Module 5: Population Dynamics
Aimee Lynn A. Barrion-Dupo
5.1 INTRODUCTION
The innate dynamism of living systems is typified through patterns and cycles explained in Modules 3 and
4, modification of components, adaptations to physiological environments, genetic regulation, and population
dynamics. This module focuses on the latter; providing an understanding of how populationsgrow and decline.
It is important to relate population growth to resource use as biogeochemical cycles through ecosystems
influence the rates at which populations of organisms reproduce. ln the same manner, the size and pattern of
distribution ofpopulations of organisms influences biogeochemical cycles. Microorganisms,for instance, are known
to be key driversof global biogeochemical cycles (ftiladsen, 2011).
The human population,meanwhile,contributes to global change byaltering biogeochemical cycles. Such
modificationsare partially a function of the growth in size and productivity of the human population. Population
size and productivity are intricately connected through both technologiesand socio-cultural activities that allow us
to harness energy as wellas feed us (Suarez and Sajise, 2010;Wright, 2005).
By the end of Module 5, you are expected to accomplish the following: 1) study the resources in this
module, and 2) accomplish module's learning tasks.
5.2 LEARNING OUTCOMES
After studying the resources and accomplishing the activities given in this module, you should be able to;
f. identify demographic processes affecting population growth;
2. differentiate factors limiting population growth, and
3. interpret constructed graphs and tables on population dynamics;
5.3 LEARNING ACTIVITIES
It was through Thomas Malthus' Essay on the Principle of Population in 1798 that the first theoretical
treatment of population dynamics was proposed. At that time, Malthus described populations to grow logistically
under ideal environmental conditions. However, he also mentioned that grovdh of populations depended on
constant resource supply. The mathematical translation of this concept was made by Pierre Frangois Verhulst in
1838, forming what is now known as the logistic equation:dN/dt = rN(1-N/K). ln this equation, N represents the
population size while r represents the intrinsic rate of increase in a given time period (t). Meanwhile, K represents
the carrying capacity, the total number of individuals of a population that the finite environment can support
(Berryman, 1992).
Alfred Lotka and Vito Volterra upgraded Verhulst's linear single-species population dynamics equation to
include the effect of another population, i.e. predator interaction. This cycling effect of predator-prey interaction is
illustrated in their dynamics (Figure 5.1).
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Figure 5.1. Cycling of predator-prey populations.
(lifted without permission Mc Graw HillCompanies)
5.3.1 Demograph ic Factors
Core to the study of population dynamics is understanding how demographic factors influence population
size. These demographic factors are namely; birth, death, immigration, and emigration. Members of a
population enter this system in two ways. One is through birth and the other through immigration. Hence, birth
and immigration cause increase in population size. ln contrast, members of this living system exit it either through
death or emigration. Both demographic processes eventually lead to the decline in population size.
How demographic factors affect population expansion and shrinking rates can be visualized through life
tables, survivorship curves, and age structures, Life tables are a record of the birth and death rates for organisms
at different life stages. A simplified graphical presentation of elements of the life table is called a survivorship
curve. Lastly, the age structure is literally a "groufie" of a population at a specific moment in time. Members of
this population are clustered accordlng to age and sex categories. Data provided by these visual records provide
useful information on the state of the population.
5.3.2Poputation Growth
As with life tables, survivorship curves, and age structures, ecologists think
of ways to show or model how population size changes in size and composition
over of time. Modelling population dynamics mathematically helps to quantify changes occurring in a population
and, importantly, to predict future changes. Describing and predicting future population changes becomes all the
more important with the human population, as the dynamics of our population directly and indirectly exert
pressure on other living systems in the biosphere (Molles, 2010).
The first population growth model represents growth of a population without environmental resistance
factors. These environmental resistance factors are limits to population growth (e.g. predators, food, mates
etc.). This continuous population increase in an unlimited environment is called the exponential growth model.
This pattern of population growth yields a J-shaped curved. However, Module 2 has demonstrated that resources
are limited and can be depleted. This causes population growth to eventually slow down and stop. The part where
population growth stops is what is termed as the carrying capacity of the environment. Garrying capacity is the
total number of individuals that the environment can support. A logistic growth model shows that when
resources get diminished, population growth rate will ultimately plateau (Molles, 2009; Stiling, 2AA2). And this
modelproduces an S-shaped population growth curve.
5.3.2Population Regulation
According to Molles (2010), environmental checks affect population growth by altering demographic
processes such as birth and death rates. These limits are classified into two types: density-dependent factors and
density-independent factors. Biotic factors like disease and predation which limit population growth are density-
dependent factors. The effects of these factors on birth and death intensifies as population increases in size. ln
contrast, density-independent factors are abiotic factors (e.9. temperature, weather, light intensity etc.) that
exert the same influence on the population regardless if the population is large or small.
Activity 1: Mind Mapping Population Dynamics Concept
Estimated Time to Finish Task 1: 90 minutes
The following resources discuss population demographics and population growth. Resource ! presents the four
demographic processes affecting population ske ii.e. birth, death, immigration, and emigration). Furthermore,
Resource ltackles how populations growth is predicted through two models: exponentialand logistic.
