354 WHITTAKER 



a. The formation and association seem no longer distinct, clearly bounded 

 entities comparable to organisms or species. With recognition of the signifi- 

 cance of vegetational continuity and the principle of species individuality, 

 these have come to be regarded as man-made classes of natural communities. 



b. Succession seems a less orderly process than in Clements' view; only a 

 part of the incessant flux of populations in natural communities can be under- 

 stood in terms of succession. Relative stability of vegetation is not determined 

 by climate alone, and varied approaches to the definition of "climax" are 

 possible. 



c. Dominant species do not control the distribution of other species and 

 characterize communities and their environments in the way assumed by 

 Clements. 



d. Since plant species are free to change their distributional relations to 

 one another through evolutionary time, evolutionary relations of communities 

 are reticulate. Natural communities do not evolve by phylogenetic descent 

 from past communities in the same sense as organisms. 



e. The concept of the community as a complex organism, central to 

 Clements' system, has been largely abandoned as inappropriate or unpro- 

 ductive. Current interpretations emphasize the functional system formed by 

 community and environment, the ecosystem. 



3. These changes in individual concepts, taken together, amount to a 

 fundamental re-orientation of the field. The deductive system of Clements 

 has broken down into the more detailed, more complex, and less coherent 

 understanding of an inductive science. Because of multiplicity of ecological 

 factors, effects of chance, and individuality of species distributions, natural 

 communities are not an area of orderly, clear-cut, exactly predictable phe- 

 nomena to which the system of Clements might be appropriate. A fundamental 

 characteristic of natural communities affecting all ecological concepts is the 

 condition of loosely ordered complexity. Ecological concepts cannot be 

 thought inherent in, or uniquely determined by, vegetation; they are the 

 means of human abstraction by which some of the diverse information about 

 natural communities can be brought into comprehensible forms. 



LITERATURE CITED 



Alechin, W. W. 1925. 1st die Pflanzenassoziation eine Abstraktion oder cine 

 Realitat? Bot. Jahrb. 60 (Beibl. 135): 17-25. 



Allee, W. C, a. E. Emerson, O. Park, T. Park, and K. P. Schmidt. 1949. Prin- 

 ciples of animal ecology. 837 pp. Saunders. Philadelphia. 



Beadle, N. C. W., and A. B. Costin. 1952. Ecological classification and nomencla- 

 ture. With a note on pasture classification by C. W. E. Moore. Proc. Linn. Soc. 

 N.S. Wales 77:61-82. 



Beard, J. S. 1953. The savanna vegetation of northern tropical America. Ecol. 

 Monog. 23:149-215. 



