Question 1

Two fish species live and compete on a coral reef.Fish A is dominant and maintains a larger population than fish B.During a very hot summer, a temperature spike occurs on the reef, killing off most of fish A's population.The fish B population then begins to increase.This scenario describes the process of

Accepted Answer

The scenario describes resource-mediated coexistence, where the reduction in the dominant species (fish A) due to an external factor (temperature spike) allows the less dominant species (fish B) to increase in population.

Question 2

Scientists reported that the reintroduction of wolves into Yellowstone National Park initiated a trophic cascade.Which factual statement best supports this conclusion?

Accepted Answer

The increase in aspen trees after wolves were reintroduced is a direct result of a trophic cascade. Wolves reduced elk populations, which in turn allowed vegetation like aspen trees to recover, demonstrating the cascading effect on the ecosystem.

Question 3

In the northern Pacific Ocean, sea otters feed on sea urchins and sea stars.Sea urchins feed on kelp, and sea stars feed on mussels.Beginning in the 1700s, sea otters were hunted for their fur and driven nearly to extinction in some areas, resulting in trophic cascades in their communities.When the fur trade ended, sea otter numbers increased and their communities began to recover.One would expect this recovery to lead to increased numbers of _______ and decreased numbers of _______.

Accepted Answer

With the recovery of sea otter populations, their predation on sea urchins and sea stars would increase, leading to a decrease in these populations. Consequently, the kelp and mussels, which are preyed upon by sea urchins and sea stars respectively, would experience reduced predation pressure and their numbers would increase.

Question 4

Two species eat the same prey, which is a limiting resource, and both their populations remain stable.Species A is removed, and the population of species B begins to increase rapidly.This suggests that the two species are _______ and the interaction is _______.

Accepted Answer

The fact that both populations remained stable when they shared the same limiting resource suggests that they are competitors. The increase in species B's population after the removal of species A suggests that species A was a competitor and was limiting the population of species B. This interaction is negative because the removal of one competitor allowed the other to thrive.

Question 5

Gopher tortoises are native to the southeastern United States.Which characteristic of gopher tortoises would best support the claim that they act as both keystone and ecosystem engineering species in their communities?

Accepted Answer

Gopher tortoises are known to dig deep burrows that provide homes for nearly 400 animal species, making them a keystone species. By digging, they also modify their habitats, which qualifies them as an ecosystem engineering species.

Question 6

An ecologist studying interaction strength in a pond set up laboratory experiments using aquaria.He set up food webs in two aquaria that included these interactions:  After populations in the aquaria stabilized, the ecologist removed the small fish from one aquarium.The population of Daphnia there immediately increased rapidly.This indicates that the interactor species (fish) had what effect on the target species (Daphnia)?

Accepted Answer

The rapid increase in the population of Daphnia after the removal of the small fish indicates that they were being strongly negatively affected by the fish. This suggests that the fish were preying on the Daphnia and limiting their population.

Question 7

Which trophic interaction in a community is an indirect interaction?

Accepted Answer

Coyotes eating pocket gophers indirectly benefits berry-producing plants because it decreases the population of a herbivore that feeds on the plants. This is an example of an indirect trophic interaction. All of the other options are examples of direct trophic interactions.

Question 8

Plant species A has only one pollinator; if the pollinator disappears, the plant is not pollinated and its numbers decline.Plant species B has multiple pollinators; if a single pollinator disappears, the remaining pollinators ensure that species B is still pollinated and its numbers remain stable.Which species shows the greatest interaction strength with its pollinators?

Accepted Answer

Species A shows the greatest interaction strength with its pollinator because its survival is highly dependent on that single pollinator species. If the pollinator disappears, the plant's numbers decline, indicating a strong, specialized interaction.

Question 9

Refer to the graph, showing the interaction between the elk population and the presence or absence of wolves in Yellowstone National Park.  Elk culling (hunting by humans) occurred until 1968.Based on this information, what factor had the most influence on the population of elk between 1926 and 1968?

Accepted Answer

The graph shows a significant decrease in elk population between 1926 and 1968, which correlates with the period of elk culling by humans. While wolf predation also had an impact on the elk population, it was not present during the entire period of decline, as wolves were largely absent from Yellowstone during the mid-1900s. Therefore, the factor that had the most influence on the elk population during this period was culling by humans.

Question 10

Beavers modify their habitat by building dams, which create wetlands, meadows, and ponds for themselves and other species.Humans also alter habitats, clearing forests and grasslands for agriculture and urban development.Beavers and humans can be considered both

Accepted Answer

Beavers and humans both act as ecosystem engineers by modifying their habitats to create new habitats for themselves and other species. Additionally, they can be considered keystone species as their presence or absence can affect the entire ecosystem.

Question 11

In the Eel River of Northern California, the food web includes the following set of interactions:  Assuming this set of interactions is controlled by a trophic cascade, what changes would be expected if the predatory fish were removed?

Accepted Answer

The answer of In the Eel River of Northern California,...

Question 12

In a salt marsh habitat, snails feed on marsh grasses, and blue crabs feed on snails.A high population of snails can graze the marsh so intensely that it becomes a mudflat.When blue crabs are present, the levels of all three species remain balanced and the marsh is healthy.What change in the salt marsh would be expected if blue crabs were removed?

Accepted Answer

Without blue crabs to control the snail population, the snails will graze the marsh grasses so intensely that it becomes a mudflat. This is known as a trophic cascade, where the removal of a top predator has ripple effects throughout the food chain.

Question 13

A trophic cascade includes which kind(s) of interactions?

