"The beauty of this experiment is that the researchers systematically vary the rules that the individual simulated prey play by, which dictates the structure of the resulting group," Parrish said. "They're like the little man behind the curtain moving three dials up and down attraction, repulsion and alignment. Then they say, 'Okay, bluegills, give it your best shot. How good are you at attacking prey based on how we set the rules?' "
This approach resulted in a "significant first step" toward a metric that can quantify how individual behaviors influence the safety of the group during a predator attack, Parrish said.
"This experiment makes some very specific predictions about what's a good configuration and what's not a good configuration, and gives some insight into what the rules of aggregation might be," she said.
"We don't know the rules prey use," Parrish said. "We can watch them, we can track them and infer what the rules are, but we don't actually know what they are. What this study did is bypass that messiness and make up the prey then see what a real predator does. That simplification is the innovation."
Once the simulation began the individual prey would swim and form groups spontaneously. Each trial consisted of 16 prey and one bluegill predator. Only the first attack by each bluegill was recorded. A new bluegill was put in the tank after the researchers restarted the simulation and the prey began moving and interacting with each other.
"Effectively, the bluegills were playing an immersive video game in which they hunted," Couzin said.
"By evolving the prey groupings, the game becomes harder and harder for the predators, as when a video game adapts to the strategy employed by the players," he said. "In a similar way, our prey 'evolved' to the mode of hunting that the bluegills exhibited, adapting better strategies that allowed them to evade hunting more effectively."'/>"/>
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