Psychologists tracking the hunting behaviour of wild leopards on the Ivory Coast have found some new evidence of the evolutionary history of primates.
Dr Klaus Zuberbuhler from the University of St Andrews and Dr David Jenny of the University of Bern, Switzerland, radiotracked a group of leopards in the tropical rainforests to investigate their predation methods, and the effect they had on their main prey of various primate species living in the forest.
Although predation is an important driving force of natural selection, its effects on primate evolution are not well understood, mainly because so little is known about the hunting behaviour of the various predators.
After tracking four wild African leopards in the Taï Forest, the psychologists found that monkeys evolved increased vigilance and a series of clever warning calls after they realised that large body size and living in large groups was no deterrent to being hunted by leopards.
“We found that the leopards preferably hunted for the various primate species living in the forest, suggesting that this predator must have been an important selective factor in the evolution of our primate ancestors. Interestingly, however, the leopards preferred the larger primate species who lived in large groups”, said Dr Zuberbuhler.
“This finding goes against current theory because it suggests that large body size and living in large groups do not adequately protect a primate against leopard predation. Large body size and large group size, in other words, are unlikely evolutionary adaptations to leopard predation.
“Instead, we suggest that the main effect of leopard predation has been on the cognitive evolution of primates. Research has shown that primates are extremely good at predicting the presence of leopards, using all kinds of indirect cues and they possess predator-specific alarm calls to warn each other about an impending threat,” he said.
The leopard is the major primate predator (other predators are chimpanzees and hawks) in the Taï forest and many other parts of the World. The team used a combination of radio-tracking devices and faecal analysis to assess the effect of leopard predation on 9 species in the Tai Forest including the Diana monkey, the Campbell’s monkey, the sooty mangabey, the putty-nosed monkey and the chimpanzee.
Dr Jenny collected 200 leopard faeces over a 2 year period in an area of 100 square kilometres, which after examination, were found to contain the remains of 23 different primate species.
In an unparalleled level of fieldwork, two male and two female forest leopards were equipped with radio-transmitters. The team’s radio-tracking data revealed insights into forest leopards hunting behaviour such as that they primarily hunt for monkeys on the ground during the day.
Faecal analyses confirmed that primates accounted for a large proportion of the leopards’ diet and revealed in detail the predation pressure exerted on the eight different monkey and one chimpanzee species. They related the species-specific predation rates to various morphological, behavioural and demographic traits that are usually considered adaptations to predation (body size, group size, group composition, reproductive behaviour, and use of forest strata).
They found that leopard predation was most reliably associated with density, suggesting that leopards hunt primates according to abundance. Contrary to predictions, leopard predation rates were not negatively, but positively, related to body size, group size and the number of males per group, suggesting that predation by leopards did not drive the evolution of these traits in the predicted way.
Instead, the team believes that the principal effect of leopard predation has been on the cognitive evolution of primate species. Thus the threat of being hunted by leopards has increased the cognitive flexibility in primates, making them evolve more sophisticated ways of dealing with the threat of predators.
The team’s findings have been published in this month’s Journal of Human Evolution.
NOTE TO EDITORS:
FOR FURTHER INFORMATION, CONTACT DR ZUBERBUHLER ON 01334 462080 OR 01382 736827 OR EMAIL kz3@st- andrews.ac.uk
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