Influence of prey foraging posture on flight behavior and predation risk: Predators take advantage of unwary prey

Foraging in animals is often associated with characteristic body postures, such as the head-down posture. When foraging conflicts with the ability to detect predators or to flee, individuals may incur a greater risk of mortality to predation than otherwise. Here we investigate the influence of different foraging postures (horizontal versus nose-down body posture) on the ability of individuals to respond to approaching predators and on the risk of mortality to predation in the guppy (Poecilia reticulata). Individuals engaged in nose-down foraging were assumed to be able to visually scan a smaller area for predators and to escape less effectively due to their body posture, and thus are more vulnerable to stalking predators than horizontally foraging ones. In a first experiment, we separately exposed nonforaging, horizontally foraging, and nose-down foraging guppies to an approaching cichlid fish predator model. Nonforaging guppies reacted sooner to and initiated flight further away from the approaching model than did foraging fish collectively and horizontally foraging individuals responded sooner to the model than nose-down foraging ones. Comparing all test guppies, nose-down foraging individuals were the most likely not to exhibit any response to the predator model. When presented with a simultaneous choice of two guppies behind a one-way mirror, individual blue acara cichlid (Aeguidens pulcher), a natural predator of the guppy, preferred to attack foraging guppies over nonforaging ones and nose-down foraging guppies over horizontally foraging individuals. In a final experiment with free-swimming cichlids and guppies, we demonstrated that individual risk of predation for guppies foraging nose down was greater than for guppies foraging horizontally, and both were at greater fisk than nonforaging guppies. This latter result is consistent with the above differences in the guppy's responsiveness to approaching predators depending on their foraging behavior, and with the finding that cichlid predators preferred fish that were less likely to show any response to them. Ou; results therefore indicate that the ability to respond to approaching predators and the risk of mortality to predation in the guppy is strongly influenced by their foraging activity, and in particular their foraging posture, and that cichlid predators preferentially select less wary and more vulnerable guppies.