Local influence of floral resource attributes on urban bumble bee foraging activity

Authors: PFEIFFER, VERA - University Of Wisconsin; ZHU, JUN - University Of Wisconsin; Poh, Karen; SIBERNAGEL, JANET - University Of Wisconsin

Submitted to: Frontiers in Sustainable Cities
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2023
Publication Date: 7/13/2023
Citation: Pfeiffer, V.W., Zhu, J., Poh, K.C., Sibernagel, J. 2023. Local influence of floral resource attributes on urban bumble bee foraging activity. Frontiers in Sustainable Cities. 5. Article 1103721. https://doi.org/10.3389/frsc.2023.1103721.
DOI: https://doi.org/10.3389/frsc.2023.1103721

Interpretive Summary: We evaluated the influence of floral cover, density, species richness, and wild plant species richness on bee counts in the city of Madison, WI. We estimated the distance at which there was similarity between the bee counts compared to the overall bee count distribution using spatial correlograms. Then, we fitted a global model to estimate the effects of the floral resource variables on average across the whole extent, and a local regression, to estimate the effects of each floral resource variable at each point in the dataset based on the data from the 20 closest points. Floral cover, species richness, and wild flowering plant species richness were all useful to predict the number of bumble bees foraging. In neighborhoods with ample floral resources, there was a heightened positive influence of wild flowering plant species richness, and a reduced effect of overall flowering plant species richness.

Technical Abstract: Urbanization diminishes the extent of uncompacted, exposed soil and the coverage of wild plant species, yet may still support diverse pollinator communities when their habitat is maintained within the built environment. Floral cover, flower species richness, and wild flowering plant richness in particular are all factors known to influence bumble bee (Bombus spp.) foraging behavior, and these factors vary across the landscape, especially across heterogeneous urban extents. This study assesses how floral resources are distributed across the city of Madison, WI and how these factors influence the distribution of foraging bumble bees. We conducted a systematic walking transect survey of bumble bees across Madison, WI. The resulting point location data associated with more than 5,000 non-lethally surveyed bumble bees were analyzed with regard to floral resource explanatory variables as well as underlying land use zoning on more than 700 transects. We used variograms and correlograms to investigate spatial autocorrelation in floral resource variables and bumble bee counts, then we fitted a generalized linear model predicting transect bee counts based on floral cover, density, species richness and wild flowering plant species richness on the distribution of foraging bees. The glm model indicated significant positive influence of flower cover, species richness, and land use zoning and weakly significant positive influence of wild plant species richness on foraging bee counts. We fitted a geographically weighted regression model to explore heterogeneity in the effects of the floral resource explanatory variables across the study extent and found that the effects of floral resource predictors on foraging bumble bee behavior may vary based on landscape context across the city.