Animal Prey Defenses

Defenses protect animals against their predators. Their scientific study is eased by classifying them according to certain criteria, for instance: ‘at which step does a defense interrupt the predation cycle?’ Taking a predation cycle that consists of the steps (1) search, (2) encounter, (3) detection, (4) attack, and (5) consumption, this criterion leads to five defense classes. For example, a hardly digestible substance increases the time period between a predator’s last meal and its next search, so it is a step 1 defense; vertical migration of lake plankton reduces encounters with predators and is a step 2 defense; camouflage is a step 3 defense, as it prevents detection by predators; warning coloration puts off predator attacks, so it is a step 4 defense; and armor is a step 5 defense, as it inhibits consumption. A second often used classification discriminates between defenses that are permanent and those that are inducible and thus phenotypically plastic, that is, only expressed in the presence of predator cues. The defenses in each class have different characteristics. For example, they are advantageous at different prey densities. Most defenses are also costly, however, so should only evolve or be expressed under certain circumstances.