470 Dynamics of the Ecosystem 



hiomass, of the members of the food cliain present at any one time 

 also form a second type of pyramid. In a land biotope the biomass of 

 the vegetation existing at the moment of observation is commonly the 

 greatest, and the biomasses of herbivores, carnivores, and further 

 links in the food chain are progressively smaller. Thus a pyramid of 

 biomasses results, but this pyramid is an indirect consequence of the 

 particular kinds of organisms present, in contrast to the production 

 pyramid which is a dynamic necessity in the operation of the eco- 

 system. In some aquatic biotopes the biomasses of some of the in- 

 habitants form a pyramid similar to the production pyramid, as in 

 Weber Lake, Wisconsin (Fig. 13.2), and on Georges Bank (Fig. 

 13.12), but in others the biomasses of fish and particularly of the 



Fig. 13.2. Pyramid of biomasses as illustrated by the weight relationships of the 

 various constituents of Weber Lake, Wisconsin. ( Juday, 1943.) 



bottom fauna are considerably greater than those of shorter-lived 

 components at lower trophic levels (Harvey, 1950, Table IV). The 

 operation of the ecosystem thus limits the relative amounts of the 

 components that may be produced, but departures from a regular 

 reduction in the biomasses of components present at any one time 

 occur because of special circumstances. 



Interdependencies within the ecosystem also exert a certain influ- 

 ence on the size of the individual organisms involved. The essential 

 plant producers vary in size from the very largest organisms in some 

 types of community to the smallest in others. The primary producers 

 in different biocenoses range from giant trees, such as the redwoods. 



