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.

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.

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.

The research aims of this thesis are to experimentally investigate how behaviours spread socially, and what factors contribute to the development of group-wide social traditions in capuchins (Cebus apella). Given the apparent convergent evolution between such monkeys and great apes, capuchin traditions are of great interest anthropologically and for a biological and psychological understanding of culture. Several studies have investigated social learning in capuchins, but few have made headway into understanding how it supports the development of traditions either in the wild or in captivity. By experimentally introducing novel foraging behaviours into several captive groups, the studies included in this thesis simulate the development of foraging behaviours so that their spread can be studied from various viewpoints. Five experiments are presented investigating: (1) the chained transmission of foraging behaviours, (2) the role of social facilitation on the rate of individual learning, (3) the fidelity of learning from localised stimulus enhancement & object-movement re-enactment, (4) the quality of individual relationships in the social transmission of novel foraging techniques, and (5) the open diffusion of group-specific foraging behaviours in capuchin monkeys. Together, these experiments explore how traditions may develop, ranging from individual learning to how behaviour patterns may spread socially based on social ties within the group.

This thesis explores social learning in mother-reared and “enculturated” capuchin monkeys (Cebus apella). At the outset a framework for understanding the social influence on learning is discussed, followed by a review of the social and cognitive abilities of capuchin monkeys, establishing the rationale for studying social learning in this species. Studies of wild capuchins suggest an important role for social learning but experiments with captive subjects have generally failed to support this. Some potential reasons for the lack of evidence in experimental settings are given. An example of using the two - method design to test social learning in acquiring behaviour by enculturated subjects is addressed. The results are related to findings with other species tested with a similar apparatus. Before testing mother-reared monkeys, an observational study of the object manipulation and tool-use repertoire of the subjects was carried out in order to facilitate the design of suitable social learning tasks for these monkeys. The first empirical study in Chapter 6 reports results of experiments with the enculturated and mother-reared capuchin monkeys employing the two -action method together with a third control group. The enculturated monkeys exhibited high fidelity copying that included the specific tool use technique witnessed while opening the foraging box. Mother-reared monkeys exhibited fidelity at a lower level, tending only to re-create the results the model had achieved. The second empirical study in Chapter 7 tested whether capuchin monkeys could show cumulative cultural learning manifested in the ability to switch from an established mode of manipulating a dipping box to a complex yet more advantageous one. Both populations were able to do so. The enculturated monkeys, as in the previous study, showed higher fidelity copying of the model. The last experiment was a preliminary study employing the “do as I do” method which was carried out with four of the enculturated monkeys. It provides suggestive evidence for at least one monkey's understanding of the task. The results of the studies are discussed in relation to previous experimental research as well as to data from capuchin monkeys in nature. The possible role of enculturation in social learning ability is considered.