Ex. 11 (2) Population Age Distribution (1)

7/30/2019 Ex. 11 (2) Population Age Distribution (1)

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Wild Thornberries HAD

CHUMACERA, KRISTINE B. Date Performed: August 1, 2013Coden, Christelle Jae D. Date Submitted: August 15, 2013

Gelera, Mariel Grace M.

Jacinto, Justine April C.

Tanalgo, Baby Lyn Ann S.

Exercise No. 11Population Age Distribution

AbstractPopulation pyramids graphically illustrate age distribution in a population. A population pyramid plots population (x-axis)

against age (y-axis). It consists of two horizontal bar graphs placed back-to-back, with the graph on the left for males and the one on theright for females. Divided into prereproductive, reproductive and post-reproductive age classes, a population pyramid shows a countrys

capability for population growth and can be used as an indicator of development. Based on their shape, the pyramids can be classified aexpansive, constictive or stationary. Using demographics and graphs generated from the United Nations Department of Economic and

Social Affairs site (http://esa.un.org/unpd/wpp/index.htm), the population pyramids of Haiti (less developed), Mexico (developing) andNorway (developed) for the year 2010 and 2015 were studied. Haiti has large percentages of younger age groups, an expansive population

for both years. Mexico has an expansive population for 2010 which aproaches a more or less equal distribution, a stationary population, in2015. Norway has stationary populations for 2010 and 2015.

Keywords: age distribution, population pyramid, expansive, constrictive, stationary

I. Introduction

Populations have an age structure, the

number or proportion of individuals in different ageclasses. The relative proportions of each age groupshow the rate of population growth. Age classes can

be divided into three stages: prereproductive,reproductive, and postreproductive (Smith and

Smith, 2012). Birth and death rates, and immigrationand emigration determine age distribution

(proportion of individuals in each age group) of apopulation. Fecundity (rate at which femalesproduce eggs), fertility (rate at which females

produce zygotes), and sex ratio (proportion of maleand female in the population) affect birth rate.Typically, expanding populations have a large

percentage of young individuals while decliningpopulations have a large percentage of old

individuals, and stable populations have a relativelyeven distribution among age groups (Campbell,2008). Age distribution of a population reflects:

history of survival (high and low periods), periods of

successful reproduction, and growth potential of apopulation (Utah State University, n.d.). Agepyramids represent the age structure of a population

at some period in time, providing a picture of therelative sizes of different age groups in a population(Smith and Smith, 2012).

Age distribution can be determined throughdifferent methods. Life tables allow for

characterization of populations in terms of age-specific mortality or fecundity. There are two typesof life tables: cohort and segment. Cohort approach

consists of all individuals born during someparticular time interval until no survivors remain. Itis the most reliable method for determining age

specific mortality. Segment (static) approach is asnap-shot of organisms alive during a certainsegment of time. It examines the whole population ata particular point in time. Life Tables allow todiscover patterns of birth and mortality, uncover

common properties shared by populations, andunderstanding of population dynamics (Weber2010)

There are generally three types of populationpyramids. Expansive population pyramids show

larger numbers or percentages of the population inthe younger age groups. These types of pyramids are

usually found in populations with very large fertilityrates and lower than average life expectancies. Theage-sex distribution of many developing countries

would probably display expansive populationpyramids. Constrictive population pyramids display

lower numbers or percentages of younger peopleThe age-sex distribution of the United States fallinto this type of pyramid. Stationary or near-stationary population pyramids display somewhaequal numbers or percentages for almost all age

groups (Abedon, 2005).Determining population age distribution is

important because it allows researchers to predict thetrend of population growth in a given population. Inthis experiment, the students will determine the age

structure of certain countries and construct age


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pyramids. The students will provide possibleexplanations to the age distributions that will beobtained and predict the future trends for that

population.

II. Materials and Methods

Population numbers were obtained from theUN population division website:

http://www.un.org/esa/population/unpop.htm .Three countries were chosen each coming from

developed, developing and less developed country.Norway, Mexico and Haiti were chosen respectively.A .CSV type of file was downloaded and wasopened using an Excel.

