Agroecosystem landscape diversity shapes wild bee communities independent of managed honey bee presence

Abstract

Large scale agricultural production can lead to a reduction in availability of habitat used by wild bees for nesting and forage and has been implicated in worldwide bee population declines. There is growing concern that further declines in wild bee populations will occur because of continued transformations of natural or seminatural landscapes into crop monocultures. Managed honey bees, often used for pollination services in agricultural systems, can compete with wild bees and are hypothesized to negatively affect their communities. Although the response of wild bees to both agriculture and honey bees (i.e., apiculture) has been studied, the relative importance of each and their potential interactions on wild bee communities are not well understood. To forecast the extent to which landscape simplification can affect wild bees and to better understand whether honey bee presence in an already disturbed landscape might further exacerbate declines, we conducted a replicated, longitudinal assessment of wild bee community richness and richness of functional guilds (e.g., floral specificity and nesting preference) in an intensively farmed region of the United States where much of the landscape is devoted to monoculture annual crop (maize and soybean) production and managed honey bee colonies co-occur. The presence of a small apiary (4 colonies) had no immediate effect on wild bee richness, suggesting honey beekeeping may not always negatively impact wild bees. Rather, landscape composition analysis showed strong responses of wild bees to land use, with communities being less speciose in landscapes with high proportions of crop production. The availability of woodland and grassland habitat, especially at the local scale (<800 m), was associated with the greatest increase in bee richness especially for rarer aboveground nesting and floral specialist species. These data suggest large scale monocultures have a greater impact on bee communities than the presence of small apiaries. The results of this research provide important information on possible solutions in agroecosystem management to support increased bee diversity where annual crop production and apiculture are practiced. Namely, mitigation of wild bee declines in such agroecosystems may benefit more from the re-integration of landscape biodiversity, with priority on the re-introduction of perennial vegetation, like that found in woodland and grassland habitats, than the restriction of honey bee apiculture. Data AvailabilityData will be archived through Iowa State Universities digital data repository.