!
On the other hand, Resource 2 complements Resource by depicting how populations grow and decline through
life tables, sulivorship curves and age struciures. elate to age structure
Resource Qelabcrates on these using the Philippine population growth as an example.
Meanwhile, Resource .-1 will help you differentiate the density-independent and density-dependent limiting factors
to population growth.
Take note of your answers to these study questions as you study the learning resources. You will have to go back
to these again at the last part of Activities 2 and 3.
1. How do demographic factors affect population size?
2. Are the effects of these factors mutually exclusive?
3. How is population growth depicted?
4. What are applications of knowing limits to population groMh?
5. Describe a density-independent factor and explain why its effect on population growth is independent of
population density.
6. How do density-dependent factors limit population growth?
Click the links be[ow to access or download all resources and study them carefully
Resource 't: Population Dvnam&s
Li n k: http:/itvup. ph/?p=3935
Estimated Time Required to View and Study: 15 minutes
Resource 2: Life Tables" Survivorship, &Aqe- Structure
Link: https:i/www.khanacademy.org/science/biologylecologylpopulation-ecology/a/life-tables-survivorship-age-
sex-structure
Estimated Time Required to Read: 5 minutes
Resource 3. Philippine Population GroMh
Link: http://tvup. phl?p=3934
Estimated Time Required to View and Study: 30 minutes
Resou rce 4: Pogu! Etiqn_Eeg qlellen
Link: https://unnrw.khanacademy.orglscience/biology/ecotogy/population-growth-and-regulation/a/mechanisms-of-
population-regu[ation
Estimated Time Required to Read: 5 minutes
Visually organize what you have learned from Resources 1-4 into a . . -:::::,:
First identify a central idea from the resources you studied. Next, create links or associations to this central idea
by adding branches to your central idea. When you are done with your mind map, partner with someone in class
and discuss your mind map.
Resource 5: Hgw_lq_make a rninelmAc Studv Tip # 6
Link: https: l1www. youtu be. comlwatch?v=YRKyWpGTSmS
Estimated Time Required to View: 1:40 minutes
Activity 2: Think Pair Share (bridge with Resources 1-4 application)
Estimated Time to Finish Task 1: 30 minutes
Read the following population cases
https://commons.wiki Case 1. You happened to observe a population of
media.orglwiki/File:Dr the Philippine flying lizards, Draco yolansthriving in the mulberry trees. One
day, you noticed that the number of adults has increased and is higher than
previously observed. What could explain this?
Case 2.lt is the start of
the rainy season. The
grassy areas near your
dorm have been flooded
and odorous ants (Iaprnoma sessl/e) living there
started to take refuge inside dorms-including
yours. ln sheer panic, you try setting up sticky
traps. After some, time, you noticed that nothing h
'.*
was happening. You tried plotting the population
growth curve of this ant species to determine if the
https://commons.wi kimedia.orglwiki/File:Od
traps are working. You ended up with the orous_house_ant_( 17434366603) jpg
exponential phase of a logistic curve.What can
you infer from your graph?
Case 3.During sembreak, you observedrats (Ra/fus noruegicus) living
in the field near your home. You noticed that while there are many
rats, you rarely observed any reproductive females. What can you
infer from this observation?
https://commons.wikimedia.org/wiki/Rattus_ncrvegicus#/med i
a/Fi le:Ratl u s_norveglcus_2.jpg
Write ciown your explanationoneach case topic prior to the
discussions. Next, pair up with a partner. You may also work with your initial partner whom you have discussed your mind
map with. Discuss and share your ideas on these cases with your partner.
Activity 3: Frgure lt Out
Estimated Time to Finish Task 1: 50 minutes
After studying Resources 14, check your understanding of the text and
videos by doing the following with your assigned group:
1, Construct a graph of the population grovrrth of the Philippines. Make use of the datafound
in:https://web.archive.orq/web/20120204171010/http:/lwww.nscb,qov.ph/secstaUd popn.asp
2. Next, plot the survivorship curve of Filipinos in 2000 using the life-table data of the Philippines.
This information can be accessed through the tink below:
http:l/apps.who. inVqho/data/view, main. LT62 1 50?lanq=en.
Your may also request your professor for an excef file of this.
3. lf you need a guide on constructing a survivorship curve, you can aceess this link for a step-by-
step guide :
http://www.afrc.uamont.edu/whited/Life%2Otables.%20survivorship%20curves,%20and%20popua
tion%20qrowth.pdf
NOTE:lf you do not have access to the internet, your professor can
provide you withelectronic and hard copies of these materials.
4. The following meeting, your group will present properly-labelled
graphs keeping in mind the guide questions listed below:
3.1 ls your graph of the Philippine population showing exponential or logistic growth?
3.2 What type of survivorship curve does the Philippine population show?
3.3 What do you think are demographic factors influencing the population growth of
Filipinos?
3.4 Cite some examples of density-dependent and density independent factors that could
influence (or has influenced) Philippine population growth.
