There is a paradigm shift concerning how urban areas are viewed as biodiversity deserts, and it is now commonly accepted that they can provide suitable habitats for some groups like bees. Most studies on urban bee communities report that pollen specialists are declining due to a lack of host plants. While specialist bees are less common in urban areas as compared to more generalist feeders, little attention has been given to the specialist species that persist in cities. This is the first meta-analysis assessing urban specialist bees at a continental scale investigating a) what specialists inhabit cities; b) what functional traits do they have; c) if there are any relationships between overall bee diversity and specialist diversity within a city; d) and what makes certain cities better supporters of specialist bees. Twelve North American (NA) cities were selected based on sufficient records of the urban bee community data. There was no city area minimum size, but we focused on cities greater than 300,000 people. Bee functional trait data was obtained from published sources and used in GLMM and Functional Dispersion analyses.
Results/Conclusions
The twelve cities range from east to west coast NA, however there was a greater concentration of cities in Eastern NA. Cleveland, Ohio, had the fewest specialists with 4 species representing 4.32% of the species pool. Austin, Texas, had the highest total abundance and percentage of specialists with 77 species or 29%. San Diego, California, also had a high percentage of specialists with 35 or 28% of the total species pool. There was a positive correlation between a city’s area and the diversity of specialist bees. Additionally, cities with more diverse bee communities also had higher diversity of specialist bees. Andrenidae and Andrena were the most represented bee family and genus, respectively. The most common functional traits are represented by medium sized, ground nesting bees flying late spring to late summer. Nesting type contributed the most to functional trait dispersion between specialists and generalists, since most specialists were ground nesters whereas most urban bee communities are dominated by cavity nesters. The common species and functional traits of specialists that persist in cities can give us a greater understanding of how bees employ resources in cities. This information is vital for conservation and urban planning to better support bees in cities.
