Re: late night thoughts: misunderstand what?

[don ohmes <d_ohmes@yahoo.com>]

Don wrote--

> There are two mechanisms here; predation driven size
increase, and the

> case where the prey, for whatever reason, can no longer increase their

> size (ie, 'predators won').

DM -- Oh, that's what you mean by "predators won". I'd have thought when
there's an arms race and the predators win, the prey dies out because the
predators are too successful; on the other hand, if the prey wins, the
predators must either switch to some other food or die out.


............ No, we are still in disagreement. Employing that most valuable 
analytical and
communicative device, the cartoon-- Assume a predation pair; an  herbivore w/ a 
red kill switch on it's neck,
and a carnivore w/ one finger. If an encountered carnivore is not tall enough
to reach the button, or close enough to detect it, the herbivore survives. If a
carnivore cannot find an herbivore that is short enough to kill, he dies.
Assume respective height variances and other variables such that selection for
height occurs; in other words a classic "arms race". In the quadruped
vs biped case, the height gained by the quadruped is accompanied by a 
proportionally
larger mass gain than is the case w/ the biped, ultimately placing the
quadruped at a disadvantage. When the herbivore hits it's mass limit, soon
there are carnivores are tall enough to reach the switch of every herbivore, as
directional selection is still occurring on their side of the equation. Classic
arms race, and the carnivores won. After all, all they had to do was lengthen
one finger, and maintain enough locomotive and sensory competence to attain
lethal proximity. Extinction does not necessarily occur, however. A large
number of 'butterfly scenarios' can be constructed. As an example, the
carnivore's population may be limited by a fortuitous new factor, allowing
sufficient herbivores to survive through the random fortune of zero predator 
proximity to
maintain viability. -- Don


DM -- As for why sauropods are so big in the first place, that may
have any number of reasons. A prime candidate is the fact that the bigger you
are, the longer you can afford fermenting food in your gut, which in turn means
that you can live off poor-quality food (such as conifer needles). If you're
just big enough, you have an unlimited food source and no competition.


........... True enough, at least in theory, and as far as I can tell.
But the laws of probability mandate that 'selective vectors' are additive, just
as events are multiplicative! Assuming that "reasons" have equal
value, two reasons to get big are more likely to result in bigness than one. In
the case of inequality, you must have the knowledge and data to determine a
level of significance before discarding one in favor of another. In reality,
you may need several vectors to occur, even occurring in the proper sequence,
for directional selection to be feasible. -- DO.


While I am at it, I would like to digress a little and point
out that while size creates relative efficiencies in resource utilization, at
some point the absolute quantity of food that must be gathered is prohibitive. 
Heh. I still say you should go out and gather some pine
needles; say, 400 kgs? There are problems that occur... -- DO.

Don