Adaptive Radiation

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, 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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adaptive radiation [ə′dap·tiv ‚rād·ē′ā·shən]

(evolution)

Diversification of a dominant evolutionary group into a large number of subsidiary types adapted to more restrictive modes of life (different adaptive zones) within the range of the larger group.

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Adaptive Radiation 

the formation of diverse organismic forms within the limits of a species or a group of related species. The term was proposed by the American scientist H. Osborn in 1915, although the idea had already been advanced by C. Darwin, who employed the term “divergence.” Adaptive radiation is fundamental to all forms of adaptogenesis and is the result of the acquisition by organisms of special accommodations—adaptations and penetrations into new adaptive zones. The main origin of adaptive radiation is found in intraspecies processes such as genetic diversity of species populations, differentiation of the species into geographical and ecological races as a result of enlargement of the territory under favorable conditions, and intraspecies contradictions.

The scale of adaptive radiation may differ from one case to another. Large-scale adaptive radiation is found in the evolution of amphibians, some aquatic forms of which have tails (Urodela), while strictly amphibious forms preserve the tail only in the larval stage (Anura), and a third group, the dry-land forms, have lost their legs and assumed a serpentine character (Apoda). Examples of small-scale adaptive radiation associated with the formation of geographical races are found in the cases of the Kamchatka great spotted woodpecker (Dendrocopus major Kamtschaticus ) and the Talysh lesser spotted woodpecker (Dendrocopus minor quadrifasciatus ) or in races of the ordinary spruce—Norway (Picea excelsa), Siberian (Picea obovata), and Finnish (Picea fennica).

A. V. IABLOKOV