Dormancy facts for kids
Dormancy is a period in an organism's life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be closely associated with environmental conditions.
There are two types of dormancy:
- Predictive dormancy occurs when an organism enters a dormant phase before the onset of adverse conditions. For example, day length and decreasing temperature are used by many plants as triggers to start dormancy before the onset of winter.
- Consequential dormancy occurs when organisms enter a dormant phase after adverse conditions arise. This is often found in areas with an unpredictable climate. Sudden changes in conditions may lead to a high mortality rate among animals relying on consequential dormancy. On the other hand, its use can be advantageous, as organisms remain active longer and are able to make greater use of available resources.
Contents
Animals
- Hibernation: Hibernation is a mechanism used by many mammals to save energy and survive 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 that 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. Although hibernation is almost exclusively seen in mammals, some birds, such as the common poorwill, may hibernate.
- Diapause: Diapause is a predictive strategy common in insects between autumn and spring.
- Aestivation: Aestivation is consequential dormancy in response to very hot or dry conditions. It is common in invertebrates, and also occurs in lungfish, salamanders, desert tortoises, and crocodiles.
- Brumation: Brumation is dormancy in reptiles similar to hibernation. It differs from hibernation in the metabolic processes involved. Reptiles usually start brumation in late autumn. They often wake up to drink water and return to "sleep". They can go for months without food.
Plants
Development from the seed
A seed, though not active, is a tiny living thing. It contains the embryo of the future plant, which is not changing or developing: it is dormant. The common idea is that the seed "sleeps" until it gets what it needs to wake up. That is not correct. Different seeds have different habits, no doubt adapted to their habitat. There are different kinds of resting stages in seeds:
- 1. Seed dormancy: means the seed does not develop for a while even when conditions are suitable.p98 Delayed germination (development) allows time for dispersal. Changes take place inside the seed which sooner or later make it germinate. The details vary hugely between species.
- 2. Seed hibernation: fails to germinate because conditions are not right. Growth is triggered by particular events in the environment. Details of the triggers are known for some, but not all, seeds. Rain, fire, ground temperature, are examples. Many seeds only germinate after they have been eaten and passed through the digestive system of an animal. This also is a dispersal method.
When a seed germinates ("wakes up"), it begins to grow into a little plant called a seedling. It uses the soft fleshy material inside the seed for nutrients (food) until it is ready to make food on its own using sunlight, water and air.
Most seeds germinate underground where there is no sunlight. The plant does not need the nutrients in soil for a few days or weeks, because the seed has all the things it needs to grow. Later, though, it will begin to need sunlight. If there is sunlight, the plant will use it to grow healthy. If there is no light, the plant will still grow for a while, but its plastids will not mature: the chlorophyll does not turn green. If the plant does not get enough light, it will eventually die. It needs light to make food for itself when the reserve in the seed runs out.
- The oldest carbon 14-dated seed that has grown into a plant was a Judean date palm seed about 2,000 years old, recovered from excavations at Herod the Great's palace on Masada in Israel. It was germinated in 2005.
- The largest seed is produced by the Coco de mer, or "double coconut palm", Lodoicea maldivica. The entire fruit may weigh up to 23 kilograms (50 pounds) and usually contains a single seed.
Trees
Typically, temperate woody perennial plants require chilling temperatures to overcome winter dormancy (rest). In some species, rest can be broken within hours at any stage of dormancy.
Tree species that have well-developed dormancy needs may be tricked to some degree, but not completely.
Going through an "eternal summer" and the resultant automatic dormancy is stressful to the plant and usually fatal. The fatality rate increases to 100% if the plant does not receive the necessary period of cold temperatures required to break the dormancy. Most plants require a certain number of hours of "chilling" at temperatures between about 0 °C and 10 °C to be able to break dormancy.
Bacteria
Many bacteria can survive adverse conditions by forming endospores, cysts, or states of reduced metabolic activity lacking specialized cellular structures. Up to 80% of the bacteria in samples from the wild appear to be metabolically inactive—many of which can be resuscitated. Such dormancy is responsible for the high diversity levels of most natural ecosystems.
Viruses
Dormancy does not apply to viruses, as they are not metabolically active. However, some viruses such as poxviruses, after entering the host, can become latent for long periods of time, or even indefinitely until they are externally activated.
Related pages
Images for kids
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Annual life cycle of sympodially growing orchids with dormancy after completion of new growth/pseudobulb, e.g., Miltonia, or Odontoglossum
See also
In Spanish: Dormancia para niños
