Contrasting demographic responses of toad populations to regionally synchronous pathogen (Batrachochytrium dendrobatidis) dynamics

We used long-term capture-recapture data from 3 boreal toad populations in western Montana to estimate how apparent survival is affected by Batrachochytrium dendrobatidis (Bd), a fungal pathogen that causes disease and has been implicated in amphibian population declines globally. Despite similar levels of Bd prevalence and synchronous pathogen dynamics among toad populations, Bd reduced apparent survival of toads in one population that declined, had no effect on survival in one population that was stationary, and Bd was associated with increased survival in one population that is near extinction. The different trends in survival were not predicted by observed sex ratios, a commonly-used tool to identify declining populations. Our results reveal surprising variation in responses to Bd and indicate pathogen prevalence was not predictive of survival or population risk, and they illustrate the complexity in understanding Bd dynamics across multiple populations and multi-host communities and identifying appropriate management actions.