Deforestation, host community structure, and amphibian disease risk

Habitat disturbances and the emergence of the chytrid fungus Batrachochytrium dendrobatidis (Bd) are linked to accelerated amphibian declines. Deforestation can directly alter amphibian community structure through abiotic and biotic mechanisms including shifts in local microclimates and species interactions. Changes in amphibian community attributes, in turn, potentially impact Bd transmission dynamics, and thus also have an indirect role in biodiversity persistence. Here, we tested whether deforestation influences Bd infections through shifts in amphibian community structure, including species richness, community composition, total host density, and host biomass. We surveyed 22 temperate and tropical amphibian communities across gradients of deforestation in the U.S. and Brazil, and we experimentally exposed a representative subsample of each amphibian community to standardized Bd zoospore loads in mesocosms under controlled microclimate. We found that denser temperate amphibian communities commonly found at pristine sites showed higher Bd loads when microclimates were held constant. In contrast, tropical amphibian communities found at pristine forest sites carried lower Bd infection loads in the absence of variable microclimates, likely due to their host species composition. Previous host exposure to the pathogen in tropical communities also played an important role in determining infection loads; we identified a negative association between Bd infection loads observed in the wild and in the laboratory. Our results highlight that deforestation can have cascading biotic effects on disease risk, and that quantifying the net contribution of host community attributes to Bd infections will help us identify specific drivers of disease and inform conservation strategies.