Mountain Wildlife - Mountain Geography: Physical and Human Dimensions - page 439

so well insulated that it does not have to increase its metabolism until a temperature of −40°C
(−40°F) is reached. (After Scholander et al. 1950: 254.)
DARKER COLORATION A well-known characteristic of cold-blooded animals and inverteb-
rates in mountains is a tendency toward darker coloration. Thus, salamanders, frogs,
lizards, and snakes are almost universally dark colored in mountains (Hesse et al. 1951;
Swan 1952; Pearson 1954; Swan and Leviton 1962; Haefeli 1968). Arthropods have
similar characteristics. Species that are light-colored below timberline become darker
above timberline; beetles that are pale brown, green, or metallic blue at lower eleva-
tions become dark brown or black at higher elevations; butterflies also display darker
coloration with attitude (Walshingham 1885; Downes 1964). In addition, body markings,
such as spots and stripes, tend to enlarge and coalesce at higher altitudes. For example,
the spots on ladybird beetles become larger, darker, and coalescent above timberline in
the Himalaya (Mani 1962).
The tendency toward darker coloration among cold-blooded animals at higher eleva-
tions apparently contributes to heat absorption and helps to protect against the greater
ultraviolet radiation. Body temperatures of cold-blooded animals basking in the sun may
exceed that of the surrounding air by 20°−30°C (36°−54°F). The temperature of the
Andean lizard Liolaemus multiformis was measured by radiotelemetry. Over a three-day
period, its internal temperature cycled between 3°C and 34°C (37.4°−93.2°F), while
temperatures in the shade ranged from −2°C to 15°C (28.4°−59°F) (Fig. 8.19; Pear-
son and Bradford 1976: 155). An equally great thermal capacity is presumed for dark-
colored invertebrates at high altitudes (Mani 1962).
COLD-HARDINESS It may seem redundant at this point to say that organisms living in cold
climates must have the ability to survive low temperatures, but cold-hardiness is itself
a major adaptation, especially in cold-blooded animals and invertebrates, which have
no way to maintain their internal temperature. Despite the efforts of reptiles, amphi-
bians, fish, and invertebrates to escape extreme cold through the use of microhabitats
and timing of activities, there are inevitably times when these organisms are subjected
to subfreezing temperatures. Consequently, they must have the ability to withstand at
least partial freezing. The frog Rana temporaria lives at higher altitudes than any other
in the Alps (2,600 m, 8,580 ft), and can withstand freezing as long as its heart is not
frozen (Hesse et al. 1951). Fish in shallow lakes that freeze to the bottom may be en-
cased in ice with no apparent damage, owing to plasma-protein concentrations that act
as antifreeze, protecting their cells from disruption (Hargens 1972). Lizards and snakes
are less well adapted to freezing and, for this reason, are less common in middle- and
high-latitude mountains.
Arthropods have the ability to supercool and retard ice nucleation, in some cases
down to −40°C (−40°F). A few insects can withstand being frozen solid, mainly in the
intermediate stages (i.e., eggs, larvae, or pupae), but the major adaptation to subfreez-
ing temperatures in insects is supercooling, achieved through the presence of glycerol,
a natural antifreeze ingredient (Smith 1958; Salt 1961, 1969). Resistance to freezing is
also related to moisture content and atmospheric pressure: The less body fluid an in-
sect has and the lower the air pressure, the more supercooling the insect displays (Salt
1956; Crawford and Riddle 1974).