1. 46
The Global Ecosystem

2. Concept 46.1 Climate and Nutrients Affect Ecosystem Function
One aspect of ecosystem function:
Net primary productivity (NPP)—rate at which an ecosystem produces primary-producer biomass.
NPP can be estimated by instruments on satellites that measure wavelengths of light reflected from the Earth’s surface.

3. Concept 46.1 Climate and Nutrients Affect Ecosystem Function
NPP varies among ecosystem types, mostly due to variation in climate and nutrient availability.
Tropical forests, swamps, and marshlands are the most productive.
Cultivated land is less productive than many natural ecosystems.

4. Figure 46.1 NPP Varies among Ecosystem Types

5. Figure 46.2 Terrestrial NPP Corresponds to Climate

6. Concept 46.1 Climate and Nutrients Affect Ecosystem Function
Discuss why NPP (net primary productivity), usually measured as grams of primary-producer biomass produced per unit of area per year, is a measure of ecosystem function. 6

7. Concept 46.1 Climate and Nutrients Affect Ecosystem Function
NPP (net primary productivity), usually measured as grams of primary-producer biomass produced per unit of area per year, is a measure of ecosystem function because
a. NPP measures the rate of exchange of materials (especially carbon) between biotic and abiotic components of ecosystems.
b. NPP measures the net rate with which solar energy is captured by an ecosystem’s primary producers.
c. Both a and b
d. None of the above
e. I don’t understand the question.
Answer: c
INSTRUCTOR NOTE:
See page 893 of the textbook.
[NOTE TO THE INSTRUCTOR: It can be useful to include an “I don’t know” or “I don’t understand the question” choice with clickers, because it can help you discover how many students really haven’t understood the concept at all. Use of this option may depend on whether you assign participation-only points or performance points (or some combination) to clicker questions in your course. If you only assign participation points, it may be useful to leave the “I don't know” choice in the question, as it gives students a penalty-free way of indicating that more time may be needed on this concept.] 7

8. Figure 46.3 Terrestrial NPP Varies with Temperature and Precipitation

9. Figure 46.3 Terrestrial NPP Varies with Temperature and Precipitation (Part 1)

10. Figure 46.3 Terrestrial NPP Varies with Temperature and Precipitation (Part 2)

11. Figure 46.4 Marine NPP Is Highest around Coastlines

12. Concept 46.1 Climate and Nutrients Affect Ecosystem Function
Compare the following maps of terrestrial and marine NPP.
With a partner or group, discuss:
What does the terrestrial pattern suggest determines terrestrial NPP?
What does the marine pattern suggest determines marine NPP?
INSTRUCTOR NOTES:
For terrestrial NPP, students should be able to come up with temperature because of the latitudinal gradient. They also might come up with precipitation if they notice the desert belt at 30 degrees N and S.
For marine NPP, students should be able to come up with near-shore versus open-ocean, and connect that with upwelling and runoff.
See Figures 46.2 and 46.4 of the textbook. 12

13. Concept 46.1 Climate and Nutrients Affect Ecosystem Function
Compare the following maps of terrestrial and marine NPP.
The patterns for terrestrial NPP suggest it is linked to
a. temperature.
b. precipitation.
c. latitude.
d. All of the above
e. None of the above
Answer: d
INSTRUCTOR NOTES:
For terrestrial NPP, students should be able to come up with temperature because of the latitudinal gradient. They also might come up with precipitation if they notice the desert belt at 30 degrees N and S.
See Figures 46.2 and 46.4 of the textbook. 13

14. Concept 46.1 Climate and Nutrients Affect Ecosystem Function
Compare the following maps of terrestrial and marine NPP.
The patterns for marine NPP suggest it is limited by
a. latitude.
b. distance from shore.
c. upwelling.
d. runoff.
e. b, c, and d
Answer: e
INSTRUCTOR NOTES:
For marine NPP, students should be able to come up with near-shore versus open-ocean, and connect that with upwelling and runoff.
See Figures 46.2 and 46.4 of the textbook. 14

15. Concept 46.1 Climate and Nutrients Affect Ecosystem Function
As winds push water across the ocean surface, water rises up from underneath the displaced water to replace it. This is called “upwelling.” Upwelling occurs in the open ocean and especially along coastlines. The water that rises up from deeper levels of the ocean is colder and rich in nutrients. These nutrients fertilize the surface waters and result in higher biological productivity. Algal blooms provide more food for fish, resulting in growth in fish populations when and where upwelling is strong. 15

