Deck 15: Mutualism and Commensalism

Question 1

In comparing agriculture practiced by humans and by leaf-cutter ants, which of these statements is the least correct?

A) Both groups grow crops, benefiting themselves and the crop species.
B) Both groups are highly dependent on food produced through agriculture.
C) Both groups have been practicing farming for about the same length of time.
D) Agriculture has allowed both groups to develop extremely high populations.

Answer 1

C

Question 2

A bird species nests in a specific kind of tree. The tree is not harmed by the bird building its nest in the tree's branches, but the bird benefits from the shelter provided by the tree and is better able to successfully raise young. This is an example of

A) mutualism.
B) endosymbiosis.
C) commensalism.
D) symbiosis.

Answer 2

C

Question 3

In one interaction, a bird feeds on the seeds of a specific plant. Some of the seeds are digested, while others pass unharmed through its digestive tract and are deposited in new locations. In a second interaction, a bird digests all of the seeds from the plant and therefore, none of the seeds are dispersed. The plant is not damaged because the number of seeds eaten is relatively small. Which term best describes both of these interactions?

A) Symbiosis
B) Facilitation
C) Mutualism
D) Commensalism

Answer 3

B

Question 4

Three examples of associations in nature include: 1) Sea anemones riding on the backs of hermit crabs where the two species protect each other from their different enemies; 2) Lactobacillus bacteria living inside the human gut, having a beneficial effect on human health; and 3) Leaf-cutting ants farming and feeding on specific fungi, which receive free food and protection. How can these three associations best be classified?

A) All three are symbioses.
B) All three are commensalisms.
C) Associations 1 and 3 are commensalisms; association 2 is a symbiosis.
D) Associations 1 and 3 are symbioses; association 2 is a commensalism.

Question 5

Which criterion is most important in determining whether an ecological relationship is a symbiosis?

A) Whether both parties benefit
B) Whether the parties are from the same kingdom
C) The degree of proximity between the two parties
D) The number of parties in the interaction

Question 6

The loss of mycorrhizae-plant associations, in both angiosperms and gymnosperms, would have which effect on the plants?

A) Plants would be able to extract more water and more nutrients from the soil.
B) Plants would be able to extract less water and fewer nutrients from the soil.
C) Plants would be better protected from pathogens.
D) Plants would be able to survive in a wider range of habitats.

Question 7

A mycorrhizal-associated fungus grows between the cells of the root of a plant, forming a mantle around the exterior of the root. This is an example of which type of association?

A) Arbuscular mycorrhizal
B) Communalistic mycorrhizal
C) Ectomycorrhizal
D) Endomycorrhizal

Question 8

Which statement describes the critical distinction between arbuscular mycorrhizae and ectomycorrhizae?

A) Ectomycorrhizae involve more penetration into root cells.
B) Arbuscular mycorrhizae often grow farther into soil and involve more penetration into root cells.
C) Arbuscular mycorrhizae form a mantle around root exteriors, whereas ectomycorrhizae only grow between root cells.
D) Arbuscular mycorrhizae are engaged in commensalisms, whereas ectomycorrhizae are engaged in mutualisms.

Question 9

Algae called zooxanthellae live in the tissues of corals. Their photosynthesis provides organic compounds that the corals use as food and the corals provide the algae with a safe place to live and with nutrients to use in photosynthesis. This relationship is best described as

A) symbiotic (+/0).
B) mutualistic (+/+).
C) commensal (+/0).
D) parasitic (+/-).

Question 10

Cord grass is a major plant in saltmarshes in southeastern United States. It provides habitat for many saltmarsh species, such as snails, crabs, conch, and mullet. Within these species, cord grass could best be described as a

A) foundation species.
B) host species.
C) nurse species.
D) parasitic species.

Question 11

An ant colony maintains and farms a species of fungus on which it feeds. The fungus, in turn, is parasitized by a bacterium. The ant/fungus interaction is _______ and the fungus/bacterium is _______.

