IELTS Listening · Cam 21

Test 3 Part 4

Today I'm going to talk about invasive species. Let me start by saying what an invasive species

Level: C1 · 97 sentences

Transcript

  1. Today I'm going to talk about invasive species.
  2. Let me start by saying what an invasive species
  3. is and what it's not.
  4. Invasive species are any animal or plant that
  5. is introduced into an environment by humans and
  6. which is then harmful to that environment.
  7. It's important to be clear that not all introduced species are invasive.
  8. Many introduced or non-native species thrive in new areas
  9. without posing any threat.
  10. In some cases, invasive species have changed the natural world beyond recognition,
  11. so let's look at the different ways they can be problematic.
  12. First of all, invasive species may eat native species,
  13. or sometimes they may bring a disease with them,
  14. which native species have never faced before
  15. and therefore have no defences against.
  16. Often the invasive species breed very quickly,
  17. which further adds to the problem of native species
  18. losing their sources of food.
  19. Species invasions are one of the biggest causes
  20. of damage in an ecosystem, actually putting its survival at risk.
  21. So how do invasive species spread?
  22. Without a doubt, the biggest cause is human activity.
  23. This could be intentional or it could be accidental,
  24. such as when people who've been on holiday in another country...
  25. come back with, say,
  26. the seeds of plants on their clothes or shoes.
  27. Plants and animals, especially insects,
  28. arrive in or on the cargo of ships
  29. and then escape into their new home.
  30. But sometimes humans deliberately move animals and plants around the world,
  31. for example, to use them to control pests on farms
  32. or to be pets.
  33. This can go very wrong if those animals and
  34. plants move into wild settings and start breeding
  35. or begin growing in ways that weren't predicted.
  36. Let's now look at an example of an invasive
  37. species here in Australia.
  38. Rinella marina is a species of toad that
  39. was deliberately introduced from Hawaii in 1935
  40. as a form of biological control.
  41. It was hoped that the toads would eat the grey-backed
  42. beetles responsible for destroying crops of sugar on many of the plantations.
  43. At first, just a handful of toads were released
  44. by scientists into Queensland,
  45. but this number soon grew as other states followed suit.
  46. Within two years, 62,000 young toads had been released into the wild.
  47. The toads did nothing to protect the plantations,
  48. but they did reproduce rapidly and could soon be
  49. found all over the northern half of the country.
  50. The toads are poisonous at every stage of their life cycle,
  51. and anything that eats them will die.
  52. My second example regarding invasive species is the United Kingdom.
  53. Actually there are more than 3,000 invasive species there,
  54. including some that are extremely common.
  55. Some invasive plants, such as Japanese knotweed,
  56. have had a devastating impact on parts of the UK.
  57. Gardeners in the 19th century considered it a beautiful ornamental plant,
  58. which it is when it's kept under control.
  59. but it's soon spread into the countryside and
  60. remains a problem even to this day as it's
  61. so hard to eradicate.
  62. Another invasive plant is rhododendrons,
  63. which can be found in UK parks and woodlands.
  64. Their introduction dates back to 1763,
  65. but they're now seen as harmful because they block out
  66. so much light that native wildflowers can't grow beneath them.
  67. And then there are grey squirrels,
  68. which are one invasive species almost everyone in the UK
  69. will have come across.
  70. They were brought to the UK from North America
  71. and introduced to private estates around the 1870s,
  72. but are now found everywhere, from forests to city squares.
  73. Grey squirrels have out-competed the smaller, native red squirrels.
  74. They both eat the same food and the grey
  75. squirrels carry a type of virus that is deadly
  76. to the red squirrels.
  77. Red squirrel populations have collapsed and there are only
  78. a handful of sites left in the UK where they're found.
  79. An important question for ecologists worldwide is what
  80. can we do to tackle the problem of invasive species?
  81. The first step in controlling invasive species is learning
  82. about the behaviour of new species coming into the country.
  83. Monitoring is an important part of this so
  84. that we can know if the new species begins
  85. to have a negative impact in its new environment.
  86. One effective way to keep track of invasive species
  87. is to create a database for the whole country.
  88. That way, all relevant authorities and agencies can share important information
  89. and take whatever actions needed.
  90. But the public also have a vital role
  91. to play in this process.
  92. They should be encouraged to photograph harmful species,
  93. because this helps with identification,
  94. and then to report when and where these were observed.
  95. But it's important to tell people not to destroy
  96. or even touch what they've found.
  97. Now, I'm going to move on to an example...