Urban wild bees benefit from flower-rich anthropogenic land use depending on bee trait and scale

Abstract

Context: Wild bees are important pollinators for wild and cultivated plants. Besides other causes, their decline has been linked to land-use change such as urbanisation. In contrast, urban habitats are discussed as potential wild bee refuges. Objectives: To expand our understanding of cities as wild bee habitats, bee responses to urban land-use types with varying foraging and nesting resources were analysed. Methods: Wild bees were sampled with pan traps at 49 study sites in a Central European city. Effects of land-use types on wild bees were examined at 12 scales ranging from 50 to 1500 m from sampling points. For analyses, bees were grouped according to their traits (e.g., size, nesting and pollen-collecting behaviour) to account for species-specific requirements. Results: Land-use types significantly affected wild bees covering all investigated scales. Anthropogenically managed flower-rich habitats, i.e., long-term allotments and cemeteries, were beneficial for most wild bee groups within varying scales between 200 and 600 m. Impervious surface affected only some of the investigated wild bee groups, mostly in a unimodal manner within a 100 m scale. Conclusions: This study shows that it is recommended for future investigations to take different scales and different bee traits into account when assessing urban habitat quality for bees. In particular, the non-linear response to impervious surface indicates positive edge effects between urban core and rural areas. Conservation measures and implementation management to support wild bees in urban areas should consider the results on scale and land use to meet species-specific demands effectively.