THE STRUGGLE FOR EXISTENCE* 283 



old and weighing 20 pounds (although four-year old salmon 

 often weigh more than 20 pounds), there would be 160,000,000 

 pounds of salmon in this third-generation crop. If these sal- 

 mon were packed in tins and should net three fourths of their 

 original weight, or 120,000,000 pounds, and should be sold 

 at ten cents per pound, they would be worth 112,000,000 ; or 

 if the inhabitants of a city of 10,000 people were to use an 

 average of one fourth of a pound per day for each person, this 

 third generation of salmon would supply this city of 10,000 

 people for 48,000 days, or for more than 131 years. 



Any given species of animal has an inherent rate of repro- 

 duction which makes enormous numbers of that species possi- 

 ble if we assume that this inherent rate is to have no limitations. 

 Many an enthusiastic resident of a city has made calculations 

 regarding the number of chickens that may grow in a small 

 number of years from a small initial number of chickens. 

 Some city residents have even moved into the country expect- 

 ing to grow chickens in numbers comparable to these inher- 

 ently possible numbers. They have found that important 

 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 condi- 

 tions 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 inher- 

 ently possible, and these bees should be housed in hives each of 

 which has 4 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 



