494 



LAND ANIMALS 



be blown away into snow or ice fields. Alpine insects habitually con- 

 ceal themselves when the winds blow and fly only when the air is 

 quiet. 



Zonation. — The regular reduction in temperature and pressure 

 with altitude, and the inverse variation in humidity, produce a zona- 

 tion of the total environment, primarily for vegetation, and secondarily, 

 in partial dependence on the vegetation, for the animal life. These 

 zones compare with the climatic zones which surround the poles, but 

 their much closer approximation in the mountains makes them more 

 immediately evident. In a single day one may climb from the lowland 

 hardwoods and conifers to the alpine and the snow zone. A regular 

 arrangement of the animal life corresponds to these climatic and vege- 



Fig. 129. — Zonal distribution of the chipmunk Eutamias, shown in a cross sec- 

 tion through the Sierra Nevada and White Mountains in California. After 

 Merriam. 



tational zones. Thus the successive zones in adjacent mountain ranges 

 may have similar faunae, as is beautifully shown by the chipmunks 

 of the Sierra Nevada and White Mountains of California (Fig. 129) . 20 

 The life zones of mountains correspond closely to the larger climatic 

 zones of the earth's surface. The changes in the land snail fauna ob- 

 servable between central Europe and Spitzbergen correspond closely to 

 those observable in the Alps from their base to the zone of permanent 

 snow. 21 In the ascent to the Abyssinian highland, the insects are es- 

 sentially Saharan up to 800 m.; between 800 and 2000 m. they are 

 Senegambian ; from 2000 to 2800 m. they are Mediterranean, and above 

 this European or even subalpine. In the Chilean Andes two small 

 species of butterflies (Argynnis modesta and A. euterpe) range to 

 lower and lower altitudes to the southward, until they are found at 

 sea level at the Straits of Magellan. 22 The most complete interrelations 

 between the circumpolar and mountain zones are to be seen in North 

 America, with its north-south mountain ranges, and animal distribu- 



