Overgrazing by purple sea urchins has caused many kelp forests along North America's west coast to be replaced by urchin...
GMAT Information and Ideas : (Ideas) Questions
Overgrazing by purple sea urchins has caused many kelp forests along North America's west coast to be replaced by urchin barrens—areas stripped of vegetation and covered in purple sea urchins. Urchins in barrens persist in a state of starvation that lessens their nutritional value—and thus their appeal—to many predators. Sarah Gravem and colleagues placed sunflower sea stars, a once-abundant predator species suffering massive population declines in recent years, in aquariums that each contained a nutritionally poor and a nutritionally rich purple sea urchin. The researchers found that the sea stars selected the nutritionally rich urchin in \(42.7\%\) of trials and the nutritionally poor urchin in \(37.5\%\) of trials, suggesting that ______
Which choice most logically completes the text?
sunflower sea stars are willing to hunt sea urchins, but if given a choice, they will prey on other more nutritious marine animals instead.
sunflower sea stars are reluctant to feed on both nutritionally poor and nutritionally rich sea urchins and are therefore unlikely to thrive in kelp forests.
sunflower sea stars are less likely to consume sea urchins in barrens than other species of sea stars are, putting sunflower sea stars at a high risk of extinction.
sunflower sea stars do not always avoid foraging on nutritionally poor sea urchins, making sunflower sea star population recovery a potentially important tool for controlling urchin barrens.
Step 1: Decode and Map the Passage
Create Passage Analysis Table
| Text from Passage | Analysis |
|---|---|
| Overgrazing by purple sea urchins has caused many kelp forests along North America's west coast to be replaced by urchin barrens—areas stripped of vegetation and covered in purple sea urchins. |
|
| Urchins in barrens persist in a state of starvation that lessens their nutritional value—and thus their appeal—to many predators. |
|
| Sarah Gravem and colleagues placed sunflower sea stars, a once-abundant predator species suffering massive population declines in recent years, in aquariums that each contained a nutritionally poor and a nutritionally rich purple sea urchin. |
|
| The researchers found that the sea stars selected the nutritionally rich urchin in 42.7% of trials and the nutritionally poor urchin in 37.5% of trials |
|
Provide Passage Architecture & Core Elements
Main Point: An experiment tested whether sunflower sea stars show strong preference for nutritionally rich over poor sea urchins, finding a modest difference in selection rates.
Argument Flow: The passage sets up an environmental problem, explains why it persists, then presents experimental data about predator behavior.
Step 2: Interpret the Question Precisely
This is a fill-in-the-blank question asking us to choose the best logical connector. The answer must create the right relationship between what comes before and after the blank.
Step 3: Prethink the Answer
- The key insight is that sunflower sea stars chose the nutritionally rich urchin only slightly more often (\(\mathrm{42.7\%}\) vs \(\mathrm{37.5\%}\) - just a \(\mathrm{5.2}\) percentage point difference)
- This shows these predators don't strongly avoid nutritionally poor urchins
- They still eat them over one-third of the time, which has implications for controlling urchin populations
sunflower sea stars are willing to hunt sea urchins, but if given a choice, they will prey on other more nutritious marine animals instead.
✗ Incorrect
- Claims sea stars prefer other marine animals instead
- The experiment only tested urchin choices - no data about other animals
- Goes beyond study scope
sunflower sea stars are reluctant to feed on both nutritionally poor and nutritionally rich sea urchins and are therefore unlikely to thrive in kelp forests.
✗ Incorrect
- Says sea stars are reluctant to feed on both types
- The data shows active selection (\(80.2\%\) combined selection rate)
- Misinterprets evidence
sunflower sea stars are less likely to consume sea urchins in barrens than other species of sea stars are, putting sunflower sea stars at a high risk of extinction.
✗ Incorrect
- Compares to other sea star species
- Study only examined sunflower sea stars
- Introduces absent information
sunflower sea stars do not always avoid foraging on nutritionally poor sea urchins, making sunflower sea star population recovery a potentially important tool for controlling urchin barrens.
✓ Correct
- Correctly states sea stars do not always avoid nutritionally poor urchins (\(37.5\%\) selection proves this) and connects to population recovery as a tool for controlling barrens
- Matches evidence and broader context