SK-54 is a curious fossil. The 1.5 million year old skullcap represents a juvenile Paranthropus robustus, one of the heavy-jawed hominins which lived in prehistoric South Africa, but there is something that makes this skull fragment particularly special. Near one of the sutures along the back of the skull are two neat puncture marks, the hallmark of a leopard.
Even though it was initially proposed that SK-54 had been murdered by another australopithecine wielding a weapon of bone or horn, in the late 1960's the paleontologist C.K. Brain was able to demonstrate that the holes almost precisely fitted with the lower canine teeth of a leopard. What's more, Brain determined that many of the accumulations of bones found in the South African cave deposits were attributable to the activities of predators, meaning that for a long span of time our ancient relatives (particularly juveniles) may have regularly been cat food. Nor were hominins the only primate fossils to be found in these accumulations. It seems that the prehistoric leopards had a taste for primates, just as some living leopards do.
In the Tai Forest of Cote d'Ivoire, leopards frequently kill and consume primate prey. It is rare that scientists observe an attack in progress, but the primate remains in big cat scat confirm that primates are a major part of the leopard diet in this forest. Along with what we know from the fossil record, these prey preferences have raised an interesting question. Have the hunting habits of leopards influenced primate evolution?
It has previously been proposed that predation has caused some primates to evolve larger body size, larger social groups, groups with more males in them, and other characteristics, and to test these ideas scientists Klaus Zuberbuhler and David Jenny used radio collars to monitor the movements of the Tai leopards and checked leopard droppings for signs of any of nine primate species living in the forest (specifically red colobus, black-and-white colobus, olive colobus, Diana monkey, lesser spot-nosed monkey, Campbell's monkey, putty-nosed monkey, sooty mangabey, and chimpanzees). By putting this information together with what was known of the natural history of each primate species, the scientists could then see if some hypotheses about the influence of predation on primate evolution held up. For instance, if the hypothesis that predation had driven large body size it would be expected that leopards would prefer smaller species, and if larger social groups were a response to predation it would be assumed that leopards would prefer primates which gathered in smaller groups or were solitary more often.
After looking at the movements and fecal samples of four Tai leopards over the course of two years (1992-1994), what the researchers found was that the big cats primarily hunted during the day, and during that time they often searched out monkey groups to stalk. That they did succeed in catching monkeys was confirmed through the 200 scat samples. The majority of prey traces in the feces were from small mammals, particularly small hoofed animals called duikers, but monkey remains were also common (about 64 occurrences, while chimpanzee remains occurring only once). Overall, this was comparable to the results from a similar study published in 1984, with the only difference being that comparatively more Diana monkeys and fewer colobus monkeys were found in the earlier study, and this was probably attributable to known fluctuations in population during that time.
With this data in hand, Zuberbuhler and Jenny could test the leopard's prey preferences against some of the previously-published hypotheses about how predation has affected primate evolution. They were surprised by the results. Leopards appeared to prefer larger monkeys over smaller ones, so it did not seem that larger body size afforded any protection from predators. Likewise, monkeys which lived in larger groups or in groups which had a larger proportion of adult males were preyed upon more often, again running counter to expectations.
The reasons for the disparity between the expectations and the habits of the Tai leopards are difficult to discern. While large body size might make a monkey more susceptible to a leopard due to lessened agility, large body size might be an effective deterrent against the birds of prey which also hunt monkeys in the forest. As for group size, whatever vigilance benefits come from being in a large group might be counterbalanced by the fact that larger groups of primates are easier to find and thus might be preferred by leopards. Rather than providing protection, the traits which were supposed to insulate the monkeys from predation might make them more vulnerable.
But what about the chimpanzees? Why, if leopards prefer larger prey in easy-to-locate groups, were chimpanzees almost absent from the sample? Perhaps they are just to large and strong to be eaten. Leopards, though powerful, are relatively small as big cats go, and they would certainly risk severe injuries if they chose to attack a healthy adult chimpanzee. In fact, at least one of the leopards tracked avoided chimpanzee groups, suggesting that the apes are a special case.
