Home – Home – Jornals – Contemporary Problems of Ecology 1999 number 1

The modern basic theoretical principles of population regulation in mammals are reviewed in this paper. Consistent with the most fruitful systemic approach, a population, as the object of study, can be understood by both investigating the dynamics of the parts of the system (individual organisms) and by examining the context of population system in more inclusive community and landscape systems whose part it is.

Terrestrial landscapes are increasingly subject to fragmentation as a result of both natural and anthropogenic influences. How animals respond to fragmentation in the real world is an important ecological issue. We provide a prospectus for research linking population dynamics of small mammals to community dynamics in patchy landscapes. Our studies in the north-eastern United States demonstrate the importance of patch quality to the population dynamics of white footed mice (Peromyscus leucopus) within oak forest patches. These studies also provide evidence for dispersal of mice from patches of high quality to neighbouring patches of lower quality when mouse densities are at or near a peak. We contrast two alternative models for characterizing such dispersal between patch types - the source

In this article we present the current state of seasonal reproduction in mammals, a phenomenon which is well known to ecologists and endocrinologists. Emphasis is placed on mechanisms of seasonal reproduction and ecological considerations, first of all concerning the Djungarian hamster (Phodopus sungorus) since its seasonal rhythms and especially its photoperiodic control, have been studied extensively.

According to theory, animals should attempt to optimize the allocation of resources among the competing demands for reproduction, growth, survival, and of course maintenance, so as to maximize lifetime reproductive output. Trade-offs between immune competence and other life-history attributes have received much of this research interest because of the potential returns to our understanding of population processes in a changing environment.
The main modern hypotheses about ecological factors and evolutionary reasons of wide range variability of immunocompetence in population of animals are reviewed in this paper.

Ovulation rate, embryo mortality, mean number of live embryos and sexual maturation rate depended significantly on the phase of water vole population dynamics. Female's reproductive capacity was the highest at the increase phase and the lowest at the decline phase. Embryo mortality and sexual maturation rate were affected pleotropically by the coat colour genes. The lower reproductive capacity of dark-brown over wintered voles at all phases of population cycle, except for the peak, was due to a higher incidence of resorption of entire litters compared to brown over wintered females. At the peak, reproductive characteristics of brown and dark-brown over wintered females did not differ. Young-of-the-year dark-brown females matured earlier than brown females at the peak and decline phases and, therefore, were more reproductively successful. Analysis of voles growth in captivity revealed that dark-brown voles grew faster than brown ones. In natural population, coat colour differences in body weight of over wintered individuals were phase-dependent. Dark-brown voles usually weighed more than brown voles in the peak and decline years. It is suggested that differences in female fertility, growth and sexual maturation rate between coat colour genotypes contribute to transformation of genetic structure and act as mechanisms maintaining coat polymorphism in cyclic water vole population.

The number of wounds on skin, social ranks of captured adult males in experimental encounters, and spatial distribution of breeding individuals were studied in a population of Arvicola terrestris (L.) during two consecutive cycles (1980-1998). The study was performed within a period of intense breeding (May and June). The level of wounding of over wintered females low and independent of population density. In over wintered males, the wounding level was positively correlated with population density. The local density of reproductively active water voles within local populations did not change regardless of population fluctuations. The nearest neighbour analysis indicated that breeding females were territorial. In the male-biased local populations, heavier males were trapped closer to females. This might reflect their advantage in male-male competition and prior access to the relatively limited reproductive resource. Male body weight significantly differed among social ranks; it was maximal in dominant individuals. Dominance capacities of homozygous brown and black, and heterozygous dark-brown over-wintered males were also compared in experimental encounters. Differences among coat colour morphs were found to be cycle-dependent. At the peak and decline phases, the percentage of dominants was higher for heterozygous dark-brown than homozygous brown males. These differences may account partly for maintenance of coat colour polymorphism within the population.

Plasma 11-hydroxicorticosteroids, progesterone, testosterone, estradiol, circulating free fatty acids, and glucose were monitored in a water vole population during 1980

Inter-annual, seasonal and individual variations in food digestibility were studied in a cyclic population of water vole. Digestibility was calculated from the data on the indigestible component (lignin + acid-insoluble ash) in food and feces. Samples were collected in natural habitats and from captured water voles maintained on a natural diet for 3-5 days after capture. Estimates of food quality were based on the data for forage fibber.
Seasonal changes in digestibility were determined by seasonal alterations in the forage but found to differ at different phases of population dynamics. After the peak there was a relative loss of digestibility in animals with no loss of food quality. This is suggested to be caused by adoptions to eating un-preferable food against a background of food depletion in winter habitats overgrazed at high density. Digestibility values started to rise at low density and these inter-annual changes in over wintered animals were positively correlated with the cyclic-related changes in the mean body weight and negatively with the plasma level of free fatty acids. Relations between the digestibility and the individual body weight, social status and breeding conditions were found. Among animals over wintered at numbers decline, dominant males and pregnant females digested food more efficiently in contrast to subordinate and non-pregnant ones. It was concluded that adjustments of digestive system of animals, among other nutritional factors, may affect the population dynamics through changes in population and individual fitness.

In 1991-1996, the time course of numbers, and the variability of the basic demographic and some ecologic-physiological indices of Siberian lemming (L. sibiricus) population in the Kolyma lowland (lower reaches of the Bolshaya Chukochya river, 70