Rare niches and the ecological equivalence of species

Debate remains on the contributions of niche and neutral processes in structuring biological communities. Temporal variation in the extent to which these two processes may jointly operate makes the problem of resolving their roles even more daunting. Here, we gain insight into this problem by using deterministic and stochastic models of competitors to investigate how the occurrence of rare niches, in what is usually a neutrally structured community, affects species diversity. Rare niches are modeled by allowing each species access to unique resources, which occur with temporal variability. While results from the deterministic model are clear (rare niches provide stable coexistence to otherwise neutral competitors), demographic stochasticity complicates this picture. Stochastic rare niche models show parameter regimes where increases in rare niches actually increase extinction risk by amplifying the variance in population counts. We also use our stochastic model to evaluate the effectiveness of current empirical methods in resolving the difference between rare niche and neutral systems. We find that in many cases, stochastic variation makes niche and neutral systems indistinguishable, allowing for the possibility of niche systems to masquerade as neutral ones. These results highlight the need to better understand how demographic stochasticity and environmental variation can affect the maintenance of species diversity.