PS 23-30 - Life-stage specific thermal tolerance explain climate vulnerability of amphibians globally

Background/Question/Methods

Global warming threatens numerous species worldwide. Ectotherms are especially at risk due to their reliance on the environment to maintain body temperature. Many ectotherms like amphibians have a complex life cycle with stages that differ in morphology, physiology, and habitat use, which could promote stage-specific thermal responsiveness. Accurately quantifying thermal metrics at different life stages is therefore essential to identify the risks associated with global warming. In this study, we provide the first systematic global analysis of stage-specific thermal tolerance of larvae and adult amphibians and estimate their vulnerability under future climate change scenarios.

We combined observational and experimental data on amphibian larvae and adults to calculate stage-specific thermal metrics for 252 species around the globe. Since data for one stage was unavailable for some species, we used phylogenetic imputation to obtain the missing metrics. We used this data to test (1) how thermal metrics are distributed across the phylogeny, (2) how thermal tolerances differ across stages, and (3) how thermal sensitivity varies with latitude. Finally, we applied climate models from the Earth System Grid Federation (ESGF) to identify (4) how the percentage of amphibians that would be at risk will change under future climate change scenarios by 2100.

Results/Conclusions

We found a strong phylogenetic signal (Pagel’s lambda p < 0.001) for both T_Max and T_Min. Furthermore, T_Max of the larval (tadpole) stage is significantly higher by 2.69°C than T_Max of adults, and the T_Range was larger for larva than for adults by 4.17°C, indicating that adults have smaller thermal niches and are more sensitive to temperature extremes. Disparity in thermal tolerance across stages might be due to the delicate water balance mechanism of adult amphibians. At a global geographic scale, we found amphibian T_Max decreased with absolute latitude while T_Min increased, leading to an increase in T_Range with absolute latitude. Accounting for species-specific microclimate, our simulations indicate that between 31.34% to 51.59% of amphibian species will experience temperatures that exceed their thermal tolerance limits by 2100 depending on the specific Shared Socioeconomic Pathway scenario is followed (SSP 1-1.9 vs SSP 5-8.5).

Our findings suggest that adult amphibians might be more susceptible to the temperature increase and thus demands more attention in conservational biology. Future work should be done to evaluate other metamorphic organisms' stage-specific thermal metrics. Our conclusion will be relevant to conservationists focusing on amphibian habitat restoration and provide reference on global warming's impact on biodiversity.