[R-sig-eco] bootstrapping diversity indices

[Kay Cecil Cichini]

hello all,

i want to know whether pooled invaded quadrats (n=6) show decreased  
diversity compared to pooled uninvaded quadrats (n=6) - or in other  
words, whether species are lacking from invaded quadrats.

to yield confidence limits i bootstrapped pooled absence/presence  
species data from 6 quadrats using inverse simpson diversity (the  
number of equally-common species required to give a particular value).  
i took the boot-samples from a vector where species identifiers were  
multiplied with nr. of occurences, and calculated simps.div. from the  
tabulated bootstrapped vectors 1000 times.

the boostrap estimates of diversity indices are known to be negatively biased.
i get bias of magnitude -4 to -9 which i use for the adjustment of the  
diversity estimates from the observed pooled values and wonder if i  
should be concerned about the magnitude of bias or not. histogramms of  
boot-samples look ok...

i also used simpson index with small sample corr. (with form:  
sum(x)*(sum(x)-1)/sum(x*(x-1))), where the bias is small but the  
estimates from the observed values tend to correct for high amounts  
(large difference to uncorrected estimates).

any pointers on how to deal with this would be greatly appreciated,
kay