[R-sig-eco] Re: ANOSIM in vegan

[Michael Gerisch]

Hi Soumi,

it just came into my mind - no idea if i am wrong: For me it sounds like your 
sampling design is not independent, as you sample 400 plots twice and you will 
have high probability that the community of a pair of similar sites is more 
equal just because it is the same site and not because of some environmental 
factors. Call it pseudoreplication or else, but i think large part of the 
"similarity" will be due to this fact. Unless you have something like an 
extreme event between the dates which sort of "reset" your communites...maybe 
then its appropriate.

But i don`t know if anosim has the assumption of independence anyway. Maybe 
there is "reanypeated measure" variant? Or maybe i am  totally wrong...

Sorry, did not want to confuse, but it would also be interesting for me.

cheers
michael

  

On Friday 12 November 2010 01:23:41 Soumi Ray wrote:
> Hi,
> 
> I have a dataset consisting of species collected from the same location
> during 2 time periods - i want to see if the community composition is
> similar during the two time periods. My entire dataset is presence/absence
> (0/1) data. There are around 23 species and 400 samples (during each time
> period, so a total of 800 samples). Will ANOSIM from the vegan package be
> an right test to apply? I was going through some papers online where they
> have used methods like db-RDA in similar situations. Would it be right to
> use it for qualitative data? Any suggestion would be of great help.
> 
> Thanks,
> 
> Soumi
> 
> 	[[alternative HTML version deleted]]
> 
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