ENVIRONMENT-COMMUNITY INTERRELATIONS 



397 



a smaller carnivore would be a krtiary consumer. 

 This concept which segregates functional niches into 

 producers, primary consumers, secondary consumers, 

 and so on, is called the food chain (Figures 20.1 and 

 20.2). The chain implies a linear order of food con- 

 sumption. 



In nature the actual functional niches do not as- 

 sume the straight-line relationship that is implied by 

 a food chain. Rather, natural niche interrelation- 

 ships, when diagramed in terms of what eats what, 

 disclose a netlike pattern of energy transfer. The 

 phenomenon represented by such a pattern is called a 

 food web (Figure 20.2). 



Functional niches are clarified by considering vari- 

 ous food pyramids, especially the production, bio- 



mass, and numbers pyramids. These pyramids all 

 stress the fact that the energy cycle in an ecosystem is 

 not 100 per cent efficient. In other words, it takes 

 more than one pound of plant materials to form one 

 pound of herbivores, and more than one pound of 

 herbivores to form one pound of carnivores. The vari- 

 ous pyramid concepts disclose the inefficiency, or 

 loss, in energy transfer in unlike ways. A production 

 pyramid from base to apex represents a food chain. 

 The base portrays the amount of organic materials, 

 usually by weight, that are produced by the plants in 

 a particular area. The level next above the base shows 

 the amount of growth that takes place in the herbi- 

 vores that consume the produced amount of plant ma- 

 terials. Progressively higher layers diagram the 



FOOD CHAINS 



4° Consumers 



killer 

 whales 



FOOD WEB 

 light 



green flagellates algae 



fishes 



ge fishes 



FOOD PYRAMID 



killer whale 



coyote 



squirrels 



herbs 



Figure 20.2 Food chain, food web, and food pyromid. Food pyramids may imply the amount of 

 food formed, weight of life in o porticulor level of the energy cycle, or the number of individual 

 organisms in each level of the energy cycle. 



