On predation.

J. Moore (j#d#.moore@canrem.com)
Sun, 22 Oct 95 11:49:00 -0500

I have posted this before, but am doing so again by request; it
outlines the general problems of predation on a transitional
hominid population:

1) We have (in chimpanzees) a model of a population that is
similar in mental and physical abilities to the transitional
hominids, which shows that they can and have survived in the face
of predation by terrestrial predators.

2) We have no such model anywhere for an aquatic population: all
such animals do one or more of the following a) swim really fast,
b) get out of the water incredibly fast, c) they are very large,
and especially d) they reproduce at a much higher rate.

On The Problem of Predation:
We've had a few varying threads on the subject of predation on early
hominids, specifically the transitional population, and in light of some
of the responses, I thought I'd make some points.

One is that predation happens, sometimes. It doesn't matter much
*unless* there's too much of it. When the animals can't at least
replace their population, there's a problem. Populations may get
smaller for a while, and often do, but if a population goes year after
year without being able to replace its numbers, it can't last.

Another is that, for the transitional population, we can surmise, from
fossil and molecular evidence of relatedness, an animal that is similar
in mental and physical abilities to chimpanzees, and so can use that
species' proven ability to survive in open savannah woodland as a model
for how our ancestors could've done the same. We can even see *how*
they might have handled land-based predators, based on how chimps do so
now. We can also see that predators such as snakes, both constrictors
and venomous, are apparently not a problem for chimps today, and
therefore likely would not have been a fatal problem for the
transitional population, although you could expect all such predators
might occasionally have been a fatal problem for some individuals.

We cannot do the same for a proposed water-based transitional
hominid population. They would've faced water-based predators which,
as has been shown in previous posts, are numerous, vicious, and do not
respond to bluff and even counterattack as readily as do land-based
mammalian predators. We also have no appropriate model for such a
water-based hominid. Animals which have survived in this environment,
spending many hours a day in the water, are either quite large or breed
prodigiously. Even animals such as African otters have several pups
each year and these pups are self-sufficient by the following year.
Even whales, which are relatively slow-breeding as animals go,
breed much faster than chimpanzees (or gorillas) or humans who
gather and hunt. This means these aquatic animals are having a
lot more young than would the transitional hominids. This also
means the population can afford to lose far more of its members
than could the transitional hominids.

The point is that avoiding all predation isn't what's needed, just
avoiding *enough* predation. What "enough" is depends on how many kids
you've got to spare. In my recent reading on crocodilians, for example,
they have a high mortality rate until they reach, for Nile Crocodiles,
about a meter in length. The first year mortality may be as high as
90%, and some mortality occurs even later. But overall, even as the
mortality rate climbs to as much as 98%, there is still a surplus in the
population, because they start with 50 eggs or so (up to 80), and have a
long reproductive lifespan. Many fish, of course, lay thousands of eggs
each year, and manage to keep a surplus despite heavy losses throughout
the lifespan. Even animals which just one, two, or three offspring each
year may do well enough if those kids mature quickly. Hominids, like
apes, had a different problem. They just didn't have that many kids, and
couldn't afford to lose many.

One other thing is what we can tell from the records of predators and
modern human populations. One thing we *can't* say is that these
predators were not a problem because they don't kill most of the human
population today. We have a population that is obviously not all
spending 4-8 hours a day in predator-filled water, and furthermore, we
have very sophisticated devices and weaponry to help deal with these
predators in places we might encounter them. Early hominids not only
didn't have shark nets and firearms, or even steel knives and spears,
they also didn't even have sharpened rocks until some 4-6 million years
after the transition had occurred. And yet we *can* see that, even with
these modern weapons, we still have *some* problems with large predators.
And in the case of the most common and likely predator of an African
water-based transitional hominid, the crocodile, we can see that, when
they get hold of humans today, even when other humans fight them with
modern spears and knives, these counteroffensive tactics are ineffective.

