The distribution of distances to the edge of species coexistence

Abstract

Here we examine how the way biotic interactions determine the robustness of species coexistence in the face of environmental perturbations. For Lotka-Volterra community models, given a set of biotic interactions, recent approaches have characterized, and applied, the probability of finding at set of species intrinsic features (e.g. growth rates) that will allow coexistence. Here we ask instead: if species do coexist, given their interactions, how fragile this coexistence should be? This change of framing allows us to derive the essential features of interactions that determine the robustness of coexistence, while not reducing it to a single number. As we illustrate on data from experimental plant community experiments, our results generate new ways to study species' contextual role in maintaining coexistence, and allows us to quantify the extent to which biotic and abiotic forces align (making coexistence more robust than expected), or oppose (making coexistence less robust than expected). Because it has both as central tenets, our work helps synthesize coexistence and ecological stability theories.