A 32-year demography of yellow-bellied marmots (Marmota flaviventris)

Yellow-bellied marmots Marmota flaviventris in the East River Valley of Col orado were live-trapped and individually marked annually from 1962 through 1993. These pooled data were used to produce a demography and life table fo r these years. Females had significantly better survivorship than males bey ond the first-year age class, and the sex ratio became progressively female biased. The major mortality factors of predation and unsuccessful hibernat ion acted evenly on all age classes as shown by the constant rates of survi vorship. The rate of senescence indicated that the probability of mortality did not increase with age. Females produced litters from ages 2 to 10 year s. Mean litter size was 4.1 and did not differ among age classes. The femal e generation length of 4.49 years was 2.4 times the life expectancy and the median survivorship. The net reproductive rate (R-o) was 0.67, yet the pop ulation did not continually decline; adjustments to these data increased R- o to 0.85. Reproductive values (V-x) were approximately equal across the re productive age classes. The polygynous mating system is both cause and effe ct of the demography. Marmot population size is affected by weather factors that influence reproduction and survival, by predation, and by movement in to and out of the study area.