Department of Zoology, University of Wisconsin, Madison, Wisconsin 53706, USA.
Ecology. 2012 Apr;93(4):803-14. doi: 10.1890/11-0967.1.
The earlier flowering times exhibited by many plant species are a conspicuous sign of climate change. Altered phenologies have caused concern that species could suffer population declines if they flower at times when effective pollinators are unavailable. For two perennial wildflowers, Tradescantia ohiensis and Asclepias incarnata, we used an experimental approach to explore how changing phenology affects the taxonomic composition of the pollinator assemblage and the effectiveness of individual pollinator taxa. After finding in the previous year that fruit set varied with flowering time, we manipulated flowering onset in greenhouses, placed plants in the field over the span of five weeks, and measured pollinator effectiveness as the number of seeds produced after a single visit to a flower. The average effectiveness of pollinators and the expected rates of pollination success were lower for plants of both species flowering earlier than for plants flowering at historical times, suggesting there could be reproductive costs to earlier flowering. 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 increases over time in the effectiveness of some pollinator taxa. Both species face the possibility of temporal mismatch between the availability of the most effective pollinators and the onset of flowering, and changes in the effectiveness of individual pollinator taxa through time may add an unexpected element to the reproductive consequences of such mismatches.
许多植物物种更早的开花时间是气候变化的一个显著标志。物候期的改变引起了人们的担忧，如果物种在有效传粉者无法到达的时间开花，它们可能会面临种群减少的风险。对于两种多年生野花，Tradescantia ohiensis 和 Asclepias incarnata，我们采用实验方法来探索物候期的变化如何影响传粉者组合的分类组成以及单个传粉者类群的有效性。在前一年发现果实结实率随开花时间而变化后，我们在温室中操纵开花起始时间，在五周的时间跨度内在野外放置植物，并通过单次访问花朵后产生的种子数量来衡量传粉者的有效性。与在历史时期开花的植物相比，两种植物的开花时间更早，传粉者的平均有效性和预期授粉成功率较低，这表明更早的开花可能会带来生殖成本。对于 A. incarnata，每周平均种子产量的差异主要归因于传粉者组合组成的变化，而对于 T. ohiensis 的差异则是由传粉者类群组成的变化以及某些传粉者类群有效性随时间的增加的综合影响所驱动。这两种植物都面临着最有效传粉者的可用性与开花起始时间之间的时间不匹配的可能性，而单个传粉者类群的有效性随时间的变化可能会给这种不匹配的生殖后果增加一个意想不到的因素。
