1. Communities and Ecosystems
Chapter 37
Communities and Ecosystems

2. Introduction Natural ecosystems are valuable because they
Natural ecosystems are valuable because they
provide natural resources,
support outdoor recreation, and
provide natural services including
buffering against hurricane damage,
recycling nutrients,
preventing erosion, and
pollinating crops.
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3. Community Structure and Dynamics Ecosystem Structure and Dynamics
Figure 37.0_1
Chapter 37: Big Ideas C h e m i c a l y n g
Energy flow
Figure 37.0_1 Chapter 37: Big Ideas
Community Structure
and Dynamics
Ecosystem Structure
and Dynamics 3

4. Figure 37.0_2
Figure 37.0_2 Only about a quarter of Earth’s land surfaces remain untouched by human alterations. 4

5. COMMUNITY STRUCTURE AND DYNAMICS
COMMUNITY STRUCTURE AND DYNAMICS
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6. 37.1 A community includes all the organisms inhabiting a particular area
Community ecology is concerned with factors that
influence species composition and distribution of communities and
affect community stability.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
2. In human society, a community might be roughly equivalent to a local population, perhaps all the people living in a town or city. The definition of a biological community is more inclusive, comprising all of the populations of organisms living close enough together for potential interaction.
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7. 37.1 A community includes all the organisms inhabiting a particular area
A biological community is
an assemblage of all the populations of organisms living close enough together for potential interaction and
described by its species composition.
The boundaries of a community vary with the research question to be investigated. For example, the boundaries of a community could be defined as
a pond or
the intestinal microbes of a pond organism.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
2. In human society, a community might be roughly equivalent to a local population, perhaps all the people living in a town or city. The definition of a biological community is more inclusive, comprising all of the populations of organisms living close enough together for potential interaction.
© 2012 Pearson Education, Inc. 7

8. 37.2 Interspecific interactions are fundamental to community structure
Interspecific interactions
are relationships with individuals of other species in the community,
greatly affect population structure and dynamics, and
can be categorized according to their effect on the interacting populations.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
2. Examples of interspecific competition are as close as the nearest lawn. Although students may be more likely to think of animal examples, the various grasses and weeds in a lawn reveal different strategies in their competition for sunlight, moisture, and soil.
3. If your class includes students with business interests, they may enjoy the following analogy. To better understand competition, students might think about fast-food restaurants in your region. Challenge your students to identify the strategies employed by these restaurants to compete with each other. As each restaurant makes changes, does the other restaurant respond? Restaurants changing strategies in response to each other is analogous to coevolution.
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9. 37.2 Interspecific interactions are fundamental to community structure
Interspecific competition occurs when populations of two different species compete for the same limited resource.
In mutualism, both populations benefit.
In predation, one species (the predator) kills and eats another (the prey).
In herbivory, an animal consumes plant parts or algae.
In parasitism, the host plants or animals are victimized by parasites or pathogens.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
2. Examples of interspecific competition are as close as the nearest lawn. Although students may be more likely to think of animal examples, the various grasses and weeds in a lawn reveal different strategies in their competition for sunlight, moisture, and soil.
3. If your class includes students with business interests, they may enjoy the following analogy. To better understand competition, students might think about fast-food restaurants in your region. Challenge your students to identify the strategies employed by these restaurants to compete with each other. As each restaurant makes changes, does the other restaurant respond? Restaurants changing strategies in response to each other is analogous to coevolution.
© 2012 Pearson Education, Inc. 9

10. Table 37.2
Table 37.2 Interspecific Interactions 10

11. 37.3 Competition may occur when a shared resource is limited
An ecological niche is the sum of an organism’s use of the biotic and abiotic resources in its environment.
Interspecific competition occurs when the niches of two populations overlap.
Competition lowers the carrying capacity of competing populations because the resources used by one population are not available to the other population.
Student Misconceptions and Concerns
1. For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
2. The concept of an ecological niche can be confusing. Ecologist Eugene Odum has suggested that an ecological niche is like an organism’s habitat (address) and its occupation combined.
Teaching Tips
1. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
2. If your class includes students with business interests, they may enjoy the following analogy. To better understand competition, students might think about fast-food restaurants in your region. Challenge your students to identify the strategies employed by these restaurants to compete with each other. As each restaurant makes changes, does the other restaurant respond? Restaurants changing strategies in response to each other is analogous to coevolution.
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12. Figure 37.3A
Figure 37.3A A Virginia’s warbler (Vermivora virginiae) 12

13. Figure 37.3B
Figure 37.3B An orange-crowned warbler (Vermivora celata) 13

14. 37.4 Mutualism benefits both partners
Reef-building corals and photosynthetic dinoflagellates illustrate the win/win nature of mutualism. Photosynthetic dinoflagellates
gain shelter in the cells of each coral polyp,
produce sugars used by the polyps, and
provide at least half of the energy used by the coral animals.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. Students who are business-oriented may also enjoy this analogy. Many corporate leaders describe the best business deals as mutualistic, fostering a win-win relationship. For example, perhaps a new company creates a marketable product from another company’s wastes.
2. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
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15. Figure 37.4
Figure 37.4 Coral polyps 15

