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{{Cleanup|date=May 2008}}[[Image:Darwin's finches.jpeg|thumb|Four of the [[Darwin's finches|13 finch species]] found on the [[Galápagos Islands|Galápagos Archipelago]], are thought to have evolved by an adaptive radiation that diversified their [[beak]] shapes to adapt them to different food sources.]]

An '''adaptive radiation''' is a rapid [[evolutionary radiation]] characterised by an increase in the morphological and ecological diversity of a single, rapidly diversifying lineage.  Phenotypes adapt in response to the environment, with new and useful traits arising.<ref name=Schluter2000>{{cite book
 | author = Schluter, D.
 | year = 2000
 | title = The Ecology of Adaptive Radiation
 | publisher = Oxford University Press
 | isbn = 
}}</ref> This is an [[evolution]]ary process driven by [[natural selection]].

==Causes of adaptive radiation==

===Innovation===
The evolution of a novel feature may permit a clade to diversify by making new areas of morphospace accessible.  A classic example is the evolution of a fourth cusp in the mammalian tooth.  This trait permits a vast increase in the range of foodstuffs which can be utilised, with species able to specialise on feeding on a range of foodstuffs. The trait arose a number of times in different groups during the Cenozoic, and in each instance was immediately followed by an adaptive radiation.<ref name=Jernvall1996>{{cite doi|10.1126/science.274.5292.1489}}</ref> Birds provide another example; the evolution of flight opened new avenues for evolution to explore, initiating an adaptive radiation.<ref>''The Origin and Evolution of Birds'' by Alan Feduccia (1999)</ref>

===Opportunity===

Adaptive radiations often occur as a result of an organism arising in an environment with unoccupied niches, such as a newly formed lake or isolated island chain.  The colonising population may diversify rapidly to take advantage of all possible niches.

In [[Lake Victoria]], an isolated lake which formed recently in the African rift valley, over 300 species of [[cichlid]] fish adaptively radiated from one parent species in just 15,000 years. 

Adaptive radiations commonly follow [[mass extinction]]s: following an extinction, many niches are left vacant.  A classic example of this is the replacement of the non-avian dinosaurs with mammals at the [[K-T extinction event|end of the Cretaceous]], and of brachiopods by bivalves at the [[P-T extinction|Permo-Triassic boundary]]..

==See also==
*[[Evolutionary radiation]] - a more general term to describe any radiation
*[[Cambrian explosion]] - the most famous evolutionary radiation

==Further reading==
*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 (continent)|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.
*Grant, P.R. 1999. The ecology and evolution of Darwin's Finches. Princeton University Press, Princeton, NJ. 
*Mayer, Ernst. 2001. What evolution is. Basic Books, New York, NY.
*Kemp, A.C. 1978. A review of the hornbills: biology and radiation. The Living Bird 17: 105-136.

==References==
{{reflist|2}}



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