Re: [R] indicator value in labdsv

From: Jari Oksanen <jarioksa_at_sun3.oulu.fi>
Date: Mon 19 Sep 2005 - 21:09:11 EST

On Mon, 2005-09-19 at 09:41 +0200, astrzelczak@ps.pl wrote:
>
> Hi,
>
> I'm trying to find out what threshold of indicator value in labadsv should be
> used to accept a specie as an indicator one? So far I assumed that indval=0.5
> is high enough to avoid any mistakes but it was based only in my intuition.
>
> I'd be greatful for any advise
>
> best regards
>

Agnieszka,

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Then about indicator value analysis. You should be more specific: there seem to be three alternatives functions for "indicator species" in labdsv. Which did you mean? At least two of these return an item called "indval", and these two alternative "indvals" are very different. For the Dufrêne-Legendre indvals, you should check the original paper (see references in the help page), and there you even have an associated "P value". In indspc, the variance of the indval clearly is dependent on species frequency. Moreover, in indspc the expected indval (and its variance) are dependent on the whole set of sites you have: these reflect the general "homogeneity" of your data set. Therefore you cannot say there that any certain value would mean that a species is a good indicator. However, it would be easy to work out standard errors for indspc indvals.

I think it would be more useful to post to some other mailing group where people are more concerned about indicator species, or to contact the package author directly (I CC this message to him).

cheers, jari oksanen

-- 
Jari Oksanen -- Dept Biology, Univ Oulu, 90014 Oulu, Finland
Ph. +358 8 5531526, cell +358 40 5136529, fax +358 8 5531061
email jari.oksanen_at_oulu.fi, homepage http://cc.oulu.fi/~jarioksa/

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Received on Wed Sep 21 02:03:40 2005

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