Editing Swarm behaviour (section)

===Mathematical models===
[[File:Metric vs topological distance in schools of fish.png|right|thumb|400px|In the [[metric distance]] model of a [[fish school]] (left), the focal fish (yellow) pays attention to all fish within the small zone of repulsion (red), the zone of alignment (lighter red) and the larger zone of attraction (lightest red). In the [[topological space|topological distance]] model (right), the focal fish only pays attention to the six or seven closest fish (green), regardless of their distance.]]
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|image1=[http://www.red3d.com/cwr/boids/ Boids simulation]
|image2=[http://www.aridolan.com/ofiles/iFloys.html iFloys simulation]
|image3=[http://www.aridolan.com/ofiles/Efloys.aspx Efloys simulation]}}
Early studies of swarm behaviour employed mathematical models to simulate and understand the behaviour. The simplest mathematical models of animal swarms generally represent individual animals as following three rules:
* Move in the same direction as their neighbours
* Remain close to their neighbours
* Avoid collisions with their neighbours

The [[boids]] computer program, created by [[Craig Reynolds (computer graphics)|Craig Reynolds]] in 1986, simulates swarm behaviour following the above rules.<ref name="Reynolds"/> Many subsequent and current models use variations on these rules, often implementing them by means of concentric "zones" around each animal. In the "zone of repulsion", very close to the animal, the focal animal will seek to distance itself from its neighbours to avoid collision. Slightly further away, in the "zone of alignment", the focal animal will seek to align its direction of motion with its neighbours. In the outermost "zone of attraction", which extends as far away from the focal animal as it is able to sense, the focal animal will seek to move towards a neighbour.

The shape of these zones will necessarily be affected by the sensory capabilities of a given animal. For example, the visual field of a bird does not extend behind its body. Fish rely on both vision and on [[hydrodynamic]] perceptions relayed through their [[lateral line]]s, while Antarctic [[krill]] rely both on vision and hydrodynamic signals relayed through [[antenna (biology)|antennae]].

However recent studies of starling flocks have shown that each bird modifies its position, relative to the six or seven animals directly surrounding it, no matter how close or how far away those animals are.<ref name="Ballerini et al">{{cite journal |doi=10.1073/pnas.0711437105 |vauthors=Ballerini M, Cabibbo N, Candelier R, Cavagna A, Cisbani E, Giardina I, Lecomte V, Orlandi A, Parisi G, Procaccini A, Viale M, Zdravkovic V |title= Interaction ruling animal collective behavior depends on topological rather than metric distance: Evidence from a field study |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=105 |issue=4 |pages=1232–7 |year=2008 |pmid=18227508 |pmc=2234121|arxiv= 0709.1916 |bibcode= 2008PNAS..105.1232B|doi-access=free }}</ref> Interactions between flocking starlings are thus based on a [[topological]], rather than a metric, rule. It remains to be seen whether this applies to other animals. Another recent study, based on an analysis of high-speed camera footage of flocks above Rome and assuming minimal behavioural rules, has convincingly simulated a number of aspects of flock behaviour.<ref>{{cite journal |vauthors=Hildenbrandt H, Carere C, Hemelrijk CK |year= 2010 |title= Self-organized aerial displays of thousands of starlings: a model |journal= Behavioral Ecology |volume= 21 |issue= 6 |pages= 1349–1359 |doi= 10.1093/beheco/arq149|doi-access= free |arxiv= 0908.2677 }}</ref><ref>{{cite journal |vauthors=Hemelrijk CK, Hildenbrandt H |year= 2011 |title= Some causes of the variable shape of flocks of birds |journal= PLOS ONE |volume= 6 |issue= 8 |page= e22479 |doi= 10.1371/journal.pone.0022479 |pmid=21829627 |pmc=3150374 |bibcode=2011PLoSO...622479H|doi-access= free }}</ref><ref>{{cite web |url=http://www.rug.nl/sciencelinx/exhibits/swarming/index|title=Zwermen en scholen - Swarming - Permanente expo - Bezoek onze expo's & workshops! - Science LinX - Rijksuniversiteit Groningen|date=10 November 2007}}</ref><ref>{{cite web |url=http://www.rug.nl/fmns-research/beso/_people/hemelrijk|title=Onderzoek aan de Faculteit Wiskunde en Natuurwetenschappen - Faculteit Wiskunde en Natuurwetenschappen - Over ons - Rijksuniversiteit Groningen|date=25 October 2012}}</ref>