Question 1

It had been thought that Brassica nigra competitively displaced the native grass Nassella pulchra, but Orrock et al. showed that it was likely apparent competition when
A) B. nigra shaded out N. pulchra.
B) N. pulchra did not germinate near B. nigra.
C) B. nigra sheltered mammal herbivores which consumed N. pulchra.
D) B. nigra had higher survival after fire than N. pulchra.
E) All of the choices are correct.

Accepted Answer

Apparent competition occurs when two species indirectly affect each other through a third party, such as a predator or herbivore. In this case, B. nigra sheltering mammal herbivores that consumed N. pulchra is an example of apparent competition, as the presence of B. nigra indirectly leads to increased predation on N. pulchra by providing shelter for the herbivores.

Question 2

In Robert Paine's studies of the Washington intertidal community, which organism proved to be a keystone species?
A) The whelk Thais
B) Acorn barnacles
C) Chitons
D) The starfish Pisaster
E) Limpets

Accepted Answer

Robert Paine's studies showed that the starfish Pisaster was a keystone species in the Washington intertidal community. When Pisaster was removed from the ecosystem, the mussel population, which is a dominant competitor for space, increased significantly and led to a reduction in the diversity of other species. This demonstrated the significant impact that one species can have on the entire community.

Question 3

The use of predaceous weaver ants to control pest insects in citrus orchards was first recorded in
A) California in the 1950s.
B) Florida in the 1920s.
C) Mexico in Mayan times.
D) China in the 17th century.
E) China in the 4th century.

Accepted Answer

The use of predaceous weaver ants to control pest insects in citrus orchards was first recorded in China in the 4th century, making it one of the earliest known forms of biological pest control.

Question 4

Cleaner wrasse are mutualists of other coral reef fishes. What benefit do they provide to those other fish?
A) They suppress diseases because they consume carcasses of dead fish.
B) They keep water oxygenated because they consume organic debris before it can rot.
C) They keep fish relatively free of externally feeding parasites.
D) They maintain fish habitat by keeping corals free of encrusting algae.
E) They reduce fish mortality by repelling large vertebrate predators.

Accepted Answer

Cleaner wrasse remove ectoparasites from other fish, providing a valuable service that helps keep their clients healthy and parasite-free.

Question 5

Which statement best sums up the relationship between density of the herbivorous snail Littorina and the diversity of algae in its habitat?
A) Highest diversity when Littorina are abundant, in all habitats
B) Highest diversity when Littorina are rare, in all habitats
C) Highest diversity when Littorina densities are intermediate, in all habitats
D) Highest diversity in tidepools when Littorina are rare, but in emergent habitats when Littorina densities are intermediate
E) Highest diversity in tidepools when Littorina densities are intermediate, but in tidepools when Littorina are rare

Accepted Answer

The answer of Which statement best sums up the relationship...

Question 6

Teja Tscharntke's studies of the food web associated with Phragmites reeds revealed that
A) only a single parasitoid species can persist exploiting a single species of herbivore.
B) only a single herbivore species can persist attacking a single species of plant.
C) predation by birds actually protects herbivores, because the birds feed on parasitoid-infested herbivore galls but not uninfested galls.
D) within local food webs, all interactions tend to be of roughly the same strength.
E) recognizing variation in interaction strength can greatly simplify the depiction of a food web.

Accepted Answer

The answer of Teja Tscharntke's studies of the food web...

Question 7

Which is the correct order of prey consumption in the Antarctic pelagic food web?
A) Krill→Diatoms→Ross seal→Crabeater seal→Killer Whale
B) Diatoms→Krill→Ross seal→Crabeater seal→Killer Whale
C) Diatoms→Squid→Emperor penguin→Leopard seal→Killer whale
D) Krill→Squid→Weddell seal→Leopard Seal→Killer whale
E) Diatoms→Squid→Krill→Emperor penguin→Leopard seal

Accepted Answer

The answer of Which is the correct order of prey...

Question 8

Kirk Winemiller, who described the feeding relations among freshwater fish in Venezuela and Costa Rica, simplified the food webs from his study sites by presenting common-fish webs. Common-fish webs
A) exclude rare species.
B) both exclude rare species and include the fish species whose aggregate abundance comprise 95% of the individuals collected.
C) exclude species that do not comprise at least 30% of the community.
D) include the fish species whose aggregate abundance comprise 95% of the individuals collected.
E) exclude species that do not comprise at least 40% of the community.

