Relative Habitat Use, Occupancy, and Species Richness of Bats Across the Gradient of Urbanization in an Arid Region

Urbanization is a primary driver of ecological change and occurs across a gradient from low- to high- density development. Wildlife species can exhibit different responses to urbanization, with some species being more sensitive than others. Further, wildlife communities can exhibit varying patterns of species richness across the gradient of urbanization, where species richness can either decrease linearly or peak at intermediate levels of urbanization, consistent with the intermediate disturbance hypothesis (IDH). For chapter one, the objective was to evaluate the response of bats to urbanization across seasons. It was predicted that bat species would exhibit different responses to urbanization and that bats would increase use of urbanized areas in the summer season, where food and water resources were assumed to be greater. For chapter two, the objective was to evaluate species richness of bats across the gradient of urbanization in the summer season. Species richness of bats was predicted to either decrease linearly or peak at moderate levels of urban intensity. To test these hypotheses, 50 sites across the gradient of urbanization were sampled during four seasons using stationary acoustic bat monitors. Fourteen bat species were identified during 1000 nightly occasions. Consistent with chapter one predictions, bat species exhibited different responses to urbanization, with most bats being sensitive to urbanization. Counter to predictions, most bats did not appear to shift their response to urbanization across seasons. However, two bats (i.e., big brown bat and Yuma myotis) exhibited higher use of urbanized areas in the summer compared to other seasons. Consistent with chapter two predictions, species richness of bats decreased with increasing urban intensity. Results from this study demonstrate that most bats in the community were sensitive to urbanization, which is potentially related to species traits and has important conservation implications. First, it is likely important to maintain high-quality undeveloped habitat with low anthropogenic disturbance in wildland areas for species that are sensitive to urbanization and to maximize species richness. In addition, for bats that are tolerant of urbanization and to increase species richness in urbanized areas, it is likely important to preserve resources in urbanized areas and increase landscape connectivity.