41 research outputs found
Plant Species\u27 Origin Predicts Dominance and Response to Nutrient Enrichment and Herbivores in Global Grasslands
Exotic species dominate many communities; however the functional significance of species\u27 biogeographic origin remains highly contentious. This debate is fuelled in part by the lack of globally replicated, systematic data assessing the relationship between species provenance, function and response to perturbations. We examined the abundance of native and exotic plant species at 64 grasslands in 13 countries, and at a subset of the sites we experimentally tested native and exotic species responses to two fundamental drivers of invasion, mineral nutrient supplies and vertebrate herbivory. Exotic species are six times more likely to dominate communities than native species. Furthermore, while experimental nutrient addition increases the cover and richness of exotic species, nutrients decrease native diversity and cover. Native and exotic species also differ in their response to vertebrate consumer exclusion. These results suggest that species origin has functional significance, and that eutrophication will lead to increased exotic dominance in grasslands
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A Tale of Two Spills: Novel Science and Policy Implications of an Emerging New Oil Spill Model
The 2010 Deepwater Horizon oil release posed the challenges of two types of spill: a familiar spill characterized by buoyant oil, fouling and killing organisms at the sea surface and eventually grounding on and damaging sensitive shoreline habitats, and a novel deepwater spill involving many unknowns. The subsurface retention of oil as finely dispersed droplets and emulsions, wellhead injection of dispersants, and deepwater retention of plumes of natural gas undergoing rapid microbial degradation were unprecedented and demanded the development of a new model for deepwater well blowouts that includes subsurface consequences. Existing governmental programs and policies had not anticipated this new theater of impacts, which thereby challenged decisionmaking on the spill response, on the assessment of natural resource damages, on the preparation for litigation to achieve compensation for public trust losses, and on restoration. Modification of laws and policies designed to protect and restore ocean resources is needed in order to accommodate oil drilling in the deep sea and other frontiers.Keywords: Ecosystem, Petroleum, Deep water horizon, Gulf of Mexico, BlowoutKeywords: Ecosystem, Petroleum, Deep water horizon, Gulf of Mexico, Blowou
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Response to Comments on "Productivity Is a Poor Predictor of Plant Species Richness"
Pan et al. claim that our results actually support a strong linear positive relationship between productivity and richness, whereas Fridley et al. contend that the data support a strong humped relationship. These responses illustrate how preoccupation with bivariate patterns distracts from a deeper understanding of the multivariate mechanisms that control these important ecosystem properties
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Plant species' origin predicts dominance and response to nutrient enrichment and herbivores in global grasslands
Exotic species dominate many communities; however the functional significance of species’ biogeographic origin remains highly contentious. This debate is fuelled in part by the lack of globally replicated, systematic data assessing the relationship between species provenance, function and response to perturbations. We examined the abundance of native and exotic plant species at 64 grasslands in 13 countries, and at a subset of the sites we experimentally tested native and exotic species responses to two fundamental drivers of invasion, mineral nutrient supplies and vertebrate herbivory. Exotic species are six times more likely to dominate communities than native species. Furthermore, while experimental nutrient addition increases the cover and richness of exotic species, nutrients decrease native diversity and cover. Native and exotic species also differ in their response to vertebrate consumer exclusion. These results suggest that species origin has functional significance, and that eutrophication will lead to increased exotic dominance in grasslands
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Predicting invasion in grassland ecosystems: is exotic dominance the real embarrassment of richness?
Invasions have increased the size of regional species pools, but are typically assumed to reduce native diversity. However, global-scale tests of this assumption have been elusive because of the focus on exotic species richness, rather than relative abundance. This is problematic because low invader richness can indicate invasion resistance by the native community or, alternatively, dominance by a single exotic species. Here, we used a globally replicated study to quantify relationships between exotic richness and abundance in grass-dominated ecosystems in 13 countries on six continents, ranging from salt marshes to alpine tundra. We tested effects of human land use, native community diversity, herbivore pressure, and nutrient limitation on exotic plant dominance. Despite its widespread use, exotic richness was a poor proxy for exotic dominance at low exotic richness, because sites that contained few exotic species ranged from relatively pristine (low exotic richness and cover) to almost completely exotic-dominated ones (low exotic richness but high exotic cover). Both exotic cover and richness were predicted by native plant diversity (native grass richness) and land use (distance to cultivation). Although climate was important for predicting both exotic cover and richness, climatic factors predicting cover (precipitation variability) differed from those predicting richness (maximum temperature and mean temperature in the wettest quarter). Herbivory and nutrient limitation did not predict exotic richness or cover. Exotic dominance was greatest in areas with low native grass richness at the site- or regional-scale. Although this could reflect native grass displacement, a lack of biotic resistance is a more likely explanation, given that grasses comprise the most aggressive invaders. These findings underscore the need to move beyond richness as a surrogate for the extent of invasion, because this metric confounds monodominance with invasion resistance. Monitoring species’ relative abundance will more rapidly advance our understanding of invasions.This is the publisher’s final pdf. The published article is copyrighted by John Wiley & Sons Ltd and can be found at: http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-2486
HOW INTERACTIONS BETWEEN ECOLOGY AND EVOLUTION INFLUENCE CONTEMPORARY INVASION DYNAMICS
The literature on biological invasions has principally focused on understanding the ecological controls and consequences of invasions. Invading populations, however, often experience rapid evolutionary changes associated with or soon after their introduction. Ecological and evolutionary processes can, therefore, potentially interact over relatively short timescales. A number of recent studies have begun to document these interactions and their effect on short-term invasion dynamics: (1) The degree to which founder effects, drift, and inbreeding alter the genetic composition of introduced populations is mediated by migration and dispersal patterns, the population dynamics of founding populations, and life history. The genetic changes associated with founding can themselves feed back on population dynamics and life history. (2) Patterns of human-mediated dispersal and landscape change can influence the frequency and pattern of hybridization, which in turn can alter invasion dynamics. These altered invasion dynamics can influence the frequency and pattern of subsequent hybridization and introgression. (3) Strong selection can rapidly generate ecotypic specialization. Dispersal patterns, founder effects, genetic system, and life history influence the rate of local adaptation, its persistence, and its distribution in a landscape. (4) Introduced populations are subject to selection on life history traits and can serve as selective pressure on the life history traits of native populations. Life history evolution in both natives and aliens can influence ecological interactions and population dynamics, which in turn can influence the evolution of life history. Too few studies have investigated these interactions to definitively assess their overall generality or to determine how the.-relative interaction strength of ecology and evolution varies across taxa or ecosystems. However, the studies that do exist report interactions from a wide breadth of taxa and from all stages in the invasion process. This suggests that ecological-evolutionary interactions may have a more pervasive influence on contemporary invasion dynamics than previously appreciated, and that at least in some situations an explicit understanding of the contemporary co-influence of ecology and evolution can produce more effective and predictive control strategies