1. Introduction to Modeling Lab: Causal Loop & Stock and Flow Models
Bio 102
Outline:
Objectives
Brief review of concepts and lab prep assignment
Building models in STELLA!

2. Learning Objectives for today’s lab
Concepts and terminology
Importance of feedback and how to use causal loops
Conceptualizing world as stocks and flows
Experience building simulation models of some basic population and community level interactions

3. Causal-Loop Models ( - ) ( + ) ( - ) ( + ) Feedback Control
(+) feedback reinforces change
(-) feedback counteracts change
Bank
Balance
Termite
Population
( + )
( + )
( - )
( + )
Fox
population
Termite
Population
( + )
( + )
Tree
Biomass
Interest
Added/month
( + )
( - )
( - )
( + )
Hare
population
( - )
Births
( + )

4. Stock and Flow Models Stock Flows Stock = state variable:
A component of a system that stores stuff
Flow = input & output = rate of change = differential equation:
The movement of stuff into or out of a stock
Stock
Births
Deaths
Population Size
Flows

5. Causal-Loops  Stocks and Flows?
Termite
Population
Tree
Biomass
( - )
( + )
Fox
population
Hare
Interest
Added/month
Births
Bank
Balance
Bank Balance
Interest

6. Causal-Loops  Stocks and Flows?
Termite
Population
Tree
Biomass
( - )
( + )
Fox
population
Hare
Interest
Added/month
Births
Bank
Balance
Termite Population
Births

7. Causal-Loops  Stocks and Flows?
Termite
Population
Tree
Biomass
( - )
( + )
Fox
population
Hare
Interest
Added/month
Births
Bank
Balance
Termite Population
Tree Biomass

8. Causal-Loops  Stocks and Flows?
Termite
Population
Tree
Biomass
( - )
( + )
Fox
population
Hare
Interest
Added/month
Births
Bank
Balance
Fox
Hare

9. Building models in STELLA
Open
Kettering 100  Open from Program Menu in Start Menu
Kettering 103  Apple computer should have been started up with Windows Operating System. Double click on STELLA program icon on desktop
Births
Deaths
Population Size