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Chapter Introduction
Lesson 1
Populations
Lesson 2
Changing
Populations
Lesson 3
Communities
Chapter Wrap-Up
How do populations
and communities
interact and change?
What do you think?
Before you begin, decide if you agree or
disagree with each of these statements.
As you view this presentation, see if you
change your mind about any of the
statements.
Do you agree or disagree?
1. Some life exists in the ice caps of the
North Pole and South Pole.
2. A community includes all organisms of
one species that live in the same area.
3. Some populations decrease in numbers
because of low birthrates.
Do you agree or disagree?
4. An extinct species has only a few
surviving individuals.
5. No more than two species can live in
the same habitat.
6. A cow is a producer because it
produces food for other organisms.
Populations
• What defines a population?
• What factors affect the size of a
population?
Populations
• biosphere
• population
• community
• competition
• limiting factor
• population
density
• biotic potential
• carrying capacity
The Biosphere and Ecological
Systems
The parts of Earth and the surrounding
atmosphere where there is life is called
the Earth’s biosphere.
The Biosphere and Ecological
Systems (cont.)
• The biosphere includes all the land of
the continents and islands, all of the
earth’s oceans, lakes, and streams, as
well as the ice caps at the North Pole
and the South Pole.
• Parts of the biosphere with large
amounts of plants or algae often
contain many other organisms as well.
What is a population?
• An ecosystem is a group of organisms
that lives in an area at one time, as
well as the climate, soil, water, and
other nonliving parts of the
environment.
• The study of all
ecosystems on
Earth is ecology.
What is a population? (cont.)
A community is all the populations of
different species that live together in the
same area at the same time.
What is a population? (cont.)
A population is all the organisms of the
same species that live in the same area
at the same time.
What is a population? (cont.)
A species is a group of organisms that
have similar traits and are able to
produce fertile offspring.
What defines a population?
Competition
• Competition is the demand for
resources, such as food, water, and
shelter, in short supply in a community.
• When there are
not enough
resources
available to
survive, there is
more competition
in a community.
Population Sizes
• Changes in environmental factors can
result in population size changes.
• A limiting factor is anything that
restricts the size of a population.
• Available sunlight is a limiting factor for
most organisms.
• Without sunlight, green plants cannot
make food, which effects animals that
eat plants.
Population Sizes (cont.)
• Temperature is a limiting factor for
some organisms.
• When the temperature drops below
freezing, many organisms die because
it is too cold to carry out their life
functions.
• Disease, predators, and natural
disasters such as fires or floods are
also limiting factors.
Population Sizes (cont.)
What factors affect the size of
a population?
Population Sizes (cont.)
• Population density is the size of a
population compared to the amount of
space available.
• One way of estimating population
density is by sample count.
Population Sizes (cont.)
population
from Latin populus, means
“inhabitants”
density
from Latin densus, means “thick,
crowded”
Population Sizes (cont.)
• A population’s biotic potential is the
largest number of offspring that can be
produced when there are no limiting
factors present.
• No population on Earth ever reaches
its biotic potential because no
ecosystem has an unlimited supply of
natural resources.
Population Sizes (cont.)
• The largest number of individuals of
one species that an environment can
support is the carrying capacity.
• A population grows until it reaches the
carrying capacity of an environment.
Carrying capacity is determined in part
by limiting factors.
Population Sizes (cont.)
• Disease, space, predators, and food are
some of the factors that limit the carrying
capacity of an ecosystem.
• The carrying capacity of an environment
is not constant because it increases and
decreases as the amount of available
resources increases and decreases.
• When the size of a population becomes
larger than the carrying capacity of its
ecosystem, overpopulation occurs.
• The population density of organisms,
including green plants and algae,
varies throughout the world.
• A community is
all the populations
of different species
that live together in
the same area at
the same time.
• The number of individuals in a
population varies as the amount of
available resources varies.
Which term refers to all the
populations of different species that
live together in the same area at the
same time?
A. a population
B. a biosphere
C. a community
D. an ecosystem
Which of these refers to anything
that restricts the size of a
population?
A. population density
B. limiting factor
C. carrying capacity
D. biosphere
Which of these increases when
there are not enough resources
available in a community for all
its organisms to survive?
A. competition
C. organisms
B. population
D. food
Do you agree or disagree?
1. The biosphere includes all parts of
Earth and the surrounding atmosphere
that support life.
2. A community includes all organisms of
one species that live in the same area.
Changing Populations
• How do populations change?
• Why do human populations change?
Changing Populations
• birthrate
• death rate
• extinct species
• endangered
species
• threatened
species
• migration
How Populations Change
• A population change can be measured
by the population’s birthrate and death
rate.
• A population’s birthrate is the number
of offspring produced over a given
period of time.
• The death rate is the number of
individuals that die over the same
period of time.
