Effects of landcover change on amphibian disease risk

Background/Question/Methods

Habitat loss and chytridiomycosis, a disease caused by the fungus Batrachochytrium dendrobatidis (Bd), are main drivers of amphibian declines worldwide. Our recent studies show that, paradoxically, amphibian populations experience higher disease risk in natural habitats in both tropical and temperate forests. Here we investigate the roles of host diversity and microclimate as potential mechanisms leading to higher Bd infections in amphibian populations sampled at breeding sites surrounded by natural vegetation. To achieve this goal we (1) tested for the effect of host species richness on pathogen occurrence, prevalence, and infection intensity using linear regressions, accounting for potential effects of environmental factors; and (2) tested for the effects of microclimatic shifts arising from deforestation on pathogen outcome by linking the effects of shade and water temperature to Bd epidemiology.

Results/Conclusions

We found that amphibian species richness was a positive predictor of Bd infections in amphibian populations even after accounting for potential effects of environmental factors such as habitat loss and regional climate. When testing for the effect of microclimate on disease risk through path analysis, we found that high habitat loss predicted lower water temperatures, which in turn predicted higher Bd prevalence and infection intensity in amphibians. Bd thrives under microclimatic conditions typical of natural forests, where diversity is high and where dozens of rare specialized amphibians are in the brink of extinction. Understanding how community attributes and microclimates affect disease outcome will help us develop appropriate management tools in the wild, and provide a more complete picture of the interaction between habitat loss and chytridiomycosis; two main factors accounting for amphibian declines worldwide.