OCCUPANCY AND ECOLOGICAL INFLUENCE OF SEMI-AQUATIC MAMMALS IN SOUTHERN ILLINOIS

Author

Derek Whipkey, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2025

Degree Name

Master of Science

Department

Zoology

First Advisor

Bastille-Rousseau, Guillaume

Second Advisor

Narr, Charlotte

Abstract

Semi-aquatic mammals play important ecological roles at the interface of terrestrial and aquatic systems. Specifically, beavers (Castor canadensis) and muskrats (Ondatra zibethicus) can modify habitat through ecosystem engineering behaviors whereas the presence of river otters (Lontra canadensis) and mink (Neovison vison) can be indicative of overall habitat quality. Given these roles, advancing our understanding of how environmental factors shape their occupancy and how semi-aquatic mammals themselves may influence surrounding communities would strengthen conservation efforts. To address this, I surveyed 67 sites across four counties in southern Illinois, USA from March – May 2023 for American beaver, muskrat, river otter, and American mink. Sites were distributed evenly between waterbody type and size. Given the elusive nature of these species, I combined two detection methods, sign surveys and camera traps, to increase detection. In chapter 1, I applied a Bayesian multi-method occupancy model that incorporates both detection methods to estimate a single occupancy probability for each target species to determine the relative importance of terrestrial and aquatic environments to semi-aquatic mammal distributions. I built candidate models of aquatic and terrestrial covariates separately to identify the most important covariates of each category. The individual top model varied by species, but a combined additive model of the top aquatic and terrestrial models provided the best overall predictions for each species. Beaver, otter, and mink occupancy showed positive associations with large waterbodies, while muskrat occupancy was positively linked to lotic systems. Additionally, muskrat and mink occupancy were positively related to increasing distance from roads. These results suggest that while aquatic and terrestrial factors have varying influences in predicting semi-aquatic mammal occupancy, considering both yields the most accurate results. All four semi-aquatic mammal species I studied were impacted by aquatic type, highlighting the importance of considering both waterbody types to better understand their distribution. In chapter 2, I quantified measures of alpha and beta diversity of terrestrial mammals detected by camera traps to measure the influence of beaver and muskrat on species diversity. I then used distance-based redundancy analysis to model diversity as a function of beaver and muskrat occupancy probability, as well as the presence of a beaver dam. The basic measure of alpha diversity, species richness, was not influenced by beaver, beaver dams, or muskrat occupancy in any of the models. Beaver dams and muskrat occupancy had a negative effect on total beta diversity and the species turnover component of beta diversity. This suggests that both beaver dams and muskrat are influential in maintaining consistent species compositions, perhaps due to the habitat modifications both enact on the landscape. Overall, this work contributes to a greater understanding of how semi-aquatic mammals interact with the landscape and surrounding communities.