First integrative trend analysis for a great ape species in Borneo

Truly Santika,Ahmat Suyoko,Roberto A Delgado,Andrew J Marshall,Stephanie Spehar,Hjalmar S Kühl,Kisar Odom,Anton Nurcahyo,Andjar Rafiastanto,Nardiyono Nardiyono,Isabelle Lackman,Graham L Banes,Maria Voigt,Albertus Tjiu,Jessie A Wells ,Max Houghton,Kerrie Mengersen,Jamartin Sihite,Kerrie A Wilson,Ari Meididit,Anne E Russon,Gail Campbell-Smith,Benoît Goossens ,Laura D'arcy ,Ashley Leiman,Musnanda Musnanda,Marc Ancrenaz,Carel P Van Schaik,Didik Prasetyo,Simon J Husson,Serge A Wich,H Hartanto ,Andi Erman,Karmele Llano Sánchez ,Nicola K Abram ,Adi H Santana,Sri Utami ,Purnomo Purnomo ,Niel Makinuddin,Lisa M Curran ,Adventus Panda,Dessy Ratnasari,Iman Sapari,Erik P Willems,Eddy Santoso,Slamet Raharjo,Erik Meijaard

doi:10.1038/s41598-017-04435-9

Abstract

For many threatened species the rate and drivers of population decline are difficult to assess accurately: species’ surveys are typically restricted to small geographic areas, are conducted over short time periods, and employ a wide range of survey protocols. We addressed methodological challenges for assessing change in the abundance of an endangered species. We applied novel methods for integrating field and interview survey data for the critically endangered Bornean orangutan (Pongo pygmaeus), allowing a deeper understanding of the species’ persistence through time. Our analysis revealed that Bornean orangutan populations have declined at a rate of 25% over the last 10 years. Survival rates of the species are lowest in areas with intermediate rainfall, where complex interrelations between soil fertility, agricultural productivity, and human settlement patterns influence persistence. These areas also have highest threats from human-wildlife conflict. Survival rates are further positively associated with forest extent, but are lower in areas where surrounding forest has been recently converted to industrial agriculture. Our study highlights the urgency of determining specific management interventions needed in different locations to counter the trend of decline and its associated drivers.

Highlights

The Bornean orangutan (Pongo pygmaeus) is one of only two great ape species found in Asia today
Our model indicates that the long-term abundance of orangutans per km2 is strongly determined by seasonal rainfall, with the species being most abundant in areas receiving intermediate rainfall during the dry season (150-250 mm per month from May to September) (Fig. 3a) and the wet season (200-400 mm per month from November to March)
Based on population census and land cover data among administrative districts in Kalimantan, we found that districts located within the intermediate rainfall zone have the socio-economic features that lead to higher propensities of hunting compared to districts located outside these zones

Summary

Introduction

The Bornean orangutan (Pongo pygmaeus) is one of only two great ape species found in Asia today. Despite strong public and scientific interest in orangutans in addition to considerable efforts and spending to conserve the species, we do not have an accurate assessment of the rate of Bornean orangutan population decline, or the drivers of this decline. 1), leading to confusion about the conservation status of the species. As for many threatened species, the rate of decline and the drivers of population change of orangutans are difficult to assess because of the species' cryptic behavior, and because surveys of orangutans are typically restricted to small geographic areas, are conducted over short time periods and employ different survey protocols. Extensive parts of the orangutan range in Borneo are remote and difficult to survey 2

Methods

Results

Discussion

Conclusion