Download Model File
Required Software
To open these system models, you will need Vensim installed on your computer. Vensim PLE (Personal Learning Edition) is free to download here.
To open Vensim, download the file above. Sometimes, Vensim will not open due to being from an unidentified developer. To bypass this issue, you will need to right-click and click "Open". Then, when Vensim opens up, go to File > Open... and select FrogsAndFlies.mdl.
To run the model, open Vensim first and then click on the link. To run the model, press the Simulate button at the top. To adjust parameters such as the Survival Rate, run Synthesim and adjust the scroll bars.
Model Description
In this model, the quantities are frogs and flies. Frogs have 5 stages of their life cycle: Eggs, New Tadpoles, Tadpoles, Young Frogs, and Frogs. The extra stages (New Tadpoles, Young Frogs) are there to make the frogs' life cycle longer than the flies. Flies have 4 stages of their life cycle: Eggs, Larvae, Pupae, and Flies.
The frogs and flies interact in a predator-prey relationship: the frogs prey on the flies. The rate of reproduction in frogs is also affected by the number of flies.
Click image to expand
This model is balanced the way it is to create a realistic portrayal of predator-prey relationships. With this model, this balance is thrown off rather easily. For example, if the death rate for frogs is too low and the predation rate for flies is too high, the frogs consume all of the flies and then die of starvation. At larger scales, this behavior is too unpredictable and the populations are almost never sustainable, so this model has been scaled down.