Mountain Wildlife - Mountain Geography: Physical and Human Dimensions - page 441

The decrease in oxygen with altitude is more or less constant, so all mountain animals
are subjected to oxygen-deficient conditions. Surprisingly little research has been done
concerning the effects of lack of oxygen on naturally high-altitude animals; some of the
earliest work was carried out in the mid-1930s (Hall et al. 1936; Kalabukov 1937).
The response of most lowland wild animals to altitude is basically similar to that ob-
served in humans (Chiodi 1964; Timiras 1964; Hock 1964c, 1970). Curiously, however,
some of the animals best adapted to high altitudes—for example, rodents, the Camelid-
ae (llama, alpaca, vicuña, guanaco), and the yak, sheep, and goats—do not display these
characteristics. The physiological characteristics of these high-altitude animals are of-
ten the opposite of those observed in sea-level animals exposed to high altitudes. The
primary contrast is that they do not show an increase in red blood cells or hemoglobin
(Hall et al. 1936; Morrison et al. 1963a, 1963b). They tend to have a larger blood-plasma
volume, but there is less oxygen in their blood and they are able to function at a very
low partial pressure of oxygen (Morrison and Eisner 1962; Bullard 1972). They do have
larger hearts and lung volumes as well as higher heart and breathing rates, just like an-
imals transported to high altitudes, but there is no increase in the number of red blood
cells or quantity of hemoglobin. Since this is one of the most conspicuous responses by
lowland species taken to high elevations, its absence in native highland animals is strik-
ing. Although the increase in the production of red blood cells and hemoglobin appears
to be the simplest means of improving oxygen transport, it must also present some dis-
advantage: perhaps that of the increased viscosity of cell-rich blood (Morrison 1964).
FIGURE 8.19 Body temperature of free-living lizard ( Liolaemus multiformis ) at an altitude of 4,300 m
(14,200 ft) in the Peruvian Andes. This lizard is able to achieve and maintain a higher temperature
(dashed line) than that of the surrounding air (solid line) by its behavior, for example, by basking
or seeking shelter according to the weather conditions. (After Pearson and Bradford 1976: 157)