|
The single predator-single prey relationship between wolves (''Canis lupus'') and moose (''Alces alces'') on Isle Royale off the coast of Lake Superior, is unique and has been the subject of detailed study for over 55 years. Isle Royale, the principal island of Isle Royale National Park in Michigan in the United States, is an isolated island with little migration of animals into and out of the island and as a national park human interaction and impact on the two species is also limited. Both the wolves and the moose first became established populations on Isle Royale in the 1900s. Over the fifty years of the study, the populations of both moose and wolves have shown repeated spikes and declines and have not settled to a balanced relationship. The moose populations have ranged from 500 to 2500 while the number of wolves has ranged from almost 50〔(【引用サイトリンク】title=About The Project: Overview )〕 down to 3. The relationship between wolves and moose on Isle Royale has been the subject of the longest research study of its type, begun in 1958.〔"Overview of the Ecology and Research of Wolves and Moose on Isle Royale." The Wolves and Moose of Isle Royale. April 16, 2006 ()〕 The wolves have been subject to inbreeding and carry a spinal deformity. As of the 2014 count, there were only 9 wolves on the island, with the 2015 count showing only 3. A review completed in 2014 determined that new wolves would not be introduced into the park to attempt a genetic rescue. Isle Royale National Park is made up of about 400 islands, and is in the northwest portion of Lake Superior. It is about 50 miles (80 km) from Michigan's shore, and 12 miles (19 km) from the Canadian shore. The main island is about 45 miles (72 km) long, and nine miles (14 km) wide at the widest point, with an area of 205 square miles (530 km²). There are no roads, and no motorized vehicles are allowed on the island. The park is closed from September to May during which the wolf-moose study personnel are the only humans resident on the island. ==Wolf-moose dynamics interactions== Because of Isle Royale being an isolated island, neither wolves nor moose were there initially. Moose swam across Lake Superior from Minnesota in the early 1900s.〔Flesher, John. "Biologist Never Tires of Watching Wolves, Moose on Isle Royale." (The Boston Globe ) March 24, 2006. April 9, 2006〕 In 1949 a pair of wolves crossed an ice bridge from Ontario to the island during a harsh winter.〔Line, Les. "In Long-Running Wolf-Moose Drama, Wolves Recover From Disaster." The New York Times March 19, 1996. April 3, 2006 ()〕 But because only one pair of wolves migrated to the island, inbreeding has posed problems to the wolves' existence. According to Rolf Peterson, a professor at Michigan Technological University and the lead wolf-moose researcher, "Moose were isolated here 100 years ago. Most of the genes are still here, but they have enough population (to compensate). There are so few wolves that they have lost genetic variability. The scientific dogma suggests that they are not going to make it."〔Weier, Anita. "Isle is Perfect Laboratory for Moose and Wolves – Their Interactions Studied Since 1958. (Saturday Extra)" The Capital Times (Madison, WI) (May 31, 2003): 1B.〕 In fact, all of the wolves' DNA on Isle Royale can be traced back to one ancestor.〔 The lack of genetic variability leads to inbreeding, and inbreeding in turn leads to mutations and fitness problems. Wolves with mutations often are violently harassed, and sometimes killed because of their differences.〔 When initially studied in 1958, many researchers believed the two species would eventually reach a population equilibrium (which is believed to be about twenty-five wolves, and 1,500 moose). They have not yet shown any sign of settling into one, instead tending to fluctuate unpredictably.〔Myers, John. "Isle Royale's Moose Numbers Continue Crash." (Duluth News Tribune ) March 10, 2006. April 2, 2006〕 The highest number of moose on Isle Royale since being researched with the interactions of wolves was 2,450 in 1995. The highest number of wolves ever recorded on the island was fifty in 1980. The most dramatic decrease in the wolf population occurred when the canine parvovirus was spread to the wolves on the island, introduced by a park visitor's dog (breaking the rules of the national park) in 1980 or 1981, causing a crash in the population; there were fifty wolves in 1980, but only fourteen by 1982.