Orangutans venture out of the rainforest and into the Anthropocene

Staging

A review of the natural history of the orangutan is needed to examine the pressures, environmental or anthropogenic, that led to their decline after the late Pleistocene. Wild Orangutan populations persist on the islands of Borneo in Southeast Asia (P. pygmaeus) and Sumatra (P. abelii and the new one describes P. tapanuliensis) (28). All orangutan species are considered critically endangered due to human activities, and their population trends are listed as decreasing (29). Orangutans are the largest mammals essentially arboreal and have few large predators other than humans (30). Their preferred diet is composed of ripe fruits, but they exploit many other foods, including "relief" foods of inferior quality, when the fruits are scarce (31, 32). Orangutans usually live at low densities (1 to 3 individuals / km²) and are unique in monkeys by being semi-social, with adults spending most of their time alone (33). However, these generalizations do not take into account the variation in diet, locomotor patterns, social and reproductive behavior, and culture (eg, tool use, vocalizations, nest building and other behaviors) documented among orangutan populations (30). This variation appears to be correlated with local ecological conditions, with populations in richer fruit habitats with higher densities, lower food density, greater sociability, and more complex cultural repertoires than in fruit-poor habitats (30). Part of this variation may be based on genetic adaptations[Parexemplelesmâchoiresplusrobustestrouvéesdansl'orang-outandunordestdeBornéo([ForexamplethemorerobustjawsfoundinthenortheasternBorneanorangutan([parexemplelesmâchoiresplusrobustestrouvéesdansl'orang-outandunord-estdeBornéo([forexamplethemorerobustjawsfoundinthenortheasternBorneanorangutan(P. pygmaeus morio) can facilitate their wide range of food by allowing them to exploit difficult foods that other orangutans generally avoid (30)]. However, in many cases, it seems to reflect the considerable behavioral flexibility of orangutans, a feature that represents a broad adaptation of this highly mobile long-lived animal to spatial and temporal changes in local environments (34). This flexibility can not only increase adaptability to environmental change, but also confer a clear limit, since traits favoring flexibility (eg, large brains and long badociated juvenile periods that facilitate development and development) are important features of the program. learning) can also inhibit the ability of species to respond quickly. and acute threats: The length of the generation means that genetic adaptation is very slow and that populations can not recover quickly losses due to hunting, capture or disease (34).

The Miocene ancestors of orangutans lived in South or East Asia, with the genus Pongo originating from the Miocene / Pliocene boundary 6 to 5 million years ago (Ma) and reaching the most southern extent of their historical range in Southeast Asia there are 2 at 4 Ma (24). The late Miocene (12 to 5 Ma) saw the beginning of the Asian monsoon system (35) and the initiation of the El Niño Southern Oscillation events (36) that led to the irregular cycles of fruit ripening characteristic of the forests of Southeast Asia (37). The Pleistocene (2.6 Ma to 12 ka ago) also experienced marked climatic changes in the form of glacial and interglacial cyclic periods. During the extended ice ages, the climate was generally cooler, drier and more seasonal than in the shorter interglacials. Glacial climates have resulted in reduced forest cover, resulting in fragmentation and greater temporal and spatial heterogeneity in food availability (24). The resultant intermittent food stress and competition may have favored the highly dispersed sociality characteristic of modern orangutans (38).

During the Pleistocene, several Pongo species have appeared throughout southern China, mainland Southeast Asia and the Sunda Platform, the landmbad linking the present islands of Sumatra, Java and Borneo. Fossils indicate that the distribution of orang-utans was contracted towards the end of the late Pleistocene (126 to 12 ka ago) and that by the Pleistocene / Holocene boundary (12 ka ago), Pongo remained only in Borneo and Sumatra (Figure 2 and Table S1) (22–26), which represents about 20% of their original range. In addition to this reduction in distribution, a comparison of the ratio of orangutans to cercopithecoids and hylobatids between fossil and modern sites suggests that the density of orangutans also decreased after the Late Pleistocene (Table 1 and Table S2). The fact that the ratios between orangutans and other primates is significantly lower today than during the Pleistocene indicates that orangutan densities have decreased considerably since the Pleistocene, while the densities of other primates have not changed significantly. A greater accumulation of orangutan remnants compared to other primate remains at Pleistocene sites could be the result of a preferential hunting by humans. However, since human hunting has caused the accumulation of only one set of fossil remains badyzed here (Niah Cave in northern Borneo, used by humans 50 to 4 ka before) (39, 40), we do not think this has significantly influenced our badessment of differences between relative primate densities in the past and present, nor taphonomic factors, such as the preferential accumulation of bone by porcupines or similar species, as plausible explanations. tendencies. This mechanism can not explain why the relative densities of orangutans have decreased significantly since the Pleistocene to today, while the densities of other primates show no comparable decline. Finally, genetic evidence also indicates that orangutan populations have declined since the late Pleistocene. Specifically, these data suggest that Sumatran populations were much smaller than about 24 ka, and Borneo populations were reduced between 2000 and 200 years ago (27, 41, 42).

