Australia Essay Research Paper Plant Life Although (стр. 1 из 2)

Australia Essay, Research Paper

Plant Life

Although only a dozen plant families are unique to Australia, there are 530 unique genera and many unique species within these genera. As the Australian fragment of prehistoric Gondwanaland drifted north, its ancient flora became the basis for the present plant systems. Increasing aridity modified this vegetation, giving much of it hardened, pointed leaves of reduced size–a condition called scleromorphy.

Australia’s native vegetation is divisible into seven types. The first type of vegetation consists of remnants of Gondwanan rain forests, with primitive flowering plants, palms, and laurels. These occur where high rainfall and high temperatures coincide with fertile, often volcanic soils, mainly in coastal north Queensland. In climax rain forests, three layers of trees appear, entangled with shrubs, lianas, and epiphytes. Closest to original Gondwanan conditions are the temperate rain forests of Tasmania, dominated by the myrtle beech and swathed in tree-ferns and mosses–called moss forests.

The second type of vegetation, communities dominated by the tall, straggly eucalyptus trees, is the most ubiquitous, forming a wide, concentric band around the desert core. Of the 500 species, two or three typically form a mosaic in one locality and intermingle with other plant associations. Eucalyptus trees are classified according to their bark types–hence the names stringybark, ironbark, bloodwood, and smoothbark (the gums that shed their outer bark annually). The most widespread is the river red gum. Mallee eucalypts survive in semiarid regions by growing multiple stems (lignotubers) from a common rootstock. The world’s tallest flowering plant is a southern eucalyptus, the mountain ash. Its height can exceed 325 feet (100 meters). Building timbers are obtained in Victoria from alpine ash and mountain ash, in New South Wales and Queensland from blackbutt, spotted gum, bluegum, and ironbark, and in Western Australia from jarrah and karri, another type of eucalypt.

A third type of plant community is dominated by wattles (the genus Acacia of the Mimosa family) and advances beyond the last eucalyptus trees into the desert. Although more than 900 species are known, vast regions are dominated by just a few, including brigalow, mulga, and gidgee. Their tannin-rich bark is used in tanning leather. One of the less attractive of the varieties of acacia is the mulga. This small tree grows on thousands of square miles of arid inland Australia. The slang term “out in the mulga” refers to the distant outback areas. Aborigines had a number of uses for this tree. Its wood provided a slow-burning fuel for cooking fires, and it was also used to make spear blades.

The golden wattle is the acacia most familiar to natives. It is the floral symbol of Australia. There is even a Wattle Day, which may be celebrated on August 1 or September 1. Eucalyptus or acacia trees are dominant over 75 percent of the continent.

Three other types of vegetation are found over smaller areas. Communities dominated by casuarinas (and Allocasuarina species, including she-oaks) occupy semiarid niches between eucalyptus and acacia woodlands. Native conifers command no large areas as they do in the Northern Hemisphere, although white cypress pine grows widely on infertile soils. Pioneer builders were gratified to discover that it withstands drought, fire, and termites. Salt-tolerant shrublands devoid of trees are found mainly along the southern edges of the arid core. Mallee, saltbush, and bluebush are common, and Banksia and Grevillea are of local importance. Finally, grasslands occur where rainfall is insufficient for larger plants. Summer-growing species tend to be more northerly and winter-growing species more southerly. Hummock grasslands (including spinifex) spread across the dunes, sandy plains, and rocky ranges of the Western Plateau.

