Biology Reference
In-Depth Information
or both groups together (group C). This full factorial design led to nine experi-
mental treatments, which were replicated four times each, making a total of 36
experimental units. The pollination treatments were applied in two consecutive
years (June-July 2003 and 2004). We controlled for the total number of pollina-
tor visits received by each plot during the two pollination seasons (1,000 visits in
2003 and 1,200 visits in 2004) to allow an unbiased comparison of pollination
efficiency among the various experimental treatments.
In August and September 2003, we counted the number of fruits on each
plant in every plot. We also counted the number of seeds per fruit on five col-
lected fruits per plant. Lastly, in April 2004 and 2005, we measured both the
number of plant species present at the seedling stage (recruitment richness)
and the total number of seedlings (recruitment density) to determine the ef-
fects of the experimental treatments on the natural recruitment of the next
plant generation.
Results
Effects on Plant Reproductive Success
The reproductive success of the two plant functional groups after the first
season is analysed in Table 1. There was a significant effect of pollination treat-
ment on the number of fruits per plant (Table 1, left; standardized means ±
standard error [SE]: syrphid -0.278 ± 0.061, bumble bee 0.221 ± 0.065, and
both 0.063 ± 0.068). Orthogonal contrasts on pollination treatment indicate
that the identity of the pollinator guild (syrphid [A] versus bumble bee [B])
had a significant effect. There was a higher fruit production in bumble bee-
pollinated communities than in those pollinated by syrphids. Moreover, the
breakdown of the interaction of pollination and plant treatments into the
orthogonal contrasts A1 versus B1 and A2 versus B2 indicates that the two
plant functional groups responded differently to the identity of the pollinator
functional group. Tubular 3 flowers (group 2) produced significantly fewer
fruits in the syrphid treatment, whereas open flowers (group 1) produced
the same amount of fruits whatever the identity of the pollinator functional
group (Figure 2A). This supports our hypothesis that bumble bees were able
to pollinate both plant functional groups whereas syrphids could only ef-
ficiently pollinate open flowers. Although the functional diversity of plant or
pollinator treatment alone had no significant effect, fruit production tended
to increase with both plant and pollinator functional diversity (contrast [A1 +
A2 + B1 + B2] versus C3; Figure 2B).
