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Physiological, emotional, and behavioral adjustment by an individual to changes in the environment.
Adaptation of a species or population to a changed environment over several generations. Also known as acclimation.



the adaptation of organisms to new conditions of existence.

Although acclimatization literally means adaptation to the climate, the term has long been used to designate adaptation of the organism not, only to new climatic conditions but also to soil conditions and new biocenoses. Acclimatization can occur in either of two ways: (1) By changing the metabolism of organisms. This type of change (modification) is not inherited and is governed by the response rate of the organism. In that case, naturalization occurs—for example, noxious and quarantine weeds and pests of a genotype with a broad response rate are capable of propagating freely over the planet—and the genetic structure of the population or species undergoes no change. (2) By changing the genetic structure of the species. This constitutes true acclimatization. A factor determining the genetic structure of the species and responsible for acclimatization is natural selection. In ontogenesis, acclimatization is determined by the richness of the gene pool of the population. Spontaneous mutations are of some importance in acclimatization, but their frequency is low. Acclimatization occurs when organisms resettle in regions or sites which are new to them or where they had previously been wiped out (reacclimatization). Acclimatization is observed when a habitat’s conditions are altered—for example, when forests are cut down or new forest stands are planted, when deserts are irrigated or swamps dried out. In those cases, some organisms migrate to other sites or perish (like plants), while others adapt to the new environmental conditions—that is, they become acclimatized. Cultivated species of animals and plants also become acclimatized through introduction (artificial acclimatization), while wild species become acclimatized under natural conditions (natural acclimatization) as they resettle in new regions— spread by migration, wandering animals, or the random transfer of plants by humans, animals, or the wind.

In antiquity, nomadic tribes moved seeds of useful wild plants with them and resettled animals, which became acclimatized under their new conditions. The resettlement of plants and animals contributed later on to the development of world trade and means of transportation. In the 18th century A. Humboldt first expressed the idea of the possibility of gradual acclimatization, termed stepwise acclimatization. A. P. de Candolle and his son A. de Candolle stated that a certain set of conditions was required for a particular species to move into new areas. The works of C. Darwin were of great significance for the development of the theory and practice of acclimatization. Much attention was devoted to acclimatization in tsarist Russia in the mid-19th century. K. F. Rul’e and his disciple A. P. Bogdanov set up a committee on acclimatization in 1857. A periodical Akklimatizatsiia began to be published in 1860 on their initiative. Writings on acclimatization by the Russian scientists E. L. Regel’ and A. N. Beketov are well known. Theoretical research in acclimatization underwent further development in the USSR. I. V. Michurin and M. F. Ivanov developed effective methods of acclimatization. The Russian zoologists B. M. Zhitkov and T. A. Manteifel’ did much work on the acclimatization of animals. N. I. Vavilov made a major contribution to the acclimatization of plants.

Plants. Acclimatization of plants always results in an expansion of the range occupied by the species. For example, the Serbian spruce, whose range was restricted to the Drina River (Yugoslavia), acclimatized readily in Northern Europe and even flourishes at the latitude of Leningrad in the USSR. The horse chestnut, whose homeland is Africa, propagated to the phytocenoses of Europe, as did the black locust, or false acacia, from North America; the Atlas cedar from Africa, the giant sequoia from North America, and the eucalyptus tree from Australia all flourish on the Black Sea coast. As a result of polymorphism and the richness of its gene pool (abundance of mutations), the lilac, which is native to Southern Europe and Asia Minor, covers a wide area. An example of natural acclimatization as a result of hybridization polyploidy is the appearance of soft wheat (Triticum aestivum ) in one of the primary centers of origin of crop plants (Southwest Asia) and the expansion of its range far to the north. Acclimatization of plants is seriously affected by such climatic factors as air temperature and humidity, quantity and distribution of precipitation, nature of snow and ice cover, and air movements; by the light status; by the type of soil and the composition of the microflora inhabiting the soil; by the nature of the biogeocenosis; and by the biological features of the plants themselves. It is known, for example, that xerophytes withstand dangerous temperature drops with greater ease than moisture-loving plants.

Acclimatization of plants is one of the major problems facing the national economy, and success in handling that problem depends to a large extent on the totality of the methods available for use. Michurin utilized hybridization of geographically and systematically remote forms in his work on the acclimatization of fruit crops and also resorted to crossing wild-growing species. The Lombardy poplar was acclimatized in Moscow through hybridization. Various agricultural techniques are used, including grafting onto stable seedling stocks, picking, pinching, irrigating and fertilizing, utilizing growth stimulants or other preparations to inhibit the growth of ovaries and protect them from late frosts, cultivating plants on irrigated soil, growing plants in the initial period of acclimatization under greenhouse conditions, and artificially heating groves.

Botanical gardens, introduction nurseries, and other scientific research institutions whose functions include building collections of local and foreign plants and introducing them into cultivation in new regions are doing much work on the acclimatization of plants in the USSR. Their activities have resulted in the acclimatization of the tea tree, citrus plants, the oil tung, the eucalyptus, the bamboo, camphor trees, the oriental persimmon, and several species of palms on the Black Sea shores of the Caucasus. The cultivation of grape vines, sweet cherries, apricots, and other fruit-bearing plants, as well as such decorative plants as the horse chestnut and various poplar species, has been moved further north. Acclimatization of trees in the Far North, where farming had been considered impossible, is particularly important. The Pamir Botanical Garden and experimental stations in mountainous regions have contributed to the acclimatization of crop plants and to the development of agriculture in high-mountain regions. Intensive work is being done on acclimatization of plants under desert conditions. New medicinal and aromatic plants are being acclimatized and introduced into cultivation. Acclimatization of tree species and bush species has enriched the available assortment of decorative plants. Important work on the transformation of plant zones is being done in the USSR through acclimatization of plants.


