[R-sig-eco] calculate "dispersion index" (betadisper, vegan)

[Eduard Szöcs]

Dear Natalie,

it should be possible to use the betadisper-result to do this.
However, a possibly faster way would be to calculate the area of the
hull directly.

Here's an example:

require(vegan)
data(dune)
data(dune.env)
MDS <- cmdscale(vegdist(dune, method = 'bray'))
plot(MDS, type = 'n')
points(MDS, col = dune.env$Management, pch = 16)


# area only for hull of NM
take <- MDS[dune.env$Management == 'NM', ]
hull <- chull(take)
lines(take[c(hull, hull[1]), ])
require(splancs)
areapl(take[c(hull, hull[1]), ])


HTH,

Eduard

On 29/07/15 19:26, Natalie wrote:
> hi all
> 
> I would like to  calculate a dispersion index or similar from the
> results of the vegan function betadisper.
> i would like to know if there is a possibility to e.g. calculate the
> volume of the community dispersion(area of the hull in the PCoA) from
> the betadisper results.
> common is to show the distance to the centroid.but I have the impression
> the dispersion within communities are not that clear,especially if you
> have similar variance.
> The program primer v5 calculates a disperion index based on  the
> similarity percentage.
> similarity percentage is not an option since it is mainly based on most
> counted species.
> 
> ideas and help are very much appreciated
> cheers natalie
> 
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-- 
Eduard Szöcs
Quantitative Landscape Ecology
Institute for Environmental Sciences
University Koblenz-Landau
Tel. +49 6341 280 31552
http://www.uni-koblenz-landau.de/en/campus-landau/faculty7/environmental-sciences/landscape-ecology/Staff/eduardszoecs