42 research outputs found
Phenological niches and the future of invaded ecosystems with climate change
In recent years, research in invasion biology has focused increasing attention on understanding the role of phenology in shaping plant invasions. Multiple studies have found non-native species that tend to flower distinctly early or late in the growing season, advance more with warming or have shifted earlier with climate change compared with native species. This growing body of literature has focused on patterns of phenological differences, but there is a need now for mechanistic studies of how phenology contributes to invasions. To do this, however, requires understanding how phenology fits within complex functional trait relationships. Towards this goal, we review recent literature linking phenology with other functional traits, and discuss the role of phenology in mediating how plants experience disturbance and stressâvia climate, herbivory and competitionâacross the growing season. Because climate change may alter the timing and severity of stress and disturbance in many systems, it could provide novel opportunities for invasionâdepending upon the dominant climate controller of the system, the projected climate change, and the traits of native and non-native species. Based on our current understanding of plant phenological and growth strategiesâespecially rapid growing, early-flowering species versus later-flowering species that make slower-return investments in growthâwe project optimal periods for invasions across three distinct systems under current climate change scenarios. Research on plant invasions and phenology within this predictive framework would provide a more rigorous test of what drives invader success, while at the same time testing basic plant ecological theory. Additionally, extensions could provide the basis to model how ecosystem processes may shift in the future with continued climate change
Nonnative grass litter enhances grazing arthropod assemblages by increasing native shrub growth
Abstract. Recent theory and research have highlighted how the brown (detritus-based) world may control the trophic structure of the green (grazing) world. Detritus can alter bottom-up control of green webs by affecting autotroph biomass and quality through its ability to alter ecosystem properties, including soil moisture and nutrient cycling. Additionally, the role of detritus as the food resource base of brown webs may subsidize omnivorous predators that can provide top-down control of green webs. Brown-green connections may be especially important following plant invasions, which often lead to increased detritus and altered food webs. I combine field experiments, observational data, and path analysis to understand how nonnative grasses impact native arthropod communities in a semiarid shrub system. Theory and correlative evidence predict that decreased shrub growth and nutritional quality, and increased feeding of detrital predators on the grazing web, would decrease the abundance of shrub arthropods. In contrast, I found nonnative litter increased shrub growth via increased soil moisture and produced a strong bottom-up increase of the grazing arthropod web; effects of detrital predators and plant quality were comparatively unimportant. I link these findings to the apparent lack of overlapping predators between the brown and green webs, and to the important abiotic role of litter in this xeric system, which increased native plants and the abundance and richness of arthropods on them
Linking the Green and Brown Worlds: the Prevalence and Effect of Multichannel Feeding in Food Webs
Recent advances in foodâweb ecology highlight that most real food webs (1) represent an interplay between producerâ and detritusâbased webs and (2) are governed by consumers which are rampant omnivores; feeding on varied prey across trophic levels and resource channels. A possible avenue to unify these advances comes from models demonstrating that predators feeding on distinctly different channels may stabilize food webs. Empirical studies suggest many consumers engage in such behavior by feeding on prey items from both livingâautotroph (green) and detritusâbased (brown) webs, what we term âmultichannel feeding,â yet we know little about how common such feeding is across systems and trophic levels, or its effect on system stability. Considering 23 empirical webs, we find that multichannel feeding is equally common across terrestrial, freshwater, and marine systems, with \u3e50% of consumers classified as multichannel consumers. Multichannel feeding occurred most often at the first consumer level, indicating that most taxa at the herbivore/detritivore level are more aptly described as multichannel consumers, and that such feeding is not restricted to predators. We next developed a simple fourâcompartment nutrient cycling model for consumers eating both autotrophs and detritus with separate parameter sets to represent aquatic vs. terrestrial ecosystems. Modeling results showed that, across terrestrial and aquatic ecosystems, multichannel feeding is stabilizing at low attack rates on autotrophs or when attack rates are asymmetric (moderate on autotrophs while low on detritus), but destabilizing at high attack rates on autotrophs, compared to herbivoryâ or detritivoryâonly models. The set of conditions with stable webs with multichannel consumers is narrower, however, for aquatic systems, suggesting that multichannel feeding may generally be more stabilizing in terrestrial systems. Together, our results demonstrate that multichannel feeding is common across ecosystems and may be a stabilizing force in real webs that have consumers with low or asymmetric attack rates
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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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 speciesâ 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 speciesâ relative abundance will more rapidly advance our understanding of invasions.This is the publisherâs 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
Data from: Scavenging: how carnivores and carrion structure communities
Recent advances in the ecology of food webs underscore
the importance of detritus and indirect predatorâprey
effects. However, most research considers detritus as an
invariable pool and predation as the only interaction
between carnivores and prey. Carrion consumption,
scavenging, is a type of detrital feeding that should have
widespread consequences for the structure and stability
of food webs. Providing access to high-quality
resources, facultative scavenging is a ubiquitous and
phylogenetically widespread strategy. In this review,
we argue that scavenging is underestimated by 16-fold
in food-web research, producing inflated predation rates
and underestimated indirect effects. Furthermore, more
energy is generally transferred per link via scavenging
than predation. Thus, future food-web research should
consider scavenging, especially in light of how major
global changes can affect scavengers
Appendix D. Two figures depicting additional path-analysis results.
Two figures depicting additional path-analysis results
Appendix B. A figure showing results of parametric MANOVA tests.
A figure showing results of parametric MANOVA tests