16. 37.5 EVOLUTION CONNECTION: Predation leads to diverse adaptations in prey species
Predation benefits the predator but kills the prey.
Prey adapt using protective strategies that include
camouflage,
mechanical defenses, and
chemical defenses.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. Rattlesnakes are a good example of a highly specialized predator. Since they are unable to move fast enough to catch their prey, rattlesnakes typically ambush them, a process facilitated by their camouflaged bodies. Rattlesnakes often feed during the cooler parts of the day, using heat-detecting facial pits to identify prey before injecting them with fast-acting venom. The prey is immediately released (perhaps to avoid damage to the snake from struggling prey), but is disabled by the venom within seconds. The rattlesnake then uses a variety of senses to track the prey the short distance to where it has collapsed.
2. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
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17. Figure 37.5A
Figure 37.5A Camouflage: a gray tree frog on bark 17

18. Figure 37.5B
Figure 37.5B Chemical defenses: the monarch butterfly 18

19. 37.6 EVOLUTION CONNECTION: Herbivory leads to diverse adaptations in plants
Herbivores and plants undergo coevolution,
a series of reciprocal evolutionary adaptations in two species,
in which change in one species acts as a new selective force on another.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. If your class includes students with business interests, they may enjoy the following analogy. To better understand competition, students might think about fast-food restaurants in your region. Challenge your students to identify the strategies employed by these restaurants to compete with each other. As each restaurant makes changes, does the other restaurant respond? Restaurants changing strategies in response to each other is analogous to coevolution.
2. Coevolution is illustrated by organisms that exhibit reciprocal evolutionary adaptations. Challenge students to explain how rewarding a pollinator with nectar has benefited some plants. Why would plants that have adaptations for only certain pollinators have an advantage? In many cases, pollinators that are restricted to certain species are more likely to transport pollen between members of that species instead of wasting pollen by taking it to other species.
3. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
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20. 37.6 EVOLUTION CONNECTION: Herbivory leads to diverse adaptations in plants
A plant whose body parts have been eaten by an animal must expend energy to replace the loss.
Thus, numerous defenses against herbivores have evolved in plants.
Plant defenses against herbivores include
spines and thorns and
chemical toxins.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. If your class includes students with business interests, they may enjoy the following analogy. To better understand competition, students might think about fast-food restaurants in your region. Challenge your students to identify the strategies employed by these restaurants to compete with each other. As each restaurant makes changes, does the other restaurant respond? Restaurants changing strategies in response to each other is analogous to coevolution.
2. Coevolution is illustrated by organisms that exhibit reciprocal evolutionary adaptations. Challenge students to explain how rewarding a pollinator with nectar has benefited some plants. Why would plants that have adaptations for only certain pollinators have an advantage? In many cases, pollinators that are restricted to certain species are more likely to transport pollen between members of that species instead of wasting pollen by taking it to other species.
3. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
© 2012 Pearson Education, Inc. 20

21. Eggs Sugar deposits Figure 37.6
Figure 37.6 Coevolution: Heliconius and the passionflower vine (Passiflora) 21

22. 37.7 Parasites and pathogens can affect community composition
A parasite lives on or in a host from which it obtains nourishment.
Internal parasites include nematodes and tapeworms.
External parasites include mosquitoes, ticks, and aphids.
Pathogens are disease-causing microscopic parasites that include
bacteria,
viruses,
fungi, or
protists.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. Pathogens are probably what most people refer to as germs. Students might believe that this general term refers to some specific type of organism.
2. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
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23. Figure 37.7
Figure 37.7 Aphids parasitizing a plant 23

24. 37.7 Parasites and pathogens can affect community composition
Non-native pathogens can have rapid and dramatic impacts.
The American chestnut was devastated by the chestnut blight protist.
A fungus-like pathogen is currently causing sudden oak death on the West Coast.
Non-native pathogens can cause a decline of the ecosystem.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. Pathogens are probably what most people refer to as germs. Students might believe that this general term refers to some specific type of organism.
2. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
© 2012 Pearson Education, Inc. 24

25. 37.8 Trophic structure is a key factor in community dynamics
The trophic structure of a community is a pattern of feeding relationships consisting of several different levels.
The sequence of food transfer up the trophic levels is known as a food chain.
The transfer of food moves chemical nutrients and energy from producers up through the trophic levels in a community.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. Students have often had prior exposure to the concepts of food webs and food chains. Present a food web (perhaps Figure 37.9) to your class and challenge them to predict the consequences of a decrease or increase in the population of one of the organisms. This activity can help students understand how difficult it is to make precise predictions about these complex systems.
2. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
© 2012 Pearson Education, Inc. 25

26. 37.8 Trophic structure is a key factor in community dynamics
Producers
are autotrophs and
support all other trophic levels.
Consumers are heterotrophs.
Herbivores are primary consumers.
Secondary consumers typically eat herbivores.
Tertiary consumers typically eat secondary consumers.
Quaternary consumers typically eat tertiary consumers.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. Students have often had prior exposure to the concepts of food webs and food chains. Present a food web (perhaps Figure 37.9) to your class and challenge them to predict the consequences of a decrease or increase in the population of one of the organisms. This activity can help students understand how difficult it is to make precise predictions about these complex systems.
2. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
© 2012 Pearson Education, Inc. 26

