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Over the last 150 years, large stretches of salmon habitat have been e

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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 10 Sep 2017, 07:50
1
pikolo2510 wrote:
hello experts,

can you explain the answer for this question?

4. 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

First of all, what exactly was the "aftermath of the Mount Saint Helens eruption"?

Quote:
[the eruption] 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.

We are looking for an answer that choice that MOST LIKELY describes the reason why the author mentioned this aftermath:

Quote:
(A) provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct

The Mount Saint Helens eruption involved an increase in straying rates and was not an example of repopulated rivers where salmon populations had become extinct. Eliminate (A).

Quote:
(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

Choice (B) is tempting, but notice that it says, "in ONE stream", whereas the Mount Saint Helens example involved "several tributaries" of the Columbia River. Thus, this example would not provide an accurate indication of the extent to which damage to ONE stream might affect the genetic structure of salmon populations. This does not seem like a LIKELY reason for including the eruption example.

Quote:
(C) provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured

The author suggests that the effect on straying rates due to human causes should be qualitatively similar to the effect on straying rates due to the Mount Saint Helens eruption. However, "no one has QUANTIFIED changes in the rate of straying as a result of the disturbances caused by humans."

The Mount Saint Helens example provides a benchmark (straying rates rose from 16 percent to 40 percent). If the effect on straying rates caused by human activities were measured, we could compare the numbers to the numbers from the eruption example. This would allow us to compare the effect of human activities to the effect of a natural phenomenon. Thus, the eruption example could in fact be used as a standard of comparison. This is a LIKELY reason for including the example, so hang on to choice (C).

Quote:
(D) show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams

The eruption example has nothing to do with salmons' homing instinct, so eliminate (D).

Quote:
(E) show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance

The Mount Saint Helens example does not explain WHY straying rates remain low in the absence of a severe environmental disturbance. In fact, the passage doesn't even tell us that this is in fact the case. Eliminate (E).

Choice (C) is the best answer.
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 10 Sep 2017, 09:45
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

Why is option-E incorrect?
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 10 Sep 2017, 12:21
pratik1709 wrote:
Hi Guys,

I found this passage extremely difficult.... Not able to eliminate answer choices for 4 out of 6 questions... And I took almost 14 mintutes of 6 question.

My worry is; what should be a strategy if this passage pops up in actual exam?

Experts : Please suggest.. bb mikemcgarry

Dear pratik1709,

I'm happy to respond. :-)

My friend, please don't bother bb--he's a busy man.

My friend, I think you need to practice reading in general. This is not about an isolated strategy. This is about building your deep understanding of English. See this article:
How to Improve Your GMAT Verbal Score

Does this make sense?
Mike :-)
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 04 Oct 2017, 21:23
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

Can experts here help me understand the process to reach answer in this one.
I was able to remove only A and ended up selecting C :(
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 16 Oct 2017, 03:42
Luckisnoexcuse wrote:
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

Can experts here help me understand the process to reach answer in this one.
I was able to remove only A and ended up selecting C :(


Luckisnoexcuse not an expert but can try to help you with this
I spent a lot of time figuring why otion e is wrong and oprion d is right.
In para 1 author states that""""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[/color]
Now according to him the habitat loss as well as population loss are both connected to the numerical effect
in the last paragraph author states thatAlthough 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.
what does this mean
it means that earlier author was talking about numbers effect on the habitat loss ((( loss of genes))
then he switches to the second paragraph and tells a whole deal about straying and then gives a particular example of Mount Saint Helens eruption. After that he makes an analogy of rate of habitat destruction by comparing the quantified analysis of mount saint Helens eruption mentioned in last lines of second paragraph to yet to be quantified analysis of human destruction of habitat by straying

So, we start the passage beliving that numerical effect is causing the habitat loss, move on to a discussion on straying as habitat loss , give an example, and in final paragraph we compare humans and mount Saint Helens eruptions rate of habitat destructions by straying
option d states that 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
You can clearly see the weakness now .The view of numerical effect to consider the loss of habitat.However, its the
straying effect that hasnt been considered ((( yet to be quantified as mentioned in last paragraph)) totally in how humans are destroying loss of habitat
Hope it helps :)
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 23 Oct 2017, 23:51
uledssul wrote:
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.
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




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




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




4. 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




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.




