COMMUNITY ORGANIZATION: METABOLISM 



509 



trophic levels: Ai, A2; A3 . • . An corre- 

 sponding to (p. 415) "producers, primary 

 consumers, secondary consumers, etc., each 

 successively dependent upon the preceding 

 level as a source of energy with the pro- 

 ducers (Ai), directly dependent upon the 

 rate of incident solar radiation as a source 

 of energy." 



This is a logical extension of the realiza- 

 tion of the vital importance of radiant 



trophic level series, the less probable will 

 be its sole dependence upon the preceding 

 trophic level as a source of energy. 



Second, there is a progressive increase 

 in the percentage loss of energy, as a con- 

 sequence of respiration, from lower to 

 higher trophic levels. For example, Linde- 

 man found that respiration energy loss with 

 respect to growth was about 33 per cent 

 for producers, 62 per cent for primary 



SOLAR RADIATION 



SOLAR RADIATION 



Fig. 167. Consumers are progressively more eflBcient in the use of their food supply in higher 

 trophic levels. (Modified after Lindeman. ) 



energy summed up by BayUss (1924, p. 

 548): "The whole existence of Uving or- 

 ganisms on the earth depends on the re- 

 ceipt of radiant energy from the sun ..." 

 This general conclusion has been applied to 

 many aspects of the community (Park, 

 1931) and was discussed previously with 

 respect to the photosynthetic key industry. 



Lindeman's development of trophic 

 levels is applicable to communities in gen- 

 eral, but was derived from his intensive 

 study of Cedar Bog Lake, Minnesota 

 (1941, 1941a), and by his reworking of 

 other limnological studies by several au- 

 thors (1942). Three of his conclusions bear 

 upon the immediate subject. 



First, the further removed an organism 

 is from the initial source of energy in the 



consumers, and close to 100 per cent for 

 secondary consumers. 



Third, consumers appear to be progres- 

 sively more efficient in the use of their food 

 supply as higher trophic levels are exam- 

 ined. This at first appears to be at var- 

 iance with the preceding generalization, 

 until it is remembered that an increased 

 activity of predators may increase their 

 chance of finding prey, as suggested by 

 Figure 167. 



We may consider a community as hav- 

 ing four or five trophic levels, each level 

 containing a variable number of species, 

 and each species containing a variable 

 number of individuals. In the formulation 

 of the concept that follows, the symbol 

 A represents a trophic level, S is a species 



