ECOLOGICAL SUCCESSION. 365 



of moisture, denser shade, and different materials for abode, 

 including the general absence of mineral soil; in fact all of the 

 factors that are supposed to influence the course and origin of 

 structural characters. The changes brought about by succession, 

 as when the beech forest displaces the oak, are disadvantageous 

 to such tiger beetles as Cicindela sexguttata because of the 

 practical disappearance of mineral soil, and the movement of 

 food species from the ground to the vegetation. Experimental 

 conditions could easily be devised which would duplicate and 

 intensify the changes alluded to, while acting upon some favorable 

 organism. If new forms appeared under the experimental con- 

 ditions any of them selected a higher level on the plants of 

 the experimental conditions, and possessed any structural char- 

 acters which enabled them to succeed there, we would have a 

 case of true adaptation paralleling the commonest type in nature. 

 It should be noted also that the fact that elementary adaptations 

 are so often adaptations to stratum speaks in favor of that view 

 of the origin of adaptations advanced by Eigenmann ('08) 

 (selection of suitable habitat by animals possessing adaptation 

 characters). The chief objection to this view seems to have been 

 that animals could not in most cases reach a suitable habitat. 

 We have noted that there are markedly graded (vertical differ- 

 ences) stratification conditions of light, temperature, circulation 

 of medium and rate of evaporation. Movement of habitat 

 preferences upward or downward is always a possibility readily 

 attainable. Should an adaptation to a particular stratum become 

 established, new lines of horizontal expansion would be thrown 

 open. Such horizontal extension of range would not usually be 

 accompanied by structural adaptations. 



We have doubtless proceeded far enough with the statement 

 of general ecological problems, to note that the training of the 

 ecologist must at present be broad. In the near future, 

 he must specialize upon some aspect of the subject, because it is 

 unusually large and its concepts especially complex. At present 

 he is called upon to know general zoology, especially general 

 physiology and behavior of organisms. He must have a working 

 knowledge of physiography, climatology, and plant ecology and 

 must be able to analyze, or at least to understand both physical 



