Ecological systems provide a number of services that support human economies and societal-well being. Biodiversity may play an important role in the provisioning of these services and understanding its effect is critical in order to mitigate the impacts of anthropogenic disturbance. Ecosystems high in species richness may stabilize the provisioning of ecosystem services if the species providing these services exhibit differential responses to the same environmental variable (herein response diversity). We examined whether the abundance of native, wild bees pollinating cultivated cranberry (Vaccinium macrocarpon) was associated with amount of agricultural land cover surrounding farms in southern New Jersey. We net-collected bees foraging on cranberry flowers at 16 farms on two different dates during peak bloom in 2009. We then related the abundance of each bee species to the amount of agricultural land cover at radii of 500, 1000, 1500, 2000, 2500, and 3500m. For each species, we used the amount of agricultural land cover at the most explanatory radius (highest Χ2) for the subsequent analysis. To test for response diversity, we used a generalized linear model with agricultural land cover and bee species identity as predictor variables, and bee abundance as the outcome variable. A significant interaction term between species and agricultural land cover indicates differential responses to agricultural land cover across bee species, i.e., response diversity.
Results/Conclusions
We collected 1230 individual bees of 46 species foraging on cranberry. Of those species, 9 had a sufficient sample sizes for this analysis (≥ 15 specimens collected and present at ≥ 3 farms). We found evidence for response diversity as the relationship between bee abundance and agricultural land cover differed among species (land cover x bee species interaction, Χ2 = 29, df = 8, p = < 0.001). Seven of the nine species (Bombus griseocollis, Bombus bimaculatus, Bombus perplexus, Augochlorella aurata, Osmia virga, Melitta americana, Lasioglossum planatum/taylori) decreased in abundance with increasing agricultural land cover; however, the magnitude of these decreases differed among species. Two species, Bombus impatiens and Xylocopa virginica, were positively associated with the amount of agricultural land cover. Previous work has demonstrated that Bombus species are highly effective pollinators of cranberry. Therefore, the diversity of responses found in this study suggests that biodiversity may stabilize pollination services across gradients of anthropogenic disturbance.
