Thesis (Ph.D.) - University of St Andrews, November 2008.

This thesis explores the seemingly simple problem of how a rainforest-dwelling primate, Cebus apella libidinosus, manages to survive in the Caatinga dry forest of north-eastern Brazil, a harsh habitat that poses a series of extreme ecological challenges for survival. Albeit a simple question, it unfolds into more complex questions regarding how ecological pressures might drive brain evolution and intelligence in primates. Although there is no "best" hypothesis to explain the evolutionary brain enlargement in higher primates, fine-grained analyses of ecology, such as those presented here provide insights into how different species deal with ecological problems that might require cognitive solutions. Capuchin monkeys are an ideal model for this inquiry. They occupy diverse habitats, and they have proven to be a cognitive puzzle. They are the only monkey to approach great apes in their ability to use tools, but apparently lack the prerequisite mental capability to understand cause and effect. The Caatinga dry forest poses a series of ecological challenges for mammals in general and primates in particular, and these are detailed in this thesis. This is the first general study of mammalian abundance and distribution in Caatinga habitats, with special reference to Cebus. I present several innovative methods for assessing plant and invertebrate biodiversity, as regards foods for the Cebus. The study population of capuchin monkeys faced more frequent and longer periods of food scarcity than does any other known capuchin population. However, the Cebus in the Caatinga circumvent the ecological constraints of low plant food availability through their proficient foraging style (destructive foraging) and through their cognitive abilities, reflected in this population's extensive and intelligent use of technology. I suggest that Old World monkeys and capuchin monkeys have undergone differential selective pressures, with 'Machiavellian intelligence' being a more prominent aspect in the brain evolution of baboons and macaques, while extractive foraging was a more important selective pressure for capuchin monkeys. The evolutionary brain enlargement observed in hominids is suggested to be a legacy of extractive foraging and that capuchin monkeys are excellent models for understanding the factors leading to brain enlargement. This thesis is concluded as an endeavour into understanding the selective forces and concatenation of events that culminated with the evolutionary brain enlargement seen in the hominins.

No description available.

Thesis (M.I.N.C.) -- Lincoln University and Georg-August University, Göttingen, 2008. / Also available via the World Wide Web.

Food cleaning behavior has been observed among laboratory squirrel monkeys. A Wilcoxon signed-ranks test showed that significantly more cleaning behavior occurred when hard monkey chow pellets and soft fruit were coated with edible debris. Monkeys removed fewer pieces of fruit from a food crock containing fruit coated with edible debris in a timed test. A principal component analysis of the food cleaning behaviors showed two underlying correlated factors. The first factor was the use of the body to clean food. The second factor was the use of the environment to clean food. Two groups of squirrel monkeys, one without previous learners and one with previous learners, were subjects in a fishing study. The presence of previous learners in the social group was not significant for monkeys fishing in water filled crocks. But there was a significant difference in the number of fishing attempts made by the No Previous Learners Group when fishing in wading pools. The Previous Learners group did not make significantly more fishing attempts fishing in wading pools than in crocks. A significant difference was observed in fishing attempts during Phase 1 and Phase 2 of the wading pool experiment for both groups. All monkeys in the group fishing experiments ate fish when it could be obtained. Monkeys who did not learn to fish successfully learned alternative behaviors to obtain fish. The Previous Learners group in the wading pool experiment were subjects in a more difficult fishing test. Significantly fewer fishing attempts were made but the number of monkeys that caught fish was larger. Caged squirrel monkeys scored a lower percentage of fishing attempts than squirrel monkeys living in a social group. While Cebus monkeys caught fish, unlike squirrel monkeys, they did not attempt to eat them.

