About this sample
About this sample
Words: 1976 |
10 min read
Published: Mar 14, 2019
Words: 1976|Pages: 4|10 min read
The species Phascolarctos cinereus, more commonly known as the koala, is a very unique and unusual animal. Although it is commonly thought of as a bear, the koala is actually a marsupial, one of the three groups of mammals, and is more closely related to the bandicoot and the American opossum than any species of bear (Smith and Harman, 1997). The koala is almost exclusively known to most people as the cute and furry animal residing throughout the continent of Australia. Although this is true for the most part, the koala is a much more intriguing animal. A turbulent journey from pre-history through todays struggle to coexist with human neighbors, very distinct mating rituals and reproductive habits, and most importantly, the destruction of their very precise habitat and the consequences this has for the existence of the koala species, are the themes to be discussed further.
Before the history of koalas is discussed in depth, a physical description of the koala is in order. Koalas, as mentioned before, are marsupials, the female having a pouch in which their young develop. Their pouch faces the rear and has a drawstring type muscle that the mother can tighten. Koalas are solitary animals, meeting only for mating purposes. Koalas are the only members of their family due to evolutionary patterns and extinction. (Phillips,1994) The koala averages between 680 and 820 millimeters in lenght from head to tail, males generally being more lenghty than females. They typically weigh between 4.9 and 14.9 kilograms, males weighing more than females and as a result of climate differences in regions, koalas from the north are smaller in length and weight than koalas from the south (Smith and Harman, 1997). Koalas are an arboreal animal, meaning they live in trees; they have a thick coat of wooly fur and are generally grey with a white underside and white speckles on the rump (Strahan, 1995).
Biologically koalas are very unique as well. As a result of being very picky eaters, koalas eat only leaves from select species of eucalyptous trees which are only found on the rich soils of the eastern coast. Because these leaves are half water, koalas never need to leave the safety of the trees to drink. The eucalyptous leaf is also high in fiber and very low in protein. This high fiber, low protein diet has caused the koala to develop a unique digestive tract that has a notably small stomach and a very large caecum. This caecum is thoght to be the equivalent of a human appendix and is where the chewed leaves are stored and symbiotic catabolism is carried out by a flora of micro-organisms that coexist within the koala. Another adaptation of koalas to the low protein diet is a very low rate of metabolism which results in a below average body temperature compared to other mammals (Phillips, 1994). The lower metabolism also accounts for the 18 hours a day that the average koala spends sleeping. Koalas also have developed an array of techniques to deal with the lower body temperature such as the thick dark fun on their backs to absorb and hold energy from sunlight. They also have a large, black nose that is moist most of the time and seems to serve as a thermostat of sorts (Wright, 2000).
Members of the marsupial class have existed in forms not much different than the koala for millions of years. Evidence has been found that indicates that many species of pre-historic marsupials were abundant in the time before the landmass Pangaea separated into the seven continents we know today. This evidence suggests that marsupials inhabited the area that today makes up the continents of Australia, South America, and Antarctica; koalas in particular evolved about 45 million years ago (Phillips, 1994). This once vast inhabitance and diversity suggests that the marsupial class may be past its prime in evolutionary history. Today marsupials numbers are quite diminished and the habitats are smaller than ever. This is most apparent in the case of the koala, whose population is decreased, in some estimates, by over ninety percent and in the which is isolated in very specific regions of Australia (Wright, 2000).
Before the arrival of Europeans in the late eighteenth and early nineteenth centuries, Australia was a very peaceful place with very little interspecies predation. But shortly after arrival, the Europeans quickly learned how easily koalas are captured and killed (Phillips, 1994). Although animals such as the dingo, European fox, goanna tree lizard, pet dogs, and some owls are known to be predators of koalas, these instances are considered rare, leaving only humans as koalas only real natural predator (Serventy, 1992). This is all too evident with the rape and pillage of the species by European settlers in shortly after arrival. Literally millions of koalas were hunted and killed for their magnificent fur. In the late 1890s, when records were first kept, upwards of 30,000 skins per year were being sent to London. These furs were not used for high- fashion clothing but as a cheap and durable fur. By the turn of the century, koala populations were completely devastated throughout the east coast. By the 1930s, koalas were extinct in South Australia and were very rare in the Mideast and north. Legislation was passed as early 1898 to prohibit the killing, but economic hardships more or less made the hunting necessary, therefore efforts to enforce the laws were ineffective (Phillips, 1994). Open hunting of koalas was again allowed between 1915 and 1920 around one million koala skins were exported per year and in 1927 a one month season was opened in which another half million koalas were slaughtered and shipped primarily to the United States. Shortly after, President Herbert Hoover signed a law permenently banning the import of koala skins, but the damage had been done, and by 1940 koalas in South Australia were extinct and very few remained in the north. The total extinction of koalas may have inadvertantly been prevented when a residents of Victoria took three koalas to Phillip Island, just off the coast of the mainland, as gifts to a resident. There the koalas flourished in the mostly vacant island and when healthy numbers eventually amassed, koalas were translocated back to the Province of Victoria in Southern Australia (Serventy, 1992). Today the koala population has dropped below 100,000 and has been distributed franmentedly throughtout the eastern coast. Development and deforestation have dictated where eucalyptous trees are left unmolested which in turn dictates where the koalas can live (Wright, 2000).
