Collaborative Research: Effects of pulsed floral resources on pollinator population dynamics

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This research will explore how one result of landscape change, the timing and availability of flowers, affects populations of bumble bees, a prominent group of native bees that pollinate many crops and wildflowers in North America. Bumble bees are important because more than one-third of the food we eat comes from crops that depend to some degree on the type of pollination they provide. Although non-native honey bees remain a cornerstone of agricultural pollination, native bees are increasingly the focus of agricultural attention in light of ongoing challenges facing honey bees. Healthy populations of native bees rely on continuous supplies of pollen and nectar. However, the availability of these floral resources has been dramatically altered by unpredictable weather associated with changing climate, and by human activities, including intensive agriculture. The investigators will study how changes in the timing and availability of flowers affect the number of bumble bees. This research is a significant advance over past studies, which used patterns of bee visits to flowers to make broad conclusions about the overall health of bee populations and communities. In contrast, the current study will focus on reproductive success of bee hives. The results will be key to developing strategies to promote robust populations of bees and ensure food security, as well as to conserve biological diversity. Specifically, the project combines manipulative field experiments and original demographic population models to assess effects of within-year resource variation (resource pulses) on population dynamics of bumble bees. The experiments will be conducted with Bombus vosnesenskii, a dominant bumble bee species in Northern California. Investigators will conduct experiments in which flower availability and timing are systematically altered. They will then measure how vital rates of individual colonies (e.g., worker production, worker survival, and queen production) depend on the availability of floral resources at different times in the colony life cycle. To ensure a consistent baseline of hive quality, all measurements will be made on lab-reared colonies started from wild-collected queens. Experimental results will be combined with demographic models to predict long-term population viability of bees under different landscape conditions. This research will answer questions about how ongoing landscape change will affect Bombus vosnesenskii and other bee species. It also will provide a previously-missing framework for population viability analysis of bees and other social insects.