Yale Environment Review

Yale Environment Review (YER) is a student-run review that provides weekly updates on environmental research findings.

Sumatran orangutan: Safe for now?

By Henk Jacobs via Shutterstock

Wich, S. A., Singleton, I., Nowak, M. G., Atmoko, S., Nisam, G., Arif, S. M., Putra, R. H., Ardi, R., Fredriksson, G., Usher, G., Gaveau, D. L. A., and Kuhl, H. S. (2016). “Land-cover Changes Predict Steep Declines for the Sumatran Orangutan” (Pongo abelii). Science Advances, 2: 1-8.  DOI: 10.1126/sciadv.1500789

Tuesday, May 23, 2017

While much research has pointed to a steady decline of the Sumatran orangutan as a consequence of habitat loss, a recent study shows population estimates are higher than previously thought. Are these higher estimates enough to preserve the species?

The future for the Sumatran orangutan (Pongo abelii) looks bleak. The International Union for the Conservation of Nature’s Red List of Threatened Species classifies this primate in the category “critically endangered.” Poaching and habitat loss are the main threats to this species’ survival. Orangutans are killed inside protected forests, but also outside when they have to cross cleared areas to reach other forest patches. Sumatran orangutans are found mainly in peat swamps and on forests with mineral soils, which are prime targets for oil palm plantations or other agricultural development. Further, governmental development plans threaten more of this species’ habitat. Knowing the number of individuals, the types of habitats the orangutans occur in, and the range over which they can be found is important for conservationists. This information can ultimately help predict how land use change will affect populations of orangutans.
In a new study, published in Science Advances, Serge Wich from the Liverpool John Moores University in the UK and other researchers estimate the population of Sumatran orangutans at more than 14,000. This more than doubles the previous estimate. The study attempted to understand the influence of different land cover changes on the orangutan populations. To do this, they had to know exactly where orangutans were found and how many existed. Population density was extrapolated from the density of nests counted while the researchers followed predetermined paths, called transects. These transects covered a much wider area than what was previously studied. They also included higher altitudes. The transect locations were randomly selected and spread evenly across the landscape to get a more accurate population estimate. The researchers developed a mathematical model that considered several predictors such as elevation, forest type, and human presence. This model was applied to each of the habitat types and used to predict future population estimates by changing the value of each predictor.
Because this study surveyed higher elevations, logged forests, and a wider area, we now know that orangutans live in a greater array of habitats. Density of orangutans was observed to be highest in peat swamps and lowland forests with mineral soils. In addition, the orangutans were found at altitudes higher than previously known. Human population density had a negative influence on orangutan density. In the nine different land change scenarios tested, all pointed towards declines in population. In 2030, there is a chance that the population could decline by 32.8 percent. Unfortunately, the researchers admit that this may be an underestimate.
Despite the higher population estimates, Sumatran orangutans still face habitat loss and endangerment. This study gives a more accurate estimate of population and greater knowledge of what habitats where the species can exist. This new information is invaluable. It provides a baseline for predicting several scenarios of land use change in the future. The researchers suggest a halt on conversion of peat swamps. This would not only halt habitat destruction but would also reduce the amount of carbon released into the atmosphere, which increases the effects of global warming. Such actions would require strict environmental impact assessments to ensure some consideration of orangutans in further development decisions. Further, the authors suggest a more strict enforcement of anti-poaching laws. Although we have a more positive population size than previously thought, there is still much to be done to ensure the Sumatran orangutan does not go extinct.