Ursidae Family Definition Essay

Defining Family Essay

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Determining family structure and dynamics as well as defining the family is a complex process. Personally, I come from a very traditional family. Much like the assumptions made by the students in the article Defining Family: Young Adults’ Perceptions of the Parent-Child Bond by Mellisa Holtzman (2008). This is what comes to mind when most people define family; a nuclear family, with married parents, and biological children. However, a family is a complex system and can take on many different forms. Today, in a world of the “postmodern family” the traditional lines of family structure are blurred. Children may come from diverse types of homes, or a couple, married or not may choose to have no children and consider…show more content…

Living with extended family members has also been publicized lately in relation to the poor economy. Young adults who typically lived on their own after college are moving back in with their parents, older adults on fixed incomes that do not go as far as they once did are living with their children. This is a definite shift in the traditional family. Having graduated and moved out on my own prior to the economic decline I have learned to live with less, but having known that was coming I would have considered living at home longer. My siblings have or are planning on moving back in with our parents after college graduation to get ahead money-wise. This is a stressor on not only the individuals as a lack of feelings of freedom, but also an adaptation by the family as a whole that was unplanned years ago. It is my belief that recognizing any family structure or definition is important, as the traditional version may be skewed in so many ways, without knowing or recognizing the “family” that people we run across may come from. We can also learn from other family definitions to build upon our own themes, rules, and beliefs. Adding stigma and prejudice toward families different from our own not only alienate the members, but can add unnecessary stress upon that family system. Stress in any family system can be seen as either an adaptation potential or a negative force. Many effects on the

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This article is about the carnivoran mammals. For other uses, see Bear (disambiguation).

Bears are carnivoranmammals of the familyUrsidae. They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout the Northern Hemisphere and partially in the Southern Hemisphere. Bears are found on the continents of North America, South America, Europe, and Asia. Common characteristics of modern bears include large bodies with stocky legs, long snouts, small rounded ears, shaggy hair, plantigrade paws with five nonretractile claws, and short tails.

While the polar bear is mostly carnivorous, and the giant panda feeds almost entirely on bamboo, the remaining six species are omnivorous with varied diets. With the exception of courting individuals and mothers with their young, bears are typically solitary animals. They may be diurnal or nocturnal and have an excellent sense of smell. Despite their heavy build and awkward gait, they are adept runners, climbers, and swimmers. Bears use shelters, such as caves and logs, as their dens; most species occupy their dens during the winter for a long period of hibernation, up to 100 days.

Bears have been hunted since prehistoric times for their meat and fur; they have been used for bear-baiting and other forms of entertainment, such as being made to dance. With their powerful physical presence, they play a prominent role in the arts, mythology, and other cultural aspects of various human societies. In modern times, bears have come under pressure through encroachment on their habitats and illegal trade in bear parts, including the Asian bile bear market. The IUCN lists six bear species as vulnerable or endangered, and even least concern species, such as the brown bear, are at risk of extirpation in certain countries. The poaching and international trade of these most threatened populations are prohibited, but still ongoing.

Etymology

The English word "bear" comes from Old Englishbera and belongs to a family of names for the bear in Germanic languages, such as Swedish björn, also used as a first name, that originate from an adjective meaning "brown".[1]

Bear taxon names such as Arctoidea and Helarctos come from the ancient Greek word ἄρκτος (arktos), meaning bear,[2] as do the names "arctic" and "antarctic", from the constellationUrsa Major, the "Great Bear", prominent in the northern sky.[3]

Bear taxon names such as Ursidae and Ursus come from Latin Ursus/Ursa, he-bear/she-bear.[3] The female first name "Ursula", originally derived from a Christian saint's name, means "little she-bear" (diminutive of Latin ursa). In Switzerland, the male first name "Urs" is especially popular, while the name of the canton and city of Bern is derived from Bär, German for bear. The Germanic name Bernard (including Bernhardt and similar forms) means "bear-brave", "bear-hardy", or "bold bear".[4][5] The Old English name Beowulf is a kenning, "bee-wolf", for bear, in turn meaning a brave warrior.[6]

