The Otherwise population growth simulator
In what now seems like an infamous episode in my early career, I once tried to deliver a sample lesson on population growth during an all-day interview for a full-time teaching position at a fairly prestigious liberal arts college. What made this interview and sample lesson a bit more challenging was that my audience of sitting faculty was not composed solely of biologists: because the position I was being interviewed for was in a Master of Arts in Teaching program, the faculty were composed of folks from all disciplines. Although the actual students I would be teaching had I gotten the job would have been science majors, the test audience for my sample lesson was basically a group of non-majors.
Let me explain to you how best to destroy your chances of getting a job through a sample lesson dedicated to population growth: let the faculty who are pretending to be your students do all the math on their own, or better yet try to teach them on-the-fly how to use a spreadsheet to do the calculations. That was my lesson, a great dry mathematical train wreck. It was not simply that many of my pretend students were somewhat befuddled by the mathematics they were asked to do; even those who easily gravitated to the math involved were so utterly bogged down in calculations that they were unable to appreciate any of the important facets of population growth that I was trying to convey. Since this disaster, I have realized that the topic of population growth can only be taught in a compelling manner if there is some sort of simulator which can quickly produce population growth trends for particular conditions. Students do not need to practice the basic mathematics that underlie population growth (either they have those mathematical skills, or they do not), they need to be able to play around with different growth parameters so that they can understand the effects these parameters have on population growth.
The kind of ideal tool that students need to understand the basics of population growth would be pretty basic itself. First of all, students should be able to see the results of their simulations quickly translated into easy-to-read graphs. For most people, seeing population growth numbers represented as either counts in a table or cartoon versions of organisms does not really capture the essence of how populations grow: graphs capture this essence. In addition, students should be able to play around with key parameters to understand how changes in these parameters affect the pattern of population growth. Really only three parameters are critical for understanding the basics of population growth: initial population size, growth rate, and carrying capacity (if any is imposed). Given that students will want to play around with different values of these three parameters so that they can understand their effects, it would also be nice for students to be able to simultaneously plot growth trends based on different parameter values.
The requirements that I lay out above for a basic population growth stimulator seem pretty bare-bones, but sadly I have not been able to find an available free online tool that meets even these simple requirements. In my ecology class I have been using a pair of online tools produced by a somewhat mysterious entity called Otherwise. These tools allow students to explore exponential growth and logistic growth using Java applets. In some ways this set of tools is pretty nice: there is the possibility of changing the growth rate and the carrying capacity, and students can retain graphs of previous simulation runs, which allows for easy comparison of different parameter values. The growth rate can be changed on the fly, which allows students to think about the effect of sudden changes in the environment.
But there are some serious shortcomings associated with this tool as well. First off is the fact that the “growth rate” is called the “birth rate”, a conceptual error in the way the program is labeled that leads to all sorts of conceptual errors in my students: right after I teach them that survival and fecundity are the components of the growth rate, the program goes and labels this rate as strictly related to fecundity (i.e. birth rate). The starting population cannot be altered from the default value of two, so the only way to compare the effect of larger starting populations is to let the simulation run up to your target population size, pause, and then run from that population as if you are starting anew. The program also is incapable of handling numbers much larger than 100,000, which limits the ability to compare faster growth rates over a longer time period. The simulator has an annoying “view habitat” option that basically just fills the screen with fish: not all that instructive! And although all platforms are vulnerable to compatibility and obsolescence problems, I find Java to be particularly troublesome and finicky, which is a minor additional downside to these Otherwise simulation tools.
In previous years I have gone searching rather half-heartedly for alternatives. Whenever I go looking, I always feel there must be something better out there. Invariably, I do not find anything. So this year I decided that I would do a very thorough web search looking for the perfect population growth simulation tool. After the search, I can say that it does not exist for free.
There are a few candidates, but all of them come with large drawbacks. The Population Growth Simulation page by Jeff Knisley does allow for control of both initial population size and growth rate, but the plotting function does not work in real time and the carrying capacity is hardwired into the simulation. This is also not the most user-friendly interface, which might cause problems for non-major ecology students. Another fairly random simulator called Simulation of the effects of natural enemies on an insect population involves complex details such as specific types of mortality, stage structured growth, and stochasticity. Stripped of some of the details, the simulator also produces basic population growth patterns, but also does not feature a real-time graph of simulation results. For some reason, the site is also littered with Google ads. And finally in the “inexplicably weird” category is McGraw-Hill’s Virtual Lab on Population Growth, which allows you to play with virtual eyedroppers but not actually see any valuable population growth patterns.
In this day and age of on-demand apps and plug-ins, it is kind of surprising that no one has bothered to make a simple teaching tool that helps users to understand the basic dynamics of population growth. But perhaps the demand or expectation of free quality software in this area is too much: if you want to pay for classroom simulation software, SimBio’s EcoBeaker Isle Royale module seems as though it contains all the features I outlined above, all at $3 a student. Am I being cheap by looking for free software? Maybe, but I also cannot imagine going through all the hassles involved in ordering this software and guiding my students through the purchasing process just for one little lab exercise.
The opportunity it ripe for someone to make a better freely-available population growth simulator!