27. 37.8 Trophic structure is a key factor in community dynamics
Detritivores derive their energy from detritus, the dead material produced at all the trophic levels.
Decomposers
are mainly prokaryotes and fungi and
secrete enzymes that digest molecules in organic materials and convert them into inorganic forms, in the process called decomposition.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. Students have often had prior exposure to the concepts of food webs and food chains. Present a food web (perhaps Figure 37.9) to your class and challenge them to predict the consequences of a decrease or increase in the population of one of the organisms. This activity can help students understand how difficult it is to make precise predictions about these complex systems.
2. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
© 2012 Pearson Education, Inc. 27

28. A terrestrial food chain An aquatic food chain
Figure 37.8_s5
Trophic level
Quaternary
consumers
Hawk
Killer whale
Tertiary
consumers
Snake
Tuna
Secondary
consumers
Mouse
Herring
Figure 37.8_s5 Two food chains (step 5)
Primary
consumers
Grasshopper
Zooplankton
Producers
Plant
Phytoplankton
A terrestrial food chain
An aquatic food chain 28

29. 37.9 Food chains interconnect, forming food webs
A food web is a network of interconnecting food chains.
Notice that
consumers may eat more than one type of producer and
several species of consumers may feed on the same species of producer.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. Students have often had prior exposure to the concepts of food webs and food chains. Present a food web (perhaps Figure 37.9) to your class and challenge them to predict the consequences of a decrease or increase in the population of one of the organisms. This activity can help students understand how difficult it is to make precise predictions about these complex systems.
2. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
© 2012 Pearson Education, Inc. 29

30. Figure 37.9 Figure 37.9 A food web 30 Quaternary, tertiary,
and secondary
consumers
Tertiary
and
secondary
consumers
Secondary
and
primary
consumers
Primary
consumers
Figure 37.9 A food web
Producers
(plants) 30

31. 37.10 Species diversity includes relative abundance and species richness
Species diversity is defined by two components:
Species richness, the number of species in a community, and
Relative abundance, the proportional representation of a species in a community.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. Diversity within a species has some of the same advantages as diversity within a community. In both situations, diversity limits the damage from a pathogen or predator specialized to attack one variation within a species or one species in a community.
2. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
© 2012 Pearson Education, Inc. 31

32. 37.10 Species diversity includes relative abundance and species richness
Plant species diversity in a community affects the species diversity of animals.
Species diversity has consequences for pathogens.
Low species diversity is characteristic of most modern agricultural ecosystems.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. Diversity within a species has some of the same advantages as diversity within a community. In both situations, diversity limits the damage from a pathogen or predator specialized to attack one variation within a species or one species in a community.
2. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
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33. Woodlot A Figure 37.10A Figure 37.10A Species composition of woodlot A33

34. Woodlot B Figure 37.10B Figure 37.10B Species composition of woodlot B34

35. Table 37.10
Table Relative Abundance of Tree Species in Woodlots A and B 35

36. 37.11 Keystone species have a disproportionate impact on diversity
A keystone species
is a species whose impact on its community is larger than its biomass or abundance indicates and
occupies a niche that holds the rest of its community in place.
Examples of keystone species in marine ecosystems include
Pisaster sea stars and
long-spined sea urchins.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. Many keystone species have been identified in ecosystems, including sea otters, elephants, freshwater bass, and Pisaster, a sea star noted in Figure 37.11B. Challenge your class to explain how the concept of keystone species impacts the efforts of conservation biologists. Why might some species be more important to conserve?
2. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
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37. Keystone Keystone absent Figure 37.11A
Figure 37.11A Arch collapse with removal of keystone 37

38. Figure 37.11B
Figure 37.11B A Pisaster sea star, a keystone species, eating a mussel 38

39. Figure 37.11C
Figure 37.11C Diadema sea urchins grazing on a reef 39

40. Figure 37.11D
Figure 37.11D A reef overgrown by fleshy seaweeds 40

41. 37.12 Disturbance is a prominent feature of most communities
Disturbances
are events that damage biological communities and
include storms, fires, floods, droughts, overgrazing, or human activity.
The types, frequency, and severity of disturbances vary from community to community.
Student Misconceptions and Concerns
1. For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
2. The idea that ecosystems are relatively stable is common. Natural disturbances of any sort (fires, earthquakes, floods, or strong storms) are typically viewed as tragic and damaging to ecosystems. Before beginning the topic of ecological disturbances, consider asking your students to briefly respond to news that a state or federal park has (a) been burned, (b) been struck by high winds and/or lightning, or (c) been temporarily flooded. In addition, consider asking what, if anything, should be done to prevent or repair this damage?
Teaching Tips
1. Before and after images of the impact and recovery of an ecosystem from a natural disaster can be more powerful than any verbal explanation of the process. Consider locating before and after images of ecosystems damaged by hurricanes, fire, or the 1980 eruption of Mt. St. Helens, to show recovery.
2. Depending upon your location and its circumstances, consider a short field trip on or near your campus to show disturbed regions and signs of recovery.
3. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
© 2012 Pearson Education, Inc. 41

