COS 230-4 - Climate futures for lizards and snakes in western North America

Abstract: Terrestrial reptiles are a diverse but relatively understudied group of vertebrates that are likely to respond to changing climates because of their ectothermic physiology, relatively small body size, and limited dispersal capabilities. In western North America, reptiles occur south of ~60 degrees north latitude where they occupy nearly all ecosystems from Canada to Mexico, apart from some of the highest altitudes and latitudes. We assessed changes to fundamental climate-niche space for lizard and snake (squamate) species under time and modeled-climate scenarios to inform natural resource managers of species and habitat projections and potential corresponding conservation issues. We compiled species-occurrence data for 186 squamate species in western North America, discarded redundant or poor-quality records, and selected species with >50 occurrence points for analyses. We used eight species-distribution modelling approaches for each of 130 species, resulting in 32 models per species for each of six time-by-climate scenarios. We then combined the highest performing models per species into a single ensemble model per scenario. Maps were generated from the ensemble models to depict the climate-niche space for each species and scenario. Patterns of species richness and niche shifts were calculated from the projections at the scale of the entire study area and for 47 individual states and provinces, Canada to Mexico. Across western North America, reptile climate-niche space was projected to move north in the future, resulting in increasing species richness within individual jurisdictions across much of western United States and Canada. Sixty-eight percent of species were projected to expand their current climate-niche space rather than to shift, contract, or remain stable. Only 8.5% of species were projected to lose climate-niche space in the future, and these species primarily occurred in Mexico and the southwestern US. We found few species were projected to go extinct at the state or province level, although species were often predicted to occupy novel areas of the state or province, novel states and provinces, and often higher elevations. Most squamate species were projected to increase their niche size in the future climate scenarios. As climate niches move northwest, species are predicted to cross administrative borders, resulting in novel conservation issues for local natural resource managers. However, information on species dispersal abilities and local landscapes (e.g., barriers) are needed to contextualize predictions relative to realized future niche expansions.