Chap. 5 



ANIMALS AND THEIR ENVIRONMENTS 



89 



basic supply. Beginning with them, smaller animals are eaten by larger ones, 

 protozoans by minute crustaceans and the fry of fishes, and these by aquatic 

 insects and so on to the large, fishes and turtles. If they die in the lake their 

 bodies are returned to the bacteria; if they are caught and taken elsewhere 

 they may become part of another food chain. In any long food chain, the 

 successive eaters are not only larger in size but fewer in number. There are 

 few sparrow hawks compared to the number of sparrows, few owls to the 

 number of field mice, one fox to dozens of rabbits. 



In communities of animals there are many more small adults than there are 

 large ones (Fig. 5.21). What seems obvious is borne out, in broad fines, by 

 analyzing a definite area of a community, counting the animals of various sizes 

 and measuring the totals by bulk or weight. The result is a pyramid of num- 

 bers. Such a pyramid applies particularly to predatory animals. It shows that 

 smaller animals have a higher reproductive capacity than large ones and are 



Open woods 



MILLIONS OF INSECTS TO ONE HAWK 



Pond 



BILLIONS OF PROTOZOANS TO ONE FISH 



Fig. 5.21. A pyramid of free living animals in one area. Plus signs express 

 abundance of types of animals. The smallest ones are most abundant. They supply 

 food to carnivores that are larger in size and fewer in number and these in turn 

 supply other carnivores that are still larger and fewer. 



