In scientific nomenclature, a synonym is a scientific name that applies to a taxon that goes by a different scientific name, although the term is used somewhat differently in the zoological code of nomenclature. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies; this name is no longer in use: it is now a synonym of the current scientific name, Picea abies. Unlike synonyms in other contexts, in taxonomy a synonym is not interchangeable with the name of which it is a synonym. In taxonomy, synonyms have a different status. For any taxon with a particular circumscription and rank, only one scientific name is considered to be the correct one at any given time. A synonym cannot exist in isolation: it is always an alternative to a different scientific name. Given that the correct name of a taxon depends on the taxonomic viewpoint used a name, one taxonomist's synonym may be another taxonomist's correct name. Synonyms may arise whenever the same taxon is named more than once, independently.
They may arise when existing taxa are changed, as when two taxa are joined to become one, a species is moved to a different genus, a variety is moved to a different species, etc. Synonyms come about when the codes of nomenclature change, so that older names are no longer acceptable. To the general user of scientific names, in fields such as agriculture, ecology, general science, etc. A synonym is a name, used as the correct scientific name but, displaced by another scientific name, now regarded as correct, thus Oxford Dictionaries Online defines the term as "a taxonomic name which has the same application as another one, superseded and is no longer valid." In handbooks and general texts, it is useful to have synonyms mentioned as such after the current scientific name, so as to avoid confusion. For example, if the much advertised name change should go through and the scientific name of the fruit fly were changed to Sophophora melanogaster, it would be helpful if any mention of this name was accompanied by "".
Synonyms used in this way may not always meet the strict definitions of the term "synonym" in the formal rules of nomenclature which govern scientific names. Changes of scientific name have two causes: they may be taxonomic or nomenclatural. A name change may be caused by changes in the circumscription, position or rank of a taxon, representing a change in taxonomic, scientific insight. A name change may be due to purely nomenclatural reasons, that is, based on the rules of nomenclature. Speaking in general, name changes for nomenclatural reasons have become less frequent over time as the rules of nomenclature allow for names to be conserved, so as to promote stability of scientific names. In zoological nomenclature, codified in the International Code of Zoological Nomenclature, synonyms are different scientific names of the same taxonomic rank that pertain to that same taxon. For example, a particular species could, over time, have had two or more species-rank names published for it, while the same is applicable at higher ranks such as genera, orders, etc.
In each case, the earliest published name is called the senior synonym, while the name is the junior synonym. In the case where two names for the same taxon have been published the valid name is selected accorded to the principle of the first reviser such that, for example, of the names Strix scandiaca and Strix noctua, both published by Linnaeus in the same work at the same date for the taxon now determined to be the snowy owl, the epithet scandiaca has been selected as the valid name, with noctua becoming the junior synonym. One basic principle of zoological nomenclature is that the earliest published name, the senior synonym, by default takes precedence in naming rights and therefore, unless other restrictions interfere, must be used for the taxon. However, junior synonyms are still important to document, because if the earliest name cannot be used the next available junior synonym must be used for the taxon. For other purposes, if a researcher is interested in consulting or compiling all known information regarding a taxon, some of this may well have been published under names now regarded as outdated and so it is again useful to know a list of historic synonyms which may have been used for a given current taxon name.
Objective synonyms refer to taxa with same rank. This may be species-group taxa of the same rank with the same type specimen, genus-group taxa of the same rank with the same type species or if their type species are themselves objective synonyms, of family-group taxa with the same type genus, etc. In the case of subjective synonyms, there is no such shared type, so the synonymy is open to taxonomic judgement, meaning that th
Populus tremuloides is a deciduous tree native to cooler areas of North America, one of several species referred to by the common name aspen. It is called quaking aspen, trembling aspen, American aspen, mountain or golden aspen, trembling poplar, white poplar, popple, as well as others; the trees have tall trunks, up to 25 meters tall, with smooth pale bark, scarred with black. The glossy green leaves, dull beneath, become golden to yellow red, in autumn; the species propagates through its roots to form large clonal groves originating from a shared root system. These roots are not rhizomes, as new growth develops from adventitious buds on the parent root system. Populus tremuloides is the most distributed tree in North America, being found from Canada to central Mexico, it is the defining species of the aspen parkland biome in the Prairie Provinces of Canada and extreme northwest Minnesota. The Quaking Aspen is the state tree of Utah; the quaking or trembling of the leaves, referred to in the common names is due to the flexible flattened petioles.