Accepted Answer

Kirk Winemiller's approach to simplifying food webs into common-fish webs involves both excluding rare species and including those fish species whose aggregate abundance comprises 95% of the individuals collected. This method allows for a more manageable and representative analysis of the feeding relationships among the most common fish in the ecosystem.

Question 9

Invasive Argentine ants have an important effect on community structure of the South African fynbos because
A) they do not disperse seeds, while native ants do.
B) they disperse seeds more effectively than do native ants.
C) they disperse seeds in different spatial patterns than do native ants.
D) as keystone species, they greatly increase the local diversity of native ants.
E) Argentine ants have invaded many communities, but not the South African fynbos.

Accepted Answer

Argentine ants disrupt the native ecosystem in the South African fynbos by not dispersing seeds, a task that native ants perform and is crucial for the propagation of various plant species.

Question 10

Martinsen, Driebe, and Whitham provided evidence for ________ with beaver consumption of cottonwoods resulting in higher densities of herbivorous beetles.
A) indirect keystone predation
B) indirect commensalism
C) apparent competition
D) keystone predation
E) indirect competition

Accepted Answer

Martinsen, Driebe, and Whitham demonstrated indirect commensalism, where beaver consumption of cottonwoods led to increased densities of herbivorous beetles, benefiting the beetles indirectly.

Question 11

A predator and its prey interact ________, but if the predator affects another species through this interaction, ecologists describe it as a(n) ________ interaction.
A) strongly; inefficient
B) directly; variable
C) weakly; diffuse
D) indirectly; keystone
E) directly; indirect

Accepted Answer

In a predator and prey interaction, the two species interact directly. However, if the predator affects another species through this direct interaction, it becomes an indirect interaction. Therefore, the best choice is E, directly; indirect. Choices A, B, C, and D do not accurately describe this relationship.

Question 12

Based on studies by Jane Lubchenco, what influence does the population density of the herbivorous intertidal snail, Littorina littorea, have on the number of algal species?
A) As snail density increases from low to medium, the number of algal species increases.
B) As snail density increases from medium to high, the number of algal species increases.
C) As snail density increases from low to medium, the number of algal species decreases.
D) As snail density increases from medium to high, the number of algal species decreases.
E) Both as snail density increases from low to medium, the number of algal species increases and as snail density increases from medium to high, the number of algal species decreases.

Accepted Answer

Jane Lubchenco's studies on the intertidal snail, Littorina littorea, demonstrate a classic example of intermediate disturbance hypothesis. At low to medium densities, the snails increase algal species diversity by preferentially consuming fast-growing algae, which allows slower-growing species to flourish. However, at high densities, the snails overgraze, leading to a decrease in algal species diversity. This shows how varying levels of herbivory can first increase and then decrease biodiversity, supporting both parts of choice E.

Question 13

In the Washington intertidal community studied by Robert Paine, the most important limiting resource is
A) space.
B) light.
C) plankton.
D) nitrogen.
E) water.

Accepted Answer

In Robert Paine's study, the most important limiting resource was found to be space, as the presence or absence of one species (the predatory sea star) had a significant impact on the diversity and abundance of other species. This suggests that competition for space was a key driver of community structure in this intertidal ecosystem.

Question 14

A keystone species is one
A) that makes up a very large proportion of total community biomass.
B) that feeds on a very large fraction of all available prey species.
C) that is fed on by a very large fraction of all predators in its community.
D) whose feeding activities have a disproportionate effect on the structure of its community.
E) that occupies the lowest level (the base) of the food web.

Accepted Answer

A keystone species is one whose feeding activities have a disproportionate effect on the structure of its community. This means that its presence or absence can greatly impact the diversity and abundance of other species in the community. Keystone species are often predators that keep the populations of their prey in check, allowing other species to thrive. Removing a keystone species can lead to cascading effects through the food web, ultimately affecting the entire ecosystem.

Question 15

Keystone species
A) appear to be common in terrestrial systems, but not in aquatic ones.
B) appear to be common in both terrestrial and aquatic systems.
C) appear to be common in aquatic systems, but not in terrestrial ones.
D) by definition, cannot occur in aquatic systems.
E) by definition, cannot occur in terrestrial systems.

Accepted Answer

Keystone species are important and influential species that have a significant impact on their ecosystem. They can exist in both terrestrial and aquatic systems. Examples of keystone species include wolves, sea otters, and beavers in terrestrial systems, and sharks, sea stars, and sea otters in aquatic systems.

Question 16

Weaver ants provide effective protection of citrus trees because they
A) remove harmful soft-scale insects (mealybugs).
B) remove all plant-feeding insects.
C) cultivate soft-scale insects, but do not allow them to feed on the trees.
D) cultivate soft-scale insects, but still allow them to be attacked by parasitoids and predators.
E) None of the choices are correct.

