Climate change has led to phenological shifts in many flowering plants and insect pollinators.  Although accumulating evidence suggests that these shifts might disrupt plant-pollinator mutualisms, few studies have documented how altered flowering phenologies affect interactions with pollinators, and experimental data are largely lacking.  I selected 14 native perennial plant species, 6 of which have exhibited shifts to earlier flowering over the last 70 years in Wisconsin and 8 of which have not.  After manipulating the flowering onset of all species in greenhouses, I placed plants in the field one and two weeks before, on, and one and two weeks after the current mean date of first bloom and observed pollinator visitation.

Results/Conclusions

Of the 6 species with historically advanced flowering, 5 received more visits when flowering was experimentally advanced.  In contrast, 7 of the remaining 8 species tended to receive more visits when flowering later in the field.  This pattern indicates that temporal mismatches between flowering onset and visitation by potential pollinators are not occurring for most of these species.  These findings further suggest that species unconstrained by pollinators have advanced their flowering times over 70 years, whereas species constrained by pollinators have not.