Not all cold blooded animals hibernate, although most amphibians do. Many warm blooded animals, like bears, also hibernate.
Hibernaculum plural form: hibernacula (Latin, "tent for winter quarters") is a word used in zoology to refer to a place of abode in which a creature seeks refuge, such as a bear using a cave to overwinter. Insects may hibernate to survive the winter. The word can be used to describe a variety of shelters used by various kinds of animals, for instance, bats, marmots and snakes.
A potential][ hibernaculum
An artificial hibernaculum or 'Bug Hotel'
An ectotherm, from the Greek εκτός (ektós) "outside" and θερμός (thermós) "hot", is an organism in which internal physiological sources of heat are of relatively small or quite negligible importance in controlling body temperature. Such organisms (for example frogs) rely on environmental heat sources, which permits them to operate at very economical metabolic rates. Some such animals live in environments in which temperatures are practically constant, as is typical of regions of the abyssal ocean. In contrast where temperature varies so widely as to limit the physiological activities of other kinds of ectotherms, many species habitually seek out external sources of heat or shelter from heat; for example, many reptiles regulate their body temperature by basking in the sun, or seeking shade when necessary in addition to a whole host of other behavioral thermoregulation mechanisms. In contrast to ectotherms, endotherms rely largely, even predominantly, on heat from internal metabolic processes.
In ectotherms, fluctuating ambient temperatures may affect the body temperature. Such variation in body temperature is called poikilothermy, though the concept is not widely satisfactory and the use of the term is declining. In small aquatic creatures such as Rotifera, the poikilothermy is practically absolute, but other creatures have wider physiological options at their disposal, and they can avoid ambient temperature changes, or moderate their effects.
Various patterns of behavior enable certain ectotherms to regulate body temperature to a useful extent. To warm up, reptiles and amphibians find sunny places and adopt positions that maximise their exposure; at harmfully high temperatures they seek shade or cooler water. In cold weather, honey bees huddle together to retain heat. Butterflies and moths may orient their wings to maximize exposure to solar radiation in order to build up heat before takeoff. Many flying insects, such as honey bees and bumble bees, also raise their internal temperatures endothermally prior to flight, by vibrating their flight muscles without violent movement of the wings (see insect thermoregulation). Such endothermal activity is an example of the difficulty of consistent application of terms such as poikilothermy and homiothermy.
In addition to behavioral adaptations, physiological adaptations help ectotherms regulate temperature. Diving reptiles conserve heat by heat exchange mechanisms, whereby cold blood from the skin picks up heat from blood moving outward from the body core, re-using and thereby conserving some of the heat that otherwise would have been wasted. The skin of bullfrogs secretes more mucus when it is hot, allowing more cooling by evaporation.][
During periods of cold some ectotherms enter a state of torpor, in which their metabolism slows or, in some cases, such as the Wood Frog, effectively stops. The torpor might last overnight or last for a season, or even for years, depending on the species and circumstances.
Ectotherms rely largely on external heat sources such as sunlight to achieve their optimal body temperature for various bodily activities. Accordingly they depend on ambient conditions to reach operational body temperatures. In contrast endothermic animals as a rule maintain nearly constant high operational body temperatures largely by reliance on internal heat produced by metabolically active organs (liver, kidney, heart, brain, muscle) or even by specialized heat producing organs like brown adipose tissue (BAT). Also as a rule, ectotherms have lower metabolic rates than endotherms at a given body mass. As a consequence, endotherms generally rely on higher food consumption, and commonly on food of higher energy content. Such requirements may limit the carrying capacity of a given environment for endotherms as compared to its carrying capacity for ectotherms.
Because ectotherms depend on environmental conditions for body temperature regulation, as a rule they are more sluggish at night and in early mornings. When they emerge from shelter, many diurnal ectotherms need to heat up in the early sunlight before they can begin their daily activities. In cool weather the foraging activity of such species is therefore restricted to the day time in most vertebrate ectotherms, and in cold climates most cannot survive at all. In lizards, for instance, most nocturnal species are geckos specialising in "sit and wait" foraging strategies. Such strategies do not require as much energy as active foraging, and do not as a rule require hunting activity of the same intensity. From another point of view, sit-and-wait predation may require very long periods of unproductive waiting. Endotherms cannot in general afford such long periods without food, but suitably adapted ectotherms can wait without expending much energy. Endothermic vertebrate species are therefore less dependent on the environmental conditions and have developed a higher variability (both within and between species) in their daily patterns of activity.
