Reading Comprehension

PT101 · S4 · P3 · Q17 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.

17.

As presented in the passage, the principles of the time theory most strongly support which one of the following predictions?

Correct
In the absence of additional
Why this is right
This answer is essentially using "Flip the Causal Difference-Maker" logic. Time Theory thinks that the reason high latitudes have fewer species is that they have been affected by a succession of ice ages (which change the local climatic conditions, which probably causes some local species to go extinct). So, by "flip the causal difference-maker" logic, "if those areas hadn't had all those ice ages disturbing their climate, then they would have had more species". That's all this answer is expressing. If the high latitudes stop having ice ages, they'll have the same climate for a longer amount of time, so more diverse species will be able to emerge there (just as they have in the undisturbed tropics).
Skill tested: Application · how this choice captures the passage's function is the move to repeat next time.
52% picked this
No future ice ages are
Too Strong: no future ice ages
This would be a bold prediction for anyone to make --- the Earth is all done with ice ages? Forever? The fact that Earth has had a succession of ice ages suggests that, if anything, ice ages are a cyclically occurring thing.
6% picked this
If no further ice ages
Unsupported: same climate
It's a pretty radical suggestion to think that climatic conditions in high latitudes would ever resemble those at tropical latitudes. Nothing in the "time theory" description suggests that ice ages have prevented high latitudes from having tropical climates, just that ice ages have prevented high latitudes from having stable climates. Because of the Earth's tilt, tropical latitudes will always receive much more direct sunlight than high latitudes; they'll always have less seasonal variation (high latitudes have nearly-always-dark winters and nearly-always-light summers); and thus they'll always have different climatic conditions from each other.
12% picked this
Researchers will continue to find
Unsupported: many more new species
There currently are many more species in the tropics than in the arctic and temperate zones, but is there any reason that "Time Theory" would have for thinking that researchers will continue to find many more new species in the tropics? Time Theory thinks, "The more time that a region stays with the same climate, the more species can develop". If higher latitudes are currently just as stable as tropical latitudes, then "time theory" would think that both latitudes are giving species a chance to learn how to adapt to those climates. Time theory is essentially saying that as an ecosystem stays in a certain climate, it gives species more time to emerge. Ice ages are disruptions to that climate, which end up killing off a bunch of species who aren't adapted to the ice age climate. For the undisturbed tropics, they just keep adding species. For the latitudes that get affected by ice ages, they add species but then lose some when the climate changes: 3 steps forward, 2 steps back. If we are in the present day and we have counted up all the species in each latitude, and if we aren't living through some ice age where the higher latitudes are having their climatic conditions affected, then all latitudes would be adding species at about the same rate. Thus, "time theory" would have no reason to think that the tropics are adding new species faster than the higher latitudes. "Time theory" isn't saying that the tropics add new species faster. It's saying that they only add species. They don't end up losing species to the turbulence of an ice age. This answer is sort of the opposite of (A). If there's no climate instability, then all climates will have new species adapting to them at roughly the same rate.
22% picked this
Future ice ages are likely
Inapplicable
Even though this answer is incredibly likely in a real world common sense way, it's not really an answer to the question stem. "Time Theory" doesn't make any prediction about if / when future ice ages will occur. It only makes predictions about what affect future ice ages would have on the species gradient.
8% picked this

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