Flower visitation of alien plants is non-linearly related to phylogenetic and floral similarity to native plants

Abstract Biological invasions are key to understanding major ecological processes that determine the formation of novel interactions. Flower visitation to alien species may be facilitated by co-flowering natives if they share similar floral traits with the latter. However, if competition for pollinators is important, flower visitation to alien species may be higher if they have traits different from those of native species. We tested whether flower visitation to alien plants depended on phylogenetic relatedness and floral similarity to native plants. In a field experiment, we simulated invaded communities by adding potted alien plants into co-flowering native communities. We recorded flower visitation to pairs of 34 alien and 20 native species totalling 151 species combinations for 3,068 hours. Flower visitation to alien species was highest when they had intermediate floral trait distances to native species, and either low or high phylogenetic distances. The alien plants received more similar flower-visitor groups to natives when they had low phylogenetic and either low or high floral trait distances to native plants. The non-linear patterns between flower visitation and similarity of the alien and native species suggest that an interplay of facilitation and competition simultaneously drives the formation of novel plant-pollinator interactions. The shapes of the relationships of phylogenetic and floral trait distances with flower visitation to alien plants were contrasting, possibly due to different strengths of phylogenetic signal among traits. We provide experimental evidence for the effects of relatedness and functional similarity to native plants on flower visitation of alien plants. We show that such effects might be non-linear, and that effects of trait dissimilarity and phylogenetic distance on pollinator-mediated interactions can reflect different mechanisms.