[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?,
or
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!
Thanks,
--
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
F:(1)-519-746-0614
ddepew at scimail.uwaterloo.ca
http://www.science.uwaterloo.ca/~ddepew
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