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Re: Theropod "migrations"



Recent data:
I don't have a citation, but I remember reading within the past year that
tests on North American Wapiti (I think) showed a fear response to Siberian
Tiger urine. The conditions of the tests appeared to be such that
ruled out the possibility that the response was generic to big cats.
The authors hypothesized that it was a genetically-programmed response
inherited from Siberian ancestors who were hunted by tigers when the
range of the tiger was much larger than at present.
In this case, the prey species appears to have a larger range than the
predator species, based on exclusion of the predator from part of
its potential range by competition with another predator - man.
Gus Derkits
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Stanley Friesen wrote:

> At 11:56 AM 4/26/99 -0500, Joseph Daniel wrote:
> >This is not really true. Physiologically, sure. Behaviorally, no. Almost all
> >predators have a "menu" of prey items that they will hunt. Animals that
> are not
> >on that list are usually ignored.
>
> In any given region this may be true, but this is often largely a *learned*
> response, not an intrinsic one.  Certainly predators show a wide variation
> in prey items between regions.
>
> > Sometimes if the predator is in extremis it
> >may go after something that is not normally a prey item but this is the
> >exception, not the rule. People are not safe from bears in the woods not
> >because
> >the bear thinks of us as food, but as competitors. Tigers and lions don't
> >make a
> >habit of attacking and eating people usually until they are old and unable to
> >hunt their regular prey and even then it is rare.
>
> The way predators treat humans is NOT a good model for the general case.
> We humans have this nasty habit of *killing* animals that kill, or even
> merely attack, other humans.  This tends to produce a strong selective
> pressure to *not* attack humans on most wild predators.
>
> >species. but, since they usually have more than one prey species, the
> >predators'
> >ranges can be bigger than the prey species.
>
> It has to go beyond that, as there are *zero* prey species in common
> between China and central North America (or there were until humans entered
> the picture).  Yet wolves lived in both places.  (And I cannot think of any
> prey species that are found in common between Europe and East Africa, so
> the same probably goes for the lion).
>
> --------------
> May the peace of God be with you.         sarima@ix.netcom.com