66 COMMUNITY FUNCTIONS— DYNAMICS OF BIOTIC FORMATION 



Related Processes. A number of functions consist of two or more 

 processes of which ecesis is ruling or decisive. This is particularly 

 true of invasion, which consists of migration and ecesis, but with its 

 final success and effect depending primarily on ecesis. This is the 

 process characteristic of succession, for which it supplies the materials 

 to be organized into the various stages as a result of reaction and 

 competition. 



The other complex functions are concerned largely with the climax 

 community, though not unknown in the later serai stages especially. 

 The most striking of these is aspection, which is characterized by 

 seasonal maxima of number or developmental behavior, in water as 

 well as on land, and with both plants and animals. Related to this 

 in terms of behavior are hibernation and estivation, ordinarily re- 

 garded as confined to animals but found in plants also, though under 

 other names. When the behavior response operates upon a daily 

 rather than a seasonal cycle, the process may be termed diurnation, 

 illustrated by the vertical movement of plankton and by the "sleep" 

 movements of flowers and leaves. Finally, the change in abundance 

 or prominence may be annual, as an expression of a larger cycle, such 

 as the eleven-year sunspot period. This is known as annuation, in 

 which the response to climatic variation may produce striking changes 

 in abundance, resulting in widespread migration or in marked differ- 

 ences in composition. Because of the importance of their roles in the 

 climax, the discussion of these functions is reserved also for 

 Chapter 6. 



Interrelations of Community Functions. Like those of the indi- 

 vidual, the functions of the community are not only most intimately 

 connected with one another, but they are also involved in a complex 

 of activities in which their simple causal relation is obscured or com- 

 pletely lost to sight. The normal sequence exists only in the simplest 

 minor communities; in others the interplay of functions is so kaleido- 

 scopic that the operation of each is difficult to discern. This is pecu- 

 liarly true of succession, which exhibits the dynamics of function at a 

 maximum. In the climax, aggregation and migration are at a low ebb, 

 and the directive processes of reaction and competition are diminished 

 and are concerned chiefly w'ith fluctuations in abundance in season 

 and year. The normal sequence comprises aggregation, migration, 

 ecesis in terms of reaction, competition and coaction, succession, diur- 

 nation, aspection, and annuation. It is obvious that the relation of 

 almost any two of these is more or less cyclic, inasmuch as migra- 

 tion makes aggregation again effective, from which further migration 

 proceeds. In the case of reaction, the ensuing competition in turn 



