Radiations can be either adaptive or non-adaptive, resulting in a variety of niches occupied by sympatric species, or in hardly any niche differentiation and species showing largely mosaic distribution patterns. The terms are useful despite the fact that intermediate situations occur.
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Alternate titles: multiple divergence
By The Editors of Encyclopaedia Britannica Article History
Table of Contentsadaptive radiation in Galapagos finches
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Key People:Henry Fairfield Osborn...[Show more]Related Topics:divergence...[Show more]
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adaptive radiation, evolution of an animal or plant group into a wide variety of types adapted to specialized modes of life. Adaptive radiations are best exemplified in closely related groups that have evolved in a relatively short time. A striking example is the radiation, beginning in the Paleogene Period [beginning 66 million years ago], of basal mammalian stock into forms adapted to running, leaping, climbing, swimming, and flying. Other examples include Australian marsupials, cichlid fish, and Darwin’s finches [also known as Galapagos finches].
Many examples of speciation by adaptive radiation are found in archipelagoes removed from the mainland. In addition to the Galapagos Islands, the Hawaiian archipelago, with its several volcanic islands and relatively small total land area, hosts an astounding number of plant and animal species that are endemic; that is, they have evolved there and are found nowhere else. More than 90 percent of the native species of Hawaiian flowering plants, land mollusks, birds, and insects are endemic.
Which of the following scenarios is NOT an example of adaptive radiation: A few marsupial species travel from South America to Australia, where they inhabit the numerous new niches, resulting in dozens of marsupial species over a relatively short amount of time After a few plant species have gone extinct in an area, a surviving plant species spreads into this same area, and its population triples in size A few mice from a single species leave the mainland and inhabit an island. Over time, the mice develop local adaptations that result in divergence of the original species After the dinosaurs went extinct, the mammals they coexisted with them see a significant increase in species