THE ANIMAL AND ITS ENVIRONMENT 



101 



Fig. 5-11. Because of the exacting environmental conditions of a desert plain, there are few plants and animals. 



But even here there is an intricate relationship between them. 



a large variety of predators such as the 

 predaceous diving beetles. Others, hke the 

 midge larvae and May fly nymphs, are con- 

 tent with the dead bodies of plants and ani- 

 mals, and are known as scavengers. Finally, 

 the organic matter that remains after all 

 animals are through with it is decomposed 

 by bacteria, known as decomposers, so that 

 the inorganic compounds that are needed 

 by the plants are restored to the water. 

 Thus the cycle is completed. 



Seasonal changes occur in the pond com- 

 munity and the animals living there must 

 adjust to them. Usually there is an abun- 

 dance of water in the pond during the 

 spring of the year, but as fall approaches 

 there may be very little water left. Con- 

 sequently animals must migrate to other 

 ponds or go into a resting stage until condi- 



tions improve. The sheet of ice which cov- 

 ers the pond during the winter excludes 

 most of the light, which results in less pho- 

 tosynthesis, hence less oxygen. If animals 

 are to survive the winter they must be able 

 to get along on minimum quantities of oxy- 

 gen as well as withstand low temperatures. 

 Each animal living permanently in such a 

 pond community is able to meet these situ- 

 ations and is found year after year in the 

 same locality. 



A desert plain. In contrast to the pond, 

 the desert environment supports only those 

 plants and animals that can survive on very 

 little or no water, except that taken with 

 the food. If we study the life existing on the 

 plains of our own Southwest, we find a 

 strange group of plants and animals, all of 

 which are adapted in one way or another 



