White-nose syndrome is an emerging disease of North American bat species associated with the presence of cold tolerant fungus Pseudogymnoascus destructans. As the disease spread across the Eastern and Southern United States over the last decade, response by bat populations has varied by species and infection severity. Diverse hypotheses for bat mortality differences have been proposed, including cave temperature dynamics, migration patterns, habitat and climatic heterogeneity, and variability in interspecific disease transmission and susceptibility to infection.
Our objective was to model the potential spread of white-nose syndrome across hibernacula sites in Montana, while exploring proposed hypotheses regarding differential bat mortality across species. Our approach uses a spatially-explicit stochastic SEIR model of infection coupled to a movement matrix of transmission to predict species and life history stage-specific survival for little brown bats (Myotis lucifugus), big brown bats (Eptesicus fuscus), and Townsend’s big-eared bats (Corynorhinus townsendii) occupying 20 cave and mine hibernacula sites. We populated our model using data on bat roost location, occupancy and environmental conditions provided by Montana Natural Heritage Program, climate information from the Montana Climate Office, and literature values for bat species and P. destructans life history parameters.
Preliminary model runs using little brown bats at 10 caves indicate that Montana hibernacula populations would respond variably to infection, with some caves experiencing a small reduction in bat numbers while other caves were reduced to a small fraction of the initial bat population. Differences were driven life by disease connectivity across the landscape predicted by bat movement distance and initial infection intensity. As observed from actual sites of infection, the longer white-nose syndrome persisted in infected hibernacula, the more likely the disease was to spread across sites and increase the total number of infected bats. We anticipate these results will change with the addition of bat species with lower average mortality from infection (Big brown bat) or that serve primarily as a vector for the disease (Townsend’s big-eared bat), and with the incorporation of Pd pathogen growth dynamics coupled to transmission dynamics within hibernacula. Our results will inform future surveillance and control efforts for white-nose syndrome in Montana. Drastic changes in bat population dynamics in Montana could have profound effects on cave ecosystem biodiversity, as well as ecosystem services in agricultural and forested lands across the state.