Nested model and variance partitioning

hi, hi all,

Dear R users,
I face to a nested pattern and despite the numerous examples in the help I

am

still confused.
I sampled bugs in different habitats within sites which were within rivers
themselves within different regions.
The habitat correspond to different substrata (not systematically present

in

all sites). For rivers and sites, I have environemental variables (e.g.

altitude

and slope of the site, drainage area and geology of the river) and I have
only 2 regions. Note that sometimes I have only one site per river.
I would like to know the part of each spatial scale described by
environmental
data in the species richness variance. For instance is the drainage area

at

the river scale that explains a large amount of species richness variance

or
the

altitude of the site, or the substratum, etc.

The design of our data is complex. What is your outcome ?

I looked into the nlme package but I did not found how to proceed

The reference document about the package nlme is certainly ?Pinheiro J. C. &
Bates D. M.  (2000) Mixed-effects models in S and S-plus. Springer Verlag,
New
York. 528 pp.?

but there is many information about this subject on the WEB (see
http://www.google.fr/search?hl=fr&q=nlme&btnG=Recherche+Google&meta=)


Regards,

Pierre




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