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THE INTERDEPENDENCE OF L1VT.N(; TIIIN(JS :,i 



It will be noted in the illustrations given that animals almost 

 mvanably feed upon others smaller than themselves. The same 

 relationship is seen in lakes or oceans where microscopic plants and 

 animals (plankton) form the food of other larger organisms, especially 

 fish. These living things form 

 definite "food chains" in 

 which larger animals feed on 

 smaller and smaller ones until 

 ultimately the lowest forms 

 subsist on tiny green plants 

 or bacteria. For example, in 

 a small pond we may find 

 billions of diatoms, unicellular 

 algae, and protozoa and feed- 

 ing on them millions of small 

 crustaceans. With them are 

 thousands of insect larvae, 

 hundreds of small fish, and a 

 few large fish, such as bass, 

 pickerel, or perch, which are 

 dependent upon all the other 

 forms of life. In this case a 

 few large animals are depend- 

 ent for food upon the development of myriads of smaller organisms, 

 the basis of this food being very simple plants. Take away any link 

 in the food chain and life in the pond becomes disorganized, with the 

 ensuing death of many of the inhabitants. 



Since smaller animals reproduce more rapidly than larger ones, 

 the food supply for those "on the top of the heap" remains fairly 

 constant. It should be borne in mind, however, that the larger 

 animals require a range of sufficient size to support them. 



Adaptations for Food-getting in Animals 



Protozoans, if ameboid, engulf their food, but in other members of 

 this group, food passes into the cell through a definite opening or 

 through the plasma membrane. Sponges and many molluscs pick 

 up microscopic food as it comes to them in water currents. Some 

 molluscs bore holes through the hard shells of bivalves, in that way 

 securing the soft parts of the animal for food. Insects have biting, 

 chewing, or sucking mouthparts, each type being fitted to utilize a 



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\\ hy will a break in the food chain often 

 cause disorganization of life in that locality ? 