The specific epithet, evokes this trembling behavior and can be translated as "like tremula", the European trembling aspen. Quaking aspen is a tall, fast growing tree 20–25 m at maturity, with a trunk 20 to 80 cm in diameter; the bark is smooth, colored greenish-white to gray, is marked by thick black horizontal scars and prominent black knots. Parallel vertical scars are tell-tale signs of elk, which strip off aspen bark with their front teeth; the leaves on mature trees are nearly round, 4–8 centimeters in diameter with small rounded teeth, a 3–7-centimeter long, flattened petiole. Young trees and root sprouts have much larger nearly triangular leaves; some species of Populus have petioles flattened along their length, while the aspens and some other poplars have them flattened from side to side along the entire length of the petiole. Aspens are dioecious, with separate male and female clones; the flowers are catkins. Quaking aspen occurs across Canada in all provinces and territories, with the possible exception of Nunavut.
In the United States, it can be found as far north as the northern foothills of the Brooks Range in Alaska, where road margins and gravel pads provide islands of well-drained habitat in a region where soils are waterlogged due to underlying permafrost. It occurs at low elevations as far south as central Indiana. In the western United States, this tree survives at elevations lower than 1,500 feet due to hot summers experienced below that elevation, is found at 5,000–12,000 feet, it grows at high altitudes as far south as Mexico. Quaking aspen grows in a wide variety of climatic conditions. January and July average temperatures range from −30 °C and 16 °C in the Alaska Interior to −3 °C and 23 °C in Fort Wayne, Indiana. Average annual precipitation ranges from 1,020 mm in Gander and Labrador to as little as 180 mm in the Alaska Interior; the southern limit of the species' range follows the 24 °C mean July isotherm. Shrub-like dwarf clones exist in marginal environments too cold and dry to be hospitable to full-size trees, for example at the species' upper elevation limits in the White Mountains.
Quaking aspen propagates itself through root sprouts, extensive clonal colonies are common. Each colony is its own clone, all trees in the clone have identical characteristics and share a single root structure. A clone may turn color earlier or in the fall than its neighbouring aspen clones. Fall colors are bright tones of yellow; as all trees in a given clonal colony are considered part of the same organism, one clonal colony, named Pando, is considered the heaviest and oldest living organism at six million kilograms and 80,000 years old. Aspens do produce seeds, but grow from them. Pollination is inhibited by the fact that aspens are either male or female, large stands are all clones of the same sex. If pollinated, the small seeds are only viable a short time as they lack a stored food source or a protective coating. Beginning in 1996, individual North American scientists noticed an increase in dead or dying aspen trees; as this accelerated in 2004, word spread and a debate over causes began.
