Monday, November 18, 2013

koala bear, The koala (Phascolarctos cinereus or inaccurately, koala bear[a]) is an arboreal herbivorous marsupial native toAustralia. It is the only extant representative of the family Phascolarctidae, and its closest living relatives are thewombats.[3] The koala is found in coastal areas of the mainland's eastern and southern regions, inhabiting Queensland,New South Wales, Victoria and South Australia. HP 3MLX8TATP40 CPU Fan It is easily recognisable by its stout, tailless body; round, fluffy ears; and large, spoon-shaped nose. The koala has a body length of 60–85 cm (24–33 in) and weighs 4–15 kg (9–33 lb). Pelagecolour ranges from silver grey to chocolate brown. Koalas from the northern populations are typically smaller and lighter in colour than their counterparts further south. It is possible that these populations are separate subspecies, but this is disputed. HP Pavilion dv7-1240us CPU Fan Koalas typically inhabit open eucalypt woodlands, and the leaves of these trees make up most of their diet. Because this eucalypt diet has limited nutritional and caloric content, koalas are largely sedentary and sleep for up to 20 hours a day. They are asocial animals, and bonding only exists between mothers and dependent offspring.  DELL yy529 CPU Fan Adult males communicatewith loud bellows that intimidate rivals and attract mates. Males mark their presence with secretions from scent glandslocated on their chests. Being marsupials, koalas give birth to underdeveloped young that crawl into their mothers'pouches, where they stay for the first six to seven months of their life. Toshiba Qosmio G40-10E CPU Fan These young koalas are known as joeys, and are fully weaned at around a year. Koalas have few natural predators and parasites but are threatened by various pathogens, like Chlamydiaceae bacteria and the koala retrovirus, as well as bushfires and droughts. Koalas were hunted by indigenous Australians and depicted in myths and cave art for millennia. SONY Vaio VGN-CR407E CPU Fan The first recorded encounter between a European and a koala was in 1798, and an image of the animal was published in 1810 by naturalistGeorge Perry. Botanist Robert Brown wrote the first detailed scientific description of the koala in 1814, although his work remained unpublished for 180 years. HP Pavilion dv6-1101au CPU Fan Koalas Popular artist John Gould illustrated and described the koala, introducing the species to the general British public. Further details about the animal's biology were revealed in the 19th century by several English scientists. Because of its distinctive appearance, the koala is recognised worldwide as a symbol of Australia. HP Pavilion dv7-1157cl CPU Fan Koalas are listed as of Least Concern by the International Union for Conservation of Nature. The Australian government lists populations in Queensland and New South Wales as Vulnerable. The animal was hunted heavily in the early 20th century for its fur, and large-scale cullings in Queensland resulted in a public outcry that initiated a movement to protect the species. HP COMPAQ NX9420 CPU Fan Sanctuaries were established, and translocation efforts moved koalas whose habitat had become fragmented or reduced to new regions. The biggest threat to their existence is habitat destruction due to agriculture andurbanisation. The word koala comes from the Dharug gula. Although the vowel 'u' was originally written in the English orthography as "oo" (in spellings such as coola or koolah), HP Mini 110-1110ET CPU Fan it was changed to "oa", possibly in error. The word is mistakenly said to mean "doesn't drink".[4] Because of the koala's resemblance to a bear, it was often miscalled the koala bear, particularly by early settlers.[5] Other names like monkey bearnative bear, and tree-bear have also been used.[4] HP Pavilion dv7-1157cl CPU Fan Indigenous names include cullawinekoolawongcolahkarborcolocoolbunboorabeeburroorbangaroopucawan,banjorah, and burrenbong; many of these mean "no drink".[6] The generic name, Phascolarctos, is derived from the Greek words phaskolos "pouch" and arktos "bear". The specific name, cinereus, is Latin for "ash coloured".HP Pavilion dv6-3163eo CPU Fan The koala was given its generic name Phascolarctos in 1816 by French zoologist Henri Marie Ducrotay de Blainville,[9] who would not give it a specific name until further review. In 1819, German zoologist Georg August Goldfuss gave it the binomial Lipurus cinereusHP Pavilion dv9740us CPU Fan Because Phascolarctos was published first, according to the International Code of Zoological Nomenclature, it has priority as the official name of the genus.