Ecological strategies of small mammals in seasonal environments

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We study the life histories of deer mice and voles in short-summer environments in southwestern Alberta where age at maturation is often delayed to one year of age, survival of nestlings is variable, and survival of adults is  high. These populations are vulnerable to disturbance because turn-over rates and recovery from declines are slow. Recent food supplementation studies showed  nutritional constraints on nestling growth and maturation as well as seasonal breeding, but had no effect on nestling or adult survival. Our recent studies of mice in individual enclosures and in the wild showed similarities in energetics and activity, but nest mortality in individual enclosures was much lower than in the wild, suggesting that predation or infanticide may be most important to nest mortality. We will initiate  new studies to investigate nest predation (weasels) and infanticide, as well as the effects of parasites on growth and maturation. Finally, responses to extra food vary with the availability of natural foods. We will use stable isotopes of carbon and nitrogen to determine if they can provide useful information about changes in natural diets within populations.  The potential is  there because  deer mice are omnivorous and 15N/14N ratios vary among trophic levels (See Kelly, 2000.Can. J. Zool.78: 1-27 for a review). Our first  use of stable isotopes  yielded more questions than answers (See R1, R3) because they may be influenced by differential absorption of isotopes, stress, and rates of metabolism over and above trophic feeding levels. Ground-truthing  under controlled conditions is needed before we can  interpret  data from field samples, so we will determine the turn-over rates of isotopes, examine the differential absorption of isotopes,  examine stable isotopes in relation to rates of metabolism and  levels of stress,  examine nitrogen isotope fractionation among isocaloric but variable protein diets, and  examine isotope fractionation between diet, mothers, and dependent offspring, all in the laboratory,  before examining  field samples for seasonal, habitat, and population differences.