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 sitesthan either urban parks or urban forests, the lowest stress habitaturban 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.

Urban stress is associated with variation in microbial species composition—but not richness—in Manhattan

“…The test was not significant for bacteria (P = 0.3473) or fungi (P = 0.13) -indicating that microbial samples from sites closer together were not necessarily more compositionally similar. Similarly, Savage et al (2015) found no effect of distance on ant community composition across Manhattan when controlling for habitat type.…”

“…Fungi are intermediate in size (typical eukaryotic cells are between 1-2 orders of magnitude larger than bacteria and archaea) and perhaps have intermediate dispersal ability relative to ants and bacteria. Both ants and fungi are common and abundant in ground communities in urban ecosystems, and previous work has shown that these groups can be sensitive to urbanization and habitat patch size (Newbound et al, 2010;Savage et al, 2015). To our knowledge, this is the first analysis of intra-city diversity patterns for microbes with direct comparison to macroorganisms.…”

“…As above, we sampled equal areas of all sites. As described in more detail in Savage et al (2015), ants were sampled by extraction from leaf-litter, such that an ant sample is a measure of the composition of ants in a standardized amount of litter on the forest floor. In each site, we collected ants using both hand collection and Winkler sifting.…”

“…In each site, we collected ants using both hand collection and Winkler sifting. Because we were focused on comparing street medians to all parks, we used a single park category in our analyses rather than splitting the sites into forests and parklands, as Savage et al (2015) did.…”

Stable isotopes reveal links between human food inputs and urban ant diets

“…New York is one of the largest and oldest urban centres in North America, and its ant fauna has been recently described [21,22]. Globally, ants are widespread and abundant in both natural [23,24] and urban ecosystems [25], and they commonly recruit to human food sources [26][27][28].…”