[10] French naturalist Anselme Gaëtan Desmarest proposed the namePhascolartos fuscus in 1820, suggesting that the brown-coloured versions were a different species than the grey ones. ACER Aspire 4743 CPU Fan Other names suggested by European authors included Marodactylus cinereus by Goldfuss in 1820, P. flindersii by René Primevère Lesson in 1827, and P. koala by John Edward Gray in 1827.[2] The koala is classified with wombats (family Vombatidae) and several extinct families (includingmarsupial tapirs, marsupial lions and giant wombats) in the suborder Vombatiformes within the orderDiprotodontia.[11] HP Pavilion dv6-2170us CPU Fan Vombatiformes is a sister group to a clade that includes macropods (kangaroos andwallabies) and possums.[12] The ancestors of vombatiforms were likely arboreal,[8] and the koala'slineage was possibly the first to branch off around 40 million years ago during the Eocene.[13] Toshiba Satellite L675-S7018 CPU Fan The modern koala is the only extant member of Phascolarctidae, a family that once included several genera and species. During the Oligocene and Miocene, koalas lived in rainforests and had less specialised diets.[14] Some species, such as the Riversleigh rainforest koala (Nimiokoala greystanesi) and some species of PerikoalaASUS F80Q CPU Fan were around the same size as the modern koala, while others, such as species of Litokoala, were one-half to two-thirds its size.[15] During the Miocene, the Australian continent began drying out, leading to the decline of rainforests and the spread of open Eucalyptuswoodlands. The genus Phascolarctos split from Litokoala in the late Miocene[14][16ACER TravelMate 4200 CPU Fan ] and had several adaptations that allowed it to live on a specialised eucalyptus diet: a shifting of the palatetowards the front of the skull; larger molars and premolars; smaller pterygoid fossa;[14] and a largergap between the molar and the incisor teeth.[17] During the Pliocene and Pleistocene, when Australia experienced changes in climate and vegetation, HP 434678-001 CPU Fan koala species grew larger.[15] Phascolarctos cinereus may have emerged as a dwarf form of the giant koala (P. stirtoni). The reduction in the size of large mammals has been seen as a common phenomenon worldwide during the late Pleistocene, and it is traditionally believed that several Australian mammals, such as the agile wallaby, resulted from this dwarfing. HP G70-120EA CPU Fan A 2008 study questions this hypothesis, noting that P. cinereus and P. stirtoni were sympatric during the middle to late Pleistocene, and possibly as early as the Pliocene.[18] The fossil record of the modern koala extends back at least to the middle Pleistocene. Toshiba Satellite A300-034 CPU Fan Traditionally, three different subspecies have been recognised: the Queensland koala (P. cinereus adustus, Thomas 1923), the New South Wales koala (P. c. cinereus, Goldfuss 1817) and the Victorian koala (P. c. victor, Troughton 1835). These forms are distinguished by pelage colour and thickness, body size and skull shape. HP 606609-001 CPU Fan The Queensland koala is the smallest of the three, with shorter, silver fur and a shorter skull. The Victorian koala is the largest, with shaggier, brown fur and a wider skull.[20][21] The boundaries of these variations are based on state borders, and their status as subspecies are disputed. Compaq Presario CQ60-301sl CPU Fan A 1999 genetic study suggests that the variations represent differentiated populations with limited gene flow between them, and that the three subspecies comprise a single evolutionarily significant unit.[21] Other studies have found that koala populations have high levels of inbreeding and low genetic variation.[ TOSHIBA Satellite L300 CPU Fan Such low genetic diversity may have been a characteristic of koala populations since the late Pleistocene.[24] Rivers and roads have been shown to limit gene flow and contribute to the genetic differentiation of southeast Queensland populations.[25] In April 2013, scientists from the Queensland University of Technology announced they had fully sequenced the koala genome. ASUS Eee PC 701 CPU Fan The koala is a stocky animal with a large head and vestigial or non-existent tail.[27][28] It has a body length of 60–85 cm (24–33 in) and a weight of 4–15 kg (9–33 lb),[28] making it among the largest arboreal marsupial.[29] Koalas from Victoria are twice as heavy as those from Queensland.[20] The species is sexually dimorphic, with males 50% larger than females. Compaq Presario CQ60-305sa CPU Fan Males are further distinguished from females by their more curved noses[29] and the presence of chest glands, which are visible as hairless patches.[30] As in most marsupials, the male koala has a bifurcated penis, and the female has two lateral vaginasand two separate uteri.[27] The male's penile sheath contains naturally occurring bacteria that play an important role infertilisation.[31] HP 637607-001 CPU Fan The female's pouch opening is tightened by a sphincter that keeps the young from falling out.