Hi Milton.
phytools has a function, ratebystate, that tests this hypothesis using
the admittedly ad hoc approach of correlating the squared contrasts &
the states at each node. To read more about this method you can see some
posts on my blog: http://blog.phytools.org/search?q=ratebystate.
Note that as this is an unpublished method it has not survived the
rigors of peer review and thus should be treated cautiously.
All the best, Liam
Liam J. Revell, Assistant Professor of Biology
University of Massachusetts Boston
web: http://faculty.umb.edu/liam.revell/
email: liam.rev...@umb.edu
blog: http://blog.phytools.org
On 4/24/2015 3:39 PM, Joe Felsenstein wrote:
Milton Tan asked:
I have a question that is perhaps esoteric, since it's on a method I don't see used
often. I am looking at the dynamics of body size evolution, and have come upon
ancestor-vs-change plots described in Alroy 2000 ("Understanding the dynamics of
evolutionary trends", Paleobiology). This is interesting because it will allow me to
see if rate of body size change depends on body size. I haven't seen this method widely
used, so for anyone unaware how this works: for each branch, you plot the ancestral state
vs. the amount/rate of change along the branch.
If the question were just whether the rate of change of the character
(body size) depended on its value, then another way would be to look
for a transformation of body size that made the instantaneous variance
of change constant. i.e., does change in log(size) or in
sqrt(size) have constant variance? There are parameterized
transformation such as y = (x^p - x^{-p})/(2p) or else y = ( x^p
- 1) / p + 1 for which you could estimate the parameter p by ML.
Joe
----
Joe Felsenstein j...@gs.washington.edu
Department of Genome Sciences and Department of Biology,
University of Washington, Box 355065, Seattle, WA 98195-5065 USA
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