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Turtle-Patch Interactions (15 min)

Now let’s make agents interact with their environment in meaningful ways.

Turtles Asking Their Current Patch Questions

Turtles can ask the patch they’re standing on for information:

ask turtles [
  let current-temp [temperature] of patch-here
  if current-temp > 50 [
    set color red      ; Turn red if on hot patch
  ]
]

Common patch queries:

Moving Based on Patch Properties

Move toward better patches:

ask turtles [
  ; Look at nearby patches
  let nearby-patches patches in-radius 2
  let best-patch max-one-of nearby-patches [resources]
  
  if best-patch != nobody [
    face best-patch     ; Turn toward resource-rich patch
    forward 1
  ]
]

Avoid dangerous areas:

ask turtles [
  let current-pollution [pollution] of patch-here
  if current-pollution > 50 [
    ; Move away from polluted areas
    let clean-patches patches in-radius 3 with [pollution < 10]
    if any? clean-patches [
      move-to one-of clean-patches
    ]
  ]
]

Turtles Modifying Their Environment

Agents don’t just respond to environment - they change it:

Consume resources:

ask turtles [
  let current-resources [resources] of patch-here
  if current-resources > 0 [
    ask patch-here [
      set resources resources - 1     ; Consume 1 unit
      set pcolor scale-color green resources 0 100  ; Update color
    ]
  ]
]

Leave traces:

ask turtles [
  ask patch-here [
    set pheromone pheromone + 1       ; Leave pheromone trail
    set pcolor scale-color yellow pheromone 0 10
  ]
]

Activity 2: Foraging

Goal: Turtles move toward resource-rich patches

to setup-foraging
  ; Create resource patches
  ask patches [
    set resources random 50
    set pcolor scale-color green resources 0 50
  ]
  
  ; Create foraging turtles
  create-turtles 20 [
    setxy random-xcor random-ycor
    set color yellow
    set energy 100
  ]
end

to go-foraging
  ask turtles [
    ; Look for nearby resource patches
    let nearby-patches patches in-radius 2
    let best-patch max-one-of nearby-patches [resources]
    
    if best-patch != nobody [
      face best-patch
      forward 1
    ]
    
    ; Consume resources on current patch
    let current-resources [resources] of patch-here
    if current-resources > 0 [
      set energy energy + current-resources
      ask patch-here [
        set resources 0
        set pcolor black  ; Mark as depleted
      ]
    ]
    
    ; Use energy to survive
    set energy energy - 1
    if energy <= 0 [ die ]
  ]
end

Run this model:

  1. Click “setup-foraging” to create resources and turtles
  2. Click “go-foraging” repeatedly and watch turtles search for food
  3. Notice how they deplete resources and change the environment

Activity 3: Erosion

Goal: Turtles modify patch values as they pass through

to setup-erosion
  ; Create terrain with different soil stability
  ask patches [
    set soil-stability 50 + random 50  ; Stability 50-100
    set pcolor scale-color brown soil-stability 50 100
  ]
  
  create-turtles 30 [
    setxy random-xcor random-ycor  
    set color white
  ]
end

to go-erosion
  ask turtles [
    ; Random movement
    right random 60 - 30
    forward 1
    
    ; Cause erosion on current patch
    ask patch-here [
      set soil-stability soil-stability - 0.5
      if soil-stability < 0 [ set soil-stability 0 ]
      set pcolor scale-color brown soil-stability 0 100
    ]
  ]
end

What happens: Watch how turtle movement creates “erosion paths” in the landscape!

Learning Objectives Achieved

By completing this tutorial, you can now:

✓ Understand the role of environment in agent-based models
✓ Create meaningful environmental visualizations
✓ Implement agent-environment interactions

What’s Next?

Now you have all the building blocks - agents, environment, and interactions. Time to put it all together into your first complete model from scratch!

Think about: What complete model would you like to build? What social phenomenon interests you? What agents and environment would you need?

Course Modules
Patch Properties and Visualization (15 min)
Course Modules
What We’ve Accomplished