[R] partial mantel tests "Ecodist"

ddepew at sciborg.uwaterloo.ca ddepew at sciborg.uwaterloo.ca
Fri May 8 16:27:03 CEST 2009

Hi all,
I'm searching for a little clarification on partial mantel tests  
(ecodist package)

I've a distance matrix (x,y), and several others containing  
environmental/chemical variables.
Based on the help file, and the package instructions I've managed to  
implement the tests as;

var1 ~ env1 + space

to partial out the effect of space and test the relationship between  
the variable of interest vs variable env1.

My questions are as follows;

1) can "raw" data be used to construct the dissimilarity matricies? or  
should they be standardized? different variables have different  
measurment scales, my inclination is to standardize, but I don't know  
if this will dampen relationships between variables.

2) If env1 and another variable are correlated, is the appropriate test
         var1 ~ env1 + env2 + space?,
  var1 ~ env1 + space and then var1 ~ env2 + space?

3) interpretation... Does the value of "r" (i.e. + or -) imply spatial  
overlap (+) or spatial exclusion (-)?

Any assistance would be greatly appreciated!


David Depew
PhD Candidate
Department of Biology
University of Waterloo
200 University Ave W
Waterloo, Ontario, Canada
N2L 3G1

T:(1)-519-888-4567 x 33895

ddepew at scimail.uwaterloo.ca

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