NetLogo User Community Models
by ellen evers (Submitted: 09/25/2008)
WHAT IS IT?
In this project, a colony of ants forages for food. Though each ant follows a set of simple rules, the colony as a whole acts in a sophisticated way.
HOW IT WORKS
When an ant finds a piece of food, it carries the food back to the nest, dropping a chemical as it moves. When other ants "sniff" the chemical, they follow the chemical toward the food. As more ants carry food to the nest, they reinforce the chemical trail.
HOW TO USE IT
Click the SETUP button to set up the ant nest (in violet, at center) and three piles of food. Click the GO button to start the simulation. The chemical is shown in a green-to-white gradient.
The EVAPORATION-RATE slider controls the evaporation rate of the chemical. The DIFFUSION-RATE slider controls the diffusion rate of the chemical. There is an on-off PLOT? switch. Turning off the plotting lets the model run faster.
If you want to change the number of ants, move the POPULATION slider before pressing SETUP.
THINGS TO NOTICE
The ant colony generally exploits the food source in order, starting with the food closest to the nest, and finishing with the food most distant from the nest. It is more difficult for the ants to form a stable trail to the more distant food, since the chemical trail has more time to evaporate and diffuse before being reinforced.
Once the colony finishes collecting the closest food, the chemical trail to that food naturally disappears, freeing up ants to help collect the other food sources. The more distant food sources require a larger "critical number" of ants to form a stable trail.
The consumption of the food is shown in a plot. The line colors in the plot match the colors of the food piles.
EXTENDING THE MODEL
Try different placements for the food sources. What happens if two food sources are equidistant from the nest? When that happens in the real world, ant colonies typically exploit one source then the other (not at the same time).
In this project, the ants use a "trick" to find their way back to the nest: they follow the "nest scent." Real ants use a variety of different approaches to find their way back to the nest. Try to implement some alternative strategies.
The ants only respond to chemical levels between 0.05 and 2. The lower limit is used so the ants aren't infinitely sensitive. Try removing the upper limit. What happens? Why?
In the UPHILL-CHEMICAL procedure, the ant "follows the gradient" of the chemical. That is, it "sniffs" in three directions, then turns in the direction where the chemical is strongest. You might want to try variants of the UPHILL-CHEMICAL procedure, changing the number and placement of "ant sniffs."
The built-in DIFFUSE primitive lets us diffuse the chemical easily without complicated code.
The primitive PATCH-RIGHT-AND-AHEAD is used so to make the ants smell in different directions without actually turning.
CREDITS AND REFERENCES
This model was developed at the MIT Media Lab using CM StarLogo. See Resnick, M. (1994) "Turtles, Termites and Traffic Jams: Explorations in Massively Parallel Microworlds." Cambridge, MA: MIT Press. Adapted to StarLogoT, 1997, as part of the Connected Mathematics Project. Adapted to NetLogo, 1998, as part of the Participatory Simulations Project.
To refer to this model in academic publications, please use: Wilensky, U. (1997). NetLogo Ants model. http://ccl.northwestern.edu/netlogo/models/Ants. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.
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