Herman Dienske

Continuous-time markov chains as models for animal behaviour

A survey is given of the application of (functions of) continuous-time Markov chains in the statistical analysis of behavioural time series.

Analysis of time-inhomogeneity in Markov chains applied to mother-infant interactions of rhesus monkeys

Abstract When studying the interaction between mother-infant pairs of rhesus monkeys, inhomogeneities appear to exist during the awake phase of the infant, even under externally constant circumstances. These inhomogeneities are obscured by the stochastic nature of the bout lengths as well as the transitions between the several behavioural acts. An accurate description of the interaction, with the changes in the behaviour during the awake phase included, is necessary in order to be able to quantify the influence of the mother on the social development of the infant and vice versa. A mathematical model is described belonging to the class of continuous time Markov chains. This model gives an adequate characterization of the behavioural processes in a restricted number of ethologically wellinterpretable parameters. New procedures for estimating these parameters are derived, as well as tests on hypotheses concerning the number and magnitude of abrupt behavioural changes of the pairs. The pervasive motivational changes prior to or after napping by infants could be described comprehensively by the parameters developed.

Habitat and Interspecific Displacement of Small Mammals in the Netherlands

In The Netherlands, 7 species of small terrestrial mammals belonging to 5 genera are so numerous that they often meet in the field. The aim of this study was to assess whether interspecies interaction leads to displacement of species from their favoured habitats. For this purpose, population densities of the species were estimated in 210 localities in which ground-water level, height of herbaceous vegetation and distance from wood edges were accurately measured. The main habitats inhabitated by the various species when distribution is not limited by other species are as follows. All species except Sorex avoid grasslands shorter than 20 cm. Sorex araneus and S. minutus occur everywhere, though more outside than within woods. Microtus agrestis and Micromys minutus avoid woods; in grasslands, they do not react to differences in moisture (ground-water level) or vegetation height. Microtus arvalis occurs only in dry grasslands and presumably avoids woods. Clethrionomys glareolus and Apodemys sylvaticus occur within woods and the adjacent grasslands up to about 30 m from the edges. Tolerance among different species within a locality of co-occurrence was the rule; 6 of the 21 pairwise species combinations were even positively associated; this probably resulted from the presence of unknown environmental characteristics attractive to both. M. arvalis and C. glareolus were negatively associated. Here, we found indirect arguments for the hypothesis that part of the localities were unattractive for only one of these species. Spatial intolerance could be assessed in Microtus arvalis and M. agrestis. When macroallopatric, these live in both tall and short vegetation; however, when in proximity, M. agrestis is restricted to grasslands with tall and M. arvalis to grasslands with short vegetation.

Differences in Play Development of Young Chimpanzees Reared in Family Groups and in Peer Groups

Rhesus and chimpanzee infants reared in family conditions showed higher levels of dominance and activity behaviours than infants reared only with their mother or with peers only. These results suggest that the greater the variety of social partners in a rearing condition, the more the individuals are able to develop social skills that will be advantageous to them in group life. We investigated how living in groups with peers only (n = 65) influenced behaviour development in chimpanzees aged from zero to ten years. Comparisons were made with the development of chimpanzees in the same age range in a semi-natural zoo group (n = 25). We expected that young chimpanzees reared in a family group, which offers more variation in social partners than a pcer group, would show more frequent and diverse social behaviour; i.e. more social play, more triadic interactions (in play) and more sex differentiation in play, than young chimpanzees reared in peer groups. We were surprised to find that the peer group situation had little effect on social behaviour. The differences in the amount of gymnastics performed by peer groups and zoo groups can be interpreted as direct effects of the environmental conditions. The lower level of triadic play in the pccr groups may have been caused by the greater opportunity for diadic play; this effect was found only in young infants. The lower level of social play in individuals aged from three to six years in the peer groups was due to the presence of one group of carly-separated females and, hence, was not an overall and long-term effect of peer group rearing conditions. The absence of a sex difference in the amount of adolescent social play in peer groups and the presence of such a sex difference in the zoo shows that the social rearing condition has indeed some effect on the development of social behaviour. The fact that separation age and peer-only rearing conditions had no more marked effects on the development of social behaviour, obviously docs not imply that separating young infants from their mother is to be recommended, for many of the possible effects of separation and peer group rearing were not studied. However, since both the number of animals studied and the number of observation periods were large, the existence of only one difference is meaningful: young chimpanzees reared in an all family group show only slightly more diversity in the development of social behaviours than do young chimpanzccs reared in peer groups.

A biological meaningful classification in child psychiatry that is based upon ethological methods

Abstract An ethological approach to behavior quantification and classification in child psychiatry is described using the prototype approach to concept formation, in which examples are considered exemplars of concepts. Data are based on a large number of psychiatric evaluations. A number of behaviors was selected and their occurrence recorded and quantified. This resulted in a number of parameters for which values were determined per child. Classification of parameters was based on a number of explicit criteria that varied in their usefulness. It appeared that a classification on the basis of biological function was most useful. This biologically meaningful classification reasonably paralleled traditional child psychiatric diagnoses. The resulting prototypes may be useful during psychiatric evaluation of children.

Detection of low dose effects of psychopharmaca: Application of a semi-Marcov model to rhesus monkey behaviour.

Behavioural testing of psycho-active drugs at lower doses is needed for medical applications and for the study of pharmacological brain mechanisms. Sensitive methods to detect effects on the time structure of behaviour are lacking. We propose a procedure based on a description within the framework of continuous time Marcov chain models. This class of models is generalized to account for constraints on the organisation of a motor pattern including the speed at which it is terminated. This leads to semi-Marcov models with transition rates that quickly increase from zero to a constant level. We describe and compare several models. As an application we consider amphetamine effects on infant rhesus monkeys. One of the models is preferred since, besides giving a good fit, it demonstrates consistent amphetamine effects that can be interpreted as short-term effects on motor constraints. Amphitamine also induced more mother-directed behaviour. We give maximum likelihood procedures for behaviour analysis based on the preferred model.

A comparison of development and deprivation in non-human primates and man

Comparisons are made between the normal behavioral development and the effects of social deprivation in rhesus monkeys, chimpanzees and man. In this sequential order of species, development is slower, mother-infant stimulations are richer and the capacities to be developed are more sophisticated. It seems likely that in the course of human evolution, social play with peers is delayed in favor of longer mother-infant interactions of increasing quality. This view is consistent with a number of indications that the vulnerability for effects of mild social deprivation is greater in man than in monkeys; especially the social play with peers seems to drop out easier in humans than in monkeys. However, studies of the development of abnormal behavior in non-human primates were insufficiently matched with the known behavioral deviations in human children. More knowledge is required of the process of behavior development under circumstances relevant to humans and of the causes of individual differences.

Studying Effects of Maternal Care in Rhesus Monkeys at Different Levels of Resolution

The ultimate aim of our study in rhesus monkeys is to detect possible effects of the type of mother-infant relationship on the developing infant. We chose to study play with peers as the most important characteristic to be influenced, as play is the most common interaction with group members in early life, and because play is probably an exercise for the development of social skills.