Evolution of dispersal and the maintenance of fragmented metapopulations

Because it affects dispersal risk and modifies competition levels, habitat fragmentation directly constrains dispersal evolution. When dispersal is traded off against competitive ability, increased fragmentation is often expected to select higher dispersal. Such evolutionary effects could favor the maintenance of the metapopulation by fostering spatial rescue effects. Using an evolutionary model, we first investigate how dispersal evolves in a metapopulation when fragmentation and aggregation of this fragmentation are fixed. Our results suggest that high fragmentation indeed selects for dispersal increase, but this effect is largely reduced in aggregated landscapes, to the point of being nonexistent at the highest aggregation levels. Contrasted dispersal strategies coexist at high fragmentation levels and with no or low aggregation. We then simulate time-varying fragmentation scenarios to investigate the conditions under which evolutionary rescue of the metapopulation happens. Faster evolution of dispersal favors the persistence of the metapopulation, but this effect is very reduced in aggregated landscapes. Overall, our results highlight how the speed of evolution of dispersal and the structuration of the fragmentation will largely constrain metapopulation survival in changing environments.