Confusion of predators does not rely on specialist coordinated behavior

Antipredatory benefits are generally considered important inthe evolution and maintenance of animal aggregations. One suchbenefit is the confusion effect: the reduced ease of prey captureexperienced by some predators resulting from an inability tosingle out and attack an individual prey from a group as a resultof cognitive or sensory limitations. Although widely cited,empirical data that do any more than demonstrate the effectare sparse. Here, we use the artificial system of humans attemptingto "capture" images on a computer screen using a computer mouseto explore several hypotheses on the properties of the confusioneffect. This system has the advantage that we can control thebehavior of the prey and eliminate the risk of confounding factorsdue to differential prey behavior and/or phenotypes in groupsof different sizes. One important result of our study is thedemonstration that the confusion effect can occur in the absenceof these confounding factors and indeed in the absence of complexcoordinated behavior between individuals in the prey group (suchas are commonly observed in schooling fish). We also demonstratefor the first time that an individual prey item can still benefitfrom the confusion effect if it is only loosely associated inspace with a larger group of similar prey. Both these resultssuggest that the confusion effect can arise under less specialistcircumstances than previously realized, and so the importanceof this mechanism in shaping aggregation by prey and predator–preyinteractions may be substantially greater than previously considered.