370 THE GEOGRAl'HICAL 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 climate, 

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

 fore seemetl impassable. 



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

 of all the animals naturally found in that region. For 

 exam])le, the fauna of New Yoi'k or Mississij^pi would be all 

 the animals found in each resijective state. The faunae 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 faunie 

 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 I)y a certain fauna. For example, we may 

 consider the state of Colorado with its fauna as a faunal 

 area. It has been sh(i\\n above that the relation of faunal 

 areas to each other depends hi'st u]ion their ])roximity. 

 Secondly, it will depend upon the baniers Ijctween these 

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

 gascar differs greatly from that of Africa, because of the 

 water l^arrier between. The fauna of California < lifters 

 much fi-om that of the states separated from it b}' the 

 mountains. 



In traveling from the Atlantic to the Pacific, across the 

 United States, thice fairly distinct regions as regai'ds the 

 fauna will lie noticed. The moist, tempei'ate region along 

 the Atlantic and in the Mississippi ^'alley, with its charac- 

 teristic animals, constitutes the lii'st region. Then, as we 

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



