A hybrid correlative-mechanistic approach for modeling and mapping winter distributions of western bat species

Abstract

Aim: The fungal pathogen Pseudogymnoascus destructans and resultant white-nose syndrome (WNS) continues to advance into western North America, infecting new bat populations, species, and hibernacula. Western North America hosts the highest bat diversity in the U.S. and Canada, yet little is known about western hibernacula and western bats’ hibernation behavior. An improved understanding of where bats hibernate in the West and the conditions that create suitable hibernacula is critical if land managers are to anticipate and address the conservation needs of WNS-susceptible species. Location: United States and Canada Taxon: bats Methods: We estimated suitability of potential winter hibernaculum sites across the ranges of five bat species occurring in the West. We estimated winter survival capacity from a mechanistic survivorship model based on bat bioenergetics and climate conditions. Leveraging the Google Earth Engine platform for spatial data processing, we used boosted regression trees to relate these estimates, along with key landscape attributes, to bat occurrence data in a hybrid correlative-mechanistic approach. Results: We show that winter survival capacity, topography, land cover, and access to caves and mines are important predictors of winter hibernaculum selection, but the shape and relative importance of these relationships vary among species. Our findings suggest that the occurrence of bat hibernacula can, in part, be predicted from readily mapped above-ground features, and is not only dictated by below-ground characteristics for which spatial data are lacking. Furthermore, our mechanistic estimate of winter survivorship was among the strongest predictors of winter occurrence probability across focal species. Main conclusions: Our findings offer an improved understanding of the likely winter distribution of bats occurring in the West, and offers a valuable baseline for assessing the potential specieslevel impacts of P. destructans as well as future climate change.