|1. Global urbanis ation is rapidly expanding and most of the world’s
humans now live in cities. Most ecologi cal studies have, however, focused on
2. To address this issue, we tested predictions from studies of protected areas
in urban ecosystems.
3. Because most cities are heterogeneo us habitat mosaics which include habi-
tats with varying levels of chronic environmental stress, we focused on predic-
tions from studies of less modi?ed ecosystems about community-wi de responses
to variation in chronic stress.
4. We sampl ed ants across Manhattan’s urban habitat mosaic, at sites with
varying levels of chronic environmental stress.
5. Many predictions derived from less modi?ed ecosystems were supported
by our ?ndings: despite being the most intensively sampled habitat, high stress
urban medians ha d less variability in ant composition –both within and among
sites – than either urban parks or urban forests, the lowest stress habitat –
urban forests-had signi?cantly 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 fre-
quently in higher stress habitats was not supported; exotic species were equally
common across all habitats.
7. These ?ndings suggest that ?ne -scale heterogeneity in the chronic stress of
urban habitats may be an underappreciated, but important structuring force for
urban animal communities.|