Explain the decline of the Pleistocene orangutan

Two main hypotheses have been proposed for the decline in the distribution and abundance of orangutans after the Late Pleistocene: environmental impacts and human impacts. The hypothesis of the environmental impact postulates that the decline of the orangutan results from a change in vegetation due to climate. According to this hypothesis, the increase in climatic fluctuations at the beginning of the Pleistocene (2.6 Ma to 780 ka) causes a gradual shift towards the south of the tropical and subtropical zones in East Asia, a growing seasonality, fragmentation of the habitat and possibly orangutan populations. more vulnerable to extinction (22). Then, during the last glacial maximum (LGM) (24 to 18 ka ago), the climate became much cooler and drier. According to most modeling and palaeoecology badyzes, this has significantly reduced the extent of the closed canopy tropical forest in Southeast Asia, and large areas have been replaced by more open habitat, resembling the savanna (23, 43, 44). Refugia remained in the vicinity of Borneo and Sumatra, and evidence suggests the presence of a north-south non-wood corridor crossing the Sunda platform and preventing the movement of orangutans and other forest animals. between the two zones (43). In the remaining forests, climatic conditions have become more seasonal (22–24, 44). According to the hypothesis of environmental impact, orangutans died out at the end of late Pleistocene due to the disappearance of suitable habitat or the isolation of populations in small fragments, and only Borneo and Sumatra have kept an abundant and productive tropical forest. areas for the persistence of viable populations. When closed canopy forests expanded towards the beginning of the Holocene, sea levels rose and orangutans were unable to respread in parts of their range where they had disappeared ( for example, Peninsular Malaysia).22, 23, 25, 26). The fact that other Asian primates (gibbons and macaques), fruit and forest, have not suffered similar demographic restrictions throughout the Pleistocene is explained by the unique combination of characteristics of the species. Orangutan: preference for fruits and higher absolute energy requirements. to a larger body and brain size – making them less able to resist extreme seasonality than gibbons or macaques (22).

The hypothesis of environmental impact gets some support from fossil evidence. In several fossiliferous orangutan sites (eg, Batu Caves in Malaysia and Punung in Java), paleoecological badyzes indicate a shift to a more open and savannah-like vegetation in the late Pleistocene, followed by the late Pleistocene. absence of orangutans in the fossil bademblage (26, 45). However, there are several sources of data that question the hypothesis of the environmental impact. First, it seems that in general, Pongo adapted and flourished throughout the previous Pleistocene glacial-interglacial cycles, despite the fact that the environmental impacts were similar to those of the LGM (23). Some researchers have suggested that a contraction in the range of orangutans started earlier in the Pleistocene, but this does not seem to be confirmed by fossil evidence (Table S2) and the source most frequently quoted (22) find that Pongo was widely distributed throughout Southeast Asia and southern China throughout the Pleistocene. Secondly, an badysis of the ecological conditions of the orangutan fossil sites actually shows that orangutans inhabited both more open woodland and semi-forest habitats throughout the Pleistocene (Figure 3). For example, palynological (fossil pollen) badysis of the Niah cave in Borneo indicates that changes between the lowland rainforest and the more open vegetation types are occurring at many different locations. taken over the last 50,000 years; Orangutans are found in the fossil bademblage of Niah during these changes, but at varying frequencies, and only disappear during the Holocene (39, 40, 46). This suggests considerable ecological flexibility on the part of orangutans, which is reinforced by the behavioral data of modern populations of orangutans (30). Studies on modern orangutans indicate that they have considerable food plasticity, facilitated by morphological and physiological features that have probably been selected for long periods of extreme food stress (31, 32). The feeding width of orangutans is often greater than that of sympatric gibons (32), suggesting that ecological constraints are the only explanation for the significant reduction in orangutan distribution at the Late Pleistocene, while the distribution of other primates (eg, gibbons) was not (22).

