In biology, the term "keystone species" refers to a species that has a disproportionately large effect on its environment relative to its abundance. These species play a critical role in maintaining the structure of an ecological community. Their presence influences the types and numbers of other species in the ecosystem. When a keystone species is removed, the ecosystem can undergo significant changes, often leading to a decline in biodiversity and the collapse of the community structure. The concept highlights how certain organisms are pivotal to the health and stability of their habitats.
🎧 リスニング講義
Professor: Let me give you a classic example. In the Pacific Northwest, the sea otter is a keystone species. Sea otters feed on sea urchins, which in turn graze on kelp forests. When otters are present, they keep the urchin population in check, allowing kelp forests to thrive. These forests provide habitat and food for many fish and invertebrates. However, in areas where otters were hunted to near extinction, urchin populations exploded. The urchins devoured the kelp, creating barren underwater areas. With the kelp gone, fish and other species lost their homes, and biodiversity plummeted. This shows how removing one species—the otter—triggered a cascade of effects that drastically altered the entire ecosystem.
❓ 質問 Using the example from the lecture, explain the concept of 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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