42. 37.12 Disturbance is a prominent feature of most communities
Communities change drastically following a severe disturbance that
strips away vegetation and
removes significant amounts of soil.
Ecological succession results from colonization by a variety of species, which are replaced by a succession of other species.
Student Misconceptions and Concerns
1. For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
2. The idea that ecosystems are relatively stable is common. Natural disturbances of any sort (fires, earthquakes, floods, or strong storms) are typically viewed as tragic and damaging to ecosystems. Before beginning the topic of ecological disturbances, consider asking your students to briefly respond to news that a state or federal park has (a) been burned, (b) been struck by high winds and/or lightning, or (c) been temporarily flooded. In addition, consider asking what, if anything, should be done to prevent or repair this damage?
Teaching Tips
1. Before and after images of the impact and recovery of an ecosystem from a natural disaster can be more powerful than any verbal explanation of the process. Consider locating before and after images of ecosystems damaged by hurricanes, fire, or the 1980 eruption of Mt. St. Helens, to show recovery.
2. Depending upon your location and its circumstances, consider a short field trip on or near your campus to show disturbed regions and signs of recovery.
3. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
© 2012 Pearson Education, Inc. 42

43. 37.12 Disturbance is a prominent feature of most communities
Primary succession begins in a virtually lifeless area with no soil.
Secondary succession occurs when a disturbance destroys an existing community but leaves the soil intact.
Student Misconceptions and Concerns
1. For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
2. The idea that ecosystems are relatively stable is common. Natural disturbances of any sort (fires, earthquakes, floods, or strong storms) are typically viewed as tragic and damaging to ecosystems. Before beginning the topic of ecological disturbances, consider asking your students to briefly respond to news that a state or federal park has (a) been burned, (b) been struck by high winds and/or lightning, or (c) been temporarily flooded. In addition, consider asking what, if anything, should be done to prevent or repair this damage?
Teaching Tips
1. Before and after images of the impact and recovery of an ecosystem from a natural disaster can be more powerful than any verbal explanation of the process. Consider locating before and after images of ecosystems damaged by hurricanes, fire, or the 1980 eruption of Mt. St. Helens, to show recovery.
2. Depending upon your location and its circumstances, consider a short field trip on or near your campus to show disturbed regions and signs of recovery.
3. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
© 2012 Pearson Education, Inc. 43

44. Figure 37.12A
Figure 37.12A Primary succession on a lava flow 44

45. Annual plants Perennial plants and grasses Shrubs Softwood trees
Figure 37.12B
Annual
plants
Perennial
plants and
grasses
Shrubs
Softwood trees
such as pines
Hardwood
trees
Figure 37.12B Stages in the secondary succession of an abandoned farm field
Time 45

46. 37.13 CONNECTION: Invasive species can devastate communities
Invasive species
are organisms that have been introduced into non-native habitats by human actions and
have established themselves at the expense of native communities.
The absence of natural enemies often allows rapid population growth of invasive species.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. The United States Department of Agriculture sponsors the National Invasive Species Information Center, which maintains a website at
2. Students who are interested in wildlife may collect an animal to keep as a pet, or to admire for a few days. This might be a good time to remind them that if they hope to return a wild animal to its natural environment, they should do so quickly and return it to within a few feet of the spot of its collection. Reintroducing an organism to a nearby environment may spread disease and potentially extend the organism’s natural range. Further, the introduction of commercial specimens from fish tanks, such as the marine algae Caulerpa dumped into the ocean, has had devastating consequences. The following web site addresses this example
3. The accidental introduction of the Brown Tree Snake into Guam during World War II has had a devastating impact on the ecology and economy of Guam. Extensive details can be found at
4. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
© 2012 Pearson Education, Inc. 46

47. 37.13 CONNECTION: Invasive species can devastate communities
Examples of invasive species include the deliberate introduction of
rabbits into Australia and
cane toads into Australia.
Student Misconceptions and Concerns
For many students, understanding ecosystems is like appreciating art. Although both are visible to the naked eye, some background is required to understand the method of composition, the significance of components, and the nature of interactions. The fundamentals introduced in this chapter are new ways to see generally familiar systems.
Teaching Tips
1. The United States Department of Agriculture sponsors the National Invasive Species Information Center, which maintains a website at
2. Students who are interested in wildlife may collect an animal to keep as a pet, or to admire for a few days. This might be a good time to remind them that if they hope to return a wild animal to its natural environment, they should do so quickly and return it to within a few feet of the spot of its collection. Reintroducing an organism to a nearby environment may spread disease and potentially extend the organism’s natural range. Further, the introduction of commercial specimens from fish tanks, such as the marine algae Caulerpa dumped into the ocean, has had devastating consequences. The following web site addresses this example
3. The accidental introduction of the Brown Tree Snake into Guam during World War II has had a devastating impact on the ecology and economy of Guam. Extensive details can be found at
4. Many students have been exposed to diverse ecosystems only through television and movies, which have likely focused on a few species. Before discussing this chapter, consider showing the class a good video (it need not be long) about an ecosystem. The video can then serve as a shared recent experience to which you can relate the content of this chapter. Alternately, you can relate some of the basics of this chapter to a local or regional example with which most students are familiar. There may even be a distinct community on your campus, such as a pond, wooded area, etc., that students could visit and return from with new insights.
© 2012 Pearson Education, Inc. 47

