Question 162·Hard·Central Ideas and Details
For decades, ecologists assumed that lichen colonization on fresh volcanic rock followed a slow, orderly sequence: a handful of hardy “pioneer” species arrive first, and only centuries later do the more delicate, moisture-dependent lichens appear. However, while surveying the young island of Anak Krakatau, researchers Hiro Tanaka and Mei Chen found evidence that upends that timeline. Samples taken from lava flows that solidified in 1993 already contained two lichen species previously considered “late-stage” colonizers, whereas the supposed pioneers were scarce. Tanaka and Chen argue that Anak Krakatau’s frequent ash fall provides trace minerals that accelerate soil formation, allowing late-stage lichens to establish themselves within just two decades.
According to the text, which choice would Tanaka and Chen most likely support?
For “According to the text, which choice would X most likely support?” questions, locate the sentence that states X’s conclusion (often introduced by verbs like “argue,” “suggest,” or “conclude”) and paraphrase it as a simple cause-and-effect claim. Then pick the answer that matches that causal logic without adding new conditions, reversing the direction of the effect, or shifting the explanation to something the passage doesn’t emphasize.
Hints
Locate their main claim
Focus on the sentence that begins with “Tanaka and Chen argue that…”. What cause do they give, and what effect does it have?
Track the cause-and-effect chain
Write the chain in three parts: ash fall → ________ → late-stage lichens appear sooner.
Watch for subtle mismatches
Be cautious of choices that (1) change the cause from ash-driven soil formation to spore arrival, or (2) claim pioneers must still dominate first, even though the passage says pioneers were scarce.
Step-by-step Explanation
Identify what changed the scientists’ view
The passage contrasts what ecologists assumed (a centuries-long sequence with pioneers first) with what Tanaka and Chen found on Anak Krakatau (late-stage lichens present on lava that solidified in 1993, with pioneers scarce). This signals that the usual timeline does not fit this island.
Find the explanation Tanaka and Chen give
Tanaka and Chen’s key claim is explicit: frequent ash fall provides trace minerals that accelerate soil formation, which then allows late-stage lichens to establish themselves within about two decades.
Translate the claim into a general statement
If ash fall enriches fresh lava with minerals and speeds soil formation, then ecological succession (at least for lichens) can proceed faster than expected on frequently ashed volcanic surfaces.
Select the choice that matches that claim
The correct choice is the one stating that frequent ash deposition can shorten the expected timeline of ecological succession by rapidly enriching otherwise barren volcanic rock.