Data from: Wild bee abundance declines with urban warming, regardless of floral density

As cities expand, conservation of beneficial insects is essential to
maintaining robust urban ecosystem services such as pollination. Urban
warming alters insect physiology, fitness, and abundance, but the effect
of urban warming on pollinator communities has not been investigated. We
sampled bees at 18 sites encompassing an urban warming mosaic within
Raleigh, NC, USA. We quantified habitat variables at all sites by
measuring air temperature, percent impervious surface (on local and
landscape scales), floral density, and floral diversity. We tested the
hypothesis that urban bee community structure depends on temperature. We
also conducted model selection to determine whether temperature was among
the most important predictors of urban bee community structure. Finally,
we asked whether bee responses to temperature or impervious surface
depended on bee functional traits. Bee abundance declined by about 41% per
°C urban warming, and temperature was among the best predictors of bee
abundance and community composition. Local impervious surface and floral
density were also important predictors of bee abundance, although only
large bees appeared to benefit from high floral density. Bee species
richness increased with floral density regardless of bee size, and bee
responses to urban habitat variables were independent of other
life-history traits. Although we document benefits of high floral density,
simply adding flowers to otherwise hot, impervious sites is unlikely to
restore the entire urban pollinator community since floral resources
benefit large bees more than small bees.