A) +/+; +/-
B) +/0; +/-
C) a+/+; +/0
D) +/0; +/+

Question 12

Refer to the table.
The table contains data on the effects of symbiosis between a fly (host) and a fungus over many years. It shows the upper and lower bounds for the effects of the association; positive numbers denote net benefits and negative numbers denote net costs. (If zero is between the upper and lower bounds, consider the effect to be zero, since it is statistically indistinguishable from zero.)

-According to the table, the relationship between the fungus and the fly in 1990 was a

A) mutualism.
B) competitive interaction.
C) commensalism.
D) host?parasite interaction.

Question 13

Refer to the table.
The table contains data on the effects of symbiosis between a fly (host) and a fungus over many years. It shows the upper and lower bounds for the effects of the association; positive numbers denote net benefits and negative numbers denote net costs. (If zero is between the upper and lower bounds, consider the effect to be zero, since it is statistically indistinguishable from zero.)

-According to the table, the relationship between the fungus and the fly in 1996 was a

A) mutualism.
B) competitive interaction.
C) commensalism.
D) host?parasite interaction.

Question 14

Refer to the table.
The table contains data on the effects of symbiosis between a fly (host) and a fungus over many years. It shows the upper and lower bounds for the effects of the association; positive numbers denote net benefits and negative numbers denote net costs. (If zero is between the upper and lower bounds, consider the effect to be zero, since it is statistically indistinguishable from zero.)

-According to the table, in what year did the relationship between the fungus and the fly first become a mutualism?

A) 1996
B) 1999
C) 2002
D) 2005

Question 15

Which factor in the association between figs and fig wasps, if true, indicates that they have gone and/or are undergoing coevolution?

A) The association is mutually beneficial.
B) The association is facultative.
C) Both species are tropical, indicating high rates of evolution.
D) Wasp reproductive behavior is highly specialized to benefit figs.

Question 16

In desert environments, many larger plants serve as "nurse" plants for smaller species that grow beneath them and benefit from their shade. Which characteristic of this association suggests that coevolution is not a major factor?

A) The association is facultative, rather than obligate.
B) The association involves commensalism, rather than mutualism.
C) A single nurse species can protect many different smaller species.
D) The association occurs only in the desert.

Question 17

All other factors being equal, which scenario is least likely to involve coevolution?

A) An obligate positive interaction in which one party lives inside the other
B) An obligate positive interaction in which the two parties are closely related
C) An obligate positive interaction in which the two parties are from different kingdoms
D) A facultative interaction in which the two parties are from different kingdoms

Question 18

Refer to the figure.
The figure shows the influence of soil temperature on the interaction between two wetland plants, forget-me-nots and cattails. Cattails have extensive air channels for transporting oxygen in their leaves, stems, and roots. Forget-me-nots lack air channels. Based on the figure, as soil temperature increased, the influence of cattails on the growth of forget-me-nots changed from

A) neutral to negative (no effect to competition).
B) positive to negative (facilitation to competition).
C) negative to positive (competition to facilitation).
D) positive to neutral (facilitation to no effect).

Question 19

Refer to the figure.
The RNE (relative neighbor effect) measures growth of a target plant species in the presence and absence of neighboring species. The figure shows graphs of the RNE at eleven sites around the world. RNE was measured at high and at low elevations at each site. RNE values above zero (blue) indicate that neighboring plants increased the growth of target species; RNE values below zero (red) indicate that neighbors decreased target species growth.

-This study showed that the presence of neighboring plants most often benefited the target plants at

A) high-elevation sites.
B) low-elevation sites.
C) sites in North America only.
D) sites in Europe only.

Question 20

Refer to the figure.
The RNE (relative neighbor effect) measures growth of a target plant species in the presence and absence of neighboring species. The figure shows graphs of the RNE at eleven sites around the world. RNE was measured at high and at low elevations at each site. RNE values above zero (blue) indicate that neighboring plants increased the growth of target species; RNE values below zero (red) indicate that neighbors decreased target species growth.

-What type of ecological interaction did plants show at high elevations and at low elevations, respectively?

