ESSAY ON STELLA

SSI3013 : ICT IN SCIENCE

TITLE :

MODELLING AND STIMULATION BY USING STELLA

GROUP:

C

PREPARED BY:

NAME ID NO. PHONE NO.

NUR ASHIKIN BINTI ALIAS D20101037459 012-3139521

LECTURER’S NAME: MR. AZMI BIN IBRAHIM

DUE DATE : 3rd DECEMBER 2012

TEACHING AND LEARNING BASED ON MODELLING AND SIMULATION

Nowadays, computer technology has evolved dramatically over the years and has
significantly changed the society. As technology advances, it transform and improves the
society. The revolution of computer technology changed the way of people thinking
especially for the computer system users, administrators and designers. Generally, they
have their own goal of highest performance at lowest cost. Here, modelling and simulation of
system design is a good preparation to deal with real work. So now, what is modelling? What
is simulation? How they work? What type of problems that suitable for simulation? How to
select simulation software? What are the benefits and disadvantages of modelling and
simulation? Everyone are keep on asking about it.
Modelling and simulation is the process of producing a model over the time to
develop data as a basic to manage or technical decisions that involved emulators,
prototypes, simulators and stimulators either statically or over. Modelling and simulation are
often used interchangeably. A model is a representation of an object, a system or idea in
some form of other than that of the entity itself. The model is looks similar but it is more
simpler than the system it represents. One of the purposes of a model is to enable us to
analyse the effect of changes to the system. On the other hand, the model should be close
approximate to the real system and do not to be so complicated because it might difficult to
be understand it.
A good model is the one that can differentiate between realism and simplicity. An
important issue in modelling is model validity. Model validation techniques includes
stimulating the model under known input conditions and compared the model with system
output. There are various types of models which are physical model (scale models,
prototype plants) and mathematical model (analytical queueing models, linear programs and
simulation). Generally, a model that intend for a simulation study is a mathemical model that
develop with the help of simulation software. Mathematical model are includes deterministic
where the input and ouput variables are fixed values, or stochastic (at least one of the ouput
variables is probabilistic), static (time is not included) or dynamic (time-varying interactions
among the variables are included). Typically, simulation models are stochastic and dynamic.
While, a simulation of a system is the operation of a model of the system which is
representation of that system. The model is amenable to manipulation which would be
impossible, too expensive or to impractical to perform on that system which it represents.
The operation of the model can be studied and the properties concerning the behaviour of
the actual system or its subsystem can be inferred. In its broadest sense, simulation also
evaluate the performance of a system. Simulations is used before an existing system built

which is to reduce the chances of failure to meet specifications and to optimize system
performance. Simulators are collection of hardware and software which are used to mimic
the behaviour of some entity. The simulation is used widely nowadays in many fields such
as in education, industry and etc.

In educational field, computer simulation is suitable to used in order relate the
classroom material with relevant experiences. It become one of the factor that contribute to a
motivation of student’s success. Thus, the educator that apply simulation during class
session, they must be well understood to used it in order to motivate the students. Not only
that, to successfully implement a computer simulation in classroom, educators also need to
consider ‘play’ factor which one of the most important motivators. This is because, simulation
is a part of teaching model. What is the advantages of using these simulation? One of them
is simulators can be used as an effective materials for teaching or demonstrating concepts of
a real system to the students. These particular true of simulators make an intelligent use of
computer graphics and animation. It dynamically shows the behavior and the relationship of
all the simulated system’s components so that the users are providing with a meaningful
understanding of the system’s nature. For example, for Physics teacher who want to teach
about circuit, by using simulation, the students can see what actually happened to the circuit
and they become more understanding towards the dynamic circuit. Besides that, simulator
used also enable students to control either to speed up, slow down, stop or even reverse the
simulation to more understanding.

Besides that, teaching with simulation method have the potential to engage students
in ‘deep learning’ that empowers understanding as opposed to ‘suface learning’ which only
requires memorization. Deep learning is refer to the students that can learnt scientific
methods including doing the experiments and simulation. Here, simulation gives students
concentrate formats to think like a scientist. Not only that, by using simulation, we can adjust
the variables that being used in the model. So, it allows the students to change the
parameter values and can observe what happens and they able to make a prediction. It also
encourage students to participate actively since these type of instructional simulations
cannot be passive learning. A well done simulation is constructed to include an extension to
a new problem or new set of parameters that requires students to extend what they have
learned in an earlier context.

