Origin of Biomes 



and Succession 



The relatively simple community considered in the 

 preceding chapter to explain the evolution of basic 

 community relationships is only a small unit in com- 

 parison with the many diverse communities of the 

 biotic world. The transition from one to many com- 

 munities appears to have occurred chiefly by the 

 processes of alternate community division and re- 

 union, brought about by geologic and climatic 

 change (together comprising geomorphic change) 

 and accompanied by simultaneous species fission. 



The normal action of geomorphic change would 

 produce such results. If a new arm of the sea, a 

 drastic change in climate, or some similar happening 

 divides a uniform ecological area, it will split the 

 range of the whole community and all the species 

 restricted to it. Each such division therefore sets the 

 stage for the formation of new daughter commu- 

 nities diff^ering in that they have many, perhaps hun- 



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