The influence of nature reserves on hoverflies and bees in agricultural areas (Diptera: Syrphidae; Hymenoptera: Apidae s.l.).

摘要

Over the last decades, biodiversity in agricultural landscapes has declined drastically. Initiatives to enhance biodiversity, such as agri-environment schemes, are often ineffective, especially in intensively farmed landscapes. Possibly, the distance to source areas is a limiting factor. We evaluated the effects of (semi-) natural habitats on biodiversity of hoverflies and bees in the surrounding, intensively managed agricultural landscape. We surveyed bees and hoverflies in 300 m long transects along ditch banks, both bordering and perpendicular to the edge of four nature reserves, forming small islands in landscapes dominated by agriculture. Species density and abundance of hoverflies declined over the first 125 m beyond the nature reserves. After these distances, no further decline was observed. Species density of the bees declined sharply already after 25 m. Therefore, species of flower-visiting insects resident in high-quality (semi-) natural habitats tend to disperse over limited distances (<150 m) into the neighbouring agricultural landscape. These results give an indication of the chance of colonization of a site in relation to the distance to a nature reserve. Agri-environment schemes focused on biodiversity conservation may therefore be most effective when implemented in the direct vicinity of (semi-) natural habitats.