Because they hang out in nests high up in trees and lead relatively solitary lives, orangutans have challenged scientists trying to study them. Now, orangutans face their own challenge, and it’s urgent.
Increasingly steep population declines over the past century or two have imperiled orangutans’ survival in northeastern Borneo, according to a new DNA analysis. In just the past few decades, the population has dropped from more than 20,000 to about 5,000 orangutans, report geneticist Benoit Goossens of Cardiff University in Wales and his colleagues. This trend coincides with extensive forest clearance that began in the 1890s and accelerated during the past 50 years, the scientists note.
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“This is the first time that a recent and alarming decline of a great ape population, brought about by [people], has been demonstrated, dated, and quantified using genetic information,” Goossens says.
DNA evidence of dwindling orangutan numbers emphasizes the need for intensive conservation efforts, the scientists conclude in the February PLoS Biology.
During a 2001 survey of the still-forested parts of a Borneo wildlife sanctuary, Goossens and his coworkers collected orangutan feces found under nests or near orangutans that they encountered. The team also collected hair from tree nests. A total of 200 individuals were identified by chemically tagging DNA segments known as microsatellites. Studies in people indicate that individual genetic differences evolve relatively quickly in microsatellites.
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The researchers used computer programs to analyze the distribution of genetic variants that had evolved within the sample and to estimate changes in population size that would have produced that distribution.
The results indicate that orangutan populations in northeastern Borneo decreased by more than 95 percent over the past 100 to 200 years. The decline was most rapid in the past few decades, the researchers report. Their new findings are consistent with a controversial 1987 report in which another investigator estimated a population of more than 20,000 after counting orangutan nests observed from a helicopter.
East Borneo orangutans, including the groups that Goossens’ team studied, face a high risk of extinction within the next few decades, the researchers conclude. Major survival threats come from forest destruction to develop oil palm–tree plantations and from illegal hunting.
The arrival of the first farmers in Borneo about 5,000 years ago apparently had little impact on the numbers of resident orangutans, Goossens’ team says.
The new investigation supports the findings of the 2004 Orangutan Population and Habitat Viability Assessment. After surveying orangutans on Borneo and Sumatra, researchers concluded that habitat loss and other factors would wipe out the animals on both islands within about 50 years.
Neither the new genetic study nor the 2004 project appears likely to spark conservation efforts, remarks anthropologist Roberto A. Delgado Jr. of Hunter College, City University of New York. “There are larger socioeconomic and political forces at play in Southeast Asia,” he says.
A proposal to expand timber harvesting is now being considered by the government of Borneo, Delgado notes. Orangutans also suffer from the illegal trade in exotic animals.