Urbanization and abundance of floral resources affect bee communities in medium-sized neotropical cities

Bees are important pollinators that have been negatively impacted by anthropogenic environmental changes, such as urbanization. In addition, urban development can reduce and degrade the natural habitat of bees by increasing the proportion of impervious surfaces, decreasing green areas and increasing the number of exotic ornamental plants. However, cities can provide refuge for bees because they provide an environment with a wide variety of nesting and foraging resources. The objective of our study was to evaluate the richness and abundance of bees, their respective functional groups, and community composition along with an urbanization gradient in 21 locations distributed among six medium-sized Brazilian cities (with populations between 80 000 and 170 000 inhabitants). We also evaluated the effect of richness, number of plants and proportion of native plants. We collected a total of 132 species of bees. Total bee richness decreased with increasing impervious cover and increased with landscape heterogeneity, which also had a positive effect on the richness of above-ground nesting bees and generalist bees. Regarding abundance data, solitary bees and belowground-nesting bees were positively influenced by the increase in grass cover. The total number of native and exotic plants collected positively influenced the total abundance of bees, as well as the abundances of eusocial bees, which nest above- and belowground, and generalists. The proportion of native plants positively influenced the total richness and abundance of specialist bees. Our results indicate that medium-sized urban areas may be home to a wide diversity of bee species, but species that nest in the soil and specialist species may be more sensitive to urbanization and the decrease in the supply of floral resources.