RE: NANFA-L-- Diversity Indicies

Hoover, Jan J ERDC-EL-MS (Jan.J.Hoover at
Thu, 29 Sep 2005 16:05:08 -0500

A few comments on this recent thread:

Diversity measures:
If you are interested in calculating diversity, take a look at these books:
Magurran ,A.E. 1988. Ecological diversity and its measurement. Princeton
University Press, 179 pp.
Ludwig, J.A. and J.F. Reynolds. 1988. Statistical ecology. John Wiley and
Sons, 337 pp. [Comes with software - assuming your computer still reads 51/2
" floppies]
Both are excellent and compliment each other nicely. They explain clearly
how to calculate various measures, strengths and weaknesses of each.

Rarefaction (sometimes called rarefraction):
Good technique for expressing diversity in a readily understandable way
(number of species/number of individuals) but it will not work for small
samples. This is because species accumulate with increasing sub-sample size
at similar or indistinguishably rapid rates; this rate of accumulation slows
down at larger sub-sample sizes at different rates. Looking at it another
way - rarefaction curves (number of species for a given sub-sample size)
converge at smaller sub-sample sizes and diverge at larger sub-sample sizes.
You need fairly large sample sizes to detect meaningful differences in
Easy-to-use software for rarefaction analyses is available at:
Reads text files (simple lists of numbers). I have used this program in the
past and it works well.

Weighting species abundance based on tolerance (or sensitivity):
Multiplying the abundance of an animal with some index of its "sensitivity,"
and then summing the products is commonly done. This is what a number of
invertebrate-based biotic indices do (like the Hilsenhoff Index). Rare,
intolerant species (indicator organisms) are given comparable or even greater
value than more abundant, tolerant species (ubiquitous organisms). I have
never seen this done with fish, but it makes a lot of sense to me, and I do
not know why you could not do it.

- Jan Hoover
just back from a 4-hour meeting on IBI development
Vicksburg, MS
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