Diverse pollinator communities enhance plant reproductive success

Abstract

Understanding the functional consequences of biodiversity loss is a major goal of ecology. Animal-mediated pollination is an essential ecosystem function and service provided to mankind. However, little is known how pollinator diversity could affect pollination services. Using a substitutive design, we experimentally manipulated functional group (FG) and species richness of pollinator communities to investigate their consequences on the reproductive success of an obligate out-crossing model plant species, Raphanus sativus. Both fruit and seed set increased with pollinator FG richness. Furthermore, seed set increased with species richness in pollinator communities composed of a single FG. However, in multiple-FG communities, highest species richness resulted in slightly reduced pollination services compared with intermediate species richness. Our analysis indicates that the presence of social bees, which showed roughly four times higher visitation rates than solitary bees or hoverflies, was an important factor contributing to the positive pollinator diversity-pollination service relationship, in particular, for fruit set. Visitation rate at different daytimes, and less so among flower heights, varied among social bees, solitary bees and hoverflies, indicating a niche complementarity among these pollinator groups. Our study demonstrates enhanced pollination services of diverse pollinator communities at the plant population level and suggests that both the niche complementarity and the presence of specific taxa in a pollinator community drive this positive relationship.

Figure 1.

Experimental design. Increasing pollinator richness up to nine species and three functional groups (FGs) (social bees (A), solitary bees (B) and hoverflies (C)), including all single-species ‘communities’, were used in a substitutive design. Three-species communities contained one or three FGs. Communities with three species from three FGs did not overlap.

Figure 2.

(a) Mean (±1 s.e.) number of seeds per fruit and (b) mean number of fruits per flower of R. sativus at different levels of pollinator FG (social bees, solitary bees, hoverflies) and species richness (see figure 1 for the experimental design).

Figure 3.

Mean (±1 s.e.) number of flower visits during 30 min of the three FGs social bees, solitary bees and hoverflies at four different daytime periods: 9.00–11.30, 11.30–14.00, 14.00–16.30, 16.30–19.00.