Ecological determinants of pathogen transmission in communally roosting species

Many animals derive benefits from roosting communally but may also face increased risk of infectious disease transmission. In spite of recent high-profile disease outbreaks in roosting animals of conservation and public health concern, we currently lack general theory for how attributes of roosting animals and their pathogens influence pathogen spread among roosts and overall population impacts on roosting species. Here we develop a model to explore how roost size and host site fidelity influence the time for a pathogen to escape from its initial roost, overall infection prevalence, and host population size, for pathogens with density- or frequency-dependent transmission and varying virulence. We find that pathogens spread rapidly to all roosts when animals are distributed among a small number of large roosts, and that roost size more strongly influences spread rate for density-dependent than frequency-dependent transmitted pathogens. However, roosting animals that exhibit high site fidelity and distribute among a large number of small roosts are buffered from population-level impacts of pathogens of both transmission modes. We discuss our results in the context of anthropogenic change that is altering aspects of roosting behavior relevant to emerging pathogen spread.