Abstract
The demographic consequences of lactational deficiency, which has been hypothesized to occur during periods of physiological stress in mammals, were assessed in Microtus montanus populations under field conditions. Comparisons are made among progeny of animals in an expanding population (= U cohort), juvenile progeny removed from high-density populations and introduced with (= M cohort) and without (= I cohort) previously crowded adults, and offspring (= F1 cohort) of voles of the I cohort. Survival rate of the I cohort was higher than the M cohort. Furthermore, males of the I cohort had a significantly higher instantaneous growth rate than the M cohort. The growth rates of females in the M and I cohorts were uniformly low. Sexual maturity was delayed in males of the M and I cohorts, though the delays were not sufficient to reduce the reproductive output. There was no significant difference in the proportions of either pregnant females or reproductive activity among cohorts. Early juvenile survival was high in the populations in which the U and I cohorts resided, whereas no juveniles survived in the M cohort's population. The observed changes in demographic parameters among the cohorts do not conform to the predictions of the lactational deficiency hypothesis. Survival and age at sexual maturity were primarily affected by seasonality, whereas individual growth, early juvenile survival, and population growth were primarily affected by adult-progeny social interactions.
Published Version
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