Summary: Feedback, Stability, Tipping Points & Resilience
- Negative feedback loops reduce change and help a system stay stable
- Positive feedback loops make change bigger and can push a system away from balance
- Stable equilibrium happens when inputs and outputs are balanced over time
- Feedback delays (lag time) can make systems overshoot and {{oscillate|Repeatedly rise and fall instead of settling at one stable level.}}
- Tipping points are thresholds where a small change causes a large (often hard to reverse) shift
- Positive feedback often drives systems toward tipping points
- After a tipping point, the system settles into a new equilibrium
- Resilience is a system’s ability to absorb {{disturbance|A sudden event that disrupts a system, such as fire, flood, disease, or pollution.}} and still keep functioning
- Resilient systems can change in the short term but stay stable in the long term
- High {{biodiversity|The variety of species in an ecosystem, including plants, animals, and microorganisms.}} usually increases resilience because there are more roles and backups (redundancy)
- Large and multiple storages act as buffers, slowing change and helping recovery
- Low resilience increases the risk of crossing tipping points
Freshwater lake example (eutrophication)
- Extra nutrients enter the lake (fertiliser/sewage)
- Algae increase quickly (algal bloom)
- Algae block sunlight → plants die
- Decomposition increases → oxygen drops
- Fish/invertebrates die → lake shifts to a low-oxygen state
Exam link: This is a positive (reinforcing) feedback loop — more nutrients → more algae → less oxygen → more ecosystem damage → conditions that favour more algae.
Humans and resilience
- Humans can reduce resilience by lowering biodiversity and shrinking storages (deforestation, monocultures, water extraction, pollution)
- When diversity/storages drop, ecosystems recover less well and tipping points become more likely
- Humans can increase resilience by protecting ecosystems, restoring diversity, and increasing storages (mixed forests, wetland restoration, soil improvement, conservation)
- Actions that increase diversity and storages usually increase resilience