ECOLOGICAL SUCCESSION. 335 



are facts of behavior, habitat-preference, community of habitat 

 preferences and laws governing the relations of organisms in com- 

 munities. The last is not a part of physiological life histories, 

 the mores conception being broader than that of physiological life 

 histories. An ecological classification is a classification upon a 

 physiological basis, but since structure and physiology are in- 

 separable, we must also note the relations of structure to ecology 

 and to ecological classification. 



II. BASIS AND METHOD OF CLASSIFICATION. 



i. Basis. 



The ecological distribution of mores is the resultant of the 

 behavior reactions of the animals constituting them, to variations 

 of environmental conditions, encountered in their movements in 

 space. According to the law of toleration (Shelford, 'n 3 ), the 

 distribution of species or mores is limited by the variation 

 of a factor or factors beyond the limit of toleration of the 

 species or mores in question. The statement of the law was 

 based upon field and experimental observations on the tiger 

 beetles, which clearly supported this view. We noted that where 

 the conditions were nearest optimum, the number of larvae was 

 greatest and where least favorable the number was smallest. It 

 appears, from field study, that the number of individuals varies 

 directly with the degree of deviation from the conditions most 

 favorable. The distribution of each species or mores is probably 

 representable by the ideal curve (see Fig. 9, p. 351) when viewed 

 with reference to all environmental factors. As we pass in 

 different directions from the point of maximum number of indi- 

 viduals, different factors or combinations of factors are seen to 

 fluctuate. The area of maximum numbers is the area of over- 

 lapping of optima of the various factors. This is called the 

 ecological optimum (Schimper, '03). The ecological optima of 

 many mores are similar, a fact well known to naturalists. The 

 fact is most evident where changes in conditions are most abrupt. 

 Ecological classification places together groups of mores with 

 similar ecological optima. 



Ecological classification, whether of groups of individuals be- 



