Resilience & Stability of Ecosystems (HL IB Environmental Systems & Societies (ESS))
Revision Note
Resilience & Stability of Ecosystems
An ecosystem’s capacity to tolerate disturbances and maintain equilibrium depends on its diversity and resilience
Diversity refers to the variety of species, genetic variations, habitats and ecological functions within an ecosystem
Resilience refers to the ability of an ecosystem to recover after a disturbance
High resilience = ecosystem quickly returns to its original state after disturbance
Low resilience = ecosystem takes a long time to recover or does not fully recover after disturbance
Greater diversity often means greater resilience—two main reasons for this include:
Species redundancy:
Multiple species perform similar roles, so if one species is lost, others can fill its ecological role
Genetic variation:
More genetic diversity within a species can help it adapt to changing conditions
Human impacts on succession
Human activities can divert the progression of succession to an alternative stable state by modifying the ecosystem through various activities, such as:
Burning
Agriculture
Grazing pressure
Resource use (such as deforestation)
These activities can have both direct and indirect impacts on the ecosystem
They lead to changes in the biotic and abiotic components, ultimately altering the course of ecological succession within the ecosystem
For example, controlled fires are often used to clear land for agricultural purposes or to manage the spread of wildfires
However, fire can have serious negative effects on the ecosystem by killing off plants, reducing soil fertility and altering nutrient cycles
Similarly, agriculture and grazing can cause soil erosion, loss of vegetation cover and changes in nutrient cycling
This can, in turn, affect the composition of the species in the ecosystem
These activities, which divert the progression of succession, may be temporary or permanent, depending upon the resilience of the ecosystem
If the human disturbance is mild and the ecosystem is highly resilient, it may be able to recover and return to its original state
If the disturbance is severe and the ecosystem is less resilient, the ecosystem will be permanently changed
This eventually leads to a new stable state with a different set of species and ecological interactions
This is one reason why it is so important to carefully consider the environmental impacts of human activities in order to minimise their negative effects on the ecosystem
It is essential to protect natural ecological processes, such as succession
Case Study
Human disturbances to succession in tropical rainforests
Even highly resilient ecosystems like tropical rainforests can shift to alternative stable states under enough human pressure
Deforestation and agriculture:
Trees removed to create grazing land
Reduces habitat complexity and leads to biodiversity loss
Disrupts nutrient cycling and changes the hydrological cycle
Causes soil erosion and loss of topsoil, leading to lower soil fertility
Results in decreased primary productivity
Can trigger the process of desertification
Mining:
It involves the removal of topsoil and vegetation
Leads to soil erosion and landslides
Chemicals used in mining can pollute water sources
Water pollution negatively impacts aquatic life within the ecosystem.
Formation of alternative stable states
Deforestation can transform tropical rainforests into savannas or grasslands
These new ecosystems are less resilient compared to rainforests
They have lower biodiversity and productivity
They have different abiotic and biotic factors from the original forest ecosystem
These new states have lower resilience and are less capable of recovering to their original forested condition
Did this page help you?