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The old belief that climatic stability accounts for the high level of

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The old belief that climatic stability accounts for the high level of  [#permalink]

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New post Updated on: 21 Apr 2019, 17:52
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New Project RC Butler 2019 - Practice 2 RC Passages Everyday
Passage # 153, Date : 18-APR-2019
This post is a part of New Project RC Butler 2019. Click here for Details


The old belief that climatic stability accounts for the high level of species diversity in the Amazon River basin of South America emerged, strangely enough, from observations of the deep sea. Sanders discovered high diversity among the mud-dwelling animals of the deep ocean. He argued that such diversity could be attributed to the absence of significant fluctuations in climate and physical conditions, without which the extinction of species should be rare. In the course of time new species would continue to evolve, and so the rate of speciation would be greater than the rate of extinction, resulting in the accumulation of great diversity. Sanders argued that the Amazon tropical rain forest is analogous to the deep sea: because the rain forest has a stable climate, extinction should be rare. Evidence that some species of rain-forest trees have persisted for some 30 million years in the Amazon basin, added to the absence of winter and glaciation, supports this view.

Recently however, several observations have cast doubt on the validity of the stability hypothesis and suggest that the climate of the Amazon basin has fluctuated significantly in the past. Haffer noted that different species of birds inhabit different corners of the basin in spite of the fact that essentially unbroken green forest spreads from the western edge to the eastern edge of the region. This pattern presented a puzzle to biologists studying the distributions of plants and animals: why would different species inhabit different parts of the forest if the habitat in which they lived had a stable climate?

Haffer proposed a compelling explanation for the distribution of species. Observing that species found on high ground are different from those on low ground and knowing that in the Amazon lowlands are drier than uplands, he proposed that during the ice ages the Amazon lowlands became a near-desert arid plain; meanwhile, the more elevated regions became islands of moisture and hence served as refuges for the fauna and flora of the rain forest. Populations that were once continuous diverged and became permanently separated. Haffer’s hypothesis appears to explain the distribution of species as well as the unusual species diversity. The ice-age refuges would have protected existing species from extinction. But the periodic geographic isolation of related populations (there have been an estimated 13 ice ages to date) would have facilitated the development of new species as existing species on the lowlands adapted to changing climates.

Although no conclusive proof has yet been found to support Haffer’s hypothesis, it has led other researchers to gauge the effects of climatic changes, such as storms and flooding, on species diversity in the Amazon basin. Their research suggests that climatic disturbances help account for the splendid diversity of the Amazon rain forest.

1. As discussed in the first paragraph of the passage, Sanders’ analogy between the deep sea and the Amazon basin involves which one of the following assumptions?

(A) Both the Amazon basin and the deep sea support an unusually high rate of speciation.
(B) Both the rain-forest trees in the Amazon basin and the mud-dwelling animals in the deep sea have survived for 30 million years.
(C) Both the deep sea and the Amazon basin have not experienced dramatic changes in climate or physical conditions.
(D) A dependable supply of water to the Amazon basin and the deep sea has moderated the rate of extinction in both habitats.
(E) The rate of speciation in the Amazon basin is equivalent to the rate of speciation in the deep sea.



2. The author of the passage would most likely agree with which one of the following statements about Haffer’s hypothesis?

(A) It provides an intriguing and complete explanation for the high rate of species diversity in the Amazon basin.
(B) It is partially correct in that a number of climatic disturbances account for species diversity in the Amazon basin.
(C) It has not yet been verified, but it has had an influential effect on current research on species diversity in the Amazon basin.
(D) It is better than Sanders’ theory in accounting for the low rate of species extinction in the Amazon basin.
(E) It provides a compelling explanation for the distribution of species in the Amazon basin but does not account for the high species diversity.



3. According to the passage, lowlands in the Amazon basin currently differ from uplands in which one of the following respects?

(A) Lowlands are desertlike, whereas uplands are lush.
(B) Lowlands are less vulnerable to glaciation during the ice ages than are uplands.
(C) Uplands support a greater diversity of species than do lowlands.
(D) Uplands are wetter than are lowlands.
(E) Uplands are more densely populated than are lowlands.



4. Which one of the following best describes the organization of the passage?

(A) A hypothesis is discussed, evidence that undercuts that hypothesis is presented and a new hypothesis that may account for the evidence is described.
(B) A recently observed phenomenon is described, an explanation for that phenomenon is discussed, and the explanation is evaluated in light of previous research findings.
(C) Several hypotheses that may account for a puzzling phenomenon are described and discounted, and a more promising hypothesis is presented.
(D) A hypothesis and the assumptions on which it is based are described, and evidence is provided to suggest that the hypothesis is only partially correct.
(E) Two alternative explanations for a phenomenon are presented and compared, and experiments designed to test each theory are described.



