Abstract:

Understanding species coexistence and the maintenance of biodiversity has long been the central interest of ecologists. The niche-based theory of community assembly has dominated community ecology for nearly a century, yet understanding of the mechanisms of species coexistence has remained elusive. The newly developed neutral theory of biodiversity has offered a promising alternative to the niche paradigm. The analytical elegance and simplicity of the neutral theory and its predictive power have made the theory widely popular. However, it is the very same simplicity of the theory (e.g. the symmetric assumption) that makes the theory vulnerable to stark criticisms. Widespread empirical evidence has shown that species in communities are not functionally symmetric; ecological equivalence is more a conceptual simplicity than a biological realism. Recognizing that niche and neutral processes do not have to diametrically oppose each other and a community is likely determined by the interplay of the two processes, ecologists currently are searching to reconcile the two theories by either incorporating drift into niche theory or niche into the neutral framework. However, this reconciliation process is still at its very early stage, we expect this direction will lead to a more complete understanding of community assembly mechanisms. In this paper, we provide a review on the brief histories of the niche and neutral theories, with the focus on comparing the distinct importance of the two theories in explaining community assembly. We discuss in details several integrated models that attempt to unify the niche and neutral theories. We argue that it is an essential step for any successful theory to withstand substantial experimental and field tests. The experimental tests of neutral theories are an important direction that has currently not received due attention.

Key words: species traits, ecological equivalence, stochasticity, species relative abundance, species abundance distribution