Biology Reference
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communities that contained only tubular flowers, recruitment richness in the two
pollination treatments that contained bumblebees was similar.
These results are in agreement with our theoretical pollination network pre-
sented in Figure 1. In our experimental system, syrphids can be considered as
specialist pollinators since they efficiently pollinate only open flowers. Bumble
bees were potentially generalists as they induced an important fruit production of
the two plant types and a good recruitment in the open- and tubular-flower plant
treatments. Our results on the reproductive success and recruitment of single-
guild plant treatments indicate that there are strong functional group identity
effects since our plant functional groups responded differently to our pollinator
functional groups.
However, the functional diversity of both the plant and pollination treatments
was also important. Plant reproductive success tended to increase with pollinator
functional diversity when the number of seeds per fruit was considered, and with
both plant and pollinator functional diversity when the number of fruits per plant
was considered (Figures 2B and 2D). Although recruitment in single-guild plant
treatments was mainly affected by the identity of functional groups, the effect of
functional diversity was dramatic in the mixed plant treatment. Natural recruit-
ment of plant communities visited by mixed pollinator guilds was largely above
that in other pollination treatments.
Pollination by syrphids alone allowed the reproduction of open flowers but
not tubular flowers, as expected from the specialisation of syrphids. More surpris-
ingly, however, bumble bees failed to be efficient generalist pollinators. Most of
their visits occurred on tubular flowers (Figure 4), resulting in a relatively poor
recruitment of open flowers. The only pollination treatment that achieved a high
recruitment of both open and tubular flowers when they were mixed, was the
one containing the two insect functional groups (Figure 3, right). When syrphids
and bumble bees simultaneously pollinated mixed plant communities, they each
focused on their target plant functional group, leading to more efficient visits and
a better distribution of visits among plant functional groups (Figure 4). Ultimate-
ly, it was the pollination treatment with both pollinator functional groups that
produced the highest richness and density of natural recruitment. Consequently,
since most natural plant communities contain both open and tubular flowers,
pollinator functional diversity should strongly enhance the persistence of these
communities.
Although our experimental system differed from natural communities, and
information about the reciprocal effects of the functional diversity of plant
communities on the diversity of pollinator communities would be useful, our
study indicates that the functional diversity of plant-pollinator interaction webs
may be critical for the persistence and functioning of ecosystems and should be
