No. 571] TERRESTRIAL ASSOCIATIONS 423 



environment, though a large number of characters do 

 result in advantage. Characters advantageous in one 

 relation may be disadvantageous or indifferent in an- 

 other relation. The origin of the characters is not at 

 present a subject which can be treated in a study of inter- 

 relations of organisms (cf. Shelford, 1912&: 342). Be- 

 havior characters appear to be of greatest importance to 

 the animal in determining its relations with other organ- 

 isms of the association, though usually these are accom- 

 panied by physiological or structural characters. The 

 animal is not adapted to a particular status in the asso- 

 ciation; its ecological constitution determines what place 

 it shall be able to find among the other animals of its sur- 

 roundings. The relations among the various animals, 

 when a state of equilibrium has been reached, are ttie 

 result of mutual accommodation on the part of all the 

 animals involved. 



D. Internal Activities of the Association 

 It has been indicated that the complex of activities 

 within the association is the synthesis of all the activities 

 of the individual organisms. Each plant and each ani- 

 mal is subjected to physical, plant and animal influences. 

 From the extreme complexity of the entire system of 

 relations within the association, it is hardly possible to 

 consider more than one or several of these at one time. 3 

 It is possible, however, to see that each species finds a 

 status within the association, according to its particular 

 combination of internal and external relations. It con- 

 tinues in fairly constant numbers from year to year. A 

 change in these numbers, if at all great, may cause a dis- 

 turbance in the association, which is quickly regulated 

 by the activities of conflicting organisms (Forbes, 1880). 

 The entire association of plants and animals, by very 



