Habitat degradation destabilizes complex metacommunities by disrupting dispersal

Habitat loss and fragmentation are rapidly reshaping ecosystems worldwide, yet their consequences for ecological stability remain unresolved. Classical theory, pioneered by Robert May, established rigorous criteria for stability; however, these apply to spatially well-mixed communities, limiting their relevance to habitat degradation. Here, we develop a metacommunity framework that integrates classical stability theory with spatial dynamics to determine how anthropogenic habitat degradation reshapes ecosystem stability. We show that metacommunities exhibit three distinct dynamical regimes following a perturbation (e.g., drought or forest fire): stable regime (perturbations decay and species persist), reactive regime (perturbations are transiently amplified, which increases extinction risk under repeated disturbances), and unstable regime (perturbations grow, causing extinctions even after a single disturbance). Dispersal fundamentally reshapes these stability transitions, converting unstable communities into reactive ones and reactive communities into stable ones. While homogeneous dispersal progressively stabilizes communities, heterogeneous dispersal maximizes stability at intermediate strengths. We further show that habitat loss and fragmentation can be comparably effective at driving species extinctions by shifting metacommunities from stable to reactive and ultimately unstable regimes, demonstrating that fragmentation per se can be as important as habitat loss. Our findings reveal that reactivity is both an early-warning signal of impending instability and a state of elevated extinction risk under recurrent disturbances. By linking stability transitions to changes in population persistence under nonlinear dynamics, our results bridge classical stability theory with spatial ecology and provide a general framework for predicting how ecological complexity and dispersal jointly govern both ecosystem stability and population persistence under habitat degradation.