Drivers of population dynamics of at-risk populations change with pathogen arrival

Abstract

Successful wildlife conservation in an era of rapid global change requires understanding determinants of species population abundance and growth. However, when populations are faced with novel stressors, factors associated with healthy and growing populations can change, necessitating a shift in conservation strategies. For example, emerging infectious diseases can cause conditions previously beneficial or neutral to host populations to increase disease impacts. Here, we paired a population dataset of 265 colonies of the federally endangered Indiana bat (Myotis sodalis) with 50.7 logger-years of environmental data to explore factors that affected colony response to white-nose syndrome (WNS), an emerging fungal disease. We found wide variation in colony responses to WNS, ranging from extirpation to stabilization and persistence. Simulating future population dynamics suggests that most extirpations have already occurred, as the pathogen has been present for several years in most colonies, and that small colonies were more susceptible to extirpation than large ones. Further, while temperature and humidity conditions of hibernacula appeared unassociated with Indiana bat colony growth prior to WNS, extirpation risk following pathogen arrival was elevated in colonies that used colder and wetter hibernacula. Additionally, rates of decline were greater in colder hibernacula, opposite the association for a sympatric bat species. Overall, this study illustrates that emerging infectious diseases can change the factors associated with host population abundance and optimal growth, including through novel environmental associations, which can vary across host species. Consideration of these shifting associations and intrinsic differences between impacted host species will be essential to successful species conservation.