Centre for Functional Biodiversity, School of Life Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermartizburg 3209, South Africa.
Biol Lett. 2019 Jul 26;15(7):20190349. doi: 10.1098/rsbl.2019.0349. Epub 2019 Jul 31.
Bird pollination systems are dominated by specialist nectarivores, such as hummingbirds in the Americas and sunbirds in Africa. Opportunistic (generalist) avian nectarivores such as orioles, weavers and bulbuls have also been implicated as plant pollinators, but their effectiveness as agents of pollen transfer is poorly known. Here, we compare the single-visit effectiveness of specialist and opportunistic avian nectarivores as pollinators of Aloe ferox, a plant that relies almost exclusively on birds for seed production. We found that the number of pollen grains on stigmas of flowers receiving single visits by opportunistic avian nectarivores was approximately threefold greater than on those receiving single visits by specialist sunbirds and about twofold greater than on those that received single visits by honeybees. The number of pollen grains on stigmas of flowers visited by sunbirds was similar to that on stigmas of unvisited flowers. These results show that opportunistic birds are highly effective pollinators of A. ferox, supporting the idea that some plants are specialized for pollination by opportunistic birds.
鸟类传粉系统主要由专门的花蜜食者主导，如美洲的蜂鸟和非洲的太阳鸟。机会主义（广义）的鸟类花蜜食者，如黄鹂、织布鸟和画眉，也被认为是植物传粉者，但它们作为花粉传播媒介的有效性知之甚少。在这里，我们比较了专门的和机会主义的鸟类花蜜食者作为 Aloe ferox 的传粉者的单次访问有效性，Aloe ferox 是一种几乎完全依赖鸟类来产生种子的植物。我们发现，接受机会主义鸟类单次访问的花朵柱头上的花粉粒数大约是接受专门的太阳鸟单次访问的花朵柱头上的花粉粒数的三倍，大约是接受蜜蜂单次访问的花朵柱头上的花粉粒数的两倍。接受太阳鸟访问的花朵柱头上的花粉粒数与未受访问的花朵柱头上的花粉粒数相似。这些结果表明，机会主义鸟类是 A. ferox 的高效传粉者，支持了一些植物专门通过机会主义鸟类进行传粉的观点。
