by Christian Yates
C.A. Yates, R. Erban, C. Escudero, I. Couzin, J. Buhl, I. Kevrekidis, P. Maini and D. Sumpter, (2009). "Inherent noise can facilitate coherence in collective swarm motion". Proceedings of the National Academy of Sciences (PNAS) 106(14) 5464-5469.
Supporting information can be found here: http://people.maths.ox.ac.uk/~yatesc/inherentnoisesupportinginformation.pdf
Among the most striking aspects of the movement of many animal
groups are their sudden coherent changes in... more
Among the most striking aspects of the movement of many animal
groups are their sudden coherent changes in direction. Recent
observations of locusts and starlings have shown that this directional
switching is an intrinsic property of their motion. Similar
direction switches are seen in self-propelled particle and other
models of group motion. Comprehending the factors that determine
such switches is key to understanding the movement of these
groups. Here, we adopt a coarse-grained approach to the study of
directional switching in a self-propelled particle model assuming an
underlying one-dimensional Fokker–Planck equation for the mean
velocity of the particles. We continue with this assumption in analyzing
experimental data on locusts and use a similar systematic
Fokker–Planck equation coefficient estimation approach to extract
the relevant information for the assumed Fokker–Planck equation
underlying that experimental data. In the experiment itself the
motion of groups of 5 to 100 locust nymphs was investigated in
a homogeneous laboratory environment, helping us to establish
the intrinsic dynamics of locust marching bands. We determine
the mean time between direction switches as a function of group
density for the experimental data and the self-propelled particle
model. This systematic approach allows us to identify key differences
between the experimental data and the model, revealing
that individual locusts appear to increase the randomness of their
movements in response to a loss of alignment by the group. We
give a quantitative description of how locusts use noise to maintain
swarm alignment. We discuss further how properties of individual
animal behavior, inferred by using the Fokker–Planck equation
coefficient estimation approach, can be implemented in the selfpropelled
particle model to replicate qualitatively the group level
dynamics seen in the experimental data.
Download (.pdf)