PrepTest 101

[lcid:3503] Prep Test 101 LSAT — Reading Comp — S4 Reading comp

Passage

Questions 15-20  .        When the same habitat types (forests, oceans,  . grasslands, etc.) in regions of different latitudes are Remaining source text redacted.
Passage walkthrough
Passage Summary

Topic: Science


Paragraph 1

  • Paragraph note
    • "Latitudinal gradient" phenomenon (more species near the equator than poles)
  • Views, minor Meta-Structures, and the author's attitude
    • Comparison:
      • When you compare a habitat type that stretches out from the north to the south, there are more species near the equator than far from the equator (first sentence)
    • Author's attitude: "probably even more pronounced" (last sentence)

Paragraph 2

  • Paragraph note
    • "Time theory" hypothesis and author's rebuttal
  • Views, minor Meta-Structures, and the author's attitude
    • Cause-and-effect relationship, according to the "time theory" hypothesis:
      • Latitudinal gradient exists because tropics haven't been interrupted by ice ages and therefore have more time to develop species (first sentence)
    • Comparison, according to the "time theory" hypothesis:
      • Tropic zones have not been affected by ice ages, while temperate and arctic zones have (first sentence)
    • Author's view:
      • The "time theory" hypothesis isn't consistent with the evidence, as arctic conditions haven't actually been interrupted by ice ages, and there is a varying range of interruption in temperate areas (last sentence)
    • Author's attitude: "However" (last sentence)

Paragraph 3

  • Paragraph note
    • Species-energy hypothesis and author's rebuttal
  • Views, minor Meta-Structures, and the author's attitude
    • Cause-and-effect relationship, according to the species-energy hypothesis:
      • Latitudinal gradient exists because tropics have more energy from the sun, which causes high biomass and lower rates of extinction (first and last sentences)
    • Author's view:
      • The causal mechanism between biomass and increased local populations remains untested, and biomass and the number of species are not necessarily correlated (second through last sentences)
    • Author's attitude: "However" (second sentence); "remains untested" (last sentence)

Paragraph 4

  • Paragraph note
    • Climatic-stability hypothesis and author's rebuttal
  • Views, minor Meta-Structures, and the author's attitude
    • Cause-and-effect relationship, according to the climatic-stability hypothesis:
      • The tropics' stable climate causes a reliable resource supply, which allows more species to coexist (first through third sentences)
    • Author's view
      • The climatic stability hypothesis describes a local process that cannot explain the regional differences along the latitudinal gradient (fourth and last sentences)
    • Example of a local process, according to the author:
      • Competition (last sentence)
    • Example of regional differences along the species gradient, according to the author:
      • Forests along the equator and forces at higher altitudes (last sentence)
    • Author's attitude: "However" (fourth sentence); "cannot account for" (fourth sentence)

Paragraph 5

  • Paragraph note
    • Rate-of-speciation hypothesis and author's endorsement
  • Views, minor Meta-Structures, and the author's attitude
    • Cause-and-effect relationship, according to the rate-of-speciation hypothesis:
      • Latitudinal gradient exists because, in the tropics, the rate of speciation (the development of new species) is higher, and the extinction rate of species is lower (last sentence)
    • Author's attitude: "most plausible hypothesis" (first sentence)

Paragraph 6

  • Paragraph note
    • How rate of speciation works
  • Views, minor Meta-Structures, and the author's attitude
    • Cause-and-effect relationship/comparisons, according to the rerate-of-speciation hypothesis:
      • Speciation occurs when subgroups become isolated and differentiate from the main population (first and second sentences)
      • Subgroups are more likely to survive in the tropics than in the arctic, causing a higher rate of speciation and a lower rate of extinction in the tropics (third and last sentences)

Main Point: The rate-of-speciation hypothesis is the best explanation for why there exists a latitudinal gradient in species distribution.

Key Lines?

Paragraph 1, Sentence 1 (P1, S1) - Description of phenomenon

P5, S1 - The author's preferred explanation

P6, S4 - How the preferred explanation actually works 

Meta-Structure?

