6 ANIMAL LIFE IN TEE YOSEMITE 



We may express the facts in another way. The large number of kinds 

 of animals present in the entire Yosemite section is due to the great range 

 of physical conditions (temperature, moisture, soil, light, and perhaps 

 others) with the accompanying diversity of vegetational features. Man 

 is able to traverse the whole gamut of these conditions, even with benefit 

 to himself by reason of the stimulus change produces, adjusting his mode 

 of dress and behavior to them and carrying his food with him. But animals 

 and plants are more or less directly in contact with the conditions around 

 them ; they are, as a rule, far less adaptable ; and they are vitally affected 

 by differences in temperature, in moisture, in food supply, and so on. The 

 interesting thin^ is that in many species the degree of sensitiveness is so 

 great that they can maintain existence only \vithin a relatively narrow 

 range of the critical conditions. 



Such underlying reasons as those just suggested help to explain what 

 impresses the traveler in ascending the west slope of the Sierras, namely, 

 the correlation, roughly, with respect both to animals and plants, of 

 zonation with altitude and, therefore, temperature. And it is because of 

 this inter-correlation that the student is led to the conclusion that it is the 

 factor of temperature which has most to do with the causation of life zones. 



Reference to our map and cross-section diagram (pis. 61, 62) will show 

 the application, to the Yosemite section, of the system of recognizing these 

 belts of animal and plant life as some naturalists have worked them out 

 and named them. Each life zone is a belt of relatively uniform constitution 

 with respect to species. At the same time, we must emphasize that there 

 is rarely an abrupt line of demarcation between any two adjoining zones. 

 There is, as a rule, along the meeting ground more or less mixing or over- 

 lapping of the specific elements. Tliis is especially true where the slope 

 is very gentle, broad, and all facing in one direction. The steeper the 

 slope, or the more abrupt the change of exposure (say from west to north), 

 the sharper will be the boundary between the two adjacent zones. 



To enter here into a further discussion of the life-zone concept is 

 not necessary. We will simply refer the inquiring reader to some of the 

 literature relating to the subject^ and confine the present treatise to the 



iC. Hart Merriam, Life Zones and Crop Zones of the United States (U. S. Dept. 

 Agric, Div. Biol. Surv., Bull. no. 10, 1898), 79 pp., 1 colored map. C. Hart Morriam, 

 Eesults of a Biological Survey of Mount Shasta, California (U. S. Dopt. Agric, Div. 

 Biol. Surv., N. Am. Fauna, no. 16, 1899), 179 pp., 5 pis., 46 figs, in text. H. M. Hall, 

 A Botanical Survey of San Jacinto Mountain (TTniv. Calif. Puhl. Bot., vol. 1, 1902), 

 l)p. 1-140, pis. 1-14. J. Grinnell, An Account of the Mammals and Birds of the Lower 

 Colorado Valley, with Especial Reference to the Distributional Probleius Presented 

 (Univ. Calif. Publ. Zool., vol. 12, 1914), pp. .'51-294, pis. 3-13, 9 figs, in text. J. Grinnell, 

 A Distributional List of the Birds of California (T'ac. Coast Avifauna, no. 11, 1915), 

 217 pp., 3 maps. H. M. Hall and J. Grinnell, T^ife Zone Indicators in California (Proc. 

 Calif. Acad. Sci., ser. 4, vol. 9, 1919), pp. 37-67. 



