Carel van Schaik - US grants

Comparative studies document the diversity of lifestyles observed across species. The usual goal of such studies is to understand the causal basis for this diversity. In the research proposed here, diversity in primate behavioral, morphological, and life history characteristics will be examined using comparative methods. This study improves on previous research in three ways. First, it makes use of the largest primate socioecological database to better document patterns across species. This database also retains information on intraspecific variation to test patterns below the species level. Second, this study investigates a recently expanded theoretical model which includes the role of conflict between males and females in primate social evolution. Finally, this research applies new methods for dealing with the statistical problems of non-independence associated with evolutionary descent. Results from these methods have already identified new patterns and invalidated some previously proposed associations among traits. Thus, this research has important implications for the empirical basis of our understanding of primate social evolution. Comparative studies have played an important role in explaining evolutionary patterns, and the present work is expected to have implications for future research and education in primatology.

This project involves a systematic investigation of behavioral differences between populations of wild orangutans (Pongo pygmaeus). The widespread tool use among orangutans at Suaq Balimbing (Sumatra, Indonesia) suggests that orangutans have population differences in behavior similar to those found in chimpanzees. Focal animal observation at three established field sites (Suaq Balimbing, Ketambe, and Cabang Panti) will answer the following questions: 1. Is there additional evidence of cultural variation in orangutans? 2. What are the minimum levels of opportunity for invention, expression and social learning that permit cultural behavior? The hypothesis that the opportunities for social learning are the critical factor in the expression of these cultural behaviors will be tested. Improved understanding of the cultural capacity of the orangutan will provide insight into the cultural capacities of the last common ancestor of the great apes and the evolution of culture as a key human adaptation.

Power in animal societies is typically studied in terms of differences in fighting abilities, or dominance. However, other more economic forms of power, or leverage, may influence an individual's power. Relationships between the sexes are particularly interesting for studying power because mating opportunities and protection services may be exchanged between males and females and often cannot be taken by force. The objective of this research is to examine some power-related factors that can lead to variation in male-female relationships. This study will examine the effects of leverage (based upon female reproductive status and the ratio of males to females) and dominance (based upon fighting ability) on male-female relationships in white sifaka.

The white sifaka is an ideal species for studying male-female relationships. First, males and females are not expected to differ in their fighting abilities because they are the same size. Nevertheless, female sifaka have priority of access to resources and often are aggressive towards males. Second, the effects of reproductive status on male-female relationships can be determined without depending upon hormone analysis because sifaka have a very short mating season. Third, services such as watching for predators, alarm calling, and defense against predators may be an important currency for exchange for sifaka. Finally, these lemurs live in social groups where the ratio of males to females varies across groups. These characteristics suggest that the effects of dominance will be reduced and that leverage effects will more easily be observed in this species.

Sex ratio, behavioral, and body size data will be collected by 4 observers on 6 focal groups with different sex ratios at Kirindy forest in Madagascar from October 2000-March 2002. Neighborhoods will be censused monthly. To estimate each individual's ability to use force, body size and condition data will be collected 4 times during the study and combined with canine size data.

The broader implications of this research include a better understanding of male-female relationships in all mammals, where a broad theoretical framework is lacking outside of mating systems. Moreover, male-female relationships have played a prominent role in hypotheses about human social evolution. The exchange of services, such as parental care and infanticide protection, may have led to some sort of bonding between the sexes. Using economic and political theory, this interdisciplinary project attempts to better understand human social evolution by testing these theories in a species where males and females are the same size, and hence, non-dominance power can best be studied.

Despite previous long-term behavioral studies, a full understanding of the social organization and reproductive strategies of orangutans has been difficult to achieve due to their extended life histories, large home ranges, predominantly arboreal lifestyles and semi-solitary natures. Because adult individuals are normally dispersed and visibility is limited within their rainforest habitats, long distance vocalizations are likely to play an important role in regulating individual relationships and social interactions, including reproduction. There is already strong and consistent behavioral and experimental evidence for an intra-sexual spacing function, but additional hypotheses such as mate attraction or protection against sexual coercion have not been tested rigorously. It is also not yet clear if reliable assessment cues are encoded in acoustic features and calling patterns or if listeners can recognize individual males and associate a signaler's identity with past performance.
This research aims to test predictions for the signal content of male long calls, examine potential functions and assess possible determinants of variation in calling behavior among Bornean and Sumatran populations. Using field recordings, focal animal sampling and carefully controlled playback experiments, this study intends to examine acoustic variation in male long calls, the patterns of calling behavior by males and behavioral responses in relation to the listener's social context, reproductive status and familiarity with the calling male. The signal content of male orangutan long calls has important repercussions for understanding female mate choice and the nature of inter-individual relationships in this endangered species.

