56 COMMUNITY FUNCTIONS— DYNAMICS OF BIOTIC FORMATION 



that leads on the one hand to further reactions upon the habitat 

 and on the other to new coactions between the associated organisms. 

 In succession these processes proceed in a chain or series which finds 

 its summation in the climax. The chain of serai communities has 

 been likened to the series of stages in the life history of an animal 

 undergoing metamorphoses with its final and most perfect stage repre- 

 sented by the adult which is comparable to the climax. The process 

 of succession has also been likened to the growth of plants, but lack 

 of detailed knowledge of both processes renders the comparison ciuite 

 ineffective. 



The functions of the biome may be viewed from the standpoint 

 of the dynamic processes, such as succession, annuation, aspection, 

 etc., or from that of the causal sequence of processes, beginning with 

 aggregation and terminating in stabilization. Both approaches are 

 desirable for a proper understanding of development and its relation 

 to the consequent structures, but the scrutiny of the single functions 

 and their correlations is much the more essential. In spite of the 

 fact that they are more or less simultaneous in operation, it is pos- 

 sible to separate them experimentally and to a certain extent by 

 observation also. 



Up to the present, the functions of the community have been stud- 

 ied chiefly with respect to the plant matrix, but it is evident that they 

 also carry over into the biome. Special studies of coactions and com- 

 petitions made from the standpoint of particular species of animals 

 confirm this conclusion. Their significance with respect to animal 

 groups is most clearly exhibited where animals are the dominants, 

 as in the marine climaxes. However, it is also well exemplified in 

 the various minor communities, such as families, colonies, and so- 

 cieties, both plant and animal, which are essential features of the 

 biotic community. The smaller and simpler the community, the more 

 readily can its functions be followed, and, in consequence, initial 

 stages in succession furnish the best opportunity for this in nature, 

 just as similar artificial groups constitute the best cultures for such 

 purposes. 



The following seven functions are considered to be the basic 

 processes in the plant matrix, and hence in the biome, even when 

 this consists primarily or wholly of animal dominants. These are 

 aggregation, ecesis (establishment), migration, reaction, coaction, com- 

 petition, and cooperation. Out of these arise certain complex proc- 

 esses, such as invasion and succession, while such phenomena as 

 diurnation, aspection, and annuation are more or less closely con- 

 nected with them. For the present purpose, at least, the most signifi- 



