Invasion Success and Community Resistance In Single and Multiple Species Invasion Models: Do the Models Support the Conclusions? (original) (raw)
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Invasion impacts diversity through altered community dynamics
Journal of Ecology, 2005
Invading plant species often alter community structure, composition and, in some instances, reduce local diversity. However, the community dynamics underlying these impacts are relatively unknown. 2 Declines in species richness with invasion may occur via displacement of resident species and/or reduction of seedling establishment by the invader. These two mechanisms differ in the demographic stage of the interaction. 3 We document turnover dynamics using long-term permanent plot data to assess the mechanism(s) of invasion impacts of four exotic species on a mixed community of native and exotic species. These mechanisms were evaluated at both the neighbourhood (1-m 2 plot) and population (individual species) scales. 4 During invasion, species richness declined with increasing invader cover for three of the four invaders. All invaders reduced colonization rates, but had no effect on extinction rates at the neighbourhood scale. Populations differed in their susceptibility to invasion impacts, with significant reductions in colonization for 10 of 25 (40%) species and increases in extinction for only 4 of 29 (14%) species. 5 At neighbourhood and population scales, influences of invasion on community dynamics were essentially the same for all invaders regardless of life-form. While individual resident species had some increase in extinction probability, community richness impacts were largely driven by colonization limitation. 6 The consistency of invasion impacts across life-forms suggests establishment limitation as a general mechanism of invasion impact. This common causal mechanism should be explored in other systems to determine the extent of its generality.
EFFECT OF COMMUNITY STRUCTURE ON INVASION SUCCESS AND RATE
Ecology, 2002
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.
Methods in Ecology and Evolution, 2014
1. In 1859, Darwin had already identified environmental constraints and competition with the native community as major drivers of invasion success. Since then, a toolbox of indices and statistical approaches has been developed and commonly applied to test for the relative importance of these drivers. This toolbox is largely based on community ecology theory with the underlying hypothesis that patterns of trait (or phylogenetic) similarities between invaders and native species permit to disentangle the signatures of competition and environmental filtering. However, so far the performance of the indices and statistical approaches has not been thoroughly evaluated, and there exists no study exploring the sensitivity of the different methods given common biases in field data. This severely hampers intercomparisons of invasion studies and ultimately prevents the elaboration of general conclusions. 2. In this study, we developed a mechanistic community assembly model to simulate invasion patterns across a range of communities and tested the performance of four different indices aiming at disentangling environmental filtering vs. competition from these patterns. Furthermore, we evaluated the sensitivity of the statistical methods to biases in the data (resulting from non-equilibrium dynamics or observation errors). 3. Our results indicated that the best performing index was mean distance to the native species (the average functional distance between the invader and all the species of the community), especially in heterogeneous landscapes. Further, we demonstrated that the detection of competition was more sensitive to the presence of biases in the data than the detection of environmental filtering. 4. In conclusion, studying invasion mechanisms based on community patterns is possible when employing the appropriate statistical method, but it is highly sensitive to the quality of the data set used.
Oikos, 2013
Competition for limited resources is considered a key factor controlling invasion success. Resource availability can be viewed in either the long or short-term. Long-term availability depends on the baseline nutrient availability in the ecosystem and how those conditions shape the ecological community. Short-term resource availability fluctuates with disturbances that alter nutrient availability and/or the density and composition of the ecological community.
Biological Invasion Theories: Merging Perspectives from Population, Community and Ecosystem Scales
Biological invasions have reached an unprecedented level and the number of introduced species is still increasing worldwide. Despite major advances in invasion science, the determinants of success of introduced species, the magnitude and dimensions of their impact, and the mechanisms sustaining successful invasions are still debated. Empirical studies show divergent impacts of non-native populations on ecosystems and contrasting effects of biotic and abiotic factors on the dynamics of non-native populations; this is hindering the emergence of a unified theory of biological invasions. We propose a synthesis that merges perspectives from population, community, and ecosystem levels. Along a timeline of ecosystem transformation driven by non-native species, from historical to human-modified ecosystems, we order invasion concepts and theories to clarify their chaining and relevance during each step of the invasion process. This temporal sorting of invasion concepts shows that each concep...
