Biology Reference
In-Depth Information
Considering recruitment density, there was also a significant effect of year,
with a higher density after the second pollination season (mean ± SE: 26.784
± 2.324 in 2004 and 31.319 ± 1.937 in 2005), and a significant effect of plant
treatment, with fewer individuals recruiting in tubular communities (Figure 3B,
centre). These year and plant-treatment effects can be explained in the same way
as for recruitment richness (see above). There was also a significant effect of polli-
nation treatment, with a lower recruitment density when plant communities were
pollinated by syrphid flies alone (means ± SE: syrphids: 24.104 ± 20.464, bumble
bees: 34.364 ± 32.781, and both 28.688 ± 21.459). This is congruent with our
results on the number of fruits produced per plant (see Table 1, contrast A versus
B). As for recruitment richness, there was a significant interaction between plant
and pollination treatments (Figure 3B). In the open-flower plant treatment, re-
cruitment density was not significantly different among pollination treatments
(Figure 3B, left). But in the tubular-flower plant treatment, recruitment density
was significantly higher in the bumble bee treatment than in the other pollination
treatments (Figure 3B, centre). Finally, in the mixed plant treatment, the same
pattern as for recruitment richness was observed: There was a higher density in the
mixed pollination treatment than in single-guild pollination treatments (Figure
3B, right).
Note that these results on natural recruitment are not an artefact caused by
sampling small quadrats in heterogeneous experimental plots since the same pat-
terns were observed when data from all quadrats in a plot were pooled.
Pollination Visitation Web in the Mixed Plant Treatment
To explain the strong effect of pollinator functional diversity on the persistence
of mixed plant communities, we carried out a log-linear analysis on the visita-
tion rate of each insect species in a given pollination treatment, for the six plant
species of the mixed plant treatment. Data from the year 2003 are illustrated in
Figure 4, and the results of the analysis on both years are presented in Table 3. In
the second year, there was a significant effect of plant functional group identity:
Tubular flowers received a higher number of visits than did open flowers (mean
visitation frequency ± SE: for open flowers 0.236 ± 0.097 and for tubular flow-
ers 0.763 ± 0.097). This is very likely due to the two well-established perennial
species, which produced a more attractive floral display during the second year
of the experiment. For the two years of the experiment, there was a significant
interaction between plant functional group and pollinator functional group. This
indicates that the two pollinator functional groups were specialised on different
plant functional groups (mean visitation frequency ± SE on open flowers and
tubular flowers, respectively: in 2003, for bumble bees 0.128 ± 0.058 and 0.433