Instead of advantages, there are disadvantages of the simulation. A disadvantage of
simulation in comparison to exact mathematical methods is stimulation cannot be used
naturally to find an optimal solution. Simulation model often used to approach complex
system analysis. However, there are many systems that cannot be modelled with

mathematical equations. Besides that, simulation model also is quite expensive since the
process must be well understood although we know that the simulation can help the
process. The most expensive part is the collection of data for the simulation.

The suitable software used for these Modelling and Simulation especially in
education is STELLA which is a system thinking for Education and Research. STELLA offers
a practical way to dynamically visualize and communicate how complex the systems and
ideas really work. STELLA is used to stimulate a system over the time, jump the gap
between theory and the real world and also it enable students to creatively change the
systems. Moreover, STELLA teach students to look for a relationships and also it create a
clear communication system inputs and outputs to demonstrate the outcomes. There are
many topics that can be construct by using STELLA. One of them is Predator-Prey
Dynamics. This topic is quiet familiar among the school’s student until the higher level of
study.

Predator-prey Dynamics

Introduction:

Community structure refers to the number and relative abundances of species in a
habitat which it changes over the time. Each community have a dynamic structure, reflected
in shifting patterns of biodiversity. Species interactions, as well as abiotic factors such as
climate and source of food will affect the the community structure. There are five type of
direct species interactions in communities. Species interact in ways that can be beneficial,
harmful, or have no effect on one another. The interaction will shifts the numbers and
abundances of the species.

Besides that, co-evolution is one of the the important parts of an organism’s
environment in other organisms. It occurs when the species are adapting to the
environments, two or more organisms evolve together to show off their strength in the
habitat, organisms make use of other organisms by eating them and mating. At the same
time, organisms coevolve with many species due to the environment that consists of many
types of organisms. Organisms have to adapt to form the relationship similar like they have
to adapt with any part of their environment. These adaptations cause changes in the
descendants which the better suited to take the advantage on the relationship and they may

be entirely different species from their ancestors. Relationships that formed through co-
evolution can be called symbiotic relationships. One of the symbiotic relationship is predator-
prey interactions.

Predator-prey interactions refers to the relative abundance of predator and prey
populations of a community which shift over the time in response to species interactions and
changing environmental conditions. Predators are consumers that gain energy and nutrients
from prey which are living organisms that predators capture, kill and eat. The quantity and
types of prey species affect predator diversity and abundance, and predator types and the
numbers do the same for prey. The extent to which predators affect prey numbers depends
on how individual predators respond to changes in prey density. Predator and prey are
evolve together. The prey is part of the predator's environment, and the predators also a part
of prey’s environment. The predator will die if there is no food, so it evolves in order to eat
the prey. The characteristics of animals that can be a predators are it have high speed to run
so that they can catch the prey quickly, it can stealth, it have ability to camouflage, it have a
good sense of smell, sight, or hearing (to detect the location of the prey), it have high
immunity to against the prey's poison, and also it have its own poison that used to kill the
prey.

As we know, the population of organisms does not remains constants. The number of
individuals within a population changes sometimes dramatically from one time to to another.
There are fluctuations that wide in variety organisms including algae, invertebrates, fish,
frog, birds, and mammals such as rodents, large herbivores and carnivores. The resources
that available plays an important role to control the fluctuations. There are three models for
responses of predators to prey density. In a type I response, the proportion of prey killed is
constant, so the number killed in any given interval depends on the prey density. For
example, the web spinning spiders and other passive predators. When the number of flies is
increase, there are more will be caught by the spider web. While, in a type II response, the
number of prey killed is depend on the capacity of predators to capture, eat and digest the
prey. As the prey density is increases, the rate of kills rises steeply at first because there are
many prey that they have to catch. However, the rate of increase become slow because the
prey cannot handle all the prey in one time. For example is the wolf will not hunt on other
animals till it finished eat and digested the caribou first. This is common in nature. This is
followed by type III response where the number of predators kills increase slowly until the
prey density exceed a certain level, then it rise rapidly and stop. These kind of response is
common in nature with three conditions. The first is the predators are switched among the
prey and it concentrate the efforts on the species. The second is the predators have to learn

the best way to capture the prey. The third is when the number of hiding places for prey is
limited. The number of predators increase when the prey density increases.

