IELTSwithJurabek

You should spend about 20 minutes on Questions 14-26, which are based on Reading Passage 2.

The Impact of Invasive Species

A Invasive species are among the leading threats to the native wildlife of most countries, with approximately 42 percent of endangered species at risk from them. Invasive species can be any kind of organism - for example, a mammal, amphibian, fish, insect or plant - that is not native to an ecosystem. Often, they reproduce and spread with great speed. Contrary to popular belief, a plant or animal classified as an invasive species does not necessarily originate in another country. For example, lake trout are native to the Great Lakes of North America, but are considered to be an invasive species in Yellowstone Lake in Wyoming because they compete with native cutthroat trout for habitat.

B When a new species is introduced into an ecosystem, native wildlife may struggle to compete with it for food and other resources. Invasive species can change the food web in an ecosystem by destroying or replacing native food sources, while providing little or no food for local wildlife. In extreme cases, the invader may prey on the native species. Above all, invasive species threaten biodiversity in many habitats. For instance, the climbing plant species kudzu (which is native to East Asia) can easily replace a habitat that had a wide range of plants with a monoculture consisting solely of kudzu, as has started to happen in the southern states of the USA.

C The phenomenon is not an exclusively modern one. Humans have always transferred a variety of species from one region to another, but the development of rapid means of transportation has increased the frequency of such introductions. Aquatic organisms can be shipped across the oceans, while insects can easily get into the wooden crates that are transported around the world in this way. In addition, climate change has enabled some invasive plant species to colonise new areas. Other invasive species include pets such as snakes or turtles which are intentionally set free into the wild.

D Invasive species do not all present the same level of threat to native ecosystems and can be classified into three types. The first of these may be introduced species which can maintain themselves in a limited range of habitats without upsetting the ecological equilibrium of the area. Some scientists have even argued that in these cases the introduction enhances the diversity of animal and plant life in that specific area. A second group of invaders present a greater threat because their spread is at the expense of one native species. The North American grey squirrel, for example, was introduced to the UK in 1876 largely because wealthy landowners thought it would be a fashionable and attractive addition to the local wildlife on their estates. It spread widely, leading directly to the dramatic decline in the population of the native red squirrel. However, it would appear that this is the only definite negative impact of the grey squirrel.

E There is a third level of threat in which the dominance of the introduced species has an extremely destructive effect on the entire ecosystem. One of the most damaging examples involved a species of comb jellyfish. Native to estuaries along the western Atlantic coast from the northern United States to the Valdes peninsula in Argentina, this species was released from a ship into the Black Sea in Eastern Europe in 1982, almost certainly by accident. The Black Sea has levels of industrial waste which are by international standards exceptionally high. Despite this, fishing boats were still able to catch healthy numbers of fish. But when the invading jellyfish underwent a population explosion in the space of just six years, the entire marine ecosystem was transformed, and fish numbers declined dramatically because they were in competition with the jellyfish, preying on exactly the same microscopic creatures. The jellyfish had a more serious impact on the ecosystem than the heavily polluted water.

F More than a century after its introduction outside its native range on the Amazon River in South America, a plant known as a water hyacinth can be found in tropical lakes, streams, and rivers around the world. Its beauty attracted botanists seeking exotic plants for botanical gardens and they imported it to a horticultural exhibition in New Orleans in 1884. Visitors were so impressed they planted it in many locations during the 1880s and 1890s, resulting in the aquatic ecosystems of the southeastern United States being progressively colonized by vast, floating, dense carpets of water hyacinth. Today it is present around the globe, damaging boat engines and even blocking cooling pipes for power plants, occasionally leading to massive blackouts. The impact of the water hyacinth on native water plants is largely undiscussed, as is unfortunately the case for most ecosystems invaded by new plant species.

G In the United States, more than 7,000 introduced species have established themselves, of which at least 15 percent cause ecological damage. As the number of invasive species expands, legislation to deal with this problem is rare or non-existent in the majority of countries. Unfortunately, ordinary people outside the scientific community have a very limited understanding of the threat posed by invasive species, which means that other environmental threats receive considerably more media attention. The introduction of new species can initially seem highly desirable, but the full extent of their impact is consistently underestimated.

H Although ultimately measures need to be taken at an international level, limited action is possible by individuals. One way is for people to plant native plants in their gardens rather than species from abroad. It is also useful to learn to identify invasive species, and report any sightings to wildlife organisations. Regularly cleaning clothing, boots, boats, tires, and any other equipment regularly used outdoors can remove insects and plant parts that may introduce invasive species into new locations.