Minor coastal plant communities include salt marsh, seagrass, and mangroves. Alpine herb fields, often flattened by the wind, are dotted with sphagnum moss bogs. Weeds introduced from outside Australia, such as wild turnip and hoary cress, compete with crops. Lantana, blackberries, bracken fern, and Paterson’s curse overrun pastures. Cape tulip and Saint-John’s-wort can poison livestock or taint food. Algae block drainage and smother plants. Only 5.3 percent of Australia’s 2,966,200 square miles (7,682,300 square kilometers) is covered in forest. Of that, 75 percent is in public domain. Forest plantations account for another 3,759 square miles (9,737 square kilometers), 69 percent of them under California radiata pine. Fine specimens of Australian flora can be seen in the National Botanic Gardens in Canberra, the Royal Botanic Gardens of Sydney and Melbourne, and Kings Park in Perth. Animal Life

Native to Australia are 250 species of mammals (half of them pouched marsupials); 750 species of birds; more than 500 species of reptiles and amphibians, including 150 species of snakes; 22,000 species of fish, but only 150 of them freshwater; 65,000 known insect species; and 1,500 species of spiders. The continent is world-famous for these zoological curiosities. It became a veritable Noah’s ark for monotremes, which include the platypus, and marsupials, saved from competition with carnivores and herbivores and free to evolve uniquely, when Australia split from Gondwanaland between 45 and 70 million years ago. By contrast, other animals drifted free with South America and Africa but became extinct when those continents encountered Northern Hemisphere landmasses that were home to predators.

When Australia drifted closer to Asia 20 million years ago, Asian animal immigrants reached northern Australia across shallow continental shelves. Bats and rodents island-hopped. The dingo, a type of wild dog, came with migrating aborigines or Asian fishermen 5,000 years ago. Other creatures used the broad land bridges which surfaced when the expansion of the ice caps resulted in lowered sea levels, linking the Australian mainland with New Guinea and Tasmania. Marine animals dispersed easily across the entire tropical and subtropical Indian and Pacific oceans. Wallace’s line, drawn in 1868 between the Indonesian islands of Bali and Lombok, marked the proximal separation of Australasian and Oriental faunas.

The present Australian fauna thus contains three main elements–those uniquely Australian (like the monotremes and lyrebirds), those of Gondwanan origin with affinities to other continents (some marsupials, the emu and cassawary, geckos, side-necked tortoises, most frogs, lungfish, and barramundis), and those which flew or floated on drifting vegetation from Asia within the last 30 million years (rodents, lizards, insects, birds, bats, and snakes), still comfortably acclimatized in tropical northern Australia.

The monotremes, an egg-laying order of mammals, include only the platypus and two species of echidnas, or spiny anteaters. Platypuses are found nowhere else in the world, not even in fossil form. Echidnas are found also in New Guinea. The platypus uses its webbed feet and broad, sensitive bill to nuzzle food from the bottoms of coastal creeks from northern Queensland to South Australia. The bill has a unique sensing device that detects changes in electrical fields. The platypus is a skilled swimmer and can remain underwater for up to five minutes at a time. It spends only a few hours of each day in the water. The males have a poisonous spur on each hind leg. Although the poison is not fatal to humans, it can cause agonizing pain.

The shy echidna uses its snout to probe for termites and insects, which adhere to the saliva on its tongue. It settles into the ground, spikes erect, when disturbed. The heavily armored echidna has small spines on the back of its head and long spines on the upper surface and sides of its body. Its clawed limbs are short and powerful. The male has a retractable spur on each hind limb that releases a weak poison. It is from this that the animal gets its name–echidna is derived from a Greek word for viper. The echidna is toothless but has a tongue up to 12 inches (30 centimeters) long, the sticky surface of which is used for catching ants.

For a study in sheer animal cunning it would be difficult to surpass the dingo, also known by the aboriginal name warrigal. It is an animal very similar in appearance to the domestic dog. It probably arrived from mainland Asia about 5,000 years ago, along with an immigration of aborigines. The dingo is a fairly large canine, growing to about 4 feet (1.2 meters) long, including its 12-inch tail. The dingo has long been the killer of the outback. It hunts kangaroos, wallabies, rabbits, and ground birds–with a special fondness for the echidna. It also runs down and kills sheep and cattle. Like wolves, these animals hunt alone or in packs. Its ferocity resulted in the elimination of the Tasmanian devil and the Tasmanian wolf from mainland Australia. The dingo carries a bounty on its head, and Queensland once erected a 3,000-mile (4,800-kilometer) fence to keep the animal out.

