obtained with the multi-locus method. This variability of population selfing rate might be explained by a mixed-mating system, allowing C. eumyota to reproduce through inbreeding and outbreeding according to mating possibilities; this trait may have favoured the rapid establishment of new populations in Europe. Web of Science Corella eumyota France Field - Observational marine Intertidal/Near Shore Invasion Hyp. Inherent Superiority Self Compatible filter 2880 Sutton, Jason R.; Stohlgren, Thomas J.; Beck, K. George 2007 Predicting yellow toadflax infestations in the flat tops wilderness of colorado journal BIOLOGICAL INVASIONS 9 7 783 793 Understanding species-environment relationships is important to predict the spread of non-native species. Yellow toadflax (Linaria vulgaris Mill.) is an invasive perennial recently found in the Flat Tops Wilderness of the White River National Forest on the western slope of the Colorado Rocky Mountains. We hypothesized yellow toadflax occurrence could be predicted from easily measured site characteristics. We used logistic regression with stepwise selection to generate a model to predict yellow toadflax occurrence on a particular plot based on that site's physical characteristics. The experimental design was a paired-plot study in two locations using circular 1,018-m(2) plots. Sixty-eight plots that did not contain yellow toadflax and 65 plots that contained yellow toadflax were sampled at the Ripple Creek site in 1999. In 2000, 54 non-toadflax plots and 55 toadflax-containing plots were sampled in the Marvine Creek site. Site characteristics sampled included: vegetation type; under-canopy light level; slope; aspect; soil properties; presence of disturbance, trails, and/or water; and total species richness. A model that correctly classified > 90% of the 242 plots sampled included two vegetation type parameters, the presence of trails, and total species richness. Yellow toadflax is most often found in areas that were open-canopy sites, along trails, and with higher species diversity plots (> 23 species). This approach can be used for other species in other areas to rapidly identify areas vulnerable to invasion. Web of Science Linaria vulgaris USA Colorado White River National Fores Field - Observational terrestrial Mountain Invasion Hyp. Community Species Richness;Disturbance primary 2881 Huels, Joerg; Otte, Annette; Eckstein, R. Lutz 2007 Population life-cycle and stand structure in dense and open stands of the introduced tall herb Heracleum mantegazzianum journal BIOLOGICAL INVASIONS 9 7 799 811 Populations of the introduced Heracleum mantegazzianum consist of dense central stands, which gradually give way to open stands towards the margins. To analyse whether open stands are due to unsuitable conditions or represent the invading front for further spread, we studied life-cycle, population dynamics, stand structure and soil conditions of open and dense stands over two transition periods. Populations decreased during the first interval but increased after the extremely dry and warm summer of 2003 during the second interval. Open stands had shorter generation times, lower height, smaller proportions of small individuals and were less in equilibrium with the environment than dense stands. In open stands, growth to higher stages was most important, while in dense stands delayed development (self-loops) had a strong effect on population growth; stasis and fecundity contributed most to the difference in lambda between stand types. By petiole extension H. mantegazzianum may raise its leaves just above the resident vegetation. Therefore, younger stages develop faster in open stands, whereas strong competition by conspecific adults leads to longer generation times and a higher proportion of small individuals in dense stands. Disturbance due to extreme climatic conditions in summer 2003 equalised population dynamics of both stand types. Life-cycle variation between stand types makes it difficult to infer simple management rules. However, our data suggest that small and/or open stands of H. mantegazzianum may eventually serve as initials for further spread after land-use changes, whereas dense stands are stable and may represent sources of propagules. Web of Science Heracleum mantegazzianum Germany Field - Observational terrestrial Deciduous Forest Invasion Hyp. Plasticity;Disturbance primary 2882 Plowes, Robert M.; Dunn, John G.; Gilbert, Lawrence E. 2007 The urban fire ant paradox: native fire ants persist in an urban refuge while invasive fire ants dominate natural habitats journal BIOLOGICAL INVASIONS 9 7 825 836 In contrast to the widespread extirpation of native fire ants (Solenopsis geminata) across southern US following the invasion by imported red fire ants (S. invicta), some residential areas of Austin form unexpected refuges for native fire ants. Ironically, these urban environments provide refuges for the native fire ants while adjacent natural habitats have been overrun by invasive fire ants. Resistance to invasive fire ants in these urban areas occurs mainly in older residential properties constructed prior to the S. invicta invasion, while more recent construction has allowed establishment by S. invicta. The invasive ability of S. invicta is often attributed to escape from parasitoids and efficient dispersal of polygyne multiple queen colonies. Here we also show the importance of landscape parameters in the invasion process, where low levels of disturbance and continuous plant cover in older residential areas form possible barriers to colonization. Dense leaf cover (high NDVI) was also found to be associated with native ant refuges. Long term residential land ownership may have resulted in lower recent disturbance levels and increased plant cover that support refuges of native fire ants. Web of Science Solenopsis invicta United States Field - Observational terrestrial Invasion Hyp. Enemy Release predator 2883 Whitcraft, Christine R.; Talley, Drew M.; Crooks, Jeffrey A.; Boland, John; Gaskin, John 2007 Invasion of tamarisk (Tamarix spp.) in a southern California salt marsh journal BIOLOGICAL INVASIONS 9 7 875 879 Exotic plants have been demonstrated to be one of the greatest threats to wetlands, as they are capable of altering ecosystem-wide physical and biological properties. One of the most problematic invaders in the western United States has been salt cedar, Tamarix spp., and the impacts of this species in riparian and desert ecosystems have been well-documented. Here we document large populations of tamarisk in the intertidal salt marshes of Tijuana River National Estuarine Research Reserve, a habitat not often considered vulnerable to invasion by tamarisk. Initial research demonstrates that there are multiple species and hybrids of Tamarix invading the estuary and that the potential impact of tamarisk within this salt marsh is significant. This highlights the need for managers and scientists to be aware of the problems associated with tamarisk invasion of coastal marine habitats and to take early and aggressive action to combat any incipient invasion. Web of Science Tamarix spp. United States California Field - Observational estuarine Invasion Hyp. Inherent Superiority;Hybridization Broad Tolerances primary 2884 Ren, Ming X.; Zhang, Quan G. 2007 Clonal diversity and structure of the invasive aquatic plant Eichhornia crassipes in China journal AQUATIC BOTANY 87 3 242 246 The information on diversity and spatial distribution of clones of an invasive clonal plant is crucial for the understanding of its clonal structure and invasive history. In this paper, random amplified polymorphic DNA (RAPD) markers were used to explore the clonal diversity and clonal structure of Eichhornia crassipes (Mart.) Solms in natural populations, and their possible effects on the plant success as an invader are also discussed. Five populations covering the entire distribution area in China were studied, sampling 43 individuals per population at an interval of I m in a sampling plot. Twelve RAPD primers produced 69 reproducible bands, with 22 being polymorphic. Only five RAPD phenotypes (clones) were detected in these five populations, but each population consisted of at least three clones, contrary to the traditional expectations that E. crassipes populations should be monoclonal. The diversity of clones within populations is thought to be mainly resulted from multiple introductions by humans. The evenness of distribution of clones varied slightly and most clones were widespread, suggesting clonal growth is the predominant mode of regeneration in all the populations. A single clone dominated each population and this clone might be the first one introduced into China or the genotype with a higher phenotypic plasticity, which could survive and reproduce via clonal growth in various habitats. The clones in each population were highly intermixed, especially in river populations, suggesting this species has a guerilla clonal structure which can be facilitated by water current. (c) 2007 Elsevier B.V. All rights reserved. Web of Science Eichhornia crassipe China Field - Observational lentic;lotic Invasion Hyp. Inherent Superiority Clonal Reproduction primary 2885 Carpintero, S.; Retana, J.; Cerda, X.; Reyes-Lopez, J.; De Reyna, L. Arias 2007 Exploitative strategies of the invasive Argentine ant (Linepithema humile) and native ant species in a southern Spanish pine forest journal ENVIRONMENTAL ENTOMOLOGY 36 5 1100 1111 The Argentine ant, Linepithema humile (Mayr, 1868), is displacing native ant species in Donana National Park (Spain). This paper discusses the results of experiments aimed at analyzing exploitation competition between the invading species and other ant species in a park community. The Argentine ant was found to implement several strategies favoring its success in exploitation competition: mass recruitment, use of various microhabitats (on the ground and in trees), and activity over a wide range of temperatures. Although these strategies were not exclusive to L. humile, their joint use, together with the large number of workers forming each *unicolony,* conferred a clear advantage for resource exploitation. Some native species were more severely affected than others by the presence of L. humile in terms of both abundance and behavior. The worst affected species were those whose ecological cbaracteristics were similar to those of the Argentine ant, e.g., Pheidole pallidula (Nylander, 1849); the species least affected was Cataglyphis floricola Tinaut, 1993, possibly because of its subordinate and thermophilous nature (little overlap of daily activity rhythms with the exotic species). Web of Science Linepithema humile Spain Donana National Park Field - Experimental terrestrial Coniferous Forest Invasion Hyp. Inherent Superiority Broad Tolerances omnivore 2886 Becker, Leandro A.; Pascual, Miguel A.; Basso, Nestor G. 2007 Colonization of the southern Patagonia ocean by exotic Chinook salmon journal CONSERVATION BIOLOGY 21 5 1347 1352 Anadromous salmonids have been particularly successful at establishing wild populations in southern Patagonia, in contrast to their limited success elsewhere outside their native ranges. The most recent such discovery is a spawning population of Chinook salmon in the Santa Cruz River, which flows into the Atlantic Ocean from Argentina. We used mitochondrial DNA analysis to discriminate between alternative potential sources of this population and were able to discard in situ introductions of fish imported directly from California in the early twentieth century. Our results showed that the fish most likely came from Puget Sound, Washington, imported into southern Chile for salmon-ranching experiments in the 1980s. This finding provides concrete evidence of colonization of Atlantic rivers from Pacific locations. The southern Pacific and Atlantic oceans provide a favorable marine environment for the success of invading salmon. In particular, the waters associated with fjords, southern channels, and the inshore portion of the Patagonian shelf provide a rather bounded, continuous waterway for exotic anadromous salmonids, rich in diverse forage species. Web of Science Oncorhynchus tshawytscha Argentina Field - Observational lotic Invasion Hyp. Empty Niche predator 2887 Bartuszevige, Anne M.; Hrenko, Rikki L.; Gorchov, David L. 2007 Effects of leaf litter on establishment, growth and survival of invasive plant seedlings in a deciduous forest journal AMERICAN MIDLAND NATURALIST 158 2 472 477 Disturbance often promotes plant invasion. Small disturbances to the forest floor expose bare soil to light which may promote seed germination and establishment. We tested the hypothesis that small disturbances to the litter layer allow invasive species to become established in forest interiors. We found that seedlings of the invasive shrub Lonicera maackii were found in sites with significantly lower leaf litter mass than regularly spaced points along a transect. We then investigated establishment and survival of L. maackii and the invasive biennial Alliaria petiolata in plots randomly assigned to three treatments: litter removed, litter added and control. Significantly more L. maackii seedlings established in the litter removed and control plots than the litter added treatments, but there was no effect on survival. Significantly more A. petiolata seedlings established in the litter removed plots than in the control or litter added treatments. Survival of established A. petiolata seedlings was significantly greater in control than in litter removed plots, but the final number of A. petiolata seedlings was greatest in the litter removed treatment. Our results confirm that bare patches of soil in the forest interior are colonization sites for invasive plant species. Web of Science Alliaria petiolata; Lonicera maackii United States Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 2888 Peterson, A. Townsend; Williams, Richard; Chen, Guojun 2007 Modeled global invasive potential of Asian gypsy moths, Lymantria dispar journal ENTOMOLOGIA EXPERIMENTALIS ET APPLICATA 125 1 39 44 Asian populations of gypsy moths, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), remain poorly characterized - indeed, they are not presently accorded any formal taxonomic status within the broader species. Their ecology is similarly largely uncharacterized in the literature, except by assumption that it will resemble that of European populations. We developed ecological niche models specific to Asian populations of the species, which can in turn be used to identify a potential geographic distributional area for the species. We demonstrated statistically significant predictivity of distributional patterns within the East Asian range of these populations; projecting the Asian ecological niche model to Europe, correspondence with European distributions was generally good, although some differences may exist; projecting the ecological niche model globally, we characterized a likely potential invasive distribution of this set of populations across the temperate zone of both Northern and Southern Hemisphere. Web of Science Lymantria dispar Asia Field - Observational terrestrial Deciduous Forest Invasion Hyp. Preadaptation to Climate herbivore 2890 West, Elizabeth J.; Bames, Peter B.; Wright, Jeffrey T.; Davis, Andrew R. 2007 Anchors aweigh: Fragment generation of invasive Caulerpa taxifolia by boat anchors and its resistance to desiccation journal AQUATIC BOTANY 87 3 196 202 We use two experiments to assess the role of anthropogenic activities in disseminating the invasive alga, Caulerpa taxifolia. First, we tested the hypothesis that the removal of fragments of C. taxifolia from an estuary would be dependent on anchor type (sand versus rock) and anchor attachment (chain versus rope). Second, we hypothesised that the viability of different sized clumps (1, 5 and 10 g dry weight) of C. taxifolia would be dependent on aerial exposure (I h, I day and 3 days) and environmental conditions (sun versus shade, damp rope versus no rope). Fragments of C taxifolia were consistently removed by anchors regardless of the anchor type; overall, 82% of anchors lowered into C. taxifolia beds removed fragments. Rock and sand anchors removed similar sized clumps of C. taxifolia (up to 15 g dry weight), while chain attachments removed significantly larger clumps compared to ropes (up to 0.5 g dry weight). Once removed from the water, fragment survivorship increased with clump size, protection from desiccation (i.e. greatest under damp shaded ropes) and decreased with length of aerial exposure. Most shaded clumps survived I h of aerial exposure, while none, irrespective of their size, survived 3 days. Our study confirms that the anchoring of vessels removes fragments of C. taxifolia from estuaries and that conditions inside anchor lockers may enhance fragment survivorship. Thus, vessels may be an important vector for dispersal of C. taxifolia within and between estuaries. (c) 2007 Elsevier B.V. All rights reserved. Web of Science Caulerpa taxifolia Australia Field - Experimental estuarine Invasion Hyp. Inherent Superiority Effective Disperser;Clonal Reproduction primary 2892 Kirkendall, Lawrence R.; Odegaard, Frode 2007 Ongoing invasions of old-growth tropical forests: establishment of three incestuous beetle species in southern Central America (Curculionidae : Scolytinae) journal ZOOTAXA 0 1588 53 62 Old- growth tropical forests are widely believed to be immune to the establishment of alien species. Collections from tropical regions throughout the world, however, have established that this generalization does not apply to inbreeding host generalist bark and ambrosia beetles. Scolytine saproxylophages are readily spread by shipping, inbreeders can easily establish new populations, and host generalists readily find new breeding material, apparently regardless of stage of forest succession. Consequently, many inbreeding scolytines are globally distributed and abundant in all forest types, often being among the dominant species in their wood- borer communities. We report the recent introductions to lower Central America of two Old World inbreeding ambrosia beetles: Xylosandrus crassiusculus, which breeds primarily in smaller diameter trunks, small branches, and twigs, and Xyleborinus exiguus, which is apparently not size selective. We also document the establishment of Euwallacea fornicatus in the region, known previously from a single collection in Panama. Xylosandrus crassiusculus and E. fornicatus are notorious agricultural and forestry pests, as are several previously established alien species in the region. Studying the spread of species such as these three new arrivals into millions of years- old faunas could help us to understand if the saproxylic communities of old- growth tropical forests are peculiarly vulnerable to invasion. Web of Science Xylosandrus crassiusculus; Xyleborinus exiguus; Euwallacea fornicatus Central America Field - Observational terrestrial Tropical Forest Invasion Hyp. Inherent Superiority;Community Species Richness Self Compatible decomposer 2893 Muth, Norris Z.; Pigliucci, Massimo 2007 Implementation of a novel framework for assessing species plasticity in biological invasions: responses of Centaurea and Crepis to phosphorus and water availability journal JOURNAL OF ECOLOGY 95 5 1001 1013 1. It is widely considered that phenotypic plasticity is important to species invasiveness. However, few empirical studies have expressly assessed the relationship between species invasiveness and their responses to environmental variability. Thoughtfully incorporating phenotypic plasticity into studies of invasiveness requires explicit links among appropriate environmental variables, traits relevant to invasion success, and comparison groups of species, populations or genotypes (competitors or close relatives) that place focal species in context. 2. We examine trait responsiveness in introduced species of Crepis and Centaurea (Asteraceae) that have been characterized by different degrees of success. Specifically, we assess the extent to which species are robust in the face of harsh environments and opportunistically responsive to favourable conditions. 3. We exposed all species to water and phosphorus availability treatments in a common glasshouse experiment and report the responses of phenological, architectural, size and fitness traits. We predicted that, compared with less invasive congeners, invasive species would more often display robust fitness in harsh environments (here, drought and no phosphorus addition) and would also be more responsive to favourable conditions (no drought and phosphorus additions). 4. In both Crepis and Centaurea we found evidence of greater stress tolerance to low phosphorous among the more invasive congeners, albeit for different components of fitness. Contrary to expectations, we observed no relationship between invasiveness and opportunism. Overall, trait responses were highly variable and largely idiosyncratic with respect to invasive categorization. 5. Consistent with basic expectations, across-environment species performance largely corresponded to degree of invasiveness. 6. Our results suggest that, even among closely related species, relationships between invasiveness and phenotypic plasticity do not necessarily reveal consistent patterns, nor do they conform to simple theoretical expectations. We suspect that phenotypic plasticity may indeed play an important role in many species invasions, but the breadth of relevant factors (which genotypes, which populations, which traits, which environments) reduces the likelihood of detecting robust general patterns. Web of Science Centaurea spp.;Crepsis spp. USA Greenhouse terrestrial Deciduous Forest Invasion Hyp. Plasticity primary 2894 Emery, Sarah M. 2007 Limiting similarity between invaders and dominant species in herbaceous plant communities? journal JOURNAL OF ECOLOGY 95 5 1027 1035 1. Limiting similarity theory predicts that successful invaders should differ functionally from species already present in the community. This theory has been tested by manipulating the functional richness of communities, but not other aspects of functional diversity such as the identity of dominant species. Because dominant species are known to have strong effects on ecosystem functioning, I hypothesized that successful invaders should be functionally dissimilar from community dominants. 2. To test this hypothesis, I added seeds of 17 different species to two different experiments: one in a natural oldfield community that had patches dominated by different plant species, and one in grassland mesocosms that varied in the identity of the dominant species but not in species richness or evenness. I used indicator species analyses to test whether invaders had higher establishment success in plots with functionally different dominant species. 3. A large percentage of invader species (47-71%) in both experiments showed no difference in affinity across the different dominant treatments, although one-third of species did show some evidence for limiting similarity. Exotic invaders had much higher invasion success than native invaders, and seemed to be inhibited by dominant species that were functionally similar. However, even these invasion patterns were not consistent across the two experiments. 4. The results from this study show that there is some evidence that dominant species suppress invasion by functionally similar species, beyond the effect of simple presence or absence of species in communities, although it is not the sole factor affecting invasion success. Patterns of invasion success were inconsistent across species and experiments, indicating that other studies using only a single species of invader to make conclusions about community invasibility should be interpreted with caution. Web of Science Many USA Michigan Field - Experimental terrestrial Old Field Invasion Hyp. Empty Niche primary 2895 Morrison, Janet A.; Mauck, Kerry 2007 Experimental field comparison of native and non-native maple seedlings: natural enemies, ecophysiology, growth and survival journal JOURNAL OF ECOLOGY 95 5 1036 1049 1. Acer platanoides (Norway maple) is an important non-native invasive canopy tree in North American deciduous forests, where native species diversity and abundance are greatly reduced under its canopy. We conducted a field experiment in North American forests to compare planted seedlings of A. platanoides and Acer saccharum (sugar maple), a widespread, common native that, like A. platanoides, is shade tolerant. Over two growing seasons in three forests we compared multiple components of seedling success: damage from natural enemies, ecophysiology, growth and survival. We reasoned that equal or superior performance by A. platanoides relative to A. saccharum indicates seedling characteristics that support invasiveness, while inferior performance indicates potential barriers to invasion. 2. Acer platanoides seedlings produced more leaves and allocated more biomass to roots, A. saccharum had greater water use efficiency, and the two species exhibited similar photosynthesis and first-season mortality rates. Acer platanoides had greater winter survival and earlier spring leaf emergence, but second-season mortality rates were similar. 3. The success of A. platanoides seedlings was not due to escape from natural enemies, contrary to the enemy release hypothesis. Foliar insect herbivory and disease symptoms were similarly high for both native and non-native, and seedling biomass did not differ. Rather, A. platanoides compared well with A. saccharum because of its equivalent ability to photosynthesize in the low light herb layer, its higher leaf production and greater allocation to roots, and its lower winter mortality coupled with earlier spring emergence. Its only potential barrier to seedling establishment, relative to A. saccharum, was lower water use efficiency, which possibly could hinder its invasion into drier forests. 4. The spread of non-native canopy trees poses an especially serious problem for native forest communities, because canopy trees strongly influence species in all forest layers. Success at reaching the canopy depends on a tree's ecology in previous life-history stages, particularly as a vulnerable seedling, but little is known about seedling characteristics that promote non-native tree invasion. Experimental field comparison with ecologically successful native trees provides insight into why non-native trees succeed as seedlings, which is a necessary stage on their journey into the forest canopy. Web of Science Acer platanoides USA New Jersey Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Superior Competitor primary 2896 van Grunsven, Roy H. A.; van der Putten, Wim H.; Bezemer, T. Martijn; Tamis, Wil L. M.; Berendse, Frank; Veenendaal, Elmar M. 2007 Reduced plant-soil feedback of plant species expanding their range as compared to natives journal JOURNAL OF ECOLOGY 95 5 1050 1057 1. As a result of global warming, species may spread into previously cool regions. Species that disperse faster than their natural enemies may become released from top-down control. We investigated whether plants originating from southern Europe and recently established in north-western Europe experience less soil pathogen effects than native species. 2. We selected three plant species originating from southern Europe that have immigrated into the Netherlands and three similar native Dutch species. All six plant species were grown in sterilized soils with a soil inoculum collected from the rhizospheres of field populations. As a control we grew a series of all six plant species with a sterilized rhizosphere inoculum. 3. We harvested the plants, added the conditioned soil to sterilized soil and grew a second generation of all six plant species in order to test for each plant pair feedback effects from the conditioned soil communities to conspecifics and heterospecifics. 4. The effect of the soil community is dependent on plant species, and is dependent on soil fertility in only one of the three pairs. 5. Soil conditioning caused less biomass reduction to exotic plant species than to native species, suggesting that exotic immigrants are less exposed to soil pathogens than similar native plant species. 6. Our results suggest that plant species that expand their range as a result of climate change may become released from soil pathogenic activity. Whether the exotics are released from soil pathogens, or whether they experience enhanced benefit from mutualistic symbionts remains to be studied. We conclude that range expansion may result in enemy release patterns that are similar to artificially introduced invasive exotic plant species. 7. The escape from enemies through range shifts changes key biotic interactions and complicates predictions of future distribution and dominance. Web of Science Heracleum mantegazzianum;Tragopogon dubius;Eragrostis pilos Netherlands Garden terrestrial Deciduous Forest;Old Field Invasion Hyp. Climate Change primary 2899 McDonald, Jennifer L.; Peterson, Mark S.; Slack, William T. 2007 Morphology, density, and spatial patterning of reproductive bowers in an established alien population of Nile tilapia, Oreochromis niloticus journal JOURNAL OF FRESHWATER ECOLOGY 22 3 461 468 In coastal Mississippi aquatic systems, Nile tilapia (Oreochromis niloticus) has been introduced via aquaculture practices and appears to have established breeding populations. However, little is known about characteristics of bowers in non-native environments or if reproductive activities vary with water temperature. Therefore, we examined bower morphology, sediment composition, density, spatial pattern, and the distribution of bowers and reproductive leks in relation to thermal gradients within a power plant cooling pond. We found that the Nile tilapia has the appropriate materials for building bowers, can establish active breeding leks, and distributes along thermal gradients. All of these attributes allow for successful invasion and establishment into non-native environments. Web of Science Oreochromis niloticus USA Mississippi Field - Observational lentic;lotic Invasion Hyp. Preadaptation to Climate herbivore 2900 Skarpaas, Olav; Shea, Katriona 2007 Dispersal patterns, dispersal mechanisms, and invasion wave speeds for invasive thistles journal AMERICAN NATURALIST 170 3 421 430 Understanding and predicting population spread rates is an important problem in basic and applied ecology. In this article, we link estimates of invasion wave speeds to species traits and environmental conditions. We present detailed field studies of wind dispersal and compare nonparametric (i.e., data-based) and mechanistic ( fluid dynamics model-based) dispersal kernel and spread rate estimates for two important invasive weeds, Carduus nutans and Carduus acanthoides. A high-effort trapping design revealed highly leptokurtic dispersal distributions, with seeds caught up to 96 m from the source, far further than mean dispersal distances (approx. 2m). Nonparametric wave speed estimates are highly sensitive to sampling effort. Mechanistic estimates are insensitive to sampling because they are obtained from independent data and more useful because they are based on the dispersal mechanism. Over a wide range of realistic conditions, mechanistic spread rate estimates were most sensitive to high winds and low seed settling velocities. The combination of integrodifference equations and mechanistic dispersal models is a powerful tool for estimating invasion spread rates and for linking these estimates to characteristics of the species and the environment. Web of Science Carduus nutans; Carduus acanthoides United States Pennsylvania Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Effective Disperser primary 2901 Alcaraz, Caries; Garcia-Berthou, Emili 2007 Life history variation of invasive mosquitofish (Gambusia holbrooki) along a salinity gradient journal BIOLOGICAL CONSERVATION 139 2 83 92 The mosquitofish (Gambusia holbrooki) is among the most invasive fish worldwide, with well documented ecological impacts on ecosystem functioning and several native taxa. Although it has been suggested that salinity limits the invasive success of mosquitofish, there are few studies on how salinity affects its ecology. We examined differences in life history traits of mosquitofish at 19 sampling sites from fresh (438 mu S/cm; ca. 0.2 parts per thousand of salinity) to polysaline waters (35.1 mS/cm; ca. 23 parts per thousand). Salinity affected the density and life history traits of both male and female mosquitofish; density showed a unimodal response to salinity, stronger for females and thus affecting the sex ratio. On the other hand, the endemic Aphanius iberus was only present in polysaline and eusaline waters, where mosquitofish were generally absent. Mosquitofish increased reproductive investment (higher gonadal mass) in oligosaline waters, at the cost of somatic condition in females. The increase in reproductive investment also implied an increase in total mass in contrast to somatic mass, demonstrating that the latter is a better indicator of condition. Females from higher salinity waters presented more embryos in advanced developmental stages, indicating earlier reproduction than in fresh water. After correction for brood and fish sizes, females from saltier environments presented heavier embryos (independently of maturation state). In summary, salinity mainly affected mosquitofish females which, despite presenting earlier maturation and higher reproductive investment, reduced their condition and density, hence supporting the hypothesis that salinity limits mosquitofish invasive success. (c) 2007 Elsevier Ltd. All rights reserved. Web of Science Gambusia holbrooki Spain Field - Observational lentic Invasion Hyp. Other herbivore 2902 Dehnen-Schmutz, Katharina; Touza, Julia; Perrings, Charles; Williamson, Mark 2007 A century of the ornamental plant trade and its impact on invasion success journal DIVERSITY AND DISTRIBUTIONS 13 5 527 534 We identify a significant relationship between domestic market-based propagule pressure, as measured both in presence in the British horticultural market and in seed prices of ornamental plant species, with success in invasion. We employ a multispecies temporal approach and use a Generalized Estimation Equation model comparing ornamental non-native species introduced into Britain which started to invade with species introduced but not known outside cultivation. Historical nursery catalogues gave information on the availability and prices of seeds of 506 ornamental species in the British horticultural market every 20 years from 1885 to 1985. Higher market frequency and cheap prices of seeds were more significant and had a greater impact on the invading probability 20 years later than at the date of listing in a nursery catalogue. Our results suggest that national economic factors are an important part of the explanation for the invasiveness of ornamental plant species, and hence for the development of potential solutions. Web of Science Many Britain Field - Observational terrestrial Invasion Hyp. Propagule Pressure primary 2903 Duyck, Pierre-Francois; David, Patrice; Quilici, Serge 2007 Can more K-selected species be better invaders? A case study of fruit flies in La Reunion journal DIVERSITY AND DISTRIBUTIONS 13 5 535 543 Invasive species are often said to be r-selected. However, invaders must sometimes compete with related resident species. In this case invaders should present combinations of life-history traits that give them higher competitive ability than residents, even at the expense of lower colonization ability. We test this prediction by comparing life-history traits among four fruit fly species, one endemic and three successive invaders, in La Reunion Island. Recent invaders tend to produce fewer, but larger, juveniles, delay the onset but increase the duration of reproduction, survive longer, and senesce more slowly than earlier ones. These traits are associated with higher ranks in a competitive hierarchy established in a previous study. However, the endemic species, now nearly extinct in the island, is inferior to the other three with respect to both competition and colonization traits, violating the trade-off assumption. Our results overall suggest that the key traits for invasion in this system were those that favoured competition rather than colonization. Web of Science Ceratitis capitata La Reunion Island Field - Observational terrestrial Tropical Forest Invasion Hyp. Inherent Superiority Superior Competitor herbivore 2904 Lafleur, Nancy E.; Rubega, Margaret A.; Elphick, Chris S. 2007 Invasive fruits, novel foods, and choice: An investigation of European starling and American Robin frugivory journal WILSON JOURNAL OF ORNITHOLOGY 119 3 429 438 We compared the feeding choices of an invasive frugivore, the European Starling (Sturnus vulgaris). with those of a native, the American Robin (Turdus migratorius). Using captive birds, we tested whether these species differ in their preferences when offered a choice between a native and an invasive fruit, and between a novel and a familiar food. We examined willingness to eat fruits of selected invasive plants and to select a novel food by measuring the time elapsed before feeding began. Both species demonstrated significant preferences for invasive fruits over similar native fruits in two of three choice tests. Both starlings and robins ate autumn olive (Elaeagnus umbellata) fruits significantly more willingly than Asiatic bittersweet (Celastrus orbiculatus). Starlings, but not robins when choosing between a novel and a familiar food, strongly preferred the familiar food. We found no differences in willingness of birds to eat a novel food when it was the only food available. These results suggest that some fleshy-fruited invasive plants may receive more dispersal services than native plants with similar fruits, and that different frugivores may be seed dispersers for different invasive plants. Web of Science Sturnus vulgaris; Turdus migratorius United States Field - Observational terrestrial Deciduous Forest Invasion Hyp. Mutualism Facilitation herbivore 2906 Mondor, Edward B.; Addicott, John F. 2007 Do exaptations facilitate mutualistic associations between invasive and native species? journal BIOLOGICAL INVASIONS 9 6 623 628 As invasive species are key threats to ecosystem structure and function, it is essential to understand the factors underlying their success. Enigmatically, mutualistic organisms are often successful in colonizing novel environments even though they commonly persist only through intricate relationships with other species. Mutualistic ants, for example, protect aphids from natural enemies while collecting carbohydrate-rich honeydew. To facilitate this interaction, ants have evolved aggressive responses to aphid alarm pheromone emissions. As invasive and native mutualists have not evolved together, however, it is unclear if this form of cross-species communication exists between these two parties thereby facilitating these novel interactions. We address this hypothesis by assessing whether the invasive Argentine ant, Linepithema humile, responds to native poplar aphid, Chaitophorus populicola, alarm signals. Here, we show that interspecific signalling does exist in this newly established mutualistic interaction. Argentine ant workers exhibit increased aggression and double the number of visits to an aphid colony after an aphid alarm signal is emitted. We suggest that pre-adaptations may facilitate the emergence of mutualistic associations between many invasive and native species. Web of Science Linepithema humile USA California Davis Field - Experimental terrestrial Invasion Hyp. Mutualism Facilitation omnivore 2908 Kercher, Suzanne M.; Herr-Turoff, Andrea; Zedler, Joy B. 2007 Understanding invasion as a process: the case of Phalaris arundinacea in wet prairies journal BIOLOGICAL INVASIONS 9 6 657 665 Invasive plants that most threaten biodiversity are those that rapidly form a monospecific stand, like the clonal grass, Phalaris arundinacea. Understanding complex and potentially interacting factors that are common in urban and agricultural landscapes and underlie rapid invasions requires an experimental, factorial approach. We tested the effects of flooding and nutrient and sediment additions (3 x 3 x 3 = 27 treatments, plus a control with no additions) on invasion of Phalaris into mesocosms containing wet prairie vegetation. We discovered a three-step invasion and degradation process: (1) initially, resident native species declined with prolonged flooding and sediment additions, and (2) prolonged flooding, sedimentation, and nutrients accelerated Phalaris aboveground growth; biomass rose to 430 times that of the control within just two growing seasons. The dramatic expansion of Phalaris in the second year resulted in the formation of monospecific stands in over one-third of the treatments, as (3) native species continued their decline in year 2. Disturbances acted alone and in combination to make the resident wetland community more invasible and Phalaris more aggressive, leading to monospecific stands. Yet, Phalaris did not always *win*: under the least disturbed conditions, the resident plant canopy remained dense and vigorous and Phalaris remained small. When anthropogenic disturbances coincide with increases in the gross supply of resources, more tolerant, fast-growing, and morphologically plastic plants like Phalaris can invade very rapidly. The fluctuating resource hypothesis should thus be refined to consider the role of interacting disturbances in facilitating invasions. Web of Science Phalaris arundinacea USA Wisconsin Garden terrestrial Grassland Invasion Hyp. Disturbance primary 2909 Bauer, Candice R.; Bobeldyk, Angela M.; Lamberti, Gary A. 2007 Predicting habitat use and trophic interactions of Eurasian ruffe, round gobies, and zebra mussels in nearshore areas of the Great Lakes journal BIOLOGICAL INVASIONS 9 6 667 678 The Laurentian Great Lakes have been subject to numerous introductions of nonindigenous species, including two recent benthic fish invaders, Eurasian ruffe (Gymnocephalus cernuus) and round gobies (Neogobius melanostomus), as well as the benthic bivalve, zebra mussel (Dreissena polymorpha). These three exotic species, or *exotic triad,* may impact nearshore benthic communities due to their locally high abundances and expanding distributions. Laboratory experiments were conducted to determine (1) whether ruffe and gobies may compete for habitat and invertebrate food in benthic environments, and (2) if zebra mussels can alter those competitive relationships by serving as an alternate food source for gobies. In laboratory mesocosms, both gobies and ruffe preferred cobble and macrophyte areas to open sand either when alone or in sympatry. In a 9-week goby-ruffe competition experiment simulating an invasion scenario with a limited food base, gobies grew faster than did ruffe, suggesting that gobies may be competitively superior at low resource levels. When zebra mussels were added in a short-term experiment, the presence or absence of mussels did not affect goby or ruffe growth, as few zebra mussels were consumed. This finding, along with other laboratory evidence, suggests that gobies may prefer soft-bodied invertebrate prey over zebra mussels. Studies of interactions among the *exotic triad*, combined with continued surveillance, may help Great Lakes fisheries managers to predict future population sizes and distributions of these invasive fish, evaluate their impacts on native food webs, and direct possible control measures to appropriate species. Web of Science Gymnocephalus cernuus;Neogobius melanostomus;Dreissena polymorpha USA Lab lotic Fundamentals predator;filter 2910 Thiengo, Silvana C.; Faraco, Fabio Andre; Salgado, Norma C.; Cowie, Robert H.; Fernandez, Monica A. 2007 Rapid spread of an invasive snail in South America: the giant African snail, Achatina fulica, in Brasil journal BIOLOGICAL INVASIONS 9 6 693 702 Beginning around 1800, but primarily since the early and mid-twentieth century, the giant African snail, Achatina (Lissachatina) fulica Bowdich, 1822, has been introduced throughout the tropics and subtropics and has been considered the most important snail pest in these regions. In Brasil, specimens probably brought from Indonesia were introduced into the state of Parana in the 1980s for commercial purposes (*escargot* farming) that were not successful. Achatina fulica is now widespread in at least 23 out of 26 Brasilian states and the Federal District, including the Amazonian region and natural reserves. Among the reasons for the species' rapid invasion are its high reproductive capacity and the tendency for people to release the snails into the wild. Achatina fulica occurs in dense populations in urban areas where it is a pest in ornamental gardens, vegetable gardens, and small-scale agriculture. Also of concern is the damage caused to the environment, and potential competition with native terrestrial mollusks. It can also act as an intermediate host of Angiostrongylus cantonensis, a nematode that can cause meningoencephalitis in people, and it may be a potential host of A. costaricensis, which causes abdominal angiostrongylosis, a zoonosis that occurs from the southern United States to northern Argentina. Management and control measures for A. fulica are under way in Brasil through a national plan implemented by the Brasilian government. Web of Science Achatina fulica Brazil Field - Observational terrestrial Urban Invasion Hyp. Inherent Superiority High Reprod. Output herbivore 2911 Zaiko, Anastasija; Olenin, Sergej; Daunys, Darius; Nalepa, Tomas 2007 Vulnerability of benthic habitats to the aquatic invasive species journal BIOLOGICAL INVASIONS 9 6 703 714 A comparative vulnerability analysis of 16 selected benthic habitat types in the SE Baltic Sea waters and the Curonian lagoon, including Klaipeda strait, was performed using long-term monitoring datasets (1980-2003) and results of several other surveys in the lagoon and the sea. Results indicated that invasive species richness (number of alien species per habitat) in lagoon habitats was significantly higher than in the sea. Habitats formed by artificial rock and stone, sand, mud, and habitats modified by zebra mussel shell deposits appeared to be the most invaded. Highest invasive species richness occurred in habitats with high native species richness indicating that the main factors driving native species distribution (such as favourable physical conditions, habitat alterations generated by human or/and biotic activities) are also driving aquatic invaders. Physical factors distinguished to be the most important for native and invasive species distribution were salinity, depth range (expressed by the maximal and minimal depths difference within a habitat), shallowness of a habitat (expressed by a minimal depth), and availability of a hard substrate. Web of Science Many Lithuania marine Intertidal/Near Shore Invasion Hyp. Disturbance 2912 Doblin, Martina A.; Coyne, Kathryn J.; Rinta-Kanto, Johanna M.; Wilhelm, Steven W.; Dobbs, Fred C. 2007 Dynamics and short-term survival of toxic cyanobacteria species in ballast water from NOBOB vessels transiting the Great Lakes - implications for HAB invasions journal HARMFUL ALGAE 6 4 519 530 We measured the presence, viability and potential toxicity of cyanobacteria in ships' ballast tanks during three domestic voyages through the North American Great Lakes. Using molecular methods, the toxin-producing forms of Microcystis and Anabaena were monitored in ballast water after ships' ballast tanks were filled at their first port of call, and at subsequent ports as ships transited the Great Lakes. Microcystis was detected in ballast water at intermediate and final ports of call in all three experiments, but the presence of Anabaena was more variable, suggesting low abundance or patchy distribution in ballast tanks. Both species were detected in ballast water up to I I days old. Detection of the microcystin synthetase gene, incyE, in ballast tanks indicated entrained cells were capable of producing microcystin, and further analyses of RNA indicated the toxin was being expressed by Microcystis, even after I I days in dark transit. These data demonstrate within-basin transport and delivery of planktonic harmful algal bloom (HAB) species to distant ports in the world's largest freshwater reservoir, with potential implications for drinking water quality. These implications are discussed with respect to management of microbial invasions and the fate of introduced phytoplankton in their receiving environment. (C) 2007 Elsevier B.V. All rights reserved. Web of Science Microcystis;Anabaena lentic Invasion Hyp. Other primary 2913 Corin, S. E.; Abbott, K. L.; Ritchie, P. A.; Lester, P. J. 2007 Large scale unicoloniality: the population and colony structure of the invasive Argentine ant (Linepithema humile) in New Zealand journal INSECTES SOCIAUX 54 3 275 282 The Argentine ant is native to South America and has spread widely across the globe. In this study, we use genetic analyses and behavioural assays to examine the colony structure of Argentine ants in New Zealand. Diet modification studies were also carried out in order to help identify what factors influence these behavioural assays. There was no aggression observed between any pairings tested across the North Island of New Zealand, though we found that diet manipulations in the laboratory could lead to low levels of aggression between previously amiable Argentine ant nests. The New Zealand population of Argentine ants was characterized by low levels of genetic variation in six microsatellite loci from their nuclear genome. Additionally, the population also lacked significant genetic structuring with no patterns of regional differentiation or isolation by distance. An analysis of molecular variation(AMOVA) found that the majority of genetic variation was present at a nest level (93% of total genetic variance), with little genetic differentiation observed within or between regions (3-4% of total genetic variance). No correlation between aggression and genetic relatedness was observed. This evidence suggests that Argentine ants in New Zealand effectively form a unicolonial population, which is likely the result of colonization from a single source population. As far as we know, this is the first country to have an entirely unicolonial population of Argentine ants. Web of Science linepithema humile New Zealand terrestrial Invasion Hyp. Other omnivore 2914 Espadaler, X.; Tartally, A.; Schultz, R.; Seifert, B.; Nagy, Cs. 2007 Regional trends and preliminary results on the local expansion rate in the invasive garden ant, Lasius neglectus (Hymenoptera, Formicidae) journal INSECTES SOCIAUX 54 3 293 301 The expansion process of the invasive garden ant, Lasius neglectus in Europe and Asia is described in terms of: a) local expansion through colony growing measured on four supercolonies (Seva, Debrecen, Buda Castle and Budateteny) from two distant and climatically different countries (Spain, Hungary), and b) regional expansion, using data from all published and several new non-native localities. Short, local distance processes (few meters to 89 m year-(1)), as colony budding, are two to five orders of magnitude smaller than long regional distances (ten km to > 1000 km). This suggests direct human intervention in the invasive spread. The regional trend also shows that the invasive garden ant has been quickly and steadily increasing the number of non native localities (77) and countries (14) it has reached during the last 30 years. Web of Science Lasius neglectus Spain;Hungary) Field - Observational terrestrial Urban Invasion Hyp. Other omnivore 2915 Malik, Riffat Naseem; Husain, Syed Zahoor 2007 Broussonetia papyrifera (L.) L'her. ex Vent.: An environmental constraint on the Himalayan Foothills vegetation journal PAKISTAN JOURNAL OF BOTANY 39 4 1045 1053 Biololgical invasion caused by the non-indigenous plant species have been considered as one of the major threat to the native vegetation and its diversity at local, regional and global level and its effect oil native forest ecosystem is regarded as one of the most critical issues confronting environmental conservationist,. This study addresses the influence of Broussonetia popyrifera oil the native surub forest at the Himalayan Foothills. Islamabad, Pakistan and its relationship,with ecological gradients which are important in terms of its spatial distribution. Floristic species composition and environmental factors were measured from 77 plots from two sites of the scrub forest at the lower elevation of Margalla Hills National Park Islamabad. Agglomerative hierarchical Cluster Analysis (CA) Was Used for species assemblage patterns and ordination analyses such as Detrended correspondence Analysis (DCA) and Canonical Correspondence Analysis (CCA) was used to establish the relationship with the underlying ecological gradients. CA divided the plots into three vegetation zones: a vegetation zone comprised of species of native scrub forest dominated by Acacia modesta; a transition vegetation zone where B. papyrifea was present either in scattered form amongst the scrub forest species or showed patchy distribution and invasive vegetation zone dominated by B. pupyrifera. Mail Whitney U-test Was Used to find out if vegetation zones identified by CA could be significantly different from each other based on the measured environmental factors. Factor Analysis (FA)/Principal Components Analysis (PCA) were Used to identify set of environmental factors/predictors, which call best discriminate vegetation zones. FA/PCA (raw varimax rotated) oil the environmental factors renders three varifactors with eigenvalues higher than 1.0 accounting for over 72% of total variance. Multivariate analyses indicated that the spatial distribution of B. papyrifera is related to edaphic factors such as the soil texture, organic matter and moisture contents. The distribution was insensitive to the topographic factors. The probable consequences of B. papyrifera invasion for future scrub forest composition and plant species diversity are also discussed.. The findings of this research will be Used in formulating scientifically sound Management and conservation strategy for the forest ecosystems of the Margalla Hills National Park Islamabad. Web of Science Broussonetia popyrifera Pakistan Islamabad Himalayan Foothills Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Other primary 2916 Von der Lippe, Moritz; Kowarik, Ingo 2007 Long-distance dispersal of plants by vehicles as a driver of plant invasions journal CONSERVATION BIOLOGY 21 4 986 996 Roadsides are preferential migration corridors for invasive plant species and can act as starting points for plant invasions into adjacent habitats. Rapid spread and interrupted distribution patterns of introduced plant species indicate long-distance dispersal along roads. The extent to which this process is due to species' migration along linear habitats or alternatively, to seed transport by vehicles has not yet been tested systematically. We tested this by sampling seeds inside long motorway tunnels to exclude nontraffic dispersal. Vehicles transported large amounts of seeds. The annual seed rain caused by vehicles on the roadsides of five different tunnel lanes within three tunnels along a single urban motorway in Berlin, Germany, ranged from 635 to 1579 seeas/m(2)/year Seeds of non-native species accounted for 50.0% of the 204 species and 54.4% of the total 11,818 seeds trapped inside the tunnels. Among the samples were 39 (19.1%) highly invasive species that exhibit detrimental effects on native biodiversity in some parts of the world. By comparing the flora in the tunnel with that adjacent to the tunnel entrances we confirmed long-distance dispersal events (>250 m) for 32.3% of the sampled species. Seed sources in a radius of 100 m around the entrances of the tunnels had no significant effect on species richness and species composition of seed samples from inside the tunnels, indicating a strong effect of long-distance dispersal by vehicles. Consistently, the species composition of the tunnel seeds was more similar to the regional roadside flora of Berlin than to the local flora around the tunnel entrances. Long-distance dispersal occurred significantly more frequently in seeds of non-native (mean share 38.5%) than native species (mean share 4.1%). Our results showed that long-distance dispersal by vehicles was a routine rather than an occasional mechanism. Dispersal of plants by vehicles will thus accelerate plant invasions and induce rapid changes in biodiversity patterns. Web of Science Many Germany Berlin Statistical/Meta-analysis terrestrial Urban Invasion Hyp. Inherent Superiority Effective Disperser primary 2917 Ward, Nicola L.; Masters, Gregory J. 2007 Linking climate change and species invasion: an illustration using insect herbivores journal GLOBAL CHANGE BIOLOGY 13 8 1605 1615 Climate change and invasive species are two of the most important ecological issues facing the world today. Yet, to date these two factors have largely been viewed independently. In order to prevent large-scale economic and environmental damage and as a first step towards predicting and preventing invasions, it is important to understand the factors affecting invasions. Here, we focus on insect herbivores and link the climate change and invasive research fields. We illustrate using existing published research that life history traits can be useful indicators of future invasive potential. However, climate change will also affect propagule pressure and the communities into which invaders will arrive. With the aid of a meta-analysis we show that climate-induced community changes are likely to increase niche-availability in the future, further exacerbating the problem of invasive species. It is timely and important that further research linking these two important ecological threats is undertaken. Web of Science Many Review/Meta-analysis terrestrial Invasion Hyp. Empty Niche;Climate Change herbivore 2918 Fumanal, Boris; Chauvel, Bruno; Sabatier, Anne; Bretagnolle, Francois 2007 Variability and cryptic heteromorphism of Ambrosia artemisiifolia seeds: What consequences for its invasion in France? journal ANNALS OF BOTANY 100 2 305 313 Background and Aims: Ambrosia artemisiifolia is a ruderal weed introduced from North America to Europe. It produces large amount of achenes which are highly heterogeneous in size. Due to the preponderant role of propagules in invasive plant processes, the achene mass variability related to germination, dispersal strategy and life history traits of offspring were investigated within this species. Methods: The variability in achene mass was quantified among six populations sampled in different habitats. The effects of achene mass variation on germination were studied. The percentages of floating and non-floating achenes were evaluated in the studied populations. The consequences of floatability on the growth and traits of the offspring were studied. Key Results: Mean achene mass ranged from 1.72 to 3.60 mg, depending on the populations, and was highly variable. Variation among achenes within plants accounted for 63-9 % of the variance, whereas variances among plants within each population (22.2 %) and among populations (13.9 %) were lower. Achene masses were also positively correlated to the total germination percentage for four populations out of six. Two kinds of achenes were distinguished: floating and non-floating. The majority of floating achenes (90 %) sank 24 It after water immersion. Whatever the population, floating achenes were lighter, more dormant and germinated faster than non-floating achenes. Plants which issued from floating achenes had better growth than those from non-floating achenes. Conclusions: The capacity of A. artemisiifolia to be invasive in Europe appears to be high, possibly due to its huge plasticity in seed mass which may help it to cope with a wide range of conditions and to establish in disturbed habitats. Furthermore, the recent invasion of southern France by A. artemisiifolia could be partially explained by water dispersal of achenes through rivers and has pinpointed its colonization potential along French rivers. Web of Science Ambrosia artemisiifolia France Field - Observational terrestrial Old Field Invasion Hyp. Plasticity primary 2921 Milton, S. J.; Wilson, J. R. U.; Richardson, D. M.; Seymour, C. L.; Dean, W. R. J.; Iponga, D. M.; Proches, S. 2007 Invasive alien plants infiltrate bird-mediated shrub nucleation processes in arid savanna journal JOURNAL OF ECOLOGY 95 4 648 661 1. The cultivation and dissemination of alien ornamental plants increases their potential to invade. More specifically, species with bird-dispersed seeds can potentially infiltrate natural nucleation processes in savannas. 