The role of climate, spatial structure, and geography in disease-related amphibian extinctions in Central and South America

Chytridiomycosis, an infectious disease caused by the fungus Batrachochytrium dendrobatidis, is implicated in mass amphibian die-offs and extinctions around the world.  This pathogen seems especially problematic in tropical regions.  For instance, in Central and South America, chytridiomycosis is the putative cause of 70 extinctions out of 113 species in the toad genus Atelopus and most of these extinctions have occurred since 1980.  Recent evidence suggests that these extinctions were more common in warm years; however, alternative hypotheses have not been carefully tested.  We evaluate the strength of the mean and variance of cloud cover, diurnal temperature range, frost frequency, ambient air temperature, minimum air temperature, maximum air temperature, vapor pressure, precipitation, and wet day frequency as regional climatic predictors of Atelopus extinctions.  In addition, we consider geographic predictors, such as the elevational range and spatial distribution of the species as factors influencing the spatiotemporal spread of these presumed chytrid-induced extinctions.  Our results revealed that the rate of Atelopus extinctions was positive in the 1980’s and negative in the 1990’s, consistent with B. dendrobatidis recently running out of susceptible species in this region.  Variability in temperature was a better predictor of extinctions than absolute temperature, a result in agreement with recent work suggesting that temperature variability might be more important than absolute temperature for susceptibility of amphibians to infection.  A more thorough comparison of the predictors will be provided during the talk.