Simple Predator-Prey Dynamics Using STELLA.

1.0 Introduction

STELLA is a program computer that was created by Robert Webb of Australia. The

programs can be manipulated and altered in various ways. The STELLA software can be

use from isee systems to model dynamic systems. Dynamics systems are usually very

complex, having many components with involved relationships. STELLA offers a practical

way to dynamically visualize and communicate how complex systems and ideas really work.

For example, STELLA can be used to model competition among different species for limited

resources or the chemical reactions of enzyme kinetics.

Moreover, thousands of educators and researchers have made STELLA to study

everything from economics to physics, literature to calculus, chemistry to public policy and

more interesting and unique STELLA has capabilities to stimulate learning. This is because

STELLA allows user to communicate how a system works, how the systems is impacted and

what are the outcomes. STELLA is a flexible computer modelling package with an easy,

intuitive interface that allows users to construct model and simulation. The model represents

the system itself whereas the simulation represents the operation of the system over time.

In addition, STELLA also can give supports in diverse learning styles with a wide

range of storytelling features. Students have variety of learning style such as auditory

learners, visual learners, tactile learners and kinesthetic learners. Everybody learns in their

own way. So, for visual learners STELLA can help in making learning more awesome and

interesting because students with visual learners learning style can discover relationships

between variables in an equation by using diagrams, charts and animation that can be found

in STELLA software. Visual learners will be able to recall what they see because they mostly

learnt by observing and enjoy working with graphs, computer graphics, graphic organizers

and text with a lot of pictures. So, STELLA is the best choices for this kind student’s learning

style to generate them be active in learning, improve their grades and make study become

more enjoyable.

Besides, STELLA auditory or verbal learner might surround visual models with words

or attach documents to explain the impact of a new environmental policy. STELLA also

suitable for student’s learning style kinesthetic and tactile learners. This is because STELLA

gives user an enormously powerful and flexible tool for creating environments that allow

people to learn by doing. Then, auditory learner also can use STELLA software in learning

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because it has multimedia supports for graphics, movies, sounds and text messages.

Overall, STELLA can be use to simulate a system over time, jump the gap between theory

and the real word because students can be able experience by their self to make experiment

and understand the theory by using STELLA.

In addition, STELLA also enables students to creatively change systems and teach

them to look for relationships based on the diagrams or graphs that appear based on the

experiment they run. This is because STELLA can clearly communicate system inputs and

outputs and demonstrate the outcomes. So that students can more understand the variables

that influence their experiment and make learning become more effective. However,

STELLA not only used for run an experiment but STELLA has widely functioned such as

built-in functions to facilitate mathematical, statistical and logic operations.

There are some benefits by using STELLA software which is the language increases

that accuracy and clarity of verbal descriptions, ambiguities diminish and communication

much more efficient and effective. Besides, the software provides a check on intuition and

also provides a vehicle for building an understanding of why. The tools facilitate putting

together in an organized and clear way the qualitative and quantitative approaches present

in the experiment. Moreover, the tool enablers an easier operation, demonstration serving as

the basis for analyzing different types of infrastructure.

STELLA is one kind of simulation that useful in teaching strategy for illustrating a

complex and changing situation. Nowadays, simulation in education is widely become

recognized as an important tool in schools and being used as medium instructional.

Simulation is also used to gain insight into their functioning and show the eventual real

effects of alternative conditions and courses of action. Next, simulation also used when the

real system cannot be engaged because it may no be accessible or may dangerous and

unacceptable to engage. The main point using simulations include acquisition of valid

resource information about the relevant selection of characteristics, behaviours and validity

of the simulation’s outcomes.

In additions, simulations promote student’s critical and evaluative thinking. This is

because STELLA simulations will encourages student think beyond of their mind and

generate analysis thinking. Besides, there are several benefits that students get by using

simulation of STELLA. For example, through simulation will include the participation of

students while using the software and promotes the constructivism learning. When students

directly involved the learning process will be more enjoyable and students acquire more

knowledge and understanding. Next, simulations are necessarily less complex compare to

present the real situations. This is because students are not necessarily to observe the

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interaction between prey and predator for several days in the real situation. In contrast, by

using stimulation of STELLA, just need to run the experiment in more comfortable and safety

environment compared to the real situation that used more student efforts and put them in

danger condition.

Furthermore, observe the interaction between prey and predator in the real situation

will cost more than running experiment using STELLA simulation. Sometimes, it is not

worthless and may cause waste of time and cost because the result students can get from

observe the real situation will end up to nothing and make them low in motivation and

disappointed in study. This is because is not easy to estimate and predict the interaction of

living thing which human cannot control their activity. In contrast, by using STELLA

simulation are often cheaper and low in cost needed. For example, install simulation

software is cheaper than buying parameters to measure the interaction between prey and

predator in the real situations.

Besides, simulations can be paused meanwhile the real life cannot. Pausing allows

more time for students to assess what’s going on. So, the learning process will be more

effective to the students. The purpose simulation in teaching and learning is gives deep

learning. This is because by using simulation engage students in deep learning that

empowers understanding compared to the learning by using text book which only will

promote students commit to memorize without understand the content. Moreover, simulation

will stimulate learner’s curiosity and create their interest toward learning process.

Most importance, simulations allow students to change parameter values and

observe the changes occurred after parameter is change. For example, size in one time lynx

harvest is the parameters change to see what happened in the hare population. Simulations

also teach students to think like scientist does. Next, simulations also help students

understand the scientific knowledge that rely on the acceptable hypothesis. Then, students

also can improve their understanding on probability and sampling theory by using simulation.

Interestingly, students can predict outcomes using simulations and make learning process

showed the progress.

