breeds [winner loser predator] ;; three species turtles-own [energy age];;turtles have energy and age globals [time] to setup ca set time 0 ask patches [set pcolor blue] ;;all patches are colored blue, water create-loser nloser ask loser [set color green set shape "tetra"] ask loser [fd (random-int-or-float 21)] create-winner nwinner ask winner [set color red set shape "heli"] ask winner [fd (random-int-or-float 21)] create-predator npredator ask predator [set shape "gamm"] ask predator [set color yellow] ask predator [fd (random-int-or-float 21)] ask turtles [set energy 10];;initial energy is 10 ask winner [set age 10];;initial age is 10 ask loser [set age 10] ask predator [set age 50];;except for predator whose age is 50 repeat npatch ;;a certain number of patches colored brown, leaves [ set pcolor-of random-one-of patches with [pcolor != brown] brown] end to go set time time + 1 ask turtles [set age age - 1] ;;deducts one year with each turn ask turtles [if (age = 0) [die]] ask loser [if (pcolor != brown) [rt random-int-or-float 360 fd random-int-or-float 41]] ask loser [if (pcolor != brown) [set energy energy - 1]] ask loser [if (pcolor = brown) and (count winner-here != 0) [die]] ;;if heli on brown patch, tetra dies ask loser [if (pcolor = brown) [set energy energy + 1]] ask loser [if (pcolor = brown) and (energy > 10) and (count loser-here < 10) [hatch lrepro [rt random-int-or-float 360 fd random-int-or-float ljmp set energy 5 set age 20]]];; reproduce only if less than 10 losers on patch ask loser [if (energy = 0) [die]] ask winner [if (pcolor != brown) [rt random-int-or-float 360 fd 1]] ask winner [if (pcolor != brown) [set energy energy - 1]] ask winner [if (pcolor = brown) [set energy energy + 1]] ask winner [if (pcolor = brown) and (energy > 10) and (count winner-here < 10) [hatch wrepro [rt random-int-or-float 360 fd wjmp set energy 5 set age 20]]] ask winner [if (pcolor = brown and count loser-here != 0) [ask loser-here [die]]];; winner kills loser here ask winner [if (energy = 0) [die]] ask predator [if (pcolor != brown) [rt random-int-or-float 360 fd random-int-or-float pjmp set energy energy - 1]] ask predator [if (pcolor = brown and count winner-here = 0 and count loser-here = 0) [set energy energy - 1]] ;;no winner, no losers, predator loses energy ask predator [if (pcolor = brown and count winner-here = 0 and count loser-here = 0) [rt random-int-or-float 360 fd random-int-or-float pjmp]];if no fungi, move on ask predator [if (pcolor = brown and count winner-here != 0) [set energy energy + 2]] ;; predator gains energy if winner here ask predator [if (pcolor = brown and count winner-here != 0) [ask winner-here [die]]];; predator kills winner here ask predator [if (pcolor = brown and count loser-here != 0) [set energy energy + 2]];; predator gains energy if loser here ask predator [if (pcolor = brown and count loser-here != 0) [ask loser-here [die]]];; predator kills loser here ask predator [if (energy = 0) [die]] ask predator [if (energy > 15) and (count predator < pmax )[hatch prepro [rt random-int-or-float 360 fd random-int-or-float 40 set energy 5 set age 50]]];;if energy > 10, produce number of new predator, grows older than winner or loser if (count loser = 0) [stop] ;;program stops when all tetra dead if (count winner = 0) [stop] ;;program stops when all heli dead do-plots end; add model procedures here to do-plots set-current-plot "Numbers" set-current-plot-pen "Loser" plot count loser set-current-plot-pen "Predator" plot count predator set-current-plot-pen "Winner" plot count winner end @#$#@#$#@ GRAPHICS-WINDOW 313 10 743 461 17 17 12.0 1 10 1 1 1 CC-WINDOW 315 462 630 582 Command Center BUTTON 22 192 77 225 NIL setup NIL 1 T OBSERVER BUTTON 94 191 157 224 NIL go T 1 T OBSERVER MONITOR 101 261 158 310 Loser count loser 3 1 MONITOR 179 260 229 309 Winner count winner 3 1 MONITOR 25 258 87 307 Predator count predator 3 1 SLIDER 17 374 109 407 nloser nloser 0 1000 400 1 1 NIL SLIDER 14 327 106 360 nwinner nwinner 0 1000 400 1 1 NIL SLIDER 16 425 108 458 npredator npredator 0 1000 0 1 1 NIL SLIDER 148 472 248 505 npatch npatch 0 1000 500 1 1 NIL PLOT 72 36 272 186 Numbers NIL NIL 0.0 100.0 0.0 100.0 true true PENS "Loser" 1.0 0 -11352576 true "Winner" 1.0 0 -65536 true "Predator" 1.0 0 -256 true SLIDER 146 378 238 411 prepro prepro 0 10 1 1 1 NIL SLIDER 147 329 239 362 wrepro wrepro 0 100 5 1 1 NIL SLIDER 147 426 239 459 lrepro lrepro 0 20 5 1 1 NIL SLIDER 767 334 859 367 ljmp ljmp 0 20 20 1 1 NIL SLIDER 761 377 853 410 pmax pmax 0 1000 250 1 1 NIL SLIDER 765 288 857 321 pjmp pjmp 0 20 20 1 1 NIL SLIDER 761 243 853 276 wjmp wjmp 0 20 1 1 1 NIL MONITOR 242 263 292 312 Time time 3 1 @#$#@#$#@ PREDATOR-MEDIATED COEXISTENCE (Felix Baerlocher, fbaerlocher@mta.ca) WHAT IS IT? This