When the same habitat types (forests, oceans, grasslands, etc.) in reg

Question

New Project RC Butler 2019  -  Practice 2 RC Passages Everyday   
Passage # 288, Date : 24-Aug-2019
 This post is a part of New Project RC Butler 2019 .  Click here for Details

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. This
 (5)  latitudinal gradient is probably even more pronounced
than current records indicate, since researchers believe
that most undiscovered species live in the tropics.

One hypothesis to explain this phenomenon, the
“time theory,” holds that diverse species adapted to
 (10)  today’s climatic conditions have had more time to
emerge in the tropical regions, which, unlike the
temperate and arctic zones, have been unaffected by a
succession of ice ages. However, ice ages have caused
less disruption in some temperate regions than in others
 (15)  and have not interrupted arctic conditions.

Alternatively, the species-energy hypothesis
proposes the following positive correlations: incoming
energy from the Sun correlated with rates of growth
and reproduction; rates of growth and reproduction
 (20)  with the amount of living matter (biomass) at a given
moment; and the amount of biomass with number of
species. However, since organisms may die rapidly,
high production rates can exist with low biomass. And
high biomass can exist with few species. Moreover, the
 (25)  mechanism proposed—greater energy influx leading to
bigger populations, thereby lowering the probability of
local extinction—remains untested.

A third hypothesis centers on the tropics’ climatic
stability, which provides a more reliable supply of
 (30)  resources. Species can thus survive even with few
types of food, and competing species can tolerate
greater overlap between their respective niches. Both
capabilities enable more species to exist on the same
resources. However, the ecology of local communities
 (35)  cannot account for the origin of the latitudinal
gradient. Localized ecological processes such as competition
do not generate regional pools of species, and it is the total
number of species available regionally for colonizing
any particular area that makes the difference between
 (40)  for example, a forest at the equator and one at 
a higher latitude.

A fourth and most plausible hypothesis focuses on
regional speciation, and in particular on rates of
speciation and extinction. According to this hypothesis,
 (45)  if speciation rates become higher toward the tropics,
and are not negated by extinction rates, then the
latitudinal gradient would result—and become
increasingly steep.

The mechanism for this rate-of-speciation
 (50)  hypothesis is that most new animal species, and
perhaps plant species, arise because a population
subgroup becomes isolated. This subgroup evolves
differently and eventually cannot interbreed with
members of the original population. The uneven spread
 (55)  of a species over a large geographic area promotes
this mechanism: at the edges, small populations spread out
and form isolated groups. Since subgroups in an arctic
environment are more likely to face extinction than
those in the tropics, the latter are more likely to survive
 (60)  long enough to adapt to local conditions 
and ultimately become new species.   1 
 C 
 1. Which one of the following most accurately expresses the main idea of the passage?

(A) At present, no single hypothesis explaining the latitudinal gradient in numbers of species is more widely accepted than any other.
(B) The tropical climate is more conducive to promoting species diversity than are arctic or temperate climates.
(C) Several explanations have been suggested for global patterns in species distribution, but a hypothesis involving rates of speciation seems most promising.
(D) Despite their differences, the various hypotheses regarding a latitudinal gradient in species diversity concur in predicting that the gradient can be expected to increase.
(E) In distinguishing among the current hypotheses for distribution of species, the most important criterion is whether a hypothesis proposes a mechanism that can be tested and validated.

2 
 E 
 2. Which one of the following situations is most consistent with the species-energy hypothesis as described in the passage?

(A) The many plants in a large agricultural tract represent a limited range of species.
(B) An animal species experiences a death rate almost as rapid as its rate of growth and reproduction.
(C) Within the small number of living organisms in a desert habitat, many different species are represented.
(D) In a tropical rain forest, a species with a large population is found to exhibit instances of local extinction.
(E) In an arctic tundra, the plants and animals exhibit a slow rate of growth and reproduction.

3 
 A 
 3. As presented in the passage, the principles of the time theory most strongly support which one of the following predictions?

