Habitat isolation shapes the recovery of aquatic insect communities from a pesticide pulse.
The role of spatial processes in ecotoxicology is largely ignored. Yet, together with species-specific sensitivities to the pollutant, spatial processes may determine community recovery and the resulting community composition after a pollution event. We investigated the isolation-specific potential for internal recovery by reproduction and external recovery by dispersal after a pesticide pulse in experimental aquatic insect communities along an isolation gradient. External recovery was important in the univoltine species and in a multivoltine species that went locally extinct but only when a source population was nearby. Internal recovery occurred in all multivoltine species and was unexpectedly stronger in more isolated communities, probably because of release from a dispersal-limited key predator. As a result, community recovery and resulting changes in composition strongly depended on isolation and species differences in the potential for external recovery through dispersal and internal recovery through reproduction. Synthesis and applications. Our results indicate that while the immediate impact of a toxicant on natural communities is shaped by species sensitivities, their recovery is primarily dependent on the degree of isolation. Risk assessment and the protection of communities under toxicant threat may improve greatly from considering the spatial context: isolated communities and communities with poor dispersers should receive extra protection to safeguard their member species. Ideally, land use planning should strive to remediate isolation of natural communities under threat in agricultural landscapes. Where this is not possible, spatial regulation of pesticide application may considerably improve protection of extant diversity.