model is based on Caswell (1978). It examines the effect of a predator on the coexistence of two competitors. The graphics window contains a variable number of brown resource patches and blue non-resource patches. Brown patches allow survival and reproduction of the two competitors, called "winner" and "loser", respectively. A third agent, "predator" preys on both winners and losers present on a brown patch. Blue patches do not contain any food, they may represent barriers between food patches. When a winner and a loser land on the same brown patch, the loser gets killed. Once a winner is established on a brown patch, it cannot be displaced, except by a predator. When a predator arrives on a brown patch, it will kill both winners and losers, and, in the process, gain energy. Newly hatched offspring wander randomly until they find a brown patch. If the patch is empty, it can be colonized by either winner and loser; if it already contains a winner, losers cannot colonize it. Predators can colonize (and will empty) any patch with losers, winners, or both. When the model is run with only winners and losers, winners almost always win, except when there are very few brown patches and the migration parameters are set very low. When a predator is added, the length of time that winner and loser can coexist, increases. By emptying patches occupied by the superior competitor, the predator creates new opportunities for the inferior competitor. Important concepts that can be illustrated are the difference between open and closed systems, equilibrium vs. nonequilibrium systems, trade-offs between rapid reproduction and wide dispersal vs. superior competitiveness, etc. An advantage of this model over Caswell's original model is that spatial arrangement of resource patches is explicit. Their numbers and arrangements,combined with mobility of the agents, can greatly influence the final outcome. In the current setup, they are distributed randomly; this could easily be modified by producing clumps of patches, separated by variable distances. The predator can be generalized to a disturbance (which would no longer allow its extinction). The model could then provide a simple illustration of the intermediate disturbance hypothesis (Connell 1978) Caswell, H. (1978) Predator-mediated coexistence: a nonequilibrium model. American Naturalist 112, 127-154. Connell, J.H.(1978) Diversity in tropical rainforests and coral reefs. Science 199, 1302-1310. HOW TO USE IT? Click the SETUP button to set up the the two competitors (winner, loser), the predator (predator) and the resources patches. Click the GO button to start the simulation. There are 11 sliders. nwinner, nloser and npredator control the initial numbers of the three species, npatches controls the initial number of brown resource patches. nrepro, wrepro, and prepro control the number of offspring released during hatching. wjmp, ljmp, pjmp controls the maximum number of fd steps that might be taken during random movement. pmax controls the upper limit where reproduction by the predator is no longer possible. (Note: Changes in the DENSITY slider do not take effect until the next SETUP.) THINGS TO NOTICE Begin with the following settings: nwinner = nwloser = 400. npredator = 0;wrepro = 5, lrepro = 5, prepro = 1, npatch = 500. pmax = 250. wjmp = 1, pjmp = 20, ljmp = 20. pmax = 250. The loser generally goes extinct within 20 - 50 turns. Now add 250 predators. Winner usually goes extinct after a few 100 turns. Now begin with 500 patches. Coexistence of all 3 species is extended. EXTENDING THE MODEL Try arranging brown patches in a certain order (e.g., a large contiguous block in the center, with a few smaller blocks distributed randomly. Replace predator by an physical/chemical disturbance (no need to reproduce). @#$#@#$#@ default true 0 Polygon -7566196 true true 150 5 40 250 150 205 260 250 ant true 0 Polygon -7566196 true true 136 61 129 46 144 30 119 45 124 60 114 82 97 37 132 10 93 36 111 84 127 105 172 105 189 84 208 35 171 11 202 35 204 37 186 82 177 60 180 44 159 32 170 44 165 60 Polygon -7566196 true true 150 95 135 103 139 117 125 149 137 180 135 196 150 204 166 195 161 180 174 150 158 116 164 102 Polygon -7566196 true true 149 186 128 197 114 232 134 270 149 282 166 270 185 232 171 195 149 186 149 186 Polygon -7566196 true true 225 66 230 107 159 122 161 127 234 111 236 106 Polygon -7566196 true true 78 58 99 116 139 123 137 128 95 119 Polygon -7566196 true true 48 103 90 147 129 147 130 151 86 151 Polygon -7566196 true true 65 224 92 171 134 160 135 164 95 175 Polygon -7566196 true true 235 222 210 170 163 162 161 166 208 174 Polygon -7566196 true true 249 107 211 147 168 147 168 150 213 150 arrow true 0 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