Accepted Answer

A trophic cascade involves both direct and indirect interactions between different trophic levels in an ecosystem. For example, the removal of top predators can indirectly result in an increase in the population of their prey, which in turn can lead to a decrease in the population of their prey's prey. This indirect effect is known as a trophic cascade, and it can have wide-ranging impacts on the structure and function of ecosystems. Trophic cascades are important because they illustrate the complex and interconnected nature of ecosystems and the many ways that organisms interact with each other.

Question 14

Corals affect their communities by producing elaborate limestone skeletons (coral reefs) that provide habitat for thousands of species and by helping to concentrate resources on the reef.Sea otters affect their communities by acting as top predators that generate trophic cascades, helping to maintain species richness, abundance, and composition.Are these animals considered keystone species or foundation species?

Accepted Answer

Corals are considered a foundation species because they create a physical structure for the community to live on and around. Sea otters are considered a keystone species because they have a disproportionate impact on the community compared to their biomass, as their presence or absence can affect the entire food web. Therefore, the correct choice is D, which states that corals are a foundation species and sea otters are a keystone species.

Question 15

Several woodpecker families inhabited dead trees, or snags, in a large backyard.They fed on many kinds of insects in the homeowner's garden.In an effort to "clean up" the backyard, the owner removed the snags.Having lost their nesting sites, the woodpecker families moved to a nearby woodland community, where they both nested and fed.There was a sudden, large boom in insect populations feeding on the garden plants.Based on this information, what is the best description of the interaction, and its strength, between the interactor species (woodpeckers) and the target species (insects)?

Accepted Answer

The woodpeckers and insects were engaged in a strong negative interaction, where the woodpeckers were controlling the insect population by feeding on them. However, the removal of snags (woodpecker nesting sites) led to the woodpeckers moving away, causing a sudden boom in insect populations.

Question 16

The reintroduction of wolves into Yellowstone Park in 1995 had a(n) _______ effect on aspen and _______ effect on elk.

Accepted Answer

The answer of The reintroduction of wolves into Yellowstone Park...

Question 17

Which statement describes an important difference between a keystone species and a foundation species?

Accepted Answer

Foundation species are typically larger and more abundant, providing structure to the ecosystem, while keystone species, though not necessarily abundant, have a disproportionately large impact on their environment.

Question 18

The intermediate disturbance hypothesis states that a community experiencing an intermediate level of disturbance will have higher species diversity than it would with low or high disturbance.What is a major justification for this hypothesis?

Accepted Answer

Low disturbance environments typically allow dominant species to outcompete other species leading to reduced species diversity. On the other hand, high disturbance environments usually lead to increased mortality rates and decreased species diversity. However, intermediate levels of disturbance disrupt the dominance hierarchy, creating opportunities for less competitive species to survive and reproduce, leading to higher species diversity compared to low and high disturbance environments. Therefore, the major justification for the intermediate disturbance hypothesis is that low disturbance would result in competitive exclusion, and high disturbance would cause more extinctions.

Question 19

Charles Darwin observed the following interactions among plants and animals in his region of England: Bees pollinate flowers and make seed production possible.Field mice prey on bee combs and nests.Cats eat field mice.From these observations, he concluded that cats could control the populations of certain flowers.On what did he base this conclusion?

Accepted Answer

Darwin observed an indirect interaction between cats and flowers through mice and bees. The cats, through predation on field mice, could indirectly impact the population of bees, which in turn could affect the pollination and seed production of certain flowers. This is an example of how complex ecological interactions can have ripple effects throughout an ecosystem.

Question 20

Many species are introduced outside their normal ranges deliberately, for specific purposes.Some of these (such as the honey bee) integrate into natural communities; others (such as the gypsy moth) reproduce out of control, become pests, and are defined as "invasive." Which of the following could be a difference in the way these two categories of introduced species changed a community's structure?

Accepted Answer

Only invasive introduced species seriously harmed native species. Noninvasive species may integrate into the native food web without causing harm, but invasive species outcompete native species for resources and disrupt the balance of the ecosystem, leading to serious harm to native species.

Quiz 56: Communities

Scientists reported that the reintroduction of wolves into Yellowstone National Park initiated a trophic cascade.Which factual statement best supports this conclusion?

Two species eat the same prey, which is a limiting resource, and both their populations remain stable.Species A is removed, and the population of species B begins to increase rapidly.This suggests that the two species are _ and the interaction is _.

Gopher tortoises are native to the southeastern United States.Which characteristic of gopher tortoises would best support the claim that they act as both keystone and ecosystem engineering species in their communities?

Which trophic interaction in a community is an indirect interaction?

Refer to the graph, showing the interaction between the elk population and the presence or absence of wolves in Yellowstone National Park. Elk culling (hunting by humans) occurred until 1968.Based on this information, what factor had the most influence on the population of elk between 1926 and 1968?

Beavers modify their habitat by building dams, which create wetlands, meadows, and ponds for themselves and other species.Humans also alter habitats, clearing forests and grasslands for agriculture and urban development.Beavers and humans can be considered both

In the Eel River of Northern California, the food web includes the following set of interactions: Assuming this set of interactions is controlled by a trophic cascade, what changes would be expected if the predatory fish were removed?

A trophic cascade includes which kind(s) of interactions?

The reintroduction of wolves into Yellowstone Park in 1995 had a(n) _ effect on aspen and _ effect on elk.

Which statement describes an important difference between a keystone species and a foundation species?

The intermediate disturbance hypothesis states that a community experiencing an intermediate level of disturbance will have higher species diversity than it would with low or high disturbance.What is a major justification for this hypothesis?