The data presented in the excel was filteredaccording to sex. Three columns were achievedtheage groups, the female populations in those age

groups, and the male population preceded with aminus (-) sign. These were copied into Powerpoint

where a pyramid was created.Barwas the chart typechosen and the gap width was reduced to 0. Theminus sign was removed on the x-axis. The tickmark labels on the Y-axis were moved to the left-hand side of the graph. The legend box and gridlines

were removed. The border around the plot area wasremoved. The oldest age groups were removed andadjustments were made so all the age-group labelsappear. A label was added to the x-axis and finally,the chart was recolored and labels of Men and

Women using text box were added.

III. Results

Figure 1. Generated population age structure of a less developedcountry, Haiti 2010

Figure 2. Generated population age structure of a less developed

country, Haiti 2015

Figure 3. Generated population age structure of a developing country,

Mexico 2010

Figure 4. Generated population age structure of a developing country,

Mexico 2015

Figure 5. Generated population age structure of a developed country,

Norway 2010


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Figure 6. Generated population age structure of a developed country,

Norway 2015

IV. Discussion

Age structure, also called population agedistribution is defined as the relative proportion of

individuals belonging to various age classes across apopulation at a certain point in time. Members of thepopulation are grouped into age classes since

generations may overlap; age may refer to timeunits (e.g. days, months, years) or to a qualitative

stage (e.g. eggs, larva, pupa) (Smith & Smith, 2012).In humans, there are three ecological ages namelydependency (pre-reproductive), reproductive, and

post-reproductive (McGraw-Hill, 2001).The length of time an organism remains in

each stage is dependent on the life history of anorganism. Organisms with short lives usually

increase rapidly between generations and thosewhich have long lives increase slowly and havelonger time spans between generations. If an

organism has variable generation times, then thelength of the pre-reproductive period has a

significant effect on the growth rate of thepopulation. If there is an effect on the growth rate ofthe population, then there would also be an effect on

the age structure. For example, if a large proportionof the population belonged to the pre-reproductive

state of the population, then it could be expected thatthe population is expanding or increasing. However,if a large proportion of the population belonged tothe post-reproductive stage, then it could beexpected that the population would be declining or

have no growth (McGraw-Hill, 2011).

There are several ways of obtaning the age

distibution of a given population. First is thehorizontal approach. This utilizes young members of

the population and following their survival duringtheir life spans. Second is the vertical approach werethe ages in the population are examined

simultaneously in one point in time. Third utilizes anindirect method which involves a life table

(McGrawhill, 2001).

The usual representation for population agedistribution is an age pyramid. It is a figure whererelative sizes of different age groups in the

population are shown. The population of each age

groups is shown as a bar extending from the certervertical line, where the bars length is dependent onthe population for the particular age class it isrepresenting. The centerline (center vertical line)separates females (on the right side) from the males

(on the left side) (McGrawhill, 2001).

Figure 7. An example of an age pyramid Retrieved from

Figure 8. Population pyramids for the different stages of demographictransition

Retrieved from

There are three main types of age pyramids

expanding population pyramid, stable populationpyramid, and the declining populationpyramid(McGraw-Hill, 2011).

Expanding population pyramids haverepresent populations with high birth rates, and the

population is undergoing exponential growth. The

concaves sides indicate the high birth rate and lowdeath rate. This is usually pyramidal in shape. This

is the usual population pyramid for less-developedcountries as seen in the exercise (Haiti). The

government in these countries may invest inincentives to use birth controls to decrease

population growth rate(McGraw-Hill, 2011)..

Stable population pyramids (bell-shaped)indicates that pre-reproductive and reproductive age

groups are mostly equal and post-reproductivegroups smallest (due to mortality). This type of

pyramid is the usual population pyramid for stable
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developed countries as seen in the exercise(Norway). The governments in countries with stable

population pyramids should maintain the currentpopulation because stable population pyramids

indicate that not only is the population stable but theeconomy as well. The current population can supportand is supported by the economy(McGraw-Hill,2011).