2. To test (i) whether invasion depends on facilitation by host trees, (ii) whether propagule pressure determines invasion probability, and (iii) whether alien host plants are better facilitators of alien fleshy-fruited species than indigenous species, we mapped the distribution of alien fleshy-fruited species planted inside a military base, and compared this with the distribution of alien and native fleshy-fruited species established in the surrounding natural vegetation. 3. Abundance and diversity of fleshy-fruited plant species was much greater beneath tree canopies than in open grassland and, although some native fleshy-fruited plants were found both beneath host trees and in the open, alien fleshy-fruited plants were found only beneath trees. 4. Abundance of fleshy-fruited alien species in the natural savanna was positively correlated with the number of individuals of those species planted in the grounds of the military base, while the species richness of alien fleshy-fruited taxa decreased with distance from the military base, supporting the notion that propagule pressure is a fundamental driver of invasions. 5. There were more fleshy-fruited species beneath native Acacia tortilis than beneath alien Prosopis sp. trees of the equivalent size. Although there were significant differences in native plant assemblages beneath these hosts, the proportion of alien to native fleshy-fruited species did not differ with host. 6. Synthesis. Birds facilitate invasion of a semi-arid African savanna by alien fleshy-fruited plants, and this process does not require disturbance. Instead, propagule pressure and a few simple biological observations define the probability that a plant will invade, with alien species planted in gardens being a major source of propagules. Some invading species have the potential to transform this savanna by overtopping native trees, leading to ecosystem-level impacts. Likewise, the invasion of the open savanna by alien host trees (such as Prosopis sp.) may change the diversity, abundance and species composition of the fleshy-fruited understorey. These results illustrate the complex interplay between propagule pressure, facilitation, and a range of other factors in biological invasions. Web of Science Many South Africa Northern Cape province Diskobolos Military Base Field - Observational terrestrial Grassland;Deciduous Forest Invasion Hyp. Mutualism Facilitation;Propagule Pressure primary 2922 Perelman, Susana B.; Chaneton, Enrique J.; Batista, William B.; Burkart, Silvia E.; Leon, Rolando J. C. 2007 Habitat stress, species pool size and biotic resistance influence exotic plant richness in the Flooding Pampa grasslands journal JOURNAL OF ECOLOGY 95 4 662 673 1. Theory and empirical evidence suggest that community invasibility is influenced by propagule pressure, physical stress and biotic resistance from resident species. We studied patterns of exotic and native species richness across the Flooding Pampas of Argentina, and tested for exotic richness correlates with major environmental gradients, species pool size, and native richness, among and within different grassland habitat types. 2. Native and exotic richness were positively correlated across grassland types, increasing from lowland meadows and halophyte steppes, through humid to mesophyte prairies in more elevated topographic positions. Species pool size was positively correlated with local richness of native and exotic plants, being larger for mesophyte and humid prairies. Localities in the more stressful meadow and halophyte steppe habitats contained smaller fractions of their landscape species pools. 3. Native and exotic species numbers decreased along a gradient of increasing soil salinity and decreasing soil depth, and displayed a unimodal relationship with soil organic carbon. When covarying habitat factors were held constant, exotic and native richness residuals were still positively correlated across sites. Within grassland habitat types, exotic and native species richness were positively associated in meadows and halophyte steppes but showed no consistent relationship in the least stressful, prairie habitat types. 4. Functional group composition differed widely between native and exotic species pools. Patterns suggesting biotic resistance to invasion emerged only within humid prairies, where exotic richness decreased with increasing richness of native warm-season grasses. This negative relationship was observed for other descriptors of invasion such as richness and cover of annual cool-season forbs, the commonest group of exotics. 5. Our results support the view that ecological factors correlated with differences in invasion success change with the range of environmental heterogeneity encompassed by the analysis. Within narrow habitat ranges, invasion resistance may be associated with either physical stress or resident native diversity. Biotic resistance through native richness, however, appeared to be effective only at intermediate locations along a stress/fertility gradient. 6. We show that certain functional groups, not just total native richness, may be critical to community resistance to invasion. Identifying such native species groups is important for directing management and conservation efforts. Web of Science Many Argentina Flooding Pampas Field - Observational terrestrial Grassland Invasion Hyp. Community Species Richness;Disturbance primary 2923 Van Kleunen, Mark; Johnson, Steven D. 2007 South African Iridaceae with rapid and profuse seedling emergence are more likely to become naturalized in other regions journal JOURNAL OF ECOLOGY 95 4 674 681 1. Plant invasions constitute a large biological problem and screening protocols are needed to assess the invasive potential of species considered for introduction. However, insufficient information is available on species characteristics associated with successful establishment outside their native range. 2. We tested experimentally whether seed and seedling emergence characteristics and early growth of seedlings are associated with naturalization of South African Iridaceae. In a common garden experiment, we compared these characteristics between 30 species that have become naturalized elsewhere and 30 congeneric species that have been introduced elsewhere but have failed to become naturalized. 3. The average seed mass did not differ between naturalized and non-naturalized species but seedlings of naturalized species emerged faster and more profusely than their non-naturalized congeners. As a consequence of fast seedling emergence, naturalized species reached a larger size early in the season than did non-naturalized species. 4. The results of our study indicate that rapid and profuse seedling emergence play important roles during naturalization, at least for Iridaceae from South Africa. Web of Science Many South Africa Garden terrestrial Invasion Hyp. Inherent Superiority Rapid Growth primary 2924 Siemann, Evan; Rogers, William E. 2007 The role of soil resources in an exotic tree invasion in Texas coastal prairie journal JOURNAL OF ECOLOGY 95 4 689 697 1. Variation in resource requirements among plant species may cause changes in community composition when resource supply rates vary. Because exotic plants may differ in their requirements compared with native plants, changes in resource levels or ratios may change their invasive potential. The concentration hypothesis, nutrient balance hypothesis and resource ratio hypothesis make different predictions regarding the effects of nutrient additions on plant communities and the success of invaders. 2. We investigated these hypotheses using Chinese tallow tree (Sapium sebiferum), which is an aggressive invader of grasslands in the southern USA. Soil nitrogen, phosphorus and potassium were manipulated in a full factorial field experiment in a Texas coastal prairie. 3. Survival of Sapium seedlings over three growing seasons was independent of all three types of nutrient additions, alone or in any combination. Adding nitrogen or potassium increased the mass and height of Sapium seedlings. Adding phosphorus increased the mass and height of Sapium seedlings only when nitrogen was also added. These results support the nutrient balance hypothesis, which assumes that higher tissue concentrations of a nutrient reflect a greater ability of a plant species to take up and/or conserve that nutrient. 4. The above-ground biomass of background prairie vegetation was independent of the addition of each type of nutrient alone or in any combination. However, the functional composition of the community shifted from graminoids to forbs with the addition of nitrogen and from graminoids to woody plants with the addition of phosphorus. These results support the concentration hypothesis, which assumes that higher tissue concentrations of a nutrient reflect a greater requirement for that nutrient. The contrasting responses of native woody vegetation and Sapium to phosphorus addition suggest that Sapium may have unusually low demands for phosphorus relative to nitrogen for a woody plant in this community. 5. These results show that potassium or nitrogen addition, perhaps in combination with phosphorus addition, has the potential to accelerate the invasion of Sapium into Texas coastal prairies. Because anthropogenic nutrient additions are common in grasslands worldwide, this may help to explain the frequent success of woody species invading grasslands. Web of Science Sapium sebiferum USA Texas Field - Experimental terrestrial Grassland Invasion Hyp. Inherent Superiority Broad Tolerances primary 2925 Valliant, Morgan T.; Mack, Richard N.; Novak, Stephen J. 2007 Introduction history and population genetics of the invasive grass Bromus tectorum (Poaceae) in Canada journal AMERICAN JOURNAL OF BOTANY 94 7 1156 1169 The invasive annual Bromus tectorum (cheatgrass) is distributed in Canada primarily south of 52 degrees N latitude in two diffuse ranges separated by the extensive coniferous forest in western Ontario. The grass was likely introduced independently to eastern and western Canada post-1880. We detected regional variation in the grass's genetic diversity using starch gel electrophoresis to analyze genetic diversity at 25 allozyme loci in 60 populations collected across Canada. The Pgm-1a & Pgm-2a multilocus genotype, which occurs in the grass's native range in Eastern Europe, is prevalent in eastern Canada but occurs at low frequency in western Canada. In contrast, the Got-4c multilocus genotype, found in the native range in Central Europe, is widespread in populations from western Canada. Overall genetic diversity of B. tectorum is much higher in eastern Canada than in the eastern U.S., while the genetic diversity in populations in western North America is similar between Canada and the U.S. The distribution of genetic diversity across Canada strongly suggests multiple introduction events. Heterozygous individuals, which are exceedingly rare in B. tectorum, were detected in three Canadian populations. Formation of novel genotypes through occasional outcrossing events could spark adaptive evolution and further range expansion across Canada of this exceedingly damaging grass. Web of Science Bromus tectorum grass Ontario western Ontario Field - Observational terrestrial Coniferous Forest Invasion Hyp. Evolution in General primary 2926 Thomsen, M. S.; McGlathery, K. J. 2007 Stress tolerance of the invasive macroalgae Codium fragile and Gracilaria vermiculophylla in a soft-bottom turbid lagoon journal BIOLOGICAL INVASIONS 9 5 499 513 Invasive species are often hypothesized to have superior performance traits. We compared stress tolerance (as change in biomass) of the invasive macroalgae Codium fragile ssp. tomentosoides and Gracilaria vermiculophylla to the native macroalgae Fucus vesiculosus, Agardhiella subulata, Hypnea musciformis and Ulva curvata in Hog Island Bay, a shallow lagoon in Virginia, USA. We hypothesized that the success of the two aliens is due to their high tolerances of turbidity, sedimentation, desiccation, grazing and nutrient enrichment. Like many lagoons, Hog Island Bay is characterized by extensive intertidal mudflats, high turbidity and sedimentation, and high densities of omnivorous mud snails. Nutrient enrichment may also become a problem as land use practices in adjacent watersheds change. Contrary to our hypothesis, C. fragile was less resistant to sedimentation, desiccation and grazing than other algae and had low growth at all light and nutrient levels. This suggests that any superior performance of this invasive species compared to native algae is probably limited to microhabitats where stress is minimal and where bivalve shells facilitate recruitment and long-term persistence. In contrast, G. vermiculophylla was resistant to desiccation, burial and grazing, and was not negatively influenced by either high or low light or nutrient levels. These traits reflect the current success of G. vermiculophylla in already invaded lagoons and estuaries, and indicates that it will likely continue its spread in European and North American turbid and tidal soft-sediment systems. Web of Science Codium fragile;Gracilaria vermiculophylla USA Virginia Hog Island Bay Field - Observational estuarine Invasion Hyp. Inherent Superiority Broad Tolerances primary 2927 Wolfe, Lorne M.; Blair, Amy C.; Penna, Brandy M. 2007 Does intraspecific hybridization contribute to the evolution of invasiveness?: an experimental test journal BIOLOGICAL INVASIONS 9 5 515 521 One of the major objectives of research on invasive species is to determine the relative importance of different evolutionary and ecological forces in the invasion process. It was recently suggested that post-introduction intraspecific hybridization between previously isolated genotypes could produce novel and/or heterotic progeny that might express enhanced invasiveness. We tested this hypothesis with Silene latifolia, a European native that has successfully invaded North America and has previously been shown to have undergone genetic change since its introduction. In a common garden experiment we compared the performance of plants derived from within and between population crosses from eight European and 18 North American populations. Results showed that there was no significant effect of crossing distance on progeny phenotype. Furthermore, progeny from within or between population crosses did not differ in size, reproductive output or survival. Collectively, these results suggest that the invasive phenotype of S. latifolia is likely the result of natural selection and/or genetic drift rather than intraspecific hybridization. Web of Science Silene latifolia USA Garden terrestrial Deciduous Forest Invasion Hyp. Hybridization primary 2928 Moody, M. L.; Les, D. H. 2007 Geographic distribution and genotypic composition of invasive hybrid watermilfoil (Myriophyllum spicatum x M-sibiricum) populations in North America journal BIOLOGICAL INVASIONS 9 5 559 570 The recent recognition of invasive hybrid watermilfoil (Myriophyllum spicatum x M. sibiricum) in North America has necessitated a more thorough evaluation of its overall distribution and occurrence in natural populations. A comprehensive survey of watermilfoil populations was conducted in five Minnesota lakes, three of which were suspected a priori to contain hybrid watermilfoil. DNA sequence data verified that hybrid plants between the nonindigenous M. spicatum L. and indigenous M. sibiricum Kom. occurred in three of the five lakes sampled. Myriophyllum spicatum was not detected in lakes where hybrids were prevalent. Further sampling of lakes in Idaho, Michigan, Minnesota, Wisconsin and Washington identified 30 additional hybrid watermilfoil populations. In only three of these populations the hybrid watermilfoil was found to co-occur with M. spicatum. To facilitate the field identification of the two parental species and their hybrid, morphological data from watermilfoil specimens collected across the United States were evaluated. We determined that leaf segment/leaf length measurements can effectively distinguish M. spicatum and M. sibiricum; however, hybrids are intermediate for these characters and such measurements frequently overlap with respect to their parental taxa. By incorporating a combined molecular and morphological approach to identifying watermilfoils, the hybrids can be identified readily and their distributions elucidated both within and between lakes. Because hybrids may respond differently to local ecological conditions than their parents, information on their presence and distribution should be of particular importance to management and conservation programs. Web of Science Myriophyllum spicatum;Myriophyllum sibiricum USA Minnesota Field - Observational lentic Invasion Hyp. Hybridization primary 2930 Casagrandi, Renato; Mari, Lorenzo; Gatto, Marino 2007 Modelling the local dynamics of the zebra mussel (Dreissena polymorpha) journal FRESHWATER BIOLOGY 52 7 1223 1238 1. The bivalve Dreissena polymorpha has invaded many freshwater ecosystems worldwide in recent decades. Because of their high fecundity and ability to settle on almost any solid substratum, zebra mussels usually outcompete the resident species and cause severe damage to waterworks. Time series of D. polymorpha densities display a variety of dynamical patterns, including very irregular behaviours. Unfortunately, there is a lack of mathematical modelling that could explain these patterns. 2. Here, we propose a very simple discrete-time population model with age structure and density dependence that can generate realistic dynamics. Most of the model parameters can be derived from existing data on D. polymorpha. Some of them are quite variable: with respect to these we perform a sensitivity analysis of the model behaviour and verify that non-equilibrial regimes (either periodic or chaotic) are the rule rather than the exception. 3. Even in circumstances where the model dynamics are aperiodic it is possible to predict total density peaks from previous peaks. This turns out to be true also in the presence of environmental stochasticity. 4. Using the stochastic model we explore the effects of age-selective predation. Quite surprisingly, larger removal rates of adults do not always result in smaller population densities and mussel biomasses. Moreover, non-selective predation can result in skewed size-frequency distributions which, therefore, are not necessarily the footprint of predators' preference for larger or smaller zebra mussels. Web of Science Dreissena polymorpha Many Theoretical/Modeling lentic Fundamentals filter 2931 Song, Li-Ying; Ni, Guang-Yan; Chen, Bao-Ming; Peng, Shao-Lin 2007 Energetic cost of leaf construction in the invasive weed Mikania micrantha HBK and its co-occurring species: implications for invasiveness journal BOTANICAL STUDIES 48 3 331 338 Construction cost (CC) is a quantifiable measure of energy demand for biomass production and is related to energy-use efficiency. Low construction cost was hypothesized to give invaders a growth advantage by utilizing energy efficiently. The present study examines the energetic cost of leaf construction in the invasive weed Mikania micrantha H.B.K. and its five common co-occurring species (Ageratum conyzoides L.,Wedelia trilobato (L.) Hitchc, Lantana camara L., Urena lobata L. and Derris trifoliata Lour.), and provides insight into the success of this invasive weed. Mikania micrantha had the lowest leaf construction cost both on a mass basis (leaf CC(mass), 1.32 g glucose g(-1)) and on an area basis (leaf CC(area) 28.80 g glucose m(-2)). Mikania micrantha dominated the studied community with 60% coverage. The low leaf CC associated with its great abundance indicated that low energetic cost might benefit its spread. Additionally, a higher specific leaf area (SLA) and lower C and N concentrations were found in M micrantha, providing it with another competitive advantage. All the six studied species could be grouped into either an invasive or a native species category. Both the mean leaf CC(area),. and CC(mass) for the invasive were lower than those for the native species though the mean leaf CC(mass) was not significantly different. The result indicated that a low energetic cost of leaf construction might generally influence invasive potential. Using discriminant analysis, leaf CC(area), was identified to be more powerful in distinguishing between invasive and native species. Therefore, leaf CC(area) might be a valuable index to predict invasiveness and has a meaningful management implication. Web of Science Mikania micrantha China. Zhuhai Qi’ao Island Lab terrestrial Invasion Hyp. Inherent Superiority Rapid Growth primary 2933 Underhill, Les G.; Hofmeyr, Jan H. 2007 Barn Swallows Hirundo rustica disperse seeds of Rooikrans Acacia cyclops, an invasive alien plant in the Fynbos Biome journal IBIS 149 3 468 471 Rooikrans Acacia cyclops is an invasive plant species in the coastal region of South Africa, especially the Fynbos Biome. It is endemic to southwestern Australia. Seeds are bird-dispersed, mostly by frugivores and granivores. We report that at one locality in South Africa, Barn Swallows Hirundo rustica, normally regarded as obligate foragers of aerial arthropods, also consumed the seeds and associated arils of Rooikrans shrubs and trees. The seeds were voided and the arils digested. Three thousand Barn Swallows in the region where this was observed conceivably consumed and voided two million Rooikrans seeds during the 5-month non-breeding period. Barn Swallows are therefore dispersers of Rooikrans seeds. Many of the bird species known to consume Rooikrans seeds are territorial, so that seeds are not dispersed far beyond existing acacia stands. Barn Swallows cover large distances between feeding areas and roosts, and could therefore disperse seeds far from existing stands. This development adds urgency to the need to eradicate Rooikrans from the Fynbos Biome. Web of Science Acacia cyclops South Africa Fynbos Biome Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Mutualism Facilitation primary;herbivore 2934 Vidra, Rebecca L.; Shear, Theodore H.; Stucky, Jon M. 2007 Effects of vegetation removal on native understory recovery in an exotic-rich urban forest journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 134 3 410 419 Urban forests represent patches of biodiversity within otherwise degraded landscapes, yet these forests are threatened by invasion by exotic plant species. We investigated the response of a forest understory to removal of four common exotic species: Elaeagnus umbellata Thunb., Lonicera japonica Thunb., Ligustrum sinense, Laur.. and Microstegium vimineum (Trin.) A. Camus in a forest within the city of Raleigh, NC, USA. In the summer of 200 1, we initiated a removal experiment with three treatments. In the *repeated removal* treatment, all understory vegetation was initially removed by clipping and new exotic seedlings were repeatedly removed every 2 weeks throughout the study period. The *initial removal* treatment involved a one-time understory vegetation removal with no further weeding. Control plots had no intervention throughout the study period. We conducted vegetation surveys of the plots prior to treatment initiation and in April and August of 2002 and 2003. With a non-metric multidimensional scaling (NMS) ordination, we were able to discern differences in species composition between the repeated removal treatment and the other two treatments. However, using repeated measures ANOVA, we found no significant differences in native species richness, cover, and abundance among treatments during most sampling periods. We also used a seedbank study to determine that while some early successional species, were present, no native shrubs and few native trees emerged from the seedbank. These results suggest that (1) repeated removal is required to decrease the importance of exotic species, especially if the site is in close proximity to a source of exotic propagules; and (2) subsequent to exotic removal, native species may not recover sufficiently without supplemental plantings. Therefore, restoration plans for urban forests should incorporate both long-term monitoring and native plant re-introduction to achieve a diverse native community. Web of Science Many USA North Carolina Raleigh Field - Experimental terrestrial Urban Invasion Hyp. Community Species Richness;Disturbance primary 2935 Lelong, Benjamin; Lavoie, Claude; Jodoin, Yvon; Belzile, Francois 2007 Expansion pathways of the exotic common reed (Phragmites australis): a historical and genetic analysis journal DIVERSITY AND DISTRIBUTIONS 13 4 430 437 Using 779 herbarium and modern specimens, we reconstructed the spread of the common reed (Phragmites australis) in Quebec, Canada, where large-scale invasion of this plant species has been reported since the 1960s. All specimens were genetically differentiated using molecular tools to identify the genotype (native or exotic). The exotic genotype (haplotype M) has been present in Quebec as early as 1916, but it was rare prior to the 1970s and was almost exclusively restricted to the shores of the St. Lawrence River. The exotic genotype spread inland only after the beginning of the 1970s. In less than 20 years, a complete shift occurred, from the dominance of native genotypes to the dominance of the exotic genotype. Today, more than 95% of common reed colonies found in Quebec are dominated by the haplotype M. It is especially abundant along roads, but colonies present in marshes are also dominated by the exotic genotype. This study provides evidence that, in Quebec, the development of the highway network in the 1960s and 1970s strongly contributed to the inland expansion of the exotic genotype. Moreover, it shows the usefulness of molecular techniques for reconstructing the spread of an invader. Without the use of molecular tools, the reconstruction of invasions of exotic taxa would be impossible because of the lack of clear phenotypic differences between genotypes. Web of Science Phragmites australis Canada Quebec Field - Observational wetland Wetland Invasion Hyp. Evolution in General;Disturbance primary 2936 Harris, Carla J.; Murray, Brad R.; Hose, Grant C.; Hamilton, Mark A. 2007 Introduction history and invasion success in exotic vines introduced to Australia journal DIVERSITY AND DISTRIBUTIONS 13 4 467 475 The ecological damage caused by invasive vines poses a considerable threat to many natural ecosystems. However, very little data are available for this potentially environmentally destructive functional group in Australia. In order to address this paucity of information, we assembled the first inventory of exotic vines that have become established in natural ecosystems across Australia. The influence that introduction history attributes, variables that relate to the introduction of a species to a new area, may have on the occurrence and distribution of exotic vines was also determined. We asked whether the continent of origin, reason for introduction, and residence time related to the prevalence and distribution of exotic vines across Australia. A total of 179 exotic climbing plant species from 40 different families were found to have become established across continental Australia. However, five families accounted for over 50% of these species. Most exotic vines originated from South America, and were introduced for ornamental purposes. The length of time in which an exotic vine had been present in its new range was significantly related to its distribution, with a positive relationship found between residence time and area of occupancy across the continent. No other introduction history attribute was significantly related to the area of occupancy, or distribution, of a species. This suggests that while the trends found among introduction history attributes are important in explaining the prevalence of exotic vines in Australia, only residence time is currently a useful predictor of their future success. Web of Science Many Australia Theoretical/Modeling;Statistical/Meta-analysis terrestrial Invasion Hyp. Other primary 2937 Ficetola, Gentile Francesco; Thuiller, Wilfried; Miaud, Claude 2007 Prediction and validation of the potential global distribution of a problematic alien invasive species - the American bullfrog journal DIVERSITY AND DISTRIBUTIONS 13 4 476 485 Predicting the probability of successful establishment and invasion of alien species at global scale, by matching climatic and land use data, is a priority for the risk assessment. Both large- and local-scale factors contribute to the outcome of invasions, and should be integrated to improve the predictions. At global scale, we used climatic and land use layers to evaluate the habitat suitability for the American bullfrog Rana catesbeiana, a major invasive species that is among the causes of amphibian decline. Environmental models were built by using Maxent, a machine learning method. Then, we integrated global data with information on richness of native communities and hunting pressure collected at the local scale. Global-scale data allowed us to delineate the areas with the highest suitability for this species. Predicted suitability was significantly related to the invasiveness observed for bullfrog populations historically introduced in Europe, but did not explain a large portion of variability in invasion success. The integration of data at the global and local scales greatly improved the performance of models, and explained > 57% of the variance in introduction success: bullfrogs were more invasive in areas with high suitability and low hunting pressure over frogs. Our study identified the climatic factors entailing the risk of invasion by bullfrogs, and stresses the importance of the integration of biotic and abiotic data collected at different spatial scales, to evaluate the areas where monitoring and management efforts need to be focused. Web of Science Rana catesbeiana Global Field - Observational;Statistical/Meta-analysis terrestrial;lentic;lotic Invasion Hyp. Preadaptation to Climate omnivore 2942 Gammon, Melinda A.; Grimsby, Jonna L.; Tsfrelson, Dina; Kesseli, Rick 2007 Molecular and morphological evidence reveals introgression in swarms of the invasive Taxa fallopia japonica, F-sachalinensis, and F-Xbohemica (Polygonaceae) in the United States journal AMERICAN JOURNAL OF BOTANY 94 6 948 956 Fallopia japonica (Japanese knotweed, Polygonaceae) is a well-known East Asian perennial that is established throughout the U.S. and Europe. Another congener, F. sachalinensis, and their hybrid, F. Xbohemica, also persist on both continents. Their invasive success is primarily attributed to their ability to spread via clonal growth. However, mounting evidence suggests invasion history and dynamics differ between continents and that sexual reproduction is more common than previously assumed. We used published morphological traits designed to distinguish the three taxa to characterize their distribution in 24 New England towns. We found continuous variation of all five traits, with 84% of our 81 individuals having at least one trait outside parental limits. Hierarchical cluster analysis, along with two chloroplast and one nuclear species-specific markers, suggests the presence of intercrossing, segregating hybrids, and likely introgression between F1 hybrids and F. japonica. Our markers also show the first evidence of bidirectional hybridization between parental taxa in the U.S., emphasizing the complex structure of populations in our region. This study is a first step toward unraveling the evolutionary forces that have made these taxa such aggressive invaders in the U.S. The data may also affect management strategies originally designed for largely monomorphic, clonal populations. Web of Science Fallopia japonica;Fallopia sachalinensis USA New England Field - Observational;Statistical/Meta-analysis terrestrial Deciduous Forest;Urban Invasion Hyp. Hybridization primary 2943 Grimsby, Jonna L.; Tsirelson, Dina; Gammon, Melinda A.; Kesseli, Rick 2007 Genetic diversity and clonal vs. sexual reproduction in Fallopia spp. (Polygonaceae) journal AMERICAN JOURNAL OF BOTANY 94 6 957 964 Although fundamental to the study of invasion mechanisms, the relationship between mode of reproduction and plant invasion is not well understood. Fallopia japonica (Japanese knotweed), a highly aggressive invasive plant in both Europe and North America, serves as a model species for examining this relationship. In Britain, F. japonica var. japonica is a single female clone reproducing solely through vegetative growth or obligate hybridization with other Fallopia spp. In the U.S., however, there is more evidence for sexual reproduction. Here, simple sequence repeat (SSR) markers were developed, and three Massachusetts populations were sampled at regular intervals. The amount of sexual and clonal reproduction in each population was determined based on within-population genetic diversity. Clonal growth was apparent, but the populations together contained 26 genotypes and had evidence of sexual reproduction. One genotype that was present in all populations matched the single aggressive British clone of F. japonica var. japonica. Also, a potentially diagnostic marker for the F. sachalinensis genome provided evidence of inter- and intraspecific sexual reproduction and introgression. These differences observed in U.S. populations compared to European populations have significant implications for management of Fallopia spp. in the U.S. and underscore the importance of regional studies of invasive species. Web of Science Fallopia japonica USA Massachusetts Field - Observational terrestrial Urban Invasion Hyp. Inherent Superiority Clonal Reproduction primary 2944 Kendra, Paul E.; Hennessey, Michael K.; Montgomery, Wayne S.; Jones, Edward M.; Epsky, Nancy D. 2007 Residential composting of infested fruit: A potential pathway for spread of Anastrepha fruit flies (Diptera : Tephritidae) journal FLORIDA ENTOMOLOGIST 90 2 314 320 Composting plant waste is a beneficial practice commonly used by American gardeners, but disposal of infested fruit directly into the environment creates a potential pathway for introduction of insect pests. This study estimates the likelihood of adult emergence for exotic fruit flies (Tephritidae) from residential composting in south Florida. Ripe grapefruits, Citrus x paradisi Macfad., were infested with the Caribbean fruit fly, Anastrepha suspensa (Loew). Half of the infested fruit was placed onto outdoor compost piles and half was maintained under controlled laboratory conditions. Adult fly emergence was recorded daily for 30 d from both the compost piles and control bins. Compost temperature, air temperature, relative humidity, and precipitation were monitored, and the study was repeated 4 times under different seasonal conditions. Despite high mortality of flies from the composted fruit relative to control fruit, the overall risk of a potentially mated female emerging from composted fruit was calculated to be similar to 10%. Of the environmental factors evaluated, compost temperature was found to have a significant effect on adult emergence. Mortality approached 100% in piles with maximum compost temperatures >= 48 degrees C. This report provides experimental data in support of quantitative risk analysis for a tephritid-compost pathway. Web of Science Tephritidae USA Florida south Florida Field - Observational terrestrial Urban Invasion Hyp. Mutualism Facilitation primary 2945 Evans, Alexander M.; Gregoire, Timothy G. 2007 A geographically variable model of hemlock woolly adelgid spread journal BIOLOGICAL INVASIONS 9 4 369 382 The hemlock woolly adelgid (HWA) (Adelges tsugae) has spread through the range of eastern hemlock (Tsuga canadensis) leaving dead hemlock trees in its wake. We combined county and previously unavailable township level infestation records with geographic variables including plant hardiness zone, elevation, forest cover type, urbanization, precipitation, temperature, and hemlock range in a geographic information system to build models linking HWA spread to the structure and characteristics of the environment. We explored the connections between site variables and spread rate using quantile regression, Tobit regression, a parametric model for heterogeneous error variance, and classification and regression tree modeling. The results show that since 1990 HWA has spread at a rate closer to 12.5 km/yr rather than the 20-30 km/yr previously estimated, however spread rates vary significantly with environmental variables. County-based data show a faster rate of range expansion in the south, 15.6 km/yr, and very slow spread in the northern part of the current range of HWA. The rate of spread based on township records for Pennsylvania and north is 8.13 km/yr. Our study suggests that HWA spreads more slowly in colder areas, with a mean minimum temperature of -26.1 degrees C (plant hardiness zone 5B) delineating areas of slower range expansion. HWA also spreads more slowly during cold years, those with lower than average mean January temperatures. Our analysis demonstrates the value of quantile regression, Tobit regression, and classification and regression tree models for understanding the spread of invasive, exotic insects. Web of Science Adelges tsugae USA Field - Observational;Theoretical/Modeling terrestrial Coniferous Forest Fundamentals herbivore 2946 Nehrbass, Nana; Winkler, Eckart; Mullerova, Jana; Pergl, Jan; Pysek, Petr; Perglova, Irena 2007 A simulation model of plant invasion: long-distance dispersal determines the pattern of spread journal BIOLOGICAL INVASIONS 9 4 383 395 Mechanisms and consequences of biological invasions are a global issue. Yet, one of the key aspects, the initial phase of invasion, is rarely observed in detail. Data from aerial photographs covering the spread of Heracleum mantegazzianum (Apiaceae, native to Caucasus) on a local scale of hectares in the Czech Republic from the beginning of invasion were used as an input for an individual-based model (IBM), based on small-scale and short-time data. To capture the population development inferred from the photographs, long-distance seed dispersal, changes in landscape structures and suitability of landscape elements to invasion by H. mantegazzianum were implemented in the model. The model was used to address (1) the role of long-distance dispersal in regional invasion dynamics, and (2) the effect of land-use changes on the progress of the invasion. Simulations showed that already small fractions of seed subjected to long-distance dispersal, as determined by systematic comparison of field data and modelling results, had an over-proportional effect on the spread of this species. The effect of land-use changes on the simulated course of invasion depends on the actual level of habitat saturation; it is larger for populations covering a high proportion of available habitat area than for those in the initial phase of invasion. Our results indicate how empirical field data and model outputs can be linked more closely with each other to improve the understanding of invasion dynamics. The multi-level, but nevertheless simple structure of our model suggests that it can be used for studying the spread of similar species invading in comparable landscapes. Web of Science Heracleum mantegazzianum Czech Republic Field - Observational;Theoretical/Modeling terrestrial Fundamentals primary 2947 Collins, A. R.; Jose, S.; Daneshgar, P.; Ramsey, C. L. 2007 Elton's hypothesis revisited: an experimental test using cogongrass journal BIOLOGICAL INVASIONS 9 4 433 443 In the 1950s Charles Elton hypothesized that more diverse communities should be less susceptible to invasion by exotic species (biodiversity-invasibility hypothesis). The biodiversity-invasibility hypothesis postulates that species-rich communities are less vulnerable to invasion because vacant niches are less common and the intensity of interspecific competition is more severe. Field studies were conducted at two sites, a logged site and an unlogged site in Santa Rosa County, Florida, U.S.A, to test Elton's hypothesis using cogongrass (Imperata cylindrica), a non-indigenous grass invading large areas of the Southeastern United States. The logged site was under 17-year-old loblolly pine prior to clear cutting. The unlogged site, a longleaf pine forest, was at the Blackwater River State Forest. Both the logged site and unlogged site showed no significant relationship between the rate of cogongrass spread and native plant species richness, functional richness, and cover of the invaded community. Increased species or functional richness may increase the use of resources; however, the extensive rhizome/root network possessed by cogongrass and its ability to thrive under shade may allow for its persistence in a diverse community. The results from both the logged and unlogged sites do not support the general hypothesis of Elton that invasion resistance and compositional stability increase with diversity. Biodiversity does not appear to be an important factor for cogongrass invasion in the southern United States. Extrinsic factors in this study prevent the ability to draw a defined causal relationship between native plant diversity and invasibility. Underlying reasons for why no relationship was observed may be simply due to the tremendous competitive ability of cogongrass or the narrow range of species richness, functional richness and cover observed in our study. Web of Science Imperata cylindrica USA Florida Blackwater River State Forest Field - Observational terrestrial Coniferous Forest Invasion Hyp. Community Species Richness primary 2948 Aronson, Myla F. J.; Handel, Steven N.; Clemants, Steven E. 2007 Fruit type, life form and origin determine the success of woody plant invaders in an urban landscape journal BIOLOGICAL INVASIONS 9 4 465 475 The spread of alien plant species is a critical ecological event worldwide, but the forces that control this spread are not well documented. Alien plant species are well known to disrupt ecological services of native ecosystems, change the composition of native habitats, and often lead to the extirpation of native flora and fauna. Here, we report on life history patterns of plant species with rapidly spreading and declining ranges in North America's major urban region. We tested for differences in life history traits between the 466 native and alien woody flora of the New York metropolitan area. We also examined the relationship between life history traits and change in distribution in the New York metropolitan area between 1900 and 2000. Native and alien species of the New York metropolitan area differ with respect to pollination vector and breeding system. However, pollination vector and breeding system are not associated with success, defined here as increasing range spread in the urban environment; instead, fruit type (dispersal), life form and origin are important determinants of success. Alien species that are deciduous trees, shrubs or vines with fleshy fruit are the most successful in increasing their distribution in this urban landscape. Newly introduced species with these characteristics are expected to have a better chance at establishing in similar urban landscapes and should be targets for intensive management. The ability to predict which alien species will become invasive is also a valuable tool for the prevention of invasions by newly introduced plant species. Web of Science Many USA New York Field - Observational terrestrial Urban Invasion Hyp. Other primary 2949 Deng, Zifa; An, Shuqing; Zhou, Changfang; Wang, Zhongsheng; Zhi, Yingbiao; Wang, Yunjing; Shi, Suhua; Chen, Lin; Zhao, Congjiao 2007 Genetic structure and habitat selection of the tall form Spartina alterniflora Loisel. in China journal HYDROBIOLOGIA 583 0 195 204 Spartina alterniflora Loisel., a highly invasive species on the Chinese coast, is a focus of increasing management concerns due to its high expansion rate in tideland and the significant damages on native ecosystems, since its introduction into China in 1979. There are both tall and dwarf forms of the species in China. The tall form with strongly invasive ability has widely expanded. Genetic variation was examined within and among three tall form S. alterniflora populations in Jiangsu Province using amplified fragment length polymorphisms (AFLP) markers. Three populations were sampled along the coastal line, and each population was divided into three subpopulations relating with the three microenvironments: Foreland, mid-marsh and upland. Genetic diversity was low at both the population level (PPB = 22%, H (E) = 0. 0657 and H (pop) = 0.099) and at the species level (PPB = 24.65%, H (T) = 0.0814 and H (sp) = 0.1225). A low level of genetic differentiation among populations was detected based on analyses of coefficients of genetic differentiation (9.51%), Shannon's diversity index (9.48%) and AMOVA (10.69%). The mean value of Gst among nine subpopulations was 22.02%. Habitat selections may occur and affect the genetic structure of S. alterniflora in the process of its spread because there are 7.2, 3.4 and 5.9% specific bands out of 158 polymorphic bands in foreland, mid-marsh, and upland, respectively. This genetic differentiation may result from seedling survival and colonization success based on the selection of specialized microhabitats. The results indicated that high capability of genetic differentiation within populations and strong adaptability of tall form S. alterniflora may be the reasons for the widespread expansion of the tall form S. alterniflora. Web of Science Spartina alterniflora China Field - Observational estuarine Invasion Hyp. Evolution in General primary 2950 Abbott, Laurie B.; Lepak, Domininka; Daniel, David L. 2007 Vegetative and reproductive phenology of African rue (Peganum harmala) in the northern Chihuahuan Desert journal SOUTHWESTERN NATURALIST 52 2 209 218 African rue (Peganum harmala) is an herbaceous perennial plain native to arid and semiarid regions of northern Africa and Asian deserts that has spread to parts of the Southwestern United States arid northern Mexico. Despite its occurrence in many geographic regions, little is known about the biology and ecology of this invasive species. We conducted field studies on 2 populations of African rue in the northern Chihuahuan Desert to describe its vegetative and reproductive phenology. Overwintering. dormant plants in both populations commenced growth in mid March, grew through May and June, and initially senesced during June and July. Shoot development was synchronous between the 2 populations, but was not related to ambient or soil temperatures or precipitation. Onset of senescence was not related to calendar date or accumulated temperature. Flower production commenced at both sites in mid April, and fruit maturation Occurred in June and July. Fruit maturation was related to calendar date and ambient temperature. In one population, senescent plants initiated new shoots in August and produced a second cohort of flowers. This renewed growth was not related to temperature, but likely triggered by midsummer precipitation. Therefore, African rue exhibits characteristic *drought evader* growth and reproduction strategies. This fundamental description of African rue phenology, provides knowledge needed to manage this invasive species. Web of Science Peganum harmala Mexico Chihuahuan Desert Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Plasticity primary 2951 Cooper, Matthew J.; Ruetz, Carl R., III; Uzarski, Donald G.; Burton, Thomas M. 2007 Distribution of round gobies in coastal areas of lake michigan: Are wetlands resistant to invasion? journal JOURNAL OF GREAT LAKES RESEARCH 33 2 303 313 Great Lakes coastal wetlands may be more resistant to invasion by certain nonindigenous species and thus serve as refuge habitats for native species. As a first step in testing this hypothesis, we investigated the distribution of round goby (Apollonia melanostomus, formerly Neogobius melanostomus) in the lower reaches of several Lake Michigan tributary systems that contain both wetland and lake habitats near their confluences with Lake Michigan. Using fyke nets, we sampled round gobies in lake and adjacent wetland habitats in four systems in 2004 and six systems in 2005. In each macrohabitat (lake or wetland), we sampled three miccrohabitats (mono-dominant stands of Nuphar, beds of submersed aquatic vegetation, and bare sediment). We found that round gob), catch was generally lower in wetland macrohabitats than adjacent lake macrohabitats and that round gobies appeared to prefer beds of submersed aquatic vegetation in lakes among the three microhabitats. The majority, of round gobies in all habitats were relatively small (< 7 cm standard length). We also found a significant negative correlation between round goby catch and distance of sampling points from the Lake Michigan shoreline in 2005, suggesting that 1) Lake Michigan nearshore waters (including the connecting navigation channels and pier areas) may be serving as round gob.), spawning and nursery habitats with subsequent dispersal into the tributary lake/lwetland complexes, and 2) round gobies may still be invading these systems from Lake Michigan. Our results provide evidence that coastal wetland habitats are more resistant to invasion by round gobies than adjacent lake habitats. Web of Science Apollonia melanostomus USA Michigan Lake Michigan wetland Wetland Invasion Hyp. Other primary 2952 Savino, Jacqueline F.; Riley, Stephen C.; Holuszko, Melissa J. 2007 Activity, aggression, and habitat use of ruffe (Gymnocephalus cernuus) and round goby (Apollonia melanostoma) under laboratory conditions journal JOURNAL OF GREAT LAKES RESEARCH 33 2 326 334 Potential negative ecological interactions between ruffe Gymnocephalus cernuus and round goby Apollonia melanostoma (formerly Neogobius melanostomus) might affect the colonization dynamics of these invasive species where they are sympatric in the Great Lakes. In order to determine the potential for ecological interactions between these species, we examined the activity, aggression, and habitat use of round gobies and ruffe in single species and mixed species laboratory experiments. Trials included conditions in which food was concentrated (in light or darkness) or scattered. Results showed that ruffe were more active than gobies, particularly when food was scattered. Activity of both species was significantly lower during darkness. Round gobies were significantly more aggressive than ruffe, and total aggression was lower in mixed species trials. Habitat use by ruffe and round gobies overlapped considerably, but we observed significant differences between species in their use of specific habitats that depended on experimental conditions. Overall, ruffe used open habitats more often than did round gobies, primarily when food was scattered. Round gobies used rocks significantly more frequently than did ruffe, but their use of rock habitat decreased during dark conditions. Ruffe were found more often in plant habitats and less often near the wall of the pool in trials during daylight with concentrated food. Activity and habitat use of ruffe and round goby did not significantly differ between single and mixed species trials. Overall, we found little evidence,for negative ecological interactions between ruffe and round goby in these laboratory experiments. Web of Science Gymnocephalus cernuus USA Great Lakes Lab lotic Fundamentals predator 2953 Frieswyk, Christin B.; Zedler, Joy B. 2007 Vegetation change in great lakes coastal wetlands: Deviation from the historical cycle journal JOURNAL OF GREAT LAKES RESEARCH 33 2 366 380 Water-level change is integral to the structure and function of Great Lakes coastal wetlands, and many studies document predictable relationships between vegetation and water level. However, anthropogenic stressors, such as invasive species, land-use change, and water-level stabilization, interact to shift the historical cycle (of native vegetation migration up- and down-slope) toward dominance by invasive Typha species. Knowing from earlier studies that water-level stabilization alters the historical vegetation cycle, we asked if similar shifts can occur where water levels are not stabilized. Using historical aerial photographs of three coastal wetlands (in Lake Michigan's Green Bay, Wisconsin), we determined that habitat dominated by Typha species has expanded to eliminate wet meadow habitat. Between 1974 and 1992, linear regressions showed strong, significant relationships of both meadow area (R(2) >= 0.894; p < 0.02) and marsh area (R(2) >= 0.784; p < 0.05) to water level in all three wetlands. In 2000, meadow area was below that predicted by the historical pattern due to the landward advance of marsh habitat during a year of decreasing water levels. In the same period, land use in the wetland watersheds converted from agriculture to urban. Urbanization and the replacement of native Typha lat folia by the invasive hybrid Typha xglauca may have overwhelmed the beneficial impact of water-level fluctuation. The documentation of vegetation shifts, as herein, is an essential step in the process of preserving and restoring ecological integrity. Web of Science Typha xglauca USA Great Lakes Field - Observational wetland Wetland Invasion Hyp. Disturbance primary 2954 Jiang, Xiao Lei; Zhang, Wei Guo; Wang, Gang 2007 Biodiversity effects on biomass production and invasion resistance in annual versus perennial plant communities journal BIODIVERSITY AND CONSERVATION 16 6 1983 1994 In a field experiment we constructed two different communities using both annual and perennial plant species, in which species diversity is experimentally manipulated. We want to test the relationships between species diversity and biomass production and invasibility and the possible mechanisms driving this relationships, especially, whether the identical mechanisms drive both diversity-production and diversity-invasibility relationships. Our results indicated that a positive diversity-production relationship and negative diversity-invasibility and production-invasibility relationships emerged in two different communities. However, the mechanisms underlying are different in two communities. In the annual communities, the observed positive diversity-production and negative diversity-invasibility relationships are linked by the sampling effect. In the perennial communities, however, the mechanism responsible for these observed relationships are the complementarity effect. Our results also found that, in addition to species diversity, species composition also play an important role in governing the observed relationship. The results of our study suggest that because species in different communities may differ in their life history, biological and physiological traits, mechanisms responsible for the observed relationship between diversity and biomass production and invasibiltiy are likely different. Web of Science Many China Field - Experimental terrestrial Invasion Hyp. Community Species Richness primary 2955 Castillo, Jesus M.; Leira-Doce, Pablo; Carrion-Tacuri, Jorge; Munoz-Guacho, Edison; Arroyo-Solis, Aida; Curado, Guillermo; Doblas, David; Rubio-Casal, Alfredo E.; Alvarez-Lopez, Antonio A.; Redondo-Gomez, Susana; Berjano, Regina; Guerrero, Giovanny; De Cires, Alfonso; Figueroa, Enrique; Tye, Alan 2007 Contrasting strategies to cope with drought by invasive and endemic species of Lantana in Galapagos journal BIODIVERSITY AND CONSERVATION 16 7 2123 2136 This study compares how Lantana camara, an invasive species, and L. peduncularis, an autochthonous one, cope with drought in Galapagos. Soil surface temperature was the abiotic environmental parameter that best explained variations in photosynthetic stress. Higher soil surface temperatures were recorded in the lowlands and in rain-shadow areas, which were also the driest areas. L. peduncularis, with a shallow root system, behaved as a drought-tolerant species, showing lower relative growth rates, which decreased with leaf water content and higher photosynthetic stress levels in the lowlands and in a northwest rain-shadow area in comparison with higher and wetter locations. Its basal and maximal fluorescences decreased at lower altitudes, reflecting the recorded drops in chlorophyll concentration. In contrast, L. camara with a deep root system behaved as a drought-avoiding species, showing leaf and relative water contents higher than 55% and avoiding permanent damage to its photosynthetic apparatus even in the driest area where it showed very low chlorophyll content. Its relative growth rate decreased more in dry areas in comparison to wetter zones than did that of L. peduncularis, even though it had greater water content. Furthermore, L. camara showed higher water contents, growth rate, and lower photosynthetic stress levels than L. peduncularis in the arid lowlands. Thus, L. peduncularis maintained lower maximum quantum efficiency of photosystem II photochemistry (F (v)/F (m)) than L. camara even at sunrise, due to higher basal fluorescence values with similar maximal fluorescence, which indicated permanent damage to PSII reaction centres. Our results help to explain the success and limitations of L. camara in the invasion of arid and sub-arid environments. Web of Science Lantana camara Ecuador Galapagos Field - Observational terrestrial Tropical Forest Invasion Hyp. Fluctuating Resources primary 2956 Hochstedler, Wendy W.; Gorchov, David L. 2007 The effects of June precipitation on Alliaria petiolata (garlic mustard) growth, density and survival journal OHIO JOURNAL OF SCIENCE 107 3 26 31 The factors that determine population dynamics of invasive plant species are not well studied. Alliaria petiolata (garlic mustard), an invasive biennial, exhibits annual fluctuation in rosette and adult density. June precipitation has been found to correlate with rosette,A. petiolata density in October and adult density the following May. Since ability to predict density would facilitate management of this invasive species, we experimentally tested the impact of precipitation on. A.. petiolata rosette growth and survival. Rain was excluded in June 2005 from thirty-six 0.8 x 0.8 m plots in a second-growth woodlot in southwest Ohio. Plots were lined to a depth of 20 cm, and randomly assigned to receive a dry (1 cm), average (10 cm) or wet (20 cm) water treatment. In the central 0.25 m(2) of each plot we assessed soil moisture, rosette root depth, root and shoot biomass, and survival. Soil moisture content, measured with a time domain reflectometer, was significantly affected by treatment. However, rosette biomass, root length, fruit production and survival did not differ among treatments. Assessment of soil water availability between treatments indicated dry treatments may not have dried the soil as much as occurs in drought years. While the hypothesis that heavier June precipitation enables rosettes to survive summer drought was not supported, it cannot be rejected based on our experiment. June precipitation is probably not a reliable predictor of A. petiolata rosette survival in years with above average precipitation; however the effect of spring drought on A. petiolata requires further investigation. Web of Science Alliaria petiolata USA Ohio Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Fluctuating Resources primary 2958 Broz, Amanda K.; Broeckling, Corey D.; He, Ji; Dai, Xinbin; Zhao, Patrick X.; Vivanco, Jorge M. 2007 A first step in understanding an invasive weed through its genes: an EST analysis of invasive Centaurea maculosa journal BMC PLANT BIOLOGY 7 0 Background: The economic and biological implications of plant invasion are overwhelming; however, the processes by which plants become successful invaders are not well understood. Limited genetic resources are available for most invasive and weedy species, making it difficult to study molecular and genetic aspects that may be associated with invasion. Results: As an initial step towards understanding the molecular mechanisms by which plants become invasive, we have generated a normalized Expressed Sequence Tag ( EST) library comprising seven invasive populations of Centaurea maculosa, an invasive aster in North America. Seventy- seven percent of the 4423 unique transcripts showed significant similarity to existing proteins in the NCBl database and could be grouped based on gene ontology assignments. Conclusion: The C. maculosa EST library represents an initial step towards looking at gene-specific expression in this species, and will pave the way for creation of other resources such as microarray chips that can help provide a view of global gene expression in invasive C. maculosa and its native counterparts. To our knowledge, this is the first published set of ESTs derived from an invasive weed that will be targeted to study invasive behavior. Understanding the genetic basis of evolution for increased invasiveness in exotic plants is critical to understanding the mechanisms through which exotic invasions occur. Web of Science Centaurea maculosa USA Lab terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 2959 Beard, Karen H. 2007 Diet of the invasive frog, Eleutherodactylus coqui, in Hawaii journal COPEIA 0 2 281 291 Because of their high densities and generalist feeding behaviors, the introduced frog, Eleutherodactylus coqui has been hypothesized to consume and potentially reduce endemic invertebrates in Hawaii. To address this hypothesis, I compared E. coqui diets to invertebrate abundances in I I sites on the Islands of Hawaii and Maui in the summer of 2004. At each site, I collected between 22 and 119 frogs from 20 x 20-m plots, and invertebrates from light traps, beating trays, and leaf litter samples. Prey items in frog stomachs were identified to order, and invertebrates collected in environmental samples were identified to the lowest taxonomic category possible. Multivariate analyses of diet content and invertebrates collected at each site suggest that most Prey was from the leaf litter. Non-native ants (Hymenoptera: Formicidae) and amphipods (Amphipoda: Talitridae) comprised 30% and 22%, respectively, of the total prey items consumed. These non-native invertebrates were more abundant in stomachs of E. coqui than in the environment indicating a preference for these species. There was little evidence that E. coqui were reducing important invertebrate pests. No mosquitoes (Diptera: Culicidae) were found in stomachs, and termites (Isoptera) comprised < 1% of the total prey items. Arthropod orders containing endemic species that appear most vulnerable to E. coqui predation include Acarina (mites), Coleoptera (beetles), Collembola (springtails), and Diptera (flies), which each made up > 2% of the diet of E. coqui. Dominant prey items in frog stomachs differed among study sites suggesting that frogs are opportunistic feeders and forage on abundant prey items. Eleutherodactylus coqui management should focus on areas with endemic invertebrates of concern because it is these locations where E. coqui may have the greatest impact. Web of Science Eleutherodactylus coqui USA Hawaii Field - Observational terrestrial Subtropical Forest Invasion Hyp. Plasticity predator 2961 Lortie, Christopher J.; Cushman, J. Hall 2007 Effects of a directional abiotic gradient on plant community dynamics and invasion in a coastal dune system journal JOURNAL OF ECOLOGY 95 3 468 481 1 Local abiotic factors are likely to play a crucial role in modifying the relative abundance of native and exotic species in plant communities. Natural gradients provide an ideal opportunity to test this hypothesis. 