IV 

 THE BALANCE OF NATURE 



The adjustment of various species of plants and animals to one 

 another under natural conditions, and the danger of suddenly disturb- 

 ing the equilibrium, have been much discussed, particularly in the 

 literature of economic ornithology, but the principles involved apply 

 with. equal force to the mammals. 1 



Perhaps there is no such thing in nature as an absolutely perfect 

 biological equilibrium a condition in which no species is either in- 

 creasing or decreasing, their relative numbers remaining constant. 

 Surely such an equilibrium, if it occurs, is temporary. Local conditions 

 are slowly but constantly changing, demanding constant re-adjust- 

 ment, which, under natural conditions, is accomplished gradually, with 

 but little disturbance of the balance. World-wide conditions also 

 change, though even more slowly. That this has been going on through- 

 out the geological ages is shown by abundant fossil evidence. At many 

 times during the past, whole faunas and floras have become extinct 

 and have been replaced by new faunas and floras, but these changes 

 have doubtless been exceedingly slow. 



The environmental changes wrought by civilized man are often 

 much more rapid. In a few decades we destroy vast forests, bring 

 under cultivation thousands of square miles of prairie soil, carry water 

 into arid regions for irrigation, drain great swamps and lakes ; destroy 

 immense herds of bison or other mammals, or myriads of pigeons, 

 obliterate the hiding and nesting places of many species and reduce 

 their food supply; introduce various other species, such as cattle, sheep, 

 English sparrows, etc., to provide competition for native species of 

 animals, and grains and other plants to provide competition with native 

 plants and to furnish new, different and perhaps better food supplies 



1 See especially Forbes, On some interactions of organisms, Bull. Illinois State Lab. 

 Nat. Hist., i, No. 3, pp. 3-18, 1880; 2d ed., 1883; The regulative action of birds upon 

 insect oscillations, ibid., i, pp. 3-32. 1883; The ornithological balance wheel, Trans. 

 Illinois Horticultural Soc., xv, 120-131, 1882. Palmer, The danger of introducing 

 noxious animals and birds," Yearbook U. S. Dept. Agric. for 1898, pp. 87-110. Gold- 

 man, The predatory mammal problem and the balance of nature, Journ. Mammalogy, 

 vi, 28-33, 1925- Adams, The conservation of predatory mammals, ibid., pp. 83-96. Hen- 

 derson, The practical value of birds, pp. 26-35, IQ 2 ?. and publications therein cited. 



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