1 



144 Adams, Ecological Succession of Birds. [ April 



There is thus a very strong convergent tendency. By convergence 

 is meant the independent production of the same kind of association 

 from diverse starting points or habitats and associations. Quite 

 minor ecological units may show similar but temporary convergent 

 tendencies in their succession. It is therefore not surprising that 

 any marked environmental dominance will tend to produce simi- 

 lar or convergent results, even in local areas. Under such cir- 

 cumstances similar associations or societies may be independently 

 and repeatedly formed by the selecting environmental influences, 

 such as, for example, are found in the numerous small lakes scat- 

 tered throughout the coniferous forests. This convergent phenome- 

 non is certainly a fertile source of confusion throughout all phases 

 of science. Perhaps the best guide through such a labyrinth will 

 be to clearly bear in mind the relative value of general and local 

 influences, and watch with an "eternal vigilance" for convergent 

 results due to diverse causes. This convergent phenomenon is 

 particularly liable to occur in the case of environments produced by 

 reversible physical conditions. It should further be stated that a 

 study of these problems from a genetic and dynamic point of view 

 will aid in recognizing such results. Under such circumstances 

 attention is primarily directed toward the dominant causes and 

 conditions of change rather than to the stages, products, and 

 results produced by them. Convergence thus viewed is the result 

 of several causes and should be considered a product rather than 

 a process. This same distinction may be made for all societies, 

 associations and formations. Convergent 'phenomena are tints 'par- 

 ticularly liable to confuse wherever products rather than genetic 

 processes receive primary emphasis. 



6. Succession and Environmental Evolution. The relation of 

 succession to general biological problems is very intimate. This 

 opens up a very extensive field which is only mentioned to indicate 

 its general relation to succession. The facts of succession and 

 evolution must ever remain far in advance of our knowledge of 

 their causes. If, however, one turns to the standard evolutionary 

 treatises and searches for a discussion of the evolution of the environ- 

 ment, as correlated with animal evolution, only the most general, 

 or the elementary and superficial phases, are as a rule discussed. 

 To be sure, certain papers and treatises take up special phases of 



