The worldwide importance of honey bees as pollinators in natural habitats

Abstract

The western honey bee (Apis mellifera) 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 A. mellifera in natural habitats. Apis mellifera 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 A. mellifera For 33% of the networks and 49% of plant species, however, A. mellifera visitation was never observed, illustrating that many flowering plant taxa and assemblages remain dependent on non-A. mellifera visitors for pollination. Apis mellifera 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, A. mellifera did not differ from the average non-A. mellifera floral visitor, though it was generally less effective than the most effective non-A. mellifera visitor. Our results argue for a deeper understanding of how A. mellifera, and potential future changes in its range and abundance, shape the ecology, evolution, and conservation of plants, pollinators, and their interactions in natural habitats.

Keywords: Apis mellifera; floral visitation; meta-analysis; plant–pollinator network; pollination; pollination effectiveness.

Figure 1.

Proportion of all floral visits contributed by the western honey bee (Apis mellifera) in 80 plant–pollinator interaction networks in natural habitats worldwide. Apis mellifera is generally considered a native species in Europe, the Middle East, and Africa; and introduced elsewhere. (Online version in colour.)

Figure 2.

The distribution of the proportion of floral visits contributed by the western honey bee (Apis mellifera) (a) across 80 plant–pollinator interaction networks in natural habitats worldwide, and (b) across plant species in 41 networks where A. mellifera was documented and where the numbers of visits to each plant species by A. mellifera and other floral visitors were available. Bars show the mean value of each bin across networks; whiskers show 95% confidence intervals.

Figure 3.

Average single-visit pollination effectiveness of the western honey bee (Apis mellifera) relative to (a) the mean effectiveness of all other floral visitor taxa, and (b) the effectiveness of the most effective non-A. mellifera taxon. p-values at the bottom-centre of each panel reflect two-sample t-test comparisons of A. mellifera relative effectiveness in non-crop (n = 18) versus crop (n = 16) plant species; p-values at the top-left reflect one-sample t-test comparisons of A. mellifera to the mean or most effective non-A. mellifera pollinator after combining data from non-crop and crop plant species. Boxes show central 50% of data and median; whiskers show quartiles ± 1.5× interquartile range, or most extreme values of data, whichever is closest to median. Points indicate extreme values.