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Passage Discussion

Passage A

Paragraph One:

The author of passage A begins by discussing the complacency with which many conservationists used to approach the issue of nonindigenous plants and animals’ invasion of new ecosystems. This complacency was based on the common view presented in a 1958 book by Charles Elton, that the habitats vulnerable to such attacks were those that were disturbed, with fewer or weaker native species. The modern view, the author says, is that the issue is more serious than previously thought, and that invasive species can also threaten undisturbed, vibrant, species-rich habitats.

Paragraph Two:

In the second and closing paragraph, the author provides two examples to show the threat that invasive plants can bring to the biodiversity of the world’s ecosystems. The first example is that of the Florida Everglades National Park, where the author says the degradation is as bad as it would be were it the result of chemical pollution. There, the nine-foot sawgrass that traditionally comprised large marsh areas and provided habitat for the unique local wildlife has been literally overshadowed by Australian melaleuca trees, which, at 70 feet tall, monopolize sunlight while blocking waterflow with leaf litter, leading to declines in the traditional wildlife. In the final sentence the author quickly provides an additional example in Australia, where diverse native reptiles disappeared after Scotch broom plants were introduced.


Several Viewpoints were presented in passage A: first, Charles Elton’s view, the perspective that many conservationists shared until recently, that disturbed habitats are most vulnerable to invasion by introduced nonindigineous species. The second perspective presented begins on line 8: it is that of modern ecologists that the threat is shared by vibrant, species rich ecosystems as well. Note that the author shares this perspective as well, making the point clearly by stating that current ecologists “realize” that species-rich habitats are threatened as well. The remainder of the passage continues the presentation of the author’s perspective.

The Structure of Passage A is as follows:
  • Paragraph 1: Present an old and an updated perspective on the danger of introducing new species to ecosystems.

    Paragraph 2: Provide two examples that show the potential hazard associated with the introduction of invasive species.
The author’s Tone is one of concern, and conviction.

The Main Point (and central Argument) presented in Passage A is that the introduction of invasive species can be devastating to the ecosystems to which the species are introduced.

Passage B

Paragraph One:

The author begins the passage by asserting that invasive plants don’t really threaten nature, but rather human perception of what nature should be. Invasive plants don’t necessarily wipe out pre-existing species; other than some important exceptions, they can increase biodiversity and add to the local species count.

Paragraph Two:

Even when invasions do bring major change to a local ecosystem, that doesn’t mean that the local ecosystem collapses, although it might hold less appeal or value for humans. According to the author, fifty years of study have shown little difference between largely native ecosystems and those comprised of introduced invasive species. The author ends the paragraph by contrasting transformative species invasions with the destructive act of forest clear cutting.

Paragraph Three:

In the final paragraph the author implies that the issue has been misrepresented. The choice is not between life and death for the ecosystem, but rather what types of species will make up its composition. There are costly and tragic exceptions, the author concedes, but generally invasive species can be introduced without detriment.


The only Viewpoint presented in passage B is that of the author, who believes that the introduction of nonindigineous species is not necessarily a threat, and can often be beneficial.

The Structure of Passage B is as follows:
  • Paragraph 1: Assert that invasive species don’t necessarily pose a threat, and such introductions can add to the local diversity,

    Paragraph 2: State that invasions don’t always mean collapse, and change might only offend certain human preferences. Contrast species introduction, which can increase diversity, with the more clearly destructive act of clear cutting forests.

    Paragraph 3: Reframe the issue as not one of life or death, but rather one of what specific species will comprise any given ecosystem. Concede that occasional extinctions are tragic, but that generally introduction of outside species can bring benefit rather than detriment.
The author’s Tone is one of skepticism regarding the claims about invasive species.

The Main Point of Passage B is also the author’s central Argument: introducing new species to an ecosystem is not necessarily hazardous and could be beneficial.

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