Proces kształtowania się struktury płciowej w populacjach nornicy rudej (Clethrionomys glareolus Schreber 1780)

Bujalska, Gabriela

doi:ISSN 0013-2969

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Tytuł: Proces kształtowania się struktury płciowej w populacjach nornicy rudej (Clethrionomys glareolus Schreber 1780) ; Struktura płciowa w populacjach nornicy rudej

Abstrakt:

A review of papers on sex ratio in populations of Clethrionomys glareolus Schreber 1780 is given. The secondary sex ratio (at the moment of birth) is almost always 1:1, only in some cases — cohorts born in the second half of the reproduction season — there is a prevalence of males (up to 72°/o of males). The tertiary sex ratio (among sexually immature individuals) varies with a tendency to male prevalence, and only in populations having a low density the sex ratio is equal to 1:1. Quarternary sex ratio (among sexually mature individuals) shows a prevalence of females in the majority of ćases. This is atf special significance far the fluctuations of populations numbers.It seems that sex ratio of individuals of a current year shows usually the prevalence of males (especially in the first months of life). When these individuals constitute 9O*/o of population the sex ratio in this category of individuals becomes even (Table I).General sex ratio (for the entire population) has a much lower variability than sex ratio in distinguished categories of individuals. This observation as well as the analysis with regard to changes in sex ratio together with increasing population numbers (with increasing population numbers differences in sex ratio tend to decrease) (Fig. 1) point -to the existence of group reactions in the population responsible for the formation of a determined sex ratio.The relation between sex ratio and demographical strategy in populations of small rodents is discussed (Fig. 2). The necessity of examining the sex ratio as regards the division into sexually mature and immature individuals and within them into cohorts of the same age has been pointed out.