Disturbance-generated competitive coexistence

Abstract

Explaining how competing species coexist remains a challenge in ecology. A major hypothesis is that disturbance opens up the opportunity for types with different “life history” strategies to coexist, allowing types better at getting to and using recently disturbed patches to coexist with better competitor types. A simple model introduced several decades ago demonstrated this, but its focus on patch dynamics (i.e. the dynamics of the number of patches a species occupies) gives limited insight into how coexistence-enabling variation arises from within-patch demographic strategies. Here we present, and demonstrate how to analyze, a partial differential equation model that captures the emergence of larger-scale competitive dynamics from within-patch population dynamics of species competing for patches subject to disturbance. We analyze key cases of the model framework, with competition acting in turn on each aspect of within-patch demography included in the model: reproduction, offspring-survival, and adult-survival. Insights arising from these analyses include: 1) variation between species on a simple reproduction-adult-survival trade-off can enable disturbance-generated coexistence, 2) variation along trade-offs with species’ robustness-to-competition can also generate coexistence 3) disturbance-generated coexistence may or may not involve classical “successional dynamics” within patches, and 4) coexistence is easier to generate at intermediate disturbance rates. Our work here provides new tools for more complete development of the theory of disturbance-generated coexistence.