Causes and process of migration

Streszczenie w języku angielskim

Bibliographical references (page 159)

Bibliografia na stronie 159

Abstract in English

Pages 151-160 ; 24 cm

Strony 151-160 ; 24 cm

Using the studies made in the Institute of Ecology, Polish Academy of Sciences, as a basis, certain selected problems of the origin and course taken by migrations of animals were discussed from the ecological standpoint. The examples referred to in the text were obtained from research on different groups of animals insects, spiders, molluscs, birds and mammals.Analysis was made of the influence exerted on the origin and course of migration by three basic groups of factors: 1) biologica! adaptation of the species which promote the migrational tendencies of individuals, 2) abiotic habitat, 3) population and biocenosis.Replacing of different species of animals, founded in the biological tendencies of the species to migration, is usually connected with reproduction. (search for suitable places for breeding), the appearance of a particular stage of development (r·eplacing of part of the population in the search for a habitat proper to the given stage of development, for food or for their hosts), or of a new generation of young individuals, e.g. in the case of birds. The course taken by this type of migration, that is, its intensivity, range, duration, is often modified by the influence of the habitat.The influence of the second group, including the action of habitat factors on migration, was analysed by considering, the migrations of animals taking place under the predominating influence of the habitat, such as changes in temperature, humidity etc. Migrations were also discussed which occur as the result of violent changes of a catastrophic character in the habitat, such as, for instance, variations in the water level in bodies of water as the result of floods. The replacing of animals caused by artificial poisoning of the habitat is given as a very particular case of this category of migrations.When considering the influence exerted on migration by the third group of factors - population and biocenosis, reference is made to cases of migration taking place under the predominating influence of population or biocenosis, or both these factors jointly, in relation to the habitat.From the population aspect analysis was made of the effect on migration of animals of the age, sex and space structure of the population and the effect of crowding. Experimental works were also taken into consideration here, especially those concerned with the effect of crowding on migration, made both under natural and under laboratory conditions.The migration caused by competitive action of species in an interconnected system, with similar ecological niches, is given as a characteristic case of migration under the influence of biocenotic action.The groups of factors discussed above (biological adaptation of the species determining the creation of migrational tendenies, abiotic habitat, population and biocenosis) may in some cases constitute a cause or a stimulus to the formation of migration, and in others modify its course. Despite the fact that in certain cases the dominating effect of the given group of factors may be pointed to as determining migration, this latter is as a rule a complex phenomenon, affected by the influence as a whole of the adaptation of the species, habitat, population and biocenosis. Migration affected by the co-acting system of the above groups of factors reacts in turn during the migration process on this system.