PRAC 5-ANIS,AMI
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Transcript of PRAC 5-ANIS,AMI
SCE 3107
Title: Understanding Population Trends
Introduction
A population is all the organisms that both belong to the same species and live in the
same geographical area. The area that is used to define the population is such
that inter-breeding is possible between any pair within the area and more probable than
cross-breeding with individuals from other areas. Normally breeding is substantially
more common within the area than across the border.
Population growth is the change in population size (N) over time, and this is determined
by births, deaths, immigration and emigration, Population growth can be modelled by a
geometric curve (that is, a non-linear curve). This will be either an S-shaped (sigmoidal)
curve or an exponential curve. If the population size doubles between each time interval
then this form of geometric growth is called exponential growth. Studies of both short-
lived and long-lived organisms have indicated that population growth, and therefore the
form and shape of population growth curves, is ultimately controlled by three factors:
1. the initial population size (N0)
2. a population growth factor (R) which measures the rate at which a population
would grow if it had unlimited resources
3. the carrying capacity (K), which is determined by environmental factors.
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TASK 1: Population of Rhinoceros
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Time interval
(t) =
Rhinoceros Population A Rhinoceros Population B
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generation
Pop size (N) Growth factor
(R)
Pop size (N) Growth factor
(R)
0 N0 = 30 N0 = 20
1 58 1.9 39 2.0
2 123 2.1 82 2.1
3 236 1.9 161 2.0
4 484 2.1 318 2.0
5 955 2.0 643 2.0
Geometric
mean
=2.0 =2.0
Table 1: Population growth oh rhinoceros
Question:
1. What type of population growth does Rhinoceros have, and why are the final
population sizes different?
The population growth of rhinoceros is exponential. In the final population sizes
different maybe because of rhinos are so isolated that they may rarely or never
meet to breed. So, the differences quite big.
2. What type of growth do each of the rhinoceros populations show:
exponential or sigmoidal ?
The growth type of the rhinoceros populations show is exponential curve.
3. Check the three factors that influence population growth. Why is there a
difference in population size between these two populations at time interval
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5? Is it due to differences in initial population size, the growth factor, or the
environment?
there are three factors that influence population growth which are the initial
population size, the growth factor, and carrying capacity which influenced by the
environment.
According to the table 1 we noted that the growth factor for both Rhinoceros
populations are quite balance and they even have the same geometric mean that
is 2 and so it would not affect the population growth. Beside that, both of the
Rhinoceros populations are living in the same area and so the environment factor
should be the same and this also would not give much influenced to their growth.
Therefore, we can say the differences in population size between the two
Rhinoceros populations at time interval 5 are due to the first factors, its initial
population. Population A has more population size than population B and so at
time interval 5, Population A also has more population size than population B
where the geometric mean for both populations are constant.
TASK 2: Population of Koala
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Time interval
(t) =
Koala Population A Koala Population B
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generation
Pop size (N) Growth factor
(R)
Pop size (N) Growth factor
(R)
0 N0 = 20 N0 = 20
1 36 1.8 31 1.6
2 63 1.8 47 1.5
3 118 1.9 66 1.4
4 212 1.8 103 1.6
5 375 1.8 150 1.5
Geometric
mean
=1.8 =1.5
Table 2: Population growth of Koala
Question :
1. What type of population growth does the Koala have, and why are the final
population sizes different?
The population growth of koala is exponential. The final population sizes different
maybe because of the of food supply problem. It is because they eat only
Eucalyptus leaves (also known as gum leaves). So when the leaves decrease or
humans clearing of the eucalypt forests there is no food supply and koala not
have their food anymore.
2. What type of growth do each of the koala populations show: exponential or
sigmoidal?
The growth type of the koala populations’ show is exponential.
3. For the two koala populations, why is there a difference in population size
at time interval 5? Is it due to differences in initial population size, the
growth factor, or the environment?
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From the table 2 the initial population size for both Koala Population A and B are
the same which is 20, so it is not the main factor which will affect the population
growth in future. The environment factor also should be the same and this also
would not give much influenced to their population growth.
Therefore, we can say the differences in population size between the two Koala
populations at time interval 5 are due to the second factors, the growth factor.
Population A has higher growth factor than Population B where the geometric
means of them are 1.8 and 1.5 respectively. Hence Population A has higher
population growth
4. In Table 2, if the data for koala population A were for the same, but under
plentiful rainfall conditions, and the data for koala population B were for
drought conditions, why might the populations show a change in the
growth factor (R) ? Remember that the growth factor R = Births – Deaths.
The populations show a change in the growth factor because of changes in the
balance of the ecosystem can lead to dieback. A decline in koala populations has
also been observed in times of drought. The death rate for koala population B is
more higher because the starvation. They don’t have enough basic need or
source in drought condition. While the population A the birth rate is higher
because they have enough sources and have a good condition to stay alive.
