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[Niklas Wahlberg]

Dear Leps-Listers,
  To continue on the metapopulation theme, I would like to remind you
that the spatial population structure of a species is not constant over
its range. For instance the species that has been discussed in this
thread (Euphydryas editha) has a so-called "mainland-island" population
structure in the San Fransisco area (as was discussed by John and
Patrick), whereas in the Sierra Nevada mountains the same species
(albeit a different subspecies) has a more classical metapopulation
structure (Thomas and Singer 1998). The main implication of this is that
one can't really generalize _even within the same species_ without
taking into account the local landscape structure.
  Also touting numbers derived from models is not a good idea in
practical conservation. Models allow us to get crucial insights into how
Nature works, but the bottom line is that they are (usually extreme)
simplifications of what really happens. This means that some factors
that might have a large effect on the dynamics of natural populations
may be missed out or wrongly modelled. The best example that is still
hanging is how to incorporate environmental stochasticity into our
models. We all know that the meteorologists have difficulties in
predicting the weather next month, so how can we rely on the
quantitative predictions of our models that are usually run for hundreds
or thousands of "generations"?!
   Nevertheless, I think that the concept of metapopulations has brought
much to conservation. A good rule of thumb is that suitable habitat that
does not have a certain species is as important as habitat that does
have the species. We've been studying a relative of E. editha, Melitaea
cinxia, for the past 7 years here in Finland. In a patch network of
several thousand suitable habitat patches there have been several
hundred local populations each year. All but a handful have gone extinct
_at least_ once during the study period (read all about it in Hanski
1999, Metapopulation Ecology.). This, I think, underlines the importance
of habitat that is empty today. It might not be tomorrow.

Cheers,
Niklas
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________________________________________________________________________

   Niklas Wahlberg                          
   Metapopulation Research Group
   Department of Ecology and Systematics    
   Division of Population Biology           
   PO Box 17 (Arkadiankatu 7)               
   00014 University of Helsinki
   Finland                                                         
   p. +358-9-191 7378, fax +358-9-191 7301  
 Check out our web-site:                    
  http://www.helsinki.fi/science/metapop/