Why do animals and birds avoid red flowers?March 17th, 2009 - 5:22 pm ICT by IANS
Sydney, March 17 (IANS) Naturalists like Charles Darwin have always thought that the appearance of flowers is dictated purely by the need to attract the various insects, mammals and birds needed for cross-pollination.
Biologists studied hakeas, a group of plants which are noted for their diverse appearance. Although many species produce relatively small, white flowers encircled by dense spiny leaves, others possess large, red flowers which are sparsely surrounded by spineless leaves.
Earlier observations suggested that while the white flowers are predominantly pollinated by insects, the showy and accessible flowers of the red variety are usually bird-pollinated.
However, showiness and accessibility bring with them a potential problem - if pollinators like birds can easily locate and access a flower, then so can large vertebrate herbivores.
Working in the species-rich heathlands around Perth in Western Australia, the University of Plymouth’s Mick Hanley and colleagues collected data on flower and foliage characteristics from 50 hakea species.
They found consistently higher levels of cyanide in the large, red flowers of bird-pollinated species compared with the spiny, white-flowered plants.
As cyanide is commonly employed by plants to deter herbivores, the obvious conclusion was that this has evolved in bird-pollinated flowers as a response to herbivore attack.
Red flowers have traditionally been seen as a means of attracting bird pollinators to the plant. But Hanley believes that the animals that eat the plants may learn to associate the colour with the bitter taste produced by the cyanide.
“The colour red acts as a warning to large vertebrate herbivores like emus, parrots and kangaroos that the flower contains distasteful or even poisonous cyanogenic compounds,” said Hanley, according to a University of Plymouth release.
The research work was funded by a British Ecological Society Small Ecological Project Grant and published in the current issue of New Phytologist.
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Tags: biologists, bitter taste, british ecological society, charles darwin, cross pollination, ecological project, foliage characteristics, heathlands, herbivores, kangaroos, mammals, naturalists, obvious conclusion, parrots, pollinators, red flowers, sydney march, university of plymouth, western australia, white flowers