Movement barriers, habitat heterogeneity or both? Testing hypothesized effects of landscape features on home range sizes in eastern indigo snakes

Animal home ranges are influenced by diverse intrinsic and extrinsic factors. For example, habitat heterogeneity may affect the spatial distribution of resources leading to larger home ranges where resources are spatially dispersed or, conversely, smaller home ranges where resources are concentrated or abundant. Other landscape features may lead to smaller home ranges by constraining or restricting animal movements. Understanding the relative importance of these two processes is increasingly important given the prevalence of anthropogenic features across contemporary landscapes. We test the relative importance of habitat heterogeneity and movement restriction on the home range size of a wide-ranging, habitat and dietary generalist, the federally threatened eastern indigo snake (Drymarchon couperi). We used data from 83 radio-tracked individuals in a multi-scale analysis of home range size as a function of multiple landscape features representing land cover and habitat heterogeneity. We found that home range size was negatively correlated to habitat heterogeneity (i.e., the standard deviation of normalized difference vegetation index [NDVI]) and urban intensity. Smaller home ranges in areas with high habitat heterogeneity and low urban intensity likely reflected reduced resource dispersion through the concentration of diverse foraging habitats. Home ranges were smallest in urban landscapes which, combined with previously documented avoidance of urban habitats by eastern indigo snakes, suggests that urban land cover restricts home range size. Our results demonstrate the importance of considering both the influence of resource dispersion and movement barriers in understanding animal space use. Moreover, we highlight the need to consider the potential role of anthropogenically subsidized resources (e.g., prey, shelter sites) to understand variation in eastern indigo snake home range sizes within urban areas.