[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Waiter, there's an ammonite in my chicken (Re: Sauroparental care)



Either I joined the thread late and therefore don't know the context, or
some list members have been getting in to the holiday punch early!

"Amniote", folks.  It's "amniote".  ;-)

<pb> (who'll be sippin' the stew in due course)
--


On Tue, 23 Dec 2003 14:02:11 -0500 Graydon <oak@uniserve.com> writes:
> On Tue, Dec 23, 2003 at 01:21:13PM -0500, John Bois scripsit:
> > 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.
> 
> Birds *are* ammonites.  Haemoglobin as the means of oxygen transport 
> is,
> like the tetrapod skeleton, ancestral.
> 
> A bracket is a way of saying something about likelihood when you 
> don't
> have any evidence.  In the case of 'red blood', we do have evidence 
> from
> the genes that code for the stuff; they're pretty much the same 
> across
> everything that bleeds red.  That means it evolved once and got 
> copied
> into descendants.  Supposing that sauropods evolved a novel form of
> oxygen transport then violates parsimony.
> 
> > > 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).
> 
> That's still not evidence they made it into sauropods (or
> ornithsicians).  They'd have to be essentially the *same* genes, 
> which
> is monumentally unlikely given that the range of parental care
> behaviours is large.
> 
> > > > 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?
> 
> Because you're ignoring size effects; "parental care" isn't an
> independent variable.  Smaller creatures make relatively larger
> reproductive investments.  So *all* modern birds are bad examples of 
> the
> choice space for sauropods.
> 
> Crocs are similarly very small by comparison, and don't have 
> parental
> care; they have a variable degree of nest defense, and some
> intermittent care of hatchlings.
> 
> > > 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.
> 
> By pointing out that it *isn't* universal?
> 
> [snip]
> > > 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.
> 
> They scramble for the water because that's where they can move and 
> eat,
> I suspect.
> 
> Also note that current sea turtle populations are very low, compared 
> to
> historical numbers; this is because people eat them.  This makes the 
> net
> effect of predation pressure worse.
> 
> > > 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.
> 
> And it probably did, but that's not the point I was trying to make.
> 
> You have an episodic food source.  It can carry the number of 
> predators
> that can survive through the *dip*, not the peak.  (Consider 
> lemmings
> and the arctic weasel population.  It's the dip, not the peak, that
> constrains the weasel population.)
> 
> If the peak is sufficiently large compared to the dip that the 
> predator
> supply is flatly incapable of eating all of the peak population of
> sauropod hatchlings, the R strategy will work fine.
> 
> > > > 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.
> 
> It's a tactic to get where they can move and eat; they're sea 
> turtles,
> they have flippers.  They would rush to the ocean without the 
> gulls.
> 
> > > 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.
> 
> Sure one can.  Those are all real costs, but they're not 
> necessarily
> high or even high-risk.
> 
> > 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.
> 
> Sure it does.  Mass.  A clutch of eggs that represents 50% of the 
> adult
> weight of the bird that laid them is a huge investment.  A clutch 
> of
> eggs that represents 0.5% of the weight of the sauropod that laid 
> them
> is not a major investment.
> 
> > > 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?
> 
> Yup.
> 
> Elephants don't have much reproductive elasticity; one female 
> elephant
> has a maximum lifetime number of offspring around ten.
> 
> Postulating 20 eggs per clutch, 1 clutch a year, and the same 40 
> year
> reproductive life, the female sauropod has 800 potential offpsring,
> probably for a smaller proportionate energy investment.
> 
> There is no particular reason to suppose that the sauropod clutch 
> was
> that small, or that egg-laying was that infrequent.
> 
> -- 
> oak@uniserve.com | Uton we hycgan    hwaer we ham agen,
>                  | ond thonne gedhencan    he we thider cumen.
>                  |   -- The Seafarer, ll. 117-118.
> 
> 


"Let's get this train outa here.  Those damn bees might be back any
minute." - General Slater, from the movie "The Swarm"


________________________________________________________________
The best thing to hit the internet in years - Juno SpeedBand!
Surf the web up to FIVE TIMES FASTER!
Only $14.95/ month - visit www.juno.com to sign up today!