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Primates have important ecological roles as seed dispersers and seed predators in tropical forests. Orangutans are large-bodied frugivores that consume a high diversity of plant species, however, relatively little is known about their ecological roles. Ecological interactions are critical processes for ecosystem dynamics, structures, and functions. This dissertation investigated Bornean orangutans’ (Pongo pygmaeus wurmbii) ecological roles by studying orangutan patterns of frugivory, seed dispersal, and seed predation, dispersed seed spatial patterns, and seed fate outcomes. This research was conducted at the Cabang Panti Research Station in Gunung Palung National Park, Borneo, Indonesia. Chapter 2 analyzes orangutan seed dispersal behavior using the seed dispersal effectiveness framework to identify which fruits orangutans are most effectively dispersing. Orangutans predated seeds more frequently than they spat or swallowed seeds. Additionally, the fruits preferred most by orangutans were highly predated. Despite the prevalence of seed predation, orangutans also frequently dispersed seeds, 71.8% of fecal samples contained seeds with a mean of 28 seeds (>2mm) per fecal sample. Chapter 3 models orangutan seed dispersal distances to understand how far orangutans are dispersing seeds across the landscape and if seeds are dispersed across habitat types. This study found orangutans dispersed seeds, on average, 400-650m. There were occasional long distance seed dispersal events, and the maximum dispersal distance was 2.2km. Both male and female orangutans dispersed seeds long distances (>1km). Unflanged male orangutans dispersed seeds the longest mean distances of the age-sex classes with the farthest mean maximum distances at the 80-hour gut retention time. In Chapter 4, the fate of seeds dispersed by orangutans is investigated along with the variation underlying the fate of dispersed seeds. Camera traps and seed tracking studies revealed the orangutan primary seed shadow was heavily reshaped post-dispersal. By 6-months post dispersal, most orangutan dispersed seeds (86-87%) had been removed, mostly by seed predators, and almost all of the remaining seeds (11-14%) had died. This dissertation reveals orangutans are involved in important ecological interactions. Orangutans disperse and predate high quantities of seeds from many plant genera, and the loss of the orangutan would likely negatively affect their natural ecosystems. / 2026-10-31T00:00:00Z

El objeto de nuestra investigación ha sido el estudio de la posible lateralidad manual (grado y direccionalidad de la misma) de los sujetos de una muestra integrada por 31 chimpancés comunes ("Pan troglodytes"), 2 chimpancés pigmeos o bonobos ("Pan paniscus") y 3 orangutanes ("Pongo pygmaeus"), todos ellos en condiciones de cautividad.Se ha observado a los individuos mientras llevaban a cabo la acción de recoger comida (y llevársela a la boca), considerando todos aquellos factores circunstanciales que pudieran incidir sobre la elección preferente de una u otra extremidad. Así, el tamaño del ítem de alimento suministrado, la posición de dicha comida respecto del sujeto, la postura adoptada por el individuo mientras realizaba la acción indicada, el lugar donde se encontraba el alimento al ser recogido y, finalmente, las condiciones de la mano no empleada para recoger comida.En algunos casos, también se han registrado otras conductas espontáneas, tales como: lanzar objetos dirigidos a un blanco, beber agua con la mano y provocar corrientes en la superficie del agua para obtener un objeto flotante sobre la misma.Asimismo, se han propuesto unas pruebas manipulativas especificas a una submuestra de sujetos (formada por 24 chimpancés comunes y 2 orangutanes), consistentes en cuatro aparatos diseñados al efecto, cuya resolución exigía el empleo de una o ambas manos en acciones secuenciales y/o simultáneas, al objeto de obtener una recompensa (un ítem de comida).Además de las preferencias manuales exhibidas por los sujetos en cada una de las acciones de resolución de los aparatos y las estrategias utilizadas para resolverlos, se contemplaba también la postura adoptada por los individuos al manipularlos, controlado la posición del sujeto respecto del aparato y la libertad de la mano no empleada en la acción.Asimismo, al evaluar los resultados obtenidos por los sujetos, se consideraron los siguientes factores: el grado de dificultad cognitivo-atencional y la componente visuoespacial de cada uno de los 4 aparatos, el control motor requerido por las diversas acciones, el número de orden de cada acción en la secuencia de resolución y la coordinación bimanual exigida.El análisis de los datos muestra que el 81 % de los 36 individuos estudiados exhibe una preferencia manual significativa diestra (17 chimpancés y 2 orangutanes) o zurda (10 chimpancés) en la acción de recoger comida.Esta preferencia manual se mantiene estable en el tiempo en los sujetos adultos -mayores de 7 años-, y es consistente en direccionalidad con las preferencias manuales mostradas por cada individuo en