Path: utzoo!attcan!uunet!shelby!apple!bionet!PUCC.PRINCETON.EDU!AEBAKER%CSUGREEN
From: AEBAKER%CSUGREEN@PUCC.PRINCETON.EDU (ann baker biology dept 303 491 5307)
Newsgroups: bionet.population-bio
Subject: geneflow:asymmetry,equilibrium
Message-ID: <9010210525.AA06820@genbank.bio.net>
Date: 21 Oct 90 04:19:39 GMT
Sender: daemon@genbank.bio.net
Lines: 30

Gene flow is likely to be asymmetric when there is a large difference
in population size between two source populations. The larger population
will donate more migrants than the small one usually, though exceptions
may exist where very small populations are unstable because they don't
have a "critical mass" to make the individuals socially cohesive. The
"critical mass" idea is from a very old paper by Gilbert and Singer
on Euphydryas butterflies (Am Natur 1960s I think). The asymmetry idea
is from simulations I do with Len Nunney on t haplotypes and on my
unpublished analyses of the rate of dispersal as a function of the
rate of population growth (house mice only).

Equilibrium seems to be what theoretical popgeneticists use as a
stopping point for their simulations. It removes the influence of
the initial starting conditions, but I have a problem with this:
in house mice living in barns or homes, the habitat is often changing
at the whim of the economics (price of corn, hay, eggs etc): the
barn is cleaned out, the chickens or corn are sold etc: often these
cleaning out periods occur every year (about 4 generations?) in house
mice (Petras and Topping 1979? JMamm for example). Can equilibrium
occur that quickly? No. Yet we run simulations for 200 generations
or so until the equilibrium is reached. I don't know a way around
this problem: the equilibrium is easily defined, the other stuff is
not, though the other stuff may be a more realistic reflection of
house mouse populations near human habitation.

ann eileen miller baker
biology department
colorado state university
fort collins 80523
aebaker@csugreen