GENERAL ZOOLOGY 



Mussels 



■ Snails 



Large aquatic 

 insects 



Fig. 19.4. Schematic diagram of predator-prey relationships in a pond community. The 

 arrows in each case lead from prey or food to predator or feeder; thev mav be interpreted as 

 meaning "eaten bv." (Adapted from V. E. Shelford, Animal Commumties in Temperate America, 

 copyright 1913 by Chicago Geographical Society, printed by permission.) 



In analyzing one of the food chains in the pond community represented in 

 Figure 19.4, we find that the microscopic green plants called algae serve as 

 food for protozoans; these, and algae, are eaten by small aquatic insects, 

 which in turn support a population of larger aquatic insects. The large 

 insects are eaten by fish called bullheads, many of which are preyed upon 

 by black bass. Adult black bass, if large enough, may be the terminal link 

 in this chain, but smaller bass are important items in the diet of the larger 

 pickerel. At almost any stage in this sequence, it is possible to follow alter- 

 nate pathways, all of which, however, lead eventually to the pickerel. 



Implicit in these intricate interrelationships are several interesting gener- 

 alities. In the first place, plants form the broad base of the food relations 

 of the community, because they alone are competent to entrap solar energy 

 in the synthesis of organic compounds; plants, then, serve as the initial 

 repositories of stored energy. In every community the plants support a 

 population of herbivorous animals which transform plant materials into animal 

 fiesh. In our example, the protozoans, the small crustaceans, mussels, snails, 

 and small insects represent the herbivorous links in the several food chains. 

 These, in turn, serve as food for various carnivorous animals, which thus 



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