How Populations Change (cont.)
• If the birthrate is higher than the death
rate, the population increases.
• If the death rate is higher than the
birthrate, the population decreases.
• When a population is in ideal
conditions with unlimited resources, it
grows in a pattern called exponential
growth.
How Populations Change (cont.)
exponential
Science Use a mathematical
expression that contains a
constant raised to a power, such
3
2
as 2 or x .
Common Use in great amounts
How Populations Change (cont.)
• During exponential growth, the larger a
population gets, the faster it grows.
• E coli bacteria are microscopic organisms
that undergo exponential growth; the
population doubles in size every half hour.
How Populations Change (cont.)
• Disease and natural disasters such as
floods, fires, or volcanic eruptions can
decrease populations.
• Predation—the hunting of organisms
for food—also reduces population size.
How Populations Change (cont.)
• If populations continue to decrease in
numbers, they disappear.
• An extinct species is a species that
has died out and no individuals are left.
• Extinctions can be caused by
predation, natural disasters, or damage
to the environment.
How Populations Change (cont.)
extinct
from Latin extinctus, means
“extinguish”
How Populations Change (cont.)
• An endangered species is a species
whose population is at risk of
extinction.
• A threatened species
is a species at risk, but
not yet endangered.
Tom Brakefield/Getty Images
How Populations Change (cont.)
• Populations also change when
organisms move from place to place.
• Migration is the instinctive seasonal
movement of a population of
organisms from one place to another.
• Ducks, geese, and monarch butterflies
are examples of organisms that
migrate annually.
How Populations Change (cont.)
List three ways populations
change.
Human Population Changes
• Human population, like all other
populations, are affected by birthrate,
death rate, and movement.
• Unlike other species, humans have
developed ways to increase the carrying
capacity of their environment.
• Scientists estimate that there were about
300 million humans on Earth a thousand
years ago.
Human Population Changes (cont.)
• Today there are more than 6 billion
humans on earth.
• As human population grows, people
need to build more houses and roads
and clear more land for crops, which
means there is less living space, food,
and other resources for other species.
• Human energy use contributes to
pollution that affects other populations.
Human Population Changes (cont.)
• Factors that keep the human birthrate
higher than its death rate include food,
resources, sanitation, and medical
care.
• Advances in agriculture have made it
possible to produce food for billions of
people.
• Today people have access to more
resources because of better
transportation methods.
Human Population Changes (cont.)
• Modern water treatment and more
effective cleaning products help
prevent the spread of disease-causing
organisms that can lead to death.
• Human populations in some parts of
the world are decreasing in size
because of factors like disease,
drought, and natural disasters.
Human Population Changes (cont.)
Like other organisms, populations of
humans might
move when
more resources
become available
in a different place.
Human Population Changes (cont.)
What makes human
populations increase or
decrease in size?
• The birthrate and the death rate of any
population affects its population size.
• The giant moa is classified as an
extinct species because there are no
surviving members.
• A population that is
at risk but not yet
endangered is a
threatened species.
Tom Brakefield/Getty Images
Which term refers to a species
that is at risk, but not yet
endangered?
A. an extinct species
B. a threatened species
C. an endangered species
D. a migrating species
What happens to a population if
the birthrate of a species is
higher than the death rate?
A. it decreases
B. it remains the same
C. it increases
D. it disappears
Which of these is the only species
capable of developing ways to
increase the carrying capacity of an
environment?
A. ducks
B. zebras
C. monarch butterflies
D. humans
Do you agree or disagree?
3. Some populations decrease in
numbers because of low birthrates.
4. An endangered species is at risk of
becoming extinct.
Communities
• What defines a community?
• How do the populations in a
community interact?
Communities
• habitat
• symbiosis
• niche
• mutualism
• producer
• commensalism
• consumer
• parasitism
Communities, Habitats, and Niches
• A community is made up of all the
species that live in the same
ecosystem at the same time.
• The place within an ecosystem where
an organism lives is its habitat.
• A habitat provides all the resources an
organism needs, including food and
shelter.
Communities, Habitats, and Niches
(cont.)
A habitat has the right temperature,
water, and other conditions the organism
needs to survive.
habitat
from Latin habitus, means “to live,
dwell”
Communities, Habitats, and Niches
• A niche is what a species does in its
habitat to survive.
(cont.)
• Different species have different niches
in the same environment.
What is a community?
Communities, Habitats, and Niches
(cont.)
• All living things use energy to
carry out life processes such as growth
and reproduction.
• How an organism obtains energy is an
important part of its niche.
• Almost all the energy available to life
on Earth originally came from the sun.
Communities, Habitats, and Niches
(cont.)
• Producers are organisms that get
energy from the environment, such as
sunlight, and make their own food.
• Consumers are organisms that get
energy by eating other organisms.
• Herbivores get their energy by eating
plants.
