How many bees fit in the city? A spatial ecological case study to conserve urban wild bees

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Pollination is crucial for biodiversity and food security, with bees playing a significant role. The growing popularity of urban beekeeping is leading to increasing honeybee densities in cities, raising concerns about competition for pollen and nectar with wild bees due to limited foraging resources in densely urbanized areas. To assess the current bee occurrences of wild and honeybees in urbanized and protected areas of a Central European city, we focused on the ecological similarities between honeybees and wild bees. We compiled an inventory of 462 wild bee species documented since 1990 in Vienna (Austria) and conducted a survey of apiary locations in cooperation with beekeepers. We calculated apiary densities and indices for species richness, rarity, and, based on flower-visiting traits, the trait similarity between honeybees and wild bees. We found that approximately four times more honeybee colonies were kept in central Vienna in 2023 than the habitat may support. In parts of Vienna’s nature conservation areas, the number of colonies also exceeded the density of 3.5 colonies per km² recommended by the literature. Results indicate a significant spatial overlap of high apiary densities and wild bee hotspots, particularly in urban nature conservation areas like Natura 2000 protected areas. In Natura 2000 areas, the trait similarity of rare wild bee species was significantly increased, indicating a potential elevated competition between wild bees and honeybees for floral resources. This study highlights the need for spatial planning to balance urban beekeeping and wild bee conservation, recommending actions to match habitat quality to apiary densities to mitigate competitive pressures.