Hedi,

When you use adonis you are testing if the communities differ between
treatments and time. Adonis tests if the position of the centroids differ
among the treatments. Betadisper tests if the communities differ in their
variance. For example, if the communities found in land1 is not different
from communities found in land2 (i.e. the position of the centroids do not
differ in adonis), they can differ in betadisper if the communities found in
land 1 are more variable than communities found in land 2 (i.e. the
distances to centroid of communities from land 1 are smaller, or bigger,
than distances of communities from land2). This can be interpreted as a
measure of beta diversity.

victor



On Thu, Jul 28, 2011 at 3:05 PM, Hedi <hedikebli@gmail.com> wrote:

> Hi,
>
> I have some trouble with interpretation of R functions: adonis and
> betadisper. I am interesting in understanding if the communities differ
> according to land use treatment (3 treatments) and time (6,12,18,24 and 30
> months). I know that adonis works on the centroids for the groupings and
> betadisper on variance, the spread of the observations about the grouping
> means/centroids. The problem is both "betadisper" and "adonis" say that the
> factor "time" is significant. So can I say that my communities are still
> different according to time?
> Actually what is the biological interpretation of the centroid of a
> community and the dispersion of a community?
>
> Thanks
>
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>



-- 
victor
_______________________________

Victor Lemes Landeiro
www.inpa.gov.br
http://ppbio.inpa.gov.br
http://ppbio.inpa.gov.br/Port/public/disciplinas
fones
(62)85764316(Oi); (62)81702517(Tim)

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