Why Macaques Minimally Interact In Palm Oil Plantations

Faced with constant threats, macaques acted more aggressively and showed reduced social bonding inside palm oil plantations, research shows.

AsianScientist (Jul. 26, 2021) – According to an international team of researchers, palm oil plantations can change the social behavior of macaques—for the worse. These findings, which may help inform appropriate measures for protecting these primates, were published in Scientific Reports.

From doughnuts to deodorant, palm oil can be found in nearly half of the packaged products we find on supermarket shelves. Driven by ravenous consumer demand, large swathes of lush tropical forest in countries like Indonesia and Malaysia have since been cleared and replaced by palm oil plantations—affecting the behavior of the creatures that once called those forests home.

Though previous studies have explored the impacts of urban or tourist areas on animal behavior, few have explored how habitats altered by humans affect the behaviors of highly social creatures like apes.

To address this question, scientists from Universiti Sains Malaysia (USM) and collaborators from Germany tracked 50 individuals from two social groups of southern pig-tailed macaques (Macaca nemestrina) in Malaysia, focusing on aggressive interactions, relationship-promoting behaviors as well as mother-infant relationships, among others.

“This is the first population of this shy species to be habituated to scientific observers. Every day, the groups walk for about three hours from the rainforest to the neighbouring plantation,” explained study co-author Dr. Nadine Ruppert from USM.

As anticipated by the researchers, the macaques used the plantation mainly as an additional food source—spending about two-thirds of their time foraging and eating palm oil fruits as well as rats. Compared to the rainforest, macaques behaved more aggressively inside the plantation, likely as the locale offers little protection from threats like humans or stray dogs.

Moreover, the monkeys within the plantation also showed almost no social bonding behaviors mutual grooming or play behavior—potentially in a bid to stay vigilant against attackers.

Conversely, the rainforest served as a safe retreat for macaques at the edge of the plantation. Protected by the nearby forest, the macaques not only displayed social interaction, but in some cases even increased it by almost three times.

The plantation also impacted the smallest social units within the group: mother-infant pairs. Both inside and at the edge of the plantation, mothers maintained more body contact with their offspring. According to the team, this could be due to developmental delays in their offspring, spurring the mothers to invest more time and energy in their children.

In turn, the extended mother-infant bonding could lengthen intervals between births in an already threatened species—potentially jeopardizing the population’s survival in the long run.

Ultimately, the study demonstrates how human-induced habitat changes can severely alter social behaviour in groups and even disrupt mother-infant relationships in the absence of regular direct contact with humans. Protecting remaining populations of these macaques, as well as their habitats, is therefore of utmost importance.

“Their protection will ultimately contribute to maintaining biodiversity and important ecosystem functions of tropical habitats,” concluded Ruppert. “Maintaining forest corridors can…enable animals to engage in essential social interactions that are essential for the long-term survival of primates and other species.”

The article can be found at: Holzner et al. (2021) Oil Palm Cultivation Critically Affects Sociality in a Threatened Malaysian Primate.


Source: Leipzig University; Photo: Anna Holzner.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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