1. IB Environmental Systems & Societies
Unit 1.1.6: Feedback

2. System Equilibria
What does this diagram show?
Stable equilibrium

3. System Equilibria What does this diagram show?
Steady state equilibrium

4. System Equilibria
How do systems maintain and/or return to equilibrium?

5. Feedbacks ↓ (+) Elephant Population Births
As an elephant population rises, how is the elephant birth rate affected?
The birth rate increases
Elephant
Population
↓ (+)
Births

6. Feedbacks (+)↑ Elephant Population Births
As elephant birth rates increase, how is the elephant population affected?
The population increases
Elephant
Population
(+)↑
Births

7. Feedbacks (+)↑↓(+) Elephant Population Births
Thus we can say that the elephant population drives the elephant birth rate that drives elephant population
Elephant
Population
(+)↑↓(+)
Births

8. ↑ Feedbacks Fear of banks crashing ↓ (+) Withdrawal Money ↓ (+)
Another example...
What happens if citizens become concerned that banks are running out of money?
Withdrawal money
Bank health suffers
Banks fail... ↑
Fear of
banks crashing
↓ (+)
Withdrawal
Money
↓ (+)
Bank Health
Banks Fail

9. Feedbacks This is called a positive feedback (open) loop.
Positive feedback leads to increasing change in a system.
The response in an open loop says "Great, more, more!" So the change in the outside environment is reinforced instead of corrected.
i.e. An action creates a result that generates more of the action, and hence more of the result.
Is this a good thing?

10. Feedbacks
Positive feedback tends to move a system away from its equilibrium state & make it more unstable, which is often destructive or even fatal.
What happens when you cut your finger?

11. Feedbacks ↓ (+) Elephant Population Deaths
As an elephant population increases, how is the proportionate death rate affected?
A proportionally larger number of elephants will die
Elephant
Population
↓ (+)
Deaths

12. Feedbacks (-) ↑ Elephant Population Deaths
As the elephant death rate increases, how is the elephant population affected?
The population decreases
Elephant
Population
(-) ↑
Deaths

13. Feedbacks (-) ↑↓(+) Elephant Population Deaths
This complimentary behaviour forms a negative feedback (closed) loop
Elephant
Population
(-) ↑↓(+)
Deaths

14. Feedbacks (-) ↑↓(+) Itch Scratch Another example...
What do you do when you’re itchy???
Scratch!
Itch
(-) ↑↓(+)
Scratch

15. Feedbacks (-) ↑↓(+) Hunger Eating Another example...
What do you do when you’re hungry???
Eat!
Hunger
(-) ↑↓(+)
Eating

16. Feedbacks
Negative feedback is a self-regulating method of control leading to the maintenance of a steady- state equilibrium, making it more stable.
A change in the outside environment is sensed, which triggers a response which opposes or corrects the change, because their action is toward the good (equilibrium) of the living system.

17. Indicate Positive (+) or negative (-)feedbacks