A) High: mutualists; low: mutualists
B) High: mutualists; low: parasites
C) High: mutualists; low: competitors
D) High: competitors; low: mutualists

Question 21

Refer to the figure.
The figure shows the RNE (relative neighbor effect) correlated to summer temperatures in alpine plants. Higher summer temperatures indicate communities at lower elevations, where plants are less stressed. The RNE is one measurement of the degree of mutualism in a community-the higher the RNE, the stronger the mutualistic interaction. Based on the data in this figure, which conclusion can be drawn about the importance of mutualism in this community?

A) Mutualism is relatively unimportant among alpine plants.
B) Mutualism becomes stronger under less stressful conditions.
C) Mutualism becomes stronger under more stressful conditions.
D) Mutualism becomes stronger at lower temperatures, but stress is not a factor.

Question 22

A bacterium provides essential amino acids to an aphid, which in turn provides sugars to the bacterium. Assuming that each partner is benefiting from the interaction, this would be an example of which type of mutualism?

A) Trophic
B) Metabolic
C) Service
D) Chemical

Question 23

A fungus increases the ability of a plant to grow under high-salt conditions. For the plant, this association is which type of mutualism?

A) Trophic
B) Formic
C) Chemical
D) Habitat

Question 24

Because leaf-cutter ants and fungi help each other overcome plant defenses, the leaf-cutter ant-fungus mutualism can be described as which type of mutualism?

A) Trophic
B) Habitat
C) Service
D) Chemical

Question 25

Which of these scenarios represents an example of habitat mutualism?

A) Bees travel among flowers, obtaining nectar and pollinating the plants.
B) Ants protect treehoppers from predators and receive honeydew as food.
C) Clownfish live among sea anemone tentacles and protect them from predators.
D) Mycorrhizae provide plants with phosphorus; plants provide microrrhizae with carbohydrates.

Question 26

Refer to the figure.
Medicago truncatula, or barrelclover, is a clover-like legume that has a mutualistic association with mycorrhizal fungi. In the experiment illustrated in the figure, fungi in contact with Medicago had access to either no phosphorus, or to either 35 or 700 ?M of phosphorus. According to the figure, how did Medicago alter the amount of carbohydrate it transferred to the fungi in response to the change in fungal phosphorus levels?

A) It increased its transfer of carbohydrate when the fungi contained phosphorus.
B) It decreased its transfer of carbohydrate when the fungi contained phosphorus.
C) It transferred more carbohydrate as the fungal phosphorus levels increased.
D) It ceased its transfer of carbohydrate when fungal phosphorus levels were zero.

Question 27

In a plant-pollinator interaction, the plant expends energy to produce colors and scents that attract the pollinator. This energy is therefore not available to use in the plant's growth and reproduction. This interaction provides evidence in favor of which statement?

A) Both partners benefit equally from the relationship.
B) Partners join mutualisms for altruistic reasons.
C) Conflicts of interest seldom exist in mutualisms.
D) Mutualisms may impose costs on the partners.

Question 28

For an ecological interaction to be a mutualism, the net benefits must

A) exceed the net costs for both partners.
B) exceed the net costs for one, but not necessarily the other, partner.
C) be less than the net costs for both partners.
D) be less than the net costs for one, but not necessarily the other, partner.

Question 29

From the act of pollinating flowers, a bee population gains the benefit of a 0.06 growth rate increase per month. However, the costs imposed by the flower (bees occasionally getting stuck, time spent pollinating the flower instead of pollinating other species, etc.) is a 0.02 reduction in growth rate per month. The flower gains benefits from the pollination that enhance its population growth rate by 0.05 per month, but it incurs costs (feeding the bees, damage done by the bees) that reduce its growth rate by 0.05 per month. In this situation, what is the best description of the relationship between the bees and the flowers?

A) A host‒parasite relationship
B) An amensalism
C) A commensalism
D) A mutualism

Question 30

The studies by Pellmyr and Huth on yuccas and yucca moths showed that

A) the mutualism evolved from a host-parasite relationship.
B) yucca plants reward moths that lay the most eggs.
C) yucca plants impose penalties on moths that lay too many eggs.
D) there is no conflict of interest between the yucca plants and the yucca moths.