Marsupials.

Of the world’s 19 marsupial families, 16 are native to Australia. They include opossums, koalas, wombats, kangaroos, and wallabies. Whereas placental mammals connect the unborn baby to the mother’s uterus, the marsupials give birth to their young at a very early stage of development, retaining, carrying, and suckling them in an abdominal pouch. A vivid example is the joey, or baby kangaroo, scrambling into the mother kangaroo’s pouch.

There are 50 species of kangaroos in Australia. These macropods have large hind legs for hopping. Their heavy tails serve as a counterbalance during locomotion and as a prop when standing upright.

Kangaroo sizes and characteristics vary widely. There are burrowing rat kangaroos, tree kangaroos with shortened hind legs and exceedingly long tails, rock wallabies with granulated footpads for gripping, pademelons, and quokkas. The largest species are the grey (or forester) kangaroo and the red kangaroo. Males of both species may exceed 8 feet (2.4 meters) from nose to tail.

Many ranchers regard kangaroos as vermin, especially during plagues. Conservationists deplore their slaughter for skins, for pet food, or simply to cut down the size of a herd. (See also Kangaroo.)

Koala is an aboriginal word meaning “it does not drink,” though these animals do drink when ill. Koalas are tree-dwelling marsupials with a home range of 14 to 15 eucalyptus trees. One tree will be an animal’s favorite. They feed exclusively on specific eucalyptus leaves which provide sufficient moisture. An exceptionally long intestine and special liver mechanism cope with the harsh oils and tannin in the leaves. Lacking the tails typical of most arboreal animals, and with pouches that open inconveniently backwards (like their closest relative, the wombat), koalas may have originated as ground-dwelling, burrowing animals.

Koalas were abundant in coastal forests from northern Queensland to southeastern South Australia. Hunters exported their pelts in large numbers (two million in 1924 alone) until public revulsion and an American ban on imports led to total protection by law. Continuing problems include habitat fragmentation–especially in their southern Queensland stronghold–serious fires, and a virulent form of the disease trachoma.

Australian opossums, or phalangers, are also arboreal marsupials. They include the cuscus, a monkeylike marsupial; the ringtail opossum, which has a prehensile tail; and the gliders, which are also called flying phalangers.

Another tree-dwelling marsupial is the tiny pygmy gliding opossum, an acrobatic, mouselike animal and the smallest marsupial adapted for gliding. One of the numerous kinds of Australian possums, it is found in eastern regions of the country. However, it is rarely seen because it is active at night and extremely furtive. It glides from tree to tree in flights that are really prolonged leaps. Membranes between its limbs have a parachute effect, and its fringed tail provides an additional airplanelike surface.

The doglike Tasmanian devil is also a marsupial. It is a slow-moving, clumsy animal that lives in open forest areas. It takes shelter in any available cover by day and scavenges for food by night. Although widely regarded as a fierce killer of animals, the Tasmanian devil is actually a poor hunter and usually feeds on carrion, much like a vulture. The animal is usually about 28 inches (71 centimeters) long with a 10-inch (25-centimeter) tail. It is mostly black, with white bands across its chest and rump. The forefeet have five toes and the rear feet have four. All of its toes are strongly clawed. (See also Marsupials.)

Reptiles.

All three orders of reptiles–crocodiles, lizards and snakes, turtles and tortoises–are well represented in Australia. The seagoing estuarine crocodile ranges from India to China and the western Pacific. It is found along the northern coasts of Australia between Broome and Maryborough, in saltwater estuaries and river mouths. Males average 16 feet (5 meters) in length but do reach 23 feet (7 meters). Crocodiles feed on fish, crabs, water rats, and occasionally on larger prey–including horses, cattle, and humans–which they first drown and then dismember. The smaller freshwater crocodile, found in the billabongs (streambeds) and lagoons of monsoonal rivers, is harmless to humans.

