3.1 Bee behaviour and Visitation Rates
As expected, two bumblebee species were the only pollinator visitors to
our experimental plants, with Bombus hortorum visiting flowers
significantly more often (mean = 0.6 ± 1.6 SD visits per flower per
hour) than B. pascuorum (mean = 0.2 ± 0.9 SD; P<0.001;
N = 1288 3-minute surveys). Overall, robbed flowers received visits at a
significantly lower rate (mean = 0.7 ± 1.7 SD visits per flower per
hour) than flowers in the control treatment (mean = 1.0 ± 2.0;
P<0.001; Fig. 2a), and this was consisted for both bumblebee
species.
We found that the average visit length to flowers was also different
when comparing robbing treatments. Visits to robbed flowers were
significantly shorter (mean = 6.6 ± 5.3 SD seconds; N = 120) than on the
control flowers (mean = 10.3 ± 9.5 SD; N = 210; P < 0.001),
with visits being on average 3.7 seconds shorter (Fig. 2b). This
reduction in visit length was consistent across bumblebee species (Fig.
3); however, visits by B. hortorum were overall of shorter
duration (mean = 7.3 ± 6.3 SD seconds; N = 232) than B. pascuorum(mean = 12.9 ± 11.2 SD; N = 98; P < 0.001; Fig. 3).
Bumblebees visited on average 50% of a control plant’s flowers on an
inflorescence (N = 52) and 42% of a robbed plant’s flowers (N = 40),
and this difference was statistically significant (P = 0.037). When
recording the number of times that plants in each treatment were
rejected by foragers, robbed plants were rejected 32 times compared with
25 times for the control; this was not significantly different (P=0.090)