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# While the most abundant and dominant species within a

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Intern
Joined: 03 Aug 2011
Posts: 45

Kudos [?]: 27 [2] , given: 17

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

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29 May 2012, 11:14
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86% (01:44) correct 14% (00:57) wrong based on 306

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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).
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:
A

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:
C

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:
B

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:
D

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

_________________

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Kudos [?]: 27 [2] , given: 17

Intern
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Kudos [?]: 27 [0], given: 17

Re: OG 13 - RC [#permalink]

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29 May 2012, 11:22
_________________

Keep your eyes on the prize: 750

Kudos [?]: 27 [0], given: 17

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Re: OG 13 - RC [#permalink]

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29 May 2012, 11:26
plz prepare more explanations
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Kudos [?]: 27 [0], given: 17

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Kudos [?]: 3 [0], given: 32

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

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10 Aug 2013, 02:39
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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.

Kudos [?]: 3 [0], given: 32

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Kudos [?]: 240 [0], given: 0

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

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21 May 2016, 00:21
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While the most abundant and dominant species within a [#permalink]

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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
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

Kudos [?]: 19 [0], given: 84

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Kudos [?]: 860 [0], given: 313

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

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29 Jun 2017, 12:22
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
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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Kudos [?]: 860 [0], given: 313

Manager
Joined: 04 Sep 2016
Posts: 174
Location: India
WE: Engineering (Other)

Kudos [?]: 19 [0], given: 84

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

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29 Jun 2017, 17:46
Hi GMATNinja

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.

WR,
Arpit

Kudos [?]: 19 [0], given: 84

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

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15 Jul 2017, 11:31
All correct. Took me around 7 mins.

Agree with the reasoning provided by jacquerc.

Kudos [?]: 3 [0], given: 142

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Kudos [?]: 28 [0], given: 311

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

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17 Jul 2017, 01:41
All correct
It was a good passage .
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Kudos [?]: 28 [0], given: 311

Re: While the most abundant and dominant species within a   [#permalink] 17 Jul 2017, 01:41
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