In biology, the term "keystone species" refers to a species whose impact on its ecosystem is disproportionately large relative to its abundance. Removing a keystone species can cause dramatic changes in the ecosystem's structure, often leading to a collapse or a cascade of extinctions. The concept emphasizes that certain organisms play a critical role in maintaining biodiversity and ecological balance, even if they are not the most numerous.
🎧 Лекция
Professor: Let me give you an example of a keystone species: the sea otter. In kelp forest ecosystems along the Pacific coast, sea otters are not the most abundant animals, but they have a huge effect. They eat sea urchins. Without otters, sea urchins multiply and eat the kelp at the base, destroying the entire forest. Kelp forests provide habitat and food for many species like fish and crabs. When otters are present, they control the urchin population, allowing kelp to thrive, which in turn supports a rich community. So the presence of a few otters keeps the whole ecosystem healthy and diverse, demonstrating the concept perfectly.
❓ Вопрос Using the example from the lecture, explain the concept of keystone species.
📊 Критерии оценки TOEFL Speaking Task 3
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.
💡 Советы
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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