Amphibian population declines, disease, and climate change

Amphibians are declining across the globe for a variety of reasons. We review the evidence for the role of climate change in triggering disease outbreaks of chytridiomycosis, an emerging infectious disease of amphibians. Growing evidence clearly indicates that chytridiomycosis is a major contributor to the global loss of amphibian diversity. Some studies find no evidence for climate change during the time of amphibian population declines, and posit chytridiomycosis as an exotic pathogen introduced into naïve populations and spreading along wave-like fronts. Other studies find that the timing of disease outbreaks is correlated with climatic events (e.g., multiple El Niño events), or a gradual increase in ambient temperature that apparently stimulates the emergence of an endemic pathogen. Both climatic anomalies and disease-related extirpations appear to be recent phenomena, and both are especially prevalent at high elevations in tropical areas; thus, it is difficult to separate their confounding effects. Compounding the problem are the widely accepted findings from lab and field studies that have shown that microenvironmental (e.g., temperature, moisture) conditions can influence disease prevalence, transmission, and growth. Some studies have taken this to mean support for climate change causing disease outbreaks. We end with a discussion of data necessary to support the hypothesis that climate change is triggering disease outbreaks. Effective conservation actions require knowledge of the essential threats to biodiversity, and possible synergistic interactions.