(A) In the absence of additional ice ages, the number of species at high latitudes could eventually increase significantly.
(B) No future ice ages are likely to change the climatic conditions that currently characterize temperate regions.
(C) If no further ice ages occur, climatic conditions at high latitudes might eventually resemble those at today’s tropical latitudes.
(D) Researchers will continue to find many more new species in the tropics than in the arctic and temperate zones.
(E) Future ice ages are likely to interrupt the climatic conditions that now characterize high-latitude regions.

4 
 E 
 4. Which one of the following, if true, most clearly weakens the rate-of-speciation hypothesis as it is described in the passage?

(A) A remote subgroup of a tropical species is reunited with the original population and proves unable to interbreed with members of this original population.
(B) Investigation of a small area of a tropical rain forest reveals that many competing species are able to coexist on the same range of resources.
(C) A correlation between higher energy influx, larger populations, and lower probability of local extinction is definitively established.
(D) Researchers find more undiscovered species during an investigation of an arctic region than they had anticipated.
(E) Most of the isolated subgroups of mammalian life within a tropical zone are found to experience rapid extinction.

5 
 D 
 5. Which one of the following inferences about the biological characteristics of a temperate-zone grassland is most strongly supported by the passage?

(A) It has more different species than does a tropical-zone forest.
(B) Its climatic conditions have been severely interrupted in the past by a succession of ice ages.
(C) If it has a large amount of biomass, it also has a large number of different species.
(D) It has a larger regional pool of species than does an arctic grassland.
(E) If population groups become isolated at its edges, they are likely to adapt to local conditions and become new species.

6 
 B 
 6. With which one of the following statements concerning possible explanations for the latitudinal gradient in number of species would the author be most likely to agree?

(A) The time theory is the least plausible of proposed hypotheses, since it does not correctly assess the impact of ice ages upon tropical conditions.
(B) The rate-of-speciation hypothesis addresses a principal objection to the climatic-stability hypothesis.
(C) The major objection to the time theory is that it does not accurately reflect the degree to which the latitudinal gradient exists, especially when undiscovered species are taken into account.
(D) Despite the claims of the species-energy hypothesis, a high rate of biological growth and reproduction is more likely to exist with low biomass than with high biomass.
(E) An important advantage of the rate-of-speciation theory is that it considers species competition in a regional rather than local context.

Source:   LSAT Official PrepTest 19   ( June 1996 ) 
 Difficulty Level:   700

unraveled · Accepted Answer

Para 1 Summary – Author introduces a phenomenon and why researchers believe in latitude gradient so.

Para 2 Summary – In this para author refers to one ‘time theory’ to explain and mentions a paradox.

Para 3 Summary – Another approach is presented with positive correlations but untested ones.

Para 4 Summary – A third theory explain climatic stability as a factor to explain the phenomenon.

Para 5 Summary – Author opines that the fourth hypothesis is the most credible.

Para 6 Summary – Finally author presents the details of the fourth hypothesis and gives reasons why it is so.

Summary – Author introduces a phenomenon and provides our different hypothesis with one being most credible.

1. Which one of the following most accurately expresses the main idea of the passage?

(A) At present, no single hypothesis explaining the latitudinal gradient in numbers of species is more widely accepted than any other. – WRONG. It goes to extreme in saying that no hypothesis is accepted though passage mentions one is most acceptable looking.
(B) The tropical climate is more conducive to promoting species diversity than are arctic or temperate climates. – WRONG. Limited scope. Only one paragraph covers the scope mentioned.
(C) Several explanations have been suggested for global patterns in species distribution, but a hypothesis involving rates of speciation seems most promising. –  CORRECT. Out of all theories presented one is most suitable. 
(D) Despite their differences, the various hypotheses regarding a latitudinal gradient in species diversity concur in predicting that the gradient can be expected to increase.- WRONG. Similar problem as that o option B. Limited scope.
(E) In distinguishing among the current hypotheses for distribution of species, the most important criterion is whether a hypothesis proposes a mechanism that can be tested and validated. – WRONG. Irrelevant. Nowhere such claim mentioned by author.

