> Is there a general formula for the spread of exotics?
There certainly seems to be a fairly deductive pathway, first people
arrive, then they spread the exotics. :-)
Seriously though, I don't really know, too many variables I think. A few
thoughts though;
Worldwide the main ones appear to be;
lack of suitable eating/angling targets (anything large and usually
pisciverous)--primarily first world
world health organisation (spreading damnbusia)--primarily 2-3rd world
peace corp voluneers (spreading tilapia)--primarily 2-3rd world-Africa
Auburn University (spreading tilapia)--anywhere
Much of this continues as I type this message and is government supported
(especially USA as I understand it).
No doubt there are others. Many are government organised and well
intentioned but often not well thought through or considered
environmentally. There are places in the US where you can call up, ask
for your damnbusia and they'll send 'em out to ya free of charge no
questions asked. They will even tell you they are not a threat to the
environment.
You should read some of the "crap" David Coates has written about PNG. He
advocates spreading tilapia and other species for the native folks to eat
because apparently the fauna is depauperate. Mind you, from what I'm told
fish do not play a big part in their diet (at least not to where it needs
to be supplemented) and fork and eeltailed catfishes are common in most of
these areas and are considered to be good eating species by most folks
standards. I don't think many follow through studies have been
undertaken to assess the success of these actions either.
Tootles
Peter Unmack