The worldwide importance of honey bees as pollinators in natural habitats

Abstract

The western honey bee (<i>Apis mellifera</i>) is the most frequent floral visitor of crops worldwide, but quantitative knowledge of its role as a pollinator outside of managed habitats is largely lacking. Here we use a global dataset of 80 published plant-pollinator interaction networks as well as pollinator effectiveness measures from 34 plant species to assess the importance of <i>A. mellifera</i> in natural habitats. <i>Apis mellifera</i> is the most frequent floral visitor in natural habitats worldwide, averaging 13% of floral visits across all networks (range 0-85%), with 5% of plant species recorded as being exclusively visited by <i>A. mellifera</i> For 33% of the networks and 49% of plant species, however, <i>A. mellifera</i> visitation was never observed, illustrating that many flowering plant taxa and assemblages remain dependent on non-<i>A. mellifera</i> visitors for pollination. <i>Apis mellifera</i> visitation was higher in warmer, less variable climates and on mainland rather than island sites, but did not differ between its native and introduced ranges. With respect to single-visit pollination effectiveness, <i>A. mellifera</i> did not differ from the average non-<i>A. mellifera</i> floral visitor, though it was generally less effective than the most effective non-<i>A. mellifera</i> visitor. Our results argue for a deeper understanding of how <i>A. mellifera</i>, and potential future changes in its range and abundance, shape the ecology, evolution, and conservation of plants, pollinators, and their interactions in natural habitats.