Feedback Processes

Types of Feedback

• Positive Feedback
  • Cause and effect move in the same direction.
  • Examples:
    • Increase leads to increase.
    • Decrease leads to decrease.
• Negative Feedback
  • Cause and effect move in opposite directions.
  • Examples:
    • Increase leads to decrease.
    • Decrease leads to increase.

Deer and Grass Example

• Less grass → Less deer
  • Positive Feedback: Decrease leads to a decrease.
• Fewer deer → More grass
  • Negative Feedback: Decrease leads to an increase.
• More grass → More deer
  • Positive Feedback: Increase leads to an increase.
• More deer → Less grass
  • Negative Feedback: Increase leads to a decrease.
• Importance: Negative feedback maintains system equilibrium.

Example of Positive Feedback Without Negative Feedback

The Water Cycle and Ice Ages

• Process:
  • Water evaporates, forms clouds, precipitates (rain/snow).
  • Snow is white, reflects sunlight, cools Earth.
• Positive Feedback Cycle:
  • Cooling → More snow → More reflection → More cooling.
  • Leads to rapid ice ages (decades, not thousands of years).
• Threshold Concept: Critical to break positive-only feedback loop.

Threshold in Ice Ages

• Initial Cooling
  • Snow expands, Earth gets colder.
• Ocean's Role
  • Takes longer to cool than land; contains more heat.
  • Gradual cooling leads to reduced evaporation and snowfall.
• End of Ice Age
  • Snow reduces through sublimation (solid to gas).
  • Ground changes from white to dark, absorbs heat, warms planet.

Threshold Concept

• Definition: Point where a different process interrupts feedback cycle.
• Pot Plant Example
  • Fertilizer initially helps growth.
  • Over-fertilization kills plant, demonstrating threshold.

Key Takeaways

• Positive feedback can lead to rapid changes when unchecked by negative feedback.
• Thresholds are crucial in breaking feedback cycles and restoring balance.
• Understanding feedback dynamics is vital for predicting and managing ecological and environmental changes.