Name ______________________________ Class ___________________ Date __________________
Interactions in Ecosystems
Study Guide A
Answer Key
6.
7.
8.
9.
10.
11.
12.
SECTION 1. HABITAT AND NICHE
1. habitat
2. niche
3. habitat: food, other lions, trees, watering
hole, wildebeest, zebra, sand, temperature,
grass, savanna; niche: all of the above plus
hunting behavior
4. niche partitioning
5. evolutionary response
6. niche partitioning
7. competitive exclusion
8. ecological equivalents
SECTION 4. POPULATION GROWTH
PATTERNS
1.
2.
3.
4.
5.
6.
7.
SECTION 2. COMMUNITY
INTERACTIONS
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
intraspecific
interspecific
interspecific
intraspecific
intraspecific
predator
mutualism
commensalism
parasitism
c
b
symbiosis
8.
9.
10.
11.
12.
13.
14.
immigration
deaths
births
emigration
grow, increase, get larger
shrink, decrease, get smaller
exponential growth should show a J-shaped
curve; logistic growth should show an
S-shaped curve
Logistic
Exponential
d
b
immigrate
density-dependent limiting factor
emigrate
SECTION 5. ECOLOGICAL
SUCCESSION
SECTION 3. POPULATION DENSITY
AND DISTRIBUTION
1.
2.
3.
4.
5.
reproductive strategy
Type II
Type III
Type I
density
dispersion
survivorship curve
1.
2.
3.
4.
5.
6.
population density
b
a
b
c
biotic changes
a, 3; b, 2; c, 1; d, 4
a, 4; b, 2; c, 1; d, 3
primary succession
secondary succession
pioneer species
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
i
Interactions in Ecosystems
Name ______________________________ Class ___________________ Date __________________
Section 1: Habitat and Niche
Study Guide A
KEY CONCEPT
Every organism has a habitat and a niche.
VOCABULARY
habitat
competitive exclusion
ecological niche
ecological equivalent
MAIN IDEA: A habitat differs from a niche.
Fill in the blank with the term that best completes the sentence.
1. A(n)__________ is the place where an organism lives.
2. A(n) __________ is how an organism lives.
3. Determine which of the ecological factors listed in the box below are part of a
lion’s habitat and which are a part of a lion’s niche. Write each item in the
correct column.
food
other lions
temperature
wildebeest
grass
sand
trees
zebra
hunting behavior
savanna
watering hole
Habitat
Niche
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
1
Interactions in Ecosystems
Section 1: Habitat and Niche
Name ______________________________ Class ___________________ Date __________________
Study Guide A continued
MAIN IDEA: Resource availability gives structure to a community.
4. Two species that are able to divide the resources in a niche without competing
are involved in ________________.
5. One species of squirrel develops larger teeth that can crack larger nuts than
another squirrel species living the same niche. This description is an example
of competitive exclusion that has resulted in _____________________.
6. Honeybees collect pollen from flowers. Butterflies collect nectar from flowers.
This relationship is an example of _____________________.
Vocabulary Check
Fill in the blank with the word or phrase that best completes the sentence.
7. The principle of ___________________________ states that when two species
compete for the same resources, one species will be better adapted to the niche
and the other species will be pushed into another niche or become extinct.
8. Species that occupy similar niches but live in different parts of the world are
called ___________________________.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
2
Interactions in Ecosystems
Section 1: Habitat and Niche
Name ______________________________ Class ___________________ Date __________________
Section 2: Community Interactions
Study Guide A
KEY CONCEPT
Organisms interact as individuals and in populations.
VOCABULARY
competition
symbiosis
commensalism
predation
mutualism
parasitism
MAIN IDEA: Competition and predation are two important ways in which
organisms interact.
Next to each situation described below, write whether it is an example of
interspecific competition or intraspecific competition.
_________________ 1. Two squirrels race up a tree to reach a hidden pile of
nuts.
_________________ 2. A hyena chases off a vulture to feast on an antelope
carcass.
_________________ 3. Different species of shrubs and grasses on the forest
floor compete for sunlight.
_________________ 4. Brown bears hunting for fish on a river’s edge fight
over space.
_________________ 5. Male big horn sheep butt heads violently in competition
for mates.
Fill in the blank with the word or phrase that best completes the sentence.
