10 Viewpoint of Modern Ecology 



sions into extensive chestnut groves of edible chestnut trees to gather 

 nuts. Now an edible chestnut tree is a rarity because a blight on this 

 species, caused by a fungus, spread throughout the northeastern states 

 and wiped out the chestnut groves between 1910 and 1930. 



If the slight, but crucial, increase in the destructive action of the 

 environment extends beyond a local area to the whole range of a 

 species, its effect becomes much more serious, and it may even result 

 in the extinction of the species. This, too, has happened, not once, 

 but many times. Within the memory of man such species as the 

 Labrador duck and the passenger pigeon have become extinct; many 

 more, such as the American bison, would have been entirely wiped 

 out if it were not for protected preserves. No one knows how many 

 species during the ages failed to meet the challenge of the environ- 

 ment. We do know that about 21,000 species of extinct vertebrates 

 and an even larger number of extinct higher plants have been de- 

 scribed. If we add to this figure a guess as to the number of extinct 

 vertebrates and higher plants whose remains were never found, and 

 of the extinct species of invertebrates and of lower plants, we shall 

 have some impression of the precariousness of existence in this world. 



As if the destructive action of the environment were not serious 

 enough under natural conditions, man has added immeasurably to it 

 as civilization has "advanced." As will appear many times in our 

 further discussions, man need not necessarily be the destroyer. With 

 an adequate understanding of ecological principles he can utilize 

 many natural resources without impairing them. In some instances 

 the abundance and variety of the natural fauna and flora have im- 

 proved as a result of man's activities. If we include cultivation, a 

 very great development of plant and animal life has, of course, been 

 brought about by the hand of man. Unfortunately the intelligent use 

 of biological resources has not been the rule. Whole populations of 

 animals and birds have been slaughtered for their fur or their feathers. 

 Grasslands have been ruined; forests have been cut down (Fig. 1.6). 



Besides direct devastation of much of our natural vegetation and 

 wildlife, we have wrought even more harm through causing serious 

 pollution of lakes, river, and harbors, irreparable damage to the soil, 

 and loss of ground-water reserves (Fig. 1.7). The sad story of man's 

 destruction of his own natural resources throughout the world has 

 been effectively told. The need for intelligent conservation and the 

 steps being taken in the United States to achieve it have been sum- 

 marized by Gustafson, Guise, Hamilton, and Ries (1949), by G. H. 

 Smith (1950), and others. Suffice it here to stress once more the fact 

 that animals and plants in nature are living dangerously. The natural 



