THE ANIMAL COMMUNITY 13 



rate of reproduction about equals the death rate. 

 Any individual may find itself in danger of being 

 eaten at any moment between hatching and ma- 

 turity. Fully mature individuals are as rare as 

 human centenarians; yet a species is only rarely 

 exterminated and each maintains itself at the 

 average number for which we have reason to 

 think there is sufficient food and shelter available 

 year after year. Two ideas explain the order 

 that is evolved in such communities. First, 

 there is the background of common interests and 

 of unconscious co-operation among all the elements 

 of the community, the nature of which will be 

 discussed later. Second, there is the struggle for 

 existence and the elimination usually of the less 

 fortunate but, at times, of the less fit animals. 



Such water communities as those culminating 

 in the black bass represent islets of older, lower 

 life in the midst of the higher, more recent life 

 of the surrounding region. Will the relationships 

 described from such a relatively simple commu- 

 nity hold for the more complex relations existing 

 among land animals .^^ This question will be 

 examined in the following chapters. 



The study of such communities, their inter- 

 relations with other communities as well as the 

 inter-actions between members of the same com- 

 munity and the relations of the communities or 



