Latency to flee from an immobile predator: effects of predation risk and cost of immobility for the prey

When a predator is immobile near an immobile prey, the probability that the predator will detect and attack increases over time. The prey’s cost of moving, thereby abandoning crypsis due to immobility, therefore decreases. Cost of not moving increases over time if movement is required for prey to conduct fitness-enhancing activities. We tested a cost-benefit model that predicts effects of factors that affect predation risk and cost of not moving on a prey’s latency to flee. Acting as simulated predators, we conducted experiments on the lizards Iberolacerta cyreni and Podarcis lilfordi. All predictions for 5 risk factors and a cost of moving factor were verified. Lizards fled sooner when the predator stood closer, approached rapidly rather than slowly before stopping, approached directly rather than indirectly, and gazed at the lizard rather than away from it, and after the second of 2 successive approaches. Latency to move was shorter in the presence than absence of a mealworm, suggesting the importance of opportunity cost of immobility. The effect of standing distance has 2 components, greater rate of detection by the predator and greater risk of being captured if detected at shorter distances. Escape theory has been highly successful in predicting how close a prey allows a predator to approach before fleeing. Our model extends an economic approach to study of escape decisions in response to an immobile predator that may be an ambush forager or an active forager that has stopped moving nearby.