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Re: Vegavis gen. nov. - new anseriform in today's Nature
On Mon, 31 Jan 2005, Graydon wrote:
> I have no difficulty imagining a whip-tail sauropod keeping an eye on
> its nest, but we're not going to find many fossils of small would-be
> nest robbers blown into fragments by apatosaurian tail strikes.
Nest guarding would be a must in my view. Provisioning hatchlings might
be difficult given the size disparity. But then again, a small
regurgitation would be mana from heaven for a throng of hatchlings.
> There are also some sauropods-in-company trackways that appear to
> indicate herding behaviour, with the smaller animals in the middle and
> the largest to the front of the direction of travel.
> Have you ever looked at the *degree* of R strategy in some fish or some
> frogs? (We can leave pine trees out of this.)
Offspring are expensive. They're even more expensive if
you have to invest in them after they hatch. But offspring are also
_valuable_ because they carry one's genes into posterity. So there is a
trade off: do I take better care of fewer offspring, or do I spend on more
offspring and throw them to the wind, the plankton, whatever. This
"choice" has got to be contingent on the specific niche--one strategy
better suited than another depending on the niche. The evidence from TE
Martin's study suggests that if organisms have their druthers (i.e.,
if predation pressure is lower) they will invest more in fewer offspring.
Another way of saying this is that a few better-prepared, more developed,
ontologically further along, etc., etc., babies have advantage over many
immature babies. But, again, this is dependent on the specific niche.
And, as you say, many organisms do fine using "Darwinian ammunition" (nice
>...you're looking at ten _thousand_ eggs, and pretty good odds two of
> them make it to stable reproductive adulthood, on average.
There may be a faulty assumption here: predators and prey control
each other's population levels with a negative feedback system.
But ecosystems are not super-organisms taking care of their health.
No doubt population oscillations occur and that they are caused by food
availability/predation, etc. But there is no reason to assume _a priori_
that predator populations could not eat every last one of a brood of even
thousands. Extant r strategists make it work by using various tactics:
concealment, remote laying/brooding, bad-tasting children, etc., etc.
Ostriches produce many offspring, 90% of which don't see their first
birthday. Those that do survive must thank specific attributes of their
niche, e.g., grass, low predator density, and their own physiological and
behavioral responses to it. I'm not knocking ostriches. They are
exceptional birds. Indeed, given their amazing speed and immunity from
predation as adults, they embody a fundamental evolutionary challenge: why
didn't dinosaurs re-establish dominance in the large animal terrestrial
niche. How do these arguments relate to sauropods? What did they do to
reduce predation so that two offspring survived? I don't believe
satiating predators was part of this because offspring could not scramble
into (for example) water like hatchling turtles. Protection must have
been part of it...but not, I would argue, a very effective part, that is
if only two of thousands survived! Concealment? Small offspring could
hide, but not that well if guarded by parents. I guess my point, finally,
is that creatures cannot just keep uping the offspring numbers
indefinitely...and that this limit plays a role when organisms in similar
niches are competing with each other. And the upshot of this (potential)
fact of evolutionary life, is that the diversity of organisms practicing
parental investment has increased!
> Which is all it really takes, and being a huge R strategist is quite
> cheap, energetically.
I don't think this computes. A pine tree invests way more than a
flowering plant in its reproductive effort (right?). Yet each individual
flowering plant offspring has more invested in it. Presumably parent
investment pays off energetically for birds as well (re: TE Martin's
> Sixty million years of mammalian predator ecologies, and at least ten
> million of dinosaurian predator ecologies. That's as well or better
> than pretty much anything else that's fully terrestrial is doing.
Truly! And yet check the minimal diversity of the body plan. There has
to be a reason for this--beyond waiting for a mass extinction as per David
M's. world view.
> Since people have subsequently found quite a number of Cretaceous
> sauropods, it's far from clear that their diversity declined.
Is nothing sacred?