| Ø | Click the Equations tool, click on the following variables and enter the equations and units of measurements as follows: |
| Rabbit Population = INTEG ( |
| births-deaths, |
| initial population) |
Units: rabbit
initial population = 1000
Units: rabbit
| birth rate= | 0.23 |
Units: fraction/Year
average lifetime = 8
Units: Year
births = Rabbit Population * birth rate
Units: rabbit/Year
| deaths = | (Rabbit Population / average lifetime) * |
| effect of rabbit crowding on deaths |
Units: rabbit/Year
carrying capacity = 1000
Units: rabbit
The variable carrying capacity is not the maximum number of rabbits that the environment can hold. Instead, carrying capacity represents the normal number of rabbits for that environment. We would use a different formulation if we wanted to represent maximum carrying capacity.
Note that we are initializing the Level with the Constant initial population rather than typing in a number. This allows us to make changes to the value during simulation experiments. Note also that the deaths equation has a multiplier effect of rabbit crowding on deaths which will change the value of deaths.
Remember: To add a variable as an initial value use the Choose Variable (Choose Initial Variable in PLE and PLE Plus) button on the Variables tab.
