Animals and their Environment
example just given, the equivalent temperature would be uncomfortably
hot (well above body temperature) even though the air temperature is not
uncomfortably high.
If windspeed in this example were increased to 3 mls, Te would decrease to 43" C. If white clothing with a, = 0.3 were worn, Te would be
36" C at u = 1 mls.
12.7 Applications of the Energy Budget
Equation
We return briefly to the animal energy budget equation (Eq. (12.1 1))
to consider some applications. The metabolic rate, latent heat loss, body
temperature, and body conductance are primarily physiological, and have
upper and lower bounds set by the physiological makeup of the animal.
By determining the limits of these variables, the extremes of environment
(T,) can be predicted that can be tolerated by the animal. The combination of minimum body temperature, maximum sustainable metabolic rate,
minimum conductance, and minimum latent heat loss defines the lower
lethal limit for the animal. The combination of maximum allowable body
temperature, minimum metabolic rate, maximum conductance, and maximum latent heat loss defines the upper lethal limit. The animal cannot
survive extended periods of time in environments below its lower lethal
limit or above its upper lethal limit. These limits define a kind of climate
space in which the animal can reside. The climate space is a function of
both air temperature and absorbed radiation.
In addition to being useful for predicting animal behavior, the energy
budget equations can be used to predict the food energy required to maintain a favorable body temperature. If the operative temperature of the
environment is specified, and the body temperature and conductance are
known, the energy budget equation can be used to compute the metabolic
rate needed to balance the energy budget. This is just the metabolic requirement for thermoregulation, but other energy sinks are usually small
compared to the requirement for thermoregulation.
Example 12.3. How much food is required for thermoregulation by a
1.5 kg rabbit in an environment with T, = O°C? Assume d = 0.1 m and
u = 1 d s .
Solution. Since T, is given, there is no need to consider the radiative
environment of the rabbit, but when considering both day and night conditions in a typical rabbit environment T, and T, are likely to be about
the same. Equation (12.11) can be used to find M. We need to know the
body temperature, the heat and vapor conductances, and the latent heat
loss. We assume body temperature is 37" C, and that the combined respiratory and skin latent heat loss is 20 percent of the metabolic rate. There
are three conductances for heat loss, the convective-radiative gHr7 the
coat g ~ ~ ,
and the tissue gHr. The convective-radiative conductance is the
example just given, the equivalent temperature would be uncomfortably
hot (well above body temperature) even though the air temperature is not
uncomfortably high.
If windspeed in this example were increased to 3 mls, Te would decrease to 43" C. If white clothing with a, = 0.3 were worn, Te would be
36" C at u = 1 mls.
12.7 Applications of the Energy Budget
Equation
We return briefly to the animal energy budget equation (Eq. (12.1 1))
to consider some applications. The metabolic rate, latent heat loss, body
temperature, and body conductance are primarily physiological, and have
upper and lower bounds set by the physiological makeup of the animal.
By determining the limits of these variables, the extremes of environment
(T,) can be predicted that can be tolerated by the animal. The combination of minimum body temperature, maximum sustainable metabolic rate,
minimum conductance, and minimum latent heat loss defines the lower
lethal limit for the animal. The combination of maximum allowable body
temperature, minimum metabolic rate, maximum conductance, and maximum latent heat loss defines the upper lethal limit. The animal cannot
survive extended periods of time in environments below its lower lethal
limit or above its upper lethal limit. These limits define a kind of climate
space in which the animal can reside. The climate space is a function of
both air temperature and absorbed radiation.
In addition to being useful for predicting animal behavior, the energy
budget equations can be used to predict the food energy required to maintain a favorable body temperature. If the operative temperature of the
environment is specified, and the body temperature and conductance are
known, the energy budget equation can be used to compute the metabolic
rate needed to balance the energy budget. This is just the metabolic requirement for thermoregulation, but other energy sinks are usually small
compared to the requirement for thermoregulation.
Example 12.3. How much food is required for thermoregulation by a
1.5 kg rabbit in an environment with T, = O°C? Assume d = 0.1 m and
u = 1 d s .
Solution. Since T, is given, there is no need to consider the radiative
environment of the rabbit, but when considering both day and night conditions in a typical rabbit environment T, and T, are likely to be about
the same. Equation (12.11) can be used to find M. We need to know the
body temperature, the heat and vapor conductances, and the latent heat
loss. We assume body temperature is 37" C, and that the combined respiratory and skin latent heat loss is 20 percent of the metabolic rate. There
are three conductances for heat loss, the convective-radiative gHr7 the
coat g ~ ~ ,
and the tissue gHr. The convective-radiative conductance is the