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Name
Date
Class
Content Vocabulary
LESSON 2
Populations and Communities
Directions: On each line, write the term from the word bank that correctly replaces the underlined words from
each sentence. NOTE: You may need to change a term to its plural form.
biotic potential
limiting factor
carrying capacity
niche
habitat
symbiotic relationship
1. Factors that can limit the growth of a population include
water, space, and food.
2. A population never reaches its potential growth in perfect
conditions with no limiting factors.
3. Instead, limiting factors cause a population to reach the
largest number of individuals of one species that an
ecosystem can support over time.
4. Mutualism, parasitism, and commensalism are examples of
different species living together in a close relationship over
a long period of time.
5. Different species live in different physical places.
6. They also have differences in their particular ways of
surviving and obtaining resources.
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Interactions of Living Things
Name
Date
Class
Lesson Outline
LESSON 2
Populations and Communities
A. Populations
1. A(n)
is all the members of one species that live in an
area at one time.
2. The size of a population can increase or decrease in response to changes in abiotic
or
factors in the environment.
3. Populations can increase when individuals move into an area or when more
individuals are
. They can
when individuals move away from an area or die.
4. Population
describes the number of organisms in an
area relative to the amount of space available.
a. Limiting factors limit the
of a population. One factor
is the lack of sufficient
such as water; some individuals
cannot survive under these circumstances.
b. Factors such as predation, competition, and disease are examples
of .
5.
.
is the potential growth of a population if it could grow
in perfect conditions with no limiting factors.
6.
is the largest number of individuals of a species that an
ecosystem can support over time.
of an area determine the area’s carrying capacity.
7. The
8.
occurs when a population becomes larger than the
ability of the area to support it.
B. Communities
1. Populations that live in the same area interact as a(n)
2.
.
in a community might compete for resources such as
space. They might also compete directly as they hunt each other for food or hide
from
.
C. Symbiotic Relationships
1. All the populations in a community share a(n)
, the
physical place where a population or an organism lives.
Interactions of Living Things
27
Name
Date
Class
Lesson Outline continued
2. A(n)
is the unique way that an organism survives,
obtains food and shelter, or avoids danger in its habitat.
3. A(n)
occurs when two different species live together
in a close relationship over a long period of time.
a.
is a symbiotic relationship in which two species
in a community help each other.
b.
is a symbiotic relationship in which one species
(the parasite) benefits while another (the host) is harmed.
c.
is a symbiotic relationship in which one species
benefits and the other is not helped or harmed.
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Interactions of Living Things
Name
Date
Class
Content Practice A
LESSON 2
Populations and Communities
Directions: On each line, write the term from the word bank that correctly completes each sentence. Each term is
used only once.
biotic potential
limiting factors
population density
carrying capacity
mutualism
population size
commensalism
niche
resources
1. If a large number of eggs hatch, the
habitat
parasitism
symbiotic
of fish increases.
2. The number of organisms in a population relative to the amount of space available
describes
.
3. Factors that keep the growth of a population in check are called
factors.
4. The potential growth of a population, if it could grow in perfect conditions with no
limiting factors, is the population’s
.
5. The largest number of individuals in one species that an ecosystem can support over
time is the
.
6. Populations interact and compete for
, such as food, water,
and living space.
7. All populations in a community share a
, the physical place
where a population or organism lives.
8. Each species in a community has a
, which is its unique
ways of surviving, obtaining food and shelter, and avoiding danger.
9. A
relationship is a close relationship in which two different
species live together in a close relationship over a long period of time.
10. A symbiotic relationship in which two species in a community help each other
is called
.
11. A symbiotic relationship in which one species benefits while another is harmed
is called
.
12. A symbiotic relationship in which one species benefits and the other is not helped
or harmed is called
30
.
Interactions of Living Things
Name
Date
Class
Content Practice B
LESSON 2
Populations and Communities
Directions: On the line before each statement, write T if the statement is true or F if the statement is false. If the
statement is false, change the underlined word to make it true. Write your changes on the lines provided.
1. When individuals in a population move away or die, the population size
decreases.
2. Population density describes the number of organisms in the community
relative to the amount of space available.
3. Water, food, competition, and disease are some of the capacity factors that can
limit the growth of a population.
4. Biotic potential is the potential growth of a population if it could grow in
perfect conditions with no limiting factors.
5. A population reaches its carrying capacity when it has the largest number
of individuals of one speices that an ecosystem can support over time.
