370 THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS 



becomes too abundant in a certain area and those on the 

 outskirts venture farther and farther in search of food. 

 Often a species is driven out by enemies, change of cUmate, 

 etc. In such cases, it may pass over barriers that hereto- 

 fore seemed impassable. 



Fauna. — Briefly speaking, the fauna of a region consists 

 of all the animals naturally found in that region. For 

 example, the fauna of New York or Mississippi would be all 

 the animals found in each respective state. The faimse of 

 two adjoining states are usually very much alike, because 

 the conditions are about the same, and, usually, there are 

 no great barriers between. On the other hand, the faunae 

 of two widely separated states like New York and Missis- 

 sippi are considerably unhke. This is due largely to the 

 difference in climate. 



Faunal areas. — A faunal area is, of course, the area or 

 region occupied by a certain fauna. For example, we may 

 consider the state of Colorado with its fauna as a faunal 

 area. It has been shown above that the relation of faunal 

 areas to each other, depends first upon their proximity. 

 Secondly, it will depend upon the barriers between these 

 faunal areas. For example, the fauna of the Island of Mada- 

 gascar differs greatly from that of Africa, because of the 

 water barrier between. The fauna of Cahfornia differs 

 much from that of the states separated from it by the 

 mountains. 



In traveling from the Atlantic to the Pacific, across the 

 United States, three fairly distinct regions as regards the 

 fauna will be noticed. The moist, temperate region along 

 the Atlantic and in the Mississippi Valley, with its charac- 

 teristic animals, constitutes the first region. Then, as we 

 reach the high plateaus of the Rockies, dry and treeless, 



