

THE STRUGGLE FOR EXISTENCE 877 



inherently possible numbers. They have found that impor- 

 tant limiting factors prevent the realization of their hopes. 



In the first place, it is clear that there is not space enough 

 for more than a small part of the new individuals to develop. 

 Every open space that offers anything like reasonable living 

 conditions for plants and animals is soon occupied by them. 

 If the fifth-year crop of sweet corn, as calculated above, were 

 planted as corn is ordinarily planted, it would require about 

 2000 times the land area of Illinois in which to plant it. If 

 one hive of honeybees were to produce for six years as rapidly 

 as inherently possible, and these bees should be housed in 

 hives each of which has four square feet as its standing place, 

 the state of Illinois would not supply standing room for the 

 total crop of bees. 



Space is too limited for any given kind of plants or animals 

 to increase very rapidly. In a rich river bottom, in a vacant 

 lot, in almost any place where plants and animals may 

 get started to grow, the struggle for space is evident. In 

 the tree tops the birds contend for nesting places (fig. 176). 

 The English sparrow has driven many native birds away 

 from their former nesting places. Agriculture has taken over 

 the territory formerly occupied by many kinds of native 

 plants and animals and has introduced other kinds of plants 

 and animals into the old haunts of native living things. 



389. Not food enough for all. The city man who would 

 make a fortune growing chickens finds that his expense for 

 feed is large, often so large that he cannot afford to raise 

 chickens ; and if the possible rates of increase are made real 

 for even a short period, it is soon evident that neither space 

 nor food is sufficient. In nature the tragedy of the shortage 

 of the food supply is frequently seen. It would be seen con- 

 stantly if it were not for the fact that one kind of living thing 

 may serve as food for one or many other kinds. When salmon 

 become quite abundant, other kinds of fish, or other animals, 

 may devour them in large numbers. In our fresh-water 



