Orangutan movement and population dynamics across human-modified landscapes: implications of policy and management

Abstract

Context Agricultural expansion is a leading cause of deforestation and habitat fragmentation globally. Policies that support biodiversity and facilitate species movement across farmland are therefore central to sustainability efforts and wildlife conservation in these human-modified landscapes. Objectives We investigated the conservation impact of several potential management scenarios on animal populations and movement in a human-modified tropical landscape, focusing on the critically endangered Bornean orangutan, Pongo pygmaeus. Methods We used an individual-based modelling platform to simulate population dynamics and movements across four possible landscape management scenarios for a highly modified oil palm-dominated landscape in Sabah, Malaysian Borneo. Results Scenarios that maximised the retention of natural forest remnants in agricultural areas through sustainability certification standards supported stable orangutan populations. These populations were up to 45% larger than those supported under development-focused scenarios, where forest retention was not prioritised. The forest remnants served as corridors or stepping-stones, increasing annual emigration rates across the landscape, and reducing orangutan mortality by up to 11%. Sensitivity analyses demonstrated that this outcome was highly contingent on minimising mortality during dispersal. Conclusions Management that promotes maximising natural forest cover through certification, such as that promoted by the Roundtable on Sustainable Palm Oil, can maintain viable orangutan populations over the lifespan of an oil palm plantation and facilitate movement among otherwise isolated populations. However, minimising hunting and negative human–orangutan interactions, while promoting peaceful co-existence between apes and people, will be imperative to insure positive conservation outcomes.

Riparian buffers can help mitigate biodiversity declines in oil palm agriculture

“…Many of the terrestrial species detected in narrow buffers are likely transient, using them for short-term refuge (Rodríguez-Mendoza and Pineda 2010), seasonal resources (Keuroghlian and Eaton 2008), or dispersal (Gray et al 2019). Nevertheless, transient use of buffers may still help populations to persist in the long term, particularly in areas where the landscape matrix is inhospitable (eg orangutans [Pongo spp]; Seaman et al 2021).…”

Mammals in an Oil Palm Dominated Landscape

“…They were, however, much less abundant in these patches, with their density reduced by almost two-thirds when compared to logged forest (Seaman et al, 2019). It is widely recognised that oil palm plantations have negative effects on orangutan populations (Ancrenaz et al, 2021;Payne & Oram, 2020), yet our data indicates that they retain a limited ability to persist in and around plantations, provided some forested areas are retained within the wider landscape (Seaman et al, 2019;Seaman et al, 2021). Orangutan nests were observed in remnant forest patches and in riparian buffers within oil palm plantations, and at distances of over 6 km from large forested areas, indicating that some orangutans are probably resident within the plantation estates (Seaman et al, 2019).…”

“…Moreover, adult females with young have been directly observed in riparian buffers (Seaman et al, 2019), possibly indicating a limited ability to reproduce in these landscapes. Our research contributes to the growing wealth of data indicating that orangutans using and living in remnant forest patches are important in maintaining gene flow in orangutan populations over large geographic areas (Ancrenaz et al, 2021;Seaman et al, 2021).…”

“…Computer modelling was used to examine the impact of competing landscape management scenarios on orangutans, with scenarios ranging from the retention of forest remnants in agricultural areas through sustainable certification standards to development-focussed scenarios where forest retention was not prioritised (Seaman et al, 2021). Even in highly fragmented landscapes it was predicted that substantial orangutan populations could be sustained for at least 40 years in areas under oil palm production when management aims to maximise the amount of forest cover, although this does not account for what might happen to the orangutan populations when oil palm replanting occurs (Seaman et al, 2021).…”

Disease Risk and Conservation Implications of Orangutan Translocations

“…Results for orangutans, on the other hand, have been markedly poor ( 40 , 41 ). However, conservation and management of orangutan populations within forest reserves and forested patches in palm oil plantations is possible if killing is avoided ( 5 , 43 , 93 ).…”