6. All the populations in a community share physical space, called a niche.
7. A habitat is the unique ways that an organism survives, obtains food and
shelter, and avoids danger.
8. A symbiotic relationship is one in which two different species live together
in a close relationship over a long period of time.
9. Leaf-cutter ants and a fungus benefit in a relationship called commensalism.
10. In a relationship called parasitism, mistletoe harms the tree from which it takes
food and water.
11. Mutualism is a symbiotic relationship in which one species benefits and the
other is not affected.
12. Populations in an ecosystem interact and compete for resources.
Interactions of Living Things
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Name
Date
Class
School to Home
LESSON 2
Populations and Communities
Directions: Use your textbook to answer each question.
1. Limiting factors restrict the size of populations.
How would the amount of water and food in an area act as limiting factors?
2. A population’s density is the number of organisms in a population relative
to the amount of space.
How can population density be a limiting factor?
3. Populations and communities are parts of ecosystems.
How are populations and communities related?
4. A symbiotic relationship occurs when two different species live together
in a close relationship for a long time.
What are three types of symbiotic relationships? What effect does each type of
relationship have on the two species involved?
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Interactions of Living Things
Name
Date
Key Concept Builder
Class
LESSON 2
Populations and Communities
Key Concept How do individuals and groups of organisms interact?
Directions: Complete this table by writing what happens to the population size on the lines provided.
Factor That Changes a Fish
Population
Does the population size increase,
decrease, or stay the same?
1. Fish are eaten by other organisms.
2. Fish swim to another location.
3. A large number of fish eggs hatch.
4. Fish die.
5. Fish are added to the lake.
6. More food is available.
Directions: Respond to each statement on the lines provided.
7. Explain what population density is in your own words.
8. Give an example of an area of your school that has a high population density and an
area that has a low population density.
Interactions of Living Things
33
Name
Date
Class
Key Concept Builder
LESSON 2
Populations and Communities
Key Concept How do individuals and groups of organisms interact?
Directions: Answer each question on the lines provided.
Limiting Factors
1. What are limiting factors?
2. What are four specific resources
that are limiting factors?
3. How do these resources limit a
population’s growth?
4. What are three other limiting
factors that are not resources?
5. What two limiting factors
involve interactions with other
populations in the community?
Question
Biotic Potential
Carrying Capacity
What is it?
6.
7.
Does a population
reach it? Explain
why or why not.
8.
9.
Can it change?
Explain why or
why not.
10.
11.
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Interactions of Living Things
Name
Date
Class
Key Concept Builder
LESSON 2
Populations and Communities
Key Concept What are some examples of symbiotic relationships?
Directions: Complete this table by writing how populations might interact with other populations
in a pond community.
Populations in a
Pond Community
How They Interact with Other Populations
1. Cattails and other
plants
2. Different
populations of
insects
3. Different
populations of
fish
4. A population of
ducks
5. A population of
turtles
Directions: Fill in the chart to compare a habitat and a niche.
Habitat
Niche
6. What is it?
7. What is it?
8. In a community, which populations share
the habitat?
9. In a community, which populations share
a niche?
Interactions of Living Things
35
Name
Date
Class
Key Concept Builder
LESSON 2
Populations and Communities
Key Concept What are some examples of symbiotic relationships?
Directions: Respond to the statement below.
1. Define symbiotic relationship.
Directions: Complete this table by writing the definition and an example of each type of symbiotic relationship.
2. Mutualism
Definition:
Example:
3. Parasitism
Definition:
Example:
4. Commensalism
Definition:
Example:
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Interactions of Living Things
Lesson 2: Populations and Communities
A. Populations
1. A(n) population is all the members of one species that live in an area at one time.
2. The size of a population can increase or decrease in response to changes in abiotic or biotic factors in the
environment.
3. Populations can increase when individuals move into an area or when more individuals are born. They can
decrease when individuals move away from an area or die.
4. Population density describes the number of organisms in an area relative to the amount of space available.
a. Limiting factors limit the growth of a population. One factor is the lack of sufficient resources such as
water; some individuals cannot survive under these circumstances.
b. Factors such as predation, competition, and disease are examples of limiting factors.
5. Biotic potential is the potential growth of a population if it could grow in perfect conditions with no limiting
factors.
6. Carrying capacity is the largest number of individuals of a species that an ecosystem can support over time.
7. The limiting factors of an area determine the area’s carrying capacity.
8. Overpopulation occurs when a population’s size becomes larger than the ability of the area to support it.
B. Communities
1. Populations that live in the same area interact as a(n) community.
2. Populations in a community might compete for resources such as space. They might also compete directly as
they hunt each other for food or hide from predators.
