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! The modeling process Benefits of modeling

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 dynamic simulation models of populations growing with and without constraints

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 ( + )

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

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

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

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

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

Building models in STELLA Open Science Center Lab  Open from Program Menu in Start Menu Computer Science Lab  double click on program icon on desktop (but not on “Bio102LabModels.stm”) Births Deaths Population Size