130 Temperature 



— 2.5°C. The maximum temperature in marine environments of any 

 size is probably represented by records of 36°C in the Persian Gulf. 

 In tide pools of the littoral zone and in shallow bodies of fresh water 

 temperatures may go higher. 



On land the record for the lowest temperature is held by a locality 

 in the north interior of Siberia where the thermometer was read at 

 — 70°C (— 93.6°F) in 1947. Temperatures almost as low were re- 

 ported for a northern outpost in the Yukon territory. At the other 

 end of the scale air temperatures ranging above 60°C (140°F) are 

 recorded in desert areas. Desert soils have been found to rise as high 

 as 84°C when exposed to the noonday sun. The water in hot springs 

 and geysers may approach 100°C, and even higher temperatures occur 

 sporadically in the very special situations presented by volcanic areas. 



Are these environmental temperatures beyond the ranges that can 

 be tolerated by animals and plants? Birds and mammals are warm- 

 blooded animals, or homoiotlierms, that maintain their own constant 

 internal temperature, and their tissues are insulated from the heat or 

 cold of the outside world. All other animals are cold-blooded forms 

 or poikilotherms. The tissues of these animals and of all plants, which 

 are also poikilothermous, tend to approach the temperature of their 

 immediate surroundings and to vary with external thermal conditions. 

 No organism can continue to live in an active condition at tempera- 

 tures below those at which its tissues freeze. As we shall see below, 

 the freezing points of living tissues differ widely, but no poikilother- 

 mous animal or plant can actually grow at continuing temperatures 

 lower than a few degrees below 0°C. At the other end of the thermal 

 scale we find certain blue-green algae and thermophilous bacteria 

 growing happily in hot springs, such as those in Yellowstone Park, at 

 80 to 88°C! However, relatively few poikilotherms can live perma- 

 nently at temperatures above about 45°C, and Brues (1927, 1939) 

 found no reliable records for poikilothermous animals above 52°C. 



It appears from the foregoing that the whole range of temperature 

 in the sea is within the limits of tolerance of many plants and animals. 

 In contrast, land temperatures may be far below or far above the 

 temperatures that can be withstood by organisms in an active condi- 

 tion. Since the range of heat conditions sustained successfully by in- 

 dividual species is very much less, temperature extremes present a 

 problem on both land and sea. The homoiothermous animals form a 

 special case since the thermal range that they can tolerate is generally 

 much greater than that of other animals and of plants, but even this 

 group has definite limits of toleration. We shall be concerned, then, 

 with the limiting action of extreme temperatures, as well as with the 



