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Question 1
E
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Question 2
D
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B
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C
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C
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E
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Over the last 150 years, large stretches of salmon habitat have been eliminated by human activity: mining, livestock grazing, timber harvesting, and agriculture as well as recreational and urban development. The numerical effect is obvious: there are fewer salmon in degraded regions than in pristine ones; however, habitat loss also has the potential to reduce genetic diversity. This is most evident in cases where it results in the extinction of entire salmon populations. Indeed, most analysts believe that some kind of environmental degradation underlies the demise of many extinct salmon populations. Although some rivers have been recolonized, the unique genes of the original populations have been lost.
Large-scale disturbances in one locale also have the potential to alter the genetic structure of populations in neighboring areas, even if those areas have pristine habitats. Why? Although the homing instinct of salmon to their natal stream is strong, a fraction of the fish returning from the sea (rarely more than 15 percent) stray and spawn in nearby streams. Low levels of straying are crucial, since the process provides a source of novel genes and a mechanism by which a location can be repopulated should the fish there disappear. Yet high rates of straying can be problematic because misdirected fish may interbreed with the existing stock to such a degree that any local adaptations that are present become diluted. Straying rates remain relatively low when environmental conditions are stable, but can increase dramatically when streams suffer severe disturbance. The 1980 volcanic eruption of Mount Saint Helens, for example, sent mud and debris into several tributaries of the Columbia River. For the next couple of years, steelhead trout (a species included among the salmonids) returning from the sea to spawn were forced to find alternative streams. As a consequence, their rates of straying, initially 16 percent, rose to more than 40 percent overall.
Although no one has quantified changes in the rate of straying as a result of the disturbances caused by humans, there is no reason to suspect that the effect would be qualitatively different than what was seen in the aftermath of the Mount Saint Helens eruption. Such a dramatic increase in straying from damaged areas to more pristine streams results in substantial gene flow, which can in turn lower the overall fitness of subsequent generations.
Large-scale disturbances in one locale also have the potential to alter the genetic structure of populations in neighboring areas, even if those areas have pristine habitats. Why? Although the homing instinct of salmon to their natal stream is strong, a fraction of the fish returning from the sea (rarely more than 15 percent) stray and spawn in nearby streams. Low levels of straying are crucial, since the process provides a source of novel genes and a mechanism by which a location can be repopulated should the fish there disappear. Yet high rates of straying can be problematic because misdirected fish may interbreed with the existing stock to such a degree that any local adaptations that are present become diluted. Straying rates remain relatively low when environmental conditions are stable, but can increase dramatically when streams suffer severe disturbance. The 1980 volcanic eruption of Mount Saint Helens, for example, sent mud and debris into several tributaries of the Columbia River. For the next couple of years, steelhead trout (a species included among the salmonids) returning from the sea to spawn were forced to find alternative streams. As a consequence, their rates of straying, initially 16 percent, rose to more than 40 percent overall.
Although no one has quantified changes in the rate of straying as a result of the disturbances caused by humans, there is no reason to suspect that the effect would be qualitatively different than what was seen in the aftermath of the Mount Saint Helens eruption. Such a dramatic increase in straying from damaged areas to more pristine streams results in substantial gene flow, which can in turn lower the overall fitness of subsequent generations.
VRC000460-01
1. The primary purpose of the passage is to
(A) argue against a conventional explanation for the extinction of certain salmon populations and suggest an alternative
(B) correct a common misunderstanding about the behavior of salmon in response to environmental degradation caused by human activity
(C) compare the effects of human activity on salmon populations with the effects of natural disturbances on salmon populations
(D) differentiate the particular effects of various human activities on salmon habitats
(E) describe how environmental degradation can cause changes in salmon populations that extend beyond a numerical reduction
1. The primary purpose of the passage is to
(A) argue against a conventional explanation for the extinction of certain salmon populations and suggest an alternative
(B) correct a common misunderstanding about the behavior of salmon in response to environmental degradation caused by human activity
(C) compare the effects of human activity on salmon populations with the effects of natural disturbances on salmon populations
(D) differentiate the particular effects of various human activities on salmon habitats
(E) describe how environmental degradation can cause changes in salmon populations that extend beyond a numerical reduction
VRC000460-02
2. It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which
(A) pristine streams that are near polluted streams become polluted themselves
(B) the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
(C) the number of salmon in pristine habitats decreases relative to the number in polluted streams
(D) an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
(E) the extinction of the salmon populations that spawn in polluted streams is accelerated
2. It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which
(A) pristine streams that are near polluted streams become polluted themselves
(B) the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
(C) the number of salmon in pristine habitats decreases relative to the number in polluted streams
(D) an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
(E) the extinction of the salmon populations that spawn in polluted streams is accelerated