Question 31

Yucca plants retain 62% of the flowers that contain up to six moth eggs, but only 11% of the flowers containing nine or more eggs. The yucca aborts these flowers before the moth eggs hatch. This process is only effective for reducing exploitation by moths if

A) moths that appear later are unable to lay eggs in the yucca flowers.
B) moths are able to lay more eggs in the unaborted flowers.
C) the moth larvae in an aborted flower all die.
D) the moth larvae in an aborted flower move to another yucca.

Question 32

An insect removes nectar from a flower without pollinating it. This is an example of

A) the insect acting as a cheater.
B) the insect extracting a penalty from the plant.
C) the plant extracting a penalty from the insect.
D) a typical mutualistic interaction between insect and plant.

Question 33

Refer to the figure.
The fruit fly Drosophila neotestacea carries a bacterial symbiont; the fly can also be infected by a nematode worm. The figure shows the number of eggs produced by female flies that are or are not infected by the nematode and that have or do not have the bacterial symbiont.

- Assuming that the nematode benefits by being inside the fly, the fly?nematode relationship, when there is no bacterial symbiont, is best described as a(n)

A) host?parasite relationship.
B) commensalism.
C) amensalism.
D) mutualism.

Question 34

Refer to the figure.
The fruit fly Drosophila neotestacea carries a bacterial symbiont; the fly can also be infected by a nematode worm. The figure shows the number of eggs produced by female flies that are or are not infected by the nematode and that have or do not have the bacterial symbiont.

-According to the figure, the bacterial symbiont

A) reduces the fecundity of female flies infected by the nematode.
B) increases the fecundity of female flies infected by the nematode.
C) increases the fecundity of female flies not infected by the nematode.
D) increases the transmission of the nematode.

Question 35

Acacia plants often have ants of the genus Pseudomymex associated with them. Removal of ant colonies from individuals of the bullhorn acacia species results in which change in the acacias?

A) They grow considerably larger.
B) Their growth is considerably stunted.
C) Their survival rate increases.
D) They form partnerships with other ant species.

Question 36

When Daniel Janzen studied the ant-acacia system by removing ant colonies from some acacias, he found much lower growth rates in the acacia after ants were removed. Which other changes were seen in the responses of the acacia to ant removal?

A) Their survival rate was higher and they were more susceptible to insect herbivores.
B) Their survival rate was higher and they were less susceptible to insect herbivores.
C) Their survival rate was lower and they were more susceptible to insect herbivores.
D) Their survival rate was lower and they were less susceptible to insect herbivores.

Question 37

What characteristics are found in Pseudomyrmex ants that depend on acacias, compared to species of Pseudomyrmex that are not associated with acacias?

A) They are more active and more aggressive.
B) They are less active and less aggressive.
C) They are more aggressive and less active.
D) They are more active and less aggressive.

Question 38

Refer to the figure.
In the study by van der Heijden and colleagues comparing the effects of differing numbers of mycorrhizal species (0?-14) on the same 15 plant species, the shoot biomass of the target plants was found to

A) increase steadily with the number of mycorrhizal fungal species.
B) increase at first and then level off as the number of mycorrhizal fungal species increased.
C) increase at first but then drop sharply as the number of mycorrhizal fungal species increased.
D) be high when only a few mycorrhizal fungal species were present and then decrease as more were added.

Question 39

Which statement describes the most likely reason that a fish associated with a cleaner fish like Labroides dimidiatus does not eat the cleaner fish, even when the cleaner fish is in its mouth?

A) The fish is being altruistic.
B) The benefit from parasite removal is greater than that from eating the cleaner fish.
C) The cleaner fish contains noxious secondary compounds that harm other fish.
D) The cleaner fish emits a chemical that makes the other fish more docile.

Question 40

Grutter tested the effect of cleaner fish on species diversity in the Great Barrier Reef by

A) adding cleaner fish to reefs that did not have them.
B) experimentally removing cleaner fish from certain reefs.
C) manipulating fish so they would not associate with cleaner fish.
D) manipulating fish so they would eat cleaner fish.

