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Difficulty: 555-605 Level,    Science,    Short Passage,                               
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Re: While the most abundant and dominant species within a particular ecosy [#permalink]
KarishmaB GMATNinja

For Q1, why E is incorrect?
(E) The fact that there is great species diversity within some habitats occupied by P. ochraceus
Author has mentioned in the last sentence that species diversity could impact the keystone species status. Why E is incorrect then. I agree that community diversity could affect when a reduction in species diversity occur but in broader terms, diversity in general could affect.

In Q4, why C is incorrect?
(C) Such an identification is likely to be less reliable as an ecosystem becomes less diverse.
Acc to last line, identification depends on a diverse environment. So a less diverse environment could affect keystone status. Why can't we infer C from this sentence.

Thank you for your time :)
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Re: While the most abundant and dominant species within a particular ecosy [#permalink]
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Question 1


Sneha2021 wrote:
url=[https://gmatclub.com:443/forum/memberlist.php?mode=viewprofile&un=KarishmaB]KarishmaB[/url] url=[https://gmatclub.com:443/forum/memberlist.php?mode=viewprofile&un=GMATNinja]GMATNinja[/url]

For Q1, why E is incorrect?
(E) The fact that there is great species diversity within some habitats occupied by P. ochraceus
Author has mentioned in the last sentence that species diversity could impact the keystone species status. Why E is incorrect then. I agree that community diversity could affect when a reduction in species diversity occur but in broader terms, diversity in general could affect.

Question 1 asks us which answer is specifically mentioned in the passage regarding P. ochraceus.

In that last sentence, the author isn't talking specifically about P. ochraceus any more. Instead, he/she is talking generally about what might keystone status for any species.

So, could great species diversity within some habitats occupied by P. ochraceus impact its keystone status? Sure! But the author doesn't mention that species diversity ACTUALLY impacts P. ochraceus's status. By contrast, the author DOES specifically mention that P. ochraceus's role is impacted by the degree to which its habitat is sheltered from waves.

(E) is out and (A) is the correct answer for question 1.

Question 4


Sneha2021 wrote:
url=[https://gmatclub.com:443/forum/memberlist.php?mode=viewprofile&un=KarishmaB]KarishmaB[/url] url=[https://gmatclub.com:443/forum/memberlist.php?mode=viewprofile&un=GMATNinja]GMATNinja[/url]

In Q4, why C is incorrect?
(C) Such an identification is likely to be less reliable as an ecosystem becomes less diverse.
Acc to last line, identification depends on a diverse environment. So a less diverse environment could affect keystone status. Why can't we infer C from this sentence.

Thank you for your time :)

Here's the exact language of question 4:
Quote:
4. The passage suggests which of the following about the identification of a species as a keystone species?

(C) then says that "such an identification is likely to be less reliable as an ecosystem becomes less diverse."

Hmm. (C) isn't directly talking about how to tell whether something is a keystone species (and your'e absolutely right that a less diverse environment could affect keystone status). This is talking about how reliable the identification is. In other words, how sure are you that a certain species is or is not a keystone?

There's nothing in the passage implying that this identification is more or less reliable in one situation or another. You could be very confident about whether something is a keystone in a very diverse environment, and equally confident about whether its a keystone in a non-diverse environment.

We can eliminate (C) for question 4 because there's nothing implying that one situation makes identifying keystone species less reliable than another.

I hope that helps!
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Re: While the most abundant and dominant species within a particular ecosy [#permalink]
4/4 in 5 minutes. I find myself more comfortable with sciences topics than with humanities topics
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Re: While the most abundant and dominant species within a particular ecosy [#permalink]
GMATNinja wrote:

Question 1


woohoo921 wrote:

Thank you for your thorough explanation. I have a few follow-up questions below after reading through your explanations.

For question 576 (the passage mentions which of the following as a factor that affects the role of P. ochraceus as a keystone species within different habitats), can someone please further clarify why Choice B is incorrect? I see why Choice C is correct. However, the passage does mention 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." So, P. ochraceus does seem to depend on the degree to which other animals prey on mussels (based on its relation to when starfish are present or absent). What am I missing?

For question 578 (which of the following, if true, would most clearly support the argument about keystone status advanced in the last sentence of the passage (lines 24-31), why doesn't Choice A fall under "community diversity" in that bats managing the size of the insect population and the size of the insect population manages the bird population? 

Thank you so much again for all of your time, help, and dedication.

Take another look t that line of the passage: "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."

"This starfish" refers to P. ochraceus. In other words, P. ochraceus IS the starfish. So, there's no interaction between P. ochraceus and other starfish. Eliminate (B) for question 1.

Question 3


The hypothesis in the last line of the passage states that context is important for determining keystone status. For example, a change in species diversity could strip a species of its keystone status, or thrusts a non-keystone species into a keystone role.

Answer choice (A) really doesn't tell us anything about species diversity. Sure, we've got bats, birds, and insects, but is that a diverse ecosystem? There's no way of knowing. Also, it really doesn't capture the idea that a change in species diversity could change keystone status. It could be that these animals have existed just like this for a long time, and the keystone species have also remained the same (instead of shifting when the context changes). Because (A) doesn't support the hypothesis that keystone status is dependent on context, you can eliminate (A).

I hope that helps!

­Dear GMAT Ninja, for Q3, in the paragraph, the author said that 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), so how about "A species of bat is primarily responsible for keeping insect populations within an ecosystem low", can we infer that this is also support for determining bad is the keystone species? 
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Re: While the most abundant and dominant species within a particular ecosy [#permalink]
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