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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