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€ T E R et al.
222 T . D I E K OT
corrected Akaike information criterion (stepAICc) for stepwise
(direction = both) model selection in R 2.14.2 (R Development
Core Team, 2012). The model yielding the lowest AICc according to this procedure always had the lowest number of predictor variables and was selected as the final model. We used Rfunction lm on final models to retrieve adjusted R2 values.

Results
Altogether, 1540 trap-nesting bees and wasps from 16
species were recorded. O. rufa was represented by 1208
individuals (78%). The remaining nine bee species contributed 247 individuals; six wasp species contributed
85 individuals. Neither across the year (t = 0.6034,
df = 8, P = 0.563) nor for the separate periods during
(t = 0.4999, df = 8, P = 0.631) nor after (t = 1.0756,
df = 8, P = 0.314) the mass flowering of oilseed rape
were abundances of O. rufa and the total of all other
trap-nesting bees and wasps significantly correlated. On
average, 66% 21 (standard deviation) of all individuals per site hatched from nests built during the mass
flowering of oilseed rape. However, early nests were
dominated by O. rufa. Once this dominant species was
excluded, 78% 31 individuals hatched from nests
built after the mass flowering of oilseed rape (332 individuals, Fig. 2).
From a total of 516 nests, hatching bees and wasps
were determined for 133 nests, 220 nests of bivoltine
species’ first generations were vacated during exposure
in the field without record, and bees or wasps died
before hatching in 163 nests. Based on the records from

133 nests with species identification, estimated species
richness of trap-nesting bees and wasps across the year
was significantly positively related to the percentage
area of oilseed rape at the 1750 m scale and seminatural
habitat at the 1500 m scale (Fig. 2a–b; Table 2). In absolute numbers, estimated species richness increased twofold from approximately three to six species with an
increase in oilseed rape from 4 to 15% and from 2.5 to 5
species with an increase in seminatural habitats from 2
to 14%. While both landscape variables were not significantly related to estimated species richness during the
mass flowering of oilseed rape, after the mass flowering
the percentage areas of oilseed rape and seminatural
habitats were significantly positively related to estimated species richness at the 2000 m and 1000 m scale,
respectively (Fig. 2c–d; Table 2). In absolute numbers,
observed species richness after the mass flowering of
oilseed rape increased from approximately two to five
species with an increase from 4 to 15% in oilseed rape
and from 2 to 17% in seminatural habitats.
Seminatural habitats were also positively related to
the abundance of trap-nesting pollinators across the
year at the 1250 m scale (Fig. 2e; Table 2) and after the
mass flowering of oilseed rape at the 1000 m scale
(Fig. 2f; Table 2).
The number of nests from which individuals of bivoltine first generations hatched in the field was significantly negatively related to the percentage area of
seminatural habitats at the 1750 m scale across the year
and during the mass flowering of oilseed rape (Fig. 2g–h;
Table 2).

Fig. 2 Percentage of individuals hatched during and after the mass flowering of oilseed rape per species. Species appear in descending order with regard to percentage of individuals hatched during mass flowering and in alphabetical order for species recorded only
after mass flowering. In addition to species’ names, their taxonomic assignment, abundance, and information on their phenology are
provided (? indicates insufficient data; III = March, IV = April, etc.; Bl€
uthgen, 1961; Westrich, 1989; Schmidt & Schmid-Egger, 1991).
© 2013 Blackwell Publishing Ltd, GCB Bioenergy, 6, 219–226