In this post Lucas Garibaldi discusses his recent Review article ‘Trait matching of flower visitors and crops predicts fruit set better than trait diversity

Sustainable management of agroecosystems is a global challenge, with more than 35 % of the Earth’s land area covered by farmland. It has been suggested that species diversity is critical for sustainability because it increases the level and stability of agroecosystem functioning, represented by measures of ecosystem services and agricultural production. There is a growing consensus that such influences of species diversity on functioning are mediated by changes in trait diversity. However, empirical evidence for the role of trait diversity on agroecosystem functioning is scarce.

T.Mahlmann, 2007
A bee on a crop flower. Photo credit: T. Mahlmann.

Trait diversity reflects the among-species variation in morphological, physiological, and behavioural traits relevant to a specific function. Hence, newly developed indices of trait diversity are expected to better predict functioning than traditional indices of species diversity. To test these ideas, we collected data on traits of flower visitors and crops, visitation rates to crop flowers per insect species, and fruit set in 469 fields of 33 crop systems all over the world. This synthesis provides a unique opportunity to test the strength of the relationship between trait and species diversity, and of the relative ability of trait versus species indices for predicting functioning, across contrasting crop systems.

If trait diversity indices predict functioning better than species diversity indices, it suggests that there are a subset of traits shared across species that are overwhelmingly important for functioning. Contrary to this idea, here we demonstrate that although trait diversity indices were positively related to crop fruit set (functioning), they did not provide greater model fit compared to species diversity indices (including both richness and evenness). Furthermore, we found very low functional redundancy among flower-visitor species, suggesting that there is not enough sharing of important traits among species to make the trait diversity indices more useful than species diversity.

Different body sizes and tongue lengths for bees, which were the main traits analysed in the paper. The genus of the bees are as follows (from bottom to top, from left to right): Bombus, Apis, Euglossa, Megalopta, Megachile, Ceratina, Coelioxys, e Nannotrigona. Photo credit: T.Mahlmann.
Different body sizes and tongue lengths for bees, which were the main traits analysed in the paper. The genus of the bees are as follows (from bottom to top, from left to right): Bombus, Apis, Euglossa, Megalopta, Megachile, Ceratina, Coelioxys, Nannotrigona. Photo credit: T. Mahlmann.

Sustainable intensification of agroecosystems represents one of the greatest challenges for humanity. To succeed in this challenge it is critical to quantify the relationship among trait diversity, species diversity, and agroecosystem functioning. In this study we show that crop fruit set, an important component of agricultural yield, can be increased through both higher species richness and evenness of flower visitors. Fruit set might be further enhanced by agricultural practices targeted to promote specific flower visitors with traits that match those of the focal crop. Indeed, trait matching showed the greatest influence on fruit set. Current management practices for greater pollination, however, focus mostly on enhancing flower-visitor abundance, often of a single species, namely Apis mellifera. Although greater abundance is an important contributor to pollination function, our results show that it cannot replace the additional benefits of species richness, species evenness, and trait matching between flower visitors and crops.

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