Sexual-Selection

Submitted by librarian on Tue, 2006-08-15 19:42. :: Category

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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 can reproduce. If two rabbits with energies above the hatch-threshold meet (land on the same patch), they reproduce. That is, an offspring is produced with 1/2 the parents’ average ‘energy’, moving randomly. Its colorgene is the average of its parents' colorgene. Parent’s ‘energy’ is set to 2/3 of their ‘energy’. If rabbit ‘energy’ goes to zero, the rabbit dies. A graph of the number of rabbits (blue) and grass (green) vs. time is activated by ‘go’ button.

‘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 before it can reproduce.

‘drought’ button kills 75% of the grass.

EXPLORATIONS

Set up and run model several times. Observe screen and statistics. Refer to graph.

What happens to the range and standard deviation of colorgenes over time? Compare results of several runs. Account for your results.

Turtle procedures



	
turtles-own [energy species [rabbit grass] colorgene dad]
;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]
   [set colorgene ((random 81) + 20)
    scale-color blue colorgene 20 100 ;scale the color to reflect colorgene
    setspecies rabbit
    setdad -1
    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)
      [grab one-of-turtles-here
          [if ((species-of partner) = rabbit) and ((energy-of partner) > (hatch-threshold))
              [setdad partner
               reproduce2]
          ]
      ]
end

to reproduce2
  setenergy-of dad ((energy-of dad) * .667)
  setenergy energy * .667
  hatch [setenergy (((energy-of dad) + energy) / 2)
         setcolorgene (((colorgene-of dad) + colorgene) / 2)
         scale-color blue colorgene 20 100
         seth random 360 jump 1]
  ifelse energy > (hatch-threshold) and (energy-of dad) > (hatch-threshold)
      [reproduce2]
      [setdad -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]
  pp3 ppd plot avg-colorgene
end

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

to avg-colorgene
   output ((sum-of-turtles-with (species = rabbit) [colorgene]) / count-turtles-with [species = rabbit])
end

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

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

to calcsd
  settemp 0
  ask-turtles [if color != black [settemp temp + ((colorgene - avgcolorgene) * (colorgene - avgcolorgene))]]
end

to calcstats
  setmincolorgene min-of-turtles-with (species = rabbit) [colorgene]
  setmaxcolorgene max-of-turtles-with (species = rabbit) [colorgene]
  setrangecolorgene (maxcolorgene - mincolorgene)
  settotalcolorgene sum-of-turtles-with (species = rabbit) [colorgene]
  setavgcolorgene (totalcolorgene / count-turtles-with [species = rabbit])
  calcsd
  setsdcolorgene sqrt ((temp / (count-turtles-with [species = rabbit])))
end

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Sexual-Selection

HOW TO USE IT

EXPLORATIONS

Turtle procedures

Observer procedures