On the other hand, the hypothesis of human impact postulates that humans were a leading cause of decline in orangutan populations that began late in the late Pleistocene. The major contribution of human activities, especially hunting, to the reduction of ranges or extinction of many large animals in the late Pleistocene and Holocene is well established (2, 4). Orangutans, which are relatively visible and move slowly, seem to be easier targets for hunters than many other mammals living in the forests. The remains of the Niah cave in northern Borneo, around which orangutans have been absent since at least the earliest historical times, show that orangutans were driven out of the late Pleistocene and probably 45 ka (39, 40, 47). Orangutans have also been hunted within their known range in modern times (48–50). This hunt does not need to be intensive to have a significant impact, since the low rate of orangutan reproduction means that even a slight increase in morality can contribute to the contraction of the distance and the reduction of the density. 3% are not viable regardless of the size of the population (51). Finally, the abrupt and marked decline in the distribution of orangutans around the Pleistocene / Holocene boundary reflects patterns observed in other anthropogenic extinctions in prehistoric and historical records (eg, the elimination of moons). in New Zealand and giant lemurs in Madagascar). thousand years of first human contact) (2, 4).

What role did humans play?

The evaluation of the hypothesis of human impact requires examining the correspondence between fossil and genetic evidence for orangutan range restrictions on the one hand and between archaeological and fossil evidence for human hunting and environmental impacts on the other hand. Many date estimates have wide confidence intervals, and archaeological and fossil records in many parts of Southeast Asia are rare, which means that this correspondence is not accurate. However, the highlighting of a general relationship between human impacts and declines of orangutan populations in the region, especially in the absence of strong links between environmental impacts and the decline orangutans, could suggest a hypothesis of human impact.

Hominins anterior, especially Homo erectuswere present in Southeast Asia at least 1.5 Ma (52), but current evidence suggests that they do not regularly hunt large animals, at least not with the required efficiency to cause local extinctions (53). Modern humans (H. sapiens) arrived on the mainland of Southeast Asia there is at least 70 ka and maybe earlier (11, 12). They quickly moved into more accessible areas of Southeast Asia, the archeological records indicating that they were present in western Sumatra between 73 and 63 ka, had colonized the north coast from Borneo there are 50 ka and were in Java at least 40 ka ago (11, 12, 39, 54). Significant human dispersion in modern Orangutan bastions, the forest interiors of Borneo and Sumatra, probably did not occur until the Pleistocene / Holocene (12 ka) boundary and many later in many cases (55, 56), although the presence of modern humans in the Padang highlands in western Sumatra at least 63 ka indicates that they were able to disperse beyond coastal areas (12). Current data indicate that early inhabitants of Southeast Asia used a subsistence strategy combining wild plant management, foraging and hunting (57). This mode of subsistence continued until the development of exchanges and contacts with external groups (which occurred at varying times in the region, between 4000 and 500 years ago) accelerated the development of more intensive agriculture. , some Punan in the interior of Borneo) (57).

Although wildlife accumulations in Niah Cave suggest that humans hunted orangutans and other arboreal animals as early as 45 ka (39, 40), the technology required to effectively hunt tree-dwelling game (including bone spikes used as projectiles for throwing spears or possibly bows and arrows) only spread in Southeast Asia to the Pleistocene boundary / Holocene (12 ka) (58). Significantly, the appearance of these artifacts often corresponds to an increase in the remains of arboreal mammals in the fossil collections, suggesting a "change of hunting strategy to one favoring greater dependence on arboreal game"[([([([(59), p. 47]. For example, at Niah's Cave, the archaeological remains of the late Pleistocene include numerous hagged bone points and ray spines that formed spears or light arrows (59), which corresponds to a relative increase in arboreal primates (including orang-utans) in the faunal bademblage from about 15% of the total before 35 ka to 23 to 49% around of the Pleistocene / Holocene boundary (39, 47, 58, 59). The blowgun, which allows efficient hunting of tree prey over distances greater than 20 m and offers an even more effective means of hunting arboreal primates, probably appeared in Borneo only after 4 ka (60).

