Resilience
Resilience
Big idea: 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.
A **{{resilient system|A system that can recover after a disturbance and avoid crossing tipping points.}}** can change in the short term but remain stable in the long term.
What does resilience look like?
Resilient systems are **dynamic**, not static. Short-term change is normal.
Examples of resilient systems
Resilient ecosystems may change in species numbers, but the system as a whole survives.
Factors that increase resilience
What reduces resilience?
Low resilience increases the risk of **tipping points**.
Factors that increase resilience
1. Diversity
**{{Diversity|A variety of species, genes, or roles within a system.}}** makes systems more resilient.
Example: If one prey species declines, predators may switch to another.
2. Size and number of storages
Large and multiple **{{storages|Places where matter or energy is held.}}** increase resilience.
Large storages act as **buffers** — they slow down change.
Example: A lake dries out more slowly than a puddle because it has a larger storage.
Resilience and feedback
Resilience and feedback
Resilient systems usually have strong **negative feedback loops** that counteract change.
Resilience vs tipping points
When resilience is low, a system may cross a **{{tipping point|A threshold beyond which a system cannot return to its original state.}}**.
After a tipping point, the system settles into a **new equilibrium**.
Human Impact on Ecosystem Resilience
Human Impact on Ecosystem Resilience
Humans can affect ecosystem resilience in **positive or negative ways**. Our aim should be to **reduce damage** and **strengthen systems** so ecosystems can cope with change.
Negative human impacts on ecosystem resilience
Human activities often **reduce resilience** by lowering **biodiversity** and **shrinking storages** such as biomass, water, and nutrients.
When diversity and storages decrease, ecosystems become **less able to recover** and more likely to cross **tipping points**.
Damage is often **delayed or hidden**, meaning humans may not react until the ecosystem is already close to collapse.
Positive human impacts on ecosystem resilience
Humans can **increase resilience** by protecting ecosystems, restoring diversity, and increasing the size and number of storages.
Resilience can also be improved in **human systems**, such as cities, by planting trees to reduce heat and store water.
Actions that increase **diversity** and **storages** usually increase ecosystem resilience.
Case study example: Freshwater lake
Case study example: Freshwater lake ecosystem (eutrophication)
A freshwater lake is usually a stable system with clear water, aquatic plants, and healthy fish populations. Its resilience depends on balanced nutrient levels and sufficient oxygen.
Human activities such as agriculture and sewage discharge can add excess nutrients (nitrates and phosphates) to the lake.
If oxygen levels fall too low, the lake can cross a **tipping point** and shift from a clear, healthy state to a polluted, low-oxygen state.
After this shift, recovery is difficult because nutrients stored in sediments continue to feed algal growth even if pollution inputs are reduced.
This is a **positive (reinforcing) feedback loop**: more nutrients → more algae → less oxygen → ecosystem damage → conditions that favour more algae.