From individual to collective information processing in fish schools
Guy Theraulaz
Centre de Recherches sur la Cognition Animale, CNRS, UMR 5169, Université Paul Sabatier,
118 route de Narbonne, 31062 Toulouse, France
Email: guy.theraulaz@univ-tlse3.fr
Webpage: http://cognition.ups-tlse.fr/_guyt/index.html
Abstract: Swarms of insects, schools of fish and flocks of birds display an impressive varietyof collective behaviors that emerge from local interactions among group members. These
puzzling phenomena raise a variety of questions about the interactions rules that govern thecoordination of individuals’ motions and the emergence of large-scale patterns. While
numerous models have been proposed, there is still a strong need for detailed experimental
studies to foster the biological understanding of such collective motion. I will present themethods that we used to characterize interactions among individuals and build models foranimal group motion from data gathered at the individual scale. Using video tracks of fish
shoal in a tank, we determined the stimulus/response function governing an individual’smoving decisions from an incremental analysis at the local scale. We found that both
attraction and alignment interactions are present and act upon the fish turning speed, yielding
a novel schooling model whose parameters are all estimated from data. We also found that themagnitude of these interactions changes as a function of the swimming speed of fish and thegroup size. The consequence being that groups of fish adopt different shapes and motions:group polarization increases with swimming speed while it decreases as group size increases.
The phase diagram of model revealed that the relative weights of the attraction and alignment
interactions play a key role in the emergent collective states at the school level. Of particularinterest is the existence of a transition region in which the school exhibits multistability andintermittence between schooling and milling for the same combination of individual
parameters. In this region the school becomes highly sensitive to any kind of perturbations
that can affect the behavior of just a single fish.
Short bio: Guy Theraulaz is a senior research fellow at the National Center for Scientific
Research CNRS) and an expert in the study of collective animal behaviors. He is also aleading researcher in the field of swarm intelligence, primarily studying social insects but also
distributed algorithms, e.g. for collective robotics, directly inspired by nature. His research
focuses on the understanding of a broad spectrum of collective behaviors in animal societies
by quantifying and then modeling the individual level behaviors and interactions, thereby
elucidating the mechanisms generating the emergent, group-level properties. He was one of
the main characters of the development of quantitative social ethology and collective
intelligence in France. He published many papers on nest construction in ant and wasp
colonies, collective decision in ants and cockroaches, and collective motion in fish schools
and pedestrian crowds. He has also coauthored five books, among which Swarm Intelligence:
From Natural to Artificial Systems (Oxford University Press, 1999) and Self-organization in
Biological Systems (Princeton University Press, 2001) that are now considered as reference
textbooks.