650 



COLLEGE ZOOLOGY 



ence from other animals, or by their own 

 physiologic makeup. Common barriers are 

 mountains, bodies of fresh or salt water, 

 open country for forest animals, and forests 

 for prairie-inhabiting species. The reverse of 

 a barrier is a highway. Apparently there are 

 routes of migration which are especially 

 favored. 



LIFE REALMS 



Life realms are natural regions of the 

 earth, distinguished by certain characteris- 

 tics such as temperature, and often have no 

 relation to political boundaries. Wallace's 

 classification of the earth into 6 large regions 

 and each of these into 4 subregions (life 



Figure 455. Zoogeographical regions of the world. Life realms are divided into zoological 

 regions and subregions. The subregions are designated by numbers for the Nearctic Realm only. 



zones), as shown in Fig. 455, is the best 

 known. It is based on the distribution of 

 mammals. For example, most of North 

 America lies within the Nearctic Realm. 

 This realm is divided into 4 subregions: (1) 

 Californian, (2) Rocky Mountain, (3) Al- 

 leghenian, and (4) Canadian. The Nearctic 

 Realm is characterized by the presence of 

 certain groups of mammals and each subre- 

 gion by distinctive species or genera belong- 

 ing to these groups. The members of each 

 large group of animals such as mammals, 



birds, and mollusks are adapted to their own 

 peculiar conditions, hence life realms and 

 life zones must be determined for each 

 group, and the precise delimitation of re- 

 gions for several groups together is prac- 

 tically impossible. 



SELECTED COLLATERAL 

 READINGS 



Alice, W.C., Cooperation Among Animals. 

 Henry Schuman, New York, 1951. 



