adaptive radiation, in biology, the evolution of an ancestral species, which was adapted to a particular way of life, into many diverse species, each adapted to a different habitat. Adaptive radiation has occurred in the evolution of many groups of organisms, and is clearly illustrated by Hawaiian honey-creepers. Another example is shown in Darwin's finches , at least 15 species of small land birds of the Galápagos Islands and Cocos Island. All of Darwin's finches derive from a single species of ground-dwelling, seed-eating finch that probably emigrated from the South American mainland. Because the environmental niches, or habitats, were unoccupied on the isolated islands, the ancestral stock was able to differentiate into diverse species; several species are ground-dwelling seedeaters, others live on cactus plants or trees and are seedeaters or insecteaters. See also competition .
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