Niche Contraction of an Endangered Frog Driven by the Amphibian Chytrid Fungus

Introduced pathogens can alter the geographic distribution of susceptible host species. For example, Batrachochytrium dendrobatidis (Bd) is a fungal pathogen that has been linked to the global decline and extinction of numerous amphibian species during the last four decades. A growing number of studies have described the distribution of Bd and susceptible hosts across the globe; however, knowledge on how Bd may shape the climatic niche of susceptible species is still missing. We estimated the effect of Bd on the geographic distribution and niche dynamics of the critically endangered lowland robber frog ( Craugastor ranoides ) in Costa Rica. We found a reduction of 98% in the geographic range of this species by 1995, following the epizootic outbreaks of Bd that affected Costa Rica in the 1980 and early 1990s. We also quantified niche contraction and found that the species is currently restricted to dry and warm environments that have been considered unsuitable for Bd. Our results contribute to the understanding of how emerging pathogens shape the climatic niches and geographic distribution of susceptible species.