Color Bunnies

Submitted by librarian on Tue, 2006-08-08 19:49. :: 5-8 | 9-12 | Standard 3: Earth and Space Science

WHAT IS IT?

Introduction

If you have not done so, run rabbits and grass model. The rabbits and grass model explores a simple ecosystem made up of rabbits and grass. The rabbits wander around randomly, and the grass grows randomly. Rabbits use up energy as they move. When a rabbit bumps into some grass, it eats the grass and gains energy. If the rabbit gains enough energy, then it reproduces by hatching a new rabbit. If it loses all of its energy, then the rabbit dies. What happens to the population of rabbits over time?

This model deals with the question, What would happen to the population if all the rabbits were not identical? Imagine that the rabbits differed in one genetically determined trait, and that the distribution of that trait was random over a given range. What would happen to the distribution of that trait in the rabbit population over time? In this model the genetically determined trait is color. Each rabbit begins the simulation with a randomly given color that is determined by a colorgene. The colorgene has a numerical value between 20 and 100. The color of the rabbit does not affect its fitness in this environment. That is, the color is cosmetic.

HOW TO USE IT

Set up

Determine the initial population number with the number slider.

‘setup’ button will distribute rabbits and grass randomly across the land.

‘show statistics’ button will activate monitors, showing you colorgene statistics; minimum, maximum, average colorgene values; as well as the range and standard deviation of colorgene values in the population.

Run

The ‘go’ button will cause the grass to grow, the rabbits to move randomly, and eat grass Rabbits are born with a randomly determined supply of ‘energy’. They use ‘energy’ to move, and gain ‘energy’ by eating grass. When their ‘energy’ is greater than the hatch-threshold (see below) they reproduce. The result is two rabbits with half the hatch threshold energy moving randomly. If rabbit energy goes to zero, the rabbit dies. A graph of number of rabbits (blue) and grass (green) vs. time is activated by ‘go’ button. Average colorgene value is plotted in black.

‘stop-it’ button stops all of this.

‘grass-rate’ slider determines how fast grass will grow. The ‘hatch-threshold’ slider determines how much ‘energy’ rabbit needs to accumulate to reproduce. ‘drought’ button kills 75% of the grass.

EXPLORATIONS

In this model the 'rabbits' reproduce asexually. Although this is not the case for real rabbits, scientists recognize that a model such as this one can accurately model population dynamics. You can imagine that we are just modeling the female rabbits and there are enough males to make them all pregnant.

Turtle procedures



	
turtles-own [energy species [rabbit grass] ]
;turtles can be of species rabbit or species grass

to setup
  setxy random screen-width random screen-height
  ifelse who < grass-rate
   [setc black ht setspecies grass]
   [setcolor random 140
    setspecies rabbit
    setenergy random 10]
  repeat 20 [grow]
end

to grow
  if species = grass [  ;only grass turtles should do this
    rt random 10 lt random 10
    fd 1
    if pc-ahead = green [stamp green]  ;grass only grows near other grass
  ]
end

to move
  if species = rabbit [       ;only rabbit turtles should do this
    takestep
    eat-grass
    reproduce
    death
  ]
end

to eat-grass  ;turn the patch to black and increase energy
  if pc = green [stamp brown setenergy energy + 1]
  if energy > 30 [setenergy  30]
end

to takestep
  rt random 50
  lt random 50
  setenergy energy - .25
  fd 1
end

to reproduce
  if energy > (hatch-threshold)
       [setenergy energy * .5
        hatch [seth random 360 jump 1]
       ]
end

to death
  if energy < 0 [die]
end

Observer procedures




globals [mincolorgene maxcolorgene rangecolorgene avgcolorgene sdcolorgene temp totalcolorgene]

to setup
  ca
  clearplot
  setbg brown
  crt number + grass-rate
  ask-patches [if (random 100) < 25 [setpc green]]
  ask-turtles [setup]
  setup-graph
end

to setup-graph
  pp1 ppreset setppc green
  pp2 ppreset setppc blue
  pp3 ppreset setppc black
  setplot-title "Rabbits and Grass"
  setplot-yrange 0 300
  setplot-xrange 0 50
end

to graph-it  ;graph the amount of grass (scaled) and turtles
  pp1 ppd plot (count-pc green) / 5
  pp2 ppd plot count-turtles-with [species = rabbit]
end

to total-rabbits
  output count-turtles-with [species = rabbit]
end



to go
 ;the movebutton, grassbutton, and graphbutton are pressed
  startmovebutton
  startgrassbutton
  startgraphbutton
end

to stop-it
  ;the movebutton, grassbutton, and graphbutton are stopped
  stopmovebutton
  stopgrassbutton
  stopgraphbutton
end

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