388 



COMMUNITY ECOLOGY: 



shodscolesiT 

 scrub ^-E± 



chaparral ^ 



juniper 

 woodland 



creosote scrub' 



tropical savanna 



Figure 19.26 The Biomes of North America. {Generalized after various sources.) 



However, a biome is not a homogeneous unit. This 

 was imphed by saying each can include different serai 

 stages and nonclimatic climaxes. In addition, a bi- 

 ome can contain several closely related but slightly 

 different climatic climaxes. This possibility stems 

 from lack of homogeneity in a single climate type. 

 Rather, each climate possesses some gradients in the 

 various factors that distinguish it. For this reason, 

 there may be strong, gradual, or abrupt, over-all 

 gradients in the area of a single climate; and these 

 climatic variations are the basis for more than a 

 single climatic climax being present. 



The biome scheme was formulated by Clements 

 and Shelford in 1939. In the scheme plants are the 

 dominant organisms and are called dominants in the 

 sense of the present book. Animals are interpreted 

 correctly as being secondary to the dominant plants, 

 but animal importance in a community is recognized 

 as influents. Although the diagnosis of biomes is made 



on the basis of the plant formation (a group of closely 

 related climax plant communities), biomes can be 

 further subdivided into associations, consociations, 

 fasciations, and societies. However, the "association" 

 of Clements and Shelford refers to a climatic climax; 

 it is not any primary or secondary climax, as is the 

 "association" in other parts of this text. In addition, 

 overlaps (ecotones) between biomes are recognized. 



Biomes are named in more than one way. Gen- 

 erally they are named on the basis of the plant forma- 

 tion alone, but names might indicate the type of vege- 

 tation and common animals. For example, the Great 

 Plains Grassland might be called either the Grass- 

 land Biome, or the Grass-Bison-Pronghorn Biome. 



The biome scheme is applicable to the entire sur- 

 face of the earth. Because a biome is a plant forma- 

 tion (plus its animals) and many plant formations 

 exist, there are more biomes than could possibly be 

 considered in a brief outline of the subject. 



