Environmental Science
Chapter 4:
Population Ecology
Mr. Manskopf
Notes also available at
http://www.manskopf.com
Population Ecology Big Ideas
In an ecosystem, the biotic and
abiotic components interact to form
an interconnected system.
 Humans classify the diversity of life
on Earth in order to better
understand their relationships.
 Population sizes change according to
changes in the environment.

Section 1: Studying Ecology
GOALS
 Distinguish between biotic and abiotic
factors in an ecosystem
 Describe how a population, community
differ from a species
 Explain the importance of habitats
What is ecology?
 The
study of
how organisms
interact with
each other and
with their
environments
What is an ecosystem?
Defining an ecosystem
Ecosystem: all the
organisms living in
an area together
 Forest Ecosystem
 Pond Ecosystem
 Vacant Lot
Ecosystem
 Desert Ecosystem

All Ecosystems are connected
How does your
ecosystem
impact the
Atlantic Ocean?
Parts of an ecosystem
Parts of an ecosystem
In order for an
ecosystem to survive
there must be certain
basic parts
 Energy
 Mineral nutrients
 Carbon dioxide
 Water
 Oxygen and more
What are some parts of this
ecosystem?
You will be conducting a study
of the interactions of
vegetation, animals, mineral
composition of the soil, and
water levels in a saltmarsh. You
are studying the saltmarsh ___.
ECOSYSTEM
Biotic vs. Abiotic
Biotic: living parts of
the ecosystem
 Plants, animals,
bacteria, etc.
Abiotic: nonliving parts
of the ecosystem
 Sunlight, soil, air,
temperature
What are some biotic AND abiotic parts of this ecosystem?
Organizing Biotic
Parts
Smallest Unit
Organism: an individual
living thing like you, a
tree, a fox, a rose
Species are groups of
organisms like red
foxes or black widow
spiders, or grizzly
bears
Species
Species: groups of
organisms that
resemble each other
in appearance,
behavior, chemistry
and genetic
makeup…able to
reproduce
 3.6 to 100 million
species (1.4 identified)
 Mostly insects/micro
 Tropical forests
Insects
751,000
Known
species
1,412,000
Plants
248,400
Population
Population: all the
members of the same
species that live in the
same place at the same
time
 Field mice living in a
corn field, grizzly bears
of Yellowstone Park
area
Community
Community: a group of
various species that
live in the same place
and interact with
each other.
 Pond Community
 Pineland Forest
Biosphere
 All
parts of the
Earth where
life is found
Giraffes, lions, zebras, hyenas,
and all the other living things of
the Serengeti make up a(n) ___
COMMUNITY
Habitat
Habitat: a place
where an
organism lives
Organisms are
well suited for
their habitat
Habitat
 Habitats
provide an
organism with
resources—
anything an
organism needs to
survive and
reproduce,
including food,
shelter, and mates.
Section 1 Review
 Distinguish
between biotic and abiotic
factors in an ecosystem
 Describe how a population,
community differ from a species
 Explain the importance of habitats
Section 2: Describing Populations
 Explain
the usefulness of tracking
population sizes
 Define population density
 Describe three ways populations can
be distributed
The Decline of the Passenger
Pigeon

How does a species
go from having
billions to extinct in
just one
century…The
Passenger Pigeon
Story.

Extinct in the wild
since 1900 and last
died in the Cincinnati
Zoo 1914.
Review: What is a population?
Population: all the
members of the same
species that live in the
same place at the same
time
 Field mice living in a
corn field, grizzly bears
of Yellowstone Park
area
Wolves in Yellowstone NP
Population Size
 Why
care about
the size of the
population?
 How can scientists
estimate the
population (say of
Elephant Seals on
a beach in CA)?
Population Size
•
The number of individuals
in a population at a given
time
•
Sudden and dramatic
decreases in population
size can indicate an
unhealthy population
headed toward extinction.
•
Ecologists often use
sampling techniques to
estimate
population
size.
Did You Know? The passenger
pigeon was once North America’s
most abundant bird. Hunting
drove them to extinction in less
than 100 years.
Mark and Recapture

Common way of
estimating population
size
Estimating Population
How can you
estimate the
population of
trees in this
valley?
WHY NOT
COUNT THEM
ALL?
WHY IS
SAMPLING
NEEDED?
Population Density
What is
population
density?
What are
advantages
and
disadvantages
of high and
low density?
Population Density
•Measure of how crowded a population is
•Larger organisms
generally have lower
population densities.
•Low population density:
More space, resources;
finding mates can be difficult
•High population density:
Finding mates is easier; tends to be more competition;
more infectious disease; more vulnerability to predators
Population Distribution
How organisms are arranged within an area:
UNIFORM
RANDMOM
Occurs when
individuals hold
territory or compete
for space. Plants in
desert
Occurs where
resources needed are
found throughout,
wildflowers in meadow
CLUMPED
Most Common.
Occurs where
resources are
together. Water hole
in desert, humans in
cities
Many bird species are territorial.
In territorial birds species, what
kind of population structure
would you expect?
UNIFORM
Population Distribution
•Random distribution:
Organisms arranged in
no particular pattern
•Uniform distribution:
Organisms evenly spaced
•Clumped distribution:
Organisms grouped near resources; most
common distribution in nature
What type of distribution?
CLUMPED
WHY?
Age Structure
•
Relative number
of organisms of each
age group within
population
•
Can be used to
predict future
population growth of
a population
•
HOW?
Sex Ratios
•
Proportion of males
to females
•
Age structure
diagrams give
information about
sex ratios.
•
For a monogamous
species, the ideal sex
ratio is 50:50.
Why is 50/50 not as
important in nonmonogamous populations?
Section 2: Describing
Populations Review
Explain the usefulness of tracking
population sizes
 Define population density
 Describe three ways populations can be
distributed
 TERMS: Population Size, Population
Density, Population Distribution, Age
Structure, Sex Ratios

Section 3: Population Growth
Describe the factors that influence
population’s growth rate
 Explain exponential and logistic growth
 Explain how limiting factors and biotic
potential affect population growth
 TERMS: survivorship curve, immigration,
emigration, exponential growth, carrying
capacity, logistic growth, biotic potential

What does this graph show?
Population Growth?

