Zooming out: How do small pollinator gardens support bumblebee (Bombus sp.) success in fragmented landscapes?

The decline of many bumblebee species can be attributed to the reduced quality and availability of habitat. Given the essential pollination services provided by bumblebees in natural and agricultural areas, there is interest in implementing conservation strategies for bumblebee communities. Currently these efforts prioritize providing floral resources from May-October through habitat augmentations, as many studies indicate these increase pollinator abundance and diversity; however, the impact at a landscape scale remains unclear. Small pollinator restorations have the potential to create stepping stones of habitat through the landscape (i.e., functional connectivity). We hypothesized that a higher degree of functional connectivity would support greater bumblebee success.

Here, we monitored five pollinator gardens in Connecticut, which fall along a gradient of green space within a 2-km radius, ranging from 8%-83%, a proxy for habitat connectivity. Weekly within the garden and at locations within the 2-km radius, we conducted vegetation surveys to assess floral resource availability and collected all bumblebees we observed within a 30-minute observation period to quantify species abundance and diversity. A non-lethal tarsal sample was collected from all Bombus impatiens workers captured during this time. DNA was extracted from each sample individually and population genetics analyses were conducted to estimate nest abundance and sibling relationships. Field and genomic data were modeled in ArcGIS to approximate connectivity of Bombus impatiens within green spaces and pollinator gardens. Results indicate that landscape composition influences bumblebee foraging behavior and success. This work will enable the creation of evidence-based recommendations for enhancing habitat connectivity in fragmented environments.