1 Escape behavior : importance , scope , and variables

Prey that do not escape when attacked by lethal predators die. Even prey that suffer nonlethal injuries inflicted by predators may incur substantial costs, such as reduced ability to reproduce, reduced social status, reduced ability to forage, and reduced ability to escape in later encounters with predators. Unsuccessful escape reduces fitness. A prey that is killed by a predator loses all fitness that might have been obtained in the future. More technically, residual reproductive value (expected remaining reproductive output over a lifetime) becomes zero when a prey is killed. Therefore predator–prey interactions have been a major force driving evolutionary changes to reduce the likelihood of predation. Numerous, often spectacular, antipredatory adaptations have evolved, including morphological defenses such as shells and other armature, weaponry, camouflage, and the ability to shed tails or other expendable body parts. In addition to such adaptations, prey that rely on escape to avoid predation must be able to make appropriate escape decisions when confronted by predators. The degree of predation risk posed by a predator that is approaching or is immobile nearby determines expected loss of fitness if the prey does not flee, i.e., the cost of not fleeing. This cost of not fleeing varies with distance between predator and prey when escape begins, and in some cases with the length of time that the predator approaches or is immobile nearby. Besides avoiding being eaten, prey must do many things to maintain themselves and increase their fitness, such as foraging and defending foraging grounds, courting, mating, and aggressively interacting with sexual rivals. When fleeing interrupts an activity that increases fitness, it imposes a cost of fleeing. Therefore each time a prey encounters a predator, the prey has a current level of fitness. The greater its fitness, the more the prey has to lose if killed. In everyday usage, escape seems to be a simple term, but misleadingly so. If we think of a prey and predator that meet, the prey may flee and/or enter refuge to escape. However, prey may employ other defenses that allow them to escape in a broad sense, including avoiding areas where predators occur, avoiding detection by predators, and a