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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 finchesDarwin's finches
or Galapagos finches
, species of small perching birds, constituting the subfamily Geospizinae of the tanager family. Not related to the true finches, this group of at least fifteen species is confined to the Galápagos Islands, except for a
..... Click the link for more information. , 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 competitioncompetition,
in biology, relationship between members of the same or different species in which individuals are adversely affected by those having the same living requirements, such as food or space. Intraspecific competition, i.e.
..... Click the link for more information. .
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