14 ECOLOGICAL FOUNDATIONS OF ZOOGEOGRAPHY 



to suspend their activities at certain seasons on account of low tem- 

 peratures. 



The upper limit of temperature is approached and sometimes ex- 

 ceeded in hot springs. For Protozoa it is about 50°C. (54.4° is the 

 highest reported by Brues), 9 for Metazoa about 45°. The temperatures 

 tolerated by desert insects and desert lizards correspond closely to 

 those endured by the animals of hot springs. 10 - u 



For individual species, the temperature range is for the most part 

 rather narrow. The range varies for different species, but is fairly con- 

 stant for a given form. The three cardinal temperatures are the 

 maximum, minimum, and optimum; the optimum temperature usually 

 lies nearer the maximum than the minimum limiting temperature. 

 The optimum may be widely different for different animals; it lies 

 between 1° and 4°C. (maximum 12-15°C.) for the eggs of trout; 

 between 14° and 20° for the eggs of carp; about 22° for frog's eggs 

 (maximum 30°, minimum nearly 0°C.) ; and at 38-39° for the fowl's 

 eggs. When the temperature range for a species is wide, the animal is 

 said to be eury thermal; when narrow, it is stenothermal. Stenothermal 

 animals in turn may be cold- or heat-tolerant. Examples of eury- 

 thermal animals are the flatworm, Planaria gonocephala (limits -j-0.5° 

 and 24°); the oyster (—2° to 20°); the snail, Limnaea truncatula, 

 which in Germany is found principally in cold springs, lives in warm 

 springs at 40° in the Pyrenees; the sperm whale, Physeter, lives in all 

 oceans; and the large predatory cats such as the puma, ranging from 

 Canada to Patagonia, or the tiger, which is equally at home in the 

 tropical jungles of India, the mountains of Central Asia up to 4000 

 meters, and northward to Irkutsk at 53° N. latitude. Stenothermal 

 warmth-tolerant animals are represented by the reef corals, which 

 flourish only at temperatures above 20°; the crustacean, Copilia 

 mirabilis (between 23° and 29°) ; the salpids, the termites, the carp 

 (which require at least 18° to breed) ; and most reptiles. Cold- 

 tolerant stenothermal forms are represented by a cave silphid beetle 

 which lives in ice grottoes where the annual temperature ranges from 

 — 1.7° to +1-0°C; 12 the pearl mussel, Margaritana niargaritifera; 

 the crustacean, Calanus finmarchicus ; trout and whitefish; and many 

 others. 



Increase of temperature to a certain point reacts favorably on the 

 life of an animal because the chemical reactions on which the release 

 of energy depends are accelerated by the rise in temperature. 13 This 

 is especially striking in the developmental stages. The rate of develop- 

 ment of the eggs of the sea urchins, Sphaer echinus and Echinus, is 

 increased 2.5 times for every rise of 10° between 2.5° and 25°. 14 The 