TASK 3: Population of Zebra
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Time interval
(t) =
generation
Zebra Population A Zebra Population B
Pop size (N) Growth factor
(R)
Pop size (N) Growth factor
(R)
0 N0 = 20 N0 = 20
1 80 4.0 50 2.5
2 230 2.9 100 2.0
3 400 1.7 220 2.2
4 500 1.3 360 1.6
5 550 1.1 460 1.3
6 580 1.1 520 1.1
7 590 1.0 550 1.1
8 595 1.0 570 1.1
9 600 1.0 580 1.0
10 600 1.0 600 1.0
Geometric
mean
=1.4 =1.4
Table 3: Population growth of zebra
Question:
1. What type of population growth does Zebra have, and how does carrying
capacity affect the final population size?
The population growth of zebra is sigmoidal. The final population size is same.
2. What type of growth does each of the populations show: exponential or
sigmoidal?
The growth type of the zebra populations show is sigmodial.
3. Which population, A or B, has the highest growth factor?
Both populations have the same growth factor.
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4. Is the growth factor (R) constant? Describe any changes that occur in R.
No, the growth factor is not constant there has some changes. For the first until
fifth time interval the growth factor is increase and for six into 10 time interval the
growth factor is decrease and the value is constant.
5. What is the carrying capacity (K or the asymptote of the curve) for each
population?
The carrying capacity for zebra A is when the population size is 600 which is at
the ninth generation. While for the for zebra B the population size not reach the
carrying capacity at the ninth generation.
TASK 4: Population of Zebra
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Time interval
(t) =
generation
Population A Population B
Pop size (N) Growth factor
(R)
Pop size (N) Growth factor
(R)
0 N0 = 20 N0 = 20
1 90 4.5 50 2.5
2 220 2.4 120 2.4
3 340 1.5 210 1.8
4 410 1.2 260 1.2
5 440 1.1 260 1.0
6 450 1.0 230 0.9
7 450 1.0 200 0.9
8 440 1.0 170 0.9
9 460 1.0 150 0.9
10 450 1.0 150 1.0
Geometric
mean
=1.4 =1.2
Table 4: Population growth of zebra
Question:
1. What type of growth do each of the Zebra populations show: exponential or
sigmoidal?
The growth type of the Zebra populations show is sigmodial.
2. Which population, A or B, has the highest growth factor?
Population A, has the highest growth factor.
3. Is the growth factor (R) constant ? Describe any changes that occur in R.
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The growth factor (R) for population A and B are not constant. The changes of R
is decrease from first generation to last generation for population A while the
growth factor for population B also decrease from first generation to ninth
generation but increase when reach at last generation.
4. Has the carrying capacity (K or the asymptote of the curve) for population
A changed? If so, in what way?
No.
5. Both zebra populations had the same initial population size. Why has one
population out-competed the other? Check the three factors that control
population growth.
There are three factors that control population growth which are initial population
size, growth factor and environment. Initial population not influence or control
population growth because it has same initial population size.
The growth factor is the factor influence and control population growth of zebra
because maybe the birth rate of the population B is low than population A while
for the death rate for population B is higher than population A.
The environment factor is the factor influence and control population growth
because Zebra's are prey to lions and spotted hyenas. Zebra is threatened by
hunting and by habitat change from ranching and other kinds of farming. Zebra
is threatened by local livestock that compete with it for water and food. Maybe
the resistance of zebra B is more lower. So in the competition they are less resist
with environment and it is now so small that environmental hazards, such as
drought, can easily affect the species.
6. If the data in Table 3 are for the two populations living separately, and in
Table 4 for the same populations living together, what has been the effect
of competition on R for both zebra populations?
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The effect of competition on R for zebra population in Table 3 is same because
the growth factor for both population zebra in Table 3 is 1.4 while the effect of
competition on R for zebra population in Table 4 is different because the growth
factor for both population A and B is 1.4 and 1.2.
Discussion
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1. What is the difference between exponential and logistic (sigmoidal)
growth?
Exponential growth (including exponential decay) occurs when the growth rate of
a mathematical function is proportional to the function's current value. In the case
of a discrete domain of definition with equal intervals it is also called geometric
growth or geometric decay (the function values form a geometric progression).
With exponential growth of a positive value its rate of increase steadily increases,
or in the case of exponential decay, its rate of decrease steadily decreases.
Exponential growth model is one that exists when the rate of growth is
proportional to the existing amount. For this, a population needs ideal conditions:
bacteria in a patria dish, radioactive decay or compound interest in a saving
amount.
