Beyond Refugia: Fish and Wildlife Exploit Thermal Heterogeneity Not Only to Survive, but Also to Thrive

At the southern extent of their range, salmonids and other fishes often rely on coldwater refugia--patches of habitat that remain physiologically suitable during periods of warm weather or low flows. Much less is known about the ecological significance of thermal heterogeneity at higher latitudes, where species are less likely to experience heat stress and more likely to be limited by the physiological constraints of cold water. Here I review a series of recent case studies that demonstrate how salmonids in Alaska actively exploit thermal heterogeneity and strongly benefit from the complementary effects of warm and cold habitats, via a variety of ecological mechanisms. Further, I show how the shifting habitat mosaic of intact floodplains can buffer the growth potential of fish from strong inter-annual variation in temperature and precipitation. While many studies attempt to predict the biological responses of fishes to climate change, more work is needed to understand how habitat features mediate this response and contribute to the resilience of freshwater ecosystems.