Eqloff and Brakel (1973) calculated evenness for a population of aquatic 

 macroinvertebrates in a stream receiving large inputs of domestic sewage. 

 Above the outfall, evenness values ranged from 0.6 to 0.7 and diversity was 

 3.0 and greater; below the outfall, evenness dropped to 0.4 and below and 

 diversity decreased to less than one. The number of species and evenness 

 appeared to be inversely related along the stream except at the outfall, where 

 both decrease. 



The evenness index has not been widely used in aquatic studies. 



SPECIES RICHNESS (SR) 



A further component of diversity, richness, was calculated in the computer 

 proqram furnished by Orr et.al. (1973), but no reference to it could be found 

 in the literature. It was calculated as follows: 



SR = d - d/log 2 N 



Species richness is more commonly calculated by summing the total number 

 of species present in a sample. 



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