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, often leading to the decline or extinction of other species. The concept highlights how certain organisms play a critical role in maintaining the structure and balance of their habitat, even if they are not the most numerous.
🎧 Conferencia de audio
Professor: Let me give you a classic example of a keystone species: the sea otter. In kelp forest ecosystems along the Pacific coast, sea otters are not the most numerous creatures, but they have a huge effect. They prey on sea urchins, which feed on kelp. Without otters, sea urchin populations explode, and they devour the kelp forests. Kelp provides shelter and food for many fish and invertebrates. When kelp disappears, those animals lose their habitat and their numbers drop sharply. But when otters are present, they keep urchin numbers in check, allowing kelp to thrive, and thus the whole ecosystem remains diverse and healthy. So, a single predator, though not abundant, is essential.
❓ Pregunta Question: Using the example from the lecture, explain the concept of a keystone species.
📊 Rúbrica 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.
💡 Consejos
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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