Accepted Answer

Weaver ants cultivate soft-scale insects for their honeydew but protect them from predators and parasitoids, indirectly protecting the citrus trees by maintaining a balance.

Question 17

Human hunters in the Amazon rain forests kill
A) large numbers of almost every mammal and bird species, for food and for skins.
B) large numbers of the smallest mammal and bird species, which are easiest to catch.
C) large numbers primarily of the largest mammal and bird species.
D) large numbers of mammals and birds, but do not greatly affect population densities.
E) only a few mammals and birds, but because humans are keystone species, these few kills greatly reduce population densities.

Accepted Answer

Human hunters in the Amazon rain forests primarily target the largest mammal and bird species, such as tapirs, deer, and peccaries, which provide more meat and are easier to spot and hunt. This has led to significant declines in the populations of these species.

Question 18

Teja Tscharntke simplified the food web associated with the wetland reed Phragmites australis by dividing the species into which of the following major trophic levels?
A) Plant, herbivore, piscivore, granivore
B) Herbivore, carnivore, detritivore, consumer
C) Herbivore, parasite, carnivore, detritivore
D) Plant, herbivore, parasite, carnivore
E) Plant, detritivore, parasite, herbivore

Accepted Answer

Teja Tscharntke simplified the food web associated with the wetland reed Phragmites australis by dividing the species into plant, herbivore, parasite, and carnivore.

Question 19

In zooplankton and intertidal communities, as the overall diversity of the food web increases, the proportion of predators in the web
A) tends to decrease.
B) tends to increase.
C) first decreases, then increases again.
D) first increases, then decreases again.
E) stays about the same.

Accepted Answer

As the overall diversity of the food web increases, the proportion of predators tends to increase because a more diverse food web supports a greater variety of prey species, which in turn can support a larger and more diverse predator population.

Question 20

In Jane Lubchenco's tidepool system, removal of the herbivorous snail Littorina led to
A) dominance of the tidepools by the unpalatable alga Chondrus.
B) replacement of Chondrus by the more palatable alga Enteromorpha.
C) replacement of Chondrus by other algae better adapted to herbivory.
D) replacement of Enteromorpha by other algae that are better competitors.
E) no marked change in the algal community.

Accepted Answer

When the herbivorous snail Littorina was removed from Jane Lubchenco's tidepool system, the more palatable alga Enteromorpha replaced the unpalatable alga Chondrus. This is because Littorina normally feeds on Enteromorpha, keeping its population in check. Without Littorina, Enteromorpha was able to outcompete Chondrus.

Quiz 17: Species Interactions and Community Structure

It had been thought that Brassica nigra competitively displaced the native grass Nassella pulchra, but Orrock et al. showed that it was likely apparent competition when

In Robert Paine's studies of the Washington intertidal community, which organism proved to be a keystone species?

The use of predaceous weaver ants to control pest insects in citrus orchards was first recorded in

Cleaner wrasse are mutualists of other coral reef fishes. What benefit do they provide to those other fish?

Which statement best sums up the relationship between density of the herbivorous snail Littorina and the diversity of algae in its habitat?

Teja Tscharntke's studies of the food web associated with Phragmites reeds revealed that

Which is the correct order of prey consumption in the Antarctic pelagic food web?

Kirk Winemiller, who described the feeding relations among freshwater fish in Venezuela and Costa Rica, simplified the food webs from his study sites by presenting common-fish webs. Common-fish webs

Invasive Argentine ants have an important effect on community structure of the South African fynbos because

Martinsen, Driebe, and Whitham provided evidence for ________ with beaver consumption of cottonwoods resulting in higher densities of herbivorous beetles.

A predator and its prey interact , but if the predator affects another species through this interaction, ecologists describe it as a(n) interaction.

Based on studies by Jane Lubchenco, what influence does the population density of the herbivorous intertidal snail, Littorina littorea, have on the number of algal species?

In the Washington intertidal community studied by Robert Paine, the most important limiting resource is

A keystone species is one

Keystone species

Weaver ants provide effective protection of citrus trees because they

Human hunters in the Amazon rain forests kill

Teja Tscharntke simplified the food web associated with the wetland reed Phragmites australis by dividing the species into which of the following major trophic levels?

In zooplankton and intertidal communities, as the overall diversity of the food web increases, the proportion of predators in the web

In Jane Lubchenco's tidepool system, removal of the herbivorous snail Littorina led to