Key Idea: Topic 2.3 explains how species share ecosystems (niches + resource use), how populations interact and change over time, what stops populations growing forever (limiting factors + carrying capacity), and how ecologists estimate population size using sampling.
✅ Niche vs habitat (exam favourite)
To describe a niche: give feeding role + interaction + conditions needed (e.g., nocturnal predator that hunts rodents, needs forest cover).
🤝 Population interactions (know the outcomes)
High niche overlap → competition increases → one species may be outcompeted or forced to change resource use.
📉 Population dynamics (patterns you must recognise)
In graphs: predators lag behind prey. Explain the lag using reproduction time and food availability.
🧱 Limiting factors & carrying capacity
If the limiting factor improves → carrying capacity increases. If it worsens → carrying capacity decreases.
📏 Measuring populations (field methods)
Lincoln Index: N = (n₁ × n₂) / m
Know assumptions: population closed, marks not lost, marked mix evenly, samples random.
1) Habitat vs niche? 2) What causes competition? 3) Define carrying capacity. 4) Difference between density-dependent and density-independent factors? 5) When do you use quadrats vs Lincoln Index?