A declining population pyramid (urn-

shaped) represents a population where the post-reproductive group is the largest and the pre-reproductive groups is the smallest. This shows thatmortality is greater that birth rate which leads todeclining populations(McGraw-Hill, 2011). The

government in countries with declining populationmay use incentives to increase population (i.e. free

health care for the second child).Other pyramid types may include the

stationary and contracting type. The stationary typeis found in countries with low natality and mortality.The contracting type is found in population where

there are lower numbers of young people. Thesepyramid types are based on factors affecting agestructure(McGraw-Hill, 2011).

One of the factors influencing the agestructure of a population is the sex ratio, or the

proportion of males relative to the proportion offemales (University of Wyoming, 2013).

On the other hand, natality is the productionof new individuals or offspring of an organism in a

population. These individuals can be formed through

birth, as in humans; hatching, as in chicken eggs;germination, as in plants; or cell division, as in lower

organisms. There are two types of natality. The first,called the maximum or absolute natality, also knownas the fecundity rate, refers to the maximum

offspring produced under most suitableenvironmental conditions. Since environmentalconditions constantly change and are never static,

this value is theoretical. It is also constant for agiven population. The second type, called the

ecological natality, is also known as the fertility rate,and means the number of offspring produced under

the existing environmental conditions. Meanwhile,mortality denotes the death of individuals in a

population. Similarly, mortality rate has two typesthe minimum mortality rate or physiologicallongevity, or the theoretical minimum death rate

under ideal conditions; and ecological mortality, theactual death rate. The vital index is the ratio of birthto death rate, expressed as percentage. The vitalindex determines the normal growth rate of a

population (Kohli et al, n.d.).

In addition to natality and mortality,immigration, and emigration also affect population

size. Immigration and birth increase population size

while emigration and death decrease it. For instanceif birth and immigration is greater than emigrationand death, the population size would increase. Agedistribution shifts depending on the ages of the

individuals migrating. For instance, if more oldpeople immigrate and more young people emigratethe distributions shifts toward the older ages (Kohlet al, n.d.).

Carrying capacity, the capacity of anecosystem to support a maximum number ofindividuals, is another factor. When population size

increases, the growth rate is reduced as the carryingcapacity is approached (Kohli et al, n.d.).

Age structure can change without changingpopulation size when the number of individual

leaving is equivalent to those entering. This mayoccur when immigration is equal to emigration, orwhen death rate is equal to birth rate. Here, the

population will be stationary, described as zero

growth. Moreover, mortality rate should always belower than the population size (Bietsch, 2012).

Other important concepts to note are sexratios and dependency ratios. Sex ratio is the ratio ofmales to females in the population. Dependencyratio is the number of people who are noteconomically active for every 100 economically

active people in a given population. The formula fordependency ratio is shown below (ColumbiaUniversity, n.d.).

Figure 9. Formula for dependency ratio

Retrieved from

In the exercise, it could be seen that Haithas an increasing population because of the

triangular form of the age pyramid. This shows thatHaiti is indeed not yet a well-developed country interms of economy. The government couldimplement family planning procedures and give

incentives to those who have less children. Mexicoa developing country, is mosty triangular buteventually becomes columnar at the basal part. This

shows that Mexico is approaching a stable pyramidtype. Norway has a columnar shaped pyramid whichimplies that it is stable in terms of population and

economy. The upper portion is triangular onlybecause of the mortality in the post-reproductive

population.

V. Conclusion and Recommendations

In conclusion, the investigators were able to

determine and compare the age structure of countries


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with varying state of economies. Factors such asnatality and mortality were correlated with theobtained data.

Age pyramids are clear visualrepresentations of the population and show the trendin age distribution and can also predict the future

population structure. These tools can also reflect theeconomy of the area of concern, such as if it is a

developing or a developed country.

It is recommended that more pyramids be

constructed with respect to time to observedifferences in the population patterns of a country

and to correlate these differences with variousfactors and events that have occurred in the yearsobserved.

