title: Phase separation driven by density-dependent movement: A novel mechanism for ecological patterns.
abstract: Many ecosystems develop strikingly regular spatial patterns because of small-scale interactions between organisms, a process generally referred to as spatial self-organization. Self-organized spatial patterns are important determinants of the functioning of ecosystems, promoting the growth and survival of the involved organisms, and affecting the capacity of the organisms to cope with changing environmental conditions. The predominant explanation for self-organized pattern formation is spatial heterogeneity in establishment, growth and mortality, resulting from the self-organization processes. A number of recent studies, however, have revealed that movement of organisms can be an important driving process creating extensive spatial patterning in many ecosystems. Here, we review studies that detail movement-based pattern formation in contrasting ecological settings. Our review highlights that a common principle, where movement of organisms is density-dependent, explains observed spatial regular patterns in all of these studies. This principle, well known to physics as the Cahn-Hilliard principle of phase separation, has so-far remained unrecognized as a general mechanism for self-organized complexity in ecology. Using the examples presented in this paper, we explain how this movement principle can be discerned in ecological settings, and clarify how to test this mechanism experimentally. Our study highlights that animal movement, both in isolation and in unison with other processes, is an important mechanism for regular pattern formation in ecosystems.
authors.affiliation: State Key Laboratory of Estuarine and Coastal Research, East China Normal University, 200062 Shanghai, PR China; Department of Estuarine and Delta Systems, Royal Netherlands Institute for Sea Research and Utrecht University, PO Box 140, 4400 AC Yerseke, The Netherlands; Center for Global Change and Ecological Forecasting, East China Normal University, Shanghai 200062, PR China. Electronic address: qxliu@sklec.ecnu.edu.cn.
authors.forename: Quan-Xing
authors.initials: QX
authors.lastname: Liu
authors.affiliation: Department of Environmental Sciences, Copernicus Institute, Utrecht University, PO Box 80155, TC Utrecht, The Netherlands.
authors.forename: Max
authors.initials: M
authors.lastname: Rietkerk
authors.affiliation: Department of Estuarine and Delta Systems, Royal Netherlands Institute for Sea Research and Utrecht University, PO Box 140, 4400 AC Yerseke, The Netherlands.
authors.forename: Peter M J
authors.initials: PM
authors.lastname: Herman
authors.affiliation: Department of Coastal Systems, NIOZ Royal Netherlands Institute for Sea Research, 1790 AB Den Burg, The Netherlands; Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, PO Box 11103, 9700 CC Groningen, The Netherlands.
authors.forename: Theunis
authors.initials: T
authors.lastname: Piersma
authors.affiliation: Department of Integrative Biology, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G 2W1, Canada.
authors.forename: John M
authors.initials: JM
authors.lastname: Fryxell
authors.affiliation: Department of Estuarine and Delta Systems, Royal Netherlands Institute for Sea Research and Utrecht University, PO Box 140, 4400 AC Yerseke, The Netherlands; Groningen Institute for Evolutionary Life Sciences, University of Groningen, PO Box 11103, 9700 CC Groningen, The Netherlands. Electronic address: Johan.van.de.Koppel@nioz.nl.
authors.forename: Johan
authors.initials: J
authors.lastname: van de Koppel
mesh_terms: D000374:Aggression; D000818:Animals; D001000:Ants; D018407:Bacterial Physiological Phenomena; D001522:Behavior, Animal; D018533:Biomass; D049872:Bivalvia; D003670:Deer; D004463:Ecology / Q000379:methods*; D017753:Ecosystem; D009068:Movement; D009235:Myxomycetes; D011156:Population Density; D011157:Population Dynamics
keywords: Collective behavior; Density-dependent movement; Phase separation; Self-organization