POPULATION ECOLOGY
Chapter 5

• Focuses on the factors that influences population’s:
Size (number of individuals)
Growth rate (rate of change of population size)
Density (number of individuals per unit area and
volume)
Population structure (relative number of individuals
different ages)
POPULATION ECOLOGY

• Is a group of individuals of same species in same area at
same time
• refers to the group in general and also to the size of the
population—the number of individuals it contains.
• a reproductive group because organisms usually breed
with members of their own population
POPULATION

Population of zebras Population of trees

Demography
is the study of populations, but most often refers to the
study of human populations
Demographics
 vital statistics of the populations, which include
population size, density, distribution and age structure.
CHARACTERISTICS OF
POPULATION

1. Population Density
is the number of
individuals of a
per unit area or
volume.
CHARACTERISTICS OF
POPULATION

2. Population Distribution
Is the dispersal of individuals across an area of interest
The availability of resources can affect where
of a species are found.
CHARACTERISTICS OF
POPULATION

Abiotic factors
sunlight &
temperature
precipitation / water
soil / nutrients
Biotic factors
other living organisms
prey (food)
competitors
predators, parasites,
disease
Resources are non-living and living components of an
environment that support living organism

Dispersion Pattern
• is the relative distribution or arrangement of its individuals
• within a given amount of space.

Why clumped?
Results from unequal
distribution of
resources
Why uniform?
Results from
interactions among
individuals of population
Why random?
Only occurs in the absence
of strong attractions or
repulsions among
individuals in a population.

3. Growth Rate
Results in population sizes
A change in the size of a population over a given
of time
Dependent upon:
natality (number of individuals born each year) and
mortality (the number of individuals that die each year
is the birth rate minus the death rate
CHARACTERISTICS OF
POPULATION

MIGRATION
Another reason the population continued to grow was that
immigration increased.
The movement of individuals between areas is called migration.
Movement into an area is immigration and movement out of an
area is emigration.
Migration between and within countries is a significant part of
population change.
The populations of many developed countries might be
decreasing if not for immigration.

These graphs have a typical shape for populations with different rates of growth. The
number of males and females in each age group are shown as opposite-facing bars.
People between 15 and 44 years of age are likely to produce children.

BIOTIC POTENTIAL
Is the fastest rate at which populations can grow and is
achieved when resources are unlimited
Depends on following factors:
1. Usual number of offspring per reproduction or
(reproductive potential)
2. Chances of survival age of reproduction
3. How often each individual reproduces
4. Age at which reproduction begins

FORECASTING POPULATION SIZE
Survivorship
is the percentage of members of a group that are likely to survive to
any given age.
Cohort is a term used to describe population members that are the
same age and have the same chances of surviving.
To predict survivorship, a demographer studies a group of people
born at the same time and notes when each member of the group
dies.
The results plotted on a graph might look like one of the types of
survivorship curves.

Survivorship curves
show how much of the
population survives to a
given age.
A Type I curve is seen in
populations where most
members survive to be
very old.
A Type III curve is seen in
populations where many
children die.

Wealthy developed
countries such as Japan
and Germany currently
have a Type I
survivorship curve
because most people
live to be very old.
Type II populations have
a similar death rate at all
ages.
Type III survivorship is the
pattern in very poor human
populations in which many
children die. Both Type I and
Type III survivorship may result
in populations that remain the
same size or grow slowly.

FORECASTING POPULATION SIZE
Age Structure
Diagrams divide a population into age groupings
Three major age groups:
• Pre-productive
• Reproductive
• Post-productive

Why pyramid shaped?
Results when pre-
reproductive group is
largest of the three
groups
Birth rate is higher
than death rate
Why bell shaped?
Results when
reproductive group
equals the size of pre-
reproductive group
Why urn shaped?
Results when the post-
reproductive group is the
largest

PATTERNS OF POPULATION GROWTH
The number of babies born each year per 1,000 women in a
population is called fertility rate
Demographers also calculate the total fertility rate, or the
average number of children a woman gives birth to in her
lifetime.
Replacement level is the average number of children each parent
must have in order to “replace” themselves in the population.
This number is about 2.1, or slightly more than 2, because not all
children born will survive and reproduce.

Birth rate means the number of new individuals that are produced by a
population in a period.
Death rate means the number of individuals that die in a given period.
 A population shrinks when birth rate is less than the death rate.
 When the birth rate is greater than the death rate, a population
grows.

The baby boom was a period of high fertility rates, and the baby bust
was a period of decreasing fertility.

TWO TYPES OF POPULATION
GROWTH
1. Logistic Growth
Occurs in population that produce a single batch of offspring in
a year
Population increases by a constant ratio from one generation to
the next
2. Exponential Growth
Occurs in nature only when populations have plenty of food and
space, and have no competition or predators.
Populations produce offspring throughout the year

Population growth is
graphed by plotting
population size over a
period of time.
Exponential population
growth will look like the
J-curve shown here.

Logistic population
will look like the
S-curve shown here.

In an ideal environment (one
that has no limiting factors)
populations grow at an
exponential rate (left).
However, for all populations,
exponential growth is curtailed
by factors such as limitations in
food, competition for other
resources, or disease. As
competition increases and
resources become increasingly
scarce, populations reach the
carrying capacity (K) of their
environment, causing their
growth rate to slow nearly to
zero (right).

CARRYING CAPACITY
The maximum number of individuals of a population that can be
maintained indefinitely by the environment.
 Maintained indefinitely refers to the ability of an ecosystem to
provide the same quantity and quality of environmental goods
and services over time.
When a population overshoots, it means the population
surpasses the carrying capacity of its environment. The death
rates will begin to surpass birth rate.

