Food Chain with 10% Energy Rule
WHAT IS IT?
The purpose of this model is to simulate the ten percent energy rule in a food chain. In food chains, the predator only gains about ten percent of the prey's energy. This pyramid effect leads to lower populations of upper-trophic-level predators. The goal of this simulation is to show how population fluxuates based on the ten percent energy rule and display the viability of a fifth trophic level in a simple food chain.
HOW IT WORKS
This model is based in Net Logo, and therefore uses a system of turtles (moving organisms that represent the population) and patches (background pixels of the environment). In this specific model, each trophic level is defined as a seperate breed or patch as follows:
Trophic Level......Description 1.......................(Producer) Green patches that represent grass 2.......................(Primary) White turtles with the "rabbit" shape 3.......................(Secondary) Blue turtles with the "wolf" shape 4.......................(Tertiary) Red turtles with the "cat" shape 5.......................(Quaternary) Magenta turtles with the "hawk" shape
This model simulates the energy transfer between trophic levels using a simple one-sto predation system. If an organism/turtle of one trophic level encounters an organism of a trophic level below it, then the prey dies and roughly ten percent of its energy is given to the predator.
Each organism begins the simulation with 1000 energy - an arbitrary amount with no corresponding scientific unit - and lose 50 energy per tick (unit of time in NetLogo). If an organism drops below 100 energy, then it dies.
Also, each trophic level has the ability to reproduce. If reproduction occurs, then one identical turtle is hatched at a location near to the organism and the organism loses one third of its energy.
In addition to the animal trophic levels, this model simulates the producer level using green, or grass, patches. These are consumed by the second trophic level and "die" or turn brown. After a selected amount of time (ticks), the grass regrows and becomes green and edible again.
Together, the predation, energy, death and reproduction features allow simulation of population change in a food chain with the ten percent energy rule applied. However, because this is a rough simulation, it is important to run the model several times to ensure more accurate prediction.
HOW TO USE IT
There are various items on the interface tab that can manipulate the simulation:
SETUP : this button resets the model and creates the world. It is necessary to set your values for each trophic level before hitting setup
GO : this toggle able button can continuously run the simulation
KILL-GRASS : this button kills all the grass
GRASS-RESPAWN RATE : this variable set the rate at which grass respawns. One value is equal to one tick that it takes for grass to respawn
XXX-AMOUNT : this sets the the amount of organisms to be spawned at the start of the simulation. These four values (one for each animal trophic level) must be set before hitting the SETUP button.
XXX-REPRODUCE : these four values correspond to each of the upper four trophic levels and is the percent chance for reproduction at a single tick. For example, if primary-reproduce is set at 50, then, at each tick, the primaries (rabbits) each have a 50% change to reproduce.
To the right of the world display, there is a graph that illustrates the amount of each breed of turtle and grass producers present over time. Also, monitors are located below the graph to display the amount of each breed and grass at a specific time.
THINGS TO TRY AND NOTICE
Since this model is aimed at multiple-tier predation, it is important to notice how population changes over time and, for each breed, in relation to other breeds.
Using this model, certain questions can be answered:
After the initial growth of the rabbits, what happens? For what two reasons might this occur?
Observe the simulation for a period of time. What do you notice about the population of each trophic level?
What happens over time to the population of Tertiary and Secondary predators if you set the Tertiary-amount to a value significantly greater that Secondary-amount? In ecology, is having more tertiary predators than secondary organisms possible?
After observing the simulation and population change, try finding values for XXX-AMOUNT and XXX-REPRODUCE at which population of trophic levels 2 through 4 begin to balance. How do these values relate to the ten percent energy rule?
Based on this model, is a fifth trophic level possible?
Using the KILL-GRASS button repeatedly, how does removing all the grass affect the population of rabbit? How does a change in the rabbit population affect other trophic levels?
EXTENDING THE MODEL
There are several additional features possible to extend this model:
Adding factors of long-term and short-term weather patterns on producers (for example, seasons).
