Question 1

When two species have evolved a mutualistic relationship, if one species begins to provide less of a benefit, we predict that the other species will

Accepted Answer

If one species begins to provide less of a benefit, it is unlikely that the other species will evolve to provide more because this would require genetic changes that may not be possible in a short amount of time. It is also unlikely that the other species would not change the benefit it provides. Instead, it is more likely that the other species will evolve to provide less of a benefit in order to conserve resources and energy.

Question 2

Garlic mustard is a plant that has been introduced to North America. It produces a chemical that kills mycorrhizal fungi in the forest where it grows. How would killing mycorrhizal fungi affect native trees in the forest?

Accepted Answer

Mycorrhizal fungi form a mutually beneficial relationship with tree roots, helping them absorb nutrients and water from the soil. If the fungi are killed by garlic mustard, the trees will be left without this important source of nutrition, which will cause reduced growth and potentially even death.

Question 3

Consider a simple food web consisting of plants, aphids, ants, and ladybird beetles. Aphids are herbivores that consume the plants, and ladybird beetles are a predator that eats aphids. The ants obtain nutritious honeydew from the aphids, and in return the ants protect the aphids from predatory insects. What is likely to happen to the ladybird beetles, aphids, and plants if the ants go extinct?

Accepted Answer

The answer of Consider a simple food web consisting of...

Question 4

A shrub species lives in low-nutrient soil that contains mycorrhizal fungi. The plant provides sugars from photosynthesis to the fungi. The fungi provide the plants with nitrogen and phosphorus. If you add enough nitrogen and phosphorus fertilizer to the soil so that the plant can maximize its reproductive success without nutrients from the fungi, would you expect the mutualism to change? Why or why not?

Accepted Answer

The answer of A shrub species lives in low-nutrient soil...

Question 5

Ants are often associated with aphids, small insects that feed on plants. The ants obtain nutritious honeydew from the aphids, and in return the ants protect the aphids from predatory insects. If the mutualism between aphids and ants broke down such that the ants no longer protected the aphids,

Accepted Answer

Without the protection from ants, aphids would be more vulnerable to predation, likely reducing their numbers and consequently the damage they inflict on plants.

Question 6

Why is the relationship between termites and the gut protozoans considered mutualism?

Accepted Answer

The protozoans in the gut of termites are able to break down the complex lignin and cellulose found in wood, which is their primary food source. This allows the termites to extract nutrients from the wood and obtain energy from the protozoans' metabolism, creating a mutually beneficial relationship known as mutualism.

Question 7

If Rhizobium bacteria were to go extinct, plants would

Accepted Answer

Rhizobium bacteria play a crucial role in fixing atmospheric nitrogen into a form that plants can use, so if they were to go extinct, plants would not be able to obtain this necessary nutrient, which could severely impact their growth and survival.

Question 8

In the mutualism between ants and trillium flowers, if the trillium stopped producing the elaiosome on its seeds, the ants would probably

Accepted Answer

The elaiosome is a nutritious structure on the seed that attracts ants to carry them back to their nest, where they eat the elaiosome and discard the seed. If the trillium stopped producing the elaiosome, the ants would no longer be attracted to the seeds and would not carry them back to their nest. Therefore, choice B is the best answer.

Question 9

If yucca plants did not selectively abort flowers with many yucca moth eggs, over several generations the frequency of moths that lay many eggs will likely

Accepted Answer

If yucca plants did not selectively abort flowers with many yucca moth eggs, the probability of more eggs and more hatching larvae would increase. This would increase the chance of competition between the larvae and a higher demand for resources from the plant. The plant would eventually be selected to abort these flowers to prioritize their own survival and reproduction, resulting in a decrease in the frequency of moths that lay many eggs. However, if the plant did not selectively abort these flowers, the frequency of moths that lay many eggs would likely increase over time.

Question 10

Of the following types of mutualisms, which would likely have the largest impact on other species if one member of the mutualism went extinct?

Accepted Answer

Specialist obligate mutualisms involve two closely dependent species where one species is very specialized to the other for survival. If one member were to go extinct, it would have a significant impact on the other species and could potentially lead to their extinction as well.

