Hi,
   There are three explantation matrixs(topography, soil and   PCNMs variation 
matrixs) and one response matrix.  And I want to know  the contribution of each 
explantation matrix to the response matrix  using the function of varpart which 
is contained in vegan package. But  there are  two questions as follows:
1) Should insignificant  variations of each explantation matrix be excluded 
prior to partitioning  using forward selection or other selection methods?

>>>>I did not get exactly what you mean when you say "insignificant variations", but 
>>>>if you mean that you have some variables within each matrix which are not 
>>>>significant, I suggested that for each matrix you used forward selection by 
>>>>"forward.sel" of R: Blanchet, F G, Legendre, P and Borcard, D (2008) Forward 
>>>>selection of explanatory variables. Ecology 89:2623-2632.

2) PCNM method could provide spectral decomposition of the spatial  
relationships among the sampling sites. The significant PCNM variations  could 
be divided into several submodels according to scales, however,  how can I 
achieve this process of dividing in R?
   Thanks for all  your attention!

>>>>As I know this dividing process of PCNM's to let's say Micro-,Meso- or 
>>>>Macro-scale that you asked is something arbitrary! So there is no R function for 
>>>>it. Have a look to these two papers:
Borcard, D, Legendre, P, Avois-Jacquet, C and Tuomisto, H (2004) Dissecting the 
spatial structure of ecological data at multiple scales. Ecology 85:1826-1832
Laliberté, E, Paquette, A, Legendre, P and Bouchard, A (2009) Assessing the 
scale-specific importance of niches and other spatial processes on beta 
diversity: a case study from a temperate forest. Oecologia 159:377-388.

Good luck,
Omid

Omid Paknia,
Institute of Experimental Ecology,
Albert-Einstein-Allee 11 
University of Ulm
D-89069 Ulm, 
Germany
http://www.uni-ulm.de/nawi/bio3/kalko/phdstud/paknia.html




________________________________
From: lgj200306 <lgj200306@163.com>
To: R-sig-ecology@r-project.org
Sent: Tue, July 13, 2010 4:45:39 AM
Subject: [R-sig-eco] Some questions about variation decomposition using function 
of varpart

Hi,
   There are three explantation matrixs(topography, soil and  PCNMs variation 
matrixs) and one response matrix.  And I want to know the contribution of each 
explantation matrix to the response matrix using the function of varpart which 
is contained in vegan package. But there are  two questions as follows:
    1) Should insignificant variations of each explantation matrix be excluded 
prior to partitioning using forward selection or other selection methods?
    2) PCNM method could provide spectral decomposition of the spatial 
relationships among the sampling sites. The significant PCNM variations could be 
divided into several submodels according to scales, however, how can I achieve 
this process of dividing in R?
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