Niche Overlap Is Not Enough: Same Overlap, Opposite Dynamics

Abstract

Niche overlap (NO) is a central concept in coexistence theory, determining the outcome of competitive interactions at equilibrium. Yet, NO is a composite quantity that collapses multiple mechanisms and thus cannot by itself capture community dynamics. We quantify this gap by analyzing one of the simplest out-of-equilibrium observables: temporal correlations in species abundances, widely used in microbial ecology. Within a generalized consumer-resource framework, we separate the mechanistic traits that shape dynamical responses and show that systems with identical NO can display opposite correlation patterns. The decisive predictor is the yield-depletion mismatch (YDM) - the mismatch between species depletion and yield dissimilarities. Analytical theory, stochastic simulations, and a reanalysis of microbial time-series consistently show that YDM, not NO, sets the sign and magnitude of abundance correlations, whereas instantaneous growth-rate correlations increase with NO. Our results suggest that other out-of-equilibrium properties, such as invasion probabilities and coexistence robustness, will likewise be largely independent of NO and instead controlled by distinct out-of-niche parameters.