Question 11

(Figure 17.22) Researchers manipulated the number of species of mycorrhizal fungi living in the soil and measured the effects on plant biomass and phosphorus uptake. Their results are shown in the figure. Based on their results, the most likely way the extinction of mycorrhizal fungi species would affect the ecosystem is to

Accepted Answer

The graph shows that as the number of mycorrhizal fungi species in the soil decreases, both plant biomass and phosphorus uptake decrease. This suggests that the extinction of mycorrhizal fungi species would reduce plant growth, making choice A the best answer. The graph does not provide any evidence to suggest that the extinction of mycorrhizal fungi would increase plant growth or reduce/increase plant extinction.

Question 12

A small forest herb does not normally develop nectaries. However, when herbivorous insects attack it, the herb develops nectaries that attract ants to the plant. Explain why this plant develops nectaries only when attacked by herbivorous insects.

Accepted Answer

The answer of A small forest herb does not normally...

Question 13

Under which circumstance do we tend to NOT see mutualism?

Accepted Answer

The answer of Under which circumstance do we tend to...

Question 14

Several animal species have gone extinct on the islands of Mauritius. These extinct animals, including the dodo bird and tortoises, once ate the fruit of many plant species. As a result of the extinction of these animals,
I. the flowers of the plants can no longer be pollinated.
II. the parental plants are strongly competing with their offspring.
III. many plants are growing together in tight groups instead of being spread over the island.

Accepted Answer

The extinction of animals like the dodo bird and tortoises, which once ate the fruit of many plant species, affects plant distribution and competition. Without these animals to eat and disperse the seeds, the seeds are more likely to fall and grow near the parent plants, leading to strong competition between parental plants and their offspring (II) and causing many plants to grow together in tight groups instead of being spread over the island (III). The statement about pollination (I) is not directly related to the role of these extinct animals, as they primarily affected seed dispersal rather than pollination.

Question 15

(Figure 17.20) Researchers experimentally removed cleaner fish from some coral reef communities and left cleaner fish present in other communities. Their results are shown in the figure. Based on these results, extinction of cleaner fish would result in _____ fish species, and each species would be _____ abundant.

Accepted Answer

The answer of  (Figure 17.20) Researchers experimentally removed cleaner...

Question 16

If cleaner fish went extinct, damselfish would

Accepted Answer

Cleaner fish help remove parasites from the damselfish. Without the cleaner fish, the damselfish would carry more parasites.

Question 17

(Figure 17.18) A group of researchers grew plants so that half of their roots were in soil with a fungus that provides benefits to the plants and the other half were in soil with a fungus that did not provide benefits to the plants. After 9 weeks of growth, they provided the plants with carbon dioxide containing a rare isotope of carbon. For four days, they evaluated how much of the carbon went to the beneficial fungus and how much of the carbon went to the nonbeneficial fungus. Some of their results are presented in the figure. Which statement(s) about this experiment is/are CORRECT?
I. At the experiment's start, the nonbeneficial fungus was taking resources from the plant.
II. After 4 days, the plant provided more resources to the beneficial fungus.
III. This is an example of how species can prevent cheating in mutualisms.

Accepted Answer

The answer of  (Figure 17.18) A group of researchers...

Question 18

Which would be a reason to use a Mann-Whitney rank sum test rather than a t-test to compare two groups?

Accepted Answer

The Mann-Whitney U test is a non-parametric test used when the data do not follow a normal distribution, making it a suitable alternative to the t-test which assumes normality of the data.

Question 19

Biologists have recently introduced wild turkeys and Aldabra tortoises to the islands of Mauritius. How have these introductions affected native plants of Mauritius?

Accepted Answer

The introduction of Aldabra tortoises and wild turkeys has helped in seed dispersal and improved germination rates, as these animals consume the fruits and help spread the seeds through their droppings.

Question 20

In Palmer's experimental manipulation of large herbivore abundance on acacia trees, he found that exclusion of large herbivores often caused the ant species Crematogaster mimosa to abandon acacia trees and the ant species C. sjostedti to move into acacia trees. What were the effects of the shift from C. mimosa to C. sjostedti on the acacia trees?

Accepted Answer

The answer of In Palmer's experimental manipulation of large herbivore...

Quiz 17: Mutualism