Environmental Systems
Modelling Assignment: Tigers and Chitals
A peer-graded modelling assignment on predator-prey dynamics.
Software and publications you need for this modelling assignment:
Software and publications you need for this modelling assignment:
- Vensim
- Bacaër (2011), p. 71-72 (if you want to get some background information)
- Berryman (1992), p. 1531 (if you want to get some background information)
Tasks
For this modelling assignment you have to simulate two variants of predator-prey systems. Each of your simulation models should be based on the given system descriptions.
Tigers, chitals and endless primary production resources
For the first modelling task, please use the following observation as basis for your model:
- Tigers and chitals share the same living space.
- Tigers only eat chitals and nothing else (i.e. no exception regardless of any circumstances).
- Chitals only eat sprouting grasses, fruits etc. (i.e. chitals are herbivores).
- While dying tigers have been observed, chitals only died because they are snatched by the tigers; the latter indicates enough food resources for the chitals.
In the setting of this task, the provided facts describe the system of interest in full. Hence, please do not add any other feature in your model.
During modelling, you will most likely face two major problems:
During modelling, you will most likely face two major problems:
- How to deal with geographical space in a null dimensional model? The sections on the Lotka–Volterra equation in Bacaër (2011), p. 71-72 or Berryman (1992), p. 1531 could help you in answering this question.
- How to link predators and prey? One solution could be, that the prey has an influence on the reproduction capacity of the predator population while the predators have an influence on the death rate of the prey. As a consequence, predators only die because they reach their average live expectancy while prey only dies because it is killed by the predators.
Please prepare the following for the assignment:
- Explain very shortly how you represent the hunting dynamics observed in the geographical space in your null dimensional model.
- Construct a stock and flow model matching the observations above.
- Use your model to simulate a time period of 24 month. Use a value of 0.1 t to initialize all of your stocks (in this case, t is tons of biomass) and use a value of 1.0 for any other auxiliary variable.
- Visualize the modelling results using an xy plot describing the population changes of tigers and chitals (y axis) over time (x axis).
Tigers, chitals and limited primary production resources
The second modelling task is closely related to the first one. Please use the following observation as basis for your model:
Please prepare the following for the assignment:
- Tigers and chitals share the same living space.
- Tigers only eat chitals and nothing else (i.e. no exception regardless of any circumstances).
- Chitals only eat sprouting grasses, fruits etc. (i.e. chitals are herbivores).
- Dying tigers and chitals have been observed; the latter indicates limited food resources for the chitals.
Please prepare the following for the assignment:
- Extend a copy of your first model to include limited food resources for the chitals.
- Use your model to simulate a time period of 120 month. Use a value of 0.1 t to initialize all of your stocks (in this case, t is tons of biomass) and use a value of 1.0 for any other auxiliary variable.
- Visualize the modelling results using an xy plot describing the population changes of tigers and chitals (y axis) over time (x axis).
- Shortly describe the major difference in the population dynamics of tigers and chitals as compared to your first simulation (you can assume, that the dynamics you observe within the first 24 month of your first simulation are representative for any other time).
Submission
Include the two stock and flow models, the visualized results as well as the short notes on the representation of geographical space and the differences between the two simulations in a single PDF file and upload the file in time via the exercises module of this course system.
The submission deadline and the upload function can be found in the section Modelling Assignment: Tigers and Chitals of the exercise module.
Review and grading
The assignment will be peer-reviewed. If you want to preserve your privacy, do not add any personal information into your submission.