522 



THE COMMUNITY 



stricted usually to trophic levels (Tables 

 44, 45, 46) in terms of glucose produced 

 or energy values for many difiFerent species, 

 each with its specific potentiality. Such 

 wholly understandable lumping of meshes 

 in the food web may hide important aca- 

 demic or practical principles. 



Mathematical treatment of energy bud- 

 gets (Juday, 1940) and efficiencies at var- 

 ious community levels (Krogh, 1934; 

 Riley, 1941, 1941a, 1944) are signs of 

 progress in the field of ecological theory. 



respect to either individuals or species, this 

 fundamental relationship between size and 

 numbers exists for the overwhelming ma- 

 jority of plants and animals. 



Many organisms are prolific. There are 

 many more seeds, spores, and eggs pro- 

 duced than germinate or hatch (pp. 236- 

 243). Furthermore, to attain sexual ma- 

 turity, the hazards of the inanimate and 

 animate portions of the community environ- 

 ment must be evaded. This tends to aug- 

 ment greatly the numbers of organisms of 



Fig. 172. Pyramid of numbers of the metazoan fauna of the forest floor stratum of Carle 

 Woods, Cook County, Illinois. (From Park, Allee, and Shelf ord.) 



Clarke, Edmondson, and Ricker (1946) 

 have provided a mathematical formulation 

 of biological productivity that may be de- 

 veloped for particular species populations. 

 When adult organisms of a community 

 are counted and measured, or even when 

 a representative sample of the community 

 is so studied, it is found that, in general, 

 the numbers of individuals present are in- 

 versely proportional to their body sizes. 

 Since each species population tends to 

 fluctuate about a mean body size, this 

 quantitative survey also demonstrates that 

 there is a progressive increase in body size 

 with a progressive decrease in population 

 size of the species present. Consequently, 

 whether the community is examined with 



small size and to decrease the numbers of 

 the relatively larger organisms. 



The differential in maturing of develop- 

 mental life history stages, as well as sea- 

 sonal and day-night intercommunity and 

 interstratal movements, tends to compHcate 

 this simple picture with respect to the ani- 

 mals present. Periodic movements are dis- 

 cussed in the next chapter. 



Such tendencies provide the background 

 for one of the more striking concepts in 

 community ecology, namely, the pyramid 

 of numbers. This is not a new concept. It 

 can be inferred from the 1887 essay of 

 Forbes and was given definite form by El 

 ton (1927, p. 69). 



When put in a graph, with size groups 



