1. Environmental Systems
Topic - 1 Systems and Models
Statements:
1.H – 1.L

2. Steady-State Equilibrium
The most stable state of a system and is a common property of most open systems in nature.
The average condition of the system remains unchanged over time.
No net change in the system… what does this mean??

3. Steady-State Equilibrium
Some systems may undergo long-term changes to their equilibrium, while retaining an integrity to the system.
Although there is continual input and output of matter and energy, the state of the system remains constant.
This can be compared to Static Equilibrium - Properties of the system are constant and unchanged over time… this does not often occur in nature.
Examples of Steady-State:
With the person sitting next to you; One person describe steady state equilibrium and the other explain an example.

4. How systems stay at Equilibrium
Systems remain balanced or unbalanced because of their feedback mechanisms.
Systems always want to be in homeostasis, or balanced, and usually have a mechanism to get there.
Feedback systems can be either negative or positive

5. Feedback Loops
Feedback Loop (IB): a relationship in which a change to one part of a system influences another part of the system in a way that either reinforces (increases) or slows the original change.
(Or) A change to a system can either increase change or take the system back to equilibrium.
Feedback loops involve time lags. Why?
Not all systems have feedback loops... there must be a change to the system first.

6. Negative Feedback Negative is Good
Occurs when a change to a system causes a response that is in the opposite direction of the output.
A self-regulating method of promoting stability…leads of steady-state equilibrium.

7. Negative Feedback Loops
Example: temperature regulation in humans involves a negative feedback loop, in which increased temperature leads to decrease in temperature by sweating.
Without this response, what would happen?

8. Example of negative feedback in the environment?
USE PREDATOR PREY

9. Positive Feedback Positive is usually Bad
Occurs when a change to a system causes more of the change to occur.
Feedback that amplifies or increases change and accelerates deviation away from equilibrium.
It is a destabilizing, vicious cycle.
Example:
System = a forest
Change to system = flame
Response = wood dries
Feedback = more fire and more wood drying, which leads to more fire, etc….

10. Positive Feedback Loops
Example: exponential population growth involves a positive feedback loop in which more individuals lead to increased numbers of births.

11. Another Example of Positive Feedback: Off-Road Vehicle Use
As vehicle use occurs, tires uproot and kill plants. This increases erosion rates and causes gullies. Erosion causes more vegetation loss. People avoid the gullies, which causes the paths to widen and more vegetation loss and erosion, etc…

12. 1J: Describe by diversity and the size of storages within systems can contribute to their resilience and affect their speed of response to change (time lags).
Resilience: the ability of a system to “bounce back” after a disturbance
Low Resilience
Smaller systems
Low diversity
Time lags shorter
High Resilience
Larger Systems
More Diversity
Results in longer time lags.

13. 1K: Define and explain the possible consequences of tipping points.
Tipping Point: when a system is pushed past the point of returning to it’s original state.
Involve positive feedback loops
Once reached there is a quick change to the system
Changes are difficult to reverse/long lasting
Examples?

14. Evaluation of Models
Strengths: (in other words, why do we use models?)
Limitations: (issues surrounding the use of models)
Discuss this with the 3 to 4 people in your area, coming up with 3 for each. Discuss as a class.

15. MODELS: STRENGTHS/BENEFITS

16. MODELS: LIMITATIONS/PROBLEMS