Question 41

In a prairie ecosystem, mycorrhizal fungi form associations with the roots of prairie grasses, such as big bluestem. When the mycorrhizae are removed, the performance of big bluestem decreases, while the performance of other prairie grasses and wildflowers increases. This effect most clearly shows the influence of mutualisms on

A) species abundance.
B) species distribution.
C) ecosystem structure.
D) ecosystem diversity.

Question 42

Refer to the figure.
In the study illustrated in the figure, van der Heijden and colleagues compared the effects of differing numbers of mycorrhizal species (0?-14) on the same 15 plant species. They measured the effects of this mycorrhizal species diversity on net primary production (measured as shoot and root biomass) and on cycling of nutrients (measured as phosphorus content). Based on the figure, what can be concluded about the effect of mycorrhizal diversity on plant ecosystems?

A) All three factors decrease, indicating that mycorrhizal diversity inhibits plant growth.
B) All three factors increase, indicating that mycorrhizal diversity improves plant growth.
C) There appears to be little change in any of the three factors; thus, mycorrhizal diversity has little effect on plant growth.
D) Shoot biomass and phosphorus content increase, but root biomass shows little change, indicating that the presence of mycorrhizae in soil depresses root growth.

Question 43

Based on Grutter's studies, we can conclude that the presence of cleaner fish

A) reduces the parasite load of other fish species.
B) decreases the abundance of other fish species.
C) decreases species diversity on the reef.
D) increases predation rates on the reef.

Question 44

When leaf-cutter ants encounter the parasitic fungus Escovopsis, they

A) enlist help from other species, including a symbiotic bacterium.
B) decrease the rate at which they weed their fungal gardens.
C) abandon the infected area and build a new nest.
D) build more crypts to combat the infection.

Question 45

A seedling begins to grow very close to a leaf-cutter ant colony. What is a possible cost or benefit of growing in that area?

A) The seedling might grow faster due to increased soil fertility around the colony.
B) Seedling growth rates might be increased by herbivory from ants.
C) The seedling would be aggressively defended by the ants.
D) The seedling would pay an energetic cost by providing nectar to the ants.

Question 46

Humans have associated with canines throughout history, and this has led to the emergence of domestic dogs. Historically, dogs helped humans defend their livestock and aided in hunting. Create a table (Table 1) that includes the following terms: symbiotic, mutualism, commensalism, parasitic, obligate/facultative, trophic mutualism, habitat mutualism, and service mutualism. Describe each term's applicability and justification in regard to the historic human/dog relationship.

Question 47

You are studying two new species that have a mutualistic relationship. How would you determine if the mutualism is facultative or obligate? What types of observational data would you collect and what type of experiment would you conduct?

Question 48

The interaction of fig trees and fig wasps is a very close obligate mutualism. In contrast, desert ironwood serves as a "nurse" species for seedlings of 165 different desert plants and shares a facultative mutualism with each. Compare and contrast these two types of relationships. What might cause the development of each?

Question 49

What types of environmental factors can cause positive associations, including mutualism and commensalism, to vary in terms of their costs and benefits? Give several environmental conditions that might impact these associations.

Question 50

Suppose a fish species lives in an environment where both food and safe living space are hard to find. How would the development of mutualistic associations benefit this fish species? Would trophic or habitat mutualisms, or both, be most beneficial? Can you think of situations in nature where such associations occur?

Question 51

Refer to the figures.
The two figures represent the results of studies on a mutualism between the plant Medicago and its partner, a mycorrhizal fungus. The top figure shows the percentage of carbohydrate transferred from the plant to the fungus, depending on the amount of phosphorus the fungus supplies to the plant. The bottom figure shows the amount of fungal phosphorus incorporated by plant roots, depending on the amount of carbohydrate supplied to the fungus. Given the information in these two figures, does the mutualism appear to be under the control of the plant or the fungus, or do both partners exercise some control?

Question 52

What is a "cheater" in a mutualistic relationship? Give an example. Under what circumstances would cheating be a benefit to the cheating party? How might the exploited partner respond?

