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.cb BIOLOGICAL ADVANTAGES OF TERRITORIALITY AND EMIGRATION

.CB John McCarthy, Stanford University


	It may sometimes be advantageous for a population to
put much of its efforts into finding new habitats at the expense
of fully populating its existing habitats.  For example, suppose
that frog ponds sometimes dry up and new frog ponds sometimes
form.  A frog population that feels crowded as soon as it has
reasonably populated a frog pond and expels its surplus population
to hop randomly across dry land is likely to quickly occupy
any new frog ponds that open up within hopping distance.  This is
advantageous for the population even though in most years no new
frog ponds arise and all the emigrants die when they have hopped
as far as possible.  More generally, any population should send emigrants
into nearby (in the general sense) ecological niches even
at the cost of losing them almost all the time.  While emigration
in space may exist as a specific evolved pattern of behavior, the
concept applies to trying new food sources and other behaviors.

	The object of this paper is give some mathematical
models that permit determining the
optimum fraction of a population's resources to be put into emigration.
Perhaps this will provide a teleological explanation of territoriality.
Perhaps we can regard regular bird migration as a development of
emigration behavior.

	A possible real example of this behavior is reported by xxx in
yyy.  It seems that mice confined to a field by fences reach stable population
levels several times those reached when young pregnant females are allowed
to emigrate.  Presumably they mostly emigrate to territory unsuitable for
mice or are prevented from surviving by predation or territoriality.  Otherwise,
immigrants would balance emigrants and the high population level would be
attained anyway.