By Kate Stone
For the past year, a research expedition has tracked endangered tigers through the Sumatran jungles and found the animals barely clinging to survival in low-density populations. The expedition findings have reawakened fears about the possible extinction of these elusive apex predators. What is the key to saving the Sumatran tigers? Protecting their habitat, researchers say.
Tigers on the neighboring islands of Java, Bali, and Singapore went extinct in the twentieth century. Their extinction led to new antipoaching efforts by people hoping to help Sumatran tigers avoid suffering the same fate. The good news is that many of those efforts have been successful. In unlogged forests, the density of tigers has increased somewhat over the last twenty years, and tigers’ numbers are twice as high, researchers have found.
The bad news is that well-protected forests are disappearing and increasingly fragmented; between 2000 and 2012, 17 percent of the Sumatran tigers’ habitat was deforested, canceling out any gains to the tigers’ chance of survival, the researchers explain. Habitat destruction for oil palm plantations was a leading culprit of deforestation.
“Our results are a mixed bag,” says Matthew Luskin, formerly of University of California, Berkeley, now a research fellow with the Smithsonian Institution at Nanyang Technological University in Singapore. “The loss of key habitat is causing significant conservation challenges for Sumatra—and in particular for this critically endangered species.”
How did researchers count the Sumatran tigers?
Obtaining information on rare, stealthy predators is not easy, especially in jungles. The research team spent a year trekking through remote Sumatran forests, mounting hundreds of cameras that automatically take pictures and video whenever an animal passes by. Individual tigers are identified by their unique pattern of stripes, allowing the researchers to track their movement.
With data from the cameras, the scientists calculated a Sumatran tiger’s home range to be roughly 150 square miles, about the three times the size of San Francisco. This is much larger than tiger home ranges in other regions such as India and indicates Sumatran tigers need larger parks to survive.
The study found that tiger densities are 47 percent higher in primary versus degraded (logged) forests, and that extensive clearing of pristine lowland forest has disproportionately reduced tiger numbers. This is no surprise; between 1990 and 2010, Sumatra lost 37 percent of its primary forest, and, as a result, tiger subpopulations also became significantly more fragmented, greatly increasing their threat of extinction in each individual forest and as a species.
Too-small jungle fragments, too-few Sumatran tigers
The research team has combined their results with data collected from other scientists to calculate the number of tigers in each remaining forest in Sumatra. They found that there are now just two habitats large enough to host more than 30 breeding female tigers. “The erosion of large wilderness areas pushes Sumatran tigers one step closer to extinction,” Luskin says. “We hope this serves as a wake-up call.”
Mathias Tobler of San Diego Zoo Global adds, “Safeguarding the remaining expanses of primary forests is now absolutely critical to ensuring tigers can persist indefinitely on Sumatra.” The most famous of these forested areas is Gunung Leuser National Park in northern Sumatra, where organizations such as the Leonardo DiCaprio Foundation work to prevent deforestation and poaching. “Large-scale reforestation is unlikely,” Tobler says. “If we are going to save Sumatran tigers in the wild, the time to act is now.”
This study was published in the journal Nature Communications with funding provided by the National Geographic Society.
—Kate Stone serves as the editor in chief of GotScience Magazine.
Featured image: A tiger poses for a camera trap in Sumatra. Credit: Matthew Luskin.
Luskin, M. S., Albert, W. R., & Tobler, M. W. (2017). Sumatran tiger survival threatened by deforestation despite increasing densities in parks. Nature Communications, 8(1). DOI:10.1038/s41467-017-01656-4. Available at: https://www.nature.com/articles/s41467-017-01656-4.
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