Chapter 16

Question 1

Tansley’s early research on competition was groundbreaking because:
A) he was the first to recognize competition as a biotic factor.
B) he was the first to suggest that plants could compete for limited resources.
C) he was the first to suggest that competition could determine the distribution of species.
D) he was the first to test experimentally the idea that competition could determine the
distribution of species.

Answer 1

D) he was the first to test experimentally the idea that competition could determine the
distribution of species.

Question 2

Which of the following did Tansley determine from his research on species in the plant genus
Galium?
A) The presence or absence of a species could be determined by competition with other
species.
B) The conditions of the environment affect the outcome of competition.
C) The present ecological segregation of species may reflect past competition.
D) all of the above

Answer 2

D) all of the above

Question 3

Individuals belonging to the same species cannot compete because cooperative and altruistic
relationships among the individuals promote the betterment of the species.
A) True B) False

Answer 3

B) False

Question 4

The resource requirements of two plant species, A and B, have been carefully studied.
Researchers have determined the levels of a particular resource required by both species that
will support equilibrium levels of each species. The level of this resource required to maintain
the equilibrium level of species A is higher than that required to maintain the equilibrium level
of species B. When these two species are placed in competition (under conditions in which this
resource is limiting), which of the two species is likely to displace the other?
A) species A B) species B

Answer 4

B) species B

Question 5

Which of the following does ecologist David Tilman consider the attribute(s) of a resource?
A) A resource is consumed, and its amount or availability is thereby reduced.
B) A resource is used by a consumer for its maintenance and growth.
C) Reduction of a resource’s availability leads to reduced population growth of a consumer.
D) all of the above

Answer 5

D) all of the above

Question 6

Which of the following is not a resource for terrestrial plants?
A) nitrogen B) light C) water D) temperature E) space

Answer 6

D) temperature

Question 7

Which of the following is not a renewable resource for a species of predatory bird?
A) prey B) water C) oxygen D) nest sites

Answer 7

D) nest sites

Question 8

Ecologists recognize three types of renewable resources, listed below. Consider the process
whereby nitrogen taken up by plants is recycled (through decomposition of plant remains) and
made available for subsequent consumption by other plants. In this context, which of the three
resource types is soil available nitrogen (as nitrate, for example)?
A) a resource with its source external to the system
B) a resource whose abundance is directly linked to uptake by consumers
C) a resource whose abundance is indirectly linked to uptake by consumers

Answer 8

C) a resource whose abundance is indirectly linked to uptake by consumers

Question 9

The competitive exclusion principle was based on which of the following research findings?
A) Competing species do not coexist indefinitely when sharing the same limiting resource in
laboratory experiments.
B) Competing species do not coexist indefinitely when sharing the same limiting resource in
their natural habitat.
C) both of the above

Answer 9

A) Competing species do not coexist indefinitely when sharing the same limiting resource in
laboratory experiments.

Question 10

The mathematical models for competition between species are based on which of the
following?
A) energy balance equation
B) exponential population growth equation
C) logistic population growth equation
D) life table equation

Answer 10

C) logistic population growth equation

Question 11

In the competition equations developed by Lotka and others, what does the term a1,2N2
Chapter 16: Competition
3
represent?
A) instantaneous rate of population increase of species 1
B) carrying capacity of the environment for species 1
C) reduction of species 1’s carrying capacity by individuals of species 1
D) reduction of species 1’s carrying capacity by individuals of species 2

Answer 11

D) reduction of species 1’s carrying capacity by individuals of species 2

Question 12

Which of the following make(s) coexistence of species 1 and 2 more likely?
A) higher values of both r1 and r2
B) lower values of both N1 and N2
C) higher values of both K2 and K1
D) lower values of both a1,2 and a2,1
E) all of the above

Answer 12

D) lower values of both a1,2 and a2,1

Question 13

Which of the following statements best expresses the condition for coexistence of two species,
according to the competition models developed by Lotka and others?
A) To coexist, species must limit themselves more than they limit each other.
B) To coexist, species must limit themselves about the same as they limit each other.
C) To coexist, species must limit themselves less than they limit each other.

Answer 13

A) To coexist, species must limit themselves more than they limit each other.

Question 14

When David Tilman grew diatoms in the genera Cyclotella and Asterionella at Si/P ratios
between 6 and 90, the two species coexisted. Why?
A) Both species were phosphorus‐limited.
B) Both species were silicon‐limited.
C) Neither species was limited by phosphorus or silicon.
D) One species was limited by phosphorus, and the other was limited by silicon.
E) Tilman continuously supplemented the cultures with individuals of the two species.

