Deck 17: Species Interactions and Community Structure

Question 1

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

Answer 1

D

Question 2

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

Answer 2

E

Question 3

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

Answer 3

E

Question 4

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.

Question 5

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

Question 6

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.

Question 7

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.

Question 8

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

A) Krill $\rightarrow$ Diatoms $\rightarrow$ Ross seal $\rightarrow$ Crabeater seal $\rightarrow$ Killer Whale
B) Diatoms $\rightarrow$ Krill $\rightarrow$ Ross seal $\rightarrow$ Crabeater seal $\rightarrow$ Killer Whale
C) Diatoms $\rightarrow$ Squid $\rightarrow$ Emperor penguin $\rightarrow$ Leopard seal $\rightarrow$ Killer whale
D) Krill $\rightarrow$ Squid $\rightarrow$ Weddell seal $\rightarrow$ Leopard Seal $\rightarrow$ Killer whale
E) Diatoms $\rightarrow$ Squid $\rightarrow$ Krill $\rightarrow$ Emperor penguin $\rightarrow$ Leopard seal

Question 9

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.

Question 10

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.

Question 11

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.

Question 12

We can infer a statistically significant difference between two population means when

A) our estimates of the two means are different.
B) the variances of the two means do not overlap.
C) the standard deviations of the two means do not overlap.
D) the 95% confidence intervals for the two means do not overlap.
E) the 95% confidence intervals for the two means are of different widths.

Question 13

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.

Question 14

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 17^th century.
E) China in the 4^th century.

Question 15

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.

Question 16

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

Question 17

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.

Question 18

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.

Question 19

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.

Question 20

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

Question 21

Removal of Pisaster starfish in the Washington intertidal leads to a decline in diversity of other invertebrate species.

Question 22

The impact of Argentine ants on species diversity in the South African fynbos is most dramatic following fires.

Question 23

Ecologists summarize feeding interactions among species in a community when they compile a _________.

Question 24

The presence of cleaner wrasse enhances diversity of fishes on coral reefs.