Different responses of bees and hoverflies to land use in an urban–rural gradient show the importance of the nature of the rural land use

Most studies focusing on the effects of urban land use on pollinators have compared urban sites with one type of rural site. However, there is a lot of variation in the amount of natural habitats or intensive agriculture in rural areas. The position of urban areas within that continuum in terms of pollinator communities remains unclear. In this work, we studied bee and hoverfly communities (abundance, diversity, and species composition) in three site types along two river systems crossing urban areas, rural areas dominated by agriculture (termed rural-agricultural) and rural areas with high amounts of semi-natural land use (termed rural-natural). Pollinators were caught in August 2011. Abundance and diversity were highest in rural-natural sites for both taxonomic groups. Our data also indicate that hoverflies and bees responded differently to the surrounding land use, with bee abundance and diversity only significantly reduced in rural-agricultural sites but not in urban sites, and hoverfly abundance and diversity only significantly reduced in urban sites but not in rural-agricultural sites. The observed differences in the response of pollinators point out the importance of incorporating different types of rural land use and clearly defining the rural end of an urban–rural gradient in getting a clear view on how urban land use affects a specific pollinator group. Year-round sampling of these pollinators would, however, probably enable a more accurate view on these responses.