Stochasticity-induced stabilization weakens in diverse communities

Abstract

Environmental stochasticity and the temporal variations of demographic rates associated with it are ubiquitous in nature. The ability of these fluctuations to stabilize a coexistence state of competing populations (sometimes known as the storage effect) is a counterintuitive feature that has aroused much interest. Here we consider the performance of environmental stochasticity as a stabilizer in diverse communities. We show that the effect of stochasticity is buffered because of the differential response of populations to environmental variations, and its stabilizing effect disappears as the number of populations increases. Of particular importance is the ratio between the autocorrelation time of the environment and the generation time. Species richness grows with stochasticity only when this ratio is smaller than the inverse of the fundamental biodiversity parameter. When stochasticity impedes coexistence and lowers the species richness, the ratio between the strength of environmental variations and the speciation (or migration) rate governs its effect.

Effects of temporal environmental stochasticity on species richness: a mechanistic unification spanning weak to strong temporal correlations

“…We derived a formula showing that the temporal correlation at which the transition occurred decreased with the community speciation rate as an inverse relationship, reflecting weaker temporal niches from the second pathway. A recent study (Pande and Shnerb 2021) also found such an inverse relationship for a different community model with TES, but using simulations that do not allow generalization of the relationship across parameter space as our formula does. Our formula indicates that TES is less likely to have a positive net effect on richness for communities with more species, such as tropical coral and tree communities.…”