Climate change and shifts in flowering time: Effects on plant-pollinator interactions

Climate change has led to phenological shifts in flowering plants and insect pollinators, causing concern that these shifts will disrupt plant-pollinator mutualisms. We investigated how flowering onset affects pollinator visitation for 14 plant species, 6 of which have exhibited shifts to earlier flowering. We manipulated flowering onset and then observed pollinator visitation. When flowering was experimentally advanced, 5 of 6 species with historically advanced flowering received more visits, whereas 7 of 8 species with unchanged flowering received fewer visits. This pattern indicates that mismatches at the onset of flowering are not occurring for most of these species and suggests that species unconstrained by pollinators have advanced their flowering, whereas species constrained by pollinators have not.;For Tradescantia ohiensis and Asclepias incarnata , we explored how flowering time affects the composition and effectiveness of the pollinator assemblage. The effectiveness of pollinators was lower for both species flowering earlier than at historical times, suggesting fitness costs. Whereas for A. incarnata differences in seed set among weeks were due to compositional changes, the differences for T. ohiensis were driven by the combined effects of compositional changes and increases in the effectiveness of some pollinator taxa. Both species face the possibility of temporal mismatch between the availability of the most effective pollinators and flowering onset, and changes in the effectiveness of pollinator taxa may add an unexpected element to the fitness consequences of such mismatches.;Using a community of 14 plant species and 22 pollinator taxa, we investigated the influence of flowering phenology, plant traits, and plant and pollinator phylogenies on interaction patterns. Although pollinator communities differed among plant species, these differences could not be explained by phylogenetic relationships among pollinators. Phylogenetically related plants were more (or less) likely to attract a greater number of pollinators, and pollinators attracted to one plant were likely to be attracted to related plants. Plant height, flower color, floral symmetry, floral display, and date of first bloom explained differences among pollinators in their visits to plants. Because some of these traits are phylogenetically related among plants, they can explain the pattern that phylogenetically related plants were similarly attractive to pollinators.