Do Monarchs need Mexican forests?
patfoley at csus.edu
Fri Apr 19 16:14:51 EDT 2002
I also am dubious about Brower's figures, but I can't find out how he
calculated them except hearsay.
Does anyone have a pointer to a Brower paper which clears this up.
Jim Taylor wrote:
> Hate to horn in, Pat, but in my other life I was a statistician. Had Brower
> said, "about three-quarters" he would have been much more believable to me.
> The astonishingly precise 74% causes me to look askance at all his figures.
> Why not 74.2%?
> Jim Taylor
> ----- Original Message -----
> From: "Patrick Foley" <patfoley at csus.edu>
> To: <monarch at saber.net>
> Cc: "Leps-l" <Leps-l at lists.yale.edu>
> Sent: Friday, April 19, 2002 10:52 AM
> Subject: Re: Do Monarchs need Mexican forests?
> > My understanding (only from quotes in the popular press) is that Brower
> > made his mortality estimates after the those of Solis and others, and
> > thus obtained higher estimates. Brower also thinks the uncertainty
> > around Monarch overwintering estimates is enormous.
> > Again, I would like to see the scientific papers that show how these
> > estimates are made. I still have little idea how trustworthy any of the
> > estimates are. Any practicing population biologist would be wary about
> > an estimate without a standard error. And any scrupulous person would
> > want to know more before he attacked the honesty of others. The evidence
> > from the popular press is that Brower made his estimates using some kind
> > of standard (over several years) approach counting dead butterflies per
> > quadrat and comparing the dead to population size estimates. This does
> > not show that his estimates are right, but it does suggest that he is
> > not just dreaming them up to drum up hysteria in the press.
> > Brower may well be wrong about his mortality estimates. But the popular
> > press articles I have seen clearly show that he is uncertain about
> > Monarch numbers. Paul, are you certain about your numbers? Do you think
> > anecdotal evidence and carefully chosen photographs are an honest
> > improvement over Brower's scientific papers?
> > Patrick Foley
> > patfoley at csus.edu
> > Patrick
> > Paul Cherubini wrote:
> > > Patrick Foley wrote:
> > >
> > > > As a population biologist I am very interested in the statistical
> > > > techniques used to estimate Monarch overwintering mortality.
> > > > What techniques did Brower use to get 74% mortality. What
> > > > techniques did the others use to get 33-47% mortality? What
> > > > were the standard errors of these estimates? Did they refer to
> > > > the same locations at the same times?
> > >
> > > Yes, the two groups (American vs Mexican biologists) measured
> > > mortality at the same locations and the same times, but I don't
> > > know anything about the techniques they used.
> > >
> > > However we can review some basic monarch census data ALL
> > > the monarch authorities agree on.
> > >
> > > 1. In the winter of 2000-2001 the overwintering monarch
> > > population in Mexico was 28 million butterflies. In the spring of
> > > 2001 ALL monarch authorities agree the size of the migration
> > > that arrived in Texas from Mexico was very small. Mike Quinn
> > > described it as "barely perceptible" to a Fort Worth, Texas
> > > newspaper reporter.
> > >
> > > 2. Just 9-10 months later, in the winter of 2001-2002 the
> > > the overwintering monarch population in Mexico was 110 million
> > > butterflies - 3.93 times as large as the overwintering population
> > > in 2000-2001 (and about 40% above the long term average
> > > of about 76 million butterflies).
> > >
> > > Now if Lincoln Brower is right and 75% of these 110 million
> > > monarchs perished in the January freeze then only 27.5 million
> > > monarchs would have survived. And it would follow that the
> > > size of the spring migration that arrived in Texas this past
> > > March and April should be near the "barely perceptible" levels
> > > that were observed last year.
> > >
> > > Now if the Mexican biologists are right and only 30% of these
> > > 110 million monarchs perished in the January freeze then
> > > 77 million monarchs would have survived. And it would follow
> > > that the size of the spring migration that arrived in Texas
> > > this past March and April should be about 2.75 times as
> > > large as the numbers that were observed last year in March
> > > - April.
> > >
> > > Well, ALL Texas monarch authorities agree there are alot more
> > > monarchs in Texas and neighboring states this spring compared
> > > to last year. (And to my knowledge not a single monarch
> > > authority has put out a press release announcing this fantastically
> > > good news).
> > >
> > > Here are just two examples:
> > ------------------------------------------------------------
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