A video game designed for predatory fish might have unraveled some lingering evolutionary questions about group formation and movement in animals, according to new research that took a unique approach to observing interactions between real and simulated animals.
Princeton University researchers report in the journal Science some of the strongest direct evidence that collective motion in animal groups such as schools of fish can evolve as a finely tuned defense against attack from predators. This dynamic has been suggested by other research, but the many variables that can drive group movement have made it difficult to observe a direct link to self-defense, explained senior researcher Iain Couzin, an assistant professor of ecology and evolutionary biology at Princeton who studies collective animal behavior.
Couzin and his colleagues developed an evolvable simulation of small prey that allowed the researchers to observe how group formation and movement alone protect against predatory attack. Couzin developed and conducted the study at Princeton with two former postdoctoral researchers from his lab, first author Christos Ioannou, now a research fellow at the University of Bristol, and Vishwesha Guttal, now an assistant professor of ecological sciences at the Indian Institute of Science.
The researchers projected the simulated prey — which appeared as small reddish dots — onto one side of a tank containing the famously ravenous bluegill sunfish. The prey interacted spontaneously with one another based on encoded behavior traits, and the researchers documented in the prey the resulting individual behaviors and group formations. In the end, the bluegills were most likely to avoid attacking simulated prey that had formed coordinated and mobile groups.
These results show that group formation itself can dissuade a predator, even if the prey — as in the simulation — are completely unaware of the danger, the researchers report. This suggests that the specific configuration of animal groups is an evolved defense in its own right, Couzin explained. The ideal configurations exhibited by the simulated prey mirror those of many animal groups, wherein individuals follow cues from their near-neighbors to coordinate collective movement.
“This sort of hybrid virtual approach has given us a way of tapping into these long-lasting questions that have really evaded standard analysis for decades,” Couzin said.
“To conduct this type of study is very intensive in terms of statistics and creating control models of what predators would have done, given the prey that were available to them in that particular situation at that time and compare that to the behavior of the real behavior,” Couzin said. “And that’s one of the reasons why these studies have been so difficult in the past using classic experimental means.”
An important aspect of the simulation is that it let the researchers control the behavior of individual prey, Couzin said. In nature, animals can respond to a predator in different and unpredictable ways — animals might react as the predator approaches or after the initial attack. In addition, group cohesion depends on the number of animals assembled and environmental factors such as terrain.
These results show that group formation itself can dissuade a predator, even if the prey — as in the simulation — are completely unaware of the danger, the researchers report. This suggests that the specific configuration of animal groups is an evolved defense in its own right, Couzin explained. The ideal configurations exhibited by the simulated prey mirror those of many animal groups, wherein individuals follow cues from their near-neighbors to coordinate collective movement.
“This sort of hybrid virtual approach has given us a way of tapping into these long-lasting questions that have really evaded standard analysis for decades,” Couzin said.
“To conduct this type of study is very intensive in terms of statistics and creating control models of what predators would have done, given the prey that were available to them in that particular situation at that time and compare that to the behavior of the real behavior,” Couzin said. “And that’s one of the reasons why these studies have been so difficult in the past using classic experimental means.”
An important aspect of the simulation is that it let the researchers control the behavior of individual prey, Couzin said. In nature, animals can respond to a predator in different and unpredictable ways — animals might react as the predator approaches or after the initial attack. In addition, group cohesion depends on the number of animals assembled and environmental factors such as terrain.
