Syllabus Edition
First teaching 2024
First exams 2026
Ecosystem Functioning & Sustainability (DP IB Environmental Systems & Societies (ESS))
Revision Note
Written by: Alistair Marjot
Reviewed by: Bridgette Barrett
Ecosystem Functioning & Sustainability
Sustainability of ecosystems
Sustainability is a fundamental property of ecosystems
It refers to the ecosystem's ability to maintain balance and productivity over time
Ecosystems naturally regulate themselves to sustain life within them
Balanced inputs and outputs
In a steady-state ecosystem, inputs and outputs are balanced
Inputs include energy, nutrients and water entering the ecosystem
Outputs include energy, nutrients and waste leaving the ecosystem
This balance ensures the ecosystem's long-term stability and resilience
These inputs and outputs can be illustrated with ecosystem flow diagrams
Flow diagrams demonstrate the movement of energy and nutrients within ecosystems
These diagrams highlight the interconnectedness of biotic and abiotic factors within an ecosystem
An ecosystem flow diagram showing a simplified form of the nutrient cycle in a tropical rainforest
Evidence of long-term sustainability
Some ecosystems have persisted for millions of years, indicating their long-term resilience and sustainability
Tropical rainforests are a prime example of long-term sustainable ecosystems
Despite changes in climate and other external factors, these ecosystems have endured
For example, the Amazon Rainforest has remained stable despite external pressures like deforestation
Its great biodiversity and complex interactions contribute to its resilience
Human impacts on ecosystem stability
Human activity can disrupt the stability of ecosystems, leading to tipping points
Tipping points are critical thresholds where small changes can trigger significant shifts in the ecosystem
These shifts can lead to the collapse of the original ecosystem and the establishment of a new equilibrium
Deforestation in the Amazon Rainforest
Deforestation involves the clearing of trees for agriculture, logging, or urban development
Deforestation reduces the generation of water vapour by plants through transpiration
Impact on climate:
Reduced transpiration leads to a decrease in the amount of water vapour in the local atmosphere
Water vapour is essential for cloud formation and precipitation (which generates a significant cooling effect) and for maintaining regional climate patterns
Consequently, deforestation disrupts local and regional climate systems
Feedback loop:
Deforestation can create a positive feedback loop where reduced precipitation leads to further forest loss
With less precipitation, the remaining forest may become more susceptible to drought and wildfires, accelerating deforestation and, as a result, generating even less transpiration and water vapour for precipitation
New equilibrium:
If deforestation continues at its current rate, it may not be long until the Amazon Rainforest reaches a new equilibrium state
This new equilibrium may feature different compositions of species, reduced biodiversity and very different climate patterns
Deforestation can drive a positive feedback look that results in an increase in the frequency of droughts and forest fires
Understanding the role of keystone species
Keystone species are organisms within an ecosystem that have a disproportionately large impact on the structure and function of the ecosystem relative to their abundance
In other words, even if they have a relatively low abundance, keystone species play critical roles in maintaining the health and long-term stability of ecosystems
The presence of keystone species can help regulate the population sizes of other species and maintain higher levels of biodiversity
The removal of keystone species can have cascading effects throughout the ecosystem, leading to significant changes in community structure and function
If their removal disrupts the ecological balance too much, this can increase the risk of ecosystem collapse
Examples of keystone species
Purple sea stars (Pisaster ochraceus) play a crucial role in controlling mussel populations along the rocky shores of the North Pacific coast
Sea stars prey on mussels, preventing them from overwhelming the ecosystem
Without sea stars, mussel populations would expand rapidly and start to dominate the ecosystem, outcompeting other species for space and resources
This would displace other intertidal organisms, leading to a decline in overall species diversity
African elephants (Loxodonta africana) play a vital role in shaping the structure and composition of savannah grasslands
Elephants feed on shrubs and trees, preventing them from becoming too dense and dominating the landscape
Their browsing behaviour creates gaps in the vegetation, promoting the growth of grasses and increasing habitat diversity—this provides habitats for a greater variety of species, increasing species diversity
Their movement and feeding activities also contributes to soil nutrient cycling by redistributing nutrients and increasing soil fertility and plant growth
Human impacts on biosphere integrity
The planetary boundaries model identifies nine key Earth system processes essential for maintaining a stable planet
These boundaries represent safe operating limits for human activity to prevent irreversible environmental changes
Changes beyond these boundaries can lead to detrimental effects on Earth's systems and human well-being
Biosphere integrity (one of the nine critical processes) refers to the overall health and diversity of life on Earth
Human activity has significantly impacted biosphere integrity, pushing it beyond critical thresholds
Disturbances to ecosystems have led to severe loss of biodiversity, disrupting ecological balance and resilience
Ecosystems and species diversity are highly interlinked, with each depending on the other:
Healthy ecosystems support diverse species populations, while diverse communities contribute to ecosystem resilience and stability
Loss of biodiversity due to human activities undermines the integrity of ecosystems, making them more vulnerable to collapse
Evidence from extinction rates
Extinction rates provide tangible evidence that the planetary boundary for biosphere integrity has been crossed
Highly accelerated rates of species extinction in recent times indicate severe disturbances to ecosystems and loss of biodiversity
Human-induced factors such as habitat destruction, pollution and climate change have driven extinction rates to unprecedented levels
Avoiding critical tipping points
Reversing the loss or "erosion" of biosphere integrity is crucial to preventing catastrophic shifts in Earth's ecosystems
Addressing ecosystem damage and species loss is essential to avoiding reaching these critical tipping points
Ecosystem conservation efforts aim to preserve the structure, function and diversity of ecosystems
By protecting ecosystems, we can slow the rate of ecosystem damage and reduce the risk of irreversible changes
Preserving species is a key factor in maintaining ecosystem integrity
Each species occupies a unique ecological niche within an ecosystem, contributing to its stability and resilience
Protecting ecosystems helps to preserve the niche requirements essential for the ongoing survival of individual species
Various conservation strategies can help to protect ecosystems and preserve species diversity, including:
Habitat conservation: protecting natural habitats from destruction and fragmentation helps maintain ecosystem integrity
Species conservation: using specific methods to protect the most endangered species is essential for biodiversity conservation
Sustainable resource management: promoting sustainable practices ensures the responsible use of natural resources without degrading ecosystems
Examiner Tips and Tricks
When using real-world examples, like the Amazon rainforest, make sure you are able to explain how human activities, such as deforestation, can disrupt ecosystem stability and lead to new equilibria.
Remember that healthy, stable ecosystems and high species diversity are highly interdependent factors that sustain each other—a decrease in one will cause a decrease in the other and vice versa.
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