Amphibian population declines at savannah river site are linked to climate, not chytridiomycosis

Amphibian populations at the Savannah River Site (SRS), South Carolina, USA, have been censused consistently for 35 years, and this Provides a time series to examine the causes Of Population fluctuations. We examined archived museum specimens of 15 anuran species collected at wetlands on the SRS for the presence of the causative agent (Batrachochytrium dendrobatidis) of chytridiomycosis, an emerging disease associated with population declines elsewhere. Infections were present in three out of 137 (2.18%) individuals; the pathogen was detected in two Rana catesbeiana and a single Rana sphenocephala, all collected between 1978 and 1981. Lesions were not consistent with the later stages of fatal chytridiomycosis. Analysis of population trajectories of nine amphibian species over 26 years at SRS showed that four species declined significantly over this period, including R. sphenocephala. However, we demonstrate that these declines are more likely caused by an increase in the number of years with insufficient rainfall and a shortened hydroperiod at the breeding site than by chytrid epidemics. This pattern appears to be linked to a drying trend at SRS through the 1990s, although it is unclear whether this was caused by climate change. This study demonstrates that the presence of B. dendrobatidis in amphibian communities where some species are declining does not always implicate chytrids as a cause of the decline. Like many other emerging pathogens, the outcome of infection can vary among individuals and populations, depending on life history traits, environmental conditions, and virulence factors of the pathogen. Our report also demonstrates the usefulness of archived museum specimens and long-term population monitoring in studying the host-parasite ecology of emerging diseases.