Dear all,

 

I'm performing RDA on plant presence/absence data, constrained by
geographical locations. I'd like to constrain the RDA by the "extended
matrix of geographical coordinates" -ie the matrix of geographical
coordinates completed by adding all terms of a cubic trend surface
regression- . 

This is the command I use (package vegan):

 

>rda(Helling ~ x+y+x*y+x^2+y^2+x*y^2+y*x^2+x^3+y^3) 

 

where Helling is the matrix of Hellinger-transformed presence/absence data

The result returned by R is exactly the same as the one given by:

 

>anova(rda(Helling ~ x+y)

 

Ie the quadratic and cubic terms are not taken into account

 

I hope you can help me with that: "how can I perform a RDA on an extended
matrix of geographical coordinates in R?".

 

Thank you very much in advance,

 

Helene Morlon

University of California, Merced

morlon.helene@gmail.com

 


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