SD07: Effects of urban warming on cucumber visitor communities and pollination success

Warmer temperatures under urbanization and climate change could push species beyond their tolerable thermal limits, causing animals to alter their foraging time or decrease their foraging activity to avoid the heat. In the case of bee pollinators, such behavioral changes could affect pollination service. However, to date, few studies have examined how varied temperatures across an urban to rural gradient impact bee communities and pollination. Using community gardens and cucumber (Cucumis savitus) as our study system, we asked whether hotter times and places within Raleigh and Durham, North Carolina experienced reduced daily pollination service. To calculate daily pollination service, we multiplied daily bee species-specific visitation rates by each species’ single visit effectiveness (the average number of conspecific pollen grains a bee of a particular species deposits in a single visit), and then summed across all visiting taxa on a given day. Pooling data across all sites and leveraging differences in temperature across all our sampling days, we found that cucumber plants received more pollination service on hotter days. These results imply that warming temperatures in the study region may increase pollination service to a certain extent. Ongoing work aims to understand why and under what conditions this is true. For instance, Bombus impatiens contributes significantly to daily service, since it visits cucumber plants frequently and has a relatively high single visit effectiveness, however on the hottest days its body temperature approaches stressful limits, suggesting there could be a point when temperatures are too hot for this important species.