Dynamics of Sex Ratio in Populations of Cyclomorphic Mammals (Rodentia, Cricetidae, Muridae)

摘要

Using the result of long-term monitoring (over 30 years) of the main population parameters of cyclomorphic mammals (genera Clethrionomys, Microtus, and Sylvaemus) in the ll'men Reserve (Chelyabinsk oblast, the Southern Urals), the phenomenology of the sex ratio and its dynamics in their natural populations are analyzed. The main factors potentially influencing the sex structure of rodents are considered, including isolation of settlements, relative abundance, population density, species-specific features, alternative types of ontogeny, exposure to extreme factors, sex-dependent asynchronous mortality, and age cross. It is shown that the analysis of sex structure in rodents should be performed taking into account the type of their ontogeny, with the CM R method (capture-marking-recapture) giving the most objective estimate of the sex ratio. An alternative approach is to analyze samples taken in autumn to winter, after the end of breeding and elimination of reproductive individuals from the population. It is concluded that the dynamics of the sex structure in murine rodents are conditioned ecologically and that no selective elimination of individuals depending on sex takes place upon overwintering. The sex ratio in cyclomorphic mammals is a variable parameter that fluctuates about the average value depending on both regular and random factors. Methodological recommendations are given for the assessment of sex structure in cyclomorphic mammals.