Taxonomy and phylogeny

The family Ursidae is one of nine families in the suborder Caniformia, or "doglike" carnivorans, within the orderCarnivora. Bears' closest living relatives are the pinnipeds, canids, and musteloids.[7] Modern bears comprise eight species in three subfamilies: Ailuropodinae (monotypic with the giant panda), Tremarctinae (monotypic with the spectacled bear), and Ursinae (containing six species divided into one to three genera, depending on the authority). Nuclear chromosome analysis show that the karyotype of the six ursine bears is nearly identical, with each having 74 chromosomes, whereas the giant panda has 42 chromosomes and the spectacled bear 52. These smaller numbers can be explained by the fusing of some chromosomes, and the banding patterns on these match those of the ursine species, but differ from those of procyonids, which supports the inclusion of these two species in Ursidae rather than in Procyonidae, where they had been placed by some earlier authorities.[8]

Evolution

The earliest members of Ursidae belong to the extinct subfamily Amphicynodontinae, including Parictis (late Eocene to early middle Miocene, 38–18 Mya) and the slightly younger Allocyon (early Oligocene, 34–30 Mya), both from North America. These animals looked very different from today's bears, being small and raccoon-like in overall appearance, and diets perhaps more similar to that of a badger. Parictis does not appear in Eurasia and Africa until the Miocene.[9] It is unclear whether late-Eocene ursids were also present in Eurasia, although faunal exchange across the Bering land bridge may have been possible during a major sea level low stand as early as the late Eocene (about 37 Mya) and continuing into the early Oligocene.[10] European genera morphologically are very similar to Allocyon, and to the much younger American Kolponomos (about 18 Mya),[11] are known from the Oligocene, including Amphicticeps and Amphicynodon.[10]

The raccoon-sized, dog-like Cephalogale is the oldest-known member of the subfamily Hemicyoninae, which first appeared during the middle Oligocene in Eurasia about 30 Mya.[10] The subfamily includes the younger genera Phoberocyon (20–15 Mya), and Plithocyon (15–7 Mya). A Cephalogale-like species gave rise to the genus Ursavus during the early Oligocene (30–28 Mya); this genus proliferated into many species in Asia and is ancestral to all living bears. Species of Ursavus subsequently entered North America, together with Amphicynodon and Cephalogale, during the early Miocene (21–18 Mya). Members of the living lineages of bears diverged from Ursavus between 15 and 20 Mya,[12][13] likely via the species Ursavus elmensis. Based on genetic and morphological data, the Ailuropodinae (pandas) were the first to diverge from other living bears about 19 Mya, although no fossils of this group have been found before about 5 Mya.[14]

The New World short-faced bears (Tremarctinae) differentiated from Ursinae following a dispersal event into North America during the mid-Miocene (about 13 Mya).[14] They invaded South America (≈1 Ma) following formation of the Isthmus of Panama.[15] Their earliest fossil representative is Plionarctos in North America (~ 10–2 Ma). This genus is probably the direct ancestor to the North American short-faced bears (genus Arctodus), the South American short-faced bears (Arctotherium), and the spectacled bears, Tremarctos, represented by both an extinct North American species (T. floridanus), and the lone surviving representative of the Tremarctinae, the South American spectacled bear (T. ornatus).[10]

