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While the most abundant and dominant species within a particular ecosy

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While the most abundant and dominant species within a particular ecosy [#permalink]

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Question 1
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59% (02:03) correct 41% (02:09) wrong based on 178

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While the most abundant and dominant species within a particular ecosystem is often crucial in perpetuating the ecosystem, a “keystone” species, here defined as one whose effects are much larger than would be predicted from its abundance, can also play a vital role. But because complex species interactions may be involved, identifying a keystone species by removing the species and observing changes in the ecosystem is problematic. It might seem that certain traits would clearly define a species as a keystone species; for example, Pisaster ochraceus is often a keystone predator because it consumes and suppresses mussel populations, which in the absence of this starfish can be a dominant species. But such predation on a dominant or potentially dominant species occurs in systems that do as well as in systems that do not have species that play keystone roles. Moreover, whereas P. ochraceus occupies an unambiguous keystone role on wave-exposed rocky headlands, in more wave-sheltered habitats the impact of P. ochraceus predation is weak or nonexistent, and at certain sites sand burial is responsible for eliminating mussels. Keystone status appears to depend on context, whether of particular geography or of such factors as community diversity (for example, a reduction in species diversity may thrust more of the remaining species into keystone roles) and length of species interaction (since newly arrived species in particular may dramatically affect ecosystems).

[Reveal] Spoiler:
A

1. The passage mentions which of the following as a factor that affects the role of P. ochraceus as a keystone species within different habitats?

(A) The degree to which the habitat is sheltered from waves

(B) The degree to which other animals within a habitat prey on mussels

(C) The fact that mussel populations are often not dominant within some habitats occupied by P. ochraceus

(D) The size of the P. ochraceus population within the habitat

(E) The fact that there is great species diversity within some habitats occupied by P. ochraceus


[Reveal] Spoiler:
C

2. Which of the following hypothetical experiments most clearly exemplifies the method of identifying species, roles that the author considers problematic?

(A) A population of seals in an Arctic habitat is counted in order to determine whether it is the dominant species in that ecosystem,

(B) A species of fish that is a keystone species in one marine ecosystem is introduced into another marine ecosystem to see whether the species will come to occupy a keystone role.

(C) In order to determine whether a species of monkey is a keystone species within a particular ecosystem, the monkeys are removed from that ecosystem and the ecosystem is then studied.

(D) Different mountain ecosystems are compared to determine how geography affects a particular species, ability to dominate its ecosystem.

(E) In a grassland experiencing a changing climate, patterns of species extinction are traced in order to evaluate the effect of climate changes on keystone species in that grassland.


[Reveal] Spoiler:
B

3. Which of the following, if true, would most clearly support the argument about keystone status advanced in the last sentence of the passage?

(A) A species of bat is primarily responsible for keeping insect populations within an ecosystem low, and the size of the insect population in turn affects bird species within that ecosystem.

(B) A species of iguana occupies a keystone role on certain tropical islands, but does not play that role on adjacent tropical islands that are inhabited by a greater number of animal species.

(C) Close observation of a savannah ecosystem reveals that more species occupy keystone roles within that ecosystem than biologists had previously believed.

(D) As a keystone species of bee becomes more abundant it has a larger effect on the ecosystem it inhabits.

(E) A species of moth that occupies a keystone role in a prairie habitat develops coloration patterns that camouflage it from potential predators.



[Reveal] Spoiler:
D

4. The passage suggests which of the following about the identification of a species as a keystone species?

(A) Such an identification depends primarily on the species’ relationship to the dominant species.

(B) Such an identification can best be made by removing the species from a particular ecosystem and observing changes that occur in the ecosystem.

(C) Such an identification is likely to be less reliable as an ecosystem becomes less diverse.

(D) Such an identification seems to depend on various factors within the ecosystem.

(E) Such an identification can best be made by observing predation behavior.

[Reveal] Spoiler: Question #1 OA
[Reveal] Spoiler: Question #2 OA
[Reveal] Spoiler: Question #3 OA
[Reveal] Spoiler: Question #4 OA

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First, I have to say that the OA for the first question is A, not E.

