Differential Susceptibility May Not Drive Chytridiomycosis Related Declines in Multi-Host Amphibian Communities

Batrachochytrium dendrobatidis (Bd) is the most catastrophic wildlife pathogen, associated with severe amphibian population declines or the extinction of over 500 species. Bd has the potential to influence the structure and dynamics of amphibian populations in multiple and compounding ways, yet few studies have investigated how Bd effects vary in communities with differential susceptibility. Here, we used temporal data from amphibian communities in temperate Tasmania, Australia, comprising four co-occurring species: the brown treefrog (Litoria ewingii), Tasmanian treefrog (L. burrowsae), common froglet (Crinia signifera), and Tasmanian froglet (C. tasmaniensis). Previous laboratory trials indicated L. burrowsae and C. tasmaniensis are susceptible to Bd, whereas L. ewingii and C. signifera act as reservoirs. Using Bayesian Markov chain Monte Carlo models, we tested whether Bd presence, the presence of reservoirs, or same-genus species influenced susceptible species across sites and years. Contrary to expectations-that Bd and reservoir hosts destabilise amphibian communities-we found no evidence of population declines in L. burrowsae or C. tasmaniensis. Instead, species appeared to coexist in a relatively stable community structure, despite Bd presence. Our findings suggest that susceptibility identified by laboratory trials might not reliably predict field disease outcomes in this system, owing to an absence of relevant extrinsic environmental variables. We postulate that pond conditions in which amphibian communities in our study occur, characterised by low temperature and pH, limit Bd growth and survival, creating a refuge from its effects. These results highlight the importance of ecological and environmental context when assessing disease impacts in wild multi-host communities, and also that climate change may threaten community resilience.