Mountain Wildlife - Mountain Geography: Physical and Human Dimensions - page 403

Temperature operates in several ways to limit life. The first and most obvious is
where it exceeds the tolerance limits of organisms. All species have an upper and lower
threshold of temperature that they can withstand and, within this range, an optimum or
preferred level. The same can be said of any environmental factor, and animals with dif-
ferent potentials, tolerances, and abilities seek out, as near as possible, their own pre-
ferred range. This is one of the basic reasons for the distributions of species on Earth.
All life exists within the fairly narrow temperature range of 0° to 50°C (32°−122°F).
Temperatures on Earth far exceed these limits, but most organisms escape the extremes
by one means or another. The absolute low-temperature limit is reached when body flu-
ids begin to freeze, usually within a few degrees below the freezing point of pure wa-
ter. The upper limit is reached when body fluids begin to undergo destructive chemic-
al change. The two effects are not equal, however. There is much greater flexibility at
the lower end of the spectrum than at the higher: High temperatures usually result in
irreversible damage and death, but cells can freeze in some animals without irrevers-
ible damage, and activity may be resumed when temperatures rise (Hesse et al. 1951).
The length of exposure and extremity of the temperature are important, of course, but
a number of creatures, especially insects, do survive winters of subfreezing temperat-
ures. During Sir John Ross's second voyage to the Canadian Arctic in 1829 to 1833, the
larvae of butterflies were found frozen to the point of brittleness. Specimens were taken
inside and allowed to thaw. The larvae became active within two hours. They were then
taken back outside into the −40°C (−40°F) weather and allowed to refreeze. The pro-
cess was repeated three times and, although there was considerable mortality, some of
the larvae still pupated in the spring (Downes 1964).