Intraspecific plant chemodiversity at the individual and plot levels influences flower visitor groups with consequences for germination success

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Abstract Chemodiversity, the diversity of specialised (secondary) metabolites, plays a crucial role in mediating interactions between plants and animals, including insect herbivores and mutualists. Chemodiversity can be observed at both the individual and the population level. However, the impacts of chemodiversity at these two levels on interactions between plants and floral visitors, mainly pollinators and floral herbivores (florivores), are only poorly understood. This study aimed to investigate the effects of chemodiversity at both individual (chemotype) and plot level on pollinators and florivores, examining their mutual interactions. To investigate these questions, we used individuals of the perennial Tanacetum vulgare differing in their terpenoid composition, representing different chemotypes. We planted individuals of five distinct chemotypes in a common garden design with homogeneous (five plants of the same chemotype) and heterogeneous (five different chemotypes) plots and observed flower visits in dependence of individual chemotype and plot type. Seeds were collected from a subset of plants and germination rates determined. Our findings revealed that chemodiversity at the plot level significantly influenced pollinator visitation, with more visits on plants of heterogeneous plots. We also observed marginally more pollinators on one of the chemotypes grown in homogeneous plots. In contrast, chemotype but not plot type had a significant effect on florivore visits. Pollinator and florivore species richness did not vary with plot type. Furthermore, a negative correlation was observed between pollinator and florivore visits in 1 year. Germination rates were positively correlated with pollinator visits and affected by chemotype but not by florivore visits or plot type. Synthesis. Our study emphasises the significance of the spatial level at which plant chemistry is perceived by flower visitors, potentially influencing the germination success of plants. Exploring the ecology of these visitors and the varying selection pressures they exert on floral chemistry can help to elucidate the evolutionary processes that maintain chemodiversity in natural environments. Read the free Plain Language Summary for this article on the Journal blog.