Abstract
Collective behaviour in flocks, crowds, and swarms occurs throughout the biological world. Animal groups are generally assumed to be evolutionarily adapted to robustly achieve particular functions, so there is widespread interest in exploiting collective behaviour for bio-inspired engineering. However, this requires understanding the precise properties and function of groups, which remains a challenge. Here, we demonstrate that collective groups can be described in a thermodynamic framework. We define an appropriate set of state variables and extract an equation of state for laboratory midge swarms. We then drive swarms through “thermodynamic” cycles via external stimuli, and show that our equation of state holds throughout. Our findings demonstrate a new way of precisely quantifying the nature of collective groups and provide a cornerstone for potential future engineering design.
Highlights
Collective behaviour in flocks, crowds, and swarms occurs throughout the biological world
Our findings demonstrate the surprising efficacy of classical equilibrium thermodynamics for quantitatively characterizing and predicting collective behaviour in biology
Even though individual midges are certainly not in equilibrium and need not obey the same rules as, for example, particles in an ideal gas, we find that the collective behaviour of ensembles of these individuals is surprisingly simple
Summary
Collective behaviour in flocks, crowds, and swarms occurs throughout the biological world. Animal groups are generally assumed to be evolutionarily adapted to robustly achieve particular functions, so there is widespread interest in exploiting collective behaviour for bio-inspired engineering This requires understanding the precise properties and function of groups, which remains a challenge. It is generally assumed that since evolution has led so many different kinds of animals to behave collectively, the performance of collective groups at whatever task they seek to achieve ought to be well beyond the capabilities of a single individual[5], while being robust to uncertain natural e nvironments[6,7] and operating without the need for top-down c ontrol[8] For these reasons, there has been significant interest both in understanding how collectivity conveys these advantages[9] and how to exploit it in engineered systems[10,11]. By applying a suitable sequence of external perturbations to the swarms, we show that we can drive them through a thermodynamic cycle in pressure–volume space throughout which our empirical equation of state holds
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