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 a cascade of changes, often leading to the collapse of the ecosystem's structure and diversity. These species often control the population of other organisms, maintain habitat, or provide critical resources. Their presence is essential for maintaining the balance of the ecosystem, even if they are not the most numerous organisms.
🎧 Conferencia de audio
Professor: Let me give you a classic example: the sea otter. In the kelp forest ecosystems off the coast of the Pacific Ocean, sea otters are a keystone species. They eat sea urchins, which are herbivores that feed on kelp. Without otters, the sea urchin population explodes, and they devour the kelp forests. This destroys the habitat for many fish, invertebrates, and other organisms that rely on the kelp. When otters are present, they keep the urchin numbers in check, allowing kelp forests to thrive, which supports high biodiversity. So even though otters are not the most abundant species, their presence or absence dramatically alters the whole ecosystem.
❓ 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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