World’s rarest great ape virtually wiped out in a century

The survival of the world’s rarest great ape – the Tapanuli Orangutan – is hanging in the balance, according to a team of scientists.

Fewer than 800 individuals remain in three increasingly disconnected groups on the island of Sumatra, Indonesia, far fewer than the 1,000 surviving mountain gorillas or the more than 2,000 Giant Pandas currently living in the wild.

“The apes are in more trouble than we previously thought,” stated Serge Wich, professor of primate biology at Liverpool John Moores University.

In a study published today, the European-Indonesian research team, estimate that the Tapanuli Orangutan only retains 2.5% of the range it occupied 130 years ago – just over 1,000 km² compared to 40,796 km² in the 1890s.

Driven into mountains

And what’s more, they suggest that their current occupied habitat is not ideal for the remaining individuals, being restricted to mountain territory only.

To estimate the historic range, the authors searched historical journal and newspaper archives and found 23 previously unpublished orangutan records, and found that many records of orangutans were outside the currently known distribution range.

Dr Onrizal, one of the co-authors from the University of Sumatera Utara, said: “Much of what we know about species trends is what ecologists have measured over the past few decades. But what is often overlooked in conservation is the deeper historical context, and that is especially important in a species-rich country like Indonesia.”

Knowing where a species occurred in historical times is important for understanding its ecology and thus informs conservation strategies, they say, while avoiding the historical angle can lead to incorrect assumptions.

“Some scientists have claimed that the Tapanuli Orangutan is a species that is specifically adapted to living at high elevations, because it currently occurs at an average altitude of 834 m above sea level”, said team leader Professor Erik Meijaard, of the Durrell Institute of Conservation and Ecology, University of Kent.

“Our study, however, indicates that the Tapanuli used to primarily inhabit lowland forest and that a combination of unsustainable hunting and forest fragmentation drove the species to extinction in those areas.”

Deforestation

The significant extent of historic forest conversion to agriculture was another surprise in the study. Documentation unearthed by the team from the 1950s showed that large parts of northern Sumatra had already been deforested for smallholder agriculture before the industrial-scale plantation developments that started in the 1970s. For example, 52% of North, South and Central Tapanuli, the Districts where the Tapanuli Orangutan now occurs, were already deforested in the 1930s.

Added Professor Wich: “Our historical analysis shows two important things. First, the Tapanuli Orangutan only retains a tiny part of its former range, where it likely became extinct because of a combination of unsustainable hunting and habitat fragmentation, and both these threats still affect the remaining populations.

“And second, the Tapanuli is not specifically adapted to highland conditions, and should occur in a full range of habitats such as peat-swamp and lowland-dryland forests for optimal likelihood of survival in the wild. The fact that this species has likely been driven to extinction in the peat-swamp forests of North Sumatra is therefore a major concern.”

Contact information:

Erik Meijaard. Email: emeijaard@gmail.com. Tel.: +31-615350744

Serge Wich. Email: S.A.Wich@ljmu.ac.uk

Onrizal. Email: onrizal@usu.ac.id

The manuscript “The historical range and drivers of decline of the Tapanuli Orangutan” is published in PLOSOne and authored by Erik Meijaard1,2,3,*, Safwanah Ni'matullah1, Rona Dennis1, Julie Sherman1,4, Onrizal5 and Serge A. Wich6

1 Borneo Futures, Bandar Seri Begawan, Brunei Darussalam

2 Durrell Institute of Conservation and Ecology, University of Kent, Canterbury, UK

3 School of Biological Sciences, University of Queensland, St Lucia, Australia

4 Wildlife Impact. Portland, Oregon, USA

5 University of Sumatera Utara, Medan, Indonesia

6 Liverpool John Moores University, Liverpool, UK