Erik P. Willems

Erik P. Willems
University of Zurich | UZH · Institut für Anthropologie und Anthropologisches Museum

PhD

About

120
Publications
29,541
Reads
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2,815
Citations
Additional affiliations
October 2003 - October 2008
Durham University
Position
  • PhD Student
September 1999 - July 2003
Utrecht University
Position
  • Master's Student

Publications

Publications (120)
Article
Patterns of primate socioecology have been used to suggest that the first truly savanna-dwelling hom-inin, Homo ergaster, lived in sizeable groups. Here, we revisit these estimates and infer additional features of the social organization of these early hominins based on anti-predator responses observed across the primate taxon. We first show that t...
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Classic socio-ecological theory holds that the occurrence of aggressive range defence is primarily driven by ecological incentives, most notably by the economic defendability of an area or the resources it contains. While this ecological cost-benefit framework has great explanatory power in solitary or pair-living species, comparative work on group...
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The Brownian bridge movement model (BBMM) provides a biologically sound approximation of the movement path of an animal based on discrete location data, and is a powerful method to quantify utilization distributions. Computing the utilization distribution based on the BBMM while calculating movement parameters directly from the location data, may r...
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The importance of between-group competition in the social evolution of animal societies is controversial, particularly with respect to understanding the origins and maintenance of cooperation in our own species. Among primates, aggressive between-group encounters are often rare or strikingly absent, a phenomenon that in some species has been ascrib...
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The long call is an important vocal communication signal in the widely dispersed, semi-solitary orangutan. Long calls affect individuals' ranging behavior and mediate social relationships and regulate encounters between dispersed individuals in a dense rainforest. The aim of this study was to test the utility of an Acoustic Location System (ALS) fo...
Preprint
Co-representation during joint action is a hallmark of human cooperation, but its origin poses a puzzle: It apparently emerges late in ontogeny (around the age of four) suggesting it is cognitively demanding, but it has also been demonstrated in several nonhuman primate species. We reassessed the ontogeny of co-representation in 2-4 years old human...
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The collection of environmental DNA (eDNA) and subsequent metabarcoding are useful tools for assessing marine fish biodiversity noninvasively. It is of particular importance to evaluate biodiversity in regions that are hard to access and thus less well studied. Sampling and preservation methods tailored to the specific circumstances are required. A...
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Play is thought to serve different purposes at different times during ontogeny. The nature and frequency of play are expected to change accordingly over the developmental trajectory and with socio-ecological context. Orangutans offer the opportunity to disentangle the ontogenetic trajectories of solitary and social play with their extended immature...
Article
In many slowly developing mammal species, males reach sexual maturity well before they develop secondary sexual characteristics. Sexually mature male orangutans have exceptionally long periods of developmental arrest. The two male morphs have been associated with behavioral alternative reproductive tactics, but this interpretation is based on cross...
Article
Bottlenose dolphins (Tursiops spp.) are found in waters around Australia, with T. trun-catus typically occupying deeper, more oceanic habitat, while T. aduncus occur in shallower, coastal waters. Little is known about the colonization history of T. aduncus along the Western Australian coastline; however, it has been hypothesized that ex-tant popula...
Preprint
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Proactive information donation is crucial for human cumulative cultural evolution. Evidence for proactive information donation in nonhuman animals is limited to a few examples, and its evolutionary origin remains debated. Here, we examine the role of cooperative breeding for the evolution of proactive information donation by comparing cooperatively...
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For small, arboreal marmoset monkeys, antipredator vigilance is essential to ensure survival. However, since antipredator vigilance is incompatible with some other behaviours, such as feeding in a head-down position, it has to be regulated efficiently within individuals and perhaps even at the group level. To investigate what drives individual diff...
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Social structuring from assortative associations may affect individual fitness, as well as population-level processes. Gaining a broader understanding of social structure can improve our knowledge of social evolution and inform wildlife conservation. We investigated association patterns and community structure of female Indo-Pacific bottlenose dolp...
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Human hyper-cooperativity and the emergence of division of labor enables us to not only solve problems effectively within a group but also collectively. Collective problem solving occurs when groups perform better than the additive performance of separate individuals. Currently, it is unknown whether this is unique to humans. To investigate the evo...
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Although curiosity has huge implications for human creativity and learning, its evolutionary roots and function in animals remain poorly understood. Modern humans, who lack natural predators, thrive with curiosity, but our ancestors faced more hazardous environments that would not necessarily favor individual curiosity. Instead, being curious may h...
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Chimpanzees live in fission-fusion social organizations, which means that party size, composition, and spatial distribution are constantly in flux. Moreover, chimpanzees use a remarkably extensive repertoire of vocal and nonvocal forms of communication, thought to help convey information in such a socially and spatially dynamic setting. One propose...
Article
Understanding determinants of differential reproductive success is at the core of evolutionary biology because of its connection to fitness. Early work has linked variation in reproductive success to differences in age,¹ rank,² or size,³,⁴ as well as habitat characteristics.⁵ More recently, studies in group-living taxa have revealed that social rel...