VI. Literature Cited

Abedon, S. 2005. Population Ecology. Ohio State

University. Retrieved 12 August 2013from< http://www.mansfield.ohio-state.edu/~sabedon/ campbl52.htm>.

Population Ecology. Utah State University.

Retrieved 12 August 2013from < http://ocw.usu.edu/biology/general-ecology/lecture8/lecture-8-population-ecology-2.html>.

Bietsch, K.E. (2012).A Guide to Stable Population.

Retrieved 14 Aug 2013 from

.

Campbell N, Reece,J. 2008. Biology. 8th ed.

Pearson Education Inc., Singapore.

Columbia University. (n.d). Demography LearningModule. Retrieved 14 Aug 2013

Kohli, R.K., Batish, D.R. and Singh, H.P. (n.d.).

Ecology. Retrieved 14 Aug 2013 from

.

McGraw-Hill. (2001). Ecology of Populations.

Retrieved 14 Aug 2013 from

Smith T, Smith R. 2012. Elements of Ecology. 8th

ed. Pearson Education Inc., Singapore.

Weber. 2010. Population Ecology. Retrieved 12August 2013from .

University of Wyoming. (2013). Population

Ecology. Retrieved 14 Aug 2013 from

.
http://www.mansfield.ohio-state.edu/~sabedon/%20campbl52.htmhttp://www.mansfield.ohio-state.edu/~sabedon/%20campbl52.htmhttp://ocw.usu.edu/biology/general-ecology/lecture8/lecture-8-population-ecology-2.htmlhttp://ocw.usu.edu/biology/general-ecology/lecture8/lecture-8-population-ecology-2.htmlhttp://ocw.usu.edu/biology/general-ecology/lecture8/lecture-8-population-ecology-2.htmlhttp://ocw.usu.edu/biology/general-ecology/lecture8/lecture-8-population-ecology-2.htmlhttp://www.columbia.edu/itc/hs/pubhealth/modules/demography/populationRatio.htmlhttp://www.columbia.edu/itc/hs/pubhealth/modules/demography/populationRatio.htmlhttp://faculty.weber.edu/jcavitt/WildlifeManagementMaterials/Lectures/Lecture%207.%20Population%20Ecology.pdfhttp://faculty.weber.edu/jcavitt/WildlifeManagementMaterials/Lectures/Lecture%207.%20Population%20Ecology.pdfhttp://faculty.weber.edu/jcavitt/WildlifeManagementMaterials/Lectures/Lecture%207.%20Population%20Ecology.pdfhttp://faculty.weber.edu/jcavitt/WildlifeManagementMaterials/Lectures/Lecture%207.%20Population%20Ecology.pdfhttp://faculty.weber.edu/jcavitt/WildlifeManagementMaterials/Lectures/Lecture%207.%20Population%20Ecology.pdfhttp://faculty.weber.edu/jcavitt/WildlifeManagementMaterials/Lectures/Lecture%207.%20Population%20Ecology.pdfhttp://faculty.weber.edu/jcavitt/WildlifeManagementMaterials/Lectures/Lecture%207.%20Population%20Ecology.pdfhttp://faculty.weber.edu/jcavitt/WildlifeManagementMaterials/Lectures/Lecture%207.%20Population%20Ecology.pdfhttp://www.columbia.edu/itc/hs/pubhealth/modules/demography/populationRatio.htmlhttp://www.columbia.edu/itc/hs/pubhealth/modules/demography/populationRatio.htmlhttp://ocw.usu.edu/biology/general-ecology/lecture8/lecture-8-population-ecology-2.htmlhttp://ocw.usu.edu/biology/general-ecology/lecture8/lecture-8-population-ecology-2.htmlhttp://ocw.usu.edu/biology/general-ecology/lecture8/lecture-8-population-ecology-2.htmlhttp://ocw.usu.edu/biology/general-ecology/lecture8/lecture-8-population-ecology-2.htmlhttp://www.mansfield.ohio-state.edu/~sabedon/%20campbl52.htmhttp://www.mansfield.ohio-state.edu/~sabedon/%20campbl52.htm

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Ex. 11 (2) Population Age Distribution (1)