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





Hi GMATNinjaTwo,

Q6 seems to be controversial here(my take is E). Other than this, I got Q4 wrong.
I narrowed it down to B and C, and then chose B. Please compare the two options and explain why B is wrong.
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 24 Oct 2017, 13:27
ShashankDave wrote:
Other than this, I got Q4 wrong.
I narrowed it down to B and C, and then chose B. Please compare the two options and explain why B is wrong.

The following post provides explanations for each answer choice in Q4. See if this helps, and, if not, please post your additional concerns: https://gmatclub.com/forum/over-the-las ... l#p1923344
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 27 Dec 2017, 21:25
Hi all,

The OA of the last question is E. Please help me explain why. Thanks a lot.
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 30 Dec 2017, 16:21
thingocanhnguyen wrote:
Hi all,

The OA of the last question is E. Please help me explain why. Thanks a lot.

This exactly what is described in the last paragraph. There is no reason (i.e. "absence of any reason) to suspect that the effect (i.e. "disturbances brought about by human activity") would be qualitatively different than what was seen in the aftermath of the Mount Saint Helens eruption (i.e. "natural causes").

The preceding paragraph describes and quantifies how the Mount Saint Helens eruption (a natural cause) increased straying rates. Although no one has quantified changes in straying rates caused by human disturbances, there is no reason to believe that the consequences of human disturbances would be much different than the consequences of the eruption (a natural cause).

I hope that helps!
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 05 Mar 2018, 03:22
Hi mikemcgarry ,

can you please explain Q2,4,5 and 6 for the passage.
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 05 Mar 2018, 03:25
uledssul wrote:
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.
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




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




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




4. 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




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.




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




-----------------------------------------------------------------------------------------------------------------

Hi mikemcgarry

Please explain Q2,4,5 and 6. I ended up marking these wrong.

Thanks,

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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 08 Mar 2018, 16:27
ucb2k7 wrote:
Hi mikemcgarry ,

can you please explain Q2,4,5 and 6 for the passage.

ucb2k7, this is certainly a challenging passage, but can you try explaining your selections for the questions that you asked about? Sometimes, attempting to explain your thought process can lead you to the correct answer. Also, I know that the always-amazing mikemcgarry (Hi Mike!) receives numerous requests for help every day, and I imagine that he'd give priority to questions that are a bit more specific and thoughtful. The more information you provide, the easier it is for all of us to help!

As discussed in our RC Guide for Beginners, try reading the passage again and focusing on structure and purpose, rather than worrying about every little detail:

Quote:
Here’s the basic structure that we recommend: stop at the end of each paragraph, and ask yourself WHY the author has written the paragraph. Your focus should be on the big picture: each paragraph’s purpose and how each paragraph connects with the previous paragraphs. If you’re crystal-clear about WHY the author has written every paragraph – and how they fit together – you’ll be in great shape for the contextual questions that you’ll inevitably see next.

See if that approach helps improve your understanding of the passage, and then give the questions another shot. Then, as I recommended above, try explaining your thought process for the ones that you miss.

You can also check out this post for an explanation of question #4.

Good luck!
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 09 Mar 2018, 13:17
1
ucb2k7 wrote:
uledssul wrote:
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.
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




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




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




4. 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




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.




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




-----------------------------------------------------------------------------------------------------------------

Hi mikemcgarry

Please explain Q2,4,5 and 6. I ended up marking these wrong.

Thanks,

ucb2k7


Hi ucb2k7!

Carolyn from Magoosh here :-) Mike can't respond right now, but I'd be happy to answer your questions :-) However, as GMATNinja mentioned, it would be really useful if you could make your questions a bit more specific. Please try to explain your thought process for each question, and mention what exactly you're having trouble understanding. That way we can provide better, more specific explanations!

Thanks! :-)
Carolyn
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 24 Apr 2018, 19:21
Quote:
4. 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

Has anyone actually seen this question in the software?? If so, please post a screenshot. Thanks!
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 20 Jun 2018, 03:22
mikemcgarry wrote:
voodoochild wrote:
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


OA D

Why is B wrong? When high straying happens, dilution is the issue. Hence, when low straying happens, dilution is not an issue at all -- what B) says. Also lines (30), " Low levels of straying are crucial, since the process provides a source of novel genes and a mechanism by which a location can be (40) repopulated should the fish there disappear. " --- implies genes are preserved -- and as the next sentence says "dilution happens" in case of high straying. Can't we infer that in case of low straying, no dilution happens and the genes are preserved?

