Reading Comprehension

PT101 · S4 · P3 · Q20 Species Gradient

A free, expert breakdown of this official LSAT Reading Comprehension question.

  • Save & drill this skill — build targeted practice sets from questions like this one

  • Video walkthroughs — watch every question solved step by step

  • 81 official LSATs — as questions, timed sections & full-length tests

Start practicing free

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.

20.

With which one of the following statements concerning possible explanations for the latitudinal gradient in number of species would the author be most likely to agree?

  1. The time theory is the

    Too Strong: least plausible

    We know that the author thinks #4 is most plausible, but we wouldn't be able to rank how she feels about the plausibility of the other three.

    5% picked this

  2. Correct

    The rate-of-speciation hypothesis addresses a

    Why this is right

    This certainly sounds worth considering on a first pass, because it's saying "the rate-of-speciation hypothesis (i.e. author's favorite) addresses a principal objection to one of the other hypotheses (is better than one of the other ones)." What was the principal objection to the climatic-stability hypothesis? It's a tough one to understand, but the final two sentences of the 4th paragraph are saying - a stable climate can't explain the origin of the gradient Okay, does rate-of-speciation hypothesis explain the origin of the gradient? Yes, the second sentence of the 5th paragraph says, "According to this hypothesis .. if X happens and isn't negated by Y, then the latitudinal gradient would result, and become increasingly steep." The author's principal objection to climatic-stability is that it "cannot account for the origin of the latitudinal gradient", whereas the rate-of-speciation hypothesis could.

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

    51% picked this

  3. The major objection to the

    Bad Objection Match

    The objection to time theory was that it argued that "more stable climate" would explain why there are more species as you go closer to the Equator, but meanwhile the arctic climate is just as stable as the Tropics. Both of have been uninterrupted by ice ages (because the arctic is always covered by ice, and during an ice age, then ice sheet never gets as far south as the Tropics), so we should be seeing as many species at the arctic latitudes as we do at the tropical latitudes. This answer is saying that the author's objection was about undiscovered species? That's nowhere in the 2nd paragraph.

    8% picked this

  4. Despite the claims of the

    Too Strong: more likely

    The species-energy hypothesis does think that a higher rate of biological growth and reproduction would lead to more biomass. But the author isn't flipping that on its head and saying, "No, higher rates of growth and reproduction are actually usually going to be accompanied by low biomass". She's just saying that it's not a super solid connection. She points out that there can be exceptions to this rule; she doesn't say that the opposite of this rule is true.

    8% picked this

  5. An important advantage of the

    Unsupported: regional competition

    Nothing in the rate-of-speciation theory talks about regional competition. The idea of competition for resources was from the 3rd theory. The rate-of-speciation does actually deal with local subgroups. It says that when you have a species spread out weirdly over a large area, the local members who live on the fringe may end up forming an isolated group that stops interacting with other members of the species. Over time, that isolated local group adapts to local conditions. Soon enough, it can no longer interbreed with the original species and so now, voila, we have a new species.

    28% picked this

Continue the review in LSAT Lab

Save this question, watch the video walkthrough, and drill similar questions in your LSAT Lab account.

Save and practice this skill
LSAT Lab

Turn this review into a targeted study plan.

Save this question, drill more like it, watch the video walkthrough, and track your progress in your LSAT Lab account.

Start practicing free