A series of corollary measures derived from the Shannoi ' were also 

 applied: 



DMAX = log (s) 



DMIN = log (N) - / n - s + A log (N - s + 1) 



on - D^AX - D 

 *^^ ~ DMAX - DMIN 



EV = D/DMAX 



where s = number of taxa in the sample, N^ = number of individuals in 



taxon i, and N = total number of individuals counted. DMAX and DMIN are 



theoretical maximum and minimum diversities. RD or redundancy is an 



expression of dominance by one or more species and is inversely proportional 



to the wealth of species. (A value of zero is obtained if each individual 



belongs to a different species and a value of one is obtained if all 



individuals belong to the same species.) EV or evenness measures the 



equality of species abundances in a sample; the greater the disparities 



among species abundances, the smaller will be the evenness. 



Another derived measure is Lloyd and Ghelardi's "equitability" (6), 



9 



S 



e = 



s 



where s' is the number of taxa required to produce the observed Shannon 

 index (D) if the taxa are distributed according to MacArthur's "broken 

 stick" model (8). Equitability is more sensitive to pollution than is 

 D; even slight levels of degradation have been found to reduce equitability 

 below 0.5 and generally to a range of 0.0 to 0.3 (4). 



