Hi Renata.
I agree with Ted - you should be able to fit an ANCOVA model with
gls(y~x+ecomorph,...,correlation=corBrownian(phy=tree)), or something
like this, where ecomorph is a factor.
Alternatively, you could use the method we devised in Revell & Collar
(2009; Evolution) in which we first reconstructed the discrete character
on the tree (in your case, this would be ecomorph), and then we fit a
model in which different covariance structure between our variables was
permitted on different branches of the tree. This method is also
implemented in my phytools package (function: evol.vcv).
All the best, Liam
--
Liam J. Revell
University of Massachusetts Boston
web: http://faculty.umb.edu/liam.revell/
email: liam.rev...@umb.edu
blog: http://phytools.blogspot.com
On 12/14/2011 3:26 PM, Theodore Garland Jr wrote:
Why not just include an interaction term between your main effect coding
variable (presumably coded as 0, 1 to indicate your two ecomorphs) and one or
more of your continuous independent variables?
Cheers,
Ted
Theodore Garland, Jr.
Professor
Department of Biology
University of California, Riverside
Riverside, CA 92521
Office Phone: (951) 827-3524
Home Phone: (951) 328-0820
Facsimile: (951) 827-4286 = Dept. office (not confidential)
Email: tgarl...@ucr.edu
http://www.biology.ucr.edu/people/faculty/Garland.html
Experimental Evolution: Concepts, Methods, and Applications of Selection
Experiments
Edited by Theodore Garland, Jr. and Michael R. Rose
http://www.ucpress.edu/book.php?isbn=9780520261808
(PDFs of chapters are available from me or from the individual authors)
________________________________________
From: r-sig-phylo-boun...@r-project.org [r-sig-phylo-boun...@r-project.org] on
behalf of Matt Pennell [mwpenn...@gmail.com]
Sent: Wednesday, December 14, 2011 12:17 PM
To: Renata Brandt
Cc: r-sig-phylo@r-project.org
Subject: Re: [R-sig-phylo] split data set and topology on PGLS
Hi Renata,
This seems to be an appropriate approach. (I am sure someone will correct
me if i am wrong in this). Phylogenetic regression in the way that you are
using it is basically to remove the statistical non-independence between
data points. Effectively what you are doing by splitting your data into two
morphologies is pruning your tree. Under Brownian motion, evolution along
any branch is independent of evolution along any other branch, so pruning
your tree will not change the correlation struction of the data.
(Similarily you can still do PGLS with incomplete sampling of species). So
as long as you can justify splitting the data up as you are, it seems fine.
cheers,
matt
On Wed, Dec 14, 2011 at 12:09 PM, Renata Brandt<renata.bra...@gmail.com>wrote:
Hello everybody.
I have some questions for you.
When performing a phylogenetic regression between two continuous traits,
the dependent trait clearly divides my data set in two distinct
morphologies. This division overlaps with what I previously thought were
two different ecomorphs. The relationship between the same traits seems to
be different for each morphology.
Now my question is:
- Is it ok to split the data set (one data table and topology for each
ecomorph) and reanalyze data to get the relationship between traits for
each group? (That is what I would do if not using a phylogenetic approach).
- If this is wrong, any hints on how should I proceed?
Many thanks. Cheers.
--
Renata Brandt
Departamento de Biologia - FFCLRP
Universidade de São Paulo
Brasil
(16) 82039533
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