Phenomenon/Explanation: This passage follows a Phenomenon/Explanation Meta-Structure. Passages that utilize this Meta-Structure follow a consistent pattern. First, the passage will describe an observable fact, behavior, or situation. Then, the author will present one or more explanations of that observable fact, behavior, or situation. That's exactly the model this passage follows. The author describes our phenomenon — the latitudinal gradient of species distribution — and then presents four hypotheses that could explain this phenomenon.

In this type of Meta-Structure, if the author says that one explanation is the best, then that's the main point of the passage. Here, the author prefers the last hypothesis, "rate of speciation." So the main point is that the rate-of-speciation hypothesis is the best explanation for why there exists a latitudinal gradient in species distribution. 

Lists: This most prominent minor Meta-Structure in this passage is a list. In fact, nearly the entire passage is dedicated to listing four separate hypotheses for the latitudinal gradient of species distribution. When the whole passage is organized around a list, we'll surely get at least a few questions about items on this list. This is why our notes must allow us to quickly determine which paragraph describes which hypothesis.

Causality: Like many science passages, cause and effect also figure heavily into this passage. Each hypothesis of the latitudinal gradient of species distribution proposes a causal mechanism to explain the phenomenon. For those of us who are less fluent in science than we'd like to be, it can help if we simplify the cause-and-effect relationships as much as possible. We've done so below for each hypothesis:

  • "Time theory": The lack of ice-age disturbance in the tropics is the cause, and more time for species to emerge in the tropics is the effect (P2, S1)
  • Species-energy: Greater energy from the sun is the cause, and more biomass, lower rates of extinction, and more species are the effects (P3, S2)
  • Climatic stability: The tropics' stable climate is the cause, and more resources and species are the effects (P4, S1-3)
  • Rate of speciation: The better chance of surviving in the tropics is the cause, and the lower rates of extinction and higher rates of survival in the tropics are the effects (P6, S4)

Last Thoughts?

The nice thing about this passage is that the middle paragraphs are formulaic. The second, third, and fourth paragraphs follow the same formula: the author describes a hypothesis and then dismisses the hypothesis with counterevidence. Even when the topics (like ecology and species distribution) are unfamiliar, noticing these patterns can help us follow the passage and decoct the structure.

Question prompt

Which one of the Remaining source text redacted.
Why the credited answer is right

Credited answer: E

The notes below walk through why it fits the stem and how to eliminate the rest.

Question Type

Science

Strategy Overview

Review the rate-of-speciation hypothesis, determine weaknesses in that claim to anticipate how to weaken it, and select the answer choice that makes the claim less convincing

Answer Anticipation

We'll approach Weaken questions in Reading Comprehension in a very similar manner as we would in Logical Reasoning. We can review the excerpt from the passage, just like we'd carefully read an argument in LR. We'll then interrogate the claim for any weaknesses, as the correct answer on both RC and LR will probably weaken the claim by exploiting a problem. Additionally, causation flaws are commonplace on Weaken questions in both RC and LR, so we should be especially mindful of those.Here, we're asked to weaken the rate-of-speciation hypothesis. So, what are the critical elements of the rate-of-speciation hypothesis? According to that hypothesis, new species emerge when subgroups become isolated, spread to new areas, and differentiate from the main population (P6, S1-2). The subgroups that spread to the tropics are more likely to survive than those that spread to the arctic, causing a higher speciation rate in the tropics (P6, S3).Are there any issues with this hypothesis? First, we should note that this is a causal claim. A subgroup spreading to the tropics causes the subgroup to have a better chance of survival, which causes the tropics' higher speciation rate. The most common way to weaken a causal claim on the LSAT is by undermining the correlation. In this case, the correct answer might show other instances in which a subgroup spreads to the tropics but has a lower chance of survival. This technique is often called "cause without the effect." Alternatively, the correct answer could show an effect produced without the supposed cause preceding it. That might involve species having a high chance of survival without spreading to the tropics. This technique is often called "effect without the cause." Either would undermine the correlation proposed by the rate-of-speciation hypothesis.That said, many things could feasibly weaken the rate-of-speciation hypothesis, so we should keep an open mind as we progress through the answer choices. We'll start by asking ourselves, "Does this weaken the hypothesis that a subgroup spreading to the tropics makes it more likely to survive?"