As for question 2, you must answer the question in relation to the information provided in the last sentence. When you see these questions that relate to specific parts of the passage, you must go to those parts and read them carefully. This question becomes difficult because the last sentence has a pretty crazy structure with a leading clause followed by some modifying text with two parenthetical statements. You have to focus on the key points: keystone status depends on the context - geography, diversity, and length of interaction.

2. Which of the following, if true, would most clearly support the argument about keystone status advanced in the last sentence of the passage?
A. A species of bat is primarily responsible for keeping insect populations within an ecosystem low, and the size of the insect population in turn affects bird species within that ecosystem. No discussion of context here.
B. A species of iguana occupies a keystone role on certain tropical islands, but does not play that role on adjacent tropical islands that are inhabited by a greater number of animal species. This shows how the geographical context (different tropical islands with different species diversities) impacts keystone status. This fits perfectly with the argument in the last sentence.
C. Close observation of a savannah ecosystem reveals that more species occupy keystone roles within that ecosystem than biologists had previously believed.While this discusses keystone roles, it doesn't talk about differences in context impacting keystone status.
D. As a keystone species of bee becomes more abundant it has a larger effect on the ecosystem it inhabits. No discussion of how context impacts keystone status.
E. A species of moth that occupies a keystone role in a prairie habitat develops coloration patterns that camouflage it from potential predators. Again, no discussion of context impacts on keystone status.
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Re: While the most abundant and dominant species within a particular ecosy [#permalink]

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1. The passage mentions which of the following as a factor that affects the role of P. ochraceus as a keystone species within different habitats?
A. The degree to which the habitat is sheltered from waves Correct. In more wave-sheltered habitats the impact of P. ochraceus is weak or nonexistent.
B. The degree to which other animals within a habitat prey on mussels
C. The fact that mussel populations are often not dominant within some habitats occupied by P. ochraceus
D. The size of the P. ochraceus population within the habitat
E. The fact that there is great species diversity within some habitats occupied by P. ochraceus


2. Which of the following hypothetical experiments most clearly exemplifies the method of identifying species, roles that the author considers problematic?
A. A population of seals in an Arctic habitat is counted in order to determine whether it is the dominant species in that ecosystem,
B. A species of fish that is a keystone species in one marine ecosystem is introduced into another marine ecosystem to see whether the species will come to occupy a keystone role.
C. In order to determine whether a species of monkey is a keystone species within a particular ecosystem, the monkeys are removed from that ecosystem and the ecosystem is then studied. Correct. A problematic way to identify a keystone is to move the species and oberve changes in the ecosystem.
D. Different mountain ecosystems are compared to determine how geography affects a particular species, ability to dominate its ecosystem.
E. In a grassland experiencing a changing climate, patterns of species extinction are traced in order to evaluate the effect of climate changes on keystone species in that grassland.



3. Which of the following, if true, would most clearly support the argument about keystone status advanced in the last sentence of the passage?
A. A species of bat is primarily responsible for keeping insect populations within an ecosystem low, and the size of the insect population in turn affects bird species within that ecosystem.No reflection of a particular geography, community diversity or length of species interaction.
B. A species of iguana occupies a keystone role on certain tropical islands, but does not play that role on adjacent tropical islands that are inhabited by a greater number of animal species. Correct. It refers to the community diversity.
C. Close observation of a savannah ecosystem reveals that more species occupy keystone roles within that ecosystem than biologists had previously believed.
D. As a keystone species of bee becomes more abundant it has a larger effect on the ecosystem it inhabits.Not related
E. A species of moth that occupies a keystone role in a prairie habitat develops coloration patterns that camouflage it from potential predators.Not related



4. The passage suggests which of the following about the identification of a species as a keystone species?
A. Such an identification depends primarily on the species’ relationship to the dominant species.
B. Such an identification can best be made by removing the species from a particular ecosystem and observing changes that occur in the ecosystem. Author mentioned this method is problematic.
C. Such an identification is likely to be less reliable as an ecosystem becomes less diverse.
D. Such an identification seems to depend on various factors within the ecosystem.Correct. Keystone status appears to depend on context.
E. Such an identification can best be made by observing predation behavior. Predation behavior also occurs in systems that do not have keystones.

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Re: While the most abundant and dominant species within a particular ecosy [#permalink]

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New post 28 Aug 2014, 06:32
NVM just saw that post above mentioned same problem I mentioned. Disregard my original post!