Note that because of historical accident, students encounter a source of possible confusion between the terminology of physics and biology. Whereas the thermodynamic terms "exothermic" and "endothermic" respectively refer to processes that give out heat energy and processes that absorb heat energy, in biology the sense is effectively inverted. The metabolic terms "ectotherm" and "endotherm" respectively refer to organisms that rely largely on external heat to achieve a full working temperature, and to organisms that produce heat from within as a major factor in controlling their bodily temperature.
A poikilotherm is an organism whose internal temperature varies considerably. It is the opposite of a homeotherm, an organism which maintains thermal homeostasis. Usually the variation is a consequence of variation in the ambient environmental temperature. Many terrestrial ectotherms are poikilothermic. However some ectotherms remain in temperature-constant environments to the point that they are actually able to maintain a constant internal temperature (i.e. are homeothermic). It is this distinction that often makes the term "poikilotherm" more useful than the vernacular "cold-blooded", which is sometimes used to refer to ectotherms more generally. Poikilothermic animals include types of vertebrate animals, specifically fish, amphibians, and reptiles, as well as a large number of invertebrate animals. The Naked mole rat is the only mammal that is currently thought to be poikilothermic.
The term derives from ancient Greek: poikilos (), meaning "varied"; and thermos (), meaning "heat".
For an important chemical reaction, poikilotherms may have four to ten enzyme systems that operate at different temperatures. As a result, poikilotherms often have larger, more complex genomes than homeotherms in the same ecological niche. Frogs are a notable example of this effect, though their complex development is likely more important.
Because their metabolism is variable and generally below that of homeothermic animals, sustained high-energy activities like powered flight in large animals or maintaining a large brain is generally beyond poikilotherm animals. The metabolism of poikilotherms favors strategies such as sit-and-wait hunting over chasing prey for larger animals with high movement cost. As they do not use their metabolisms to heat or cool themselves, total energy requirement over time is low. For the same body weight, poikilotherms need a half to a tenth of the energy of homeotherms.
It is comparatively easy for a poikilotherm to accumulate enough energy to reproduce. Poikilotherms at the same trophic level often have much shorter generations than homeotherms: weeks rather than years.][ Such applies even to animals with similar ecological roles such as cats and snakes.
This difference in energy requirement also means that a given food source can support a greater density of poikilothermic animals than homeothermic animals. This is reflected in the predator-prey ratio which is usually higher in poikilothermic fauna compared to homeothermic ones. However, when homeotherms and poikilotherms have similar niches, and compete, the homeotherm can often drive poikilothermic competitors to extinction, because homeotherms can gather food for a greater fraction of each day.
Poikilotherms succeed in some habitats, such as islands and hot deserts, or distinct bioregions (such as the small bioregions of the Amazon basin). These biomes often do not have enough food to support a viable breeding population of homeothermic animals. In these habitats, poikilotherms such as large lizards, crabs and frogs supplant homeotherms such as birds and mammals.
In medicine, loss of normal thermoregulation in humans is referred to as "poikilothermia". This is usually seen with sedative and hypnotic drugs or in 'compartment syndrome'. For example, barbiturates, ethanol, and chloral hydrate may precipitate this effect.][ REM sleep is also considered a poikilothermic state in humans.
Hibernation is a state of inactivity and metabolic depression in endotherms. Hibernation refers to a season of heterothermy that is characterized by low body temperature, slow breathing and heart rate, and low metabolic rate. Although traditionally reserved for "deep" hibernators such as rodents, the term has been redefined to include animals such as bears and is now applied based on active metabolic suppression rather than based on absolute body temperature decline. Many experts believe that the processes of daily torpor and hibernation form a continuum and utilize similar mechanisms. Hibernation during the summer months is known as aestivation. Some reptile species (ectotherms) are said to brumate, or undergo brumation, but any possible similarities between brumation and hibernation are not firmly established.
Often associated with low temperatures, the function of hibernation is to conserve energy during a period when sufficient food is unavailable. To achieve this energy saving, an endotherm will first decrease its metabolic rate, which then results in a decreased body temperature. Hibernation may last several days, weeks, or months depending on the species, ambient temperature, time of year, and individual's body condition.
Before entering hibernation, animals need to store enough energy to last the entire winter. Larger species become hyperphagic and eat a large amount of food and store the energy in fat deposits. In many small species, food caching replaces eating and becoming fat. Some species of mammals hibernate while gestating young, which are either born while the mother hibernates or shortly afterwards.