5. The author of the passage mentions the number of ice ages in the third paragraph most probably in order to

(A) provide proof that cooler and drier temperatures are primarily responsible for the distribution of species in the Amazon
(B) explain how populations of species were protected from extinction in the Amazon basin
(C) explain how most existing species were able to survive periodic climatic disturbances in the Amazon basin
(D) suggest that certain kinds of climatic disturbances cause more species diversity than do other kinds of climatic disturbances
(E) suggest that geographic isolation may have occurred often enough to cause high species diversity in the Amazon basin



6. The passage suggests that which one of the following is true of Sanders’ hypothesis?

(A) He underestimated the effects of winter and glaciation in the Amazon basin on the tropical rain forest.
(B) He failed to recognize the similarity in physical conditions of the Amazon lowlands and the Amazon uplands.
(C) He failed to take into a count the relatively high rate of extinction during the ice ages in the Amazon basin.
(D) He overestimated the length of time that species have survived in the Amazon basin.
(E) He failed to account for the distribution of species in the Amazon basin.




7. Which one of the following is evidence that would contribute to the “proof” (Highlighted) in the passage?

(A) Accurately dated sediment cores from a freshwater lake in the Amazon indicate that the lake’s water level rose significantly during the last ice age.
(B) Data based on radiocarbon dating of fossils suggest that the Amazon uplands were too cold to support rain forests during the last ice age.
(C) Computer models of climate during global ice ages predict only insignificant reductions of monsoon rains in tropical areas such as the Amazon.
(D) Fossils preserved in the Amazon uplands during the last ice age are found together with minerals that are the products of an arid landscape.
(E) Fossilized pollen from the Amazon lowlands indicates that during the last ice age the Amazon lowlands supported vegetation that needs little water rather than the rain forests they support today.



  • Source: LSAT Official PrepTest 11 (June 1994)
  • Difficulty Level: 650

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Originally posted by nitya34 on 05 Mar 2009, 10:29.
Last edited by SajjadAhmad on 21 Apr 2019, 17:52, edited 5 times in total.
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Re: The old belief that climatic stability accounts for the high level of  [#permalink]

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Re: The old belief that climatic stability accounts for the high level of  [#permalink]

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New post 19 Apr 2019, 07:21
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1. As discussed in the first paragraph of the passage, Sanders’ analogy between the deep sea and the Amazon basin involves which one of the following assumptions? we are looking for the similar line "because the rain forest has a stable climate"

(A) Both the Amazon basin and the deep sea support an unusually high rate of speciation - out of scope
(B) Both the rain-forest trees in the Amazon basin and the mud-dwelling animals in the deep sea have survived for 30 million years. - this is not the assumption. it is the proof. Out of scope
(C) Both the deep sea and the Amazon basin have not experienced dramatic changes in climate or physical conditions. - similar to our prediction
(D) A dependable supply of water to the Amazon basin and the deep sea has moderated the rate of extinction in both habitats. - out of scope
(E) The rate of speciation in the Amazon basin is equivalent to the rate of speciation in the deep sea. - out of scope

2. The author of the passage would most likely agree with which one of the following statements about Haffer’s hypothesis?

(A) It provides an intriguing and complete explanation for the high rate of species diversity in the Amazon basin. - Inconsistent
(B) It is partially correct in that a number of climatic disturbances account for species diversity in the Amazon basin. - author did not said that it is correct. Inconsistent
(C) It has not yet been verified, but it has had an influential effect on current research on species diversity in the Amazon basin. - as explained in last para
(D) It is better than Sanders’ theory in accounting for the low rate of species extinction in the Amazon basin. - no comparison is done - Inconsistent
(E) It provides a compelling explanation for the distribution of species in the Amazon basin but does not account for the high species diversity. - author writes about the compelling explanation. He is not agreeing to it which is asked in the question. Hence Inconsistent.

3. According to the passage, lowlands in the Amazon basin currently differ from uplands in which one of the following respects?

(A) Lowlands are desertlike, whereas uplands are lush. - Inconsistent
(B) Lowlands are less vulnerable to glaciation during the ice ages than are uplands. - Inconsistent
(C) Uplands support a greater diversity of species than do lowlands. - out of scope
(D) Uplands are wetter than are lowlands. - this is stated in the passage.
(E) Uplands are more densely populated than are lowlands. - out of scope

4. Which one of the following best describes the organization of the passage?

(A) A hypothesis is discussed, evidence that undercuts that hypothesis is presented and a new hypothesis that may account for the evidence is described. - this is the main idea and organization of the passage.
(B) A recently observed phenomenon is described, an explanation for that phenomenon is discussed, and the explanation is evaluated in light of previous research findings. - Inconsistent
(C) Several hypotheses that may account for a puzzling phenomenon are described and discounted, and a more promising hypothesis is presented. - Inconsistent
(D) A hypothesis and the assumptions on which it is based are described, and evidence is provided to suggest that the hypothesis is only partially correct. - Inconsistent
(E) Two alternative explanations for a phenomenon are presented and compared, and experiments designed to test each theory are described. - out of scope

5. The author of the passage mentions the number of ice ages in the third paragraph most probably in order to - we are looking for the similar line "But the periodic geographic isolation of related populations (there have been an estimated 13 ice ages to date) would have facilitated the development of new species as existing species on the lowlands adapted to changing climates."