Can the OA be modified to reflect the correct answer? I didn't see Kyle's post until after I had posted about this issue. Don't want others to overlook our posts and experience the same confusion.

I only googled and stumbled upon the right answer because I couldn't understand why I was wrong (chose A). But of course, afterwards I found out Kyle already stated that in the post above mine. Thanks.

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New post 28 Aug 2014, 13:43
I wish I had the ability to fix the OA, but it has to be the original poster or perhaps some staff member.

I often find myself doing google searches as well when I doubt the OA...nice move...

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Re: While the most abundant and dominant species within a particular ecosy [#permalink]

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New post 29 Aug 2014, 00:43
This one was tough for me. Time taken 10 mins. :(

1. The passage mentions which of the following as a factor that affects the role of P. ochraceus as a keystone species within different habitats?
A. The degree to which the habitat is sheltered from waves
>>P. ochraceus occupies an unambiguous keystone role on wave-exposed rocky headlands, in more wave-sheltered habitats the impact of P. ochraceus predation is weak or nonexistent, and at certain sites sand burial is responsible for eliminating mussels.

B. The degree to which other animals within a habitat prey on mussels
>>certain sites sand burial is responsible for eliminating mussels.
C. The fact that mussel populations are often not dominant within some habitats occupied by P. ochraceus
D. The size of the P. ochraceus population within the habitat
E. The fact that there is great species diversity within some habitats occupied by P. ochraceus

2. Which of the following, if true, would most clearly support the argument about keystone status advanced in the last sentence of the passage?
Keystone status appears to depend on context, whether of particular
geography or of such factors as
community diversity (for example, a reduction in species diversity may thrust more of the remaining species into keystone roles) and
length of species interaction (since newly arrived species in particular may dramatically affect ecosystems).
A. A species of bat is primarily responsible for keeping insect populations within an ecosystem low, and the size of the insect population in turn affects bird species within that ecosystem.
>>community diversity. What troubles me in this is "affects bird species within that ecosystem." Does this mean, BS r thriving .

B. A species of iguana occupies a keystone role on certain tropical islands, but does not play that role on adjacent tropical islands that are inhabited by a greater number of animal species.
>>I don't see mentioned anything like that in para. As per OG this is OA. Can anyone elucidate this.. I believe PO habitat is an example for the GC. I am correct?
C. Close observation of a savannah ecosystem reveals that more species occupy keystone roles within that ecosystem than biologists had previously believed.
D. As a keystone species of bee becomes more abundant it has a larger effect on the ecosystem it inhabits.
E. A species of moth that occupies a keystone role in a prairie habitat develops coloration patterns that camouflage it from potential predators.

3. The passage suggests which of the following about the identification of a species as a keystone species?
A. Such an identification depends primarily on the species’ relationship to the dominant species.
B. Such an identification can best be made by removing the species from a particular ecosystem and observing changes that occur in the ecosystem.
C. Such an identification is likely to be less reliable as an ecosystem becomes less diverse.
D. Such an identification seems to depend on various factors within the ecosystem.
>>Correct. Keystone status appears to depend on context .....

E. Such an identification can best be made by observing predation behavior.
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Re: While the most abundant and dominant species within a particular ecosy [#permalink]

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New post 30 Aug 2014, 02:36
xserenity114 wrote:
NVM just saw that post above mentioned same problem I mentioned. Disregard my original post!

Can the OA be modified to reflect the correct answer? I didn't see Kyle's post until after I had posted about this issue. Don't want others to overlook our posts and experience the same confusion.

I only googled and stumbled upon the right answer because I couldn't understand why I was wrong (chose A). But of course, afterwards I found out Kyle already stated that in the post above mine. Thanks.



What exactly do you want me to modify in OAs?
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Re: While the most abundant and dominant species within a particular ecosy [#permalink]

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New post 15 Sep 2014, 23:22
akshaygaur wrote:
xserenity114 wrote:
NVM just saw that post above mentioned same problem I mentioned. Disregard my original post!

Can the OA be modified to reflect the correct answer? I didn't see Kyle's post until after I had posted about this issue. Don't want others to overlook our posts and experience the same confusion.

I only googled and stumbled upon the right answer because I couldn't understand why I was wrong (chose A). But of course, afterwards I found out Kyle already stated that in the post above mine. Thanks.



