title: Finite-size scaling as a way to probe near-criticality in natural swarms.
abstract: Collective behavior in biological systems is often accompanied by strong correlations. The question has therefore arisen of whether correlation is amplified by the vicinity to some critical point in the parameters space. Biological systems, though, are typically quite far from the thermodynamic limit, so that the value of the control parameter at which correlation and susceptibility peak depend on size. Hence, a system would need to readjust its control parameter according to its size in order to be maximally correlated. This readjustment, though, has never been observed experimentally. By gathering three-dimensional data on swarms of midges in the field we find that swarms tune their control parameter and size so as to maintain a scaling behavior of the correlation function. As a consequence, correlation length and susceptibility scale with the system's size and swarms exhibit a near-maximal degree of correlation at all sizes.
authors.affiliation: Istituto Sistemi Complessi, Consiglio Nazionale delle Ricerche, UOS Sapienza, 00185 Rome, Italy and Dipartimento di Fisica, Università Sapienza, 00185 Rome, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Attanasi
authors.affiliation: Istituto Sistemi Complessi, Consiglio Nazionale delle Ricerche, UOS Sapienza, 00185 Rome, Italy and Dipartimento di Fisica, Università Sapienza, 00185 Rome, Italy and Initiative for the Theoretical Sciences, The Graduate Center, 365 Fifth Avenue, New York, New York 10016 USA.
authors.forename: Andrea
authors.initials: A
authors.lastname: Cavagna
authors.affiliation: Istituto Sistemi Complessi, Consiglio Nazionale delle Ricerche, UOS Sapienza, 00185 Rome, Italy and Dipartimento di Fisica, Università Sapienza, 00185 Rome, Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Del Castello
authors.affiliation: Istituto Sistemi Complessi, Consiglio Nazionale delle Ricerche, UOS Sapienza, 00185 Rome, Italy and Dipartimento di Fisica, Università Sapienza, 00185 Rome, Italy and Initiative for the Theoretical Sciences, The Graduate Center, 365 Fifth Avenue, New York, New York 10016 USA.
authors.forename: Irene
authors.initials: I
authors.lastname: Giardina
authors.affiliation: Istituto Sistemi Complessi, Consiglio Nazionale delle Ricerche, UOS Sapienza, 00185 Rome, Italy and Dipartimento di Fisica, Università Sapienza, 00185 Rome, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Melillo
authors.affiliation: Istituto Sistemi Complessi, Consiglio Nazionale delle Ricerche, UOS Sapienza, 00185 Rome, Italy and Dipartimento di Informatica, Università Sapienza, 00198 Rome, Italy.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Parisi
authors.affiliation: Istituto Sistemi Complessi, Consiglio Nazionale delle Ricerche, UOS Sapienza, 00185 Rome, Italy and Dipartimento di Fisica, Università Sapienza, 00185 Rome, Italy.
authors.forename: Oliver
authors.initials: O
authors.lastname: Pohl
authors.affiliation: DeFENS, Università degli Studi di Milano, 20133 Milano, Italy.
authors.forename: Bruno
authors.initials: B
authors.lastname: Rossaro
authors.affiliation: Istituto Sistemi Complessi, Consiglio Nazionale delle Ricerche, UOS Sapienza, 00185 Rome, Italy and Dipartimento di Fisica, Università Sapienza, 00185 Rome, Italy.
authors.forename: Edward
authors.initials: E
authors.lastname: Shen
authors.affiliation: Istituto Sistemi Complessi, Consiglio Nazionale delle Ricerche, UOS Sapienza, 00185 Rome, Italy and Dipartimento di Fisica, Università di Roma 3, 00146 Rome, Italy.
authors.forename: Edmondo
authors.initials: E
authors.lastname: Silvestri
authors.affiliation: Istituto Sistemi Complessi, Consiglio Nazionale delle Ricerche, UOS Sapienza, 00185 Rome, Italy and Dipartimento di Fisica, Università Sapienza, 00185 Rome, Italy.
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Viale
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D002683:Chironomidae; D003627:Data Interpretation, Statistical; D008954:Models, Biological; D013816:Thermodynamics