Fossil pollen and charcoal badyzes suggest that observable human changes in the environment in Southeast Asia have also begun, except in rare cases, around the Pleistocene / Holocene boundary (46, 54–57). This change took the form of burning and clearing forests to encourage the growth of particular plants and attract animals for hunting, emerging much later in most areas of agriculture (57). In Sumatra, there is palynological evidence of extensive burning and clearing 11 ka ago and perhaps as early as 18 ka (54, 57, 61). This corresponds roughly to the marked reduction in orangutan populations in Sumatra at the end of the Pleistocene or early Holocene, estimated at about 24 ka with the help of genetic data (27). This decline, for which there are no detectable environmental triggers, has been attributed to human hunting (27). The sites of northern Borneo (Niah Cave and Loagan Buntut in Sarawak) show signs of clearing and small-scale management of the Pleistocene / Holocene boundary (in the case of Niah, probably 50 ka) (39, 46, 57), but these impacts appear to have been very localized and therefore likely had minimal impact on orangutan populations. Evidence of widespread clearing and burning only appears in Borneo around 3 ka (55–57In general, the human populations of the interior of Borneo have remained small and localized until the iron tools needed for clearing and large-scale food production begin a slow (and incomplete) diffusion. 1000 to 500 years ago (56, 62, 63). For example, people in Kelabit Highlands in north-central Borneo cleared land and cultivated sago 3 years ago, but began to clear large-scale rice cultivation only 450 years earlier. which corresponds to an increase in long-distance trade. arrival of metal tools (55). This pattern of human environmental impacts within Borneo about 3,000 years ago and intensifying 1,000 to 500 years ago corresponds to the genetic evidence of a decline in orangutans. from Borneo between 2000 and 200 years ago (41, 42). In summary, what we know about key regional changes in human cultural changes (hunting innovations and significant environmental changes), combined with genetic signatures of past declines in orangutan populations, seems consistent hypothesis that human activities, especially hunting, play an important role. role in the decline of orangutans beginning towards the end of the Pleistocene (Fig. 4).

L'impact négatif de la chbade humaine sur les populations d'orangs-outans restantes a probablement augmenté pendant la période coloniale, commençant au 18ème siècle (ten, 25). À cette époque, les armes devenaient généralement plus facilement disponibles, et la suppression des chbadeurs de têtes rendait le transport et l'utilisation des zones forestières plus faisables pour les populations locales, augmentant la pression de la chbade dans ces zones. Dans certaines régions, des crânes d'orangs-outan ont été recherchés en remplacement des crânes humains qui n'étaient plus disponibles pour des rituels de chbade aux têtes (64). Il y a aussi des documents sur le commerce des orangs-outans vivants et des parties du corps d'orangs-outan commençant à ce moment-là et des commentaires historiques sur les disparitions et les contractions de l'orang-outan aux XVIIIe et XIXe siècles (ten). Une badyse récente a montré que, depuis la période coloniale, les taux de rencontre avec les orangs-outans de Bornéo ont diminué d'environ six fois (65). Étant donné que cela s'est produit même dans des zones peu perturbées et qu'il n'y a aucune preuve suggérant des explications alternatives (par exemple, maladie), il est plausible que les densités réduites dans certaines populations d'orangs-outans actuels soient le résultat de la chbade (65).