What exactly do you want me to modify in OAs?


Hii Akshay,
the official answer of first question is A..Please change that..
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New post 03 Jun 2015, 08:54
can someone pls explain Why option c is wrong? as the passage mentioned that "mussel population, which in the absence of starfish can be a dominant species"...Thanks :)

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New post 22 Jun 2015, 05:55
katzzzz wrote:
can someone pls explain Why option c is wrong? as the passage mentioned that "mussel population, which in the absence of starfish can be a dominant species"...Thanks :)


The question is asking what factors affect the keystone status of the starfish. The fact that mussels are not dominant in some areas is an EFFECT of the starfish in the keystone role, not something that AFFECTS the keystone status. The sheltering from waves does affect the keystone status - making choice A correct.

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Re: While the most abundant and dominant species within a particular ecosy [#permalink]

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New post 10 Sep 2015, 10:51
Hi everyone,¨

I came accross this thread because, when working on this passage in the 2016 OG, I answered A to Q1 and was surprised to see B as the OA in the guide. Can anybody confirm if there is a mistake in the 2016 OG? I assume from the date of this post that this passage was already in previous OG versions, where the OA was A... am I wrong?

Many thanks!!

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Re: While the most abundant and dominant species within a particular ecosy [#permalink]

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New post 24 Jun 2017, 22:46
GMATNinja
I am finding it difficult to stay engaged in passage, especially ones like this.
Can you help implementation of taking notes by identifying passage structure based on
your post: https://gmatclub.com/forum/experts-topi ... l#p1857560
Can you explain last sentence of passage and Q3 in light in your understanding?
In playing more safely to not deviate from author's view I am trying to do exactly what is not recommended: facts - facts - facts; and hence missing crucial flow.
WR,
Arpit
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While the most abundant and dominant species within a particular ecosy [#permalink]

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adkikani wrote:
GMATNinja
I am finding it difficult to stay engaged in passage, especially ones like this.

Can you help implementation of taking notes by identifying passage structure based on your post: https://gmatclub.com/forum/experts-topi ... l#p1857560

Can you explain last sentence of passage and Q3 in light in your understanding?

In playing more safely to not deviate from author's view I am trying to do exactly what is not recommended: facts - facts - facts; and hence missing crucial flow.
WR,
Arpit

In this passage, it is tricky to apply the techniques recommended in the Ultimate RC Guide for Beginners because we only have one paragraph!

In this case, you might break down the passage into logical chunks and ask yourself WHY the author has written each chunk:

Quote:
While the most abundant and dominant species within a particular ecosystem is often crucial in perpetuating the ecosystem, a “keystone” species, here defined as one whose effects are much larger than would be predicted from its abundance, can also play a vital role. But because complex species interactions may be involved, identifying a keystone species by removing the species and observing changes in the ecosystem is problematic.

Okay, so it looks like the author is trying to introduce/define the concept of a "keystone" species and to tell us that identifying/studying a keystone species using a seemingly simple approach is actually problematic. So you might jot down: "introduce/define "keystone" species; identifying/studying K.S. by removing/observing is problematic".

Great, that gives us an idea of WHY the author wrote that first chunk. Even though we might not completely understand every detail, let's move on to the next chunk:

Quote:
It might seem that certain traits would clearly define a species as a keystone species; for example, Pisaster ochraceus is often a keystone predator because it consumes and suppresses mussel populations, which in the absence of this starfish can be a dominant species. But such predation on a dominant or potentially dominant species occurs in systems that do as well as in systems that do not have species that play keystone roles.

The purpose of this chunk is described in the first sentence. The author wants us to realize that even though it might seem that certain traits would clearly define a species as a keystone species, those traits do not necessarily indicate that we have a keystone species. So you might jot down: "cannot determine K.S. solely by identifying certain traits".

Quote:
Moreover, whereas P. ochraceus occupies an unambiguous keystone role on wave-exposed rocky headlands, in more wave-sheltered habitats the impact of P. ochraceus predation is weak or nonexistent, and at certain sites sand burial is responsible for eliminating mussels. Keystone status appears to depend on context, whether of particular geography or of such factors as community diversity (for example, a reduction in species diversity may thrust more of the remaining species into keystone roles) and length of species interaction (since newly arrived species in particular may dramatically affect ecosystems).

