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555-605 (Medium)|   Long Passage|   Science|                        
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KarishmaB
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In the Sonoran Desert of northwestern Mexico and southern Arizona, t 19 Jun 2022, 04:04
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woohoo921
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saby1410
Hi,
ChiranjeevSingh VeritasKarishma GMATNinja AnishPassiTGC GMATNinjaTwo
They can be dietary generalists whose fidelity to a particular species depends on the availability of alternative food sources. Or, they can be dietary specialists, but their abundance may vary widely from year to year, resulting in variable pollination of their preferred food species. Finally, they
may be dietary specialists, but their abundance may be chronically low relative to the availability of flowers.

In the above line what role does Contrasting word But plays. What is contrast in the line.
how they arrive to tell that they may be dietary specialists( Finally, they may be dietary specialists)
What is the role of BUT in last sentence and What purpose this line(but their abundance may be chronically low relative to the availability of flowers.) serves.

Look at a simpler example first:

Following are the reasons you shouldn't trust him to help you:
1. He may be a bad person.
2. He may be a good person but he may be busy with helping others.
3. He may be a good person but he may not know what to do.


On the same lines, the passage is listing the various reasons why pollinators can be unreliable.

1. They can be dietary generalists (they eat anything) whose fidelity to a particular species depends on the availability of alternative food sources. (so if they get some other food sources, they may not pollinate and hence that makes them unreliable)

2. They can be dietary specialists, but their abundance may vary widely from year to year, resulting in variable pollination of their preferred food species.

This is in contrast to point 1 above. They could be dietary specialists (not generalists) such that they would eat the nectar of this cacti only so they would be reliable, but their numbers may vary from year to year so that would make them unreliable.

3. They may be dietary specialists, but their abundance may be chronically low relative to the availability of flowers.

Another reason could be that their number could be lower than what is required to pollinate all flowers. So this would make them unreliable.

KarishmaB
I am a bit confused on how the passage refers to "nectar-feeding bats" and then just "bats". Why wouldn't the GMAT repeat the "nectar-feeding" part, or is that just to be assumed at this point?

Also, to clarify for #527 (according to the passage, present-day columnar cacti in the Sonoran Desert differ from their close relatives in southern Mexico in that the Sonoran cacti), is the support for Choice E found here: "Yet the flowers of the Sonoran Desert cacti have evolved to remain open after sunrise" --> in that the "yet" indicates the difference?

avigutman
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The passage tells us why the flowers of the Sonoran Desert cacti have evolved to remain open after sunrise (hence, allowing pollination by bees and birds). It tells us why these cacti are not completely reliant on the nectar-feeding bats.
During the explanation, when the passage mentions 'bats,' we know which bats it is talking about. Using 'nectar-feeding' again and again can get pretty tedious if there is no distinction being made among different types of bats.


Quote:

Also, to clarify for #527 (according to the passage, present-day columnar cacti in the Sonoran Desert differ from their close relatives in southern Mexico in that the Sonoran cacti), is the support for Choice E found here: "Yet the flowers of the Sonoran Desert cacti have evolved to remain open after sunrise" --> in that the "yet" indicates the difference?
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In the Sonoran Desert of northwestern Mexico and
southern Arizona, the flowers of several species of
columnar cacti—cardon, saguaro, and organ
pipe—were once exclusively pollinated at night by
(5)
nectar-feeding bats, as their close relatives in arid
tropical regions of southern Mexico still are. In these
tropical regions, diurnal (daytime) visitors to columnar
cactus flowers are ineffective pollinators because,
by sunrise, the flowers' stigmas become unreceptive
(10)
or the flowers close. Yet the flowers of the Sonoran
Desert cacti have evolved to remain open after sunrise,
allowing pollination by such diurnal visitors as bees and
birds.


We are told that Sonoran desert cacti were once pollinated exclusively by bats and those in southern Mexico are still pollinated exclusively by bats.
But the Sonoran desert cacti have evolved to remain open in the day to allow pollination by birds and bees too.
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In the Sonoran Desert of northwestern Mexico and southern Arizona, t 18 Dec 2022, 07:53
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GMATNinja - Why cant option D be right?