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Sexual coercion is widespread in the animal kingdom. Its direct forms, including harassment and forced copulation, have largely been investigated as an expression of (alternative) male reproductive strategies, rather than the result of a sexual conflict between the sexes. Likewise, the frequent occurrence of forced copulations in orang-utans (Pongo...
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Consolation has been observed in several species, including marmoset monkeys, but it is often unclear to what extent they are empathy-based. Marmosets perform well in at least two of three components of empathy-based consolation, namely understanding others and prosociality, but it is unknown to what extent they show matching with others. We, there...
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Recent studies find increasing evidence for vocal accommodation in nonhuman primates, indicating that this form of vocal learning is more prevalent than previously thought. Convergent vocal accommodation (i.e. becoming more similar to partners) indicates social closeness. At the same time, however, becoming too similar may compromise individual rec...
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Investigations into cooperative partner choice should consider both potential and realised partners, allowing for the comparison of traits across all those available. Male bottlenose dolphins form persisting multi-level alliances. Second-order alliances of 4-14 males are the core social unit, within which 2-3 males form first-order alliances to seq...
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What information animals derive from eavesdropping on interactions between conspecifics, and whether they assign value to it, is difficult to assess because overt behavioral reactions are often lacking. An inside perspective of how observers perceive and process such interactions is thus paramount. Here, we investigate what happens in the mind of m...
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Sexual coercion, in the form of forced copulations, is relatively frequently observed in orangutans and generally attributed to their semi-solitary lifestyle. High ecological costs of association for females may be responsible for this lifestyle and may have prevented the evolution of morphological fertility indicators (e.g., sexual swellings), whi...
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Species relationships in the bottlenose dolphin (genus Tursiops Gervais, 1855) are controversial. We carried out a comprehensive osteological study of 264 skulls, including type specimens, and 90 postcranial skeletons of Tursiops spp. to address taxonomic uncertainties in Australia using two-dimensional (2D) measurements, and three-dimensional geom...
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Female orangutans exhibit natal philopatry, living in stable home ranges that overlap with those of their maternal relatives. Using data collected from 2003 to 2017 at Tuanan in Central Kalimantan, Indonesia, we take a longitudinal approach to better understand the mechanisms of female philopatry and the factors that influence the home range establ...
Article
Male alliances are an intriguing phenomenon in the context of reproduction since, in most taxa, males compete over an indivisible resource, female fertilization. Adult male bottlenose dolphins (Tursiops aduncus) in Shark Bay, Western Australia, form long-term, mul-tilevel alliances to sequester estrus females. These alliances are therefore critical...
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The acoustic properties of vocalizations in common marmosets differ between populations. These differences may be the result of social vocal learning, but they can also result from environmental or genetic differences between populations. We performed translocation experiments to separately quantify the influence of a change in the physical environ...
Article
Orangutans (Pongo spp.) are reported to have extremely slow life histories, including the longest average interbirth intervals of all mammals. Such slow life history can be viable only when unavoidable mortality is kept low. Thus, orangutans’ survivorship under natural conditions is expected to be extremely high. Previous estimates of orangutan lif...
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In numerous social species, males direct aggression towards female group members during intergroup fights, and this behaviour is commonly thought to function as mate guarding, even though males often target non-receptive females. In studying intergroup fights in a wild population of vervet monkeys, we found that male intragroup aggression was prima...
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Pongo pygmaeus morio, a subspecies of orangutan founded east Kalimantan is steadily declining and classified as endangered. A reintroduction program was recently established. We monitored the reintroduced individuals during their first year post-release at Kehje Sewen Forest in East Kalimantan to document the adjustment to their new habitat. Here,...
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Investigating the mechanisms underlying individual variation in cognitive performance is a crucial step towards understanding the structure and evolution of cognition. In this study, we investigated phenotypic plasticity of 61 Bornean, Pongo pygmaeus, and Sumatran, Pongo abelii, orang-utans to gain insight into how rearing history shapes problem-so...
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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 endange...
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In social species, fighting in intergroup conflicts is one of the riskiest cooperative activities group members engage in, particularly for individuals of the smaller sex. In a number of species, female group members are significantly smaller than males, so the costs associated with intergroup aggression outweigh the potential benefits and females...
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Non-human animals sometimes show marked intraspecific variation in their cognitive abilities that may reflect variation in external inputs and experience during the developmental period. We examined variation in exploration and cognitive performance on a problem-solving task in a large sample of captive orang-utans (Pongo abelii & P. pygmaeus, N =...
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In many solitary mammalian species, females live alone in relatively small home ranges whereas males roam widely and converge around, and compete for matings with fertile females. In primates, orangutans are the only diurnal semi solitary species showing this roving male promiscuity mating system. Here, we develop and test hypotheses about the natu...
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Group-level cooperation often poses a social dilemma in which joint action may be difficult to achieve. Theoretical models and experimental work on humans show that social incentives, such as punishment of defectors and rewarding of cooperators, can promote cooperation in groups of unrelated individuals. Here, we demonstrate that these processes ca...
