Evolutionary Adaptation and the Challenges of Climate Change for Salmon Conservation

A pivotal question in the debate on the consequences of climate change for biodiversity is whether species will be able to adapt fast enough to their changing environments. The challenge is to determine rates of phenotypic change necessary to prevent extinction under different climate scenarios, and the likelihood of these rates being realized given understanding of the various mechanisms through which species can adapt. I will describe a novel simulation modeling approach to this problem, which merges ecological, quantitative genetic, and demographic considerations. The model was applied to explore potential evolutionary changes in upriver migration timing and the consequences for population persistence in sockeye salmon Oncorhynchus nerka in the Fraser River, Canada, under scenarios of future climate warming. Adult sockeye salmon are highly sensitive to increases in water temperature during their arduous upriver migration, raising concerns about the fate of these ecologically, culturally, and commercially important fish stocks in a warmer future. Our results suggest that realistically fast evolution of river entry timing could allow salmon in this system to avoid increasingly frequent stressful temperatures, with the odds of population persistence increasing in direct proportion to the magnitude of additive genetic variance. The rates of evolution required to maintain persistence under simulated scenarios of moderate to rapid river warming are plausible based on theoretical expectations, heritability estimates for salmonid phenology traits, and documented microevolutionary rates in salmon and other species. As a means to build resilience to ongoing climate change, management efforts should focus on maintaining evolutionary potential within populations, in addition to conserving key habitats and minimizing additional stressors where possible. More generally, our results demonstrate the importance and feasibility of considering evolutionary processes, in addition to ecological processes, when projecting population responses to environmental change.