PT101.S4.P3.Q16 > Analytics

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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)

16.

Which one of the following ██████████ ██ ████ ██████████ ████ ███ ██████████████ ██████████ ██ █████████ ██ ███ ████████

The many plants ██ █ █████ ████████████ █████ █████████ █ ███████ █████ ██ ████████

This isn’t consistent with the species-energy hypothesis, because it involves lots of biomass (many plants) but only a limited range of species. The hypothesis thinks lots of biomass should be correlated with lots of species.

An animal species ███████████ █ █████ ████ ██████ ██ █████ ██ ███ ████ ██ ██████ ███ █████████████

This isn’t the most consistent, because this point is brought up as the author’s criticism of the species-energy hypothesis.

21%

Within the small ██████ ██ ██████ █████████ ██ █ ██████ ████████ ████ █████████ ███████ ███ ████████████

This isn’t consistent with the species-energy hypothesis, because it involves low biomass (small number of organisms) but lots of species. The hypothesis thinks low biomass should be correlated with fewer species.

In a tropical ████ ███████ █ ███████ ████ █ █████ ██████████ ██ █████ ██ ███████ █████████ ██ █████ ███████████

This isn’t consistent, because the species-energy hypothesis believes greater energy should lower the probability of local extinction. But (D) involves a large population that exhibits local extinction.

In an arctic ███████ ███ ██████ ███ ███████ ███████ █ ████ ████ ██ ██████ ███ █████████████

Consistent, because the species-energy hypothesis tries to explain the fewer number of species in the arctic by citing to the rate of growth and reproduction. According to the theory, lower rates of growth and reproduction should be correlated with fewer species.

60%

PrepTest 101 - Section 4 - Passage 3 - Question 16

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