48. Frontier of rabbit spread 1860
Figure 37.13A
600 km
1980
1910
1910
1900
1910
1920
1920
1910
1890
1900
Figure 37.13A The spread of rabbits in Australia
1910
1880
1920
1920
1890
1870
1880
Key
1870
Frontier of rabbit spread
1860 48

49. Figure 37.13B
Figure 37.13B A familiar sight in early 20th-century Australia 49

50. Figure 37.13C
Figure 37.13C A cane toad (Bufo marinus) 50

51. ECOSYSTEM STRUCTURE AND DYNAMICS
ECOSYSTEM STRUCTURE AND DYNAMICS
© 2012 Pearson Education, Inc. 51

52. 37.14 Ecosystem ecology emphasizes energy flow and chemical cycling
An ecosystem consists of
all the organisms in a community and
the abiotic environment with which the organisms interact.
In an ecosystem,
energy flow moves through the components of an ecosystem and
chemical cycling is the transfer of materials within the ecosystem.
Student Misconceptions and Concerns
Without an understanding of basic physics and the inefficiency of aerobic metabolism, students might not understand how chemical energy in food is lost as heat. Consider expanding upon the explanations given in the book.
Teaching Tips
1. The heat generated as a by-product of metabolism, which is quite evident during strenuous exercise, is much like the heat produced by a running automobile engine. In both circumstances, heat is a by-product of the fuel-burning process.
2. Energy flow through an ecosystem is analogous to the flow of fuel through a car or electricity through a vacuum cleaner. These systems will not work without a steady input. NASA, however, must rely upon some closed systems for its spacecrafts. Students might enjoy investigating the recycling of gases and fluids in these systems.
© 2012 Pearson Education, Inc. 52

53. 37.14 Ecosystem ecology emphasizes energy flow and chemical cycling
A terrarium
represents the components of an ecosystem and
illustrates the fundamentals of energy flow.
Student Misconceptions and Concerns
Without an understanding of basic physics and the inefficiency of aerobic metabolism, students might not understand how chemical energy in food is lost as heat. Consider expanding upon the explanations given in the book.
Teaching Tips
1. The heat generated as a by-product of metabolism, which is quite evident during strenuous exercise, is much like the heat produced by a running automobile engine. In both circumstances, heat is a by-product of the fuel-burning process.
2. Energy flow through an ecosystem is analogous to the flow of fuel through a car or electricity through a vacuum cleaner. These systems will not work without a steady input. NASA, however, must rely upon some closed systems for its spacecrafts. Students might enjoy investigating the recycling of gases and fluids in these systems.
© 2012 Pearson Education, Inc. 53

54. Light energy Chemical energy Chemical elements
Figure 37.14 C h e m i c a l y n g
Energy flow
Light
energy
Chemical
energy
Heat
energy
Figure A terrarium ecosystem
Chemical
elements
Bacteria,
protists,
and fungi 54

55. 37.15 Primary production sets the energy budget for ecosystems
Primary production
is carried out by producers,
is the amount of solar energy converted to chemical energy by an ecosystem’s producers for a given area and during a given time period, and
produces biomass, the amount of living organic material in an ecosystem.
Different ecosystems vary in their
primary production and
contribution to the total production of the biosphere.
Teaching Tips
Challenge students to explain why the areas of greatest primary production are near the equator. (Answer: Primary production is a consequence of photosynthesis. Regions near the equator receive the highest levels of solar input.)
© 2012 Pearson Education, Inc. 55

56. Algal beds and coral reefs
Figure 37.15
Open ocean
Estuary
Algal beds and coral reefs
Desert and semidesert scrub
Tundra
Temperate grassland
Cultivated land
Boreal forest (taiga)
Savanna
Temperate deciduous forest
Figure Net primary production of various ecosystems
Tropical rain forest
500
1,000
1,500
2,000
2,500
Average net primary productivity (g/m2/yr) 56

57. 37.16 Energy supply limits the length of food chains
A caterpillar represents a primary consumer.
Of the organic compounds a caterpillar ingests, about
50% is eliminated in feces,
35% is used in cellular respiration, and
15% is used for growth.
Teaching Tips
Why do food chains and webs typically have only three to five levels? This question, which is seldom considered by students, is addressed directly in this section of the chapter. It can spark a good opening discussion before a lecture on food chains and food webs.
© 2012 Pearson Education, Inc. 57

58. Plant material eaten by caterpillar 100 kilocalories (kcal) 35 kcal
Figure 37.16A
Plant material
eaten by caterpillar
100 kilocalories (kcal)
Figure 37.16A The fate of leaf biomass consumed by a caterpillar
35 kcal
Cellular
respiration
50 kcal
Feces
15 kcal
Growth 58

