Simulistics

Stage 2: Extending the model to represent a population of trees

Thu, 28/02/2008 - 18:25 — administrator

Step 1

Draw a submodel box to completely enclose your model diagram.

Click on the submodel tool on the toolbar
Move the mouse to the top left of your model diagram
Drag the mouse (i.e. depress the mouse button and move the mouse) to the bottom-right of your model diagram

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Stage 1: Modelling the growth of a single tree

Thu, 28/02/2008 - 18:23 — administrator

Step 1	Add a compartment to the desktop, and rename it size.
Step 2	Draw a flow into the size compartment, and rename it growth.

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Individual-based modelling of a population of trees

Thu, 28/02/2008 - 18:21 — administrator

Introduction

The main aim of this tutorial is to introduce you to individual-based modelling.

System Dynamics (or “compartment-flow”) modelling generally does not represent individuals in a population. Instead, all the individuals are lumped together and represented by a single value: the number of individuals in a population, the total weight of all the individuals, or the total amount of some substance they contain (water, carbon or nitrogen, for example).

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Stage 5: Bonus section: re-visiting the classic predator-prey model.

Thu, 28/02/2008 - 17:36 — administrator

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Stage 4: Sketching biologically meaningful relationships

Thu, 28/02/2008 - 17:34 — administrator

What we now have are some variables in our model (eaten per fox and rfox) for introducing biologically-meaningful relationships. The influence arrows we have drawn to these two variables expresses the biologically-reasonable assumptions that:

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Stage 3: Re-casting the model diagram

Thu, 28/02/2008 - 17:32 — administrator

The present model is based on a number of assumptions that are biologically unsound. For example, it assumes that the number of rabbits eaten per fox is directly proportional to the number of rabbits, so doubling the number of rabbits doubles the number eaten per fox — even if there are millions of rabbits around!