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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.

Sustainable agricultural landscapes by definition provide high magnitude and stability of ecosystem services, biodiversity and crop productivity. However, few studies have considered landscape effects on the stability of ecosystem services. We tested whether isolation from florally diverse natural and semi-natural areas reduces the spatial and temporal stability of flower-visitor richness and pollination services in crop fields. We synthesised data from 29 studies with contrasting biomes, crop species and pollinator communities. Stability of flower-visitor richness, visitation rate (all insects except honey bees) and fruit set all decreased with distance from natural areas. At 1 km from adjacent natural areas, spatial stability decreased by 25, 16 and 9% for richness, visitation and fruit set, respectively, while temporal stability decreased by 39% for richness and 13% for visitation. Mean richness, visitation and fruit set also decreased with isolation, by 34, 27 and 16% at 1 km respectively. In contrast, honey bee visitation did not change with isolation and represented > 25% of crop visits in 21 studies. Therefore, wild pollinators are relevant for crop productivity and stability even when honey bees are abundant. Policies to preserve and restore natural areas in agricultural landscapes should enhance levels and reliability of pollination services.

Habitat loss and fragmentation in agricultural landscapes lead to severe declines of abundance and richness of many insect species in the remaining isolated semi-natural habitats. We analysed possible barrier effects of large hedges and corridor effects of narrow grass strips that were hypothesized to affect foraging and dispersal of hymenopterans. We selected calcareous grasslands in the vicinity of Gottingen (Germany), which harbour high Hymenoptera diversity and are starting points for foraging and dispersal in the landscape. We installed pan traps to sample bees (i) on the grasslands; (ii) on grassland edges behind adjacent hedges (potential barriers) and without hedges; (iii) on grass strips in 100 m distance to the grassland, which were connected or unconnected to the grassland; and (iv) unconnected (isolated) grass strips in 300 m and 750 m distance to test for corridor and isolation effects on abundance and species richness of foraging wild bees. Additionally we provided trap nests for bees, wasps and their parasitoids on the grasslands and the strips. Species abundance and richness declined with increasing isolation from grasslands for foraging solitary bees, trap-nesting bees, wasps and parasitoids, but not for foraging bumblebees. Hedges did not confine movement of foraging bees. We found no mitigating effects of (100 m) corridor strips on any of the observed groups. We conclude that conservation of semi-natural habitats as sources of bee and wasp diversity is important and that grass strips act as sinks rather than corridors when high quality patches are nearby.

Bees provide essential pollination services that are potentially affected both by local farm management and the surrounding landscape. To better understand these different factors, we modelled the relative effects of landscape composition (nesting and floral resources within foraging distances), landscape configuration (patch shape, interpatch connectivity and habitat aggregation) and farm management (organic vs. conventional and local-scale field diversity), and their interactions, on wild bee abundance and richness for 39 crop systems globally. Bee abundance and richness were higher in diversified and organic fields and in landscapes comprising more high-quality habitats; bee richness on conventional fields with low diversity benefited most from high-quality surrounding land cover. Landscape configuration effects were weak. Bee responses varied slightly by biome. Our synthesis reveals that pollinator persistence will depend on both the maintenance of high-quality habitats around farms and on local management practices that may offset impacts of intensive monoculture agriculture. Bees provide essential pollination services that are potentially affected both by local farm management and the surrounding landscape. To better understand these different factors, we modelled the relative effects of landscape composition (nesting and floral resources within foraging distances), landscape configuration (patch shape, interpatch connectivity and habitat aggregation) and farm management (organic vs. conventional and local-scale field diversity), and their interactions, on wild bee abundance and richness for 39 cropsystems globally. Bee abundance and richness were higher in diversified and organic fields and in landscapes comprising more high-quality habitats; bee richness on conventional fields with low diversity benefited most from high-quality surrounding land cover. Landscape configuration effects were weak. Beeresponses varied slightly by biome. Our synthesis reveals that pollinator persistence will depend on boththe maintenance of high-quality habitats around farms and on local management practices that may offsetimpacts of intensive monoculture agriculture.