Besides estuarine crocodiles, the only Australian animals that will feed on humans are sharks and, of course, mosquitos and fleas. Crocodile-skin handbags and shoes were once highly prized luxury items, but crocodile hunting has been completely banned in Western Australia and the Northern Territory since 1971 and in Queensland since 1974. Crocodile farms, several of them run by aborigines, now market meat.

Australia’s 450 species of lizard probably originated in tropical Asia. Today they are the dominant predators in desert ecosystems. The largest of them is the desert perenty, averaging 5.2 feet (1.6 meters) but known to reach 8.2 feet (2.5 meters). Fossil monitor lizards, called goannas, at 20 feet (6 meters) and 1,300 pounds (600 kilograms), were twice as big as today’s record-holder, the Komodo dragon. Curiosities include the gecko, whose padded, adhesive digits enable it to move and rest on ceilings. Geckoes are able to snap off their still-wriggling tails to distract predators while making their escape. Among the dragon lizards are the thorny devil, the water dragon, and the spectacular frill-necked lizard, which unfolds its ruff like an umbrella when alarmed. Skinks with smooth, silky scales are common sights in suburban gardens.

Of Australia’s marine turtles, the largest is the leathey, or luth, turtle, up to 10 feet (3 meters) in length and 1,100 pounds (500 kilograms) in weight. Among reptiles, only the estuarine crocodile exceeds it in size. Marine turtles thrive in the warm tropical seas, coming ashore–vulnerable to human predators–to lay scores of eggs in chambers dug into beach sand. An extraordinary navigational sense permits turtles to return to the very beach where they were hatched.

Australia is the only continent where venomous snakes outnumber the nonvenomous, though only 20 or so of the 160 species (including 32 of sea snakes) are fatal to humans. Among the nonvenomous are blind or worm snakes, tree snakes, file snakes, and 13 species of pythons that suffocate their prey by constriction. The longest is the amethystine, or rock, python, which averages 11 1/2 feet (3.5 meters), and whose maximum length is 28 feet (8.5 meters). The most widespread is the common carpet snake.

All 65 species of venomous snakes are front-fanged elapids. Venom is secreted from modified saliva glands at the base of grooved, hollow fangs. It kills either by destroying the linings of blood vessels, causing blood to clot, destroying the red blood cells, or, in the case of neurotoxins, paralyzing nerves that control the heart and lungs. Australia’s most dangerous snakes are the tiger snake, the Eastern brown snake, the mulga or king brown snake, death adders, the red-bellied black snake, the taipan, and its look-alike, the fierce or giant brown snake. The latter’s neurotoxic venom can kill 100,000 mice, making it the most deadly of all the world’s land snakes. Antivenins developed in the Commonwealth Serum Laboratories, if administered promptly, can now counteract most of these venoms.

Insects.

Other poisonous animals include the Sydney funnelweb spider, which spins a silken tube at the entrance to its burrow and has killed unsuspecting gardeners; the trapdoor spider, which seals its burrow with a plug of earth; and the red-back spider; which lurks in outhouses under toilet lids. Many of Australia’s 80,000 known insect species also sting.

The largest insect nests are the towering termites’ nests, or termitaria, some of which surpass 23 feet (7 meters) in height, connected to food sources by 110 yards (100 meters) of tunnels and galleries. Those built in the Northern Territory by the compass, or magnetic, termite are aligned north-south to minimize exposure to the tropical sun.

Birds.

Of the world’s more than 8,000 species of birds, about 750 are found in Australia. Of these, 368 are peculiar to Australia, 125 are nonbreeding visitors, and 20 or so were introduced, usually by human migrants longing for the birdsongs of their homelands. Acclimatized birds include the house sparrow, starling, song thrush, blackbird, pigeon, and, from India, the mynah and red-whiskered bulbul. Although Australia has 19 of the 25 orders of living birds, it lacks woodpeckers, vultures, true finches, and flamingos. Many of the indigenous birds originated in Asia or Gondwanaland. Many still live in New Guinea, among them the birds of paradise, bowerbirds, and spangled drongo.


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