Resource-use plasticity governs the causal relationship between traits and community structure in model microbial communities

Resolving the relationship between species’ traits and their relative abundance is a central challenge in ecology. Current hypotheses assume relative abundances either result from or are independent of traits. However, despite some success, these hypotheses do not integrate the reciprocal and feedback interactions between traits and abundances to predictions of community structure such as relative abundance distributions. Here we study how plasticity in resource-use traits govern the causal relationship between traits and relative abundances. We adopt a consumer-resource model that incorporates resource-use plasticity that operates to optimize organism growth, underpinned by investment constraints in physiological machinery for acquisition of resources. We demonstrate that the rate of plasticity controls the coupling strength between trait and abundance dynamics, predicting species’ relative abundance variation. We first show how plasticity in a single species in a community allows all other non-plastic species to coexist, a case of facilitation emerging from competitive interactions where a plastic species minimizes its similarity with competitors and maximizes resource-use efficiency in its environment. We apply this environment-competition trade-off to predict trait-abundance relationships and reveal that initial traits are better predictors of equilibrium abundances than final trait values. This result highlights the importance of transient dynamics that drive species sorting. The temporal scale of transients determines the strength of species sorting due to the emergence of ‘ecological equivalence’ at equilibrium. We propose trait-abundance feedback as an eco-evolutionary mechanism linking community structure and assembly, highlighting trait plasticity’s role in community dynamics.