In biology, the term 'keystone species' refers to a species that has a disproportionately large effect on its environment relative to its abundance. Removing a keystone species can cause a cascade of changes, often leading to the collapse of the ecosystem. Classic examples include predators that control prey populations, thereby maintaining the balance of other species in the habitat.
🎧 リスニング講義
Professor: Let me give you a classic example—sea otters in the Pacific kelp forests. Sea otters are a keystone species. They eat sea urchins, which normally graze on kelp. Without otters, urchin populations explode, and they devour the kelp, destroying the forest. This kills the habitat for fish and other organisms. When otters were hunted to near extinction in some areas, the kelp forests vanished. But when otters were reintroduced, they controlled the urchins again, and the kelp forests recovered. This shows how a single predator can shape an entire ecosystem.
❓ 質問 Using the example from the lecture, explain the concept of a keystone species.
📊 TOEFLスピーキング評価基準
Delivery: Fluency, pronunciation, intonation
Language Use: Grammar, vocabulary, sentence variety
Topic Development: Accurately explain the reading concept and restate the lecture examples
Scored 0-30 based on holistic scoring (original 0-4, scaled to 30). 30s preparation, 60s response.
💡 解答のヒント
Note the core concept definition from the reading (usually 1-2 sentences)
Record 1-2 specific examples the professor uses in the lecture
Start with the concept definition, then explain with lecture examples
Use template phrases: "The reading defines... The professor illustrates this by..."
Keep within 60s; ensure clarity and fluency
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