D4.2 - Stability and Change

D4.2 - Stability and Change in Ecosystems

Guiding Questions

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

  • What changes caused by humans threaten the stability of ecosystems?

D4.2.1: Stability as a Property of Natural Ecosystems

  • Natural ecosystems can illustrate stability and continuity over millions of years.

    • Example ecosystems: Tropical rainforests, desert ecosystems.

    • The Kalahari desert, estimated to be 60 million years old.

D4.2.2: Requirements for Stability in Ecosystems

  • Stable ecosystems require:

    • A continuous supply of energy (e.g., solar energy).

    • Efficient recycling of nutrients (e.g., nitrogen and phosphorus cycles).

    • Genetic diversity to adapt to changes.

    • Climatic variables need to remain within tolerance levels.

D4.2.3: Deforestation of the Amazon Rainforest

  • Example of a tipping point in ecosystem stability.

  • Importance of expansive rainforest areas for:

    • Generation of atmospheric water vapor via transpiration.

    • Influencing cooling, air flows, and rainfall patterns.

  • Uncertainty over minimum area essential for sustaining ecological processes.

  • Students should be able to calculate percentage change from initial to current rainforest area.

Tipping Points

  • Defined as critical thresholds leading to irreversible changes in ecosystems.

Amazon Rainforest at a Tipping Point

  • The impact of deforestation since the 1970s:

    • Approximately 20% of the Amazon has been deforested.

    • Impacts wind and rainfall patterns influencing climate change.

D4.2.4: Use of Mesocosms in Ecosystem Studies

  • Mesocosms: Controlled experimental systems simulating natural ecosystems.

  • Allows variable manipulation while studying ecological interactions.

  • Importance of following IB Experimental guidelines to minimize harm to organisms.

D4.2.5: Role of Keystone Species

  • Keystone species have a disproportionate effect on community structure.

  • Example: Wolves in Yellowstone ecosystem increase biodiversity.

  • Their removal can lead to ecosystem collapse.

D4.2.6: Sustainability of Resource Harvesting

  • Definition: sustainable rate of harvesting should be lower than the rate of replacement.

  • Terrestrial plant example: Silver Top Palm in the Bahamas—sustainably harvested for traditional products.

  • Marine fish example: Sustainable fishing practices ensure fish populations do not decline over time.

Sustainable Fishing Practices

  • Utilizes selective methods to maximize catches while maintaining population health.

  • Maximum Sustainable Yield: The largest catch that can be harvested without depleting stock.

Monitoring Fish Stocks

  • Methods for assessing fish populations:

    • Capture-mark-release-recapture.

    • Use of echo sounders.

    • Analysis of fish catch data.

D4.2.10: Effects of Plastic Pollution

  • Plastics are non-biodegradable materials impacting marine ecosystems.

  • Types:

    • Macroplastics: Larger, visible debris (>1mm).

    • Microplastics: Smaller pieces resulting from the breakdown of macroplastics (<1mm).

  • Real-life impacts:

    • Laysan albatrosses dying from ingesting plastics.

    • Sea turtles mistaking plastic bags for food, leading to ingestion and harm.

D4.2.11: Rewilding and Ecosystem Restoration

  • Rewilding aims to restore natural processes by reintroducing apex predators and keystone species.

  • Hinewai Reserve in New Zealand: Example of managed natural ecosystem restoration.

D4.2.12: Ecological Succession

  • Ecological succession: Progressive changes in an ecosystem over time due to species interaction.

  • Primary Succession: Starts from bare rock or soil following disturbances (e.g., glacial retreat).

  • Secondary Succession: Follows disturbances that leave soil intact (e.g., wildfires).

D4.2.15: Climax Communities and Arrested Succession

  • Climax community: Stable community reached at the end of succession unless disturbed.

  • Arrested Succession: Factors, such as grazing or drainage, prevent progression to climax communities.

  • Examples:

    • Grazing livestock hinder further plant growth and regeneration.

    • Draining wetlands reduces biodiversity and alters ecological trajectories.