TOEFL iBT Writing. In this integrated writing task, you will write a response to

Now listen to part of a lecture on this topic in a biology class.
Most invasive species are the result of human activity, either accidental or intentional. Introduced species will quickly take over when they out-compete native species and have no natural predators. A recent invader in North America is the zebra mussel, which arrived in the ballast water of a cargo ship from the Caspian Sea. Within ten years, the mussels spread through the entire Mississippi River system, where they compete with the native shellfish for space, and with the native fish for food.
Some ecosystems are especially likely to be taken over by invasive species. Island ecosystems, for example, are separated from others by distance, and this makes them likely to have open niches, where introduced species might flourish. An example of this is the invasion of Guam by the brown tree snake. Guam had no native snake species, so all of its native birds had adapted to life without these predators. When the brown tree snake arrived—probably in air cargo from another Pacific island—it quickly established itself, feeding on the defenseless birds. The result was a massive invasion of snakes and the decimation of the native bird populations.
A well-known invasive plant is the kudzu vine. Kudzu was introduced into the United States from Asia in the nineteenth century. At first, it was promoted as an ornamental plant and food crop for animals. Then the government encouraged farmers to plant kudzu as a way to reduce soil erosion. The southeastern states have nearly perfect conditions for kudzu to grow out of control: hot, humid summers and mild winters. Furthermore, the plant has no natural predators. For these reasons, the once-promoted plant is now considered a pest weed.
Summarize the points made in the lecture, explaining how they support points made in the reading.