GMATNinja
felixduan320

Thanks for sharing this. A few things. Wouldn't the term "generalist", which suggests that they can pollinate more than one flower, indicate that a generalist would pollinate according to preference, and not abundance? It would make more sense for a specialist to prioritize abundance, since they can only feed on a select few flowers, whereas a generalist has more choices and can therefore be more picky. This would make Answer C more correct.

In addition, Answer A specifically mentions "at times significantly lower", whereas the excerpt in the passage quotes "their abundance may be CHRONICALLY low relative to the availability of flowers". It seems to be the passage is suggesting the only chronically low abundance would be a reliability issue, but if it happens once in a while ("at times"), the effects are not significant enough to warrant the "unreliable" label.

Let me know if the above makes sense. Based on the logic above, I am still struggling to understand why B is correct and not C. Thank you!
The passage tells us that a generalist can be an unreliable pollinator because its "fidelity to a particular species depends on the availability of alternative food sources."

This tells us that a generalist doesn't really have a preference for which plant it eats -- it just eats whatever is most readily available. Let's say that out of plants X, Y, and Z, only plant X is available. Generalists will just eat plant X and be happy to do so! Now say that plants Y and Z move into the area -- the generalist doesn't remain faithful to plant X, but eats whatever is most convenient. Plant X will not get as much attention from the generalist -- so from plant X's perspective, the generalist is an unreliable pollinator when other plants are available for it to feed on.

The main point is that the generalist doesn't choose what it eats based on preference -- it chooses based on availability.

Take another look at (C):
Quote:
C. A dietary generalist for whom that flower’s nectar is not a preferred food but is the most consistently available food [is an unreliable pollinator].
Based on the discussion above, we know that generalists decide what to eat based on availability. So, it will reliably eat (and therefore pollinate) "the most consistently available food." This is essentially the opposite of answer choice (C), so (C) is incorrect.

To understand why (B) is correct, take a look at the two reasons identified in the passage to explain why a specialist may be an unreliable pollinator:
  • "their abundance may vary widely from year to year, resulting in variable pollination of their preferred food species." OR
  • " their abundance may be chronically low relative to the availability of flowers."

Now take a look at answer choice (B):
Quote:
B. A dietary specialist whose abundance is at times significantly lower than that of the flower
You are correct to point out that (B) doesn't align well with a case in which the specialist population is "chronically low." However, this answer choice does fit nicely with the other case, in which the specialists' "abundance may vary widely." Because (B) specifically tells us that the specialist's abundance is "at times significantly lower than that of the flower," we can say that it is not consistently available to pollinate all of the flowers. Therefore, this particular specialist is an unreliable pollinator, and (B) is correct.

I hope that helps!
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In the Sonoran Desert of northwestern Mexico and southern Arizona, t 21 Dec 2022, 11:18
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Question 2


kittle
GMATNinja - Why cant option D be right?

GMATNinja

The passage tells us that a generalist can be an unreliable pollinator because its "fidelity to a particular species depends on the availability of alternative food sources."

This tells us that a generalist doesn't really have a preference for which plant it eats -- it just eats whatever is most readily available. Let's say that out of plants X, Y, and Z, only plant X is available. Generalists will just eat plant X and be happy to do so! Now say that plants Y and Z move into the area -- the generalist doesn't remain faithful to plant X, but eats whatever is most convenient. Plant X will not get as much attention from the generalist -- so from plant X's perspective, the generalist is an unreliable pollinator when other plants are available for it to feed on.

The main point is that the generalist doesn't choose what it eats based on preference -- it chooses based on availability.

Take another look at (C):
Quote:
C. A dietary generalist for whom that flower’s nectar is not a preferred food but is the most consistently available food [is an unreliable pollinator].
Based on the discussion above, we know that generalists decide what to eat based on availability. So, it will reliably eat (and therefore pollinate) "the most consistently available food." This is essentially the opposite of answer choice (C), so (C) is incorrect.

To understand why (B) is correct, take a look at the two reasons identified in the passage to explain why a specialist may be an unreliable pollinator:
  • "their abundance may vary widely from year to year, resulting in variable pollination of their preferred food species." OR
  • " their abundance may be chronically low relative to the availability of flowers."

