Patrick: Structure of Diatom Communities 



361 



cent chancL- of not shifting their position in the curve (Preston, 1948) and, 

 therefore, will remain a part of the community. 



However, if the kinds of species in similar sections of various rivers are ex- 

 amined, a great variation as to the kinds of species is seen as described by 

 Patrick (1961). Also, in studies of the same area of the Savannah River at 

 about the same season (late August, early September) of the year in different 

 years, only 34 per cent of the species were common to both studies. A sim- 

 ilar, but not as great, variation is seen when two different areas in the same 



Table 2 



Savannah River 



Summary of Catherwood Diatometer Readings at Station 1 



October 1953 to January 1958 



Date 



Specimen number 

 in modal interval 



Oct. 1953 



Jan. 1954 

 Apr. 1954 

 July 1954 

 Oct. 1954 



Jan. 1955 

 .\l)r. 1955 

 July 1955 

 Oct. 1955 



Jan. 1956 

 .Vpr. 1956 

 July 1956 

 Oct. 1956 



Jan. 1957 

 .\pr. 1957 

 July 1957 

 "Oct. 1957 



Jan. 1958 



(Apr. 1954-1958 averages) 



4-8 

 2-4 

 2-4 



4-8 



4-8 

 2-4 

 2-4 

 2-4 



2-4 

 4-8 

 2-4 

 2-4 



2-4 

 2 4 

 4-8 

 2-4 



2-4 



Species in mode 



22 



19 

 24 

 23 

 21 



19 



25 

 20 



27 



30 



35 

 24 

 23 



29 



21 

 29 



25 



27 

 24 



Species observed 



150 



151 

 169 



153 

 142 



132 

 165 

 132 

 171 



185 

 215 

 147 

 149 



177 

 132 

 181 



157 



152 

 151 



Species in theo- 

 retical universe 



178 



181 

 200 

 193 

 168 



166 

 221 



180 

 253 



229 

 252 

 185 

 206 



233 

 185 

 203 

 232 



212 



194 



Table 3 

 Dominant Species in Two Areas, Guadalupe River 



