CASE STUDY: Biomass Dynamics

Background:

In this model, we wish to investigate the flow of biomass through a simple ecosystem. In this ecosystem, there are three biomass sources and sinks -- dead grass, herbivores, and decomposers. Herbivores eat the dead grass, the decomposers decompose the dead grass, and the herbivore decomposes at some time after death. The following rate constants are known from experimental data:

Herbivore eating grass: 0.01 grass units per time period

Grass decomposing: 0.005 grass units per time period

Herbivore decomposing: 0.001 herbivore units per time period

At the beginning of the simulation, we have 100 units of dead grass, 5 decomposers, and 5 herbivores. We wish to run this simulation for 10 time periods.

Points to consider:

This is a closed ecosystem -- nothing comes in or out other than the three players. As such, your model should have a circular look to it. Think carefully as well to the direction of the arrows on the flows.

A graph of the run of this model for 5 time periods is shown below. Use this graph to check the validity of your own model. Note carefully the units on the "y" axis.

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