Species assembly in model ecosystems, I: Analysis of the population model and the invasion dynamics
Journal of Theoretical Biology, 2011
Recently we have introduced a simplified model of ecosystem assembly for which we are able to map out all assembly pathways generated by external invasions in an exact manner. In this paper we provide a deeper analysis of the model, obtaining analytical results and introducing some approximations which allow us to reconstruct the results of our previous work. In particular, we show that the population dynamics equations of a very general class of trophic-level structured food-web have an unique interior equilibrium point which is globally stable. We show analytically that communities found as end states of the assembly process are pyramidal and we find that the equilibrium abundance of any species at any trophic level is approximately inversely proportional to the number of species in that level. We also find that the per capita growth rate of a top predator invading a resident community is key to understand the appearance of complex end states reported in our previous work. The sign of these rates allows us to separate regions in the space of parameters where the end state is either a single community or a complex set containing more than one community. We have also built up analytical approximations to the time evolution of species abundances that allow us to determine, with high accuracy, the sequence of extinctions that an invasion may cause. Finally we apply this analysis to obtain the communities in the end states. To test the accuracy of the transition probability matrix generated by this analytical procedure for the end states, we have compared averages over those sets with those obtained from the graph derived by numerical integration of the Lotka-Volterra equations. The agreement is excellent.
Community ecology theory as a framework for biological invasions
Trends in Ecology & Evolution, 2002
Biological invasions are having a major impact on the Earth's ecosystems [1], giving urgency to a better understanding of the factors that affect them. Some recent reviews have considered invasions from a variety of viewpoints, including the characteristics of invaders [2], the characteristics of invaded communities [3], resources [4,5] and natural enemies [6]. As these issues are not independent, it is essential to find a means of considering them jointly. Towards this goal, a theoretical framework for invasion ecology based on community ecology theory is proposed here. We show how this framework applies to the analysis
Scale Dependent Effects of Biotic Resistance to Biological Invasion
Ecology, 2003
As nonindigenous species continue to displace native species and disrupt ecosystems, understanding the degree to which native species richness affects the vulnerability of communities to nonindigenous species invasions has grown in importance. Native and exotic species diversity are often positively correlated in large-scale observational studies, but negatively correlated in small-scale experimental studies. This discrepancy suggests that the scale of invasion studies may be an important influence on their outcomes. Using a competition-based model that exhibits a negative relationship on a small scale, we show that changes in the number of available resources across communities can cause invasion success to become positively correlated with native species diversity at larger scales. The strength of the positive correlation, however, depends on the relationship between niche breadth and species diversity in natural communities. Adding species to a community or removing resources has a similar effect-increasing the sum of interspecific interaction strengths, which decreases invasion success.
Mechanistic reconciliation of community and invasion ecology
Community and invasion ecology have mostly grown independently. There is substantial v www.esajournals.org 1 February 2021 v Volume 12(2) v Article e03359 and testing hypotheses. Our framework paves the way for a similar transition in invasion ecology, to better capture the dynamics of multiple alien species introduced in complex communities. Reciprocally, applying insights from invasion to community ecology will help us understand and predict the future of ecological communities in the Anthropocene, in which human activities are weakening species' natural boundaries. Ultimately, the successful integration of the two fields could advance a predictive ecology that is urgently required in a rapidly changing world.
Permanence via invasion graphs: incorporating community assembly into modern coexistence theory
Journal of Mathematical Biology
To understand the mechanisms underlying species coexistence, ecologists often study invasion growth rates of theoretical and data-driven models. These growth rates correspond to average per-capita growth rates of one species with respect to an ergodic measure supporting other species. In the ecological literature, coexistence often is equated with the invasion growth rates being positive. Intuitively, positive invasion growth rates ensure that species recover from being rare. To provide a mathematically rigorous framework for this approach, we prove theorems that answer two questions: (i) When do the signs of the invasion growth rates determine coexistence? (ii) When signs are sufficient, which invasion growth rates need to be positive? We focus on deterministic models and equate coexistence with permanence, i.e., a global attractor bounded away from extinction. For models satisfying certain technical assumptions, we introduce invasion graphs where vertices correspond to proper subs...