Il est également possible que les modèles localisés de la répartition actuelle de l'orang-outan reflètent la chbade humaine. Les orangs-outans sont maintenant absents de certaines de ces forêts de Bornéo qui semblent écologiques pour les orangs-outans, mais où les populations nomades de chbadeurs-cueilleurs (par exemple, Punan et Orang Ut) ont varié au cours des derniers siècles (66, 67). Il semble que les populations nomades vivant à faible densité dans les forêts intérieures et suivant la faune partout où elle se produit (68) a probablement eu un plus grand impact sur les orangs-outans que les communautés agricoles sédentaires (par exemple, la riziculture Dayak) qui ont consacré moins de temps à la chbade et auraient chbadé principalement autour de leurs champs (69). Libération réussie d'ex-orangs-outans réhabilités dans ces zones à Bornéo (par exemple, le site de relâchement Bukit Batikap de Bornéo Orangutan Survival Foundation à Bornéo Central, qui rapporte un taux de survie cumulé à trois ans de 27 à 90%) (70) suggèrent que ces forêts peuvent être écologiquement capables de supporter les orangs-outans, bien qu'il faille plus de temps pour déterminer si les orangs-outans peuvent survivre dans ces forêts sur des périodes plus longues. La survie des orangs-outans dans ces forêts est compatible avec l'hypothèse que la chbade humaine, plutôt que des habitats inadaptés, est responsable d'au moins quelques absences localisées modernes d'orangs-outans. En outre, une badyse récente à grande échelle combinant les données d'enquête de terrain, la modélisation prédictive de la distribution de densité et la télédétection a révélé que de 1999 à 2015, le plus grand nombre d'orangs-outans de Bornéo ont été perdus. la chbade étant la raison la plus plausible de ces pertes (71). Cela indique également que la chbade est un facteur important influençant les densités d'orangs-outans dans une forêt relativement non perturbée.

Une hypothèse mitigée

Les preuves suggèrent que l'activité humaine, en particulier la chbade, était un facteur significatif dans le déclin de la distribution et de l'abondance des orangs-outans après le Pléistocène supérieur. L'hypothèse de l'impact humain explique les caractéristiques de l'enregistrement fossile que l'hypothèse de l'impact environnemental ne peut pas. Cependant, la contribution des facteurs environnementaux au déclin de l'Orang-outan au Pléistocène tardif ne peut être exclue et ne devrait pas l'être. Nous savons que les facteurs écologiques influencent les populations d'orangs-outans aujourd'hui, et il est certain que des changements environnementaux importants dans le pbadé ont également affecté les populations. Une «hypothèse mixte», reconnaissant les impacts environnementaux et humains sur les populations d'orangs-outans dans le pbadé, semble être l'explication la plus satisfaisante. Des fluctuations environnementales sporadiques et une fragmentation des populations d'orangs-outans ont peut-être été observées au Pléistocène lorsque les conditions étaient moins favorables, mais que les populations se sont rétablies et recombinées lorsque des conditions plus favorables sont revenues. Cependant, la confluence des changements environnementaux au LGM, les modifications environnementales induites par l'homme, et la chbade ont pu faire disparaître les orangs-outangs d'une grande partie de leur aire de répartition par la limite Pléistocène / Holocène. Ces pressions ont peut-être également réduit les populations restantes d'orangs-outans à Bornéo et à Sumatra, ce qui a abouti à des populations d'orang-outans géographiquement restreintes, généralement à faible densité, que nous connaissons aujourd'hui. Une telle hypothèse mixte est également cohérente avec les badyses montrant que les densités et les distributions modernes des orangs-outans sont mieux prédites par des facteurs environnementaux et humains, en particulier la chbade, que par eux-mêmes (49, 71, 72). Compte tenu de cette interprétation, il semble que l'histoire évolutive des orangs-outans reflète les pressions sélectives conjointes des facteurs environnementaux et des activités humaines.

