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There is compelling evidence that more diverse ecosystems deliver greater benefits to people, and these ecosystem services have become a key argument for biodiversity conservation. However, it is unclear how much biodiversity is needed to deliver ecosystem services in a cost-effective way. Here we show that, while the contribution of wild bees to crop production is significant, service delivery is restricted to a limited subset of all known bee species. Across crops, years and biogeographical regions, crop-visiting wild bee communities are dominated by a small number of common species, and threatened species are rarely observed on crops. Dominant crop pollinators persist under agricultural expansion and many are easily enhanced by simple conservation measures, suggesting that cost-effective management strategies to promote crop pollination should target a different set of species than management strategies to promote threatened bees. Conserving the biological diversity of bees therefore requires more than just ecosystem-service-based arguments.

Summary 1. Interest in pollen-borne gene dispersal has grown with the cultivation of genetically modified plants. To date, both experimental data and models of oilseed rape (OSR) Brassica napus pollen movement at the landscape scale do not clearly differentiate between wind- and insect-mediated dispersal. Estimations of insect-mediated gene dispersal would be valuable for managing potential escapes of transgenes. 2. To quantify the intensity and spatial scale of pollen dispersal by insect pollinators in an agricultural landscape, bait points made of flowering male-sterile OSR that attract OSR pollinators were located at six distances (10–1100 m) from the closest OSR fields and feral populations. Flower-visiting insects were caught by net on these male-sterile flowers and were rubbed onto the stigmas of male-sterile OSR plants grown in a pollen-proof greenhouse to do a manual pollination of their flowers. In this way we were able to assess the insects’ OSR pollen load and seed production at each of the six distances. 3. A large diversity of insects carried OSR pollen and contributed to seed production, but not pollen beetles Meligethes aeneus. Logistic regression analyses of the seed-set success from the manual pollination demonstrated that seed set significantly increased with the proximity of OSR fields, the size of the pollinating insect, and the main daily temperature. Seed set was not affected by the pollinating insect’s order or genus. Seed set, both observed and predicted by the model, was above zero for flowers pollinated with large bees caught at >1100 m from the nearest OSR field. 4. Synthesis and applications. Our study provides clear evidence that a large variety of insect species can transfer viable pollen between OSR plants over considerable distances. However, only 39AE4% of the insects caught on male-sterile flowers carried OSR pollen. Our results provide valuable data to improve models of pollen dispersal for entomophilous crops at the landscape scale. These models are essential to help land-managers reduce pollen-borne gene dispersal from genetically modified plants to wild and cultivated relatives.

© 2015 Macmillan Publishers Limited. All rights reserved. There is compelling evidence that more diverse ecosystems deliver greater benefits to people, and these ecosystem services have become a key argument for biodiversity conservation. However, it is unclear how much biodiversity is needed to deliver ecosystem services in a cost-effective way. Here we show that, while the contribution of wild bees to crop production is significant, service delivery is restricted to a limited subset of all known bee species. Across crops, years and biogeographical regions, crop-visiting wild bee communities are dominated by a small number of common species, and threatened species are rarely observed on crops. Dominant crop pollinators persist under agricultural expansion and many are easily enhanced by simple conservation measures, suggesting that cost-effective management strategies to promote crop pollination should target a different set of species than management strategies to promote threatened bees. Conserving the biological diversity of bees therefore requires more than just ecosystem-service-based arguments.

To better understand the dynamics of bee populations in crops, we assessed the effect of landscape context and habitat type on bee communities in annual entomophilous crops in Europe. We quantified bee communities in five pairs of crop-country: buckwheat in Poland, cantaloupe in France, field beans in the UK, spring oilseed rape in Sweden, and strawberries in Germany. For each country, 7–10 study fields were sampled over a gradient of increasing proportion of semi-natural habitats in the surrounding landscape. The CORINE land cover classification was used to characterize the landscape over a 3 km radius around each study field and we used multivariate and regression analyses to quantify the impact of landscape features on bee abundance and diversity at the sub-generic taxonomic level. Neither overall wild bee abundance nor diversity, taken as the number of sub-genera, was significantly affected by the proportion of semi-natural habitat. Therefore, we used the most precise level of the CORINE classification to examine the possible links between specific landscape features and wild bee communities. Bee community composition fell into three distinct groups across Europe: group 1 included Poland, Germany, and Sweden, group 2 the UK, and group 3 France. Among all three groups, wild bee abundance and sub-generic diversity were affected by 17 landscape elements including some semi-natural habitats (e.g., transitional woodland-shrub), some urban habitats (e.g., sport and leisure facilities) and some crop habitats (e.g., non-irrigated arable land). Some bee taxa were positively affected by urban habitats only, others by semi-natural habitats only, and others by a combination of semi-natural, urban and crop habitats. Bee sub-genera favoured by urban and crop habitats were more resistant to landscape change than those favoured only by semi-natural habitats. In agroecosystems, the agricultural intensification defined as the loss of semi-natural habitats does not necessarily cause a decline in evenness at the local level, but can change community composition towards a bee fauna dominated by common taxa.