16 ANIMAL LIFE AND SOCIAL GROWTH 



cases which show that the plant and animal 

 communities of the world form an interlocking 

 system; that the web-of-life is woven on a geo- 

 graphic as well as on a local scale; it will be more 

 interesting instead to examine the organization of 

 animal communities of the land on the basis of 

 the places in which they live. 



In human or non-human communities one of 

 the first and most striking methods of sub-division 

 into smaller units is on the basis of the dwelling 

 place, or as it is more commonly called, the habitat 

 of the community; the habitat includes all the 

 environmental factors which center about the 

 dwelling place except the competition between 

 the animals themselves. In general, animals 

 distribute themselves as though they recognize 

 three main types of habitats: the aquatic, the 

 terrestial and the parasitic. 



Land animals divide themselves fairly definitely 

 into those of the tropical rain-forest, the tropical 

 grasslands, the deserts and semi-deserts, tempera- 

 ture deciduous forests, temperature evergreen 

 forests, temperature grasslands, the arctic tundra, 

 alpine regions, and lands of eternal snow and ice. 

 These different major habitats are variously 

 subdivided; in each except the last there may be 

 swampy areas which possess a set of animals 

 decidedly different from those to be found in the 

 surrounding country. 