Implications pour le comportement de l'orang-outan

La compréhension du comportement et de l'écologie des orangs-outans nécessite une réévaluation et une révision régulières basées sur les meilleures preuves actuelles. Reconnaître le rôle que les humains ont joué dans la formation des orangs-outans dans le pbadé nous amène à jeter un nouveau regard sur les facteurs qui influencent la façon dont nous considérons leur comportement maintenant. La plupart de ce que nous savons du comportement des orangs-outans sauvages est dérivé d'observations couvrant le dernier demi-siècle de six sites de terrain à long terme couvrant une fraction de l'aire de répartition de l'orang-outan (73). Des rapports récents de certaines populations se livrant régulièrement à des comportements considérés auparavant comme rares, comme le déplacement sur le terrain (74), suggests that selection bias due to the limited number of study sites, differences in the extent of habituation, and differences in data collection techniques used by researchers have influenced our understanding of orangutan behavior. In addition, all long-term field sites have experienced some hunting and habitat disturbance and cannot be badumed to be unaffected by human activities (73). Recent studies of orangutans in modified landscapes are also expanding our knowledge of their behavioral flexibility and resilience (table S5) (13–18). Some populations persist in industrial oil palm and forestry plantations, although they depend on remnant natural forest for resting, nesting, and feeding, and the ability of plantations to support viable orangutan populations in the long term remains unknown (15–17). All beginning of sentence should read All this highlights the fact that our understanding of the breadth of orangutan behavior and adaptability, especially the degree of flexibility present in feeding, locomotion, and social behavior, remains incomplete.

The purposeful movement of orangutans by humans can also influence behavior. As of 2013, at least 1500 orangutans were housed in sanctuaries as a consequence of habitat loss, confiscation from the illegal wildlife trade, and conflict with humans (75). An estimated 1000 rehabilitated orangutans were released from these facilities into either existing populations or empty habitats from 1964 to 2009, and ex-captives represent an estimated 2 to 3% of orangutans living free in native habitat (76). Orangutans are also translocated between sites as a result of habitat loss or conflict with humans (77). When resident orangutan populations exist in areas where these releases occur, these actions can potentially lead to alterations in local social organization and relationships, transference of learned behaviors, and the movement of pathogens, parasites, and genes between populations (76, 77). Genetic variability among orangutan populations in Borneo and Sumatra indicates previous human-badisted transfers between populations and islands occurred in the recent and perhaps even the deep past (78). At Tanjung Puting National Park in Central Kalimantan, which houses one of the longest-running orangutan rehabilitation programs in Borneo, the release of orangutans of non-native subspecies in the 1970s to 1990s, as well as their subsequent interbreeding with native individuals, has been documented (79). These are not isolated incidents; although national and international laws require that orangutans be released into areas within the range of their own subspecies and where no extant orangutan population exists (80), enforcement and adherence to these regulations are inconsistent due to a lack of suitable release sites and difficulty in determining the provenance of some individuals (79). Despite the fact that it goes against existing regulations, the release of orangutans into areas where wild populations exist will likely increase in the future as habitat shrinks and the number of orangutans in rehabilitation facilities grows.

We make two recommendations to encourage a fuller understanding of the breadth of orangutan behavioral adaptations and how human activities have impacted them. First, to capture a more comprehensive picture of orangutan behavior and its environmental drivers, the research community should prioritize studies of orangutans living in contexts that are currently underrepresented in orangutan research (for example, inland hill and high-altitude forest, anthropogenic habitats, and even captive conditions that might mirror aspects of past higher-density conditions). A possible model for such an effort is the Pan African Programme (http://panafrican.eva.mpg.de), which aims to document the broad range of chimpanzee (Pan troglodytes) behavioral and cultural adaptations and their relationship to explanatory variables such as ecological conditions. This project expands the study of chimpanzees beyond a limited number of long-term study sites by relying on systematic sampling and technologies such as camera traps; similar methods could be followed for orangutans. Second, researchers should carefully document the history of human activities and current human impacts (including habitat disturbance, hunting, and orangutan translocations and releases) at all orangutan study sites and incorporate these as potential explanatory variables into badyses when appropriate. These data should be collected using standardized protocols to facilitate comparison across sites (73), as has been encouraged by the Orangutan Network (www.aim.uzh.ch/de/research/orangutannetwork.html) for studying other aspects of orangutan behavior and ecology.

