238 CLIMAX AND SERE 



dominance resulted from cultural accomplishments such as the produc- 

 tion of steel (Shelford, 1935). But civilized man has also become a 

 reactor through extensive development of human culture. Lumber- 

 ing, as a direct coaction, and grazing, as an indirect one, produce re- 

 action only incidentally, but fire, clearing, cultivation, draining, flood- 

 ing, and construction regularly react on soil conditions and often 

 extend over wide stretches. 



It is evident that influence, like dominance, depends upon the life 

 form, and in a large degree upon size and abundance as well. This 

 is particularly true of the basic coactions that concern shelter and 

 food material. In all such relations, the animal typically assumes 

 the active role and the plant a passive one, and hence it is not desir- 

 able to treat the plant as an influent, unless it is parasitic or poisonous. 

 Coactions of introduced parasitic plants have at times produced strik- 

 ing results, e.g., the chestnut blight which has practically destroyed 

 the typical dominant of the oak-chestnut association. In water, some 

 animals play the part of dominants, as distinct from that of influents 

 taken by others. However, influence is more commonly exerted upon 

 other animals than on plants, though plankton-eaters devour both the 

 plant and animal members of the microplankton. 



Kinds of Dominants. Apart from the obvious distinction of 

 dominants as plant or animal, land or sea, climax or serai, they have 

 been distinguished on the basis of their role in the community (Clem- 

 ents, 1916, 1920, 1928; Shelford, 1935). The major division in land 

 communities is into dominants and subdominants, and it is probable 

 that this applies to some aquatic ones also, especially in the benthic 

 climaxes. The term codominant has been variously employed, usually 

 for one of several dominants. In this sense it appears to be super- 

 fluous, and it is here proposed to utilize it for dominant species be- 

 longing to the other kingdom, such as seaweeds in the ocean and carp 

 in ponds. 



From the standpoint of the food nexe of lake and ocean, the minute 

 forms of the plankton possess an importance quite out of proportion 

 to their size. In recognition of this fact, they have been termed ve- 

 dominants {ve-, small), a treatment further justified by their direct 

 response to the hydroclimate and their reciprocal reaction upon it. 

 Similar small or microscopic organisms take the leading part in the 

 short succession, or senile {-ulus, diminutive), typical of dead plants 

 and animals, logs, food masses, etc. To these, the term dominule is 

 applied, in taking account at the same time of their role and size. 



The Dominant. According to the prevailing interpretation, a 

 dominant is an organism with such definite relations to climate and 