Answer 14

D) One species was limited by phosphorus, and the other was limited by silicon.

Question 15

In David Tilman’s experiments with diatoms in the genera Cyclotella and Asterionella, he found
that Cyclotella was equally limited by silicon and phosphorus at a ratio of Si/P = 6, and that
Asterionella was equally limited by the two elements at a ratio of Si/P = 90. When he grew the
two species at a Si/P ratio exceeding 90 (455 in his experiment), which species excluded the
other?
A) Cyclotella
B) Asterionella
C) Neither; the two species coexisted.

Answer 15

B) Asterionella

Question 16

In David Tilman’s experiments with diatoms in the genera Cyclotella and Asterionella, he found
that Cyclotella was equally limited by silicon and phosphorus at a ratio of Si/P = 6, and that
Asterionella was equally limited by the two elements at a ratio of Si/P = 90. When he grew the
two species at a Si/P ratio below 6 (0.6 in his experiment), which species excluded the other?
A) Cyclotella
B) Asterionella
C) Neither; the two species coexisted.

Answer 16

A) Cyclotella

Question 17

Which of the following is a limiting resource for barnacles growing on rocky intertidal areas?
A) food B) water C) mates D) space

Answer 17

D) space

Question 18

Which of the following experimental approaches did Joseph Connell use to determine the
cause(s) of vertical zonation in two species of barnacles along the Scottish coast?
A) introduction of exotic barnacle species
B) introduction of exotic substrates, such as used tires
C) introduction of barnacle parasites
D) removal of one or the other of the species of barnacles
E) removal of macroscopic algae

Answer 18

D) removal of one or the other of the species of barnacles

Question 19

In the rocky intertidal zone of the Scottish coast, which factors were found to control the
vertical zonation of barnacles?
A) competition
B) differential tolerance of stressful conditions
C) allelopathy
D) predation
E) A and B
F) C and D

Answer 19

E) A and B

Question 20

In the lower rocky intertidal zone of the Scottish coast, the barnacle Balanus is a much more
effective competitor than the barnacle Chthamalus. What aspect of competition does this
situation illustrate?
A) facilitation
B) asymmetry
C) allelopathy
D) mutualism

Answer 20

B) asymmetry

Question 21

According to P. J. Grubb and David Tilman, plants compete __________ intensely when mineral
elements are less abundant in the soil.
A) more B) less

Answer 21

A) more

Question 22

Based on the results of various competition experiments reviewed in Chapter 16, what can we
conclude about our ability to predict the outcome of competition?
A) Competition appears to be pervasive, and the outcomes of competition are consistent and
highly predictable.
B) Competition appears to be pervasive, but how it is manifested depends very much on the
characteristics of the interacting species and their habitats.

Answer 22

B) Competition appears to be pervasive, but how it is manifested depends very much on the
characteristics of the interacting species and their habitats.

Question 23

Anyone watching a hummingbird feeder has observed that individual hummingbirds will chase
away other hummingbirds, as well as insects, that attempt to visit the feeder. Such encounters
are examples of:
A) interference competition B) exploitative competition C) neither of the above

Answer 23

A) interference competition

Question 24

A group of children at a birthday party sit around a table covered with pieces of candy. Each
child must gather candy, one piece at a time, as fast as possible. No child is permitted to
impede the access of another child to the remaining candy on the table. When the table has
been cleared, the child with the most pieces of candy is declared the winner. This is an example
of:
A) interference competition B) exploitative competition C) neither of the above

Answer 24

B) exploitative competition

Question 25

Where shrubs (such as Salvia) and grassland meet in dry areas in southern California, there is
often a few feet of bare ground separating the two. Which of the following mechanisms has
been proposed to explain this observation?
A) allelopathic inhibition of shrubs by grasses
B) allelopathic inhibition of grasses by shrubs
C) reduced soil moisture where bedrock is close to the surface
D) high levels of heavy metals (Ni, Cr) in the soil
E) very low nitrogen levels in the soil

Answer 25

B) allelopathic inhibition of grasses by shrubs

Question 26

What additional factor (beyond that referenced in the previous question) appears to play a role
in maintaining the bare areas between shrubs and other plants in dry areas in southern
California?
A) selective mortality caused by frequent fires
B) selective herbivory by rabbits
C) contrasting properties of soils derived from different rock types
D) flooding caused by heavy rains
E) use of herbicides by highway maintenance crews

Answer 26

B) selective herbivory by rabbits

Question 27

One of the first scientists to recognize that grazing can maintain a high diversity of potentially
competing species in grasslands was __________.
A) Robert Paine B) Joseph Connell C) A. G. Tansley D) Charles Darwin