Article
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Males in a number of group-living species fight in intergroup conflicts to defend access to food resources, a seemingly paradoxical behaviour, given that this resource does not usually limit male fitness directly. We investigated the mechanism(s) driving apparent male food defence in wild vervet monkeys (Chlorocebus aethiops pygerythrus) by testing...
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Cultural species can - or even prefer to - learn their skills from conspecifics. According to the cultural intelligence hypothesis, selection on underlying mechanisms not only improves this social learning ability but also the asocial (individual) learning ability. Thus, species with systematically richer opportunities to socially acquire knowledge...
Method
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ESM from Female monkeys use both the carrot and the stick to promote male participation in intergroup fights
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In many social species, group members cooperate to defend a communal home range. Fighting in between-group conflicts carries an opportunity cost, a risk of injury or death, and the possibility of exploitation by free-riding group members. As a result, it is rare that all group members fight in a given between-group conflict, and individual particip...
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Among primates, orangutans are unique in having pronounced male bimaturism leading to two fully adult morphs that differ in both physical appearance and behavior. While unflanged males have a female-like appearance, flanged males have the full suite of secondary sexual characteristics, including cheek flanges and a large throat sac. So far, hormona...
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Group-living animals often do not maintain territories, but instead have highly overlapping ranges, even though in principle these are economically defendable. We investigate whether this absence of range defence reflects a collective action problem, since a territory can be considered a public good. In a comparative analysis comprising 135 primate...
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In most mammals, females pay for reproduction by dramatically increasing net energy intake from conception to mid- or late lactation. To do this, they time their reproductive events in relation to environmental cycles so that periods of peak food availability coincide with peak demand or are used to build energy stores. This timing is not possible...
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The geographic distribution of Bornean orang-utans and its overlap with existing land-use categories (protected areas, logging and plantation concessions) is a necessary foundation to prioritize conservation planning. Based on an extensive orang-utan survey dataset and a number of environmental variables, we modelled an orang-utan distribution map....
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In trajectory data a low sampling rate leads to high uncertainty in between sampling points, which needs to be taken into account in the analysis of such data. However, current algorithms for movement analysis ignore this uncertainty and assume linear movement between sample points. In this paper we develop a framework for movement analysis using t...
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Female philopatry in mammals is generally associated with ecological and sometimes social benefits, and often with dispersal by males. Previous studies on dispersal patterns of orangutans, largely non-gregarious Asian great apes, have yielded conflicting results. Based on 7 years of observational data and mitochondrial and nuclear DNA analyses on f...
Article
Philopatry and sex-biased dispersal have a strong influence on population genetic structure, so the study of species dispersal patterns and evolutionary mechanisms shaping them are of great interest. Particularly nongregarious mammalian species present an underexplored field of study: despite their lower levels of sociality compared to group-living...
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Ecological factors have been shown to be important for brain size evolution. In this comparative study among catarrhine primates, we examine two different ways in which seasonality may be related to brain size. First, seasonality may impose energetic constraints on the brain because it forces animals to deal with periods of food scarcity (Expensive...
Technical Report
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Discussions in this group focused on a particular problem that arises in animal movement ecology: how to link data describing movement (i.e. sequential GPS-coordinates collected on wild and free-ranging animals) with geographical and environmental context (i.e. properties of the internal and external environment within which the animals move). Our...
Article
Although geographic variation in an organism's traits is often seen as a consequence of selection on locally adaptive genotypes accompanied by canalized development [1], developmental plasticity may also play a role [2, 3], especially in behavior [4]. Behavioral plasticity includes both individual learning and social learning of local innovations (...
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In contrast to most primate species, including the other great apes, orangutans maintain a fission-fusion social system in the wild without being part of a stable community. In zoos, however, they are kept in permanent groups, usually consisting of one adult male and several females. In zoo orangutans, we predict higher levels of glucocorticoids an...
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In social species that cooperatively defend territories the decision to retreat or attack in contests between groups is likely to depend on ecological and social factors. Previous studies have emphasized the importance of the encounter location or the size of competing groups on the outcome. In addition, the identity of the intruder, whether famili...
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Paternity success of high-ranking primate males is affected by the number of males and the number of fertile females and their cycle synchrony. Female vervets in the wild show strong reproductive seasonality and do not advertise the ovulatory period with conspicuous signals or behavior. Because this makes it difficult for males to monopolize fertil...
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The Southeast Asian Sunda archipelago harbors a rich biodiversity with a substantial proportion of endemic species. The evolutionary history of these species has been drastically influenced by environmental forces, such as fluctuating sea levels, climatic changes, and severe volcanic activities. Orangutans (genus: Pongo), the only Asian great apes,...