[R] indicator value in labdsv

Jari Oksanen jarioksa at sun3.oulu.fi
Mon Sep 19 13:09:11 CEST 2005

On Mon, 2005-09-19 at 09:41 +0200, astrzelczak at 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


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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 Dufrêne-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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