THE ANIMAL COMMUNITY 9 



scramble for food with almost all the other fishes 

 of the lake and, in fact, not only with the other 

 fishes but with the insects and larger crustaceans 

 as well. Mollusks are not in such direct compe- 

 tition, but they do compete since they feed upon 

 the minute organisms which the smaller crusta- 

 ceans themselves use as food. 



In their turn the small bass become food for 

 other fishes as well as for turtles, water snakes, 

 wading and diving birds, large beetles, dragon-fly 

 nymphs and giant water bugs; even the lowly 

 fresh water hydra feed upon the small black bass 

 at every opportunity. 



An illustration of more remote and unexpected 

 rivalries is found in the relation of the black bass 

 to the green plant called bladderwort which fills 

 acres of the ponds of northern Illinois. Small 

 bladders, several hundreds to the plant, grow on 

 its leaves and give the basis for its common 

 name. They serve as tiny traps for the capture 

 of minute animals. The plant has no roots or- 

 dinarily and lives largely on the animals taken 

 in its bladders. Ten of these sacs, taken at ran- 

 dom, yielded 93 different species of small crusta- 

 ceans and insect larvae. Hence the bladderwort 

 competes with fishes for food and, by consuming 

 large amounts of this food, helps keep down the 

 number of black bass in an otherwise favorable 



