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  • Writer's pictureJolene Pappas

Population Dynamics

Updated: Oct 21, 2021

There are many versions of population dynamics simulations out there. I've used a hands-on paper-based simulation with squares of paper to represent the prey and note cards as the predators. This lets students study the basic pattern of population changes between a predator and prey, but it is time consuming to cycle through enough generations to observe a pattern and so it is difficult to work in much in the way of inquiry. I think the paper-based simulation is a great introduction for introductory ecology, but for my honors high school groups, I wanted more student choice in design and analysis.

Other freely available online population dynamics simulations include:

A search for "population dynamics simulation" or "predator prey simulation" will yield additional results. Even though there are options out there, I wanted to do my own. Partially because, if I was going to have a website with biology simulations, this seemed like one I should put my own spin on. Also, for my own classroom use, I had specific things I wanted from a simulation, that I wasn't always getting with the other options. I wanted my simulation to be sustainable (everything doesn't die off) with the default settings, have random factors (so the results aren't the same each time), and represent producer, predator, and prey.

I also wanted a simulation that was fairly simple and intuitive for students to use and interpret. In the interest of freely manipulating the settings and variables, I did not base my simulation on a specific real-world example (such as the classic Isle Royale). However, there is an opportunity to integrate historical data into lessons that work with this simulation. I pair this with the impact that the reintroduction of wolves has had on the Yellowstone ecosystem. I use the article Lessons from the wild lab by V. Morell (Science, 347 (6228), 1302-1307) as a reference (a subscription to Science is needed for access to the full article, but there are other resources that detail recent Yellowstone data as well). It is important that students understand that this simulation is a very simplified representation of an ecosystem. As stated in the simulation introduction, "real community population dynamics are more complex than what is represented in this simulation."

Population dynamics simulation ecology lab. User can manipulate variables including starting population and reproduction rates
Population dynamics simulation

The virtual lab that I have prepared for this simulation is a fairly open inquiry. Students are asked to play with the simulation to become familiar with the parameters and then they choose their own questions to test. The most difficult part of this for students seems to be selecting a dependent variable. The worksheet gives them several examples, but this is an area where some students may need guidance before jumping into data collection. The goal of this worksheet is more about practicing experimental design and data collection than about learning any specific information about population dynamics. In the future, I may add additional worksheets that introduce more guided labs to teach specific content and concepts. And, of course, teachers are welcome to use the simulation to design their own lessons as needed.

Now onto some details about the simulation. The user can control the starting populations for both the predator (ranging from 10-100) and the prey (100-2000). The amount of plants is represented by "relative plant abundance" and ranges from 25-100. The predator and prey population numbers are not limited to their max starting options over the course of the simulation, but the plant abundance is treated as a percent and cannot exceed 100. The number of generations (10-100) can also be selected.

Rather than representing reproduction as a rate, I chose to simplify it by calling it "relative reproduction" and it is presented on a scale of 1 to 6. This value represents the amount of offspring produced for each surviving prey. Similarly, herbivory and predation are presented as relative values, both on a scale of 1 to 8. This represents the amount of plants or prey that need to be eaten in order for an individual to survive. The simulation is also simplified in that all organisms involved have synced up life cycles. Each generation covers an entire life cycle for the plant, prey, and predator.

Graph showing plant, predator, and prey values for a population dynamics simulation
Population dynamics graph

There is a lot going on in the resulting graph. Each of the three populations have significantly different ranges so it is necessary to use three different y-axes. Fortunately, it's pretty easy to retrieve data because hovering the mouse over any point on the graph causes the values to be displayed. Clicking on one of the lines in the key will remove the line from the graph completely, simplifying the view.

Plotly.js graph for the population dynamics simulation.
Simplified population dynamics graph. Clicking on a line in the key removes/replaces a data series.

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