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Exotic Invasions (exotic + invasion)

Distribution by Scientific Domains

Life Sciences	100%

Distribution within Life Sciences

Ecology & Organismal Biology	50%

Selected Abstracts

Anthropogenic impacts upon plant species richness and net primary productivity in California

ECOLOGY LETTERS, Issue 2 2005
John W. Williams
Abstract We assess the importance of anthropogenic land-use, altered productivity, and species invasions for observed productivity,richness relationships in California. To this end, we model net primary productivity (NPP) c. 1750 AD and at present (1982,1999) and map native and exotic vascular plant richness for 230 subecoregions. NPP has increased up to 105% in semi-arid areas and decreased up to 48% in coastal urbanized areas. Exotic invasions have increased local species diversity up to 15%. Human activities have reinforced historical gradients in species richness but reduced the spatial heterogeneity of NPP. Structural equation modelling suggests that, prior to European settlement, NPP and richness were primarily controlled by precipitation and other abiotic variables, with NPP mediating richness. Abiotic variables remain the strongest predictors of present NPP and richness, but intermodel comparisons indicate a significant anthropogenic impact upon statewide distributions of NPP and richness. Exotic and native species each positively correlate to NPP after controlling for other variables, which may help explain recent reports of positively associated native and exotic richness. [source]

Potential selection in native grass populations by exotic invasion

MOLECULAR ECOLOGY, Issue 8 2006
BRIAN A. MEALOR
Abstract Ecological impacts of invasive plant species are well documented, but the genetic response of native species to invasive dominance has been often overlooked. Invasive plants can drastically alter site conditions where they reach dominance, potentially exerting novel selective pressures on persistent native plant populations. Do native plant populations in old exotic invasions show evidence of selection when compared to conspecific populations in adjacent, noninvaded areas? We employ amplified fragment length polymorphism (AFLP) analysis to screen a large number of loci from two native grass species (Hesperostipa comata (Trin. & Rupr.) Barkworth and Sporobolus airoides Torr.) that occur in old infestations of the invasive forb Acroptilon repens. We then compare observed locus by locus FST values with distributions of FST estimated from simulation models under expectation of neutrality. We also compare the proportion of loci possibly linked to selection and those not linked to selection which exhibit parallel trends in divergence between two community types (invaded, noninvaded). Few loci (H. comata, 2.6%; S. airoides, 8.7%) in the two native grasses may be linked to genes under the influence of selection. Also, loci linked to selection showed a greater portion of parallel trends in divergence than neutral loci. Genetic similarities between community types were less than genetic similarity within community types suggesting differentiation in response to community alteration. These results indicate that a small portion of scored AFLP loci may be linked to genes undergoing selection tied to community dominance by an invasive species. We propose that native plants in communities dominated by exotic invasives may be undergoing natural selection. [source]

A meta-analysis of biotic resistance to exotic plant invasions

ECOLOGY LETTERS, Issue 10 2004
Jonathan M. Levine
Abstract Biotic resistance describes the ability of resident species in a community to reduce the success of exotic invasions. Although resistance is a well-accepted phenomenon, less clear are the processes that contribute most to it, and whether those processes are strong enough to completely repel invaders. Current perceptions of strong, competition-driven biotic resistance stem from classic ecological theory, Elton's formulation of ecological resistance, and the general acceptance of the enemies-release hypothesis. We conducted a meta-analysis of the plant invasions literature to quantify the contribution of resident competitors, diversity, herbivores and soil fungal communities to biotic resistance. Results indicated large negative effects of all factors except fungal communities on invader establishment and performance. Contrary to predictions derived from the natural enemies hypothesis, resident herbivores reduced invasion success as effectively as resident competitors. Although biotic resistance significantly reduced the establishment of individual invaders, we found little evidence that species interactions completely repelled invasions. We conclude that ecological interactions rarely enable communities to resist invasion, but instead constrain the abundance of invasive species once they have successfully established. [source]

Potential selection in native grass populations by exotic invasion

Microsatellite loci for Ponto-Caspian gobies: markers for assessing exotic invasions

MOLECULAR ECOLOGY RESOURCES, Issue 2 2009
KEVIN A. FELDHEIM
Abstract We developed and tested eight polymorphic microsatellite loci for Ponto-Caspian ,neogobiin' gobies, many of which are invasive in Eurasia and North America, whose study will aid understanding of the population genetics underlying their success. We tested samples from one to two locations from 12 taxa in the recently revised genera Babka, Benthophilus, Mesogobius, Neogobius = Apollonia, Ponticola and Proterorhinus; including the bighead, Caspian, knout, monkey, racer, round, tadpole and tubenose gobies; and taxa from introduced vs. native populations, those diverging between fresh and marine waters, and those differentiated between the Black and Caspian Seas. Populations conformed to Hardy,Weinberg equilibrium expectations, averaging five to 15 alleles per locus and 0.11 to 0.67 mean heterozygosity. Allelic variation significantly differentiated among all taxa and populations. [source]

Negative native,exotic diversity relationship in oak savannas explained by human influence and climate

OIKOS, Issue 9 2009
Patrick L. Lilley
Recent research has proposed a scale-dependence to relationships between native diversity and exotic invasions. At fine spatial scales, native,exotic richness relationships should be negative as higher native richness confers resistance to invasion. At broad scales, relationships should be positive if natives and exotics respond similarly to extrinsic factors. Yet few studies have examined both native and exotic richness patterns across gradients of human influence, where impacts could affect native and exotic species differently. We examined native,exotic richness relationships and extrinsic drivers of plant species richness and distributions across an urban development gradient in remnant oak savanna patches. In sharp contrast to most reported results, we found a negative relationship at the regional scale, and no relationship at the local scale. The negative regional-scale relationship was best explained by extrinsic factors, surrounding road density and climate, affecting natives and exotics in opposite ways, rather than a direct effect of native on exotic richness, or vice versa. Models of individual species distributions also support the result that road density and climate have largely opposite effects on native and exotic species, although simple life history traits (life form, dispersal mode) do not predict which habitat characteristics are important for particular species. Roads likely influence distributions and species richness by increasing both exotic propagule pressure and disturbance to native species. Climate may partially explain the negative relationship due to differing climatic preferences within the native and exotic species pools. As gradients of human influence are increasingly common, negative broad-scale native,exotic richness relationships may be frequent in such landscapes. [source]