The subfamily Ursinae experienced a dramatic proliferation of taxa about 5.3–4.5 Mya, coincident with major environmental changes; the first members of the genus Ursus appeared around this time.[14] The sloth bear is a modern survivor of one of the earliest lineages to diverge during this radiation event (5.3 Mya); it took on its peculiar morphology, related to its diet of termites and ants, no later than by the early Pleistocene. By 3–4 Mya, the species Ursus minimus appears in the fossil record of Europe; apart from its size, it was nearly identical to today's Asian black bear. It is likely ancestral to all bears within Ursinae, perhaps aside from the sloth bear. Two lineages evolved from U. minimus: the black bears (including the sun bear, the Asian black bear, and the American black bear); and the brown bears (which includes the polar bear). Modern brown bears evolved from U. minimus via Ursus etruscus, which itself is ancestral to the extinct Pleistocenecave bear. Species of Ursinae have migrated repeatedly into North America from Eurasia as early as 4 Mya during the early Pliocene. The polar bear is the most recently evolved species and descended from the brown bear around 400,000 years ago.[16][17][18]

Phylogeny

The bears form a clade within the Carnivora. The red panda is not a bear but a musteloid. The cladogram is based on molecular phylogeny of six genes in Flynn, 2005.[19]

The phylogeny of extant bear species is shown in a cladogram based on complete mitochondrial DNA sequences from Yu et al., 2007.[20] The giant panda, followed by the spectacled bear are clearly the oldest species. The relationships of the other species are not very well resolved, though the polar bear and the brown bear form a close grouping.[8]

Classification

Extant species are shown in bold, extinct taxa are marked †.[21]

Physical characteristics

Size

The bear family includes the most massive extant terrestrial members of the order Carnivora.[a] The polar bear is considered to be the largest species,[30] with adult males weighing 350–700 kg (772–1,543 lb) and measuring 2.4–3 metres (7 ft 10 in–9 ft 10 in) in total length.[31] The smallest species is the sun bear, which ranges 25–65 kg (55–143 lb) in weight and 100–140 cm (39–55 in) in length.[32] Prehistoric North and South American short-faced bears were the largest species known to have lived. The latter estimated to have weighed 1,600 kg (3,500 lb) and stood 3.4 m (11 ft) tall.[26][25] Body weight varies throughout the year in bears of temperate and arctic climates, as they build up fat reserves in the summer and autumn and lose weight during the winter.[33]

Morphology

Bears are generally bulky and robust animals with short tails. They are sexually dimorphic with regard to size, with males typically being larger.[34][35] Larger species tend to show increased levels of sexual dimorphism in comparison to smaller species.[35] Relying as they do on strength rather than speed, bears have relatively short limbs with thick bones to support their bulk. The shoulder blades and the pelvis are correspondingly massive. The limbs are much straighter than those of the big cats as there is no need for them to flex in the same way due to the differences in their gait. The strong forelimbs are used to catch prey, to excavate dens, to dig out burrowing animals, to turn over rocks and logs to locate prey, and to club large creatures.[33]

Unlike most other land carnivorans, bears are plantigrade. They distribute their weight toward the hind feet, which makes them look lumbering when they walk. They are capable of bursts of speed but soon tire, and as a result mostly rely on ambush rather than the chase. Bears can stand on their hind feet and sit up straight with remarkable balance. Their front paws are flexible enough to grasp fruit and leaves. Bears' non-retractable claws are used for digging, climbing, tearing, and catching prey. The claws on the front feet are larger than those on the back and may be a hindrance when climbing trees; black bears are the most arboreal of the bears, and have the shortest claws. Pandas are unique in having a bony extension on the wrist of the front feet which acts as a thumb, and is used for gripping bamboo shoots as the animals feed.[33]

Most mammals have agouti hair, with each individual hair shaft having bands of colour corresponding to two different types of melanin pigment. Bears however have a single type of melanin and the hairs have a single colour throughout their length, apart from the tip which is sometimes a different shade. The coat consists of long guard hairs, which form a protective shaggy covering, and short dense hairs which form an insulating layer trapping air close to the skin. The shaggy coat helps maintain body heat during winter hibernation and is shed in the spring leaving a shorter summer coat. Polar bears have hollow, translucent guard hairs which gain heat from the sun and conduct it to the dark-coloured skin below. They have a thick layer of blubber for extra insulation, and the soles of their feet have a dense pad of fur.[33] Other than the bold black-and-white pelage of the panda, bears tend to be uniform in colour, although some species may have markings on the chest or face.[36]