Fil: Garibaldi, Lucas Alejandro. Universidad Nacional de Río Negro (Sede Andina) y Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); Argentina. Fil: Steffan Dewenter, Ingolf. University of Würzburg. Biocentre. Department of Animal Ecology and Tropical Biology; Germany. Fil: Winfree, Rachael. Rutgers University. Evolution and Natural Resources. Department of Ecology; USA. Fil: Aizen, Marcelo A. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche (CRUB). Instituto de Investigaciones en Biodiversidad y Medioambiente (INIBIOMA). Laboratorio Ecotono; Argentina. Fil: Bommarco, Riccardo. Swedish University of Agricultural Sciences. Department of Ecology; Sweden. Fil: Cunningham, Saul A. CSIRO Ecosystem Sciences; Australia. Fil: Kremen, Claire. University of California. Environmental Sciences Policy and Management; USA. Fil: Carvalheiro, Luísa G. University of Leeds. School of Biology; UK. Naturalis Biodiversity Center; Netherlands. Fil: Harder, Lawrence D. University of Calgary. Department of Biological Sciences; Canada. Fil: Afik, Ohad. Hebrew University of Jerusalem. Robert H. Smith Faculty of Agriculture, Food and Environment. Department of Entomology; Israel. Fil: Bartomeus, Ignasi. Rutgers University. Department of Entomology, Evolution and Natural Resources; USA. Fil: Benjamin, Faye. Rutgers University. Evolution and Natural Resources. Department of Ecology; USA. Fil: Boreux, Virginie. Leuphana University. Institute of Ecology; Germany. Department of Environmental Systems Science; Switzerland. Fil: Cariveau, Daniel. Rutgers University. Evolution and Natural Resources. Department of Ecology; USA. Fil: Chacoff, Natacha P. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e IML. Instituto de Ecología Regional; Argentina. Fil: Dudenhöffer, Jan H. Agroscope Reckenholz-Tänikon Research Station ART. Ecological Farming Systems; Switzerland. Fil: Freitas, Breno M. Universidade Federal do Ceará. Departamento de Zootecnia–CCA; Brazil. Fil: Greenleaf, Sarah S. University of California. Environmental Sciences Policy and Management; USA. Fil: Hipólito, Juliana. Universidade Federal da Bahia. Departamento de Zoologia. Instituto de Biologia; Brazil. Fil: Holzschuh, Andrea. University of Würzburg. Biocentre. Department of Animal Ecology and Tropical Biology; Germany. Fil: Howlett, Brad. New Zealand Institute for Plant and Food Research; New Zealand. Fil: Isaacs, Rufus. Michigan State University. Department of Entomology; USA. Fil: Javorek, Steven K. Atlantic Food and Horticulture Research Centre. Agriculture and Agri-Food Canada; Canada. Fil: Kennedy, Christina M. Nature Conservancy. Development by Design Program; USA. Fil: Krewenka, Kristin M. Georg-August-University. Department of Crop Sciences. Agroecology; Germany. Fil: Krishnan, Smitha. ETH Zürich. Department of Environmental Systems Science; Switzerland. Fil: Mandelik, Yael. Hebrew University of Jerusalem. Robert H. Smith Faculty of Agriculture, Food and Environment. Department of Entomology; Israel. Fil: Mayfield, Margaret M. University of Queensland. School of Biological Sciences and Ecology Centre; Australia. Fil: Motzke, Iris. Leuphana University. Ecosystem Functions. Institute of Ecology; Germany. Georg-August-University. Department of Crop Sciences. Agroecology; Germany. Fil: Munyuli, Theodore. National Center for Research in Natural Sciences. Department of Biology; Democratic Republic of Congo. Fil: Nault, Brian A. Cornell University. Department of Entomology. New York State Agricultural Experiment Station; USA. Fil: Otieno, Mark. University of Reading. School of Agriculture, Policy and Development; UK. Fil: Petersen, Jessica. Cornell University. Department of Entomology. New York State Agricultural Experiment Station; USA. Fil: Pisanty, Gideon. Hebrew University of Jerusalem. Robert H. Smith Faculty of Agriculture, Food and Environment. Department of Entomology; Israel. Fil: Potts, Simon G. University of Reading. School of Agriculture, Policy and Development; UK. Fil: Rader, Romina. Stockholm University. Department of Physical Geography and Quaternary Geology; Sweden. Fil: Ricketts, Taylor H. University of Vermont. Gund Institute for Ecological Economics; USA. Fil: Rundlöf, Maj. Swedish University of Agricultural Sciences. Department of Ecology; Sweden. Lund University. Department of Biol-ogy; Sweden. Fil: Seymour, Colleen L. South African National Institute of Biodiversity. Applied Biodiversity Research Division; South Africa. Fil: Schüepp, Christof. University of Bern. Institute of Ecology and Evolution, Community Ecology; Switzerland. University of Koblenz-Landau. Ecosystem Analysis; Germany. Fil: Szentgyörgyi, Hajnalka. Jagiellonian University. Institute of Environmental Sciences; Poland. Fil: Taki, Hisatomo. Forestry and Forest Products Research Institute. Department of Forest Entomology; Japan. Fil: Tscharntke, Teja. Georg-August-University. Department of Crop Sciences. Agroecology; Germany. Fil: Vergara, Carlos H. Universidad de las Américas Puebla. Departamento de Ciencias Químico-Biológicas; Mexico. Fil: Viana, Blandina F. Universidade Federal da Bahia. Instituto de Biologia. Departamento de Zoologia; Brazil. Fil: Wanger, Thomas C. Georg-August-University. Department of Crop Sciences. Agroecology; Germany. Fil: Westphal, Catrin. Georg-August-University. Department of Crop Sciences. Agroecology; Germany. Fil: Williams, Neal. University of California. Department of Entomology; USA. Fil: Klein, Alexandra M. Leuphana University. Ecosystem Functions. Institute of Ecology; Germany. The diversity and abundance of wild insect pollinators have declined in many agricultural landscapes. Whether such declines reduce crop yields, or are mitigated by managed pollinators such as honey bees, is unclear. We found universally positive associations of fruit set with flower visitation by wild insects in 41 crop systems worldwide. In contrast, fruit set increased significantly with flower visitation by honey bees in only 14% of the systems surveyed. Overall, wild insects pollinated crops more effectively; an increase in wild insect visitation enhanced fruit set by twice as much as an equivalent increase in honey bee visitation. Visitation by wild insects and honey bees promoted fruit set independently, so pollination by managed honey bees supplemented, rather than substituted for, pollination by wild insects. Our results suggest that new practices for integrated management of both honey bees and diverse wild insect assemblages will enhance global crop yields.