[32] The pelage of the koala is thicker and longer on the back, and shorter on the belly. The ears have thick fur on both the inside and outside.[29] The back fur colour varies from light grey to chocolate brown.[27] HP Pavilion dv7-3067nr CPU Fan The belly fur is whitish; on the rump it is dappled whitish, and darker at the back.[28] The koala has the most effective insulating back fur of any marsupial and is highly resilient to wind and rain, while the belly fur can reflect solar radiation.[33] The koala's curved, sharp claws are well adapted for climbing trees. HP Pavilion dv5-1210ez CPU Fan The large forepaws have two opposable digits (the first and second, which are opposable to the other three) that allow them to grasp small branches. On the hindpaws, the second and third digits are fused, a typical condition for members of Diprotodontia, and the attached claws (which are still separate) are used for grooming.[34] Compaq Presario CQ50-211nr CPU Fan As in humans and other primates, koalas have friction ridges on their paws.[35] The animal has a sturdy skeleton and a short, muscular upper body with proportionately long upper limbs that contribute to its climbing and grasping abilities. Additional climbing strength is achieved with thigh muscles that attach to the shinbone lower than other animals.[36] HP G56-114SA CPU Fan The koala has acartilaginous pad at the end of the spine that may make it more comfortable when it perches in the fork of a tree. The koala has one of the smallest brains in proportion to body weight of any mammal,[37] being 60% smaller than that of a typical diprotodont. SONY Vaio VGN-CR21Z/N CPU Fan The brain's surface is fairly smooth, typical for a "primitive" animal.[38] It occupies only 61% of the cranial cavity[37]and is pressed against the inside surface by cerebrospinal fluid. The function of this relatively large amount of fluid is not known, although one possibility is that it acts as a shock absorber, cushioning the brain if the animal falls from a tree.[38] HP Pavilion dv7-4060eo CPU Fan The koala's small brain size may be an adaptation to the energy restrictions imposed by its diet, which is insufficient to sustain a larger brain.[37] Because of its small brain, the koala has a limited ability to perform complex, unfamiliar behaviours. For example, when presented with plucked leaves on a flat surface, Toshiba Satellite M70-252 CPU Fan the animal cannot adapt to the change in its normal feeding routine and will not eat the leaves.[39] The koala's olfactory senses are normal, and it is known to sniff the oils of individual branchlets to assess their edibility.[37] Its nose is fairly large and covered in leathery skin. Its round ears provide it with good hearing[32] and it has a well-developed middle ear.[14] Toshiba Satellite A100-455 CPU Fan A koala's vision is not well developed,[32] and its relatively small eyes are unusual among marsupials in that the pupils have vertical slits. The koala has several adaptations for its eucalypt diet, which is of low nutritive value, of high toxicity and high in dietary fibre.[40] HP Pavilion dv5-2112br CPU Fan The animal's dentition consists of the incisors and cheek teeth (a single premolar and four molars on each jaw), which are separated by a large gap (a characteristic feature of herbivorous mammals). The incisors are used for grasping leaves, which are then passed to the premolars to be snipped at the petiole before being passed to the highly cusped molars, DELL BFB0505HA CPU Fan where they are shredded into small pieces.[41] Koalas may also store food in their cheek pouches before it is ready to be chewed.[42] The partially worn molars of middle-aged koalas are optimal for breaking the leaves into small particles, resulting in more efficient stomach digestion and nutrient absorption in the small intestine,[43] HP Pavilion dv6-3299en CPU Fan which digests the eucalyptus leaves to provide most of the animal's energy.[41] A koala sometimes regurgitates the food into the mouth to be chewed a second time.[44] Unlike kangaroos and eucalyptus-eating possums, koalas are hindgut fermenters, and their digestive retention can last for up to 100 hours in the wild, or up to 200 hours in captivity.[41SONY Vaio VGN-NW11Z/T CPU Fan ] This is made possible by the extraordinary length of their caecum—200 cm (80 in) long and 10 cm (4 in) in diameter—the largest proportionally of any animal.[45] Koalas can select which food particles to retain for longer fermentation and which to pass through. Large particles typically pass through more quickly, as they would take more time to digest.[41] Toshiba Satellite L550-20W CPU Fan While the hindgut is proportionally larger in the koala than in other herbivores, only 10% of the animal's energy is obtained from fermentation. Since the koala gains a low amount of energy from its diet, its metabolic rate is half that of a typical mammal,[40] although this can vary between seasons and sexes.