16. Concept 46.1 Climate and Nutrients Affect Ecosystem Function
Fisheries are directly impacted by the strength of upwelling. Without nutrients from the upwelling, there are few phytoplankton, and with few phytoplankton, little food for fish.
Off California, upwelling of cold water has become less common since What do you predict will result if less upwelling is indeed a long-term trend?
INSTRUCTOR NOTES:
Winds blowing across the ocean surface displace water. Water then rises up from beneath the surface to replace the displaced water. This process is known as “upwelling.” Upwelling occurs in the open ocean and along coastlines. Water that rises to the surface as a result of upwelling is typically colder than bottom water and is rich in nutrients. These nutrients “fertilize” surface waters, thus these surface waters often have high biological productivity. Therefore, good fishing grounds typically are found where upwelling is common. (The reverse process, called “downwelling,” occurs when wind causes surface water to build up along a coastline and the surface water eventually sinks toward the bottom). 16

17. Concept 46.1 Climate and Nutrients Affect Ecosystem Function
Fisheries are directly impacted by the strength of upwelling. Without nutrients from the upwelling, there are few phytoplankton, and with few phytoplankton, little food for fish.
Off California, upwelling of cold water has become less common since Which of the following scenarios might you predict if less upwelling is indeed a long-term trend?
a. Fisheries will benefit.
b. Fish populations will decline as the strength of upwelling decreases.
c. More nutrients will likely rise to the surface.
d. Phytoplankton growth will decrease as upwelling weakens.
e. Both b and d
Answer: e
(Water that rises to the surface as a result of upwelling is typically colder than bottom water and is rich in nutrients. These nutrients “fertilize” surface waters, thus these surface waters often have high biological productivity. Therefore, good fishing grounds typically are found where upwelling is common. If trade winds weaken as a result of climate change upwelling strength will decline, and fisheries will be adversely affected—less algae, less fish.) 17

18. Figure 46.5 Chemical Elements Cycle among Compartments of the Biosphere

19. Figure 54.20 Review: Generalized scheme for biogeochemical cycles

20. Figure 46.6 The Global Water Cycle

21. Figure 46.7 The Global Nitrogen Cycle

22. Figure 46.8 Where Does the Extra Nitrogen Come From?

23. Figure 46.8 Where Does the Extra Nitrogen Come From? (Part 1)

24. Figure 46.8 Where Does the Extra Nitrogen Come From? (Part 2)

25. Figure 46.9 High Nutrient Input Creates Dead Zones

26. Figure 46.9 High Nutrient Input Creates Dead Zones

27. Figure 46.10 The Global Carbon Cycle

28. Figure 46.11 Earth’s Radiation Balance

29. Figure 46.12 Atmospheric Greenhouse Gas Concentrations Are Increasing

30. Figure 46.12 Atmospheric Greenhouse Gas Concentrations Are Increasing (Part 1)

31. Figure 46.12 Atmospheric Greenhouse Gas Concentrations Are Increasing (Part 2)

32. Figure 46.13 Global Temperatures Are Increasing

33. Figure 46.14 Global Precipitation Patterns Have Changed

34. Apply the Concept, Ch. 46, p. 905

35. Figure 46.15 Climate Change Affects Life Histories

36. Plant photosynthesis (gross primary productivity)
Concept Biological, Geological, and Chemical Processes Move Materials through Ecosystems
Discuss which of the following processes results in a net flux that removes carbon from the atmospheric pool of carbon:
Plant respiration
Plant photosynthesis (gross primary productivity)
Burning of fossil fuels 36

37. b. Plant photosynthesis (gross primary productivity)
Concept Biological, Geological, and Chemical Processes Move Materials through Ecosystems
Which of the following processes results in a net flux that removes carbon from the atmospheric pool of carbon?
a. Plant respiration
b. Plant photosynthesis (gross primary productivity)
c. Burning of fossil fuels
d. All of the above
e. None of the above
Answer: b
(Only photosynthesis removes carbon dioxide from the atmospheric pool of carbon. Plant respiration and burning of fossil fuels add carbon dioxide to the atmospheric pool [i.e., cause a net flux adding to the atmospheric carbon pool].) 37

38. Concept 46.3 Certain Biogeochemical Cycles Are Especially Critical for Ecosystems
The Northern Hemisphere of Earth has a greater land surface than that of the Southern Hemisphere, and more of Earth’s plants (especially forests) occur in the Northern Hemisphere.
Discuss the pattern of seasonal variation in CO2 levels seen in this Mauna Loa, Hawaii graph, and discuss how plant photosynthesis and respiration can explain this predictable seasonal pattern.
INSTRUCTOR NOTES:
Photosynthesis and respiration affect CO2 seasonality. It is important to point out to students that the x-axis labels indicate the start of the year (January).
It is also important to point out that marine photosynthesis and respiration do not contribute as immediately to atmospheric CO2 as does terrestrial photosynthesis/respiration—marine CO2 is dissolved in water and doesn’t contribute to the atmospheric pool except through outgassing—so marine exchange lags behind terrestrial exchange.
GRAPHIC SOURCE:
NOAA 38

