Fitness declines toward range limits and local adaptation to climate affect dispersal evolution during climate-induced range shifts

Sherpa Romeo yellow journal (pre-print only, accepted for publication)

Dispersal ability will largely determine whether species track their climatic niches during climate change, a process especially important for populations at contracting (low-­latitude/low-­elevation) range limits that otherwise risk extinction. We investigate whether dispersal evolution at contracting range limits is facilitated by two processes that potentially enable edge populations to experience and adjust to the effects of climate deterioration before they cause extinction: a) climate-­‐induced fitness declines toward range limits, and b) local adaptation to a shifting climate gradient. We simulate a species distributed continuously along a temperature gradient using a spatially explicit, individual-­‐ based model. We compare range-­‐wide dispersal evolution during climate stability vs. directional climate change, with uniform fitness vs. fitness that declines toward range limits (RLs), and for a single climate genotype vs. multiple genotypes locally adapted to temperature. Dispersal decreased toward stable RLs when range-­‐wide fitness was uniform, but increased when fitness declined toward RLs, due to highly dispersive genotypes maintaining sink populations at RLs, increased kin selection in smaller populations, and an emergent fitness asymmetry that favoured dispersal in low-­‐quality habitat. However, this initial dispersal advantage at low-­‐fitness RLs did not facilitate climate tracking, as it was outweighed by an increased probability of extinction. Locally-­‐adapted genotypes benefited from staying close to their climate optima; this selected against dispersal under stable climates but for increased dispersal throughout shifting ranges, compared to cases without local adaptation. Dispersal increased at expanding RLs in most scenarios, but only increased at the range centre and contracting RLs given local adaptation to climate.