Print PageThe earlier flowering times exhibited by many plant species are a conspicuous and widespread sign of climate change. Altered flowering phenologies have caused concern that species could suffer population declines if they begin flowering at times when effective pollinators are unavailable. For two perennial wildflowers with advanced flowering, Tradescantia ohiensis and Asclepias incarnata, we used an experimental approach to investigate two components of pollination success: (1) the effectiveness of individual pollinator species, and (2) the species composition of the pollinator assemblage. We manipulated flowering onset in greenhouses, placed plants in the field over the span of five weeks, and measured the effectiveness of pollinator species by the number of seeds produced after a single visit to a flower. To investigate how the pollinator assemblage responded to shifts in flowering time, we analyzed how pollinator composition and visitation patterns changed over time for these species.
Results/Conclusions
The average effectiveness of pollinators visiting T. ohiensis and A. incarnata was lower for plants flowering earlier than for plants flowering at historical times, resulting in lower seed set per visit and suggesting that there may be costs to shifts in flowering onset.Whereas for A. incarnata differences in average seed set among weeks were due primarily to changes in the composition of the pollinator assemblage, the differences for T. ohiensis were driven by the combined effects of compositional changes and within-species increases in effectiveness over time.The previously under-appreciated changes in the effectiveness of the same pollinator taxa through time may complicate the assessment of potential plant-pollinator mismatches in phenology caused by climate change.
