Ecology of Plants and of Animals 13 



However, the environment sometimes changes so as to allow huge 

 variations in the numbers of organisms, such as plagues of mice or 

 insect pests, as will be discussed later. More generally, however, 

 the fluctuations in the surroundings and in the abundance of plants 

 and animals are less violent. In the great majority of these unspec- 

 tacular oscillations it is nevertheless the environment that is exerting 

 the vital control of the numbers of each species. In order to discover 

 the causes of fluctuations, which are sometimes of great economic 

 importance, a clear understanding of the essential relations between 

 the organism and its environment must be obtained. 



The everyday action of the environment in curtailing the geographi- 

 cal spread and the abundance of organisms has other significant 

 effects. The production of more young plant seedlings and young 

 animals than can survive causes a continual struggle for existence, 

 with the resulting survival of the fittest. These are essential factors 

 in the evolutionary process— as was pointed out by a prominent "ecol- 

 ogist" by the name of Darwin, long before the term ecology came into 

 common use. Through its influence on the individual the environ- 

 ment indirectly controls the natural community. It determines the 

 complexion of the whole population by determining which species 

 can exist in each area and the relative numbers of each. Through the 

 control of feeding, growth, and other activities of each living com- 

 ponent, the environment regulates the dynamic operation of the 

 community. 



THE DEVELOPMENT OF ECOLOGY 



The Ecology of Plants and of Animals 



The term "oecology" was first used by the German zoologist Haeckel 

 in 1869. The word did not appear again until 1895, when a report 

 on ecological plant geography was published by Warming, a Danish 

 botanist. The term in its modern spelling was taken up again later 

 by the zoologists. In those early days and for a long period there- 

 after botanists and zoologists were often working quite separately. 

 It is not surprising, therefore, that plant ecology and animal ecology 

 tended to develop independently, but it is unfortunate that this divi- 

 sion into two separate fields tended to persist. We have now come to 

 realize that a proper understanding of the ecology of animals neces- 

 sarily involves a consideration of the plants of the environment, and 

 that a study of the ecology of plants would be incomplete without in- 

 cluding the influence of animals. However, ecologists, and biologists 