The same species can be keystone in some habitats and not keystone in other habitats. Keystone status depends not solely on certain traits but rather on context (i.e. geography and community diversity). The purpose of this chunk is to explain that "keystone status depends on habitat/geography, community diversity, and other factors".

Okay, so we have

Chunk 1: "introduce/define "keystone" species; identifying/studying K.S. by removing/observing is problematic"
Chunk 2: "cannot determine K.S. solely by identifying certain traits"
Chunk 3: "keystone status depends on habitat/geography, community diversity, and other factors"

Now, what is the purpose of the passage as a whole? It seems like the author wants to introduce the concept of a keystone species and then explain and provide evidence to support that determining keystone status is not a simple task. So, for the purpose of the passage, you might write: "introduce/define "keystone" species; show that determining keystone status is complex".

Hopefully that helps you get your head around this complicated passage without getting bogged down in the details!

See if question #3 makes more sense in light of this analysis. As a starting point, remind yourself of the purpose of that chunk (chunk #3).

I hope that helps!
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Re: While the most abundant and dominant species within a particular ecosy [#permalink]

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New post 29 Jun 2017, 17:46
Hi GMATNinja

Thanks for your detailed explanations.
For the second chunk, how did you decide to start with no keyword
at start. (I am assuming you started third chunk, seeing moreover)

I got to OA thanks to reading explanations. But I want to confirm correct reasons.
I chose B based on geographical factors and not community diversity. Hope I am correct.

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Re: While the most abundant and dominant species within a particular ecosy [#permalink]

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New post 15 Sep 2017, 07:46
KyleWiddison wrote:
First, I have to say that the OA for the first question is A, not E.

As for question 2, you must answer the question in relation to the information provided in the last sentence. When you see these questions that relate to specific parts of the passage, you must go to those parts and read them carefully. This question becomes difficult because the last sentence has a pretty crazy structure with a leading clause followed by some modifying text with two parenthetical statements. You have to focus on the key points: keystone status depends on the context - geography, diversity, and length of interaction.

2. Which of the following, if true, would most clearly support the argument about keystone status advanced in the last sentence of the passage?
A. A species of bat is primarily responsible for keeping insect populations within an ecosystem low, and the size of the insect population in turn affects bird species within that ecosystem. No discussion of context here.
B. A species of iguana occupies a keystone role on certain tropical islands, but does not play that role on adjacent tropical islands that are inhabited by a greater number of animal species. This shows how the geographical context (different tropical islands with different species diversities) impacts keystone status. This fits perfectly with the argument in the last sentence.
C. Close observation of a savannah ecosystem reveals that more species occupy keystone roles within that ecosystem than biologists had previously believed.While this discusses keystone roles, it doesn't talk about differences in context impacting keystone status.
D. As a keystone species of bee becomes more abundant it has a larger effect on the ecosystem it inhabits. No discussion of how context impacts keystone status.
E. A species of moth that occupies a keystone role in a prairie habitat develops coloration patterns that camouflage it from potential predators. Again, no discussion of context impacts on keystone status.

IMO E in Q1 is wrong because of "within some habitats occupied by P . Orchraceus". Occupy here means take control

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Re: While the most abundant and dominant species within a particular ecosy [#permalink]

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New post 03 Oct 2017, 18:01
omidsa wrote:
While the most abundant and dominant species within a particular ecosystem is often crucial in perpetuating the ecosystem, a “keystone” species, here defined as one whose effects are much larger than would be predicted from its abundance, can also play a vital role. But because complex species interactions may be involved, identifying a keystone species by removing the species and observing changes in the ecosystem is problematic. It might seem that certain traits would clearly define a species as a keystone species; for example, Pisaster ochraceus is often a keystone predator because it consumes and suppresses mussel populations, which in the absence of this starfish can be a dominant species. But such predation on a dominant or potentially dominant species occurs in systems that do as well as in systems that do not have species that play keystone roles. Moreover, whereas P. ochraceus occupies an unambiguous keystone role on wave-exposed rocky headlands, in more wave-sheltered habitats the impact of P. ochraceus predation is weak or nonexistent, and at certain sites sand burial is responsible for eliminating mussels. Keystone status appears to depend on context, whether of particular geography or of such factors as community diversity (for example, a reduction in species diversity may thrust more of the remaining species into keystone roles) and length of species interaction (since newly arrived species in particular may dramatically affect ecosystems).

