Wild pollinators, bees in particular, may greatly contribute to crop pollination and provide a safety-net against declines in commercial pollinators. However, the identity, life history traits and environmental sensitivities of main crop pollinator species have received limited attention. These are crucial for predicting pollination services of different communities and for developing management practices that enhance crop pollinators. We sampled wild bees in three crop systems (almond, confection sunflower and seed watermelon) in a mosaic Israeli Mediterranean landscape. Bees were sampled in field/orchard edges and interiors, and in semi-natural scrub surrounding the fields/orchards. We also analysed land cover at 50-2500 m radii around fields/orchards. We used this data to distinguish crop- from non-crop pollinators based on a set of life history traits (nesting, lecty, sociality, body size) linked to habitat preference and crop visitation.
Results/Conclusions
Bee abundance and species richness decreased from the surrounding semi-natural habitat to the field/orchard interior, especially across the semi-natural-field edge ecotone. Thus, although rich bee communities were found near fields, only small fractions crossed the ecotone and visited crop flowers in substantial numbers. The bee assemblage in agricultural fields/orchards and on crop flowers was dominated by ground-nesting bees of the tribe Halictini, which tend to nest within fields. Bees' habitat preferences were determined mainly by nesting guild, whereas crop visitation was determined mainly by sociality. Lecty and body size also affected both measures. The percentage of surrounding semi-natural habitat at 250-2500 m radii had a positive effect on wild bee diversity in field edges, for all bee guilds, while at 50-100 m radii, only above-ground nesters were positively affected. In sum, we found that crop- and non-crop pollinators are distinguished by behavioral and morphological traits. Hence, analysis of life-history traits of bee communities can help assess the pollination services they are likely to provide (when taking into account single-visit pollination efficiency). The ecotone between agricultural fields and surrounding habitats is a major barrier that filters many bee species, particularly with regard to their nesting requirements. Thus greater attention should be given to management practices that encourage pollinators to live and nest, and not only forage, within fields.