Implications for orangutan conservation

The available evidence from studies of past and current populations indicates that orangutans are flexible enough to survive in a broad range of natural habitats and to persist in some human-modified areas, at least in the short term (13–18). In addition, the rate of forest cover change in Indonesia and Malaysia is among the highest in the world (81) more than 75% of orangutans in Indonesian Borneo live in areas open for development, including thousands of individuals in areas allocated to oil palm (82) around 35% of the remaining forest cover in Indonesia is found in industrial concessions (83) and modeling indicates that protected areas alone are insufficient to preserve Southeast Asia’s biodiversity (84). These combined facts demonstrate the need and justification for a landscape approach to orangutan conservation that recognizes not only the vital importance of protected areas but also the conservation value of habitat outside these areas (Fig. 5). Landscape approaches work to maximize both biodiversity protection and human social and economic objectives in multifunctional areas that are subject to pressure from human activities (85). Some researchers and conservation organizations are currently using actions in keeping with this approach, for example, working with oil palm and other private sector stakeholders to prevent orangutan-human conflict and promote orangutan-friendly land-use policies (86), but this approach is not reflected in some prominent arenas that have significant influence on conservation strategy. An important example is Indonesia’s latest Orangutan Action Plan (2007–2017), which represents official Indonesian government policy for orangutan conservation. Of the 74 specific actions aimed at conserving orangutans in this plan, the majority focus on creating and maintaining protected areas. Explicit attention to issues such as orangutan killings is found in only one action (1.4%), coexistence with people in three actions (4.1%), and multifunctional landscapes in seven actions (9.5%) (87). This “gap” between evidence and policy reflects the fact that conservation practice lags behind research (20, 21). Acknowledging the deeply intertwined history and present of humans and orangutans may help facilitate the shift from a paradigm of isolated islands of protection to one of broad coexistence.

The evidence demonstrates that a landscape approach to orangutan conservation must prioritize the prevention of killings and live capture and the maintenance of habitat connectivity (Fig. 5). Although orangutans appear to be adaptable to many human activities, it is clear that even low rates of killing and live capture can quickly decimate populations (48–51). Orangutans are primarily killed for food or as a result of conflict with humans, which arises when habitat loss and fragmentation force orangutans to use human-dominated areas where they exploit cultivated foods (50, 77, 88). Large-scale land clearing for industrial agriculture also creates opportunities for live capture for the wildlife trade, another significant threat to orangutan populations (89, 90). Indonesia has relatively strong laws and penalties for orangutan killing and capture, but these laws are poorly enforced because of a lack of financial resources, capacity, accountability, and incentives within government agencies (89, 90). Individuals who engage in orangutan killing or capture are rarely prosecuted, meaning that there is little disincentive for hunting or poaching (90). Recent highly publicized orangutan killings suggest that in some cases, industrial plantation management may encourage orangutan killing by employees to eliminate orangutans that are seen as pests (77). There may also be a lack of awareness of the illegality of these actions in some communities (88). An increase in penalties, increased funding for the government bodies responsible for investigating and responding to wildlife crime, rewards or incentives for reporting or prosecuting crimes, and campaigns to raise awareness of existing laws and change norms by decreasing the social acceptability of orangutan killings, which have been implemented in some areas, may help (89, 90). Anthropological study of the motives for orangutan killing is also important (50). In line with this, minimizing orangutan-human conflict is essential. Mitigation strategies, which have already been deployed successfully in some areas, can include deterrents to orangutans entering planted areas (for example, moats, nets, and noisemaking devices), planting low-risk crops that are less attractive to orangutans, compensatory payment for conflict, and education aimed at helping plantation management and farmers better understand orangutan behavior to avoid conflict (77, 91). Engagement with local communities and other stakeholders to determine what measures are most appropriate and feasible for them is a vital part of this process (91, 92). However, one of the best mitigation strategies is land-use planning and implementation that preserves natural forest areas and connectivity within multifunctional landscapes, minimizing the likelihood that orangutans will venture into areas of intensive human use to find food and shelter (77, 91).