VRC000460-03
3. According to the passage, human activity has had which of the following effects on salmon populations?
(A) An increase in the size of salmon populations in some previously polluted rivers
(B) A decline in the number of salmon in some rivers
(C) A decrease in the number straying salmon in some rivers
(D) A decrease in the gene flow between salmon populations that spawn in polluted streams and populations that spawn in pristine streams
(E) A decline in the vulnerability of some salmon populations to the effects of naturally occurring habitat destruction
3. According to the passage, human activity has had which of the following effects on salmon populations?
(A) An increase in the size of salmon populations in some previously polluted rivers
(B) A decline in the number of salmon in some rivers
(C) A decrease in the number straying salmon in some rivers
(D) A decrease in the gene flow between salmon populations that spawn in polluted streams and populations that spawn in pristine streams
(E) A decline in the vulnerability of some salmon populations to the effects of naturally occurring habitat destruction
4. [Not An official Question]The author mentions the “aftermath of the Mount Saint Helens eruption” most likely in order to
(A) provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct
(B) indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere
(C) provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured
(D) show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams
(E) show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance
(A) provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct
(B) indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere
(C) provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured
(D) show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams
(E) show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance
VRC000460-05
5. The author's argument that increased straying can "lower the overall fitness of subsequent generations" (see hightlited text) is based on which of the following assumptions?
(A) A disturbance of salmonid spawning streams caused by human activity could increase the straying rate of affected salmonid populations as much as the aftermath of the Mount Saint Helens eruption did.
(B) In the streams in which the straying salmonids spawn, these straying salmonids would amount to no more than 40 percent of the total spawning population
(C) Salmonids in some streams benefit from particular local adaptions.
(D) Nonenvironmental factors have no effect on salmonid straying rates.
(E) At least some of the streams in which straying salmonids would spawn are pristine, affected by neither natural nor artificial disturbances.
5. The author's argument that increased straying can "lower the overall fitness of subsequent generations" (see hightlited text) is based on which of the following assumptions?
(A) A disturbance of salmonid spawning streams caused by human activity could increase the straying rate of affected salmonid populations as much as the aftermath of the Mount Saint Helens eruption did.
(B) In the streams in which the straying salmonids spawn, these straying salmonids would amount to no more than 40 percent of the total spawning population
(C) Salmonids in some streams benefit from particular local adaptions.
(D) Nonenvironmental factors have no effect on salmonid straying rates.
(E) At least some of the streams in which straying salmonids would spawn are pristine, affected by neither natural nor artificial disturbances.
VRC000460-07
6. Which of the following does the author mention as support for the view that environmental disturbances caused by human activity could increase straying rates?
(A) The existence of salmon populations in rivers where the elimination of salmon habitat by human activity had previously made the fish extinct
(B) The results of studies measuring the impact on straying rates of habitat loss caused by human activity
(C) The potential for disturbances in one environment to cause the introduction of novel genes into salmon populations in neighboring areas
(D) The weaknesses in the view that the extinction of entire salmon populations is the only mechanism by which human destruction of salmon habitat reduces genetic diversity in salmon
(E) The absence of any reason for believing that disturbances brought about by human activitiy would differ in their effects from comparable disturbances brought about by natural causes
6. Which of the following does the author mention as support for the view that environmental disturbances caused by human activity could increase straying rates?
(A) The existence of salmon populations in rivers where the elimination of salmon habitat by human activity had previously made the fish extinct
(B) The results of studies measuring the impact on straying rates of habitat loss caused by human activity
(C) The potential for disturbances in one environment to cause the introduction of novel genes into salmon populations in neighboring areas
(D) The weaknesses in the view that the extinction of entire salmon populations is the only mechanism by which human destruction of salmon habitat reduces genetic diversity in salmon
(E) The absence of any reason for believing that disturbances brought about by human activitiy would differ in their effects from comparable disturbances brought about by natural causes
26 Jul 2012, 06:38
Kudos
Bookmarks
Q10:
It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which
a. pristine streams that are near polluted streams become polluted themselves
b. the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
c. the number of salmon in pristine habitats decreases relative to the number in polluted streams
d. an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
e. the extinction of the salmon populations that spawn in polluted streams is accelerated
As given in line 20 “Although some rivers have been recolonized, the unique genes of the original populations have been lost.” This refers that some streams have been initially “DE SALMONed” i.e Salmons fail to return to their natal streams in order to spawn because of some environmental degradation of the stream but somehow the stream was restored and finally recolonized. That’s exactly what option D says (If the stream recovers, an environmentally degraded stream could be recolonized).