3.5 When do you think willa population collapse?
Scoring Rubric for Task 1: Figure lt Out
Categories Yes Partly No Remarks
(2 fis) (1 pt) (o pt)
Comprehension
'1. Discussionreflects a good perception of key
ideas from the module and resources
2. Discussion connects the topic to related ideas
and concepts
Presentation of Graphs
1. Graphs are clearly, concisely presented
2. Graphs are neat and properly labelled
I nterpretation of Graphs
1. Related data to moduie concept clearly
2" Described and evaluated trends observed
from the data plotted
Etiquette
1. The group responds to theirpeers' questions
Courteously
2. The group displays a openess to consider
novel and even contradictory ideas
Communication Skills
1. Data presentation and discussion is presented in
correct, academic language
2. Dala presentation displayminimal grammar,
spelling errors
Sub-total
SYNTHESIS
From this module, you should be able to realize the importance and applications of knowing why and how populations
grow and shrink. Such knowledge and understanding can help you relate the complex interwoven connections between
population dynamics and the sustainable use of biological resources. However, keep in mind that with appreciation comes
action too, hence you were asked to address some incendiary questions.
SELF-ASSESSMENT:
Estimated Time to Finish Self-Assessment: 5 minutes
After studying the module resources and accomplishing all the learning tasks for this module, check whether you
were able to do the following:
L- identify demographic processes influencing population dynamics
i: discuss how population size increases and decreases
t-I distinguish factors limiting population growth
il explain the relationship population dynamics with resource use
Multimedia Resources:
Below are multimedia resources (videos, slide presentations, etc.) to help reinforce your learning on Population Dynamics.
Demographic Transition
(Khan Acaderny {24M, April2S). Demographic Transition ffideo fitel.}
https: //www. youtu be. com/watch ?v=6 P2 bs PWC RvM
Manila- 20 Million and Risinq
(Leelee {2412, October 12}.Manila 20 Million and Rising ffideo filel.)
https://www.youtube. com/watch?v=Ku DDvYhmCTE
Population Dvnamics
(Khan Academy (2014, Apri27). Population Dynamics Mdeo filel.)
https://www. voutu be. com/watch?v=4CAQ N -nc8Ac
Population Ecoloqv
(Bozeman $cience (2015, Cctober 1). Population Ecology [Video file].]
https://www. youtube. com/watch?v=PQ-CQ3CQE3q
Links:
Resource 1: Population Dynamics
Link: http://tvup. ph/?p=3935
Resource 2: Lrte Tables, Survivorship, & Age- Structure
Link: https://www.khanacademv.orq/science/bioloqv/ecoloqv/population-ecologv/a/life-tables-survivorship-age-sex-
structure
Resource 3. Philippine Population Growth
Link: http://tvup. ph/?p=3934
Resource 4: Population Regulation
Link: hflps://www.khanacademy.orq/science/bioloqy/ecoloqv/population-qrowth-and-requlation/a/mechanisms-of-
poou lation-reou lation
Resouree 5: How to make a mind map Study Tip # 6
Link: https://www. voutu be. com/watch?v=YRKvWp6TSmS
Human Population Growth and the Demographic Transition
Link: https://www. ncbi.nlm. nih.gov/pmc/articles/PMC2781 829/
References:
1) Albe(in,W., P. Marullo,M. Aigle,C. Dillmann,D, de Vienne,M. Bely, and D.Sicard.
2011. Population Size Drives lndustrial Saccharomyces cerevisiae Alcoholic
Fermentation and ls under Genetic Control. Applied and Environmental
IVI icrobiology : 27 7 2-27 84.
2) Berryman, AA. 1992. The origins and evolution of predator-prey theory. Ecology.
73(5): 1 530-1 535.
3) Barrion-Dupo ALA, Banaay CGB, Lambio lAF, Maranan FS, Rabena MAF, Flores
RJD, Deyto RC, Fajardo AM, Lit lLJr. 2013. Effect of population density on
larval dispersion and pit construction of the antlion, Myrmeleonangustipennis
Banks (Neuroptera: Myrmeleontidae). Asian Journal of Biological
Sciences.vol.6(2): 31 -1 37.
4) Bongaarts, J. 2009. Human population growth and the demographic transition. Phil.
Trans. R. Soe. B (2009) 364,2985-2990. doi:10.10981rs1b.2009.0137.
5) Madsen, E.L. 2011. lvlicroorganisms and their roles in fundamental biogeochemical
cycles. Current Opinion in Biotechnology. 22:456464.
6) Molles, M. C. Jr. 2010. Ecology: Concepts and Applications. Sth edition. Boston:
WCB/McGraw-Hill. 230-26'1 .
7) Stiling, P.2OA2. Ecology. Upper Saddle River, NJ: Prentice Hall, pp.66-88.
8) Suarez, R.K. and P.E. Sajise. 2010. Deforestation, Swidden Agriculture and Philippine
Biodiversity. Philip Sciletters . 3(1):91-99.
9) Wright, R.T. 2005. Environmental Science. Upper Saddle River, N.J.:
Pearson/Prentice Hall, pp.76-78.
