Ecological strategies of small mammals in seasonal environments

我们在艾伯塔省西南部的短夏环境中研究了鹿鼠和田鼠的生活史，在那里，成熟年龄往往推迟到一岁，雏鸟的存活率可变，成体的存活率也很高。这些人口很容易受到干扰，因为周转率和从下降中恢复的速度很慢。最近的食物补充研究表明，营养限制了雏鸟的生长和成熟以及季节性繁殖，但对雏鸟或成鸟的存活没有影响。我们最近对单独围栏中的小鼠和在野外的小鼠进行的研究显示，它们在能量和活动方面相似，但单独围栏中的巢死亡率比野外低得多，这表明捕食或杀婴可能是巢死亡率最重要的因素。我们将启动新的研究，以调查巢穴捕食(黄鼠狼)和杀婴，以及寄生虫对生长和成熟的影响。最后，对额外食物的反应随天然食物的可获得性而不同。我们将使用碳和氮的稳定同位素来确定它们是否能提供有关种群内自然饮食变化的有用信息。但潜力是巨大的，因为鹿鼠是杂食性动物，15N/14N比率因营养水平而异(见Kelly，2000。Can)。J.Zool.78：1-27用于评论)。我们第一次使用稳定同位素产生了比答案更多的问题(见R1，R3)，因为它们可能受到同位素的不同吸收、压力和高于营养摄食水平的新陈代谢速度的影响。在我们能够解释来自野外样本的数据之前，需要在受控条件下进行地面实况调查，因此，我们将确定同位素的周转率，检查同位素的差异吸收，检查稳定同位素与代谢率和压力水平的关系，检查等卡路里但可变的蛋白质饮食中的氮同位素分馏，以及检查饮食、母亲和依赖的后代之间的同位素分馏，所有这些都在实验室进行，然后再检查田野样本的季节性、栖息地和种群差异。

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.