2. Which one of the following situations is most consistent with the species-energy hypothesis as described in the passage? 
Answering the question requires a proper understanding of that part of passage. 
(A) The many plants in a large agricultural tract represent a limited range of species. – WRONG. Species energy and range correlation is not discussed anywhere n the passage.
(B) An animal species experiences a death rate almost as rapid as its rate of growth and reproduction. – WRONG. Death rate is not discussed in the passage. Though the option is close.
(C) Within the small number of living organisms in a desert habitat, many different species are represented. – WRONG. Similar to option A this one suffers from drawing incorrect correlation. 
(D) In a tropical rain forest, a species with a large population is found to exhibit instances of local extinction. – WRONG. It goes opposite to what one of the theories in the passage claims.
(E) In an arctic tundra, the plants and animals exhibit a slow rate of growth and reproduction. –  CORRECT. Initially, though got stuck between this option and B but as reasoned in B eliminated it and chose E. Also here only growth and reproduction is discussed i.e. within scope.

3. As presented in the passage, the principles of the time theory most strongly support which one of the following predictions? 
 This is a must be true/inference type of question. Though got it WRONG in timed situation and marked D after POE.  
(A) In the absence of additional ice ages, the number of species at high latitudes could eventually increase significantly. – CORRECT. Ice ages have affected arctic a lot and hence less number of species. On the other side, had this not been the case i.e. had ice ages not affected the arctic region it would have had high number of species.
(B) No future ice ages are likely to change the climatic conditions that currently characterize temperate regions. – WRONG. ‘Time theory’ concerns species not climatic conditions only since species adapt to them.
(C) If no further ice ages occur, climatic conditions at high latitudes might eventually resemble those at today’s tropical latitudes. WRONG. Again same issues as that o option ‘B’.
(D) Researchers will continue to find many more new species in the tropics than in the arctic and temperate zones. –  WRONG. Marked this option correct with an understanding that since species have more time to adapt in tropics than arctic and temperate zones, researchers would find many species, but that’s not the case here. Instead the option goes a little more out of scope when it says that ‘many more species’ would be found. How many is not mentioned in this theory.  
(E) Future ice ages are likely to interrupt the climatic conditions that now characterize high-latitude regions. – WRONG. It may be true but what about species. It does not talk about them.

4. Which one of the following, if true, most clearly weakens the rate-of-speciation hypothesis as it is described in the passage? 
A clear understanding of paragraphs 5 and 6 can help find the answer here.
(A) A remote subgroup of a tropical species is reunited with the original population and proves unable to interbreed with members of this original population. – WRONG. It strengthens the rate-of-speciation hypothesis by claiming similar results as mentioned in the theory.
(B) Investigation of a small area of a tropical rain forest reveals that many competing species are able to coexist on the same range of resources. – WRONG. Neither weakens nor strengthens the rate-of-speciation hypothesis. Rate-of-speciation hypothesis does not mentioned competing species.
(C) A correlation between higher energy influx, larger populations, and lower probability of local extinction is definitively established. – WRONG. Larger population and energy nlux s part of species – energy theory.
(D) Researchers find more undiscovered species during an investigation of an arctic region than they had anticipated. – WRONG. This is close to the answer but undiscovered species are not new species. 
(E) Most of the isolated subgroups of mammalian life within a tropical zone are found to experience rapid extinction. –  CORRECT. Rapid extinction in tropics is exactly opposite to the rate-of-speciation hypothesis’s claim hence correct.