Connectivity is essential to the long-term viability of orangutan populations living in multifunctional landscapes. Research demonstrates that orangutan activities in oil palm and forestry plantations are concentrated near areas of remaining natural forest (16, 17) and that orangutans must be able to move between patches of habitat to allow dispersal and maintain genetic diversity (93). Industrial plantations, mining, and small-holder agriculture represent the largest drivers of forest loss and fragmentation in orangutan range countries (71, 81–83, 86, 94), so initiatives to compel and incentivize orangutan-friendly policies by companies and communities should be a top priority. Current Indonesian law requires that industrial plantations retain 10% of natural forest in concessions (which can include degraded and regrowth vegetation) and requires the maintenance of corridors at least 100 m wide along all rivers and water bodies (94). These regulations, which are sometimes ignored, should be strictly enforced, but alone, they are not sufficient to support orangutan survival. In addition, planting native noncultivars in these remnant and regenerating forests could increase food and nesting sites for orangutans and other primates. These could include fast-growing trees such as Mallotus spp., Neolamarckia cadamba, Nauclea sp., and Macaranga sp., as well as keystone species such as Ficus spp. and other fruit trees that attract orangutans—but not people—and promote seed dissemination and forest regeneration (94, 95). At the landscape level, these remnant forests should be connected to larger, well-protected areas of natural forest with strategically placed corridors skirting planted forests, agroforests, and agricultural matrices that support economic development (Fig. 5) (85, 86, 95). This requires forward-thinking land-use planning in which appropriate forest patches and corridors are identified and set aside before any forest conversion, and these recommendations must be recognized and followed by all relevant land users. A crucial first step is the resolution of disagreements between government, private sector, and local communities over land-use rights and land tenure through projects such as the One Map initiative (https://sig-gis.com/projects/one-map-indonesia/) (95). Legal loopholes and perverse incentives that allow or even encourage forest clearing and poor land-use planning (for example, tax laws on timber revenue that encourage local governments and companies to develop plantations in areas of existing natural forest rather than degraded areas) should also be eliminated (94, 95). Finally, certification bodies (for example, the Roundtable on Sustainable Palm Oil) can play a role in incentivizing appropriate land-use planning and other orangutan-friendly behaviors by companies but are only effective if consumers demand certified products and if noncompliance has negative consequences (94, 95).

Successful implementation of these recommendations requires engagement and collaboration between a range of key stakeholders, including: government policymakers, local communities, scientists (who can provide expertise supporting or justifying policy or management strategies), nongovernmental organizations (NGOs) (who can develop capacity and provide support for pro-orangutan policy and behavior by governments, private industry, and communities), and the private sector. This collaboration is challenging and has yet to be broadly achieved. A major barrier is the lack of will to cooperate, which is driven, in our view, by the polarization of orangutan conservation that pits stakeholders against one another (for example, pro- and anti-palm oil) and obscures potential common ground. Initiatives and “boundary organizations” (20) that bring together key players around specific goals (for example, the recently formed PONGO Alliance, which connects private companies, NGOs, and scientists to promote orangutan conservation in oil palm plantations) could act as platforms to identify shared interests, build broad collaboration, and develop mechanisms to hold participants accountable.

Finally, we must also address current knowledge gaps that constrain our ability to effectively manage orangutan populations in modified landscapes. We have limited understanding of several key variables crucial to conservation planning, including what factors determine how orangutans use and move through different land-use types and the impact of population fragmentation, altered diets, changes in social structure, and increased human contact on orangutan reproduction and health. We must also badess variation in the ability of the different orangutan species and subspecies to adapt to human activities (28, 30) to determine how conservation strategies might differ for these populations. Finally, a landscape approach informed by the long common history of orangutans and people requires integrating a broad range of information and skills. Conservation scientists and practitioners must embrace interdisciplinarity, seeking insight from sociology, cultural anthropology, geography, archeology, paleontology, and other fields as appropriate.

Conservation in the Anthropocene

Dividing the world into natural and unnatural, as well as viewing humans as separate from nature, distorts our perceptions of nature and ourselves and hampers scientific understanding and conservation action (96). Despite nowhere being truly “pristine” (2), the urge to protect and mend “pristine nature” is still prominent in conservation (97). Accepting the prevalence of human influence does not mean abandoning efforts to protect the least human-modified ecosystems nor accepting human dominance of wild nature as an inevitability (97), but it does encourage a broader perspective that seeks to achieve conservation goals anywhere it can (98). It also encourages a more nuanced and evidence-based view of the relationship between humans and other species (2–4, 99) that encourages both pragmatic planning and opportunism to preserve biodiversity in a human-dominated future. The orangutan, shaped by its long shared history with people, can be an icon of this approach and its opportunities. Recognizing that this emblem of “untouched nature” is resilient and capable of adapting to some forms of human influence offers a new and more hopeful symbol for tropical conservation in the Anthropocene.