Woodland and floral richness boost bumble bee density in cranberry resource pulse landscapes

Authors: PFEIFFER, VERA - University Of Wisconsin; SILBERNAGEL, JANET - University Of Wisconsin; GUÉDOT, CHRISTELLE - University Of Wisconsin; Zalapa, Juan

Submitted to: Landscape Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2019
Publication Date: 4/2/2019
Citation: Pfeiffer, V., Silbernagel, J., Guédot, C., Zalapa, J.E. 2019. Woodland and floral richness boost bumble bee density in cranberry resource pulse landscapes. Landscape Ecology. 34(5):979. https://doi.org/10.1007/s10980-019-00810-1.
DOI: https://doi.org/10.1007/s10980-019-00810-1

Interpretive Summary: We sampled bumble bees using genetic markers at fourteen cranberry marshes before, during, and after the cranberry bloom in central Wisconsin. We quantified floral richness and surrounding land cover and assessed their effects on individual bumble bees and their colonies. The percentage of forest or conversely cultivated land best predicted bumble bee abundance. The interspersion of meadow through the surrounding landscape and the total bog edge were also useful to explain bumble bee abundance. Floral richness was the primary factor influencing individual bumble bee abundance during bloom, as well as the change in colony abundance accounting for detection. Additionally, landscapes with large agricultural field sizes and very clumpy forest had a decrease in colony detection probability during the bloom. We suggest that cranberry growers can use this information to justify maintaining forested land and interspersed meadow around cultivated crops. This action will promote bumble bee colony abundance, and bolstering floral richness locally will draw in more bees when floral resources are abundant, thus enriching their pollination services.

Technical Abstract: Native pollinators provide an important ecosystem service for many pollination-dependent fruit crops, and require nesting and foraging resources in proximity to target crop plants. Additionally, pollination services provided by wild bees may fluctuate temporally due to foraging preferences that may shift based on surrounding habitat and floral resources throughout the season. This study investigates how floral resources and landscape context influence bumble bee colony density and fluctuation around and during the resource pulse created by the target crop bloom. We sampled bumble bees using genetic markers at fourteen cranberry marshes before, during, and after the cranberry bloom in central Wisconsin. We quantified floral richness and surrounding land cover and assessed their effects on individual and colony density using linear regression models and variance partitioning. The percentage of forest or conversely cultivated land best predicted individual and colony density during almost all temporal extents. The interspersion of meadow through the surrounding landscape and the total bog edge were also useful to explain variance in top regression models for bumble bee density. Floral richness was the primary factor influencing individual density during bloom, as well as the change in colony density accounting for detection. Additionally, landscapes with large agricultural field sizes and very clumpy forest experienced a decrease in colony detection probability during the bloom. We suggest that maintaining forested land and interspersed meadow around cultivated fruit crops is important to promote bumble bee colony abundance, and bolstering floral richness locally will draw in more bees when floral resources are abundant.