This module requires one or more columns of abundance data with taxa down the rows. The main purpose is to compare diversities in several samples.
The validity of comparing diversities across samples can be criticized because of arbitrary choice of diversity index. One sample may for example contain a larger number of taxa, while the other has a larger Shannon index. A number of diversity indices may be compared to make sure that the diversity ordering is robust. A formal way of doing this is to define a family of diversity indices, dependent upon a single continuous parameter (Tothmeresz 1995).
PAST uses the exponential of the so-called Renyi index, which depends upon a parameter α. For α=0, this function gives the total species number. α=1 (in the limit) gives an index proportional to the Shannon index, while α=2 gives an index which behaves like the Simpson index.
The program can plot several such diversity profiles together. If the profiles cross, the diversities are non-comparable. The bootstrapping option (giving a 95% confidence interval) is based on 2000 replicates.
Reference
Tothmeresz, B. 1995. Comparison of different methods for diversity ordering. Journal of Vegetation Science 6:283-290.