〔 The population of the two species as of 2005 was 540 moose, which is the lowest recorded, and thirty wolves, which is considered rather high. In 2008, the number of moose was 700, and the number of wolves were 23. The density of the two species is very much dependent on the density of proper forage. Because a moose's diet is 59% balsam fir, any change in its density affects the density of moose.〔McLaren, B.E., and R.O. Peterson. "Wolves, moose, and tree rings on Isle Royale. (Isle Royale National Park, Michigan)." Science 266.n5190 (Dec 2, 1994): 1555(4).〕 The consistent presence of moose on Isle Royale since 1900 has led to a dramatic decline in understory growth of balsam fir. As of 2002, understory growth of balsam fir was at 5%, which is down 40% from 19th century rates, when it was recorded at 46%.〔 The reliance of moose on balsam fir has led to a much higher concentration of the species on the east side of the island, where the plant is more plentiful.〔Wilmers, CC, ES Post, RO Peterson, & JA Vucetich. 2006. Disease mediated switch from top-down to bottom-up control exacerbates climatic effects on moose population dynamics. Ecology Letters 9: 383–389.〕 Birch and aspen trees, which are much healthier for moose, used to grow plentifully on the island, but have now mainly been replaced by the less nutritious balsam fir. Because balsam fir does not fulfill the amount of moisture moose need in their diet, they have recently been spotted eating snow, which is a very rare occurrence.〔 They have also been sighted eating lichens, which is another very strange occurrence; researcher Rolf Peterson has compared it to eating dust.〔 When the moose population grows too high, the balsam fir population crashes, which leads to a crash in the moose population. This leads to the continuing "see-sawing" of the moose population on the island. Crashes in balsam fir growth lead to malnutrition, which is one of the most common killers, both directly and indirectly of moose. When there are too many moose for the amount of balsam fir, then many moose, especially young moose become plagued with malnutrition, which leads to arthritis. Moose commonly die either directly from malnutrition, or, because they become emaciated, and slowed down by arthritis, they are picked out by a wolf pack as easy prey, and are killed. The most common cause of malnutrition in moose is when calves are born during a winter with deep enough snow that browsing for proper forage is very difficult.〔 Wolves pick out moose prey which they can outrun, and bring down. Moose in their prime years commonly outrun wolves in a hunt; moose can cross snow two feet deep at 20 mph (32 km/h) and outrun wolves if the snow is soft.〔 Even if wolves can catch up to a moose, they cannot always bring it down; researchers have found many bruises and scars on wolves that have not been successful when trying to kill healthy moose.〔 Wolves pick out young moose calves, old moose, or moose plagued with disease or injury in order to increase their chances in successfully killing one. The typical moose that a wolf kills is about 12 years old, and suffers from arthritis, osteoporosis, or peridontitis, and in some cases all of them.〔"Isle Royale is a study in moose and wolves." Akron Beacon Journal (Akron, OH) (Dec 29, 2005): NA.〕 Though moose are often infected by various diseases, approximately 80% to 90% of moose deaths on Isle Royale can be attributed to wolves.〔Peterson, R.O., R.E. Page, and K.M. Dodge. "Wolves, moose, and the allometry of population cycles." Science 224 (June 22, 1984): 1350(3).〕 Because moose make up nine-tenths of an Isle Royale wolf’s diet (the remainder being snowshoe hare and beaver), finding a young, old or sickly moose is imperative for survival.〔 The average number of moose a wolf kills a month is between 0.44 and 1.69.〔Vucetich, JA & RO Peterson. 2004. Long-term population and predation dynamics of wolves on Isle Royale. Pages 281–292 in Biology and Conservation of Wild Canids, edited by D. Macdonald & C. Sillero-Zubiri, Oxford University Press.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Wolves and moose on Isle Royale」の詳細全文を読む スポンサード リンク
|