Question 1

The number of trophic levels in most communities is limited by

Accepted Answer

The loss of energy between trophic levels restricts the number of trophic levels in most communities. As energy is transferred from one level to another, a significant amount of energy is lost as heat, which limits the carrying capacity of the ecosystem. This makes it difficult for higher trophic levels to be sustained, resulting in a limited number of trophic levels in most communities.

Question 2

The reintroduction of wolves into Yellowstone in 1995 had _______ effect on aspen and _______ effect on elk.

Accepted Answer

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

Question 3

Grain is eaten by cows, and cows are eaten by humans. If the ecological transfer efficiency between each trophic level is 10 percent, how much grain is required to produce 70 kg of human biomass?

Accepted Answer

Ecological transfer efficiency is 10%, so 10% of the grain eaten by cows is transferred to cow biomass, and 10% of the cow biomass eaten by humans is transferred to human biomass. Therefore, to produce 70 kg of human biomass, 70/0.1/0.1 = 70,000 kg of grain is required.

Question 4

The introduction of a large predatory fish into a lake will lead to declines in the populations of smaller fish; this decrease in the smaller fish will lead to an increase in the plankton on which they feed. This phenomenon is called

Accepted Answer

The introduction of a predatory fish into a lake causes a trophic cascade, which is the phenomenon whereby the removal or addition of a top predator in an ecosystem leads to changes in the abundance or behavior of other species, ultimately affecting the entire ecosystem. In this case, the introduction of the predatory fish leads to a decline in the population of smaller fish, which in turn leads to an increase in the plankton population as the smaller fish are no longer consuming them, resulting in a trophic cascade.

Question 5

Beavers affect communities by

Accepted Answer

Beavers have a significant impact on their communities by altering the patterns of vegetation, creating meadows and ponds through their dams, and affecting the availability of food sources for other animals by eating certain types of plants. Therefore, all of the given choices are correct.

Question 6

Which of the following statements about wolves in Yellowstone National Park is true?

Accepted Answer

The disappearance of wolves in Yellowstone led to an increase in elk populations, which over-browsed young aspen trees, causing their reduction. This is an indirect effect, as wolves are not the only predators of moose and elk.

Question 7

A termite mound alters the environment in such a way that it creates new habitats for a variety of organisms. In constructing these mounds, therefore, termites can be considered

Accepted Answer

Termites alter the physical environment by excavating soil and creating structures that hold moisture, which creates new habitats for other organisms. This makes them ecosystem engineers, as they alter and create habitats within the ecosystem.

Question 8

In which of the following communities would one expect to see greater energy flow into primary consumers than into primary producers?

Accepted Answer

The open ocean has less primary production due to low nutrient availability, so the energy flow is generally greater into primary consumers (zooplankton) than into primary producers (phytoplankton). In contrast, both forests and grasslands have high primary production, so energy flow would be expected to be greater into primary producers than primary consumers.

Question 9

Which of the following always has a "pyramidal" shape (i.e., decreasing values at higher trophic levels)?

Accepted Answer

Pyramids of energy always have a pyramidal shape because energy is lost as it flows through trophic levels due to inefficiencies in energy transfer and metabolic processes. As a result, there is less energy available at higher trophic levels, leading to a pyramidal shape in the energy pyramid. Pyramids of number and biomass do not always have a pyramidal shape as they can be inverted or columnar depending on the ecosystem being studied.

Question 10

In which of the following communities would one expect to see more biomass in primary consumers than in primary producers?

Accepted Answer

In open ocean ecosystems, the phytoplankton (primary producers) are often limited by nutrients and light, resulting in lower biomass. However, primary consumers such as zooplankton can still thrive and have higher biomass due to their ability to efficiently filter feed on the abundant phytoplankton. In contrast, in forest and grassland ecosystems, the primary producers (plants) typically have higher biomass than the primary consumers (herbivores).

Question 11

If gross primary productivity is 120 units per day, and the respiration rate is 30 units per day, net primary productivity is _______ units per day.

Accepted Answer

Net primary productivity (NPP) is the amount of energy that is left over after plants have undergone cellular respiration. NPP = Gross primary productivity - Respiration rate. 
Using the given values, NPP = 120 units/day – 30 units/day = 90 units/day. Therefore, the correct answer is C) 90.

Question 12

Suppose that the gamma diversity for a marshy habitat and the gamma diversity for a sandy habitat are comparable for a particular geographic region, but the alpha diversity for marshy habitats tends to be much greater than the alpha diversity for sandy habitats. We could conclude that

Accepted Answer

If the gamma diversity is comparable between the two habitat types, but the alpha diversity is much greater for marshy habitats, it suggests that there is less turnover in species composition among marshy habitats than among sandy habitats. This implies that beta diversity is lower in marshy habitats, as the species present are more consistent across sites.

Question 13

In most communities, which of the following is greater in tertiary consumers as compared to secondary consumers?

Accepted Answer

Tertiary consumers occupy a higher trophic level than secondary consumers and thus tend to have a greater body size. This is because they require more energy to sustain themselves and energy is lost at each trophic level, resulting in fewer organisms at higher levels. Reproductive rates and number of species tend to decrease at higher trophic levels, while total biomass may vary depending on the specific ecosystem.

Question 14

For most communities, species richness will _______ if fertilizer is added when productivity is low, and it will _______ if fertilizer is added when productivity is high.

Accepted Answer

The answer of For most communities, species richness will _______...

Question 15

Which of the following resulted from Robert Paine's removing the predator sea star from parts of the intertidal zone?

Accepted Answer

Paine's removal of the predator sea star from parts of the intertidal zone resulted in a decrease in species richness and an increase in the abundance of one species of mussel, Mytilus californianus.

Question 16

As productivity increases, species richness in a community

Accepted Answer

At first, as productivity increases, there is more energy and resources available to support a greater number of species. However, as productivity continues to increase, a few dominant species may outcompete and exclude other species, leading to a decrease in species richness. This pattern is known as the productivity-diversity relationship.

Question 17

Suppose you were going up the west coast of Australia and observed that there are many species of termites in any one community, and the species composition changed little between communities. You would conclude that for these termites,

Accepted Answer

The observation that there are many species of termites in any one community suggests that the alpha diversity is high. The fact that the species composition changes little between communities indicates that the beta diversity is low. Therefore, for these termites, the alpha diversity is high, and the beta diversity is low.

Question 18

Which of the following factors reduces the efficiency of energy transfer between trophic levels?

Accepted Answer

All of the above factors can reduce the efficiency of energy transfer between trophic levels. Lack of availability of some biomass means that not all of the primary producers are consumed by herbivores, resulting in less energy being available for the next trophic level. Heat loss is a natural consequence of energy transfer as organisms generate heat during metabolic processes, and this heat is lost to the environment. Indigestibility of some biomass means that some food may not be fully broken down or absorbed, resulting in less energy being available for the consuming organism and reduced efficiency of energy transfer.

Question 19

If secondary consumers are the highest trophic level in a community, how many trophic levels are in the community (not counting decomposers)?

Accepted Answer

Secondary consumers are the third trophic level, following primary producers (first level) and primary consumers (second level).

Question 20

A species that exerts an influence on a community that is much greater than its abundance would lead one to expect is called a(n)

Accepted Answer

A keystone species can have a large impact on the community structure and function, even if it is not very abundant. Removing a keystone species can cause significant changes in the community as a whole, whereas the loss of a less influential species may have little effect.

Quiz 57: Community Ecology