Question 53

Forest fragmentation and habitat loss is increasing around the world. Many species living in forests are "forest specialists." These specialists can only survive in certain types of trees, or in certain microclimates found only in a particular forest type; that is, they have facultative mutualisms with certain species in the forests. One of these is the white-backed woodpecker, a rare European species found in old-growth deciduous forests. Others include more than 20,000 types of wood beetles, which require specific types of oaks as their habitat. Predict what will happen to these mutualisms, and to the distribution and abundance of species, as forest fragmentation and habitat loss continues.

Question 54

A coral reef ecosystem provides food and habitat for a variety of species. Discuss, with examples, how a coral reef might increase species diversity in the shallow ocean habitat.

Question 55

Would positive associations be expected to change ecosystem processes in any way, other than effects on species diversity? For example, could mutualisms or commensalisms affect nutrient cycling, photosynthesis, or other key processes? If so, explain how this might happen, with examples.

Question 56

Refer to the figure.
Leaf-cutter ant colonies, which farm fungi for food, are often infested with a specialized parasitic fungus called Escovopsis. Under normal conditions, the ants periodically "weed" their fungal gardens, removing unwanted materials and organisms. The figure illustrates results of an experiment showing what happens to weeding behavior when the ant colony is exposed to water, to Trichoderma (a generalist fungal parasite), and to Escovopsis. What does this figure suggest about the mutualism between leaf-cutter ants and the fungi they farm?

Question 57

A bear accidentally carries the seeds of a weedy plant in its fur. Transporting the seeds neither helps nor harms the bear, but is beneficial to the plant. This is an example of a(n)

A) mutualism.
B) commensalism.
C) symbiosis.
D) amensalism.

Question 58

Refer to the table.
The table contains data on the effects of a symbiosis between a bee (host) and a bacterium over many years. The table shows the upper and lower bounds for the effects of the association; positive numbers denote net benefits and negative numbers denote net costs. (If zero is between the upper and lower bounds, consider the effect to be zero, since it is statistically indistinguishable from zero.) According to the table, the relationship between the fungus and the fly in 1988 was a

A) mutualism.
B) competitive interaction.
C) host‒parasite interaction.
D) commensalism.

Question 59

Refer to the table.
The table contains data on the effects of a symbiosis between a bee (host) and a bacterium over 22 years. The table shows the upper and lower bounds for the effects of the association; positive numbers denote net benefits and negative numbers denote net costs. (If zero is between the upper and lower bounds, consider the effect to be zero, since it is statistically indistinguishable from zero.) According to the table, this interaction first become a commensalism in

A) 1993.
B) 1997.
C) 2001.
D) 2005.

Question 60

Bromeliads and other tropical plants live in and on rainforest trees, obtaining food and living space from the trees but not helping or harming them. What type of association do trees and bromeliads have, and how much coevolution is occurring to maintain this relationship?

A) Mutualism; little or no coevolution
B) Mutualism; significant coevolution
C) Commensalism: little or no coevolution
D) Commensalism; significant coevolution

Question 61

Scientists have studied the value of positive interactions in ecosystems by measuring the "relative neighbor effect" (RNE), or the effect that neighboring species have on the growth of a target species. Given the usual purposes of positive interactions, in which ecosystem would the neighboring plant species be most likely to help a target species?

A) Rainforest
B) Desert
C) Prairie
D) Deciduous forest

Question 62

A wasp pollinating a plant in exchange for food is an example of

A) both a service mutualism and a habitat mutualism.
B) both a service mutualism and a trophic mutualism.
C) both a habitat mutualism and a trophic mutualism.
D) only a trophic mutualism.

Question 63

Spider crabs live on the ocean floor in shallow areas and greenish-brown algae live on their backs. This provides the algae with a home and the algae's greenish-brown color helps the crab blend in and stay safe from predators. This association can be considered a mutualism because

A) both partners receive a net benefit.
B) the association is an altruistic one.
C) one partner benefits and the other is not harmed.
D) the crab obtains a greater net benefit than the algae.