39. Concept 46.3 Certain Biogeochemical Cycles Are Especially Critical for Ecosystems
Which of the following statements could explain the seasonal variation in CO2 levels in the atmosphere?
a. Atmospheric CO2 levels increase during the Northern Hemisphere summer because plants respire more at this warmer time.
b. Atmospheric CO2 levels decrease during the Northern Hemisphere winter because plants photosynthesize more at this colder time.
c. The greater total terrestrial biomass in the Northern Hemisphere compared with the Southern Hemisphere drives these seasonal CO2 patterns.
d. All of the above
e. None of the above
Answer: c
(Answers a and b are incorrect because Northern Hemisphere plants photosynthesize most in summer, and respire most in winter, so the reverse is true: atmospheric CO2 levels decrease in summer and increase in winter as a result of this seasonal shift from photosynthesis to respiration. It has been said that the northern forests thus act like the “lungs of the Earth.” CO2 undergoes a regular seasonal cycle, reflecting the seasonal growth and decay of land plants in the Northern Hemisphere.) 39

40. c. I don’t understand the question.
Concept Certain Biogeochemical Cycles Are Especially Critical for Ecosystems
Do the seasonal shifts in CO2 levels that result from seasonal differences in photosynthetic rates predominating in the Northern Hemisphere explain the trend for annual CO2 levels (increasing over time, in this graph from 2006 to 2011)?
a. Yes
b. No
c. I don’t understand the question.
Answer: b
INSTRUCTOR NOTES:
CO2 undergoes a regular seasonal cycle, reflecting the seasonal growth and decay of land plants in the Northern Hemisphere.
Normally balanced by natural processes (sources and sinks), carbon dioxide levels in the atmosphere would have changed little if human activities had not added an amount every year.
However, the overall trend for rising CO2 is driven by the burning of fossil-fuels, causing a net flux of carbon being added to the atmospheric pool of carbon and creating a warming trend as a result of the greenhouse effect (more gases equal more heat trapped).
How do we know that the warming trend has an anthropogenic cause? Scientists have several lines of evidence to go by, including atmospheric carbon having a different isotopic fingerprint when it is derived from fossil fuel versus natural sources (e.g., volcanoes).
[NOTE TO THE INSTRUCTOR: It can be useful to include an “I don’t know” or “I don’t understand the question” choice with clickers, because it can help you discover how many students really haven’t understood the concept at all. Use of this option may depend on whether you assign participation-only points or performance points (or some combination) to clicker questions in your course. If you only assign participation points, it may be useful to leave the “I don't know” choice in the question, as it gives students a penalty-free way of indicating that more time may be needed on this concept.]
GRAPHIC SOURCE:
NOAA 40

41. Concept 46.4 Biogeochemical Cycles Affect Global Climate
Discuss the validity of the following statements regarding the greenhouse effect:
Prior to the industrial revolution (starting around 1880), Earth had no carbon dioxide in its atmosphere.
The composition and thickness of a planet’s atmosphere affect its surface temperatures.
Air temperature is the only factor influenced by the changing composition of Earth’s atmosphere. 41

42. Concept 46.4 Biogeochemical Cycles Affect Global Climate
Which of the following statements are true regarding the greenhouse effect?
a. Prior to the industrial revolution (starting around 1880), Earth had no carbon dioxide in its atmosphere.
b. The composition and thickness of a planet’s atmosphere affect its surface temperatures.
c. Air temperature is the only factor influenced by the changing composition of Earth’s atmosphere.
d. All of the above
e. None of the above
Answer: b
(Mars’s thin atmosphere means it’s a very cold planet, whereas Venus with a thick atmosphere, is very hot. Refer to page 903 of the textbook.)
Answer a is not true because carbon dioxide has existed in the atmosphere for millenia, it’s just the proportion of gases in it that has changed over time, most recently with a large influx of extra carbon dioxide and other anthropogenically derived green house gases.
Answer c is not true because precipitation and storm intensity are also expected to change, not just air temperature. Sea surface temperature, changed ocean currents, and changes in acidity and salinity are some of the changes predicted for the marine environment. 42

43. Concept 46.5 Rapid Climate Change Affects Species and Communities
Corals, which secrete calcareous skeletons that over time form the large physical structure of reef communities, rely on a mutualism with a photosynthetic alga, and without this mutualism they cannot grow. Reefs have the highest biodiversity within marine ecosystems, and are important for supporting fisheries. Reef organisms have evolved over hundreds of millions of years to cope with recurring disturbance, damage, and destruction, followed by recovery or regrowth. However, recent climate change appears to be occurring at rates faster than reefs can tolerate.
Reefs are temperature-sensitive and a rise in temperature as small as 1 degree Celsius can result in “bleaching,” as algae react to the warmer water by producing oxygen compounds that are toxic to the coral, resulting in the coral ejecting their algal support system, leaving the reefs starved of nutrients and deathly white. 43