las restantes conductas espontáneas consideradas.También podernos hablar de patrones de lateralidad manual individuales en 25 de los 26 sujetos que resolvieron, al menos, un aparato, en función de la preferencia manual exhibida y la consistencia inter-acciones en la direccionalidad de dicha preferencia. En los chimpancés: 8 diestros, 5 diestros mixtos, 1 zurdo mixto y 9 zurdos; en los orangutanes: 1 diestro y 1 diestro mixto. Estos patrones individuales coinciden, en la mayoría de los casos, con las preferencias manuales exhibidas en las conductas espontáneas.De acuerdo con los resultados obtenidos, tanto la edad como la especie parecen ser aspectos relevantes al considerar la lateralidad manual de los sujetos.Así, en los sujetos jóvenes se observa la utilización de la boca en acciones manipulativas simples, una inestabilidad temporal de las preferencias manuales y una cierta dificultad de comprensión y ejecución de las tareas que requieren una coordinación bimanual simultánea. En los adultos, en cambio, se observa una consistencia en el tiempo de las preferencias manuales exhibidas y una direccionalidad diestra de las mismas en la mayoría de los individuos.Las características morfo-conductuales de la especie influyen decisivamente en la realización de la tarea e indirectamente pueden afectar a los patrones de coordinación y lateralidad manual de los sujetos. Así, los orangutanes utilizan, de forma coordinada y eficiente, manos, pies y boca en algunas de las acciones de resolución de los aparatos y exhiben prensiones de precisión digital que no incluyen el empleo del pulgar.Asimismo, se comprueba que hay una serie de factores en las conductas observadas y/o en las tareas propuestas, que facilitarían la expresión de la lateralidad manual, mientras otros tenderían a dificultarla.Entre los primeros cabe destacar: el alto grado de control motor, especialmente la realización de prensiones digitales de precisión; el uso simultáneo y coordinado de ambas manos en acciones con exigencias motoras diversas y, finalmente, la adopción de posturas que implican una reorientación de todo el cuerpo hacia el objetivo final de la acción.En cuanto a los segundos, hay que considerar: la novedad de la tarea y la presencia de una componente visuo-espacial importante -que interfiere en la expresión de la lateralidad manual de los sujetos, especialmente entre aquellos que presentan una preferencia manual diestra- y la complejidad cognitiva de la tarea -particularmente si se traba ja con individuos jóvenes-.A la luz de los resultados obtenidos, creemos posible afirmar que el estudio de la lateralidad manual de los chimpancés y de los orangutanes, nos proporciona modelos homólogos muy válidos para intentar comprender el origen y desarrollo de esta especialización conductual.Ninguno de los datos aportados por nuestro trabajo nos indica una ruptura de orden cualitativa entre las preferencias manuales de los póngidos estudiados y las de los seres humanos. La mayoría de los sujetos de nuestra muestra están manualmente lateralizados y se observa una ligera tendencia hacia el dextrismo -significativa entre los adultos-. / A study on possible manual laterality was carried out on a sample, comprising 31 common chimpanzees ("Pan trogldyytes"), 2 pygmy chimpanzees ("Pan paniscus"), and orang-utans ("Pongo pygmaeus"), all under conditions of captivity.The individuals were observed while engaged in food-reaching activity. In addition, specific manipulative tests were set up for a subsample of subjects (comprising 24 common chimpanzees and orang-utans), consisting of four apparatus whose solution demanded the use of one or both hands in sequential and/or simultaneous actions for the purpose of obtaining a reward (a food item).Analysis of the data shows that the majority of the individuals studied (81%) displayed a significant manual preference in food-reaching activity.Individual manual laterality patterns may also be spoken of in 25 of the 26 subjects completing at least one apparatus (9 left-handed, 1 mixed left-handed, 6 mixed right-handed, and 9 right-handed). The left/right direction of these preferences coincides, in 96% of the individuals, to that shown in their spontaneous behaviour.Both age and the morpho-behavioural characteristics of the species would seem to be significant aspects when considering the manual laterality of the subjects. It was also shown that there are some factors in the behaviour observed and/or the tasks set up that tend to facilitate the expression of the subjects' manual laterality whereas others tend to inhibit it.In the light of the results obtained, it can be stated that the study of manual laterality in chimpanzees and orang-utans provides homologous models that are valid for understanding the origin and development of that behavioural specialization. None of the data obtained points to a qualitative break between the manual preferences of the apes studied and those of human beings. Most of the subjects in the sample are manually lateralized, and there is a slight tendency towards right-handedness - one which becomes significant in the case of adults.

