Relationship of habitat variables and observation data on muskrat occupancy in an urban green space waterway : a case study from Forest Park, St. Louis, USA
Authors:   , McCloud Matthew David 
Published: October 2023

Urban green spaces (UGS) are high value areas that strive to serve both ecological and social goals. Quality stewardship of these areas require that all components affecting the ultimate site goals be addressed in not only the planning and development of an UGS but also in the day to day management of the area. My research was prompted by park stewards looking for a non-lethal method in which to manage an ever-growing muskrat population. To address this topic, my research established twenty study sites located throughout the Linear Connected Waterway System (LCWS) in Forest Park located in St. Louis, MO. Research began by monitoring how these sites changed over time and the site variables that made them more similar/dissimilar to each other and how this change affected the suitability of the sites to support muskrat occupancy using the established muskrat Habitat Suitability Index (HSI). The HSI quantifies habitat variables crucial to the support of muskrat occupancy. A Similarity/Dissimilarity analysis of sites was conducted through Bray-Curtis ordination and showed two main clusters of sites. Group one (Axis one) identified that vegetation stand density and bank slope were correlated for the site cluster whereas Group two (Axis two) identified proximity to disturbance and percent aquatic vegetation being responsible for the clustering of the remaining study sites. The next goal was to generate HSI scores for each of the twenty sample sites and analyze changes observed in the terrestrial and aquatic vegetation over time that affected the sites suitability for muskrat occupancy. Data showed that seasonal and yearly fluctuations of these two variables showed a corresponding change in the sites' habitat suitability score being most pronounced by the availability of aquatic vegetation. Next, muskrat absence/presence data was collected and analyzed to determine if any of the site classification variables could be used to predict muskrat occupancy. Analysis was conducted using three generalized linear models which identified that a site's density of aquatic vegetation and proximity to disturbance were most supportive in predicting a sites muskrat occupancy. The last question this research addressed was whether specific water quality components, phosphorus and nitrogen, could be used to predict the potential level of aquatic vegetation support. Monthly water samples showed that during the regional growing season nitrogen was generally found to be at a level of low enrichment whereas phosphorus was recorded consistently at highly enriched levels. These levels both supported the assumption that the capacity for higher densities of aquatic vegetation was possible thus the capacity to support higher muskrat occupancy. All of the data generated during this research reinforced the importance of proper UGS planning and monitoring and the perils, both financially and ecologically, managers may face if plans don't fully consider all potential flora and fauna occupancy. Renovation and establishment of urban green spaces presents the potential for undesirable effects brought about by unchecked, historically native wildlife species. Habitats that are not ecologically balanced can result in unanticipated problems, such as species overpopulation, that can result in habitat damage or the overall destruction of the habitat type. An ecologically balanced UGS is one in which proper biological checks and balances are in place allowing the habitat to develop through natural processes while supporting sustainable populations of naturally occurring organisms. This process can only occur if organisms do not exceed the habitat's carrying capacity. Without naturally occurring mechanisms such as predators and habitat fluctuations, species population levels can become unsustainable when they reach carry capacity thus depleting an areas abiotic and biotic resources potentially negatively affecting not only the target species but other species that occupy the space. Addressing this habitat degradation can lead to additional cost to UGS managers in maintaining these highly valued urban green spaces through constant remediation efforts. However, through careful monitoring and habitat design many of these habitats can be sustained with minimal cost and disruption. Current research has shown that properly designed habitats allow for natural succession to occur while facilitating the control of varying species populations. These strategies address problems that urban resource managers throughout the world face when managing designed habitats in which natural processes have been manipulated. Investing limited time and money into reestablishing urban ecosystems without appreciating these potential pitfalls could lead to the eventually loss of the valued resource and the societal benefits they provide.