This is a series of simple programs which cover a variety of topics in environmental science. The individual programs are titled Energy Flow, Carbon Cycle, Ozone Depletion, Island Biogeography, Population Momentum, Max. Sustainable Yield, and Rock Cycle. What each program does is described below. All the modules are simulations, with the user interface done through hypercard. For those of you unfamiliar with hypercard, its an interface which is designed to look like a series of index cards, where you flip from one card to the next to get from one topic to the next. Each module lets you set one or more variables of the simulation (using sliders which you move with the mouse), run it, and then look at the results either as a table or on graphs. In some of the simulations you are asked to predict what the output graph will look like before you actually run it. There is a minimal amount of text explaining each model, along with some cute sound effects and speech which hilight some actions. The simulations were all written in Stella (see the entry on Stella below), and each module lets you look at a schematic of its model.

In general, these are quite nicely done programs. The user interface is quite simple and consistent across all modules, although because its done in Hypercard there is a lot of flipping back and forth from one screen to another. The text on screen is enough to guide most students through the simulation, though there is very little background material in most of the modules. A very nice feature of some of the modules is that they ask the student to predict what will happen before running the model, and then superimpose the real results on top of the predictions. These programs would all work well as 1 hour computer labs or in discussion sections in an introductor ecology or environmental science course. They are too simple to be used for more extensive labs. Individual descriptions and reviews follow.

The Energy Flow module puts the student in charge of managing the Silver Springs Ecosystem, which consists of producers, herbivores, predators, decomposers, and top predators. As a manager, you control the number of tourists coming through the system, which controls how many bread crumbs get fed to the herbivores, and so controls the energy flow through the whole system. Your job is to keep exactly 10 top predators around for five years, and especially not to let top predators get too low or too high, by regulating the flow of tourists. The aim of the module is to demonstrate that management is hard, especially when there are time lags between the input that you control (bread crumbs) and the output that you desire (10 top predators). The program serves this purpose, although it wonÕt take too long for an observant student to get it right.

Th Carbon Cycle module demonstrates the basic parts of the global carbon cycle. The model includes burning fossil fuels, decomposing of organic matter, respiration, net destruction of vegetation, and carbon escaping from the oceans as source of carbon and gross primary productivity and the oceans as sinks. You are shown a schematic of all these sources and sinks, and clicking on any one of them will bring up a short explanation of its role. The student is given the mission of keeping global atmospheric carbon dioxide below 720 e15 grams, by adjusting each of the sinks and sources. After running the model and comparing the results to your predictions, you can get explanations of some of the features of the results such as why there are yearly oscillations in the carbon cycle and the effects of the different sources and sinks. This module works nicely as a simple introduction to the sources and sinks of carbon dioxide in the world, and their relative magnitudes. It is also a nice introduction to how modelling of this sort is done. Since these C02 models are in the news a lot as part of the debate on the greenhouse effect, the content of the program should be interesting to students in a variety of introductory classes. I see a potential problem, however, if the teacher does not make it clear that this is only a caricature of how the real world works (especially since the model is so simple, and does not include connections even between the variables which exist such as vegetation destruction and GPP), and would also want to make clear that while you can change things in the model such as CO2 flux into and out of the oceans, GPP, etc., in real life there are no slide bars on these things. Still, if the teacher makes these points, the program should serve as a good integrater and solidifier of both how a nutrient cycles on a global basis, and some of the variables involved in the debate on the greenhouse effect.

The Island Biogeography module is a simple demonstration of the theory of island biogeography. It gives a short introduction to the theory with the requisite three graphs showing effects of distance from mainland and size of islands, then lets the student play with a simple model of species colonization and extinction, where you can adjust the distance of an island from the mainland and the size of the island, let the model run for some preset amount of time, then look at graphs of number of species, colonization, extinction and turnover rates over time. At the end are a series of questions about the results from the model, with the option to go back and rerun the model to check your answers.

The Population Momentum module explores how the worlds human population grows. After a short introduction on population growth and U.N. predictions of this growth, theprogram presents you with a model of an age-structured population. The population has 11 categories, including three pre-reproductive ages, four reproductive ages, and four post-reproductive ages. You can set the number of individuals in each class, and an overall reproductive rate for the population. As you run the model the population structure is shown changing in a horizontal bar graph (the classical representation of population structure). At the end are several questions about the results of the model, with the option of going back and rerunning the simulation to answer them. The thrust of the introductory text and the questions is that even with just a replacement rate of reproduction, the human population can grow quite a bit before reaching equilibrium. Look at BioQUESTÕs Demography for another program with the same idea but a somewhat more flexible model.

The Max. Sustainable Yield module lets students try to harvest fish using two different harvesting strategies, fixed quotas, and variable effort, using a very simplistic model. There are several screens of introductory material which discuss fixed quota and variable effort harvesting strategies, using graphs of population size vs. recruitment to show how each of these work. You can then try each of these strategies out on a model of a fish population. The model is of logistic growth, with the parameters of the growth fixed. Before running the model, you can set the initial population size, and either the amount harvested per year (fixed quota) or the rate of harvesting (variable effort). When you are done playing with the model, the program asks you several questions about the resource management strategies you just played with. This program would work best after students have been introduced to some theory on population growth (ie. what a population size vs. recruitment rate graph shows) and harvesting strategies. Even then, a problem with this program is that the model has no probabalistic elements in it, and so if you pick the right values, both harvesting strategies work just as well. Without chance, you have to play around and imagine for yourself that chance was acting to see the greater risk inherant in harvesting by quota than by a variable effort strategy. There is also no graph of amount harvested per year, so you cannot look at how efficient your harvesting strategy is. However, the program works as a very basic introduction to these concepts.

The Ozone Depletion and Rock Cycle modules are similar to the others, but since they are only peripherally concerned with biology I do not review them here.

Computer: Macintosh, also needs Hypercard 2.2 or higher (will not work with Hypercard player).

Source: Wm. C. Brown,
Publishers, Business and Educational Technologies,
2460 Kerper Boulevard,
P.O. Box 539,
Dubuque, Iowa, 52004-0539.
1-800-258-2371.

Cost: High (plus cost of Hypercard from Apple).

Last update 22nd of January 1996