Why are there so few whales, but so many
bacteria?
Factors the Determine
Population Growth
A population’s relative
birth and death rates
(mortality and natality)
affect how it grows.
 More births than
deaths = population
increase
 More deaths than
births = population
decrease

Survivorship
Individuals of
different ages have
different probabilities
of dying
 Survivorship curves
show how the
likelihood of death
varies with age.

Type I
survivorship
curves are for
species that have
a high survival
rate of the young,
live out most of
their expected life
span and die in old
age. Humans are a
good example of a
species with a
Type I survivorship
curve
Type II survivorship curves are for species that have a
relatively constant death rate throughout their life span. Death
could be due to hunting or diseases. Examples of species
exhibiting a Type II survivorship curve are coral, squirrels,
honey bees and many reptiles.
Type III
survivorship
curves are found
in species that
have many
young, most of
which die very
early in their life.
Plants, oysters
and sea urchins
are examples of
species that have
Type III
survivorship
curves.
If a tree wants to successfully reproduce, how many seeds
should it spread?
If a couple in India knows for sure there child will survive to
adulthood, will they decide to have more or less children do
you think?
Immigration/Emigration
•
In addition to births and deaths, population
growth is affected by immigration and
emigration—individuals moving into and out of
a population.
•
Migration, seasonal movement into and out of
an area, can temporarily
change population size.
Population Calculations
Net population Change =
(births + immigration) – (deaths + emigration)
There are 300 people living in a village, 50
children are born, 20 people die, 10 immigrate
and 2 emigrate. What is the new population?
Calculating Growth Rate
•
Determined by the following equation:
(birthrate + immigration rate) – (death rate +
emigration rate)
•
Growing populations have a positive growth
rate; shrinking populations have a negative
growth rate.
•
Usually expressed in terms of individuals per
1000
Current human growth rate 1.25% down from
2.2% in 1963
Every spring, many species of
bird travel north to the Arctic to
breed, and in the fall travel
south again for the winter. This
is an example of _____
MIGRATION
How Populations Grow

What
resources
are
available to
the
population?
Patterns of Growth
EXPONETIAL GROWTH
•
Population increases by
a fixed percentage
every year.
•
Normally occurs only
when small populations
are introduced to an
area with ideal
environmental conditions
•
Rarely lasts long
WHAT SHAPE
DOES
EXPONENTIAL
GROWTH LOOK
LIKE?
Starts slowly, then
takes off – “JShaped Curve”
Why doesn’t exponential growth
last long?
Limiting Factors
Limiting Factor
Principle: too much or
too little of any abiotic
factor can limit or
prevent growth of a
population, even if all
other factors are near
or above optimum.


Why are there no citrus
fruit growing in NJ?
Why do trees grow
toward the sky?
What Might Be Some Limiting
Factors in the Ocean?

Limiting factors

may include:
•
Salinity
•
Ph
•
Sunlight
•
Dissolved oxygen
•
Temperature
Carrying Capacity
Limiting Factors lead to
Carrying Capacity: the
largest population an
environment can
sustain.
What is the maximum
amount of wolves
that can be sustained
in Yellowstone?
Logistic Growth
Carrying Capacities
are NOT fixed
A population of wolves is reintroduced
into Yellowstone National Park. For the
first decade, the wolf population grows
exponentially. Then, the population
growth slows. The new pattern is
known as ___
LOGISTIC GROWTH
In the example above, where wolves are
reintroduced to Yellowstone National Park, the
number of elk and other prey species within
the park are _____ Limiting Factors
Biotic Potential
•An organism’s maximum ability
to produce offspring in ideal
conditions
•Many factors influence biotic
potential, including gestation
time and generation time.
•Organisms with high biotic potential
can recover more
quickly from population declines than
organisms with low biotic potential.
Biotic Potential
Scorpion Fish
 Mature 3-5 years
 Release 50,000 to
100,000 eggs
 Once fertilized take
12-16 days to hatch
 HIGH BIOTIC
POTENTIAL
Orangutans
 Females Mature 10
years
 Birth to single babies
once every eight
years
 LOW BIOTIC
POTENTIAL
Section 3 Population Growth
Review
Describe the factors that influence
population’s growth rate
 Explain exponential and logistic growth
 Explain how limiting factors and biotic
potential affect population growth
 TERMS: survivorship curve, immigration,
emigration, exponential growth, carrying
capacity, logistic growth, biotic potential

Chapter 4 Big Ideas
In an ecosystem, the biotic and
abiotic components interact to form
an interconnected system.
 Humans classify the diversity of life
on Earth in order to better
understand their relationships.
 Population sizes change according to
changes in the environment.

Think About: Essays
Explain how limiting factors and biotic
potential interact to regulate the
population growth of a species.
 What are some of the benefits for humans
of keeping track of the population sizes of
wild species?