An example of carrying
capacity is shown by
the dashed yellow line
in the graph. This line
seems to be a limit on
the size of the example
population (blue line).

LIMITING FACTORS OF POPULATION
1. Density-dependent Factors
Includes factors that are related to population size
Operate only when the population density reaches a certain level
(exponential growth)
Operate most strongly when a population is large and dense
They do not affect small, scattered populations as greatly
 Include: competition, predation, parasitism, disease

LIMITING FACTORS OF POPULATION
2. Density-independent Factors
Affect all populations in similar ways, regardless of the
population size.
Examples of density-independent limiting factors include:
unusual weather
natural disasters
seasonal cycles
certain human activities—such as damming rivers and clear-
cutting forests

REPRODUCTIVE STRATEGIES
R – ADAPTED SPECIES
 Short life
 Rapid growth
 Early maturity
 Many, small offspring
 Little parental care and protection
 Little investment in individual offspring
 Adapted to unstable environment
 Pioneers, colonizers
 Niche generalist
 Prey
 Regulated by intrinsic factors
 Low trophic level
K – ADAPTED SPECIES
 Long life
 Slower growth
 Late maturity
 Few, large offspring
 High parental care or protection
 High investment in individual offspring
 Adapted to stable environment
 Late stages of succession
 Niche specialist
 Predators
 Regulated mainly by extrinsic factors
 High trophic level

r – strategist
produces a J-curve
while k – strategist
produces S-curve

HIGHLIGHTS OF THE PHILIPPINE
POPULATION 2015 CENSUS OF POPULATION
Release Date: Thursday, May 19, 2016
The population of the Philippines as of August 1, 2015 was
100,981,437, based on the 2015 Census of Population (POPCEN
2015).
The 2015 population is higher by 8.64 million compared with the
population of 92.34 million in 2010, and by 24.47 million
compared with the population of 76.51 million in 2000.

HIGHLIGHTS OF THE PHILIPPINE
POPULATION 2015 CENSUS OF POPULATION

HIGHLIGHTS OF THE PHILIPPINE
POPULATION 2015 CENSUS OF POPULATION
The Philippine population increased by 1.72 percent annually, on
average, during the period 2010 to 2015. By comparison, the rate
at which the country’s population grew during the period 2000 to
2010 was higher at 1.90 percent.

HIGHLIGHTS OF THE PHILIPPINE
POPULATION 2015 CENSUS OF POPULATION
Of the country’s 18 administrative regions, Region IV-A
(CALABARZON) had the biggest population in 2015 with 14.41
million, followed by the National Capital Region (NCR) with 12.88
million, and Region III (Central Luzon) with 11.22 million. The
combined population of these three regions accounted for about
38.1 percent of the Philippine population in 2015.
The Autonomous Region in Muslim Mindanao (ARMM) was the
fastest growing region with an average annual population
growth rate (PGR) of 2.89 percent.

HIGHLIGHTS OF THE PHILIPPINE
POPULATION 2015 CENSUS OF POPULATION
The country has 81 provinces. Of these provinces, Cavite was the
most crowded in 2015 with 3.68 million persons, followed by
Bulacan (3.29 million), and Laguna (3.04 million).
Batanes was the smallest province in terms of population size
with 17,246 persons. Two other provinces posted a population
size of less than 100,000. These are Siquijor (95,984) and
Camiguin (88,478).

HIGHLIGHTS OF THE PHILIPPINE
POPULATION 2015 CENSUS OF POPULATION
The Philippines has 33 highly urbanized cities (HUCs).
Four of these HUCS had surpassed the one million population
mark, namely:
Quezon City (2.94 million),
City of Manila (1.78 million),
Davao City (1.63 million), and
Caloocan City (1.58 million).

CURRENT PHILIPPINE POPULATION
102 617 303 Current population
51 460 843
Current male
population (50.1%)
51 156 462
Current female
population (49.9%)
1 694 438 Births this year
473 311 Deaths this year
-102 587
Net migration this
year
-177
Net migration
today
1 118 552
Population growth
this year
1 928
Population growth
today
Source : United Nations Department of Economic and Social Affairs: Population Division

PROBLEMS OF RAPID GROWTH
Rapidly growing population can use resources faster than the
environment can renew them
Standards of living decline when wood is removed from local
forests faster than it can grow back, or when wastes overwhelm
local water sources.
Vegetation, water, and land are the resources most critically
affected by rapid growth.

PROBLEMS OF RAPID GROWTH
The makeshift
housing shown here
is one consequence
of unmanaged
growth.

PROBLEMS OF RAPID GROWTH
Unsafe Water
In places that lack infrastructure, the local water supply may be
used not only for drinking and washing but also for sewage
disposal.
As a result, the water supply becomes a breeding ground for
organisms that cause diseases such as dysentery, typhoid, and
cholera.

PROBLEMS OF RAPID GROWTH
The Rio Grande,
shown in this figure is
one example of an
unsafe water source
used by many people.

PROBLEMS OF RAPID GROWTH
Impacts on Land
Growing populations may have a shortage of arable lands, which
is land that can be used to grow crops.
Growing populations also make trade-offs between competing
uses for land such as agriculture, housing, or natural habitats.
Much of the world’s population is undergoing urbanization,
which means that more people are living in cities than in rural
areas.

PROBLEMS OF RAPID GROWTH
Impacts on Land
People often find work in the cities but move into
suburban areas around the cities.
This suburban sprawl leads to traffic jams, inadequate
infrastructure, and the reduction of land for farms, ranches, and
wildlife habitat.
Meanwhile, housing within cities becomes more costly, more
dense, and in shorter supply.

PROBLEMS OF RAPID GROWTH