Question 1

Owls eat rats, mice, shrews, and small birds. Assume that, over a period of time, an owl consumes 5,000 J of animal material. The owl loses 2,300 J in feces and owl pellets and uses 2,500 J for cellular respiration. What is the production efficiency of this owl?

Accepted Answer

To find the production efficiency, we need to subtract the energy lost in feces and pellets and energy used in cellular respiration from the energy consumed. 
Energy consumed = 5,000 J 
Energy lost in feces and pellets = 2,300 J 
Energy used in cellular respiration = 2,500 J 
Energy available for growth and reproduction = Energy consumed - energy lost in feces and pellets and energy used in cellular respiration 
= 5,000 - 2,300 - 2,500 J 
= 1,200 J 
Production efficiency = (Energy available for growth and reproduction / Energy consumed) x 100% 
= (1,200 / 5,000) x 100% 
= 24% 
Therefore, the production efficiency of this owl is 7.4%, which is closest to option B.

Question 2

How does inefficient transfer of energy among trophic levels result in the typically high endangerment status of many top-level predators?

Accepted Answer

Top-level predators typically have small populations due to their position at the top of the trophic pyramid. Inefficient transfer of energy among trophic levels means that there is less energy available at the top of the food chain, which makes it harder for top-level predators to find enough food to sustain their populations. This, in turn, makes them more susceptible to endangerment.

Question 3

Suppose you are studying the nitrogen cycling between vegetation, sediments, and water in a pond ecosystem over the course of a month. While you are collecting data, a flock of 100 Canada geese lands and spends the night during a fall migration. What could you do to eliminate error in your study as a result of this event?

Accepted Answer

Option C is the best choice as it takes into account the impact of the Canada geese on the nitrogen cycling in the ecosystem. By calculating the amount of nitrogen consumed and eliminated by the geese during their overnight stay and adding/subtracting this value to the ecosystem's nitrogen budget, it is possible to account for any changes in the nitrogen balance. Options A and B do not consider both nitrogen consumption and elimination and may lead to inaccurate results. Option D is not a practical or feasible solution for eliminating the error in the study.

Question 4

What advantage would there be for an ecosystem ecologist to measure net ecosystem production (NEP) instead of net primary production (NPP)?

Accepted Answer

NEP accounts for the total carbon balance of an ecosystem, including respiration by all organisms, providing insight into carbon storage and overall ecosystem carbon dynamics.

Question 5

For most terrestrial ecosystems, pyramids composed of species abundances, biomass, and energy are similar in that they have a broad base and a narrow top. The primary reason for this pattern is that ________.

Accepted Answer

Pyramids of species abundances, biomass, and energy are similar because at each step, energy is lost from the system. This occurs because energy is transformed into biomass and work, and some of it is lost as heat during cellular respiration. This loss of energy limits the amount of biomass that can be supported at higher trophic levels, resulting in the characteristic pyramid shape.

Question 6

Many of the organisms in the ocean are nutrient-limited. If you wanted to investigate this phenomenon, one reasonable approach would be to ________.

Accepted Answer

Experimentally enriching some areas of the ocean and comparing their productivity to that of untreated areas would allow for a direct investigation into the role of nutrient limitation in ocean productivity. This would provide concrete evidence on whether or not many organisms are nutrient-limited in the ocean. A, C, and D are also possible approaches, but they are not as direct or focused on nutrient limitation as option B.

Question 7

Use the following figure to answer the question.

After looking at the figure, what can be said about productivity in this ecosystem?

Accepted Answer

The answer of Use the following figure to answer the...

Question 8

Which statement best describes what ultimately happens to the chemical energy that is consumed but not used to produce new biomass in the process of energy transfer between trophic levels in an ecosystem?

Accepted Answer

Energy not used in biomass production is eventually lost as heat due to cellular respiration, aligning with the second law of thermodynamics which states that energy transformations are not 100% efficient, leading to the dissipation of energy as heat.

Question 9

Why does a vegetarian leave a smaller ecological footprint than an omnivore?

Accepted Answer

The answer of Why does a vegetarian leave a smaller...

Question 10

You own 300 acres of patchy temperate forest mixed with grassy meadows. Which one of the following actions would increase the net primary productivity of the area the most?

