Physiological, Behavioral, and Genetic Responses to the Thermal Environment 14-1 the Role of the Animal in Thermal Energy Exchange

A homeothermic animal maintains a balance between its heat production and the physical processes of heat exchange with its environment by regulating its physiology and behavior. The complexity of heat transfer is beyond comprehension, but the characteristics of heat transfer for different animals in different habitats can be determined through analytical procedures. For example, evaporation losses are more important at high temperatures when vapor-pressure deficits are high, but little research has been done on evaporative loss from wild animals. A series of thermal analyses, mostly for white-tailed deer, are presented in this chapter. It is difficult to illustrate dynamic heat exchange in two-dimensional graphs, but insight into the relative importance of different modes of heat exchange contributes to our understanding of the basic energy relationships between an animal and its environment. The heat loss described in Chapter 13 must be balanced by an animal's heat production if homeothermy is to be maintained. An animal can either increase its heat production or reduce its heat loss to maintain homeothermy. These are regulated in several ways, both behaviorally and physiologically. The predicted energy balance, using a model, is discussed in this chapter, along with responses and adaptations described by others studying homeothermy and energy exchange. Before going on to specific responses, however, let us consider the concept of a "critical thermal environment" in relation to thermal energy exchange.