Energy: Carbon as a Fuel and a Tissue Constituent

The energy of plants and animals is contained in carbohydrates, proteins and lipids. Energy gain and loss by animals can be considered in terms of gross, digestible, metabolizable and net energy. Energy expenditure can be measured using calorimetry with captive animals or with the doubly labeled water technique in free-living animals. Animals vary in their basal metabolic rate (BMR), maintenance requirements (up to 2 × BMR), and the additional requirements for thermoregulation, activity, reproduction and growth. Total energy expended in the field therefore varies from 2 to 7 × BMR. The potential for growth in a population during the year is related to the body condition of individuals within that population. This chapter describes various techniques available to wildlife managers to objectively evaluate body condition of animals. Body condition varies with seasonal changes in food supply and with life history of the species. The time and amount of energy and nutrients required for reproduction and growth vary with allocation of body stores or diet to parental investment, and with the number of offspring and their rate of growth.