Intersecting urban and latitudinal gradients: Impacts on ant diversity

Increasing urban temperatures related to the urban heat island effect are associated with widespread biodiversity declines. Because cities are broadly distributed by latitude and embedded within diverse climates, the effects of urban heat could vary geographically. Here we studied ant communities within four US cities that span a latitudinal gradient from Massachusetts to North Carolina. We sampled urban ants using baits placed at the base of a single common tree species along an urban temperature gradient within each city. When pooling results across all cities, ant species richness increased towards the equator, which is consistent with longstanding latitude-diversity gradients. Within each city, however, we observed consistent declines in ant species richness with increasing temperature that did not vary with latitude. Our results contrast with studies of other urban taxa that have found worsening effects of urban heat in low latitude cities and sometimes positive effects in high latitude cities.