CLIMAX FRESH-WATER COMMUNITIES 301 



Influents. These prey on other organisms and do not affect the 

 habitat as the dominants do: 



Pomoxis sparoides (Lac.) Black crappie 

 Hiiro floridana {Microptcnis salmoides) 



(Le S.) Large-moutliod black bass 



Cambarus propinquus (Gir.) Crayfish 



Chelydra serpentina (L.) Snapping turtle 



Chrysemys marginata (Ag.) Painted turtle 



Plankton. The j^lankton contains many genera of diatoms and 

 other types of algae, which settle slowly to the bottom and 

 produce a brown layer. There are many Protozoa, rotifers, and crus- 

 taceans of which certain typical forms are conspicuous in their proper 

 seasons, namely: two protozoans, Condonella cratera and Ceratium 

 hirundinclla; rotifers of the genera Brachionus, Synchaeta, Polyarthra, 

 and Keratella; various cladocerans, particularly Moina affinis, Daph- 

 nia longispina, and Bosmina longirostris; and three copepods, Diapto- 

 mus pallidus, D. siciloides, and Cyclops bicuspidatus (Eddy, 1934). 



The Nature of Dominance. The species that constitute this com- 

 munity appear to be very closely knit together. The frequency with 

 which all the fishes except the bass and crappie are found to eat duck- 

 weed, bloodworms (Chironomidae), Hexagenia and sphaerids, Campe- 

 loma, mussels, detritus, and mud is quite remarkable (Forbes, 1878, 

 etc.). The crappie may feed largely upon plankton, but the bass 

 preys on the 3"oung of other fishes and on minnows that occur asso- 

 ciated with them. A trematode parasite {Crespidostomum cooperi 

 Hop.) (Hopkins, 1934:62-73) has Hexagenia and sphaerids as its al- 

 ternate hosts, and a fish as the final host. 



The pool community in favorable conditions, such as are presented 

 in sluggish portions of rivers of the Mississippi drainage, represents 

 fragments of a true climax. The role of the fishes such as the various 

 suckers, several catfishes, buffalo group and other bottom feeders, 

 which often eat vegetation, mud, and detritus, is such as to remove 

 plants or prevent their increase and therefore maintain the terrige- 

 nous bottom suitable for themselves. They also increase turbidity and 

 make conditions less favorable for plants by this means (see Coker, 

 1929,0.6). 



The European carp possesses the qualities of a climax dominant, 

 but probably not to a greater degree than many of the American silu- 

 rids, catastomids, cyprinitls, etc. There have always been complaints 

 about carp and fishes of like habit increasing turbidity and driving 

 out other fishes. Cahn (1929) described the effect of the carp when 



