Shape a woodland pool, choose which animals go in it, then run a whole year to find out which ones survive well, which ones survive less well, and which ones cannot survive at all.
Data format
Finishing a year adds one row per animal you put in, with Animal, Weeks of Water, Number That Made It, How It Did, and Fish in the Pool. Rows build up across years, so several pools can be compared; running the same pool again adds nothing. A bar graph of Number That Made It by Animal reads out one pool. Plotting Number That Made It against Weeks of Water across several pools separates the animals that need a long-lasting pool from the ones that do not.
Every animal starts with the same number in the pool, 8 of each. At the end of the year the sim reports how many of those 8 made it, and describes each animal as having survived well, survived less well, or not survived at all. The number is the evidence and the description is the claim it supports. Because the sim follows one batch of each animal through a single year, the number can only go down, and no animal breeds partway through.
Model details
Two things are deliberately not to scale. A whole year plays in about 26 seconds, so a week goes by roughly every half second and the summer drawdown you watch over a few seconds really takes months. And the animals are drawn far larger than life against the pool: a mosquito larva is about half a centimetre long in real life and would be invisible at the size this pool is drawn, so every animal is scaled up until it can be seen and counted. The pool, the basin and the water line are in proportion to each other; the animals in them are not.
Everything in this sim hangs off one quantity: how many weeks the pool holds water. A deeper basin holds water longer, and trees shade the water so it lasts longer still. Each animal needs the water to last a certain number of weeks in order to finish growing up. Mosquitoes need about 2 weeks, fairy shrimp about 3, wood frogs about 9, and spotted salamanders about 13.
Two predators cut across that. If you open the channel to the creek, fish swim in, and because the pool no longer empties they stay all year and eat almost everything else. If the pool holds water for a long time without a channel, dragonfly nymphs settle in instead, and fairy shrimp have no defence against them. This is why a pool that holds water forever is not the best pool for everyone.
Mosquitoes need only about 2 weeks of water, so every pool in this sim is long enough for them. What changes their fortunes is who else is in the pool: tadpoles and salamander larvae eat mosquito larvae. That means a pool stocked with frogs and salamanders produces far fewer mosquitoes than a pool stocked with nothing, which surprises most people.
A pool joined to the creek is still full of water in midwinter, so it freezes over. The ice is only a lid: water is heaviest at 4 degrees Celsius, so the coldest water sits on top as ice while the bottom of the pool stays a few degrees above freezing. The fish spend the winter down in that water, barely moving, and are still there in spring. What actually endangers fish under ice is not the cold but the air running out, because ice and snow block the light so the plants stop making oxygen. A pool joined to a moving creek keeps getting fresh water, which is another reason the channel is what lets a fish population last.
Mosquitoes go through four stages: egg, larva, pupa, and flying adult. The larva hangs at the surface breathing through a tube at its tail, the comma-shaped pupa also sits at the surface but does not feed, and the adult climbs out of the pupa at the water surface and flies away. Adults live only a few weeks, which is why they are gone from the scene long before winter.
Standards
3-LS4-3 Construct an argument with evidence that in a particular habitat some organisms can survive well, some survive less well, and some cannot survive at all.
Design intent
- The student shapes the habitat rather than the animals, so the result is theirs to argue about.
- There is no pool that suits every animal at once. Giving the pool more water is what wipes most of it out.
- How many of each animal are left is meant to be read by looking at the pool, not off a chart.
- The three outcomes use the performance expectation's own wording, so the claim students construct is the claim the standard asks for.
Discussion prompts
- Which animals survived well in this pool, and what is your evidence?
- Which animal survived less well? What would it have needed?
- Which animal could not survive at all here, and why not?
- Can you build a pool where every animal survives well at once? Why not?
- Looking at a pool full of water in spring, can you tell whether fish will be in it? What else would you need to know?
How do I explore?
- Drag the Depth label, or the round knob beside it, up or down to set how deep the pool is. Three dotted lines show you where Shallow, Medium and Deep are.
- Tap the forest floor to plant trees. It goes None, Some, Dense, and then back to None. The three dots show you where you are. Trees shade the water and slow it down from drying up.
- Find the dotted line running out of the pool and click Dig the channel. That joins the pool to the creek. Click Fill in the channel to close it again.
- Tap an animal to put it in the pool or take it out.
- Press Play to run a whole year. While the year is running you cannot change the pool, because that would spoil your test. Press reset when you want to build a different one.
What should I do/notice?
- Watch the water line on the cut side go down through the summer. Where does the water go?
- 8 of each animal go into the pool. Count how many climb out onto the bank, then run it again with a different pool and count again.
- Try opening the channel to the creek. What moves in, and what happens to everyone else?
- Try to build one pool that is good for all four animals at the same time.
What about the data?
When a whole year finishes, your table fills in on its own. Each animal you put in gets one row. The row says which animal it is, how many weeks the pool held water, how many of its 8 made it, how it did, and whether fish got in. You do not have to press anything.
The rows add up as you go, so build a different pool and run another year. Then you can compare them. Running the very same pool twice does not add the same rows again. Try a bar graph of Number That Made It for each Animal. Then try graphing Number That Made It against Weeks of Water and see which animals need a long-lasting pool and which do not.