Adding multiple organisms in one trophic level to create a complex food web rather than a simple food chain.
Creating a more comprehensive reproduction system in which two organisms are required to reproduce.
Wolf Sheep Predation Model (in the Biology Section of Models Library)
CREDITS AND REFERENCES
This simulation was created by Joshua Abraham as part of Tracy High School's Biology curriculum.
Credit to: Del Pabalan for advising this modeling project.
Uri Wilensky for his "Wolf Sheep Predation" model that acted as a basis for this model.
This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/4.0/.
Comments and Questions
breed [primaries primary] ; creates the four breeds for trophic levels 2-5 breed [secondaries secondary] breed [tertiaries tertiary] breed [quaternaries quaternary] globals [eat-energy] ; global variable to store the energy transferred between trophic levels turtles-own [energy] ; stores long-term energy on each turtle patches-own [countdown] ; variable to count ticks for grass respawn rate to setup ca reset-ticks create-world trophic-setup end to create-world ; sets up the geography ask patches [ set pcolor green] ; creates grass ask patches with ; visuals for the sky and sun [pycor > 45] [set pcolor white] ask patches with [(pycor >= 55) and (pxcor <= -55)] [set pcolor yellow] end to trophic-setup ; creates trophic levels 2-5 set-default-shape primaries "rabbit" ; sets default shape of all primaries to rabbit ask n-of primary-amount patches with ; sprouts primaries only on grass [(pcolor = green) and (pycor > -64) and (pycor < 45)] ; and far enough away from borders of grass [sprout-primaries 1 [set color white set size 3] ] set-default-shape secondaries "wolf" ; sets default shape of all secondaries to wolf ask n-of secondary-amount patches with ; sprouts secondaries only on grass [(pcolor = green) and (pycor > -64) and (pycor < 45)] [sprout-secondaries 1 [set color blue - 3 set size 3] ] set-default-shape tertiaries "cat" ; default shape of all tertiaries to cat ask n-of tertiary-amount patches with ; sprouts only on grass [(pcolor = green) and (pycor > -64) and (pycor < 45)] [sprout-tertiaries 1 [set color red - 3 set size 2] ] set-default-shape quaternaries "hawk" ; default shape of all quaternaties to hawk ask n-of quaternary-amount patches with ; sprouts only on grass [(pcolor = green) and (pycor > -64) and (pycor < 45)] [sprout-quaternaries 1 [set color magenta set size 2] ] ask turtles [set energy 1000] ; sets baseline energy level for all turtles end to go movement ; bounce and move procedure trophic-primary ; controls the four animal trophic levels trophic-secondary trophic-tertiary trophic-quaternary reproduction ; controls reproduction rates ask patches [grow-grass] ; begins grass regrowth death ; procedure for death of turtles wait .2 tick if count primaries = 0 [stop] ; stops simulation if all primaries die end to kill-grass ; button to set all grass patches to dead ask patches with [pcolor = green] [set pcolor brown] ; sets all green patches to brown end to movement ask turtles [ ; sets random heading for all turtles during each tick ifelse (ycor > 44) or (ycor < -62) [set heading (heading + 150 + random 60)] [rt 150 lt 150 ] ] ask primaries [fd 1] ; primaries' movement ask secondaries [ ; secondaries' movement fd 1 + random 2 ; moves them sometimes faster to catch primaries if pcolor = yellow ; prevents extended movement from bringing turtles off grass [set ycor ycor + 20] if pcolor = white [set ycor ycor + 20] ] ask tertiaries [ ; tertiaries' movement fd 2 + random 2 ; faster movement for catching tertiaries if pcolor = yellow ; prevents extended movement from bringing turtles off grass [set ycor ycor + 20] if pcolor = white [set ycor ycor + 20] ] ask quaternaries [ ; quaternaries' movement fd 3 ; faster movement to catch tertiaries if pcolor = yellow ; prevents