The logistics is a different kind of behavior which is more realistic to population
not in ideal conditions: the rate of growth is proportional to the amount but there
is also a damping factor due to competition and limited resources. This model
works that at first the rate of growth getting faster then it slows down since there
are too many individual competing on limited space. When this population
reaches its equilibrium state, the rate of growth is zero and if there will be no
interactions; the size of the population will stay constant.
2. How do populations gain and lose individuals?
If the birth rate and the immigration rate high, it will increases the population of
individuals while if the death rate and emigration rate increases, it will decreases
the population of individuals.
3. What are the characteristics of a population which has a high intrinsic rate
of increase?
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When there are unlimited physical environment factors, the decreasing of prey
population and the population is out-competed in competition for resource, the
population growth will increase. The Law of the Minimum states that population
growth is limited by any resource like food, shelter, water supply, space
availability, and (for plants) soil and light in the shortest supply. Population
growth decreases when the population is eliminated by other population when
competition for physical environment factor occurred. Besides that, the
increasing of prey population may decrease the population growth.
The population that have high intrinsic rate of increase for sure can breed easily
and can adapt well in a habitat. Besides that , when its breed the number of the
young or the birth rate must be higher so that the death rate will not influence or
affect the population size even the rate of death is high. Another characteristic is
the antibody of the species is tough so they will not easily get sick . If a species
do not have tougher antibody, it will easily get sick and will die.
Births equal to deaths, a stable population size usually means that the rate of
death of its members is equal to the rate of birth. For example, organisms with a
tendency to produce large numbers of offspring also have a tendency to lose an
equally large number of offspring whereas those which produce few offspring
likely engage in a reproductive strategy which results in a much higher likelihood
of survival for any given offspring.
4. What are the environmental factors which act to (1) increase population
growth and (2) decrease population growth?
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The environmental factor which acts to decrease population growth is habitat
destruction. Destruction of habitats leads directly to a reduction in the number of
individuals present in a given population.
Destruction of habitat also leads to high probability of extinction. Following
habitat destruction, resulting populations are left in small, isolated fragments. The
probability of extinction among these isolated populations is high due to their
inherently small size. The likelihood of repopulation from other fragments may be
reduced due to the habitat isolation, a second consequence of habitat
destruction. Habitat destruction also has a tendency to affect other, especially
downstream ecosystems. Excessive erosion from clear cut forests clogs the
steams in which salmon hatch and develop thus helping decimate salmon
populations. Habitat destruction tends to turn mature ecosystems into disturbed
ecosystems. Since some organisms are well adapted to growth in disturbed
ecosystems. Habitat destruction also tends to favour the growth of some
organisms while disfavouring the growth of many others (particularly, K
strategists).
Some environmental factors affecting population growth include, bacteria and
disease for example West Nile, natural disasters fort example Tsunamis and
unbalanced Predator Prey relationship For Ex. A Decline in the population foxes
will cause in increase in the hair population
5. What happens if the population size exceeds the carrying capacity?
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Natural Selection will take it course meaning some will die. If the population size
exceeds the carrying capacity the birth rate will drops then the death rate will
increases, then the population returns to the normal carrying capacity. The
process will be repeated continuously. If the population size increase more than
the carrying capacity, the graph will decrease means that the population size
decrease again since the habitat cannot supply enough basic needs source.
6. Why is a random change in K from year to year a problem for management
of commercially exploited wild populations?
If the random change in K from year to year it will influence the population of wild
populations. For instance, if carrying capacity fish is low so the population growth
of the fish will low or decrease. So the income for fisherman will decrease
because the size population growth of fish is small. While if the carrying capacity
fish high so the population growth of the fish high or increases. So the income for
fisherman will increases because the size population growth of fish wide.
7. What will you do if there is a good season and deer populations for the
next season are predicted to overshoot carrying by 20 %?
Actually, we should control the deer harvesting activity. When we control this
activity, the population growth of dear will increases and the growth of deer will
achieve the carrying capacity level.
Conclusion
The shape of population growth curves, is ultimately controlled by three factors:
the initial population size (N0)
a population growth factor (R) which measures the rate at which a population
would grow if it had unlimited resources
the carrying capacity (K), which is determined by environmental factors.
SCE 3107
REFERENCES
https://www.savethekoala.com/koalasendangered.html
http://www.greatlakes.local-e.nsw.gov.au/environment/9815/9817.html
http://cheddarbay.com/0000koala/koala.html
http://www.wwf.org.my/about_wwf/what_we_do/species_main/rhino/index.cfm
http://www.africaguide.com/wildlife/zebra.htm
http://en.wikipedia.org/wiki/Plains_Zebra
http://www.awf.org/content/wildlife/detail/zebra
http://www.encyclopedia.com/doc/1O8-Sshapedgrowthcurve.html
http://wiki.answers.com/Q/List_4_contributing_factors_that_affect_population