Fine‐scale heterogeneity across Manhattan's urban habitat mosaic is associated with variation in ant composition and richness

Abstract

1. Global urbanisation is rapidly expanding and most of the world's humans now live in cities. Most ecological studies have, however, focused on protected areas.
2. To address this issue, we tested predictions from studies of protected areas in urban ecosystems.
3. Because most cities are heterogeneous habitat mosaics which include habitats with varying levels of chronic environmental stress, we focused on predictions from studies of less modified ecosystems about community‐wide responses to variation in chronic stress.
4. We sampled ants across Manhattan's urban habitat mosaic, at sites with varying levels of chronic environmental stress.
5. Many predictions derived from less modified ecosystems were supported by our findings: despite being the most intensively sampled habitat, high stress urban medians had less variability in ant composition –both within and among sites – than either urban parks or urban forests, the lowest stress habitat – urban forests‐had significantly more accumulated species and a higher number of unique species than higher stress habitats, and urban parks, which have intermediate levels of chronic environmental stress, also had intermediate levels of variation in among‐site species composition, accumulated species richness, and the incidence of unique species. The most common species also differed across Manhattan's urban habitat mosaic.
6. Nevertheless, the prediction that exotic species would occur more frequently in higher stress habitats was not supported; exotic species were equally common across all habitats.
7. These findings suggest that fine‐scale heterogeneity in the chronic stress of urban habitats may be an underappreciated, but important structuring force for urban animal communities.