No insect, disease, or environmental condition is yet identified as a joint cause. Trees adjacent to one another are stricken or not. In other instances, entire groves have died. Many areas of the Western US have experienced increased diebacks which are attributed to ungulate grazing and wildfire suppression. At high altitudes where grasses can be rare, ungulates can browse young aspen sprouts and prevent those young trees from reaching maturity; as a result, some aspen groves close to cattle or other grazing animals, such as deer or elk, have few young trees and can be invaded by conifers, which are not browsed. Another possible deterrent to aspen regeneration is widespread wildfire suppression. Aspens are vigorous resprouters and though
Pine nuts called piñón or pinoli, are the edible seeds of pines. About 20 species of pine produce seeds large enough to be worth harvesting. In Europe and places with a Mediterranean climate, two species in particular are harvested. Four other species, Siberian pine, Siberian dwarf pine, Chinese white pine and lacebark pine, are used to a lesser extent. Russia is the largest producer of Pinus sibirica nuts in the world followed by Mongolia which produces over 10,000 tonnes of forest grown nuts annually, the majority of harvest is exported to China. Afghanistan is an important source of pine nuts, behind Korea. Pine nuts produced in Europe come from the stone pine, cultivated for its nuts for over 5,000 years, harvested from wild trees for far longer; the Swiss pine is used to a small extent. In North America, the main species are three of the pinyon pines: Colorado pinyon, single-leaf pinyon, Mexican pinyon; the other eight pinyon species are used to a small extent, as are gray pine, Coulter pine, Torrey pine, sugar pine and Parry pinyon.
Here, the nuts themselves are known by the Spanish name for the pinyon pine: piñón. In the United States, pine nuts are harvested by Native American and Hispano communities in the Western United States and Southwestern United States, by the Uto-Aztecan Shoshone, Navajo, Hopi and Hispanos of New Mexico. Certain treaties negotiated by tribes and laws in Nevada guarantee Native Americans' right to harvest pine nuts, the state of New Mexico protects the use of the word piñon for use with pine nuts from certain species of indigenous New Mexican pines. For those seeking to grow edible landscapes, these are the more used species. Old World Pinus armandii – Chinese white pine Pinus bungeana – lacebark pine Pinus cembra – Swiss pine Pinus gerardiana – Chilgoza pine Pinus koraiensis – Korean pine Pinus pinea – Mediterranean stone pine Pinus pumila – Siberian dwarf pine Pinus sibirica – Siberian pine New World Pinus cembroides – Mexican pinyon Pinus culminicola – Potosi pinyon Pinus edulis – Two-needle piñon or Colorado pinyon Pinus johannis – Johann's pinyon Pinus monophylla – Single-leaf pinyon Pinus orizabensis – Orizaba pinyon Pinus quadrifolia – Parry pinyon Pinus remota – Texas pinyon or papershell pinyo The pine nut species will take a time that depends on the exact species to complete its maturity.
For some American species development begins in early spring with pollination. A tiny cone, about the size of a small marble, will form from mid-spring to the end of summer; the cone will commence growth until it reaches maturity near the end of summer. The mature piñon pine cone is ready to harvest ten days. A cone is harvested by placing it in a burlap bag and exposing it to a heat source such as the sun to begin the drying process, it takes about 20 days until the cone opens. Once it is open and dry, the seed can be extracted in various ways; the most common and practical extraction method used is the repeated striking of the burlap bag containing the cone against a rough surface to cause the cone to shatter, leaving just the job of separating by hand the seed from the residue within the bag. Another option for harvesting is to wait until the cone opens on the tree and harvest the cone from the piñon pine, followed by the extracting process mentioned above. Fallen seed can be gathered beneath the trees.
In the United States, millions of hectares of productive pinyon pine woods have been destroyed due to conversion of lands, in China, destructive harvesting techniques and the removal of trees for timber have led to losses in production capacity. The elevation of the pinyon pine is an important determinant of the quantity of pine cone production, therefore, will determine the amount of pine nuts the tree will yield. American Pinyon pine cone production is most found at an elevation between 6,000 feet and 8,500 feet, ideally at 7,000 feet; this is due to higher temperatures at elevations lower than 6,000 feet during the spring, which dry up humidity and moisture content that provide for the tree throughout the spring and summer, causing little nourishment for pine cone maturity. Although there are several other environmental factors that determine the conditions of the eco-system, without sufficient water the trees tend to abort cones. High humidity encourages cone development. There are certain topographical areas found in lower elevations, such as shaded canyons, where the humidity remains constant throughout the spring and summer, allowing pine cones to mature and produce seed.
