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Abstract:
Recently, numerous inducible defenses against predators have been described for freshwater animals. Prey have been found to be phenotypically plastic and are able to respond to chemical stimuli released by predators (kairomones). Inducible defenses can consist of morphological structures, life-history adaptations and behavioral responses. Various groups of animals develop spines, protective body shapes, stronger shells, or ''neck teeth''. Animal life-histories can be adaptive via changes in energy allocation to growth or reproduction, which will depend on the predator type that causes highest mortality either in juvenile or adult stages. Diel vertical migration of zooplankton is the most conspicuous predator avoidance behavior found to be controlled by a chemical stimulus. Defensive mechanisms may be costly - thus in a variable environment, chemical induction of phenotypic responses provides a rapid and efficient way of applying defences only when they are needed
