6-7 



H' = Z p. log p. 

 i=l 



where: p. = proportion of the i species in the sample. The Brillouin 

 index is calculated as: 



.. 1 -, N! 



log 



N ^ n ' n^! . . . n ! 

 12 s 



where : N = total individuals 

 S = number of species 

 n. = number of individuals for the i species. 



These two diversity indices have been used somewhat inter- 

 changeably by ecologists and the decision as to which is appropriate 

 is based upon theoretical considerations best siammarized by Pielou 

 (1966, 1975). It is convenient to consider H (Brillouin) as repre- 

 senting the diversity present in the sample itself and H' (Shannon- 

 Weaver) to be an estimator of the diversity in the population from which 

 the sample is drawn. In practice, the choice of an index is not of 

 prime importance because both are highly correlated (r = 0.9725 for a 

 random sample of data from the present study) . 



J', or evenness, is a measure of how equally the various 

 component species are represented in the population in terms of their 

 numerical density, and is calculated from: 



J = 



log 



s 



where: s = number of species. 



H' is the highest value that H' can assxame given a certain 

 max 



number of species. This occurs when the J' value is at a maximum, which 

 is when all species are represented equally. H' is calculated by: 



1 -, 1 

 H = - — r— log — — - = log 



max S ^ S ^s 



