Explorations

This file gives some play suggestions for the Scenarios included in the Gecko GrassWorld demo. For what it all means, please see the Discussion instead. The Help reader explains how to operate the gizmos on the screen. Further readings are listed in References.

Scenario: Unstable Quickie

This is the scenario automatically launched when Gecko is loaded, and shown in the sphere pictures in the Discussion. If you try it a few times (click Restart), you'll find the spiders eat off all the grasshoppers very quickly.

  1. Use one spider instead of two:
    1. Click Parameters
    2. Select Spider
    3. Change "initNumber" to 2 and click "OK"
    4. Click on Restart
    How much longer do the grasshoppers last? If any are still alive by the stop time, you can click on Continue, and optionally change the stop time via RunControl.
  2. A theory: if there are no spiders to control the grasshoppers, the grasshoppers will kill off all the plants and then die of starvation. True?
  3. Another theory: with no grasshoppers and no spiders, and the faster reproductive advantage of Plant over BigPlant, [...your theory here...] Try it. [Hint: look at biomass over the long haul. You can speed things up for the long haul by setting the display cycle to 20.]
  4. Would a bigger reproductive advantage for Plant help? How about a breedsize on Plant of 5 and on BigPlant of 10? If you added a grasshopper at time 1000, would either plant species benefit?
  5. If BigPlant's breeding radius is set high enough, it can keep growing even past its breeding radius. This is because it only spawns one child per timestep, and if it's big enough, it can get more resources than needed for a seed.
  6. There are other funky parameters here. Click on Scenarios | Unstable Quickie again to get back to the original settings, and try some of them.
    1. Gopper veer is fun. It's expressed in radians, so the default of 3.77 = 216 degrees. Try .785, or about 45 degrees.
    2. Spider smell radius is fun, though this scenario might be too small to grow it. Try setting it down instead. Note that smell radius is a multiplier on the spider's current size, not an absolute radius. If it were absolute, the default settings would mean the spider couldn't smell as far as he could eat.

Scenario: 2 Plants + Gopper + Spider

  1. The last scenario had 2 Plants + Gopper + Spider. What's different?

Scenario: Plant/Gopper/Spider (orig basic3)

This is the original Gecko test case, with us since Gecko's prototype in 1994. The goal is to have a stable 3 trophic level model exhibit a "trophic cascade". That means that plant biomass should be highest with no grazers present. With grazers but no grazer predators, plant biomass should be lower. With grazers and their predators, plant biomass should be intermediate between the two other levels.

This scenario is bigger and slower than the other two. If you make it much smaller, though, it may not stay stable (all 3 species persist) very well.

  1. Want to demonstrate the trophic cascade to yourself? (Kinda tedious.)
  2. To turn on further statistics, click RunControl. Try looking at Plant | Biomass Theft. This plot shows the amount of Plant biomass eaten by goppers (y-axis) vs. standing Plant biomass (x-axis.) Leave it on through a few boom/bust cycles.
  3. Change Gopper veer to 6.28, that being roughly 360 degrees. How do the dynamics change?

Ginger Booth, September 17, 1999