Bee-Mediated Pollen Transport Across Five Urban Landscape Features: Buildings Are Important Barriers

Urbanization alters insect pollinator diversity and foraging ranges, while also providing novel pollinator habitats. Common urban landscape features, such as roads and buildings, may alter the ability of insect pollinators to move and forage throughout the urban landscape. In this study, we aimed to quantify the effects of common urban landscape features on insect pollinator movement. We focused on roads, buildings, forest fragments, lawns, and community gardens. We studied five community garden sites and the landscape features surrounding them in Raleigh, North Carolina, USA. To measure pollinator movement across each feature, we placed clusters of potted cucumber plants on either side of a feature and added fluorescent dye powder to the stamens of the flowers. After 7 h, we collected and counted the number of fluorescent dye powder grains transferred to each cucumber stigma. We conducted 10-min visitation observations at each cluster to assess the pollinator community and to assess whether low visitation was linked to low dye transfer. Buildings had the lowest estimated dye transfer, roads and gardens were intermediate, and lawns and forest fragments had the highest estimated dye transfer. Although plants associated with buildings also had low visitation rates, visitation overall was a poor predictor of dye transfer. The most common visitors observed were Apis mellifera, Bombus spp., and Xylocopa virginica, indicating our results are likely primarily representative of these large, generalist bee species. Our study highlights the heterogeneity of urban spaces to pollinators. We demonstrate which features facilitate and inhibit movements of pollinators and thereby provide an empirical basis to map and assess functional landscape connectivity. This information can help cities identify and create connected networks of habitat for essential pollinators using geospatial methods, and can inform research about resource accessibility and foraging energetics for urban pollinators.