[leps-talk] Credible sources

[Paul Cherubini]

Patrick Foley wrote:

> If we are to get a clearer and more honest picture of the Monarch's
> status and prospects, we need a _quantitative_ description of the
> changes in critical winter habitat.   We need to ask 1) how does monarch
> winter survivorship depend on the amounts of land in old growth,
> secondary growth,  clear cut and milpas?
                                                                                               
Pat, I'm not sure what you mean by "critical winter habitat"?   None
of the monarch forests today in Mexico are virgin 120+ year old
growth type forests. They are are all young 30 - 60 year old regrowth
despite their pristine-like appearance
http://www.saber.net/~monarch/chincuadis.JPG  And for decades this
massively altered forest has been sufficiently good habitat to support the
massive monarch migration / overwintering phenomenon we still see today,
with no sign of the population increasing or decreasing
http://www.saber.net/~monarch/mexicopop.jpg   Likewise, the massive
crop monocultures of the upper Midwest
http://www.saber.net/~monarch/iowaland.jpg have provided sufficiently
good breeding habitat to support the massive monarch migration.
                                                                                                                                                                                                      
Have the monarchs abandoned any of the mountains in Mexico due
to any cause such as forest alteration?  NO.  Have the numbers of
monarchs decreased on any of the mountains?  NO.   Have certain
forest densities / structures been conclusively linked to butterfly
survivorship or mortality during storms / freezes? NO.  After winters with
high storm related mortality, such as 1981-82, 1991-92, 1995-96 and
2000-01, was the size of the butterfly population returning to Mexico the
following autumn always average or above average in size? YES.
After winters such as 2001-2002 with a catastrophically high level (75%)
of storm related mortality was the size of the butterfly population
returning to Mexico the following autumn average in size?
YES.  Thus, in view of these facts, what biological justification is there
to describe the overwintering habitat in Mexico as "critical", "fragile",
etc. anymore than if someone should describe the summer breeding crop
monoculture habitat of the monarch
http://www.saber.net/~monarch/iowaland.jpg 
as "critical" and "fragile." And considering that the size of the
overwintering population in Mexico has remained stable despite radical
changes in forest age and structure (from all virgin to all
regrowth) do we really need to know precisely how forest age and
structure affects butterfly survivorship in order to "get a clearer
and more honest picture of the Monarch's status and prospects"?
Or is it more reasonable to conclude the monarch migration is no
imminent danger of extinction?

Paul Cherubini

 
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