Now take a look at answer choice (B):
Quote:
B. A dietary specialist whose abundance is at times significantly lower than that of the flower
You are correct to point out that (B) doesn't align well with a case in which the specialist population is "chronically low." However, this answer choice does fit nicely with the other case, in which the specialists' "abundance may vary widely." Because (B) specifically tells us that the specialist's abundance is "at times significantly lower than that of the flower," we can say that it is not consistently available to pollinate all of the flowers. Therefore, this particular specialist is an unreliable pollinator, and (B) is correct.

I hope that helps!
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Dietary generalists decide whether to eat something based on the availability of alternative food sources. (D) talks about dietary generalists who prefer the flower in question over other available foods. If they would rather eat this flower, then they will be reliable pollinators, not unreliable pollinators.

I hope that helps!
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In the Sonoran Desert of northwestern Mexico and southern Arizona, t 25 Dec 2024, 10:43
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Hi,
For the first question i just have one doubt, the correct answer choice does not contain "Southern Arizona" whereas the passage does.
GMATNinja

Question 2


T1101
Dear Verbal Expert,

even after reading the discussion I am still not able to fully understand Question 2... I understand why B is correct, but I do not understand why C is incorrect. Is it because of the "not a preferred food"? The passage never talks about explicitly about preference.

Thank you in advance!!!

(Book Question: 440)
According to the passage, which of the following types of nectar-feeding pollinators is likely to be an unreliable pollinator of a particular cactus flower?
A. A dietary specialist whose abundance is typically high in relation to that of the flower
B. A dietary specialist whose abundance is at times significantly lower than that of the flower
C. A dietary generalist for whom that flower???s nectar is not a preferred food but is the most consistently available food
D. A dietary generalist for whom that flower???s nectar is slightly preferred to other available foods
E. A dietary generalist that evolved from a species of dietary specialists
The passage does mention preference explicitly in lines 22-24:


Or, they can be dietary specialists, but their abundance may vary widely from year to year, resulting in variable pollination of their preferred food species.

However, the role of preference is implied throughout the passage.

  • The distinction between "generalist" and "specialist" begins with the premise that animals pollinate food species (in other words, animals pollinate what they feed on).
  • Some pollinators (the generalists) pollinate whatever food species are available, while other pollinators (the specialists) do have a special preference, which can only be satisfied by a narrow range of food species.

So how we do we eliminate choice (C)? Well, here's the author says when describing reasons what could make a pollinator unreliable:


Pollinators can be unreliable for several reasons. They can be dietary generalists whose fidelity to a particular species depends on the availability of alternative food sources.

According to the passage, a dietary generalist will be faithful to a particular food species if it's available. They don't have special food preferences. If they're feeding on a certain type of nectar, but an alternative food sources become available, then the generalists will begin pollinating that alternative food source instead. Is that what choice (C) says?

Quote:
C. A dietary generalist for whom that flower's nectar is not a preferred food but is the most consistently available food
(is likely to be an unreliable pollinator of that flower).
Nope. (C) tells us that this flower is the most consistently available food for that generalist. If that's true, then we'd expect the generalist to be a reliable pollinator for this flower, because the generalist pollinates whatever is available.

But choice (C), as it's written, states that the generalist is likely to be an unreliable pollinator for this flower.

This contradicts the expected behavior of generalists -- so we must eliminate it.

I hope this helps!
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In the Sonoran Desert of northwestern Mexico and southern Arizona, t 07 Jan 2025, 11:29
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shvm_sin7
Hi,

For the first question i just have one doubt, the correct answer choice does not contain "Southern Arizona" whereas the passage does.
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The first sentence of the passage states: "In the Sonoran Desert of northwestern Mexico and southern Arizona..."

There's no need to repeat that geographic description every time the desert is mentioned. Anytime we see "Sonoran Desert", we know that refers to a desert in northwestern Mexico and southern Arizona. (A very beautiful one, incidentally.)

Hopefully that answers your question, but let us know if not!
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In the Sonoran Desert of northwestern Mexico and southern Arizona, t 10 Apr 2026, 06:46
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