‘Pest’ monkeys save palm oil industry millions

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Monkeys save the palm oil industry hundreds of millions each year by killing damaging pests, according to researchers in Liverpool, UK.

The finding could see pig-tailed macaques turn villain to hero in South-East Asia where they are vilified by palm oil farmers.

“It’s a classic case of my enemy’s enemy is my friend,” stated Dr Antje Engelhardt, Associate Professor in Primate Behaviour and Conservation at Liverpool John Moores University.

Farmers have a long history of conflict with macaques in countries like Malaysia and Indonesia – the heart of the global industry – where the forager’s presence is considered detrimental to crop yields and profits.

Yet the new data suggests that on the contrary, macaques act as biological pest control by feeding on plantation rats, with each macaque group estimated to reduce rat populations by about 3,000 per year.

More profitable

“It soon became clear to us that if used for rodent control in place of the conventional method of poison, macaques could provide an important ecosystem service and enhance palm oil sustainability,” said Dr Engelhardt.

“In short, farms with macaques are going to be potentially more profitable than ones without.”

The area of primary rainforest converted into oil palm plantations has dramatically increased over the past decades to cover 18.7 million hectares of land worldwide. Malaysia alone produces 19.5 million tons of the stuff - 30% of world production.

As monkeys lose their forest homes, they roam onto the plantations, eating or damaging oil palm fruits.

The team, which included researchers from the University of Leipzig, Universiti Sains Malaysia and the Max Planck Institute for Evolutionary Anthropology, investigated both the role of macaques as crop pest and as biological pest control, and presented the first data on macaques’ net impact in the journal Current Biology.

They found macaques eat significant quantities of oil palm fruit – a large group (=44) would eat 12.4 tonnes in a year, roughly 0.5% of production in their home range. Nevertheless, this damage was up to 17-fold lower than the crop damage reported for rats.

Further, an extrapolation of foraging data estimated a consumption rate of 3,135 rats per year per macaque group, not least because they actively search for rats, mostly by removing persistent leaf bases (boots) from oil palm trunks.

A plantation regularly visited by pig-tailed macaques could reduce crop damage from 10% to less than 3% (2.1% by rats; 0.56% by macaques), corresponding to a yield increase equal to crops grown over approximately 406,000 hectares (approximately US$ 650 million per year).

Human-animal conflict

Dr Nadine Ruppert, of Universite Sains Malaysia, concluded: “Our results have important implications for mitigating human-wildlife conflicts by encouraging farmers and palm oil companies to protect primates in their natural habitat.

“To maintain biodiversity with less felling is a win-win situation for productivity and the indigenous animal population.”

- Pig-tailed macaques were listed as Vulnerable in their latest survey (IUCN 2008, [7]), however, given the dramatic decline of their natural habitat, macaque population size is assumed to have further decreased during the past decade.


Towards more sustainable palm oil: macaques can contribute to greener practices when used as biological pest control is published on October 21, 2019 in Current Biology https://www.cell.com/current-biology/fulltext/S0960-9822(19)31171-6 and authored by:

Anna Holzner1,2,3, Nadine Ruppert2,6*, Filip Swat2, Marco Schmidt1, Brigitte M. Weiß1,3, Giovanni Villa2, Asyraf Mansor2, Shahrul Anuar Mohd Sah2, Antje Engelhardt4, Hjalmar Kühl3,5, Anja Widdig1,3,5

1 Behavioural Ecology Research Group, Institute of Biology, University of Leipzig, 04103 Leipzig, Germany

2 School of Biological Sciences, Universiti Sains Malaysia, 11800 Pulau Pinang, Malaysia

3 Department of Primatology, Max Planck Institute for Evolutionary Anthropology, 04103 Leipzig, Germany

4 Faculty of Science, School of Natural Sciences and Psychology, Liverpool John Moores University, Liverpool L3 3AF, UK

5 German Center for Integrative Biodiversity Research, 04103 Leipzig, Germany


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