Centre for Functional Biodiversity, School of Life Sciences, University of KwaZulu-Natal, Pietermaritzburg, South Africa.
Plant Biol (Stuttg). 2022 Aug;24(5):806-814. doi: 10.1111/plb.13433. Epub 2022 May 25.
Bird pollination systems are diverse, ranging from narrow-tubed flowers pollinated by specialist nectarivores such as hummingbirds and sunbirds, to relatively open flowers pollinated by opportunistic (i.e. generalist) nectarivores. The role of opportunistic avian nectarivores as pollinators has historically been under-appreciated. A key aspect to understanding the importance of opportunistic birds as pollinators is to investigate how efficiently they transfer pollen among flowers. Here, we document the pollination and breeding systems of Schotia brachypetala, a southern African tree known as the 'weeping boer-bean' on account of its prolific production of dilute hexose-dominated nectar. The cup-shaped flowers of this tree attract a large number of bird species, including both opportunistic and specialist nectarivores. We identified floral visitors using observations and camera traps and quantified the floral traits responsible for animal attraction. We documented the breeding system, used selective pollinator exclusion to test the contribution of birds to fecundity, and performed supplemental pollination to test for pollen limitation. Single-visit pollen deposition trials were undertaken to determine the efficacy of bird pollinators. Controlled hand-pollination experiments showed that S. brachypetala is genetically self-incompatible and therefore dependent on pollinators for seed production. Supplemental hand-pollination experiments showed that natural fecundity is limited by either the amount and/or the quality of pollen on stigmas. Flowers from which birds but not insects were experimentally excluded set fewer seeds than open control flowers. Opportunistic birds deposited more pollen per visit than did specialist sunbirds. We conclude that S. brachypetala has a generalized bird pollination system that mainly involves opportunistic nectarivores.
鸟类传粉系统多种多样，从由蜂鸟和太阳鸟等专门吸食花蜜的鸟类传粉的细管花，到由机会主义（即一般性）吸食花蜜的鸟类传粉的相对开放的花。机会主义食蜜鸟类作为传粉者的作用在历史上一直被低估。理解机会主义鸟类作为传粉者的重要性的一个关键方面是研究它们在花朵之间传递花粉的效率。在这里，我们记录了南部非洲一种名为“哭泣的农民豆”的树的传粉和繁殖系统，因为其大量产生稀有的己糖主导的花蜜而得名。这种树的杯状花吸引了大量的鸟类物种，包括机会主义和专门吸食花蜜的鸟类。我们通过观察和相机陷阱识别了花卉访客，并量化了吸引动物的花卉特征。我们记录了繁殖系统，使用选择性传粉者排除来测试鸟类对繁殖力的贡献，并进行了补充授粉以测试花粉限制。进行了单次访问花粉沉积试验以确定鸟类传粉者的功效。控制性的人工授粉实验表明，S. brachypetala 在遗传上是自不亲和的，因此依赖传粉者来产生种子。补充人工授粉实验表明，自然繁殖力受到柱头花粉数量和/或质量的限制。与开放对照花相比，从实验中排除鸟类但不排除昆虫的花设置的种子较少。机会主义鸟类每次访问时沉积的花粉量多于专门的太阳鸟。我们的结论是，S. brachypetala 具有广义的鸟类传粉系统，主要涉及机会主义的食蜜鸟类。
