Definition
Resilience of a system
Resilience is a system’s ability to resist disturbances, recover, and maintain stability instead of reaching a tipping point that leads to a new equilibrium.
- Resilience applies to both ecological and social systems, allowing them to adapt, survive, and function despite external shocks.
- It involves two key aspects:
- Resistance: The ability to withstand disturbances without significant change.
- Recovery: The ability to bounce back to its original state after a disturbance.
Factors Affecting System Resilience
- Resistance: The ability to withstand stress or change without breaking down.
- Recovery: The speed and efficiency with which a system returns to its original state after a disturbance.
- Adaptability: The capacity to reorganize or adjust processes to cope with new conditions.
- Redundancy: The presence of multiple species or components performing similar roles, ensuring function if one fails.
- Feedback control: The system’s ability to use negative feedback loops to restore balance.
Example
Coral reefs exposed to repeated bleaching events struggle to recover, leading to ecosystem collapse.
Common Mistake
- A common mistake is assuming that all human interventions reduce resilience.
- In reality, actions like reforestation or sustainable agriculture can enhance it.
Ecological vs Social Resilience
| Ecological Resilience | Social Resilience |
|---|---|
| Maintains ecosystem functions like nutrient cycling, energy flow, and biodiversity. | Maintains ecosystem functions like nutrient cycling, energy flow, and biodiversity. |
| Driven by biodiversity, storage capacity, and feedback mechanisms. | Driven by institutions, culture, education, and technology. |
| Example: Coral reefs recovering after bleaching. | Example: A community rebuilding after a natural disaster. |
Why is Resilience Important?
- Stability: Resilient systems maintain equilibrium and avoid tipping points.
- Adaptation: They can adjust to new conditions, such as climate change or economic shifts.
- Sustainability: Resilience supports long-term survival and functionality.
Common Mistake
Don't confuse resilience with resistance.
- Resistance = ability to withstand change.
- Resilience = ability to recover after change.
Diversity and resilience
- Biodiversity enhances resilience through redundancy.
- Multiple species perform similar ecological functions.
- When one species declines, another can fulfill its role (e.g., pollination, nutrient cycling).
- Diverse ecosystems distribute risk.
- Not all species respond identically to stress.
Example
In tropical rainforests, if one pollinator species declines, others can continue pollination, maintaining ecosystem productivity.
Common Mistake
- Don't confuse diversity with abundance.
- A system with many individuals of a single species is less resilient than one with fewer individuals spread across multiple species.
Storage Size and System Stability
- Storage refers to the quantity of energy, matter, or biomass contained in a system component (e.g. trees, soil, water).
- Large storages act as buffers, slowing the rate of change and providing stability against disturbances.
- Smaller storages respond more quickly to inputs or losses, leading to less stable systems.
Example
Puddle vs. Lake
- A puddle has a small water storage and it heats, cools, or evaporates quickly, showing low stability.
- A lake has a much larger storage, so temperature and water level changes occur slowly, giving greater resilience.
Note
- High diversity + large storages = high resilience
- Low diversity + small storages = low resilience
Case study
North American Prairie Systems
- Native tallgrass prairies once stretched across central North America, characterized by:
- Deep, organic-rich soils
- Complex food webs
- High species diversity and strong negative feedbacks.
- Periodic fires maintained stability.
- Plants regrew from underground meristems.
- When prairies were replaced with monoculture wheat farming, system diversity and resilience declined:
- Low diversity increased vulnerability to pests and diseases.
- Loss of root biomass reduced soil nutrient storage.
- Artificial fertilizers temporarily replaced natural nutrient cycling but weakened long-term stability.
Human Effect on the Resilience of Ecosystems
- Humans influence resilience by reducing biodiversity, altering storages, and accelerating change beyond natural recovery rates.
- When diversity or storages are reduced, ecosystems become more vulnerable to disturbances and less able to recover.
1. Deforestation
- Removes carbon and nutrient storages in biomass and soil.
- Reduces photosynthesis, primary productivity, and carbon sequestration capacity.
- Disturbed forests lose nutrients quickly through erosion and leaching, as thin tropical soils cannot retain them.
- Leads to lower resilience, slower recovery, and increased vulnerability to drought and climate change.
Example
Tropical Rainforests
- High diversity and biomass storage make them resilient.
- Logging and fires destroy tree biomass (main carbon store).
- Loss of producers disrupts food webs and species niches.
- Soil nutrients are rapidly lost after tree removal, leading to long-term degradation.
2. Conversion to Monocultures
Definition
Monoculture
An artificial system growing a single species of crop with minimal biodiversity, resulting in low resilience.
- Replacement of diverse ecosystems with single-crop systems (e.g. soybean, wheat).
- Decreases genetic and species diversity → increases vulnerability to pests and diseases.
- Requires artificial inputs (fertilizers, pesticides) to maintain productivity.
- Low resilience due to dependence on human management.
3. Dam Construction
- Alters water storages and flow regimes.
- Downstream ecosystems receive less water, affecting wetlands and aquatic biodiversity.
- Reduces overall system resilience and may cause loss of habitat or species displacement.
4. Overfishing
- Depletes fish populations faster than they can recover.
- Disrupts food webs and nutrient cycling.
- Leads to loss of a major biological storage of energy and biomass in aquatic ecosystems.
5. Invasive Species
- Outcompete native species and reduce biodiversity.
- Simplify food webs, making ecosystems less adaptable to environmental change.
- Increase likelihood of ecosystem collapse after disturbance.
Case study
Tropical Rainforest Deforestation
- Tropical rainforests have high biodiversity and large carbon storage in biomass.
- When trees are removed:
- Carbon storage declines → less capacity to absorb CO₂.
- Soils lose nutrients quickly through erosion and leaching.
- Food webs shorten, reducing stability.
- Recovery becomes slow or impossible → loss of resilience.
Tip
- Link human activities to both decreased storage (energy or matter) and reduced diversity.
- These are the two key mechanisms by which humans reduce resilience.
Self review
- Describe how biodiversity contributes to the resilience of an ecosystem.
- Compare the resilience of grasslands and tropical rainforests to disturbance.
- Explain how the size of storages affects stability using the lake–puddle analogy.
- Discuss how human activities reduce resilience in ecosystems.
