CHAPTER 5 

 AGGREGATION, CO^IPETITION AND CYCLES 



General Relations. The process of aggregation lies at the basis of 

 social life in the biotic community, and hence it exhibits the most 

 intimate relations with the other functions of the complex organism. 

 It is the very essence of the association of organisms in the dynamic 

 sense, and is primarily concerned with the integration of all the group- 

 ings, from the simplest family of plants or animals to the most highly 

 differentiated climax. Like all community functions, it is the collec- 

 tive response of organisms to their environment, and in its turn it 

 produces social patterns of all degrees of complexity. For plants, its 

 general features have been elaborated by Clements (1901, 1916) ; for 

 animals, its operation has been treated in much detail by Allee (1931). 

 As with the other concepts of ecology, it now becomes necessary to 

 examine it from the biotic standpoint and to make such modifications 

 in it as the community life of plants and animals renders desirable. 



The purpose of the present chapter is to discuss aggregation as a 

 social process, to treat its significance in cooperation and competition, 

 and to trace its relation to population numbers and movements and 

 the consequences that flow from this. It is evident that reaction is 

 dependent in the first degree upon aggregation, since this alone makes 

 it possible to combine the effects of individual organisms into a cumu- 

 lative and permanent whole. A somewhat similar relation obtains 

 in respect to coaction. Though the latter may concern but two indi- 

 viduals, as in the case of food or reproduction, this is aggregation in its 

 simplest form, from which all other forms arise directly or indirectly. 

 The kind and degree of aggregation will determine whether coopera- 

 tion or competition will rule in the resulting community, or whether 

 they will alternate in space or time, as in the stages of succession. 

 The connection with migration is even more intimate, since the two 

 processes exhibit constant reciprocal action. All mixed aggregation, 

 that is, every community unit above the rank of family, depends 

 upon the operation of migration, while in the opposite direction the 

 increasing pressure of numbers due to aggregation is probably the 

 chief inciting cause for movement. In turn, ecesis or establishment 



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