Landscape heterogeneity
Landscape heterogeneity should have a positive effect on pollinators, as
heterogeneous landscapes provide more niches with a higher diversity of
food resources and nesting sites (Fahrig et al. 2011, Hopfenmüller et
al. 2014). We predicted that generalist hoverflies benefit more from
landscape heterogeneity compared to wild bees, as they forage across a
wider range of habitats (H2). In our study, wild bees were positively
affected by landscape heterogeneity at intermediate spatial scales
(340-780m). Similar, hoverfly abundance was positively affect at small
scales (100-140m). However, at large scales (<750m), landscape
heterogeneity had continuously a negative effect on hoverflies. We
expect that the observed negative relationship of hoverflies to
landscape heterogeneity is primarily driven by hoverfly responses to a
limitation of other resources in the landscape (see above), since both
landscape heterogeneity and arable field cover are negatively related to
each other at large scales. Hence, positive effects of landscape
heterogeneity may only be important for hoverflies, if landscape
heterogeneity is uncorrelated to arable field cover (as in our study for
small spatial scales). In conclusion, we found no support for the
hypothesis 2, which may be reasoned by specifics of our landscape,
though negative correlations between arable field cover and landscape
heterogeneity should be present in many areas worldwide (Tscharntke et
al. 2012).