Spatial and temporal influence of oilseed-rape and semi-natural habitats on wild bees in permanent grasslands.
Résumé
Wild bees need continuous food resources throughout the season as found in semi-natural habitats (SNH). Oilseed rape (OSR) fields provide a short but rewarding food resource used by some species. The aim of this study was to understand the effects of landscape area covered by OSR (%OSR) and SNH (%SNH) on species richness and abundance of three different sociality functional groups captured in permanent grasslands. We found that in SNH-rich landscape, %SNH and %OSR significantly impacted bee abundance but not species richness. Responses greatly depended on bee sociality: %SNH enhanced eusocial bee abundance in the late season, but reduced other social bee abundance suggesting a dilution effect. The %OSR had a global positive effect on eusocial species but a negative effect on other social bees in permanent grasslands, illustrating a competition between OSR and SNH for other social bees. Our results highlighted the relevance of temporal approaches