[R-sig-eco] Do I have to standardise my explanatory data before doing a RDA?

[Constanze Keye]

Dear list members,

I struggle over a few things whilst doing a RDA for the last couple of days. Could please somebody enlighten me?

  1.  Do I have to standardise my explanatory data before doing a RDA (function rda, vegan)?
  2.
I know that�s a normal procedure before RDA, but I found this post in the r-sig forum: https://stat.ethz.ch/pipermail/r-sig-ecology/2010-April/001196.html
Now, I'm not sure if I can/should skip standardisation before RDA using the vegan package, or if I did understand something wrong here?

2.  Why are all my species always clustered in the very middle of my RDA plot ? If I use function 'triplot.rda' from https://raw.githubusercontent.com/zdealveindy/anadat-r/master/scripts/NumEcolR2/triplot.rda.R , they are much more spaced around the plot and some of them seem to correlate well with my explanatory variables...

Sorry, if these questions are a bit basic, but I�m still trying to get my head around the whole subject of RDA.

Cheers,
Conny


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