Elliott Susan E, Irwin Rebecca E
Biology Department, Dartmouth College, Hanover, New Hampshire 03755 USA.
Am J Bot. 2009 May;96(5):912-9. doi: 10.3732/ajb.0800260. Epub 2009 Apr 13.
Variation in flowering plant density can have conflicting effects on pollination and seed production. Dense flower patches may attract more pollinators, but flowers in those patches may also compete for pollinator visits and abiotic resources. We examined how natural and experimental conspecific flowering plant density affected pollen receipt and seed production in a protandrous, bumble bee-pollinated wildflower, Delphinium barbeyi (Ranunculaceae). We also compared floral sex ratios, pollinator visitation rates, and pollen limitation of seed set from early to late in the season to determine whether these factors mirrored seasonal changes in pollen receipt and seed production. Pollen receipt increased with natural flowering plant density, while seed production increased across lower densities and decreased across higher flower densities. Experimental manipulation of flowering plant density did not affect pollinator visitation rate, pollen receipt, or seed production. Although pollinator visitation rate increased 10-fold from early to late in the season, pollen receipt and seed set decreased over the season. Seed set was never pollen-limited. Thus, despite widespread effects of flowering plant density on plant reproduction in other species, the effects of conspecific flowering plant density on D. barbeyi pollination and seed production are minor.
开花植物密度的变化对授粉和种子生产可能产生相互矛盾的影响。密集的花斑可能吸引更多传粉者，但这些花斑中的花朵也可能竞争传粉者的访问和非生物资源。我们研究了自然和实验条件下同种开花植物密度如何影响一种雄性先熟、由熊蜂授粉的野花——巴氏翠雀花（毛茛科）的花粉接收和种子生产。我们还比较了花期从早期到晚期的花的性别比例、传粉者访花率以及种子结实的花粉限制，以确定这些因素是否反映了花粉接收和种子生产的季节性变化。花粉接收量随自然开花植物密度的增加而增加，而种子产量在较低密度下增加，在较高花密度下减少。对开花植物密度的实验操作并未影响传粉者访花率、花粉接收量或种子产量。尽管传粉者访花率在花期从早期到晚期增加了10倍，但花粉接收量和种子结实率在整个花期却下降了。种子结实从未受到花粉限制。因此，尽管开花植物密度对其他物种的植物繁殖有广泛影响，但同种开花植物密度对巴氏翠雀花授粉和种子生产的影响较小。