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 wrote:
The author's argument that increased straying can "lower the overall fitness of subsequent generation" (see highlighted text) is based on which of the following assumptions?
a) a disturbance of salmonid spawning streams caused by human activtity will increasing 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 total spawning population
c) Salmonids in some streams benefit from particular local adaptations
d) Nonenvironmental factors have no effect
e) At least some of the streams in which straying salmonids would spawn are pristine, affected by neither natural nor artificial disturbances.


OA C


Why is E) wrong? Also what support do we have for C) To me, "lowering the overall fitness" implies less likely to pass Darwin's "survival of the fittest" Hence, such adaptations are in fact bad -- 180 to what the OA is :( 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.

You're correct in your understanding of "fitness" --- we are talking about Darwinian fitness here.

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 :-)





Hi Mike,

Could you please explain why the correct option is C and not E for the below question.

4. 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
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 30 Oct 2018, 05:12
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 activitity would differ in their effects from comparable disturbances brought about by natural causes
ABC to me are really confusing! They are not even complete sentences.
Plus I do not have a clue about how to choose? Can someone please help!
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Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 01 Nov 2018, 08:46
Rebekah wrote:
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 activitity would differ in their effects from comparable disturbances brought about by natural causes
ABC to me are really confusing! They are not even complete sentences.
Plus I do not have a clue about how to choose? Can someone please help!


hey Rebekah

lets read the question once more. :)

Which of the following does the author mention as support for the view that environmental disturbances caused by human activity could increase straying rates?

Now ask yourself a question, how author can support his claim? by providing examples right ? so in which paragraph did author put an example ? in the second paragraph, the last sentence: see below

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.

note it is not a environmental disturbance caused by human. it is caused by volvanic eruption, which skyrocketed rates of straying to more than 40%


now lets move on to the third pararagraph. see below first sentence

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.


so author mentions here that environmental disturbances caused by volcanic eruptions is equivalent to the environmental disturbance caused by human.


hence correct answer is E

The absence of any reason for believing that disturbances brought about by human activitity would differ in their effects from comparable disturbances brought about by natural causes

:)
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Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 01 Nov 2018, 11:53
manishk30 wrote:
mikemcgarry wrote:
voodoochild wrote:
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


OA D

Why is B wrong? When high straying happens, dilution is the issue. Hence, when low straying happens, dilution is not an issue at all -- what B) says. Also lines (30), " Low levels of straying are crucial, since the process provides a source of novel genes and a mechanism by which a location can be (40) repopulated should the fish there disappear. " --- implies genes are preserved -- and as the next sentence says "dilution happens" in case of high straying. Can't we infer that in case of low straying, no dilution happens and the genes are preserved?

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 wrote:
The author's argument that increased straying can "lower the overall fitness of subsequent generation" (see highlighted text) is based on which of the following assumptions?
a) a disturbance of salmonid spawning streams caused by human activtity will increasing 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 total spawning population
c) Salmonids in some streams benefit from particular local adaptations
d) Nonenvironmental factors have no effect
e) At least some of the streams in which straying salmonids would spawn are pristine, affected by neither natural nor artificial disturbances.


OA C


Why is E) wrong? Also what support do we have for C) To me, "lowering the overall fitness" implies less likely to pass Darwin's "survival of the fittest" Hence, such adaptations are in fact bad -- 180 to what the OA is :( 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.

You're correct in your understanding of "fitness" --- we are talking about Darwinian fitness here.

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 :-)





Hi Mike,

Could you please explain why the correct option is C and not E for the below question.

4. 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




hi there,

Since 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



The author provides standard of comparison because you dont need measure qualitatively the effect of human activity when comparing it with volacanic eruption - i.e. both negative effects are qualitatively similar - the statement is based on previous (assumed) experiences, knowledge etc


its like comparing forests fires caused by extremely hot weather, vs forests fires caused by human activity :) the negative effects are similar.



this is how i understand :)
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