Figure 1: Depiction of the disembodied simulation. Prey seek to forage as much as possible while avoiding being captured by the predator. If none of the prey in the group are vigilant, the target prey is captured 100% of the time. Model of predators and prey 6 We designed this model to capture certain features of natural predators and to control for potentially complicating factors. First, to ensure that predator attacks are not trivially predictable we simulate predators that attack at intervals that are normally distributed around a specific attack rate. Thus, predator attacks are randomly distributed throughout the 2,000-time-step duration of the simulation. To model the fact that larger groups of prey often attract more attacks from predators—a realistic cost of group living known as the attraction effect [37]—we scale this attack rate with the group size, such that the group experiences 5 predator attacks for every prey initially in the group over the course of the simulation. This scaling factor also allows us to control for the dilution effect , which has been In this model, prey fitness is directly related to the amount of time it spends foraging, where a single round of foraging increases prey fitness by 1.0. However, prey vigilance determines whether a predator’s attack on the prey is successful. These two options— foraging and vigilance—are assumed to be mutually exclusive. Thus, prey must evolve to maximize their food intake while remaining vigilant enough to survive the entire simulation, which is akin to the maximum possible life span of the prey. this study. Vigilant prey (10% capture chance) Foraging prey (+1 fitness per update) (30% capture chance due to vigilant prey) Approaching predator (Attack rate proportional to prey group size) Ta rg et  p re y 10  u pd at es  be fo re  a tta ck