^° 1908^^1 Adams, Ecological Succession of Birds. 143 



The relatively slow rate of change in many environmental proc- 

 esses and the relative stability of the climax biota/ is doubtless 

 the basis for the current view that such conditions are relatively 

 constant or fixed ; but that change and not constancy is the normal 

 and usual condition in nature is quite evident upon a moment's 

 reflection. Almost every one notices these changes after an absence 

 of a few years from a region. Thus intimacy tends to blind us to 

 changes unless a habit of giving attention to them is deliberately 

 cultivated. For this reason some find it almost impossible to recog- 

 nize environmental changes or to comprehend their significance. 

 It is therefore of practical value to clearly recognize under what 

 conditions changes may be most readily perceived. Therefore the 

 importance of the study of local influences is emphasized, and the 

 necessity recognized of distinguishing the dominance of geographic 

 and relatively stable conditions or formations as contrasted with 

 those due to local and often relatively changeable conditions. Then 

 among these changes we must distinguish those which are mere 

 fluctuations and those which are indicative of the true progressive 

 succession. This is mainly accomplished by attention to general 

 relations and the subordination of minor details. 



5. Environmental and Assockitional Convergence. At the pres- 

 ent imperfect stage of ecological development, comparison must 

 furnish us the most important and general clues to the processes 

 of succession; and undoubtedly this method must long remain as 

 our main guide on account of its comprehensive application and 

 the magnitude of the problem to be solved. It is therefore desira- 

 ble that the limitations of the method should be clearly borne in 

 mind. It is often assumed that the implied successions of a given 

 place are the same as those which have developed at that place in 

 the evolution of the present climax. But as we })ositively know that 

 many different causes are able to produce the same or very similar 

 results, such conclusions must be received with due caution. That 

 the dominant geographic conditions tend to override local influences 

 seems very fairly established because diverse local or original condi- 

 tions are transformed into the climax or dominant type. This clearly 

 shoM^s that in time diverse local influences have flowed into the gen- 

 eral environmental trend or current and have become a part of it. 



1 For the migrations of climax societies, cf. Adams, '05. 