2 In a coastal dune system in northern California, we used comparative and experimental studies to evaluate how a wind and soil texture gradient influences the relative abundance of native and exotic plant species in this community. 3 We detected small-scale spatial variation in soil texture along a 200-m gradient from relatively sheltered to more exposed. Sand coarseness significantly increased with exposure while soil nitrate levels significantly decreased. The more extreme end of the gradient was also subject to greater wind speeds and less soil moisture. 4 The plant community consistently responded to this gradient in the 7 years censused. Species richness decreased with exposure, cover of natives decreased and cover of exotics increased at the more extreme end of the gradient. 5 A single-season wind-shelter experiment similarly shifted the balance between native and exotic species. Shelters decreased the relative density of exotic species and increased the relative density of natives regardless of position on the gradient. 6 These comparative and manipulative findings both suggest that a single factor, wind, at least partially explains the success of exotic species in a coastal dune plant community. This supports the hypothesis that local abiotic conditions can explain differences in invasibility within a plant community. Web of Science Many USA California Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority Broad Tolerances primary 2962 Siemens, Tania J.; Blossey, Bernd 2007 An evaluation of mechanisms preventing growth and survival of two native species in invasive bohemian knotweed (Fallopia x bohemica, Polygonaceae) journal AMERICAN JOURNAL OF BOTANY 94 5 776 783 Restoring native diversity to habitats dominated by invasive plants requires improved understanding of mechanisms that allow introduced plants to retain dominance. We used a factorial transplant experiment to assess whether light limitation, nutrient limitation, or allelopathic interference by Fallopia Xbohemica reduces growth or survival of Eupatorium perfoliatum or Acer saccharinum. Increased light improved A. saccharinum performance but had no effect on E. perfoliatum growth. Increased light had no effect on A. saccharinum survival but improved E. perfoliatum survival. Activated carbon addition had short-term benefits allowing E. perfoliatum plants to grow for 4 wk and increased A. saccharinum leaf width but not biomass. Nutrient addition had no beneficial effect on transplants. These results in combination with the outcome of a cutting experiment suggest that F. Xbohemica achieves competitive superiority primarily by limiting access to light. Species-specific effects and significant interaction effects particularly of light and activated carbon suggest additional mechanisms. Allelopathic interference or interaction with microbial soil organisms may contribute to the lack of native species in populations of F. Xbohemica. Restoration efforts should combine selective F. Xbohemica control with soil amendments (such as activated carbon) to assess their potential to facilitate return of native species to invaded habitats. Web of Science Fallopia Xbohemica USA Lab terrestrial Invasion Hyp. Inherent Superiority Rapid Growth primary 2963 Ostry, M. E.; Moore, M. 2007 Natutral and experimental host range of Sirococcus clavigignenti-juglandacearum journal PLANT DISEASE 91 5 581 584 The fungus Sirococcus clavigignenti-juglandacearum causes butternut canker in North America and is riot known to kill or seriously affect tree species other than butternut (Juglans cinerea). However, this putative exotic pathogen has been found on branches of black walnut (J. nigra) and heartnut (J. ailantifolia var. cordiformis), raising questions regarding the potential host range of the pathogen and its spread to new areas on tree hosts other than butternut. Results of artificial inoculations of several hardwood species indicated that the pathogen, although not causing lethal cankers, has the ability to colonize and survive in the wood of several genera, including Quercus Carya, Corylus, Prunus, and Castanea. Several commercially important Persian walnut (J. regia) cultivars tested were moderately or highly susceptible, underscoring the importance of preventing the movement of the pathogen into commercial Juglans plantations in California, where its ability to cause disease and damage trees is unknown. Evidence for the presence of variation in aggressiveness among isolates of S. clavigignenti-juglandacearum was detected based on differences in canker lengths resulting from inoculations with two isolates of the pathogen. In a field test of several previously named butternut cultivars, all were found to be highly susceptible to the disease, calling into question the value of these selections for nut production or future restoration uses. Web of Science Sirococcus clavigignenti-juglandacearum USA California terrestrial Deciduous Forest Invasion Hyp. Plasticity pathogen 2964 Saltonstall, Kristin; Stevenson, J. Court 2007 The effect of nutrients on seedling growth of native and introduced Phragmites australis journal AQUATIC BOTANY 86 4 331 336 Differing responses to abiotic stresses and increased nutrient availability may play a role in the invasion and spread of introduced Phragmites australis Cav. (Trin.) ex. Steud. and the decline of native P.a. americanus Saltonstall, P.M. Peterson & Soreng in North America. We present results from an outdoor experiment where native and introduced P. australis seedlings were grown under two nutrient treatments. Both subspecies responded positively to increased nutrients but introduced plants clearly outperformed natives, growing taller, producing more stems, and had three to four times higher biomass. The biomass of introduced R australis growing in low nutrients was similar to that of the native in high nutrients. Aboveground:belowground biomass ratios were nearly 1.25 for both native and introduced plants across treatments and reflect the high investment P. australis seedlings place on shoot production in their first year of growth. Our results also demonstrate that introduced P. australis can have explosive growth over a single growing season, even when established from seed. This implies that management of young, newly established populations may be prudent where introduced P. australis is considered undesirable, irregardless of whether eutrophication is an issue. (c) 2006 Elsevier B.V. All rights reserved. Web of Science Phragmites australis USA Maryland Garden wetland Wetland Invasion Hyp. Inherent Superiority Rapid Growth primary 2965 Larson, Daniel 2007 Reproduction strategies in introduced Nymphoides peltata populations revealed by genetic markers journal AQUATIC BOTANY 86 4 402 406 To determine whether introduced Nymphoides peltata populations reproduced vegetatively or sexually, microsatellites were used to study the genetic structure of the species in Sweden. Leaves from 156 plants and seeds from 4 plants were sampled from 7 water-systems and analysed. A total of 10 genotypes were found among the 156 leaves. Seeds accounted for one additional genotype per seed. Lack of genetic variation and entirely vegetative reproduction dominated in the introduced N. peltata populations although sexual reproduction was found in one water-system. However, even where the species reproduced sexually, vegetative reproduction constituted an important part of the total reproduction. (c) 2006 Elsevier B.V. All rights reserved. Web of Science Nymphoides peltata Sweden Field - Observational lentic Invasion Hyp. Inherent Superiority Clonal Reproduction primary 2966 Wilson, John R. U.; Yeates, Alice; Schooler, Shon; Julien, Michael H. 2007 Rapid response to shoot removal by the invasive wetland plant, alligator weed (Alternanthera philoxeroides) journal ENVIRONMENTAL AND EXPERIMENTAL BOTANY 60 1 20 25 Resprouting plants provide an interesting test to the generality of plant allometric relationships. The ability to rapidly resprout after disturbance also makes weeds more difficult to control. We performed a glasshouse experiment to investigate regrowth of an invasive plant (alligator weed, Alternanthera philoxeroides (Martins) Grisebach) after an experimental mowing treatment. Nutrient levels and biomass accumulation were measured weekly for five weeks, and carbohydrate levels were measured when regrowth was quickest. After five weeks, the biomass of treatment plants was similar to that expected from a growth curve fitted to undamaged control plants. Treatment plants, however, had a higher below-ground biomass, and a higher ratio of stem to leaf biomass than expected. The regrowing material also had a lower nutrient concentration. Both the rapid regrowth and the change in morphology make the mechanical control of alligator weed more difficult, and may, in part, be responsible for the invasiveness of this plant. (c) 2006 Elsevier B.V. All rights reserved. Web of Science Alternanthera philoxeroides USA Greenhouse wetland Wetland Invasion Hyp. Inherent Superiority Rapid Growth primary 2967 Bulleri, Fabio; Branca, Maria Giovanna; Abbiati, Marco; Airoldi, Laura 2007 Development of reproductive structures in the introduced green alga, Codium fragile ssp tomentosoides, in the northern Adriatic Sea journal EUROPEAN JOURNAL OF PHYCOLOGY 42 2 137 144 Biological invasions are among the most important drivers of global change. The introduced green alga, Codium fragile ssp. tomentosoides, has become an important component of low-shore assemblages on hard coastal defence structures along the north-west coast of the Adriatic Sea. We investigated the temporal dynamics, the spatial scales of variation and the effects of wave exposure on the abundance of reproductive structures of C. fragile. Furthermore, we assessed whether the reproductive output of C. fragile was correlated with the density of thalli. On the landward side of breakwaters, gametangia were found on thalli of C. fragile from June to September in both 2003 and 2004. Although there was some variation among breakwaters, the abundance of gametangia of C. fragile was greater on the landward than on the seaward side of breakwaters. Scales of variation in the number of gametangia and density of thalli of C. fragile were similar, with most of the variability occurring at a scale of tens of cm. Little variation emerged at larger (tens or hundreds of in) or smaller scales (within thalli, cm). The results of this study indicate that the provision of sheltered rocky habitats has been crucial for the establishment of C. fragile in the northern Adriatic Sea, enabling the alga to grow and reproduce. Processes operating at small spatial scales are responsible for patterns of variation in the number of gametangia and density of thalli of C. fragile. The tendency for a positive correlation between density of thalli and reproductive output in C. fragile in August suggests that greater densities of plants could ameliorate harsh environmental conditions during daytime low tides, fostering reproduction. Web of Science Codium fragile Greece Field - Observational marine Invasion Hyp. Inherent Superiority High Reprod. Output primary 2968 Glasby, Tim M.; Connell, Sean D.; Holloway, Michael G.; Hewitt, Chad L. 2007 Nonindigenous biota on artificial structures: could habitat creation facilitate biological invasions? journal MARINE BIOLOGY 151 3 887 895 We identified different distributions of marine nonindigenous species (NIS) and native species on some artificial structures versus natural reefs and using experimental manipulations, revealed some possible causal mechanisms. In well-established subtidal assemblages, numbers of NIS were 1.5-2.5 times greater on pontoons or pilings than on rocky reefs, despite the local species pool of natives being up to 2.5 times greater than that of NIS. Conversely, on reefs and seawalls, numbers of native species were up to three times greater than numbers of NIS. Differential recruitment to different positions and types of surfaces appeared to influence distribution patterns. NIS recruited well to most surfaces, particularly concrete surfaces near the surface of the water, whilst natives occurred infrequently on wooden surfaces. The position of rocky reefs and seawalls close to the shore and to the seabed appeared to make them favourable for the recruitment of natives, but this positioning alone does not hinder the recruitment of NIS. We argue that pontoons and pilings represent beachheads (i.e. entry points for invasion) for many nonindigenous epibiota and so enhance the spread and establishment of NIS in estuaries. Habitat creation in estuaries may, therefore, be a serious threat to native biodiversity. Web of Science Many Australia Sydney Harbor Field - Observational marine Invasion Hyp. Other primary;filter 2969 Decottignies, Priscilla; Beninger, Peter G.; Rince, Yves; Riera, Pascal 2007 Trophic interactions between two introduced suspension-feeders, Crepidula fornicata and Crassostrea gigas, are influenced by seasonal effects and qualitative selection capacity journal JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 342 2 231 241 The effects of season and qualitative selection capacity on trophic relationships between two sympatric invasive suspension-feeders, Crepidula fornicata and Crassostrea gigas, were investigated in Bourgneuf Bay (France) from January 2003 to June 2004. Carbon and nitrogen stable isotopic deviations, delta C-13 and delta N-15, of common Atlantic slippersnails and Pacific oysters were analysed relative to isotopic composition and availability of end-members. Slippersnail deviations were less variable over the sampling period compared with those of oysters. Significant differences between delta C-13 and delta N-15 of C. fornicata and C. gigas were found from winter to early summer, and linked to major isotopic changes in oysters. We identified three distinct seasonal periods: January to March when oysters were N-15-enriched compared to slippersnails and to themselves at other times of the year, April to June-July when oysters showed a N-15-depletion and a more marked C-13-depletion compared to slippersnails and to themselves at other times of the year, and July-August to December when both species presented similar carbon and nitrogen deviations. Species-specific differences in qualitative selection capability may explain these seasonal differences in isotopic deviations. Whereas the isotopic composition of the indiscriminate suspension-feeding slippersnails reflects the composition of the seston throughout the year, the oyster is capable of qualitative selection. The oyster isotopic compositions are consistent with a facultative activation of selection mechanisms under conditions of qualitative and quantitative food limitation, notably the preferential ingestion and assimilation of the dominant organic source in the suspended pool. We conclude that C. fornicata and C gigas are trophic competitors only in winter and spring at this site, where detrital end-members are major POM components. These results underscore (1) the importance of long-term (annual) studies in the evaluation of potential trophic competition, and (2) the necessity to include the qualitative selection capacities of suspension-feeders in future interpretations of trophic relationships in marine coastal ecosystems. (c) 2007 Published by Elsevier B.V. Web of Science Crepidula fornicata;Crassostrea gigas France Bourgneuf Bay Field - Observational marine Fundamentals filter 2970 Sala, Anna; Verdaguer, Dolors; Vila, Montserrat 2007 Sensitivity of the invasive geophyte Oxalis pes-caprae to nutrient availability and competition journal ANNALS OF BOTANY 99 4 637 645 Background and Aims Invasion by alien plants may be partially related to disturbance-related increases in nutrient availability and decreases of competition with native species, and to superior competitive ability of the invader. Oxalis pes-caprae is an invasive winter geophyte in the Mediterranean Islands that reproduces vegetatively via bulbs. An investigation was made into the relative responses of O. pes-caprae and the native annual grass Lolium rigidum to nutrient availability and to competition with each other in order to understand patterns of invasion in the field. Because Oxalis accumulates oxalic acid in its leaves, which could ameliorate soil phosphorous availability, field observations were made to determine whether the presence of Oxalis alters soil P availability. Methods A full-factorial glasshouse experiment was conducted with nutrient availability (high and low) and competition (Lolium alone, Oxalis alone, and Lolium and Oxalis together). Plant performance was assessed by determining (1) above- and below-ground biomass at the time of Oxalis maximum biomass and (2) reproductive output of Oxalis and Lolium at the end of their respective growth cycles. Measurements were also taken for leaf N and P content. Soil samples were taken in the field from paired Oxalis-invaded and non-invaded plots located in Menorca (Balearic Islands) and available P was determined. Key Results High nutrient availability increased Oxalis and Lolium vegetative biomass and reproductive output to a similar degree. Competition with Lolium had a much stronger negative effect on Oxalis bulb production than reduced nutrients. Lolium was a superior competitor than Oxalis; the latter did not affect Lolium maximum biomass and spike production. Significantly greater soil-P availability in Oxalis-invaded field soils relative to paired non-invaded soils suggest that Oxalis influences soil P cycling. Conclusions Oxalis is a poor competitor. This is consistent with the preferential distribution of Oxalis in disturbed areas such as ruderal habitats, and might explain its low influence on the cover of native species in invaded sites. The results also suggest that certain disturbances (e.g. autumn ploughing) may greatly enhance Oxalis invasion. Web of Science Oxalis pes-caprae Spain Menorca Greenhouse terrestrial Invasion Hyp. Disturbance 2971 Grotkopp, Eva; Rejmanek, Marcel 2007 High seedling relative growth rate and specific leaf area are traits of invasive species: Phylogenetically independent contrasts of woody angiospernis journal AMERICAN JOURNAL OF BOTANY 94 4 526 532 Understanding, causal factors of exotic species invasions is important not only for prevention and prioritizing control efforts, but also for providing valuable insights into the underlying biology of contrasting- life-history strategies. In seedling growth analyses, invasive woody species were compared with less-invasive woody species commonly cultivated in California using phylogenetically Corrected procedures (12 phylogenetically independent contrasts). Invasive species were hypothesized to have highher seedling relative growth rates (RGRs) and specific leaf areas (SLAs) than did related less-invasive species. In phylogenetically independent contrasts conducted among taxa within families, high seedling RGRs and SLAs have significant positive associations with woody plant invasiveness. For contrasts containing species invasive in mediterranean regions, invasive species had significantly larger root biomass allocation than did less-invasive species. Optimization of fast seedling growth (high RGR) associated with opportunistic resource acquisition (high SLA) and increased root allocation to survive summer drought may be critical for the success of plant invaders in regions with inediterranean climates. Web of Science Many USA California terrestrial Invasion Hyp. Inherent Superiority Rapid Growth primary 2972 Poulin, Jessica; Sakai, Ann K.; Weller, Stephen G.; Nguyen, Tan 2007 Phenotypic plasticity, precipitation, and invasiveness in the fire-promoting grass Pennisetum setaceum (poaceae) journal AMERICAN JOURNAL OF BOTANY 94 4 533 541 Invasiveness may result from genetic variation and adaptation or phenotypic plasticity, and genetic variation in fitness traits may be especially critical. Pennisetum setaceum (fountain grass, Poaceae) is highly invasive in Hawaii (HI), moderately invasive in Arizona (AZ), and less invasive in southern California (CA). In common garden experiments, we examined the relative importance of quantitative trait variation, precipitation, and phenotypic plasticity in invasiveness. In two very different environments, plants showed no differences by state of origin (HI, CA, AZ) in aboveground biomass, seeds/flower, and total seed number. Plants from different states were also similar within watering treatment. Plants with supplemental watering, relative to unwatered plants, had greater biomass, specific leaf area (SLA), and total seed number, but did not differ in seeds/flower. Progeny grown from seeds produced under different watering treatments showed no maternal effects in seed mass, germination, biomass or SLA. High phenotypic plasticity, rather than local adaptation is likely responsible for variation in invasiveness. Global change models indicate that temperature and precipitation patterns over the next several decades will change, although the direction of change is uncertain. Drier summers in southern California may retard further invasion, while wetter summers may favor the spread of fountain grass. Web of Science Pennisetum setaceum USA California;Hawaii;Arizona Garden terrestrial Grassland Invasion Hyp. Plasticity primary 2973 Geng, Yu-Peng; Pan, Xiao-Yun; Xu, Cheng-Yuan; Zhang, Wen-Ju; Li, Bo; Chen, Jia-Kuan; Lu, Bao-Rong; Song, Zhi-Ping 2007 Phenotypic plasticity rather than locally adapted ecotypes allows the invasive alligator weed to colonize a wide range of habitats journal BIOLOGICAL INVASIONS 9 3 245 256 Both phenotypic plasticity and locally adapted ecotypes may contribute to the success of invasive species in a wide range of habitats. Here, we conducted common garden experiments and molecular marker analysis to test the two alternative hypotheses in invasive alligator weed (Alternanthera philoxeroides), which colonizes both aquatic and terrestrial habitats. Ninety individuals from three pairs of aquatic versus terrestrial populations across southern China were analyzed, using inter simple sequence repeat (ISSR) marker, to examine population differentiation in neutral loci. Two common gardens simulating aquatic and terrestrial habitats were set up to examine population differentiation in quantitative traits. We found no evidence of population differentiation in both neutral loci and quantitative traits. Most individuals shared the same ISSR genotype. Meanwhile, plants from different habitats showed similar reaction norms across the two common gardens. In particular, plants allocated much more biomass to the belowground roots in the terrestrial environment, where alligator weed may lose part or all of the aboveground shoots because of periodical or accidental disturbances, than those in the aquatic environment. The combined evidence from molecular marker analysis and common garden experiments support the plasticity hypothesis rather than the ecotype hypothesis in explaining the adaptation of alligator weed in a wide range of habitats. Web of Science Alternanthera philoxeroides China Garden terrestrial;lentic Invasion Hyp. Plasticity;Preadaptation to Climate primary 2974 DeFalco, Lesley A.; Fernandez, George C. J.; Nowak, Robert S. 2007 Variation in the establishment of a non-native annual grass influences competitive interactions with Mojave Desert perennials journal BIOLOGICAL INVASIONS 9 3 293 307 Competition between native and non-native species can change the composition and structure of plant communities, but in deserts, the highly variable timing of resource availability also influences non-native plant establishment, thus modulating their impacts on native species. In a field experiment, we varied densities of the non-native annual grass Bromus madritensis ssp. rubens around individuals of three native Mojave Desert perennials-Larrea tridentata, Achnatherum hymenoides, and Pleuraphis rigida-in either winter or spring. For comparison, additional plots were prepared for the same perennial species and seasons, but with a mixture of native annual species as neighbors. Growth of perennials declined when Bromus was established in winter because Bromus stands had 2-3 months of growth and high water use before perennial growth began. However, water potentials for the perennials were not significantly reduced, suggesting that direct competition for water may not be the major mechanism driving reduced perennial growth. The impact of Bromus on Larrea was lower than for the two perennial grasses, likely because Larrea maintains low growth rates throughout the year, even after Bromus has completed its life cycle. This result contrasts with the perennial grasses, whose phenology completely overlaps with (Achnatherum) or closely follows (Pleuraphis) that of Bromus. In comparison, Bromus plants established in spring were smaller than those established in winter and thus did not effectively reduce growth of the perennials. Growth of perennials with mixed annuals as neighbors also did not differ from those with Bromus neighbors of equivalent biomass, but stands of these native annuals did not achieve the high biomass of Bromus stands that were necessary to reduce perennial growth. Seed dormancy and narrow requirements for seedling survivorship of native annuals produce densities and biomass lower than those achieved by Bromus; thus, impacts of native Mojave Desert annuals on perennials are expected to be lower than those of Bromus. Web of Science Bromus madritensis USA California Field - Experimental terrestrial Grassland Invasion Hyp. Fluctuating Resources primary 2975 Jongejans, Eelke; Skarpaas, Olav; Tipping, Philip W.; Shea, Katriona 2007 Establishment and spread of founding populations of an invasive thistle: the role of competition and seed limitation journal BIOLOGICAL INVASIONS 9 3 317 325 Successful plant invasions require both the founding and local spread of new populations. High plant densities occur only when founding plants are able to disperse their seeds well locally to quickly colonize and fill the new patch. We test this ability in a 7-year field experiment with Carduus acanthoides, an invasive weed in several North American ecosystems. Founder plants were planted in the center of 64 m(2) plots and we monitored the recruitment, distribution pattern, mortality, and seed production of the seedlings that originated from these founding plants. Competing vegetation was clipped not at all, once, or twice each year to evaluate the importance of interspecific competition. More seedlings recruited in the intermediate once-clipped plots, and these seedlings also survived better. The control plots had fewer microsites for seedling recruitment; clipping a second time in September stimulated grasses to fill up the gaps. The number of C. acanthoides recruits and their median distances from the founder plants were also explained by the initial seed production of the founding plants. Overall, the experiment shows that the success of founder plants can fluctuate strongly, as 55% of the plots were empty by the sixth year. Our study suggests that the local invasion speed following initial establishment depends strongly on both the propagule pressure and availability of suitable microsites for seedling recruitment and growth. Web of Science Carduus acanthoides USA Field - Experimental terrestrial Grassland Invasion Hyp. Propagule Pressure primary 2976 Dawson, Kathryn; Veblen, Kari E.; Young, Truman P. 2007 Experimental evidence for an alkali ecotype of Lolium multiflorum, an exotic invasive annual grass in the Central Valley, CA, USA journal BIOLOGICAL INVASIONS 9 3 327 334 One of the characteristics of highly invaded ecosystems is that exotic species are often poor invaders of edaphically severe sites, which become refuges for native flora. To investigate the invasive potential of Lolium multiflorum (Per.) into alkali sites in California, an ex-situ reciprocal transfer experiment was carried out using seeds from populations of L. multiflorum taken from three sites differing in alkalinity (and inundation), including alkali sink soils (pH 8.5) and sink matrix soils (pH 7.4) located within meters of each other, and non-sink soils (pH 5.0) located several km away. Survivorship, plant height, leaf number and seed production were assessed. In addition, a native composite, Hemizonia pungens (Hick.), commonly found on alkali sinks was also sampled at the sink and sink matrix microsites. Lolium multiflorum plants grown from alkali sink and sink matrix seeds produced fewer leaves and seeds but were taller than plants grown from non-alkali seeds, the latter perhaps an adaptation to frequently inundated soils. Non-alkali genotypes fared poorly in sink soils for all traits, both in comparison to their growth on non-sink soils, and in comparison to the sink and sink edge genotypes. This suggests the existence of L. multiflorum ecotypes adapted to inundated alkali sinks, a genotypic difference that occurs on a broad spatial scale (kilometers), but not so obviously on the micro-site scale (meters) between sink and sink matrix populations. These data suggest that the absence of exotic invasives from alkali sites may be temporary if they are evolving tolerance for these severe sites, and this may threaten the future of the native alkali specialists that currently find refuge in these sites. Web of Science Lolium multiflorum USA California Field - Experimental terrestrial Chaparral/Shrublands Invasion Hyp. Evolution of Increased Competitive Ability primary 2977 Mony, C.; Koschnick, T. J.; Haller, W. T.; Muller, S. 2007 Competition between two invasive Hydrocharitaceae (Hydrilla verticillata (L.f.) (Royle) and Egeria densa (Planch)) as influenced by sediment fertility and season journal AQUATIC BOTANY 86 3 236 242 Competition between two invasive plants of similar growth form, Hydrilla verticillata (L.f.) (Royle) and Egeria densa (Planch), was studied in response to season and sediment fertility. These two invasive species were grown in outdoor concrete tanks in monocultures, and mixtures. Five fertilization rates were tested for monocultures and two for mixtures where six combinations of planting densities were used in two seasons (spring and fall). Monitoring of plant biomass was made at the end of each of these 2-month-experiments. In contrast to E densa, clear seasonal patterns in biomass production and in reproductive allocations of H. verticillata were evident. Competitive pressure for both species was lower during the fall experiment. Biomass production increased with fertilization for H. verticillata in monocultures and changes either in allocative ratios or in tuber production patterns were shown in response to nutrient availability. However, E. densa growth was not affected by fertilization. In most cases, H. verticillata was a better competitor than E. densa except when sediment was pure sand. Competition occurred mainly for nutrient uptake rather than for light harvesting. These results suggest that despite the similar ecology, H. verticillata may outcompete E. densa in many situations, probably due to its higher plasticity. (c) 2006 Elsevier B.V All rights reserved. Web of Science Hydrilla verticillata;Egeria densa USA Florida Garden lentic Fundamentals primary 2978 Hansen, Dorte L.; Lambertini, Carla; Jampeetong, Arunothai; Brix, Hans 2007 Clone-specific differences in Phragmites australis: Effects of ploidy level and geographic origin journal AQUATIC BOTANY 86 3 269 279 Phragmites australis (Cav.) Trin. ex Steud. is virtually cosmopolitan and shows substantial variation in euploidy level and morphology. The aim of this study was to assess clone-specific differences in morphological, anatomical, physiological and biochemical traits of P. australis as affected by the geographic origin, the euploidy level (4x, 6x, 8x and 12x), and to assess differences between native and introduced clones in North America. Growth, morphology, photosynthetic characteristics, photosynthetic pigments and enzymes were measured on 11 geographically distinct clones propagated in a common environment in Denmark. Any differences between the measured parameters were caused by genetic differences between clones. Overall, the largest differences between clones were found in ontogeny, shoot morphology and leaf anatomy. The North Swedish clone was adapted to short growing seasons and sprouted very early in the spring but senesced early in July. In contrast, clones from southern regions were adapted to warmer and longer growing seasons and failed to complete the whole growth-cycle in Denmark. Some clones from oceanic habitats with climatic conditions that do not differ much from conditions at the Danish growth site did flower in the common environment. The octoploid genotype in general had larger dimensions of leaves, taller and thicker shoots and larger cell sizes than did the hexaploid and tetraploid clones. The dodecaploid clone was neither bigger than the octoploid, nor significantly different from tetraploid and hexaploid clones in most of the morphological characters observed. Stomatal density decreased with increasing ploidy level, while length of guard cells increased. Tetraploid clones generally had morphometric dimensions, similar to hexaploids. Hence, polyploidy did not always result in an increase in plant size, probably because the number of cell divisions during development is reduced. Four North American clones were included in the study. The clone from the Atlantic Coast and the supposed invasive European clone resembled each other. The Gulf Coast clone differed from the rest of the clones in having leaf characters resembling Phragmites mauritianus Kunth. Thus, morphological characters are not unmistakable parameters that can be used to discriminate between introduced and native clones. The physiological and biochemical processes also differed between clones, but these processes showed considerable phenotypic plasticity and were therefore very difficult to evaluate conclusively. It is concluded that P. australis is a species with very high genetic variability which is augmented by its cosmopolitan distribution, clonal growth form and the large variation in chromosome numbers. It is therefore not surprising that large genetically determined differences in ontogeny, shoot morphology and leaf anatomy occur between clones. (c) 2006 Elsevier B.V. All rights reserved. Web of Science Phragmites australis Denmark;USA;Sweden Garden wetland Wetland Invasion Hyp. Other primary 2980 O'Doherty, Daniel C.; Sherwood, Alison R. 2007 Genetic population structure of the Hawaiian alien invasive seaweed Acanthophora spicifera (Rhodophyta) as revealed by DNA sequencing and ISSR analyses journal PACIFIC SCIENCE 61 2 223 233 Acanthophora spicifera (Vahl) Borgesen is the most widespread and invasive alien macroalga on coral reefs throughout the main Hawaiian Islands. This alga disperses from harbors and ports to coral reefs throughout the state, producing high quantities of biomass that affect a wide range of reef flora and fauna. Population samples of A. spicifera from across the main Hawaiian Islands were collected and compared through two kinds of analyses: DNA sequencing (based on a variable region of the nuclear large subunit ribosomal RNA gene, and the mitochondrial cox 2-3 spacer region) and fragment techniques (Inter-Simple Sequence Repeats [ISSRs]). DNA sequencing revealed no variation for the two markers, even when collections from other areas of the Pacific and Australia were included. In contrast, ISSR analyses revealed highly structured Hawaiian populations of A. spicifera with a substantial range of both within- and among-population variation, with individual plants forming discrete clusters corresponding to geographic locality. Web of Science Acanthophora spicifera USA Hawaii Field - Observational marine Intertidal/Near Shore Invasion Hyp. Evolution in General primary 2982 Von Holle, Betsy; Motzkin, Glenn 2007 Historical land use and environmental determinants of nonnative plant distribution in coastal southern New England journal BIOLOGICAL CONSERVATION 136 1 33 43 The factors that influence the invasion of natural habitats by normative plants remain poorly understood. We investigated abiotic, biotic, and human influences on the distribution and abundance of normative species in coastal upland habitats of southern New England and adjacent New York, US. We censused vegetation and sampled soils in 776, 20 x 20 In plots in natural areas and constructed a spatially referenced GIS database of the region that included land-use history, distance from roads, and surficial geology. Our results indicate that the modern distribution of normative plants is influenced by multiple, interdependent current and historical factors. Glaciolacustrine landforms had greater nonnative species richness and cover than beach-dune, moraine, and glacial outwash sand plain landforms. Extant open-canopied areas (i.e., grasslands, dunes, heather barrens, and old fields) harbored significantly greater normative species richness and cover than closed-canopy forests, heathlands, and shrublands. Additionally, soil calcium levels and native species richness were positively associated with normative species richness. Sites that were cultivated historically or experienced other soil disturbance had higher normative species richness than areas without soil disturbance. Overall, abiotic, biotic and historical land use affected levels of normative species richness whereas normative cover was largely associated with abiotic conditions, particularly soil characteristics. Because many rare coastal sandplain plants reach their greatest abundance on extant open-canopied habitats, efforts to restore native plants will involve tradeoffs between the benefits of expanded habitat for these species and increased risk of invasion by normative species. (C) 2006 Published by Elsevier Ltd. Web of Science Many USA New York;Conneticut Field - Observational terrestrial Deciduous Forest Invasion Hyp. Community Species Richness;Disturbance primary 2983 Castellano, Steven M.; Boyce, Richard L. 2007 Spatial patterns of Juniperus virginiana and Lonicera maackii on a road cut in Kentucky, USA journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 134 2 188 198 We investigated the spatial patterns of several woody species that colonize disturbed sites, including the native Juniperus virginiana and the exotic Lonicera maackii. Our study site was on a road cut in northern Kentucky, USA, that faced NW and consisted of nine contiguous 25-m(2) quadrats. The positions of all woody plants : 50 cm in height were measured. Spatial patterns were quantified and compared with Ripley's K and the pair correlation function, which analyze the distribution of interplant distance at varying scales. For each woody plant, we also measured height, soil depth, and photosynthetically active radiation (PAR); the latter two measurements were taken at the four cardinal directions. Ripley's K showed that J. virginiana was distributed randomly, while L. maackii was clustered. Both J. virginiana and L. maackii were distributed independently of each other. Smaller L. maackii individuals clustered with larger ones, but this pattern was not seen in J. virginiana. Neither species appeared to associate with the other species. Mann-Whitney tests showed that L. maackii was found in areas of lower light than J. virginiana but there was only a weak indication of differences in soil depth means between these two species. These two species colonize disturbed sites in very different manners. L. maackii potentially facilitates establishment of its own species, whereas J. virginiana seedlings can only establish at some distances from parent trees. The different physiological requirements and growth forms of the two species appear to explain the lack of interaction between them. Though this project was limited to one study site, the methods can be used for multiple site analysis or on sites of varying size. Web of Science Lonicera maackii USA Kentucky terrestrial Old Field Fundamentals primary 2987 Kalwij, J. M.; Milton, S. J.; McGeoch, M. A. 2007 Road verges: Corridors for plant invasions - A spatial hierarchical approach journal SOUTH AFRICAN JOURNAL OF BOTANY 73 2 293 294 Web of Science Many South Africa Theoretical/Modeling;Review terrestrial Invasion Hyp. Disturbance primary 2988 Gittenberger, Adriaan 2007 Recent population expansions of non-native ascidians in The Netherlands journal JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 342 1 122 126 Over the last 50 yrs seven non-native ascidians have settled in The Netherlands, concentrated in the two periods 1974-1977 and 1991-2004 (i.e., Styela clava, Aplidium glabrum, Diplosoma listerianum, Didemnum sp., Botrylloides violaceus, Molgula complanata and Peraphora japonica). The year of the introduction of B. violaceus remains a matter of dispute because many of the Botrylloides specimens that are recorded in western Europe, have been identified as the closely resembling species B. leachi. Only Didemnum sp. has become a true invasive species and has become a threat to native ecosystems, especially in the province of Zeeland, by its ability to overgrow virtually all hard substrata present. This includes rocks, stones, sand, algae and almost all sessile marine animals. The sudden population expansion of the didemnid from 1996 onward, coincided with the cold winter of 19951996, which caused decreased population sizes of many marine animals. The resulting increase in the availability of suitable substrates for settlement and the strong decrease of grazing sea urchins, may have triggered the population expansion. Studying its population dynamics, the optimal growing temperature for Didemnum sp. appears to be 14-18 degrees C. Virtually all colonies die when the water temperature gets colder than 5 degrees C. Colonies growing on live marine animals seem to be more resistant to the cold, than those growing on rocks, stones and plants. Two potential predators of the didemnid have also been recorded in Dutch waters: the gastropods Trivia arctica and Lamellaria sp. (c) 2006 Elsevier B.V. All rights reserved. Web of Science Many The Netherlands Field - Observational marine Intertidal/Near Shore Fundamentals filter 2989 Altman, Safra; Whitlatch, Robert B. 2007 Effects of small-scale disturbance on invasion success in marine communities journal JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 342 1 15 29 Introductions of non-indigenous species have resulted in many ecological problems including the reduction of biodiversity, decline of commercially important species and alteration of ecosystems. The link between disturbance and invasion potential has rarely been studied in the marine environment where dominance hierarchies, dynamics of larval supply, and resource acquisition may differ greatly from terrestrial systems. In this study, hard substrate marine communities in Long Island Sound, USA were used to assess the effect of disturbance on resident species and recent invaders, ascidian growth form (i.e. colonial and solitary growth form), and the dominant species-specific responses within the community. Community age was an additional factor considered through manipulation of 5-wk old assemblages and 1-yr old assemblages. Disturbance treatments, exposing primary substrate, were characterized by frequency (single, biweekly, monthly) and magnitude (20%, 48%, 80%) of disturbance. In communities of different ages, disturbance frequency had a significant positive effect on space occupation of recent invaders and a significant negative effect on resident species. In the 5-wk community, magnitude of disturbance also had a significant effect. Disturbance also had a significant effect on ascidian growth form; colonial species occupied more primary space than controls in response to increased disturbance frequency and magnitude. In contrast, solitary species occupied significantly less space than controls. Species-specific responses were similar regardless of community age. The non-native colonial ascidian Diplosoma listerianum responded positively to increased disturbance frequency and magnitude, and occupied more primary space in treatments than in controls. The resident solitary ascidian Molgula manhattensis responded negatively to increased disturbance frequency and magnitude, and occupied less primary space in treatments than in controls. Small-scale biological disturbances, by creating space, may facilitate the success of invasive species and colonial organisms in the development of subtidal hard substrate communities. (c) 2006 Elsevier B.V. All rights reserved. Web of Science Diplosoma listerianum USA New York Long Island Sound Field - Experimental marine Intertidal/Near Shore Invasion Hyp. Disturbance filter 2990 Agius, Brad P. 2007 Spatial and temporal effects of pre-seeding plates with invasive ascidians: Growth, recruitment and community composition journal JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 342 1 30 39 Many shallow water subtidal habitats in Massachusetts, USA have recently been invaded by five non-indigenous ascidian species: Ascidiella aspersa, Botrylloides violaceus, Didemnum sp., Diplosoma listerianum and Styela clava. This study examined the effects of seawater temperature, as a proxy for climate change, on B. violaceus and D. listerianum and the impact these ascidians have on native sessile fouling communities. Field experiments were conducted over a four month period at two locations (Lynn and Woods Hole, MA) to examine growth dynamics over regional thermal and geographic ranges. Invasive ascidians occupied as much as 80% of the primary substratum and accounted for the majority of species richness. B. violaceus and D. listerianum growth were similar at both study sites, but initial colony growth of D. listerianum was positively affected by temperature. B. violaceus and D. listerianum exhibited rapid two-week growth rates during the summer months with more rapid growth at the warmer Woods Hole site. Competition for space between B. violaceus and D. listerianum typically resulted in neutral borders between colonies. Overgrowth occurred if the colony of one species was disproportionably larger than the colony of the other species. Recruitment and growth of native species influenced the long-term composition of experimental communities more than the pre-seeding with B. violaceus or D. listerianum colonies. Elevated temperatures, however, increased initial growth of B. violaceus and D. listerianum and may have facilitated the species success to invade the communities during crucial periods of introduction. With projected global climate change, a rise in sea surface temperatures may exacerbate the cumulative impacts of invasions on benthic communities and facilitate the invasion of other non-native ascidian species. (c) 2006 Elsevier B.V. All rights reserved. Web of Science Many USA Massachusetts Field - Experimental marine Intertidal/Near Shore Invasion Hyp. Community Species Richness filter 2991 Osman, Richard W.; Whitlatch, Robert B. 2007 Variation in the ability of Didemnum sp to invade established communities journal JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 342 1 40 53 Over the past 30 years southern New England, USA has been invaded by several species of ascidians, including Botrylloides violaceus, Diplosoma listerianum, Styela clava, and Ascidiella aspersa. These species have become dominate in coastal embayments and marinas but are usually absent from more open water coastal areas. A colonial ascidian, Didemnum sp. has invaded southern New England during the past 10 years and we first observed this species in eastern Long Island Sound in 2000. It has become the dominant at several field sites while remaining in low abundance at others. We conducted an experiment at two places, a protected marina and an open coast site, to examine its ability to compete with the established fouling community. Small colonies of Didemnum were transplanted onto panels with communities that varied in age from one to four weeks old and these treatments along with controls with only Didemnum were exposed at both sites. In most treatments Didemnum became a dominant species in the communities at both sites but it reached higher abundances at the open coast site. Potential causes of the observed differences are predation on other species of ascidians at the open coast site reducing recruitment of these species and competition, lower tolerance for elevated temperatures at the marina site, or other environmental parameters that might affect growth rates. (c) 2006 Published by Elsevier B.V. Web of Science Diplosoma listerianum USA New England Field - Experimental marine Intertidal/Near Shore Invasion Hyp. Community Species Richness filter 2992 Dijkstra, Jennifer; Harris, Larry G.; Westerman, Erica 2007 Distribution and long-term temporal patterns of four invasive colonial ascidians in the Gulf of Maine journal JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 342 1 61 68 Invasive ascidians are a growing concern for ecologists and natural resource managers, yet few studies have documented their short- and long-term temporal patterns of abundance. This study focuses on the invasion of the Gulf of Maine by the colonial ascidians Botryllus schlosseri, Botrylloides violaceus, Diplosoma listerianum and Didemnum sp. A. We examined the time of arrival and potential vectors for these four invasive ascidians using survey data (collected from 1969 onwards) and literature documentation. We also compared the dominance and seasonal patterns of abundance of these species using data from two identical panel studies; one conducted from 1979 to 1980, the other from 2003 to 2005. Didemnum and Botrylloides were most likely first introduced into the Damariscotta River, Maine in the early 1970's through oyster aquaculture while Botryllus and Diplosoma were probably transported by commercial and recreational vessels. The overall abundance of colonial ascidians has increased since 1979 and 1980. Botryllus was the only invasive colonial ascidian present during the 1979 to 1980 study and accounted for an average of 6.16% cover on panels. From 2003 to 2005, the more recently arrived colonial ascidians Botrylloides and Didemnum accounted for 7.38% and 2.08% cover respectively, while Botryllus covered only 1.16%. Our results reveal a shift in seasonal abundance between 1979 to 1980 and 2003 to 2004. In 1979 and 1980, colonial ascidians had the highest percent cover in fall and winter while in 2003 and 2005 they bad highest percent cover in summer and fall. Seasonal patterns of space occupation by colonial ascidians were correlated with seasonal changes in seawater temperature. (c) 2006 Elsevier B.V. All rights reserved. Web of Science Didemnum listerianum.;Botrylloides violaceus;Botryllus schlosseri USA Maine Field - Observational marine Intertidal/Near Shore Fundamentals filter 2993 Simoncini, Melissa; Miller, Robert J. 2007 Feeding preference of Strongylocentrotus droebachiensis (Echinoidea) for a dominant native ascidian, Aplidium glabrum, relative to the invasive ascidian Botrylloides violaceus journal JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 342 1 93 98 Subtidal benthic communities show distinct patterns of community structure related to substrate angle. Suspension-feeding invertebrate communities often dominate vertical and undercut rock surfaces, while macroalgae dominate horizontal surfaces. One factor that may shape this pattern is sea urchin grazing, which is often more intense on horizontal surfaces. The native Gulf of Maine ascidian Aplidium glabrum, like other native ascidians, is generally restricted to vertical and undercut rock walls, whereas the introduced ascidian Botrylloides violaceous is often abundant on horizontal surfaces. We tested the hypothesis that this pattern could be due to differing predation intensity on these two ascidians by Strongylocentrotus droebachiensis, a dominant omnivore in the Gulf of Maine. Feeding preference of S. droebachiensis on the native A. glabrum vs. B. violaceous was estimated in the laboratory and in field experiments. Laboratory results show that S. droebachiensis prefers to feed on the native ascidian A. glabrum over B. violaceous. In the field, potential differences in the impact of S. droebachiensis on the two species were masked by the much greater growth rate of B. violaceus compared to A. glabrum. These results may help explain observed patterns in ascidian distribution in the Gulf of Maine, and ultimately the overall success of B. violaceus as a major invader throughout New England. (c) 2006 Elsevier B.V. All rights reserved. Web of Science Aplidium glabrum USA Maine Field - Experimental;Field - Observational marine Intertidal/Near Shore Invasion Hyp. Enemy Of My Enemy filter 2994 Castro, Silvia; Loureiro, Joao; Santos, Conceicao; Ater, Mohammed; Ayensa, Garbine; Navarro, Luis 2007 Distribution of flower morphs, ploidy level and sexual reproduction of the invasive weed Oxalis pes-caprae in the western area of the Mediterranean region journal ANNALS OF BOTANY 99 3 507 517 Background and Aims Oxalis pes-coprae is a widespread invasive weed in regions with a Mediterranean climate. In its native habitat (southern Africa) this species has been reported as heterostylous with trimorphic flowers and a self- and morph-incompatible reproductive system. In most of the areas invaded, only a pentaploid short-styled morphotype that reproduces mainly asexually by bulbils is reported, but this has only been confirmed empirically. This study aims to analyse the floral morph proportions in a wide distribution area, test the sexual female success, and explain the causes of low sexual reproduction of this species in the western area of the Mediterranean Basin. Methods Fifty-five populations of O. pes-caprae were sampled in the Iberian Peninsula and Morocco to evaluate the floral morph ratio and individual fruit set. In plants from a dimorphic population, hand-pollination experiments were performed to evaluate the effect of the pollen source on pollen tube growth through the style. The ploidy level and genome size of individuals of each floral morph were analysed using flow cytometry. Key Results From the populations studied 89.1% were monomorphic, with most of them containing the short-styled (SS) floral morph, and 10.9% were dimorphic containing long-styled (LS) and SS morphs. In some of these, isoplethy was verified but no fruit production was observed in any population. A sterile form was also recorded in several populations. Hand-pollination experiments revealed that pollen grains germinated over recipient stigmas. In intermorph crossings, pollen tubes were able to develop and fruit initiation was observed in some cases, while in intramorph pollinations, pollen tube development was sporadic and no fruit initiation was observed. All individuals within each floral form presented the same DNA ploidy level: SS plants were pentaploid and LS and the sterile form were tetraploid. Conclusions The low or null sexual reproduction success of this species in the area of invasion studied seems related with the high frequency of monomorphic populations, the unequal proportion of floral morphs in dimorphic populations and the presence of different ploidy levels between SS and LS morphs. The discovery of the occurrence of an LS floral morph and a sterile form, whose invading capacity in these areas is as yet unknown, will be valuable information for management programmes. Web of Science Oxalis pes-caprae Spain;Morocco Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority Clonal Reproduction primary 2995 Condeso, T. Emiko; Meentemeyer, Ross K. 2007 Effects of landscape heterogeneity on the emerging forest disease sudden oak death journal JOURNAL OF ECOLOGY 95 2 364 375 Sudden oak death is an emerging forest disease caused by the pathogen Phytophthora ramorum that is invading the west coast of the United States and semi-natural areas in Europe. This disease causes lethal stem infections in oaks (Quercus spp.) and tanoak (Lithocarpus densiflorus), as well as non-lethal foliar infections in a range of other species. We investigated two questions to evaluate the effect of landscape structure on