Roads are partial barriers to foraging solitary bees in an urban landscape

Understanding how animals navigate novel heterogeneous landscapes is key to predicting species responses to land-use change. Roads are pervasive features of human-altered landscapes, known to alter movement patterns and habitat connectivity of vertebrates like small mammals and amphibians. However, less is known about how roads influence movement of insects, a knowledge gap that is especially glaring in light of recent investments in habitat plantings for insect pollinators along roads verges and medians. In this study, we experimentally investigate behavioral avoidance of roads by a solitary bee and explore whether landscape factors are associated with bee movement in urban Massachusetts, USA. Using mark-recapture surveys, we tracked individual solitary bee (Agapostemon virescens) foraging movements among floral patches separated by roads or grass lawn. We found that roads acted as partial barriers to movements of foraging bees, with road crossings nearly half as likely as along-road movements (36% vs. 64%). Movement probabilities were negatively associated with distance and the proportion of roadway between patches, and positively associated with higher floral resource density at the destination patch. Importantly, our findings also suggest that while roads impede bee movement, they are not complete barriers to dispersal of bees and/or transfer of pollen in urban landscapes. In the context of green space design, our findings suggest that prioritizing contiguous habitat and ensuring higher floral densities along road edges may enhance resource access for pollinators and mitigate the risk of ecological traps.