This project will investigate the factors that limit the development of efficient tap-foraging skills in immature aye-ayes (Daubentonia madagascariensis) at the Duke University Primate Center (DUPC). Using experimental methods, this study will assess the age at which adult-level foraging proficiency is reached, and will determine whether lack of experience, small body size, and/or poor neuromuscular control prevent young aye-ayes from foraging efficiently. Results will test whether the time needed to learn complex foraging skills can explain the remarkably slow development of the aye-aye.
Study of the ontogeny of lemur foraging efficiency has important implications for understanding the evolution of slow development, or slow life history, in other primates, including humans. Human life history features, including a long juvenile period and lifespan, may be explained by a dietary shift towards more specialized, hard-to-obtain foods (e.g. meat, larvae). Additionally, human behaviors, such as food sharing with offspring, can be associated with slow life history. Recently, anthropologists have begun to test this hypothesis with long-term data from hunter-gatherer groups, with specific attention to the relative importance of experience and size to foraging efficiency. Following in this vein, the proposed project will be among the first to experimentally test hypotheses for life history evolution. Because aye-ayes, like humans, are also characterized by a relatively slow life history and a specialized, nutrient-rich diet, this study is directly relevant to our understanding of derived human life history traits.
More broadly, this research project will provide multiple opportunities for promoting education and participation in research. Preliminary data have been collected with the help of three student research assistants trained in behavioral observations and data collection techniques using hand-held computers. The proposed research will continue to provide opportunities for education and training of student research assistants. Additionally, the DUPC is an educational facility that provides information about lemurs and their ecosystems to thousands of visitors annually. Visitors to the center will have the opportunity to observe data collection sessions and to learn about this research project via educational materials.
This research is also more broadly applicable to understanding human dietary development. Like non-human primates and other mammals, humans have been observed to learn about food socially. Eating patterns, including obesity and dieting, appear to develop gradually throughout childhood. Understanding the development of foraging behaviors in non-human primates can help us understand the underlying stages of human dietary development, and may provide insight into preventative treatment of food-related disorders.
Finally, this research will provide helpful information for the reintroduction of aye-ayes and other mammals into the wild, and thus has important implications for conservation. While the release of animals within their current or former range is becoming increasingly important in conservation and wildlife management, primates in particular appear to rehabilitate less successfully than other mammals. Discerning how primates learn to forage will help us predict at what age young animals reach foraging proficiency adequate for independent survival, and whether reintroduced animals will be able to forage in a novel environment. This is particularly relevant for the aye-aye, which is highly threatened by habitat loss and hunting.

This project will contribute broadly to our growing knowledge of great ape behavioral ecology and genetics, while furthering the study of human origins through an investigation of cultural behavior on two sides of a dispersal barrier. The identification of arbitrary signal variation and rudimentary symbol use in orangutans suggests that previous studies may only have scratched the surface of existing cultural variation in this lineage, a phenomenon that is inherently interesting to humans and therefore capable of generating significant interest in orangutan conservation. Because animals cannot cross dispersal boundaries, cultural variants should reflect the history of diffusion from the locations(s) of innovation until blocked by a dispersal barrier. This project will test the ability of a cultural interpretation to account for patterns of behavioral variation exhibited by wild Bornean orangutans (Pongo pygmaeus wurmbii) ranging on either side of a 150m-wide river in Central Kalimantan, which currently serves as an effective barrier for orangutan dispersal in the study region, but offers opportunities for gene flow at its more narrow headwaters. The synchronized study of orangutans on opposite sides of a river barrier offers an exceptional opportunity to empirically evaluate the assumptions of a cultural interpretation for behavioral variation (based on opportunities for social learning), while holding both ecological variation and genetic relatedness constant. This project will assess the impact of social learning on the presence of skills required for orangutan survival and local adaptation, which are critical to the success of reintroduction efforts currently underway. It will also give us a greater understanding of the ecological and social contexts that favor cultural solutions for orangutans in particular situations but not in others, which will give us insight into the likely extent of culture in the last common ancestor of the great apes.

More broadly, this project will aid conservation initiatives by documenting the extent to which geographic variation in wild orangutan behavior is maintained by social transmission and, therefore, the extent to which reintroduced or translocated animals have difficulty achieving full adaptation to local conditions. This research will provide numerous opportunities for promoting student training and participation in research. Preliminary data were collected with the help of a Duke University undergraduate student as well as several local Indonesian assistants and university students. The proposed research will continue to provide training for Indonesian students and assistants and will promote international collaboration with Indonesian, European, and American counterparts. The orangutan is presently confined to highly fragmented populations in small forest patches on the islands of Borneo and Sumatra. Despite its formally protected status, the orangutan has become a critically endangered species, the extinction of which is anticipated within the next two decades due to the continuing threat of timber exploitation and human encroachment throughout its range. It is critical that this research be carried out soon, because there is a danger that as habitat devastation continues, individual orangutan populations with unique local traditions will vanish, resulting in lost opportunities to document the full extent of cultural behavior in wild orangutans.