Lab 03 (III): The overshoot deer population model
Submit the lab before June 21st 2024, 20:00
Introduction
Now that we are familiar with the basics of the Kaibab deer herd case, we are now moving towards more complex models. This part is based on two main sources: (1) chapter 21 of the book Modelling the Environment1, (2) a suite of pre-defined models that we will explore and modify in this lab. All pdfs and models are available on moodle. Make sure that you really invest the time and energy needed for the reading as well as for the different models – both elements, in particular the models, are much more complex compared to what you worked with thus far. Be prepared that it will take you some time until you understand the details of the models!
The overarching question of this lab is What is meant by the ‘overshoot’ of the deer population?. To do that, we will examine the models M21.3.mdl
, M21.5.mdl
, M21-7.mdl
, M21-9.mdl
, M21-12.mdl
and M21-15.mdl
and reproduce the simulations that are described in the book chapter. Again: be prepared that this will take you some time. Some of the models will show a warning related to the extrapolation outside the value range of the look-up tables – feel free to either ignore those warnings. Though, if you can think about ways to fix them, feel free to do so.
Exercise I: The concept of fullness.
Focus now on the full model M21-15.mdl
in Vensim At first, we want to think about the concept of fullness in the context of bioproductivity (i.e., primary productivity). Run the model, and visualize the two relevant variables related to fullness in the context of bioproductivity. After that, answer the following question:
Exercise II: Exploring effects of a wolve population on deer populations.
Now, we want to expand the model from above. Specifically, we want to specify the deer’s predator and replace the lookup tables (lookup for predators, lookup for 2nd shape, etc.) by a wolve population model, similar to what you have seen in model M2.mdl
of lab 3(II). To do so, replace the lookup tables by a population model for wolves that matches the following criteria:
The births of wolves are determined by the amount of deer killed per predator per year and a factor
<1
that develops in a meaningful way across the range of potential deer kills.Introduce the same ruleset for the deaths of wolves
The factors should be chosen in a way that the model produces an oscillating pattern for both predator and prey stocks. You can achieve this either by try-and-error or through the SyntheSim
functionality.
The wolves’ population should start with 150 individuals.
Exercise III: Introducing hunting pressure.
In this last exercise of the lab, we want to explore the impact that hunting wolves has on standing biomass in the system. Do that considering the following criteria:
the number of hunted wolves must be only dependent on the size of the wolves’ population and a hunting rate (which has to be found; see below)
Increase the model’s run time to 100 years.
Find (and report) the maximum rate (rounded, no comma) of annual wolf hunts possible so that the standing biomass does not collapse entirely.
Once you are done, provide the information below.
Ford, A. (1999). Modelling the Environment (2nd Edition). Island Press. 488 pages↩︎