When resources are limited, the population will decline because each individuals are
compete each other to get it. The bottom-up control helped the population around carrying
capacity. Besides that, the predation can also affect the size of prey population by act as the
top-down controller. Thus, the interaction between these two forms of population are work
together to alter the population over the time. By knowing this, the ecologist can predict the
long term-effects of predation on a prey population. The presence of parasites and disease
also affect the population dynamics.

There are some cases where the time lag in the predator’s are response to the prey
density and cause a cyclic changes in abundance of predators and prey. If the prey density
are lower, the number of predators also reduce. Thus, the prey are in safe condition and
have increase in numbers, However, this situation gives opportunity to the predators to
increase in number and causes the prey decline and the cycle starts again.

Based on predator-prey models, the building blocks of the bio-ecosystems are
biomasses are develop their resource masses. The species are compete and evolve each
other and disperse in order to survive. By depending on their specific setting of applications,
the species can have the forms of resource-consumer, plant-herbivore, parasite-host, tumor
cells (virus)-immune system. They also faced the general loss-win interaction and also can
have the applications out of the ecosystems. When there are competitive interactions, they
are often in some forms predator-prey interactions.

The Lotka-Volterra model describes the interactions between two species in an
ecosystem which is a predator and a prey. This is shown the first-species model. The
population changes and the predator population changes are describing by using
mathematical equations. As we know, the populations are always changing. The changes
are may because of human interfering the food web or habitats or even human do not
disturbing the habitat, the population will naturally changes either goes up and down or
fluctuate. One of the most famous example of population changes is the predator-prey
population cycle of the showshoe hare and lynx.

The snowshoe hare in North America is a common species of mammals that related
to rabbit. Snowshoe hare is the smallest member of genus Lepus. It belongs to family
Leporidae. Generally, hares have longer ears, longer hind feet and even the tail is short, but
it is more longer than rabbits. The used of name is always misapplied to particular species.

The sizes of body of the hares is depend on the species which can helps to dissipate excess
body heat. Snowshoe hare have two colour pattern where throughout the summer, it will turn
to brown and during winter, it turn into white so that it can get a better camouflage with the
snow. The snowshoe hares depends on grasses, berries, twigs, bark and leaves to survive.
It have high rates of reproduction where there are multiple large litter are produced each
year. The young hares are born fully furred and their eyes are open to enable it to hop for a
few minutes after birth. Hares serves as a diets of carnivorous birds, mammals and reptiles.
For human, hares provide food and fur.

While lynx is a wild cat in north America which have similar looks like a large house
cat with a short tail and prominent tufts on its ears. It belongs to family Felidae. It have long
leg, large pawed cats with tufted ears, hairy soles and a broad, short head. There are coats
that formed a bushy ruff on its neck with a cream colour that mottled with brown and black.
The tip of the tail and the tufts of the ears are black in colour. During winter season, the fur is
dense and soft till and is sought by human for trimming garments. Lynx is a nocturnal and
silent animals except for during mating season. It live alone or in small groups. It climbs and
swim well and feed on birds and other small mammals. The Canada lynx are too depend on
snowshoe hare for food. The lynx lies in wait its favourite prey, snowshoe hare. When there
are hare, the lynx move, bounding from its cover and starts to chase the hare and trying to
evade it adversary. Then, its population increases and decreases every 9 or 20 years which
relative to the population of its prey. Lynx breed at the end of winter or early of spring
season. There are four young is born after gestation period which is about two months. Lynx
are very secretive and even experienced hunters rarely see one in the wild. Its range
overlaps with the snowshoe hare, on which it almost exclusively preys upon. So, how
Modelling and Simulation are apply in Predator-prey dynamics?

