ECOLOGIE - ENVIRONNEMENT

Landscape composition is assumed to modify spatial foraging patterns of bees in agricultural ecosystems which subsequently influence pollination services provided to crops. However, empirical evidence to support this prediction is scarce.

We investigated the influences of semi-natural habitats and nesting resources on concentration effect and waylaying effect of bees, as well as their consequences on crop pollination in landscapes. Ninety-seven vetch patches with independent gradients of size and distances to nesting sites were selected from 11 agricultural landscapes with independent gradients of surrounding semi-natural habitats and nesting resources. Semi-natural habitats and nesting resources were quantified either by field inspections or from satellite images; flower visitor densities and vetch pollination services were measured across overall flowering seasons.

The proportion of semi-natural habitats did not modify the concentration effect or waylaying effect of the abundant and highly social honey bees or the solitary species Anthophora waltoni. The increase in area of brick walls, acting as nesting resources of A. waltoni, increased the concentration effect and the waylaying effect. For other solitary bees, the proportion of semi-natural habitats and the proportion of buildings did not influence the concentration effect or the waylaying effect. Honey bee density, A. waltoni density and other solitary bee density positively predict vetch pollination services. The landscape-modified concentration effect and waylaying effect cascaded to vetch pollination by modifying A. waltoni density. Our findings indicated that landscape composition could modify the spatial foraging patterns of bees and influence pollination services provided to crops, but those varied among different taxonomic groups.