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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 30 Oct 2018, 06:12
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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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 01 Nov 2018, 09:46
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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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 01 Nov 2018, 12:53
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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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 23 Apr 2019, 00:40
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.

Hi GMATNinja
I got the above question wrong and while articulating my confusion here , I ended up with a better reasoning.(As you have mentioned this in one of your previous posts here)

Here is my reasoning :

The author says INCREASED straying could lower the fitness of the subsequent generations(presumably in the foreign habitat.

So Does that mean the author thinks "Normal Straying increases/benefits the local fitness?"

If so, then C would be the answer.

Please tell me whether my reasoning is correct. Or please add on to it if my should have been better
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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 18 Jul 2019, 12:38
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.

I am trying to understand the answer to this question and i read an explanation by mikemcgarry in a previous post. So as per my understanding "lower the overall fitness of subsequent generations" this is caused by straying of salmon from damaged areas to more pristine areas(as mentioned in the last paragraph) and high rates of straying can dilute local adaptations.(as mentioned in second paragraph) Hence we can infer that salmonids in some streams benefit from particular local adaptations. Can someone please confirm if my thinking is correct?
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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 18 Jul 2019, 19:40
VeritasKarishma GMATNinja VeritasPrepHailey generis

Can you please explain how in the below question the answer is D???

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
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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 19 Jul 2019, 23:32
1
Look at the second paragraph:

"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."


Some salmon do not return to their natal stream. They stray to nearby streams. Low levels of straying are crucial since they provide a mechanism to repopulate if the fish disappear in the nearby streams.

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
(D) an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
So if the old population of some nearby stream disappears because of degraded stream, straying can repopulate if the stream recovers.



warrior1991 wrote:
VeritasKarishma GMATNinja VeritasPrepHailey generis

Can you please explain how in the below question the answer is D???

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

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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 Jul 2019, 16:13
Passage map: Overall the passage describes genetic diversity as another unintended consequence of severed environmental disruptions to Salmon Habitats
P1: to describe the extent of the problem and non-obvious
p2: To argue that large scale disturbances in one locale impact another
p3: To state the potential human cause of straying

Q1
E is correct - quite clear from the 1st - 2nd sentence in P1
A - no conventional explanation therefore incorrect
B - no common misunderstanding therefore incorrect
C - no, not to compare, but to argue that humans can have the same effect
D - no, the argument routinely refers to one environmental effect and humans as one potential cause of this effect

Q2
Inference -refer back and infer.
We are told that some salmon stray to other streams and that this straying is crucial as it provides a source of novel genes and a way by which a location, presumably the disturbed one, can be repopulated if the fish in that disturbed population disappear.

We are then asked to infer what straying provides:
A - it does not state anywhere that pristine streams become polluted by straying populations -incorrect
B - no, we are in fact told the opposite - that dilution occurs.
C - no. We aren't told anything on the population numerical impact
D - Yes. As we are told, VERY INDIRECTLY, "a location can be repopulated".
E - No. We have no basis for this statement.

Q3
Detail - refer back.
We are told of the impact on human activity in the first and last paras. The obvious impact is the numerical effect: decrease in population of polluted environments.
A is incorrect- we are only told that the populace decreases in polluted rivers, nothing of an "increase" in "previously polluted" streams
B is correct - this statement - " the decline in the number of salmon in SOME rivers" (the polluted ones) is the stated effect
C is incorrect because we aren't given a quantitative link between straying and human impact
D is incorrect because we are in fact told the opposite in the last para - "substantial gene flow"
E is incorrect because we are told that humans' increase the vulnerability of salmons by increasing the likelihood of their populace straying

Q5
Which of the following must be true in order for the argument to be true? That's the question.
The argument: A dramatic increase in straying from damaged streams to more pristine streams increases gene flow, lowering the fitness of subsequent generations.

A - This is not required for the argument to be true because humans could SIMPLY cause straying e.g. 1-2% straying rate and the fitness of subsequent generations of the salmon impacted could still be lowered
B - Again, this quantity is not necessarily assumed in arguing that the overall fitness decreases
C must be true because if it weren't true then it wouldn't matter if salmons inter-bred. The argument is that "fitness" (or how good something is) essentially decreases, so if decreasing is bad, what must be true? Keeping genes pure must be true.
D is incorrect - NO - humans are PART of the cause, not ALL of the cause
E is incorrect - no this is the opposite. What's inferred by E is that some of the straying salmon DONT decrease the fitness.


Q6
The potential for humans to impact straying is discussed in P3 by the statement - "although NO ONE has QUANTIFIED changes in the rate of straying as a result of...humans" "there is no reason to believe that the effect would be qualitatively different".

A is not mentioned or supported
B is incorrect because no such studies exist
C is mentioned in the passage, but it is not mentioned in support of the argument that humans increase or cause straying rates. For this reason, C is incorrect.
D is incorrect. Firstly it is the weakness in the view that humans ONLY decrease populations - the whole premise of the passage is that HUMANS DO OTHER THINGS i.e. "increase Straying". Second, "extinction" generally isn't supported. Third, destruction actually INCREASES genetic diversity (mixing).
E is incorrect - The way it is worded can be off-putting. But E essentially states that the "absence" of any "reason (evidence)" does not negate the argument that humans cause straying.
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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 Jul 2019, 07:11
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DiyaDutta wrote:
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.

I am trying to understand the answer to this question and i read an explanation by mikemcgarry in a previous post. So as per my understanding "lower the overall fitness of subsequent generations" this is caused by straying of salmon from damaged areas to more pristine areas(as mentioned in the last paragraph) and high rates of straying can dilute local adaptations.(as mentioned in second paragraph) Hence we can infer that salmonids in some streams benefit from particular local adaptations. Can someone please confirm if my thinking is correct?


Manas1212 wrote:
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.

Hi GMATNinja
I got the above question wrong and while articulating my confusion here , I ended up with a better reasoning.(As you have mentioned this in one of your previous posts here)

Here is my reasoning :

The author says INCREASED straying could lower the fitness of the subsequent generations(presumably in the foreign habitat.

So Does that mean the author thinks "Normal Straying increases/benefits the local fitness?"

If so, then C would be the answer.

Please tell me whether my reasoning is correct. Or please add on to it if my should have been better

Sorry for not replying sooner, Manas1212! I think you are both on the right track here...

The passage specifically tells us that "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."

But the very next sentence says, "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." According to the author, high rates of straying are bad because they dilute any local adaptations that are present. Okay, that sounds reasonable enough... but what if those local adaptations do not actually benefit the salmonids in any way?

For example, maybe a local population has developed a certain color in response to certain characteristics of the local water. If that change in color doesn't actually help the salmon at all, then it would be an example of a local adaptation that does not actually benefit the salmonids.

But if salmonids in some streams DO benefit from particular local adaptions, then passing those traits to future generations would obviously improve the overall fitness of future generations. Now if a bunch of non-local salmonids come in and diluate those adaptations, a lower percentage of the next generation will have that beneficial adaptation. That would of course lower the overall fitness of future generations.

It might seem a bit ridiculous at first, but unless we assume that salmonids in some streams benefit from particular local adaptions, then we can't argue that increased straying would be harmful to the fitness of future generations. That's why (C) is correct!

warrior1991 wrote:
VeritasKarishma GMATNinja VeritasPrepHailey generis

Can you please explain how in the below question the answer is D???

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

Have you checked out this post? If that doesn't help, let us know what you are struggling with (be as specific as possible!).
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Re: Over the last 150 years, large stretches of salmon habitat have been e   [#permalink] 23 Jul 2019, 07:11

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