CHAPTER II. THE HABITAT 
CoNcErT 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, 
al! 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. — 
