coevolution
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WHAT IS IT?
This model simulates the process of coevolution.
HOW IT WORKS
- There are prey and predator populations in the model. The population size can be adjusted by the "number-of-prey" and "number-of-predators" sliders. Once the user sets up the population sizes, they remain stable over time. There are three pairs of predator-prey relationships to try.
- Each predator will hunt five times each tick. It has to get two successful hunts to survive. In each hunt, users may or may not allow the predators to identify the slowest prey in their hunting range. When "spot-the-slowest-prey" is off, the predator randomly picks one prey. It kills the prey if its speed is higher than that of the prey. When "spot-the-slowest-prey" is on, the predator picks the slowest prey. It kills the prey if its speed is higher than that of this prey.
- The prey only dies when it is preyed on by the predators.
- In each tick, both populations are re-established based on the survivors. The speed of new prey and predators are around the average speed of the survivors, with some variations determined by the relevant speed mutation.
- Mutation of speed for prey or predator can be controlled by the relevant sliders. Note it does not determine the mutation direction but only represents the extent to which the offspring can mutate. So the mutation can lead to either a faster or a slower runner.
- Users may add faster or slow prey/predators into the simulation, which are either slower or faster than the min/max speed of the existing prey/predators.
- This simulation does not consider the energy cost of prey or predators. The hunting success is solely determined by speed difference.
HOW TO USE IT
- Press on "set/reset" to set the simulation.
- Press on "run/pause" to run or pause the simulation.
- Sliders can be adjusted before and while running the simulation.
THINGS TO TRY
- Alter the speed mutation of prey and predator to observe the results.
- Turn on and off predator's ability to spot the slowest prey.
CREDITS AND REFERENCES
This model is made by Dr. Lin Xiang at Weber State University. If you mention this model in a publication, we ask that you include the citations below.
Xiang, L. (2018). Coevolution. Department of Zoology, Weber State University, Ogden, UT.
This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc-sa/4.0/.
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Click to Run Model
breed [prey a-prey] breed [predators predator] turtles-own [speed hit erg] predators-own[keen] globals[prey-mean-speed predator-mean-speed slowest-prey-speed slowest-predator-speed] ;------ to setup ca setup-prey setup-predators setup-habitat do-plotting do-plotting-1 reset-ticks end to prey-traits if species = "Shark-fish" [ set color 84 set shape "fish" set size 1.25] if species = "Falcon-duck" [ set color 36 set shape "bird side" set size 1.25] if species = "Wolf-elk" [set color 22 set shape "elk" set size 2.25] end to predator-traits if species = "Shark-fish" [set color 2 set size 4 set shape "shark"] if species = "Falcon-duck" [ set color 33 set shape "hawk" set size 2.5] if species = "Wolf-elk" [set color 0 set shape "wolf" set size 1.25] end to set-speed if species = "Shark-fish" [ set speed 1 + random-float 1] if species = "Falcon-duck" [ set speed 9 + random-float 1] if species = "Wolf-elk" [set speed 3 + random-float 1] end to setup-prey create-prey Number-of-Prey [prey-traits set-speed setxy random-xcor random-ycor] end to setup-predators create-predators Number-of-Predators [predator-traits set hit 0 set-speed setxy random-xcor random-ycor] end to setup-habitat ask patches [if species = "Shark-fish" [ set pcolor 105] if species = "Falcon-duck" [ set pcolor 88] if species = "Wolf-elk" [set pcolor green] ] end ;------------ to go if years = 0 [user-message "input the years"] if ticks >= years [stop] setup-habitat ask prey [prey-traits] ask predators [predator-traits] move predation predator-death if count prey = 0 [user-message "There is no prey." stop ] if count predators = 0 [user-message "There is no predator." stop ] reproduction energy-back do-plotting do-plotting-1 tick end to move ask turtles [rt random 45 lt random 45 fd 1] end to predation ask predators [ set hit 0 ifelse spot-the-slowest-prey? [repeat 5 [ let meal one-of prey with [speed = min [speed] of prey] if meal != nobody [if [speed] of meal < [speed] of self [ set hit hit + 1 ask meal [die] ] ]]] [repeat 5 [ let meal one-of prey if meal != nobody [if [speed] of meal < [speed] of self [ set hit hit + 1 ask meal [die] ] ]]] ] end to predation-1 ask predators [ set hit 0 ifelse spot-the-slowest-prey? [repeat 5 [ let possible-meal prey in-radius 10 ;Given the radius, the predator only hunts a subgroup of the population. This allows some slow prey survive at some point. if possible-meal != nobody [ let meal one-of prey with [speed = min [speed] of possible-meal] if meal != nobody [if [speed] of meal < [speed] of self [ set hit hit + 1 ask meal [die] ] ]]]] [repeat 5 [ let meal one-of prey in-radius 10 if meal != nobody [if [speed] of meal < [speed] of self [ set hit hit + 1 ask meal [die] ] ]]] ] end to predator-death ask predators with [hit < 3] [die] end to reproduction set prey-mean-speed mean [speed] of prey set predator-mean-speed mean [speed] of predators create-prey Number-of-Prey - count prey [prey-traits ifelse random 2 = 0 [set speed prey-mean-speed + random-float Prey-speed-mutation][set speed prey-mean-speed - random-float Prey-speed-mutation] setxy random-xcor random-ycor] create-predators Number-of-Predators - count predators [predator-traits ifelse random 2 = 0 [set speed predator-mean-speed + random-float Predator-speed-mutation][set speed predator-mean-speed - random-float Predator-speed-mutation] setxy random-xcor random-ycor] end to energy-back ;This procedure is not in use. ask patches [if pcolor = 0 [if species = "Shark-fish" [ set pcolor 105] if species = "Falcon-duck" [ set pcolor 88] if species = "Wolf-elk" [set pcolor green] ] ] end to add-fast-prey create-prey 1 [setxy random-xcor random-ycor prey-traits set speed max [speed] of prey + random-float 0.5] end to add-slow-prey set slowest-prey-speed min [speed] of prey if slowest-prey-speed <= 0 [user-message "Have reached the slowest speed" stop] create-prey 1 [setxy random-xcor random-ycor prey-traits set speed slowest-prey-speed - random-float 0.3 ] end to add-fast-predator create-predators 1 [setxy random-xcor random-ycor predator-traits set speed max [speed] of predators + random-float 0.5] end to add-slow-predator set slowest-predator-speed min [speed] of predators if slowest-predator-speed <= 0 [user-message "Have reached the slowest speed" stop] create-predators 1 [setxy random-xcor random-ycor predator-traits set speed slowest-predator-speed - random-float 0.3] end to do-plotting set-current-plot "Prey Speed Distribution" set-plot-x-range (round min [speed] of turtles - 1) (round max [speed] of turtles + 1) histogram [speed] of prey end to do-plotting-1 set-current-plot "Predator Speed Distribution" set-plot-x-range (round min [speed] of turtles - 1) (round max [speed] of turtles + 1) histogram [speed] of predators end
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