Question 129·Hard·Central Ideas and Details
In a recent ecological study, Sarah Kumara and colleagues investigated how certain seabird species distribute themselves across newly formed volcanic islands. Earlier models suggested that seabirds wait decades for vegetation to establish before colonizing. However, Kumara's team documented terns and boobies nesting within two years of an eruption, taking advantage of nutrient-rich ash layers for burrows and feeding on insect swarms drawn by residual heat. The researchers argue that the birds' early arrival accelerates soil development by depositing guano, thereby speeding subsequent plant establishment.
According to the passage, which choice best describes the effect Kumara and colleagues propose early seabird colonization has on newly formed volcanic islands?
For central-idea/detail questions, locate the exact sentence that states the researchers’ claim (often introduced by verbs like “argue” or “propose”). Paraphrase it into a simple cause-and-effect chain, then choose the option that matches both the direction of the effect (speeding vs. slowing) and the stated mechanism (here, guano adding nutrients), eliminating choices that introduce unstated mechanisms or revert to the earlier model the study challenges.
Hints
Use the last sentence
The researchers’ proposed effect is stated directly in the final sentence, beginning with “The researchers argue…”
Track the cause-and-effect chain
Identify what the birds add to the island and what that addition changes (soil first, then plants).
Watch for the mechanism
The passage gives a specific mechanism (guano deposition). Choose the option that matches that mechanism rather than inventing a different one.
Step-by-step Explanation
Locate where the effect is described
Look for the sentence that states the researchers’ claim about the impact of early seabird arrival. In the final sentence, the passage says the birds' early arrival “accelerates soil development by depositing guano, thereby speeding subsequent plant establishment.”
Paraphrase the claim in your own words
The researchers’ proposed chain of effects is:
- Birds arrive early.
- They deposit guano (nutrient-rich droppings).
- This accelerates soil development.
- Faster soil development leads to faster plant establishment.
Match to the choice that restates the claim
The correct choice must reflect that early seabird colonization speeds plant establishment because it adds nutrients (guano) that help soil form faster. The option that says this is: It catalyzes plant establishment by providing additional nutrients.