Where is the UK's pollinator biodiversity? The importance of urban areas for flower-visiting insects

TLDR

Insect pollinators are essential but threatened, and while urban areas may support pollinators, their relative value compared to farmland and nature reserves is unclear and warrants inclusion in national conservation strategies. We compared pollinator communities using quantified flower‑visitation networks across 36 1‑km² sites in urban, farmland, and nature reserve landscapes. Flower‑visitor abundance and species richness did not differ among urban, farmland, and reserve sites, yet bee species richness was higher in urban areas, hoverfly abundance was greater in farmland and reserves, urban assemblages were more spatially homogeneous, farmland exhibited higher network specialization, and urban pollinators foraged from more plant species but a smaller proportion of available species, suggesting higher generality alongside higher specialization driven by greater plant richness.

Abstract

Insect pollinators provide a crucial ecosystem service, but are under threat. Urban areas could be important for pollinators, though their value relative to other habitats is poorly known. We compared pollinator communities using quantified flower-visitation networks in 36 sites (each 1 km(2)) in three landscapes: urban, farmland and nature reserves. Overall, flower-visitor abundance and species richness did not differ significantly between the three landscape types. Bee abundance did not differ between landscapes, but bee species richness was higher in urban areas than farmland. Hoverfly abundance was higher in farmland and nature reserves than urban sites, but species richness did not differ significantly. While urban pollinator assemblages were more homogeneous across space than those in farmland or nature reserves, there was no significant difference in the numbers of rarer species between the three landscapes. Network-level specialization was higher in farmland than urban sites. Relative to other habitats, urban visitors foraged from a greater number of plant species (higher generality) but also visited a lower proportion of available plant species (higher specialization), both possibly driven by higher urban plant richness. Urban areas are growing, and improving their value for pollinators should be part of any national strategy to conserve and restore pollinators.