Functional flower traits and their diversity drive pollinator visitation
Abstract
Recent studies have shown that the diversity of flowering plants can enhance pollinator richness and visitation frequency and thereby increase the resilience of pollination. It is assumed that flower traits explain these effects, but it is still unclear which flower traits are responsible, and whether pollinator richness and visitation frequency are more driven by mass-ratio effects (mean trait values) or by trait diversity. Here, we analyse a three-year data set of pollinator observations collected in a European grassland plant diversity experiment (the Jena Experiment), with comprehensive flower trait measurements including reward, morphological and chemical traits. Overall functional diversity did not affect pollinator species richness but reduced visitation frequency. When looking at individual flower traits separately, single trait diversity of flower reflectance and flower morphology were important predictors of pollinator visitation frequency, and, independent of total flower abundance, community-weighted means of flower height, area, reflectance, nectar-sugar concentration and nectar-amino acid concentration strongly affected both pollinator species richness and visitation frequency. Our results challenge the idea that functional diversity always positively affects ecosystem functions, but demonstrate that both single trait diversity and mass-ratio effects of flower traits play an important role for diverse and frequent flower visits.
What the paper shows and why it matters (AI-generated)
Plant diversity is known to boost pollinator visitation, but this three-year grassland experiment asks a sharper question: is it the diversity of flower traits that matters, or just the average trait values across the community? Both turn out to matter, and not always as ecosystem-function orthodoxy would predict — overall trait diversity actually reduced visitation frequency in this dataset, while specific traits like flower height, colour and nectar chemistry mattered more via their community-weighted mean. That distinction has shaped how the pollinator-conservation field since thinks about plant-mix design, cited widely across restoration studies choosing species for pollinator support.