the mystery of Vanessa unidirectional migration

[Ron Gatrelle]

For this type of "migration" I still like the term dispersal. The NA
monarch, to me, is a classic example of true migration. A journey in mass
to select area, and return. Dispersal is an evolutionary event all its
own - which is why it works so well. In fact, in the long run, because of
its flexibility, it seems much more conducive to species survival than
classic migration. I would think that dispersal, evolutionarily, must
always be a phase that precedes the development true migration.  And that
highly structured migration could be called over evolved dispersal - for it
has lost flexibility?

Let me put it this way. Migration is an element of mass dispersal in a more
flexible manner. Pure x to y to x migration seems so locked into a pattern
that, by its precise structure, it makes the organism too vulnerable to a
cataclysmic event. (Wouldn't the fight to maintain the Monarch's Mexican
overwintering area support this? The message is that if this tiny spot on
the earth is lost so is the species. If this area is not "saved" the NA
Monarch will become extinct. If the Monarch will not become extinct, then
all that is being done is an effort to preserve an evolutionary phenomenon
and not a species.)  In dispersal no one spot, or region is essential. The
chaotic or random elements of dispersal are its safeguard. A shotgun effect
that costs the life of many individuals but insures that the organism will
always "hit a (not the) target". In reading these posts I have been waiting
for the word dispersal to come up and Liz has done so.

So, for me, I would say the spring mass dispersals of   x  is taking place
in a migratory fashon.  I  would say that Monarch's  migrate using a
dispersal pattern of such and such. (My right brain just thinks these
events are pretty neat and like to see and hear about them.)

Other comments and thoughts?

Ron

----- Original Message -----
From: "Liz Day" <beebuzz at kiva.net>
To: <leps-l at lists.yale.edu>
Sent: Monday, April 30, 2001 9:57 PM
Subject: the mystery of Vanessa unidirectional migration


> I don't understand what advantage this bug gains by migating north every
> spring, if the adults don't then migrate back south in the fall, and (?)
> thus their offspring are instead killed off by winter.  Isn't this
genetic
> suicide?   I understand dispersion is good, but it seems like consistent
> directional dispersion in a direction that is ultimately death would be
> selected against, eventually.   What is going on?  I must not be seeing
the
> whole picture.
>
> Thanks,
>
> -------------------------------------------------------------
> Liz Day
> Indianapolis, Indiana, central USA  (40 N, ~86 W)
> USDA zone 5b.  Winters ~20F, summers ~85F.  Formerly temperate deciduous
> forest.
> daylight at kiva.net
> www.kiva.net/~daylight
> -------------------------------------------------------------
> "It is quite remarkable, when you think of it, that if you tell somebody
to
> buy something and dump it on or squirt it on, he will almost certainly do
> it, after a fashion. But if you suggest that he observe something or
think
> about something or learn about something, he almost certainly will
> not. Yet those gardens we admire are never the results of dumping and
> squirting: they are always the result of muddling things about in the
brain
> and the eye."
> -- from _The Essential Earthman_, by the late Henry Mitchell
>
>
>
>
>  ------------------------------------------------------------
>
>    For subscription and related information about LEPS-L visit:
>
>    http://www.peabody.yale.edu/other/lepsl
>
>


 
 ------------------------------------------------------------ 

   For subscription and related information about LEPS-L visit:

   http://www.peabody.yale.edu/other/lepsl