[Reveal] Spoiler:
A

1. The passage mentions which of the following as a factor that affects the role of P. ochraceus as a keystone species within different habitats?

(A) The degree to which the habitat is sheltered from waves

(B) The degree to which other animals within a habitat prey on mussels

(C) The fact that mussel populations are often not dominant within some habitats occupied by P. ochraceus

(D) The size of the P. ochraceus population within the habitat

(E) The fact that there is great species diversity within some habitats occupied by P. ochraceus



Passage: Keystone Species

Question: Detail Factor

The Simple Story


First, the passage defines a particular term: a keystone species is one whose effects are much larger than would be predicted from its abundance. In other words, this type of species has a larger impact on the ecosystem than would normally be expected.

How do you know for sure that a species is a keystone species? According to the passage, you can’t just remove that keystone species from the environment to see what happens. “It might seem” that a certain characteristic would define a keystone species, but the language it might seem signals that the author is going to disagree. Sure enough, the author provides a certain example about a possible keystone predator and then shows how that predator may or may not be a keystone species.

The author finally concedes that this question depends on two things: context (with an example given) and length of species interaction (with further elaboration given).

Sample Passage Map

This passage contains just one paragraph, so think about how to delineate different parts of it on your Map. Here is one way to map this passage. (Note: abbreviate as desired!)

KS: >> effect than expctd

Mid: How to ID KS? Hard.

2 things: context + interaction length

The “Mid” designation means “the whole middle of the passage is about this.” KS is an abbreviation for keystone species and ID is an abbreviation for identify.

Step 1: Identify the Question

The language mentions which of the following in the question stem indicates that this is a Detail question. Your job is to find this detail in the passage: what factor affects the role of the P thing as a KS in different habitats?

Step 2: Find the Support

Scan for the P thing; it’s introduced in line 12.

“It might seem that certain traits would clearly define a species as a keystone species; for example, Pisaster ochraceus is often a keystone predator because it consumes and suppresses mussel populations, which in the absence of this starfish can be a dominant species. But such predation on a dominant or potentially dominant species occurs in systems that do as well as in systems that do not have species that play keystone roles. Moreover, whereas P. ochraceus occupies an unambiguous keystone role on wave‐exposed rocky headlands, in more wave‐sheltered habitats the impact of P. ochraceus predation is weak or nonexistent, and at certain sites sand burial is responsible for eliminating mussels.”

Step 3: Predict an Answer

The first two sentences talk about P as a KS, but the example doesn’t discuss different habitats until the third sentence, beginning moreover. In one location, P has an unambiguous keystone role, but in another area, P’s predation is weak or nonexistent, so it can’t be playing a keystone role there.

What aspect of the habitats influence this difference? In the first location, there are a lot of waves. In the second, the area is sheltered from the waves.

Step 4: Eliminate and Find a Match

(A) CORRECT. This choice reflects the circumstances described in the passage. When the area is exposed to the waves, P can be a keystone species. When the area is sheltered from the waves, P is much less central to the system.

(B) The example does not address what other animals are preying on the mussels or how that would affect P’s status as a KS.

(C) The passage does state that P consumes and suppresses mussel populations, which could be dominant in the absence of this starfish, suggesting that mussels are not dominant when P is present. However, the next sentence indicates that such predation on a potentially dominant species in not a guarantee of status as a KS in a given habitat.

(D) This choice is a trap. While it makes logical sense that a large population would have a significant impact on an ecosystem, the first sentence specifically defines a KS as one whose effects are much larger than would be predicted from its abundance. In other words, the species is having a much larger impact than you would expect based on its population size—but the effects don’t necessarily vary based on population size itself.