Q11:
According to the passage, human activity has had which of the following effects on salmon populations?
a. An increase in the size of salmon populations in some previously polluted rivers
b. A decline in the number of salmon in some rivers
c. A decrease in the number straying salmon in some rivers
d. A decrease in the gene flow between salmon populations that spawn in polluted streams and populations that spawn in pristine streams
e. A decline in the vulnerability of some salmon populations to the effects of naturally occurring habitat destruction
As given in opening lines “Over the last 150 years, large stretches of salmon habitat have been eliminated by human activity: Line mining, livestock grazing, timber harvesting, and agriculture as well as recreational and urban development. The numerical effect is obvious: there are fewer salmon in degraded regions than in pristine ones;” This clearly refers that human activity caused decline in number of salmons in some river (B)
Q12:
The author mentions the “aftermath of the Mount Saint Helens eruption” (lines 73-74) most likely in order to
a. provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct
b. indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere
c. provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured
d. show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams
e. show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance
As given in last para “Although no one has quantified changes in the rate of straying as a result of the disturbances caused by humans, there is no reason to suspect that the effect would be qualitatively different than what was seen in the aftermath of the Mount Saint Helens eruption”, author is clearly comparing the effect of human activity with that of environmental degradation.
a. provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct – Not an example of any process of repopulation
b. indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere – not talking about any particular stream
c. provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured - YES
d. show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams – Clearly out
e. show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance – Clearly out
It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which
a. pristine streams that are near polluted streams become polluted themselves
b. the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
c. the number of salmon in pristine habitats decreases relative to the number in polluted streams
d. an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
e. the extinction of the salmon populations that spawn in polluted streams is accelerated
As given in line 20 “Although some rivers have been recolonized, the unique genes of the original populations have been lost.” This refers that some streams have been initially “DE SALMONed” i.e Salmons fail to return to their natal streams in order to spawn because of some environmental degradation of the stream but somehow the stream was restored and finally recolonized. That’s exactly what option D says (If the stream recovers, an environmentally degraded stream could be recolonized).
Q11:
According to the passage, human activity has had which of the following effects on salmon populations?
a. An increase in the size of salmon populations in some previously polluted rivers
b. A decline in the number of salmon in some rivers
c. A decrease in the number straying salmon in some rivers
d. A decrease in the gene flow between salmon populations that spawn in polluted streams and populations that spawn in pristine streams
e. A decline in the vulnerability of some salmon populations to the effects of naturally occurring habitat destruction
As given in opening lines “Over the last 150 years, large stretches of salmon habitat have been eliminated by human activity: Line mining, livestock grazing, timber harvesting, and agriculture as well as recreational and urban development. The numerical effect is obvious: there are fewer salmon in degraded regions than in pristine ones;” This clearly refers that human activity caused decline in number of salmons in some river (B)
Q12:
The author mentions the “aftermath of the Mount Saint Helens eruption” (lines 73-74) most likely in order to
a. provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct
b. indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere
c. provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured
d. show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams
e. show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance
As given in last para “Although no one has quantified changes in the rate of straying as a result of the disturbances caused by humans, there is no reason to suspect that the effect would be qualitatively different than what was seen in the aftermath of the Mount Saint Helens eruption”, author is clearly comparing the effect of human activity with that of environmental degradation.
a. provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct – Not an example of any process of repopulation
b. indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere – not talking about any particular stream
c. provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured - YES
d. show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams – Clearly out
e. show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance – Clearly out
17 Oct 2012, 10:17
Kudos
Bookmarks
voodoochild
B is quite wrong because the passage makes very clear --- when a stream is polluted, straying happens, which means dilution happens. The passage describes clearly the straying that resulted from the Mount St. Helen's eruption, and then around line (70) says that the effect of pollution probably would be about the same as what they saw at Mount St. Helen's. When the stream is polluted, the salmon can't use it to spawn, so they stray.
voodoochild
You're correct in your understanding of "fitness" --- we are talking about Darwinian fitness here.
To me, the conclusion is that straying because of human effects causes bad things to Salmon in pristine streams. What's the support? Straying causing the dilution of the gene pool. I couldn't find that answer choice. The passage says "high rates of straying can be problematic because misdirected fish may interbreed with the existing stock to such a degree that any local adaptations that are present become diluted." In other words, the salmon in those pristine areas had adaptions particular suited to those areas, which made them quite fit, and along come a bunch of salmon from the polluted stream next door, and they genetically dilute the salmon of that pristine stream, making them less adapted to that unique niche, and hence less fit. That passage is enormous support for (C)
(E) is a typically GMAT RC distractor, and you fell for the bait. It is a statement that's true in general, but not relevant to the argument. Suppose we said that there was no such thing as a "pristine" perfect place for salmon --- suppose even the environments with zero pollution had natural challenges. Well, then, the salmon in those environments, over the centuries, would adapt to those particular conditions and be quite fit, and then if others stray into their unique stream and interbreed with them, it will reduce the fitness of that population.
Does all this make sense?
Mike
that's awesome!! To read the paragraph itself it took 6 mins for me 
Any tips sir..