You should spend about 20 minutes on Questions 27-40, which are based on Reading Passage 3 below.

Music soothes and awes – and may help us heal

Tapping into the brain's ability to process music, researchers are using songs and sounds in novel ways

Dan Ellsey, 33, was sitting in his wheelchair, his virtually useless arms and weak torso strapped to the chair for safety. As we were introduced, he arched his back, grinned broadly and aimed the power of his dark brown eyes at me, as if eye contact were his only means of transcending the prison of his body.

But it isn't. In the last few years, Ellsey, who was born with cerebral palsy, has discovered another, almost miraculous way of expressing himself: composing music with a special computerized system called Hyperscore. For Ellsey, as for most human beings, music has almost inexplicable power. It can rouse armies to battle, soothe babies to sleep, communicate peaks of joy and depths of sorrow that mere words cannot.

Why evolution would have endowed our brains with the neural machinery to make music is a mystery. "It's unclear why humans are so uniquely sensitive to music. Certainly, music shares many features with spoken language, and our brains are particularly developed to process the rapid tones and segments of sound that are common to both," said neurologist and author Dr Oliver Sacks, whose latest book is Musicophilia: Tales of Music and the Brain. "Some researchers," he added in an e-mail interview, "think that in primitive cultures, music and speech were not distinct. Other researchers debate which came first in evolution, speech or song." What is clear is that the brain is abundantly wired to process music.

Scientists at the Montreal Neurological Institute and Hospital, for instance, have found dramatic evidence on brain scans that the chills, or visceral feelings of awe, that people report when listening to their favorite music are real. Reactions to music appear to vary greatly. Music that a person likes, but not music that is disliked, activates the higher thinking centers in the brain's cortex and, perhaps more importantly, the "ancient circuitry, the motivation and reward system," according to experimental psychologist Robert Zatorre, a member of the Montreal team. This primeval part of the brain also governs basic drives such as hunger, thirst and sex, suggesting that the brain may consider music on a par with them.

Music has the power not just to awe but also to heal. If a person has a stroke on the left side of the brain, where the speech centers in most people are, that "wipes out a major part of communication," said Dr Gottfried Schlaug, chief of the Cerebrovascular Disorder Division and Stroke Recovery Laboratory at Beth Israel Deaconess Medical Center. But if the right side, where a lot of music is processed, is intact, some stroke patients can use melodic intonation therapy, which involves singing using two tones relatively close in pitch, to communicate. Schlaug's research suggests that with intensive therapy, some patients can even move from this two-tone singing back to actual speech.

Stroke patients with gait problems also profit from music therapy. At the Center for Biomedical Research in Music at Colorado State University in Fort Collins, director Michael Thaut and his team have shown that people who are partially paralyzed on one side of the body can be retrained to walk faster and in a more coordinated way if they practice walking rhythmically, cued by music or a metronome. Combining rhythmic training with physical therapy also helps stroke patients recover gait faster. "Music helps us organize our movement," said Kathleen Howland, a music therapist who teaches at Lesley University in Cambridge in the USA. In fact, researchers have found that auditory signals are more powerful than visual signals in coordinating movement in healthy people.

Patients undergoing colonoscopy seem to feel less pain and need fewer sedative drugs if they listen to music during the procedure, according to several studies. But not all studies have been so clear-cut. A 2007 review by the Cochrane Collaboration, a nonprofit, international organization that evaluates medical research, pooled data from 51 pain studies and concluded that, although listening to music can reduce the intensity of pain and the need for narcotic drugs, the benefit, overall, was small.

A number of studies, however, show that music therapy can reduce pain, such as a 2001 study on burn patients, whose burns must be frequently scraped to reduce dead tissue. Music therapy may improve mental state and functioning in people with schizophrenia, and communication in children with autistic spectrum disorders, according to Cochrane reviews. Babies, as any parent knows, clearly respond to music. Premature infants who listen to lullabies learn to suck better and gain more weight than those who don't get music therapy. Deforia Lane, director of music therapy at the University Hospitals Ireland Cancer Center in Cleveland, has found an improvement in immune response among hospitalized children who played, sang and created music, compared with children who did not get music therapy. Indeed, the list of potential benefits from music therapy seems long. And for people such as Ellsey, the benefits can be nothing short of liberating.