44. Concept 46.5 Rapid Climate Change Affects Species and Communities
If climate change is predicted to raise ocean temperatures by 1–3°C by the year 2050, what impact do you expect this might have on coral reef ecosystems?
Discuss. 44

45. Concept 46.5 Rapid Climate Change Affects Species and Communities
If climate change is predicted to raise ocean temperatures by 1–3°C by the year 2050, which of the following outcomes might you expect?
a. More bleaching events will occur.
b. Corals will be less able to grow.
c. Coral reefs may almost entirely disappear by 2050.
d. Fisheries will decline.
e. All of the above
Answer: e
INSTRUCTOR NOTES:
You might also point out to students that temperature is not the only climate change impact on coral reefs. Increased carbon dioxide absorption by marine waters also results in acidification of the water, which results in difficulty for marine organisms that rely on a calcareous shell or external skeleton. Experimental work has shown that on average, corals decrease their calcification rates by 30% with doubled atmospheric CO2 concentrations (Kleypas, 2006).
Extension question: The dying of coral reefs has the potential to further exacerbate and perhaps accelerate the rate of climate change. Can you think of a reason why?
Answer: Corals and their mutualistic algae convert CO2 from the atmosphere into the calcaerous shells that form the reef. When the temperature is too high for this symbiosis to function, there is no conversion of CO2 to calcium in the hard external skeleton of the coral, reducing the amount of CO2 that is “fixed” in this way.
“The future is horrific,” says Charlie Veron, an Australian marine biologist who is widely regarded as the world’s foremost expert on coral reefs. “There is no hope of reefs surviving to even mid-century in any form that we now recognize. If, and when, they go, they will take with them about one-third of the world's marine biodiversity. Then there is a domino effect, as reefs fail so will other ecosystems. This is the path of a mass extinction event, when most life, especially tropical marine life, goes extinct.”
Alex Rogers, a coral expert with the Zoological Society of London, talks of an “absolute guarantee of their annihilation.”
And David Obura, another coral expert and head of CORDIO East Africa, a research group in Kenya, is equally pessimistic: “I don’t think reefs have much of a chance. And what’s happening to reefs is a parable of what is going to happen to everything else. These are desperate words, stripped of the usual scientific caveats and expressions of uncertainty, and they are a measure of the enormity of what's happening to our reefs.”
If climate change is not stopped, coral bleaching is set to steadily increase in frequency and intensity all over the world until it occurs annually by 2030—2070.This would devastate coral reefs globally to such an extent that they could be eliminated from most areas of the world by Current estimates suggest that reefs could take hundreds of years to recover. The loss of these fragile ecosystems would cost billions of dollars in lost revenue from tourism and fishing industries, as well as damage to coastal regions that are currently protected by the coral reefs that line most tropical coastlines.
SOURCES: 45

46. c. I don’t understand this question.
Concept Ecological Challenges Can Be Addressed through Science and International Cooperation
Do you think that indefinite economic growth is possible given the ecological limits of our planet?
a. Yes
b. No
c. I don’t understand this question.
Answer: b
(We cannot continue indefinite growth on a planet with finite resources.)
INSTRUCTOR NOTES:
This question is intended to spur class discussion, rather than for use as a clicker question, although you may wish to poll the class to see if they understand the concept.
Extension question:
Continual economic growth—ever-increasing production and consumption of goods and services— is the goal and drives policies in nearly every nation on Earth. Explain the ecological dilemma that we face living on a planet with finite resources to create those goods and services.
Hints:
Think about our biogeochemical cycles, which are processes that continually “recycle” Earth’s finite resources.
Think about the links between economic growth, human population growth, and per capita as well as total human consumption of resources.
Extension exercises:
Ask students to develop a list of human actions that would help to reduce production of greenhouse gases (human population size may be one topic to discuss in relation to this).
Consolidate class list of actions, and then ask students to prioritize (in groups) the relative importance of different actions and ways of implementing them.
Ask students to discuss why international cooperation is mentioned in this section of the text.
[NOTE TO THE INSTRUCTOR: It can be useful to include an “I don’t know” or “I don’t understand the question” choice with clickers, because it can help you discover how many students really haven’t understood the concept at all. Use of this option may depend on whether you assign participation-only points or performance points (or some combination) to clicker questions in your course. If you only assign participation points, it may be useful to leave the “I don't know” choice in the question, as it gives students a penalty-free way of indicating that more time may be needed on this concept.] 46