Landscape context and pollinator composition
The specific landscape context may modulate the observed responses of
pollinators. Although we are confident that similar findings (and
correlations between landscape predictors) can be expected in other
regions, we would like to highlight that our study area belongs to the
most intensified landscapes in Europe (for comparison: 39 % of the
total land area of the EU is cropland, around our study patches mean of
60%) with a long history of intensive fertilization and pesticides
input. Therefore, we assume that the past land-use intensification
already had a tremendous effect on the species pool in the area and the
species composition in our study is only a small subset of the species
pool of some decades ago. The comparison with previous studies in our
study area (Hahn 2002, Saure and Berger 2006) indicates that on the one
hand oligolectic bee species disappeared (see above), but also common
hoverflies. We observed remarkably low ratios between hoverflies and
wild bee individuals compared to studies of similar study systems (our
study 1419 wild bees vs. 214 hoverflies, ratio = 0.15; Mudri-Stojnić et
al. 2012: ratio 0.83, Jauker et al. 2009: ratio: 0.82, Jauker et al.
2019: ratio 0.95). In particular, generalist aphidophagous species (e.g.Eupeodes corollae , Sphaerophoria scripta ) that occur in
high densities (e.g. Hahn 2002 for our landscape, Bankowska 1980), are
underrepresented in our study, which concurs with the decline of common
hoverfly species (Hallmann et al. 2021). These deviations are most
likely a consequence of the high land-use intensity in our study region,
which is the main factor for the current insect decline (Wagner et al.
2021) and question the hypothesis that hoverflies are less vulnearble
than wild bees.