Species Distribution Modeling Reveals Insights into the Occurrence of a Locally Rare Snake at the Periphery of its Geographic Range

Habitat management and species conservation plans are increasingly important as biodiversity losses increase. For many species, we lack the necessary data to implement habitat management or conservation plans because the species may be rare or difficult to detect, particularly at the periphery of geographic ranges. This may be especially true for snakes. For example, Pygmy Rattlesnakes (Sistrurus miliarius) have state-level protection at the northern terminus of the range but what little is known about the species in this region is derived from just 30 observations collected over the past 40 yr. This leaves considerable uncertainty regarding conservation status and establishes a need to better understand habitat suitability and their geographic distribution. Therefore, the objectives of our study were to determine landscape-scale environmental variables that influence patterns of distribution for S. miliarius in the northern extent of its range via the Maxent Species Distribution Algorithm coupled with on-site monitoring via standardized road-cruising transects (n = 43) to evaluate model suitability. The resulting species distribution model showed that suitable habitat (similar to 2045.96 km(2)) was composed primarily of riparian areas that exist in isolated patches. These habitats were primarily composed of sandy soils and low-elevation forested areas. Our on-site monitoring, informed by our modeling efforts, resulted in 12 new records for the species (an increase of 28.57%). Collectively, our species distribution model suggests that suitable habitat for S. miliarius within our study area is restricted to riverine or riparian habitats associated with the Lower Tennessee River Valley. The methods used in this study employ a strategy to better understand suitable habitat for rare or secretive species that occur across large geographic areas.