Variation in forest patch habitat quality for white-footed mice driven by invasive plants in an urbanizing landscape

The habitat quality of urban forest patches is determined by the composition and structure of vegetation which in turn affects the quality of trophic resources and shelter provided for wildlife species. In addition, urban development in the landscape surrounding forest patches can affect species' movement between patches, further influencing habitat quality. Understanding how species respond to variation in habitat quality among urban forest patches is especially important for species that contribute to ecosystem services and disservices for urban residents. Here, we assessed habitat quality provided by urban forest patches for white-footed mice (Peromyscus leucopus) because they are one of the key reservoir species for Lyme disease and they influence disease dilution ecosystem services provided by mammal communities. We examined variation in vegetation composition and structure in forest patches across a gradient of landscape-scale urban development in and around Philadelphia, PA, USA. In particular, we focused on shifts in vegetation composition and structure associated with invasive understory shrubs given their prevalence in our study system. We then quantified the numerical (index of relative abundance) and morphological responses of white-footed mice to variation in habitat quality. While we observed no significant effects of environmental variables on our index of mouse relative abundance in forest patches, environmental variables associated with vegetation structure and composition were associated with shifts in mouse morphology. Most notably, mice were larger at sites with more invasive shrub species. This indicates that invasive understory shrubs may be creating higher-quality habitat for white-footed mice. Because larger-bodied mice are likely to feed more ticks, this result has significant implications for Lyme disease dynamics in urban areas, such as amplified transmission.