Animals. It is generally known that thousands of both harmful and useful species of animals have propagated beyond the confines of their natural ranges over the earth. For example, over 180 species of pests (the Hessian fly, the appleworm, the corn borer, and many timber pests) have penetrated into the USA from other countries. The Colorado potato beetle, which has become one of the most dangerous and harmful pests to hit potato crops, came to Europe from America. The widespread gray and black rats are relatively recent newcomers to a large part of their present range; their resettlement was an indirect result of human activity. Species which find no serious competitors in their new habitats flourish with special vigor—for example, the European starling spread over the USA, Canada, South Africa, Australia, and New Zealand within a space of 60 years. Acclimatization on islands takes place with relative ease for the same reason (islands are characterized by depleted biocenoses and absence of competitors). In New Zealand, for example, imported species of animals now completely dominate the wild: over 50 percent of the mammals and birds are from Europe, Asia, and North America, including deer—the red, axis, sambar, Virginia, and fallow deer and the moose—wild boars, two species of rats, larks, thrushes, finches, and goldfinches.

In economic practice, acclimatization is caused by the artificial resettlement of useful wild or agricultural animals. Experiments on acclimatization of wild mammals in various countries have been carried out on 160 species. There are now 32 species of mammals resettled in the USSR, and acclimatized mammals account for over 10 percent of fur production. Muskrat acclimatization has been particularly profitable, with the range of muskrat in the USSR now exceeding the area it occupied in its native USA and in Canada. The American mink has taken well to acclimatization in several areas, as have the raccoon dog, the coypu, and the deer. Several species of birds have made successful resettlement—for instance, the gray partridge, Daurian and willow ptarmigan, and pheasant. Unique work on acclimatization is being done at the Askaniia-Nova Preserve, where over 80 types of mammals and 350 types of birds are being investigated. Acclimatization of fish is also of great importance. The resettlement, restocking, and acclimatization of carp, bream, whitefish, bonefish, and other species in internal reservoirs of the USSR yield an annual crop of over 10,000 tons of a most valuable product.

Acclimatization of food organisms—various invertebrates, predominantly worms, shellfish, mollusks, and crabs—increases the productivity of water reservoirs. For example, acclimatization of invertebrates stocked at Tsimlianskoe Reservoir has resulted in 1,500 tons of fish yearly. The nereis annelid, acclimatized in the waters of the Caspian Sea, has become the basic nutrient for sturgeon and Sevruga sturgeon. Acclimatization is accompanied not only by changes in the way of life of animals but also by changes in their morphological and physiological features: through improvements in the stability of animals under changes in temperature, light status, environmental humidity, atmospheric pressure, the air’s gas composition, and the potential available food supply. Adaptive reactions caused by relatively slight changes in their conditions of existence enhance the resistance of animals to various environmental changes—for example, maintaining some mammals at a temperature of 10°C enhances their stability to temperatures below - 15°C. Success in acclimatization depends on the selection of subjects and the length of time over which acclimatization is carried out. Natural selection of those individuals most completely adapted to unusual conditions of existence takes place in the new environment. The phenology of multiplication and the animal’s development conforms to the new seasonal and diurnal rhythms. Acclimatization can be considered completed when the species acquires the ability to maintain its population level under the new environmental conditions and to restore it after periods of depression. Changes in morphological and physiological features in response to acclimatization are expressed with particular clarity in fish but are also manifested in mammals. Acclimatization may also mean changes in the marketable qualities of animal furs—for example, changes in the quality of fur of the Teleut squirrel, coypu, and marmot during the acclimatization process. Stocking a species range with particularly valuable forms to improve the quality of the local animal population does not necessarily bring about the desired results, since the newcomers change in the direction of the aboriginal strains; for example, stocking the Urals with the most valuable eastern sables failed to produce the expected results, since the quality of fur in the acclimatized sables deteriorated. Acclimatization also plays a major role in restoring the original range of animals, once it has been curtailed as a result of human activities (reacclimatization). For example, in the 1920’s the population of riverine beavers in the USSR was no greater than 1,000. As a result of expensive resettlement of the animals from Byelorussia and from the Voronezh’ Preserve, riverine beaver are now found in 48 regions; the total number of beavers has increased to 40,000. Sable, squirrels, two species of rabbits, desman, and other commercially valuable species of animals have also become reacclimatized. Auroch herds are being successfully restored.


Agricultural animals. Humans themselves play a major role in the acclimatization of agricultural animals that have undergone a prolonged and complicated process of domestication, since the concept of environment applicable to such animals includes, in addition to natural factors, such agricultural and economic factors as the chemical composition of the fodder, feeding levels, maintenance of the animals, prevention of sicknesses, and breeding. If these and the new environmental conditions contrast sharply, the acclimatization process, particularly in the case of commercially valuable breeding stocks, takes place under great tension and frequently ends in failure.

Successful acclimatization of agricultural animals requires not only attention to climatic conditions in a new habitat but also efforts to provide the imported animals with the proper types of fodder and food, food allowances with adequate nutrients, suitable barn and stall accommodations, and improved maintenance conditions. If the animals imported into the new area acclimatize poorly, they are crossed with local stocks, with animals carefully selected for health, constitution, and productivity, using breeding studs certified to produce easily acclimatizing progeny. Acclimatizing animals are prevented from degeneration by crossing them with already acclimatized animals of the same breeds, using different forms of selection, and also by resorting to interspecific crossing. One crucial method for overcoming the difficulties encountered in acclimization is hybridization. The progeny of the imported animals possess broader adaptive capacities, since their process of adaptation begins at early stages of development, when the organism is most flexible.


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