CHAPTER IV 

 HABITATS 



WE have seen in the last chapter that the habitat 

 of every animal can be divided for convenience 

 into three parts : the animal community, the vegeta- 

 tion, and the physical factors. It is sometimes said 

 that animal ecology is only the study of the physi- 

 ology of whole organisms instead of the physiology 

 of particular organs or organ systems. But it can 

 easily be seen that this is a very limited view to take 

 of the subject, since such physiological studies, 

 although of great importance, cover only part of the 

 environmental complex that determines the con- 

 ditions in which an animal can live and breed. 

 Ecology covers such a wide field, and experimental 

 work is usually so difficult and costly and takes 

 so many years to complete, that it is not surpris- 

 ing to find that a large specialized section of 

 ecological research has grown up, which deals only 

 with the effects of physical factors upon animals. 

 It is clear that in applying such data to the ex- 

 planation of animal distribution and numbers in the 

 field, the vegetation and the mode of organization 

 of animal communities must also be taken into 

 account. We have dealt briefly with animal inter- 

 relations, and something has now to be said about 

 vegetation. 



In surveying the possible habitats available for 

 animals, we are struck by the dominant influence of 

 vegetation in creating large and comparatively uni- 



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