400 Relations between Species 



than its own growth, the first species will cause the elimination of 

 the second from the area. (2) If the two species have somewhat 

 different demands on the environment so that they inhabit different 

 niches, the two species may continue to coexist in the area. (3) If 

 the two species are dependent one upon the other, as parasite and 

 host or predator and prey, the aggressor may eliminate the other 

 species and then turn to other types of food. (4) If the attacking 

 species is unable to destroy all the other species and is able to survive 

 periods of low abundance of the other species, the two species may 

 continue to live in the area in either a steady or a fluctuating equi- 

 librium. For a further discussion of these intricate relations of com- 

 petition the reader may consult Hutchinson and Deevey (1939), 

 Solomon (1949), or Allee et al. (1949, Ch. 22). 



The survey of interrelations that has been presented in this chapter 

 has revealed the extraordinarily varied and complex nature of the 

 dealings of one species with another. We have delineated relations 

 of mutual assistance, of toleration, and of antagonism; we have re- 

 viewed the special circumstances of parasitism and of predation and 

 have considered various ecological effects of competition between 

 specific types of organisms. In the natural community many indi- 

 viduals of many species of both plants and animals are typically 

 present. It is our next task to consider the operation, organization, 

 and alteration of the commvmity as a whole in which each individual 

 is responding not only to influences from all neighboring species but 

 also to concomitant influences from others of its own species and from 

 the chemical and physical features of the environment. 



( 



I 