5. Which one of the following inferences about the biological characteristics of a temperate-zone grassland is most strongly supported by the passage? 
 Marked B which is WRONG after POE between ‘B’ and ‘D’. Again a proper understanding of passage would help to answer the question.  
(A) It has more different species than does a tropical-zone forest. – WRONG. Tropical zone forest would have most different species. Refer paragraph 4 which states that tropic climate’s stability is the reason behind coexistence of various species.
(B) Its climatic conditions have been severely interrupted in the past by a succession of ice ages. –  WRONG. ‘Severely’ is opposite to ‘less’ as mentioned in Para 2 – Time theory. 
(C) If it has a large amount of biomass, it also has a large number of different species. – WRONG. Though it refers to untested mechanism(refer para 3), it draws a negative correlation.
(D) It has a larger regional pool of species than does an arctic grassland. – CORRECT. Since arctic would have least latitude gradient and tropics the most, temperate would have better than arctic, thus larger regional pool. In timed situation however, eliminated it.
(E) If population groups become isolated at its edges, they are likely to adapt to local conditions and become new species. – WRONG. Inference is true for tropics but for temperate it can’t be established. Refer Para 2 and 4 combined.

6. With which one of the following statements concerning possible explanations for the latitudinal gradient in number of species would the author be most likely to agree? 
 Marked D which is WRONG. Again a must be true/inference type question. It states that author most likely agrees with the following options when used to explain the latitudinal gradient in terms of number of species. May be this is the toughest among all.
 (A) The time theory is the least plausible of proposed hypotheses, since it does not correctly assess the impact of ice ages upon tropical conditions. – WRONG. Time theory does mention the difference between tropics and temperate/arctic and thus latitudinal gradient. Impact of Ice ages is not factor here so incorrect.
(B) The rate-of-speciation hypothesis addresses a principal objection to the climatic-stability hypothesis. – CORRECT. In para 4 the statement ‘ecology of local communities cannot account for the origin of the latitudinal gradient’ raises a limitation to explain which para 6 elaborates using ‘small populations spread out and formation of isolated groups’ explains latitudinal gradient.
(C) The major objection to the time theory is that it does not accurately reflect the degree to which the latitudinal gradient exists, especially when undiscovered species are taken into account. – WRONG. Author would disagree here since nowhere he/she is concerned with the accuracy aspect of latitudinal gradient using time theory. Author does mention in the intro about ‘undiscovered species’ that are believed to be living in arctic and also never opines about ‘Time theory’.
(D) Despite the claims of the species-energy hypothesis, a high rate of biological growth and reproduction is more likely to exist with low biomass than with high biomass. –  WRONG. Marked this option correct since the question looks more convoluted and author agrees with species-energy hypothesis. But how would author disagree with this option I am still unclear. 
(E) An important advantage of the rate-of-speciation theory is that it considers species competition in a regional rather than local context. – WRONG. Though initially confused about this option, since author would disagree with this option. However in the last line of the passage ‘Since subgroups in an arctic environment are more likely to face extinction than those in the tropics, the latter are more likely to survive long enough to adapt to local conditions and ultimately become new species’ author provides enough reasons that population difference (latitudinal gradient) would exist between arctic and tropic.

Have still doubt on last question. Waiting for experts’ explanation on this answer.

Dhruvnneo · Answer

2. Which one of the following situations is most consistent with the species-energy hypothesis as described in the passage?

(A) The many plants in a large agricultural tract represent a limited range of species.
(B) An animal species experiences a death rate almost as rapid as its rate of growth and reproduction.
(C) Within the small number of living organisms in a desert habitat, many different species are represented.
(D) In a tropical rain forest, a species with a large population is found to exhibit instances of local extinction.
(E) In an arctic tundra, the plants and animals exhibit a slow rate of growth and reproduction.

Moreover, the mechanism proposed—greater energy influx leading to bigger populations , thereby lowering the probability of local extinction—remains untested.
my answer was wrong as i choose D instead of E. but later on giving more thought i realised we can deduce the answer E from this line.

Hope i'm right.

Dhruvnneo · Answer

please explain Q3.

In Q5 why correct option is D and not B.
B) Its climatic conditions have been severely interrupted in the past by a succession of ice ages.
(D) It has a larger regional pool of species than does an arctic grassland.

i choose option B as it is mentioned in the para. 
 However, ice ages have caused less disruption in some temperate regions than in others (15) and have not interrupted arctic conditions.

unraveled · Answer

Refer explanation above.

Sajjad1994 · Answer

Dhruvnneo  here is the explanation.

Explanation

2. Which one of the following situations is most consistent with the species-energy hypothesis as described in the passage?

