Individual variation in the behaviour of pigs—noise or functional coping strategies?

Abstract

Consistent individual variation in behaviour, creating within-species categories of individuals, is predicted from game theory and has been observed in studies of coping behaviour in rodents. I suggest that four properties of individual variation are particularly important to clarify in order to extrapolate from rodents to other species: (1) intra-situational consistency, i.e. the behavioural consistency between different exposures to the same situation; (2) inter-situational consistency, i.e. the consistency in reaction to different situations; (3) distribution of individuals, i.e. whether it is normal or bimodal; (4) genetic base for the distribution. I suggest that extrapolation of coping theory to other species demands demonstrations of high intra- and inter-sitution consistency, a bimodal distribution and genotypic differences between groups of individuals. Reviewing some of the data within the field, I conclude that there are good indications of distinct coping types of individuals among rodents, but not among pigs. This can be explained by ecological differences between the species and/or by domestication effects. There is a strong need for increased theoretical and empirical work that ties functional and mechanistic aspects of individual variations together.