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Re: Built Like a Race Horse, Slow as an Elephant?



Also, historical contingency plays a role in relative speeds of predators and prey. North American pronghorn (the only remaining antilocaprids) run substantially faster than all extant predators (well, except perhaps SUVs on the interstate...). It's been hypothesized that they evolved to be this fast as a response to the recently extinct North American cheetahs, but regardless they are currently far faster than selective pressures would dictate they need to be (unless, perhaps, there is some sexual preference for fast mates...THAT brings up a whole slew of off-color joke possibilities...).

So not only is Dawkins overgeneralizing, but the principal only works on time-averaged relations; it can't cope with predicting the specifics of a predator/prey relationship, and certainly won't precisely place an absolute top speed on T. rex.

Sheesh, I sound like Gould...

Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com

-----Original Message-----
From: koreke77@yahoo.de
To: dinosaur@usc.edu
Sent: Mon, 15 Jan 2007 7:44 AM
Subject: RE: Built Like a Race Horse, Slow as an Elephant?

I'm sure there've been studies, but this situation
is covered by the
Life-Dinner Principle, named (I think by Krebs and
Dawkins)

While basically correct, Dawkins is once again getting carried away throwing too many things into one pot. It works like that in short/medium chase one-on-one encounters (or some cases thereof, lynxes/bobcats for example. Cheetahs, it don't; they have gone great lengths in evolution to be able to outrun anything which seems a bit pointless if L/D held true in their case).

If you have a pack of predators, a herd of prey, or
both, and/or ambush predators or long-distance
chasers, there are additional twists making it not
strictly true.

For example, wildebeest fleeing from a pack of hyenas
are not outrunning the predators but each other (then
again, this IS Life/Dinner, but on a population level,
but it only works because some individuals cannot keep
up with the predator). For ambush predators, the
prey's optimal strategy has failed in the moment the
predator attacks, and so on.

I don't know whether there are actual empirical
studies that compare a wide range of predator
strategies. And whether this can be applied to
terrestrial theropods is another question.

FWIW, the requirements from the prey's side is that at
least some individuals have to be able to get away by
whatever means on a regular basis. From the predator's
side, it's more straightforward: being able to outrun
some prey individuals on a regular basis.

Gazelles for example are probably the ideal mammalian
prey in African grasslands, being fairly mediocre in
about all defensive aspects. They have to cope with
about as many predator strategies as one can imagine.
So they keep their eyes peeled for anything funny
going on (like too many ostrich heads being "up" at
the same time) and tend to get it going before anyone
else does.

Life/Dinner is an underlying principle forcing
evolution into one direction in some but not all cases
of terrestrial predators and their prey, as long as no
other "desideratae" overrule/cap it (such as
functional constraints).

Regards,

Eike






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