Influence of social tolerance on social learning
von Anna Viktoria Schnöll
Datum der mündl. Prüfung:2014-10-08
Betreuer:Prof. Dr. Peter M. Kappeler
Gutachter:Prof. Dr. Peter M. Kappeler
Gutachter:Prof. Dr. Julia Ostner
EnglischOne outstanding feature of modern human societies is the complex cultural behaviour they exhibit. Although we do not find comparable capacities for culture in other species, some elements of culture are present in the animal kingdom as well. Recent research has described behavioural traditions in primates, cetaceans, other mammals, birds and fish. Because these traditions tend to be simpler than the ones we find in humans, research on animal traditions can provide new insights into the evolution of human culture. However, the origin of traditions in animals is still poorly understood. It has been suggested that there are several steps that have to be passed through on the way towards a tradition. The raw materials for a tradition are innovations, thus new behavioural variants that are not present yet in the repertoire of a species. We still lack information on the frequency of innovative behaviour in different populations of animals in the wild, because reports on them are rare. In this thesis I describe an incident of a potential feeding innovation in redfronted lemurs (Eulemur rufifrons).Social learning is the key mechanism for the formation of traditions, because it allows the spread of new behaviours within groups. However, the social environment of a group, in which an innovation occurs, can either facilitate or constrain the transmission via social learning. High social tolerance levels in egalitarian societies are suggested to favour the homogenous and quick spread of new information. In despotic societies, in contrast, the transmission is proposed to be limited to subgroups, because social tolerance is restricted to certain dyads within the group, like kin or friends. Social tolerance is described as the probability that individuals can stay in close proximity during a competitive situation with little or no aggression. Although there are theoretical models on the influence of social tolerance on the pattern and speed of social transmission, we still lack comparable empirical data. Therefore, in the main part of my thesis, I investigate the influence of social tolerance on social learning by comparing two lemur species: rather egalitarian redfronted lemurs and hierarchical structured ringtailed lemurs (Lemur catta). In a first step, I measure the social tolerance level of both species by using a co-feeding experiment, in which wild groups of lemurs were confronted with a clumped food resource within an experimental arena. Afterwards the results of the experiment were validated by observational data. During the experiment I found that more redfronted lemurs were feeding simultaneously and were able to stay in close proximity during a competitive situation than ringtailed lemurs, suggesting that redfronted lemurs are more socially tolerant. During the observational study, redfronted lemurs spent more time in close proximity than ringtailed lemurs, but I did not find a species difference in co-feeding. Additionally, both approaches yielded the same species difference in the outcome of aggression, with fewer agonistic interactions being decided between redfronted lemurs than between ringtailed lemurs. I therefore conclude that close proximity as well as outcome of aggression can serve as consistent measures of social tolerance. Subsequently, I conducted a social diffusion experiment with redfronted lemurs and ringtailed lemurs to study possible differences in the pattern and speed of learning. Therefore, I confronted the study groups with feeding boxes that could be opened with two alternative techniques (“lifting” or “sliding”) and a knowledgeable demonstrator for one of the techniques. The results of the experiment revealed faster learning as well as a further spread of the new skills in the more tolerant species compared to the less tolerant species. These results suggest that social tolerance indeed influences the amount of learning opportunities. This phenomenon is probably caused by closer proximity between individuals, which allows them to observe in greater detail. There was no species difference in the homogeneity of the transmission, but I find a generally positive influence of the number of contacts an individuals had with the demonstrator on the possibility of learning, again highlighting the importance of proximity in this context. Affiliative relationships in contrast did not promote learning. I was only able to find weak evidence for social learning during the experiment: the subjects did not imitate the technique used by the demonstrator but they might have learned that the feeding boxes contain food and can be opened. In this case simple learning mechanisms might be at work, like observational conditioning or emulation. Additionally, the tolerant species was able to scrounge from a more diverse set of producers, which might have facilitated learning. Another aspect that is still poorly understood is the longevity of traditions over time. Although we know that some animal traditions, like the famous sweet potato washing in Japanese macaques, can persist over more than 50 years, we lack information on the underlying mechanisms leading to stable behavioural patterns. Especially experimental research in this area can help to identify them. To this end, I investigated in my thesis the stability of an experimentally introduced tradition over time in wild redfronted lemurs. I conducted an additional social diffusion experiment over three experimental years with feeding boxes that could be opened in two different ways (“pushing” or “pulling”). Less than half of the participants preferred one technique to the other one in this time interval. The remaining individuals exhibited fluctuating preferences. The low level of difficulty and/or the low object specificity of the task might have caused this instability. The majority of lemurs additionally scrounged. Thus, redfronted lemurs appear to use the two techniques flexibly but also scrounged opportunistically to get access to the rewards, indicating that traditions might be stabilized by multiple factors. The results of my thesis indicate that these two species of group-living lemurs are able to innovate and information can spread within their groups. However, they are either unable to form long-lasting traditions or there is simply no need for them in the wild. Furthermore my study suggests a facilitating effect of social tolerance levels on learning. High levels of social tolerance seem to result in further spread of new behaviours as well as increased speed of learning. My thesis is the first comparative study on the influence of social tolerance on social learning and intends to contribute to a better understanding of the development of traditions in animals, and possibly also in humans. However, more comparative studies with other species are needed to get a full comprehension of the influence of the social environment on social learning.
Keywords: Animal traditions; Culture; Malagasy lemurs