Climate change and amphibians demographics: Can we identify common mechanisms across species and regions?
There is an urgent need for conservation action to address amphibian declines. Although threats to amphibian populations might be locally idiosyncratic, global factors such as climate change are also likely contributors to declines. To better coordinate conservation efforts at national and international scales, it may be useful to identify consistent relationships, across species and regions, between demographic rates and broad-scale environmental factors. We initiated such an effort by gathering 30 long-term mark-recapture datasets from 11 species (5 frogs, 3 toads, 1 salamander and 2 newts) in North America and Western Europe. We investigated the effects of temperature and water availability on adult survival and recruitment in one of the few meta-analyses of capture-recapture data from a single group of organisms spanning multiple regions of the world.
For most amphibians, extreme temperatures and dehydration are important stressors that are driven by climate. Our goal was to identify commonalities and differences among different amphibian species and populations in their demographic response to these potential stressors. We tested a priori hypotheses developed around these potential environmental stressors, using an information-theoretic approach. We used the Pradel temporal-symmetry method to model the mark-recapture data and estimate adult survival and recruitment, while controlling for imperfect detection. To assess the relative importance of each covariate, we used model AIC weights and a deviance-ratio approach to quantify proportions of variance explained.
Preliminary results (from U.S. sites only; n=22) provide us some first insights. As expected, no single covariate stands out as the main driver of demographic variation across species. Each population shows specific responses that are likely the results of complex interactions between the species’ ecology and local site characteristics. Some generalities were apparent for ranid frogs. Mortality of adults and juveniles seems mainly affected by high temperature events and the extent of winters, which suggests high susceptibility to temperature anomalies. For other groups, no general pattern is apparent, partly due to the limited number of datasets available. No clear contrast between groups (e.g., frog vs. toad) was apparent. As we add additional regions and datasets to the analysis we hope to be able to discern patterns useful to amphibian conservation. Our approach provides a basis for investigating broad-scale drivers of demographic perturbation in amphibians and will provide a benchmark for other similar broad-scale studies.