CHAPTER XXV 



THE ANIMAL AND ITS ENVIRONMENT 

 (By A. 0. Weese, University of Oklahoma) 



Ecology is that division of biology which has to do with the rela- 

 tions between organisms and their environment. The environment 

 of an organism, for convenience, may be divided into two parts, the 

 nonliving, including physical, chemical, and climatic factors, and 

 the living, including other organisms of the same and of different 

 kinds. The science of ecology, in a sense, is as old as man, because 

 from the very beginning of his conscious existence it was necessary 

 that man take cognizance of the fact that his environment was made 

 up in part of plants and animals and that these organisms in turn 

 had relations to their environment. It was not until comparatively 

 recently, however, that ecology came to be recognized as a separate 

 department of biology. Modern ecology may be said to have begun 

 with the recognition of the community. Plants and animals are 

 distributed as they are over the surface of the earth, not because 

 of any chance coincidence, but because of a combination of circum- 

 stances, one of which is the fitness of the physical environment for 

 the proper completion of their life histories and another of which 

 is the presence of such other organisms as are necessary to furnish 

 food and to provide other requisite conditions. We can think of a 

 community of organisms in much the same way as we think of a 

 community of human beings. The analogy cannot be followed too 

 closely, for, after all, human beings are much alike while the organ- 

 isms in an ecological community are of many different kinds, having 

 different requirements in detail as- to food and environmental con- 

 ditions. We shall arrive at a better concept if we think of a human 

 community as made up, not only of butchers and bakers and candle- 

 stick makers, each with their particular functions as producers and 

 as consumers, but also of the domestic animals which furnish mate- 

 rials for food or clothing or which perform labor, the household 

 pets and pests, the cultivated plants which are utilized in the manu- 

 facture of food, clothing or shelter, and the host of wild animals 

 and plants which enter into some relation with those previously 



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