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Dormancy is a period in an organism's life cycle when growth, development, and (in animals) physical activity is temporarily suspended. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be closely associated with environmental conditions. Organisms can synchronize entry to a dormant phase with their environment through predictive or consequential means. Predictive dormancy occurs when an organism enters a dormant phase before the onset of adverse conditions. For example, photoperiod and decreasing temperature are used by many animals to predict the onset of winter. Consequential dormancy occurs when organisms enter a dormant phase after adverse conditions have arisen. This is commonly found in areas with an unpredictable climate. While very sudden changes in conditions may lead to a high mortality rate among animals relying on consequential dormancy, its use can be advantageous, as organisms remain active longer, and are therefore able to make greater use of available resources.
- Main article: Hibernation
Hibernation is a mechanism used by many animals to escape cold weather and food shortage over the winter. Hibernation may be predictive or consequential. An animal prepares for hibernation by building up a thick layer of body fat during late summer and autumn which will provide it with energy during the dormant period. During hibernation the animal undergoes many physiological changes, including decreased heart rate (by as much as 95%) and decreased body temperature. Animals that hibernate include bats, ground squirrels and other rodents, mouse lemurs, the European Hedgehog and other insectivores, monotremes and marsupials.
Diapause is a predictive strategy that is predetermined by an animal's genotype. Diapause is common in insects, allowing them to suspend development between autumn and spring, and in mammals such as the red deer, where a delay in attachment of the embryo to the uterine lining ensures that offspring are born in spring, when conditions are most favorable.
- See also: Mammalian embryonic diapause
- Main article: Estivation
Estivation is an example of consequential dormancy in response to very hot or dry conditions. It is common in invertebrates such as the garden snail and worm but also occurs in other animals such as the lungfish. The period of dormancy that bears experience during the winter is also called estivation.
- Main article: Brumation
Reptiles generally begin brumation in late fall (more specific times depend on the species). They often wake up to drink water and return to "sleep". They can go months without food. Reptiles may want to eat more than usual before the brumation time but eat less or refuse food as the temperature drops. However, they do need to drink water. The brumation period is anywhere from one to eight months depending on the air temperature and the size, age, and health of the reptile. During the first year of life, many small reptiles do not fully brumate, but rather slow down and eat less often. Brumation should not be confused with hibernation; when mammals hibernate, they are actually asleep; when reptiles brumate, they are less active, and their metabolism slows down so they just do not need to eat as often. Reptiles can often go through the whole winter without eating. Brumation is triggered by lack of heat and the decrease in the hours of daylight in winter.
- Main article: Torpor
Torpor is a short-term reduction of body temperature to an ambient level during periods of inactivity, often lasting only a few hours. Animals that experience torpor include small birds such as hummingbirds and some small mammals such as bats.
- Scholar team (2002) SQA Adv. Higher Biology; Environmental Biology. p 93-95 Heriot Watt University
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