Communal decision-making and patterns of aggregation

Jean-Louis Deneubourg

Unit of Social Ecology, ULB, Brussels, Belgium

Patterns of aggregation, resulting from individual responses to conspecifics modulated by environmental heterogeneity, are widespread social phenomena. During their resting periods, cockroaches aggregate in shelters that are an important environmental resource. Their selection is governed not only by their physical characteristics but also by social inter-attraction. This insect is an example that a self-organized process leads to optimal site selection and spatial patterns without any general knowledge of the resources. The dynamics of aggregation is based on the interplay between a positive feed-back based on modulation of the individual resting time in a shelter as a function of the number of conspecifics present in their close neighbourhood, and a negative feed-back based on the probability to joint the shelter. This dynamics leads to multiple spatial organizations. The transitions between different spatial organizations of the population correspond to successive bifurcations leading to multiple steady states. These collective choices are similar in their complexity and flexibility to those of eusocial insects. These results point to the existence of a generic self-organized dynamics of pattern formation in fragmented environment independently of the level of sociability of animal groups. Similar collective responses should be found in many others group-living organisms that present amplifications mechanisms based on inter-attraction.