The effect of tree supply on death rate depends upon a ratio comparing the number of trees that are actually available per person per year to the desired number of trees per person per year. Create two new converters: first, actual number of trees available per person and second, desired number of trees per person (which you can set as 0.5). Connect these two new converters to the effect of tree supply on death rate. Double-click on effect of tree supply on death rate. Define the effect equation as actual number of trees available per person / desired number of trees per person (Notice that the units cancel.) Click Become Graphical Function. We want to define this effect of tree supply on death rate converter as a graphical function so the output value will change based on the ratio of the number of trees available over time.

How do you think the number of trees affects the death rate? For example, what do you think happens to the death rate when there are plenty of trees (relative to what people need to survive)? What happens to the death rate if there are very few trees (relative to what people need to survive)? What if there are just enough trees? Draw your answer on the graph below.