Can floral traits predict an invasive plant's impact on native plant–pollinator communities?

Abstract

Summary The possession of certain floral traits can determine which insects visit a plant species. If two species possess similar floral traits that determine shared flower visitors, floral traits can be said to mediate plant–plant interactions. Such indirect interactions are important for understanding fundamental relationships of plant communities, such as competition and facilitation but thus far have only been tested within a native community context. We test whether floral‐trait similarity can be used to predict interactions between an invasive plant and co‐occurring native species in South Africa's Cape Floristic Region. We surveyed flower visitation at invaded and uninvaded plots across four sites and correlated floral‐trait similarity between invasive and native species with both invasion impact on native flower visitation and flower visitor overlap of natives and the invasive species. Similarity of all traits (categorical and continuous) and categorical traits alone explained invasion impact (flower visitor overlap) between the native and invasive species. The majority of flower visitor overlap was attributed to the native honeybee Apis mellifera subsp. capensis. This study is the first to show that floral traits can be used to predict novel plant–plant interactions, even amongst ecologically generalized flower visitors and plants and to predict potential impacts of an invasive species on native flowering communities. However, floral traits were not useful for predicting changes in visitation to plant species. Synthesis. Results advance our understanding of the role of plant traits in ecological communities and reveal that they are important in mediating not only plant–pollinator interactions but also plant–plant interactions. Our findings also shed light on invasive–native plant interactions via pollinators and have the potential to predict certain invasion impacts.