Species Distribution Modeling of the Threatened Blanding's Turtle's (Emydoidea blandingii) Range Edge as a Tool for Conservation Planning

Delineating a species range is challenging because many factors interact at multiple spatial scales to affect a species distribution. Species distribution models (SDM) can be used to identify factors most associated with a species presence and, therefore, potentially define a range edge. We evaluated the utility of two popular SDM approaches, maximum entropy models (e.g., MaxEnt) and generalized linear models (GLM), for determining the range edge for the threatened Blanding's Turtles, Emydoidea blandingii, in northeastern New York, USA. Using the mapping and analysis software ArcGIS, we constructed and validated SDMs using presence/absence records (GLM) and presence/background records (MaxEnt) with 11 environmental predictor variables. Because of the limits imposed by the low number of absences, we found that GLM was not as successful as MaxEnt at predicting habitat suitability for rare and cryptic species like E. blandingii. Our results also indicated that a distinct environmentally induced range edge is associated with factors related to elevation. Both GLM and MaxEnt models also projected the presence of suitable habitat outside of the current range, including locations with known disjunct populations. We conclude that a presence/background SDM approach such as MaxEnt is valid when accurate data on locational absences are lacking, as is typical for rare, cryptic species. Using SDM to understand factors that shape the range edge can aid in planning habitat conservation and management of threatened species such as E. blandingii.