19. COMMUNITIES OF ORGANISMS 



E. W. Fager 



1. Introduction 



The species composition and general qualitative characteristics of level- 

 bottom benthic communities have recently been thoroughly reviewed (Thorson, 

 1957). There are also recent, less detailed, reviews of the communities of rocky 

 intertidal regions (Doty, 1957) and of sand beaches (Hedgpeth. 1957), and an 

 excellent introduction to the concepts of community and ecosystem (Hedgpeth, 

 1957a). Each of these has an extensive bibliography from which can be obtained 

 references giving the details of particular communities. Very little seems to 

 have been done with the community ecology of plankton or abyssal benthic 

 organisms. In view of the preceding, no attempt has been made to present a 

 complete review of the published work on marine communities in this chapter. 

 Instead, the emphasis is on the identification, description and analysis of 

 communities. Most of the more recent development and use of formal ways 

 of identifying and describing communities has been done by plant ecologists 

 and students of soil fauna. Similarly, the analysis of communities in terms of 

 energy relations has been most completely worked out in freshwater habitats. 

 Thus many of the ideas and methods discussed will be from these fields. While 

 it is true that one cannot assume that everything done in freshwater or ter- 

 restrial ecology is directly applicable to the marine environment, general 

 ecological concepts, such as food webs, pyramid of numbers, trophic levels, 

 etc., do apply in the latter, no matter where they may have been developed. 

 There may seem to some to be too much space devoted to the problem of the 

 identification and description of communities. The writer believes that one 

 cannot adequately study something until it can be fairly objectively identified 

 and described. In this view, the structural aspects of a community are as 

 important as, but no more important than, the functional aspects ; both are 

 necessary before an even approximately complete understanding of the com- 

 munity is possible. As is evident in the section on community theory (page 433), 

 the separation between structure and function is purely formal and convenient ; 

 in fact, they are completely interwoven in the community. 



It is probably as well to state at the start that the writer believes there 

 are such things as communities in the sense of recurrent organized systems of 

 organisms with similar structure in terms of species presence am abundances, 

 and that it is possible and meaningful to identify and study them, always with 

 the fact firmly in mind that they are open systems. The oppos f e viewpoint 

 is that there are only randomly assembled collections of organisms whose 

 ecological tolerances allow them to exist in a particular environment, that each 

 collection is an individual point on a continuum and that any grouping of 

 them is, at best, artificial. Evidence supporting this view is presented later. 



Precise and complete repetition of species composition and of relative 

 abundances of all species present probably never occurs and, therefore, in- 

 dividual assemblages will appear more or less dissimilar when compared in 



{MS received August, 1900] 41.1 



