Quantitative analyses reveal interactions of community plants and insect flower visitors are associated with relative composition of nectar amino acids

Trait-based analyses that elaborate the biological mechanisms underlying species interactions are crucial for predicting the structure of community plants and animals. Flower nectar, a sugar-rich solution, is fundamental to linking flowers and animal visitors for most plants. However, there is a paucity of knowledge regarding the influence of nectar micro-components, such as amino acids (AAs), and their relative composition on foraging decisions of flower visitors within a community context.We quantitatively calculated the relative composition of 21 AAs of nectars from 40 species and recorded the visitation frequency of their 207 species of insect visitors (15 functional groups from five orders) in a species-rich alpine meadow. Phylogenetically generalized mixed models with Bayesian estimation were used to detect the influence of nectar AAs on the visitation frequency of flower visitors from the different groups.Our results indicated that the increase of gamma-aminobutyric acid (GABA) and methionine in nectar enhanced the visitation of social bees, the dominant flower visitors in this meadow. Furthermore, the AAs in nectar that affect visitation frequency varied among different functional groups of Dipteran, e.g., hoverfly, mucoid fly, meat fly, and horsefly. Their different diet sources and life history strategies (e.g., feeding larvae or not) may explain the preferring or disliking of nectar AAs.Our findings suggest a way that flower reward may structure plant-pollinator interactions in communities with diverse species, which enriches the understanding of mechanisms for biodiversity maintenance.