Over a 16-year period, about half of the orangutans living on the island of Borneo were lost as a result of changes in land cover. That's according to estimates reported in Current Biology showing that more than 100,000 of the island's orangutans disappeared between 1999 and 2015.

A Bornean orangutan [Credit: Marc Ancrenaz]

Many of those losses were apparently driven by the demand for logging, oil palm, mining, paper, and associated deforestation. However, many orangutans have also disappeared from more intact, forested areas, the researchers say. Those findings suggest that hunting and other direct conflicts between orangutans and people remain a major threat to the species.

"The decline in population density was most severe in areas that were deforested or transformed for industrial agriculture, as orangutans struggle to live outside forest areas," says Maria Voigt of the Max Planck Institute for Evolutionary Anthropology in Germany. "Worryingly, however, the largest number of orangutans were lost from areas that remained forested during the study period. This implies a large role of killing."

To estimate changes in the size of the orangutan population over time, Voigt, along with Serge Wich from Liverpool John Moores University in the UK and their colleagues representing 38 international institutions, compiled field surveys conducted from 1999 to 2015. They extrapolated the overall size of the island's population from the number of orangutan nests observed throughout the species' range in Borneo.

This photograph shows where Bornean forest was cleared for road development  [Credit: Marc Ancrenaz]

All told, the team observed 36,555 nests. They estimated a loss of 148,500 Bornean orangutans between 1999 and 2015.The data also suggest that only 38 of the 64 identified spatially separated groups of orangutans (known as metapopulations) now include more than 100 individuals, which is the accepted lower limit to be considered viable.

In order to identify the likely causes of those losses, the researchers relied on maps of estimated land-cover change over the same period that have been made possible by advances in remote sensing technology. The comparison of orangutan and habitat losses suggests that land clearance caused the most dramatic rates of decline. However, a much larger number of orangutans were lost in selectively logged and primary forests. That's because while the rates of decline were less precipitous in those areas, that's also where far more orangutans are found, the researchers explain.

By 2015, they report, about half of the orangutans estimated to live on Borneo in 1999 were found in areas in which resource use has since caused significant changes to the environment. Based on predicted future losses of forest cover and the assumption that orangutans ultimately cannot survive outside forest areas, the researchers predict that over 45,000 more orangutans will be lost over the next 35 years.

This photograph shows where Bornean forest was cleared for a factory  [Credit: Marc Ancrenaz]

They say that effective partnerships with logging companies and other industries are now essential to the Bornean orangutan's survival. Public education and awareness will also be key.

"Orangutans are flexible and can survive to some extent in a mosaic of forests, plantations, and logged forest, but only when they are not killed," Wich says. "So, in addition to protection of forests, we need to focus on addressing the underlying causes of orangutan killing. The latter requires public awareness and education, more effective law enforcement, and also more studies as to why people kill orangutans in the first place."

They note that Indonesia and Malaysia are both currently developing long-term action plans for orangutan conservation. By taking into account past failures, the hope is that new strategies to protect orangutans can be developed and implemented.

Source: Cell Press [February 15, 2018]

How did Borneo get its elephant? This could be just another of Rudyard Kipling's just so stories. The Bornean elephant is a subspecies of Asian Elephants that only exist in a small region of Borneo. Their presence on this southeastern Asian island has been a mystery. Now, in a study published in Scientific Reports, a research team led by Lounès Chikhi from Instituto Gulbenkian de Ciência (IGC, Portugal) and CNRS, Université Paul Sabatier (France), and Benoit Goossens, from Cardiff University (Wales), and Sabah Wildlife Department (Malaysia), found that elephants might have arrived on Borneo at a time of the last land bridge between the Sunda Islands in Southeast Asia.

The Bornean elephant is the smallest of all elephants. It is also said to be the gentlest. It can only be found in the north  of Borneo in a area representing less than 5 percent of the island, mainly in the state of Sabah (Malaysia)  [Credit: Rudi Delvaux]

Until recently, two opposing theories have been under debate to explain the origin of Bornean elephants: they could have been recently introduced by humans, maybe 300 years ago, or they could have diverged from Asian elephants a long time ago. Indeed, there are historic records reporting that, in the 17th century, neighbour Sultans offered elephants as gifts to the Bornean Sultan. Current elephants would thus be non-native elephants that turned feral. On the other hand, about 15 years ago a genetic study showed that the DNA of Bornean elephants was very different from that of other Asian elephants, suggesting a very ancient separation, on the order of 300,000 years ago. However, no elephant fossils have yet been discovered in Borneo, even though fossils from other large mammals such as orang-utans have been found.

To shed light on the mystery of Bornean elephant's origin, Chikhi and Goossens' team used genetic data analysis and computational modelling to study the past demographic history of these animals. It is very difficult to track ancient demographic history of animals, even more when there are no fossil records to guide the work. "What we did was to create computational models for different scenarios that might have happened. Then, we compared the results from these models with the existing genetic data, and used statistical techniques to identify the scenario that best explained the current genetic diversity of the elephant population in Borneo," explains Lounès Chikhi.

"Our results suggest that the most likely scenario to have occurred is a natural colonization of Borneo around 11,400 to 18,300 years ago. This period corresponds to a time when the sea levels were very low and elephants could migrate between the Sunda Islands, a Southeastern Asia archipelago to which Borneo belongs. We cannot exclude more complex scenarios, but a historical human introduction seems very improbable, and so does a very ancient arrival," adds Reeta Sharma, researcher at the IGC and first co-author of the paper.

With less than 2000 individuals surviving today in an increasingly fragmented environment, and with regular news of poisoned or killed Bornean elephants, the future is grim for this endangered species. "Its very limited geographic distribution and reduced genetic diversity compromise the future of the population. Understanding their origins and past demography will be useful for the development of a long-term conservation strategy, especially at the time we, Sabah Wildlife Department, and partners are drafting a new 10-year State Action Plan for the Bornean elephant," said Goossens. The researcher notes "in the light of the recent killings of elephants in the state for ivory trade and during conflicts, Sabahans must realise that it is their natural patrimony that is targeted, they need to stand for their wildlife and condemn those who kill those magnificent creatures. We should take pride of our wildlife, elephants are part of Sabah's patrimony and we cannot afford losing more animals."

Source: Instituto Gulbenkian de Ciencia [January 17, 2018]