Specialization and Foraging Efficiency of Solitary Bees

Abstract

The specialist bee, Hoplitis anthocopoides, foraged for pollen from Echium vulgare, its preferred plant, more efficiently than did four generalist species. Efficiency was measured as the weight of pollen (the larval food) harvested from Echium flowers per unit handling time, divided by the weight of the discrete pollen mass required to rear one offspring. This measure of efficiency corresponds more closely to reproductive output than does the usual measure, net energy gained per unit time. The specialists produced more potential offspring per unit handling time because they manipulated flowers faster and collected more pollen per flower than did generalists. The specialists also flew between flowers more rapidly than did the generalists. The specialists did not defend the flowers against generalists. These results support the assumption in models of resource partitioning and optimal foraging theory, and in hypotheses explaining the evolution of pollen—specializing bee species, that specialists are more efficient at using their preferred resources than are generalists.