Predator/Prey Simulation
for Investigating Emergent
Behavior
Jay Shaffstall
Introduction
Overview of emergent behavior
Evolution & emergent behavior
Predator/Prey simulation
Outcomes
Emergent Behavior
An emergent behavior is a behavior that is
not programmed into the system.
An emergent behavior evolves over time
from more primitive behaviors.
The classic example: ant colony
Emergent Behavior
The ant colony looks like it is strongly
organized…each ant does a job to keep the
colony healthy.
In reality, each ant is responding to local
rules. Each ant decides what to do next
based on what is in its immediate area.
An ant has no concept of the colony.
Emergent Behavior
So emergent behavior is behavior that arises
from the interaction of a lot of local
behaviors.
Another example is how cities seemingly
organize into neighborhoods, even though
each individual is making decisions based
on what is best for them.
Evolution & Emergent Behavior
Evolution allows a population to adapt to its
environment over time.
Environmental pressure
Characteristics
Natural selection
Evolution is the process of a species
adapting to environmental changes
Does nothing for the individual
Evolution & Emergent Behavior
Over time, individuals may start to
cooperate in local ways.
This local cooperation leads to emergent
behavior, in which widely separated
individuals appear to be working toward the
same purpose
Predator/Prey Simulation
A predator/prey simulation provides a
simple environment in which evolution can
happen
There are three types of organisms in the
simulation
Plants
Prey
Predators
Predator/Prey Simulation
Each organism has its own genetic
structure.
One gene for the prey, for example, might
control how far the prey can move in one
action
Each organism also has rules for how it
interacts with its local environment
Predator/Prey Simulation
Each organism can breed to produce more
organisms.
The organisms that live long enough to
breed are considered to be “fit”, and pass on
their genetic characteristics to their
children.
Over time, the children become more and
more “fit”
Predator/Prey Simulation
Stages of development
Environment
Invasive plants
Crippled prey
Nice predators
No more lemmings
A complete simulation
Predator/Prey Simulation
Goals of the simulation:
Provide an environment in which evolution
could take place for predators and prey
See what emergent behaviors come out of the
local behaviors
Outcomes
The first non-testing run of the simulation
took about 15 hours, and generated around
10 gigabytes of data.
Let’s look at a sample of the displays. This
sample is from the 8th step of the
simulation.
Outcomes
That was from the 8th step, where we still
have the initial random distribution of
animals and plants.
Let’s look at a display from the 5600th step,
about 15 hours later.
Outcomes
But what happened between those steps?
Did evolution take place?
Let’s look at a population graph for that run.
120000
100000
80000
60000
40000
20000
0
Cycle
5569
5105
4641
4177
3713
3249
2785
2321
1857
1393
929
465
Plants
Prey
Predators
1
Population
Predator/Prey Populations
Outcomes
Clearly, evolution did not take place.
So, when the program doesn’t work like you
expected, you find out why.
The big question is why didn’t the prey
population increase when the plant
population increased?
Consider this zoomed in part of the 5600th
step.
Outcomes
The failure of prey to reproduce is the key
problem with the simulation as it is written.
Because of that, we do not see evolution
Without evolution, we don’t see emergent
behavior
Conclusion
I set out to write a simulation to investigate
emergent behavior
Much bigger project than I thought, but also
a lot of fun
I recommend future students to look at
projects dealing with emergent behavior
Conclusion
To learn from my mistakes:
Capstone paper available at
http://cs.franklin.edu/~shaffsta/paper.zip