Living with the enemy: Facilitating amphibian coexistence with disease

Globalization has facilitated the emergence and spread of novel pathogens, representing a major conservation challenge. The amphibian disease chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis, epitomizes this unprecedented threat, being responsible for declines and extinctions of amphibians worldwide. Chytridiomycosis has had both immediate catastrophic impacts during initial epidemics, as well as more variable, ongoing effects as the pathogen transitions to endemicity in its new distribution. Where B. dendrobatidis is now endemic, effective management actions are needed to prevent further extinctions of species. Yet, after nearly 20 years of research, management solutions remain rare or largely untested. Here, we highlight the potential for mitigation strategies focused on the environmental part of the host-pathogen-environment triangle to facilitate coexistence with the pathogen. We provide an extensive literature review to demonstrate that environmental conditions and demographic processes can strongly mediate the impact of B. dendrobatidis, and the capacity of amphibian populations to withstand disease-associated mortality. In particular, novel management approaches to achieve coexistence could focus on manipulating environmental conditions to decrease suitability for B. dendrobatidis and/or increase demographic resilience to disease-associated mortality. Such strategies include translocation to, or creation of, environmental refuges, and habitat manipulation to increase recruitment and offset elevated adult mortality. We argue that responding to chytridiomycosis requires a conceptual readjustment of our baselines to recognize that endemic B. dendrobatidis infection is the 'new normal' in surviving populations of many susceptible amphibian species. We conclude with recommendations for research and management actions that can help achieve coexistence of amphibian species susceptible to B. dendrobatidis.