132 MICHIGAN SURVEY, 1908. 



3. A formation or climax society is composed of a relatively (and 

 usually absolutely) limited number of species which, are dominant in a 

 given environment of geographic extent. Such dominance, in general, 

 implies extensive range, relative abundance, and ability to indefinitely 

 succeed or perpetuate itself under given conditions. 



4. Where dominance obtains, avian variety is limited so that the 

 greatest diversity occui*s where local influences prevail, and at the mar- 

 gins of the formation. 



5. Correlated environmental and biotic dominance produces what 

 may be considered a Tjiotic Mse, stratum, or optimum, from which de- 

 partures may be considered less favorable. This is a relative equilibrium, 

 resulting from complete environmental and biotic adjustment, under 

 given conditions. 



6. In each formation there is a normal inter-adjustment of the avian 

 species and individuals, in addition to the adjustment with the domi- 

 nant physical environment. The former is dominated by their structure, 

 habits, and the instincts or behavior; hence the colonial breeding or 

 spacing, migTation, etc. 



7. Each large environmental area or formation tends to have a full 

 complement or set of species, of diverse but supplementary ecological 

 character, such as water, shore or inland birds. One set is likely to be 

 dominant. ■ 



8. Eelative stability in an association is correlated with the climax 

 dominance, and generally watli extreme and slowly changing local in- 

 fluences. Fluctuation is correlated with intermediate conditions. 



9. Diveraified associations and isolation are greatest with imperfect 

 dominance, but dominance itself prodiices isolation of the climax as- 

 sociation. This diversification produces associations surrounded by 

 others and hence their isolation. 



10. The taxonomic elements in different formations vary much, but 

 there are close analogies in the kinds of taxonomic and ecological groups 

 in different formations, — as the Mniotiltidae of the New are represented 

 bv the 8vlviidae of the Old World. Cf. Osborn '02. LeConte, '50, 

 p. 230. Vf. Xo. 7. 



11. The roughly zonal arrangement of societies about the climax 

 society (formation) or the environmental optimum, is primarily due 

 either to local reversals, the lagging influence of local or neutral condi- 

 tions, or to the influence of adjacent formations. This is a result of 

 the retardation of the complete cycle of successions. 



12. The primain' environmental conditions tend to encroach upon 

 all others. The local conditions thus tend to become transformed in 

 the direction of the dominant environment and to be appropriated by 

 it. The corresponding avain associations are thus given a definite 

 dynamic trend. 



13. The mobility of birds during the breeding season is very generally 

 overestimated. The presence of the nest and young renders them for a 

 time relatively sedentary. There are many causes influencing this, such 

 as other individuals, proximity of food for young, homing, instinct, etc. 