Discussion:

Graph 1 : The relationship between Snowshoe hare and Lynx

In order to run the simulation, firstly, we have to set with the zero number of removal
Lynx. Since, there is no Lynx, so we can predict that there is no predation occur among Lynx
and snowshoe hares. Based on the Graph 1, the interactions between Snowshoe hares and
Lynx are constant. This is show that the population of both species are stable. Lynx do not
disturbed the snowshoe hares population growth. Each snowshoe hares gives rise to a
constant number of offspring per year. In other words, there are no limiting factors that
interfere the snowshoe hares population growth apart from lynx. Besides that, each lynx eats
a constant proportion of the snowshoe hares population per year. That’s mean that if we
doubling the snowshoe hares population, thus the number eaten per lynx also doubles. It is
regardless on the size of snowshoe hare’s population. Lynx reproduction also is directly
proportional to snowshoe hares consumed. Another way to describe this is there are certain
number of snowshoe hares consumed will results in one new predator or one prey
consumed will produces some fraction of a new predator. Moreover, there are constant
proportion of the lynx population dies per year which are the death rate of lynx is
independent of the amount of food available. They live in peace, harmony and equilibrium.

Next, we adjust the reading of the number Lynx harvest up to 200 (Graph 2) and we
doubled it into 400 (Graph 2). What can we predict that, as the number of snowshoe hares
increase, the number of Lynx also increase. So, Graph 2 and Graph 3 shows the
population’s growth and decline through time of both Lynx and Snowshoe hares. From the
graph, we can see that the snowshoe hares population leads the lynx population through
cycle. From the beginning, the lynx cannot detect a decrease in snowshoe hares
immediately, so it will experience the difficulties of finding prey. Due to the declining of food
supply, starvation, mortality as well as difficulty to produce young are occurred, so it cause
the lynx to response. However, the snowshoe hares does respond immediately to the Lynx
declining numbers. There are more snowshoe hares are left alive because there are fewer
Lynx are catching, killing and eating fewer of them, but to increase in numbers, snowshoe
hares have to reproduce and it takes time so there is a lag in the response of each
population to the changes that takes place in other.

Graph 4

Lastly, the number of Lynx harvest is adjust up to 750, the maximum value. The
prediction can be made is there are higher number of hares will consumed due to the high
number of Lynx harves. As the number of hares increase, Lynx also increased. From the
graph, we can see that the snowshoe hares population leads the lynx population through

cycle. Suddenly, there are decline in hares population. This is may because of diet of hares
decrease that lead to hares die off and Lynx have to turn to other prey. The lynx are picky
and many starve to death, so there are lack of predators and allow the vegetation to grows
back and the Snowshoe hare rejuvenates. Since there are more hares and nutrition
available, the Lynx population grows and the cycle begins. However, it brings stress for
hares and a downword spiral in their population like a roller coaster cycle. But, the lynx
maintain riding its up and down.

Conclusion:

The balance of natural processes is extremely delicate. They are affected by many
environmental and external factors such as food web, vegetation adaptations, trapping and
prey preference that affect the population of Lynx.

References:

Randy L.Bell and Lara K. Smetana, retrieved at
http://cs.explorelearning.com/docs/tech_sec_science_chapter_3.pdf on 24th November,
2012.

http://www.cs.mun.ca/~donald/msc/node6.html retrieved on 15th November 2012.

http://www.eg.bucknell.edu/~xmeng/Course/CS6337/Note/master/node1.html retrieved on
15th November 2012.

http://www.inf.utfsm.cl/~hallende/download/Simul-2
2002/Introduction_to_Modeling_and_Simulation.pdf retrieved on 7th November 2012.

http://home.ubalt.edu/ntsbarsh/simulation/sim.htm#rintroduction retrieved on 7th November
2012.

http://www.systems-thinking.org/modsim/modsim.htm retrieved on 7th November 2012.

http://en.wikipedia.org/wiki/Modeling_and_simulation retrieved on 7th November 2012.

http://en.wikipedia.org/wiki/Computer_simulation retrieved on 7th November 2012.

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