Influence of detectability and ability to escape on natural selection of conspicuous autotomous defenses

Antipredatory adaptations in which a predator's attack is diverted to body parts that may be sacrificed or are less vulnerable sometimes depend upon the conspicuousness of the body part attacked. The predator's attention is drawn to the emphasized part, which serves as a decoy. Such defenses appear paradoxical in that they increase the probability of detection. However, they simultaneously increase the probability of postdetectional escape enough to decrease the overall probability of being killed. Based on probabilities of detection and of escape following detection, a simple model predicts the conditions in which autotomy and related defenses are favored. For a conspicuous decoy, equilibrium values of the increases in probabilities of detection and of escape following detection are given. Data on the conditional probability of escape after detection are discussed for the scincid lizards Eumeces fasciatus and E. laticeps, which have brightly colored autotomous tails. Versions of the model that split the predator–prey encounter into several successive stages are outlined briefly and illustrated by the data for the two lizard species. Strategies for measuring the probabilities and testing the model's predictions are considered.