Resource overlap and possible competition between honey bees and wild beesin central Europe

Evidence for interspecific competition between honey bees and wild bees was studied on 15 calcareous grasslands with respect to: (1) foraging radius o f honey bees, (2) overlap in resource use, and (3) possible honey bee effec ts on species richness and abundance of flower-visiting, ground-nesting and trap-nesting wild bees. The grasslands greatly differed in the number of h oney bee colonies within a radius of 2 km and were surrounded by agricultur al habitats. The number of flower-visiting honey bees on both potted mustar d plants and small grassland patches declined with increasing distance from the nearest apiary and was almost zero at a distance of 1.5-2.0 km. Wild b ees were observed visiting 57 plant species, whereas honey bees visited onl y 24 plant species. Percentage resource overlap between honey bees and wild bees was 45.5%, and Hurlbert's index of niche overlap was 3.1. In total, 1 849 wild bees from 98 species were recorded on the calcareous grasslands. N either species richness nor abundance of wild bees were negatively correlat ed with the density of honey bee colonies (within a radius of 2 km) or the density of flower-visiting honey bees per site. Abundance of flower-visitin g wild bees was correlated only with the percentage cover of flowering plan ts. In 240 trap nests, 1292 bee nests with 6066 brood cells were found. Nei ther the number of bee species nor the number of brood cells per grassland was significantly correlated with the density of honey bees. Significant co rrelations were found only between the number of brood cells and the percen tage cover of shrubs. The number of nest entrances of ground-nesting bees p er square metre was not correlated with the density of honey bees but was n egatively correlated with the cover of vegetation. Interspecific competitio n by honey bees for food resources was not shown to be a significant factor determining abundance and species rich ness of wild bees.