(A) provide proof that cooler and drier temperatures are primarily responsible for the distribution of species in the Amazon - Inconsistent
(B) explain how populations of species were protected from extinction in the Amazon basin - out of scope
(C) explain how most existing species were able to survive periodic climatic disturbances in the Amazon basin - out of scope
(D) suggest that certain kinds of climatic disturbances cause more species diversity than do other kinds of climatic disturbances - out of scope
(E) suggest that geographic isolation may have occurred often enough to cause high species diversity in the Amazon basin - similar to what we are looking for.

6. The passage suggests that which one of the following is true of Sanders’ hypothesis?

(A) He underestimated the effects of winter and glaciation in the Amazon basin on the tropical rain forest. - out of scope
(B) He failed to recognize the similarity in physical conditions of the Amazon lowlands and the Amazon uplands. - out of scope
(C) He failed to take into a count the relatively high rate of extinction during the ice ages in the Amazon basin. - out of scope
(D) He overestimated the length of time that species have survived in the Amazon basin. - out of scope
(E) He failed to account for the distribution of species in the Amazon basin. - as stated in the 2nd para

7. Which one of the following is evidence that would contribute to the “proof” (Highlighted) in the passage? We are basically looking for the answer choice which provides the evidence for the distribution of species hypothesis by Haffer to be valid

(A) Accurately dated sediment cores from a freshwater lake in the Amazon indicate that the lake’s water level rose significantly during the last ice age. - Inconsistent. rise in water level does not account as a evidence for distribution of species
(B) Data based on radiocarbon dating of fossils suggest that the Amazon uplands were too cold to support rain forests during the last ice age. - same as above
(C) Computer models of climate during global ice ages predict only insignificant reductions of monsoon rains in tropical areas such as the Amazon. - out of scope
(D) Fossils preserved in the Amazon uplands during the last ice age are found together with minerals that are the products of an arid landscape. - opposite
(E) Fossilized pollen from the Amazon lowlands indicates that during the last ice age the Amazon lowlands supported vegetation that needs little water rather than the rain forests they support today. - this line can be the evidence or proof for the hypothesis to hold valid
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Re: The old belief that climatic stability accounts for the high level of  [#permalink]

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New post 24 Apr 2019, 05:11
1
All correct in 11 mins 40 seconds, including 3 mins 30 seconds to read.

Para 1- climatic stability leads to high level of species diversity, Sanders compares Amazon to deep sea
Para 2- doubts on the stability hypothesis, Haffer - distributions of plants and animals
Para 3- Haffer's explanation- lowland and upland
Para 4- no conclusive proof but researchers are exploring and concur

1. As discussed in the first paragraph of the passage, Sanders’ analogy between the deep sea and the Amazon basin involves which one of the following assumptions?
(C) Both the deep sea and the Amazon basin have not experienced dramatic changes in climate or physical conditions.

Sanders argued that the Amazon tropical rain forest is analogous to the deep sea: because the rain forest has a stable climate, extinction should be rare

2. The author of the passage would most likely agree with which one of the following statements about Haffer’s hypothesis?
(C) It has not yet been verified, but it has had an influential effect on current research on species diversity in the Amazon basin

Although no conclusive proof has yet been found to support Haffer’s hypothesis, it has led other researchers to gauge the effects of climatic changes, such as storms and flooding, on species diversity in the Amazon basin

3. According to the passage, lowlands in the Amazon basin currently differ from uplands in which one of the following respects?
(D) Uplands are wetter than are lowlands.

Amazon lowlands are drier than uplands

4. Which one of the following best describes the organization of the passage?
(A) A hypothesis is discussed, evidence that undercuts that hypothesis is presented and a new hypothesis that may account for the evidence is described.

5. The author of the passage mentions the number of ice ages in the third paragraph most probably in order to
(E) suggest that geographic isolation may have occurred often enough to cause high species diversity in the Amazon basin

the more elevated regions became islands of moisture and hence served as refuges for the fauna and flora of the rain forest. Populations that were once continuous diverged and became permanently separated. Haffer’s hypothesis appears to explain the distribution of species as well as the unusual species diversity. The ice-age refuges would have protected existing species from extinction. But the periodic geographic isolation of related populations (there have been an estimated 13 ice ages to date) would have facilitated the development of new species as existing species on the lowlands adapted to changing climates.


6. The passage suggests that which one of the following is true of Sanders’ hypothesis?
(E) He failed to account for the distribution of species in the Amazon basin.

Haffer noted that different species of birds inhabit different corners of the basin in spite of the fact that essentially unbroken green forest spreads from the western edge to the eastern edge of the region.

7. Which one of the following is evidence that would contribute to the “proof” (Highlighted) in the passage?
(E) Fossilized pollen from the Amazon lowlands indicates that during the last ice age the Amazon lowlands supported vegetation that needs little water rather than the rain forests they support today.

he proposed that during the ice ages the Amazon lowlands became a near-desert arid plain; meanwhile, the more elevated regions became islands of moisture and hence served as refuges for the fauna and flora of the rain forest.
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Re: The old belief that climatic stability accounts for the high level of   [#permalink] 24 Apr 2019, 05:11
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