In population genetics, 'migration'
is movement among populations, rather than
periodic movement of individuals between one place and
another.
(A) The Mainland / Island
Model assumes that offshore islands receive
unidirectional migration from the Mainland. (B) The Island
Model assumes that a species is divided into
multiple sub-populations, each of which is connected to all
of the others (this resembles an island archipelago).
(C) The alternative Stepping-Stone Model assumes
that sub-populations are connected only to adjacent
sub-populations, in a nearest-neighbor grid. (D) A
River or Path Model assumes
that each sub-population is connected only to those on
either side of it, in linear sequence. (E) A more complex
model may use different allele frequencies q and
different migration rates m to achieve more
complex results.
The models are drawn so as to suggest land
islands surrounded by water. They are
however equally applicable to ponds / lakes connected
by watercourses. Model D in is readily
adapted to a riverine model with unidirectional
migration due to downstream flow.