Protective Adaptations

in animals, the morphological, physiological, or ethological characteristics that ensure survival in the struggle for existence—that is, the preservation of the life of the individual and its offspring.

Morphological protective adaptations comprise all types of protective coloration and forms of animals, as well as organs of passive and active defense against enemies. These include the spines of some fish (for example, porcupine fish and sticklebacks), porcupines, hedgehogs, and sea urchins; the hairs of caterpillars; the strong armor of boxfish, tortoises, and armadillos; the chitinous shells of many arthropods and the shells of mollusks; the skeletons of sponges and coral; the horns of ungulates; and the poison organs of spiders, scorpions, scolopendra, fish, snakes, bees, and wasps. At various stages of their development, animals are protected from un-favorable external environmental conditions by egg and embryonic membranes, cocoons, feathers, hair, scales, and a fatty layer of skin.

Physiological protective adaptations include the poisonous properties of the lymph, blood, or skin of inedible species and the excretions from malodorous glands of bedbugs, beetles, skunks, and beavers, which frighten away enemies. Some animals discharge poisonous or malodorous fluids (for example, bombardier and darkling beetles) or the contents of an ink gland (for example, cuttlefish). The storage of reserves of nutritive substances and the binding of metabolic water by some animals ensures survival in times of unfavorable seasonal conditions.

Ethological protective adaptations are manifested in various defensive reactions, including fleeing from enemies, hiding in shelters (burrows, runs, nests, and shells), and standing perfectly still. The feigning of death by some insects and of injury by birds, in order to lead an enemy away from the nest or the brood, as well as the shedding (autotomy) of tails, extremities, and other parts of the body by lizards, crayfish, daddy longlegs, and worms are also examples of this type of protective adaptation. Other examples are the frightening cries, hisses, and threatening poses of some animals.

Vertical and horizontal movements of animals (fish, birds, and mammals), the instinct for building nests and other shelters, and food storage can also be classified as protective adaptations. Formed through an evolutionary process, protective adaptations are beneficial to an organism only under the conditions of its natural environment.