Animals and their Environment
small that effects of g,, and g,, are negligible by comparison, as shown
in Ch. 7. Table 7.2 gives some animal skin conductances. Table 12.1
gives a more extensive listing. Note that species living in arid environments tend to have the lowest vapor conductances. Little is known about
the variability of these numbers or their dependence on environmental
moisture or temperature. Much additional research is needed in this area.
Accurate estimates of skin-diffusive conductance are important, both for
accurate energy budget predictions and for water budgets of animals. The
importance of skin water loss is illustrated by the fact that it accounts
for 75 percent or more of the total water loss even for the desert tortoise
(Schmidt-Nielsen, 1969).
To illustrate the magnitude of hE,, we find the rate of skin water loss
for a camel under circumstances similar to those for which hEr was found.
If skin temperature is 36"C, then e, = 5.9 H a . Assuming e, = 1 kPa,
and using the skin conductance for camel from Table 12.1 gives
J
mol
5.9 kPa - 1 kPa
hE, = 44000 - x 0.0032 - x
W
= 6.9 - .
mol
m 2 s
101 kPa
m 2
The effect of coat and boundary layer conductance have been ignored,
but their effect is small when the skin conductance is so low. If we assume
hEr = 0.1M and M = 50 w/m2, then hE, = 5 w/m2. The skin latent
heat loss is larger than this value and, in fact, makes up about 58 percent
of the total. The total latent heat loss is around 20 percent of M. These
percentages are probably fairly typical for resting endotherms that are not
heat-stressed. For poikilotherms under similar conditions one typically
assumes M = h E.
As the animal becomes heat-stressed, latent heat loss increases, generally by some active process such as sweating or panting. There is no
general approach to the calculation of latent heat loss under these conditions since animal responses are so varied. The approach would need
to be fitted to the particular species being studied. In Ch. 13 we look at
TABLE 12.1. Skin conductance to vapor for non-heat stressed
animals
Mammals
white rat
human
camel
white footed mouse
spiney mouse
Reptiles
caiman
water snake
pond turtle
box turtle
iguana
mmol mP2 s-I
10.6
5.4
3.2
3.0
2.8
Reptiles (cont.) mmol m-2 s-'
gopher snake
1.0
chuckawalla
0.34
desert tortoise
0.34
Birds
sparrow
5.4
budgerigar
4.9
zebra finch
4.1
village weaver
3.3
poor-will
3.1
roadrunner
2.4
painted quail
2.1
small that effects of g,, and g,, are negligible by comparison, as shown
in Ch. 7. Table 7.2 gives some animal skin conductances. Table 12.1
gives a more extensive listing. Note that species living in arid environments tend to have the lowest vapor conductances. Little is known about
the variability of these numbers or their dependence on environmental
moisture or temperature. Much additional research is needed in this area.
Accurate estimates of skin-diffusive conductance are important, both for
accurate energy budget predictions and for water budgets of animals. The
importance of skin water loss is illustrated by the fact that it accounts
for 75 percent or more of the total water loss even for the desert tortoise
(Schmidt-Nielsen, 1969).
To illustrate the magnitude of hE,, we find the rate of skin water loss
for a camel under circumstances similar to those for which hEr was found.
If skin temperature is 36"C, then e, = 5.9 H a . Assuming e, = 1 kPa,
and using the skin conductance for camel from Table 12.1 gives
J
mol
5.9 kPa - 1 kPa
hE, = 44000 - x 0.0032 - x
W
= 6.9 - .
mol
m 2 s
101 kPa
m 2
The effect of coat and boundary layer conductance have been ignored,
but their effect is small when the skin conductance is so low. If we assume
hEr = 0.1M and M = 50 w/m2, then hE, = 5 w/m2. The skin latent
heat loss is larger than this value and, in fact, makes up about 58 percent
of the total. The total latent heat loss is around 20 percent of M. These
percentages are probably fairly typical for resting endotherms that are not
heat-stressed. For poikilotherms under similar conditions one typically
assumes M = h E.
As the animal becomes heat-stressed, latent heat loss increases, generally by some active process such as sweating or panting. There is no
general approach to the calculation of latent heat loss under these conditions since animal responses are so varied. The approach would need
to be fitted to the particular species being studied. In Ch. 13 we look at
TABLE 12.1. Skin conductance to vapor for non-heat stressed
animals
Mammals
white rat
human
camel
white footed mouse
spiney mouse
Reptiles
caiman
water snake
pond turtle
box turtle
iguana
mmol mP2 s-I
10.6
5.4
3.2
3.0
2.8
Reptiles (cont.) mmol m-2 s-'
gopher snake
1.0
chuckawalla
0.34
desert tortoise
0.34
Birds
sparrow
5.4
budgerigar
4.9
zebra finch
4.1
village weaver
3.3
poor-will
3.1
roadrunner
2.4
painted quail
2.1