59. 37.16 Energy supply limits the length of food chains
A pyramid of production shows the flow of energy
from producers to primary consumers and
to higher trophic levels.
Only about 10% of the energy stored at each trophic level is available to the next level.
Teaching Tips
Why do food chains and webs typically have only three to five levels? This question, which is seldom considered by students, is addressed directly in this section of the chapter. It can spark a good opening discussion before a lecture on food chains and food webs.
© 2012 Pearson Education, Inc. 59

60. Tertiary consumers Secondary consumers Primary consumers Producers
Figure 37.16B
Tertiary
consumers
10 kcal
Secondary
consumers
100 kcal
Primary
consumers
1,000 kcal
Producers
Figure 37.16B An idealized pyramid of production
10,000 kcal
1,000,000 kcal of sunlight 60

61. 37.18 Chemicals are cycled between organic matter and abiotic reservoirs
Ecosystems are supplied with a continual influx of energy from the
sun and
Earth’s interior.
Except for meteorites, there are no extraterrestrial sources of chemical elements.
Thus, life also depends on the recycling of chemicals.
Student Misconceptions and Concerns
Students are unlikely to have any prior knowledge of biogeochemical cycles. Although some transfers between the biotic and abiotic components of ecosystems, such as the use of fertilizer on plants, may be known to them, the broader fact that the biosphere is a self-cycling system is not appreciated by most students. Before you lecture, consider asking your students to explain how carbon, phosphorus, and nitrogen cycle through the atmosphere. Pre-testing your students on their knowledge can confirm both what they understand and what they may need explained to them in more detail.
Teaching Tips
As you discuss the importance of the biogeochemical cycles, consider explaining the basic label information provided on a container of plant fertilizer. Consider an example that might be used on houseplants, and therefore more likely to be familiar to students. Typically, plant fertilizers contain various forms of nitrogen and phosphorus, which are essential chemicals for growth.
© 2012 Pearson Education, Inc. 61

62. 37.18 Chemicals are cycled between organic matter and abiotic reservoirs
Biogeochemical cycles include
biotic components,
abiotic components, and
abiotic reservoirs, where a chemical accumulates or is stockpiled outside of living organisms.
Biogeochemical cycles can be
local or
global.
Student Misconceptions and Concerns
Students are unlikely to have any prior knowledge of biogeochemical cycles. Although some transfers between the biotic and abiotic components of ecosystems, such as the use of fertilizer on plants, may be known to them, the broader fact that the biosphere is a self-cycling system is not appreciated by most students. Before you lecture, consider asking your students to explain how carbon, phosphorus, and nitrogen cycle through the atmosphere. Pre-testing your students on their knowledge can confirm both what they understand and what they may need explained to them in more detail.
Teaching Tips
As you discuss the importance of the biogeochemical cycles, consider explaining the basic label information provided on a container of plant fertilizer. Consider an example that might be used on houseplants, and therefore more likely to be familiar to students. Typically, plant fertilizers contain various forms of nitrogen and phosphorus, which are essential chemicals for growth.
© 2012 Pearson Education, Inc. 62

63. Consumers Producers Decomposers Nutrients available to producers
Figure 37.18
Consumers 3 2
Producers
Decomposers 1
Nutrients
available
to producers 4
Figure A general model of the biogeochemical cycling of nutrients
Abiotic
reservoirs
Geologic processes 63

64. 37.19 The carbon cycle depends on photosynthesis and respiration
Carbon is
the major ingredient of all organic molecules and
found in
the atmosphere,
fossil fuels, and
dissolved in carbon compounds in the ocean.
The return of CO2 to the atmosphere by respiration closely balances its removal by photosynthesis.
The carbon cycle is affected by burning wood and fossil fuels.
Student Misconceptions and Concerns
Students are unlikely to have any prior knowledge of biogeochemical cycles. Although some transfers between the biotic and abiotic components of ecosystems, such as the use of fertilizer on plants, may be known to them, the broader fact that the biosphere is a self-cycling system is not appreciated by most students. Before you lecture, consider asking your students to explain how carbon, phosphorus, and nitrogen cycle through the atmosphere. Pre-testing your students on their knowledge can confirm both what they understand and what they may need explained to them in more detail.
Teaching Tips
1. As you discuss the importance of the biogeochemical cycles, consider explaining the basic label information provided on a container of plant fertilizer. Consider an example that might be used on houseplants, and therefore more likely to be familiar to students. Typically, plant fertilizers contain various forms of nitrogen and phosphorus, which are essential chemicals for growth.
2. As rising atmospheric carbon dioxide levels affect global climate, carbon cycling has become an increasingly important issue. If your course will not cover Module 38.5, on global warming, consider including a brief discussion of the topic here.
© 2012 Pearson Education, Inc. 64

65. CO2 in atmosphere Burning Photosynthesis Cellular respiration
Figure 37.19
CO2 in atmosphere 5
Burning 3
Photosynthesis
Cellular respiration 1
Plants, algae,
cyanobacteria
Higher-level
consumers 2
Wood
and
fossil
fuels
Primary
consumers
Figure The carbon cycle
Decomposition
Wastes; death
Plant litter;
death 4
Decomposers
(soil microbes)
Detritus 65

