Patrick: Structure of Diatom Communities 



363 



of genera such as Pinnularia, Adinella, Anomoeoneis and Surirella. Thus, we 

 have a community composed of fewer species with populations that are much 

 more variable in size (figure 2). The truncated normal curve representing 

 the structure of the community has a much lower mode, fewer observed spe- 



40 

 35 



<" 30 



UJ 



in 



^ 20 



o 



a 15 

 m 

 2 10 



o 



INDIVIDUALS 

 INTERVALS 



1-2 2-4 4-8 8-16 16-32 32-64 64" 128- 256" 512" 1024- 2048-4096" 8192-16384-32768- 



128 256 512 1024 2048 4096 B 1 92 16384 32768 65536 



= 1 



10 II 



12 



13 14 15 16 



Figure 2. Egg Harbor River, N.J. 



40 

 35 



<^ 30 



UJ 



o 



Q. 25 

 "- 20 



o 



Q: I 5 



UJ 

 CQ 



2 10 



INDIVIDUALS = 1-2 2-4 4-8 8-16 16-32 32-64 64" 128" 256- 512" 1024- 2048-4096" 8192-16384-32768- 

 iinuiviuuml;^ l^g 255 512 1024 2048 4096 8192 16384 32768 65536 



INTERVALS =0 



10 II 12 13 14 



15 



Figure 3. Back River, Maryland 



cies, a much greater a^, which means more variability in the sizes of the diatom 

 populations, and covers more intervals, because a few species have very large 

 populations. 



This is the type of curve often found for the structure of diatom populations 

 which are subjected to pollution (figure 3). In both cases one or more eco- 



