Abstract
Understanding the impacts of global climate change on biodiversity is critical to its conservation. Existing frameworks within evolutionary biology can help us predict whether, and under what conditions, adaptation may be a sufficient means for population persistance in a changing environment. Here, we consider the relevance of mountain ranges as natural systems for studying this process. Mountains compress environmental variation into short geographic distances, allowing adaptation across divergent environments to be studied at tractable spatial scales and, importantly, often in the presence of ongoing gene flow between markedly different habitats. We review empirical evidence for local adaptation across elevational gradients and argue that systems of migration-selection balance provide a particularly useful framework for connecting altitude adaptation to rapid climate adaptation. However, the analogy between altitude adaptation and climate adaptation is conditional. Elevation is a composite of temperature, oxygen availability, precipitation, radiation, and other environmental variables, only some of which are relevant to anthropogenic climate change. Moreover, inferring temporal evolutionary responses from spatial differentiation relies on a space-for-time substitution that may not always be valid. We argue that the greatest value of mountain systems therefore lies in using elevational gradients to explore whether responses to spatially varying selection can translate into evolutionary rescue. Integrating genomic and phenotypic approaches with experimental validation will be particularly important for determining when existing local adaptation provides populations with the capacity to keep pace with climate change.