David Bapst wrote --
> Let's say that there exists a worker who is measuring several different
> traits across a number of species and then testing for correlations among
> these traits. The first test is body size versus growth rate and they use
> independent contrasts or PGLS to test for a the correlation, accounting for
> phylogeny. Both of these traits are inherited, evolving variables. Now
> let's say they'd like to test for the relationship between growth rate and
> some metric of the anthropogenic degradation of that species' habitat. Now
> what? It is even valid to apply PIC to the habitat degradation metric even
> though it is not an inherited, evolving trait? It's unclear to me.
...
> One explanation I know of is that when we apply phylogenetic comparative
> methods to these quasi-traits to consider their relationship to another
> trait, we are assuming that these variables are actually the result of some
> underlying, unobserved set of traits which are evolving along the
> phylogeny.
I don't have an easy answer to this: it is a serious issue. One is assuming
that the environmental variable is evolving along the phylogeny according to a
Browian motion process. This may well not be a reasonable assumption.
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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