A novel metric for species vulnerability and coexistence in spatially-extended ecosystems

Abstract: We develop a theoretical framework to understand the persistence and coexistence of competitive species in a spatially explicit metacommunity model with a heterogeneous dispersal kernel. Our analysis, based on methods from the physics of disordered systems and non-Gaussian dynamical mean field theory, reveals that species coexistence is governed by a single key parameter, which we term competitive balance. From competitive balance, we derive a novel metric to quantitatively assess the vulnerability of a species, showing that abundance alone is not sufficient to determine it. Rather, a species' vulnerability crucially depends on the state of the metacommunity as a whole. We test our theory by analyzing two distinct tropical forest datasets, finding excellent agreement with our theoretical predictions. A key step in our analysis is the introduction of a new quantity - the competitive score - which disentangles the abundance distribution and enables us to circumvent the challenge of estimating both the colonization kernel and the joint abundance distribution. Our findings provide novel and fundamental insights into the ecosystem-level trade-offs underlying macroecological patterns and introduce a robust approach for estimating extinction risks.