Effects of population density and other factors on maturation of young of the year (by the example of bank vole - Clethrionomys glareolus Schreber)

The present work is directed to study of changes of intensity of maturation of young of the year depending on population density. Since 1999for 2011 years once in a season in second half of July took samples of local population bank vole (Clethrionomys glareolus Schreber). Reproductive status voles on a condition of reproductive system determined. The pregnant and parous females, having placental scar and/or embryos in uterus, and males with weight of the testis more than 150 mg with the advanced epididymis were ranked to sexually mature individuals. Each time after year ofa middle abundance occurred year high-density, therefore years of middle population density were increase phases. For the years of a low abundance followed peak years or one behind another, this has allowed to consider theirs as phase of decline (depressions). Age of animals determined under the form and sizes of the second upper tooth. For the analysis used young bank voles only in the age from 1.5 month, as sexually mature individuals in our samples meet since this age. Total investigated of young of the year has made 443 individuals. As among young voles the grown-ups individuals had age 3.5 month and among overwintered animals youngest were not younger 9.5 month, hence for the period of supervision of winter reproduction was not. The infringements of monotony of a curve reflecting dependence ofa share sexually mature among young of the yearfrom its indexes of abundance in July, occur within the limits of low and middle values population density of bank vole. The high values of a proportion mature young of the year, expressed at population of density are less 8 ind./ ha, within the limits of area 8-19 ind./ha decrease and remain low. This is connected to influence on an investigated parameter of abnormal weather conditions in first half summer and/or of the raised share red-backed (Clethrionomys rutilus Pall.) and red-sided voles (Clethrionomys rufocanus Sundevall) in community. The adverse weather conditions approximately equally suppress puberty, both males, and females young of the year. But the increased share red-backed and red-sided voles in community in the greater measure works on young females of the bank vole, than on males. Under abnormal weather conditions the effect of the raised share closely-related of species in community is not shown. The new increase of share sexually mature individuals up to a previous level occurs at population density within the limits of 20-30 ind./ha. Substantially it is connected to favorable weather conditions in those years, when the level population density was in the indicated limits. Density-dependent mechanisms of population self-regulation begin to work already at middle population density as seasonal inhibition of puberty females young of the year. In a complete measure their action is shown, when population density exceeds 40 ind./ha, therefore a share reproductively-active young voles comes nearer to zero.