the spread of P. ramorum: (i) does the spatial pattern of forested habitat predict P. ramorum disease severity, and is this relationship scale-dependent; and (ii) what influence does spatial pattern have on the optimal microclimate conditions for P. ramorum reproduction? We mapped the spatial distribution of suitable forest habitat for P. ramorum and established 86 randomly located field plots within a 20-km(2) region of northern California. For each plot, we quantified P. ramorum disease severity and measured the abundance of woody species. Disease severity in each plot was examined in relation to the surrounding landscape structure measured for nested landscapes of increasing scale. P. ramorum disease severity was greatest in plots surrounded by a high proportion of contiguous forest, after accounting for plot-level variables of host abundance, elevation, canopy cover and microclimate. The explanatory power of the model increased with increasing scale up to 200 m, but was not significant at scales less than 50 m. High disease severity was associated with lower temperatures in the field than the laboratory-determined optimal range for pathogen reproduction. Variation in microclimate conditions was explained by elevation, not the pattern of host vegetation, indicating that spatially varying disease severity was not a function of microclimate-related edge effects on pathogen growth and survival. Both landscape-scale configuration and local composition of host habitat are related to the severity of this destructive forest disease. Increased disease severity within contiguous woodlands may have a considerable impact on the composition of such woodlands, with cascading effects on the population dynamics of both host and pathogen. Web of Science Phytophthora ramorum USA California Field - Observational;Theoretical/Modeling terrestrial Deciduous Forest Fundamentals pathogen 2997 Parker, Matthew A.; Wurtz, Anna K.; Paynter, Quentin 2007 Nodule symbiosis of invasive Mimosa pigra in Australia and in ancestral habitats: a comparative analysis journal BIOLOGICAL INVASIONS 9 2 127 138 Ninety isolates of root nodule bacteria from an invasive Mimosa pigra population in Australia were characterized by PCR assays and by sequencing of ribosomal genes. All isolates belonged to the same bacterial genus (Burkholderia) that predominates on M. pigra in its native geographic range in tropical America. However, the Australian Burkholderia strains represented several divergent lineages, none of which had a close relationship to currently known Burkholderia strains in American M. pigra populations. Inoculation of M. pigra with Australian strains resulted in equal or higher plant growth and nodule nitrogenase activity (measured by acetylene reduction assays) relative to outcomes with bacteria from M. pigra's native geographic region. The main difference in symbiotic phenotype for bacteria from the two regions involved responses to an alternate Mimosa host species: Central American strains failed to fix nitrogen in association with Mimosa pudica, while most Australian Burkholderia isolates tested had high nodule nitrogenase activity in association with both Mimosa species. Invasive M. pigra populations in Australia have therefore acquired a diverge assemblage of nodule bacteria that are effective nitrogenfixing symbionts, despite having a broader host range and a distant genetic relationship to bacterial strains found in the plant's ancestral region. Web of Science Mimosa pigra Australia Field - Observational terrestrial Deciduous Forest Invasion Hyp. Mutualism Facilitation primary 2998 Kota, Nathan L.; Landenberger, Rick E.; McGraw, James B. 2007 Germination and early growth of Ailanthus and tulip poplar in three levels of forest disturbance journal BIOLOGICAL INVASIONS 9 2 197 211 Increasing rates of forest disturbance may provide greater opportunity for invasion of normative species, thereby altering the successional trajectory of native plant communities. In the eastern U.S., invasive Ailanthus altissima and native Liriodendron tulipifera have similar life histories and niches and often co-occur. To examine how disturbance affects the establishment of these species, we performed field experiments to evaluate the response of sown seeds and transplanted seedlings to three levels of disturbance on north- and south-facing aspects. L. tulipifera germination was severely limited by low seed viability and had significantly lower germination than A. altissima in all sites. The effect of disturbance regime on A. altissima germination depended on aspect in the second growing season. In contrast, mean seedling survival, biomass, leaf area and leaf area ratio were greater for L. tulipifera in all field sites. Overall, the north-facing selective cut forest provided a disproportionately large number of suitable microsites for L. tulipifera establishment. Collectively, this study demonstrated that different timber harvest practices produce heterogeneous mosaics of suitable microsites for germination and establishment. Limited L. tulipifera germination may be a serious constraint to population establishment if seeds are deposited for the first time immediately after a disturbance event. However, if sufficient viable seeds of both species exist, L. tulipifera out-performs the invasive in the first two years following disturbance. This may explain why A. altissima has shown explosive population growth in a limited number of sites in the past century. Web of Science Ailanthus altissima USA Field - Experimental terrestrial Coniferous Forest Invasion Hyp. Disturbance primary 2999 Burns, Jean H.; Halpern, Stacey L.; Winn, Alice A. 2007 A test for a cost of opportunism in invasive species in the Commelinaceae journal BIOLOGICAL INVASIONS 9 2 213 225 Many invasive species can respond opportunistically to favorable growing conditions. In a previous work, we found that invasive species in the family Commelinaceae were more opportunistic than their noninvasive congeners and could therefore outperform noninvasive relatives in an environment with abundant resources and no competition. Contrary to the expectation that superior performance under favorable conditions comes at the cost of reduced performance under stressful conditions, invasive species did not perform more poorly relative to noninvasive congeners under any conditions we examined. Here we expand our search for potential costs of opportunism in invasive species to additional environmental conditions in which invasive taxa have been shown or predicted to perform poorly. We grew four invasive and four noninvasive species in environments consisting of all possible combinations of high and low soil resources and presence and absence of clipping (removal of aboveground biomass). We also fed leaves of each species to a generalist herbivore to assess resistance to herbivory. We found that the advantage of invasive species is reduced but not eliminated by low soil resources and clipping. At low soil resources, invasive species produced softer leaves than noninvasive species and might therefore be less resistant to generalist herbivory than noninvasive species, although a direct comparison of resistance in a no-choice bioassay revealed no difference. The invasive species outperformed noninvasive species only under the most favorable conditions, and the noninvasive species did not outperform the invasive species in any environment. Web of Science Many terrestrial Invasion Hyp. Enemy Release;Inherent Superiority Superior Competitor primary 3000 Richardson, Bryce A.; Zarnbino, Paul J.; Klopfenstein, Ned B.; McDonald, Geral I.; Carris, Lori M. 2007 Assessing host specialization among aecial and telial hosts of the white pine blister rust fungus, Cronartium ribicola journal CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE 85 3 299 306 The white-pine blister rust fungus, Cronartium ribicola Fisch. in Rabenh., continues to spread in North America, utilizing various aecial (primary) and telial (alternate) hosts, some of which have only recently been discovered. This introduced pathogen has been characterized as having low genetic diversity in North America, yet it has demonstrated a capacity to invade diverse environments. The recent discovery of this rust fungus on the telial host Pedicularis racemosa Dougl. ex Benth., raises questions of whether this host association represents a recent acquisition by C. ribicola or a long-standing host association that was overlooked. Here we explore two questions: (i) is host specialization detectable at a local scale and (ii) is the capacity to infect Pedicularis racemosa local or widespread? Genetic analysis of C. ribicola isolates from different aecial and telial hosts provided no evidence for genetic differentiation and showed similar levels of expected heterozygosity within a geographic population. An inoculation test showed that diverse C. ribicola sources from across North America had the capacity to infect Pedicularis racemosa. These results support a hypothesis that ability to infect Pedicularis racemosa is common in C. ribicola from North America. Utilization of Pedicularis racemosa by C. ribicola may be dependent on the co-occurrence of this host, inoculum, and favorable environments. Web of Science Cronartium ribicola USA Field - Observational terrestrial Coniferous Forest Fundamentals pathogen 3002 Walsh, Maureen G.; Dittman, Dawn E.; O'Gorman, Robert 2007 Occurrence and food habits of the round goby in the profundal zone of southwestern Lake Ontario journal JOURNAL OF GREAT LAKES RESEARCH 33 1 83 92 Little is known about the ecology of round goby (Neogobius melanostomus), an invasive benthic fish, in the profundal zone of the Great Lakes. In April 2002-2005 we caught increasing numbers of round gobies with a bottom trawl in the 45-150 m depth range of southwestern Lake Ontario. In 2005, we examined gut contents of 30 round gobies from each of three depths, 55, 95, and 130 m, and qualitatively compared gut contents with density of benthic invertebrates determined by Ponar grabs. Round goby guts contained mostly Dreissena spp. and opposum shrimp, Mysis relicta (Mysis); the frequency of occurrence of dreissenids in guts decreased with depth, whereas the frequency of occurrence of Mysis in guts increased with depth. Abundance of these invertebrates in the environment followed the same pattern, although dreissenids of optimum edible size (3-12 mm) were still abundant (1,373/m(2)) at 130 m, where round gobies primarily consumed Mysis, suggesting that round gobies may switch from dreissenids to more profitable prey when it is available. Other food items were ostracods and fish, with ostracods generally eaten by smaller round gobies and fish eaten by larger round gobies. Occurrence and increasing abundance of round gobies in the profundal zone and predation on Mysis by round goby could have far-reaching consequences for the Lake Ontario fish community. Web of Science Neogobius melanostomus USA Michigan Field - Observational marine Benthic Invasion Hyp. Plasticity predator 3003 Akasaka, Munemitsu; Tsuyuzaki, Shiro; Hase, Akira 2007 Annual growth of invasive Larix kaempferi seedlings with reference to microhabitat and ectomycorrhizal colonization on a volcano journal JOURNAL OF PLANT RESEARCH 120 2 329 336 To investigate the seedling growth of a biologically invasive larch Larix kaempferi (Lamb.) Carr. on Mount Koma, Japan, seedlings were excavated from three microhabitats (bareground = BA, Salix reinii patch = SP, and Larix understory = LU) in three elevational zones. Seedlings showed the highest ectomycorrhizal (ECM) colonization percentage in the most shaded microhabitat, LU. ECM colonization percentages in BA and SP were found to decrease with decreasing elevation. These results inferred that the ECM colonization percentages were related to seedling growth, particularly in BA and SP. However, the annual seedling growth was not synchronized with the increases in either elevational gradients. Although ECM colonization was most evident in LU, the seedling growth was the lowest. We concluded that the effects of ECM colonization on seedling growth were reduced mostly by microhabitat characteristics. Web of Science Larix kaempferi Japan Mount Koma Field - Observational terrestrial Coniferous Forest Fundamentals primary 3004 Sugiura, Shinji; Yamazaki, Kazuo 2007 Migratory moths as dispersal vectors of an introduced plant-pathogenic fungus in Japan journal BIOLOGICAL INVASIONS 9 2 101 106 The plant-pathogenic fungus Claviceps paspali infects florets of the dallisgrass Paspalum dilatatum and induces the plant to produce honeydew (containing massive amounts of conidia), which in turn attracts insects for dispersal of the fungal spores. In Japan, the association between C. paspali and its host plant is common, although both P. dilatatum and C. paspali are introduced species. To determine the dispersal agents of the introduced C paspah, we examined which insects sapped the P. dilatatum honeydew produced by C paspali. The study was conducted from September to October 2003 in central Japan. Adults of 48 moth species and two lacewing species visited infected spikelets of P. dilatatum and sapped the honeydew at night. The dominant moths, which carried C. paspali conidia on their proboscises, migrate long distances every year. Therefore, migratory moths may transmit C paspali spores from diseased to healthy host plants and may have spread C. paspali to other areas in Japan where C paspali did not previously exist. Web of Science Claviceps paspali terrestrial Grassland Invasion Hyp. Mutualism Facilitation pathogen 3005 Williams, Moira C.; Wardle, Glenda M. 2007 The spatial pattern of invading Pinus radiata journal PROCEEDINGS OF THE LINNEAN SOCIETY OF NEW SOUTH WALES 128 0 111 122 The spatial pattern of invading populations can provide insight into mechanisms of invasion and help establish the potential for further spread of a species. Pinus radiata has successfully invaded native vegetation across southeastern Australia. The small scale spatial pattern of invading Pinus radiata was investigated within two dry Eucalypt woodlands adjacent to commercial plantations in the upper Blue Mountains, NSW Australia. This study aimed to identify the presence of a second generation of pines in order to determine the sustainability of the invading population. We looked for evidence of 1) clustering of pine seedlings; 2) positive associations between pine seedlings and reproductive pines. Spatial analysis of 20 m by 20 m plots using dispersion indices and Ripley's K function revealed clustering of pine seedlings at distances of up to 450 m from the plantation. Bivariate analysis found significant positive association between seedlings and reproductive pines in two plots. Further evidence for self propagation was Provided by the correlation between seedling abundance and cone abundance. These results suggest that the invading population is sustainable in the long term and is capable of spreading further into the native vegetation. Web of Science Pinus radiata Australia Field - Observational terrestrial Coniferous Forest Invasion Hyp. Inherent Superiority Self Compatible primary 3006 Dupont, Lise; Bernas, Damien; Viard, Frederique 2007 Sex and genetic structure across age groups in populations of the European marine invasive mollusc, Crepidula fornicata L. (Gastropoda) journal BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY 90 2 365 374 In long-lived species, variance in allele frequencies over time may vary according to the number of generations contributing to progeny. Here, we investigate the temporal stability of genetic diversity and structure in relation to sex and age in introduced populations of Crepidula fornicata, an exotic gastropod that successfully invaded Europe. This protandrous species has the potential to change sex from male to female according not only to age, but also to local sex ratio (social environment). This mechanism may adjust the reproduction efficiency across different cohorts and thus decrease the likelihood of genetic drift in the following generations. Based on crude demographic structure analysis in two spatially closed introduced French populations, we demonstrate that recruitment is discontinuous. Although timing of sex change is different across populations, both populations have a similar age structure characterized by distributions of males and females changing across generations. Using five microsatellite loci, we show that both populations display a temporal genetic homogeneity and a stability in genetic diversity indices across age groups examined. Our results highlight that the social control of sex change in C. fornicata has strong implications to the maintenance of high genetic diversity by enhancing breeding across several generations at each reproductive season. (c) 2007 The Linnean Society of London. Web of Science Crepidula fornicata France Field - Observational marine Invasion Hyp. Plasticity herbivore 3007 Garnas, Jeffrey R.; Drummond, Francis A.; Groden, Eleanor 2007 Intercolony aggression within and among local populations of the invasive ant, Myrmica rubra (Hymenoptera : Formicidae), in coastal Maine journal ENVIRONMENTAL ENTOMOLOGY 36 1 105 113 Myrmica rubra L. was introduced into New England in the early 20th century, and at present, has a patchy distribution in parts of northeastern North America, including records from 31 communities in Maine. M. rubra is highly polygynous, and colonies reproduce vegetatively, forming dense local populations where conditions are favorable. Using mobile nests and baited arenas in a series of field aggression bioassays, we tested patterns of internest tolerance within and among local populations on Mt. Desert Island, ME. We found that foragers originating from fragments of the same colony or from neighboring nests retained a high level of intraspecific tolerance over several months, whereas significant intercolony aggression among workers was present between colonies within the same local patch separated by approximate to 10 m. Within populations, aggression score values were found to increase linearly with internest distance within a site. Aggression was highest between colonies from spatially different populations on the island and was higher still when nests were assayed against colonies at an off-island site 70 km away in Castine, ME. These data strongly suggest a multicolonial organization within and among local populations of M. rubra in parts of its introduced range. These findings contradict the loss of intraspecific aggression and unicolonial social structure over large geographic areas that have previously been observed in other invasive ant species, particularly Linepithema humile Mayr. Web of Science Myrmica rubra USA Maine Field - Observational terrestrial Invasion Hyp. Other omnivore 3008 Dehnen-Schmutz, Katharina; Touza, Julia; Perrings, Charles; Williamson, Mark 2007 Teh horticultural trade and ornamental plant invasions in Britain journal CONSERVATION BIOLOGY 21 1 224 231 Ornamental horticulture has been recognized as the main pathway for plant invasions worldwide. We examined the link between propagate pressure created by the presence of ornamental plants in the market and their ability to escape from cultivation and establish in the wild. A random sample of 534 non-native ornamental species on sale in nineteenth century Britain showed that 27% of these species were recorded growing outside cultivation and 30% of those were established. Species that had escaped from cultivation were more frequently on sale both in the nineteenth century and today than nonescaping species. We used logit regression models to identify biological and socioeconomic variables that affect species' abilities to escape cultivation and become established, Frequencies in the market in the nineteenth century and today were good explanatory variables that distinguished escaping from nonescaping species, whereas for the transition from casual to established status these two socioeconomic variables were either absent or only of weak significance. Biological characteristics that increased the probability that a species would escape from cultivation were species height, a European native range, and being an annual. Climbing plants and species intolerant of low temperatures were less likely to escape. In contrast, the establishment probability was greater if the species belonged to a genus native to Britain and increased as the number of continents in a plants native range increased. Annual plants had a reduced probability of establishment. Market presence, prices, and the date of introduction are among the socioeconomic factors that have had important effects on the observed course of invasions. Web of Science Many United Kingdom Field - Observational terrestrial Invasion Hyp. Propagule Pressure primary 3009 Tiebre, Marie-Solange; Vanderhoeven, Sonia; Saad, Layla; Mahy, Gregory 2007 Hybridization and sexual reproduction in the invasive alien Fallopia (Polygonaceae) complex in Belgium journal ANNALS OF BOTANY 99 1 193 203 Background and Aims The knotweed complex, Fallopia spp. (Polygonaceae), belongs to the most troublesome invasive species in Europe and North America. Vegetative regeneration is widely recognized as the main mode of reproduction in the adventive regions. However, the contribution of sexual reproduction to the success of these invasive species has only been detailed for the British Isles. An examination was made as to how hybridization may influence the sexual reproduction of the complex in Belgium and to determine how it may contribute to the dispersal of the species. Methods Studies were made of floral biology, reproductive success, seed rain, seed bank, germination capacity, seedling survival and dispersal capacity in order to characterize the reproductive biology of the species. Moreover, chromosome counts and flow cytometry were used to assess the hybrid status of seedlings produced by sexual reproduction. Key Results In the area investigated, extensive sexual reproduction by hybridization within the complex, including one horticultural species, was demonstrated. A small percentage of seeds may be dispersed outside the maternal clone (> 16 m) allowing the formation of genetically differentiated individuals. Seed germination was possible even after a winter cold period. Conclusions The extensive sexual reproduction by hybridization could further contribute to the dramatic invasive success of knotweeds in Belgium and should not be underestimated when considering control and management measures. Web of Science Fallopia japonica var. japonica; F. sachalinensis-F. x behemica Belgium Field - Observational terrestrial Invasion Hyp. Hybridization primary 3010 Mwangi, Peter N.; Schmitz, Martin; Scherber, Christoph; Roscher, Christiane; Schumacher, Jens; Scherer-Lorenzen, Michael; Weisser, Wolfgang W.; Schmid, Bernhard 2007 Niche pre-emption increases with species richness in experimental plant communities journal JOURNAL OF ECOLOGY 95 1 65 78 In plant communities, invasion resistance may increase with diversity because empty niche space decreases simultaneously. However, it is not clear if this only applies to exotic species or also to native species arriving at a site with few other native species during community assembly. We tested the latter by transplanting four native species into experimental grassland communities varying in species richness form 1-16 (-60) species. In addition, we tested the hypothesis that invasion is less successful if the invading species belongs to a functional group that is already present in the community. The test invaders included a grass species (Festuca pratensis, FP), a short (Plantago lanceolata, PL) and a tall herb species (Knautia arvensis, KA), and a legume species (Trifolium pratense, TP). The same four functional groups also occurred alone or in all possible combinations in the different experimental communities. The overall performance of the transplants was negatively related to the logarithm of the species richness of host communities. Plant biomass declined by 58%, 90%, 84% and 62% in FP, PL, KA and TP, respectively, from monocultures to 16-species mixtures, indicating lower invasiveness of the two herbs than of the grass and the legume. Resident grasses showed a strong negative effect on the performance of all test invaders, whereas resident small and tall herbs had neutral, and resident legumes had positive effects. The case of the legumes indicates that contributions to invasion resistance need not parallel invasiveness. Communities containing resident species of only one functional group were most inhibitive to transplants of the same functional group. These results indicate that invasion resistance of experimental plant communities is related to the degree of niche overlap between resident species and invaders. This niche overlap can be high due to generally low amounts of empty niche space in species-rich resident communities or due to the occurrence of the same functional group as the one of the invader in the resident community. Stronger within-than between-functional-group invasion resistance may be the key mechanism underlying diversity effects on invasion resistance in grassland and other ecosystems at large. Web of Science Festuca pratensis;Plantago lanceolata;Knautia arvensis;Trifolium pratense Germany Field - Experimental terrestrial Grassland Invasion Hyp. Community Species Richness primary 3012 Kollmann, Johannes; Frederiksen, Lise; Vestergaard, Peter; Bruun, Hans Henrik 2007 Limiting factors for seedling emergence and establishment of the invasive non-native Rosa rugosa in a coastal dune system journal BIOLOGICAL INVASIONS 9 1 31 42 The relative importance of seed, habitat and microhabitat limitation has rarely been investigated for invasive non-native species, although this is critical for their effective management and for predicting future range expansion. Rosa rugosa is an abundant non-native shrub in coastal habitats of NW Europe; it is common along the Baltic coast but more scarce in exposed dunes of the North Sea. To investigate whether invasion of exposed dunes is limited by seed, habitat and microhabitat limitation, seedling emergence and establishment were examined in a factorial sowing, transplant and disturbance experiment. Twenty plots were randomly placed in each of five dune habitats (white dune, Empetrum dune, grey dune, outer dune heath, inner dune heath), and studied over 2 years. Seedling emergence in control subplots was zero in all habitats, whereas 96% and 98% of the undisturbed and disturbed seeded subplots produced seedlings. Disturbance had a positive effect on emergence and subsequent survival in white dune, outer and inner dune heath. Seedling survival and growth, and growth of transplanted seedlings, were markedly lower in grey dune. These findings indicate that establishment of R. rugosa is seed-limited in coastal dune habitats, and that the species is able to establish in both active and fixed dunes once seeds have arrived. Although differential seedling emergence and growth indicate that habitats differ in their degree of invasion susceptibility by R. rugosa, the positive influence of small-scale disturbance suggests microhabitat limitation in some dune habitats as well. Dune management should aim to reduce seed production and dispersal of R. rugosa in near-natural sites, and anthropogenic changes of habitat dynamics should be prevented. Web of Science Rosa rugosa Denmark Baltic coast terrestrial Chaparral/Shrublands Invasion Hyp. Disturbance primary 3013 Mondor, Edward B.; Tremblay, Michelle N.; Messing, Russell H. 2007 Morphological and ecological traits promoting aphid colonization of the Hawaiian Islands journal BIOLOGICAL INVASIONS 9 1 87 100 Species introductions into novel habitats, especially island ecosystems, can have devastating effects on ecosystem function and stability. Though none are native, at least 96 aphid species can now be found on one or more of the Hawaiian Islands. As aphids cause direct feeding damage and transmit plant viruses, it is important to identify the traits that have enabled these particular species to successfully colonize the archipelago. To address this question, nine morphological and ecological traits that may contribute to successful colonization were assessed for aphids present in Hawaii. As a comparative null model, we assessed the same traits for heterospecific congeners which are not present in the archipelago, but are present elsewhere in the world. Here we report that traits with higher frequencies among colonizing aphid species are: small apterae size, broad host range, anholocycly (i.e., permanent parthenogenesis), and presence in continental USA. Small aphids arriving from the mainland US and capable of feeding on numerous plant species may be intercepted less often by plant protection agents. It is also likely that asexually reproducing species are well suited to the Hawaiian subtropical climate, thereby eliminating the need for sexual phases and egg-laying for overwintering. By understanding the traits that enable aphids to successfully colonize remote islands, it is our hope that plant protection efforts may be enhanced, thereby reducing damage to native ecosystems. Web of Science Many USA Hawaii Field - Observational terrestrial Tropical Forest Invasion Hyp. Inherent Superiority High Reprod. Output;Effective Disperser;Clonal Reproduction herbivore 3014 Foxcroft, L. C.; Hoffmann, J. H.; Viljoen, J. J.; Kotze, J. J. 2007 Environmental factors influencing the distribution of Opuntia stricta, an invasive alien plant in the Kruger National Park, South Africa journal SOUTH AFRICAN JOURNAL OF BOTANY 73 1 109 112 Opuntia stricta (Cactaceae), an alien weed, has invaded an area of more than 35 000 ha in the Skukuza region of the Kruger National Park [KNP]. The distribution of the plant and features of the environment were used to identify biotic and abiotic factors which may be affecting the distribution and density of the plant. A Canonical Community Analysis revealed that none of the environmental factors that were monitored influenced the distribution or abundance of O. stricta in KNP. There were no apparent natural barriers that might limit the occurrence of O. stricta within the KNP. The study provides insight into the relationship between the invader and host environment, showing that there is a high probability that, unless there is appropriate intervention, O. stricta will eventually colonise the entire KNP. (c) 2006 SAAB. Published by Elsevier B.V. All rights reserved. Web of Science Opuntia stricta South Africa Kruger National Park Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Preadaptation to Climate primary 3015 Daws, M. I.; Hall, J.; Flynn, S.; Pritchard, H. W. 2007 Do invasive species have bigger seeds? Evidence from intra- and inter-specific comparisons journal SOUTH AFRICAN JOURNAL OF BOTANY 73 1 138 143 Shifts in seed mass associated with the process of plant invasion may potentially enhance the competitiveness of introduced species and contribute to invasiveness. Here we test this premise using two complementary approaches. Firstly we compare the seed mass of 114 species from 31 families in both their native and introduced ranges. Secondly we compare the seed mass of 376 co-occurring native and invasive species from two families (Asteraceae and Poaceae) from California. Our results demonstrate that across the 31 families there is a significant tendency for seed mass to increase from the native to invasive ranges. In addition, the analysis on the two families revealed that such a shift in seed mass may contribute to invasive species having, on average, a higher seed mass than co-occurring native species in the same family. Consequently, these results suggest that invasion-associated upward shifts in seed mass may foster plant invasions by increasing the competitiveness of invasive species relative to natives. (c) 2006 SAAB. Published by Elsevier B.V. All rights reserved. Web of Science Many World Statistical/Meta-analysis terrestrial;estuarine;wetland Invasion Hyp. Inherent Superiority Effective Disperser primary 3016 White, Ian R.; Backhouse, David 2007 Comparison of fungal endophyte communities in the invasive panicoid grass Hyparrhenia hirta and the native grass Bothriochloa macra journal AUSTRALIAN JOURNAL OF BOTANY 55 2 178 185 Communities of fungal endophytes from roots, stems and leaves of the introduced grass Hyparrhenia hirta (Coolatai grass) and the native species Bothriochloa macra (redgrass) were compared at two sites to identify characteristics that may be associated with invasiveness of H. hirta. The most frequently isolated fungi from both hosts were species of Nigrospora, Alternaria, Cladosporium, Phoma, Epicoccum, Fusarium and Periconia. Most of these occurred at a similar frequency in the two hosts, although Nigrospora sphaerica was much more frequently isolated from H. hirta at both sites. There was little support for the hypothesis that the introduced species (H. hirta) would have a less diverse endophyte community than the native species. There was a greater degree of dominance by the most frequent species in communities from H. hirta than from B. macra, leading to lower diversity indices, but no significant difference in species richness. Cluster analysis of the endophyte communities suggested that host had a greater influence than site on community structure, and that this was expressed mostly in the relative frequency of fungi isolated from stems and leaves, with very similar fungal communities present in the roots of both species at both sites. Analysis of co-occurrence showed no evidence that competition among fungi affected community structure within individual plants. The dominance of N. sphaerica in H. hirta was therefore due to fungus - plant interactions rather than fungus - fungus interactions. Interactions with N. sphaerica could potentially affect the population ecology of H. hirta. Web of Science Hyparrhenia hirta Australia New South Wales Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Mutualism Facilitation primary 3019 Wada, Takashi; Matsukura, Keiichiro 2007 Seasonal changes in cold hardiness of the invasive freshwater apple snail, Pomacea canaliculata (Lamarck) (Gastropoda : Ampullariidae) journal MALACOLOGIA 49 2 383 392 We investigated the cold hardiness of a South American freshwater apple snail, Pomacea canaliculata, which began to invade Japanese paddy fields in the early 1980s. Pomacea canaliculata exhibited apparent seasonal fluctuation in its cold hardiness. Snails collected from submerged paddy fields in summer were less tolerant to cold, and none survived exposure to 0 degrees C for five days. With decreasing temperature, together with drainage of its habitat in autumn, P. canaliculata developed cold hardiness, attaining almost 100% survivorship after exposure to 0 degrees C for five days in December. The snails resting in drained fields were approximately nine times more cold tolerant than those collected from submerged fields, based on the time to 50% mortality at 0 degrees C. Snails overwintering in aquatic conditions also acquired cold hardiness. Web of Science Pomacea canaliculata Japan Field - Observational terrestrial Old Field Invasion Hyp. Inherent Superiority Broad Tolerances herbivore 3020 Pratt, Paul D.; Rayamajhi, M. B.; Silvers, C. S.; Ferriter, A. P. 2007 Naturalization and biomass allocation of the invasive tree Melaleuca quinquenervia in wetlands of the Bahamas journal JOURNAL OF AQUATIC PLANT MANAGEMENT 45 0 8 16 The myrtaceous tree Melaleuca quinquenervia (Cav.) Blake occurs naturally along Australia's eastern coast and has been internationally disseminated for ornamental and agroforestry purposes. We describe the naturalization of M. quinquenervia in the Bahamas and compare stand characteristics to other populations in the exotic tree's native and adventive ranges. Naturalized M. quinquenervia stands were assessed at single locations on Grand Bahama, New Providence and Andros Island. We conclude that M. quinquenervia is at an incipient stage of invasion at these locations, based on the small spatial distribution of stands and the relatively smaller size class distributions at each site. Densities of the M. quinquenervia stands varied dramatically among sites, ranging from 11,800 to 105,800 trees per ha and fell within the range of stands observed in other adventive ranges, including Florida (USA) where the tree is among the most insidious invaders of natural areas. M. quinquenervia trees in the Bahamas have greater biomass dedicated to reproductive structures than other adventive ranges. The number of capsular fruit produced per cm of infructescence is similar among adventive ranges but markedly greater in comparison to its native range of Australia. As a result of invasion, native plant diversity was negatively correlated with increases in M. quinquenervia densities. Consistent with many plant invasions, the most probable seed sources for these naturalized populations are nearby ornamental plantings. We predict that timely implementation of appropriate control tactics at this early stage of invasion with adequate follow-up efforts and continued vigilance will greatly enhance the probability of averting a large scale M. quinquenervia invasion in the Bahamas. Web of Science Melaleuca quinquenervia Bahamas Field - Observational wetland Subtropical Forest Invasion Hyp. Propagule Pressure primary 3021 Kang, Misun; Ciborowski, Jan J. H.; Johnson, Lucinda B. 2007 The influence of anthropogenic disturbance and environmental suitability on the distribution of the nonindigenous amphipod, Echinogammarus ischnus, at Laurentian Great Lakes coastal margins journal JOURNAL OF GREAT LAKES RESEARCH 33 0 198 210 Invasion ecology offers a unique opportunity to examine drivers of ecological processes that regulate communities. Biotic resistance to nonindigenous species establishment is thought to be greater in communities that have not been disturbed by human activities. Alternatively, invasion may occur wherever environmental conditions are appropriate for the colonist, regardless of the composition of the existing community and the level of disturbance. We tested these hypotheses by investigating distribution of the nonindigenous amphipod, Echinogammarus ischnus Stebbing, 1899, in co-occurrence with a widespread amphipod, Gammarus fasciatus Say, 1818, at 97 sites across the Laurentian Great Lakes coastal margins influenced by varying types and levels of anthropogenic stress. E. Ischnus was distributed independently of disturbance gradients related to six anthropogenic disturbance variables that summarized overall nutrient input, nitrogen, and phosphorus load carried from the adjacent coastal watershed, agricultural land area, human population density, overall pollution loading, and the site-specific dominant stressor, consistent with the expectations of regulation by general environmental characteristics. Our results support the view that the biotic facilitation by dreissenid mussels and distribution of suitable habitats better explain E. ischnus' distribution at Laurentian Great Lakes coastal margins than anthropogenic disturbance. Web of Science Echinogammarus ischnus USA Great Lakes Field - Observational lotic Invasion Hyp. Disturbance omnivore 3023 Johnston, Frances M.; Pickering, Catherine M. 2007 Effects of density on above and below ground biomass of the native alpine grass Poa fawcettiae and the environmental weed Achillea millefolium journal NORDIC JOURNAL OF BOTANY 25 4 167 175 Competition between Poa Jawcettiae Vickery, the dominant native snowgrass, and the invasive herbaceous Achillea millefolium L., was examined in three glasshouse experiments. The first experiment investigated the potential for intraspecific competition in plants by growing them in pots with low and high density. The second experiment examined the potential for inter-specific competition at low, medium and high density. In the third experiment plants in pots where either roots or shoots of the species could not compete were compared to those where root and shoot competition was possible. Achillea millefolium plants produced more than four times the biomass of P. fawcettiae plants. As a result the two species responded differently. In the A. millefolium monocultures both root and shoot biomass per plant declined at high density. By contrast, P. fawcettiae biomass was not affected. In mixed species pots, P. fawcettiae had no effect on the biomass of A. millefolium plants, while P. fawcettiae shoot and root biomass per plant decreased when grown with A. millefolium at all densities tested. Root competition from A. millefolium appears to be the main cause of the decrease in biomass of P. fawcettiae. The results imply that A. millefolium may have a competitive advantage over P. Jawcettiae in the Australian Alps. Web of Science Achillea millefolium Australian Australian Alps. Greenhouse terrestrial Mountain Invasion Hyp. Inherent Superiority Superior Competitor primary 3024 Loacker, Klaus; Kofler, Werner; Pagitz, Konrad; Oberhuber, Walter 2007 Spread of walnut (Juglans regia L.) in an Alpine valley is correlated with climate warming journal FLORA 202 1 70 78 Since the Roman time, the walnut tree (Juglans regia L.) has been cultivated in gardens and orchards in large parts of Europe, but only since Karl The Great (742-814) the walnut tree has been introduced to Tyrol (Austria) and other Alpine regions in Central Europe. As late as the beginning of the 20th century no wild populations but only cultivated trees are reported for inner Alpine valleys of Tyrol. Recently, however a striking increase of growing sites and individuals of J. regia has been detected within the Inn valley and other inner Alpine valleys of the Eastern Alps. In addition, climate warming, specifically milder winters since 1970 have been recorded within the study area (Innsbruck, Tyrol, Austria). Therefore, a dendroccological study at four study sites in surroundings of Innsbruck dominated by Scots pine (Pinus sylvestris L.) and/or Norway spruce (Picea abies (L.) Karst.) forests was initiated to examine more closely, if influence of climate warming favoured spread of this deciduous tree. Together, the four study sites encompassed 30 ha, where in total 651 J regia trees were analysed. Mapping of trees indicated that > 90% grew on south and south-west-facing slopes. Evaluation of the age structure revealed that > 48% of the analysed J. regia trees were younger than 10 years, > 72% younger than 20 years and > 92% younger than 30 years. Analysis of climate conditions in years of germination revealed a striking correspondence between the number of germinated trees and winter (December-February) minimum temperatures (r = 0.43; p < 0.01) and the number of frost days (December-February) < -5 degrees C (r = 0.40; p < 0.01), which can be related to frost sensitivity during seedling stage. In summary, results of this study provide evidence that climate warming after 1970 favoured establishment of J. regia within this inner Alpine valley. (c) 2006 Elsevier GmbH. All rights reserved. Web of Science Juglans regia Austria Tyrol Field - Observational terrestrial Mountain Invasion Hyp. Climate Change primary 3025 Williams, Amity L.; Wills, Karen E.; Janes, Jasmine K.; Schoor, Jacqueline K. Vander; Newton, Paul C. D.; Hovenden, Mark J. 2007 Warming and free-air CO2 enrichment alter demographics in four co-occurring grassland species journal NEW PHYTOLOGIST 176 2 365 374 Species differ in their responses to global changes such as rising CO2 and temperature, meaning that global changes are likely to change the structure of plant communities. Such alterations in community composition must be underlain by changes in the population dynamics of component species. Here, the impact of elevated CO2 (550 mu mol mol(-1)) and warming (+2 degrees C) on the population growth of four plant species important in Australian temperate grasslands is reported. Data collected from the Tasmanian free-air CO2 enrichment (TasFACE) experiment between 2003 and 2006 were analysed using population matrix models. Population growth of Themeda triandra, a perennial C-4 grass, was largely unaffected by either factor but population growth of Austrodanthonia caespitosa, a perennial C-3 grass, was reduced substantially in elevated CO2 plots. Warming and elevated CO2 had antagonistic effects on population growth of two invasive weeds, Hypochaeris radicata and Leontodon taraxacoides, with warming causing population decline. Analysis of life cycle stages showed that seed production, seedling emergence and establishment were important factors in the responses of the species to global changes. These results show that the demographic approach is very useful in understanding the variable responses of plants to global changes and in elucidating the life cycle stages that are most responsive. Web of Science Hypochaeris radicata;Leontodon taraxacoides Australia Field - Observational terrestrial Grassland Invasion Hyp. Climate Change primary 3026 Leishman, Michelle R.; Haslehurst, Tammy; Ares, Adrian; Baruch, Zdravko 2007 Leaf trait relationships of native and invasive plants: community- and global-scale comparisons journal NEW PHYTOLOGIST 176 3 635 643 Leaf carbon capture strategies of native and exotic invasive plants were compared by examining leaf traits and their scaling relationships at community and global scales Community-level leaf trait data were obtained for 55 vascular plant species from nutrient-enriched and undisturbed bushland in Sydney, Australia. Global-scale leaf trait data were compiled from the literature for 75 native and 90 exotic invasive coexisting species. At the community level, specific leaf area (SLA), foliar nitrogen and phosphorus (N-mass and P-mass) and N:P ratio were significantly higher for exotics at disturbed sites compared with natives at undisturbed sites, with natives at disturbed sites being intermediate. SLA, N-mass and P-mass were positively correlated, with significant shifts in group means along a common standardized major axis (SMA) slope. At the global scale, invasives had significantly higher N-mass, P-mass, assimilation rate (A(mass) and A(area)) and leaf area ratio (LAR) than natives. All traits showed positive correlations, with significant shifts in group means along a common slope. For a given SLA, invasives had higher A(mass) (7.7%) and N-mass (28%). Thus, exotic invasives do not have fundamentally different carbon capture strategies from natives but are positioned further along the leaf economics spectrum towards faster growth strategies. Species with leaf traits enabling rapid growth will be successful invaders when introduced to novel environments where resources are not limited. Web of Science Many Australia Sydney Statistical/Meta-analysis terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority Rapid Growth primary 3027 Di Nino, F.; Thiebaut, G.; Muller, S. 2007 Phenology and phenotypic variation of genetically uniform populations of Elodea nuttallii (Planch.) H. St John at sites of different trophic states journal FUNDAMENTAL AND APPLIED LIMNOLOGY 168 4 335 343 The morphological variation of E. nuttallii (Planch.) H. St John, a clonal aquatic macrophyte introduced in Europe, was investigated along a eutrophication gradient in a Northern Vosges stream (NE France). Studies of morphological plasticity in clonal plants have analysed responses to habitat quality in terms of spacer length and branching intensity. The capacity for these parameters to respond to environmental quality has been interpreted as an expression of foraging behaviour, as it confers the potential to intensify the placement of ramets in the more favourable patches of a heterogeneous environment. In our study, the first step consisted in testing the Foraging Concept applied to plant morphology as an adaptation to the acquisition of resources (De Kroon & Hutchings 1995). Eight morphological traits of individuals of E. nuttallii were studied monthly at three sites to document morphological plasticity according to a trophic gradient. A significant difference in morphological traits appeared among the dates and among the sites. A seasonal pattern of the growth of E. nuttallii was established. In agreement with the prediction of the foraging hypothesis, there was a difference in internode and in photosynthetic surface among sites. Plants growing in oligotrophic water were long and thin, while plants growing in mesotrophic water were shorter and more robust, with a greater leaf surface. The second step consisted in investigating the degree of genetic diversity among Elodea nuttallii plants in Northern Vosges streams by analysing twenty-seven samples using Amplified Fragment Length Polymorphic (AFLP) markers. Altogether 258 AFLP markers were scored using 5 primer pairs. The average proportion of shared AFLP fragments was higher than 99.80%. These results establish that E. nuttallii propagates clonally in Northern Vosges streams. They exclude morphological variations due to the presence of ecotypes, and show an only phenotypic adaptation. Web of Science Elodea nuttallii France Vosges Field - Observational lotic Invasion Hyp. Plasticity primary 3028 Morrison, Janet A.; Lubchansky, Heather A.; Mauck, Kerry E.; McCartney, Kelly-Marie; Dunn, Brian 2007 Ecological comparison of two co-invasive species in eastern deciduous forests: Alliaria petiolata and Microstegium vimineum journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 134 1 1 17 Many communities invaded by one non-native plant species also are invaded by others due to a shared response to environmental factors that promote invasive species generally, such as fragmentation, disturbance, and proximity to seed sources. Direct comparison of these co-invasive species in their shared communities therefore is necessary for understanding the ecology of invaded communities, particularly if management resources must be prioritized. We compared ecological characteristics of two of the most important co-invasive herb layer species in forests of the eastern United States, Alliaria petiolata (garlic mustard, a C-3 biennial herb native to Europe) and Microstegium vimineum (Japanese stilt-grass, a C-4 annual grass native to east Asia). Both are invasive across a wide geographic range, establish dense stands under varying canopy covers, and are associated with lower native herb layer diversity and abundance. However, A. petiolata has attracted much greater attention from the scientific and management communities. Our research had three related components aimed at understanding which species may be a greater threat. We conducted a greenhouse experiment with shaded and unshaded growing conditions, in which M. vimineum grew much greater shoot biomass (although total biomass was similar) and photosynthesis rates for M. vimineum generally exceeded those for A. petiolata. We also did a large field experiment using transplants grown from seed. Microstegium vimineum had greater survivorship, less insect herbivory, larger mass, and higher photosynthesis rates than first-year A. petiolata. In addition, we studied a co-invaded natural community. Both species' percent cover were variable across the site but had no relationship to photosynthetically active radiation (PAR) levels. Microstegium vimineum had higher cover in 2001 and by 2005 had increased dramatically over A. petiolata in co-invaded plots. In the summer months M. vimineum had greater photosynthesis rates (measured in situ with a Li-Cor 6400) and were matched only by A. petiolata's early spring rates. These results indicate that in forests where they co-invade M. vimineum may have greater potential for spread than A. petiolata and deserves increased attention from both scientists and forest managers. Web of Science Alliaria petiolata;Microstegium vimineum USA Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority primary 3029 Huebner, Cynthia D.; McQuattie, Carolyn; Rebbeck, Joanne 2007 Mycorrhizal associations in Ailanthus altissima (Simaroubaceae) from forested and non-forested sites journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 134 1 27 33 Ailanthus altissima tree seedlings were excavated from each of two habitats: (1) a forest adjacent to a trail and stream and (2) a non-forested steep, barren slope adjacent to a major highway. Each seedling root system was examined for colonization by mycorrhizal structures using light microscopy and transmission electron microscopy. The roots were colonized by one or more endomycorrhizal fungi with Arum-type colonization. Endomycorrhizal colonization of the seedlings from the non-forested site (65.2%) was significantly greater than that of the seedlings from the forested site (37.9%). Colonization by intercellular hyphae and vesicles was significantly greater in the non-forested habitat than the forested habitat. This exotic invasive species may benefit from the rapid colonization of endomycorrhizae in more extreme open environments. Web of Science Ailanthus altissima USA Field - Observational terrestrial Deciduous Forest;Old Field Invasion Hyp. Mutualism Facilitation primary 3032 Jordan, SM; Neumann, RM; Schultz, ET 2004 Distribution, habitat use, growth, and condition of a native and an introduced catfish species in the Hudson River estuary journal JOURNAL OF FRESHWATER ECOLOGY 19 1 59 67 White catfish (Ameiurus catus) is native to the Hudson River and is now coexisting with the recently established channel catfish (Ictalurus punctatus). These species were sampled from four freshwater reaches and four habitat types of the Hudson River estuary to assess whether the two species overlapped in their habitat use, and whether any impact on the native species was evident. Catfishes were sampled in 1998 and 1999 using baited hoop nets (N = 708 net nights). Catch-per-unit-effort (CPUE, number of fish per net night; total catch = 368) of white catfish was significantly different among reaches and habitat types; CPUE was greatest in the upstream reach, and in offshore shoal habitat. Channel catfish (total catch = 344) were more abundant in offshore shoal habitats in upriver reaches, but were more abundant in nearshore and tributary mouth habitats in downstream reaches. Individuals of both species were largest upstream. Individual condition (as relative weight, Wr) varied with reach in white catfish, and was low in a downstream reach; in contrast, Wr did not vary among reaches in channel catfish. White catfish grew slowly compared to channel catfish. Relative to populations in other water bodies in North America, Hudson River fishes of both species grew slowly in their first year, but otherwise grew at expected rates. Channel catfish are becoming more abundant in the Hudson River, as white catfish appear to decline. Channel catfish establishment may be facilitated by greater flexibility in habitat use. Web of Science Ictalurus punctatus USA New York Hudson River Field - Observational lotic Invasion Hyp. Plasticity herbivore 3033 Gherardi, F; Daniels, WH 2004 Agonism and shelter competition between invasive and indigenous crayfish species journal CANADIAN JOURNAL OF ZOOLOGY-REVUE CANADIENNE DE ZOOLOGIE 82 12 1923 1932 Several crayfish species behave as biological invaders. Their establishment in an area has frequently been accompanied by the reduction or elimination of indigenous species. A laboratory study was designed to investigate whether the invasive crayfish Procambarus clarkii (Girard, 1852) is dominant over the indigenous (to Delaware) crayfish Procambarus acutus acutus (Girard, 1852) in either the absence or the presence of a shelter as a limited resource. As expected, we found that P. clarkii is more aggressive than the similarly sized P. a. acutus, thus confirming previous studies that demonstrated an inherent dominance of the invasive over the indigenous crayfish. We then hypothesized that species showing a lower preference for an offered shelter (P. clarkii) should be less motivated to defend it. To the contrary, in a competitive context P. clarkii excluded P. a. acutus from the shelter but did not use the resource. Caution must be used in extrapolating these laboratory studies to the field, and future studies should analyze multiple factors, including the autoecology of the two species and their reproductive potential and recruitment patterns. However, our results might help in highlighting the risks for freshwater biodiversity created by the uncontrolled translocations of P. clarkii and other similar invasive species. Web of Science Procambarus clarkii USA Delaware Lab lotic Invasion Hyp. Inherent Superiority Superior Competitor omnivore 3034 Holker, F; Volkmann, S; Wolter, C; van Diik, PLM; Hardewig, I 2004 Colonization of the freshwater environment by a marine invader: how to cope with warm summer temperatures? journal EVOLUTIONARY ECOLOGY RESEARCH 6 8 1123 1144 The burbot Lota lota (L.) is the only member of the cold-stenothermal marine family Gadidae that invaded freshwater. To evaluate the evolutionary strategy allowing the invasion of freshwater habitats with high temperature amplitudes, we determined seasonal variations of the energy budget for juvenile burbot from the River Oder, Germany. Food consumption during summer was not sufficient to meet the animal's energetic requirements. During winter and spring, energy uptake surpassed the metabolic energy flux and left surplus energy for growth. Burbot growth is maintained throughout the year by two mechanisms: (1) growth that is reflected predominantly in length throughout the summer, when energy-rich liver tissue must be metabolized to provide energy, and (2) a synthesis of liver reserves during winter, when energy uptake exceeds energy dissipation. In contrast to most freshwater fish, which reduce growth rates during the winter months, the evolutionary burden of being cold-adapted, inherited from its marine ancestors, enables L. lota to maintain somatic growth throughout the year. Web of Science Lota lota Germany River Oder Field - Observational lotic Invasion Hyp. Inherent Superiority Broad Tolerances predator 3035 Nagasaka, M 2004 Changes in biomass and spatial distribution of Elodea nuttallii (Planch.) St. John, an invasive submerged plant, in oligomesotrophic Lake Kizaki from 1999 to 2002 journal LIMNOLOGY 5 3 129 139 Distribution of pure Elodea nuttallii vegetation was surveyed from 1999 to 2002, immediately after the most recent expansion of the species in Lake Kizaki, Japan. During 2001 and 2002, areas of E. nuttallii vegetation rapidly diminished and the summer plant height decreased wherever the vegetation remained. The organic matter content, total phosphorus, and extracted P of the sediment from the vegetation bed were measured. A linear relationship was observed between the extracted P in the sediment and the biomass. The extracted P significantly decreased in the shallow littoral vegetation bed, where the biomass clearly diminished. A fertilization experiment using the shallow littoral sediment collected in the vegetation bed was conducted in 2001. In this experiment, apical shoots of E. nuttallii were planted in pots with fertilized sediment (nitrogen, phosphorus, and potassium additions). The growth of E. nuttallii shoots was significantly enhanced by enrichment with phosphorus alone. The ecological implication of sediment phosphorus limitation is discussed in relation to the cause of decline in the E. nuttallii population in Lake Kizaki. Web of Science Elodea nuttallii Japan Lake Kizaki lentic Fundamentals primary 3036 Peck, SL; McQuate, GT 2004 Ecological aspects of Bactrocera latifrons (Diptera : Tephritidae) on Maui, Hawaii: Movement and host preference journal ENVIRONMENTAL ENTOMOLOGY 33 6 1722 1731 Bactrocera latifrons is a tephritid fruit fly that invaded the Hawaiian Islands in 1983 and has since spread throughout the island chain. Its invasion was facilitated by the invasion of two previous nonendemic species of solanaceous plants: Solarium torvum and Solarium linnaeanum. This study explored three aspects of B. latirfrons biology: (1) the short-term temporal patterns of wild flies were examined in invasive populations of S. torvum; (2) B. latifrons host preference for two principal wild hosts, S. torvum and S. linnaeanum; and (3) the movement of B. latifrons among host patches of established populations of S. torvum in Iao Valley, Maui, HI. For the third objective, we conducted a mark-release-recapture study using flies dyed with a phosphorescing marker and flies marked with a vertebrate protein. The laboratory studies suggest the flies prefer ovipositing in S. linnaeanum to S. torvum and that survival in S. linnaeanum is higher than in S. torvum. Trap catches in the dispersal study did not exceed 200 In during the 6-wk course of the study, suggesting that dispersal rates are similar to those seen in other tephritid fruit fly species. Web of Science Bactrocera latifrons USA Hawaii Field - Observational terrestrial Subtropical Forest Invasion Hyp. Mutualism Facilitation herbivore 3038 Lichstein, JW; Grau, HR; Aragon, R 2004 Recruitment limitation in secondary forests dominated by an exotic tree journal JOURNAL OF VEGETATION SCIENCE 15 6 721 728 Question: What factors limit woody plant recruitment in a mosaic landscape where former agricultural lands are dominated by the invasive tree Ligustrum lucidum (Oleaceae)? Location: Subtropical northwestern Argentina. Methods: In secondary forest patches, we measured (1) tree, shrub and liana abundance in different size classes; (2) seed rain of Ligustrum and two native trees and (3) topographic, soil and light variables. We used spatial autoregressive models to test for effects of Ligustrum dominance and environment on native plant abundance in each size class. We used multiple regression on resemblance matrices to quantify the relative importance of spatial (e.g. dispersal) and environmental effects on native species composition. Results: Native tree abundance in the smallest size class was unrelated to Ligustrum canopy dominance, while native tree abundance in larger size classes and native liana abundance were negatively correlated with Ligustrum dominance. Native species composition was both environmentally and spatially structured, suggesting that some species are dispersal limited. Seed rain was spatially correlated with conspecific basal area for one of two native species, but not for Ligustrum. Conclusions: Native tree recruitment appears to be limited primarily by sapling mortality in patches dominated by the invasive Ligustrum. Ligustrum does not appear to be dispersal limited in our study area and is likely to continue spreading. Invaded patches may persist for hundreds of years. Web of Science Ligustrum lucidum Argentina Field - Observational terrestrial Old Field Invasion Hyp. Propagule Pressure primary 3039 Martel, C; Guarini, JM; Blanchard, G; Sauriau, PG; Trichet, C; Robert, S; Garcia-Meunier, P 2004 Invasion by the marine gastropod Ocinebrellus inornatus in France. III. Comparison of biological traits with the resident species Ocenebra erinacea journal MARINE BIOLOGY 146 1 93 102 Invasive species impacts on native species and communities have been widely recognised for decades and may involve important economical losses. In this study, we examined two marine muricid gastropods: an invader, Ocinebrellus inornatus, and a resident, Ocenebra erinacea. Both species co-occur on French Atlantic coasts and probably have economical impacts on oyster farming areas of the Charente-Maritime region of France. In previous studies, we investigated the introduction source and the expansion patterns of O. inornatus, using molecular markers. However, these studies are not sufficient to fully understand the expansion dynamics of the exotics. The present framework is devoted to comparing life-history traits between the introduced and resident species. Our results first showed that O. inornatus has more favourable traits, such as a better mean growth rate and a higher reproductive effort, in comparison with O. erinacea. These traits may explain the invader establishment and, partly, its spread along the coast of France. Secondly, the resident species drilled a higher rate of oysters than the invader. Finally, the establishment of O. inornatus in France does not seem to be at the expense of O. erinacea because: (1) resources are not limiting in oyster farming areas and (2) there does not appear to be competition by interference between the species. Web of Science Ocinebrellus inornatus France Field - Observational marine Intertidal/Near Shore Invasion Hyp. Inherent Superiority Rapid Growth;High Reprod. Output herbivore 3040 Perez-Bote, JL 2004 Feeding ecology of the exotic red swamp crayfish, Procambarus clarkii (Girard, 1852) in the Guadiana River (Swiberian Peninsula) journal CRUSTACEANA 77 0 1375 1387 The feeding ecology of the red swamp crayfish, Procambarus clarkii was studied from October 1999 to September 2000 in the River Guadiana, the fourth largest river in the Iberian Peninsula. Analysis of the gut contents of 1225 individuals [15.8-172.3 mm total length (TL)] from 23 sites showed a diet dominated by plants [Relative Importance Index (RI) 50.34] and animals (RI 31.25), followed by amorphous material (RI = 12.21) and sand (RI 6.20). Animal food items were represented by insects, mainly dipterans (RI = 34.59) and ephemeropterans (RI = 16. 