66. 37.20 The phosphorus cycle depends on the weathering of rock
Organisms require phosphorus for
nucleic acids,
phospholipids, and
ATP.
Student Misconceptions and Concerns
Students are unlikely to have any prior knowledge of biogeochemical cycles. Although some transfers between the biotic and abiotic components of ecosystems, such as the use of fertilizer on plants, may be known to them, the broader fact that the biosphere is a self-cycling system is not appreciated by most students. Before you lecture, consider asking your students to explain how carbon, phosphorus, and nitrogen cycle through the atmosphere. Pre-testing your students on their knowledge can confirm both what they understand and what they may need explained to them in more detail.
Teaching Tips
1. As you discuss the importance of the biogeochemical cycles, consider explaining the basic label information provided on a container of plant fertilizer. Consider an example that might be used on houseplants, and therefore more likely to be familiar to students. Typically, plant fertilizers contain various forms of nitrogen and phosphorus, which are essential chemicals for growth.
2. Discussing the movements of water through your local community can help students better understand the concept of biogeochemical cycling. You may want to ask students to consider all of the possible inputs of water into your community as well as the possible routes of exit.
3. As noted in Module 37.20, phosphate contamination of aquatic systems typically leads to increased algal growth and potentially disastrous fish kills.
© 2012 Pearson Education, Inc. 66

67. 37.20 The phosphorus cycle depends on the weathering of rock
The phosphorus cycle does not have an atmospheric component.
Rocks are the only source of phosphorus for terrestrial ecosystems.
Plants absorb phosphate ions in the soil and build them into organic compounds.
Phosphates are returned to the soil by decomposers.
Phosphate levels in aquatic ecosystems are typically low enough to be a limiting factor.
Student Misconceptions and Concerns
Students are unlikely to have any prior knowledge of biogeochemical cycles. Although some transfers between the biotic and abiotic components of ecosystems, such as the use of fertilizer on plants, may be known to them, the broader fact that the biosphere is a self-cycling system is not appreciated by most students. Before you lecture, consider asking your students to explain how carbon, phosphorus, and nitrogen cycle through the atmosphere. Pre-testing your students on their knowledge can confirm both what they understand and what they may need explained to them in more detail.
Teaching Tips
1. As you discuss the importance of the biogeochemical cycles, consider explaining the basic label information provided on a container of plant fertilizer. Consider an example that might be used on houseplants, and therefore more likely to be familiar to students. Typically, plant fertilizers contain various forms of nitrogen and phosphorus, which are essential chemicals for growth.
2. Discussing the movements of water through your local community can help students better understand the concept of biogeochemical cycling. You may want to ask students to consider all of the possible inputs of water into your community as well as the possible routes of exit.
3. As noted in Module 37.20, phosphate contamination of aquatic systems typically leads to increased algal growth and potentially disastrous fish kills.
© 2012 Pearson Education, Inc. 67

68. Uplifting of rock Weathering of rock Phosphates in rock Animals Plants
Figure 37.20 6
Uplifting
of rock 3
Weathering
of rock
Phosphates
in rock
Animals
Plants
Runoff 1
Assimilation
Figure The phosphorus cycle 2
Phosphates
in soil
(inorganic)
Detritus
Phosphates
in solution 5
Precipitated
(solid) phosphates 4
Decomposers
in soil
Rock
Decomposition 68

69. 37.21 The nitrogen cycle depends on bacteria
Nitrogen is
an ingredient of proteins and nucleic acids,
essential to the structure and functioning of all organisms, and
a crucial and often limiting plant nutrient.
Nitrogen has two abiotic reservoirs:
1. the atmosphere, of which about 80% is nitrogen gas, and
2. soil.
Student Misconceptions and Concerns
Students are unlikely to have any prior knowledge of biogeochemical cycles. Although some transfers between the biotic and abiotic components of ecosystems, such as the use of fertilizer on plants, may be known to them, the broader fact that the biosphere is a self-cycling system is not appreciated by most students. Before you lecture, consider asking your students to explain how carbon, phosphorus, and nitrogen cycle through the atmosphere. Pre-testing your students on their knowledge can confirm both what they understand and what they may need explained to them in more detail.
Teaching Tips
The nitrogen-fixing bacteria living in the roots of soybeans add nitrogen to the soil. Corn does not enjoy this same relationship with bacteria. However, by rotating corn and soybean crops, farmers can allow corn crops to use some of the nitrogen fixed by the soybean crop in the previous year. Such rotation has other benefits. Since corn is a monocot and soybeans are dicots, few pests attack both corn and soybeans. Thus, crop rotation also helps to control the pest populations that target each type of plant, reducing the need for other pest-fighting strategies.
© 2012 Pearson Education, Inc. 69