Explanation

According to the  “species-energy theory,”  the rate of species growth and reproduction is highest at the equator because it gets the highest quantity of sunlight. Conversely, the rate of species growth and reproduction is lowest at the north and south poles because they get the lowest quantity of sunlight. Hence, a slow rate of growth and reproduction in an arctic landscape would be consistent with this theory.

(A), (B), (C), (D)  None of these choices reflects the relationship that’s at the heart of the  “species-energy theory” : the relationship between the amount of sunlight and the rate of species growth and reproduction.

Answer: E

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

Explanation

The  “time theory”  essentially argues that fewer species exist in temperate and arctic zones than in tropical zones because past ice ages have limited the number of species that have emerged in the former zones. One implication of this line of reasoning is that the number of species living in these zones could increase in the absence of future ice ages.

(B)  If anything, the  ‘‘time theory”  suggests that climatic conditions in temperate zones could be affected by future ice ages.

(C)  The  “time theory”  addresses the issue of the number of species that could emerge in different climatic zones, not whether climatic conditions in these zones could converge.

(D)  focuses on a detail in  Para 1 — that isn’t concerned with the  “time theory.”

(E)  The  “time theory”  doesn’t argue that future ice ages are a certainty.

Answer: A

Hope it helps

Kanvi · Answer

please explain question 6

devavrat · Answer

In this statement it says that the subgroup of mammalian life is isolated. Speciation theory does state that subgroup isolated will face rapid extinction

Can u pls explain?
Option C states that the energy theory is established so then our premise that speciation theory is correct falls apart and weakens the speciation theory

Sajjad1994 · Answer

Explanation

6. With which one of the following statements concerning possible explanations for the latitudinal gradient in number of species would the author be most likely to agree?

Difficulty Level:   700

Explanation

The author claims that the  “climatic stability theory”  simply cannot account for the  “latitudinal gradient in number of species”  in a given type of habitat while the  “rate of speciation theory”  can do so.

(A)  The author dismisses the  “time theory,”  the  “species-energy theory,”  and the  “climatic stability theory”  in favor of the  “rate-of-speciation theory” ; but he never mentions which of these three theories he finds least plausible.

(C)  The author’s objection to the  “time theory”  has to do with this theory’s inability to account adequately for the effects of past ice ages.

(D)  While the author acknowledges that  “high production rates can exist with low biomass,”  he doesn’t claim that they are more likely to exist with low biomass than with high biomass.

(E)  The author never makes a regional versus local distinction with respect to the ability of the  “rate-of-speciation theory”  to explain the  “latitudinal gradient.”

Answer: B

Hope it helps

devavrat · Answer

SajjadAhmad

Can u pls explain question 4

Posted from my mobile device

Sajjad1994 · Answer

Explanation

4. Which one of the following, if true, most clearly weakens the rate-of-speciation hypothesis as it is described in the passage?

Difficulty Level:   650

Explanation

The  “rate-of-speciation theory”  is based on the idea that tropical regions contain more species than other regions because  “subgroups”  in the tropics are more likely to avoid extinction than  “subgroups”  in other regions. The discovery that  “subgroups”  in the tropics actually experienced rapid extinction would, therefore, call into question the validity of this theory.

(A)  Since the  “rate-of-speciation theory”  has nothing to do with breeding ability per se, this discovery would have no direct bearing on the theory.

(B)  This finding would support the validity of the  “climatic stability theory,”  but would neither strengthen nor weaken the  “rate-of-speciation theory.”

(C)  Same as  (B)

(D)  Since the  “rate-of-speciation theory”  has nothing to do with the absolute number of species in a given region, the discovery of previously unknown species in an arctic region would not necessarily weaken the theory. Remember, this theory is concerned with the relative numbers of species across different latitudes.

In  Strengthen/Weaken  questions, always make sure you’re clear about whether you’re to strengthen or weaken something. Often, a wrong answer will do the opposite of what the question asks, and you could fall for a choice like this if you’re unsure about the task at hand.