6. A bobcat catching a young rabbit is an example of a(n) ______________-prey
interaction.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
3
Interactions in Ecosystems
Section 2: Community Interactions
Name ______________________________ Class ___________________ Date __________________
Study Guide A continued
MAIN IDEA: Symbiosis is a close relationship between species.
Complete the chart by filling in the type of symbiotic relationship
in the description.
Symbiotic
Relationship
Description
Example
7. _______________ Both organism A and
organism B benefit from
their interaction.
Long-nosed bat feeds on
cactus fruit, and helps
spread the cactus seeds.
8. _______________ Organism A benefits from Mites find a home in
an interaction with organism human eyelashes but do no
B. Organism B does not
harm to the human.
benefit, nor is it harmed.
9. _______________ Organism A benefits from
its interaction with organism
B. Organism B is harmed by
the interaction.
A tapeworm absorbs
nutrients from a mammal’s
digestive system, reducing
the amount of food
available to the mammal.
Fill in the blank with a word or phrase that best completes the sentence.
10. A parasite differs from a _________________ because it keeps its prey alive
as long as possible.
a. ectoparasite
b. endoparasite
c. predator
d. symbiont
11. A tapeworm that lives in the digestive system of its host is an example
of a(n) _________________
a. ectoparasite
b. endoparasite
c. predator
d. symbiont
Vocabulary Check
Fill in the blank with the word or phrase that best completes the sentence.
12. A close ecological relationship between two or more organisms of different
species that live in direct contact with one another is ___________________.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
4
Interactions in Ecosystems
Section 2: Community Interactions
Name ______________________________ Class ___________________ Date __________________
Section 3: Population Density and Distribution
Study Guide A
KEY CONCEPT
Each population has a density, a dispersion, and a reproductive strategy.
VOCABULARY
population density
population dispersion
survivorship curve
MAIN IDEA: Population density is the number of individuals that live in a
defined area.
1. Fill in the blank to complete the equation.
Number of individuals

Area (units 2 )
2. Circle the letter next to the situation that would explain an increase in the
population density of a population of deer.
a. an increase in the number of deer predators
b. a decrease in the area of deer habitat
c. an increase in the area of deer habitat
d. a decrease in the number of deer in the area
MAIN IDEA: Geographic dispersion of a population shows how individuals in a
population are spaced.
Circle the letter of the term that correctly describes the type of
population dispersion.
3. Individual organisms live close together, making it easier for them to find
mates and protect each other.
a. clumped dispersion
b. uniform dispersion
c. random dispersion
d. standard dispersion
4. Individuals live at a specific distance from each other to avoid competition for
limited resources.
a. clumped dispersion
b. uniform dispersion
c. random dispersion
d. standard dispersion
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
5
Interactions in Ecosystems
Section 3: Population Density and Distribution
Name ______________________________ Class ___________________ Date __________________
Study Guide A continued
5. Individuals are spread out in no particular pattern.
a. clumped dispersion
b. uniform dispersion
c. random dispersion
d. standard dispersion
MAIN IDEA: Survivorship curves help to describe the reproductive strategy
of a species.
Fill in the blank with the term or phrase that best completes the sentence.
6. An organism’s _____________________ _______________ reflects the way
it produces offspring and helps the population survive.
Number of survivors
120
100
80
60
40
20
0
10 20 30 40 50 60 70 80 90 100
Percentage of maximum life span
Look at each of the survivorship curves shown above. Next to the type of
organism described below, write whether it is an example of Type I, Type II, or
Type III survivorship.
_________ 7. Birds, small mammals, and other small animals have a survival rate
that stays about the same from birth to death.
_________ 8. Fish, amphibians, and plants produce large numbers of young. The
young of these organisms have a high death rate.
_________ 9. Lions and other large mammals care for their young. The young of
these organisms have a high survival rate.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
6
Interactions in Ecosystems
Section 3: Population Density and Distribution
Name ______________________________ Class ___________________ Date __________________
Study Guide A continued
Vocabulary Check
Fill in the blank with the word or phrase that best completes the sentence.
10. Population __________________ describes the number of individual
organisms per unit area or volume.
11. Population __________________ describes the way a population is spread out
over
an area.
12. A ____________________ ______________ helps describe the reproductive
strategy of a species.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
7
Interactions in Ecosystems
Section 3: Population Density and Distribution
Name ______________________________ Class ___________________ Date __________________
Section 4: Population Growth Patterns
Study Guide A
KEY CONCEPT
Populations grow in predictable patterns.
