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 (see illustration). Another example is shown in Darwin's finches, 14 species of small land birds of the Galápagos Islands. All the 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; 3 species are ground-dwelling seedeaters, 3 live on cactus plants and are seedeaters, 1 is a tree-dwelling seedeater, and 7 are tree-dwelling insecteaters. See also competition.
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