Size of the overwintering monarch populations - published dat a.
rjparcelles at yahoo.com
Tue Oct 14 10:43:54 EDT 2003
--- Mark Walker <MWalker at gensym.com> wrote:
> John Shuey wrote:
> > The size of the returning fall migration is the end product of summer
> > weather, habitat, and luck in the US and Canada. Environmental trends in
> > the states and provinces control the number of monarchs that return to
> > Mexico. Remember that even monarchs are insects (yes - even monarchs) -
> > and
> > fluctuations of 1-2 (or more) orders of magnitude in population size
> > during
> > the breeding season SHOULD BE EXPECTED. So the difference between
> > overwintering populations covering 12 hectares versus 2 hectares has more
> > to
> > do with summer in northern North America than winter in the Mexican
> > highlands. Granted, the number of monarchs leaving the Mexican highlands
> > each spring influences the number returning each fall, but variable
> > reproductive success in the north would mask that initial influence in
> > most
> > years.
> > The critical measure of phenomenon extinction seems likely to be the
> > percent
> > survival of monarchs during the overwintering phase. So that if the
> > %-survival is decreasing over time (mortality is positively correlated
> > with
> > forest loss/thinning) - then you have would have a disturbing trend. (and
> > this is what Brower et al have been talking about in most of the
> > literature - not the absolute size of the population that returns to
> > Mexico,
> > but how much of those butterflies survive to head back north).
> I don't agree with this at all. By your own admission we're talking about
> indicators for extinction here, not the health of a particular overwintering
> site. Why would %mortality at one location be a better extinction warning
> indicator than the trending of overall health and population size of the
> overall returning migration? While it is agreed that a high mortality at a
> site where so many Monarchs are concentrated would indeed be an issue of
> concern, the proof of whether or not the insect can sustain such a blow
> would be determined by the overall effects on the following year's
> population. Even Brower and Taylor would agree with this, as they've cited
> this expected result as part of their annual predictions.
> In my view, until someone demonstrates a strong correlation between high
> mortality and a resulting depleted Monarch population, we cannot presume any
> cause and effect. In the meantime, I will continue to support Monarch
> overwintering site habitat protection and monitoring - because it is
> prudent. But I am yet to be convinced that freezing butterflies in Mexico
> necessarily equate to the extinction of this obviously robust butterfly.
> Mark Walker.
While I naturally would be displeased if the Monarch declined or went extinct,
the chances being slim for this "weedy" species; the factor that concerns me
the most is preservation of the winter habitat for the phenomenom it is.
Imagine seeing millions of such a colorful insect massed together! Logging
practices in Mexico are only surpased in ignorance in the US.
Ecotourism is a factor that can certainly aid the endemic people in the area.
Bob Parcelles, Jr
Pinellas Park, FL
Ecologist/Ethologist, RJP Associates
CEO, PROactive Ecology Solutions Group (PESG)
Institute of Ecological and Environmental Studies (IEES)
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