David Kleijn, Rachael Winfree, Ignasi Bartomeus, Luísa G. Carvalheiro, Mickael Henry, Rufus Isaacs, Alexandra-Maria Klein, Claire Kremen, Leithen K. M'Gonigle, Romina Rader, Taylor H. Ricketts, Neal M. Williams, Nancy Lee Adamson, John S. Ascher, András Báldi, Péter Batáry, Faye Benjamin, Jacobus C. Biesmeijer, Eleanor J. Blitzer, Riccardo Bommarco, Mariette R. Brand, Vincent Bretagnolle, Lindsey Button, Daniel P. Cariveau, Rémy Chifflet, Jonathan F. Colville, Bryan N. Danforth, Elizabeth Elle, Michael P. D. Garratt, Felix Herzog, Andrea Holzschuh, Brad G. Howlett, Frank Jauker, Shalene Jha, Eva Knop, Kristin M. Krewenka, Violette Le Féon, Yael Mandelik, Emily A. May, Mia G. Park, Gideon Pisanty, Menno Reemer, Verena Riedinger, Orianne Rollin, Maj Rundlöf, Hillary S. Sardiñas, Jeroen Scheper, Amber R. Sciligo, Henrik G. Smith, Ingolf Steffan-Dewenter, Robbin Thorp, Teja Tscharntke, Jort Verhulst, Blandina F. Viana, Bernard E. Vaissière, Ruan Veldtman, Kimiora L. Ward, Catrin Westphal, Simon G. Potts

• 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 areThere 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.…