Monarch extinction / serendipity

[Martha V. Lutz & Charles T. Lutz]

Paul Cherubini wrote:

"Also, monarch migratory populations have recovered
very rapidly - in a matter of 4-5 months - following rare events of
catastrophic storm related mortality at the overwintering sites in both
California and Mexico."


For some reason this reminded me of the Epilogue of the movie "Schindler's
List," in which the fates of various characters are brought up to date.
The movie concludes by stating that there were fewer than 4000 Jews in
Poland at the time the movie was made, while there were 6000+ descendants
of the Jews Schindler saved.

I transferred that thought over to the Monarchs, and wondered:  by what
mechanisms do species (not just Monarchs--or Jews) repopulate from a
reduced population after some natural or perhaps unnatural catastrophe?

I am guessing that one big factor is a reduction in density-related
moartality factors.  Has anyone looked at that in Monarchs?  Clearly, not
every female Monarch produces X eggs (how many is typical of Monarchs?  My
Saturniids tend to lay 100-300+; I have heard 20-40 for Monarchs) and all
of them survive to become adults and reproduce in their turn.  Many eggs,
larvae, and pupae must perish and never contribute to the next generation.
Many factors surely contribute to this mortality.

Which of these factors are diminished in a reduced population, thereby
increasing individual fitness values of the survivors?  I'm betting on more
sites for appropriate oviposition and on reduced cannibalism as at least
two possible factors.  If females have more plants on which no other female
has yet laid eggs, they can scatter eggs more sparsely, and consequently
the eggs and young larvae are less likely to be eaten by their own
kind--something that apparantly is fairly common among Monarchs in crowded
conditions.

Any validity to this idea?  Any other ideas about density-dependent
mortality factors (contagious disease is an obvious one) that would be
diminished and thereby encourage rapid population recovery?

Just a few random thoughts on a cold Sunday morning in Iowa!  (Where my
teen son plans to destroy me over six miles later this morning . . . but
that's okay because I've already established my evolutionary fitness!)

In Stride,
Martha

P.S.  Typing this with no contact lenses in, so have fun with typos.  My
vision is 20/200 uncorrected!



 
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