Climate Relicts: Past, Present, Future

Populations left behind during climate-driven range shifts can persist in enclaves of benign environmental conditions within an inhospitable regional climate. Such climate relicts exist in numerous plant and animal species worldwide, yet our knowledge of them is fragmented and lacks a general framework. Here we synthesize the empirical evidence considering (a) relict habitats, (b) abiotic and biotic constraints on population dynamics, (c) mechanisms promoting population persistence, and (d) uncertainties concerning their future prospects. We identify three major types of climate relicts: (a) those constrained primarily by climate-driven abiotic factors, (b) those restricted to areas that are inaccessible to antagonistic species for climatic reasons, and (c) those requiring a host or mutualistic species that is itself limited by climate. Understanding the formation and functioning of climate relicts is essential for their conservation and for our understanding of the response of species and populations to climate change.