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

Abstract

Yellow-bellied marmots Marmota¯aviventris 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 signi®cantly better survivorship than males beyond the ®rst-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 (R o ) was 0.67, yet the population did not continually decline; adjustments to these data increased R o to 0.85. Reproductive values (V x ) 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 in¯uence reproduction and survival, by predation, and by movement into and out of the study area.

Yellow-Bellied Marmot Population Dynamics: Demographic Mechanisms of Growth and Decline

“…The projected population growth rate () estimated from the age-structured model was 0.97 Ϯ 0.03, and agreed closely with that reported by Schwartz et al (1998). Ecology,Vol.…”

“…Age of first reproduction of a female was determined as the age at which the first litter of a female emerged from the natal burrow. Litter size was estimated from the number of pups that emerged from a natal burrow (Schwartz et al 1998). Fate and reproductive history of each female was monitored until she disappeared from the study area.…”

“…Poor condition is expressed as insufficient fat to both survive the hibernation and reproduce (Andersen et al 1976). Finally, the major causes of yellow-bellied marmot mortality are predation and failure to survive hibernation (Schwartz et al 1998, Schwartz andArmitage 2002). Low survival in 1981 was the consequence of heavy badger predation that resulted in the disappearance of at least 25 young and three adults (Armitage 2004).…”

Can individual variation in phenotypic plasticity enhance population viability?

“…Juveniles are born after about 32 days of gestation and are weaned in early July when first emerging from the natal burrow after about four weeks of lactation (Armitage, 1998). Litter sizes vary between 1 and 8, with a 1:1 sex ratio (Schwartz et al, 1998).…”

A reanalysis of apparent survival rates of Indiana myotis (Myotis sodalis)

“…Empirical estimation of overwinter survival rates is hampered by several logistical limitations including the need for long-term data sets with intensive trapping effort in spring and autumn (e.g., in ground squirrels), sample-size limitations of radiotelemetric methods, or the inherent difficulty of capturing and recapturing individuals consistently enough for demographic analysis (e.g., in bats). Therefore, estimates of overwinter survival rates are available for only a limited number of species (e.g., Meaney et al 2003;Schwartz et al 1998;Sendor and Simon 2003), and generally are only available for a single population of a species under a specific set of environmental conditions.…”