1.3 Equilibrium and Feedback - Review

Equilibrium and Feedback Review

This is another incredibly important topic and students absolutely need to learn the definitions of positive and negative feedback. They are guaranteed on every exam. These are also fundamental concepts that can be used to explain almost everything in ESS. Once you have the definition, then you need to be able to give examples. First learn some examples but then try to apply this model to other situations and see if you can explain that to a friend. A positive feedback loop should always results in an amplification (an increase) in change - usually something just keeps getting worse. A negative feedback loop should always dampen down change and return the system to its equilibrium.

1. What is an equilibrium?

  • The balance between inflow and output of energy is constant over time

  • No net change in storage within the system through time.

  • Under changing conditions negative feedback mechanisms can create new internal distributions of energy and material within the system.

2. Explain how humans are impacting the equilibria of systems?

Much of the concern over human impacts on the environment centres on the rapid rate of change induced by many human activities, which can disturb system stability and bring unwanted and unforeseen side-effects.

3. Define positive feedback

  • +ve feedback loops are destabilizing

  • They serve to amplify change in the same direction.

  • Amplification takes place away from the equilibrium

  • This can drive a system toward a tipping point where a new equilibrium is adopted.

  • These are alternative stable states.

4. Define negative feedback

  • Negative feedback loops are stabilizing

  • They occur when the output of a process inhibits or reverses the operation of the same process in such a way as to reduce change—it counteracts deviation.

  • It suppresses system changes promoted by external factors

  • This self-regulation is homeostasis and explains stability in systems.

  • leads to the maintenance of a steady-state 

5. Describe an example of positive feedback

Global warming leads to an increase in temperatures > this melts ice caps > the albedo in the region decreases > so more solar radiation is absorbed > leading to more infra-red radiation > leading to an increase in global temperatures... more ice melts etc

6. Describe an example of negative feedback

There is an increase in hares > this leads to an increase in lynx > the lynx eat more hares and so the number of hares decrease (dampening down change)

There is an increase in global CO2 levels > this leads to an increase of photosynthesis > this uses more CO2 and therefore global CO2 levels decrease again (unfortunately this feedback loop is hampered by the effect of increased temperatures reducing photosynthetic activity).

There is an increase in global temperatures > this leads to more evaporation and cloud formation > the clouds reflect more solar radiation back to space > decreasing global temperatures

7. What is an alternative stable state?

Both states are in an equilibrium but the the conditions may be very different in each state. The location is the same.

8. What is a tipping point and how does it occur?

Inputs may start a positive feedback loop whereby the changes are amplified. Beyond a certain point, a tipping point is reached, and the system moves to a new alternative state in a new equilibrium.

9. Describe a non-catastrophic alternative stable state formation

It can also be the result of random stochasitic differences that occur during the development of a system. Succession is thought to be able to result in many alternative stable states depending upon these stocastic differences, i.e. the climax community may be slightly different depending upon the inputs during the process of succession.

10. Give an example of a catastrophic tipping point leading to an alternative stable state.

Coral bleaching can lead to a stable state where the coral is dead and the reef dies

Global warming may lead to an ice free arctic or "hot-house earth"

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