CHAPTER TWENTY-FOUR. 

 THE RATE OF REPRODUCTION. 



1. How Fast Must Organisms Propagate? Reproduction 

 is to keep the species going. To accomplish this, as we 

 have seen in former chapters, each pair must during their 

 life bring to maturity at least two individuals. If they 

 succeed in doing more than this the species increases in 

 numbers; if they do less the species diminishes. On the 

 average this is what each species does. Some may be 

 gaining, but if they do, it is probably at the expense of 

 other species. If a certain species of birds temporarily 

 increases in a locality, the insects on which they feed will 

 grow fewer there. On the other hand, if the birds 

 should decrease the insects are likely to increase. The 

 sum of life on the earth probably does not increase or 

 decrease greatly from generation to generation. Man, at 

 present, is increasing in numbers; and so, perhaps, are 

 those plants and animals that he cultivates for his uses. 

 But the forest trees, the wild plants, the song and game 

 birds, and the larger wild animals are decreasing with his 

 progress. Thus the total life remains about the same. 



2. What Determines the Rate of Reproduction? How 

 many offspring a plant or animal must produce that two 

 may come to maturity will depend on the favorable or 

 unfavorable conditions through which the young must go 

 to reach maturity. Among these are the climatic 

 conditions which favor or endanger the young, the amount 

 of the food supply and the ease of getting it, and the 



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