ECOLOGY OF ISLE ROYALE. 147 



which, from its very nature, must be as extensive as are the causes of 

 change does not appear to have been clearly recognized by all students of 

 biotic succession. For this reason there are certain principles of suc- 

 cession which are well established in other sciences, but which have not 

 been applied to biotic succession. In human society, for example, there 

 are many institutions whose formation, development and perpetuation 

 clearly illustrate the laws of succession which also apply, not only to 

 plants and animals, but to geologic phenomena as well. It is not at 

 all surprising therefore that under these various guises their common 

 features are easily overlooked and even denied by some students. 



In the study of the animal environment some knowledge of the gen- 

 eral principles of succession, not worked out in detail for birds 

 but already well established elsewhere, ought to be suggestive and 

 possibly valuable in the study of avian succession. Though such gener- 

 alizations are primarily of a provisional and suggestive character, yet 

 investigation should be stimulated rather than retarded by them. Such 

 descriptive characteristics and principles are stated briefly in a form 

 convenient for testing and criticism and should be useful as are cri- 

 teria in the study of geographic origin. So far as known to the writer 

 only two authors have attempted to formulate principles of biotic suc- 

 cession, and these have been limited to plants. The first is by the Dan- 

 ish ecologist Warming ('90, Oekologische Pflanzeu Geographic, pp. 360- 

 361), and the second by Clements ('05), whotee treatment merits special 

 attention. Cowles ('01) has done much to put the idea of succession 

 upon a genetic basis. In the present outline only those features and 

 principles are mentioned which are thought to be of a more or less 

 general character, and those particularly applicable to animals. This 

 list needs to be greatly prolonged, and the interrelations of these char- 

 acteristics must be determined as well as their relative value and appli- 

 cation to various ecological groups and in diverse regions. The fol- 

 lowing suggestions can only outline the problems involved. At this 

 stage, differentiation is particularly desirable. Processes and pro- 

 ducts bear the same namra and must be understood accordingly; thus 

 the processes of dominance lead to the product dominance. Dynami- 

 cally considered, the process .is primary, but used in a structural sense 

 such terms refer to products. 



1. Starting with any given set of environmental conditions and or- 

 ganisms, these become a cause and condition of future changes. All 

 changes are cumulative and form a continuous series or process. 



2. J^o sharp line can be drawn between cause and conditions in 

 succession as their relations are often reversible. A cause at one time 

 may be ai condition at another, and vice versa. 



3. The formation or association itself must be considered as an 

 essential part of the complete environment, and should be so under- 

 stood when reference is made to the environment, cf. No. 1. 



4. A given formation in its dominance tends to encroach upon all 

 minor habitats and associations. These minor habitats tend to be- 

 come cumulatively changed convergently toward the climax environ- 

 ment or formation. This is a process of eliminating diversity and thus 

 establishing dominance. 



5. Where complete environmental and biotic adjustment has taken 



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