Honey bees (Apis mellifera) modify plant-pollinator network structure, but do not alter wild species’ interactions

Honey bees (Apis mellifera) are widely used for honey production and crop pollination, raising concern for wild pollinators, as honey bees may compete with wild pollinators for floral resources. The first sign of competition, before changes appear in wild pollinator abundance or diversity, may be changes to wild pollinator interactions with plants. Such changes for a community can be measured by looking at changes to metrics of resource use overlap in plant-pollinator interaction networks. Studies of honey bee effects on plant-pollinator networks have usually not distinguished whether honey bees alter wild pollinator interactions, or if they merely alter total network structure by adding their own interactions. To test this question, we experimentally introduced honey bees to a Canadian grassland and measured plant-pollinator interactions at varying distances from the introduced hives. We found that honey bees increased the network metrics of pollinator and plant functional complementarity and decreased interaction evenness. However, in networks constructed from just wild pollinator interactions, honey bee abundance did not affect any of the metrics calculated. Thus, all network structural changes to the full network (including honey bee interactions) were due only to honey bee-plant interactions, and not to honey bees causing changes in wild pollinator-plant interactions. Given widespread and increasing use of honey bees, it is important to establish whether they affect wild pollinator communities. Our results suggest that honey bees did not alter wild pollinator foraging patterns in this system, even in a year that was drier than the 20-year average.

Methods
In southern Alberta, Canada we established eighteen 30 x 2 m transects at 100 m, 500 m, and 5000 m distances on either side of each of 3 clusters of honey bee hives for a total of six replicates. Between May 28 and August 28, 2019, observers visited each transect and surveyed insect flower visitation almost once per week for a total of 10 collection rounds. All insects that visibly contacted the anthers or stigma of open flowers were collected with a hand net and placed in labelled individual vials, frozen, and identified to species in the lab. Associated flowers were identified to species. The data were entered in Excel and processed and cleaned in R/Rstudio.

The data provided includes interaction data from nineteen transects (originally 18 but F5000 was replaced with G5000 mid-season). Interactions are recorded between pollinators and plants and the dataset also includes flower species abundance data for each transect sampled. Additionally, transect locations and locations of the bee hives placed are included.

The data provided also includes measured functional trait data from bees caught from the hand-caught dataset.

Later, some of the pinned insect specimens' body sizes were measured and contributed to the paper: "Pollinator intraspecific body size variation and sociality influence their interactions with plants". 2024. Functional Ecology. Authored by Peralta, Guadalupe; Resasco, Julian; Worthy, Sydney; Frost, Carol; Guevara, Angie; Manning, Isabella; Cagnolo, Luciano; Burkle, Laura.

To take body size measurements, the selected specimens were photographed from the dorsal side with a Nikon COOLPIX 8400 Digital Camera mounted on an OLYMPUS SZX16 stereo microscope. A ruler was placed adjacent to and in the same plane as the insect’s dorsal surface during photography. The images were then imported into ImageJ, calibrated using the ruler as a scale bar, and measured using the line tool to manually delineate the intertegular distance, which is the distance spanning between the wing bases. Only intergegular distances were analyzed in the above paper. However, other distances measured for some specimens included: thorax length (as viewed dorsally and measured along the midpoint), head width, head length, abdomen length, and body length.