Re: Some evolution questions

Top posting for a one line reply to say thanks for a very detailed and very
interesting explanation





"J.J. O'Shea" <try.not.to@xxxxxxxxxxx> wrote in message
news:0001HW.C250F1B2004167AEF0284648@xxxxxxxxxxxxxxxxxxxxxxxxx
On Sun, 22 Apr 2007 08:38:15 -0400, alwaysaskingquestions wrote
(in article <5913a3F2gr8aqU1@xxxxxxxxxxxxxxxxxx>):

Whilst I accept the overall thrust of your post, that particular point
seems
a bit over simplistic to me.

From http://www.blueplanetbiomes.org/savanna.htm

"The savanna has a large range of highly specialized plants and animals.
They all depend on the each other to keep the environment in balance.
There
are over 40 different species of hoofed mammals that live on the savannas
of
Africa. Up to 16 different species of browsers (those who eat leaves of
trees) and grazers can coexist in one area. They do this by having their
own
food preferences, browsing/grazing at different heights, time of day or
year
to use a given area, and different places to go during the dry season.

These different herbivores provide a wide range of food for carnivores,
like
lions, leopards, cheetahs, jackals and hyenas. Each species has its own
preference, making it possible to live side by side and not be in
competition for food."

Does the principle of slight behaviour modifications allowing species to
exist side by side not apply to closely related species?

Of course it does. There are just a few complicating factors.

1 humans are large omnivores. This means that, unlike the various hoofed
mammals noted above, they can eat a _large variety of different
foodstuffs_.
The large mammals noted above are not just herbivores, but _specialist_
herbivores. As _specifically noted_ in the excerpt you quoted, they eat
_specific_ plants, or even _specific parts_ of specific plants... and
leave
the other plants, or the rest of the plant, alone. This is not necessarily
the case with an omnivore. As omnivores eat a _wide variety_ of foods,
they
compete in a _wide variety_ of niches... and there just ain't that many
spots
open for large plains omnivores. Especially when you consider that humans
ain't the only large plains omnivores. Pigs, for example, are also
omnivores,
and there are some pretty damn big pigs roaming the world in general and
the
savanna in particular. Hell, humans ain't even the only large _primate_
omnivores; chimps are primarily vegetarian, but aren't that picky about
what
kind of vegetation. Baboons are smaller than either chimps or humans, and
aren't that picky, either.

2 while it is certainly _true_ that the various predators on the savanna
_prefer_ one or two types of prey... a kill is a kill and the various
predators aren't at all adverse to muscling in on someone else's kill if
they
feel they can get away with it... even if that kill is something they'd
not
normally hunt themselves. The primary reason that male lions are the size
they are is that they're the pride's anti-hyena (and anti-other-male-lion)
defence... and even they give way if a _large_ hyena pack arrives. African
Hunting Dogs (Lycaon pictus) are much smaller than lions or hyenas, but
travel in packs of up to 100, which means that when a large pack makes a
kill
the lions and hyenas stay away... which is not the case when a small pack
makes a kill. They usually go for smaller animals, under 100 kg in weight,
but have been known to chase, catch, and kill just about anything under
rhino
size if the pack is big enough. This includes animals that lions would
normally chase... but the lions are smart enough to not want to annoy a
100-strong pack of hunting dogs and back the hell off if the hunting dogs
decide they want some wildebeest or zebra today instead of their usual
impala.

3 humans, (and many other primates, including chimps and baboons) like
lions,
hunting dogs, wolves, and hyenas, are pack animals. Large packs need more
food than just a single individual. This means that food sources which a
single individual might ignore _will_ be used. It also means that food
sources which a single individual could not possibly tackle can be used...
and will be. Normally, animals wildebeest and larger size would be safe
from
attack by an animal our size, they're just too big to handle and a single
human would have problems defending the kill from other predators,
especially
hyenas. This is not so when a dozen or more humans are hunting in
cooperative
packs. Adult elephant are safe from attack from even lions, they're just
too
big and powerful, unless they're sick. Humans can and do hunt elephant
with
paleolithic technology.

Humans are, if not the top, then at least one of the top three, predators
in
any terrestrial ecosystem. (And, given tools such as boats and nets, don't
do
too badly on the water, either.) Humans are also pretty good at converting
vegetable matter mass to large omnivore body mass. Humans occupy _several_
major niches in any ecosystem they're part of. Another, closely related,
species would be in direct competition with humans for a lot of those food
sources.

You'll note that the living non-human large primates have a rather limited
range while humans have an extremely large range. This is not a
coincidence.

--
email to oshea dot j dot j at gmail dot com.



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