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Re: Harmonious depredations




I'm not saying it does.  I am saying predation limits the areas that
oviparous species nest.  In the case of ostriches, this has been, and
remains, places with or near grass.

No, John, it isn't. That is my chief problem with your argument - you are very highly selective of your facts. Ostriches do NOT - repeat NOT - only nest in grassy areas. They can and do nest on open bare ground on grassless plains and deserts, in areas where there are still nest predators. These nest sites will not vanish into the ether simply because of your hypotheses.


The ostrich's mating system has been shaped (according to Bertram) by
predation.  Ostriches are a living example of the tyranny of predation on
large oviparous species.

What you fail to recognize it that ostriches, whatever the effect of predation on their nesting behaviour, evolved and thrived, and continue to do so today, in continental areas with highly successful egg predators, and did so without requring that all nests be cryptically concealed. So did rheas and emus. If nest predators did not exterminate these creatures I see absolutely no reason why dinosaurs could not have done the same. In fact, they clearly did do so for millions of years.


 Far from avoiding this evidence, I embrace
it.  It demonstrates my argument perfectly.  However, if I am to maintain
that ovivory has a primary role in structuring/limiting large oviparous
communities, I must explain the continued existence of the ostrich.  I do
so with the authority of the field's leading researcher who says ostrich
nests are extremely difficult to find because they nest in grass at low
predator density.  Dinosaurs didn't have grass to nest in.  Do you want me
to _ignore_ this evidence?

No, I want you to put it in perspective. Does Bertram say anywhere that his study applies to all ostrich populations? Does he claim that what you say about crypticity applies to all ostrich populations? It may be absolutely true that ostriches in Bertram's study area lay hard-to-find nests, but that has nothing to do with what they do elsewhere.


No.  No.  No!!!  Most of their nests are located inspite of grass.  But a
critical number survives.  My point is that grass provides that margin, a
margin dinosaurs did not have!

Then why are there still ostriches in near-grassless areas?

I am simply stating as a fact that the medium of grass was unavailable to
dinosaurs.  I am sure crypticity was employed.  But, without grass, it
could not have been as effective.

Why would bracken or other ferns be less effective than grass?

 Supporting evidence for this position
is that ONLY ONE large (ratite-size) bird nests in an area where grass is
not a significant part of its range.

This is, as I have stated before, untrue. There are three species of living cassowary, not one. Also, moas and elephant-birds appear to have been forest-dwellers. Also, Ostriches and Emus also nest in extensive areas where grass - or at least long, concealing grass - is NOT prevalent.


And I claim that grass was critical in all of this.  Ostriches do not
appear before grass.

So what? Neither did people, or gorillas, or oscine songbirds, or baleen whales.


The crypticity stems from being lost in space.  A predator scans the
horizon in the Serengeti, and sees nary an ostrich.  They are there, but,
from a distance, they appear not to be.  I suggest the rhea is
similar.  As with the ostrich, it is not the aerial aspect but the
horizontal which is important.  From a distance this behavior would not
make the nest more visible.

Thouhg this has some validity it would not apply to, say, Egyptian Vultures.

Anecdotal.

OK, do better.

I had better say that I am getting, frankly, tired of saying the same things over and over, and do not intend to prolong this (nor do I sense much patience for it on the list). You aer convinced you are right, and nothing anyone else will do or say will change your mind (and I would note that you do not seem to have attracted any support on this list at least). I will therefore (if I can practice self-restraint) confine future replies largely to pointing out incorrect factual claims (as I did in some extended recent posts you have not answered - on giant tortoise distribution, for example).
--
Ronald I. Orenstein Phone: (905) 820-7886
International Wildlife Coalition Fax/Modem: (905) 569-0116
1825 Shady Creek Court
Mississauga, Ontario, Canada L5L 3W2 mailto:ornstn@home.com