Different responses of pollinator groups to crop field boundary-interior gradients – A meta-analysis

Mean field sizes in agricultural landscapes have increased significantly over the past decades due to agricultural intensification with negative consequences for biodiversity. We conducted a meta-analysis to investigate and summarize how distance from the field boundary, i.e. the crop field edge or margin, affects pollinator communities. We studied pollinator species richness and abundance, as well as differences among taxonomic groups (butterflies, flies, wild bees), the effect of agri-environment schemes (with or without management), and crop types (entomophilous vs. non-entomophilous crops). Our meta-analysis documents in this first synthesis (35 studies, 162 datapoints) that pollinator species richness and abundance were generally higher at field boundaries and decreased toward field interiors. Species richness was more strongly (medium effect) affected by distance from the boundary than abundance (small effect). Butterflies (medium effect) and flies (small effect) showed a stronger distance decay than wild bees including bumblebees. Agri-environment schemes implementation created a larger ecological contrast between the field boundary and the interior, resulting in a stronger distance decay of pollinator species richness (medium effect) and abundance (small effect). Pollinator species richness and abundance were higher at field boundaries in non-entomophilous than in entomophilous crops with medium and small effects, respectively. We conclude that decreasing field size and thereby increasing edge length may enhance pollinator richness and, to a lesser extent, abundances in agricultural landscapes. This pattern likely reflects the greater availability of suitable field-boundary habitats and food resources, particularly when cereal field boundaries are enhanced with flower strips.