302 AQUATIC CLIMAX COMMUNITIES 



introduced into one of the artificial pobls formed by a dam in Wis- 

 consin. At the .end of a few years, this fish had successfully removed 

 essentially all the rooted vegetation, uncovering the silt bottom to 

 which it is best fitted, whereupon it became the most abundant fish. 

 The basses, sunfish, plant- and insect-eating fishes were reduced to a 

 few scattered individuals. The carp in this case acted as a dominant, 

 actually transforming a habitat into one in which it lives to best ad- 

 vantage and changing the composition of the community almost com- 

 pletely. Unfortunately, this experiment has not been carried out with 

 native species. 



The native fishes of the pools are referred to as digging or plow- 

 ing the bottom. Of the buffaloes, Forbes and Richardson (1909) state 

 that they are reported to "plow steadily along with their heads buried 

 in the mud, — a search for small mollusca and insect larvae living in 

 the mud." The carp suckers (Carpiodes) eat a greater amount of 

 mud than the nearly related buffalo fish. The same authors refer to 

 the use of the sturgeon's hard beak to stir up the mud in its search 

 for food, the intestines being generally more or less filled with mud. 

 The bullheads and catfishes of the climax are obvious inhabitants of 

 the mud bottom in still water. They feed on aquatic insects, mollusks, 

 and detritus. The fishes of this class are abundant in the larger slug- 

 gish rivers. 



These fishes, as is readily seen from their habits, stir up the loose 

 fiocculent bottom detritus and mud and increase turbidity in the 

 same manner as the introduced carp. Turbidity is unfavorable to 

 plant growth, and the fishes do much to maintain silt and organic 

 materials in suspension. It is the activities of the fishes of the Missis- 

 sippi drainage that justify placing them among the foremost dom- 

 inants of the river climax. 



In permanent communities, terrestrial plants play the important 

 role as dominants through reaction in situ. The plant reaction in the 

 climax consists in producing conditions suitable for their own survival 

 and continuous reproduction. The general effect of the large pool 

 fishes is the same, though it is brought about by an entirely different 

 set of processes; the most important are probably the increase of tur- 

 bidity and destruction of plants either in adult form or as seedlings or 

 seeds. Mechanical disturbance of the soil is in itself also important, 

 but this process has not been evaluated. 



It must be remembered that any portion of a community separated 

 from the river channel, such as an oxbow, takes an immediate start 

 as a land sere, characterized by increases in vegetation and the ex- 

 tinction of the terrigenous bottom community. This separation and 



