Question 1

Which of the following best describes the difference between a population and a community in ecological terms?

Accepted Answer

A population is a group of interacting individuals of a particular species, while a community is an assemblage of all populations of organisms living close enough together for potential interaction.

Question 2

Eastern bluebird populations declined after the introduction of non-native house sparrows and European starlings, all of which nest in tree cavities. Which interspecific interaction best explains this decline?

Accepted Answer

Interspecific competition, because the species compete for the same limited nesting resource.

Question 3

Which of the following is an example of mutualism?

Accepted Answer

Coral and photosynthetic dinoflagellates exchanging nutrients and shelter.

Question 4

Why is predation considered a powerful factor in the adaptive evolution of prey species?

Accepted Answer

Predation exerts selective pressure, favoring prey with adaptations such as camouflage, mechanical, or chemical defenses.

Question 5

A plant produces a bitter-tasting chemical that deters herbivores. In evolutionary terms, why do humans have taste receptors for bitter chemicals?

Accepted Answer

To avoid consuming potentially toxic substances produced by plants as a defense against herbivory.

Question 6

Which of the following best describes the role of decomposers in an ecosystem?

Accepted Answer

They secrete enzymes that digest organic materials and convert them into inorganic forms, recycling nutrients.

Question 7

If all decomposers in an ecosystem suddenly stopped functioning, what would be the most immediate consequence for the carbon cycle?

Accepted Answer

Organic matter would accumulate, and the recycling of carbon to the atmosphere would be greatly reduced.

Question 8

Which of the following statements about food webs is correct?

Accepted Answer

A food web is a network of interconnecting food chains, and some consumers may occupy multiple trophic levels.

Question 9

Which of the following best explains why tropical rain forests contribute a much higher percentage to Earth's net primary production than deserts, despite covering similar surface areas?

Accepted Answer

Rain forests have higher rates of photosynthesis due to abundant sunlight, water, and nutrients.

Question 10

A pyramid of production shows that only about 10% of the energy at each trophic level is available to the next. If a field of corn produces $$10,000$$ kcal of energy, how much energy would be available to secondary consumers?

Accepted Answer

$$100$$ kcal

Question 11

Which of the following is a key difference between the phosphorus cycle and the carbon cycle?

Accepted Answer

The phosphorus cycle is primarily local because it depends on the weathering of rocks, while the carbon cycle is global due to its atmospheric reservoir.

Question 12

Which of the following best defines a keystone species?

Accepted Answer

A species whose impact on its community is larger than its biomass or abundance indicates, maintaining community structure.

Question 13

Which of the following events would most likely initiate primary succession?

Accepted Answer

A volcanic eruption that creates new rock surfaces with no soil.

Question 14

Why does demand for meat tend to drive up the prices of grains, fruits, and vegetables?

Accepted Answer

Because meat production requires large amounts of grain for animal feed, reducing the supply available for direct human consumption.

Question 15

Which of the following best describes the process of nitrogen fixation?

Accepted Answer

Conversion of nitrogen gas ($$N_2) to $$compounds usable by plants, such as ammonium ($$NH_4$$^+$$) and nitrate (NO_3$^-$$), by bacteria.

Question 16

A lake receives excessive fertilizer runoff, leading to rapid eutrophication. What is the most likely sequence of events that will occur?

Accepted Answer

Increased nutrients → algal blooms → oxygen depletion → loss of fish species.

Question 17

Which of the following is NOT an ecosystem service provided by natural ecosystems?

Accepted Answer

Production of fossil fuels.

Question 18

Which of the following best explains why invasive species can devastate native communities?

Accepted Answer

They establish themselves at the expense of native species, often lacking natural predators or controls in the new environment.

Question 19

Which of the following statements about energy flow and chemical cycling in ecosystems is correct?

Accepted Answer

Energy flows through ecosystems and is eventually lost as heat, while chemicals are recycled within ecosystems.

Question 20

Which of the following best describes the concept of sustainability in ecosystem management?

Accepted Answer

Developing, managing, and conserving resources to meet current needs without compromising future generations' ability to meet theirs.

Communities and Ecosystems: Structure, Dynamics, and Human Impact

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