Climate Change, Fragmentation, and Habitat Resilience: Complex Effects on Headwater Trout Population Persistence

Increasing connectivity among habitats and subpopulations has been suggested to increase population resilience to climate change.  However, increasing connectivity between subpopulations has complex, context-dependent effects on persistence.   We used long-term data on movement and population vital rates to develop a spatially-explicit population model for stream-dwelling brook trout, and used the model to evaluate alternative connectivity and habitat resilience (relative temperature increase) scenarios.  We found that while increasing connectivity reduced extinction risk in some scenarios, this effect was strongly dependent on both the relative temperature resilience of tributary vs. mainstem habitats, as well as the direction (one-way vs. two-way) and magnitude of movement rates.  In scenarios where fish were able to leave, but not return to, resilient habitat, we found that increasing connectivity increased extinction risk.  These results underscore the importance of evaluating and predicting thermal habitat resilience under climate change and the need to incorporate this information into prioritization and conservation decisions.