Question 64

Most wasps are carnivores, but one group feeds on pollen and nectar and pollinates the flowers they visit. Wasps are less efficient than bees at pollination because their bodies are not covered with fuzzy hairs and therefore, pollen is less likely to stick to them. But masarine wasps specialize in pollinating certain species, including beardtongues (Penstemon sp.). Given this information, how will the costs and benefits of masarine wasp-plant mutualisms likely compare to those of bee-plant mutualisms?

A) Costs and benefits will be about the same for both mutualisms.
B) Wasp-plant mutualisms will have higher costs and higher benefits.
C) Wasp-plant mutualisms will have higher costs and lower benefits.
D) Wasp-plant mutualisms will have lower costs and lower benefits.

Question 65

Which species has been documented as imposing penalties on individuals of its mutualistic partner that are engaged in overexploitation?

A) Figs of the fig-fig wasp system
B) Fig wasps of the fig-fig wasp system
C) Yucca plants of the yucca-yucca moth system
D) Yucca moths of the yucca-yucca moth system

Question 66

In Daniel Janzen's study of the ant-acacia association, which question was Janzen attempting to answer?

A) Is the ant-acacia association a mutualism or a commensalism?
B) Is the ant-acacia association obligate or facultative?
C) How long can the acacia survive if ants are removed?
D) Do the services provided by the ants benefit the acacias?

Question 67

Refer to the figure.
In Grutter's studies in the Great Barrier Reef off of Australia, he measured the number of fish species and the number of individual fish on the parts of the reef where cleaner fish were present (controls) and where cleaner fish had been removed (experimental). Based on the figures, what is the best conclusion that can be drawn regarding the effects of cleaner fish on reef fish abundance and diversity?

A) The presence of cleaner fish decreases both fish abundance and diversity.
B) The presence of cleaner fish increases both fish abundance and diversity.
C) The presence of cleaner fish increases fish abundance but decreases diversity.
D) The presence of cleaner fish decreases fish abundance but increases diversity.

Question 68

Refer to the figure.
What is the best description of the relationship identified by van der Heijden et al. between the average shoot biomass of the target plants and the number of mycorrhizal fungal species associated with them?

A) When the number of species is small, shoot biomass is also low; as the number of species increases, shoot biomass also increases.
B) When the number of species is small, shoot biomass is low; as the number of species increases, shoot biomass rapidly increases, then begins to level off.
C) When the number of species is small, shoot biomass is low; when the number of species is moderate, shoot biomass is high; when the number of species is high, shoot biomass is low.
D) The number of species has no effect on shoot biomass.

Question 69

Refer to the figure.
In the study by van der Heijden et al. of mycorrhizal fungi, the root biomass of the target plants (shown in the figure) was found to

A) increase at first and then level off as the number of fungal species was increased.
B) increase steadily as the number of fungal species was increased.
C) be highest when the fungal species were at an intermediate level.
D) be high when there were only a few fungal species present and then decrease as more were added.

Question 70

Leaf-cutter ants are part of a complex system of species associations. These include a(n) _______ with fungi, which they cultivate in gardens within their nests; a(n) _______ with a parasitic fungus (Escovopsis) that invades and destroys fungal gardens; and a(n) _______ with a bacterium living on the ant's body that produces a chemical that inhibits Escovopsis. These three associations are, respectively,

A) mutualism; host-parasite interaction; mutualism
B) mutualism; mutualism; host-parasite interaction
C) mutualism; host-parasite interaction; commensalism
D) commensalism; host-parasite interaction; host-parasite interaction

Question 71

Many people think leaf-cutter ant colonies provide a large benefit to rainforest ecosystems. Which of these statements does not provide evidence to support this assumption?

A) Nitrogen fixation in fungal gardens of leaf-cutter ant colonies is very high.
B) Refuse areas of ant colonies contain about 48 times the nutrients in leaf litter.
C) Leaf-cutter ants till the soil near their colonies, allowing plant roots to penetrate more easily.
D) Leaf-cutter ants reduce above-ground net primary productivity by harvesting leaves; their effect on root growth is unknown but is likely positive.