Mechanisms of Maintenance of Species Diversity

TLDR

Stable coexistence is achieved through equalizing mechanisms that reduce fitness differences and stabilizing mechanisms that amplify negative intraspecific interactions, such as resource partitioning, frequency‑dependent predation, and environmental fluctuations. The study aims to broaden the view of diversity maintenance by incorporating species turnover into models of unstable coexistence. Coexistence mechanisms operate in two major ways: equalizing mechanisms minimize average fitness differences, while stabilizing mechanisms increase negative intraspecific interactions relative to interspecific ones.

Abstract

▪ Abstract The focus of most ideas on diversity maintenance is species coexistence, which may be stable or unstable. Stable coexistence can be quantified by the long-term rates at which community members recover from low density. Quantification shows that coexistence mechanisms function in two major ways: They may be (a) equalizing because they tend to minimize average fitness differences between species, or (b) stabilizing because they tend to increase negative intraspecific interactions relative to negative interspecific interactions. Stabilizing mechanisms are essential for species coexistence and include traditional mechanisms such as resource partitioning and frequency-dependent predation, as well as mechanisms that depend on fluctuations in population densities and environmental factors in space and time. Equalizing mechanisms contribute to stable coexistence because they reduce large average fitness inequalities which might negate the effects of stabilizing mechanisms. Models of unstable coexitence, in which species diversity slowly decays over time, have focused almost exclusively on equalizing mechanisms. These models would be more robust if they also included stabilizing mechanisms, which arise in many and varied ways but need not be adequate for full stability of a system. Models of unstable coexistence invite a broader view of diversity maintenance incorporating species turnover.