The historical range and drivers of decline of the Tapanuli orangutan

Abstract

The Tapanuli Orangutan (Pongo tapanuliensis) is the most threatened great ape species in the world. It is restricted to an area of about 1,000 km2 of upland forest where fewer than 800 animals survive in three declining subpopulations. Through a historical ecology approach involving analysis of newspaper, journals, books and museum records from the early 1800s to 2009, we demonstrate that historically Pongo tapanuliensis inhabited a much larger area, and occurred across a much wider range of habitat types and at lower elevations than now. Its current Extent of Occurrence is 2.5% and 5.0% of the historical range in the 1890s and 1940s respectively. A combination of historical fragmentation of forest habitats, mostly for small-scale agriculture, and unsustainable hunting likely drove various populations to the south, east and west of the current population to extinction. This happened prior to the industrial-scale forest conversion that started in the 1970s. Our findings indicate how sensitive P. tapanuliensis is to the combined effects of habitat fragmentation and unsustainable take-off rates. Saving this species will require prevention of any further fragmentation and killings or other removal of animals from the remaining population. Without concerted action to achieve this, the remaining populations of P. tapanuliensis are doomed to become extinct within several orangutan generations.

Disease Risk and Conservation Implications of Orangutan Translocations

“…• Pathogen risk mitigation strategies do not appear to be consistently applied; lack of crowd control at rescue and release events, lack of PPE use, and limited pathogen surveillance pose notable risks of pathogen transfer to rehabilitant and wild populations • Orangutans are Critically Endangered. Deforestation, habitat fragmentation and killing are most pressing needs • Translocation is often viewed as the preferred solution despite higher cost and risks • Diverse stakeholder needs • Wicked complexity of orangutan conservation issues (5), (9,10), (39), (40,41), (42) What are the management goals and decisions needed? How will the risk analysis help?…”

“…Orangutan metapopulations are at risk from these same factors and may be harmed by removal of animals by wild-to-wild translocation. In areas of orangutan distribution where habitats have been degraded, fragmented or deforested, ecosystem functions are likely also compromised ( 5), (40,41), ( 43), (42) Are there any policy or regulation considerations?…”

“…One Tapanuli orangutan was translocated into a wild population during the pandemic, despite an estimated total species population of 760 animals or fewer, and the concomitant extreme risk posed by potential disease transmission into such a limited population. This animal was previously translocated in 2019 and had moved back into an area around humans ( 42 ).…”

Population Status of Tapanuli Orangutan (Pongo tapanuliensis) within the Renewable Energy Development and its Management Implications

“…Historically, Tapanuli orangutans were found from the upland of West Toba lake in North Sumatra to the Bukit Tinggi district, West Sumatra (Meijaard et al, 2021). The current population was found within the Batang Toru ecosystem, North Sumatera.…”

“…Those potential natural corridors shall be protected, and an artificial corridor could be added to facilitate orangutans' movement, specifically among the small forest patches (Ancrenaz et al, 2021). It was analyzed that one of the causes of the declining orangutans' population is hunting (Meijaard et al, 2011;Meijaard et al, 2012;Davis et al, 2013;Abram et al, 2015;Voigt et al, 2018;Meijaard et al, 2021). Moreover, Wich et al (2012) observed that hunting for Sumatran orangutan often occurred within lower geographical elevation.…”