At elevations above 8,500 feet, the temperature drops, dras
Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 millionths of a metre to 33.6 metres and have complex interactions with each other and their environments, forming intricate food webs. The category includes humans, but in colloquial use the term animal refers only to non-human animals; the study of non-human animals is known as zoology. Most living animal species are in the Bilateria, a clade whose members have a bilaterally symmetric body plan; the Bilateria include the protostomes—in which many groups of invertebrates are found, such as nematodes and molluscs—and the deuterostomes, containing the echinoderms and chordates.
Life forms interpreted. Many modern animal phyla became established in the fossil record as marine species during the Cambrian explosion which began around 542 million years ago. 6,331 groups of genes common to all living animals have been identified. Aristotle divided animals into those with those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between animal taxa. Humans make use of many other animal species for food, including meat and eggs. Dogs have been used in hunting, while many aquatic animals are hunted for sport.
Non-human animals have appeared in art from the earliest times and are featured in mythology and religion. The word "animal" comes from the Latin animalis, having soul or living being; the biological definition includes all members of the kingdom Animalia. In colloquial usage, as a consequence of anthropocentrism, the term animal is sometimes used nonscientifically to refer only to non-human animals. Animals have several characteristics. Animals are eukaryotic and multicellular, unlike bacteria, which are prokaryotic, unlike protists, which are eukaryotic but unicellular. Unlike plants and algae, which produce their own nutrients animals are heterotrophic, feeding on organic material and digesting it internally. With few exceptions, animals breathe oxygen and respire aerobically. All animals are motile during at least part of their life cycle, but some animals, such as sponges, corals and barnacles become sessile; the blastula is a stage in embryonic development, unique to most animals, allowing cells to be differentiated into specialised tissues and organs.
All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. During development, the animal extracellular matrix forms a flexible framework upon which cells can move about and be reorganised, making the formation of complex structures possible; this may be calcified, forming structures such as shells and spicules. In contrast, the cells of other multicellular organisms are held in place by cell walls, so develop by progressive growth. Animal cells uniquely possess the cell junctions called tight junctions, gap junctions, desmosomes. With few exceptions—in particular, the sponges and placozoans—animal bodies are differentiated into tissues; these include muscles, which enable locomotion, nerve tissues, which transmit signals and coordinate the body. There is an internal digestive chamber with either one opening or two openings. Nearly all animals make use of some form of sexual reproduction, they produce haploid gametes by meiosis.
These fuse to form zygotes, which develop via mitosis into a hollow sphere, called a blastula. In sponges, blastula larvae swim to a new location, attach to the seabed, develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement, it first invaginates to form a gastrula with a digestive chamber and two separate germ layers, an external ectoderm and an internal endoderm. In most cases, a third germ layer, the mesoderm develops between them; these germ layers differentiate to form tissues and organs. Repeated instances of mating with a close relative during sexual reproduction leads to inbreeding depression within a population due to the increased prevalence of harmful recessive traits. Animals have evolved numerous mechanisms for avoiding close inbreeding. In some species, such as the splendid fairywren, females benefit by mating with multiple males, thus producing more offspring of higher genetic quality; some animals are capable of asexual reproduction, which results
North America is a continent within the Northern Hemisphere and all within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the west and south by the Pacific Ocean, to the southeast by South America and the Caribbean Sea. North America covers an area of about 24,709,000 square kilometers, about 16.5% of the earth's land area and about 4.8% of its total surface. North America is the third largest continent by area, following Asia and Africa, the fourth by population after Asia and Europe. In 2013, its population was estimated at nearly 579 million people in 23 independent states, or about 7.5% of the world's population, if nearby islands are included. North America was reached by its first human populations during the last glacial period, via crossing the Bering land bridge 40,000 to 17,000 years ago; the so-called Paleo-Indian period is taken to have lasted until about 10,000 years ago. The Classic stage spans the 6th to 13th centuries.
