Abstract
Theoretical studies of ecosystem models have generally concluded that large numbers of species will not stably coexist if the species are all competing for the same limited set of resources. Here, we describe a simple multi-trait model of competition where the presence of N resources will lead to the stable coexistence of up to 2N species. Our model also predicts that the long-term dynamics of the population will lie on a neutral attractor hyperplane. When the population shifts within the hyperplane, its dynamics will behave neutrally, while shifts which occur perpendicular to the hyperplane will be subject to restoring forces. This provides a potential explanation of why complex ecosystems might exhibit both niche-like and neutral responses to perturbations. Like the neutral theory of biodiversity, our model generates good fits to species abundance distributions in several datasets but does so without needing to evoke inter-generational stochastic effects, continuous species creation or immigration dynamics. Additionally, our model is able to explain species abundance correlations between independent but similar ecosystems separated by more than 1400 km inside the Amazonian forests.
Highlights
Understanding species coexistence has been a long-standing problem in ecological research
In 1970 Robert May considered more complex competition models, where species could have direct effects on each other’s dynamics, and found that stable coexistence would not occur unless species become increasingly decoupled from one another as species diversity increased [2]
We find that when limited by N resources, our model will lead to a stable coexistence of up to 2N species
Summary
Understanding species coexistence has been a long-standing problem in ecological research. Models have started to emerge which are able to explain coexistence in complex ecosystems if species interactions are constrained to have a certain structure. Posfai et al recently described a chemostat model in which constraint structure imposed by cellular trade-offs facilitated coexistence of a large number of species even in homogeneous and resource-poor environments [5]. A very different model of competition for growth space in trees leads to stable coexistence of species [6,7]. The problem of large-scale species coexistence has not yet been solved in general. Both the chemostat model and the zerosum growth space competition model rely on rather specific assumptions about underlying competition dynamics. We show that our model correctly predicts the approximate magnitude of species abundance correlations between similar but dynamically independent ecosystems
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