Adaptive radiation
Adaptive radiation is an evolutionary process whereby a single ancestral species or form diversifies or speciates into several or many related forms or species. The basic form of the different descendant taxa are similar, but each is adapted for a particular environmental niche.
The presence of over 250,000 species of beetles, the 14 different species of Darwin's finches on the Galápagos Islands, the over 25,000 types of teleost fishes, and the different marsupials in Australia are considered to be examples of adaptive radiation (Luria et al. 1981).
Causes of adaptive radiation
The vigorous phase of diversification characteristic of adaptive radiation is linked to a new design, particularly when it is tied to movement in to a new ecological space, such as an unoccupied territory or a new mode of life, such as the development of flight by insects more than 300 million years ago (Luria et al. 1981).
Opportunity
Isolated ecosystems, such as archipelagos and mountain areas, can be colonized by a species which, upon establishing itself, undergoes rapid divergent evolution. Monotremes and marsupials are examples of geographic isolation. Monotremes evolved before the evolution of placental mammals, and they are found today only in Australia, an island. Marsupials, which also evolved before the appearance of placental mammals are also common in Australia. In Australia, marsupials evolved to fill many ecological niches that placental mammals fill on other continents.
isolaed for 50 mililion years marsupials in Austrail other contentines (partial exception of Soputh America), mostly placentals.
Richard Leakey (see below) wrote, "Biologists who have studied the fossil record know that when a new species evolves with a novel adaptation, there is often a burgeoning of descendent species over the next few million years expressing various themes on that initial adaptation - a burgeoning known as adaptive radiation. The Cambridge University anthropologist Robert Foley has calculated that if the evolutionary history of the bipedal apes followed the usual pattern of adaptive radiation, at least sixteen species should have existed between the group's origin 7 million years ago and today."
Extinction
Adaptive radiation can also occur after mass extinctions. The best example of this is after the Permian-Triassic extinction event, where biodiversity increased massively in the Triassic. The end of the Ediacaran and the beginnings of multicellular life lead to adaptive radiations and the genesis of new phyla in the Cambrian period.
ReferencesISBN links support NWE through referral fees
- Wilson, E. et al. Life on Earth, by Wilson,E.; Eisner,T.; Briggs,W.; Dickerson,R.; Metzenberg,R.; O'brien,R.; Susman,M.; Boggs,W.; (Sinauer Associates, Inc., Publishers, Stamford, Connecticut), c 1974. Chapters: The Multiplication of Species; Biogeography, pp 824-877. 40 Graphs, w species pictures, also Tables, Photos, etc. Includes Galápagos Islands, Hawaii, and Australia subcontinent, (plus St. Helena Island, etc.).
- Leakey,Richard. The Origin of Humankind - on adaptive radiation in biology and human evolution, pp. 28-32, 1994, Orion Publishing.
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