[R-sig-eco] adonis and temporal changes

[Pierre THIRIET]

Dear Valérie,

If I remember well, your design includes:
Isolation categories: 3 levels
Sites: nested within Isolation categories (10 levels, a total of 30 sites)
How many replicates per site and time?
Time:? how many years you have? Only one sampling per year? Within sites 
and years, samples were random or it is always exactly the same area you 
sample (e.g. permanent quadrats)?

for adonis, consider that strata is for constraining permutations, which 
is different than terms in the formulae.

Chears,
Pierre

Le 18/02/2013 11:17, v_coudrain at voila.fr a écrit :
> Dear all,
> I would like to test changes in species dissimilarity matrices over time, taking into account that the measurement are repeated in each site over years. I used the
> adonis function: adonis(diss.matrix~year, strata=site). However if I do the same model entering site as an additional fixed effect (this was applied this way in a
> paperI read): adonis(diss.matrix~site+year, strata=site), I get exactly the same estimate for year, but the variance explained is much higher. I am a bit lost regarding
> how much of the variance in dissimilarity is really explained by temporal changes.
> Thank you very much
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