Data from: Pollinator visitation rate and effectiveness vary with flowering phenology

Premise of the Study – Flowering time may influence pollination
success and seed set through a variety of mechanisms, including seasonal
changes in total pollinator visitation or the composition and
effectiveness of pollinator visitors. Methods – We investigated
mechanisms by which changes in flowering phenology influence pollination
and reproductive success of Mertensia
ciliata (Boraginaceae). We manipulated flowering onset of potted
plants and assessed the frequency and composition of pollinator visitors,
as well as seed set. We tested whether floral visitors differed in their
effectiveness as pollinators by measuring pollen receipt and seed set
resulting from single visits to virgin flowers. Key Results –
Despite a five-fold decrease in pollinator visitation over four weeks, we
detected no significant difference in seed set among plants blooming at
different times. On a per-visit basis, each bumblebee transferred more
conspecific pollen than did a solitary bee or a fly. The proportion of
visits by bumblebees increased over the season, countering the decrease in
visitation rate so that flowering time had little net effect on seed set.
Conclusions – This work illustrates the need to consider
pollinator effectiveness, along with changes in pollinator visitation and
species composition to understand the mechanisms by which phenology
impacts levels of pollination.

研究背景——开花时间可通过多种机制影响授粉成功率与结籽率，具体包括传粉者总访花量的季节波动，以及传粉者类群组成与传粉有效性的变化。
研究方法——本研究围绕开花物候变化对缘毛滨紫草（Mertensia ciliata，紫草科Boraginaceae）的授粉过程与繁殖成功的影响机制展开探究。我们对盆栽植株的开花起始时间进行人工调控，并评估传粉者的访花频率、类群组成以及结籽率。此外，通过对未访花（即从未接受过任何传粉的花朵）进行单次传粉访问后测量其花粉接收量与结籽率，以此验证不同花部访客的传粉有效性是否存在差异。
主要结果——尽管在四周内传粉者的访花频次下降了五倍，但不同开花时段的植株结籽率并未出现显著差异。以单次访花计，每只熊蜂传递的同种花粉量均高于独居蜂与蝇类。随着季节推移，熊蜂的访花占比逐渐上升，抵消了访花速率下降的影响，因此开花时间对结籽率的净效应极小。
研究结论——本研究表明，若要阐明物候变化影响授粉水平的内在机制，需同时考量传粉有效性、传粉者访花量变化以及类群组成的改变。