The Pre-Columbian era ended in 1492, the transatlantic migrations—the arrival of European settlers during the Age of Discovery and the Early Modern period. Present-day cultural and ethnic patterns reflect interactions between European colonists, indigenous peoples, African slaves and their descendants. Owing to the European colonization of the Americas, most North Americans speak English, Spanish or French, their culture reflects Western traditions; the Americas are accepted as having been named after the Italian explorer Amerigo Vespucci by the German cartographers Martin Waldseemüller and Matthias Ringmann. Vespucci, who explored South America between 1497 and 1502, was the first European to suggest that the Americas were not the East Indies, but a different landmass unknown by Europeans. In 1507, Waldseemüller produced a world map, in which he placed the word "America" on the continent of South America, in the middle of what is today Brazil, he explained the rationale for the name in the accompanying book Cosmographiae Introductio:... ab Americo inventore... quasi Americi terram sive Americam.
For Waldseemüller, no one should object to the naming of the land after its discoverer. He used the Latinized version of Vespucci's name, but in its feminine form "America", following the examples of "Europa", "Asia" and "Africa". Other mapmakers extended the name America to the northern continent, In 1538, Gerard Mercator used America on his map of the world for all the Western Hemisphere; some argue that because the convention is to use the surname for naming discoveries, the derivation from "Amerigo Vespucci" could be put in question. In 1874, Thomas Belt proposed a derivation from the Amerrique mountains of Central America. Marcou corresponded with Augustus Le Plongeon, who wrote: "The name AMERICA or AMERRIQUE in the Mayan language means, a country of perpetually strong wind, or the Land of the Wind, and... the can mean... a spirit that breathes, life itself." The United Nations formally recognizes "North America" as comprising three areas: Northern America, Central America, The Caribbean.
This has been formally defined by the UN Statistics Division. The term North America maintains various definitions in accordance with context. In Canadian English, North America refers to the land mass as a whole consisting of Mexico, the United States, Canada, although it is ambiguous which other countries are included, is defined by context. In the United States of America, usage of the term may refer only to Canada and the US, sometimes includes Greenland and Mexico, as well as offshore islands. In France, Portugal, Romania and the countries of Latin America, the cognates of North America designate a subcontinent of the Americas comprising Canada, the United States, Mexico, Greenland, Saint Pierre et Miquelon, Bermuda. North America has been referred to by other names. Spanish North America was referred to as Northern America, this was the first official name given to Mexico. Geographically the North American continent has many subregions; these include cultural and geographic regions. Economic regions included those formed by trade blocs, such as the North American Trade Agreement bloc and Central American Trade Agreement.
Linguistically and culturally, the continent could be divided into Latin America. Anglo-America includes most of Northern America and Caribbean islands with English-speaking populations; the southern North American continent is composed of two regions. These are the Caribbean; the north of the continent maintains recognized regions as well. In contrast to the common definition of "North America", which encompasses the whole continent, the term "North America" is sometimes used to refer only to Mexico, the United States, Greenland; the term Northern America refers to the northern-most countries and territories of North America: the United States, Bermuda, St. Pierre and Miquelon and Greenland. Although the term does not refer to a unifie
Bryce Canyon National Park
Bryce Canyon National Park is an American national park located in southwestern Utah. The major feature of the park is Bryce Canyon, which despite its name, is not a canyon, but a collection of giant natural amphitheaters along the eastern side of the Paunsaugunt Plateau. Bryce is distinctive due to geological structures called hoodoos, formed by frost weathering and stream erosion of the river and lake bed sedimentary rocks; the red and white colors of the rocks provide spectacular views for park visitors. Bryce Canyon National Park is much smaller, sits at a much higher elevation than nearby Zion National Park; the rim at Bryce varies from 8,000 to 9,000 feet. The Bryce Canyon area was settled by Mormon pioneers in the 1850s and was named after Ebenezer Bryce, who homesteaded in the area in 1874; the area around Bryce Canyon was designated as a national monument by President Warren G. Harding in 1923 and was redesignated as a national park by Congress in 1928; the park covers 35,835 acres and receives fewer visitors than Zion National Park or Grand Canyon National Park due to Bryce's more remote location.
