The Mortality, Fertility and Rate of Natural Increase of the Vole (Microtus agrestis) as Observed in the Laboratory

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Abstract
98 [male][male] and 46 [female][female], observed from the age of 3 weeks, had a mean length of life under laboratory conditions of 34.57 [plus or minus]1.343 wks. Life tables are calculated giving mortality and size of remaining population at 8-wk. intervals. The sex ratio of 505 young at weaning was 50.89 [plus or minus] 222% of [male][male]. Of [female][female] which passed the whole of their adult lives paired with [male][male] the mean number of daughters born per 8 wks. per [female] (a measure of fertility) was greatest at the age of 12-20 wks. The rate of natural increase, calculated for a population subject to the observed age-schedules of mortality and fertility and when the appropriate age-distribution was established, was 87.7 per thousand per wk., or roughly a power of multiplying 10 times in 6 mos. Application of these results is made to natural conditions and the influences of an intermittent breeding season and varying environment are briefly discussed.

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