Dr. Gail Langellotto, Professor of Urban and Community Horticulture at Oregon State University, was the first speaker in the “Urban Garden Ecology” section at the 2019 IUWC. Dr. Langellotto has been conducting research in garden ecosystems since her first faculty job at Fordham University. An entomologist by training, when she moved to the Bronx she was initially stumped when considering which insects would be best to study in the heart of New York City. Quickly she realized that urban gardens are a perfect location to study insect diversity and conservation, and continues to investigate these systems today. 
Urbanization is currently one of the most ubiquitous threats to biodiversity. However, in some areas urbanization been found to actually increase bee diversity and abundance, an observation hypothesized to be due to the presence of gardens and the floral resources they provide.
Via a literature review, Dr. Langellotto investigated several components of bee communities in urban gardens. A) How many bee species can be found in urban gardens? B) How comparable are garden bee communities across different eco-regions? C) Do gardens ecologically filter bees?
Dr. Langellotto searched for studies that sampled the bee communities in gardens (either home or community gardens), identified bees to species levels, and were performed in the United States. Through 2014, this yielded seven studies that fit these criteria.
Overall, 213 unique bee species were identified across all seven of these studies. To address how comparable these garden bee communities are, Dr. Langellotto performed a cluster analysis of bee presence/absence data, to look at the dissimilarity between groups. In fact, the sampled bee communities did segregate into two groups – comprising of eastern and western locations. In addition, these species were fairly similar to the bee species identified in other types of habitat (e.g. farm and natural area) from studies conducted over the same time period, suggesting gardens have the ability to provide habitat for the larger regional pool of bees.
However, Dr. Langellotto did find a few differences when examining the ecological characteristics of sampled bees. Differences were found at the family level; sampled gardens had significantly fewer Andrenidae (mining bees) than non-garden sites, in both the eastern and western United States. Bees in this family are spring fliers, nest in soil, and tend to be floral specialists.
Gardens also had fewer soil nesting bees and more cavity nesting species, suggesting that many gardens are not good habitat for soil nesters. In general, urban areas shift bee communities towards cavity nesters because these species are able to effectively use anthropologically provided substrates, while urban areas tend to have very little available bare soil for soil nesters. While this is great for cavity nesting species, the lack of soil nesting bees in urban areas is concerning because these species comprise about 70% of all bee diversity!
This review is exciting for those of us interested in urban ecology. It suggests that gardens have a high potential for providing habitat for pollinators in urban areas – but that gardeners and urban land managers should be mindful of maintaining patches of bare ground in an attempt to provide nesting habitat for soil nesting bees, in addition to providing the floral resources that all bees need.
Featured image “Bee and Beelette” by vapour trail is licensed under CC BY-ND 2.0