In the lowlands of Southeast Asia, the island of Borneo faces rates of primary forest degradation and deforestation exceeding tropical forests across the globe. For critically endangered Bornean orangutans (Pongo pygmaeus wurmbii), habitat loss greatly threatens the long-term stability of remaining populations. With rates of forest loss and fragmentation on the rise, it is critical we explore the role of anthropogenically-modified landscapes in conserving wild orangutans. Here I investigate orangutan habitat quality within Gunung Palung National Park (GPNP), in Borneo, Indonesia, focusing on the conservation value of a secondary forest with a history of logging. Orangutans in GPNP flexibly inhabit a range of habitats within the primary forest, suggesting the nearby secondary forest could provide population support if sufficient resources are available. Monthly phenology and focal follow data were utilized to assess feeding behavior in relation to food availability. While overall fruit availability was consistently higher in the primary forest, the abundance and fruiting frequency of preferred foods were significantly greater in the secondary forest. The fruiting pattern of preferred resources also significantly predicted orangutan presence. These findings suggest post-disturbance landscapes, if safeguarded and able to become secondary forest, could be vital areas of refuge for Bornean orangutans across an ever-changing landscape.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20557号 / 理博第4315号 / 新制||理||1620(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 友永 雅己, 准教授 後藤 幸織, 教授 平井 啓久 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Orangutans serve as an important species in hominoid studies given their relatedness to the genus Homo, a flagship taxon chosen to represent forest conservation efforts in Indonesia, and an intriguing model for studying alternative reproductive tactics. Despite interest in the species and their importance to their environment, orangutans are exceptionally challenging to study in the wild and captivity. In this dissertation, I investigated the life history of great apes under human care and the growth/ developmental patterns of orangutans. Studbooks, records of all births and deaths of captive animals, compose the largest life history datasets for great apes. I compared the following life history variables for the four great ape species housed in the United States: age at first successful reproduction, interbirth intervals, prenatal death rate, twinning rate, number of offspring, age at last reproduction, and lifespan. Results showed species-specific differences in median age at first birth among females, age at first successful fertilization among males, and number of offspring sired by males and produced by females. The four great ape species had similar ages at last birth among females, age at last successful fertilization among males, and interbirth intervals. Overall, I found that great apes have similar reproductive stages of their lives and capabilities when living with low ecological risk despite some of the differences that exist in their life history parameters. These findings can be used in comparative studies of humans and their most recent living biological ancestors. Next, I investigated the process of flanging in male orangutans. Male bimaturism is one of the most intriguing aspects of orangutans’ biology, yet there is still much that is unknown about the flanging process. All males begin as an unflanged male with the potential to flange at a random timepoint in their lifetime. I conducted a longitudinal study of two males, Budi who flanged and Kembali who remained unflanged, housed at the Toronto Zoo. For Budi, flanging lasted approximately two years. In this time, he increased in body size by approximately 78%, increased his testosterone levels, grew cheek flanges, and began long calling. Throughout flanging, his cortisol levels also increased and his C-peptide of insulin levels fluctuated, both signs of the energetic cost associated with flanging. These findings highlight the extent to which flanging affects male orangutans in terms of their morphology, physiology, and behavior. Lastly, I investigated differences in muscle mass amongst the three adult morphs of orangutans (females, unflanged males, flanged males). Adult unflanged males are approximately the same body size as adult females whereas adult flanged males are approximately twice the size of adult unflanged males and females. Thus, I predicted flanged males would have the greatest estimated lean body mass (ELBM) followed by unflanged males and females. To test this hypothesis, I analyzed creatinine and specific gravity in a large dataset of urine samples from orangutans under human care from zoos in the United States and a smaller dataset from wild Bornean orangutans at Gunung Palung National Park (GPNP) in West Kalimantan, Indonesia. While my predictions were supported by mean ELBM values, I did not find that the different age-sex classes of adult orangutans were statistically different from one another. When we analyzed both datasets together, however, we found that flanged males had significantly higher ELBM compared to all other age-sex classes and that wild orangutans have significantly lower ELBM compared to their captive counterparts. Given the variation in body size amongst age-sex classes, I believe that sex differences in muscle mass will be distinguishable with a larger sample size. Collectively, these findings in my dissertation highlight differences amongst the life history patterns of great apes, which have classically been viewed as being largely similar to one another, and the distinctiveness of having three adult morphs in a primate species. / 2025-06-27T00:00:00Z

Five captive Bornean orangutans (Pongo pygmaeus) were observed in order to better understand their spatial selection, behavior, and interaction with their environment and each other. A newly introduced adult male's interactions with a female group containing two adults, one adolescent, and one juvenile, was documented. Visual observations were performed to document individual behaviors, along with any interactions with silvery langur monkeys, public crowd levels, temperature, and enrichment props. Methods included 15 observation periods, 0.5-3 hours in length each, during which behaviors were verbally and visually confirmed using a HD video camera. Spatial locations of each individual were recorded every three minutes during each observation period. The orangutan enclosure was measured and mapped using terrestrial laser scanning (TLS), and observed behaviors and spatial locations were georeferenced to the resulting 3D model depicting the exhibit. Results were summarized as time-activity budgets and were geo-visualized using 3D plots and density maps. This research demonstrated how the application of spatiotemporal and behavioral analysis coupled with TLS and three-dimensional modelling can be used to better study captive primates. These types of studies are important as zoos increasingly become home to great ape species.

