ECOLOGY OF ISLE ROYALE. 149 



17. Widespread physically uniform conditions favor a dominant 

 Wotic formation. Climate may neutralize topographic diversity, or 

 topography the climate. Baseleveling and other geological processes 

 which favor the production of uniform conditions will favor dominance. 

 (Adams, Amer. Nat., 35, p. 842). 



18. From an evolutionary standpoint the eali,er stages of succession 

 are liable to be struggles with the- physical environment; later, in the 

 intermediate state of "storm and stress," the competition is most di- 

 verse and intense, and may thus be a fertile sourcQ of adaptive changes 

 and individual adjustments, through severe selection; and finally in 

 the stage of dominance, the competition is also biotic and physical, but 

 under relatively simpler conditions. Permanence of new characters may 

 be favored by habitat isolation and thus favor polytypic or divergent 

 evolution. 



19. In succession the adjustments and modifications of species may 

 be accomplished by a change from one society to another as well as 

 by individual modifications or adjustment within the society. 



20 Pioneer invaders, except in social species, are generally isolated 

 and increase progressively with dominance. Of. Warming, No. 1. 



21. Species and individuals in the early stages of succession or of 

 societies are relatively few, increase in the intermediate stage, and 

 are again reduced in number with dominance and in the climax society. 

 Of. Warming, No. 2. Clements VI. (3, 5). 



22. The species of open (unforested) formations are only pioneer 

 societies in forested formations and vice versa. Cf. Warming, No. 5. 



23. The less sedentary species, those less inclined to regularly re- 

 turn to old nesting sites, and young birds tend to become pioneers and 

 thus extend the breeding range. Cf. Warming No. 4. Dixon, '97, p. 

 91. 



24. Pioneers generally come from near by and from similar condi- ■ 

 tions. Cf. Clements III, (3). 



25. Extension of range takes place mainly at the unoccupied margin. 

 This may mean unilateral or radiate extension. Cf. Clements V, (5). 



26. The succession from the aquatic association to the forest is 

 probably an ancient one.. In this there is a general succession from the 

 less to the more specialized kinds of birds. Cf . Warming No. 2 ; Clements 

 VI (4). 



VII. Some Advantages op a Knowledge op the Laws op Succession. 



The study of succession implies a detailed knowledge of the field 

 relations of birds, and as this has received so little attention as a sub- 

 ject of special study, it is perhaps worth while to. mention briefly some 

 of the practical and scientific advantages which we may reasonably 

 expect will result from the development of this phase of investigation. 



The current discussions of environments are generally very frag- 

 mentary and chaotic, and the careful study of bird habitats and suc- 

 cession will greatly improve this phase of ecology. Here is a field of 

 study in need of distinct recognition as a subject worthy of detailed 

 investigation, in addition to those lines already current. When once 

 this field is developed, then and only then will it be possible to in- 



