COMMUNITY ORGANIZATION: METABOLISM 



521 



Community biomass is important. It is 

 closely associated with the productivity of 

 the community, with its biological effi- 

 ciency as compared \\'ith other communi- 

 ties of the same type, and as compared 

 with communities of different types. 



We have no complete biomass data for a 

 given community, and will not have until 

 the food web is known and the pyramid 

 worked out. We are especially in need of 



organic matter in four Wisconsin lakes 

 (Fig. 176). In this investigation it was 

 found that the plants in two hard-water 

 lakes weighed from three to five times as 

 much as the plants of two soft-water lakes, 

 and that the soft-water lakes had about 

 one-fourth as many species of large aquatic 

 plants as the hard-water communities. 



This is an interesting conclusion. It shows 

 again that the inanimate, physical part 



Fig. 176. Diagram of biomass and dissolved 

 The weight of each constituent is proportional 

 diagram was on a scale of 1 kilogram/hectare = 



a single, complete biomass. Not only (1) 

 is there a great deal of taxonomy involved 

 before the equation: bi + b2 + bi ■ • • + 

 b„= B is solved, but we are in need of in- 

 formation concerning (2) the several bio- 

 masses of the several life history stages of 

 each species, and (3) the biomasses of 

 parasites in relation to those of their hosts. 

 A sufficient body of such data can then be 

 used to great theoretical advantage. 



At present one of the best approaches to 

 community biomass is that of Juday 

 (1942), in which the weight of the sum- 

 mer standing crop of plants and animals 

 was estimated and related to the dissolved 



organic material in Weber Lake, Wisconsin, 

 to the total area of the triangle. The original 

 = 4.9 sq. mm. of graph paper. (From Juday.) 



of the community is a material influence 

 in regulating the biological part of the 

 community. This has been stressed in the 

 chapter on stratification. In the study by 

 Juday we see the striking effect of the 

 chemical composition of the medium upon 

 the biomass at the first trophic level. 



Excluding the fishes, the animal popula- 

 tion of the hard-water lakes weighed two to 

 three times that of the animal populations 

 of the soft-water lakes. This is to be ex- 

 pected, since the primary consumers would 

 be directly affected by the biomass of the 

 producers, and the secondary consumers ac- 



