Reading Comprehension

PT101 · S4 · P3 · Q19 Species Gradient

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When the same habitat types (forests, oceans, grasslands, etc.) in regions of different latitudes are compared, it becomes apparent that the overall number of species increases from pole to equator.

Topic

The increase in species diversity from poles to equator: why there are more species in the tropics than at higher latitudes.

Framework

Answer / Explain

Main Point

The passage explores several hypotheses to explain why there are more species near the equator than near the poles but favors the idea that higher speciation (and not higher extinction) in the tropics best explains this pattern. (Most valuable sentence: Last sentence of P5: )

P1: The Pattern—Latitudinal Diversity Gradient

Scientists have noticed that as you move from the poles toward the equator, the number of species in similar habitats increases, with the effect likely being even bigger than currently known.

P2: The Time Theory Hypothesis

One idea ("time theory") says tropical regions have more species simply because they've had more time without disruptive ice ages for new species to evolve, but this doesn't fully account for differences among various regions.

P3: The Species-Energy Hypothesis

Another hypothesis suggests that more sunlight in the tropics means higher growth and reproduction rates, which could lead to more biomass and thus more species, but the supposed chain of cause-and-effect has several weak links and is unproven.

19.

Which one of the following inferences about the biological characteristics of a temperate-zone grassland is most strongly supported by the passage?

  1. It has more different species

    Contradicted, if anything

    Because of the species latitudinal gradient, we know that temperate grassland has fewer species than tropical grassland. We don't really know how to compare temperate grassland to tropical forest.

    2% picked this

  2. Its climatic conditions have been

    Too Strong: severely interrupted

    We can only say that temperate zones have been affected by ice ages. The final sentence of the 2nd paragraph says that "ice ages have caused less disruption in some temperate regions than in others". So we can't just assume that any ol' temperate grassland had its climate severely interrupted by an ice age.

    23% picked this

  3. If it has a large

    Too Strong: if / then

    In the 3rd paragraph, the author says that "high biomass can exist with few species", so we can't say that "if it has high biomass, it has a large number of species".

    5% picked this

  4. Correct

    It has a larger regional

    Why this is right

    This goes off the first sentence of the passage. When you compare an arctic grassland to a temperate grassland to a tropical grassland, you'll keep seeing increasingly more species as you go towards the tropics and fewer species as you go towards the poles. Since an arctic grassland is closer to the poles and a temperate grassland is closer to the equator, the temperate grassland will have more species than the arctic grassland.

    Skill tested: Inference · how this choice captures the passage's function is the move to repeat next time.

    53% picked this

  5. If population groups become isolated

    Too Strong

    Too Strong: likely to adapt Relative vs. Absolute From the final two sentences of the passage, we could probably speculate that isolated species at the edge of a temperate grassland would be more likely to adapt to local conditions and speciate than would isolated species at the edge of an arctic grassland. But the last sentence isn't saying that any habitat is such that isolated species are likely to adapt. It's only saying that in the tropics, an isolated species would have a better chance, not necessarily a better-than-50% chance.

    17% picked this

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