10), crayfish (RI = 15.14), and fish (RI = 11.40). Classes I (TL <= 40 mm) and 11 (TL = 40.1-80 mm) had a diet dominated by animals and amorphous material. Classes III (TL = 80.1-120 mm) and IV (TL > 120 mm) had a diet dominated by plants and amorphous material. Plants were consumed by all classes throughout the year, being most important for classes III and IV in autumn and winter. For classes I and II, animal diets are important throughout the year with increasing consumption in autumn and winter. Crayfish fragments were found throughout the year in all classes with more importance in spring and summer for classes III and IV. Similarly, fish were found in the guts of the crayfish throughout the year, this prey being more important in classes III and IV in the cold seasons. The diets of males and females were very similar, although females consumed more plants (RI = 48.72) than males (RI = 46.58). In contrast, males consumed more animal prey than females (RI = 32.36 and RI = 31.30, respectively). Differences in diet between males and females were not significant (G = 0.189, df: 3, P = 0.973). Web of Science Procambarus clarkii Spain River Guadiana Field - Observational lotic Fundamentals omnivore 3052 Kercher, SM; Zedler, JB 2004 Flood tolerance in wetland angiosperms: a comparison of invasive and noninvasive species journal AQUATIC BOTANY 80 2 89 102 We assessed the biomass production, biomass allocation patterns, height growth, and root airspace of seventeen wetland plant taxa, including two potentially invasive species, grown under high nutrient conditions and subjected to four hydrologic regimes: constant drawdown, cyclic flooding and drawdown, cyclic flooding and drought, and constant flooding for the duration of the experiment (similar to10 weeks). We found that: (1) the potentially invasive reed canary grass (Phalaris arundinacea) and broadleaf cattail (Typha latifolia) responded to treatments similarly; both outgrew the other perennial species in all four hydrologic regimes; (2) Phalaris had the highest levels of root airspace of all the taxa; (3) the grasses and graminoids nearly always tolerated flooding better than the broadleaf forbs, perhaps in part due to greater quantities of root airspace; and (4) the species that were most sensitive to flooding are typically found in drier, groundwater-fed, and more nutrient-poor environments. We hypothesize that Phalaris and Typha, which are both tall and productive, should be competitive dominants under a variety of hydrologic conditions, at least where nutrients are abundant, as in urban and agricultural landscapes. Eight of the noninvasive taxa tolerated flooding but produced less biomass and/or were shorter or shorter-lived than Phalaris and Typha. Among the five taxa that were most sensitive to flooding were slow-growing habitat specialists; such species will likely experience declines in areas that become impounded or experience greater volumes of runoff. (C) 2004 Elsevier B.V. All rights reserved. Web of Science Phalaris arundinacea USA Wisconsin madison Garden wetland Wetland Invasion Hyp. Inherent Superiority Broad Tolerances;Rapid Growth primary 3053 Carlsson, N; Kestrup, A; Martensson, M; Nystrom, P 2004 Lethal and non-lethal effects of multiple indigenous predators on the invasive golden apple snail (Pomacea canaliculata) journal FRESHWATER BIOLOGY 49 10 1269 1279 1. We investigated the individual and combined effects of two predators (the climbing perch, Anabas testudineus, and the wetland crab, Esanthelphusa nimoafi) indigenous to wetlands in Laos, on the behaviour and survival of the invasive South American golden apple snail (Pomacea canaliculata). The snail is considered a pest, consuming large amounts of rice and other aquatic vegetation in the region. 2. Snail avoidance reactions to released predator chemical cues were investigated in aquaria while the effects of predators on a mixed snail population were studied in field enclosures that contained native aquatic plants (Salvinia cucullata, Ludwigia adscendens and Ipomoea aquatica). 3. In the aquaria experiment, neonate (2-3 mm) and medium-sized snails (8-10 mm) responded to fish chemical cues by going to the surface, whereas adult snails (35-40 mm) went to the bottom. In contrast, no size class of snails reacted to chemical cues released by crabs. 4. In the field experiment, fish reduced the abundance of neonate snails, and crabs reduced the abundance of all size classes. The effect of the combined predators could not be predicted from the mortality rate observed in single predator treatments. The survival of neonate and medium-sized snails was greater and of adults less than expected. The presence of predators did not affect egg production. Snails consumed significant amounts of plants despite the presence of predators. 5. Our findings suggest that some indigenous Asian predators have lethal and sublethal effects on P. canaliculata that depend on snail size and predator type. When in the presence of several predators the response of snails to one predator may either increase or decrease the vulnerability of snails to the others. Web of Science Pomacea canaliculata Laos Lab wetland Wetland Invasion Hyp. Enemy Release herbivore 3054 Spyreas, G; Ellis, J; Carroll, C; Molano-Flores, B 2004 Non-native plant commonness and dominance in the forests, wetlands, and grasslands of Illinois, USA journal NATURAL AREAS JOURNAL 24 4 290 299 Non-native species constitute one of the greatest threats to our indigenous biota. We used data from vegetation surveys of ground, shrub, and canopy strata from 1997-2001 at 399 randomly selected forests, wetlands, and grasslands to elucidate non-native plant pervasiveness throughout Illinois. The dominant non-native species in the ground layer of forests was Lonicera japonica Thunb., in wetlands it was Phalaris arundinacea L., in prairie grasslands it was Poa pratensis L., and across all grasslands it was Festuca arundinacea Schreb. Though rarely recognized as exotic, several of the most prevalent non-natives were introduced ecotypes or cultivars of cosmopolitan species. Conversely, some well-known exotics were surprisingly uncommon. Non-native species were more dominant in the ground cover (9% forests, 33% wetlands, 36% prairie grasslands, 76% secondary grasslands) than in the shrub and canopy strata across the state. Non-native ground cover varied regionally in forests and wetlands while, overall, the southern third of the state had significantly lower non-native cover. These regional patterns may be related to isolation from metropolitan areas, historical disturbances, current land use, unique edaphic features, as well as species-specific distributions for the most successful invaders. Our results show the extent to which non-native species have permeated Illinois habitats and replaced native plant communities. Web of Science Lonicera japonica;Phalaris arundinacea;Festuca arundinacea;Poa pratensis USA Illinois Field - Observational terrestrial;wetland Grassland;Deciduous Forest;Wetland Invasion Hyp. Community Species Richness primary 3055 Kercher, SM; Carpenter, QJ; Zedler, JB 2004 Interrelationships of hydrologic disturbance, reed canary grass (Phalaris arundinacea L.), and native plants in Wisconsin wet meadows journal NATURAL AREAS JOURNAL 24 4 316 325 Twelve wet meadows in Dane County, Wisconsin showed vegetation patterns that correlate with hydrologic disturbance and presence of a clonal invasive grass, Phalaris arundinacea L., at two scales, 4500-m(2) (0.45 ha) *sites* and 1-m(2) plots. Sites with indicators of hydrologic disturbance had lower species richness and diversity than reference sites, and species richness, diversity, and mean coefficients of conservatism (Mean C) were inversely related to the abundance of Phalaris on sites. Within 1-m(2) plots, 5.5 +/- 0.4 (SE) species coexisted with Phalaris, while about twice as many coexisted with two widespread native graminoids: 11.5 +/- 0.3 with Carex stricta Lam. and 10.6 +/- 0.3 with Calamagrostis canadensis (Michx.) Beauv. Cover of Phalaris was approximately six times higher in plots on sites with disturbance indicators than on reference sites. Overall, plots with either Phalaris or hydrologic disturbance had 2/3 the species of plots lacking Phalaris on reference sites, as well as lower diversity and Mean C. These results suggest a strong negative effect of hydrologic disturbance or presence of Phalaris on the quantity and quality of species in a wetland. When Phalaris and disturbance indicators co-occurred, the difference was more severe. Plots with Phalaris on disturbed sites had 1/3 the species of reference plots and the lowest diversity and Mean C. Species were grouped into seven *response types* based on apparent sensitivity to the presence of Phalaris and hydrologic disturbance. Only the clonal grass Phragmites australis (Cav.) Trin. ex Steud. responded positively to the combination of Phalaris and hydrologic disturbance. Web of Science Phalaris arundinacea USA Wisconsin Field - Observational wetland Wetland Invasion Hyp. Disturbance primary 3056 Ward, MD; Labisky, RF 2004 Post-dispersal germination success of native black gum (Nyssa sylvatica) and introduced camphor tree (Cinnamomum camphora) in Florida, USA journal NATURAL AREAS JOURNAL 24 4 341 344 This study evaluated: (1) whether the germination success of the introduced and invasive camphor tree (Cinnamomum camphora (L.) Nees & Eberm) was greater than that of the native black gum tree (Nyssa sylvatica var biflora Wait.), thereby providing camphor a competitive ecological edge for invading natural plant communities; and (2) whether the passage of seeds through the gut of birds enhanced germination success of the two tree species. Germination of de-pulped (control) black gum seeds (13.0%) differed (P < 0.05) from similarly treated camphor seeds (6.0%). Germination of camphor seeds passed through the gut (treatment) of fish crows (Corvus ossifragus Wilson) and European starlings (Sturnus vulgarius L.) did not differ (P > 0.05) from de-pulped seeds. However, germination of black gum seeds was enhanced (P < 0.05) by passage through fish crows (22.5%), but depressed (P < 0.05) by passage through starlings (4.0%). These findings suggest that at least some indigenous plant species may have a competitive edge over introduced plant species. However, the role of birds in ingesting and dispersing seeds of invasive exotic plants represents an inescapable threat to natural plant communities. Web of Science Cinnamomum camphora USA Florida Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Mutualism Facilitation primary 3058 Silliman, BR; Bertness, MD 2004 Shoreline development drives invasion of Phragmites australis and the loss of plant diversity on New England salt marshes journal CONSERVATION BIOLOGY 18 5 1424 1434 The reed Phragmites australis Cav. is aggressively invading salt marshes along the Atlantic Coast of North America. We examined the interactive role of habitat alteration (i.e., shoreline development) in driving this invasion and its consequences for plant richness in New England salt marshes. We surveyed 22 salt marshes in Narragansett Bay, Rhode Island, and quantified shoreline development, Phragmites cover, soil salinity, and nitrogen availability. Shoreline development, operationally defined as removal of the woody vegetation bordering marshes, explained >90% of intermarsh variation in Phragmites cover. Shoreline development was also significantly correlated with reduced soil salinities and increased nitrogen availability, suggesting that removing woody vegetation bordering marshes increases nitrogen availability and decreases soil salinities, thus facilitating Phragmites invasion. Soil salinity (64%) and nitrogen availability (56%) alone explained a large proportion of variation in Phragmites cover, but together they explained 80% of the variation in Phragmites invasion success. Both univariate and aggregate (multidimensional scaling) analyses of plant community composition revealed that Phragmites dominance in developed salt marshes resulted in an almost three-fold decrease in plant species richness. Our findings illustrate the importance of maintaining integrity of habitat borders in conserving natural communities and provide an example of the critical role that local conservation can play in preserving these systems. In addition, our findings provide ecologists and natural resource managers with a mechanistic understanding of how human habitat alteration in one vegetation community can interact with species introductions in adjacent communities (i.e., flow-on or adjacency effects) to hasten ecosystem degradation. Web of Science Phragmites australis USA Rhode Island estuarine Wetland Invasion Hyp. Disturbance primary 3061 Walters, AC; Mackay, DA 2004 Comparisons of upper thermal tolerances between the invasive argentine ant (Hymenoptera : Formicidae) and two native Australian ant species journal ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA 97 5 971 975 The Argentine ant, Linepithema humile (Mayr), is a significant pest species, having become established on almost every continent, particularly in areas with a Mediterranean climate. In its introduced range, the Argentine ant has been associated with reductions in the abundance and diversity of native ant and nonant invertebrate fauna, as well as the interruption of ant-plant mutualisms. The distribution of Argentine ants has been correlated with particular abiotic factors, including soil moisture, relative humidity, disturbance, and particular soil and vegetation types. This study assessed the importance of temperature on the survival of Argentine ants and two native ant species (Iridomyrmex *rufoniger* and Rhytidoponera *convexa*) in the laboratory. Workers were placed in incubators of varying temperatures (25, 32, 40, 45, 47, and 50degreesC), and counts of the numbers dead and alive were recorded after 1, 2, and 3 h. The results showed that all species displayed almost 100% survival at 25, 32, 40, and 45degreesC, but at 47degreesC the mortality rate of all species increased, with Argentine ants experiencing 100% mortality after 3 h. At 50degreesC, Argentine ants displayed no survival at 1 h, whereas the Iridomyrmex exhibited approximate to50% survival after 3 h. These results may have significant implications in Australia, where the ground surface temperatures may become very high during the summer, potentially limiting the spread of Argentine ants. Web of Science Linepithema humile Australia Field - Observational terrestrial Invasion Hyp. Inherent Superiority Broad Tolerances omnivore 3062 Garcia-Serrano, H; Escarre, J; Sans, FX 2004 Factors that limit the emergence and establishment of the related aliens Senecio inaequidens and Senecio pterophorus and the native Senecio malacitanus in Mediterranean climate journal CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE 82 9 1346 1355 Three series of seed addition experiments in natural sites and in common experimental conditions are described to compare the effect of disturbance, water availability, and habitat type on the emergence and establishment of the two alien congeners Senecio inaequidens D.C. and Senecio pterophorus D.C. and the native Senecio malacitanus Huter. The emergence of the three species was favored by disturbance, while establishment was enhanced by water availability. Habitat also had a dramatic effect on emergence, with more seedlings germinating under the shrubs and in the forest. However, only the plants that emerged in the open annual grassland survived until the adult stage, some of which flowered, mostly S. inaequidens. The emergence of the alien S. pterophorus was lower than that of the other species, but once established it produced significantly more biomass than the others. The effect of disturbance and water availability on emergence and establishment does not explain the differences in invasive capacity between the two aliens and the native; however, some traits, such as the biomass production of S. pterophorus and the early flowering of S. inaequidens, can contribute to the capacity of the two aliens to colonize new habitats. Web of Science Senecio inaequidens;Senecio pterophorus Spain terrestrial Invasion Hyp. Disturbance primary 3064 Estoup, A; Beaumont, M; Sennedot, F; Moritz, C; Cornuet, JM 2004 Genetic analysis of complex demographic scenarios: Spatially expanding populations of the cane toad, Bufo marinus journal EVOLUTION 58 9 2021 2036 Inferring the spatial expansion dynamics of invading species from molecular data is notoriously difficult due to the complexity of the processes involved. For these demographic scenarios, genetic data obtained from highly variable markers may be profitably combined with specific sampling schemes and information from other sources using a Bayesian approach. The geographic range of the introduced toad Bufo marinus is still expanding in eastern and northern Australia, in each case from isolates established around 1960. A large amount of demographic and historical information is available on both expansion areas. In each area, samples were collected along a transect representing populations of different ages and genotyped at 10 microsatellite loci. Five demographic models of expansion, differing in the dispersal pattern for migrants and founders and in the number of founders, were considered. Because the demographic history is complex, we used an approximate Bayesian method, based on a rejection-regression algorithm. to formally test the relative likelihoods of the five models of expansion and to infer demographic parameters. A stepwise migration-foundation model with founder events was statistically better supported than other four models in both expansion areas. Posterior distributions supported different dynamics of expansion in the studied areas. Populations in the eastern expansion area have a lower stable effective population size and have been founded by a smaller number of individuals than those in the northern expansion area. Once demographically stabilized, populations exchange a substantial number of effective migrants per generation in both expansion areas, and such exchanges are larger in northern than in eastern Australia. The effective number of migrants appears to be considerably lower than that of founders in both expansion areas. We found our inferences to be relatively robust to various assumptions on marker. demographic, and historical features. The method presented here is the only robust, model-based method available so far, which allows inferring complex population dynamics over a short time scale. It also provides the basis for investigating the interplay between population dynamics, drift, and selection in invasive species. Web of Science Bufo marinus Australia Theoretical/Modeling terrestrial Fundamentals omnivore 3065 MacNeil, C; Dick, JTA; Johnson, MP; Hatcher, MJ; Dunn, AM 2004 A species invasion mediated through habitat structure, intraguild predation, and parasitism journal LIMNOLOGY AND OCEANOGRAPHY 49 5 1848 1856 With field, laboratory, and modeling approaches, we examined the interplay among habitat structure, intraguild predation (IGP), and parasitism in an ongoing species invasion. Native Gammarus duebeni celticus (Crustacea: Amphipoda) are often, but not always, replaced by the invader Gammarus pulex through differential IGP. The muscle-wasting microsporidian parasite Pleistophora mulleri infects the native but not the invader. We found a highly variable prevalence of P. mulleri in uninvaded rivers, with 0-91% of hosts parasitized per sample. In addition, unparasitized natives dominated fast-flowing riffle patches of river, whereas parasitized individuals dominated slower-flowing, pooled patches. We examined the survivorship of invader and native in single and mixed-species microcosms with high, intermediate, and zero parasite prevalence. G. pulex survivorship was high in all treatments, whereas G. duebeni subsp. celticus survivorship was significantly lower in the presence of the invader. Further, parasitized G. duebeni subsp. celticus experienced near-total elimination. Models of the species replacement process implied that parasite-enhanced IGP would make invasion by G. pulex more likely, regardless of habitat and parasite spatial structure. However, where heterogeneity in parasite prevalence creates a landscape of patches with different susceptibilities to invasion, G. pulex may succeed in cases where invasion would not be possible if patches were equivalent. The different responses of parasitized and unparasitized G. duebeni subsp. celticus to environmental heterogeneity potentially link landscape patterns to the success or failure of the invasion process. Web of Science Gammarus pulex Ireland Field - Observational lotic Invasion Hyp. Enemy Release omnivore 3066 Ricciardi, A; Whoriskey, FG 2004 Exotic species replacement: shifting dominance of dreissenid mussels in the Soulanges Canal, upper St. Lawrence River, Canada journal JOURNAL OF THE NORTH AMERICAN BENTHOLOGICAL SOCIETY 23 3 507 514 During the early 1990s, 2 Eurasian macrofouling mollusks, the zebra mussel Dreissena polymorpha and the quagga mussel D. bugensis, colonized the freshwater section of the St. Lawrence River and decimated native mussel populations through competitive interference. For several years, zebra mussels dominated molluscan biomass in the river; however, quagga mussels have increased in abundance and are apparently displacing zebra mussels from the Soulanges Canal, west of the Island of Montreal. The ratio of quagga mussel biomass to zebra mussel biomass on the canal wall is correlated with depth, and quagga mussels constitute > 99% of dreissenid biomass on bottom sediments. This dominance shift did not substantially affect the total dreissenid biomass, which has remained at 3 to 5 kg fresh mass /m(2) on the canal walls for nearly a decade. The mechanism for this shift is unknown, but may be related to a greater bioenergetic efficiency for quaggas, which attained larger shell sizes than zebra mussels at all depths. Similar events have occurred in the lower Great Lakes where zebra mussels once dominated littoral macroinvertebrate biomass, demonstrating that a well-established and prolific invader can be replaced by another introduced species without prior extinction. Web of Science Dreissena polymorpha Canada Montreal Field - Observational lotic Invasion Hyp. Inherent Superiority Superior Competitor filter 3067 Lee, PLM; Patel, RM; Conlan, RS; Wainwright, SJ; Hipkin, CR 2004 Comparison of genetic diversities in native and alien populations of hoary mustard (Hirschfeldia incana [L.] Lagreze-Fossat) journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 165 5 833 843 Increased selfing and inbreeding and, consequently, depauperate genetic diversities are commonly expected for alien colonies. We compared RAPDs data for native (southern Europe) and alien (British Isles) populations of hoary mustard (Hirschfeldia incana). This species is normally out-breeding, but it is capable of self-fertilization. Contrary to the common expectations, genetic diversities in native and alien populations were similar, without any strong evidence of decreased levels of genetic diversities in alien populations. A variety of factors may have contributed to this observation, including high variation in founding groups, founders originating from multiple H. incana source populations, and high rates of past and/or current gene flow. A review of other studies showed that this pattern of similar genetic diversities in native and alien populations was not unusual but has been regularly observed in other invasive plant species. Web of Science Hirschfeldia incana United Kingdom terrestrial Fundamentals primary 3070 Meyer, JY; Lavergne, C 2004 Beautes fatales: Acanthaceae species as invasive alien plants on tropical Indo-Pacific Islands journal DIVERSITY AND DISTRIBUTIONS 10 6 333 U4 Most, if not all, alien plant species of the family Acanthaceae (acanths) found in tropical islands were intentionally introduced as garden ornamentals, because of their showy coloured flowers, bracts or leaves. Some have 'escaped' gardens and have naturalized in human-disturbed areas as weeds, adventives, or ruderal species. A few species have successfully invaded secondary and relatively undisturbed native wet forests. This paper reviews the naturalized alien acanths in tropical islands, and focuses on the currently invasive and potentially invasive species. This study is based on recent (1994-2004) botanical surveys and field observations conducted in several tropical oceanic islands of the Pacific and Indian Oceans, and on bibliographical searches of other tropical islands and countries. A total of 52 acanth species are naturalized in the Indo-Pacific islands; 26 of them are native to Asia, 18 to tropical America, and only 8 to Africa. The number of naturalized acanths in selected tropical oceanic and continental islands varied from 7 to 25 species and the rate of naturalized acanths (number of naturalized species/number of introduced species) from 27% to 62%. We recorded eight major invasive species: the erect herbs or shrubs Justicia carnea, Odontonema strictum, Phlogacanthus turgidus, Sanchezia speciosa and Strobilanthes hamiltonianus form dense monospecific thickets in the understorey of wet forests; the woody vine Thunbergia grandiflora smothers native trees; the creeping herb Hemigraphis alternata forms dense carpets that totally cover the ground; and the herb Ruellia brevifolia colonizes the understorey of closed-canopy wet forest. We also discuss eight potentially or incipient invasive acanths which are subspontaneous or sparingly naturalized, but which are not yet considered invasive. Most of the currently invasive acanths are sterile, the lack of fruit production being explained by the absence of pollinators and/or to their particular floral structure and reproduction modes. They reproduce vegetatively by stem fragmentation or by root suckers, and their range expansion is thus relatively slow. Their success may be attributed to their long (50-100 years) residence times, and long-distance dispersal by humans. Many potentially invasive acanths are newly introduced ornamentals that produce seeds, thus constituting potentially greater threats. The Acanthaceae is not yet recognized as an 'aggressive' plant family (e.g. compared to the Fabaceae, Melastomataceae, Poaceae, or Rosaceae). It is, however, one of the most popular ornamental families in the Tropics, and should receive more attention because of the increasing number of current and incipient invasive species found in tropical islands. Web of Science Many Indo-pacific islands terrestrial Tropical Forest Invasion Hyp. Inherent Superiority;Other Clonal Reproduction primary 3072 Kollmann, J; Banuelos, MJ 2004 Latitudinal trends in growth and phenology of the invasive alien plant Impatiens glandulifera (Balsaminaceae) journal DIVERSITY AND DISTRIBUTIONS 10 6 377 385 Geographical differentiation of populations can be interpreted as a result of adaptive processes in response to environmental gradients and biotic interactions. Such adaptations are particularly interesting in invasive alien species which have been present in an area for a relatively short time. There are few observations of latitudinal trends in alien plants, and no account exists for Impatiens glandulifera, a problematic annual weed in most countries of central and north-western Europe. Here we describe variation in growth and phenology in 26 populations of this species from nine European regions in a common garden in Denmark. Above-ground biomass (an estimate of fecundity), height and basal diameter were lower in the northern populations which were first to produce flowers. Some differences were also observed in biomass allocation to leaves, flowers and fruits, albeit without a latitudinal pattern. The latitudinal trends in growth and survival disappeared in a field experiment, probably due to suboptimal site conditions. Most variation in plant traits was explained by differences among regions with some minor effects of populations within regions. Besides latitude, no other geographical, climatic or population trait correlated with the observed differences in growth and phenology. Differences in latitude may mainly represent variation in length of the growing season. The causes and potential consequences of such latitudinal trends for population dynamics and dispersal of alien plants are discussed. Web of Science Impatiens glandulifera Denmark Field - Experimental;Garden terrestrial Invasion Hyp. Plasticity primary 3073 Espinosa-Garcia, FJ; Villasenor, JL; Vibrans, H 2004 The rich generally get richer, but there are exceptions: Correlations between species richness of native plant species and alien weeds in Mexico journal DIVERSITY AND DISTRIBUTIONS 10 6 399 407 Studies on the resistance of communities to plant invasions at different spatial scales have yielded contradictory results that have been attributed to scale-dependent factors. Some of these studies argue either for or against Elton's notion of biotic resistance against invasions through diversity. We studied the correlation between alien weeds and native species, dividing the latter group into weedy and non-weedy species, integrating various factors that influence diversity into an analysis on the scale of the federal states of Mexico. The resulting multiple-regression models for native and alien weed species are robust (adjusted R(2) = 0.87 and R(2) = 0.69, respectively) and show a strong partial correlation of the number of weed species (native and alien) with the number of non-weed native species. These results agree with studies showing a positive correlation between the number of native and alien species on larger scales. Both models also include human population density as an important predictor variable, but this is more important for alien weeds (beta = 0.62) than for native weeds (beta = 0.32). In the regression model for native weed species richness, the non-cultivated (fallow) area (beta = 0.24) correlated positively with native weed richness. In the model for alien weed species richness, the native weed species richness was an important variable (beta = -0.51), showing a negative partial correlation (r(part) = -0.4). This result is consistent with Elton's biotic resistance hypothesis, suggesting that biotic resistance is scale independent but that this may be masked by other factors that influence the diversity of both weeds and non-weeds. Web of Science Many Mexico Statistical/Meta-analysis;Review terrestrial Invasion Hyp. Community Species Richness primary 3074 Rambuda, TD; Johnson, SD 2004 Breeding systems of invasive alien plants in South Africa: does Baker's rule apply? journal DIVERSITY AND DISTRIBUTIONS 10 6 409 416 According to Baker's Rule, plant species capable of uniparental reproduction are more likely to be successful colonists than are self-incompatible or dioecious species. Controlled pollination experiments carried out on 17 invasive alien plant species in South Africa revealed that 100% were either self-compatible or apomictic, and that 72% of these were capable of autonomous self pollination. The distribution of breeding systems among these invasive aliens is thus strongly skewed towards uniparental reproduction. While all 13 woody species in our survey showed a capacity for uniparental reproduction, this mode of reproduction is very rare among woody plants in general. Thus Baker's rule, which has generally been considered for short-lived herbaceous plants, may also apply to invasive shrubs and trees. The study species exhibited high levels of fruit set (median = 71.5%). Supplemental hand-pollination experiments carried out on five of the species showed that pollen availability did not limit fruit set. Further work is needed to establish the exact role of uniparental reproduction in various stages of the invasion process. In particular, we need to know whether uniparental reproduction provides reproductive assurance at the population establishment stage (as originally envisaged by Baker) or whether it plays a further role in alleviating pollen limitation in small and established populations. Web of Science Many South Africa Lab terrestrial Invasion Hyp. Inherent Superiority Effective Disperser primary 3075 Kuhn, I; Brandenburg, M; Klotz, S 2004 Why do alien plant species that reproduce in natural habitats occur more frequently? journal DIVERSITY AND DISTRIBUTIONS 10 6 417 425 The invasion process can be divided into several phases. We consider invasion patterns related to two aspects of the invasion process: the spread of a species in Germany as counted by the number of occupied grid cells, and the degree of naturalization in Germany (i.e. whether a plant species is exclusively naturalized in human-made habitats or also in (semi-)natural habitats). Although in Germany the area of natural habitats is smaller than that of human-made habitats, the area of occupancy of the respective alien plant species is the opposite. We tested whether both patterns could be explained by niche-breadth variables, namely the number of inhabited habitat types, and vegetation formations, the range of human impact levels, the number of inhabited continents, the number of inhabited floristic zones (climatic zones), and the amplitude of oceanity. Tests were conducted across species and across phylogenetically-independent contrasts, using generalized linear models, in particular, hierarchical partitioning. The number of occupied grid cells could be explained by niche-breadth variables, especially by number of habitats, number of formations, and amplitude of oceanity. Contrary to our expectations, none of these variables could explain the degree of naturalization in cross-species analyses, and amplitude of oceanity is the only stably significant variable that explains the degree of naturalization when analysing phylogenetically-independent contrasts. We conclude that the degree of naturalization is probably independent from niche breadth, and that properties of a larger area of occupancy, i.e. sample size (or propagule pressure), could be responsible for this pattern. Web of Science Many Germany Statistical/Meta-analysis Invasion Hyp. Propagule Pressure primary 3080 Badano, EI; Pugnaire, FI 2004 Invasion of Agave species (Agavaceae) in south-east Spain: invader demographic parameters and impacts on native species journal DIVERSITY AND DISTRIBUTIONS 10 6 493 500 Several mechanisms have been proposed to explain the success of invasive species in new environments. A species may become invasive when a new site provides the potential for positive rates of population growth. This may be the case of several Agave species introduced to Spain in the 1940s. In this paper we document factors that promote large increases of populations of these species, and their effects on native plant communities in two sites of SE Spain. Results showed higher rhizome and bulbil production, and higher establishment rates by agaves in sandy soils than in clay soils. In their native habitats, agaves have low establishment rates and sandy soils are rare. This suggests that sandy soils are an opportunity which releases the clonal reproduction of Agave. The effects of agaves on the physiological performance and reproduction of native species were negative, positive or neutral, depending on the size and rooting depth of neighbours. Assemblages of native species growing within Agave stands had lower diversity than non-invaded sites. Our data show that Agave stands have positive growth rates in SE Spain, and suggest that sandy soils are a niche dimension enhancing the invasion in these new habitats. Web of Science Agave Spain Field - Observational terrestrial Chaparral/Shrublands Impacts;Invasion Hyp. Empty Niche primary 3081 Villanueva, R; Roubik, DW 2004 Why are African honey bees and not European bees invasive? Pollen diet diversity in community experiments journal APIDOLOGIE 35 5 481 491 We studied resource use and competition by varieties of a honey bee, Apis mellifera, through re-introducing European A. m. ligustica in experimental apiaries in a habitat 'saturated' by African ( or hybrid African and European) honey bees that naturally colonized forest in the Yucatan Peninsula of Mexico. Over 171 pollen species comprised honey bee diets. The Morisita-Horn similarity index ( highest similarity = 1.0) between the two honey bee races was 0.76 for pollen use and, from the average daily volume usage by colonies of each bee subspecies, 0.55 for taxon-specific intensity of use. Although using more plant species, the European bee specialized much more heavily on a few plants than did African honey bees. By re- analysis of pollen pellets collected by locally-adapted ( Mexican) European honey bees for one year, at the same experimental sites and using the same pollen traps as our studies, before the arrival of invasive honey bees in S. Mexico, we infer that resident bees may respond to exotic honey bee competition by shifting flower choice and by increasing resource specialization. We also show that replicated, quantitative pollen analysis is a powerful tool that may be applied to understanding diet diversity of bees. Web of Science Apis mellifera Mexico Yucatan Field - Observational terrestrial Invasion Hyp. Plasticity herbivore 3083 DeWalt, SJ; Hamrick, JL 2004 Genetic variation of introduced Hawaiian and native Costa Rican populations of an invasive tropical shrub, Clidemia hirta (Melastomataceae) journal AMERICAN JOURNAL OF BOTANY 91 8 1155 1163 Clidemia hirta is one of the most common woody invasive plants in mesic to wet forests in Hawaii, where it was introduced around 1940. The species is relatively uncommon by comparison in its native range of Central and South America and some Caribbean Islands. We examined genetic variation in allozymes of 20 C. hirta populations on four Hawaiian Islands to determine the introduction history. For comparison, we measured genetic variation in 20 native populations across Costa Rica. Mean levels of genetic variation in Hawaiian and Costa Rican populations were low compared to other woody or introduced plants (11.5-12.5% polymorphic loci, 2.05-2.50 alleles per polymorphic locus, and 0.045-0.063 expected heterozygosity). Most genetic diversity was held within rather than among populations in both areas (G(ST) = 0.120 and 0.271 in Hawaii and Costa Rica, respectively). Hawaiian populations had a high degree of genetic similarity, and no genetic differentiation was found among the four Hawaiian Islands sampled. These patterns of genetic variation in Hawaii suggest that no intraspecific hybridization of genotypes from different parts of the native range has occurred and that introductions to the different islands came from the same or similar source populations. The low levels of genetic diversity in parts of both the native and introduced ranges suggest that genetic variation is unrelated to invasiveness in C. hirta. Web of Science Clidemia hirta USA Hawaii Field - Observational terrestrial Tropical Forest Invasion Hyp. Evolution in General primary 3084 Mistri, M; Rossi, R; Fano, EA 2004 The spread of an alien bivalve (Musculista senhousia) in the Sacca di Goro Lagoon (Adriatic Sea, Italy) journal JOURNAL OF MOLLUSCAN STUDIES 70 0 257 261 The Asian date mussel, Musculista senhousia (Mytilidae), which is endemic in the western Pacific, appeared and became abundant in the Sacca di Goro, a brackish lagoon in the Po River Delta (northern Adriatic Sea, Italy) in the early 1990s. The course of the invasion was documented through a macrobenthic monitoring programme at three sites in the Sacca. From 1994, when the new mussel was first collected, M. senhousia spread throughout the lagoon and, within a few years, reached densities exceeding 10,000 individuals m(-2). Mussel effects on biodiversity were assessed by comparing macrobenthic community structure and composition: over a 5-year period some changes in the macrobenthic community seem to be apparent, suggesting a positive effect of the mussel on the number of species and benthic richness. Considering trophic guilds, significant positive correlations were found between M. senhousia and detritivores and herbivores, while suspension feeders probably suffered competition from the mussel. Musculista senhousia was initially successful because it exploited a naturally disturbed, sparsely occupied environment. The well-dated documentation of the first collections, increasing abundance and spread of M. senhousia at our study sites provided an opportunity to observe a biological invasion of a habitat in progress. Web of Science Musculista senhousia Italy Adriatic Sea Field - Observational marine Invasion Hyp. Disturbance filter 3086 Bimova, K; Mandak, B; Kasparova, I 2004 How does Reynoutria invasion fit the various theories of invasibility? journal JOURNAL OF VEGETATION SCIENCE 15 4 495 504 Questions: 1. How does species richness of recipient communities affect Reynoutria invasion? 2. How does Reynoutria invasion change host community structure? 3. Are there any differences in habitat preferences among three closely related Reynoutria taxa? 4. How does the genetic structure of Reynoutria populations change along the course of a river? Location: River Jizera basin, north Bohemia, Czech Republic. Methods: Nine 0.25 km(2) plots were chosen along the river. Within each plot all main habitat types were determined and sampled using the Braun-Blanquet scale to determine the invasibility of various communities. The patches invaded by Reynoutria taxa and surrounding Reynoutria-free vegetation in the same habitat type were sampled as releve pairs to compare the composition of invaded and non-invaded vegetation. In addition, to characterize the genetic structure of Reynoutria populations along the river, 30 samples front different clones were collected. Results and conclusions: 1. The species richness of communities has no influence on the success of Reynoutria invasion in the area studied. The combination of environmental conditions and propagule spread is more important to the invasion success than the number of species in the host community. 2. Reynoutria invasion greatly reduces species diversity. 3. R. japonica invaded more habitat types than R. sachalinensis and R. X bohemica. The hybrid R. x bohemica outcompetes the parental taxa at sites where both taxa co-occur. 4. Isozyme analysis revealed phenotype variability in the hybrid in contrast to the parental taxa. Different hybrid phenotypes are distributed randomly on the middle and lower reaches of the River Jizera; one of them dominates and the other three occur occasionally. This pattern supports the hypothesis that sexual reproduction occasionally occurs within Reynoutria taxa. Web of Science Fallopia japonica Czech Republic Field - Observational terrestrial Riparian Invasion Hyp. Community Species Richness;Hybridization;Plasticity primary 3090 Morgan-Richards, M; Trewick, SA; Chapman, HM; Krahulcova, A 2004 Interspecific hybridization among Hieracium species in New Zealand: evidence from flow cytometry journal HEREDITY 93 1 34 42 Hieracium pilosella ( Asteraceae) was accidentally introduced to New Zealand about 100 years ago. Since then it has become an aggressive weed, and an unexpected degree of genetic and genome size variation has been detected; features that might result from interspecies hybridization. We investigated the possibility that H. pilosella has hybridized with related taxa. Of the four other subgenus Pilosella species introduced to New Zealand, H. praealtum is the most abundant and, on morphological and distributional evidence, most likely to be the other parent. Flow cytometry was used to estimate relative genome size for 156 Hieracium plants collected from the wild. Plants assigned to either parental or hybrid morphotypes were found to comprise tetraploid and pentaploid individuals using genome size measurements, and this was confirmed with direct mitotic chromosome counts for a subset of plants. The haploid DNA content of H. praealtum was approximately 22% larger than that of H. pilosella. Putative hybrids that were tetraploid had mean genome sizes equivalent to two H. pilosella and two H. praealtum haploid chromosome sets, implying they were hybrids arising from the fertilization of two reduced gametes. Similar results were obtained from tetraploid hybrids produced by controlled pollination. However, the majority of field hybrids were pentaploid with a genome size equivalent to four H. pilosella and one H. praealtum haploid chromosome sets. We infer that these are not first-generation hybrids but represent successful backcrossing with H. pilosella and/or hybrid-hybrid crossing, and that sexual tetraploid hybrids have been the parents. We note that populations putatively of H. pilosella often comprise apomictic pentaploid hybrids. Significantly, our data indicate the emergence of sexual hybrids that provide further opportunity for gene flow among taxa in this complex. Web of Science Hieracium pilosella New Zealand terrestrial Invasion Hyp. Hybridization primary 3094 Owens, CS; Smart, RM; Stewart, RM 2004 Low temperature limits of giant salvinia journal JOURNAL OF AQUATIC PLANT MANAGEMENT 42 0 91 94 Giant salvinia (Salvinia molesta D.S. Mitchell) growing in three outdoor research ponds survived two north Texas winters during 1999-2000 and 2000-2001. The first winter was mild, with only one major freezing event. The second winter had three major freezing events, but again small numbers of the plants survived. Acute low-temperature exposure of the plants in a controlled study demonstrated that formation of ice results in decreased survival of giant salvinia. All the plants exposed for 48 hours to air temperatures of -16C were killed while those exposed for 48 hours at -3C survived apparently due to incomplete ice formation in the water of the containers. Web of Science Salvinia molesta USA Texas Garden lentic Invasion Hyp. Inherent Superiority Broad Tolerances primary 3096 Fetene, M; Beck, EH 2004 Water relations of indigenous versus exotic tree species, growing at the same site in a tropical montane forest in southern Ethiopia journal TREES-STRUCTURE AND FUNCTION 18 4 428 435 The objective of the study was to compare the water relations of two indigenous [Podocarpus falcatus (Thunb.) Endl., Croton macrostachys Hochst. ex. Del.] and two exotic tree species (Eucalyptus globulus Labille., Cupressus lusitanica Miller) growing in the same location in the montane Munessa State Forest, southern Ethiopia. Stem flow was measured with Granier type thermal dissipation probes. Sap flux, normalized per unit sapwood area, and the total sapwood areas of the particular trees were used to estimate daily transpiration. Maximum daily transpiration values (60 kg water) were recorded for Croton when at full foliage. After shedding most of its leaves in the dry season transpiration was reduced to 8 kg per day. Eucalyptus had the next highest transpiration (55 kg), in this case at the peak of the dry season. It transpired 4-5 times more than Podocarpus and Cupressus trees of similar size. Maximum stem flux density was tree-size dependent only in Croton. Diurnal patterns of stem flux indicated that Croton, Eucalyptus and Podocarpus, in contrast to Cupressus, responded more directly to light than to atmospheric water pressure deficit. At high VPD (>1.0 kPa) stem flux reached a plateau in Croton and Podocarpus indicating stomatal limitation. Per unit leaf area Croton had the highest and Podocarpus and Cupressus the lowest daily transpiration rates. In summary, the pioneer tree Croton had the lowest and Podocarpus the highest water use efficiency. The contribution of the study to the understanding of the role of each tree species in the hydrology of the natural forest and the plantations is discussed. Web of Science Eucalyptus globulus;Cupressus lusitanica Ethiopia Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Broad Tolerances primary 3097 Symstad, AJ 2004 Secondary invasion following the reduction of Coronilla varia (Crownvetch) in sand prairie journal AMERICAN MIDLAND NATURALIST 152 1 183 189 I investigated the effect of Coronilla varia invasion and subsequent reduction oil the plant community and soil nitrogen availability in a degraded Illinois sand prairie. The presence of C. varia significantly increased soil nitrogen availability and significantly decreased native species richness and cover, hilt neither helped nor hindered a common non-native grass, Poa pratensis. One year after the drastic reduction of C. varia, soil nitrogen remained somewhat elevated and native species richness and cover low, but P pratensis cover increased nearly six-fold. These results Suggest that C. varia's impact might be continued through altered soil nitrogen. More important, however, was the strong response of P. pratensis, which could hinder restoration efforts by competing with native species. Web of Science Coronilla varia USA Field - Observational terrestrial Grassland Invasion Hyp. Disturbance primary 3098 Maki, K; Galatowitsch, S 2004 Movement of invasive aquatic plants into Minnesota (USA) through horticultural trade journal BIOLOGICAL CONSERVATION 118 3 389 396 The extent to which invasive aquatic plants move via accidental inclusion in aquatic plant orders or sale of prohibited species is unknown. Forty orders were placed to 34 aquatic plant vendors across the US between May and September 2001 to determine the prevalence of movement into Minnesota via horticultural trade. Federal noxious weeds or Minnesota prohibited exotic species were acquired 92% of the time they were ordered and included Alternanthera sessilis, Butomus umbellata, Hydrocharis morsus-ranae, Potamogeton crispus, and Lythrum salicaria. Ninety three percent of orders received from aquatic plant vendors contained a plant or animal species not specifically requested; 10% of these purchases contained federal noxious weeds or Minnesota exotic species. Lemna minor was the most common incidental receipt found per taxa and per purchase, although Hydrilla verticillata, Lythrum salicaria, Salvinia molesta, and Potamogeton crispus (all prohibited taxa) were also found. Misidentified plants were found in 18% of the orders; unordered seeds in 43%. The sale and transport of prohibited aquatic plants likely presents the greatest risk associated with the aquatic plant trade. Other important factors include misidentification leading to the unintentional sale of invasive plants and the incidental inclusion of species during translocation. (C) 2003 Elsevier Ltd. All rights reserved. Web of Science Many USA Minnesota Field - Observational lentic;lotic Invasion Hyp. Other primary 3099 Dobbin, BF; Leao, BFD; Tidon, R 2004 Newly invading species exploiting native host-plants: the case of the African Zaprionus indianus (Gupta) in the Brazilian Cerrado (Diptera, Drosophilidae) journal ANNALES DE LA SOCIETE ENTOMOLOGIQUE DE FRANCE 40 4 285 290 The African Zaprionus indianus (Diptera, Drosophilidae) was introduced into the Neotropical Region by the end of the 1990's, and it became abundant in several types of altered and natural environments. In the Cerrado, the second South American biome in extension, it has been found mainly in open vegetation and during the rainy season. In the current work, we showed that Z indianus utilizes a major native fruit of the Brazilian Cerrado (Solanum lycocarpum) primarily, all over the fructification period and states of fruit's decay, confirming the adaptative versatility of this invading fly in new environments. Web of Science Zaprionus indianus Brazil Field - Observational terrestrial Invasion Hyp. Plasticity herbivore 3102 Meyer, SE; Nelson, DL; Carlson, SL 2004 Ecological genetics of vernalization response in Bromus tectorum L. (Poaceae) journal ANNALS OF BOTANY 93 6 653 663 Background and Aims Bromus tectorum (cheatgrass or downy brome) is an exotic annual grass that is dominant over large areas of former shrubland in western North America : To flower in time for seed production in early summer, B. tectorum plants generally require vernalization at winter temperatures, either as imbibed seeds or as established seedlings. Methods Variation in response to increasing periods of vernalization as seeds or seedlings for progeny of ten full-sib families from each of four B. tectorum populations from contrasting habitats was studied. Key Results As vernalization was increased from 0 to 10 weeks, the proportion of plants flowering within 20 weeks increased, weeks to initiation of flowering decreased, and seed yield per plant increased, regardless of whether plants were vernalized as seeds or seedlings. Most of the variation was accounted for by differences among populations. Plants of the warm desert population flowered promptly even without vernalization, while those of the cold desert, foothill and montane populations showed incremental changes in response variables as a function of vernalization period. Populations differed in among-family variance, with the warm desert population generally showing the least variance and the cold desert population the most. Variation among populations and among families within populations decreased as vernalization period increased, whereas the non-genetic component of variance showed no such pattern. Conclusions Variation in vernalization response was found to be adaptively significant and apparently represents the result of contrasting selection regimes on a range of founder genotypes. (C) 2004 Annals of Botany Company. Web of Science Bromus tectorum USA Field - Experimental terrestrial Grassland Invasion Hyp. Evolution in General primary 3103 Suehs, CM; Affre, L; Medail, F 2004 Invasion dynamics of two alien Carpobrotus (Aizoaceae) taxa on a Mediterranean island: II. Reproductive strategies journal HEREDITY 92 6 550 556 This study compares sexually and asexually produced fruit set, seed production, biomass, germination, and seedling size in Carpobrotus acinaciformis and C. edulis following controlled pollination experiments in order to evaluate the potential role of reproductive traits with respect to the invasive potential of these taxa. C. edulis is slightly agamospermic, completely self-fertile, slightly preferentially self-compatible, experiences no inbreeding depression, and has low hybrid vigour. In contrast, C. acinaciformis does not have reliable agamospermy, is only slightly self-fertile and self-compatible, experiences a slight inbreeding depression, and has a strong hybrid vigour. Both taxa have relatively low, although significantly different germination frequencies, and insignificantly different seedling sizes. Owing to the high performance in hybridisation as compared to all other controlled pollinations in C. acinaciformis, as well as a large amount of previously demonstrated introgression, we refer to the population studied on the island of Bagaud (France) as C. affine acinaciformis. We conclude that both C. edulis and C. affine acinaciformis should be considered as harmful invasive plants in the Mediterranean Basin, the former because of the flexibility of its mating system and high seed production, and the latter because of its strong clonality, high hybrid vigour, and potential for continued introgression from C. edulis genes. These differences require different control strategies, while the avoidance of sympatry is a distinct priority. Web of Science Carpobrotus acinaciformis;Carpobrotus edulis France Bagaud Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority;Hybridization Self Compatible primary 3104 MacDougall, AS; Turkington, R 2004 Relative importance of suppression-based and tolerance-based competition in an invaded oak savanna journal JOURNAL OF ECOLOGY 92 3 422 434 1. Invasive species dominate many ecosystems but the competitive strategies underlying this dominance are unclear. Are invasive species generalist competitors, or do they only thrive in certain environments? Do they occur mainly post-disturbance or can they persist throughout succession? 