A fundamental challenge in ecology is to understand the mechanisms that govern species diversity.  Numerical simulations have suggested that complex niche-structured models produce species abundance distributions (SADs) that are qualitatively similar to those of very simple neutral models that ignore differences between species.  However, in the absence of an analytical treatment of niche models, it is not known whether the two classes of model produce the same patterns via different mechanisms or whether biodiversity is, in fact, decoupled from niche structure. 

Results/Conclusions

Here we provide an analytical proof that the neutral model and a strong niche model give rise to exactly the same asymptotic form of SAD in the limit as diversity becomes large, and we demonstrate the validity of our result by comparing neutral- and niche-model predictions to data from a Panamanian tropical forest.  Our results show that neutral theory is a parsimonious and mathematically valid model for predicting and understanding macroscopic patterns of biodiversity in high-diversity communities, but that it cannot be used to infer an absence of niche structure or to understand ecosystem function and that it may not be valid in low-diversity communities.