Reconciling community-level responses of wild bees to highly anthropized landscapes

Abstract

As central-place foragers, wild bees are key witnesses of landscape transformations. Despite a prolific literature on their conservation, the impact of urbanization on bee communities remains unclear, yielding highly context-dependent results. In contrast, few data are available to assess the effectiveness of protected areas in conserving bee diversity. Our study aimed at quantifying the effect of land cover components and site protection status on the conservation value of bee communities within a highly anthropized landscape. We analyzed 6105 specimens across 91 sites, including protected areas, in the industrial belt of Hainaut, Belgium. We compared the effects of land cover components and site protection for several definitions of conservation value, including diversity indices and the number of threatened species. We found that urbanization increased diversity when abundance-based indices were examined, while simultaneously reducing the richness of threatened species. Flower-rich grasslands did not improve diversity indices, but they increased the number of threatened species. Forested areas were negatively associated with all diversity metrics except the number of threatened species. Similarly, protected areas displayed lower indices of diversity, but not fewer threatened species. This pattern aligns with the predominance of forested areas around protected sites. Our results suggest that the decline of threatened species in urban environments may be masked by high diversity among abundant species, a pattern detectable only through multiple metrics of conservation value. In addition, we reveal that existing networks of protected areas in the landscape may not be able to mitigate this decline, as reserves are not necessarily designed for the conservation of all species and may be biased towards certain types of environments.