Swarms of visitors

If you would like to meet with ACCS visitors, Jérôme Buhl and/or Audrey Dussutour, please contact Jim Hanan: jim@maths.uq.edu.au.


'Seminar: Thursday 23 November, 10:30 Morning Tea, 11:00am seminar

Place: Room 621/622, GP South (Building 78)

Speaker: Audrey Dussutour, Postdoctoral Fellow, School of Biological Sciences, University of Sydney

Title: "Moving in the crowd: Ants hold the key to traffic chaos."

The collective displacement of assemblies of organisms is certainly one of the most spectacular phenomena one can observe in nature. A column of army ants, a swarm of locusts, a herd of migrating wildebeests, a flock of birds or a shoal of fish can sometimes comprise several millions of individuals. Collective displacements are characterized by a high degree of coordination among individuals. A higher proximity between individuals is generally beneficial, because it promotes cooperation by facilitating the exchanges of information that is essential for the maintenance of group cohesion. Too much proximity however can lead to a high concentration of individuals. Detrimental effects may then occur and lead to a failure in the functioning of the group, which will affect the individuals in turn. In extreme cases, a high density may even lead to a total standstill of group activity.

Ants provide an excellent model for the study of collective movement because of their highly social organization that functions in a completely decentralized manner.

My work deals with the organization of collective movements in ants in presence of environmental heterogeneities, particularly in situations involving crowding. We chose two species of ants, characterized by different degrees of polymorphism, as well as by their mode of food transport. Our aim is to identify the link between the behavioral rules observed at the scale of the individual and the spatio-temporal organization observed at the scale of the group. Independently of the species, we found that the regulation of traffic in crowding situations depends both on interattraction processes, via the communication through the chemical trail, and on dispersion phenomena. These latter vary as a function of the size of the individuals and of the task they achieve, but give rise to comparable organisations in the species studied. The originality of this work lies in the fact that it shows that the mechanisms of dispersion allowing the regulation of the traffic and the prevention of crowding are a by-product of the interattraction processes.


Seminar: Wednesday 22 November. 3:30 Afternoon Tea, 4:00pm seminar

Place: Room 621/622, GP South (Building 78)

Speaker, Jerome Buhl, Postdoctoral Fellow, School of Biological Sciences, The University of Sydney

Title: From disorder to order in animal collective motion

Abstract: Despite the huge difference in the scale of animal aggregations and the cognitive abilities of group members, the similarities in the patterns they produce have suggested that general principles may underlie collective motion. Recent models of "Self-Propelled Particles" have predicted that mass migrating animal groups may share group-level properties irrespective of the type of animals in the group. One key prediction is that as the density of animals in the group increases, a rapid transition occurs from disordered movement of individuals within the group to highly aligned collective motion. Understanding such a transition is crucial to the prediction and control of mobile swarming insect pests such as the desert locust in which the formation of cohesive marching groups of wingless nymphs can lead to disastrous outbreaks. By studying locust groups in the laboratory experiments, we were able confirm the prediction of a rapid transition from disordered to ordered movement and identify a critical density for the onset of coordinated marching in locust nymphs. Since SPP models underlie many theoretical predictions about how groups form complex patterns, avoid predators, forage, and make decisions, these results have fundamental implications for how we understand all aspects of the motion of animal groups.

Research interests:
Collective behaviour in animal societies with a particular interest on collective movements, aggregation and synchronisation; self-organisation; evolution of sociality; mathematical biology and modelling

World-class basic and applied inter-disciplinary research on questions fundamental to understanding, designing and managing complex systems
© 2009 The ARC Centre for Complex Systems, Australia