626 General and Applied Biology 



provision to carry on the race by producing protected or resistant eggs. 

 Such factors as these naturally affect the ecologic relationships of ani- 

 mals under these conditions. A covering of ice on a body of water not 

 only affects the animals directly but also indirectly by altering the oxy- 

 gen and food supply. This explains why many animals come to holes 

 cut in the ice. Many fishes can be caught in this manner through holes 

 in the ice. 



It is a well-known fact that all types of plants cannot exist in the same 

 temperature. Since temperatures vary in different environments, a 

 plant must be placed in its required thermal environment or be killed be- 

 cause of this ill-adjustment. 



(b) Light: Certain animal protoplasms are so constructed as to be 

 unable to tolerate excess light, while others require large quantities to 

 exist. In fact, some species seem to require the stimulation given by light 

 in order to carry on many of their metabolic processes efficiently. Light 

 naturally acts as an important factor in animal distribution directly. 

 Indirectly, animals are affected by the presence of plants which require 

 light for their existence. In other words, certain animals depend upon 

 plants for food, protection, and oxygen. In turn, these plants depend 

 upon the proper amount of light. Hence, animals are indirectly and 

 directly influenced by the quantity and quality of light. Certain types 

 of animals move around only in daylight (diurnal), while others do so 

 only at night (nocturnal). In this case the presence or absence of light 

 is a factor in the ecologic relationships of such animals. 



Certain plants require a maximum of light, some require a medium 

 amount, while still others require a minimum, or possibly none at all 

 (such as mushrooms, bacteria) . Plants will successfully locate them- 

 selves in the proper quantity and quality of light which suits their par- 

 ticular and specific requirements. 



(c) Wind: The direction and velocity of the wind undoubtedly are 

 very decided factors in the dispersal of certain animals. Very strong 

 wind mav also affect the water in which animals live so that it mav be 

 a factor in the distribution of such aquatic forms. The wind may affect 

 them in various ways. It may cause injury to them directly. It may 

 stir up the sediment in water so that animals may be influenced by it. 

 The action of the wind also may influence the oxygen content of the air 

 or of the water in which they live and thus be a factor in their distribu- 

 tion. Winds also may affect the temperature and moisture content of 

 an environment and thus may directly influence animals or plant dis- 



