CHAPTER III 



THE ANIMAL ENVIRONMENT: ITS GENERAL NATURE AND ITS 

 CHARACTER IN THE AREA OF STUDY 



I. Nature and Classification of Environments (35a, 55, 58) 1 



The environment is a complex of many factors, each dependent 

 upon another, or upon several others, in such a way that a change in any 

 one effects changes in one or more others. The most important environ- 

 mental factors are water, atmospheric moisture, light, temperature, 

 pressure, oxygen, carbon dioxide, nitrogen, food, enemies, materials 

 used in abodes, etc. In nature the combinations of these in proportions 

 requisite for the abode of a considerable number of animals are called 

 " environmental complexes " (55). It is our purpose to consider animals 

 as inhabiting environmental complexes, rather than to isolate their 

 responses to various single factors. The consideration of environmental 

 complexes in any comprehensive way would consume much space and 

 require extensive and special knowledge of many fields. Accordingly, 

 we can present here only the briefest outline of some of the principles of 

 classification, and the important features. 



If one is to understand the most elementary principle of the classi- 

 fication of environments, he must recognize the distinction between 

 local and (55, 58a) climatic environmental complexes. Local complexes 

 are often referred to as secondary or minor conditions or as edaphic or 

 soil conditions. The climate, and such features as types of vegetation 

 covering large areas, e.g., steppe, deciduous forest, etc., are commonly 

 regarded as climatic. Opposed to these, and lying within them, are the 

 local conditions, such as streams, lakes, soils, exposure, etc, which are 

 only indirectly dependent upon climate. The idea can be better illus- 

 trated by the desert than by our own region. For example, in the 

 Mohave Desert, the climatic conditions may be characterized as hot 

 and arid. Within this desert are a few streams fed by mountain rain- 

 fall. These streams are local conditions in themselves, and produce 

 others, such as moist soil, and types of vegetation which do not belong 

 to the desert. Within the area about Chicago are represented two 

 geographic complexes, the savanna and the deciduous forest, and lying 



1 Numbers in the text in parentheses refer to references in the Bibliography 

 (PP. 325-36). 



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