Answer 27

D) Charles Darwin

Question 28

In his study of invertebrate animal communities on rocky intertidal areas in the state of
Washington, Robert Paine found that removal of a predator (Pisaster, the sea star) led to
__________ in community diversity.
A) an increase B) no change C) a decrease

Answer 28

C) a decrease

Question 29

Peter Morin of Rutgers University stocked artificial ponds with tadpoles of toads in the genera
Scaphiopus (spadefoot toad) and Bufo (southern toad) and a frog, Hyla (spring peeper). What
was the outcome of competition among these three species in the absence of predation? (Hint:
Refer to Figure 16.18.)
A) spadefoot toads were nearly eliminated C) spring peepers were nearly eliminated
B) southern toads were nearly eliminated D) all three species declined

Answer 29

C) spring peepers were nearly eliminated

Question 30

In Peter Morin’s study of coexistence among toad and frog tadpoles, presence in ponds of a
predatory newt at high levels (eight individuals) resulted in: (Hint: Refer to Figure 16.18.)
A) enhanced survival of both toads (Scaphiopus and Bufo)
B) enhanced survival of the frog (Hyla)
C) elimination of all tadpoles

Answer 30

B) enhanced survival of the frog (Hyla)

Question 31

What was the principal finding from Peter Morin’s study of coexistence among toad and frog
tadpoles?
A) Predation can eliminate all competing prey from a community.
B) Predation can reduce numbers of prey without altering their competitive relationships.
C) Predation can reverse the outcome of competition among prey species.

Answer 31

C) Predation can reverse the outcome of competition among prey species.

Question 32

What causes the negative effect on some species of coral when certain algae are growing in the
vicinity?
A) The algae consume oxygen, limiting growth of the corals.
B) The algae produce toxic compounds that have an allelopathic effect on the corals.
C) The algae produce polysaccharides, which stimulate microbial growth, which in turn
consume oxygen, limiting the growth of the corals.
D) The algae attract large fish, which in turn feed on the corals.

Answer 32

C) The algae produce polysaccharides, which stimulate microbial growth, which in turn
consume oxygen, limiting the growth of the corals.

Question 33

In the coral reef experiment referred to in the previous question, what treatment did
researchers apply to the system?
A) herbicide
B) fungicide
C) antibiotic
D) fertilizer

Answer 33

C) antibiotic

Question 34

Two closely related species of fish occupy a 100‐km section of a river. The temperature of this
section of the river increases gradually from 5°C upstream to 10°C downstream. One species
(fish A) is found in the cooler, upper 50 km of the stream and the other species (fish B) is found
in the warmer, lower 50 km of the stream. There is no overlap in the distributions of fishes A
and B. Why do these two species have nonoverlapping distributions?
A) Each species competitively excludes the other from its section of the river.
B) The two species have distinctive and nonoverlapping habitat requirements.
C) It is impossible to answer this question without conducting experimental studies of this
system.

Answer 34

C) It is impossible to answer this question without conducting experimental studies of this
system.

Question 35

__________ occurs when an individual of one species uses or defends a resource in a way that
reduces the availability of that resource to an individual of another species.

Answer 35

Interspecific competition

Question 36

Agricultural chemist __________ articulated the idea called “the law of the minimum” in 1840.

Answer 36

Justus von Liebig

Question 37

For a resource to be __________ for a particular population of a species, it must be required by
that species and it must be in sufficiently short supply that an increase in the level of the
resource would result in an increase in the population.

Answer 37

limiting

Question 38

Peace and Grubb found that fertilized Impatiens plants responded (with enhanced growth) to
increased light levels more than unfertilized plants, thus establishing the __________ nature of
nutrition and light.

Answer 38

synergistic

Question 39

When two resources together enhance the growth of a consumer population more than the
sum of both individually, the resources are said to be __________.

Answer 39

synergistic

Question 40

__________ is the hypothesis that two or more species cannot coexist on a single resource that
is scarce relative to the demand for it.

Answer 40

The competitive exclusion principle

Question 41

We find the constant terms a12 and a21, called __________, in the paired equations modeling
population dynamics of two competing species.

Answer 41

competition coefficients

Question 42

When competitors interact directly by aggressively defending resources, we refer to the
situation as __________ competition.

Answer 42

interference

Question 43

The direct inhibition of one species by another using noxious or toxic chemicals is __________.

Answer 43

allelopathy

Question 44

Interactions between competing species that are mediated by consumers are often referred to
as __________ competition.

Answer 44

apparent