PrepTest 101 - Section 4 - Passage 3 - Question 17

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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. ████ ███████████ ████████ ██ ████████ ████ ████ ██████████ ████ ███████ ███████ █████████ █████ ███████████ ███████ ████ ████ ████████████ ███████ ████ ██ ███ ████████

Phenomenon · Latitudinal biodiversity gradient

The phenomenon is that around the poles, there aren't that many species and as we move closer to the equator, i.e., as we move along the latitude or the different width bands of the earth towards the equator, we find more and more species.

Hypothesis 1 · Time theory

The tropics (closer to equator) had more time for species to emerge uninterrupted by ice ages.

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Challenge to Hypothesis 1 · But arctics are also uninterrupted by ice ages

And not all temperate regions have been disrupted equally, yet they all tend to have fewer species than the tropics.

Hypothesis 2 · Species-energy

Equator (and tropics) gets more solar energy which leads to higher reproduction rates which leads to higher biomass which leads to more speciation.

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Challenge to Hypothesis 2 · But these conditions aren't necessarily connected

High reproduction doesn't have to lead to high biomass if individuals have short life spans. High biomass doesn't have to lead to more speciation.

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Challenge to Hypothesis 2 · Untested mechanism

The causal chain is speculative.

Hypothesis 3 · Climatic stability in tropics

Climatic stability means reliable supply of resources which means more species can tolerate overlap in their niches.

Challenge to Hypothesis 3 · Local ecology doesn't explain the latitudinal gradient

Hypothesis 4 · Regional speciation

Hypothesis is that speciation rates are higher towards the tropics and not negated by extinction rates. Hence, there's a net increase over time in the number of species. Author thinks this hypothesis is the "most plausible."

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Mechanism for Hypothesis 4 · Isolation of population subgroups

New species form when isolated subgroups evolve separately. Subgroups in tropics more likely to survive and adapt into new species than in arctic.

Passage Style

Critique or debate

Phenomenon-hypothesis (RC)

17.

As presented in the passage, ███ ██████████ ██ ███ ████ ██████ ████ ████████ ███████ █████ ███ ██ ███ █████████ ████████████

In the absence ██ ██████████ ███ █████ ███ ██████ ██ ███████ ██ ████ █████████ █████ ██████████ ████████ ██████████████

Supported, because if the arctic area were subject to fewer ice ages, then there should be more time for new species to emerge, just as there was in the tropics (according to time theory).

43%

No future ice ████ ███ ██████ ██ ██████ ███ ████████ ██████████ ████ █████████ ████████████ █████████ ████████

No support for the idea that time theory predicts no future ice ages.

10%

If no further ███ ████ ██████ ████████ ██████████ ██ ████ █████████ █████ ██████████ ████████ █████ ██ ███████ ████████ ██████████

Not supported, because even if no further ice ages occur, time theory would predict only that there would be more time for species at all latitudes to emerge. But this doesn’t imply a belief about “climatic conditions” generally, such as temperature, amount of rain, wind, etc.

16%

Researchers will continue ██ ████ ████ ████ ███ ███████ ██ ███ ███████ ████ ██ ███ ██████ ███ █████████ ██████

Not supported, because time theory doesn’t hold that ice ages are continuing to disrupt the arctic and temperate areas. Ice ages happened in the past, and time theory believes they help explain the current diversity or lack of diversity of species. But whether ice ages will happen in the future is unknown, so we don’t know whether there will continue to be more new species discovered in the tropic compared to higher latitudes.

24%

Future ice ages ███ ██████ ██ █████████ ███ ████████ ██████████ ████ ███ ████████████ █████████████ ████████

No support for the prediction about future ice ages. Time theory doesn’t hold that ice ages are continuing to disrupt the arctic and temperate areas. Ice ages happened in the past, and time theory believes they help explain the current diversity or lack of diversity of species. But whether ice ages will happen in the future is unknown,

PrepTest 101 - Section 4 - Passage 3 - Question 17

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