Biology Reference
In-Depth Information
To experimentally test the effect of functional diversity on the functioning
and persistence of plant-pollinator communities, we defined functional groups of
plants and pollinators based on morphological traits. For plants, two functional
groups with three species each were defined according to accessibility of floral
rewards (pollen and nectar; see Figure 1). The first group (group 1) included
Matricaria officinalis, Erodium cicutarium, and Raphanus raphanistrum, which
have easily accessible floral rewards and will be called “open flowers.” The second
group (group 2), called “tubular flowers,” included Mimulus guttatus, Medicago
sativa, and Lotus corniculatus, all of which present floral rewards hidden at the
bottom of a tubular corolla. For pollinators, two functional groups were defined
according to mouthparts length (Figure 1). The first group (group A) included
three species of syrphid flies (Diptera) with short mouthparts: Saephoria sp., Epi-
syrphus balteatus, and Eristalis tenax. The second group (group B) included three
species of bumble bees with longer mouthparts: Bombus terrestris, B, pascuo-
rum, and B, lapidarius. Note that in this case a functional trait (long mouthparts)
and a phylogenetic group are confounded. Preliminary observations showed that
these six insect species contribute up to 70% of all pollinating visits to flowers
in our study area in France. Constructing a plant-pollinator network with these
four functional groups leads to a nested structure with specialists interacting with
generalists (Figure 1, third column). In principle, syrphid flies cannot efficiently
pollinate tubular flowers because their mouthparts are too short.
Figure 1.
Experimental Pollination Web.
Summary of
the characteristics upon which functional groups of pollinators (left) and plants (right) were based.
In the middle, the arrows linking insect heads to flower types show the theoretical pollination network when all
functional groups are present.
At the beginning of spring 2003, we set up 36 4-m2 caged experimental plant
communities. There were three plant treatments following a “substitutive” design
[26]. Two of them contained one of the two plant functional groups alone (group
1 or 2), whereas the third contained both plant functional groups in combina-
tion (group 3). We applied three different pollination treatments to each plant
treatment, by introducing each pollinator functional group alone (group A or B),
