title: Initiation and spread of escape waves within animal groups.
abstract: The exceptional reactivity of animal collectives to predatory attacks is thought to be owing to rapid, but local, transfer of information between group members. These groups turn together in unison and produce escape waves. However, it is not clear how escape waves are created from local interactions, nor is it understood how these patterns are shaped by natural selection. By startling schools of fish with a simulated attack in an experimental arena, we demonstrate that changes in the direction and speed by a small percentage of individuals that detect the danger initiate an escape wave. This escape wave consists of a densely packed band of individuals that causes other school members to change direction. In the majority of cases, this wave passes through the entire group. We use a simulation model to demonstrate that this mechanism can, through local interactions alone, produce arbitrarily large escape waves. In the model, when we set the group density to that seen in real fish schools, we find that the risk to the members at the edge of the group is roughly equal to the risk of those within the group. Our experiments and modelling results provide a plausible explanation for how escape waves propagate in nature without centralized control.
authors.affiliation: Department of Mathematics , Uppsala University , Uppsala 75106, Sweden ; Department of Ecology and Genetics , Uppsala University , Uppsala 75106, Sweden.
authors.forename: James E
authors.initials: JE
authors.lastname: Herbert-Read
authors.affiliation: School of Biological Sciences , The University of Sydney , Sydney, New South Wales 2006, Australia ; The Charles Perkins Centre , The University of Sydney , Sydney, New South Wales 2006, Australia ; School of Agriculture , The University of Adelaide , South Australia 5005, Australia.
authors.forename: Jerome
authors.initials: J
authors.lastname: Buhl
authors.affiliation: College of Physics and Electronic Engineering , Chongqing Normal University , Chongqing City 400047, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Hu
authors.affiliation: School of Biological Sciences , The University of Sydney , Sydney, New South Wales 2006, Australia.
authors.forename: Ashley J W
authors.initials: AJ
authors.lastname: Ward
authors.affiliation: Department of Mathematics , Uppsala University , Uppsala 75106, Sweden ; Department of Ecology and Genetics , Uppsala University , Uppsala 75106, Sweden.
authors.forename: David J T
authors.initials: DJ
authors.lastname: Sumpter
keywords: collective animal behaviour; escape waves; fish schools; self-organization