We know how chimpanzees, so alike in mental and physical abilities to
our early ancestors, handle land-based predators, and we know that they
have been effective enough at doing so to survive in the presence of
these predators. We also know that we do not have effective measures
against water-based predators even today (other than staying out of the
water), and have no appropriate, applicable model for our ancestral
population which shows us an effective strategy for dealing with this

***** How chimpanzees react to predators *******************************

In fact, predation is not much of a problem overall for chimps, which
might seem odd until you look at what you face when you face a chimp.
What you face is not just a chimp, but a group of chimps. A group
of strong, howling, stick and/or rock throwing gang of vicious
little hominoids. They kill baboons and leopard cubs (with
leopard-mommy present) with no more armament or natural ability than
australopithecines had. They are not defenseless out there, and
neither were australopithecines. In fact, even lone chimps have been
seen sleeping overnight on the ground in areas frequented by leopards,
which further suggests that they don't have much trouble with such

What we see when we look at predation on chimpanzees, those animals
so similar in size and intelligence to our early ancestors, is that
they have more severe problems (ie. they get killed) with leopards
in more heavily forested areas. In more open wooded savannah they
show little concern with leopards. Perhaps Adrian Kortlandt's
experiments during the 1960s would give us a clue as to why this is:

During the 1960s Dr. Kortlandt, a Dutch researcher, did a number of
experiments with wild chimpanzees in natural populations in Africa. One
of these was to see how different populations of chimps react to
predators. To do this, he used a stuffed leopard dummy with electrically
moveable head and tail. A baby chimpanzee doll was placed in the
leopard's front paws and the dummy was placed where it would be
encountered by mixed groups of chimpanzees, including females with young,
in all the experiments. Several populations of chimpanzees were so
tested several times, including groups in two different jungle areas,
and a group of savannah woodland chimpanzees. All the chimp groups
reacted by picking up sticks as clubs, breaking small trees and tree
limbs to use as clubs, and throwing these at the leopard dummy. An
interesting difference emerged between the jungle chimps and the
savannah chimps. The jungle chimps, while aggressive toward the
leopard, were uncoordinated in their attacks and when throwing objects,
never actually hit the leopard.

Dr. Kortlandt observed:
"The results with savannah chimpanzees, however, were quite different.
They grabbed the largest of the available clubs, which was 2.10 m long,
and they tore down small trees of about the same length; they slashed
viciously at the leopard with these. With the aid of the film we made,
we could measure impact velocities of approximately 90 km/h, which would
have been sufficient to break the back of a live leopard. In addition,
there was teamwork in evidence during these attacks, again in contrast
to what we observed in the jungle chimpanzees. During the final attack
the dummy was encircled by five chimpanzees, while two others stood in
readiness at some distance, in case they should be needed. Then the
leader grabbed the tail of the leopard and ran away, tossing the
predator so that the head flew from the body.
"With that, the enemy was considered 'dead'. The apes showed no more
fear of it, and the youngsters were allowed to touch it. The attacks on
its head, however, continued during the whole day.
"A side effect of the experiment was the observation that the savannah
chimpanzees more often walked erect than do the jungle chimpanzees."

Perhaps this difference is the result of being able to see your
potential predators, an great advantage over having them sneak up on you

Chimpanzees do not seem to be overly afraid of big cats; besides the
cases of chimpanzees occasionally sleeping on the ground while in
leopard country, there are other reports that show their reaction.
Dr. Kortland did another test in the sixties with a stuffed leopard
with a chimp doll in its paws; two female chimps threw sticks at it,
apparently distressed at the plight of the "youngster". Bands of
chimps have been spotted screaming at lions (from a distance) but
holding their ground.

Then there was that leopard den. A band of chimps went over to a
leopard den (sounds like "a gorilla walked into a bar..."), well, they
really did (if I remember the time and place correctly it was at Mahale
in 1982) and started screaming up a storm outside the den. This chimp
group included not only adult males, but also females and young. From
the sounds inside, the researchers observing this determined the mother
leopard was inside at the time (but they didn't crawl in and check for
some reason ;-). A couple of male chimps did, however, and dragged out
one of the leopard's babies and beat it to death.

Chimpanzees are not so afraid of large cats as we might reasonably
suppose them to be. (That's understatement, in case you don't
recognize it.)

Jim Moore (j#d#.moore@canrem.com)

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