Botany and Zoology Department, Stellenbosch University, Matieland, South Africa.
Oecologia. 2011 Jun;166(2):543-53. doi: 10.1007/s00442-010-1879-7. Epub 2010 Dec 19.
The co-occurrence of plant species within a community is influenced by local deterministic or neutral processes as well as historical regional processes. Floral trait distributions of co-flowering species that share pollinators may reflect the impact of pollinator preference and constancy on their assembly within local communities. While pollinator sharing may lead to increased visitation rates for species with similar flowers, the receipt of foreign pollen via interspecific pollinator movements can decrease seed set. We investigated the pattern of community flower colour assembly as perceived by native honeybee pollinators within 24 local assemblages of co-flowering Oxalis species within the Greater Cape Floristic Region, South Africa. To explore the influence of pollinators on trait assembly, we assessed the impact of colour similarity on pollinator choices and the cost of heterospecific pollen receipt. We show that flower colour is significantly clustered within Oxalis communities and that this is not due to historical constraint, as flower colour is evolutionarily labile within Oxalis and communities are randomly structured with respect to phylogeny. Pollinator observations reveal that the likelihood of pollinators switching between co-flowering species is low and increases with flower colour similarity. Interspecific hand pollination significantly reduced seed set in the four Oxalis species we investigated, and all were dependant on pollinators for reproduction. Together these results imply that flower colour similarity carries a potential fitness cost. However, pollinators were highly flower constant, and remained so despite the extreme similarity of flower colour as perceived by honeybees. This suggests that other floral traits facilitate discrimination between similarly coloured species, thereby likely resulting in a low incidence of interspecific pollen transfer (IPT). If colour similarity promotes pollinator attraction at the community level, the observed clustering of flower colour within communities might result from indirect facilitative interactions.
一个群落中植物种的共存受到局部确定性或中性过程以及历史区域过程的影响。具有共同传粉者的共花期物种的花部特征分布可能反映了传粉者偏好和恒定性对其在当地群落中组装的影响。虽然传粉者共享可能会导致具有相似花朵的物种的访问率增加，但通过种间传粉者运动接收外来花粉会降低结实率。我们在南非大开普花卉区 24 个共花期 Oxalis 物种的本地集合中，调查了本地蜜蜂传粉者对群落花颜色组装的模式。为了探索传粉者对特征组装的影响，我们评估了颜色相似性对传粉者选择的影响以及异质花粉接收的成本。我们表明，Oxalis 群落中花的颜色明显聚类，并且这不是由于历史限制造成的，因为 Oxalis 内的花颜色在进化上是不稳定的，并且群落在系统发育上是随机结构的。传粉者观察表明，传粉者在共花期物种之间转换的可能性很低，并且随着花颜色的相似性增加而增加。我们研究的四个 Oxalis 物种的种间人工授粉显着降低了结实率，并且所有物种都依赖传粉者进行繁殖。这些结果表明，花颜色相似性具有潜在的适应成本。然而，传粉者高度花朵恒定性，并且尽管蜜蜂感知到的花颜色极其相似，但仍然如此。这表明其他花部特征有助于区分颜色相似的物种，从而可能导致种间花粉转移（IPT）的发生率较低。如果颜色相似性促进了社区层面的传粉者吸引力，那么群落内花颜色的观察到聚类可能是间接促进相互作用的结果。
