[R-sig-eco] envfit and adonis restricted permutations

[Gavin Simpson]

On Tue, 2011-06-28 at 16:27 -0700, Steve Leonard wrote:
> Thanks Gavin, that is really helpful.
> 
> I'm still a bit uncertain re your parting words:
> 
> "These results, at first blush, would suggests to me that easting
> and northing effects are in the parts of the dissimilarity matrix not
> represented well by the 3-d nMDS solution."
> 
> If this was the case, wouldn't easting and northing have low r2 values in
> envfit results?

The restricted permutation test is telling you that there is nothing
special about the r2 values for those covariates in the envfit case.

That was speculation; as I said, the two techniques are testing very
different things so it is difficult to make definitive statements.
Remember in nMDS all you are doing is getting a low dimensional mapping
that best fits the *rank* ordering of the dissimilarities between you
samples. adonis is able to work with the actual dissimilarities. In
terms of the rank ordering mapping, easting and northing do not appear
to be important, yet they are able to "explain" significant amounts of
the "variance" in the actual dissimilarities.

G

> 
> Steve
> 
> 
> 
> 
> 
> -----
> Dr Steve Leonard
> Research Fellow
> Department of Zoology| La Trobe University | Bundoora, 3086 Australia
> T: +61 3 9479 2773 | M: +61 429 418 388 | F: +61 3 9479 1551 | W: www.latrobe.edu.au/zoology/
> 
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