New insights into how animals travelling in groups make decisions have been provided by a team of researchers including Professor Nigel Franks of Bristol University’s School of Biological Sciences.
The findings of the team, led by Dr Iain Couzin of the Oxford University Department of Zoology and Princeton University, are published in Nature today [3 February 2005].
Animals that forage or travel in large groups, such as honeybees, fish, hoofed mammals and birds, have to make collective decisions about which direction to take, despite there often being very few individuals in the group that know the direction in which to go to find food or to follow a migration route. Some animals are known to use signals to communicate information within a group, for instance the famous ‘waggle-dance’ of the honeybee. However, in large migrating groups, where crowding means individuals can only see the animals that are closest to them, it is unlikely that signalling can explain their movements.
The team used a computer model based on observations of real-life animal groups to show how information can be transferred within groups which neither use signalling nor know which individuals, if any, have information about where to go. Surprisingly, the model revealed that the larger the group, the smaller the proportion of informed animals needed to guide it, and that only a very small proportion of animals in the know is required to achieve great accuracy.
The model also demonstrated that animal groups are capable of coming to an accurate consensus decision when informed individuals in the group have different preferences about which way to travel, even though these individuals have no knowledge about whether they are in the majority or minority.
Dr Couzin, who conducted the research with colleagues from Princeton and the Universities of Leeds and Bristol, said: “The direction an informed individual decides to take lies in a balance between two influences: the desire to achieve a goal such as reaching a known food source, and the interaction with the animals around them. This even applies to the pedestrian walking down the street, who automatically balances the desire to follow the quickest route to a chosen destination with local conditions caused by the movement and position of other pedestrians around them.
“Using a computer model allows us to observe and better understand the patterns that exist in group movements. Our model provides new insights into the mechanisms of effective leadership and decision-making in biological systems, and has broad implications for our understanding of information transfer in groups, from the interaction of cells to the movements of grouping robots.”
'Effective leadership and decision-making in animal groups on the move’ by Iain Couzin, Jens Krause, Nigel Franks and Simon Levin is published in Nature on Thursday 3 February 2005.