Urbanization is on the rise worldwide, and in the face of global pollinator declines, can have a big impact on ecosystem functioning and services. Yet, little is known about how pollinators respond to urbanization. A common way to tackle this question is to address it from a taxonomic view, i.e. species diversity. However, while nearly one third of Missouri’s bee fauna is found within St. Louis City, the specific aspects of the environment that bees are responding to are unknown. What are the differences in richness and function that are allowing bees to be in certain parts of the city while not others?
We assessed bees’ functional diversity relative to patterns of distribution within the city of St. Louis. We sampled 9 community gardens across a range of habitats within the urban core. Sampling was done weekly from May to late September 2013 to 2016, at a rate of 0.25 person per hour hectare for all bee species using aerial nets. Specimens were mounted, labeled and identified to species. Species were sorted by functional traits including lecty (generalist or specialist forager), nest location, body size, abundance, flight period, and sociality. We also documented floral diversity and habitat structure within gardens.
Roughly 40 bee species representing 5 families and 21 genera were collected. Early mid July to late August was the peak of species abundance and diversity. Species richness declined from north to south across the city. Highest species richness was found in the north side (34 species) where empty lots and abandoned houses surrounded many sites. Alternatively, the south side had the lowest species richness (16 species), sites were surrounded by inhabited homes with manicured lawns. Bees collected included generalist (44%) and specialist (22%) foragers, as well as kleptoparasitic (21%); native (92%) and non-native (8%); solitary (84%) and social (16%); below (60%) and above ground (40%) nesters. Early spring bees were missing, which we believe is due to the lack of spring flowering plant taxa in our collection sites. We argue that using functional-trait diversity in addition to taxonomic diversity reveals general patterns of distribution within urban areas that will improve our understanding of the distribution of bee species within an urban environment. In addition to understanding how bees are responding to changes in environment, our results have significance for understanding community functioning and ecosystem services in an urban landscape.