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Re: Built Like a Race Horse, Slow as an Elephant?
Whether or not herd animals are "competing" with each other or are
hunted individually, the arms race must be intraspecies. What is at
issue is the average fitness of fleet versus nonfleet herd animals
relative to each other, in both cases. The same will be true of the
predators - slower (or less cooperative, and so forth for whatever
adaptation makes them successful hunters) predators will be selected
out in virtue of not being fit enough to capture food. The
competition here is between variants in each species, although the
actual chase is between members of different species. Selection
drives to fixation or equilibrium variants in a population. If the
prey were not social, the competition between them would still occur.
It's the frequency of that "allele" or variant in the local
population that changes due to predation. Arms races are between two
interacting species. Competition is between two members of the same
population of a species.
On 17/01/2007, at 8:49 AM, Sim Koning wrote:
I understand what you are saying Dann, but I think you are both
partly correct. Just because an animal is in a herd, does not mean
it won’t occasionally find itself alone or singled out; I think in
that case, it would be an arms race, because it is not trying to
outrun nearby members of its herd, but the predator itself. For
example, cheetahs usually single out a gazelle before it actually
starts chasing it, and if you notice, most of the other gazelles
that are nearby aren’t even running that fast because once the
cheetahs begins chasing its prey, it won’t have enough energy to
switch targets and begin a chase with a slower gazelle that it sees
out of the corner of its eye. So in the case of cheetahs, it is
very much an arms race.
Now lions are different, lions will scatter a herd and will
rapidly switch targets, eventually singling out the slowest animal.
So, like you said, Zebra are competing with each other, not the
lion. Cape hunting dogs and hyenas will also switch targets and
single out the slowest animal as well.
There are some predators that are actually slower than their prey,
but they still catch them because they have greater endurance, cape
hunting dogs are an example of this. In fact I believe sub adult
springbok only pronk in front of cape hunting dogs, though this may
just be a sign of excitement rather than a demonstration of their
I’m sorry if some of you already brought up these points, I haven’t
really been keeping track of this discussion until now.
From: Dann Pigdon <email@example.com>
To: DML <firstname.lastname@example.org>
Subject: Re: Built Like a Race Horse, Slow as an Elephant?
Date: Wed, 17 Jan 2007 09:05:40 +1100
Andrew Simpson writes:
--- Dann Pigdon <email@example.com> wrote:
Actually, it was almost certainly a
pronghorn/pronghorn arms race. There would always have been far
more pronghorns than
cheetahs, so cheetah predation on a population of slow coaches
still not have been enough to threaten their long-term survival.
I doubt pronghorns would have evolved to run as fast
as a cheetah (or as close as their biology would have allowed)
avoid the occasional bit of cheetah predation. I think it's more
pronghorns evolved to run fast to compete with each other.
It's like the old saying goes: if you and a friend
are chased by a tiger, you don't have to outrun the tiger. You
just have to
outrun your friend...
I'm not sure I'm following you Dann. How are the
Pronghorns evolving speed? Are you saying that the
North American Cheetah are or are not responsible?
Because the Proghorns can't make themselves faster and
have no reason too unless something is chasing them or
if there is an advantage to getting somewhere quicker.
(A quickly dwindling food source perhaps).
Cheetahs (and other less speedy predators) are the indirect cause,
however it was almost certainly not an 'arms race' between
predator and prey. Where herd animals are concerned, they only
have to out run the slowest members of the herd. Hence the
competition for speediness is between animals of their own
species, not directly between predator and prey.
The evolution of horns seems to have followed a similar pathway.
Antelopes use their horns against each other (or as sexual
displays) far more often than they do defending themselves against
predators with them. Therefore the development of steadily bigger
or sharper horns may not have been an 'arms race' against
predators, but rather due to intraspecies interactions.
The only antelope predatory defense that I can think of that seems
a direct response to predation is the practice of pronking. Rather
than demonstrate speed and strength to a predator directly by
evading them (a huge waste of energy), pronking allows an antelope
to demonstrate it's fittness to a predator without excessive
energy loss. When an antelope pronks, it is communicating directly
to the predator, rather than competing with herd members.
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"Darwin's theory has no more to do with philosophy than any other
hypothesis in natural science." Tractatus 4.1122