Question 110·Medium·Central Ideas and Details
Wildlife ecologist Maria Santos wanted to understand why some mangrove forests rebound quickly after tropical cyclones while others languish. Examining post-storm data from 120 Pacific coastal mangrove sites, she measured the recovery of leaf canopy and the retention of soil nutrients. The sites containing a greater mix of mangrove species regained full canopy cover months sooner and lost far fewer nutrients than less-diverse stands. Santos concluded that species diversity is a major driver of mangrove resilience following severe storms.
Which choice best states the main idea of the text?
For main-idea questions on short passages, first restate the passage in one simple sentence: who is doing what, and what did they find or conclude? Then quickly scan the answer choices and eliminate any that (1) introduce details or comparisons not mentioned (like new regions, “permanent” effects, or extra variables), (2) contradict the stated conclusion, or (3) zoom in on a detail the passage never discusses. Finally, choose the option that matches both the key findings and the author’s conclusion, not just a minor detail.
Hints
Locate the conclusion sentence
Look at the last sentence of the passage that begins “Santos concluded…”—this tells you how she interprets her results. Any correct answer must reflect that conclusion.
Connect results to the big idea
What two specific things did Santos measure after the storms, and how did these differ between more-diverse and less-diverse mangrove sites? The correct answer should include both what she found and what that implies.
Watch for information that isn’t in the passage
Do any choices mention topics like permanent changes, other oceans or regions, or details about individual species’ leaf chemistry? If so, check whether the passage ever talks about those ideas before choosing them.
Step-by-step Explanation
Restate what the passage says in your own words
First, quickly summarize the passage:
- Research question: Why do some mangrove forests rebound quickly after tropical cyclones while others recover slowly?
- Method: Santos examined data from 120 Pacific mangrove sites, measuring how quickly leaf canopy recovered and how well soil nutrients were retained after storms.
- Key result: Sites with a greater mix of mangrove species regained full canopy months sooner and lost far fewer nutrients than less-diverse sites.
- Conclusion: Santos concluded that species diversity is a major driver of mangrove resilience after severe storms.
Identify the central idea that ties everything together
Now ask: What is the main point the author wants you to take away?
- The entire passage builds toward Santos’s conclusion, which interprets her data.
- The results link higher species diversity to better recovery (faster canopy return and less nutrient loss) after storms.
- So the main idea must combine: (1) the comparison of more-diverse vs. less-diverse forests, and (2) the idea that this difference shows how biodiversity strengthens resilience.
Check each option against the passage details
Evaluate each choice by asking, “Does the passage actually say this?”
- Some wrong choices will introduce new details that never appear (like other regions or permanent effects).
- Others may focus on something very narrow (like leaf chemistry of individual species) that the passage never mentions.
- Eliminate any answer that:
- Mentions permanent changes or effects that the passage doesn’t describe.
- Talks about Atlantic mangroves (the passage only mentions Pacific sites).
- Brings up leaf chemistry variations among individual species, which is not discussed.
- Keep the one choice that accurately reflects both the specific findings (canopy and nutrients, more vs. less diverse forests) and the overall conclusion about resilience.
Match the best summary to the passage
The only option that accurately captures Santos’s findings (more-diverse forests recover canopy sooner and lose fewer nutrients than less-diverse ones) and her conclusion (that species diversity drives resilience, supporting the idea that biodiversity strengthens ecosystems) is Choice A: “Santos's study indicates that mangrove forests with more species bounce back more quickly and retain nutrients better after storms, reinforcing the view that biodiversity strengthens ecosystem resilience.”