Hello all,
I have some questions about the drift model implemented in geiger to test for a
trend in increasing or decreasing trait values over time. I'm curious how to
interpret the drift parameter, as well as whether BM is nested within BM. Is
there a citation I can read for more information? I haven't seen the parameters
of the drift model described anywhere explicitly, though perhaps I have missed
it. It seems similar to the test for a directional pressure implemented in
Pagel 1997, but I don't see any mention of the drift parameter.
Additionally, I'm curious if there's a good way to incorporate a drift model
into ancestral state reconstruction? I imagine I can transform the branch
lengths based on the drift parameter somehow and simply reconstruct ancestral
trait states under BM, but I'm unsure how to do the branch length
transformation for a drift model given that I'm not entirely sure what the
drift parameter represents.
Thanks all,
Milton Tan
Auburn University
Department of Biological Sciences
PhD Candidate
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