Relative importance of traits, climate, and threats to extinction risk in salamanders

Caudata (salamanders) is a highly threatened taxonomic group with over 60% of species estimated to be threatened. However, the species traits and extrinsic factors underlying their population decline and high extinction risk remain unclear. We conducted the first global comparative analysis to investigate which factors are associated with an increased risk of decline and extinction in salamanders. We addressed the following questions: Is extinction risk randomly distributed among salamander families, and if not, which families contain more threatened species than would be expected by chance; which species traits and extrinsic factors are important in determining the extinction risk in salamanders; and are the key factors for population decline consistent with those for extinction risk in salamanders? To determine which ecological characteristics and extrinsic factors best predict extinction risk and population decline in salamanders, we employed phylogenetic generalized least squares (PGLS) models and phylogenetic logistic regression (PGLM) models, respectively. Threatened salamanders were nonrandomly distributed across nine families, among which Cryptobranchidae and Hynobiidae contained significantly more threatened species than expected. Key predictors of salamander extinction risk were breeding strategy, geographic range size, minimum elevation, human threat index, and protected area coverage. Although geographic range size, climate change, and human threats were the most important predictors of salamander extinction risk and population decline, the effect of geographic range size was the opposite between the PGLS and PGLM models. Our results suggest that priority management should focus on extinction-prone families, particularly Cryptobranchidae and Hynobiidae, and salamanders with small range sizes and sensitivity to human disturbance or climate instability.