Checkerspot on the news

Neil Jones Neil at
Mon May 8 14:20:09 EDT 2000

In article <391376FE.4083 at>
           cherubini at "Paul Cherubini" writes:

> > Sally Daniels wrote:
> > I heard something on the news this morning about a checkerspot. They said
> > that the Army Corps of Engineers gave a permit to a developer in San Jose,
> > CA to put in a shopping mall. And now they will have to wait a year to start
> > construction because of the checkerspot. What will waiting a year do? Do
> > they plan to move the checkerspot?
> Pierre A Plauzoles wrote:
> > I haven't heard aboiut this one, I suspect that you are on the right track.
> > Stupid, ignorant move in my opinion. 
> According to a story in the San Jose [California] Mecury News:
> " the developer, William Lyon Homes Inc. has argued the butterfly has 
> not been observed on the property for at least five years and that
> 71 acres of the 575-acre property will be preserved for the butterfly, and about> half of the entire parcel will be turned over to an environmental trust for
> conservation purposes."
> Paul Cherubini

Well the developer's argument about the species' absence has little weight
when the known mathematical models of the species population dynamics are
taken into account.
It actually matters little whether the butterfly is present in any period
rather whether the site is suitable and reasonably close to an occupied one.

As I have said before checkerspot populations exist in metapopulations.
These are linked groups of colonies where individual colonies become extinct
to be eventually colonised from their neighbours. The classical model of
dynamics postulates that  the number of occupied patches P at a given time
t is given by dP/dt=cP(1-p)-eP where c and e are colonisation and
extinction rates.

What can be clearly seen from the mathematics is that EMPTY habitat is a
fundamentally inherant component of the system. So suitable but unoccupied 
habitat in the vicinity of occupied habitat must be conserved.

In fact if the mathematics is expanded on and worked up then the most modern
experssion of it is the Incidence Function Model developed by Professor
Ilkka Hanski at Helsinki. I know at least one of his team is subscribed
so if I get it wrong I will be corrected.
The model is far too complex to state in an email but it can be simplified
to an approximation that states that 3 times the Square root of the habitat
patches need to be occupied in order for the system to be stable.
It can be seen from this that there could be an awful lot of empty but 
necessary habitat in the system.

Neil Jones- Neil at
"At some point I had to stand up and be counted. Who speaks for the
butterflies?" Andrew Lees - The quotation on his memorial at Crymlyn Bog
National Nature Reserve

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