The tropic factor and local chorological structure of the population of rodents as exemplified by bank voles

Problems of organization and dynamics of the species population of vertebrate animals remain debatable and take a special significance after origination of metapopulation ecology. The trophic factor is one of the main ecological factors. Therefore, great importance of quantitative estimation of its contribution to functioning "stations of surviving" still exists as, most probably, such stations play the main role in the formation of local chorological structure of the species population of rodents. Thereupon, the exact quantitative estimation of the processes of formation and functioning of basic elementary chorological units of the species population by the example of the bank vole (Clethrionomys glareolus Schreber, 1780) was the purpose of our work. For this aim, under conditions of a typical southern taiga in the Middle Urals within the framework of continuous (from 1983 to 2014) monitoring studies, all-the-year-round field experiments with the use of strictly dosed additional food supply were conducted. We used a technique of lifelong marking and repeated catching of rodents on stationary unenclosed control and experimental plots with the sizes from 0.5 to 1 ha. Annually, from 2 to 5 catching series on each plot were carried out from February till December. For all the period of field experiments we caught and marked more than 500 bank voles and fixed more than 1500 animal trappings. As a result of simultaneous use of both regression and stochastic methods, the phenomenon of returnable rotation of the population of rodents with the formation of central and peripheral transitive zones was revealed for the first time. We established that the number of voles in the central zone with supplemental food was significantly above (t-student criterion = 11.2; p <0.01) in comparison with the neighboring peripheral zone without supplemental food. Such way of using the territory provides the species population, during the snow period, with the most effective consumption of trophic resources with maintaining the local abundance at a maximum level. Within the bounds of our conceptual approach, station environment of surviving, artificially formed with the help of using supplemental food, can be considered as adequate analogue to stations of surviving unfavorable conditions, what is real-life in nature. On the basis of such autonomic and discretely located stations there is a formation and functioning of the dynamical network consisting from elementary chorological units of the species population of rodents. The obtained results allow considering autonomous settlements of rodents in the sizes from 1 to several hectares as local gradient continuums of the species population. We found out that the leading ecological factor of forming elementary chorological units of the species population is the trophic factor. We showed that after reaching the necessary level of food supply there is obligatory formation of constantly functioning elementary chorological units of population on the basis of genetic continuity of several consecutive generations. Formation of elementary units begins in the autumn at the stage of localization of the bank vole population and comes to an end in the spring before snow cover melting and before the beginning of reproduction processes when the sizes of separate units become minimum. After this, the annual stage of dispersion or expansion of the species population of bank voles begins which is then appropriately replaced by the following stage of localization with obligatory formation of successive network of renewed elementary chorological units of the species population.

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