Bears have small rounded ears so as to minimise heat loss, but neither their hearing or sight are particularly acute. Unlike many other carnivorans they have colour vision, perhaps to help them distinguish ripe nuts and fruits. They are unique among carnivorans in not having touch-sensitive whiskers on the muzzle; however, they have an excellent sense of smell, better than that of the dog, or possibly any other mammal. They use smell for signalling to each other (either to warn off rivals or detect mates) and for finding food. Smell is the principal sense used by bears to locate most of their food, and they have excellent memories which helps them to relocate places where they have found food before.[33]

The skulls of bears are massive, providing anchorage for the powerful masseter and temporal jaw muscles. The canine teeth are large but mostly used for display, and the molar teeth flat and crushing. Unlike most other members of the Carnivora, bears have relatively undeveloped carnassial teeth, and their teeth are adapted for a diet that includes a significant amount of vegetable matter.[33] Considerable variation occurs in dental formula even within a given species. This may indicate bears are still in the process of evolving from a mainly meat-eating diet to a predominantly herbivorous one. Polar bears appear to have secondarily re-evolved carnassial-like cheek teeth, as their diets have switched back towards carnivory.[37] Sloth bears lack lower central incisors and use their protusible lips for sucking up the termites on which they feed.[33] The general dental formula for living bears is: 3.1.2–4.23.1.2–4.3.[33] The structure of the larynx of bears appears to be the most basal of the caniforms.[38] They possess air pouches connected to the pharynx which may amplify their vocalisations.[39]

Bears have a fairly simple digestive system typical for carnivorans, with a single stomach, short undifferentiated intestines and no cecum.[40][41] Even the herbivorous giant panda still has the digestive system of a carnivore, as well as carnivore-specific genes. Its ability to digest cellulose is ascribed to the microbes in its gut.[42] Bears must spend much of their time feeding in order to gain enough nutrition from foliage. The panda, in particular, spends 12–15 hours a day feeding.[43]

Distribution and habitat

Further information: List of carnivorans by population

Extant bears are found in sixty countries primarily in the Northern Hemisphere and are concentrated in Asia, North America, and Europe. An exception is the spectacled bear; native to South America, it inhabits the Andean region.[44] The sun bear's range extends below the equator in Southeast Asia.[45] The Atlas bear, a subspecies of the brown bear was distributed in North Africa from Morocco to Libya, but it became extinct around the 1870s.[46]

The most widespread species is the brown bear, which occurs from Western Europe eastwards through Asia to the western areas of North America. The American black bear is restricted to North America, and the polar bear is restricted to the Arctic Sea. All the remaining species of bear are Asian.[44] They occur in a range of habitats which include tropical lowland rainforest, both coniferous and broadleaf forests, prairies, steppes, montane grassland, alpine scree slopes, Arctic tundra and in the case of the polar bear, ice floes.[44][47] Bears may dig their dens in hillsides or use caves, hollow logs and dense vegetation for shelter.[47]

Behaviour and life history

Brown and American black bears are generally diurnal, meaning that they are active for the most part during the day, though they may forage substantially by night.[48] Other species may be nocturnal, active at night, though female sloth bears with cubs may feed more at daytime to avoid competition from conspecifics and nocturnal predators.[49] Bears are overwhelmingly solitary and are considered to be the most asocial of all the Carnivora. The only times bears are encountered in small groups are mothers with young or occasional seasonal bounties of rich food (such as salmon runs).[50][51] Fights between males can occur and older individuals may have extensive scarring, which suggests that maintaining dominance can be intense.[52] With their acute sense of smell, bears can locate carcasses from several kilometres away. They use olfaction to locate other foods, encounter mates, avoid rivals and recognise their cubs.[33]