2. We tested the relative importance of resource acquisition (competitive suppression ability) and the ability to tolerate reduced resource levels (competitive tolerance ability) among four C3 perennial grass species in an invaded oak savanna. Two species (Poa pratensis and Dactylis glomerata) are exotic invaders and are thought to have replaced the two native species (Bromus carinatus and Elymus glaucus) as dominants. 3. Using glasshouse and field experiments we tested whether the two strategies were maintained with changing resource levels and successional conditions, and their relative roles in explaining exotic dominance. 4. The relative importance of suppression- and tolerance-based competition shifted with neighbour density, burning and planting order. Further, the relative importance of particular plant traits changed depending on the imposed conditions, and the exotic dominants were only competitively superior under certain circumstances. 5. Competitive suppression ability was maintained with changing resource levels but was confined to post-disturbance conditions. When planting of neighbours was delayed, the early establishing targets were dominant regardless of species, fertility and neighbour density. 6. Competitive tolerance ability determined long-term patterns of relative abundance and coexistence, but only under the current field conditions of low fertility and limited disturbance. Alteration of these conditions changed the relative abundance of the four grasses, and would probably reconfigure species patterns in the oak savanna community generally. 7. Exotic dominance is presently determined by tolerance-based competitive traits interacting with the long-term absence of disturbance. Dominance is therefore contingent on the interaction of competitive strategies, resource availability and disturbance history rather than any one factor alone. 8. Exotic flora dominate all stages of succession in this savanna because there exists both early (suppression) and late (tolerance) successional specialists. The identity of the dominant changes with succession based on the competitive strategy it employs. This result highlights the importance of examining the historical context of invaded communities and tracking their successional status over time. Web of Science Poa pratensis;Dactylis glomerata Canada British Columbia Duncan Field - Experimental;Greenhouse terrestrial Savanna Invasion Hyp. Inherent Superiority;Disturbance Superior Competitor primary 3105 Bossdorf, O; Schroder, S; Prati, D; Auge, H 2004 Palatability and tolerance to simulated herbivory in native and introduced populations of Alliaria petiolata (Brassicaceae) journal AMERICAN JOURNAL OF BOTANY 91 6 856 862 The European herb garlic mustard (Alliaria petiolata) is a serious invader of North American deciduous forests. One explanation for its success could be that in the absence of specialized herbivores, selection has favored less defended but more vigorous genotypes. This idea was addressed by comparing offspring from several native and introduced Alliaria populations with respect to their palatability to insect herbivores and their tolerance to simulated herbivory. Feeding rates of a specialist weevil from the native range were significantly greater on American plants, suggesting a loss of resistance in the introduced range. In contrast, there was significant population variation but no continent effect in the feeding rates of a generalist caterpillar. After simulated herbivory, A. petiolata showed a substantial regrowth capacity that involved changes in plant growth, architecture, and allocation. Removal of 75% leaf area or of all bolting stems reduced plant fitness to 81% and 58%, respectively, of the fitness of controls. There was no indication of a difference in tolerance between native and introduced Alliaria populations or of a trade-off between tolerance and resistance. Web of Science Alliaria petiolata USA Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Enemy Release primary 3106 Hager, HA; Vinebrooke, RD 2004 Positive relationships between invasive purple loosestrife (Lythrum salicaria) and plant species diversity and abundance in Minnesota wetlands journal CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE 82 6 763 773 Plant species invasions may result from, and cause, changes in the vegetation community and abiotic environment. It is often hypothesized that nonnative plant invaders suppress the diversity of native species. We examined relationships of vegetation and environmental gradients associated with the nonnative invasive wetland plant Lythrum salicaria L. to determine whether L. salicaria invasion is associated with reduced diversity and abundance of resident plant species in the wetland community. Vegetation and environmental variables were surveyed in 10 wetlands defining a gradient of L. salicaria abundance. In addition, relationships among variables were compared between invaded, Lythrum-dominated and uninvaded, Typha-dominated patches within 6 of the 10 invaded wetlands. Contrary to expectations, ordination results showed that plant diversity was higher in invaded than in uninvaded patches. Lythrum salicaria replaced other plant density and biomass on a one-to-one basis. The ordination results generated an unexpected competing set of testable hypotheses regarding whether L. salicaria invades diverse plant communities or enhances plant community diversity. Web of Science Lythrum salicaria USA Minnesota Field - Observational wetland Wetland Invasion Hyp. Community Species Richness primary 3111 Baret, S; Maurice, S; Le Bourgeois, T; Strasberg, D 2004 Altitudinal variation in fertility and vegetative growth in the invasive plant Rubus alceifolius Poiret (Rosaceae), on Reunion island. journal PLANT ECOLOGY 172 2 265 273 Rubus alceifolius Poiret (Rosaceae) was introduced to the island of Reunion in the southeastern Indian Ocean about 1850 and is now highly invasive. This bramble, native from southeastern Asia and Malaysia, has invaded a wide variety of habitats (lowland rainforest, mountain and submountain rainforest, Acacia heterophylla rainforest) from sea level to 1700 m. It is suspected to be monoclonal so, its remarkable success may be due in part to great phenotypic plasticity. On Reunion, bud, flower, fruit and seed production, the duration of the flowering period and the importance of the seed bank were found to be negatively correlated with elevation (50-1500 m a.s.l.). At a lowland site, fruit production in mature stands averaged between 30 and 80 fruits/m(2) during 1999 and 2000. No fruit set occurred above 1100 m. This fruit production pattern was similar over two years. Although the number of leaves per unit area is similar along the whole gradient studied, decrease of fruit set in upland areas might be compensated for by an increase in vegetative growth. Temperature variation is very sharp along the elevation gradient and may control the fruit and the seed production. Fruit production allows establishment of new populations all around the island via bird dissemination. Once established, R. alceifolius maintains dense patches that can grow vegetatively. Our results may be relevant for eradication programs that should take into account variation in reproductive strategy in lowland vs. highland habitats. Web of Science Rubus alceifolius Reunion Field - Observational terrestrial Invasion Hyp. Inherent Superiority Effective Disperser;Clonal Reproduction primary 3114 Zettler, JA; Taylor, MD; Allen, CR; Spira, TP 2004 Consequences of forest clear-cuts for native and nonindigenous ants (Hymenoptera : Formicidae) journal ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA 97 3 513 518 Currently, the southern United States produces more timber than any other region in the world. Entire timber stands are removed through a harvesting method called clear-cutting. This common forestry practice may lead to the replacement of native ant communities with invasive, nonindigenous species. In four deciduous forest sites in South Carolina, we monitored the change in ant species richness, diversity, and abundance immediately after forest clearing for a period of 15 mo to 2 yr and determined the incidence of colonization of the red imported fire ant Solenopsis invicta into these four newly disturbed sites. Each site consisted of an uncut, forested plot and a logged, pine-planted plot. Fire ants were collected in clear-cuts as early as 3 mo postcutting, and by the end of the experiment, they were found in all four treatment sites. Our study is the first to document, through a controlled experiment, that clear-cutting alters ant species assemblages by increasing S. invicta and Pheidole spp. Populations and significantly reducing native ant numbers. Long-term studies are needed to assess how replacing native deciduous forests with pine monocultures affects ant assemblages. Web of Science Solenopsis invicta USA South Carolina Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance omnivore 3116 Gilbert, M; Gregoire, JC; Freise, JF; Heitland, W 2004 Long-distance dispersal and human population density allow the prediction of invasive patterns in the horse chestnut leafminer Cameraria ohridella journal JOURNAL OF ANIMAL ECOLOGY 73 3 459 468 1. After its initial discovery in Macedonia in 1985, during the last 19 years the leafminer moth Cameraria ohridella has invaded most of Central and Western Europe. The species, which causes aesthetic damage to horse chestnuts, is generally observed first in highly populated locations before colonizing the countryside. This pattern is consistent with a stratified dispersal process combining long-distance movements and local diffusion. 2. Using large-scale spatial data on damage caused by Cameraria ohridella in Germany, three stochastic spatial models of spread are compared: a diffusion model, a leptokurtic dispersal model and a stratified dispersal model that assumes a two-scale dispersal process. In addition, the association between human population and moth invasion is tested in this last model by linking long-distance infestation probability to human population density. Finally, these spatial models constructed with data from Germany are tested at the European scale and compared to historical records of first occurrence. 3. The fat-tailed dispersal kernel models (leptokurtic and stratified dispersal models) allowing for long-distance dispersal provide better predictions than the diffusion model. Among these models, the stratified dispersal model incorporating the effect of human population density provides the best description of the spread of Cameraria ohridella in Germany in predictive (lowest sum of squared errors) and qualitative (similar fractal dimension) terms. 4. The roles of short-distance and long-distance dispersal in Cameraria ohridella invasion ecology in relation to human population are discussed, together with the models' scale-dependence and limitations. Web of Science Cameraria ohridella Germany Field - Observational terrestrial Deciduous Forest;Urban Invasion Hyp. Inherent Superiority;Disturbance Effective Disperser primary 3117 Nunes da Cunha, C; Junk, WJ 2004 Year-to-year changes in water level drive the invasion of Vochysia divergens in Pantanal grasslands journal APPLIED VEGETATION SCIENCE 7 1 103 110 In recent decades, cattle ranchers of the Pantanal of Mato Grosso, Brazil, have pointed to the accelerated spread of several herbaceous and woody plant species that invade natural and artificial pastures (campos). It has been speculated that overgrazing by an increasing number of cattle, lack of grazing in abandoned areas, or large-scale changes in environmental conditions may be the reason for this invasion. This study focuses on ecological and ecophysiological aspects of Vochysia divergens (cambara), a flood-tolerant tree that began spreading in the Pantanal during the last 30 years and is considered a very aggressive invasive plant. The study shows that the spread of cambard can be related to natural multi-years wet periods. During multi-years dry periods the species is reduced by the increasing impact of fires in the Pantanal. This points to the great importance of multi-years climatic events on the vegetation cover of the Pantanal and indicates a very dynamic development in plant communities. Web of Science Vochysia divergens Brazil Mato Grosso Field - Observational terrestrial Grassland Invasion Hyp. Disturbance primary 3118 Marchetti, MP; Moyle, PB; Levine, R 2004 Invasive species profiling? Exploring the characteristics of non-native fishes across invasion stages in California journal FRESHWATER BIOLOGY 49 5 646 661 1. The global spread of non-native species is a major concern for ecologists, particularly in regards to aquatic systems. Predicting the characteristics of successful invaders has been a goal of invasion biology for decades. Quantitative analysis of species characteristics may allow invasive species profiling and assist the development of risk assessment strategies. 2. In the current analysis we developed a data base on fish invasions in catchments throughout California that distinguishes among the establishment, spread and integration stages of the invasion process, and separates social and biological factors related to invasion success. 3. Using Akaike's information criteria (AIC), logistic and multiple regression models, we show suites of biological variables, which are important in predicting establishment (parental care and physiological tolerance), spread (life span, distance from nearest native source and trophic status) and abundance (maximum size, physiological tolerance and distance from nearest native source). Two variables indicating human interest in a species (propagule pressure and prior invasion success) are predictors of successful establishment and prior invasion success is a predictor of spread and integration. 4. Despite the idiosyncratic nature of the invasion process, our results suggest some assistance in the search for characteristics of fish species that successfully transition between invasion stages. Web of Science Many USA California Field - Observational;Theoretical/Modeling lentic;lotic Invasion Hyp. Propagule Pressure herbivore;omnivore 3120 Sole, M; Durka, W; Eber, S; Brandl, R 2004 Genotypic and genetic diversity of the common weed Cirsium arvense (Asteraceae) journal INTERNATIONAL JOURNAL OF PLANT SCIENCES 165 3 437 444 In many clonal species, seedling establishment is restricted to early successional stages when recruitment is still possible. Then, one expects that adapted genotypes become dominant and genotypic and genetic diversity should decrease with time. We investigated genotypic and genetic diversity within recently founded and established populations of the common weed Cirsium arvense. We used highly polymorphic amplified fragments length polymorphism (AFLP) markers. All populations were multiclonal and highly diverse ( the proportion of distinguishable genotypes was 0.73 +/- 0.25 [mean +/- SD]). Clonal evenness was variable and ranged from 0.2 to 1. Independent of successional stage, we found on the small geographic scale of our study (< 5 km) a considerable differentiation between populations (&UPhi;(SC) = 0.63). This amount of differentiation was similar between founder and established populations and could result from selection in the early stage of succession as well as founder effects. Contrary to the general expectation, genotypic and genetic diversity were maintained through time, and molecular variance did not differ between successional stages (1.9 &PLUSMN; 0.89 vs. 2.5 &PLUSMN; 1.41). We suggest that this pattern is a consequence of the particular reproductive system of C. arvense that combines clonality with dioecy. The combination of clonal reproduction with the recruitment of sexually outcrossed seedlings in the first years allows the species to perform efficient colonizations even with founder effects, to undergo selection without loss of diversity, and to persist locally. This strategy appears to be very efficient in C. arvense and may have contributed to the worldwide success of this species. Web of Science Cirsium arvens USA terrestrial Invasion Hyp. Inherent Superiority Clonal Reproduction primary 3121 Lanzoni, A; Accinelli, G; Bazzocchi, GG; Burgio, G 2004 Biological traits and life table of the exotic Harmonia axyridis compared with Hippodamia variegata, and Adalia bipunctata (Col., Coccinellidae) journal JOURNAL OF APPLIED ENTOMOLOGY 128 4 298 306 As part of an environmental risk assessment study of exotic natural enemies used in inundative biological control, life-history characteristics of Harmonia axyridis (Pallas), Hippodamia variegata (Goeze) and Adalia bipunctata (L.) (Col., Coccinellidae) were quantified under laboratory conditions at 25degreesC on Myzus persicae (Sulzer) as prey. Comparative studies showed significant differences among pre-adult development times: H. axyridis developed slower ((X) over tilde = 19.8 days) than H. variegata ((X) over tilde = 18.1 days) and A. bipunctata ((X) over tilde = 18.4 days). Differences were also evident in the duration of egg, larval and pupal stages. No measurable differences among the three species were found for fecundity, oviposition rate and adult longevity. Harmonia axyridis exhibited the longest pre-oviposition ((X) over tilde = 7.4 days) and interoviposition ((X) over tilde = 3.6 days) periods and the shortest oviposition period ((X) over tilde = 13.7 days). The Bieri model was used to describe age-specific fecundity for the three species of coccinellids. The intrinsic rate of increase (r(m)), net reproductive rate (R-0) and mean generation time (T) were higher for H. variegata (r(m) = 0.114, R-0 = 52.75, T = 41.88 days) than for H. axyridis (r(m) = 0.089, R-0 = 26.27, T = 38.81 days) or A. bipunctata (r(m) = 0.081, R-0 = 18.49, T = 40.06 days). Our findings show that the biological traits of H. axyridis do not seem to be factors that may contribute to the invasiveness of this coccinellid. Web of Science Harmonia axyridis terrestrial Invasion Hyp. Inherent Superiority predator 3124 Davis, HG; Taylor, CM; Civille, JC; Strong, DR 2004 An Allee effect at the front of a plant invasion: Spartina in a Pacific estuary journal JOURNAL OF ECOLOGY 92 2 321 327 1 Spartina alterniflora sets very little viable seed at the leading edges of an invasion in Willapa Bay, Washington, USA, where it was introduced c. 100 years ago. This largely outbreeding, rhizomatous grass recruits into previously unoccupied areas at low density, so young plants initially grow isolated from one another but eventually coalesce to form continuous meadows. 2 Isolated recruits set approximately one-tenth the seed of meadow plants at five sites, spread over the 230 km(2) of Willapa Bay mudflats, and this seed germinated at only one-third the rate observed in meadow plants. 3 The consistent patterns suggested that the low seed set in the isolated plants was largely due to the demographic effects of density. Differences between sites in the incidence and amount of seed set and germination rate indicated, however, that there was some environmental influence. 4 These data imply that plants in newly invaded, low-density areas produce little viable seed until rhizomatous growth brings them into close contact. This Allee effect could substantially reduce the rate of invasion. Web of Science Spartina alterniflora USA Washington Willapa Bay Field - Observational estuarine Intertidal/Near Shore Invasion Hyp. Inherent Superiority Clonal Reproduction primary 3125 Bertolino, S; Mazzoglio, PJ; Vaiana, M; Currado, I 2004 Activity budget and foraging behavior of introduced Callosciurus finlaysonii (Rodentia, Sciuridae) in Italy journal JOURNAL OF MAMMALOGY 85 2 254 259 We studied seasonal activity patterns and feeding behavior of a population of Finlayson's squirrel (Callosciurus finlaysonii) native to Indochina and introduced into Italy. Squirrels spent the majority of active time foraging, switching between resources according to availability. In winter, they fed mainly on buds or stripped bark, shifting to flowers when plants bloomed in spring, and to mature seeds and fruits from June to October. By November-December, bark-stripping became progressively more important. This activity accounted for 36.5% of the yearly feeding time. The flexibility to exploit a wide range of foods, the ability to change food habits throughout the year, and hoarding behavior are factors that could indicate a proclivity to use different habitats successfully. Web of Science Callosciurus finlaysonii Italy Field - Observational terrestrial Deciduous Forest Invasion Hyp. Plasticity herbivore 3127 Buckley, P; Dussart, G; Trigwell, JA 2004 Invasion and expansion of Corophiidae (Amphipoda) in the Stour Estuary (Kent, Uk) journal CRUSTACEANA 77 0 425 433 The Kentish Stour Estuary has been subject to a continuous monitoring programme since June 1996. In September 1998, the exotic amphipod Chelicorophium curvispinum appeared in the upper, freshwater reaches of the estuary. At the same time, the population size of the native Corophium volutator dramatically increased in the lower part of the estuary. A third species, Corophium multisetosum, appeared near the limit of saline penetration in September 1999. Possible reasons for this multi-specific colonization, such as increases in salinity, temperature, chlorophyll a, and changes in anthropogenic impacts on the estuary, are discussed. Web of Science Chelicorophium curvispinum United Kingdom Kent Stour Estuary Field - Observational estuarine Invasion Hyp. Disturbance omnivore 3129 Xu, KY; Ye, WH; Cao, HL; Deng, X; Yang, QH; Zhang, Y 2004 The role of diversity and functional traits of species in community invasibility journal BOTANICAL BULLETIN OF ACADEMIA SINICA 45 2 149 157 The invasion of exotic species into assemblages of native plants is a pervasive and widespread phenomenon. Many theoretical and observational studies suggest that diverse communities are more resistant to invasion by exotic species than less diverse ones. However, experimental results do not always support such a relationship. Therefore, the hypothesis of diversity-community invasibility is still a focus of controversy in the field of invasion ecology. In this study, we established and manipulated communities with different species diversity and different species functional groups (16 species belong to C-3, C-4, forbs and legumes, respectively) to test Elton's hypothesis and other relevant hypotheses by studying the process of invasion. Alligator weed (Alternanthera philoxeroides) was chosen as the invader. We found that the correlation between the decrement of extractable soil nitrogen and biomass of alligator weed was not significant, and that species diversity, independent of functional groups diversity, did not show a significant correlation with invasibility. However, the communities with higher functional groups diversity significantly reduced the biomass of alligator weed by decreasing its resource opportunity. Functional traits of species also influenced the success of the invasion. Alternanthera sessilis, in the same morphological and functional group as alligator weed, was significantly resistant to alligator weed invasion. Because community invasibility is influenced by many factors and interactions among them, the pattern and mechanisms of community invasibility are likely to be far subtler than we found in this study. More careful manipulated experiments coupled with theoretical modeling studies are essential steps to a more profound understanding of community invasibility. Web of Science Alternanthera philoxeroides China Garden terrestrial Invasion Hyp. Community Species Richness primary 3131 Cassey, P; Blackburn, TM; Russell, GJ; Jones, KE; Lockwood, JL 2004 Influences on the transport and establishment of exotic bird species: an analysis of the parrots (Psittaciformes) of the world journal GLOBAL CHANGE BIOLOGY 10 4 417 426 Most studies of exotic species invasions only consider the factors that affect the establishment of populations following release, yet this is only one step on the invasion pathway. Different factors are likely to influence which species are transported and released. Here, we examine the influence of species traits on the successful transition of species through several stages in the introduction pathway (transport, release, and establishment), using parrots (Aves: Psittaciformes) as a model system. We use a species-level supertree of parrots to test for phylogenetic auto-correlation in the introduction process. Our analyses find that different sets of variables are related to the probability that a species enters each stage on the invasion pathway. The availability of individuals for transport and release seems to be most important for passage through these stages, but has no obvious effect on establishment following release. Rather, establishment success is higher for sedentary species, and species with broad diets. Web of Science Parrots, various genera Field - Observational;Theoretical/Modeling terrestrial Invasion Hyp. Other omnivore 3146 Lee, CS; Cho, HJ; Yi, H 2004 Stand dynamics of introduced black locust (Robinia pseudoacacia L.) plantation under different disturbance regimes in Korea journal FOREST ECOLOGY AND MANAGEMENT 189 3 281 293 Black locust (Robinia pseudoacacia L.) was introduced to South Korea from North America in the 19th Century and was heavily used in the 1960s for reforestation of denuded mountains after the extensive deforestation during the Japanese occupation periods and the Korean War. Nationwide distribution of black locust tended to positively correlate with human population size and/or density of the administrative districts considered. Results from field survey on the representative vegetation types, Quercus acutissima and Q. mongolica communities in lowland and upland, respectively, show that black locust have invaded other vegetation beyond originally planted zones in lowland but not the upland vegetation. Black locust occurs from the bases to summits of mountains in the urban centers, whereas its range is restricted to mountain bases in urban outskirts and rural areas. Although native oaks (Quercus spp.) are usually succeeding black locust colonies, changes to native vegetation are often interrupted by frequent disturbance by human activities, as evident from persistent sprouts and expansions of black locust suckers in the disturbed areas, such as urban center and rural areas. Responses of the black locust plantation in terms of stand dynamics to different disturbance intensities also reflected such trends. Our results suggest a correlation between disturbance regimes and occurrence of black locusts. We recommend incorporating this correlation to the management plan for control of black locust. (C) 2003 Elsevier B.V. All rights reserved. Web of Science Robinia pseudoacacia South Korea terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 3155 Braks, MAH; Honorio, NA; Lounibos, LP; Lourenco-De-Oliveira, R; Juliano, SA 2004 Interspecific competition between two invasive species of container mosquitoes, Aedes aegypti and Aedes albopictus (Diptera : Culicidae), in Brazil journal ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA 97 1 130 139 As a result of numerous successful invasions by both Aedes albopictus (Skuse) and Ades aegypti (L.), the current worldwide distributions of these mosquito species overlap. Shared larval habitats and shifts in the distribution and abundance of resident A. albopictus or A. aegypti after the establishment of the other species suggest that competitive displacement occurs. Experiments on larval competition between North American populations of the two species showed that A. albopictus has the competitive advantage under local field conditions, which apparently accounts for displacement of A. aegypti from much of the United States after the invasion of A. albopictus. The role of competition, and potential shifts of competitive advantage in different parts of their worldwide ranges are unknown, but variation due to intraspecific or environmental differences is possible. In the current study, we measured the performance of larvae of Brazilian populations of A. albopictus and A. aegypti competing under field conditions in Rio de Janeiro, Brazil. Finite rates of increase for each species were estimated and the effects of species composition, larval density, and leaf litter resource levels were determined. A. albopictus maintained positive population growth at higher combined densities and lower per capita resource availability than did A. aegypti. A. albopictus showed higher survivorship than A. aegypti under all treatments and leaf litter resource levels. These results indicate that in Brazil, just as in North America, A. albopictus is a superior larval competitor to A. aegypti when exploiting leaf litter resources. Our results further suggest that this competitive advantage for A. albopictus is likely to be independent of mosquito population origin, local environmental conditions, and local differences in the types of leaves that form the resource base of the aquatic habitats of larvae. Web of Science Aedes albopictus;Ades aegypti Brazil Rio de Janeiro Field - Experimental terrestrial Invasion Hyp. Inherent Superiority Superior Competitor herbivore;predator 3157 Trewick, SA; Morgan-Richards, M; Chapman, HM 2004 Chloroplast DNA diversity of Hieracium pilosella (Asteraceae) introduced to New Zealand: Reticulation, hybridization, and invasion journal AMERICAN JOURNAL OF BOTANY 91 1 73 85 The European hawkweed Hieracium pilosella is a successful invader and a troublesome weed in New Zealand. The systematics of the genus Hieracium is extremely complex and contentious, probably due to recent speciation, hybridization, polyploidy. and diverse reproductive strategies. In the first chloroplast DNA survey of the group, we sequenced 285 plants (including H. pilosella and 12 other species of subgenus Pilosella) from New Zealand and Europe for 900 bp of trnL-trnF. Eleven haplotypes were identified with much sharing among species. Three haplotypes (A, D, G) were found in seven, three, and four species, respectively, but two species (H. lactucella and H. auricula) had single, private haplotypes. Our cpDNA data for subgenus Pilosella are consistent with the group's having incomplete lineage sorting and/or recent reticulate evolution. Six haplotypes were identified in H. pilosella, four of these unique to this taxon in our sample. In New Zealand, haplotype A was common and occurred in plants of different ploidy (i.e., 4X, 5X, 6X), whereas haplotypes C, B, and M were restricted to 4X, 5X, and 6X plants, respectively. The distribution of haplotype variation suggests that some or all of the H. pilosella seeds accidentally introduced into New Zealand probably came from east Europe rather than the United Kingdom and that a minimum of four lineages were introduced. Within New Zealand, hybridization of H. pilosella with a related taxon (probably H. praealtum) has occurred at least three times, involving both obligate sexual tetraploids and facultative apomictic pentaploids of H. pilosella. Web of Science Hieracium pilosella New Zealand Field - Observational terrestrial Invasion Hyp. Hybridization primary 3162 Barton, AM; Brewster, LB; Cox, AN; Prentiss, NK 2004 Non-indigenous woody invasive plants in a rural New England town journal BIOLOGICAL INVASIONS 6 2 205 211 We investigated the abundance of non-indigenous woody invasive plants in Farmington, Maine, a rural New England town in a forested landscape. We found 12 invasive species and more than 7 patches per kin from surveys on 33 transects (54.3 km) along field edges, abandoned railroad right-of-ways, roadsides, and riparian zones. Invasive abundance was apparently lower than for more developed areas of the northeastern US, where, in contrast to western Maine, invasives have extensively penetrated forest interiors. Invasive abundance increased with the amount of landscaping and proximity to town, suggesting a close association between local horticulture and the spread of woody invasives. Invasive abundance and diversity were highest in riparian areas, probably due to relatively high levels of propagule pressure. Species differed in the extent of invasiveness, ranging from those still dependent on planted parent trees to fully invasive populations. The invasive species recorded in this study have caused environmental and economic damage elsewhere. The lower levels of invasiveness in Farmington are likely a result of the isolation, small human population, and forested landscape rather than low levels of invasibility. This suggests the potential for future risks, and the importance of intervention while populations can still be eradicated or controlled. Web of Science Many United States Maine Farmington Field - Observational terrestrial Riparian;Old Field Invasion Hyp. Propagule Pressure primary 3163 Ayres, DR; Smith, DL; Zaremba, K; Klohr, S; Strong, DR 2004 Spread of exotic cordgrasses and hybrids (Spartina sp.) in the tidal marshes of San Francisco Bay, California, USA journal BIOLOGICAL INVASIONS 6 2 221 231 Four species of exotic cordgrass (Spartina sp.) occur in the San Francisco estuary in addition to the California native Spartina foliosa. Our goal was to map the location and extent of all non-native Spartina in the estuary. Hybrids of S. alterniflora and S. foliosa are by far the most numerous exotic and are spreading rapidly. Radiating from sites of deliberate introduction, S. alterniflora and hybrids now cover ca. 190 ha, mainly in the South and Central Bay. Estimates of rate of aerial increase range from a constant value to an accelerating rate of increase. This could be due to the proliferation of hybrid clones capable of rapid expansion and having superior seed set and siring abilities. The total coverage of 195 ha by hybrids and other exotic cordgrass species is slightly less than 1% of the Bay's tidal mudflats and marshes. Spartina anglica has not spread beyond its original 1970s introduction site. Spartina densiflora has spread to cover over 5 ha at 3 sites in the Central Bay. Spartina patens has expanded from 2 plants in 1970 to 42 plants at one site in Suisun Bay. Spartina seed floats on the tide, giving it the potential to export this invasion throughout the San Francisco estuary, and to estuaries outside of the Golden Gate. We found isolated plants of S. alterniflora and S. densiflora in outer coast estuaries north of the Bay suggesting the likelihood for the San Francisco Bay populations to found others on the Pacific coast. Web of Science Spartina alterniflora;Spartina foliosa USA California San Francisco Estuary Field - Observational estuarine Invasion Hyp. Hybridization primary 3164 Unmack, PJ; Fagan, WE 2004 Convergence of differentially invaded systems toward invader-dominance: time-lagged invasions as a predictor in desert fish communities journal BIOLOGICAL INVASIONS 6 2 233 243 To what extent do patterns of invasion in one region generalize to other regions? Answering this question is a key goal of invasion biology because it underlies whether we can make progress via comparative studies or must instead cope with a large set of unique cases. Here we quantify similarities and differences in the historical development of normative fish assemblages of two North American desert drainages, one with many normative fishes (Gila Basin, principally southwestern USA), and one with few (Yaqui Basin, principally northwestern Mexico). The two river basins are similar in size, physiography, and ecology, but because of differences in the timing of regional development, we hypothesized that richness and geographic spread of normative fishes in the Yaqui are time-lagged relative to the Gila, and that a slow, but steady increase of normative fish occurrence is underway in the Yaqui, similar to what has already occurred in the Gila. Using the comprehensive SONFISHES database, we found that increases in the regional richness of extant normative species over time have been roughly linear in both basins. Meanwhile, previously established species have continued to spread spatially, such that the cumulative number of reach records for normative species has increased roughly exponentially in both systems. The current status of normatives in the Yaqui is remarkably similar to what was evident from the Gila in the past at a comparable level of sampling effort. For all measures of invasion dynamics we examined, a time lag of similar to 40-50 years exists between the Gila and Yaqui. The majority of extant normative fishes are known piscivores, and many have high levels of parental care, a life history trait that affords considerable advantages over native fishes. These results predict that, absent strong action now, the presently abundant native fish fauna of the Yaqui may become increasingly imperiled over the next several years, with a future similar to the Gila, where most native fishes are either extirpated, threatened, or substantially reduced in range, at least partially due to normative fishes. We recommend immediate actions to identify and protect high priority portions of the Yaqui Basin from further normative fish invasion before further degradation occurs. Web of Science Many USA Gila Basin Field - Observational lotic Invasion Hyp. Other herbivore 3167 Facon, B; Machline, E; Pointier, JP; David, P 2004 Variation in desiccation tolerance in freshwater snails and its consequences for invasion ability journal BIOLOGICAL INVASIONS 6 3 283 293 The freshwaters of Martinique (French West Indies) have recently been invaded by snails belonging to the Thiaridae family (Gastropoda; Prosobranchia). Eight distinct Thiarid lines have been successively introduced in Martinique, and are still in the process of sequentially replacing one another within local habitats, revealing a range of increasing invasive abilities. Our aim was to test whether the variation in invasive ability can be partly explained by a specific life-history trait, desiccation tolerance, which might be important in view of the typical instability of tropical freshwater habitats. We therefore tested desiccation tolerance in both juveniles and adults under laboratory conditions. Our data show that, although all Thiarid lines resist desiccation quite well, they exhibit extreme variation in the degree of tolerance. These differences are mostly mediated by individual size, but are definitely of genetic origin given that our individuals were of similar ages and were raised under standardized laboratory conditions. The overall invasive success of a line in Martinique, deduced from field surveys, does not correlate with its desiccation tolerance. However, desiccation tolerance does seem to be a limiting factor for the invasion of the small fraction of habitats that are most exposed to drought. More generally, our study exemplifies the possibility that the invasion differential among habitats, rather than a general invasion ability, be predicted according to a particular life-history trait, within a set of closely related invasive taxa. Web of Science Many Eastern Caribean Martinique Lab lentic;lotic Invasion Hyp. Inherent Superiority Broad Tolerances herbivore 3168 Kellogg, CH; Bridgham, SD 2004 Disturbance, herbivory, and propagule dispersal control dominance of an invasive grass journal BIOLOGICAL INVASIONS 6 3 319 329 Despite the dramatic changes invasive plants cause to ecosystems and communities, factors that control dominance of invasive species after establishment in a community are poorly understood. Most active management relies on catastrophic disturbances of invasive-dominated communities to increase richness and diversity of plant communities. This study examines the importance of propagule dispersal and deer herbivory on continued dominance of Phalaris arundinacea after a non-catastrophic, short-term disturbance to monotypic stands of this invasive grass. The disturbance caused no change in R arundinacea cover among treatments during any year of the study and, thus, simulates disturbance intensity more likely to be encountered in unmanaged settings. Despite the small disturbance, the combinations of disturbance + seeding and disturbance + seeding + deer exclusion caused greater species richness than controls even three years after disturbance. Increased invasion of P. arundinacea stands caused few effects on the dominant, as R arundinacea biomass was unaffected after the first year. Selective herbivory by deer of species other than R arundinacea increased the effects of disturbance and seeding, and aided in continued dominance of the grass. The tolerance of R arundinacea for direct anthropogenic effects, including poor water quality and hydroperiod fluctuations, and indirect effects, such as increased herbivory by historically high deer populations, indicates the complexity of determining persistence of invasive species. Web of Science Phalaris arundinacea USA Indiana Field - Observational wetland Grassland Invasion Hyp. Inherent Superiority;Disturbance Effective Disperser primary 3169 Howard, TG; Gurevitch, J; Hyatt, L; Carreiro, M; Lerdau, M 2004 Forest invasibility in communities in southeastern New York journal BIOLOGICAL INVASIONS 6 4 393 410 While biological invasions have been the subject of considerable attention both historically and recently. the factors controlling the susceptibility of communities to plant invasions remain controversial. We surveyed 44 sites in southeastern New York State to examine the relationships between plant community characteristics, soil characteristics, and normative plant invasion. Soil nitrogen mineralization and nitrification rates were strongly related to the degree of site invasion (F = 30.2, P < 0.0001 and F = 11.8, P < 0.005, respectively), and leaf C : N ratios were negatively correlated with invasion (R-2 = 0.22, P < 0.0001). More surprisingly, there was a strong positive relationship between soil calcium levels and the degree of site invasion (partial r = 0.70, P < 0.01), and there were also positive relationships between invasion and soil magnesium and phosphorus. We found, in addition, a positive factor-ceiling relationship between native species diversity and invasive species diversity. This positive relationship between native and invasive diversity contradicts earlier hypotheses concerning the relationships between species diversity and invasion, but supports some recent findings. Cluster analysis distinguished two broad forest community types at our sites: pine barrens and mixed hardwood communities. Invaders were significantly more abundant in mixed hardwood than in pine barrens communities (Mann-Whitney U = 682.5, P < 0.0001). Even when evaluating the mixed hardwood communities alone, invasion remained significantly positively correlated with soil fertility (calcium. magnesium, and net nitrogen mineralization rates). Soil texture and pH were not useful predictors of the degree to which forests were invaded. Nitrogen and calcium are critical components of plant development. and species better able to take advantage of increased nutrient availability may out-perform others at sites with higher nutrient levels.These results have implications for areas such as the eastern United States, where anthropogenic changes in the availability of nitrogen and calcium are affecting many plant communities. Web of Science Many USA New York Field - Observational terrestrial Deciduous Forest;Coniferous Forest Invasion Hyp. Community Species Richness primary 3170 Beckstead, J; Augspurger, CK 2004 An experimental test of resistance to cheatgrass invasion: limiting resources at different life stages journal BIOLOGICAL INVASIONS 6 4 417 432 Variable densities of an invasive species may represent variation in invasion resistance. due to variation in resource availability. This study determined. whether low- and high-density cheat-grass (Bromus tectorum L.) patches within a shadscale-bunchgrass community of western Utah, USA, can be explained by variation in resource availability. It also explored the possible role of seed limitation and enemy pressure on invasion patterns. Two parallel field experiments were conducted: (1) increasing resources within low-density cheatgrass patches and, conversely; (2) reducing resources within high-density cheatgrass patches. Treatments were applied at three life stages separately and across all stages. In low-density cheatgrass patches (assumed to represent high resistance), a disturbance that reduced soil compaction had the strongest positive effect, significantly increasing biomass by 250% and density by 104% in comparison to the control. The second strongest effect was reducing neighbors (native grasses), which significantly increased cheatgrass biomass and density. These results indicate that resources are present in low-density cheatgrass patches, but they are unavailable without disturbance and/or are exploited by competitors, and hence represent resistance to invasion. In high-density cheatgrass patches (assumed to represent low resistance), nitrogen availability was important in maintaining cheatgrass densities. Reducing nitrogen (via sucrose addition) significantly decreased density (by 37%) but not biomass. Life stages of cheatgrass were differentially affected by these resource manipulations. In addition, herbivore (primarily grasshoppers) and pathogen (head smut) pressures were documented to affect cheatgrass density, but did not explain resistance patterns. Instead, we found that differential resource availability explains the observed variation in cheatgrass density, and variation in natural resistance. Web of Science Bromus tectorum USA Utah Field - Experimental terrestrial Grassland Invasion Hyp. Disturbance primary 3171 Hager, HA 2004 Differential effects of Typha litter and plants on invasive Lythrum salicaria seedling survival and growth journal BIOLOGICAL INVASIONS 6 4 433 444 Invasive species are a problem because of their detrimental ecological and economic effects. Increased disturbance caused by human impacts is hypothesized as a primary factor promoting the spread of invaders. Plants and plant litter can have important effects on plant colonization and community composition by affecting seedling survival and growth. I examined the hypothesis that invasion of non-native Lythrum salicaria in Typha-dominated marshes is disturbance-dependent. If so, the removal of Typha plants or litter would increase the survival and growth of L. salicaria seedlings. Additionally, the removal of both plants and litter could result in an additive or synergistic effect on the establishment of L. salicaria. Alternatively, L. salicaria may be a successful invader because it has a high capacity to establish and grow regardless of neighbours. In this case, L. salicaria would be expected to perform well even in plants and litter. Strategies for managing L. salicaria will depend on which factors promote invasion. I measured the differential effects of plants and litter, alone and in combination. on the survival and growth of L. salicaria seedlings transplanted into marshes. The presence of plants and litter did not affect seedling survival in relatively dry wetland sites, indicating that L. salicaria seedlings have the capacity to persist in the presence of neighbouring Typha spp. competitors. However, removal of both plants and litter allowed increased growth of L. salicaria seedlings in drier wetlands. Therefore, growth was facilitated by disturbance that removed all vegetation. Small disturbances (0.6 m(2)) decreased competitive suppression by native Typha spp. neighbours and resulted in significant increases in growth. Disturbance of wetlands at risk of invasion by L. salicaria should be avoided. Web of Science Lythrum salicaria USA MInnesota Field - Experimental wetland Wetland Invasion Hyp. Disturbance primary 3172 Raffaele, E 2004 Susceptibility of a Patagonian mallin flooded meadow to invasion by exotic species journal BIOLOGICAL INVASIONS 6 4 473 481 Mallin wetland meadows are highly diverse, rare habitats in western Patagonia that are believed to be particularly susceptible to disturbance. I tested the hypothesis that exotic species reduce the rate and extent of recolonization by native species after disturbances. Open patches (50 x 50 cm) were subjected to artificial seeding with propagules of two exotic species. Cover of individual species in each plot was measured over the four following austral summers (1990-1993) and two late summers (1995 and 1998). The effect of a particular exotic species was not the same for all native species. For some native species. the presence of an exotic species in the plots was associated with a significant increase in cover, while a significant decrease in cover was observed for other species. Native species richness and diversity were not significantly affected by the introduction and establishment of exotic species. In addition, the failure of the exotic species to establish in the undisturbed control plots further suggests that the undisturbed mallin is resistant to invasion by exotic species. The results suggest that the small-scale changes that occurred in this community due to exotic species during recolonization were transient and almost undetectable after eight years. Web of Science Trifolium repens;Taraxacum officinale Argentina Patagonia Field - Experimental terrestrial Mountain Invasion Hyp. Community Species Richness primary 3173 Brandon, AL; Gibson, DJ; Middleton, BA 2004 Mechanisms for dominance in an early successional old field by the invasive non-native Lespedeza cuneata (Dum. Cours.) G. Don journal BIOLOGICAL INVASIONS 6 4 483 493 Researchers studying invasive plants often concentrate their efforts on predictive models thought to callow invasive plants to dominate native landscapes. However, if an invasive is already well established then experimental research is necessary to provide the information necessary to effectively manage the species. Prescribing appropriate management strategies without prior experimental research may not only be ineffective but also may squander limited resources or have the unintended consequence of furthering spread. Lespedeza cuneata (Dum. Cours.) G. Don. is a well-established invasive plant of old fields and tall-grass prairie in the US. Managers suspect this species shades-out native plants and this is proposed as its primary mechanism for dominance. Using field experiments we tested probable factors allowing the species to establish itself and, once established, interfere in old field plant communities. We also examined the effects of two common anthropogenic disturbances (mowing and nutrients) on L. cuneata growth and establishment. When L. cuneata was treated (clipping, herbicide and stem pull-back) there was a significant increase in species richness and native species cover. Stem density and canopy cover of L. cuneata increased significantly with mowing frequency but-decreased with nutrient input. We suggest that mowing benefits L. cuneata while also hindering woody competition. Results also indicate L. cuneata is less prevalent on nutrient enriched soils than on unamended soil. Lespedeza cuneata appears to suppress native plants by shading them out and it can subsequently take over grassland communities. Since it has a varying response to human induced disturbances and may actually benefit from mowing, land managers should be cautious when utilizing this as a management tool. Web of Science lespedeza cuneata USA Field - Observational terrestrial Old Field Invasion Hyp. Inherent Superiority;Disturbance Rapid Growth primary 3175 Lundholm, JT; Larson, DW 2004 Dominance as an overlooked measure of invader success journal BIOLOGICAL INVASIONS 6 4 505 510 Recent multi-habitat studies across a range of spatial scales have shown that species-rich habitats are often highly invasible by exotic species. The primary measures of 'invasion' in these and other studies are invader richness and the absolute cover or biomass of invaders. We argue that the relative biomass or cover of invaders (dominance) is an important but overlooked measure of plant invasion. We re-analyzed data presented in five previous studies to evaluate whether exotic relative abundance is positively correlated with native richness. There were either no relationships or negative relationships between native richness and relative exotic cover calculated from three spatial scales (1, 1000 and 4000 m(2)). Thus while the original studies reported high exotic richness or absolute cover in habitats rich in native species, native richness did not predict the degree to which exotics had become dominant or abundant relative to natives. Absolute measures of exotic cover reported in the original studies underestimated relative exotic cover in habitats with low native species richness. High exotic dominance in areas of low native richness may indicate that exotic richness and dominance are controlled by different factors. We conclude that it is useful for researchers to measure both invader richness and invader dominance when trying to understand the environmental factors that are associated with plant invasions. Web of Science Many USA Statistical/Meta-analysis terrestrial Invasion Hyp. Community Species Richness primary 3176 Dietz, H; Wirth, LR; Buschmann, H 2004 Variation in herbivore damage to invasive and native woody plant species in open forest vegetation on Mahe, Seychelles journal BIOLOGICAL INVASIONS 6 4 511 521 Enemy release of introduced plants and variation in herbivore pressure in relation to community diversity are presently discussed as factors that affect plant species invasiveness or habitat invasibility. So far few data are available on this topic and the results are inconclusive. We compared leaf herbivory between native and invasive woody plants on Mahe, the main island of the tropical Seychelles. We further investigated variation in leaf herbivory on three abundant invasive species along an altitudinal gradient (50-550m a.s.l.). The median percentage of leaves affected by herbivores was significantly higher in native species (50%) than in invasive species (27%). In addition, the species suffering from the highest leaf area loss were native to the Seychelles. These results are consistent with the enemy release hypothesis (ERH). While the invasive species showed significant and mostly consistent variation in the amount of leaf damage between sites, this variation was not related to general altitudinal trends in diversity but rather to local variation in habitat structure and diversity. Our results indicate that in the Seychelles invasive woody plants profit from herbivore release relative to the native species and that the amount of herbivory, and therefore its effect on species invasiveness or habitat invasibility, may be dependent on local community structure and composition. Web of Science Many Republic of Seychelles Mahe Field - Observational terrestrial Deciduous Forest Invasion Hyp. Enemy Release primary 3179 Osunkoya, OO; Bujang, D; Moksin, H; Wimmer, FL; Holige, TM 2004 Leaf properties and construction costs of common, co-occurring plant species of disturbed heath forest in Borneo journal AUSTRALIAN JOURNAL OF BOTANY 52 4 499 507 The leaf properties and construction costs ( CC) are reported for eight indigenous heath (kerangas) forest species and three invasive (exotic) species of Acacia. Both groups of species co-occur and colonise disturbed lowland tropical heath rainforest habitats in Brunei, Borneo Island. Across species, CC mass-based increased with nitrogen (N) and heat of combustion (H-C), and decreased with ash content. CC area-based showed similar trends ( although weaker in strength) in addition to significant positive correlation with leaf mass per unit area (LMA). Within the native species, the CCs of the shrub and small tree species were lower and significantly different from those of medium-sized tree species. Given the invasive success of the three acacias, it is hypothesised that these species may require less energy for biomass construction than do the native species. Within similar life growth form, no difference in CC mass-based was detected between the native trees and the invasive acacias. For CC area-based, the invasive Acacia species had a higher value. These findings failed to uphold our hypothesis. LMA and leaf N and phosphorus (P), but not potassium (K), were higher in the invasive acacias. The higher N and LMA could have been the cause of higher CC area-based in the invasive acacias. From the ordination of 11 species on the basis of leaf properties, the invasive and native species are more likely to be found in different groupings-although some native species seem more affiliated with the invasive than with their own guild, especially Alphitonia and Macaranga. Web of Science Acacia auriculiformis; Acacia cicinnata; Acacia mangium Borneo Island Field - Observational terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Superior Competitor primary 3182 Heller, NE 2004 Colony structure in introduced and native populations of the invasive Argenine ant, Linepithema humile journal INSECTES SOCIAUX 51 4 378 386 The Argentine ant, Linepithema humile, severely decreases the abundance and diversity of native ant fauna in areas where it invades, but coexists with a more diverse assemblage of ants in its native range. The greater ecological dominance of L. humile in the introduced range may be associated with differences in colony structure and population density in the introduced range relative to the native range. In this study, I compared aspects of L. humile's colony structure, including density, the spatial pattern of nests and trails, and patterns of intraspecific aggression in parts of the introduced and native ranges. I also compared the number of ant species coexisting with L. humile. Introduced and native populations did not differ significantly in nest density, ant density, nest size, and nearest-neighbor distances. In three of the four study populations in the native range and all of the study populations in the introduced range, colonies were organized into supercolonies: they consisted of multiple, interconnected nests that were dense and spatially clumped, and aggression among conspecifics was rare. In one population in the native range, colonies were organized differently: they occupied single nest sites, nests were sparse and randomly dispersed, and ants from neighboring nests were aggressive toward each other. Species richness was significantly higher in the native range than in the introduced range, even in areas where L. humile formed dense supercolonies. The results suggest that differences in species coexistence between ranges may due to factors other ant species in the native range. Web of Science Linepithema humile USA California Field - Observational terrestrial Invasion Hyp. Community Species Richness omnivore 3183 Bjaerke, MR; Rueness, J 2004 Effects of temperature and salinity on growth, reproduction and survival in the introduced red alga Heterosiphonia japonica (Ceramiales, Rhodophyta) journal BOTANICA MARINA 47 5 373 380 We determined temperature and salinity responses in culture of a Norwegian isolate of the introduced red alga Heterosiphonia japonica. The species was eurythermal, surviving temperatures between 0degreesC and 30degreesC, with adult plants showing slightly higher temperature tolerance than carposporelings. Optimal growth conditions