1.2B Negative feedback loops Notes

1. Feedback refers to processes in which the output or result of a system influences its own operation.
2. Negative feedback loops are mechanisms that counteract change, helping systems maintain stability and equilibrium.
3. They play a critical role in both natural ecosystems and human physiological systems, preventing extreme fluctuations that could threaten survival.
4. Negative feedback loops are essential to homeostasis (in biological systems) and equilibrium (in ecological and planetary systems).

Mechanism of Negative Feedback

1. Begins with a system in equilibrium, where inputs and outputs are balanced.
2. A disturbance or external factor disrupts this balance (for example, a change in temperature, population size, or resource availability).
3. The system responds in a way that reduces or reverses the initial change, restoring stability.
4. This regulation ensures that systems fluctuate around an average condition rather than moving progressively away from it.

Carbon Cycle and Climate Regulation

1. An environmental-scale feedback loop.
2. When CO₂ levels increase:
   1. Higher temperatures enhance plant photosynthesis and biomass growth.
   2. Increased plant uptake reduces atmospheric CO₂.
   3. This moderates the greenhouse effect.
3. When CO₂ decreases: Cooler conditions slow photosynthesis, allowing CO₂ to build up again.
4. This stabilizing process prevents Earth’s climate from diverging dramatically over short timescales.

Hydrological Cycle and Cloud Feedback

1. Increased global temperatures enhance evaporation → more cloud formation.
2. Clouds reflect incoming solar radiation (high albedo), which reduces heating.
3. As the planet cools, evaporation and cloud formation decrease again.
4. This negative feedback moderates the Earth’s temperature within narrow limits.

Forest Canopy Regeneration

1. When strong winds or storms blow down trees, gaps appear in the forest canopy.
2. Increased sunlight stimulates rapid growth of understory plants and saplings.
3. New vegetation fills the gap, re-establishing canopy cover and restoring the microclimate.
4. This demonstrates self-restoration through negative feedback.

Temperature Regulation in the Human Body

1. Human homeostasis offers a biological analogy for environmental feedback.
2. When body temperature rises, mechanisms such as sweating and vasodilation cool the body.
3. When the temperature drops, shivering and vasoconstriction increase heat production and retention.
4. These opposing processes stabilize body temperature around 37°C, a biological steady-state equilibrium.

Daisyworld Model

1. Developed by James Lovelock and Andrew Watson as part of the Gaia hypothesis, which proposes that life on Earth helps regulate environmental conditions.
2. Daisyworld is a computer simulation of a hypothetical planet orbiting a star with gradually increasing luminosity (heat).
3. The model shows how life can stabilize planetary temperature through negative feedback mechanisms.

Structure of the Model

1. The planet is inhabited only by black daisies and white daisies:
   1. Black daisies absorb sunlight and warm the planet.
   2. White daisies reflect sunlight and cool the planet.
2. The rest of the surface is bare ground, which has an intermediate reflectivity (albedo).
3. The temperature of Daisyworld depends on the balance between absorbed sunlight and heat radiated into space.

Equilibrium in Ecosystems

1. Equilibrium is crucial in ecosystems because it ensures stability, resilience, and sustainability in the face of natural and human-induced changes.
2. It allows systems to function efficiently and maintain life-supporting conditions.

Types of Equilibrium

1. Steady-State Equilibrium

1. Common in open natural systems such as ecosystems.
2. Inputs (e.g., energy, matter) are equal to outputs over time, but small fluctuations occur around an average condition.
3. Maintained by negative feedback loops that keep variables (temperature, population, nutrient levels) within stable limits.

2. Stable Equilibrium

1. Occurs when the system returns to its original state after disturbance.
2. Small-scale disturbances (e.g., death of a tree, flood event) trigger recovery mechanisms that restore balance.

3. Developing (Dynamic) Equilibrium

1. Some ecosystems evolve through stages, establishing temporary equilibriums during ecological succession.
2. As conditions change (soil depth, light availability, species composition), the ecosystem transitions from one equilibrium state to another until reaching the climax community.

Equilibrium and Stability in Open Systems

1. Negative feedback loops ensure that open systems (e.g., ecosystems, climate systems) do not move permanently away from equilibrium.
2. Fluctuations are normal and necessary, as they allow systems to respond to environmental change while avoiding collapse.
3. Systems that cannot self-regulate (e.g., under excessive human pressure) may lose equilibrium entirely, resulting in unstable or new equilibria.

Negative Feedback in Succession

1. During primary succession, pioneer species modify the environment—adding organic matter, retaining moisture, and altering soil chemistry.
2. These changes make conditions suitable for new species, gradually shifting equilibrium toward a more stable community.
3. Negative feedback prevents any one species from becoming overly dominant, ensuring balanced progression toward the climax community.