Hibernation among rodents has been extensively studied for decades. Species of ground squirrel, marmot, prairie dog, dormouse, and hamster have all been shown to demonstrate hibernation. These animals all exhibit the classic hibernation pattern where body temperature remains at ambient for days to weeks, followed by a brief (<24hr) return to higher body temperature.
While hibernation has long been studied in rodents, namely ground squirrels, no primate or tropical mammal was known to hibernate prior to animal physiologist Kathrin Dausmann of Philipps University of Marburg, Germany, and coworkers presenting evidence that the Fat-tailed Dwarf Lemur of Madagascar hibernates in tree holes for seven months of the year. Malagasy winter temperatures sometimes rise to over , so hibernation is not exclusively an adaptation to low ambient temperatures. The hibernation of this lemur is strongly dependent on the thermal behaviour of its tree hole: if the hole is poorly insulated, the lemur's body temperature fluctuates widely, passively following the ambient temperature; if well insulated, the body temperature stays fairly constant and the animal undergoes regular spells of arousal.][ Dausmann found that hypometabolism in hibernating animals is not necessarily coupled to a low body temperature.][
Bears do not hibernate very differently from either rodents or primates. They rely on active metabolic suppression rather than a decreased body temperature to save energy over winter. Despite their lack of body temperature change, bears have an impressive hibernation physiology. They are able to recycle their proteins and urine, allowing them to stop urinating for months.
Obligate hibernators are defined as animals that spontaneously, and annually, enter hibernation regardless of ambient temperature and access to food. Obligate hibernators include many species of ground squirrels, other rodents, mouse lemurs, the European Hedgehog and other insectivores, monotremes and marsupials. These undergo what has been traditionally called "hibernation": the physiological state where the body temperature drops to near ambient (environmental) temperature, and heart and respiration rates slow drastically. The typical winter season for these hibernators is characterized by periods of torpor interrupted by periodic, euthermic arousals, wherein body temperatures and heart rates are restored to euthermic (more typical) levels. The cause and purpose of these arousals is still not clear.
The question of why hibernators may experience the periodic arousals (returns to high body temperature) has plagued researchers for decades, and while there is still no clear cut explanation, there are a myriad of hypotheses on the topic. One favored hypothesis is that hibernators build a 'sleep debt' during hibernation, and so must occasionally warm up in order to sleep. This has been supported by evidence in the arctic ground squirrel. Another theory states that the brief periods of high body temperature during hibernation are used by the animal to restore its available energy sources. Yet another theory states that the frequent returns to high body temperature allow mammals to initiate an immune response.
Hibernating arctic ground squirrels may exhibit abdominal temperatures as low as -2.9 °C, maintaining sub-zero abdominal temperatures for more than three weeks at a time, although the temperatures at the head and neck remain at 0 ˚C or above.
Historically there was a question of whether or not bears truly hibernate. Since they experience only a modest decline in body temperature (3-5°C) compared with what other hibernators undergo (32°C+). Many researchers thought that their deep sleep was not comparable with true, deep hibernation. This theory has been refuted by recent research in captive black bears.
Unlike obligate hibernators, facultative hibernators only enter hibernation when either cold stressed or food deprived, or both. A good example of the differences between the two types of hibernation can be seen among the prairie dogs; where the white-tailed prairie dog is an obligate hibernator and the closely related black-tailed prairie dog is a facultative hibernator.
Historically, Pliny the Elder believed swallows hibernated, and ornithologist Gilbert White pointed to anecdotal evidence in The Natural History of Selborne that indicated as much. Birds typically do not hibernate, instead utilizing torpor. One known exception is the Common Poorwill (Phalaenoptilus nuttallii), first documented by Edmund Jaeger.
Fish are ectothermic, and so, by definition, cannot hibernate because they cannot actively down-regulate their body temperature or their metabolic rate. However, they can experience decreased metabolic rates associated with colder environments and/or low oxygen availability (hypoxia) and can experience dormancy. For a couple of generations][ during the 20th century it was thought that basking sharks settled to the floor of the North Sea and became dormant. Research by Dr David Sims in 2003 dispelled this hypothesis, showing that the sharks actively traveled huge distances throughout the seasons, tracking the areas with the highest quantity of plankton. The epaulette sharks have been documented to be able to survive for long periods of time without oxygen, even being left high and dry, and at temperatures of up to . Other animals able to survive long periods without oxygen include the goldfish, the red-eared slider turtle, the wood frog, and the bar-headed goose. However, the ability to survive hypoxic or anoxic conditions is not the same, nor closely related, to endotherm hibernation.