Communities, Habitats, and Niches
• Carnivores get their energy by
eating other consumers.
(cont.)
• Omnivores, such as most humans, get
their energy by eating producers and
consumers.
• Detritivores get their energy by eating
dead organisms or parts of dead
organisms.
Energy Flow
A food chain is a
way of showing
how energy
moves through a
community.
A food web
shows many
food chains
within a
community
and how
they overlap.
Energy Flow (cont.)
Identify a food chain in a
community near your home.
List the producers and
consumers in your food
chain.
Relationships in Communities
• The populations that make up a
community interact with each other in a
variety of ways.
• Some species have feeding
relationships, meaning they either eat
or are eaten by another species.
Relationships in Communities (cont.)
• Predators help prevent prey
populations from growing too large for
the carrying capacity of the ecosystem.
• The members of some populations, like
meerkats, work together in cooperative
relationships for their survival.
Relationships in Communities (cont.)
• A close relationship between two or
more organisms of different species that
live in direct contact is called
symbiosis.
• A symbiotic relationship in which both
partners benefit is called mutualism.
Relationships in Communities (cont.)
A symbiotic
relationship that
benefits one species
but does not harm or
benefit the other is
commensalism.
Carol & Don Spencer/Visual Unlimited/Getty Images
Relationships in Communities (cont.)
• A symbiotic relationship that benefits
one species and harms the other is
parasitism.
• In parasitism, the species that benefits
is the parasite, and the species that is
harmed is the host.
Relationships in Communities (cont.)
List five ways species in a
community interact.
• Each organism in a community has its
own habitat and niche within the
ecosystem.
• Within a community, each organism
must obtain energy for life processes.
Some organisms are producers and
some are consumers.
• Some organisms
have cooperative
relationships and
some have symbiotic
relationships.
Carol & Don Spencer/Visual Unlimited/Getty Images
What type of organism gets
energy from the environment to
make its own food?
A. consumers
B. carnivores
C. producers
D. herbivores
Which type of organism gets
energy by eating both producers
and consumers?
A. omnivores
B. detritivores
C. herbivores
D. carnivores
A food chain helps illustrate how
which of these moves through a
community?
A. food
B. water
C. life
D. energy
Do you agree or disagree?
5. No more than two species can live in
the same habitat.
6. A cow is a producer because it
produces food for other organisms.
Key Concept Summary
Interactive Concept Map
Chapter Review
Standardized Test Practice
A community contains
many populations that
interact in their energy
roles and in their
competition for
resources. Populations
can increase, decrease,
and move, affecting the
community.
Lesson 1: Populations
• A population is all the organisms of the same
species that live in the same area at the same time.
• Population sizes vary due to limiting factors such as
environmental factors and available resources.
• Population size usually does not exceed the
carrying capacity of the ecosystem.
Lesson 2: Changing Populations
• Populations of living things can increase, decrease,
or move.
• Populations can decrease until
they are threatened,
endangered, or extinct.
• Human population size is
affected by the same three
factors as other populations—
birthrate, death rate, and environment.
Tom Brakefield/Getty Images
Lesson 3: Communities
• A community is all the populations of different
species that live together in the same area at the
same time.
• The place within an ecosystem
where an organism lives is its
habitat and what an organism
does in its habitat to survive is
its niche.
• Three types of relationships
within a community are
predator-prey, cooperative,
and symbiotic.
Carol & Don Spencer/Visual Unlimited/Getty Images
What term refers to all the
organisms of the same species
that live in the same area at the
same time?
A. biosphere
B. population
C. community
D. limiting factor
Which term refers to the largest number
of offspring that can be produced when
there are no environmental factors
restricting the size?
A. limiting factor
B. population density
C. carrying capacity
D. biotic potential
Which term refers to the instinctive
seasonal movement of a population
of organisms from one place to
another?
A. movement
B. extinction
C. migration
D. predation
What do scientists call a species
whose population is at risk of
extinction?
A. an endangered species
B. an extinct species
C. a threatened species
D. a dying species
Which term refers to everything a
species does in its habitat to
survive?
A. population
B. niche
C. symbiotic relationship
D. parasite
What is the name for the parts of
Earth and the surrounding
atmosphere where life exists?
A. community
B. population
C. biosphere
D. ecosystem
Which of these refers to the size
of a population compared to the
amount of space available?
A. population density
B. biotic potential
C. limiting factor
D. carrying capacity
What term refers to the number
of offspring produced by a
population over a given period
of time?
A. death rate
B. exponential growth
C. birthrate
D. migration
What general term do scientists use
to describe the close relationship
between two or more organisms of
different species that live in direct
contact?
A. mutualism
C. parasitism
B. commensalism
D. symbiosis
In parasitism, which species
benefits?
A. parasite
B. host
C. partner
D. predator