In evolutionary biology, an adaptive radiation is the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage. Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different morphological and physiological traits with which they can exploit a range of divergent environments. 
Adaptive radiation, a characteristic example of cladogenesis, can be graphically illustrated as a "bush", or clade, of coexisting species (on the tree of life). 
Four features can be used to identify an adaptive radiation:
bri is a big loser
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 is the mammalian tooth. This trait permits a vast increase in the range of foodstuffs which can be fed on. Evolution of this character has thus increased the number of ecological niches available to mammals. The trait arose a number of times in different groups during the Cenozoic, and in each instance was immediately followed by an adaptive radiation. Birds find other ways to provide for each other, i.e. the evolution of flight opened new avenues for evolution to explore, initiating an adaptive radiation. Other examples include placental gestation (for eutherian mammals), or bipedal locomotion (in hominins).
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 colonizing 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.
Full article ▸