AUTHORS: Thomas L Anderson, Department of Biological Sciences, Southern Illinois University Edwardsville
ABSTRACT: Documenting species occurrences in different habitat patches across spatiotemporal gradients is critical for understanding demographic trends. Species occurrence information also can help inform management actions by determining what patches constitute consistently occupied areas versus more infrequently used areas. Identification of the drivers of consistently occupied patches is also critical to infer high quality habitats. We monitored the occurrence of ringed (Ambystoma annulatum), a Species of Conservation Concern, and marbled (A. opacum) salamanders across an 11-year period (2012-2022) at Fort Leonard Wood, Missouri. We surveyed 55 wetlands for the presence of each species during the larval period using a combination of minnow traps and dipnets. We analyzed occupancy using single-species multi-season occupancy models from the spOccupancy package in R. We compared the fit of spatial models, which account of spatial autocorrelation in state processes, with non-spatial models. We use a combination of habitat variables (e.g., canopy cover and hydroperiod) and climatic variables (e.g., drought or winter severity) to predict occupancy patterns. We found that non-spatial models fit the data better than the spatial models for both species. Using the non-spatial models, both species showed significant declines in occupancy over time. For marbled salamanders, occupancy probabilities were higher in years with reduced drought severity indices (i.e., wetter conditions) and semi-permanent wetlands compared to permanent wetlands. For ringed salamanders, occupancy probabilities tended to be higher in permanent wetlands, but no other habitat features or climate variables strongly affected ringed salamander occupancy. Further research on aspects of potential declines in these species’ occupancy at this study site are needed to identify potential mechanisms.
