Division of Natural Sciences and Engineering, University of South Carolina Upstate, Spartanburg, SC 29303, USA.
Oecologia. 2012 Feb;168(2):449-58. doi: 10.1007/s00442-011-2094-x. Epub 2011 Aug 11.
Plant species vary greatly in the degree to which floral morphology restricts access to the flower interior. Restrictiveness of flower corollas may influence heterospecific pollen receipt, but the impact of floral morphology on heterospecific pollen transfer has received little attention. We characterized patterns of pollinator visitation and quantities of conspecific and heterospecific pollen receipt for 29 species with a range of floral morphologies in a prairie community dominated by the introduced plant Euphorbia esula (leafy spurge) which has an unrestrictive morphology. Pollinator overlap was significantly greater between Euphorbia and other unrestrictive flowers than restrictive flowers. Compared to flowers with restrictive morphologies, unrestrictive flowers received significantly more Euphorbia pollen, more heterospecific pollen from other sources, and a greater diversity of pollen species, but not more conspecific pollen. However, stigmatic surface area was significantly larger for flowers with unrestrictive morphologies, and the density of Euphorbia and other heterospecific pollen per stigmatic area did not significantly differ between flower types. These findings suggest that the smaller stigma size in restrictive flowers partly accounts for their decreased heterospecific pollen receipt, but that restrictiveness also allows species to increase the purity of pollen loads they receive. Given that restrictive flowers receive fewer heterospecific pollen grains but at a higher density, the effect of restrictiveness on fecundity depends on whether absolute quantity or density of heterospecific pollen affects fecundity more. Our results also indicate that abundant neighbors are not necessarily important heterospecific pollen sources since Euphorbia pollen was rarely abundant on heterospecifics.
植物物种在花朵形态限制进入花朵内部的程度上差异很大。花被的限制性可能会影响异交花粉的接收，但花朵形态对异交花粉传递的影响却很少受到关注。我们描述了在以引入植物 Euphorbia esula（刺叶霸王）为主的草原群落中，29 种具有不同花朵形态的物种的传粉者访问模式和同属和异属花粉的接收量。Euphorbia 和其他非限制性花朵之间的传粉者重叠明显大于限制性花朵。与具有限制性形态的花朵相比，非限制性花朵接收了更多的 Euphorbia 花粉、更多来自其他来源的异交花粉和更多种类的花粉，但接收的同属花粉却没有更多。然而，非限制性花朵的柱头表面积明显更大，且每单位柱头面积上 Euphorbia 和其他异交花粉的密度在花朵类型之间没有显著差异。这些发现表明，限制性花朵中较小的柱头大小部分解释了它们接收异交花粉减少的原因，但限制也允许物种增加它们接收的花粉负荷的纯度。鉴于限制性花朵接收的异交花粉粒较少，但密度较高，限制对繁殖力的影响取决于绝对数量或异交花粉密度对繁殖力的影响更大。我们的结果还表明，丰富的邻居不一定是重要的异交花粉源，因为 Euphorbia 花粉在异交种上很少丰富。