Answer: E

Hope it helps

devavrat · Answer

Most of the isolated subgroups of mammalian life within a tropical zone are found to experience rapid extinction.

It says isolated
Does it not relate with speciation theory??

Posted from my mobile device

auradediligodo · Answer

Hi everyone,
Took 5 minutes to read, write down paragraphs summaries and main point. Got 5/6 correct

P1: Latitudinal gradient
P2: Time's theory and drawbacks 
P3: Species-energies hypothesis and drawbacks
P4: Tropic-climate stability theory and drawbacks
P5: Regional speciation theory (favored by the author)
P6: Explanation of P5's theory

MP: Present, discuss theories about the latitudinal gradient and select one theory as the best

-------------------------------------------------------------------------------------------------------------------------------------------
  
 1 . Which one of the following most accurately expresses the main idea of the passage?

Pre-thinking
 Refer to main point above to analyze each answer choice

(A) At present, no single hypothesis explaining the latitudinal gradient in numbers of species is more widely accepted than any other.
 The passage does not talk about acceptance at all. Hence this choice is incorrect

(B) The tropical climate is more conducive to promoting species diversity than are arctic or temperate climates.
 This choice might be tempting but let's ask ourselves what is the purpose of the author while writing the passage. Is it to state this claim or to propose different theories and discuss the best one? Most reasonably the second one. Hence this choice is incorrect

(C)   Several explanations have been suggested for global patterns in species distribution, but a hypothesis involving rates of speciation seems most promising.
 The passage indeed discussed different explanations and suggested one out of all as the best one. Hence this choice is correct

(D) Despite their differences, the various hypotheses regarding a latitudinal gradient in species diversity concur in predicting that the gradient can be expected to increase.
 This is not the main focus on the passage. The passage was not written to prove this common factor among all the theories. Hence incorrect

(E) In distinguishing among the current hypotheses for distribution of species, the most important criterion is whether a hypothesis proposes a mechanism that can be tested and validated.
 This is out of the scope of the passage. Hence incorrect

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2 . Which one of the following situations is most consistent with the species-energy hypothesis as described in the passage?

Pre-thinking
 This theory is discussed in paragraph three. Simply by comparing the answer choices with the description of the theory in the paragraph should help us selecting the right answer.

(A) The many plants in a large agricultural tract represent a limited range of species.
 let's break down this correlation: many the plants-->limited range of species.
Now look for similar information in P3:
" and the amount of biomass with number of
species."
Here you can see that the correlation is opposite to what is stated in this answer choice. Hence incorrect

(B) An animal species experiences a death rate almost as rapid as its rate of growth and reproduction.
 This choice suggests that death rate for a given species is fast as G%R rate.
Now let's look at P3:
"rates of growth and reproduction
(20) with the amount of living matter (biomass) at a given
moment;"
The passage on the other hand suggests correlation between the two elements but it does not suggests similar rates. Hence incorrect

(C) Within the small number of living organisms in a desert habitat, many different species are represented.
 Same reasoning for choice A. Hence incorrect

(D) In a tropical rain forest, a species with a large population is found to exhibit instances of local extinction.
 Large population---> instances of local extinction.
Let's find similar information in P3:
"greater energy influx leading to
bigger populations, thereby lowering the probability of
local extinction—remains untested."
The passage states that there should be  fewer  instances of extinction. Hence incorrect

(E)   In an arctic tundra, the plants and animals exhibit a slow rate of growth and reproduction.
 The theory at hand promotes the idea that the amount of sun is correlated with G&R rate. Since in the arctic tundra we can expect a low amount of sun we can also expect a slow rate of growth and reproduction .Hence correct.

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

Pre-thinking
 Let's focus on this portion of P2:"holds that diverse species adapted to
(10) today’s climatic conditions have had more time to
emerge in the tropical regions, which, unlike the
temperate and arctic zones, have been unaffected by a
succession of ice ages."

