Climate disequilibrium of fishes along elevation and latitudinal gradients: Implications for climate tracking

Abstract

AbstractAimDifferences in realized and fundamental thermal niches can reveal how temperature constrains species distributions. Because climate‐induced range shifts assume that temperature influences distribution limits (i.e. climate equilibrium assumption), understanding the factors that determine the realized thermal niche of species is critical for understanding their climate tracking abilities.LocationGlobal, and the Great Plains–Rocky Mountain region, U.S.A.TaxonMarine and freshwater fishes.MethodsThermal niches were evaluated for two scales: Globally (n = 95 species) andacross the Great Plains–Rocky Mountain region, U.S.A (n = 28 species). We used a combination of realized and fundamental cold limit, thermal niche data to investigate how fish species overfill or underfill their distribution limit along elevation and latitudinal gradients in the context of four hypotheses about dispersal and movement.ResultsFirst, freshwater species were not more likely than marine species to underfill their latitudinal cold‐edge limit, despite restricted dispersal in freshwater environments from biogeographic barriers. Second, biological traits of dispersal ability were not associated with patterns of overfilling or underfilling along latitudinal gradients, aside from migratory species being more likely to overfill their cold‐edge limits. Third, similar biological traits were not associated with freshwater fishes overfilling or underfilling their cold‐edge, elevation limit with respect to their cold‐edge latitudinal limit. Fourth, 78% of freshwater fish species (22 of 28) were observed underfilling their elevation limit relative to their latitudinal limit.Main conclusionsOur results reveal that the climate equilibrium assumption is not satisfied for half of marine and freshwater fishes along thermal‐spatial gradients and is largely unrelated to dispersal and movement. Freshwater fishes appear particularly limited in their distribution potential along elevation gradients, given the strong patterns of elevation underfilling.