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22 Apr 2020, 13:22
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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
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
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. Why have these cacti expanded their range of
pollinators by remaining open and receptive in daylight?
This development at the northernmost range of
columnar cacti may be due to a yearly variation in the
abundance-and hence the reliability-of migratory
nectar-feeding bats. 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. 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.
Recent data reveals that during spring in the
Sonoran Desert, the nectar-feeding bats are
specialists feeding on cardon, saguaro, and
organpipe flowers. However, whereas cactus-flower
abundance tends to be high during spring, bat
population densities tend to be low except near
maternity roosts. Moreover, in spring, diurnal cactus-
pollinating birds are significantly more abundant in
this region than are the nocturnal bats. Thus, with bats
being unreliable cactus-flower pollinators, and daytime
pollinators more abundant and therefore more reliable,
selection favors the cactus flowers with traits that
increase their range of pollinators. While data suggest
that population densities of nectar-feeding bats are
also low in tropical areas of southern Mexico, where
bats are the exclusive pollinators of many species
of columnar cacti, cactus-flower density and bat
population density appear to be much more evenly
that population densities of nectar-feeding bats are
also low in tropical areas of southern Mexico, where
bats are the exclusive pollinators of many species
of columnar cacti, cactus-flower density and bat
population density appear to be much more evenly
balanced there: compared with the Sonoran Desert's
cardon and saguaro, columnar cacti in southern Mexico
produce far fewer flowers per night. Accordingly,
despite their low population density, bats are able to
pollinate nearly 100 percent of the available flowers.
Q 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
A. have flowers that remain open after sunset
B. are pollinated primarily by dietary specialists
C. can be pollinated by nectar-feeding bats
D. have stigmas that are unreceptive to pollination at night
E. are sometimes pollinated by diurnal pollinators
I am confused between Option A and Option E, as both can be derived from the passage. Please clarify the correct answer and also, how to approach questions where two options look correct?
southern Arizona, the flowers of several species of
columnar cacti-cardon, saguaro, and organ
pipe-were once exclusively pollinated at night by
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
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. Why have these cacti expanded their range of
pollinators by remaining open and receptive in daylight?
This development at the northernmost range of
columnar cacti may be due to a yearly variation in the
abundance-and hence the reliability-of migratory
nectar-feeding bats. 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. 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.
Recent data reveals that during spring in the
Sonoran Desert, the nectar-feeding bats are
specialists feeding on cardon, saguaro, and
organpipe flowers. However, whereas cactus-flower
abundance tends to be high during spring, bat
population densities tend to be low except near
maternity roosts. Moreover, in spring, diurnal cactus-
pollinating birds are significantly more abundant in
this region than are the nocturnal bats. Thus, with bats
being unreliable cactus-flower pollinators, and daytime
pollinators more abundant and therefore more reliable,
selection favors the cactus flowers with traits that
increase their range of pollinators. While data suggest
that population densities of nectar-feeding bats are
also low in tropical areas of southern Mexico, where
bats are the exclusive pollinators of many species
of columnar cacti, cactus-flower density and bat
population density appear to be much more evenly
that population densities of nectar-feeding bats are
also low in tropical areas of southern Mexico, where
bats are the exclusive pollinators of many species
of columnar cacti, cactus-flower density and bat
population density appear to be much more evenly
balanced there: compared with the Sonoran Desert's
cardon and saguaro, columnar cacti in southern Mexico
produce far fewer flowers per night. Accordingly,
despite their low population density, bats are able to
pollinate nearly 100 percent of the available flowers.
Q 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
A. have flowers that remain open after sunset
B. are pollinated primarily by dietary specialists
C. can be pollinated by nectar-feeding bats
D. have stigmas that are unreceptive to pollination at night
E. are sometimes pollinated by diurnal pollinators
I am confused between Option A and Option E, as both can be derived from the passage. Please clarify the correct answer and also, how to approach questions where two options look correct?
Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Reading Comprehension (RC) Forum
Still interested in this question? Check out the "Best Topics" block below for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
shameekv1989
22 Apr 2020, 13:41
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gargipratapsingh
gargipratapsingh
You can find the discussion at https://gmatclub.com/forum/in-the-sonor ... l#p1869453 - You can post a question there and get a response or your query might have already been addressed
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22 Apr 2020, 15:33
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Discussed here: in-the-sonoran-desert-of-northwestern-mexico-and-southern-arizona-t-242586.html
You can post your doubts on the above-mentioned thread
Kindly go through the rules before posting : rules-to-post-on-the-verbal-forum-208733.html
This topic is locked and archived
You can post your doubts on the above-mentioned thread
Kindly go through the rules before posting : rules-to-post-on-the-verbal-forum-208733.html
This topic is locked and archived
Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Reading Comprehension (RC) Forum
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
