Diet of chewing gum turns lively marmosets into lazy layabouts

Earth 2 September 2015
Diet of chewing gum turns lively marmosets into lazy layabouts

When the going gets tough, the marmosets get lazy (Image: Antonio Mendes Pontes)

A group of monkeys has survived an ecological disaster – but only by turning from active networkers into boring layabouts.

The common marmoset, Callithrix jacchus, is a squirrel-sized monkey from coastal north-eastern Brazil. Under normal circumstances it dines on soft fruits and insects that it forages for in the forest.


But, on the Pernambuco State coast, the forest has been largely stripped of the monkeys’ preferred tree species. The area has a long history of sugar cane cultivation and logging, which has reduced its cover to small fragments that rarely exceed 100 hectares.

Insects are also scarce now. Locals use agricultural sprays heavily and winds then waft these insecticides into the forests.

Herbert Pinheiro and Antonio Mendes Pontes from the Federal University of Pernambuco in Brazil have shown how the marmosets managed to survive the drastic changes.

Digestion nap

The marmosets in the three forest fragments they looked at had radically changed their diet, switching from energy-rich fruits and insects to tree gum. While gum is readily available, it normally only makes up a tiny proportion of their diet.

But here, with precious little else to eat, monkeys spend more than 97 per cent of their foraging time eating gum.

The gum is from the Pau Pombo tree (Tapirira guianensis), a member of the cashew family. Pau Pombos are of little use for construction or firewood and so are common in forests like these, where more useful species have already been felled.

But, while gum might be just a bark-gnaw away, it´s extremely indigestible. So monkeys spend around a third of the day resting while digesting the gum, at the expense of other activities such as grooming and social bonding.

“That even such an adaptable species has to modify its ecology so radically to survive in these near-sterile forests is astonishing,” says Pontes.

With Pau Pombos so abundant, at least the monkeys don’t have to travel far to feed, and because the area is poor in wildlife, including predators, they can doze and digest the gum in peace.

Survival uncertain

“This shows how primates can modify their biology to survive in disturbed areas,” says Sarah Boyle of Rhodes College in Memphis, Tennessee. “Even then, their conservation outlook could be grim unless the habitat improves. Small forest fragments still need to be connected and habitat quality improved to ensure the conservation of such primates in the long-term.”

Another recent study found that primates can do surprisingly well in damaged environments: the chimpanzee population in a human-dominated area linking two forest reserves in Uganda, the Budongo and Bungoma forests, is three times bigger than thought. It is estimated that there are almost 320 chimps living there.

“This is very surprising given the fragmentation of forests in this region and the high human population density,” said lead author Maureen McCarthy from the University of Southern California, in a press release. “Chimpanzees, therefore, appear surprisingly resilient and can survive even in degraded habitats if they are not hunted.”

“However,” she added, “their future survival remains uncertain if protection is not afforded to them and habitat loss continues unabated.”

Journal reference: International Journal of Ecology, DOI: 10.1155/2015/685816; BMC Ecology, DOI: 10.1186/s12898-015-0052-x

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