160 



ANALYSIS OF THE ENVIRONMENT 



Allee (1923, 1934) decided that the charac- 

 ter of the sea bottom was the single envi- 

 ronmental factor most closely associated 

 with community distribution. With the de- 

 tails still freshly in mind, he concluded 

 (1923, p. 246): "The character of the sea 

 bottom .... the most obvious, the long- 

 est used, is still the least treacherous single- 

 factor index of httoral distribution in this 

 region. It should be used with discretion 



(1922), for the bottom-dwelling fishes 

 near Tortugas, and MacGinitie (1939), 

 particularly for the coast of California, 

 also emphasized the importance of the 

 physical character of the bottom in ani- 

 mal distribution. On the other hand, 

 Shelf ord and his associates (1935), in dis- 

 cussing the distribution of some biotic com- 

 munities on the Pacific coast of North 

 America, concluded that "the general hy 



Fig. 31. Total population in thousands per square yard in relation to the type of substratum 

 in Lake Erie. ( Redrawn from Krecker and Lancaster. ) 



Fig. 32. Number of species of animals per square yard in relation to diflFerent kinds of sub- 

 strata. (Redrawn from Krecker and Lancaster.) 



since a rock well back on a (tidal) flat 

 supports a different set of animals from 

 one on an exposed point, but the correc- 

 tions are obvious and easily applied." The 

 small community on such a rock differs 

 decidedly from those on the surrounding 

 sand or mud. Among others, Petersen 

 (1913, 1915), for the bottom communi- 

 ties of the coast of Denmark, Longley 



drographic conditions (submarine climate) 

 are more important than land of bottom 

 materials in determining the character of 

 benthic communities." Controlling factors 

 may well differ in different situations. It is 

 probable, however, that if the "general hy- 

 drographic conditions" were broken down 

 into constituent parts, the character of the 

 bottom, the world over, would be found to 



