Animals and their
Environment
12
The principles discussed thus far become more meaningful as they are
applied to problems in nature. The first problem considered is that of describing the fitness of the physical environment for survival of an animal
whose requirements we specify. Survival of the animal can depend on
many factors; we consider only those related to maintaining body temperature within acceptable limits and those related to maintaining proper
body water status. Even these aspects are only discussed to a limited
extent. For example, maintenance of body temperature in endotherms
(animals which maintain body temperature through internal metabolic
heat production) involves production of metabolic heat. Stored chemical
energy from the animal's food is used to produce the heat, so availability
of food in the environment could be construed as part of the animal's
physical environment. Food availability does not enter into our discussions in this way, but we do compute the amount of food an endotherm
needs in order to maintain constant body temperature. Food requirements
are of interest to those modeling ecosystems as well as those managing
range lands for wild or domestic animals.
12.1 The Energy Budget Concept
The question of whether or not an animal can maintain its body temperature within acceptable limits can be stated in another way which makes it
more amenable to analysis. It can be asked whether heat loss can be balanced by heat input and production at the required body temperature. We
are well prepared to describe heat inputs and heat losses for a system, so
the problem is easily solved, at least in principle. An equation stating that
heat inputs minus heat losses equals heat storage for a system is called
an energy budget equation. As an example of an energy budget, consider
a representative unit area of the surface of an animal that is exposed to
the atmosphere. The energy budget of this surface is the sum of the heat
inputs and losses. Thus:
Environment
12
The principles discussed thus far become more meaningful as they are
applied to problems in nature. The first problem considered is that of describing the fitness of the physical environment for survival of an animal
whose requirements we specify. Survival of the animal can depend on
many factors; we consider only those related to maintaining body temperature within acceptable limits and those related to maintaining proper
body water status. Even these aspects are only discussed to a limited
extent. For example, maintenance of body temperature in endotherms
(animals which maintain body temperature through internal metabolic
heat production) involves production of metabolic heat. Stored chemical
energy from the animal's food is used to produce the heat, so availability
of food in the environment could be construed as part of the animal's
physical environment. Food availability does not enter into our discussions in this way, but we do compute the amount of food an endotherm
needs in order to maintain constant body temperature. Food requirements
are of interest to those modeling ecosystems as well as those managing
range lands for wild or domestic animals.
12.1 The Energy Budget Concept
The question of whether or not an animal can maintain its body temperature within acceptable limits can be stated in another way which makes it
more amenable to analysis. It can be asked whether heat loss can be balanced by heat input and production at the required body temperature. We
are well prepared to describe heat inputs and heat losses for a system, so
the problem is easily solved, at least in principle. An equation stating that
heat inputs minus heat losses equals heat storage for a system is called
an energy budget equation. As an example of an energy budget, consider
a representative unit area of the surface of an animal that is exposed to
the atmosphere. The energy budget of this surface is the sum of the heat
inputs and losses. Thus: