Conclusion
In conclusion, we observed contrasting and scale-dependent responses of
wild bees and hoverflies to measures of land-use intensification, with
no particular effects of local flower diversity of plants. As a
consequence, pollination service on dry grasslands should change with
the surrounding landscape. In homogeneous landscapes with a high share
of arable field cover, insect pollination should occur less frequent,
due to lower numbers of wild bee individuals and species. Although
hoverflies concentrate particularly in these landscapes at dry
grasslands they cannot compensate absence of wild bees, as they are less
specialized to particular flower types and appear only in late summer in
reasonable amounts (see also Brandt et al. 2017). Moreover, the
comparison with historical data indicate that species composition and
abundance of both guilds already shrunk in our study area, presumably
due to high land-use intensification. In order to achieve a better
understanding of how land-use intensification affects pollinators, we
advocate to a) acknowledge that landscape effects may differ between
landscapes and b) analyze therefore possibly confounding landscape
parameters across scales.