for carposporelings were 19-25degreesC and 30 psu. Growth rates at 20 psu and 30 psu did not differ significantly, but a marked reduction in the development of tetrasporangial stichidia was observed at 20 psu. At 15 psu, growth was poor and no stichidia were produced. Ten psu was lethal. Vegetative reproduction by fragmentation was common. Sporelings survived at least 40 days in darkness under various temperature conditions. The wide tolerance limits to temperature and salinity, high specific growth rates and effective propagation by fragmentation suggest that H. japonica will continue to disperse northwards and eastwards along the Norwegian coast, but that spread into the Kattegat and Baltic Sea will be controlled by low salinities and freezing winter temperatures. The life history of the Norwegian isolate was completed in culture, and a Polysiphonia type of life history was observed at 12degreesC and 17degreesC, whereas only tetrasporangial and vegetative specimens have been observed in field collections. Web of Science Heterosiphonia japonica Norway Lab marine Invasion Hyp. Inherent Superiority Broad Tolerances primary 3184 Cecere, E; Petrocelli, A; Verlaque, M 2004 Morphology and vegetative reproduction of the introduced species Hypnea comuta (Rhodophyta, Gigartinales) in the Mar Piccolo of Taranto (Italy), Mediterranean Sea journal BOTANICA MARINA 47 5 381 388 Hypnea cornuta, a species previously introduced into the eastern Mediterranean Sea, has been discovered recently in the Mar Piccolo of Taranto (southern Italy). The specimens are in good agreement with Indo-Pacific descriptions and reference material. It is highly probable that H. cornuta has been introduced either from eastern Mediterranean or Indo-Pacific populations via ship traffic or shellfish transfers (mussels). Since being introduced, H. cornuta has given rise to a stable both attached and free-floating population throughout the Mar Piccolo. Both attached and unattached plants are described. Field and culture observations have confirmed the reproductive role of the stellate branchlets as propagules. Vegetative reproduction both by propagules and. fragmentation seems to be the only mode of reproduction in the Mar Piccolo. Web of Science hypnea cornuta Italy marine Invasion Hyp. primary 3185 Costa-Leonardo, AM; Arab, A 2004 Reproductive strategy of Coptotermes gestroi (Isoptera : Rhinotermitidae) in Brazil journal SOCIOBIOLOGY 44 1 123 125 The termite Coptotermes gestroi (Wasmann) (Rhinotermitidae) is an exotic species in Brazil. This species forms colonies headed by primary reproductives, however, non-functional neotenics are commonly found even in the presence of the imaginal pair. The presence of nonfunctional neotenics in C. gestroi colonies may correspond to a strategy of this termite species for rapid colonization in foreign areas, instead of a response to chemical control methods. Web of Science Coptotermes gestroi Brazil terrestrial Invasion Hyp. herbivore 3188 Alyokhin, AV; Yang, PJ; Messing, RH 2004 Oviposition of the invasive two-spotted leafhopper on an endemic tree: Effects of an alien weed, foliar pubescence, and habitat humidity journal JOURNAL OF INSECT SCIENCE 4 0 The two-spotted leafhopper, Sophonia rufofascia (Kuoh and Kuoh), is an exotic pest from South-East Asia that attacks a wide variety of plant species in Hawaii. Myrica faya Aiton is an aggressive exotic weed that displaces and excludes native plants in Hawaiian forests. It has been argued that because of the high nutritional quality of its foliage, M. faya might facilitate leafhopper invasion of native Hawaiian ecosystems that were originally dominated by the endemic tree Metrosideros polymorpha (Gaudichaud). In the present study, we quantified suitability of M. faya and M. polymorpha as ovipositional hosts for S. rufofascia. Overall, leafhoppers preferred to deposit their eggs into the foliage of M. faya. M. faya presence in the area did not affect leafhopper oviposition on M. polymorpha. Foliar pubescence provided good protection of hirsute morphotypes of M. polymorpha. At the same time, glabrous M. polymorpha morphotypes were quite suitable for leafhopper oviposition. There was no difference in the abundance of leafhopper eggs along a precipitation gradient. Our results confirm that invasion of native Hawaiian forests by the weed M. faya will facilitate their invasion by S. rufofascia. Because of the broad host range characteristic of the two-spotted leafhopper, this build-up may adversely affect a number of endemic plant species growing in native forests. Web of Science Sophonia rufofascia USA Hawaii Field - Observational terrestrial Tropical Forest Invasion Hyp. Mutualism Facilitation primary;herbivore 3190 Jin, L; Gu, YJ; Xiao, M; Chen, JK; Li, B 2004 The history of Solidago canadensis invasion and the development of its mycorrhizal associations in newly-reclaimed land journal FUNCTIONAL PLANT BIOLOGY 31 10 979 986 This study examined the associations between an invasive alien plant ( Solidago canadensis L.) and arbuscular mycorrhizal fungi (AMF) in relation to the invasion history of S. canadensis on Chongming Island, China. A significant positive correlation was found between invasion time and AMF colonisation rate. The total number of AMF species increased with increasing invasion time and was positively related to the number of plant species occurring in plant communities, suggesting that the invasion time and plant diversity influence the diversity of AMF species. The relative abundance of two dominant AMF species, Glomus mosseae and G. constrictum, varied systematically with invasion time. In dry habitats, the relative abundance of G. mosseae increased with the invasion time of S. canadensis, while that of G. constrictum decreased with the invasion time. However, these relationships did not exist in the wet habitats. Our results suggest that certain AMF species might have helped S. canadensis colonise newly-reclaimed habitats and that succession of belowground AMF communities may occur concomitantly with the development of the aboveground plant communities. Web of Science Solidago canadensis China Chongming Island Field - Observational terrestrial Deciduous Forest Invasion Hyp. Mutualism Facilitation primary 3191 Compton, JA; Kerfoot, WC 2004 Colonizing inland lakes: Consequences of YOY fish ingesting the spiny cladoceran (Bythotrephes cederstroemi) journal JOURNAL OF GREAT LAKES RESEARCH 30 0 315 326 Recently the exotic cladoceran Bythotrephes cederstroemi colonized inland lakes in the Upper Peninsula of Michigan, facing warmer temperatures and greater exposure to smaller fish than in coastal waters of Lake Superior. However, the long caudal appendage (spine) of Bythotrephes protects it against young-of-the-year (YOY)fish predation. After experience, small fish (30-60 mm TL) develop aversion behavior, explaining why this prey item rarely occurs in their stomachs, despite ingestion of other prey species with core body lengths between 2-3 mm. Here we compare laboratory and field size-dependent feeding patterns for YOY of two common fish species (yellow perch, Perca flavescens; bluegills, Lepomis macrochirus) with field patterns from a typical bait-fish species (spottail shiner, Notropis hudsonius). Behavioral responses of bluegills indicate that deterrence is not a simple linear function of spine length, but that longer spines offer disproportionate protection, explaining why long spines are present at birth. Stomach contents of small perch (30-60 mm TL) confirm size-dependent avoidance, with only occasional consumption of Bythotrephes and rare puncture of stomach walls. However, examples of ingestion and frequent stomach puncture were found in the thinner-walled stomachs of spottail shiners. Out of 140 small fish collected when this species encountered high densities of Bythotrephes, 77 had Bythotrephes in stomachs or lower digestive tracts, and 50 (65%) had spines protruding through gut walls. Clearly, this bait-fish species is capable not only of ingesting large numbers of Bythotrephes, but of receiving injury in the process. Web of Science Bythotrephes cederstroemi USA Michigan Field - Observational lentic Invasion Hyp. Novel Weapons herbivore 3192 Lougheed, VL; Stevenson, RJ 2004 Exotic marine macroalga (Enteromorpha flexuosa) reaches bloom proportions in a coastal lake of Lake Michigan journal JOURNAL OF GREAT LAKES RESEARCH 30 4 538 544 The exotic marine algae Enteromorpha flexuosa subsp. flexuosa and subsp. paradoxa were first observed in Muskegon Lake during autumn 2003. In September 2003, the littoral zone had between 10 and 80% cover of macroalgae, which grew largely on submerged macrophytes, and was composed almost entirely of Enteromorpha. Enteromorpha formed dense mats, fouled the boat motor and was found washed up in large quantities on the shoreline. Eleven other waterbodies in the region were surveyed: two others had Enteromorpha composing 5 to 20 % of the macroalgal community, four had no apparent macroalgae and the remaining five were dominated by Cladophora. Possible reasons for the success of Enteromorpha in these coastal lakes include nutrient enrichment, a history of industrial activity resulting in increased salinity of the water, as well as an absence of grazing pressure. Potential effects on littoral zone food webs are uncertain; however, we found low epiphytic diatom densities on Enteromorpha, which is a concern in these systems where epiphytic diatoms are important components of the food web. Currently, this new macroalgal invader has been found in only three coastal waterbodies of Lake Michigan; however, it is possible that Enteromorpha could spread beyond its current range, if it has not already done so. Given its ability to form nuisance blooms in a coastal lake of Lake Michigan and its reported impacts in marine systems, it is imperative that the possible impacts of this invasive marine macroalga on the Great Lakes ecosystem be determined. Web of Science Enteromorpha flexuosa USA Michigan Muskegon Lake Field - Observational lentic Invasion Hyp. Enemy Release;Disturbance primary 3194 Cole, PG; Weltzin, JF 2004 Environmental correlates of the distribution and abundance of Microstegium vimineum, in east Tennessee journal SOUTHEASTERN NATURALIST 3 3 545 562 We conducted a landscape-level survey of Microstegium vimineum (Trin.) A. Camus (Japanese grass, Nepal grass) at the Oak Ridge National Environmental Research Park to: (1) document the distribution of this species, (2) measure several important characteristics of the populations and invaded habitats, (3) identify biotic and abiotic environmental factors that may limit its distribution, and (4) quantify its response to environmental gradients. We found that M. vimineum exhibits the broad environmental tolerance of many *weedy* species, and it appears that no single variable explains presence or performance. Presence of M. vimineum was correlated only with soil pH, whereas M. vimineum performance was positively correlated with canopy openness and biomass of other species. Explanatory variables differed among sites, which suggests that other factors (such as disturbance or dispersal) may be locally important, or that different factors may interact to control the distribution and performance of this species at any given site. The nearly ubiquitous presence of M. vimineum along roads and trails in the study area, and the frequent incursion of roadside populations into adjacent forested habitat, highlights the importance of early control of source populations at forest edges. Web of Science Microstegium vimineum USA Tennessee Oak Ridge National Environmental Research Park Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 3195 Kimball, ME; Miller, JM; Whitfield, PE; Hare, JA 2004 Thermal tolerance and potential distribution of invasive lionfish (Pterois volitans/miles complex) on the east coast of the United States journal MARINE ECOLOGY-PROGRESS SERIES 283 0 269 278 The occurrence of lionfish (Pterois volitans/miles) complex on the southeast United States shelf represents one of the first documented invasions of a Pacific marine fish species into the western Atlantic Ocean. Temperature has been proposed as a possible factor limiting the range of this introduction. To examine this hypothesis, temperature-tolerance studies were conducted following the chronic lethal minimum protocol, with death as the endpoint. Overall, the mean chronic lethal minimum was 10.0degreesC and mean temperature at feeding cessation was 16.1degreesC. Rate of temperature decrease and acclimation temperature did not have a significant effect on chronic lethal minimum or temperature at feeding cessation. When combined with mean February water temperatures, lionfish thermal tolerance data indicated that lionfish could overwinter on the southeast United States continental shelf, with a northern limit of Cape Hatteras and an inshore limit coincident with the mean 12degreesC isotherm, which equates to a 10degreesC minimum water temperature. The mean 12degreesC bottom isotherm also runs along the continental shelf break (200 m isobath), marking the offshore limit for lionfish on the southeast United States continental shelf. The current southern limit of the invasion is not bound by temperature, as lionfish could survive (but have not yet been reported) on the Florida coast south of Miami, throughout the Gulf of Mexico and Caribbean Sea, extending into the southern hemisphere. Possible reasons for the constrained southern limit may include planktonic transport mechanisms, patterns of juvenile and adult movements, and the initial lionfish introduction site. Web of Science Pterois volitans;Pterois miles USA western Atlantic Ocean Field - Observational marine Invasion Hyp. Inherent Superiority Broad Tolerances predator 3196 Bolton, TF; Graham, WM 2004 Morphological variation among populations of an invasive jellyfish journal MARINE ECOLOGY-PROGRESS SERIES 278 0 125 139 The Australian spotted jellyfish Phyllorhiza punctata appeared in the Northern Gulf of Mexico in spectacular numbers during the summer of 2000. P. punctata was first described from Eastern Australia, although its native habitat probably extends across Northern Australia and into SE Asia. Among invasive marine species, P. punctata has a relatively well-documented history of invading tropical and subtropical environments. Despite this, there is no direct evidence of translocation routes or the mechanisms by which translocation has occurred. The invasion of the Northern Gulf of Mexico has been theorized to represent an inevitable distributional shift of an invasive hub population in the Caribbean Sea facilitated by periodic oceanographic connections between the regions, or by the transportation of benthic scyphistomae on the hulls of ships. Regardless of the translocation mechanism, the relatively close geographical proximity of the Caribbean to the Northern Gulf of Mexico makes this theory conceptually appealing. Based on a 'hub and spoke' model of marine bio-invasion, we postulated that populations of P. punctata from regions more geographically distant than those from the Caribbean and the Gulf of Mexico have been separated for longer periods of time; therefore, populations from the Caribbean and the Gulf of Mexico would bear greater morphological similarity to each other than to those of other regions due to higher levels of underlying genetic relatedness. We used multivariate analyses to compare the morphological similarity of 6 populations of R punctata distributed between the Gulf of Mexico, Caribbean and the east and west coasts of Australia. Contrary to our expectations, analyses showed that populations from the Caribbean and the Gulf of Mexico are the least similar to each other. The analyses suggest that the invasive population in the Gulf of Mexico is most likely to have originated from geographically disparate populations in either Australia or the west coast of the United States. Populations from Australia and the west coast of the United States were the most similar to each other, while the Caribbean population bore the least similarity to all other populations. Web of Science Phyllorhiza punctata USA Gulf of Mexico Field - Observational marine Fundamentals predator 3197 Martel, C; Viard, F; Bourguet, D; Garcia-Meunier, P 2004 Invasion by the marine gastropod Ocinebrellus inornatus in France. II. Expansion along the Atlantic coast journal MARINE ECOLOGY-PROGRESS SERIES 273 0 163 172 Dispersal ability is key to the spreading of exotic species to new areas. Herein, we focus on the expansion processes along the French Atlantic coast of an exotic marine gastropod, Ocinebrellus inornatus, first detected in the Marennes-Oleron bay in 1995. Unlike many aquatic invaders, O. inornatus lacks a swimming larval stage. This feature may reduce its ability to expand within the area of introduction unless counterbalanced by human-mediated spreading. By analyzing the genetic diversity at 7 allozyme markers, we compared the genetic diversity and structure of 9 French, 3 American and 5 Asian (native) populations. The genetic differentiation between populations within each area was low and of similar magnitude. However, a genetic isolation by coastline distances was detected in Asia only. We draw 2 main conclusions from these results. First, the settlement of new populations along the French Atlantic coast is not associated with drastic founder events. Second, expansion along the French coast is enhanced by oyster-farming activities. Web of Science Ocinebrellus inornatus France Marennes-Oleron Field - Observational marine Intertidal/Near Shore Invasion Hyp. Other herbivore 3200 Trifilo, P; Raimondo, F; Nardini, A; Lo Gullo, MA; Salleo, S 2004 Drought resistance of Ailanthus altissima: root hydraulics and water relations journal TREE PHYSIOLOGY 24 1 107 114 Drought resistance of Ailanthus altissima (Mill.) Swingle is a major factor underlying the impressively wide expansion of this species in Europe and North America. We studied the specific mechanism used by A. altissima to withstand drought by subjecting potted seedlings to four irrigation regimes. At the end of the 13-week treatment period, soil water potential was -0.05 MPa for well-watered control seedlings (W) and -0.4, -0.8 and -1.7 MPa for drought-stressed seedlings (S) in irrigation regimes S 1, S2 and S3, respectively. Root and shoot biomass production did not differ significantly among the four groups. A progressively marked stomatal closure was observed in drought-stressed seedlings, leading to homeostasis of leaf water potential, which was maintained well above the turgor loss point. Root and shoot hydraulics were measured with a high-pressure flow meter. When scaled by leaf surface area, shoot hydraulic conductance did not differ among the treated seedlings, whereas root hydraulic conductance decreased by about 20% in S I and S2 seedlings and by about 70% in S3 seedlings, with respect to the well-watered control value. Similar differences were observed when root hydraulic conductance was scaled by root surface area, suggesting that roots had become less permeable to water. Anatomical observations of root cross sections revealed that S3 seedlings had shrunken cortical cells and a multilayer endodermal-like tissue that probably impaired soil-to-root stele water transport. We conclude that A. altissima seedlings are able to withstand drought by employing a highly effective water-saving mechanism that involves reduced water loss by leaves and reduced root hydraulic conductance. This water-saving mechanism helps explain how A. altissima successfully competes with native vegetation. Web of Science Ailanthus altissima Greenhouse terrestrial Invasion Hyp. Inherent Superiority Broad Tolerances herbivore 3204 Culver, CS; Kuris, AM 2004 Susceptibility of California gastropods to an introduced South African sabellid polychaete, Terebrasabella heterouncinata journal INVERTEBRATE BIOLOGY 123 4 316 323 The outer surfaces of the shells of living marine gastropods are often colonized by other organisms. However, only one species, the sabellid worm Terebrasabella heterouncinata, is able to settle in the aperture of living gastropods. Native to South Africa, and introduced to California, this worm is a pest of abalone aquaculture and has been a threat to native gastropods in California. We investigated the intrinsic susceptibility of 15 marine gastropods from California to this apertural fouling organism. Intrinsic susceptibility was significantly different among gastropod species. Overall, caenogastropods tended to be more resistant than were the vetigastropods and patellogastropods. This suggests that variability in susceptibility could be due to characteristics associated with closely related gastropod hosts. However, this only partially explained the variation in susceptibility to individuals of T. heterouncinata. Intrinsic susceptibility was not associated with potential host species from similar habitats. We discuss host susceptibility to T. heterouncinata, including implications for potential control of this pest species, and for understanding factors enabling this polychaete to inhabit the apertural region, an area typically free of all other epibionts. Web of Science Terebrasabella heterouncinata USA California Field - Observational marine Invasion Hyp. Inherent Superiority filter 3205 Morewood, WD; Hoover, K; Neiner, PR; McNeil, JR; Sellmer, JC 2004 Host tree resistance against the polyphagous wood-boring beetle Anoplophora glabripennis journal ENTOMOLOGIA EXPERIMENTALIS ET APPLICATA 110 1 79 86 Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae: Lamiini) is an invasive wood-boring beetle with an unusually broad host range and a proven ability to increase its host range as it colonizes new areas and encounters new tree species. The beetle is native to eastern Asia and has become an invasive pest in North America and Europe, stimulating interest in delineating host and non-host tree species more clearly. When offered a choice among four species of living trees in a greenhouse, adult A. glabripennis fed more on golden-rain tree (Koelreuteria paniculata Laxmann) and river birch (Betula nigra L.) than on London planetree (Platanus x acerifolia (Aiton) Willdenow) or callery pear (Pyrus calleryana Decaisne). Oviposition rate was highest in golden-rain tree, but larval mortality was also high and larval growth was slowest in this tree species. Oviposition rate was lowest in callery pear, and larvae failed to survive in this tree species, whether they eclosed from eggs laid in the trees or were manually inserted into the trees. Adult beetles feeding on callery pear had a reduced longevity and females feeding only on callery pear failed to develop any eggs. The resistance of golden-rain tree against the larvae appears to operate primarily through the physical mechanism of abundant sap flow. The resistance of callery pear against both larvae and adults appears to operate through the chemical composition of the tree, which may include compounds that are toxic or which otherwise interfere with normal growth and development of the beetle. Unlike river birch or London planetree, both golden-rain tree and callery pear are present in the native range of A. glabripennis and may therefore have developed resistance to the beetle by virtue of exposure to attack during their evolutionary history. Web of Science Anoplophora glabripennis Greenhouse terrestrial Invasion Hyp. Empty Niche herbivore 3206 Klocker, CA; Strayer, DL 2004 Interactions among an invasive crayfish (Orconectes rusticus), a native crayfish (Orconectes limosus), and native bivalves (Sphaeriidae and Unionidae) journal NORTHEASTERN NATURALIST 11 2 167 178 The introduction of the rusty crayfish, Orconectes rusticus, has large effects on freshwater communities by displacing native crayfish species and altering macroinvertebrate communities. We used laboratory studies of aggression, shelter use, and feeding to examine the relationship between O. rusticus and a crayfish native to the Northeast, Orconectes limosus, along with these species' consumption of native bivalves. Orconectes rusticus dominated O. limosus in aggression trials, and shelter trials showed that dominant crayfish obtained shelter over subordinate crayfish. Both species of crayfish consumed freshwater mussels (Unionidae) and fingernail clams (Sphaeriidae), preferring prey of smaller size and those that were not buried. These findings suggest that the invasion of O. rusticus may pose a threat to native crayfish and the already threatened bivalves of the Northeast. Web of Science Orconectes rusticus USA Lab lotic Invasion Hyp. Inherent Superiority Superior Competitor omnivore 3207 Dark, SJ 2004 The biogeography of invasive alien plants in California: an application of GIS and spatial regression analysis journal DIVERSITY AND DISTRIBUTIONS 10 1 1 9 The spatial distribution of invasive alien plants has been poorly documented in California. However, with the increased availability of GIS software and spatially explicit data, the distribution of invasive alien plants can be explored. Using bioregions as defined in Hickman (1993), I compared the distribution of invasive alien plants (n = 78) and noninvasive alien plants (n = 1097). The distribution of both categories of alien plants was similar with the exception of a higher concentration of invasive alien plants in the North Coast bioregion. Spatial autocorrelation analysis using Moran's I indicated significant spatial dependence for both invasive and noninvasive alien plant species. I used both ordinary least squares (OLS) and spatial autoregressive (SAR) models to assess the relationship between alien plant species distribution and native plant species richness, road density, population density, elevation, area of sample unit, and precipitation. The OLS model for invasive alien plants included two significant effects; native plant species richness and elevation. The SAR model for invasive alien plants included three significant effects; elevation, road density, and native plant species richness. The SAR model for noninvasive alien plants resulted in the same significant effects as invasive alien plants. Both invasive and noninvasive alien plants are found in regions with low elevation, high road density, and high native-plant species richness. This is in congruity with previous spatial pattern studies of alien plant species. However, the similarity in effects for both categories of alien plants alludes to the importance of autecological attributes, such as pollination system, dispersal system and differing responses to disturbance in the distribution of invasive plant species. In addition, this study emphasizes the critical importance of testing for spatial autocorrelation in spatial pattern studies and using SAR models when appropriate. Web of Science Many USA California Theoretical/Modeling terrestrial Invasion Hyp. Community Species Richness;Propagule Pressure;Disturbance primary 3211 Widmer, TL; Guermache, F 2004 Filtrates of rhizosphere bacteria suppressive to Centaurea solstitialis seed germination journal ZEITSCHRIFT FUR PFLANZENKRANKHEITEN UND PFLANZENSCHUTZ-JOURNAL OF PLANT DISEASES AND PROTECTION 0 0 497 502 Centaurea solstitialis (yellow starthistle) is an invasive weed in the United States that infests millions of hectares of rangelands, roadsides, and recreation areas. It is not completely understood why weeds often become invasive when transported to a new ecosystem. Many factors may be involved including soil microorganisms that influence plant growth and seed germination. Yellow starthistle (YST) roots removed from four sites in southern France were washed in distilled water. Individual bacterial colonies were isolated from the root wash and plated on nutrient agar. Sixteen isolates were grown on two different media for 1 week at 25degreesC at either 150 or 250 rpm. The resulting culture was centrifuged and the supernatant adjusted to pH 7.2. The effect of the cell-free filtrates on the germination of YST seeds from France and the United States were tested by placing seeds on filter paper moistened with the bacterial filtrate in Petri plates. Five isolates showed some inhibition dependent upon the shaker speed and media used. Isolates 2(8) and 3(11) shaking at 250 rpm and 1(10) and 4(15) shaking at 150 rpm reduced germination of only French YST seeds. Isolate 2(10), identified as Streptomyces griseus, grown in a medium recommended for Streptomyces spp. at 250 rpm and isolate 4(15), identified as an Actinomycete, grown in a basic nutrient broth medium at 250 rpm inhibited both French and American YST seeds. The other eleven isolates showed no or limited inhibition of germination. These results suggest soil bacteria produce metabolites that inhibit YST seed germination and there is some response difference in the French and American seeds. Web of Science Centaurea solstitialis USA Lab terrestrial Grassland Invasion Hyp. Enemy Release primary 3220 Pintor, Lauren M.; Brown, Joel S.; Vincent, Thomas L. 2011 Evolutionary Game Theory as a Framework for Studying Biological Invasions journal AMERICAN NATURALIST 177 4 410 423 Although biological invasions pose serious threats to biodiversity, they also provide the opportunity to better understand interactions between the ecological and evolutionary processes structuring populations and communities. However, ecoevolutionary frameworks for studying species invasions are lacking. We propose using game theory and the concept of an evolutionarily stable strategy (ESS) as a conceptual framework for integrating the ecological and evolutionary dynamics of invasions. We suggest that the pathways by which a recipient community may have no ESS provide mechanistic hypotheses for how such communities may be vulnerable to invasion and how invaders can exploit these vulnerabilities. We distinguish among these pathways by formalizing the evolutionary contexts of the invader relative to the recipient community. We model both the ecological and the adaptive dynamics of the interacting species. We show how the ESS concept provides new mechanistic hypotheses for when invasions result in long- or short-term increases in biodiversity, species replacement, and subsequent evolutionary changes. Web of Science Theoretical/Modeling;Review Fundamentals 3222 Schrey, A. W.; Grispo, M.; Awad, M.; Cook, M. B.; McCoy, E. D.; Mushinsky, H. R.; Albayrak, T.; Bensch, S.; Burke, T.; Butler, L. K.; Dor, R.; Fokidis, H. B.; Jensen, H.; Imboma, T.; Kessler-Rios, M. M.; Marzal, A.; Stewart, I. R. K.; Westerdahl, H.; Westneat, D. F.; Zehtindjiev, P.; Martin, L. B. 2011 Broad-scale latitudinal patterns of genetic diversity among native European and introduced house sparrow (Passer domesticus) populations journal MOLECULAR ECOLOGY 20 6 1133 1143 Introduced species offer unique opportunities to study evolution in new environments, and some provide opportunities for understanding the mechanisms underlying macroecological patterns. We sought to determine how introduction history impacted genetic diversity and differentiation of the house sparrow (Passer domesticus), one of the most broadly distributed bird species. We screened eight microsatellite loci in 316 individuals from 16 locations in the native and introduced ranges. Significant population structure occurred between native than introduced house sparrows. Introduced house sparrows were distinguished into one North American group and a highly differentiated Kenyan group. Genetic differentiation estimates identified a high magnitude of differentiation between Kenya and all other populations, but demonstrated that European and North American samples were differentiated too. Our results support previous claims that introduced North American populations likely had few source populations, and indicate house sparrows established populations after introduction. Genetic diversity also differed among native, introduced North American, and Kenyan populations with Kenyan birds being least diverse. In some cases, house sparrow populations appeared to maintain or recover genetic diversity relatively rapidly after range expansion (< 50 years; Mexico and Panama), but in others (Kenya) the effect of introduction persisted over the same period. In both native and introduced populations, genetic diversity exhibited large-scale geographic patterns, increasing towards the equator. Such patterns of genetic diversity are concordant with two previously described models of genetic diversity, the latitudinal model and the species diversity model. Web of Science Passer domesticus USA;Kenya Field - Observational terrestrial Fundamentals omnivore 3223 Carmona-Catot, Gerard; Benito, Josep; Garcia-Berthou, Emili 2011 Comparing latitudinal and upstream-downstream gradients: life history traits of invasive mosquitofish journal DIVERSITY AND DISTRIBUTIONS 17 2 214 224 Aim Variation of life history traits along spatial gradients is poorly understood in invasive species and particularly in freshwater fish. We aimed to examine life history variation in a highly invasive fish (Gambusia holbrooki) along latitudinal and upstream-downstream river gradients and to assess the effects of age on this variation. We hypothesized similar responses in populations inhabiting environments more favourable to this species (lower latitudes and lower reaches of rivers). Location European rivers from southern Spain to southern France. Methods We sampled mosquitofish from the lowest reaches of ten river basins along 6 degrees of latitude in the Mediterranean region and seven sites along the upstream-downstream gradient in three of the rivers. We examined abundance, population structure, size-at-age and other life history traits along these gradients. Results As hypothesized, lower reaches and lower latitudes both resulted in higher reproductive effort and lower body condition of mosquitofish. However, these patterns explained low per cent variation, were nonlinear and strongly depended on fish age. Independently of fish size, age groups differed in reproductive effort, in the gonadal weight-size relationship and its variation along spatial gradients. Mean size-at-age (or overall body size) did not vary with latitude (so the intra-specific version of Bergmann's rule or its converse does not apply) and in contrast increased upstream in rivers. Main conclusions Our findings suggest that for life history traits of freshwater organisms, river longitudinal variation plays a role as important as climate, with often differential effects. Our results also illustrate the poor knowledge of spatial variation of many life history traits, which precludes the understanding and prediction of biological invasions in a rapidly changing world. Web of Science Gambusia holbrooki Spain;France Field - Observational lotic Invasion Hyp. Plasticity predator 3224 Diamantidis, Alexandros D.; Carey, James R.; Nakas, Christos T.; Papadopoulos, Nikos T. 2011 Ancestral populations perform better in a novel environment: domestication of Mediterranean fruit fly populations from five global regions journal BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY 102 2 334 345 Geographically isolated populations of a species may differ in several aspects of life history, morphology, behaviour and genetic structure as a result of adaptation in ecologically diverse habitats. We used a global invasive species, the Mediterranean fruit fly (medfly), to investigate whether adaptation to a novel environment differs among geographically isolated populations that vary in major life history components, such as life span and reproduction. We used wild populations from five global regions (Kenya, Hawaii, Guatemala, Portugal and Greece). Adult demographic traits were monitored in the F(2), F(5), F(7) and F(9) generations in captivity. Although domestication in constant laboratory conditions had a different effect on the mortality and reproductive rates of the different populations, a general trend of decreasing life span and age of first reproduction was observed for most medfly populations tested. However, taking into account the longevity of both sexes, age-specific reproductive schedules and average reproductive rates, we found that the ancestral Kenyan population kept the above life history traits stable during domestication compared with the other populations tested. These findings provide important insights into the life history evolution of this model species, and suggest that ancestral medfly populations perform better than the derived, invasive ones in a novel environment. (C) 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102, 334-345. Web of Science Ceratitis capitata Global Field - Observational terrestrial Fundamentals herbivore 3225 Yang, Suann; Ferrari, Matthew J.; Shea, Katriona 2011 Pollinator Behavior Mediates Negative Interactions between Two Congeneric Invasive Plant Species journal AMERICAN NATURALIST 177 1 110 118 Simultaneously flowering plant species may indirectly interact with each other by influencing the quantity of pollinator visitation and/or the quality of pollen that is transferred. These effects on pollination may depend on how pollinators respond to floral resources at multiple levels. In this study, we demonstrate pollinator-mediated negative interactions between two invasive plants, Carduus acanthoides and Carduus nutans. Using constructed arrays of the two species, alone and in mixture, we quantified pollinator visitation at the patch and individual plant levels and measured seed production. We found that co-occurrence of our species led to a shift in pollinator services at both levels. Greater interference occurred when arrays were small and spacings between neighboring plants were large. A spatially explicit movement model suggests that pollinator foraging behavior, which mediates the interactions between plants, was driven by floral display size rather than species identity per se. Pollinator behavior significantly reduced the proportion of seed set for both species relative to that in single-species arrays. Overall, the dependence of pollinator behavior on patch size, spacing between plants, and patch composition can lead to pollinator-mediated plant interactions that range from facilitative to competitive. Web of Science Carduus acanthoides;Carduus nutans USA Garden terrestrial Fundamentals primary 3226 Cadotte, Marc W.; Borer, Elizabeth T.; Seabloom, Eric W.; Cavender-Bares, Jeannine; Harpole, W. S.; Cleland, Elsa; Davies, Kendi F. 2010 Phylogenetic patterns differ for native and exotic plant communities across a richness gradient in Northern California journal DIVERSITY AND DISTRIBUTIONS 16 6 892 901 Aim Increasingly, ecologists are using evolutionary relationships to infer the mechanisms of community assembly. However, modern communities are being invaded by non-indigenous species. Since natives have been associated with one another through evolutionary time, the forces promoting character and niche divergence should be high. On the other hand, exotics have evolved elsewhere, meaning that conserved traits may be more important in their new ranges. Thus, co-occurrence over sufficient time-scales for reciprocal evolution may alter how phylogenetic relationships influence assembly. Here, we examined the phylogenetic structure of native and exotic plant communities across a large-scale gradient in species richness and asked whether local assemblages are composed of more or less closely related natives and exotics and whether phylogenetic turnover among plots and among sites across this gradient is driven by turnover in close or distant relatives differentially for natives and exotics. Location Central and northern California, USA. Methods We used data from 30 to 50 replicate plots at four sites and constructed a maximum likelihood molecular phylogeny using the genes: matK, rbcl, ITS1 and 5.8s. We compared community-level measures of native and exotic phylogenetic diversity and among-plot phylobetadiversity. Results There were few exotic clades, but they tended to be widespread. Exotic species were phylogenetically clustered within communities and showed low phylogenetic turnover among communities. In contrast, the more species-rich native communities showed higher phylogenetic dispersion and turnover among sites. Main conclusions The assembly of native and exotic subcommunities appears to reflect the evolutionary histories of these species and suggests that shared traits drive exotic patterns while evolutionary differentiation drives native assembly. Current invasions appear to be causing phylogenetic homogenization at regional scales. Web of Science Many USA California Field - Observational terrestrial Chaparral/Shrublands Fundamentals primary 3227 Coyle, David R.; Jordan, Michelle S.; Raffa, Kenneth F. 2010 Host Plant Phenology Affects Performance of an Invasive Weevil, Phyllobius oblongus (Coleoptera: Curculionidae), in a Northern Hardwood Forest journal ENVIRONMENTAL ENTOMOLOGY 39 5 1539 1544 We investigated how host plant phenology and plant species affected longevity, reproduction, and feeding behavior of an invasive weevil. Phyllobius oblongus L. (Coleoptera: Curculionidae) is common in northern hardwood forests of the Great Lakes Region. Adults emerge in spring, feed on foliage of woody understory plants, and oviposit in the soil. Preliminary data indicate that adults often feed on sugar maple, Acer saccharum Marshall, foliage early in the season, then feed on other species such as raspberry, Rams spp. Whether this behavior reflects temporal changes in the quality of A. saccharum tissue or merely subsequent availability of later-season plants is unknown. We tested adult P. oblongus in laboratory assays using young (newly flushed) sugar maple foliage, old (2-3 wk postflush) sugar maple foliage, and raspberry foliage. Raspberry has indeterminate growth, thus always has young foliage available for herbivores. Survival, oviposition, and leaf consumption were recorded. In performance assays under no-choice conditions, mated pairs were provided one type of host foliage for the duration of their lives. In behavioral choice tests, all three host plants were provided simultaneously and leaf area consumption was compared. Adults survived longer on and consumed greater amounts of young maple and raspberry foliage than old maple foliage. P. oblongus preferred young maple foliage to old maple foliage early in the season, however, later in the growing season weevils showed less pronounced feeding preferences. These results suggest how leaf phenology, plant species composition, and feeding plasticity in host utilization may interact to affect P. oblongus population dynamics. Web of Science Phyllobius oblongus USA Great Lakes Field - Observational;Lab terrestrial Deciduous Forest Fundamentals herbivore 3228 Gomez, Jonatan J.; Gozzi, Ana C.; Macdonald, David W.; Gallo, Emilce; Centron, Daniela; Cassini, Marcelo H. 2010 Interactions of exotic and native carnivores in an ecotone, the coast of the Beagle Channel, Argentina journal POLAR BIOLOGY 33 10 1371 1378 In coasts bordering highly productive seas, there can be a flux of resources to the terrestrial ecosystem, and terrestrial carnivores can use marine prey extensively. Two native, endangered species (otter Lontra provocax and culpeo fox Pseudalopex culpaeus lycoides) and two exotic species (mink Neovison vison and grey fox Pseudalopex griseus) inhabit the Beagle coast. The objectives of this paper are: (1) to describe the diet, habitat use and distribution of otters, mink and foxes on the coast of the Beagle channel and (2) to discuss the role of marine resources in the ecological interactions among these species. Diet was determined from the analysis of 245 faeces, and distribution was established from sign surveys. Marine prey occurred in the scats of 98.3, 70.4, 35.5 and 18.2% of otters, mink, culpeo and grey foxes, respectively. Other terrestrial species also use marine resources in Southern Patagonia. All this evidence suggests that the Fueguian coastal channels provide an illuminating example of allochthonous food subsidies from the sea. In the community of four sympatric predators, two native (and endangered) and two exotic, coexistence appears to be facilitated by a renewing marine food subsidy. Web of Science Neovison vison;Pseudalopex griseus Argentina Beagle coast Field - Observational terrestrial Chaparral/Shrublands Fundamentals predator 3229 Vacher, Corinne; Daudin, Jean-Jacques; Piou, Dominique; Desprez-Loustau, Marie-Laure 2010 Ecological integration of alien species into a tree-parasitic fungus network journal BIOLOGICAL INVASIONS 12 9 3249 3259 The diversification of species and their interactions during the course of evolution has produced ecological networks with a complex topology. This topology influences the current functioning of ecosystems. It is therefore important to investigate whether the species introduced recently by human activities have merged seamlessly into recipient ecological networks by developing interactions quantitatively and qualitatively similar to those of native species, or whether their establishment has altered the topology of the networks. We tackled this issue in the case of a well resolved interaction network between 51 forest tree taxa and 154 pathogenic fungal species. We found that alien and native species with similar phylogenetic histories and life-history strategies had similar types and numbers of interactions. Our results also suggest that the clustered architecture of the network has not been altered by the integration of alien species. It therefore seems that a few centuries have been sufficient for the network to assimilate the newly introduced species. This rapid integration was unexpected for a plant-pathogen network, because selection acts continually on plants, favouring the emergence of defences against new pathogens and impeding the development of new interactions. However, it was recently shown that perturbation of the structure of ecological networks might be overlooked if species interactions are not quantified. The tree-parasitic fungus network considered in this study is binary. We might therefore end up with different results by using quantitative data. Web of Science Many Statistical/Meta-analysis;Review terrestrial Deciduous Forest;Coniferous Forest Fundamentals primary;pathogen 3230 Sidorovich, Vadim E.; Polozov, Alexey G.; Zalewski, Andrzej 2010 Food niche variation of European and American mink during the American mink invasion in north-eastern Belarus journal BIOLOGICAL INVASIONS 12 7 2207 2217 Understanding processes allowing the co-existence of ecologically similar species is important but difficult to study in community ecology. Introductions of alien species are unplanned experiments allowing investigation of co-adaptation of both native and invasive species over a short period. We analysed food niche differentiation between native European mink and alien American mink after invasion of the latter species in Belarus. European mink feed mainly on crayfish, frogs and fish whereas American mink prefer small mammals, fish and frogs. The diet of both species varied between seasons and during the period of alien mink invasion. Concurrent with the progress of American mink invasion, the European mink food niche has narrowed to feeding mainly on frogs, with the proportion of aquatic prey (fish and crayfish) in their diet drastically reduced. In contrast, the American mink food niche became wider during invasion. The breadth was stable but included a varied proportion of different prey categories: namely an increased proportion of aquatic prey and a decreased proportion of water vole and waterfowl. The increase in abundance of American mink saw a decrease in the proportion of larger prey in their diet. When American mink preyed more often on frogs, food niche overlap of both predators increased. This result suggests that arrival of an alien competitor reduced food abundance (exploitative competition) and caused a change in native mink diet. Web of Science Neovison vison Belarus Field - Observational terrestrial Deciduous Forest Invasion Hyp. Plasticity predator 3231 Sugiura, Shinji 2010 Species interactions-area relationships: biological invasions and network structure in relation to island area journal PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES 277 1689 1807 1815 The relationship between species number and island area is a fundamental rule in ecology. However, the extent to which interactions with exotic species and how the structure of species interactions is related to island area remain unexplored. Here, I document the relationship between island area and (i) interactions with exotic species and (ii) network structure of species interactions in the context of mutualistic interactions between ants and extrafloral nectary-bearing plants on the oceanic Ogasawara (Bonin) Islands, Japan. Pooled data contained 122 interactions among 19 plant (including five exotic) and 23 ant (including 20 exotic) species. Of the observed interactions, 82.8 per cent involved at least one exotic species, ranging from 68.2 to 86.4 per cent among islands. The number of links including exotic species increased in proportion to island area, although the number of links excluding exotic species did not. These results indicate that the number of interactions with exotic species increased in proportion to island area. Connectance, or the proportion of interactions actually observed among all possible interactions, decreased with island area. Nestedness, an asymmetry index in the species interaction network, also decreased with island area. Therefore, island area affects both the number of interactions with exotic species and the network structure. Web of Science Many Japan Ogasawara Islands;Bonin Field - Observational terrestrial Fundamentals primary;herbivore 3233 Jahodova, Sarka; Trybush, Sviatlana; Pysek, Petr; Wade, Max; Karp, Angela 2007 Invasive species of Heracleum in Europe: an insight into genetic relationships and invasion history journal DIVERSITY AND DISTRIBUTIONS 13 1 99 114 Several species of the genus Heracleum (Umbelliferae) were introduced into Europe from south-west Asia in the 19th century and are now widespread in many countries. At least three invasive taxa with unresolved relationships to one another are thought to occur in Europe: Heracleum mantegazzianum Sommier & Levier, H. sosnowskyi Manden, and H. persicum Desf. ex Fischer. They are tall plants forming extensive stands with a high cover. To elucidate genetic relationships between the species, and gain insight into their invasion history, samples were collected from native ranges in Asia and invaded ranges of the three species in Europe and analysed using amplified fragment length polymorphism. Five other Heracleum species were also studied and in total, 189 samples from 72 populations were analysed. The results confirmed that there are three distinct tall Heracleum species invading in Europe. Within each of the three species, plants collected in the invaded range are genetically close to those from their native ranges. A close genetic relationship between the three invasive Heracleum species in Europe was also found. A high overall genetic variability detected in the invaded range suggests that the majority of invading populations were not affected by a genetic bottleneck and that rapid evolution, drift, or hybridization played a role in genetic structuring of invading populations. For H. mantegazzianum, genetic distance of populations in the native range significantly decreased with geographical distance, but not in the invaded range. It is likely that the current pattern of genetic diversity in Europe resulted from multiple introductions of all three species. Web of Science Heracleum spp. Europe Field - Observational terrestrial Deciduous Forest Invasion Hyp. Evolution in General primary 3469 Baret, S; Le Bourgeois, T; Strasberg, D 2005 How would Rubus alceifolius, an intrusive exotic species, progressively colonize the entirety of a humid tropical forest journal CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE 83 2 219 226 Few quantitative studies confirm or refute actual theories on the capacity of exotic species to invade and colonize new environments. To evaluate these theories, we tested some biological traits of an invasive bramble (Rubus alceifolius Poiret), known for the importance of its sexual reproduction on lowlands, at La Reunion (Indian Ocean). We studied R. alceifolius seed distribution in one of the last tropical lowland rainforests of the island. Seed count was greater under R. alceifolius patches (> 10 000 seed/m(2)) than in understoreys not colonized by the bramble (approximately 3000 seed/m(2)). In R. alceifolius patches, localized within gaps, our results showed that seed-rain and seed-bank before and after the fruit period decreased significantly from the center to the edge of the gap. This pattern was certainly due to the variation in luminosity, which decreased from the center of the gap to the edge. We conclude that seed dispersal of this species within the forest is mainly via running water. A number of seeds (10%-20%) were able to wait for a new opening in which to germinate. A small proportion of these seeds remained viable in the soil for many years. Monospecific R. alceifolius patches can be considered nurseries and are the main source for colonization of new areas within the forest. Our quantitative results confirm that copious sexual reproduction, a large soil seedbank, and a high germination rate are biological traits that greatly contribute to the invasiveness of this plant. They also provide important information for forestry services establishing adapted control plans. Web of Science Rubus alceifolius La Reunion Field - Experimental terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority;Plasticity High Reprod. Output primary 3470 Bartsch, MR; Bartsch, LA; Gutreuter, S 2005 Strong effects of predation by fishes on an invasive macroinvertebrate in a large floodplain river journal JOURNAL OF THE NORTH AMERICAN BENTHOLOGICAL SOCIETY 24 1 168 177 We assessed the effects of fish predation on zebra mussels (Dreissena polymorpha) in Navigation Pool 8 of the Upper Mississippi River from 13 May to 5 October, 1998. Concrete-block samplers were deployed at 18 randomly chosen sites in the main-channel border, with 6 sites in the upper, middle, and lower segments of the pool. Two blocks, 1 of which was enclosed in a cage to exclude large predatory fishes, were deployed at each site. After 145 d, blocks were retrieved from 12 of the 18 sites, and zebra mussels were found on all blocks. Densities of zebra mussels were higher on caged blocks than uncaged blocks, and the magnitudes of the differences varied spatially. Mean mussel densities on uncaged blocks were reduced by 66%, 86%, and 20% compared to caged blocks in the upper, middle, and lower pool segments, respectively, over the 145-d interval. Mean daily instantaneous zebra mussel mortality rates from large predators ranged from 0.0016 to 0.0138. Similarly, biomass of zebra mussels was higher on caged than uncaged blocks. Mean mussel biomass on uncaged blocks was reduced by 64% pool-wide, relative to biomass on caged blocks. Zebra mussels were consumed by at least 6 fish taxa including redhorse stickers (Moxostoma spp.), common carp (Cyprinus carpio), bluegill (Lepomis macrochirus), quillback carpsucker (Carpiodes cyprinus), flathead catfish (Pylodictis olivaris), and freshwater drum (Aplodinotus grunniens). Fish predation had an important moderating effect on zebra mussel demography in Pool 8. Web of Science Dreissena polymorpha USA Mississippi Field - Experimental lotic Invasion Hyp. Enemy Release filter 3471 Bergmann, GT; Motta, PJ 2005 Diet and morphology through ontogeny of the nonindigenous Mayan cichlid 'Cichlasoma (Nandopsis)' urophthalmus (Gunther 1862) in southern Florida journal ENVIRONMENTAL BIOLOGY OF FISHES 72 2 205 211 We evaluated diet and morphology through ontogeny for a freshwater population of the Mayan cichlid 'Cichlasoma (Nandopsis)' urophthalmus (Gunther 1862) in Florida's Big Cypress National Preserve. This species is a generalist predator throughout ontogeny. Fish remained the primary prey item throughout ontogeny, but there was a shift from detritus and ostracods among juveniles to algae, gastropods (snails), decapods, Hymenoptera, and adult Diptera among adults. All morphological variables grew isometrically except total molariform tooth area and pharyngeal jaw mass, which exhibited positive allometry. Despite a moderately robust adult pharyngeal jaw apparatus, this species does not specialize on hard prey at this south Florida site. Compared to its native range in Mexico, fish in Florida have undergone a pronounced niche shift with the diet being dominated by fish and snails, probably due to greater availability. The invasive success of C. urophthalmus does not appear to be related to ontogenetic morphological shifts or dietary specialization. Rather, its successful and rapid colonization of southern Florida might in part be related to its generalized and opportunistic feeding habits and morphology. Web of Science Cichlasoma urophthalmus USA Florida Big Cypress National Preserve Field - Observational lotic Invasion Hyp. Plasticity predator 3472 Brock, MT; Weinig, C; Galen, C 2005 A comparison of phenotypic plasticity in the native dandelion Taraxacum ceratophorum and its invasive congener T-officinale journal NEW PHYTOLOGIST 166 1 173 183 We compared plastic responses to variation in the light environment for sympatric populations of native and exotic dandelion species, Taraxacum ceratophorum and Taraxacum officinale. Plasticity in leaf size, inflorescence height, reproductive phenology and dispersal-related traits were measured under experimentally altered light quality (red : far-red light ratio, R : FR) and light intensity (photosynthetically active radiation, PAR). To test whether differences in means and reaction norms of dispersal-related traits between species affected colonization potential, we created seed-dispersal models based on seed-fall rate and release height. Differences in plasticity between species were not systematic, but varied in direction and magnitude among traits. Taraxacum officinale produced larger leaves that exhibited greater plasticity in size under variable light intensity than T. ceratophorum. Plasticity in scape length at flowering occurred in relation to R : FR ratio in both species, but tended to be greater in T. ceratophorum. Seed-bearing scapes of T. officinale were taller and more canalized in height across light regimes than scapes of T. ceratophorum. Seeds of T. officinale were smaller than seeds of T. ceratophorum. Models predict greater dispersal in T. officinale within open and vegetated habitats. In contrast to the idea that plasticity promotes invasiveness, results suggest that the lack of plasticity in dispersal-related traits enhances the colonization potential of T. officinale. Web of Science Taraxacum officinale USA Pennsylvania Field - Experimental terrestrial Mountain Invasion Hyp. Plasticity primary 3473 Brown, JS; Eckert, CG 2005 Evolutionary increase in sexual and clonal reproductive capacity during biological invasion in an aquatic plant Butomus umbellatus (Butomaceae) journal AMERICAN JOURNAL OF BOTANY 92 3 495 502 To test the hypothesis that increased allocation to reproduction is selected during biological invasion, we compared germination, survival, growth, and reproduction of native vs. introduced populations of the invasive aquatic plant Butomus umbellatus in a common greenhouse environment. Although seedling emergence and establishment did not differ consistently, survival thereafter was twice as high for eight introduced North American than eight native European Populations. As predicted, introduced plants were more likely to produce sexual inflorescences and clonal asexual vegetative bulbils, and they invested much more biomass in both reproductive modes. Higher reproductive investment was due to higher proportional allocation of biomass rather than larger plant size. These results are consistent with selection for increased reproduction during range expansion. However, population genetic surveys indicate that recruitment from seed rarely occurs in introduced populations. Hence increased sexual allocation is not an adaptive response to invasion. Although increased clonal reproduction may be advantageous in expanding populations, genetic evidence from introduced populations of B. umbellatus suggests that increased clonal allocation may have arisen via stochastic processes during long-distance transport or a selective filter right at introduction, rather than incremental natural selection during range expansion. Web of Science Butomus umbellatus Canada Ontario Greenhouse lentic Invasion Hyp. Inherent Superiority Clonal Reproduction primary 3474 Buschmann, H; Edwards, PJ; Dietz, H 2005 Variation in growth pattern and response to slug damage among native and invasive provenances of four perennial Brassicaceae species journal JOURNAL OF ECOLOGY 93 2 322 334 1 The EICA (evolution of increased competitive ability) hypothesis suggests that release from natural enemies and pathogens results in higher vigour of invasive plants as a result of the selection of less defended but rapidly growing genotypes. Slug diversity and abundance appear to be low in North America compared with Europe, and we therefore hypothesized that release from slug herbivory contributes to the invasiveness of European Brassicaceae species in North America. 