Reading Passage 2
You should spend about 20 minutes on Questions 14-26, which are based on Reading
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 lecal 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 south east 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 Valdés 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 south eastern 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 unstudied, 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 causetecological 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.
Questions 14-18
Reading Passage 2 has eight paragraphs, A-H.
Which paragraph contains the following information?
Write the correct letter, A-H, in boxes on your answer sheet.
14 a suggestion that people have moved numerous species across the globe
throughout history
15 an example of how an ecosystem can be damaged very rapidly
16 a description of what can be done to restrict the spread of invasive species
17 a reference to the lack of research on the effects of some invasive species
18 a mention of a current lack of public awareness of the problem of invasive species
19 that an introduced species may benefit a specific ecosystem
Questions 20-21
Choose TWO letters, A-E.
Write the correct letters in boxes 20 and 21 on your answer sheet.
Which TWO reasons for the spread of invasive species are mentioned in the text?
A the wish to eliminate undesirable native species
B the recent expansion of international trade in agricultural products
C a lack of checks on some of the cargo on board ships
D the deliberate release of non-native animals
E an extension of their geographical range as a result of global warming
Questions 22-23
Choose TWO letters, A-E.
Write the correct letters in boxes 22 and 23 on your answer sheet.
Which TWO statements does the writer make about the water hyacinth?
A lt is native to almost every region of the world
B It was brought to North America in the late nineteenth century.
C Its beauty has led people to ignore the negative effects it has.
D Its spread has caused some practical problems in recent years.
E Scientists recommended its introduction to the USA.
Questions 24-26
Complete the sentences below.
Choose ONE WORD ONLY from the passage for each answer.
Write your answers in boxes 24-26 on your answer sheet.
24 Kudzu has reduced the .............. of certain areas in the south east of the USA.
25 Some introduced species present a low level of threat if they remain within a small
area and do not disturb the .... ..............0f the surrounding ecosystem.
26 The effect of invasive jellyfish in the Black Sea was greater than that .................. of
from factories.
Answers and Explanations
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Questions 14–18
Which paragraph contains the following information?
14. A suggestion that people have moved numerous species across the globe throughout history
Answer: C
Explanation: Paragraph C mentions that humans have historically transferred species from one region to another. It highlights the role of transportation and deliberate introductions, such as pets being released into the wild.
15. An example of how an ecosystem can be damaged very rapidly
Answer: E
Explanation: Paragraph E describes the introduction of comb jellyfish in the Black Sea. Within six years, their population exploded, transforming the ecosystem and leading to a sharp decline in fish numbers.
16. A description of what can be done to restrict the spread of invasive species
Answer: H
Explanation: Paragraph H outlines practical measures to prevent the spread of invasive species, including planting native plants, cleaning equipment, and reporting sightings to wildlife organizations.
17. A reference to the lack of research on the effects of some invasive species
Answer: F
Explanation: Paragraph F highlights that the impact of water hyacinth on native water plants is largely unstudied, as is the case with most ecosystems invaded by new plant species.
18. A mention of a current lack of public awareness of the problem of invasive species
Answer: G
Explanation: Paragraph G states that ordinary people have limited understanding of the threat posed by invasive species, leading to less attention compared to other environmental issues.
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Questions 19
That an introduced species may benefit a specific ecosystem.
Answer: D
Explanation: Paragraph D mentions that some introduced species can enhance the diversity of animal and plant life in specific areas if they maintain themselves without upsetting the ecological equilibrium.
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Questions 20–21
Which TWO reasons for the spread of invasive species are mentioned in the text?
Answer: C and D
Explanation:
- C: Paragraph C explains that insects and other organisms can travel unnoticed in cargo such as wooden crates shipped worldwide.
- D: Paragraph C also mentions the deliberate release of non-native animals like pets, such as snakes or turtles, into the wild.
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Questions 22–23
Which TWO statements does the writer make about the water hyacinth?
Answer: B and D
Explanation:
- B: Paragraph F states that the water hyacinth was brought to North America in the late 19th century, specifically for a horticultural exhibition in 1884.
- D: Paragraph F mentions practical problems caused by the spread of the water hyacinth, such as damaging boat engines and blocking cooling pipes for power plants, leading to blackouts.
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Questions 24–26
Complete the sentences below.
24. Kudzu has reduced the _______ of certain areas in the south-east of the USA.
Answer: biodiversity
Explanation: Paragraph B explains that kudzu replaces habitats with diverse plant species, creating a monoculture and reducing biodiversity.
25. Some introduced species present a low level of threat if they remain within a small area and do not disturb the _______ of the surrounding ecosystem.
Answer: equilibrium
Explanation: Paragraph D discusses introduced species that maintain themselves without disturbing the ecological equilibrium of an area.
26. The effect of invasive jellyfish in the Black Sea was greater than that _______ from factories.
Answer: pollution
Explanation: Paragraph E contrasts the impact of invasive jellyfish with industrial pollution, emphasizing that jellyfish caused more damage to the ecosystem.