VOCABULARY
immigration
logistic growth
limiting factor
emigration
carrying capacity
density-dependent limiting factor
exponential growth
population crash
density-independent limiting factor
MAIN IDEA: Changes in a population’s size are determined by immigration,
births, emigration, and deaths.
Choose a word from the box below that best completes the sentence.
births
emigration
deaths
immigration
1. Resources are very abundant in a particular area. Individuals may move
into a population in this area to take advantage of the abundant resources.
The movement of individuals into a population from another area is called
________________.
2. A very cold winter has left many deer in a population hungry and sick.
By the end of the winter, this population will likely decrease because of
________________.
3. A deer population experiences growth when the rate of reproduction increases.
This change in population size is due to _________________.
4. Humans build new houses in a territory inhabited by deer. Many members of
the deer population move away and join herds in other areas. This movement
of individuals out of a population is called _________________.
Fill in the blank with a word that best completes the sentence.
5. When plenty of resources are available, a population is likely to __________.
6. When few resources are available, a population is likely to __________.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
8
Interactions in Ecosystems
Section 4: Population Growth Patterns
Name ______________________________ Class ___________________ Date __________________
Study Guide A continued
MAIN IDEA: Population growth is based on available resources.
7. Draw a curve in each space to show the type of population growth described.
Rapid
population
growth when
resources are
abundant
Logistic growth
Exponential growth
Slow growth is
followed by
exponential
growth, then the
size of the
population
stabilizes
Fill in the blank with the type of population growth described in the sentence.
8. ____________ growth shows a carrying capacity.
9. ____________ growth is at risk for a population crash because of resource
depletion.
MAIN IDEA: Ecological factors limit population growth.
Circle the letter of the phrase that best completes the sentence.
10. One example of a density-independent limiting factor is
a. competition.
b. predation.
c. parasitism and disease.
d. a natural disaster.
11. One example of a density-dependent limiting factor is
a. human activity.
b. competition.
c. unusual weather.
d. a natural disaster.
Vocabulary Check
Fill in the blank with the term or phrase that best completes the sentence.
12. Individual organisms ____________________ when they move into a
population.
13. A limiting factor that is affected by population density is a
__________________________________.
14. Individual organisms ____________________ when they move out of a
population.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
9
Interactions in Ecosystems
Section 4: Population Growth Patterns
Name ______________________________ Class ___________________ Date __________________
Section 5: Ecological Succession
Study Guide A
KEY CONCEPT
Ecological succession is a process of change in the species that make up a
community.
VOCABULARY
succession
pioneer species
primary succession
secondary succession
MAIN IDEA: Succession occurs following a disturbance in an ecosystem.
Fill in the blank with the phrase that best completes the definition of
ecological succession.
1. Ecological succession is the sequence of ________________ that regenerate a
damaged community or create a new community in an area that was
previously uninhabited.
2. Below are statements that describe the four main steps of primary succession.
Write a number from 1 through 4 beside each step, to indicate the order in
which these steps take place.
_____ a. Seeds of flowers and shrubs grow into plants that offer habitat for
small animals and continue to build soil.
_____ b. Lichen and mosses break down rock. As they die, their decayed
bodies begin to build soil.
_____ c. Wind, rain and ice begin to break down rock surfaces.
_____ d. Larger plants and animals move into the area as the soil layer gets
thicker.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
10
Interactions in Ecosystems
Section 5: Ecological Succession
Name ______________________________ Class ___________________ Date __________________
Study Guide A continued
3. Below are statements that describe the four main steps of
secondary succession.
Write a number from 1 through 4 beside each step, to indicate the order in
which these steps take place.
_____ a.
_____ b.
_____ c.
_____ d.
Evergreen trees grow larger and hardwood trees begin to grow.
Weed and wildflower seeds take root in the soil.
A disturbance destroys a community.
Shrub and evergreen tree seedlings begin to grow.
Vocabulary Check
Fill in the blank with the word or phrase that best completes the sentence.
4. Ecological succession that begins in an area without an existing community
of plants is called __________________________.
5. Ecological succession that begins in an area that already had an existing
community of plants and animals is called ____________________________.
6. The first species to appear in a previously uninhabited area are called
___________________________.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
11
Interactions in Ecosystems
Section 5: Ecological Succession