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How insects promote crop pollination remains poorly understood in terms of the contribution of functional trait differences between species. We used meta-analyses to test for correlations between community abundance, species richness and functional trait metrics with oilseed rape yield, a globally important crop. While overall abundance is consistently important in predicting yield, functional divergence between species traits also showed a positive correlation. This result supports the complementarity hypothesis that pollination function is maintained by non-overlapping trait distributions. In artificially constructed communities (mesocosms), species richness is positively correlated with yield, although this effect is not seen under field conditions. As traits of the dominant species do not predict yield above that attributed to the effect of abundance alone, we find no evidence in support of the mass ratio hypothesis. Management practices increasing not just pollinator abundance, but also functional divergence, could benefit oilseed rape agriculture. ; This study was funded by the Natural Environment Research Council (NERC) under research programme NE/N018125/1 ASSIST–Achieving Sustainable Agricultural Systems www.assist.ceh.ac.uk. ASSIST is an initiative jointly supported by NERC and the Biotechnology and Biological Sciences Research Council (BBSRC). Additional funding for field studies was from the Wessex Biodiversity Ecosystem Services Sustainability (NE/J014680/1) project within the NERC BESS programme. Other data sets were generated from research funded by: (a) the Insect Pollinators Initiative programme funded by BBSRC, Defra, NERC, the Scottish Government and the Wellcome Trust, under the Living with Environmental Change Partnership; (b) Defra project BD5005: Provision of Ecosystem services in the ES scheme; and (c) Irish Government under the National Development Plan 2007–2013 administered by the Irish EPA.

Pollinators face multiple pressures and there is evidence of populations in decline. As demand for insect-pollinated crops increases, crop production is threatened by shortfalls in pollination services. Understanding the extent of current yield deficits due to pollination and identifying opportunities to protect or improve crop yield and quality through pollination management is therefore of international importance. To explore the extent of "pollination deficits," where maximum yield is not being achieved due to insufficient pollination, we used an extensive dataset on a globally important crop, apples. We quantified how these deficits vary between orchards and countries and we compared "pollinator dependence" across different apple varieties. We found evidence of pollination deficits and, in some cases, risks of overpollination were even apparent for which fruit quality could be reduced by too much pollination. In almost all regions studied we found some orchards performing significantly better than others in terms of avoiding a pollination deficit and crop yield shortfalls due to suboptimal pollination. This represents an opportunity to improve production through better pollinator and crop management. Our findings also demonstrated that pollinator dependence varies considerably between apple varieties in terms of fruit number and fruit quality. We propose that assessments of pollination service and deficits in crops can be used to quantify supply and demand for pollinators and help to target local management to address deficits although crop variety has a strong influence on the role of pollinators. ; This project was funded by the Sustainable Pollination in Europe Super-B COST Action (FA1307), Project Kennisimpuls Bestuivers (funded by the Dutch Ministry of Agriculture, Nature and Food Quality; BO-43-011.06-007), BBSRC, Defra, NERC, the Scottish Government and the Wellcome Trust, under the Insect Pollinators Initiative (BB/I000348/1), the "Sustainable Management of Orchard Pollination Services" Project (BB/P003664/1), the Stapledon Memorial Trust, the Volkswagen Foundation "Identifying functional pollinator biodiversity and threats to its decline in Georgia and Kyrgyzstan" (AZ: 86880), Georgian National Science Foundation "Functional pollinator biodiversity and their number, decline and threats in Georgia" (DO/372/10-101/14), the NKFIH project (FK123813), the Bolyai János Fellowship of the MTA, the ÚNKP-19-4-SZIE-3 New National Excellence Program of the Ministry for Innovation and Technology, the Hungarian Scientific Research Fund OTKA 101940, Northern Ireland Department of Agriculture and Rural Affairs, BiodivERsA/FACCE-JPI (agreement# BiodivERsA-FACCE2014-74) EcoFruit project, Swedish Research Council Formas (grant# 2014-1784), German Federal Ministry of Education and Research (PT-DLR/BMBF) (grant# 01LC1403), the Spanish Ministerio de Economía y Competitividad (MINECO) (project# PCIN-2014-145-C02), The Worshipful Company of Fruiterers, Natural Science and Engineering Research Council of Canada and the Fonds de recherche nature et technologies du Québec, Hort Innovation Pollination Fund project PH15001: Healthy bee populations for sustainable pollination in horticulture, Smith Lever and Hatch Funds administered by Cornell University Agricultural Experiment Station and by a USDA-AFRI grant (USDA 2010-03689, B.N. Danforth, PI), the Walloon Region (Belgium) Direction générale opérationnelle de l'Agriculture, des Ressources naturelles et de l'Environnement (DGO3) for the Modèle permaculturel project on biodiversity in micro-farms, FNRS/FWO joint program EOS—Excellence Of Science CliPS: Climate change and its impact on Pollination Services (project 30947854), MinECo and FEDER (INIA-RTA2013-00139-C03-01), Formas (grant #2014-1784), Sainsbury's Supermarkets Ltd (BB/K012843/1) and RR acknowledges the receipt of a fellowship from OECD Co-operative Research Programme: Biological Resource Management for Sustainable Agricultural Systems in 2016