Lawrence H. Kobblns 



A FOOD CHAIN 



Beginning with the simplest chlorophyl-bearing plants, each organism eats, and in 

 turn is eaten. Animals generally get their food from those that are smaller. Each 

 takes what he can and gives only what he must 



vantages over larger animals. Wolves will attack a herd of cattle or deer. 

 The driver ants, which always travel in vast regiments, will attack large 

 animals — lizards, snakes, and even cattle. If the latter cannot escape the 

 swarm by running away, the countless ants will sting it to death and carry 

 off the flesh bit by bit. Not all flesh-eaters, however, are compact and ener- 

 getic fighters. The whale, for example, takes into its mouth a fraction of the 

 ocean, filters out most of the water, and finally swallows some hundred pounds 

 of small fry. 



As we should expect, a species that serves as food must be more numerous 

 than another which feeds upon it. It is estimated, for example, that one Hon 

 may kill as many as forty or fifty zebras in the course of a year. Since many 

 zebras must die every year without waiting for lions to kill them, the ratio of 

 zebras to lions must be much greater if zebras are to survive — or, for that 

 matter, if the lions are to survive. For if lions destroy too much of their food 

 supply, it will go hard with them the following season. To be sure, lions can 

 feed on other animals besides zebras; but the principle is still the same. 



The food chain is in a sense endless. Or rather, it goes round and round, as 

 we saw in considering food cycles. A single shrub may have on it millions of 

 plant lice. These plant lice furnish food for thousands of insects and spiders. 



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