Amphibians reveal unexpectedly large differences in potential climate change responses among ecologically similar habitat specialists

Abstract

Climate change is substantially impacting earth’s biodiversity, with a massive number of affected species that are difficult to study comprehensively. An “indicator species” approach that generalizes species-specific climate change impacts to broader groups (e.g., ecological groups) could theoretically help overcome this challenge and streamline climate-smart conservation planning. We assessed this approach’s viability using four specialist amphibians (Ascaphus montanus, Dicamptodon copei, Plethodon idahoensis, and Plethodon vandykei), for which we expected convergent forecasted trajectories under climate change given that all four species belong to the same group of narrowly groundwater-dependent amphibians in the Pacific Northwest, USA. Using boosted regression trees, we constructed species distribution models (SDMs) for each species and (if applicable) major intraspecific lineage, then forecasted species’ trajectories under two climate change scenarios (SSP370 and SSP585) and timeframes (mid-century and late-century). Contrary to our expectation, potential trajectories varied widely among species; most notably, a late-century three-fold potential gain in highly-suitable areas for P. idahoensis was contrasted with a potential three-fold loss for the sister species P. vandykei. Further, lineage-specific SDMs for P. vandykei suggested negligible climate change vulnerability for coastal populations but major vulnerability for Cascades populations. Thus, divergent climate change projections persisted even at an intraspecific scale. Based on our findings, the use of climate change “indicator species” to represent broader groups can be misleading, even within narrowly-defined groups wherein organisms have considerable genetic and ecological overlaps. Lastly, species-tailored variables (e.g., stream or cliff-face seep refugial properties) had consistently high explanatory power, yet many lacked the necessary data to forecast future species’ trajectories, highlighting an important future research need.