2 In common garden and glasshouse experiments we compared life history and fitness parameters in native (NP) and introduced (IP) provenances of four invasive Brassicaceae species (Barbarea vulgaris, Bunias orientalis, Cardaria draba, Rorippa austriaca) that were subjected to herbivory by Arion lusitanicus. In climate chamber bioassays we investigated slug damage to seedlings and leaf discs using the same sources of plant material. 3 In all species except B. orientalis we found significant but not always consistent differences in growth and reproductive characteristics between IP and NP plants. Plants of B. vulgaris and R. austriaca from the introduced range had a considerably higher growth rate than those from the native range. While IP plants of the non-clonal B. vulgaris allocated more resources to seed production than NP plants, the IP plants of the clonal R. austriaca showed a decreased number of seeds. 4 Contrary to expectation, there were no differences between NP plants and IP plants in the number of damaged leaves and leaf area consumed by slugs, or in the proportion of seedlings damaged and killed. Nor were there interaction effects between slug treatments and provenance. 5 The results suggest that there are genetically based differences in growth and reproductive parameters between NP and IP plants. As there were no differences in herbivore damage between the provenances, this genetic differentiation is probably due to factors such as competition rather than herbivore effects. 6 In order to make progress in understanding why some species become invasive, more comparative experimental studies are needed that investigate how different kinds of antagonists (generalist and specialist herbivores and pathogens) influence the performance of plants at different life stages. Web of Science Barbarea vulgaris;Bunias orientalis;Cardaria draba;Rorippa austriaca USA Great Lakes Greenhouse;Garden terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 3475 Bustamante, RO; Simonetti, JA 2005 Is Pinus radiata invading the native vegetation in central Chile? Demographic responses in a fragmented forest journal BIOLOGICAL INVASIONS 7 2 243 249 Forest fragmentation facilitates the invasion of exotic species. This threat may be especially severe if forest fragments are surrounded by plantations of exotic species like Pinus radiata, an aggressive colonizer and shade-intolerant tree that has invaded successfully several native ecosystems of the southern hemisphere. In this study, we experimentally tested if the conditions of a successful seedling establishment P. radiata are fulfilled at the Coastal Maulino forest, an endemic fragmented forest of central Chile. Results demonstrated that seeds are dispersed into the native forests, however seedling establishment occurs only at the edges. We conclude that this exotic species is not invading native forests up to date. However, we suggest to conduct evaluations of seed rain and seedling establishment in the long term, in order to monitor the fate of this exotic species in fragmented native forest of Central Chile. Web of Science Pinus radiata Chile Coastal Maulino forest Field - Observational terrestrial Deciduous Forest Invasion Hyp. Disturbance primary 3476 Carpenter, D; Cappuccino, N 2005 Herbivory, time since introduction and the invasiveness of exotic plants journal JOURNAL OF ECOLOGY 93 2 315 321 1 We tested the enemy release hypothesis for invasiveness using field surveys of herbivory on 39 exotic and 30 native plant species growing in natural areas near Ottawa, Canada, and found that exotics suffered less herbivory than natives. 2 For the 39 introduced species, we also tested relationships between herbivory, invasiveness and time since introduction to North America. Highly invasive plants had significantly less herbivory than plants ranked as less invasive. Recently arrived plants also tended to be more invasive; however, there was no relationship between time since introduction and herbivory. 3 Release from herbivory may be key to the success of highly aggressive invaders. Low herbivory may also indicate that a plant possesses potent defensive chemicals that are novel to North America, which may confer resistance to pathogens or enable allelopathy in addition to deterring herbivorous insects. Web of Science Many Canada Ottawa Field - Observational terrestrial Invasion Hyp. Enemy Release primary 3478 Castillo, JM; Rubio-Casal, AE; Redondo, S; Alvarez-Lopez, AA; Luque, T; Luque, C; Nieva, FJ; Castellanos, EM; Figueroa, ME 2005 Short-term responses to salinity of an invasive cordgrass journal BIOLOGICAL INVASIONS 7 1 29 35 Salinity is one of the main chemical factors in salt marshes. Studies focused on the analysis of salinity tolerance of salt marsh plants are very important, since they may help to relate their physiological tolerances with distribution limits in the field. Spartina densiflora is a South America cordgrass, which has started its invasion of the European coastline from the southwestern Iberian Peninsula. In this work, short-term responses in adult tussocks of S. densiflora from southwestern Spain are studied over a wide range of salinity in a greenhouse experiment. Our results point out that S. densiflora has a high tolerance to salinity, showing high growth and net photosynthesis rates from 0.5 to 20 ppt. S. dens flora showed at the lowest salinity (0.5 ppt) high levels of photoinhibition, compensated by higher levels of energy transmission between photosystems. Adaptative mechanisms, as those described previously, would allow it to live in fresh water environments. At the highest salinity (40 ppt), S. densiflora showed a high stress level, reflected in significant decreases in growth, net photosynthesis rate and photochemical efficiency of Photosystem II. These responses support S. dens flora invasion patterns in European estuaries, with low expansion rates along the coastline and faster colonization of brackish marshes and river banks. Web of Science Spartina densiflora Spain Greenhouse estuarine Invasion Hyp. Inherent Superiority Broad Tolerances primary 3481 Cheplick, GP 2005 Biomass partitioning and reproductive allocation in the invasive, cleistogamous grass Microstegium vimineum: Influence of the light environment journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 132 2 214 224 Biomass partitioning and allocation to chasmogamous (CH) and cleistogamous (CL) reproduction were investigated in the invasive, summer annual Microstegium vimineum in relation to light conditions. This shade-tolerant grass weed of Asian origin forms dense populations in the understory of moist deciduous forests in eastern North America. In autumn each flowering tiller produces one terminal raceme with CH spikelets and 2 to 7 sheath-enclosed axillary racemes with CL spikelets at the uppermost nodes. In a greenhouse, plants were reared from seed families collected from individuals in subpopulations of shady (2 to 8 % full sun) or sunny, edge habitats. At maturity, tillers of the shade subpopulation showed greater allocation to leaves, but reduced allocation to CH and CL, compared to those from the sunny subpopulation, suggesting adaptive differentiation to light conditions in the field. Maternal family (within subpopulation) had a significant effect on CH allocation and the mean mass of CH and CL seeds. For mature tillers collected directly from the field habitats, allocation to CH and CL was lowest, and allocation to leaves was greatest, in deep shade. CH and CL allocation averaged 16 % and 11 %, respectively, in the sunny habitat, but only 6 % and 7 % in the shady habitat. There was no evidence of a trade-off in allocation to CH vs. CL in field-collected or greenhouse tillers; in fact, there was a significant positive correlation of CH with CL allocation. The ability to grow and allocate limited resources to seed production in CH and CL spikelets under deep shade where other herbs are uncommon, is crucial to the success of M. vimineum as an aggressive colonizer of disturbed forests. Web of Science Microstegium vimineum USA Field - Observational;Greenhouse terrestrial Deciduous Forest Invasion Hyp. Inherent Superiority Self Compatible primary 3482 Cole, PG; Weltzin, JF 2005 Light limitation creates patchy distribution of an invasive grass in eastern deciduous forests journal BIOLOGICAL INVASIONS 7 3 477 488 Species interactions and their indirect effects on the availability and distribution of resources have been considered strong determinants of community structure in many different ecological systems. In deciduous forests, the presence of overstory trees and shrubs creates a shifting mosaic of resources for understory plants, with implications for their distribution and abundance. Determination of the ultimate resource constraints on understory vegetation may aid management of these systems that have become increasingly susceptible to invasions by non-native plants. Microstegium vimineum (Japanese grass) is an invasive annual grass that has spread rapidly throughout the understory of forests across the eastern United States since it was first observed in Tennessee in 1919. M. vimineum occurs as extensive, dense patches in the understory of eastern deciduous forests, yet these patches often exhibit sharp boundaries and distinct gaps in cover. One example of this distributional pattern was observed relative to the native midstory tree Asimina triloba (pawpaw), whereby dense M. vimineum cover stopped abruptly at the drip line of the A. triloba patch and was absent beneath the A. triloba canopy. We conducted field and greenhouse experiments to test several hypotheses regarding the causes of this observed pattern of M. vimineum distribution, including allelopathy, seed dispersal, light limitations, and soil moisture, texture, and nutrient content. We concluded that light reduction by the A. triloba canopy was the environmental constraint that prevented establishment of M. vimineum beneath this tree. Whereas overstory tree canopy apparently facilitates the establishment of this shade-tolerant grass, the interaction of overstory canopy with midstory canopy interferes with M. vimineum by reducing the availability of sunflecks at the ground layer. It is likely that other midstory species influence the distribution and abundance of other herb-layer species, with implications for management of understory invasive plant species. Web of Science Microstegium vimineum USA Field - Experimental;Greenhouse terrestrial Deciduous Forest Fundamentals primary 3485 Diederich, S 2005 Differential recruitment of introduced Pacific oysters and native mussels at the North Sea coast: coexistence possible? journal JOURNAL OF SEA RESEARCH 53 4 269 281 Pacific oysters (Crassostrea gigas Thunberg 1793) have been introduced into the Wadden Sea (North Sea), where they settle on native mussel beds (Mytilus edulis L.), which represent the only extensive insular hard substrata in this soft-sediment environment. As abundances of C. gigas rose, some mussel beds became increasingly overgrown with oysters, whereas others did not. Field experiments revealed that recruitment of C. gigas was higher in the lower intertidal than in the upper subtidal zone, that it was higher on conspecifics than on mussels, and that it was not affected by barnacle epigrowth except when settling on mussels. Mussel recruitment is known from inter- and subtidal zones. It occurred equally on oyster and mussel shells but showed a clear preference for barnacle epigrowth over clean shells. Assuming that settlement and recruitment are key processes for species abundances on the North Sea coast, it is predicted that the positive feedback in oyster settlement will lead to rapid reef formation of this invader at the expense of mussel beds. Mussels, however, may escape competitive exclusion by settling between or on the larger oysters especially when barnacles are abundant. Experimental patches with mussels were more often covered by fucoid algae (Fucus vesiculosus forma mytili Nienburg) than patches with oysters, and oyster recruitment was poor underneath such algal canopies. Thus, fucoids may provide the native mussels with a refuge from the invading oysters and the two bivalves may coexist, provided food is not limiting. (c) 2005 Elsevier B.V. All rights reserved. Web of Science Crassostrea gigas North Sea Wadden Sea Field - Experimental;Field - Observational marine Fundamentals filter 3489 Facon, B; Jarne, P; Pointier, JP; David, P 2005 Hybridization and invasiveness in the freshwater snail Melanoides tuberculata: hybrid vigour is more important than increase in genetic variance journal JOURNAL OF EVOLUTIONARY BIOLOGY 18 3 524 535 Many invasive taxa are hybrids, but how hybridization boosts the invasive process remains poorly known. We address this question in the clonal freshwater snail Melanoides tuberculata from Martinique, using three parental and two hybrid lines. We combine an extensive field survey (1990-2003) and a quantitative genetic experiment to show that hybrid lines have outcompeted their parents in natural habitats, and that this increased invasiveness co-occurred with pronounced shifts in life-history traits, such as growth, fecundity and juvenile size. Given the little time between hybrid creation and sampling, and the moderate standing genetic variance for life-history traits in hybrids, we show that some of the observed trait changes between parents and hybrids were unlikely to arise only by continuous selection. We therefore suggest that a large part of hybrid advantage stems from immediate heterosis upon hybridization. Web of Science Melanoides tuberculata Martinique Field - Observational;Lab lotic Invasion Hyp. Hybridization herbivore 3493 Green, AJ; Sanchez, MI; Amat, F; Figuerola, J; Hontoria, F; Ruiz, O; Hortas, F 2005 Dispersal of invasive and native brine shrimps Artemia (Anostraca) via waterbirds journal LIMNOLOGY AND OCEANOGRAPHY 50 2 737 742 North American brine shrimp Artemia franciscana have been exported worldwide since the 1950s for use in aquarium trade and fish farming. Aquaculture is expanding along the Mediterranean coast, leading to the release of A. franciscana into native Artemia populations. A. franciscana was first detected in 1981 in Portugal and has since spread to saltworks along the East Atlantic flyway used by shorebirds. Once A. franciscana becomes established in a locality, native Artemia tend to disappear. To test whether migratory shorebirds can disperse invasive and native Artemia between wetlands, we extracted Artemia cysts from feces and pellets collected at Castro Marim (Portugal) and Cadiz Bay (Spain) during southward migration. We found that large numbers of viable eggs of A. franciscana and native Artemia partheno-genetica were dispersed by Redshank Tringa totanus, Blacktailed Godwit Limosa limosa, and other shorebirds migrating through the Iberian Peninsula. This is the most extensive field demonstration to date that invertebrates can disperse readily via gut passage through birds. Web of Science Artemia franciscana Portugal; Spain Field - Observational marine Invasion Hyp. Inherent Superiority Effective Disperser filter 3494 Griswold, MW; Lounibos, LP 2005 Does differential predation permit invasive and native mosquito larvae to coexist in Florida? journal ECOLOGICAL ENTOMOLOGY 30 1 122 127 1. The hypothesis that selective predation on larvae of the invasive Aedes albopictus (Skuse) could account for its stable coexistence with the native mosquito species and inferior competitor Ochlerotatus triseriatus (Say) in Florida treeholes and container systems was tested experimentally. 2. Functional responses of the two dipteran predators Toxorhynchites rutilus (Coquillett) and Corethrella appendiculata (Grabham) were evaluated separately for A. albopictus and O. triseriatus prey. Both predators exhibited type II functional responses and consistently consumed more of the invasive species. Handling time of T. rutilus feeding upon O. triseriatus was significantly longer than when preying upon the invasive species. 3. When either predator species was offered varying ratios of the two prey species, A. albopictus was consumed preferentially. The absence of a prey ratio effect on preference indicated that switching probably does not occur. 4. The higher maximum feeding rate upon, and preference for, A. albopictus suggests that differential predation may foster coexistence of the invasive and native mosquito prey species in Florida. Web of Science Aedes albopictus United States Florida Lab terrestrial Invasion Hyp. Other parasite 3495 Gruner, DS 2005 Biotic resistance to an invasive spider conferred by generalist insectivorous birds on Hawai'i Island journal BIOLOGICAL INVASIONS 7 3 541 546 A central problem for ecology is to understand why some biological invasions succeed while others fail. Species interactions frequently are cited anecdotally for establishment failure, but biotic resistance is not well supported by quantitative experimental studies in animal communities. In a 33-month experiment on Hawaii Island, exclusion of native and alien forest birds resulted in a 25- to 80-fold increase in the density of a single non-indigenous spider species (Theridiidae: Achaearanea cf. riparia). Caged plots held large aggregations of juveniles and more large-bodied individuals, suggesting potential reproductive individuals are more susceptible to bird predation. Most examples of biotic resistance involve competition for limiting resources among sessile marine animals or terrestrial plants. The present results show that generalist predators can limit the success of introductions, even on oceanic islands, generally assumed less resistant to invasion. Web of Science Achaearanea cf. riparia United States Hawaii Field - Experimental terrestrial Subtropical Forest Invasion Hyp. Other predator 3497 Kim, KD 2005 Invasive plants on disturbed Korean sand dunes journal ESTUARINE COASTAL AND SHELF SCIENCE 62 2 353 364 The sand dunes in coastal regions of South Korea are important ecosystems because of their small size. the rare species found in this habitat, and the beautiful landscapes they create. This study investigated the current vegetative status of sand dunes on three representative coasts of the Korean peninsula, and on the coasts of Cheju Island, and assessed the conditions caused by invasive plants. The relationships between the degree of invasion and 14 environmental variables were studied. Plots of sand dunes along fine transects perpendicular to the coastal lines were established to estimate vegetative species coverage. TWINSPAN (Two-Way Indicator Species Analysis), CCA (Canonical Correspondence Analysis), and DCCA (Detrended Canonical Correspondence Analysis) were performed to classify communities on sand dunes and assess species composition variation. Carex kobomugi, Elymus mollis, and Vitex rotundifolia were found to be the dominant species plotted on the east. the west. and the peripheral coasts of Cheju Island, respectively. Vegetation on the south coast was totally extinct. The 19 communities. including representative C. kobomugi, C. kobomugi-Ixeris repens, C. kobomugi-Oenothera biennis, E. mollis, Lolium multiflorum-Calystegia soldanella, and V. rotundifolia kobomugi, were all classified according to TWINSPAN. Oenothera biennis and L. multiflorum were exotics observed within these native communities. CCA showed that invasive native and exotic species distribution was segregated significantly, according to disturbance level, exotic species number, gravel, sand and silt contents. as well as vegetation size. It further revealed that human disturbance can strongly favor the settlement of invasive and exotic species. Restoration options to reduce exotic plants in the South Korean sand dune areas were found to be the introduction of native plant species from one sand dune into other sand dune areas. prohibition of building and the introduction of exotic soils, and conservation of surrounding sand dune areas. (C) 2004 Elsevier Ltd. All rights reserved. Web of Science Many South Korea Field - Observational terrestrial Invasion Hyp. Community Species Richness;Disturbance primary 3498 Klein, J; Ruitton, S; Verlaque, M; Boudouresque, CF 2005 Species introductions, diversity and disturbances in marine macrophyte assemblages of the northwestern Mediterranean Sea journal MARINE ECOLOGY-PROGRESS SERIES 290 0 79 88 In the process of species introduction, the traits that enable a species to establish and spread in a new habitat, and the habitat characteristics that determine the susceptibility to introduced species play a major role. Among the habitat characteristics that render a habitat resistant or susceptible to introductions, species diversity and disturbance are believed to be the most important, It is generally assumed that high species richness renders a habitat resistant to introductions, while disturbances enhance their susceptibility. In the present study, these 2 hypotheses were tested on NW Mediterranean shallow subtidal macrophyte assemblages. Data collection was carried out in early summer 2002 on sub-horizontal rocky substrate at 9 sites along the French Mediterranean coast, 4 undisturbed and 5 highly disturbed. Disturbances include cargo, naval and passenger harbours, and industrial and urban pollution. Relationships between species richness (point diversity), disturbances and the number of introduced macrophytes were analysed. The following conclusions were drawn: (1) there is no relationship between species introductions, diversity and disturbance for the macrophyte assemblages; (2) multifactorial analyses only revealed the biogeographical relationships between the native flora of the sites. Web of Science Many France Field - Observational marine Invasion Hyp. Community Species Richness;Disturbance primary 3499 Lambrecht-McDowell, SC; Radosevich, SR 2005 Population demographics and trade-offs to reproduction of an invasive and noninvasive species of Rubus journal BIOLOGICAL INVASIONS 7 2 281 295 Do trade-offs between growth and reproduction differ between an invasive and noninvasive plant species and how do such trade-offs relate to population demographics? To help address these questions, we compared demographics for an invasive plant species, Rubus discolor, with a noninvasive congener, R. ursinus, in several populations of varying density. Removal of floral buds from reproductive canes increased the size of juvenile canes that arose from clonal sprouting in R. ursinus, suggesting a trade-off between current reproduction and growth. Removal of floral buds had no effect on growth of R. discolor. R. ursinus displayed trade-offs between reproduction (sexual and vegetative) and future growth based on negative correlations between leaf area production and both clonal sprouting and seedling production during the previous year. R. discolor did not exhibit these trade-offs. Both species had high population growth rates in low-density populations, but exhibited little or no growth in high-density populations. A life table response experiment was used to determine the underlying cause for the effect of density on population growth. For R. ursinus, lack of population growth in high-density populations was due primarily to increased mortality of clonally sprouting canes, while for R. discolor, it was due to decreased clonal cane production. Elasticity analysis revealed that clonal growth was more important than sexual reproduction for population growth of both species. However, elasticity values for sexual reproduction in R. discolor were greater in high- than low-density populations. This suggests an increased reliance on sexual reproduction in populations that had reached stable sizes, which could increase the capacity of R. discolor to disperse to new sites. Elasticity analyses were also used to simulate the efficacy of various control strategies for R. discolor. Control of this species could be attained by reducing clonal production within existing populations while reducing seed production to limit establishment of new populations. Web of Science Rubus discolor United States Oregon Field - Experimental;Field - Observational terrestrial Invasion Hyp. Other primary 3504 Macleod, CJ; Parish, DMB; Duncan, RP; Moreby, S; Hubbard, SF 2005 Importance of niche quality for Yellowhammer Emberiza citrinella nestling survival, development and body condition in its native and exotic ranges: the role of diet journal IBIS 147 2 270 282 The niche hypothesis predicts that some introduced species establish and spread successfully because their new environment provides expanded niche opportunities compared with their native environments. By investigating nestling survival, growth and body condition in relation to diet composition and prey abundance, we tested the prediction that the success of Yellowhammers Emberiza citrinella in New Zealand could be explained by the availability of better quality food resources in its introduced range compared with its native range. We found that Yellowhammer nestlings in New Zealand were larger and heavier than those in Britain, but that nestling survival and body condition did not differ between countries. The preferred prey items, which had some influence on nestling development and survival, were more prevalent in the diet of nestlings in New Zealand, suggesting that nestlings in the introduced range had a superior quality diet. However, there was little evidence to support the prediction that the preferred prey were more abundant in the introduced range, implying that some other factor such as prey accessibility or adult fitness may account for the differences in diet between countries. Web of Science Emberiza citrinella New Zealand Field - Observational terrestrial Invasion Hyp. Other omnivore 3505 Meiners, SJ 2005 Seed and seedling ecology of Acer saccharum and Acer platanoides: A contrast between native and exotic congeners journal NORTHEASTERN NATURALIST 12 1 23 32 The exotic tree, Acer platanoides, is increasing in forests of northeastern North America, largely within the range of its native congener, Acer saccharum. A combination of field and controlled experiments was used on seeds and seedlings of these congeners to determine species characteristics that may be contributing to these floristic changes. Acer platanoides experienced lower rates of seed predation than A. saccharum in field experiments. Differences in the dispersal and allocation characteristics of the two species were small and not likely to explain the relative success of A. platanoides. Greenhouse-grown seedlings of A. platanoides were much larger than those of A. saccharum because of differences in seed size, not differences in growth rate. These data suggest that preferential seed predation and initial seed size differences may explain greater relative success in Acer platanoides seedlings. Web of Science Acer platanoides United States New Jersey Field - Experimental;Greenhouse terrestrial Deciduous Forest Invasion Hyp. Enemy Release;Inherent Superiority primary 3506 Memmott, J; Craze, PG; Harman, HM; Syrett, P; Fowler, SV 2005 The effect of propagule size on the invasion of an alien insect journal JOURNAL OF ANIMAL ECOLOGY 74 1 50 62 1. The movement of species from their native ranges to alien environments is a serious threat to biological diversity. The number of individuals involved in an invasion provides a strong theoretical basis for determining the likelihood of establishment of an alien species. 2. Here a field experiment was used to manipulate the critical first stages of the invasion of an alien insect, a psyllid weed biocontrol agent, Arytainilla spartiophila Forster, in New Zealand and to observe the progress of the invasion over the following 6 years. 3. Fifty-five releases were made along a linear transect 135 km long: 10 releases of two, four, 10, 30 and 90 psyllids and five releases of 270 psyllids. Six years after their original release, psyllids were present in 22 of the 55 release sites. Analysis by logistic regression showed that the probability of establishment was significantly and positively related to initial release size, but that this effect was important only during the psyllids' first year in the field. 4. Although less likely to establish, some of the releases of two and four psyllids did survive 5 years in the field. Overall, releases that survived their first year had a 96% chance of surviving thereafter, providing the release site remained secure. The probability of colony loss due to site destruction remained the same throughout the experiment, whereas the probability of natural extinction reduced steeply over time. 5. During the first year colonies were undergoing a process of establishment and, in most cases, population size decreased. After this first year, a period of exponential growth ensued. 6. A lag period was observed before the populations increased dramatically in size. This was thought to be due to inherent lags caused by the nature of population growth, which causes the smaller releases to appear to have a longer lag period. Web of Science Arytainilla spartiophila New Zealand Field - Experimental terrestrial Invasion Hyp. Propagule Pressure herbivore 3509 Myers, CV; Anderson, RC; Byers, DL 2005 Influence of shading on the growth and leaf photosynthesis of the invasive non-indigenous plant garlic mustard [Alliaria petiolata (M. Bieb) Cavara and Grande] grown under simulated late-winter to mid-spring conditions journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 132 1 1 10 MYERS, C. V., R. C. ANDERSON, AND D. L. BYERS (Behavior, Ecology, Evolution, and Systematics Section, 4120 Department of Biological Sciences, Illinois State University, Normal, IL 61790-4120). Influence of shading on the growth and leaf photosynthesis of the invasive non-indigenous plant garlic mustard [Alliaria petiolata (M. Bieb) Cavara and Grande] grown under simulated late-winter to mid-spring conditions. J. Torrey But. Soc. 132: 1-10. 2005.Plasticity in photosynthetic response to varied light conditions likely contributes to the successful spread and domination of eastern deciduous forest ground layers by the invasive, non-indigenous plant species Alliaria petiolata. We examined the effects of growing plants with no shading, or under 30% or 60% black shade cloth on leaf photosynthetic rates, maximum rates of leaf photosynthesis (A(max)) and stomatal conductance (g(Smax)), light compensation point, above and below ground biomass, chlorophyll content and specific leaf mass of A. petiolata grown under simulated late-winter to mid-spring conditions of temperature, photoperiod, and irradiance in a growth chamber. The 0% shade treatment plants exhibited a significantly greater leaf photosynthetic rate than the 60% shade treatment plants between 800 and 1600 mu mol circle m(-2)circle s(-1) photosynthetically active photon flux density (PPFD). Leaf A(max) was significantly greater for plants grown under no shade than for plants grown under either the 30 or 60% shade treatments and g(Smax) was higher for plants grown under no shade than plants in the 60% shade treatment. Plants grown under 0 and 30% shade produced significantly more biomass and had greater specific leaf mass than plants grown under 60% shade. Leaves of the 60% shade treatment had significantly greater chlorophyll a and b content than leaves of the 0 and 30% shade treatments. Our results indicate that A. petiolata displays a plastic response to varied light levels in a way that would likely increase its success in invading eastern deciduous forest ground layers. Web of Science Alliaria petiolata United States Lab terrestrial Deciduous Forest Invasion Hyp. Plasticity primary 3511 Parisod, C; Trippi, C; Gallad, N 2005 Genetic variability and founder effect in the pitcher plant Sarracenia purpurea (Sarraceniaceae) in populations introduced into Switzerland: From inbreeding to invasion journal ANNALS OF BOTANY 95 2 277 286 Background and Aims The long-lived and mainly outcrossing species Sarracenia purpurea has been introduced into Switzerland and become invasive. This creates the opportunity to study reactions to founder effect and how a species can circumvent deleterious effects of bottlenecks such as reduced genetic diversity. inbreeding and extinction through mutational meltdown. to emerge as a highly invasive plant. Methods A population genetic survey by random amplified polymorphism DNA markers (RAPD) together with historical insights and a field pollination experiment were carried out. Key Results At the regional scale. S. purpurea shows low structure (theta(st) = 0.072) due to a recent founder event and important subsequent growth. Nevertheless. multivariate statistical analyses reveal that. because of a bottleneck that shifted allele frequencies, most of the variability is independent among populations. In one population (Tenasses) the species has become invasive and genetic analysis reveals restricted gene flow and family, structure (theta(st) = 0.287). Although inbreeding appears to be high (F-is > 0.410 from a Bavesian estimation). a field pollination experiment failed to detect significant inbreeding depression upon F-1 seed number and seed weight fitness-trots. Furthermore. crosses between unrelated individuals produced F-1 seeds with significantly reduced fitness. thus showing local outbreeding depression. Conclusions The results suggest that. under restricted gene flow among families. the species may not only have rapidly purged deleterious alleles. but also have undergone some form of selection for inbreeding due to co-adaptation between loci. (C) 2004 Annals of Botany Company. Web of Science Sarracenia purpurea Switzerland Field - Experimental;Lab terrestrial Wetland Invasion Hyp. Evolution in General primary 3512 Peperkorn, R; Werner, C; Beyschlag, W 2005 Phenotypic plasticity of an invasive acacia versus two native Mediterranean species journal FUNCTIONAL PLANT BIOLOGY 32 10 933 944 The phenotypic plasticity and the competitive ability of the invasive Acacia longifolia v. the indigenous Mediterranean dune species Halimium halimifolium and Pinus pinea were evaluated. In particular, we explored the hypothesis that phenotypic plasticity in response to biotic and abiotic factors explains the observed differences in competitiveness between invasive and native species. The seedlings' ability to exploit different resource availabilities was examined in a two factorial experimental design of light and nutrient treatments by analysing 20 physiological and morphological traits. Competitiveness was tested using an additive experimental design in combination with N-15-labelling experiments. Light and nutrient availability had only minor effects on most physiological traits and differences between species were not significant. Plasticity in response to changes in resource availability occurred in morphological and allocation traits, revealing A. longifolia to be a species of intermediate responsiveness. The major competitive advantage of A. longifolia was its constitutively high shoot elongation rate at most resource treatments and its effective nutrient acquisition. Further, A. longifolia was found to be highly tolerant against competition from native species. In contrast to common expectations, the competition experiment indicated that A. longifolia expressed a constant allocation pattern and a phenotypic plasticity similar to that of the native species. Web of Science Acacia longifolia Mediterranean Greenhouse terrestrial Chaparral/Shrublands Invasion Hyp. Inherent Superiority;Plasticity Superior Competitor;Rapid Growth primary 3514 Pino, J; Font, X; Carbo, J; Jove, M; Pallares, L 2005 Large-scale correlates of alien plant invasion in Catalonia (NE of Spain) journal BIOLOGICAL CONSERVATION 122 2 339 350 Identification of the main correlates of the invasion process is a fundamental step in alien species management at the regional scale. This paper explores the main climatic, territorial, and anthropic correlates of alien plant species richness and percentage in Catalonia (NE of Spain), by means of GIS techniques. We used floristic data collected in FLORACAT per UTM 10 km x 10 km to set up the number and the percentage of alien species. The association of these variables with climate, topography, landscape, human settlement, and geographic position was explored by means of stepwise regression models applied on the axes obtained from principal component analysis. The significance of the resulting correlates was tested using the modified t test of Dutilleul to remove the effects of spatial autocorrelation. PCA reduced the 22 variables to 12 principal components (PC) that explained 90% of the cumulative variance. Regression models were highly significant and captured a high proportion of total variance (adjusted r(2) = 0.70 for alien species richness and r(2) = 0.56 for alien species percentage). Both alien species richness and percentage were mainly correlated to PC summarising variables concerning climate, habitat and landscape heterogeneity, and potential anthropogenic disturbance. However, while these PC exhibited similar weights on alien species richness, species percentage was mainly determined by climate. Implications for conservation are discussed considering a future scenario of climate warming and increasing land use change in Mediterranean areas. (C) 2004 Published by Elsevier Ltd. Web of Science Many Spain Catalonia Statistical/Meta-analysis terrestrial Invasion Hyp. Preadaptation to Climate;Disturbance;Other primary 3515 Poulin, J; Weller, SG; Sakai, AK 2005 Genetic diversity does not affect the invasiveness of fountain grass (Pennisetum setaceum) in Arizona, California and Hawaii journal DIVERSITY AND DISTRIBUTIONS 11 3 241 247 Pennisetum setaceum (Poaceae) is a perennial bunch grass that invaded the United States during the 20th century and is highly invasive in Hawaii, moderately invasive in Arizona, and not yet invasive in southern California. Pennisetum setaceum is apomictic, a condition that is normally associated with low genetic variation within populations, but even moderate levels of genetic variation among populations could account for differences in invasiveness. To determine whether genetic factors are causing the variable invasion success, we used Inter-Simple Sequence Repeat markers (ISSRs) to examine genetic variation in populations from the three areas. Screening of 16 primers revealed no genetic variation within any population or between any geographical areas, a pattern consistent with complete apomixis. Variation in invasion success appears unrelated to genetic differences among populations. Differences in the seasonal timing of rainfall among the regions may be the cause of variable invasiveness of fountain grass. Alternatively, differences in timing of introduction or duration of lag phase may have limited invasiveness in Arizona and southern California. Web of Science Pennisetum setaceum United States Arizona; California; Hawaii Field - Observational;Lab terrestrial Invasion Hyp. Other primary 3517 Rinella, MJ; Sheley, RL 2005 Influence of soil water availability on competition among leafy spurge (Euphorbia esula) and grasses journal WESTERN NORTH AMERICAN NATURALIST 65 2 233 241 Some pertorbations differentially influence invasive plant and grass production. For example, growth regulator herbicides and biological control agents can dramatically reduce leafy spurge production while having little or no influence oil grass production, and overgrazing can reduce grass production while not substantially influencing leafy spurge production because cattle typically ingest little or no leafy spurge. To predict how grass production will respond to a perturbation that influences only leafy spurge and to predict how leafy spurge production will respond to a perturbation that affects only grasses, competitive relationships must be understood. Seeding mixtures of leafy spurge and 2 grasses were planted in experiments and grown for 127 days to determine whether different water application regimes influenced competition among these 3 species. Competition became less intense as the number of water applications increased. If this finding holds true under field conditions, then it indicates that competition is less intense in years and locations with numerous precipitation events. Competitive interactions (i.e., competition coefficients) were less variable when water was applied more frequently, hot the ability of models to account for variation in plant weight (i.e., r(2)) was not influenced by the frequency of water application. This suggests that models will predict invasive plant and grass biomass with equal accuracy in years with few or many precipitation events. Competitive effects were similar regardless of grass species, which suggests that grasses might be considered collectively in predicting response to perturbations in the field. Web of Science Euphorbia esula United States Greenhouse terrestrial Invasion Hyp. Inherent Superiority Superior Competitor primary 3523 Stastny, M; Schaffner, U; Elle, E 2005 Do vigour of introduced populations and escape from specialist herbivores contribute to invasiveness? journal JOURNAL OF ECOLOGY 93 1 27 37 1 Plant species may become invasive due to a lack of natural enemies (e.g. herbivores) in their introduced range. Absence of herbivores may result in selection for the loss of costly herbivore-resistance traits, which are expected to show a trade-off with vigour or competitive ability (the evolution of increased competitive ability, or EICA, hypothesis). 2 We conducted a common garden experiment in Switzerland, in which we compared herbivore resistance and vigour of Senecio jacobaea plants exposed to the specialist flea beetle Longitarsus jacobaeae, for four populations originating within the native range (Europe), and four from regions where it had been introduced (New Zealand, USA) and was unaffected by L. jacobaeae. Our predictions were that, compared with plants from the native populations, plants from introduced populations would experience greater herbivory (due to loss of resistance traits), and exhibit more vigorous growth. 3 As expected, we found that introduced S. jacobaea grew larger, and had greater reproductive output, than plants from the native range. Larger plants experienced more feeding damage, and introduced plants were consumed more even when size differences were controlled. Introduced plants also exhibited a greater relative ability to reproduce after damage was sustained, i.e. higher tolerance to herbivory. 4 Contrary to predictions, however, plants from introduced populations had higher total pyrrolizidine alkaloid production (chemical defence against herbivores). 5 Although plants from introduced ranges exhibited life-history traits consistent with EICA predictions, similar phenotypes were common in one of the populations from the native range, suggesting that EICA may not fully explain the invasion success of S. jacobaea. 6 Our results imply that increased competitive ability (vigour) of invasive plants may be associated with changes in resistance as well as tolerance to herbivory, and both types of anti-herbivore defence may need to be examined simultaneously to advance our understanding of invasiveness. Web of Science Senecio jacobaea Switzerland Garden terrestrial Invasion Hyp. Evolution of Increased Competitive Ability primary 3524 Thomas, JR; Gibson, DJ; Middleton, BA 2005 Water dispersal of vegetative bulbils of the invasive exotic Dioscorea oppositifolia L. in southern Illinois journal JOURNAL OF THE TORREY BOTANICAL SOCIETY 132 2 187 196 Riparian corridors promote dispersal of several species of exotic invasives worldwide. Dispersal plays a role in the colonization of exotic invasive species into new areas and this study was conducted to determine if the invasiveness of Dioscorea oppositifolia L. (Chinese yam) is facilitated by secondary dispersal of vegetative diaspores (bulbils) by water. Since seed production of this plant has not been observed in the United States, bulbils represent the only means of dispersal to new habitats. Dispersal was monitored by placing aquatic traps, tethered bulbils, and painted bulbil caches in a tributary of Drury Creek, Giant City State Park, Illinois. Results indicate that high-energy flow in the creek accelerated secondary dispersal of bulbils downstream and onto the floodplain. The longest recorded dispersal distance was 206.2 in downstream. Dispersal distance of tethered bulbils was not related to rainfall or flow velocity in the creek; however the total number of bulbils trapped was positively related to flow velocity. We conclude that secondary dispersal by water in streams can facilitate dispersal of vegetative bulbils of this exotic species. Web of Science Dioscorea oppositifolia United States Illinois Field - Observational lotic Riparian Invasion Hyp. Other primary 3526 Travis, JMJ; Hammershoj, M; Stephenson, C 2005 Adaptation and propagule pressure determine invasion dynamics: insights from a spatially explicit model for sexually reproducing species journal EVOLUTIONARY ECOLOGY RESEARCH 7 1 37 51 Propagule pressure is often considered to be one of the key factors determining the probability that a species becomes invasive. However, there has been relatively little work, either empirical or theoretical, that has tested this assertion. Here, we develop a patch occupancy model for diploid organisms that reproduce sexually, and use it to investigate the dynamics of an introduced species. The model produces some interesting insights: If the introduced individuals are already well-adapted to the wild conditions, then the number of escapees is always larger when there are more introductions. However, when the introduced individuals are relatively poorly adapted to the natural conditions, this is often not the case. Under these conditions, the most rapid invasion occurs for an intermediate number of introductions. When the number of introductions is high, adaptation to local conditions is dramatically slowed and in some cases a well-adapted population never establishes. Thus, high propagule pressure does not necessarily lead to greater invasability. We believe that the model framework described in this paper can be a powerful tool for biologists interested in the genetics and evolution of invasive species, and spatially structured populations in general. Web of Science Theoretical/Modeling terrestrial Invasion Hyp. Propagule Pressure 3527 Vasquez, EA; Glenn, EP; Brown, JJ; Guntenspergen, GR; Nelson, SG 2005 Salt tolerance underlies the cryptic invasion of North American salt marshes by an introduced haplotype of the common reed Phragmites australis (Poaceae) journal MARINE ECOLOGY-PROGRESS SERIES 298 0 1 8 A distinct, non-native haplotype of the common reed Phragmites australis has become invasive in Atlantic coastal Spartina marshes. We compared the salt tolerance and other growth characteristics of the invasive M haplotype with 2 native haplotypes (F and AC) in greenhouse experiments. The M haplotype retained 50 % of its growth potential up to 0.4 M NaCl, whereas the F and AC haplotypes did not grow above 0.1 M NaCl. The M haplotype produced more shoots per gram of rhizome tissue and had higher relative growth rates than the native haplotypes on both freshwater and saline water treatments. The M haplotype also differed from the native haplotypes in shoot water content and the biometrics of shoots and rhizomes. The results offer an explanation for how the M haplotype is able to spread in coastal salt marshes and support the conclusion of DNA analyses that the M haplotype is a distinct ecotype of R australis. Web of Science Phragmites australis United States Greenhouse wetland Wetland Invasion Hyp. Inherent Superiority Broad Tolerances primary 3528 Vila-Gispert, A; Alcaraz, C; Garcia-Berthou, E 2005 Life-history traits of invasive fish in small Mediterranean streams journal BIOLOGICAL INVASIONS 7 1 107 116 We compared the life-history traits of native and invasive fish species from Catalan streams in order to identify the characters of successful invasive fish species. Most of the exotic fish species were characterized by large size, long longevity, late maturity, high fecundity, few spawnings per year, and short reproductive span, whereas Iberian native species exhibited predominantly the opposite suite of traits. Species native to the southeastern Pyrenees watershed were also significantly different from species native to the rest of the Iberian Peninsula but not native to this watershed. Iberian exotic species come predominantly from large river basins, whereas Catalan streams (and other small, coastal river basins) correspond to basins and streams of a smaller size and different hydrology, with differences in species composition and life-history traits of fish. The occurrence and spread of invasive species was not significantly related to life-history traits but to introduction date. The successful prediction of future invasive species is limited due to small differences in life-history and ecological traits between native and exotic species. Fecundity, age at maturity, water quality flexibility, tolerance to pollution and habitat seem the most discriminating life-history variables. Web of Science Many Spain Statistical/Meta-analysis lotic Invasion Hyp. Inherent Superiority Superior Competitor;High Reprod. Output herbivore;omnivore;predator 3529 Vivian-Smith, G; Panetta, FD 2005 Seedling recruitment, seed persistence and aspects of dispersal ecology of the invasive moth vine, Araujia sericifera ( Asclepiadaceae) journal AUSTRALIAN JOURNAL OF BOTANY 53 3 225 230 We investigated germination, seedling emergence and seed persistence of the invasive moth vine (Araujia sericifera Brot.) under controlled and field conditions in south-eastern Queensland. Fresh seed showed high viability (99.5%) and germinated readily, with 97.2% of all recorded germinations occurring within 14 days. Mean germination rates ranged from 74 to 100% across the range of temperature (10/20 degrees C, 15/25 degrees C and 20/30 degrees C alternating 12-h thermoperiods) and light (0- and 12-h photoperiods) treatments. Germination was significantly reduced only under cool, dark conditions. In a 24-month field experiment, seedling emergence was greatest for seeds buried at 1 cm (mean = 96.3%), intermediate for seeds buried at 5 cm (mean = 62.7%) and least for surface-sown seeds (mean = 30.7%). Seed persistence under field conditions was low, declining rapidly to 3.9% at 6 months and to 0.67% at 24 months. Moth vine's capacity to germinate readily and the rapid depletion of seeds under field conditions indicate that the species has a transient seed bank in south-eastern Queensland. In an additional experiment testing the capacity of seeds for secondary dispersal by water, the mean floating time of seeds was 15.4 days, suggesting that water could act as a secondary dispersal vector, contributing to long-distance dispersal. We recommend that surveillance methods for detecting moth-vine populations should consider both water-flow patterns and wind direction. Web of Science Araujia sericifera Australia Queensland Field - Experimental;Lab terrestrial Invasion Hyp. Inherent Superiority primary 3530 Von Holle, B 2005 Biotic resistance to invader establishment of a southern Appalachian plant community is determined by environmental conditions journal JOURNAL OF ECOLOGY 93 1 16 26 1 Tests of the relationship between resident plant species richness and habitat invasibility have yielded variable results. I investigated the roles of experimental manipulation of understorey species richness and overstorey characteristics in resistance to invader establishment in a floodplain forest in south-western Virginia, USA. 2 I manipulated resident species richness in experimental plots along a flooding gradient, keeping plot densities at their original levels, and quantified the overstorey characteristics of each plot. 3 After manipulating the communities, I transplanted 10 randomly chosen invaders from widespread native and non-native forest species into the experimental plots. Success of an invasion was measured by survival and growth of the invader. 4 Native and non-native invader establishment trends were influenced by different aspects of the biotic community and these relationships depended on the site of invasion. The most significant influence on non-native invader survival in this system of streamside and upper terrace plots was the overstorey composition. Non-native species survival in the flooded plots after 2 years was significantly positively related to proximity to larger trees. However, light levels did not fully explain the overstorey effect and were unrelated to native survivorship. The effects of understorey richness on survivorship depended on the origin of the invaders and the sites they were transplanted into. Additionally, native species growth was significantly affected by understorey plot richness. 5 The direction and strength of interactions with both the overstorey (for non-native invaders) and understorey richness (for natives and non-natives) changed with the site of invasion and associated environmental conditions. Rather than supporting the hypothesis of biotic resistance to non-native invasion, my results suggest that native invaders experienced increased competition with the native understorey plants in the more benign upland habitat and facilitation in the stressful riparian zone. Web of Science Many United States Virginia terrestrial Deciduous Forest;Riparian Invasion Hyp. Community Species Richness primary 3531 Walker, S; Wilson, JB; Lee, WG 2005 Does fluctuating resource availability increase invasibility? Evidence from field experiments in New Zealand short tussock grassland journal BIOLOGICAL INVASIONS 7 2 195 211 The theory of fluctuating resource availability proposes that the susceptibility of a plant community to invasion by new species (i.e., invasibility) depends upon conditions of intermittent resource enrichment coinciding with the presence of invading propagules. We compared the response of a rapidly invading forb (Hieracium pilosella L.) between different experimental treatments in a short tussock grassland in New Zealand, over 6-12 years, to determine whether the theory explains differences in invasibility. The theory predicts that environments subject to periodic resource enrichment will be more invasible than those with more stable resource-supply rates. In our study, H. pilosella did not increase more rapidly in treatments subject to periodic resource pulses (fertiliser and water) than in those with more stable resource supplies. Also contrary to the predictions of the theory, the rate of invasion of H. pilosella did not increase following an increase in the rate of supply of water or nutrient resources, or following treatments that temporarily reduced resource uptake in the community, including grazing. H. pilosella did not increase immediately following abrupt increases in water and nutrient supply and removal of the dominant grass species with herbicide, as predicted by the theory, although temporary increases in resident exotic guilds indicated that the intensity of competition for resources was reduced. Neither H. pilosella nor resident exotic guilds showed increased cover growth rates following resumed grazing. The rate of invasion by H. pilosella was not correlated with species richness, a result consistent with one of the predictions of the theory. Therefore, short-lived events that temporarily reduced or suspended competition did not appear to determine the invasion success of this particular species in this region. In New Zealands perennial short tussock grasslands, the characteristics of the resident plant community may be more critical than resource fluctuations in determining invasion success of H. pilosella. Invasion of H. pilosella may be most successfully controlled here by promoting a successional physiognomic shift to a taller, shrub-and-tussock-dominated canopy that competitively excludes low-growing forbs. Web of Science Hieracium pilosella New Zealand Field - Experimental terrestrial Grassland Invasion Hyp. Fluctuating Resources primary 3559 Byers, JE 2000 Competition between two estuarine snails: Implications for invasions of exotic species journal ECOLOGY 81 11 1225 1239 Web of Science Batillaria attramentaria USA California Northern California Field - Experimental marine Intertidal/Near Shore Invasion Hyp. Inherent Superiority herbivore 3562 Chambers, Jeanne C.; Roundy, Bruce A.; Blank, Robert R.; Meyer, Susan E.; Whittaker, A. 2007 What makes Great Basin sagebrush ecosystems invasible by Bromus tectorum? journal ECOLOGICAL MONOGRAPHS 77 2 117 145 Web of Science Bromus tectorum USA Nevada; Utah Field - Observational terrestrial Chaparral/Shrublands Invasion Hyp. Fluctuating Resources primary 3581 Forsyth, DM; Duncan, RP 2001 Propagule size and the relative success of exotic ungulate and bird introductions to New Zealand journal AMERICAN NATURALIST 157 12 583 595 Web of Science Field - Observational;Review;Meta-analysis terrestrial Invasion Hyp. Propagule Pressure herbivore;omnivore 3588 Grotkopp, E; Rejmanek, M; Rost, TL 2002 Toward a causal explanation of plant invasiveness: Seedling growth and life-history strategies of 29 pine (Pinus) species journal AMERICAN NATURALIST 159 9 396 419 Web of Science Pinus spp. Field - Observational terrestrial Coniferous Forest Invasion Hyp. Inherent Superiority Rapid Growth primary 3590 Hastings, A; Cuddington, K; Davies, KF; Dugaw, CJ; Elmendorf, S; Freestone, A; Harrison, S; Holland, M; Lambrinos, J; Malvadkar, U; Melbourne, BA; Moore, K; Taylor, C; Thomson, D 2005 The spatial spread of invasions: new developments in theory and evidence journal ECOLOGY LETTERS 8 2 91 101 Web of Science Theoretical/Modeling;Review 3592 Hector, A; Dobson, K; Minns, A; Bazeley-White, E; Lawton, JH 2001 Community diversity and invasion resistance: An experimental test in a grassland ecosystem and a review of comparable studies journal ECOLOGICAL RESEARCH 16 11 819 831 Web of Science Many Garden;Review terrestrial Grassland Invasion Hyp. Community Species Richness primary 3603 Levine, JM; Adler, PB; Yelenik, SG 2004 A meta-analysis of biotic resistance to exotic plant invasions journal ECOLOGY LETTERS 7 3 975 989 Web of Science Review;Meta-analysis Invasion Hyp. Other 3606 Liu, Hong; Stiling, Peter 2006 Testing the enemy release hypothesis: a review and meta-analysis journal BIOLOGICAL INVASIONS 8 13 1535 1545 Web of Science Review;Meta-analysis Invasion Hyp. Enemy Release 3650 van Kleunen, Mark; Weber, Ewald; Fischer, Markus 2010 A meta-analysis of trait differences between invasive and non-invasive plant species journal ECOLOGY LETTERS 13 6 235 245 Web of Science Review;Meta-analysis primary 3651 Veltman, CJ; Nee, S; Crawley, MJ 1996 Correlates of introduction success in exotic New Zealand birds journal AMERICAN NATURALIST 147 9 542 557 Web of Science Many Review;Meta-analysis terrestrial Invasion Hyp. Propagule Pressure herbivore;omnivore;predator