Positional behavior is the measurable and observable link between the biology and behavior of an animal in its environment. In this dissertation, I examine ontogenetic patterns of positional behavior in infant, juvenile, and adult white-faced capuchins (Cebus capucinus) and mantled howling monkeys (Alouatta palliata) inhabiting the same tropical forest in Costa Rica. During growth and development ontogenetic changes in body size, limb proportions, and motor skills are likely to influence locomotion and posture through the arboreal canopy. I collected data on positional behavior, activity, prehensile-tail use, branch size, branch angle, and crown location during a 12 month period at Estación Biológica La Suerte in northeastern Costa Rica. The data set is comprised of 401.3 hours of data on Cebus capucinus and 554.3 hours of data on Alouatta palliata totaling 955.7 hours of data or 57,344 individual activity records.Life history timing and differences in rates of growth did not predictably influence the development of adult-like positional behaviors in Cebus and Alouatta. In both species, infancy was characterized by high proportions of dorsal, ventral, and side riding on the mother with smaller proportions of independent positional modes observed during play, explore, active posture, and feed/forage. Young Cebus resembled the adult pattern of positional behavior by six months of age while howlers exhibited significant differences in several positional behavior categories through 24 months of age. The positional repertoire of both species revealed similarities in the types of modes used during feed/forage and travel in juveniles and adults. For example, in juvenile and adult age categories of Cebus, feeding and foraging included high proportions of quadrupedal walk, sit, and squat in conjunction with climbing, leaping, and suspensory behaviors. In howlers, the degree to which coordination and increases in body mass during ontogeny as limiting factors in the development of adult-like positional competence is unclear. Data presented here suggest that the environment exerts different pressures on growing Cebus and Alouatta that may relate to diet, energy expenditure, foraging skill, and/or social learning.

Many studies have documented adverse affects to inequitable situations in non-human primates. The behaviors that have predominantly been examined include food taking, collecting, giving, and refusals between the primate subjects and the experimenters. However, no studies had looked at the affective responses to inequity in primates. In a recent study, four-year old children who were rewarded inequitably accepted the reward, however they showed affective signs of dissatisfaction. For this study, we looked for affective displays in capuchins during inequitable exchange tasks. We predicted that the capuchins that were experiencing inequity would show more signs of agitation and aggression than those in equitable situations. We saw no increase in agitation or aggression when subjects were treated inequitably. There was higher aggression towards partners who received the lower reward in inequitable situations and less agitation seen by partners during frustration controls. Future studies may find our hypothesized results using different methodologies.

Humans have a tendency to engage in economically irrational behaviors such as gambling, which typically leads to long-term financial losses. While there has been much research on human gambling behavior, relatively little work has been done to explore the evolutionary origins of this behavior. To examine the adaptive pressures that may have led to this seemingly irrational behavior in humans, nonhuman primates were tested to explore their reactions to gambling type scenarios. Several experiments based on traditional human economic experiments were adapted for use with a wider variety of primate species including chimpanzees and capuchin monkeys. This allowed for testing multiple species using similar methodologies in order to make more accurate comparisons of species abilities. This series of tasks helps to elucidate risky decision-making behavior in three primate species.

Many studies have documented adverse affects to inequitable situations in non-human primates. The behaviors that have predominantly been examined include food taking, collecting, giving, and refusals between the primate subjects and the experimenters. However, no studies had looked at the affective responses to inequity in primates. In a recent study, four-year old children who were rewarded inequitably accepted the reward, however they showed affective signs of dissatisfaction. For this study, we looked for affective displays in capuchins during inequitable exchange tasks. We predicted that the capuchins that were experiencing inequity would show more signs of agitation and aggression than those in equitable situations. We saw no increase in agitation or aggression when subjects were treated inequitably. There was higher aggression towards partners who received the lower reward in inequitable situations and less agitation seen by partners during frustration controls. Future studies may find our hypothesized results using different methodologies.

The aim of this thesis is to examine the cognitive processes of social learning from the bottom up. In the field of comparative psychology, an overemphasis on understanding complex cognitive processes in nonhuman animals (e.g. empathy, imitation), may be detrimental to the study of simpler mechanisms. In this thesis, I report five studies of simple cognitive processes related to social learning. A series of experiments with human children and capuchin monkeys (Sapajus sp.), examined action imitation and identified a possible role for associative learning in the development of this ability. An analysis of observational data from captive capuchins explored a number of lesser-studied social learning phenomena, including behavioural synchrony, the neighbour effect, and group-size effects. The results of this study emphasise the importance of exploring behaviour at a number of levels to appreciate the dynamic nature of social influence. Two final experiments examined social contagion in capuchin monkeys, and highlight the importance of describing the relationship between behaviour and emotion to properly understand more complex social cognition. Together, these studies demonstrate how approaching human and nonhuman behaviour from the bottom up, as well as from the top down, can contribute to a better comparative science of social learning.