| Ø | With the Equations tool selected, click on effect of rabbit crowding on deaths. |
Under the Type label there are two drop down boxes, one showing Auxiliary, the other showing Normal.
| Ø | Click on the drop down box showing Normal and select with Lookup. |
This creates a Lookup table embedded within the Auxiliary variable.
| Ø | Click on the Variables tab then click on the variable Rabbit Population in the list. |
| Ø | Type a divide by symbol (/) then click on carrying capacity. |
effect of rabbit crowding on deaths = WITH LOOKUP(
Rabbit Population/carrying capacity
As Rabbit Population changes, the effect of rabbit crowding on deaths will change according to the shape of the Lookup function. Now we need to create the actual table of figures or graph that describes the Lookup.
| Ø | Click on the button As Graph in the Equation Editor (below the Type boxes). The Graph Lookup Editor opens: |
| Ø | Click on the left hand New (values) box near the bottom left corner and type in 0 then press the Enter key. The cursor moves to the right hand box; type 0.9 and press Enter again. The cursor moves back to the left hand box and the old numbers are moved to the input/output columns making way for new numbers to be entered. |
| Ø | Continue typing in the rest of the pairs of values below, pressing the Enter key each time a value is typed. The graph will draw itself. |
(0,0.9), (1,1), (2,1.2), (3,1.5), (4,2)
| Ø | Alternatively, you can sketch the graph using the pointer by clicking on the graph to add points, and dragging the points to reposition them on the graph. You will first need to set the X-max and Y-max values to 4 and 2 respectively. |
| Ø | Click on the button Reset Scaling to set the X and Y scales to your points. |
Do not worry about getting the exact numerical values for points shown in the figure if you are adding points with the mouse. The shape of the curve is more important that the exact values. But do set (1,1) exactly because this is a reference point: when Rabbit Population is equal to carrying capacity, there is no change on the normal rate of deaths.
