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Re: Sauroparental care




On Tue, 23 Dec 2003, Graydon wrote:

> On Tue, Dec 23, 2003 at 08:46:16AM -0500, John Bois scripsit:
> > On Mon, 22 Dec 2003, Graydon wrote:

> > But the bracket is important.  How do you rate such brackets?  I imagine
> > the bracket is strong enough for you to agree that sauropods had red blood
> > without any direct evidence.
>
> That's not the bracket.  That's 'common descent from an ammonite
> ancestor'.

I thought the bracket in this case was, then, ammonites and birds.

> Talking about the phylogenetic bracket to set a rough, doubtful, range
> on probable behaviours is a very different thing that looking at common
> descent for basics of biochemical composition, and much less confident.

Common descent is what makes any bracket relevant.  And, at some level, at
some future time, hypotheses regarding the biochemical nature of parental
investment may be testabl (e.g., shared parental investment genes in both
birds and crocs).

> > Parental care isn't as strong of course--but it _is_ strong.
>
> It's a very tenuous inference.

How is it tenuous if within the bracket it is almost universal?

> Parental care has a cost.  This cost is not obviously, or always, lower
> than the cost of producing lots and lots of offspring.

This is what we are discussing--but how do you respond to the fact of its
universality.

> > Why would a species give it up?  Certainly there are
> > exceptions--megapodes are presumably secondarily non parental
> > (right?)--so what is the argument for sauropods as an exception?
> > Which is the "little green men" argument: parental or non-parental?
>
> A species would give up parental care if, as a matter of statistical
> averages, more offspring got into the future where they themselves
> survived to breed from more R-strategist parents than more K-strategist
> parents -- if the survival chances are even very marginally higher for
> producing 80 eggs and walking away instead of 50, and stepping on some
> of the offspring, say.

I agree that those are those are the sorts of calculations that are made.
But, after they are made, the result is almost always (w/in relevant
clades) go wqith parental investment.

> The bracket is an *inference*, it's not *evidence*.  It's permission to
> make the supposition, not evidence of the behaviour.

I agree.

> Essentially unchanged bauplan for a hundred and twenty-odd million years
> is a pretty solid argument that whatever strategies they had were good
> ones.

Yes.

> It works for turtles in an aquatic environment with a greater proportion
> of predators than a terrestrial ecosystem; why wouldn't it work for
> sauropods?

Then why do they scramble for the water?  Predation must be
lower--locally, at least.

> All you have to do is to assume that the number of predators is a little
> too low to always get a perfect kill off.  That's very easy if the egg
> laying is seasonal, because the predators have to get through the lean
> season, and can't carry maximal numbers to the next hatching.

On the contrary, a big crop of unprotected growing sauropods could support
a few predators w for a number of yewars.

> > Firstly, "R-strategy" is only a relative term.  To a crab turtles look
> > like K strategists.  Secondly, as argued above, if turtles stayed on
> > land they would not survive.
>
> They get eaten in the ocean, too.

They scramble to get in the ocean.  This is a survival tactic, right?  I
don't imagine such a trait could survive if the rush to the ocean didn't
pay reproductive dividends.

> The available fossil sauropod clutches have very large numbers of eggs
> in them.  That's not what a trending-K strategist egg layer is observed
> to do, that's what a trending-R strategist egg layer is observed to do.

20 eggs is R strategy only in a relative sense.  One can't overestimate
the cost of courting, mating, traveling to nest sites, etc.  At the very
least, you can't make a statement that for sauropods eggs were cheap,
plentiful, and not limiting.  I mean, you can make it...but it doesn't
have evidenciary support.

> Elephants are compulsory K strategists because they are mammals, for
> one, and for two, they aren't wildly successful, reproductively; they
> have narrow reproductive margins and deal very badly with the
> introduction of novel predators, as evidenced by North America's (and
> the rest of the world's) lack of mammoth.

The novel predator is man?