Our research focuses on four regions of the Americas that have each played an important role in understanding the causes and consequences of catastrophic amphibian declines. These systems are complementary in terms of amphibian assemblage richness, history of Bd emergence, climate conditions, and the role of additional anthropogenic stressors. By leveraging similarities and differences across systems, we can develop a general model of the conditions that promote resilience to this emerging infectious disease across scales.
Panama has long served as one of the best examples of the devastating impacts of chytridiomycosis. The system’s response there clearly fits an epizootic pattern, where the arrival of Bd into previously naïve amphibian communities resulted in disease-induced mass mortality. Prior to these outbreaks, sites in Panama had high species richness (50-70 species) and abundances. Bd is now widespread, and several iconic species, like Panamanian Golden Frogs (Atelopus varius & A. zeteki) and Panama Rocket Frogs (Colostethus panamansis), were driven to near extinction.
The Sierra Nevada, California
The Sierra Nevada are another example of an epizootic outbreak region. This montane ecosystem in California is characterized by low amphibian diversity (dominated by three species) and high historical amphibian abundance. Unlike Panama where Bd spread rapidly, Bd is thought to have arrived to this region in the last 70 years and has spread slowly. Several species, including Mountain Yellow-Legged Frogs (Rana muscosa & R. sierrae), have been decimated by Bd and are listed as ‘endangered’ under the U.S. Endangered Species Act. Climate change and non-native predatory fish are additional threats.
Atlantic Forest of Brazil
Of our four systems, the Atlantic Forest of Brazil has experienced the most habitat loss, with more than 85% of land area cleared for agriculture, cattle ranching, or urbanization. Still, the region harbors hundreds of endemic species, most of which occur in thousands of small forest fragments. This system exhibits both epizootic and enzootic host-pathogen dynamics. Some of this complexity is explained by the unusual presence of multiple Bd lineages, some of which may have a long history in the region (>100 years), while others appear to have arrived more recently. Bd is widespread in Brazil, and dozens of amphibian species declined in the late 1970s coincident with increased Bd prevalence.
In contrast to the Sierra Nevada and Panama, Eastern North America shows enzootic disease dynamics. Our study site in Pennsylvania takes advantage of >70 years of work on amphibian ecology at Pitt’s biological field station, the Pymatuning Lab of Ecology (PLE). The host community in this region is of intermediate diversity (26 species). Bd prevalence and load vary, but Bd infection has been detected in all amphibian species sampled. Amphibians here are also affected by climate and land use changes.