Survival and reproductive value of different cohorts in the muskrat population (Ondatra zibethicus L.)
N.S. Korytin, V.V. Shiryaev
Section: Population ecology
A few demographic parameters of the muskrat population have been obtained. The study is based on data from trapping muskrat samples (total 2018 individuals) and information on the fertility of 868 females. Variation in the cohort’s survival rate and reproductive value were studied for the first time on the basis of the muskrat population age distribution in the Ili River delta. The females specific survival rate was slightly higher than males in all age intervals. Both males and females survival rate was dramatically reduced starting at the age 1+. Maximal specific survival rate in the 0+ – 1+ age interval is typical for animals of the first cohort, minimal – for the second, which is most numerous. The picture of specific survival rate changes as cohort is growing older. In older age classes, the maximum survival rate turn out to last, third cohort. So, in the last age class the largest part of individuals belong to the third cohort (75%). As a result, the largest number of offspring is brought by females of this cohort (1.24–1.57 times more than representatives of the first and second cohorts). This is indicating the highest reproductive value of the third cohort females. No significant discrepancy in the fertility of females from different cohorts were found. That is, differences in the reproductive value of muskrats belonging to different cohorts arise due to the difference in specific survival rate. The number of representatives of the first two cohorts, which survived for the next year, is quite enough to form the population parent number. The muskrat retains the mechanism of forming next year reproductive core, which is typical to small voles, but it does not have a determining value for it.
ISSN 1995-4301
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