Government views Monarch Butterfly Releases as a threat to We stern Milkweeds
monarch at saber.net
Sat Dec 8 14:34:42 EST 2001
Dr. Pat Foley http://www.csus.edu/indiv/f/foleyp/index.html wrote:
> Clearly Bruce and Paul want to have it both ways: 1) Our techniques
> are so bad that we won't even sample the release effects and 2) The
> old flawed techniques are giving way to new and improved techniques.
Pat, Dr. Bruce Walsh http://nitro.biosci.arizona.edu/ wrote:
> unless the released material makes up a significant fraction of the local
> breeding population (at least over 1 percent and likely over 5 percent),
> it is unlikely to be obtained in a random population sample.
So how about if we try and model the probability of sampling a released
monarch? Since Dr, Karen Oberhauser studies monarchs in Minneapolis,
Minnesota, let look at that area.
The greater Minneapolis-St. Paul metropolitan area measures 25 x 25
miles = 625 square miles. Roughly 700,000 people live in this area.
The local monarch breeding population in this area of 625 square miles
in late summer contains roughly.62,500 monarchs (i.e. there are about
5,000,000 monarchs in the lower two thirds of Minnesota in late
summer = an area of 50,000 square miles =100 monarchs per square mile)
Approximately 200,000 monarch butterflies are shipped interstate to all
parts of the USA each year by butterfly breeders. Since the USA population
is 270,000,000, and the Minneapolis area population is 700,000, roughly
518 monarchs out of those 200,000 get shipped to Minneapolis each year.
These 518 are shipped gradually over the course of a 5 month
period, May-Sept, or an average of 104 butterflies shipped per month.
So we are looking at roughly 208 total monarchs shipped by monarch breeders
to the greater Minneapolis area (625 square miles) during August and September
with a local monarch population of 62,500. So the released material would
make up .03% of the local breeding population. This is substantially below the
1% - 5% or more fraction mentioned by Bruce Walsh. In reality, the fraction
would be much. much lower than .03% since the southward fall migration in
in the Minneapolis area begins in earnest on Aug. 24.
My conclusion, based on this model is that the chance that monarch
releases could disrupt the genetic structure of the local monarch breeding
population in the Minneapolis area in late summer is negligible. It follows
that the chance that a researcher might catch a released monarch when taking
a random population sample is negligible.
Pat, if you don't agree can you provide us with a reasonable model that
demonstrates the validity of Dr. Karen Oberhauser's concern; i.e. that
a modest amount of human assisted shipping of Maine monarchs to
Minnesota (or vice versa) in late summer has a slight chance
of disrupting the genetic structure of the recipient monarch population
and could make it difficult for a researcher to study that structure?
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