In documentaries, textbooks, and other popular accounts predation is often shown as having a major influence on the evolution. Nothing so poignantly sums up the "struggle for existence" as images of a pride of lions taking down a zebra, a Nile crocodile snapping at wildebeest in the Mara River, a spider wrapping up a fly, or a great white shark closing its jaws on a seal. Yet, as the study of leopards in the Tai Forests suggests, the actual influence of predation on prey species may not be as simple as an arms race of increasing speed, larger body size, or other characteristics outlined in popular examples. Traits thought to protect prey species may, in some cases, prove to be liabilities, and so greater attention must be paid to who predators are hunting and why.
This is not to say the leopards and other predators have had no effect on primate evolution whatsoever, of course. Primates, including our own ancestors, have had to face numerous predators during the course of evolutionary history, and the fact that many primates have evolved anti-predation strategies (such as predator-specific alarm calls) illustrates that predation precipitates some change. No doubt predation had some influence on our own ancestors, too, and I can only imagine how prehistoric hominins, wandering a landscape populated by a wider diversity of carnivores than is seen today, coped with the presence of so many dangerous animals.
Zuberbühler, K.; Jenny, D. (2002). Leopard predation and primate evolution Journal of Human Evolution, 43 (6), 873-886 DOI: 10.1006/jhev.2002.0605
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Do leopards hunt primates in the trees or on the ground? In your recent post on margays and tamarins, the margay approached the tamarins via liana, presumably (?) in the canopy.
I guess I'm wondering, if feline primate predation is mainly arboreal, would that be enough to offer a terrestrial primate an advantage?
HP; Interesting you should mention that. The authors state:
"... it might be that leopards preferred preying on large groups because there is a greater possibility of monkeys
being on the ground. The sooty mangabeys provide an interesting example. This terrestrial species forms very large groups of up to 100 individuals but suffers substantially from leopard predation, even when controlled for the effects of their low population density and large body size."
While leopards are adept climbers, it would seem that they prefer attacking prey which is on or close to the ground. (Margays, by contrast, would be more arboreal hunters.) The fact that birds of prey hunt monkeys in the Tai Forest, as well, means that they are in danger at multiple levels of the forest, with leopards being more of a danger close to the ground and raptors being more of a danger while in the trees.
Hrmm. . . so my "Run away!" hypothesis of bipedalism is shot down in its infancy. Still, I asked a good question! Not bad for a layman.
And of course, any contemporary pattern of feline/primate predation from South America can't tell us much about predator/prey relations in Africa. But now I'm really curious about lion/baboon encounters, or even tiger/macaque.
If you decided to do a whole series on hot feline-on-primate action, I wouldn't be disappointed. :) For all the heat the cable channels take for fetishizing sharks, I think the whole cat/ape thing is morbidly fascinating.
I don't know if it is a good question or not or even a good comparison, but I've read that amongst cougars the mother's diet influences the kittens diet and choice of prey. Is it possible that Leopards hunt or choose prey in a similar fashion? That is one family group might prefer primates while another would avoid them? Might it also be possible that if two predators are competing in the same niche one is more capable of getting it's choice of prey? To be frank, I'm also a lay person but I seem to also recall reading somewhere of caves in South America where the remains of prehistoric humans covering a significant span of time were found. I thought the predators were generations of jaguars. Wouldn't it also be possible that a variety of felines might choose different primates for different reasons...lions/baboons, leopards/chimps, jaguars/human...or some combination there of? I'm just suggesting that a feline choice of primate might be similar across a variety of feline/primate pairings. I do realize i might just be a raving lunatic as well...I'm completely uneducated and my reading/viewing is moderate at best.
The obvious (to me, anyway) alternative hypothesis is that the evolution of human intelligence and relatively large brains in humans and other primates occurred precisely in response to that diversity of threats. If each thing that's trying to kill you needs a specific countermeasure, then you need a big brain to remember all the countermeasures and figure out which countermeasure a specific situation calls for.
I have no idea what you'd look for in the fossil record to actually test that hypothesis, though.
