CHAPTER 11. THE HABITAT 



Concept and Analysis 



27. Definition of the habitat. The habitat is the sum of all the forces or 

 factors present in a given area. It is the exact equivalent of the term en- 

 vironment, though the latter is commonly used in a more general sense. As 

 an ecological concept, the habitat refers. to an area much more definite in 

 character, and more sharply limited in extent than the habitat of species as 

 indicated in the manuals. Since the careful study of habitats has scarcely 

 begun, it is impossible to recognize and delimit them in an absolute sense. 

 Visible topographic boundaries often exist, but in many cases, the limit, 

 though actual, is not readily perceived. Contiguous habitats may be sharply 

 limited, or they may pass into each other so gradually that no real line of 

 demarcation can be drawn. Whatever variations they may show, however, 

 all habitats agree in the possession of certain essential factors, which are 

 universally present. On the other hand, a few factors are merely incidental 

 and may be present or absent. The relative value and amount of these is 

 probably similar for no two habitats, though the latter readily fall into 

 groups with reference to the amount of some particular factor. 



28. Factors. The factors of a habitat are water-content, humidity, light, 

 temperature, soil, wind, precipitation, pressure, altitude, exposure, slope, 

 surface (cover), and animals. To these should be added gravity and polarity, 

 which are practically uniform for all habitats, and may, in consequence, be 

 ignored in this treatise. Length of season, while it plays an important part 

 in vegetation, is clearly a complex and is to be treated under its constituents. 

 Of the factors given, all are regularly found in each habitat, though some 

 are not constantly present. The first five, water-content, humidity, light, 

 temperature, and soil are the most important, and any one may well serve 

 as a basis for grouping habitats into particular classes with reference to 

 quantity. As will be pointed out later, however, water-content and light 

 furnish the most striking differences between habitats, and offer the best 

 means of classification. As habitats are inseparable from the formations 

 which they bear, the discussion of the kinds of habitats is reserved for 

 chapter IV. 