(E) The passage mentions species diversity (line 27) only as a general example of how a reduction in diversity could impact keystone roles in an ecosystem. It does not address species diversity specifically with respect to the P examples.
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While the most abundant and dominant species within a particular ecosy [#permalink]

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New post 03 Oct 2017, 18:08
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omidsa wrote:
While the most abundant and dominant species within a particular ecosystem is often crucial in perpetuating the ecosystem, a “keystone” species, here defined as one whose effects are much larger than would be predicted from its abundance, can also play a vital role. But because complex species interactions may be involved, identifying a keystone species by removing the species and observing changes in the ecosystem is problematic. It might seem that certain traits would clearly define a species as a keystone species; for example, Pisaster ochraceus is often a keystone predator because it consumes and suppresses mussel populations, which in the absence of this starfish can be a dominant species. But such predation on a dominant or potentially dominant species occurs in systems that do as well as in systems that do not have species that play keystone roles. Moreover, whereas P. ochraceus occupies an unambiguous keystone role on wave-exposed rocky headlands, in more wave-sheltered habitats the impact of P. ochraceus predation is weak or nonexistent, and at certain sites sand burial is responsible for eliminating mussels. Keystone status appears to depend on context, whether of particular geography or of such factors as community diversity (for example, a reduction in species diversity may thrust more of the remaining species into keystone roles) and length of species interaction (since newly arrived species in particular may dramatically affect ecosystems).
3. Which of the following, if true, would most clearly support the argument about keystone status advanced in the last sentence of the passage?

(A) A species of bat is primarily responsible for keeping insect populations within an ecosystem low, and the size of the insect population in turn affects bird species within that ecosystem.

(B) A species of iguana occupies a keystone role on certain tropical islands, but does NOT play that role on adjacent tropical islands that are inhabited by a greater number of animal species.

(C) Close observation of a savannah ecosystem reveals that more species occupy keystone roles within that ecosystem than biologists had previously believed.

(D) As a keystone species of bee becomes more abundant it has a larger effect on the ecosystem it inhabits.

(E) A species of moth that occupies a keystone role in a prairie habitat develops coloration patterns that camouflage it from potential predators.



Passage: Keystone Species

Question: Strengthen

The Simple Story


First, the passage defines a particular term: a keystone species is one whose effects are much larger than would be predicted from its abundance. In other words, this type of species has a larger impact on the ecosystem than would normally be expected.

How do you know for sure that a species is a keystone species? According to the passage, you can’t just remove that keystone species from the environment to see what happens. “It might seem” that a certain characteristic would define a keystone species, but the language it might seem signals that the author is going to disagree. Sure enough, the author provides a certain example about a possible keystone predator and then shows how that predator may or may not be a keystone species.

The author finally concedes that this question depends on two things: context (with an example given) and length of species interaction (with further elaboration given).

Sample Passage Map

This passage contains just one paragraph, so think about how to delineate different parts of it on your Map. Here is one way to map this passage. (Note: abbreviate as desired!)

KS: >> effect than expctd

Mid: How to ID KS? Hard.

2 things: context + interaction length

The “Mid” designation means “the whole middle of the passage is about this.” KS is an abbreviation for keystone species and ID is an abbreviation for identify.

Step 1: Identify the Question

The words if true and most clearly support indicate that this is a Strengthen question. You can answer this one in the same way that you answer Strengthen the Argument Critical Reasoning questions.

Step 2: Find the Support

The question provides a specific line reference:

Keystone status appears to depend on context, whether of particular geography or of such factors as community diversity (for example, a reduction in species diversity may thrust more of the remaining species into keystone roles) and length of species interaction (since newly arrived species in particular may dramatically affect ecosystems).

Step 3: Predict an Answer

The author claims that keystone status depends on two things: context and length of species interaction. What new information would support this claim?

Step 4: Eliminate and Find a Match

(A) These examples do not specifically address geography, community diversity, or the length of interaction among different species.

(B) CORRECT. This example discusses two matters of context mentioned in the passage: geography (different islands) and community diversity (some islands have a greater number of species).

(C) This choice states only that some scientists were wrong about some previous conclusions; it does not address how one can try to determine whether a species has earned keystone status.

(D) This example does not specifically address geography, community diversity, or the length of interaction among different species.

(E) This example does not specifically address geography, community diversity, or the length of interaction among different species.
_________________

"Be challenged at EVERY MOMENT."

“Strength doesn’t come from what you can do. It comes from overcoming the things you once thought you couldn’t.”

"Each stage of the journey is crucial to attaining new heights of knowledge."

Rules for posting in verbal forum | Please DO NOT post short answer in your post!

Kudos [?]: 1189 [1], given: 417

While the most abundant and dominant species within a particular ecosy   [#permalink] 03 Oct 2017, 18:08
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