The equilibrium theory of biodiversity dynamics: a general framework for scaling species richness and community abundance along environmental gradients

Abstract

Large-scale temporal and spatial biodiversity patterns have traditionally been explained by multitudinous particular factors and a few theories. However, these theories lack sufficient generality and problematically do not address fundamental interrelationships and coupled dynamics between resource availability, community abundance, and species richness. We propose the equilibrium theory of biodiversity dynamics (ETBD) to address these linkages, including the biodiversity-ecosystem functioning (BEF) relationship and phenomena such as niche complementarity, facilitation, and ecosystem engineering. It shows how tipping points and alternative stable states in both diversity and community abundance emerge from nonlinear BEF relationships and the dependence of origination and extinction on population size. ETBD predicts how the strength of the BEF affects scaling relationships between species richness and (meta)community abundance along different environmental gradients. Using data on global-scale variation in tree species richness, we show how the general framework is useful for clarifying the role of speciation, extinction, resource availability, and temperature in driving biodiversity patterns such as the latitudinal diversity gradient.