28 ANIMAL LIFE AND SOCIAL GROWTH 



spite exceptions, there is much truth in the belief. 

 In Wisconsin lakes, for example, the size attained 

 by yellow perch appears to be directly related 

 to the size of the body of water in which they live. 

 Similarly with larger mammals, those on small 

 islands, are smaller when fully grown than are their 

 relatives on the nearby mainland where their ranges 

 are less restricted. In many cases the dwarfing 

 in the smaller ranges is definitely related to the 

 decreased amount of food available but other 

 factors such as the accumulations of wastes, are 

 certainly effective. There is evidence that active 

 animals limited to a narrow habitat may be so 

 stimulated by repeated contacts with the habitat 

 margin or with other animals enclosed in the same 

 narrow island space that dwarfing results from 

 such over-stimulation. 



In summary of this section it may be stated 

 that a habitat niche is a special habitat in which a 

 given animal lives; or, more generally stated, 

 it is an area, large or small, in which the principal 

 relations of the habitat conditions and the living 

 forms related to them, are uniform. Groups of 

 similar niches may be united into a more general 

 habitat; in the excessively dry regions, rock desert, 

 sandy desert, gravelly desert, alkali desert and 

 arid regions with fertile soil, all are thought of as 

 forming the more generalized habitat we call a 