Accepted Answer

Planting 500 new trees would increase the net primary productivity of the area the most because trees are primary producers, and they would increase the amount of photosynthesis occurring in the area. Adding fertilizer might increase productivity temporarily, but it could also have negative long-term effects on the ecosystem. Introducing rabbits could lead to overgrazing and a decrease in plant productivity, while relocating deer could disrupt the balance of the ecosystem and potentially reduce productivity.

Question 11

Which one of the following correctly ranks these organisms in order from lowest to highest percent in production efficiency?

Accepted Answer

The answer of Which one of the following correctly ranks...

Question 12

How is net ecosystem production (NEP) typically estimated in ecosystems?

Accepted Answer

Net ecosystem production is typically estimated by measuring gas exchange from vegetation as well as estimates of respiration by all other organisms. This involves measuring the amount of carbon dioxide taken up during photosynthesis and the amount of carbon dioxide released during respiration. The difference between these two values gives an estimate of the net ecosystem production.

Question 13

During a year, plants never use 100% of the incoming solar radiation for photosynthesis. What is a reasonable explanation for this?

Accepted Answer

Plants do not intercept all incoming light, as some light will strike water, bare soil, or rock.

Question 14

Which trophic level is most vulnerable to extinction?

Accepted Answer

Tertiary consumers are at the top of the food chain and rely on all lower levels for energy, making them more vulnerable to changes and disruptions in the ecosystem.

Question 15

Which of the following ecosystems would likely have the largest net primary productivity per hectare and why?

Accepted Answer

Grasslands have a high net primary productivity per hectare due to rapid growth of plants, low amount of standing crop biomass due to consumption by herbivores, and rapid decomposition. The other ecosystems listed have lower net primary productivity due to factors such as limited sunlight or low nutrient availability.

Question 16

Consider the food chain of grass → grasshopper → mouse → snake → hawk. About how much of the chemical energy fixed by photosynthesis of the grass (100 percent) is available to the hawk?

Accepted Answer

The transfer of energy between trophic levels in a food chain is not very efficient, with much energy lost to waste heat, respiration, and other metabolic processes. As a result, only about 10% of the energy in one trophic level is typically available to the next level. This is known as the 10% rule. Hence, the energy available to the snake from the mouse would be 0.1%, energy available to the mouse from the grasshopper would be 1%, and energy available to the grasshopper from the grass would be 10%. Therefore, the energy available to the hawk from the grass is only about 0.01%.

Question 17

If you applied a fungicide to a cornfield, what would you expect to happen to the rate of decomposition and net ecosystem production (NEP)?

Accepted Answer

Fungicides target fungi, many of which are decomposers that break down organic matter. By reducing fungal populations, the decomposition rate would decrease. This could lead to more organic material being retained within the ecosystem, potentially increasing the net ecosystem production (NEP) as more carbon is stored in biomass rather than being released through decomposition.

Question 18

Which of the following is primarily responsible for limiting the number of trophic levels in most ecosystems?

Accepted Answer

Only about 10% of energy is transferred from one trophic level to the next, leading to a decrease in available energy and a limited number of trophic levels. This phenomenon is known as ecological efficiency, and it ultimately limits the number of trophic levels in most ecosystems.

Question 19

Which of the following is an accurate statement regarding mineral nutrients in soils and their implication for primary productivity?

Accepted Answer

Phosphorous is often unavailable to producers due to leaching, which can limit primary productivity. Globally, nitrogen is actually the most limiting nutrient to primary productivity, not phosphorous (option A). Adding a nonlimiting nutrient may not necessarily stimulate primary productivity, as the availability of other nutrients may still be limiting (option B). The statement in option D is not accurate, as soil productivity depends on a variety of factors beyond pH.

Question 20

Why is it that satellites, using wavelength reflectance technology, detect variable levels of productivity across Earth's oceans, rather than an increase toward the equator?

Accepted Answer

NPP (net primary productivity) can differ in Earth's open oceans due to various factors such as variability in depth, the presence of coral reefs or ocean currents. Therefore, satellites using wavelength reflectance technology detect variable levels of productivity across Earth's oceans rather than an increase toward the equator. Temperature and light intensity also play a role, but these factors alone do not account for the variability in NPP. The fourth choice is incorrect because satellites do not measure water vapor emission by transpiring producers.

Quiz 55: Ecosystems and Restoration Ecology