I don't have references on hand, but there are reports of groups of chimps attacking and killing leopards who got too close. The lesson, perhaps, is that group size matters less than group reactions - at a guess, those large groups of mangabeys scattered in individual flight when the leopard turned up?
It seems to me than many of the early line humans were not particularly large or strong, and hand unimpressive teeth. So what tool kit did they have which made them successful in an environment much more dangerous than Africa today? I wonder if they could throw hard and accurately. Has anyone looked at their anatomy with this question in mind?
Here is this leopard looking at some Australopithicenes. The leopard realizes if she attacks she will receive a number of 95-100 MPH rocks bounced off her head, so she looks elsewhere.
@ mike olsen: the book "Ghosts of Tsavo" by Philip Caputo suggests human predation by Lions may be a cultural behaviour (although it raises a number of other theories I don't subscribe to, I have no reason to question this one). Jim Corbett also suggested man-eating was a learned trait passed generationally in tigers.
Whilst this is little more than anecdotal there is a pride of lions that specialises in elephant predation that Darren has addressed on Tetzoo which certainly seems to have a "family tradition" of going after specific prey.
I actually just read a new article on the "ghosts of Tsavo" and why exactly those lions ate humans (well, why one of them did). It suggests drought and a changing ecosystem (due to the decline of elephants) reduced the lions' prey animals, and hence made humans more attractive for weaker lions. The article can be found at:
http://magazine.jhu.edu/2010/03/lions-share/
#7: That's what I was thinking. Maybe leopard predation gave rise to the split-finger fastball.
Dom - Caputo's book seems to suggest that in at least a couple of areas around Tsavo man-eating has more of a history than just those two lions but rather that humans are basically a regular occasional part of the diet which at times of stress on other prey populations (he gives another example of a viral outbreak affecting wildebeest) became a more regular choice.
Its worth a read for the passage on the killing of the maneater of mfuwe if nothing else.
"Have the hunting habits of leopards shaped primate evolution?"
Duh, ya think?
And don't discount the role of venomous snakes in shaping primate evolution, either. And hyaenids. And...
It would be interesting to see if those remains contain traces of Toxoplasma Gondii DNA.
On an unrelated note, it seems odd to me to assume the abilities and especially behavior of leopards to be unchanging for the period over which they study the purported adaptations of primates in response.
I'm not entirely happy with the use of 'preference' here. Successful predation would be a function of such factors as abundance of prey, encounters/detection (e.g. leopards picking up a scent trail), the predators choice to follow a detected prey or not (f.i. preference) and susceptibility of prey (physical features and behavioural predator avoidance strategies). Overrepresentation in feces might just reflect higher susceptibility, not necessarily true preference.
Larger and faster prey may still be more susceptible if they (as mentioned above) are less agile, have less effective antipredator behaviours or less coordinated group behaviours.
Still exciting reading, though :-)
Or maybe we went more aquatic as a response to predation that would blur the lines for most big cats and certainly wolves and hyenas our ability to swim has to come from somewhere, although jaguars and leopards will hunt in water it can't possibly be as preferential as forest floor meaning our predation rate dropped it could also possibly explain bi-pedalism due to the fact even chimps walk up-right in water.
Or maybe we went more aquatic as a response to predation that would blur the lines for most big cats and certainly wolves and hyenas our ability to swim has to come from somewhere, although jaguars and leopards will hunt in water it can't possibly be as preferential as forest floor meaning our predation rate dropped it could also possibly explain bi-pedalism due to the fact even chimps walk up-right in water.
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two predators are competing in the same niche one is more capable of getting it's choice of prey? To be frank, I'm also a lay person but I seem to also recall reading somewhere of caves in South America where the remains of prehistoric humans covering a significant span of time were found. I thought the predators were generations of jaguars
happy with the use of 'preference' here. Successful predation would be a function of such factors as abundance of prey, encounters/detection (e.g. leopards picking up a scent trail), the predators choice to follow a detected prey or not (f.i. preference) and susceptibility
do the ever eat other leopards