236 



CLIMAX AND SERE 



and increasing turbidity. This reduces or eliminates the vegetation, 

 and such fishes dominate through both coaction and reaction. The 

 marine cases cited by Petersen (see page 350) are probably pure co- 

 actions. 



The concept of dominance has heretofore been limited to plants 

 on land, and reaction, competition, and response manifested in the 

 plant matrix itself have formed the threefold basis. In the sea, a 

 parallel series of i)li('nomcna may readily be recognized among corals. 



A^ 



v'^". 



•'^ C 



'••' p 





'%..,-l'' ''i 



Fig. 53a. — Dccr-browsed area marked off at the time the cxclosure fence was 

 built in 1927 (Fig. 53£>). A, B, and C, mark clumps of overbrowsed aspen stems. 

 (Courtesy U. S. Forest Sendee, W. G. Mann, Supervisor. Photo by H. L. 



Andrews, 1936.) 



Since the equipment of sessile organisms differs more or less in all 

 three respects noted above, there are corresponding differences in the 

 degree of dominance. These are reflected primarily by the life forms 

 and secondarily by size, abundance, or both. On land, at least, the 

 first is peculiarly decisive as to the period of dominance, and hence 

 regularly marks the distinction between the dominants of climax and 

 sere, and the successive stages of sere. 



By contrast with plants, land animals exhibit very little direct 

 structural response to the habitat, but exert more or less reaction upon 

 it, chiefly through disturbing the soil. Their competition is mainly 

 connected with shelter and food coactions, and not with reaction. On 