Answer choices

  1. A
    A remote subgroup of Remaining source text redacted.
    Why choice A is not credited

    (A) Does this weaken the hypothesis that a subgroup spreading to the tropics makes it more likely to survive?

    No. The rate-of-speciation hypothesis posits that subgroups will be unable to interbreed with the original population (P6, S2) — that's how speciation occurs! This is consistent with the rate-of-speciation hypothesis, so we should eliminate (A).

  2. B
    Investigation of a small Remaining source text redacted.
    Why choice B is not credited

    (B) Does this weaken the hypothesis that a subgroup spreading to the tropics makes it more likely to survive?

    No. This has little to do with subgroups or the likelihood of their survival, so experienced test-takers would table or eliminate this choice without reviewing the passage.

    If we took the time to assess this choice, we'd realize that it is about competition in local areas, which was a factor in the climatic stability hypothesis (P4, S2). The author says these local explanations cannot account for the origin of the species gradient (P4, S3). So, this answer choice is entirely irrelevant to the rate-of-speciation hypothesis.

  3. C
    A correlation between higher Remaining source text redacted.
    Why choice C is not credited

    (C) Does this weaken the hypothesis that a subgroup spreading to the tropics makes it more likely to survive?

    Not quite. Like (B), this doesn't bring up subgroups or their survival, so decisive test-takers would table or eliminate this choice without spending too much time thinking about (C).

    For others, (C) is a tempting choice because it seems to affirm the species-energy hypothesis. If a correlation between energy influx, larger populations, and lower probability of local extinction is definitively proven, it's easy to assume that the species-energy hypothesis is vindicated and the rate-of-speciation hypothesis is disproven.

    But that leap isn't justified for a few reasons. First, the author never said the species-energy and rate-of-speciation hypotheses are mutually exclusive. They could both be true. For instance, the species-energy hypothesis could explain why subgroups have a better chance of survival in the tropics, while the rate-of-speciation hypothesis explains how those subgroups emerge along the latitudinal gradient. Second, even if (C) is true, the species-energy hypothesis is not necessarily vindicated. As the author points out, even if energy influx and large populations are correlated, that doesn't necessarily mean there are more species (P4, S3). Therefore, even if (C) is true, we still might need the rate-of-speciation hypothesis to describe the high number of species in the tropics compared to the arctic.

  4. D
    Researchers find more undiscovered Remaining source text redacted.
    Why choice D is not credited

    (D) Does this weaken the hypothesis that a subgroup spreading to the tropics makes it more likely to survive?

    Not quite. Like (B) and (C), this doesn't bring up subgroups or their chances of surviving. Well-prepared test-takers would table or eliminate this without expending too much time or energy considering its merits.

    Still, many test-takers select this option, perhaps because they think it undermines the entire idea of the latitudinal gradient of species and thus undermines any theory that attempts to explain that phenomenon.

    That line of reasoning doesn't hold up, however. (D) only says that researchers find more species in the arctic than they thought they would. That doesn't mean the latitudinal gradient doesn't exist. Even with these extra species, there could still be far fewer species in the arctic than in the tropics. Moreover, even if the latitudinal gradient is less pronounced than previously thought, that wouldn't give us any reason to doubt the rate-of-speciation hypothesis. That explanation could still account for the (less severe) gradient.

  5. E
    Most of the isolated Remaining source text redacted.
    Why choice E matches the stem

    (E) Does this weaken the hypothesis that a subgroup spreading to the tropics makes it more likely to survive?

    Finally, yes. As we anticipated, this undermines the correlation between subgroups spreading to the tropics and those subgroups' higher chances of survival. This shows that subgroups have become isolated in a tropical zone, but they don't have a high survival rate. (This is an example of "cause without the effect.") In fact, they experience "rapid extinction." This undermines the rate-of-speciation hypothesis's argument that subgroups in the tropics are more likely to survive and become species. If the subgroups in the tropics die, they aren't going to turn into new species, and the whole idea of the differing rates of speciation between the tropics and the arctic begins to fall apart.

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