Abstract
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.
Highlights
How insects promote crop pollination remains poorly understood in terms of the contribution of functional trait differences between species
For this reason only abundance and species richness metrics were derived for mesocosm studies
Theses meta-analyses found evidence in support of the complementarity hypothesis that predicts that communities with nonoverlapping trait distributions would be more likely to promote pollination
Summary
How insects promote crop pollination remains poorly understood in terms of the contribution of functional trait differences between species. While overall abundance is consistently important in predicting yield, functional divergence between species traits showed a positive correlation This result supports the complementarity hypothesis that pollination function is maintained by non-overlapping trait distributions. Meta-analyses provide a statistical approach for integrating results from independent studies lacking consistent methodologies but testing a common hypothesis Using this approach, we test if differences between pollinator communities resulting from functional differences in morphology and behaviour explain variation in crop yield in addition to that explained by simple yield-abundance relationships. We test the extent to which (2) pollination is determined by the effect traits of the numerically dominant species, a test of the mass ratio hypothesis[4,7,21,22] We infer this by testing for correlations between yield and community weighted trait means of the pollinators. Community weighted mean values of several effects traits do show correlations with oilseed rape yield, taken individually within the meta-analyses these traits do not predict yield above that attributed to the effect of abundance alone
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