Ecosystem Functioning & Sustainability (DP IB Environmental Systems & Societies (ESS))

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