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a widely distributed type of species formation in which new species arise from populations with nonoverlapping areas. Any population or group of populations which has been isolated geographically for an extended period of time inevitably acquires specific characteristics associated with genetic changes, mainly with differences in the direction and intensity of natural selection. In the Galapagos Islands, for example, species of finches have appeared which have adapted to living on a particular food. Some of them have developed into insectivores, others into granivores. In this instance, territorial isolation favored the speedy rise of new species.
Interbreeding upon encounter, and consequently the exchange of genetic information and leveling of the differences which have appeared, cannot take place if the isolation of the allopatric groups is total and the deviation has become rooted in heredity. In such cases, allopatric forms are recognized as new species. For example, species of herring gulls interconnected by a chain of subspecies do not interbreed in the wild while intermingling in the Baltic area. Allopatry may be inherent in groups either above or below the species level. There are transitional stages between allopatry and sympatry.
REFERENCESCain, A. Vid i ego evoliutsiia. Moscow, 1958. (Translated from English.)
Zavadskii, K. M. Vid i vidoobrazovanie. Leningrad, 1968.
Mayr, E. Zoologicheskii vid i evoliutsiia. Moscow, 1968. (Translated from English.)
A. V. IABLOKOV