Lecture Notes: Stability and Change in Ecosystems

Key Themes

• Continuity and Change: Focus on how ecosystems maintain stability over time and how they may change.
• Stability: Ecosystems like the Borneo lowland rainforest have persisted for millions of years.

Factors Contributing to Ecosystem Stability

• Constant Energy Supply: Typically from the Sun.
• Nutrient Cycling: Essential cycles include:
  • Carbon
  • Nitrogen
  • Phosphorus
• Genetic Variation: Within species is critical to withstand selective pressures.
• Stable Climate: Consistent temperature and precipitation are necessary.

Disruptions to Ecosystems

• Removal of Materials: Example - Deforestation.
• Removal of Species: Example - Poaching impacting biodiversity.
• Eutrophication: Excess nutrients causing algae blooms and affecting oxygen levels.
• Climate Change: Significantly impacts sensitive ecosystems like coral reefs.

Recovery and Tipping Points

• Recovery: Some ecosystems stabilize after disruption.
• Tipping Point: A critical level of disturbance causing irreversible changes, exemplified by the Amazon rainforest.
  • Positive Feedback Loops: Deforestation leads to less transpiration, drought, and fires.

Mesocosms

• Definition: Miniature ecosystems for controlled experiments.
• Types:
  • Closed Systems: Ideal for mimicking Earth’s nutrient cycling.
  • Open Systems: Still useful but less controlled.
• Advantages:
  • Allow for isolation of variables.
  • Enable multiple trials.
• Disadvantages:
  • Cannot perfectly replicate complex natural interactions.

Keystone Species

• Definition: Species with significant impact on ecosystem stability.
• Importance: Their removal can lead to ecosystem collapse.
• Case Study:
  • Paine's Sea Star Experiment:
    • Removal of sea stars led to dominance by mollusks.
    • Resulted in diminished diversity and fewer types of photosynthetic organisms.
    • Demonstrates the broad impact of keystone species on ecosystems.