The vertebrate fossil record of Cement Creek Cave, Colorado, spans from ≫ 45,000 yr ago to the present and represents the richest stratified series of high-elevation (≫ 2900 m) mammal remains known from the late Quaternary of North America. Stable carbon and oxygen isotope analyses of tooth enamel were used to assess potential ecological responses of two species found commonly throughout the cave, Yellow-bellied marmots (Marmota flaviventris) and Bushy-tailed woodrats (Neotoma cinerea), to late Quaternary climate and environmental changes of the Southern Rocky Mountains. Results indicate that despite such perturbations, the dietary ecologies of both species were maintained across this period. Neither taxon shifted to consuming C4 taxa or different C3 functional groups; similarly, no significant shifts in surface water use were detected. Variations in enamel δ13C were observed, however, that represent the physiological responses of high-elevation plants to changing levels of late Quaternary atmospheric CO2. While our findings extend both the geographic and elevational record of this plant CO2 response, they simultaneously highlight the ecological stability of high-elevation M. flaviventris and N. cinerea during climate changes of late Quaternary magnitude.

Yellow-bellied marmots Marmota flaviventris were live-trapped and marked in the East River Valley of Colorado from 1962 to 1998. For females, static life tables were calculated each year from 1967, when ages were well known, to 1997. Population density was determined, and from life tables calculations were made of: survivorship of young, yearlings and adults; percentage of females producing litters; mean and variance of litter size; net reproductive rate (Ro); and generation length. From climate records a set of 14 annual weather variables was developed that described temperature, precipitation and lengths of growing season and winter. Data from 1981 and 1996 were not used since weather data contained extreme outliers in date of last snow cover. Univariate correlation matrices were calculated among weather variables, among demographic variables, and between weather and demographic variables. Mean temperature in 24 of 29 years was cooler than long-term average temperature. Generation length increased during the years of the study. Weather data were used as independent variables with each dependent demographic variable to calculate nine multiple correlation and regression models. Models explained from 0% to 58% of the variation in demography. Significant factors in each model were mostly interpreted as affecting availability of energy necessary for successful hibernation and reproduction.

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