--Bruce Stallsmith
along the Tennessee
Huntsville, AL, US of A
>From: "Hoover, Jan J ERDC-EL-MS" <Jan.J.Hoover at erdc.usace.army.mil>
>Reply-To: nanfa-l at nanfa.org
>To: <nanfa-l at nanfa.org>
>Subject: RE: NANFA-L-- Diversity Indicies
>Date: 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
>diversity.
>Easy-to-use software for rarefaction analyses is available at:
>http://www.uga.edu/~strata/software/Software.html
>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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