In 2016, Bryce Canyon received 2,365,110 recreational visitors, representing an increase of 35% from the prior year. Bryce Canyon National Park lies within the Colorado Plateau geographic province of North America and straddles the southeastern edge of the Paunsaugunt Plateau west of the Paunsaugunt Fault. Park visitors arrive from the plateau part of the park and look over the plateau's edge toward a valley containing the fault and the Paria River just beyond it; the edge of the Kaiparowits Plateau bounds the opposite side of the valley. Bryce Canyon was not formed from erosion initiated from a central stream, meaning it technically is not a canyon. Instead headward erosion has excavated large amphitheater-shaped features in the Cenozoic-aged rocks of the Paunsaugunt Plateau; this erosion exposed colorful pinnacles called hoodoos that are up to 200 feet high. A series of amphitheaters extends more than 20 miles north-to-south within the park; the largest is Bryce Amphitheater, 12 miles long, 3 miles wide and 800 feet deep.
A nearby example of amphitheaters with hoodoos in the same formation but at a higher elevation, is in Cedar Breaks National Monument, 25 miles to the west on the Markagunt Plateau. Rainbow Point, the highest part of the park at 9,105 feet, is at the end of the 18-mile scenic drive. From there, Aquarius Plateau, Bryce Amphitheater, the Henry Mountains, the Vermilion Cliffs and the White Cliffs can be seen. Yellow Creek, where it exits the park in the north-east section, is the lowest part of the park at 6,620 feet; the national park is located in southwestern Utah about 50 miles northeast of and 1,000 feet higher than Zion National Park. The weather in Bryce Canyon is therefore cooler, the park receives more precipitation: a total of 15 to 18 inches per year. Yearly temperatures vary from an average minimum of 9 °F in January to an average maximum of 83 °F in July, but extreme temperatures can range from −30 to 97 °F; the record high temperature in the park was 98 °F on July 14, 2002. The record low temperature was −28 °F on December 10, 1972.
Little is known about early human habitation in the Bryce Canyon area. Archaeological surveys of Bryce Canyon National Park and the Paunsaugunt Plateau show that people have been in the area for at least 10,000 years. Basketmaker Anasazi artifacts several thousand years old have been found south of the park. Other artifacts from the Pueblo-period Anasazi and the Fremont culture have been found; the Paiute Indians moved into the surrounding valleys and plateaus in the area around the same time that the other cultures left. These Native Americans hunted and gathered for most of their food, but supplemented their diet with some cultivated products; the Paiute in the area developed a mythology surrounding the hoodoos in Bryce Canyon. They believed. At least one older Paiute said his culture called the hoodoos Anka-ku-was-a-wits, Paiute for "red painted faces", it was not until the late 18th and the early 19th century that the first European Americans explored the remote and hard-to-reach area. Mormon scouts visited the area in the 1850s to gauge its potential for agricultural development, use for grazing, settlement.
The first major scientific expedition to the area was led by U. S. Army Major John Wesley Powell in 1872. Powell, along with a team of mapmakers and geologists, surveyed the Sevier and Virgin River area as part of a larger survey of the Colorado Plateaus, his mapmakers kept many of the Paiute place names. Small groups of Mormon pioneers followed and attempted to settle east of Bryce Canyon along the Paria River. In 1873, the Kanarra Cattle Company started to use the area for cattle grazing; the Church of Jesus Christ of Latter-day Saints sent Scottish immigrant Ebenezer Bryce and his wife Mary to settle land in the Paria Valley because they thought his carpentry skills would be useful in the area. The Bryce family chose to live right below Bryce Amphitheater—the main collection of hoodoos in the park. Bryce grazed his cattle inside what are now park borders, reputedly thought that the amphitheaters were a "helluva place to lose a cow." He built a road to the plateau to retrieve firewood and timber, a canal to irrigate his crops and w
Hibernation is a state of inactivity and metabolic depression in endotherms. Hibernation refers to a season of heterothermy characterized by low body temperature, slow breathing and heart rate, low metabolic rate, it is most observed during the winter months. 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 any absolute decline in body temperature. Many experts believe that the processes of daily torpor and hibernation form a continuum and utilize similar mechanisms; the equivalent during the summer months is aestivation. Associated with low temperatures, hibernation functions to conserve energy when sufficient food is unavailable. To achieve this energy saving, an endothermic animal decreases its metabolic rate and thereby its body temperature. Hibernation may last days, weeks, or months depending on the species, ambient temperature, time of year, the individual's body condition.