Feeding

Most bears are opportunistic omnivores and consume more plant than animal matter. They eat anything from leaves, roots, and berries to insects, carrion, fresh meat, and fish, and have digestive systems and teeth adapted to such a diet.[44] At the extremes are the almost entirely herbivorous giant panda and the mostly carnivorous polar bear. However, all bears feed on any food source that becomes seasonally available.[43] For example, Asiatic black bears in Taiwan consume large numbers of acorns when these are most common, and switch to ungulates at other times of the year.[53]

When foraging for plants, bears choose to eat them at the stage when they are at their most nutritious and digestible, typically avoiding older grasses, sedges and leaves.[41][43] Hence, in more northern temperate areas, browsing and grazing is more common early in spring and later becomes more restricted.[54] Knowing when plants are ripe for eating is a learned behaviour.[43] Berries may be foraged in bushes or at the tops of trees, and bears try to maximize the number of berries consumed versus foliage.[54] In autumn, some bear species forage large amounts of naturally fermented fruits, which affects their behaviour.[55] Smaller bears climb trees to obtain mast (edible reproductive parts, such as acorns).[56] Such masts can be very important to the diets of these species, and mast failures may result in long-range movements by bears looking for alternative food sources.[57] Brown bears, with their powerful digging abilities, commonly eat roots.[54] The panda's diet is over 99% bamboo,[58] of 30 different species. Its strong jaws are adapted for crushing the tough stems of these plants, though they prefer to eat the more nutritious leaves.[59][60]Bromeliads can make up to 50% of the diet of the spectacled bear, which also has strong jaws to bite them open.[61]

The sloth bear, though not as specialised as polar bears and the panda, has lost several front teeth usually seen in bears, and developed a long, suctioning tongue to feed on the ants, termites, and other burrowing insects they favour. At certain times of the year, these insects can make up 90% of their diets.[62] Some species may raid the nests of wasps and bees for the honey and immature insects, in spite of stinging from the adults.[63] Sun bears use their long tongues to lick up both insects and honey.[64] Fish are an important source of food for some species, and brown bears in particular gather in large numbers at salmon runs. Typically, a bear plunges into the water and seizes a fish with its jaws or front paws. The preferred parts to eat are the brain and eggs. Small burrowing mammals like rodents may be dug out and eaten.[65][54]

The brown bear and both species of black bears sometimes take large ungulates, such as deer and bovids, mostly the young and weak.[53][66][65] These animals may be taken by a short rush and ambush, though hiding young may be stiffed out and pounced on.[54][67] The polar bear mainly preys on seals, stalking them from the ice or breaking into their dens. They primarily eat the highly digestible blubber.[68][65] Large mammalian prey is typically killed by a bite to the head or neck, or (in the case of young) simply pinned down and mauled.[54][69] Predatory behaviour in bears is typically taught to the young by the mother.[65]

Bears are prolific scavengers and kleptoparasites, stealing food caches from rodents, and carcasses from other predators.[41][70] For hibernating species, weight gain is important as it provides nourishment during winter dormancy. A brown bear can eat 41 kg (90 lb) of food and gain 2–3 kg (4.4–6.6 lb) of fat a day prior to entering its den.[71]

Communication

Bears produce a number of vocal and non-vocal sounds. Tongue-clicking, grunting or chuffing many be made in cordial situations, such as between mothers and cubs or courting couples, while moaning, huffing, sorting or blowing air is made when an individual is stressed. Barking is produced during times of alarm, excitement or to give away the animal's position. Warning sounds include jaw-clicking and lip-popping, while teeth-chatters, bellows, growls, roars and pulsing sounds are made in aggressive encounters. Cubs may squeal, bawl, bleat or scream when in distress and make motor-like humming when comfortable or nursing.[38]

Polar bear (left) and sun bear, the largest and smallest species respectively, on average.

Despite being quadrupeds, bears can stand and sit as humans do
Brown bear feeding on infrequent, but predictable, salmon migrations in Alaska
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