Re: Herbivore protection

[John Bois <jbois@umd5.umd.edu>]

On Sat, 7 Jun 1997, Stanley Friesen wrote:

> Hmm, I could be wrong about that point, it has been awhile since I read the
> article, and that wasn't the main point anyhow.  Though whatever the
> nesting sites were, they were vulnerable to human mass cultivation.

Perhaps, since both of us aren't quite sure of our info, we should
postpone this.  But the P. pigeon, since it is the only species cited
which "unequivocally" (my word) demonstrates the phenomenon of predator
satiation, remains relevant to us.  So I will try and find more on its
evolutionary ecology and report back when I do. I still argue that
colonial dinosaurs gathered together at the same place in order to resist
predation rather than satiate it.  And I
still argue that all egg-laying  vertebrate species _intentionally_ seek
places of low predator density first.  I mean P. pigeons almost certainly
would not choose nesting sites, initially, at random.  I bet they are
operating under some optimizing regimes.  My guess would be this: normally
they are open-field foragers.  They don't nest there because they would be
sitting ducks.  So, where to nest?  The place with forage and protection.
Trees afford more protection than fields.  This is especially true if you
are the prey of a swift diving bird.  Perhaps at egg time you can even
forego forage after you lay down some fat.  Further protection for these
birds may be gained by congregating in the same time _and_ place.  But
here comes the analogy police again.  This does not mean that dinos would
be under similar selection pressures.  (see below)

> What would happen is that the herds of hadrosaurs would move with the
> seasons to where food is most abundant, *crossing* the more localized, and
> less easily shifted, territories of the individual predators and predator
> packs.  This is what happens in East Africa today.  The lions do NOT follow
> the herds.

I question the analogizing of today's preds. with yesterday's.
Territoriality evolves in response to very specific ecological conditions.
The pred/prey structure of the cretaceous was altogether different.  So
were communal relationships.  Territoriality would be expected only in a
place where there is something worth defending.  If all of your food has
gone off to some remote site there is no point defending anything.  On the
other hand, if there are lots of prey for all the predators (say at a
nest-site) there is also no point in being territorial.  These ideas are
fairly well understood and I would be glad to cite some studies.  Again,
in the cretaceous these imperatives _could_ lead to a surplus of predators
at the nest _and_ a train of predators _too_ the nest.