[41] HP Pavilion dv7-4183sf CPU Fan The koala conserves water by passing relatively dry faecal pellets high in undigested fibre, and by storing water in the caecum. The koala's geographic range covers roughly 1,000,000 square kilometres (390,000 sq mi), and 30 ecoregions.[46] HP Pavilion dv7-3190ev CPU Fan It extends throughout eastern and southeastern Australia, encompassing northeastern, central and southeastern Queensland, eastern New South Wales, Victoria and southeastern South Australia. The koala was introduced near Adelaide and on several islands, including Kangaroo Island and French Island.[1] HP KSB06105HA CPU Fan The population on Magnetic Island represents the northern limit of its range.[46] Fossil evidence shows that the koala's range stretched as far west as southwestern Western Australia during the late Pleistocene. They were likely driven to extinction in these areas by environmental changes and hunting by indigenous Australians.[47] HP G62-244CA CPU Fan In Queensland, koalas are unevenly distributed and uncommon except in the southeast, where they are numerous. In New South Wales, they are abundant only in Pilliga, while in Victoria they are common nearly everywhere. In South Australia, koalas were extirpated by 1920 and subsequently re-introduced.[1] HP Pavilion dv7-3190ei CPU Fan Koalas can be found in habitats ranging from relatively open forests to woodlands, and in climates ranging from tropical to cool temperate.[29] In semi-arid climates, they prefer riparian habitats, where nearby streams and creeks provide refuge during times of drought and extreme heat. HP G62-244CA CPU Fan Koalas are herbivorous, and while most of their diet consists of eucalypt leaves, they can be found in trees of other genera, such as AcaciaAllocasuarinaCallitrisLeptospermum and Melaleuca.[49] Although the foliage of over 600 species ofEucalyptus is available, the koala shows a strong preference for around 30.[50] ASUS A6000R CPU Fan They tend to choose species that have a highprotein content and low proportions of fibre and lignin.[43] The most favoured species are Eucalyptus microcorys,E. tereticornis, and E. camaldulensis, which, on average, make up more than 20 percent of their diet.[51] Despite its reputation as a fussy eater, HP Pavilion dv7-6011sg CPU Fan the koala is more generalist than some other marsupial species, like the greater glider. Since eucalypt leaves have a high water content, the koala does not need to drink often;[49] its daily water turnover rate ranges from 71 to 91 millilitres per kilogram of body weight. Toshiba Satellite L300D-01P CPU Fan Although females can meet their water requirements from eating leaves, larger males require additional water found on the ground or in tree hollows.[43] When feeding, a koala holds onto a branch with hindpaws and one forepaw while the other forepaw grasps foliage. Small koalas can move close to the end of a branch, but larger ones stay near the thicker bases.[52] Compaq Presario CQ60-409CA CPU Fan Koalas consume up to 400 grams (14 oz) of leaves a day, spread over four to six feeding sessions.[53] Despite their adaptations to a low-energy lifestyle, they have meagre fat reserves and need to feed often.[54] Because they get so little energy from their diet, koalas must limit their energy use and sleep 20 hours a day;[55] HP Mini 110-3010sf CPU Fan only 4 minutes a day are spent in active movement.[56] They are predominantly active at night and spend most of their waking hours feeding. They typically eat and sleep in the same tree, possibly for as long as a day.[57] On warm days, a koala may rest with its back against a branch or lie on its stomach or back with its limbs dangling.[55] Toshiba Satellite L645D-S4056 CPU Fan During cold, wet periods, it curls itself into a tight ball to conserve energy.[57] On windy days, a koala will find a lower, thicker branch to rest on. While it spends most of the time in the tree, the animal will descend to the ground to move to another tree, walking on all fours.[55] The koala usually grooms itself with its hind paws, but sometimes uses its forepaws or mouth. Toshiba Satellite M70-142 CPU Fan Koalas are asocial animals and spend just 15 minutes a day on social behaviours. In Victoria,home ranges are small and have extensive overlap, while in central Queensland they are larger and overlap less.[59] Koala society appears to consist of "residents" and "transients", the former being mostly adult females and the latter males. Resident males appear to be territorial anddominate others with their larger body size.[60] DELL Inspiron E1505 CPU Fan

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