Risk of extinction increases towards higher elevations across the world's amphibians

Aim

Life in mountains is associated with multiple features that increase the risk of demographic collapses in populations – small geographic ranges, short breeding seasons, specialization to harsh climates – leading to the hypothesis that extinction risk is exacerbated in species inhabiting higher elevations. Here, we implement the first test of this hypothesis across the amphibian tree of life – the tetrapods with the largest proportion of montane species, and nature's most threatened animals.

Location

Global.

Time Period

Present.

Major Taxa Studied

Class Amphibia.

Methods

We collated a dataset spanning 8042 species from across all three amphibian orders (Anura, Caudata and Gymnophiona). We preformed phylogenetic logistic regressions to test the predictions that extinction risk increases with elevation, and whether this effect is caused by factors previously hypothesised to drive high-elevation declines, including restrictions on species' geographic ranges, variation in their life histories and the presence of infectious disease.

Results

Globally, extinction risk increases towards higher elevations. At order-level, this relationship holds for frogs and salamanders. Even when controlling for geographic range size, life histories and infectious disease, extinction risk increases with elevation for amphibians combined and frogs globally, and in the Americas. In contrast, whereas extinction risk is greater among high-elevation Eurasian amphibians, this relationship is explained by larger body sizes and lower fecundity.

Main Conclusions

Our analyses indicate that after considering factors previously thought to explain the increase in extinction risk towards higher elevations (e.g., geographic range size, disease), elevation remains a significant predictor of amphibian extinction risk. Given that the only available tests of this hypothesis in other tetrapods (birds and reptiles) conflict with our findings, we suggest that physiological or life-history features of amphibians may explain this observed phenomenon.