(A)   In the absence of additional ice ages, the number of species at high latitudes could eventually increase significantly.
 This information is clearly supported by the passage. Hence correct

(B) No future ice ages are likely to change the climatic conditions that currently characterize temperate regions.
 This choice is very extreme due to the usage of "no future ice ages" and this information is not supported by the theory. Hence incorrect

(C) If no further ice ages occur, climatic conditions at high latitudes might eventually resemble those at today’s tropical latitudes.
 This information is clearly not supported by the information given in P2. The only conclusion that can be inferred is that without ice ages there would be an increase in the climatic conditions. Hence incorrect

(D) Researchers will continue to find many more new species in the tropics than in the arctic and temperate zones.
 Not supported by the theory. Hence incorrect

(E) Future ice ages are likely to interrupt the climatic conditions that now characterize high-latitude regions.
 Inconsistent because of the usage of "to interrupt". The best replacement here would be "to slow down". Hence incorrect

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4 . Which one of the following, if true, most clearly weakens the rate-of-speciation hypothesis as it is described in the passage?

Pre-thinking
 Let's refer to the last two paragraphs to analyze the answer choices 
 "The mechanism for this rate-of-speciation
(50) hypothesis is that most new animal species, and
perhaps plant species, arise because a population
subgroup becomes isolated." 
 What if most new animal species arise even when a population subgroup is not isolated. This scenario would for sure undermine the theory. 
 
"The uneven spread
(55) of a species over a large geographic area promotes this
mechanism:"
What if the mechanism works even when there is no uneven distribution. This scenario would undermine the theory as well.

(A) A remote subgroup of a tropical species is reunited with the original population and proves unable to interbreed with members of this original population.
 This answer has no impact on the theory. Hence incorrect

(B) Investigation of a small area of a tropical rain forest reveals that many competing species are able to coexist on the same range of resources.
 This answer choice does not affect the argument at all. Hence incorrect

(C) A correlation between higher energy influx, larger populations, and lower probability of local extinction is definitively established.
 Low probability of local extinctions are not discussed at all in the theory so this choice does not affect the theory. Hence incorrect

(D) Researchers find more undiscovered species during an investigation of an arctic region than they had anticipated.
 Out of scope. Hence incorrect

(E)   Most of the isolated subgroups of mammalian life within a tropical zone are found to experience rapid extinction.
 This would undermine the argument based on the reasoning done during pre-thinking. Hence correct

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5 . Which one of the following inferences about the biological characteristics of a temperate-zone grassland is most strongly supported by the passage?

Pre-thinking
 .
#1It will have a lower latitudinal gradient than the tropic zone and higher than the arctic zone.
#2 Species in the temperate zone will face more extinction than in the tropic zone and less than the arctic zone

(A) It has more different species than does a tropical-zone forest.
 Not in line with pre-thinking. Hence incorrect

(B) Its climatic conditions have been severely interrupted in the past by a succession of ice ages.
 Severely is too extreme here. Hence incorrect

(C) If it has a large amount of biomass, it also has a large number of different species.
 This is not always true and the opposite is mentioned in the passage. Hence incorrect

(D)   It has a larger regional pool of species than does an arctic grassland.
 In line with pre-thinking. Hence correct

(E) If population groups become isolated at its edges, they are likely to adapt to local conditions and become new species.
 Not enough information are given to infer this statement. Hence incorrect

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6 . With which one of the following statements concerning possible explanations for the latitudinal gradient in number of species would the author be most likely to agree?

Pre-thinking
 Let's evaluate the answer choices

(A) The time theory is the least plausible of proposed hypotheses, since it does not correctly assess the impact of ice ages upon tropical conditions.
  Least plausible  makes this answer wrong since there is no information that can support this statement. Hence incorrect

(B)   The rate-of-speciation hypothesis addresses a principal objection to the climatic-stability hypothesis.
 This might be it. The climatic stability hypothesis states that supply of resources explains why in the tropics there is more stability and hence more species. But the rate-of-speciation hypothesis states that because of the harsher condition in the arctic region it is more probable that the species in the tropics will turn into new species. (" Since subgroups in an arctic
environment are more likely to face extinction than
those in the tropics, the latter are more likely to survive
(60) long enough to adapt to local conditions and ultimately
become new species.")
Hence correct