Hibernation induction trigger (HIT) is a bit of misnomer. Although research in the 1990s hinted at the ability to induce torpor in animals by injection of blood taken from a hibernating animal, further research has been unable to reproduce this phenomenon. Despite the inability to induce torpor, there are substances in hibernator blood that can lend protection to organs for possible transplant. Researchers were able to prolong the life of an isolated pig's heart with a HIT. This may have potentially important implications for organ transplant, as it could allow organs to survive for up to 18 or more hours, outside the human body. This would be a great improvement from the current 6 hours.
This supposed HIT is a mixture derived from serum, including at least one opioid-like substance. DADLE is an opioid that in some experiments has been shown to have similar functional properties.
There are many research projects currently investigating how to achieve "induced hibernation" in humans. The ability for humans to hibernate would be useful for a number of reasons, such as saving the lives of seriously ill or injured people by temporarily putting them in a state of hibernation until treatment can be given (compare induced coma). In addition, hibernation would be useful for humans during various proposed plans for interstellar travel in the future. Similar to human hibernation, suspended animation deals with the slowing of life processes in general, by external means and without termination.
Hibernation, and the species that are able to utilize it, have become fantastic models for many different human diseases. Hibernators make natural models for stroke, ischemia-reperfusion injury, diabetes, obesity, and depression.
A tappen is an obstruction, or indigestible mass, found in the intestines of bears and other animals during hibernation. Also referred to as a "rectal plug." They make it difficult for the animal to defecate during hibernation, but are often passed with great pain in the spring time.
Seed hibernation is different from seed dormancy. While seed dormancy can be defined as "a seed not germinating when conditions, e.g. light, water/nutrient availability or the presence of activating substances like smoke, are favourable", hibernation is the ability of a seed to remain in hibernation when there is a lack of things essential to its development (water, sunlight, nutrients, etc.) or in harsh conditions (extreme cold, extreme heat, hard ground, etc.). There is no specific time limit in which a seed may hibernate; the oldest seeds that have been found to be viable are of the Date Palm (Phoenix dactylifera): several seeds found in the Israeli fortress of Masada were radiocarbon dated to be 2000 years old. One seed was still able to germinate (Sallon et al., 2008 Science). When conditions are right for the particular type of seed, they can come out of hibernation and grow.
Seeds display hibernation for very short periods of time every year. In autumn, seeds produced in summer may have a chance to grow while the soil is still warm, but instead do not grow until spring. The seeds have chemicals encoded into them that will not allow them to germinate until the soil warms up again, a sign of spring. This is called after ripening.
Seeds may also go into hibernation for other causes. Many pines have adapted to forest fires that destroy trees by creating pine cones that open in extreme heat (fire) and release seeds coated with a material that will break down only in extreme heat. The seeds hibernate until this happens.
Seeds of the Canna Lily, and other plants, have a hard coating that must be broken down by contact with rough rock, soil, etc. before they begin to grow. Until the shell is broken and water reaches the seed, the seed remains dormant.
When released, some seeds (especially those in a desert environment) must wait for rain before the seed is triggered out of hibernation and begins to grow.
There are many other causes of dormancy. It is an unclear phenomenon; the limits of seed hibernation are still unknown, and many triggers have yet to be discovered.
↑ Peter Scott, Lecturer in Plant Developmental Biology, University of Sussex
Winter rest (from the German term Winterruhe) is a state of reduced activity of plants and warm-blooded animals living in extratropical regions of the world during the more hostile environmental conditions of winter. In this state, they save energy during cold weather while they have limited access to food sources.
Deciduous trees lose their foliage in the winter. Tree growth rings are a result of winter rest, as there is rapid growth in the warmer spring, then slower growth later in the year.
Perennial and biennial herbaceous plants lose their frost-sensitive, above-ground parts before the winter, and regrow in the spring. Herbaceous plants that are annual, producing seeds before the winter, can also be considered to have winter rest in some form, because their seeds may stay inactive over the winter before germinating. Annual plants which have seeds that germinate before winter also have winter rest.Winter cereals, for example, which are sown in the fall and germinate before the frost, become dormant during the winter and actually require a few weeks of cold before they are able to flower.
Winter rest in an animal is different from true hibernation, since the metabolism is not reduced drastically. The body temperature is not significantly lowered, however the heart rate is reduced. This means that animals like the raccoon can quickly become active again if temperatures rise or the snow melts. Other animals that winter rest are badgers and brown bears.
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