While the most abundant and dominant species within a particular ecosy

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

Question 1

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

Here's the exact language of question 4:

(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!

4/4 in 5 minutes. I find myself more comfortable with sciences topics than with humanities topics

­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? 

Question 3

­Choice (B) works because it's evidence that context matters: in one geography, the iguana is a keystone species, but in another geography, it isn't.

Choice (A), on the other hand, does not illustrate how context matters. And keeping insect populations low is not the same as reducing species diversity. If you start with, say, 50 species and then reduce all of their populations, you'd still have 50 species -- so there would be no change in the species diversity.

If we were told that the bat became a keystone species ONLY AFTER there was a reduction in species diversity, then we'd have some support for the last sentence. But that's not what we get in choice (A).

For more on (A) vs (B), check out this post: https://gmatclub.com/forum/while-the-mo ... l#p2708389.