(C) The major objection to the time theory is that it does not accurately reflect the degree to which the latitudinal gradient exists, especially when undiscovered species are taken into account.
 No information supports this statement. Plus undiscovered species are used in another context and for another purpose. Hence incorrect

(D) Despite the claims of the species-energy hypothesis, a high rate of biological growth and reproduction is more likely to exist with low biomass than with high biomass.
 Likelihood is not discussed. Hence incorrect

(E) An important advantage of the rate-of-speciation theory is that it considers species competition in a regional rather than local context.
 Such advantage is never highlighted, that is to say that there is no information that leads us to think this. Hence incorrect

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It is a good day to be alive, cheers!

Diya52 · Answer

Hi SajjadAhmad,

Can you post the explanation for Q1?

Sajjad1994 · Answer

Explanation

1. Which one of the following most accurately expresses the main idea of the passage?

Difficulty Level:   600

Explanation

After reviewing and dismissing three possible theories for global species diversity in the first four paras, the author discusses and endorses a fourth theory—the  “rate-of-speciation theory” —in the last two paras.

(A)  While the author provides his own view about which theory he considers to be most valid, he never comments on what scientists in general think.

(B)  This choice focuses on a detail in para 2 and 4.

(D)  According to the passage, only the  “rate-of-speciation theory”  predicts an increase in the gradient (under certain conditions).

(E)  The author finds the  “rate-of-speciation theory”  more compelling than the others on the basis of its substance, rather than its testability. Only in regard to the  “species-energy theory”  does he bring up the issue of testability.

In global questions, the correct answer must be broad enough to encompass the contents of the entire passage, yet narrow enough to refer to its specific contents.

Answer: C

Hope it helps

hero_with_1000_faces · Answer

Hi  auradediligodo  @SajjadAhmad; would need appreciate some help

For question 6.

However, the ecology of local communities (35) cannot account for the origin of the latitudinal gradient.
Localized ecological processes such as competition  do not generate regional pools of species , and it is the total
number of species available regionally for colonizing.

(B) The rate-of-speciation hypothesis addresses a principal objection to the climatic-stability hypothesis.
 
The principal objection is  ecological processes do not generate regional pools of species ; however rate speciation addresses his by stating how new gene pole is generated through isolation.

Is my understanding correct or am I missing the bulls eye completely.

mimishyu · Answer

For Q6
Hi,I have the way of thinking same as  hero_with_1000_faces

Is it, from sentences in para4&5 we can infer that (B) is the correct answer???
However, the ecology of local communities cannot account for the origin of the latitudinal gradient.Localized ecological processes such as competition do not generate regional pools of species,

A fourth and most plausible hypothesis focuses on“regional”
 speciation

KabxW · Answer

I completed it in 11 minutes with all 6 correct. I found this a bit difficult than actual GMAT RCs. Can anyone comment on my accuracy and time?

sam12rawat · Answer

Hi, this seemed like a really tough RC Passage. Took me 11 minutes to read and take notes, and 20 min 23 sec in total to answer all the questions (including the 11 min reading time). Could anybody please comment how likely is a test taker to get such a passage in the GMAT? I usually solve RC passages in 8-11 minutes.

Sajjad1994 · Answer

Hello sam12rawat

LSAT RC passages are lengthier and harder than the GMAT passages so you cannot perfectly compare them both. There is no doubt that official LSAT RC passages are of fine quality and a good practice alternative for the GMAT but keep in mind they are not from the official GMAT. Use them just as a practice tool if you are preparing for the GMAT.

A rough idea of time management is that a short passage (of up to 250 words) should take your 2:30 to 3 minutes to read and 0:40 to 1:00 a question. A long passage (of up to 350-370 words) should take your 3:30 to 4 minutes to read and 0:40 to 1:00 a question. One other rough idea is that a long passage with 4 questions should take 7-8 minutes and a short passage with 3 questions should take 5-6 minutes.

Good Luck!

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