Science behind the app

Floqua has been developed based on scientific research at the University of York. The research background for Floqua is studies and simulations of flocking birds and the social interactions in groups of animals. The aim of Floqua is to have fun, while attracting interest in the science on which it is based. Floqua can also be used as a tool in eduction to teach principles of animal behaviour. At York, Floqua will be used to aid outreach at schools, and spread our excitement of biology!

Why Study Animal Groups and Flocks?

Awklet Flock by D. Dibenski.
Source: Wikimedia Commons.

Studying how animals live in groups and work together is of fundamental importance if we are to fully understand how animals behave. Living in groups - such as flocks, herds, swarms, or shoals - provides many advantages to animals including escaping from predators and foraging for food. Forming a flock helps the group to stay together and coordinate their actions. A flock does not have a particular size. Some creatures, such as starlings, can form flocks with thousands of members. Other creatures such as sticklebacks and guppies form much smaller groups of only 5 or 10 members.

There are many reasons why we want to understand collective behaviour and group living. This knowledge can assist in controlling groups of animals such as locusts, which sweep across thousands of kilometres, destroying vegetation and crops. We can use computer models to predict how humans navigate through crowds and change their collective movement. This can help to improve safety in sudden events such as evacuations, or contagious social behaviour. Studies are currently looking at how monitoring social interactions and group movements can help us to improve the welfare of livestock. Sheep and other livestock are more social than you might think! The mechanisms of flocking are also used to control swarms of robots which can be used to provide communications and aid in disaster recovery.

Structured social interactions are also important in such systems. Dolphins, for example, form strong 'friendships' and their social position (who they know) can have a strong effect on their survival. In human crowds, considering social ties (e.g. to family members or friends) in models can potentially improve their ability to recommend escape route design, or monitor when an event (e.g. crowd violence) might occur.

Flocking

The complexity of the flock behaviour is the result of social interactions among many individuals. Only slight tweaks to the behaviour of individuals can change the overall collective behaviour of the group. Each animal only knows what is happening directly around it, in that it is able to see and sense the other animals close to it. No individual understands the behaviour of the entire flock, and there are often no leaders.

Computer simulations have been important scientific tools for understanding how flocks work. Individual animals are modelled with simple rules for how they interact with other animals close to them. Then multiple individuals are placed in a group and the collective behaviour observed (and often matched to observations of real flocks). One of the earliest computer models was Craig Reynolds' Boids.

A boid represents an animal, and there are three types of behaviour that a boid can perform:

  • Separation: A boid will fly away from other boids that it is too close to.
  • Alignment: A boid will adjust the direction of its flight to match the direction of the boids around it.
  • Cohesion: A boid will steer towards the average position of the other boids around it.

Each boid has a circular zone surrounding it, and any boids within that zone influence its behaviour. This zone is shown in the diagram where the boid is the blue circle in the centre. The boids have a blind spot area behind them. Boids do not pay attention to individuals outside of their zone of vision or in their blind spot.

Couzin and his colleagues expanded Reynolds' model to separate the three behaviours into three distinct zones. They appear concentrically around the individual. The separation behaviour is controlled by the repulsion zone which is found nearest to the individual. If a creature has another individual within this zone then the creature will be repulsed away from that individual. The cohesion behaviour is controlled by the attraction zone, furthest from the individual. If there is an individual within this zone then the creature will head towards it. If there are a number of individuals here then the creature will fly towards the average position of all of them. The alignment is controlled by the orientation zone. When an individual is in this zone the creature will align itself with the individual and head in the same direction.

The Floqua game uses the same principles (see figure to the right). Each fish has a zone of repulsion (red circle), orientation (green circle), and attraction (black circle). All fish will interact with other fish (including the player's fish) within their own personal zones.

Social networks

When we talk about social networks, we tend to be thinking of websites such as Twitter and Facebook. Social network is a much more general term meaning the structure of a group of individuals. The 'Friendswheel' app on facebook demonstrates this: you and your friends are represented as 'nodes' (circles) and connections (lines between nodes) represent a friendship. Many group-living animals are also highly dependent on structured social interactions with certain other individuals (such as family members, or familiar individuals). These networks represent how the individuals interact within the group.

Imagine that you and your friends are walking in a protest crowd marching through the streets. In following the crowd, you align yourself in the same direction as those around you. However, within the crowd you are more likely to move in the direction of your friends in order to stay together. Thus, your position in the crowd is related to the position of your friends, and if the crowd splits into two, your choice of which crowd to follow will also be affected by your preference to be near your friends. Everyone else is moving in the same way: they are moving with the crowd, but preferentially moving alongside their friends. From this the overall crowd structure and collective movement remains, but strong substructures exist within the group. Similar processes occur in non-human animals. These are exactly the rules applied in Floqua to capture the effects of fish with different social connections.

In animal groups the network represents the preferences between individuals to move and coordinate with each other, and affects the behaviour of the shoal (see the research paper "Social networks and models for collective motion in animals" (.pdf)). The collective behaviour of the flock changes based on the social structure. If everyone is strongly connected to one individual, for example, then that individual has a good possibility of 'leading' the group through its high social position.

Fish in Floqua have different personalities ('behavioural syndromes' in biology) and social position. The network diagram on the left demonstrates an example of social network preferences for the 'creepy fish' (you will be introduced to different types of fish in the game!). This fish has a strong preference for all other individuals (except the predator!). None of the other individuals like creepy fish though. The thickness of the line represents the strength of the preference, and the arrows the direction of the preference. In Floqua, although you are trying to lead the other fish, they do not all have a strong social preference for you. This is why recruiting a popular fish to your flock can help you to keep your flock together. Less popular fish may provide no benefit or may actually repel the fish in your flock.

Want to know more?

There is a short press article about one of our scientific models of flocks on sciencedaily.com.

The scientific papers "Social networks and models for collective motion in animals" (.pdf) and "The impact of social networks on animal collective motion" (.pdf) provide more depth on the influence of social structure on flocks.

If you have any questions about the work or enquiries about studying in this field then please contact Dr Dan Franks: daniel.franks@york.ac.uk or visit his webpage.

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