The collective movement of animals in a group is a fascinating research topic for many scientists. Understanding these collective behaviors can sometimes inspire the development of strategies to promote positive social change, as well as technologies that mimic nature.
Many studies describe swarming behavior as a self-organizing process in which individuals in a group continually adjust their direction and speed to eventually achieve “collective” movement. However, this perspective fails to take into account the hierarchical structure exhibited by many animal groups and the potential benefits of having a “leader” lead the way.
Luis Gómez-Nava, Richard Bon and Fernando Peruani, three researchers at Université Côte d’Azur, Université de Toulouse and CY Cergy Paris Université, recently used physics theory to study the collective behavior of small flocks of sheep. Their results, published in natural physicsshow that by alternating between the roles of leader and follower, the herd ultimately achieves a form of “collective intelligence”.
“In most sociable animal systems, collective movement is not a continuous process but occurs in episodes: phases of collective movement are interrupted, for example, to rest or to feed,” Peruani told Phys.org. “Nonetheless, most collective studies of movement, including experimental and theoretical, consider groups that remain in motion from start to finish. Additionally, it is often assumed that swarming behavior requires individuals to constantly negotiate direction of movement. “
The main goal of the recent work by Peruani and his colleagues was to study the collective motion of an animal system in a way that explicitly takes into account the temporal aspect of the observed self-organized process, specifically that phases of collective motion have a beginning and an end. In addition, the team wanted to take an alternative and holistic perspective, viewing the movement of the group of animals as a collection of ‘collective phases’.
“From this perspective, questions about the mechanisms of information exchange and consensual decision-making take on a new dimension,” explained Peruani.
In their experiment, Peruani and his colleagues closely examined the spontaneous behavior of small groups of sheep over different time intervals. They analyzed the trajectories of individual flock members and calculated the animals’ overall spatial order and orientation, while also assessing correlations between the speeds at which individual animals moved.
“We first showed that none of the existing flocking models, or extensions thereof, agree with our observations,” Peruani said. “Then we analyzed how information traveled through the group, identified an interaction network that matched the data, and examined what information is transmitted through that network.”
Interestingly, Peruani and his colleagues found that the interaction network representing the behavior of the observed herds was highly hierarchical. They also showed that the only information disseminated through this network is that related to the position of the sheep within the group.
Using their findings, the researchers built a model of collective animal movement that focuses on two key cognitive processes. These processes are the selection of a leader to lead the herd for a period of time and the mechanism underlying herd navigation.
“It is important that each collective movement phase has a temporal leader,” explained Peruani. “We examined the mathematical properties of the resulting model to identify the benefits of the revealed collective strategy. I believe that the main contribution is this: the animals, from using a hierarchical interaction network to move together for a while, gives the temporal leader full control of the group, but there is also a rapid change in temporal leaders.
Essentially, the researchers’ findings suggest that sheep alternate between the roles of leader and follower as they move in herds. So leaders only lead the group for a certain amount of time before control of the group is transferred to another sheep.
“If a temporal leader has knowledge relevant to the group (e.g. the way out of a maze or the location of a food source), then the temporal leader will be able to lead the group efficiently,” Peruani said. All group members use this knowledge. It is worth noting that this only works if all individuals follow the temporal guide without asking.”
The findings collected by Peruani and his colleagues shed new light on the dynamics underlying the collective movement of small flocks of sheep. However, in order to investigate to what extent these results can be generalized, further experiments with larger herds and different animals must be carried out.
“We asked ourselves: If there is a temporal leader in each moment, how does the group share and process information that each individual member of the group may have? Can the group summarize information to improve their ability to accurately navigate to a distant location? In short, does the group exhibit collective intelligence?” Peruani said. “We have demonstrated that by regularly rotating the temporal leader, the group is able to pool information and demonstrate collective intelligence.”
Overall, the recent work by this research team highlights the possibility that some naturally occurring collective animal strategies utilize both hierarchical and democratic organizational schemes. In the future, their observations could inspire new studies examining the physics and biology underlying these intriguing collective animal behaviors.
“We are now investigating collective movement with groups of different agents,” Peruani added. “Specifically, we compare the spontaneous behavior of groups of lambs, young sheep and adult sheep to examine whether sheep learn to follow temporal leaders and act as a unit over time. We also study how groups behave in complex environments such as mazes or arenas with different food fields that can create a conflict of interest within group members. And more generally, we study how collectives distribute and process information using various statistical mechanics tools.”
Luis Gómez-Nava et al, Intermittent collective movement in sheep results from alternation of leader and follower roles, natural physics (2022). DOI: 10.1038/s41567-022-01769-8
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Quote: Physics Study Shows Sheep Flocks Alternate Leaders and Attain Collective Intelligence (2022 November 17) Retrieved November 17, 2022 from https://phys.org/news/2022-11-physics-sheep-flocks-alternate- leader.html
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