Ok, I did not have clear that Lambda is calculated over the residuals
values of the correlation...
Thank you very much for the links you sent me, they will be very useful
Cheers
Adrian
2013/8/8 Alejandro Gonzalez alejandro.gonza...@ebd.csic.es
Hola Adrián,
Here is my grain of sand. The lambda parameter you estimate gives you an
idea of the evolutionary co-variance between all the traits included in the
model, its the same interpretation as for the single trait, but in the case
of multiple traits it provides information on the evolutionary co-variance
as lambda estimates the phylogenetic signal of the residuals of the
regression. An important point to add is that it is the evolutionary
co-variance given the model of evolution, in this case Brownian motion,
which has its underlying assumptions. You can look at recent papers by
Tomas Hansen on this issue.
There is quite a bit of literature on the subject, I can venture to
recommend a few papers and maybe others in the list can add more:
Martins and Hansen 1997 Phylogenies and the comparative method: a general
approach to incorporating phylogenetic information into the analysis of
interspecific data. American Naturalist 149
Rholf 2006 A comment on phylogenetic correction. Evolution 60: 1509-1515
Revell 2010 Phylogenetic signal and linear regression on species data.
Methods in Ecology and Evolution 1: 319-329
Revell et al 2008 Phylogenetic signal, evolutionary process and rate.
Systematic Biology 57: 591-601
Freckleton et al 2002 Phylogenetic analysis and comparative data: a test
and review of evidence American Naturalist 160: 712-726
Freckleton 2009 Seven deadly sins of comparative analysis. J Evol Biol
22: 1367-1375
Cheers
Alejandro
On 8, Aug 2013, at 2:33 PM, Adrián Arellano Davín wrote:
Hi all,
First of all, I am very much a newbie in phylogenetics, so the question I
will ask may be a bit naïve. Here it is:
I want to correlate some phenotypic traits of several species of animals.
Let's say, body mass and brain size. To account for the non-independence of
the points, I must use PGLS. One way to do this is searching a lambda
parameter that maximises the likelihood of my tree under a Brownian Model
of evolution.
I think I can understand the meaning of having a lambda value for one
phenotypic trait. And I think it makes sense because it gives you a rough
idea of what kind of evolution is going on. But, what is the purpose of
calculating a lambda for several traits at the same time? Does it make
sense at all? Is it just a mathematical trick with no biological meaning?
Thanks in advance
Adri
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Alejandro Gonzalez Voyer
Post-doc
Estación Biológica de Doñana
Consejo Superior de Investigaciones Científicas (CSIC)
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Spain
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