Smithsonian Conservation Biology Institute Scientists Find Forest Corridors Are Key to Maintaining Healthy Sloth Bear Populations

By using DNA extracted from sloth bear scat, a team of Smithsonian Conservation Biology Institute (SCBI) researchers found that forest corridors between protected areas in the bears’ native habitats are vital to maintaining a genetically diverse population. The team, including John Seidensticker, Jesus Maldonado, Trishna Dutta and Sandeep Sharma from SCBI and Hemendra Singh Panwar from the Peace Institute Charitable Trust, studied sloth bear populations in four wildlife reserves in India. The work was published May 6 in the PLoS-One paper “Genetic variation, structure, and gene flow in a sloth bear (Melursus ursinus) meta-population in the Satpura-Maikal landscape of Central India.”

“Our study shows that despite their sensitivity to habitat fragmentation, maintaining connectivity can protect sloth bears by preventing the negative impacts of genetic isolation,” said Trishna Dutta, SCBI research fellow and lead author. “The bottom line is clear: Corridors in this landscape are functional and are being used by many different species—sloth bears, leopards and tigers—and the protection of the corridors is vital for their continued survival.”

Studying the genetics of wild animals is a difficult proposition. Not only are sloth bears elusive, but it is difficult to tell individuals apart. Unlike tigers and leopards, these bears do not have unique coat patterns, so researchers cannot use camera traps to track individuals.

For decades, SCBI researchers have lead the world in an innovative, noninvasive alternative to trapping animals for studying genetics: They extract DNA samples from scat and hair that the animals leave behind. This technique allows researchers to study the animal populations in an unintrusive way and to sample far more animals than they would otherwise be able to access.

“Noninvasive techniques allow us to study elusive carnivores from a wide range of habitats by collecting these samples,” said Jesus Maldonado, SCBI geneticist. “From these, we are able to tell how an animal moves through a landscape and the genetic diversity within the population.”

The four wildlife reserves the team studied—Kanha Tiger Reserve, Pench Tiger Reserve, Bori-Saptura Tiger Reserve and Melghat Tiger Reserve—have been set aside primarily for the protection of tigers, but they are also home to other carnivores. The team found that the sloth bears in the reserves comprise two populations that are each connected by corridors: Bori-Satpura and Melghat form one population, and Kanha and Pench form another.

The researchers found that compared to other bear species, this population of sloth bears displayed a moderately high level of genetic diversity, which is an indication of a healthy population. Evidence of genetic mixing in the sloth bear population, along with scats found in corridors between the reserves, show that sloth bears use these corridors as conduits to move from one area to another. Previous research by SCBI scientists found that sloth bears are sensitive to the size and degree of isolation between forest patches. The results of this study support the argument that it is vital to keep the pathways between the reserves open to wildlife.

However, these corridors lack the formal protection of reserves. Humans use the same forest corridors used by bears for farming and livestock, which can result in human-animal conflict. Another looming threat to sloth bears and their habitat is human population, and the infrastructure, development and energy needs that a growing human population requires, such as transportation networks and mining for coal and other minerals.

Native to India, Nepal, Sri Lanka and Bangladesh, sloth bears are vulnerable to extinction. According to the International Union for Conservation of Nature, less than 20,000 sloth bears remain in their range countries.  

Headquartered in Front Royal, Va., SCBI facilitates and promotes veterinary and reproductive research as well as conservation ecology programs based at Front Royal, the National Zoo and at field research stations and training sites worldwide. Its scientists are leaders in applying advanced biomedical approaches, including assisted reproductive technologies and germplasm cryopreservation, for enhancing the demographic and genetic diversity of endangered species. SCBI scientists train students to become leaders in the conservation field. The National Zoo and Conservation Biology Institute is a part of the Smithsonian Institution, the world’s largest museum and research complex.

Zoo visitors can see four sloth bears—two adults and two juveniles—at the Asia Trail exhibit.

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SI-226-2015