Cooperative Fish and Wildlife Research Units Program: Arizona
Education, Research and Technical Assistance for Managing Our Natural Resources

Range-wide species conservation efforts are facilitated by spatially explicit esti-mates of habitat suitability. However, species-environment relationships oftenvary geographically and models assuming geographically constant relation-ships may result in misleading inferences. We present the first range-wide hab-itat suitability model (HSM) for the federally threatened eastern indigo snake(Drymarchon couperi) as a case study illustrating an approach to account forknown latitudinal variation in habitat associations. Specifically, we modeledhabitat suitability using interactive relationships between minimum wintertemperature and several a priori environmental covariates and compared ourresults to those from models assuming geographically constant relationships. Wefound that multi-scale models including interactive effects with winter tempera-ture outperformed single-scale models and models not including interactiveeffects with winter temperature. Our top-ranked model had suitable range-widepredictive performance and identified numerous large (i.e.,≥1000 ha) potentialhabitat patches throughout the indigo snake range. Predictive performance wasgreatest in southern Georgia and northernFlorida likely reflecting more restric-tive indigo snake habitat associations inthese regions. This study illustrates howmodeling interactive effects between temperature and environmental covariatescan improve the performance of HSMs across geographically varying environ-mental gradients.