Anuran Population Declines Occur on an Elevational Gradient in the Western Hemisphere.

Although the best known cases of enigmatic amphibian population declines come from mountains, the broader relationship between declines and elevation has not been well examined. We analyzed data from the Global Amphibian Assessment (GAA) and minimum and maximum elevation range data to study the association between elevation and population status for 1,918 anuran species in the Western hemisphere (i.e., north, central, and south America and adjacent islands). multifactorial analysis with generalized additive models indicated that enigmatic declines increase consistently with elevation, even after accounting for geographic range area, spatial autocorrelation, and species phylogenetic relationships. Although the GAA data are coarse, we found a continuous increase in the percentage of species experiencing enigmatic declines with increasing elevation, starting at sea-level, suggesting that declines in mountains may simply be the upper end of a continuum. establishing the existence of a strong elevational gradient in population declines will help focus amphibian decline research on factors that could possibly produce such a pattern, such as the role of temperature in disease dynamics.