To experimentally test the eect of functional diversity on the functioning and persistence of plant-pollinator communities, we dened functional groups of plants and pollinators based on morphological traits. For plants, two functional groups with three species each were dened according to accessibility of oral rewards (pollen and nectar; see Figure 1). e rst group (group 1) included Matricaria o cinalis, Erodium cicutarium, and Raphanus raphanistrum, which have easily accessible oral rewards and will be called “open owers.” e second group (group 2), called “tubular owers,” included Mimulus guttatus, Medicago sativa, and Lotus corniculatus, all of which present oral rewards hidden at the bottom of a tubular corolla. For pollinators, two functional groups were dened according to mouthparts length (Figure 1). e rst group (group A) included three species of syrphid ies (Diptera) with short mouthparts: Saephoria sp., Episyrphus balteatus, and Eristalis tenax. e second group (group B) included three species of bumble bees with longer mouthparts: Bombus terrestris, B, pascuorum, 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 owers 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 ies cannot e ciently pollinate tubular owers because their mouthparts are too short.