Ecosystem disturbances are a significant and ongoing threat to wildlife, caused by both natural environmental changes and human impacts. These disturbances can have a range of impacts, but one of the most crucial is on the wildlife habitat. In tropical forests, one such disturbance that is occurring at an alarming rate is peat fires. Peatfires impact the forest structure and fragmentation, which in turn directly relate to the wildlife habitat, ultimately threatening the population and even risking extinction for certain species. Of particular concern is the population of orangutans in Indonesia, which is at risk due to the impact of peat fires. This research used an agent-based modelling approach to explore the impact of ecosystem disturbances on wildlife habitat. The focus was on the orangutan population in tropical forests affected by peat fires. A systematic review of agent-based models revealed a shift towards a more mechanistic representation of entities in wildlife response to disturbances. However, fire disturbances and primate species such as orangutans still have a limited number of models. To address this gap, two agent-based models are presented: PeatFire, a model of the ignition and spread of tropical peatfire, validated using data from a fire pattern in South Sumatra; and the BORNEO model, which simulates the movement behaviour of orangutans in a disturbed forest using real tree inventory data and orangutan tracking data from the Sebangau forest in Central Kalimantan. The models were calibrated and validated using state-of-the-art methods and high-performance computing. The study demonstrates the ability of ABM to tackle complex research problems in various fields, including wildlife response to disturbances. The models developed in this study are important examples of the shift towards a more mechanistic representation of agents in ABM, and contribute to advancing the field in this direction. The research offers insights into the impact of ecosystem disturbances on wildlife habitat and highlights the potential of ABM in addressing these issues.

A central issue in the study of primate communication is the extent to which individuals adjust their behaviour to the attention and signals of others, and manipulate others’ attention to communicate about external events. I investigated whether 13 chimpanzees (Pan troglodytes spp.), 11 bonobos (Pan paniscus), and 7 orangutans (Pongo pygmaeus pygmaeus) followed conspecific attention and led others to distal locations. Individuals were presented with a novel stimulus, to test if they would lead a conspecific to detect it in two experimental conditions. In one the conspecific faced the communicator, while another required the communicator to first attract the attention of a conspecific. All species followed conspecific attention, but only bonobos in conditions that required geometric attention following and that the communicator first attract the conspecific‘s attention. There was a clear trend for the chimpanzees to selectively produce a stimulus directional ‘hunching’ posture when viewing the stimulus in the presence of a conspecific rather than alone (the comparison was statistically non-significant, but very closely approached significance [p = 0.056]), and the behaviour consistently led conspecifics to look towards the stimulus. An observational study showed that ‘hunching’ only occurred in the context of attention following. Some chimpanzees and bonobos consistently and selectively combined functionally different behaviours (consisting of sequential auditory-stimulus-directional-behaviours), when viewing the stimulus in the presence of a non-attentive conspecific, although at species level this did not yield significant effects. While the design did not eliminate the possibility of a social referencing motive (“look and help me decide how to respond”), the coupling of auditory cues followed by directional cues towards a novel object, is consistent with a declarative and social referential interpretation of non-verbal deixis. An exploratory study, which applied the ‘Social Attention Hypothesis’ (that individuals accord and receive attention as a function of dominance) to attention following, showed that chimpanzees were more likely to follow the attention of the dominant individual. Overall, the results suggest that the paucity of observed referential behaviours in apes may owe to the inconspicuousness and multi-faceted nature of the behaviours.