6. Stability and Change D4.2

Stability & Change

  • Guiding Question: What features of ecosystems allow stability over unlimited time periods?

Stability as a Property of Natural Ecosystems

  • Illustration of Ecosystem Stability:

    • Some ecosystems have shown continuity over millions of years.

    • Examples include Old Growth Forests, Temperate forests, parts of the Amazon, and Boreal Forests.

  • Requirements for Stability:

    • Continuous supply of energy.

    • Effective recycling of nutrients.

    • High genetic diversity for population robustness.

    • Climatic variables must remain within tolerance levels.

  • Deforestation of Amazon Rainforest:

    • Serves as an example of a possible tipping point in ecosystem stability.

    • A large area of rainforest is needed to generate atmospheric water vapor via transpiration, contributing to local cooling and rainfall.

    • Uncertainty regarding the minimum area necessary to sustain these processes.

  • Using Models to Investigate Stability:

    • Mesocosms:

      • Experimental ecosystems in sealed or open tanks to investigate stability.

      • Successful aquatic or microbial ecosystems preferred over terrestrial ones.

      • MUST adhere to IB experimental guidelines for care and maintenance.

  • Role of Keystone Species:

    • Keystone species have a disproportionate impact on community structure.

    • Their removal can lead to ecosystem collapse.

  • Assessing Sustainability of Resource Harvesting:

    • Sustainability defined as the rate of harvesting being lower than the rate of replacement.

    • Examples of renewable resources should include one terrestrial plant and one marine fish.

  • Factors Affecting Agricultural Sustainability:

    • Considerations include soil erosion, nutrient leaching, supply of fertilizers, pollution from agrochemicals, and carbon footprint.

  • Eutrophication in Aquatic Ecosystems:

    • Caused by leaching of nitrogen and phosphate fertilizers leading to imbalances and increased Biochemical Oxygen Demand (BOD).

  • Biomagnification of Pollutants:

    • Understanding accumulation of toxins like DDT and mercury in higher trophic levels.

  • Plastic Pollution in Oceans:

    • Persistence in the environment due to nonbiodegradability.

    • Notable adverse effects on marine life.

  • Restoration of Natural Processes (Rewilding):

    • Methods include reintroduction of apex predators, connectivity restoration of habitats, and minimizing human impacts.

    • Example: Hinewai Reserve in New Zealand.

Steady Conditions for Stability

  • Stability defined as the ability to maintain processes over time; reliant on rainfall, sunlight, and warmth.

  • Some ecosystems persist undisturbed for millions of years.

Resistance and Resilience

  • Definitions:

    • Resistance: Ability of an ecosystem to remain unchanged despite disturbances.

    • Resilience: Ecosystem's ability to recover from disturbances.

  • Importance of balance in community structure for maintaining stability.

Investigating Ecosystem Variables in Mesocosms

  • Considerations for Setting Up Mesocosms:

    • Choice of container (glass or plastic).

    • Transparency of materials used.

    • Selection of organisms for a sustainable community.

    • Maintaining oxygen supply.

Tipping Points and Ecosystem Disturbances

  • Critical disturbances may lead to a tipping point beyond which recovery is difficult.

  • Positive Feedback Loops: Influence stability and resilience, e.g., the water cycle.

Deforestation as a Tipping Point Example

  • Amazon rainforest's deforestation linked to reduced rainfall due to habitat loss and increased drought.

  • Critical feedback mechanisms influenced by disturbances in the ecosystem.

Engagement with Mapping and Data Analysis

  • Use of external resources to visualize and analyze biodiversity and impact of tree cover loss in the Amazon.