70. 37.21 The nitrogen cycle depends on bacteria
Nitrogen fixation
converts N2 to compounds of nitrogen that can be used by plants and
is carried out by some bacteria.
Student Misconceptions and Concerns
Students are unlikely to have any prior knowledge of biogeochemical cycles. Although some transfers between the biotic and abiotic components of ecosystems, such as the use of fertilizer on plants, may be known to them, the broader fact that the biosphere is a self-cycling system is not appreciated by most students. Before you lecture, consider asking your students to explain how carbon, phosphorus, and nitrogen cycle through the atmosphere. Pre-testing your students on their knowledge can confirm both what they understand and what they may need explained to them in more detail.
Teaching Tips
The nitrogen-fixing bacteria living in the roots of soybeans add nitrogen to the soil. Corn does not enjoy this same relationship with bacteria. However, by rotating corn and soybean crops, farmers can allow corn crops to use some of the nitrogen fixed by the soybean crop in the previous year. Such rotation has other benefits. Since corn is a monocot and soybeans are dicots, few pests attack both corn and soybeans. Thus, crop rotation also helps to control the pest populations that target each type of plant, reducing the need for other pest-fighting strategies.
© 2012 Pearson Education, Inc. 70

71. Nitrogen (N2) in atmosphere
Figure 37.21
Nitrogen (N2) in atmosphere 8
Plant
Animal 6
Assimilation
by plants 1 5
Denitrifiers 3
Nitrogen-fixing
bacteria in
root modules
Nitrates
in soil
(NO3)
Detritus
Figure The nitrogen cycle
Decomposers
Free-living
nitrogen-fixing
bacteria
Nitrifying
bacteria 4 7
Ammonium (NH4)
in soil 2 71

72. 37.22 CONNECTION: A rapid inflow of nutrients degrades aquatic ecosystems
In aquatic ecosystems, primary production is limited by low nutrient levels of
phosphorus and
nitrogen.
Over time, standing water ecosystems
gradually accumulate nutrients from the decomposition of organic matter and fresh influx from the land, and
primary production increases in a process known as eutrophication.
Student Misconceptions and Concerns
Students are unlikely to have any prior knowledge of biogeochemical cycles. Although some transfers between the biotic and abiotic components of ecosystems, such as the use of fertilizer on plants, may be known to them, the broader fact that the biosphere is a self-cycling system is not appreciated by most students. Before you lecture, consider asking your students to explain how carbon, phosphorus, and nitrogen cycle through the atmosphere. Pre-testing your students on their knowledge can confirm both what they understand and what they may need explained to them in more detail.
Teaching Tips
The studies of the Hubbard Brook Experimental Forest (described well at and in the previous edition of this Concepts textbook) provide an opportunity to explain how basic principles of scientific investigation are applied to ecological studies. Consider discussing the difficulties of conducting these broad experiments in other locations, where water cycling may not be so restricted and other biogeochemical cycles not as well defined.
© 2012 Pearson Education, Inc. 72

73. 37.22 CONNECTION: A rapid inflow of nutrients degrades aquatic ecosystems
Eutrophication of lakes, rivers, and coastal waters
depletes oxygen levels and
decreases species diversity.
In many areas, phosphate pollution leading to eutrophication comes from
agricultural fertilizers,
pesticides,
sewage treatment facilities, and
runoff of animal waste from feedlots
Student Misconceptions and Concerns
Students are unlikely to have any prior knowledge of biogeochemical cycles. Although some transfers between the biotic and abiotic components of ecosystems, such as the use of fertilizer on plants, may be known to them, the broader fact that the biosphere is a self-cycling system is not appreciated by most students. Before you lecture, consider asking your students to explain how carbon, phosphorus, and nitrogen cycle through the atmosphere. Pre-testing your students on their knowledge can confirm both what they understand and what they may need explained to them in more detail.
Teaching Tips
The studies of the Hubbard Brook Experimental Forest (described well at and in the previous edition of this Concepts textbook) provide an opportunity to explain how basic principles of scientific investigation are applied to ecological studies. Consider discussing the difficulties of conducting these broad experiments in other locations, where water cycling may not be so restricted and other biogeochemical cycles not as well defined.
© 2012 Pearson Education, Inc. 73

74. 37.22 CONNECTION: A rapid inflow of nutrients degrades aquatic ecosystems
Eutrophication of aquatic systems may also result from increased levels of nitrogen from
feedlots and
applications of large amounts of fertilizer.
Student Misconceptions and Concerns
Students are unlikely to have any prior knowledge of biogeochemical cycles. Although some transfers between the biotic and abiotic components of ecosystems, such as the use of fertilizer on plants, may be known to them, the broader fact that the biosphere is a self-cycling system is not appreciated by most students. Before you lecture, consider asking your students to explain how carbon, phosphorus, and nitrogen cycle through the atmosphere. Pre-testing your students on their knowledge can confirm both what they understand and what they may need explained to them in more detail.
Teaching Tips
The studies of the Hubbard Brook Experimental Forest (described well at and in the previous edition of this Concepts textbook) provide an opportunity to explain how basic principles of scientific investigation are applied to ecological studies. Consider discussing the difficulties of conducting these broad experiments in other locations, where water cycling may not be so restricted and other biogeochemical cycles not as well defined.
© 2012 Pearson Education, Inc. 74

75. Figure 37.22A
Figure 37.22A Algal growth on a pond resulting from nutrient pollution 75

76. Winter Summer G u l f o M e x i c G u l f o M e x i c Figure 37.22B
Figure 37.22B Concentrations of phytoplankton in winter and summer. Red and orange indicate highest concentrations.
Winter
Summer 76