Quantifying exposure of amphibian species to heat waves, cold spells, and droughts.

Globally, amphibians face severe threats, such as climate change and associated extreme events. Our goal was to quantify global amphibian exposure to 3 classes of extreme events: heat waves, cold spells, and droughts. We used the MERRA-2 extreme climate events data and the standardized precipitation-evapotranspiration index database to investigate where these events have increased over the last 40 years. We used the International Union for Conservation of Nature (IUCN) database of global amphibian distributions (7202 species) to calculate the level of exposure to extreme events for each species, classifying species as exposed if their distribution had ≥50% overlap with areas experiencing substantial increases of extreme events. To assess whether exposure is associated with amphibian declines, we used logistic regression to analyze the relationship between extreme event exposure and status changes on the IUCN Red List. Heat waves and droughts increased notably in Amazonia, Madagascar, and Europe. Among the 3 classes of events, exposure was highest to heat waves (40% of species exposed), followed by droughts (16% exposed). Exposure to different event classes was uneven with respect to geography and taxonomy. Some areas (e.g., Amazonia, Madagascar) and families (e.g., Mantellidae, Rhinodermatidae) had nearly 100% of constituent species classified as exposed to at least one event class. Exposure to heat waves (odds ratio 1.8) and droughts (odds ratio 1.7) was associated with status deteriorations since 2004. Our findings provide insight into amphibian biodiversity hotspots and taxonomic groups that may be particularly susceptible to extreme climate events, suggesting that these events play a causative role in ongoing declines. Understanding the aspects of species biology that influence susceptibility to extreme events, as well as interactions with other factors (e.g., disease), will be important for understanding the role of climate change in driving amphibian declines.