6 GENERAL BIOLOGY 



Balance in Nature. To the careful observer the face of 

 nature changes little from decade to decade. There are 

 giants and weaklings in every natural community, but 

 every species is strong enough to keep on living. There 

 are shifts of place, but rarely is one lost in the shifting. 

 Casualties may devastate a valley or a hill slope, but, left 

 to itself, it is soon depopulated. 



And there is order and progress in the shifting. The 



fungi growing 

 on this stump 

 (fig. i) and the 

 beetles boring in- 

 side it, are not 

 the same species 

 that will feed 

 there when it is 

 half rotted; nor 

 is any one of 

 these the same 

 that will mix its 

 di s i n t egrati n g 

 fragments with 



arly stage of decay; the Soil. There 



will be other 

 stumps with sound wood in them waiting for the descend- 

 ents of those now at work on this one. The conditions for 

 the life of all are fairly constant, and all are capable of 

 making such shifts as these conditions demand. The 

 balance is maintained by limitations of food and shelter 

 and increase of enemies, serving to prevent the undue 

 multiplication of any species. 



Man is the only disturber of the natural balance of any 

 consequence. He plows under the mixed population of the 

 prairie and gives the soil all over to corn. He finds the 



FIG. 1. Oak stump in a 

 shelf fungi on the bark. 