Before entering hibernation, animals need to store enough energy to last through the duration of their dormant period as long as the entire winter. Larger species become hyperphagic, eating a large amount of food and storing the energy in fat deposits. In many small species, food caching replaces becoming fat; some species of mammals hibernate while gestating young, which are born either while the mother hibernates or shortly afterwards. For example, female polar bears go into hibernation during the cold winter months in order to give birth to their offspring; the pregnant mothers increase their body mass prior to hibernation, this increase is further reflected in the weight of the offspring. The fat accumulation enables them to provide a sufficiently warm and nurturing environment for their newborns. During hibernation, they subsequently lose 15–27% of their pre-hibernation weight by using their stored fats for energy. True hibernation is restricted to endotherms. Still, many ectothermic animals undergo periods of dormancy which are sometimes confused with hibernation.
Some reptile species are said to brumate, but possible similarities between brumation and hibernation are not established. Many insects, such as the wasp Polistes exclamans, exhibit periods of dormancy which have been referred to as hibernation, despite their ectothermy. Obligate hibernators are animals that spontaneously, annually, enter hibernation regardless of ambient temperature and access to food. Obligate hibernators include many species of ground squirrels, other rodents, mouse lemurs, European hedgehogs and other insectivores and marsupials These species undergo what has been traditionally called "hibernation": a physiological state wherein the body temperature drops to near ambient temperature, heart and respiration rates slow drastically; the typical winter season for obligate hibernators is characterized by periods of torpor interrupted by periodic, euthermic arousals, during which body temperatures and heart rates are restored to more typical levels. The cause and purpose of these arousals is still not clear.
One favored hypothesis is that hibernators build a "sleep debt" during hibernation, so must warm up to sleep. This has been supported by evidence in the Arctic ground squirrel. Other theories postulate that brief periods of high body temperature during hibernation allow the animal to restore its available energy sources or 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. There was a question of whether or not bears hibernate since they experience only a modest decline in body temperature compared with the much larger decreases seen in other hibernators. Many researchers thought that their deep sleep was not comparable with true, deep hibernation, but recent research has refuted this theory in captive black bears. Unlike obligate hibernators, facultative hibernators only enter hibernation when either cold-stressed, food-deprived, or both.
A good example of the differences between these two types of hibernation can be seen in prairie dogs: the white-tailed prairie dog is an obligate hibernator and the related black-tailed prairie dog is a facultative hibernator. While hibernation has long been studied in rodents, namely ground squirrels, no primate or tropical mammal was known to hibernate until the discovery of hibernation in the fat-tailed dwarf lemur of Madagascar, which hibernates in tree holes for seven months of the year. Malagasy winter temperatures sometimes rise to over 30 °C, so hibernation is not an adaptation to low ambient temperatures; the hibernation of this lemur is dependent on the thermal behaviour of its tree hole: if the hole is poorly insulated, the lemur's body temperature fluctuates passively following the ambient temperature. Dausmann found that hypometabolism in hibernating animals is not coupled with low body temperature. Hibernating bears are able to recycle their proteins and urine, allowing them both to stop urinating for months and to avoid muscl