Key Idea: Topic 2.2 explains **how ecosystems are organised**, and why some ecosystems can **recover (resilience)** while others cross **tipping points** and collapse.
✅ Core definitions (exam must-know)
If a question mentions **abiotic factors**, it is about an **ecosystem**, not just a community.
🌍 Ecosystems as systems & scale
🛡️ What increases resilience?
Memorise the chain: **Disturbance → resilience → recovery**.
🦸 Keystone species
⚠️ Low resilience & tipping points
High marks come from linking ideas: biodiversity ↓ → resilience ↓ → tipping point risk ↑.
**Community vs ecosystem:** A **community** includes only the **living organisms** in an area, while an **ecosystem** includes the community **plus abiotic factors** such as soil, water, and climate. **Three factors that increase ecosystem resilience:** • **High biodiversity** (more species = more alternative pathways) • **Complex food webs** (less dependence on one species) • **Genetic diversity** within populations (greater adaptability) **Keystone species & trophic cascade:** A **keystone species** has a **disproportionately large effect** on its ecosystem. Removing it can cause a **trophic cascade**, where changes at one trophic level affect multiple other levels.