CHAPTER 5 



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THE ANIMAL AND ITS ENVIRONMENT 



So far we have considered the origin of 

 animal life in a physical world, centering 

 our attention on the animal itself rather 

 than the environment in which it thrives. 

 Since the animal is an integral part of its 

 environment, it is necessary to devote some 

 attention to this relationship, which is the 

 study of ecology. Our particular emphasis 

 will be on animal ecology, although no 

 ecological study can entirely ignore the 

 role played by the plants. 



Great variations in the environments of 

 the world are caused by such physical 



factors as light, temperature, and moisture, 

 all of which have a profound effect upon 

 the physical and physiological character- 

 istics of animals. These physical factors not 

 only determine the kinds of animals that 

 are able to survive in certain regions but 

 are also instrumental in building up associa- 

 tions between animals and plants. Thus 

 the problem in ecology is twofold: first, to 

 consider the individual animal in terms of 

 certain physical factors in its environment; 

 second, to study the relationship between 

 animals living together. 



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