On the other hand, the curiosity of students will lead them to explore and satisfy their

curiosity. So their will self motivated to run an experiment and exposed themselves to

investigate the variables that influences the changes to occur in the experiment. Simulations

also can improve students’ ability to apply particular concepts in problem solving. When

students can solve the problem actually they already develops their creative thinking and

learning process will be more effective and beneficial.

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2.0 Content of STELLA (Simple Predator-Prey Dynamics).

A predator is an organism that consumes another organism. While the prey is the

organism which predators eat. For example, in this simulation by using STELLA software,

the lynx is the predator and prey refer to the hare. Predator and prey are evolving together.

The prey is part of the predator’s environment and the predator will die if it does not

consume food. So, predator evolves whatever is necessary in order to eat the prey.

Likewise, the predator is part of the prey’s environment and the prey dies if it is eaten by

predator. So, it evolves whatever is necessary to avoid being eaten.

A population is refers to the group of organism of the same species that live in the

same area at the same time. The predators tend to regulate the prey population or vice

versa. While populations ecology is study of how members of a population interact with their

environment. Moreover, population ecology considers the number of individuals of a

particular species that are found in an area and the dynamics of the population is study the

changes in population on how and why those numbers increase or decrease over time.

However, population growth is a change in the number of individuals in a population.

Positive growth occurs when the number of individuals in a population increases. Whereas,

negative growth occurs when the number of individuals in a population decreases. Factors

that effect on the rate of population growth are birth rates, death rates, immigration and

emigration. Birth rates or known as natality is the addition of organism to the population

through reproduction that will cause the population growth to increase. While, death rates or

known as mortality is lose of organisms from the population due to death. This death rate will

cause the population growth to decrease.

In addition, a population’s growth rate (per capita increase) equals birth rate minus

death rate. Zero population growth will occur when birth rate is equal to death rate. The

maximum number of offspring that an organism can produce under ideal conditions known

as biotic potential. The ideal condition allows a maximum birth rate and a minimum death

rate. Biotic potential cannot be sustained because some form of environmental resistance

will eventually limit further population growth. Biotic potential can determines the age

beginning of reproduction, how often reproduction occurs and how many offspring are born

at a time.

Environmental resistance refer to the combination of biotic and abiotic factors that

limit the size of the population. When populations become large, they tend to run out of

some limiting resource such as food, water, light, oxygen and space. When this situation

occurred, it will limit further populations growth and pushes down on a growth curve. Thus,

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prevent populations from growing exponentially or achieving their biotic potential. The

balance between biotic potential and environmental resistance defines the carrying capacity

for a particular organism with a given set of environmental resources.

The carrying capacity is the maximum population size that can be sustained over a

relatively long period of time by a particular environment. Once population growth slows and

maintains a nearly steady level the population is said to be at the carrying capacity for the

environment. The constant population rarely exist. Actually, population numbers fluctuate

because conditions within habitats constantly change due to predation, competition,

diseases and seasonal, climatic differences which affect the availability of light, water and

food. Moreover, carrying capacity often serves as the basis for sustainable development. If

carrying capacity exceeded, living organisms must adapt to new levels of consumption or

find alternative resources.

Next, natural selection favors more effective predators and more evasive prey. This

mean predators such as lynx that have dominant characteristics like agile in hunting prey like

hare will survive longer than lynx that weak in hunting because they must have enough

resources to survive and breed. Prey that evasive means that hare which be able to avoid

from being killed by predator. The evasive hare will survive and breed for the continuous life

span. Based on the theory, when prey are numerous their predators increase in numbers.

While, reducing in prey population will cause the number of predator to decline. The prey

population eventually recovers, starting a new cycle.

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Results:

Based on the graph above, when the size of one time lynx harvest is equal zero the system

in stable condition with both lynx and hare in a balance such that for each population, births

is offset by deaths.

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Based on the graph above, when the size of one time lynx harvest is equal 90, the system in

unstable condition between lynx and hare in an imbalance such that for each population.

The population of hare have a little bit changes compare when the size of one lynx harvest

equal to zero. This is because predators (lynx) tend to regulate the prey (hare) population

and vice versa. So, by this simulation students can repeat anytime and can explore the

experiment to get information on how the changes will occur.

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Based on the graph above, when the size of one time lynx harvest is equal 380, the system

in unstable condition between lynx and hare in an imbalance such that for each population.

The graph showed that greater lynx consume hare compare graph before this. The number

of hares killed per lynx per year is assumed to depend on hare density. The greater density

of hares in the ecosystem, the larger the number of hares consumed per lynx per year.

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Based on the graph above, when the size of one time lynx harvest is equal 640, the system

in unstable condition between lynx and hare in an imbalance such that for each population.

The graph showed that greatest lynx consume hare compare other graph. However, at initial

of the graph showed lynx sudden drop and more lynx die. More precisely, some fraction of

the lynx populations dies each year. The fraction is determined by the density of the hare

population in the ecosystems. A higher density of hares means fatter, happier and longer-

lived lynx. On the other hand, as population density of hares declines, a larger portion of the

lynx population will die of malnutrition and starvation.

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Conclusion:

Based on the experiment predator-prey dynamics, using STELLA simulation actually

allow students to change parameter values and observe the changes occurred after

parameter is change. Moreover, students understand the concepts when the number of

hares killed per lynx (per year) increases with the density of hares in the ecosystems.

According to understanding, the most important part is promotes student’s critical and

evaluative thinking and at the same time student be able to make prediction for the outcome.

For example, when density is zero means there is no hares, so kills per lynx per year must

be zero. Lastly, when students can make prediction they will feel happy to learn something

and make the learning process more effective.

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