extended movement from bringing turtles off grass [set ycor ycor + 20] if pcolor = white [set ycor ycor + 20] ] end to trophic-primary ask primaries [ set energy energy - 50 ; reduces energy for metabolism ] ask primaries [ if pcolor = green ; if pcolor is green [set pcolor brown ; kill the grass set energy energy + 150] ; and increase energy ] end to trophic-secondary ask secondaries [ catch-primary ; initiates predation procedure set energy energy - 50 ; metabolism rate over time ] end to trophic-tertiary ask tertiaries [ catch-secondary ; initiates predation procedure set energy energy - 50 ; metabolism rate over time ] end to trophic-quaternary ask quaternaries [ catch-tertiary ; initiates predation procedure set energy energy - 50 ; metabolism rate over time ] end to catch-primary let prey one-of primaries in-radius 3 ; grabs a random primary close by set eat-energy sum [energy] of primaries in-radius 3 ; sets energy transfer variable to energy of that primary if prey != nobody ; was one found? if yes, [ ask prey [ die ] ; kill it set energy energy + (eat-energy / 10) ] ; get energy from eating - division creates the ten percent rule end to catch-secondary if any? secondaries in-radius 6 ; predation chase feature [face one-of secondaries in-radius 6] ; chases secondaries further than eating radius let prey2 one-of secondaries in-radius 3 ; grabs random secondary close by set eat-energy sum [energy] of secondaries in-radius 3 ; sets energy transfer variable to energy of that secondary if prey2 != nobody ; was one found? if yes, [ ask prey2 [ die ] ; kill it set energy energy + (eat-energy / 7) ] ; and gain energy from eating - division is approximate for ten percent end to catch-tertiary ; same procedure for catching teriaries if any? tertiaries in-radius 6 ; chasing feature [face one-of tertiaries in-radius 6] let prey2 one-of tertiaries in-radius 3 ; look for tertiaries close by set eat-energy sum [energy] of tertiaries in-radius 3 ; set energy transfer varaible if prey2 != nobody ; checks if there is a tertiary [ ask prey2 [ die ] ; if so, kills it and set energy energy + (eat-energy / 8) ] ; gives the quaternary energy end to grow-grass ; patch procedure to regrow grass if pcolor = brown [ ; countdown for brown patches (dead grass) ifelse countdown <= 0 [ set pcolor green set countdown grass-respawn-rate ] ; countdown is based on grass-respawn-rate slider [ set countdown countdown - 1 ] ] end to reproduction ask primaries [if random-float 100 < primary-reproduce [ ; throw "dice" to see if you will reproduce set energy (energy * 2 / 3) ; divide energy between parent and offspring hatch-primaries 1 [ rt random-float 360 fd 1 ] ; hatch an offspring and move it forward 1 step ] ] ask secondaries [if random-float 100 < secondary-reproduce [ ; throw "dice" to see if you will reproduce set energy (energy * 2 / 3) ; divide energy between parent and offspring hatch-secondaries 1 [ rt random-float 360 fd 1 ] ; hatch an offspring and move it forward 1 step ] ] ask tertiaries [if random-float 100 < tertiary-reproduce [ ; throw "dice" to see if you will reproduce set energy (energy * 2 / 3) ; divide energy between parent and offspring hatch-tertiaries 1 [ rt random-float 360 fd 1 ] ; hatch an offspring and move it forward 1 step ] ] ask quaternaries [if random-float 100 < quaternary-reproduce [ ; throw "dice" to see if you will reproduce set energy (energy * 2 / 3) ; divide energy between parent and offspring hatch-quaternaries 1 [ rt random-float 360 fd 1 ] ; hatch an offspring and move it forward 1 step ] ] end to death ask turtles [if energy < 100 [die]] ; if energy is below a threshold, the turtle dies end ;; Model created by Joshua Abraham ;; email@example.com ;; Based on Wolf Sheep Predation Model in Models Library ;; Created at Tracy High School
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