C. Symbiotic Relationships
1. All the populations in a community share a(n) habitat, the physical place where a population or an organism
lives.
2. A(n) niche is the unique way that an organism survives, obtains food and shelter, or avoids danger in its
habitat.
3. A(n) symbiotic relationship occurs when two different species live together in a close relationship over a long
period of time.
a. Mutualism is a symbiotic relationship in which two species in a community help each other.
b. Parasitism is a symbiotic relationship in which one species (the parasite) benefits while another (the
host) is harmed.
c. Commensalism is a symbiotic relationship in which one species benefits and the other is not helped
or harmed.
Content Vocabulary (page 26)
1. Limiting factors
2. biotic potential
3. carrying capacity
4. symbiotic relationship
5. habitats
6. niches
Content Practice A (page 30)
1. population size
2. population density
3. limiting factors
4. biotic potential
5. carrying capacity
6. resources
7. habitat
8. niche
9. symbiotic
10. mutualism
11. parasitism
12. commensalism
Content Practice B (page 31)
1. T
2. F; population
3. F; limiting
4. T
5. T
6. F; habitat
7. F; niche
8. T
9. F; mutualism
10. T
11. F; commensalism
12. T
School to Home (page 32)
1. A certain supply of water and food is needed to support each member of a population. Increasing the number of
individuals in a population beyond a certain number would mean that some individuals would get less food than they need
or none at all. As a result, some individuals would die.
2. When populations are too dense, some individuals discover that it is harder to get the resources they need to survive.
3. Communities are made up of many different populations.
4. Mutualism is a symbiotic relationship in which both species benefit. In parasitism, one species (the parasite) benefits
while the other species (the host) is harmed. In commensalism, one species is helped while the other is not helped or
harmed.
Key Concept Builder (page 33)
1. decrease
2. decrease
3. increase
4. decrease
5. increase
6. increase
7. Possible answer: Population density is the number of individuals in a certain amount of space.
8. Possible answer: The hallways have a high population density before classes begin. The principal’s office has a low
population density.
Key Concept Builder (page 34)
1. factors that can limit the growth of a population
2. food, water, space, shelter
3. Possible answer: If there are not enough resources, some individuals cannot survive, which limits the population’s
growth.
4. predation, competition, disease, availability of nesting sites, parasitism
5. competition and predation
6. Biotic potential is the potential growth of a population if it could grow in perfect conditions with no limiting factors.
7. Carrying capacity is the largest number of individuals that can survive in an area over a long time.
8. No; Possible answer: Almost no population reaches its biotic potential because perfect conditions almost never exist.
9. Yes; Possible answer: Carrying capacity is based on the resources available and other limiting factors.
10. No; Possible answer: It is based on perfect conditions that do not exist and do not change.
11. Yes; Possible answer: It is based on limiting factors, which can change. If limiting factors change, carrying capacity
changes.
Key Concept Builder (page 35)
1. Possible answer: Plant populations might compete for space and light. Other populations eat the plants.
2. Possible answer: Insects might eat the plants or other populations of insects. They are eaten by fish, ducks, turtles, and
other populations.
3. Possible answer: Different populations of fish might compete for food and space. They could eat plants, insect, or other
fish. They could be eaten by other populations.
4. Possible answer: Ducks might eat plants and insects.
5. Possible answer: Turtles might eat fish, insects, and plants.
6. the physical place where a population or organism lives
7. the unique ways that an organism survives, obtains food and shelter, and avoids danger in its habitat
8. All the populations in the community share the habitat.
9. Organisms in the same population share a niche.
Key Concept Builder (page 36)
1. a relationship in which two different species live together in a close relationship over a long period of time
2. a symbiotic relationship in which two species in a community benefit from the relationship; Possible answer: Leaf-cutter
ants provide fungus with food and in turn use the fungus for food.
3. a symbiotic relationship in which one species (the parasite) benefits while another (the host) is harmed; Possible
answer: Mistletoe grows in the branches of some trees and sends roots into the tree’s tissue to get food and water. The
tree is weakened and eventually killed.
4. a symbiotic relationship in which one species benefits and the other is not helped or harmed; Possible answer: A plant
produces cockleburs that stick to a passing animal. The plant benefits because its seeds are spread to a large area by the
animal. The animal does not benefit and is not harmed.