Bee foraging behavior as predictor of plant reproduction and gene flow

Bee foraging behavior influences plant reproduction and gene flow, and variation in behavior among bee species can differentially influence these processes. We report on variation in tripping rate and residence among bee species. Tripping rate is the proportion of flowers whose anthers and stigma are released following a bee visit, a mechanism common in plants from the Fabiaceae and Lamiaceae families. Residence illustrates the number of flowers visited in succession within a foraging bout by a bee species. Bees visiting alfalfa flowers differ in tripping rate, with leafcutting bees, Megachile rotundata, having a higher tripping rate, followed by bumble bees, Bombus impatiens, and finally honey bees, Apis mellifera. We expect higher tripping rate to lead to higher seed set and the slope of the relationship between number of bee visits and seed set is steeper for leafcutting bees, followed by bumble bees and last, honey bees. We also predict higher tripping rates to limit gene flow, and observed a steeper pollen deposition slope for leafcutting bees relative to bumble bees. Leafcutting bees also had shorter residence relative to bumble bees and honey bees. Within a bee species, greater residence can limit gene flow. Among bee species, however, the pattern of pollen deposition has a greater influence on gene flow relative to residence. We conclude that the tripping rate of a bee species on a plant species can help predict its relative impact on seed production and gene flow.