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Re: "Wonderful Life" - repeated. (fwd)
John Bois wrote:
[could people please include at least the name of the person they are
replying to, thanks - chris]
> 1. There is no EVIDENCE tying dinosaur extinction to anything.
Are you saying it happened for absolutely no reason?
> 2. Primates were arboreal and ultimately may well have been able
> to outcompete dinosaurs in this medium.
Okay, then why did all the big terrestrial species go extinct?
Mammals may have gotten big towards the end, but there is no indication
that any got lagre enough to be giving any but the smallest dinosaur
species a hard time.
> Their diversity was
> decreasing, and something was driving an unhealthy arms race--the
> trend towards bigness. And challenges don't come only from
> things bigger.
What is so unhealthy about bigness? It obviously hadd benefits at
some time that were great enough to outweigh the hazards. Why do you
think that changed?
> What I do know for sure is this: non-stealthy egg laying is
> today, by and large, an unsuccessful strategy. This is because
> there are creatures around which can exploit it. My _opinion_
> remains that their were also such creatures around towards the
> end of the Cretaceous.
There is a scale on which reproductive strategies fall. At one end
are "r" startegies, which involve putting little care into lots of
young. A good example are clams, which lay millions of eggs. EVen if
99% of them die, only TWO need to survive, on the average, for the
polulation to increase. THat is a SUCCESSFUL strategy. If you put $100
dollars into a slot machine and win $1,000,000, I don't htink you would
say all those other pulls were wasted efforts. If you handn't made them,
you wouldn't have made the last one that made you a millionaire. And
considering that millions of eggs are layed in high r species, the
chances aren't that bad.
At the other end are "K" strategies, in which relatively few young
are produced, but a high investment is made in keeping them individually
alive and safe. This is more like putting a whole lot of your money on a
bet in a poker match with only a few other players about as good as
you are. Your chances of winning are pretty good, and even if you loose
a lot of money, you can try again in a bit. Again, evolutionarily K
strategists only have to win a couple times for poluation to increase.
They just play less often. Primates, particularly humans, are high on
the K scale. It has been argued in fact that apes have gotten too high,
(although I don't agree) and that the risks of infant death are too high
for the size of the bet.
Reptiles and birds are somewhere in between. They lay lots of eggs,
but they also care for the young to a pretty high degree. Its all a
question of balance between between how much you bet and how likely each
individual bet is to win. Birds and reptiles may lay thier eggs out in
the open (risk), but they also care for the eggs and young to a fair
degree (increasing the lieklyhood of winning) and they lay quite a few eggs
(bets). It doesn't matter if most of the eggs get gobbled up, as long as
a few get through to keep the species at an even keel. Don;t assume that
a reproductive strategy is bad just because infant mortality is high. It
only has to be successful in absolute, not relative terms.