^°190^^] Adams, Ecological Succession of Birds. 125 



field workers. It is desirable to know the validity of these forma- 

 tions, their internal ecological relations and djuamic tendencies, 

 their relation to dominant environmental influences, etc. A com- 

 plete list is not attempted, and some of the statements may be only 

 fragments of larger generalizations; but it is just such relations as 

 these which will develop if the entire subject is considered critically 

 and synthetically. Some of the leading characteristics of these 

 larger environmental units and their avian forviatums may be 

 briefly outlined as follows: — 



1. The dominance of a limited number of physical conditions 

 or complexes, as climate, topography, vegetation, animals, etc., 

 in a given area produces the primary environmental units and 

 formations. 



2. Secondary environmental dominance is shown by a secondary 

 avian association. Thus in the Northeastern biotic center there is 

 a secondary dominance due to water basins in the forest area. 



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

 (and usually absolutely) limited number of species which are domi- 

 nant in a given environment of geographic extent. Such domi- 

 nance, 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 occurs where local influences prevail, and at 

 the margins of the formation. 



5. Correlated environmental and biotic dominance produces 

 what may be considered a biotic base, stratum, or optimum, from 

 which departures 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 dominant physical environment. The former is dominated 

 by their structure, habits, and instincts or behavior; hence the 

 colonial breeding or spacing, migration, 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 

 i? likely to be dominant. 



