Comparative 

 Evolution of Biomes 



Each major biome occurs over a considerable portion 

 of the earth, and the various biomes differ from each 

 other in their individual characteristics. Some, such 

 as the northern coniferous forest or taiga, have an 

 almost continuous range, whereas others such as the 

 tropical rain forest occur as widely separated frag- 

 ments. In some of the fragmented biomes the indi- 

 vidual parts may be taxonomically similar; in others 

 they may be markedly different. 



Geomorphic changes of the earth's surface have 

 continued to divide certain ecological areas and to 

 effect a congregation of others. These actions on 

 world-wide biomes have at times been on a truly 

 grand scale, both in geographic extent and in the 

 tremendous amounts of time involved in separations 

 or unions. Abundant examples from the fields of evo- 

 lutionary change and biogeography illustrate the fact 

 that, during this time, each phylogenetic line may 



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