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RECAST Activity: Examples
The simulation will play out in a number of ways, depending on how the variables are manipulated. The goal of the simulation is to "reveal the causal structure" within ecological succession. As students are guided through the activity worksheet in manipulating different variables, they will come to understand how changes on scales large and small (bears and earthworms) and over long and short periods of time can cause fundamental changes over time.
If the conditions remain at the default settings of the simulation (all animal and plant species are present, the soil is sufficiently rich with nutrients, and the climate is sufficiently temperate and precipitous), the ecosystem will look very much the same after 50 or 100 years, only with maybe more trees. If the students move the time variable forward and keep all the other variables constant, the simulation should depict something like the following two images:
If, however, one or more variables are manipulated - even slightly - and drawn out over 100 years, the ecosystem "down the line" will look markedly different. These more interesting simulations will highlight the species and substrate changes that occur over time as non-obvious succession takes place. What changes might cause the ecosystem to look like the image below after 100 years?
There are, of course, many answers to this question. In the activity worksheet, students will first be asked to take a look at the beginning and end states of their ecosystems and try to figure out what happened in-between. This is intended to be difficult; how can you know what happened unless you track changes over time? They will then have the opportunity to view a time-lapse animation that shows all of the stages of succession over time, and reason about the same thing. A juxtaposition of these two reasoning methods - "snapshot" and "video" reasoning - should demonstrate the superiority of the latter for understanding the causal structures of ecological succession.
For students to truly understand the causal structures within ecological succession, they must be able to ascertain how end-states come about by reasoning about changes in the ecosystem over time. In order to do this in the simulation, they must be able to visualize intermediate states. The following two images are examples of what students might expect to see as intermediate steps in the time-lapse animations. Seeing that the trees were destroyed, either by logging or by fire, in these two examples will give students a better idea of how to connect the primary and end states of their ecosystem.
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