One thing that differentiates marsupials from other mammals is actually their anatomy and physiology of reproduction. All marsupials lack a complete placenta which permits the transfer of nutrients from mother to embryo in most mammals. In marsupials, a yolk sac-like placenta is formed through which an outer memberane surrounding the embryo develops. This is called an amion. Female marsupials, including koalas, have aduplicate reproductive system. For example, they have two vaginas spread sufficiently apart so as to allow the urinary tract to pas between them. When the birth is underway the offsring usually travel out via a third passage, the birth canal, wich runs from the point of connection between the two uteri to the urogenital cavity (Phillips, 1995). The reproductive rituals of koalas are also highly unique. The breeding season begins in the summer and the onset iks heralded by bellowing of the meales. These low-pitched, snoring in halations and exhalations can be heard for up to 600 meters and serve to advertise the presence of one male to others and to receptive females (Strahan, 1995). When considering sex, koalas are unlike almost all other mammals in the fact that the actual courting is initiated and carried out by the female rather than the male although the male advertises himself through his bellows. Foreplay is elaborate and can be very rough and is usually initiated by the female holds onto her tree and begins a jerking motion while she flaps her ears. What follows is a sequence in which the female seems to attack the male and bite his neck. This lasts for about 15 minutes and culminates in intercourse and copulation which last a couple of minutes at the most. The female raises her rump while the male penetrates. the female then appears to experience an orgasmic sequence of contractions after the male has withdrawn, throwing her head back wildly(Phillips, 1995). The female is usually in heat for about one or two days so it is consequential that this mating ritual take place promptly since female koalas only reproduce once a year.
The gestation period for the koala is about 34-36 days, then the baby koala makes its way from the urogenital opening to the marsupial pouch where it will further develop for the next six months by attaching itself to one of the mammary teats inside. The average lifespan of koalas seems to range from ten to 18 years, with the male lifespan generally shorter than the females. There is a noticeable trend of decreasing lifespans with the increased deforestation and development of Australias eucalyptous forests (Phillips, 1995).
There is a raging debate throughout Australia, and throughout the world for that matter, about the endangered status of koalas and if they should even be considered endangered. The vital eucalyptous forests of the koala are being cleared at record pace, which leaves the dependent koala less and less habitat in which survival is possible. This deforestation also creates small, isolated forests of the species, which without the trees that once surrounded, cannot move geographically, which can be devastating if a deadly bacterium such as chlamydia is introduced (Phillips, 1995) As reported on the website of ABCNews, the rapidly expanding koala population their numbers are doubling every three years is stripping Australia's nature preserves of eucalyptus trees, the animals' only food source. At this reproduction rate, the koala population will outpace the growth of new trees, and the vegetation will be overwhelmed. As the forests die, the koalas will starve, as many already are (2001). This is exactly the view taken by most non-environmentalists, where the problem lies in the exploding population rather than the rapid decrease in forests habitable by koalas caused by deforestation and development of highway systems. Some solutions these people have devised include shooting the koalas which is illegal, relocation, and sterilization. All of these solutions are worthless without the realization that some habitat needs to be preserved. Relocation is not really feasible because there is a lack of highly forrest that acccomdates the koala to begin with and sterilization is difficult and highly expensive. There are many groups in Australia devoted to the continued existence of the koala such as the Australian Koala Foundation (AKF). Groups such as the AKF realize the issue is not with overpopulation of the species, but with the ignorance and possible overpopulation of the Homo sapiens (Wright 2000).
Koalas are a highly unique and specialized species to say the least. They have survived a long and, until recently, peaceful past. Although currently in the climax of a heated debate, concerning the subject of endangeredness, no progress is being made to take the blame off the koalas and focus continues to be on what can be done to directly effect the growing numbers of the animals. With assistance from organizations like AFK, the general public will eventually come to understand that the most effective method of controlling the koala population is through the indirect effect caused by the halting of deforestation and preservation of the eucalyptous forests that are the foundation of koala life.
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