FOOD RELATIONS 



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or on plants and moving away when the food gives out. Such a 

 food chain or cycle would be seen in the warblers which eat insects 

 living in trees, as plant lice and boring beetles. The warblers 

 are in turn preyed upon by hawks. In the same forest there may 

 be mice, whose chief food is acorns, and the mice are eaten by 

 owls. This is another example of a food cycle. 



Sometimes we have a sudden invasion of an animal after food, 

 | such as the locust. The 

 famous plague of grass- 

 hoppers in Utah in early 

 pioneer days was stopped 

 by a similar migration of 

 gulls from the Great Salt 

 Lake which came to feed on 

 the grasshoppers. Thus a 

 balance of life is maintained. 



Ecological successions 

 have already been spoken 

 of. When, for example, a 

 lake area dries up, different 

 animals come to occupy the 

 marsh and forest land, tak- 

 ing the place of the water 

 forms of life. Man has 

 played a very large part in 

 attracting new animal forms 

 into regions that he has 

 irrigated or reclaimed for 

 agriculture. Here are an 

 entirely new set of animals 

 which feed upon the intro- 

 duced plants. 



Life succession in a hay 

 infusion. Still another ex- 

 ample of an ecological suc- 

 cession may be seen in a hay infusion. If we place a wisp of 

 hay or straw in a small glass jar nearly full of water, and leave 



Cliff Bray 

 The people of Salt Lake City, Utah, erected this 

 monument in commemoration of the service done 

 by the gulls in the destruction of grasshoppers. 



