508 



THE COMMUNITY 



plants and animals hold each other in a 

 state of biological equilibrium. This is an 

 extension of the principle of biotic balance 

 to embrace the whole community. 



This is not to say that communities are 

 always in static equilibrium. Rather, they 

 are in a condition of flux in all their strata, 

 and within each stratum the species popula- 

 tions are in almost continual readjustment 

 to each other and to the varying physical 

 portion of their environments. We may 

 postulate safely that in any community, at 

 any time, analysis would demonstrate some 

 of its components in imbalance with respect 

 to other components. This is no less true 

 of organismal metabolism than it is of com- 

 munity metabolism. The unbalance may be 

 of varying degree and duration. If serious, 

 such maladjustment in organisms leads to 

 impairment of function and eventually to 

 organismal death, and in communities to 

 community death. Usually, the unbalance 

 is relatively small and ephemeral and oc- 

 curs frequently at many widely separated 

 parts of the organism and community. 

 Rectification of these temporary points of 

 unbalance is essential to optimal health and 

 vigor. The result is biotic balance and is 

 achieved in communities by complex regu- 

 lation of these oscillations. 



We have examined this important aspect 

 of ecology previously, in terms of predator- 

 prey regulation (p. 370). The principle of 

 balance has a still broader application. It is 

 one of the major influences maintaining the 

 character and independence of the whole 

 community. It may be an underlying cause 

 of commimity development and succession 

 (Chap. 29) in which a pioneer community 

 finally reaches a condition of unbalance 

 which it may not rectify, and the invading 

 or succeeding organisms gradually, through 

 time, develop a new community. 



In the particular sense in which the con- 

 cept of the major community is used in this 

 book (p. 436), the several species popu- 

 lations hold each other in a system of 

 checks and balances to the end that their 

 intraspecies and interspecies mutualisms 

 (p. 245) and competitions (p. 368) pro- 

 duce a self-sustaining assemblage of organ- 

 isms. This is essential for a full apprecia- 

 tion of the Darwinian web of life concept. 

 It is implied in the community concept, 

 from the early views of Mobius (1880) 

 and Forbes (1887) to the present moment. 



The biotic potential of Chapman (1928) 

 and the trophodynamic limnology of Eggle- 

 ton (1939), Lindeman (1942), and Hutch- 

 inson (1944) reflect this general point of 

 approach. Modern symposia, monographs, 

 and textbooks are, or should be, leavened 

 by its timelessness. For an opposing point 

 of view, see Bodenheimer (1938). 



The pattern of survival may be found in 

 the complex interrelations between the 

 several species populations of a community. 

 For example, in the first part of the pres- 

 ent chapter it was shown that the basic 

 trophic relations were between plants and 

 the physical portion of the environment 

 (pp. 495-507). The catabolism of a com- 

 munity is largely a consequence of the ac- 

 tivities of herbivores and carnivores. The 

 chief groups of herbivores and carnivores 

 were enumerated in the discussion of 

 stratification (pp. 441-494). There remains 

 the integration of these several bodies of 

 data into the catabolism of the whole com- 

 munity. 



In the present state of our ignorance this 

 can be only partially and imperfectly 

 achieved by a discussion of (1) food 

 chains, (2) food webs, (3) pyramids of 

 numbers, and (4) biomasses. 



The food chain is both an artificial and 

 a convenient concept. In the true sense of 

 the term, a food chain almost never exists 

 in nature as a complete entity. It presup- 

 poses a linear series of species in which A 

 is fed upon by B, B by C, and so on to N, 

 with N having few, or no enemies, A-B-C- 

 N. One end of such a chain is composed 

 of predators, the other end of photosyn- 

 thetic and chemosynthetic plants, and the 

 intermediate species populations or links in 

 the chain are herbivores or carnivores, de- 

 pending on the complexity of the food 

 chain. 



If these taxonomic links of food chains 

 are grouped into energetic categories, we 

 have, following the terminology of Thiene- 

 mann (1926, 1926a), producers (organisms 

 that synthesize protoplasms from inorganic 

 compovmds by energy derived from photo- 

 synthesis) and consumers (organisms that 

 feed upon producers and resynthesize a 

 portion of the latter into different proto- 

 plasms). 



Lindeman (1942) used this terminology 

 to further factor the feeding interrelation- 

 ships into a series of more or less discrete 



