Biology Reference
In-Depth Information
Table 3.
Analysis of Visitation Rates.
Discussion
Previous studies on the diversity of plant-pollinator interaction webs were either
descriptive [16], carried out on a single plant species [6,7,28-30], or based on
simulation [21] and theoretical approaches [22,31]. To our knowledge, this is
the first experimental evidence that the persistence of a plant community can be
affected by a loss of diversity of its pollinating fauna. Of course, our experimental
communities differed from natural ones in several respects. Among other things,
the interaction networks we studied were much simpler than those occurring in
nature; in particular, they contained fewer species in each trophic level. But such
simplifications from natural situations are often necessary to carry out controlled
experiments.
In plant communities that contained only open flowers, plants produced fewer
seeds per fruit in the bumblebee treatment than in the syrphid treatment (Figure
2C), but this was compensated by a sufficiently high fruit production, leading to
a richness and density of natural recruitment that was similar to the other pollina-
tion treatments (Figure 3A and 3B left). Thus, in these communities, all pollina-
tion treatments were equally effective in the long term.
In plant communities that contained only tubular flowers, syrphids were in-
efficient pollinators; fruit production was very low (Figure 2A) and insufficient
to allow a good natural recruitment. Bumble bees were the most effective pol-
linators (Figure 3A and 3C, centre). Note that in the bumble bee treatment, the
very high value of average recruitment density was due to three measurements in
two replicates, in which only M. guttatus seedlings were recorded at a very high
density (more than 150 seedlings per quadrat). To test the effect of these outliers,
we removed them and repeated our analysis. The same significant effects were
observed, except for the effect of pollination treatment, which became margin-
ally significant (p = 0.0645). The new mean number of seedlings per quadrat for
this experimental treatment was 32.17 ± 4.55 (SE), which is still slightly above
the value for the pollination treatment with both pollinator groups. For plant
