Introduction Many drugs are derived from plants. For example,

Introduction Many drugs are derived from plants. For example,
morphine, a powerful pain reliever, comes from opium poppies, a chemical found in certain Ephedra species relieves the symptoms of asthma, and a drug from foxglove is used to treat congestive heart failure. Common plant stimulants include caffeine, found in coffee berries, tea leaves, and kola nuts, and nicotine in tobacco leaves.

Introduction Researchers are eagerly testing newly discovered compounds that show pharmaceutical promise against cancer and infectious diseases such as malaria and HIV, as pain relievers and sedatives, to promote weight loss, and for many other uses.

Introduction But why do plants make these substances?
What is the adaptive value? In a community, populations of many different species interact with each other, and some of these relationships are potentially harmful.

Figure Figure Why do plants make drugs? (photo: foxglove)

Chapter 37: Big Ideas Community Structure and Dynamics
Figure Chapter 37: Big Ideas Figure Chapter 37: Big Ideas Community Structure and Dynamics Ecosystem Structure and Dynamics

Community Structure and Dynamics

37.1 A community includes all the organisms inhabiting a particular area
In the hierarchy of life, a population is a group of interacting individuals of a particular species. The next step up is a biological community, an assemblage of all the populations of organisms living close enough together for potential interaction. Ecologists define the boundaries of the community according to the research questions they want to investigate. 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  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.  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.

A community can be described by its species composition. Community ecologists seek to understand how abiotic factors and interactions between populations affect the composition and distribution of communities and investigate community dynamics, the variability or stability in the species composition of a community caused by biotic and abiotic factors. 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  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.  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.

Community ecology is necessary for the conservation of endangered species and the management of wildlife, game, and fisheries, is vital for controlling diseases, such as malaria, bird flu, and Lyme disease, that are carried by animals, and has applications in agriculture, where people attempt to control the species composition of communities they have established. 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  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.  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.

37.2 Interspecific interactions are fundamental to community structure
are relationships with individuals of other species in the community and greatly affect population structure and dynamics. In Table 37.2, interspecific interactions are classified according to the effect on the populations concerned. 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  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.  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.  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. Active Lecture Tips  See the Activity Students as Parasites of Their Parents on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity A Chance Discovery of Endosymbiosis? A Case Study on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Table 37.2 Table 37.2 Interspecific interactions

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  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.  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.  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. Active Lecture Tips  See the Activity Students as Parasites of Their Parents on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity A Chance Discovery of Endosymbiosis? A Case Study on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

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 and both populations need a resource that is in short supply. In general, 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  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.  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  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.  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.

Figure 37.3a Figure 37.3a A Virginia’s warbler (Vermivora virginiae)

Figure 37.3b Figure 37.3b An orange-crowned warbler (Vermivora celata)

37.4 Mutualism benefits both partners
Reef-building corals and photosynthetic dinoflagellates provide a good example of how mutualists benefit from their relationship. Photosynthetic dinoflagellates gain a secure shelter that provides access to light, produce sugars by photosynthesis that provide at least half of the energy used by the coral animals, and use the coral’s waste products, including carbon dioxide (CO2) and ammonia (NH3), a valuable source of nitrogen for making proteins. 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  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.  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.

Video: Clownfish and Anemone

Figure 37.4 Figure 37.4 Coral polyps

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  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.  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.

Video: Seahorse Camouflage

Figure 37.5a Figure 37.5a Camouflage: a gray tree frog on bark

Figure 37.5b Figure 37.5b Chemical defenses: the monarch butterfly

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, often the substances that we use medicinally or for other purposes. 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  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.  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.  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.

Like the chemical defenses of animals, toxins in plants tend to be distasteful, and herbivores learn to avoid them. Some plants even produce chemicals that cause abnormal development in insects that eat them. 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  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.  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.  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.

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 species, and the resulting adaptations of the second species in turn affect the selection of individuals in the first species. Figure 37.6 illustrates an example of coevolution between an herbivorous insect (the caterpillar of the butterfly Heliconius) and a plant. 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  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.  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.  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.

Heliconius Eggs Decoy eggs Figure 37.6
Figure 37.6 Coevolution: Heliconius and the passionflower vine (Passiflora) Decoy eggs

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. Plants are also attacked by parasites, including nematodes and aphids, that tap into the phloem and suck plant sap. 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  Pathogens are probably what most people refer to as germs. Students might believe that this general term refers to some specific type of organism.  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.

Figure 37.7 Figure 37.7 Aphids parasitizing a plant

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. 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  Pathogens are probably what most people refer to as germs. Students might believe that this general term refers to some specific type of organism.  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.

37.8 Trophic structure is a key factor in community dynamics
Every community has a trophic structure, 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. This 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. Active Lecture Tips  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 work in small groups 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.

Producers are autotrophs that support all other trophic levels. Consumers are heterotrophs. Herbivores are primary consumers. Secondary consumers on land typically eat herbivores and in aquatic ecosystems typically eat zooplankton. 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. Active Lecture Tips  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 work in small groups 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.

Video: Shark Eating a Seal

A terrestrial food chain An aquatic food chain
Figure 37.8 Quaternary consumers Killer whale Hawk Tertiary consumers Snake Tuna Secondary consumers Mouse Herring Figure 37.8 Two food chains Primary consumers Zooplankton Grasshopper Producers Plant Phytoplankton A terrestrial food chain An aquatic food chain

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. Active Lecture Tips  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 work in small groups 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.

37.9 VISUALIZING THE CONCEPT: Food chains interconnect, forming food webs
A more realistic view of the trophic structure of a community is a food web, a network of interconnecting food chains. A consumer may eat more than one type of producer, and several species of primary consumers may feed on the same species of producer. Some animals weave into the food web at more than one trophic level. 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. Active Lecture Tips  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 work in small groups 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.

Figure 37.9-1 A food web (step 1)
Producers provide the chemical energy and nutrients used by all other members of the food web. Figure A food web (step 1) Prickly pear cactus Saguaro cactus Mesquite Producers (plants) Brittlebush

Nutrient Transfer Figure 37.9-2 Figure 37.9-2 A food web (step 2)
Producers provide the chemical energy and nutrients used by all other members of the food web. Gila woodpecker Grasshopper mouse Primary consumer Primary consumer Grasshopper Harris’s antelope squirrel Desert kangaroo rat Harvester ants Figure A food web (step 2) Prickly pear cactus Saguaro cactus Mesquite Producers (plants) Brittlebush Nutrient Transfer From To Producers Primary consumers

Producers provide the chemical energy and nutrients used by all other members of the food web. Red-tailed hawk Elf owl Gila woodpecker Western diamondback Primary and secondary consumer Grasshopper mouse Praying mantis Secondary consumer Collared lizard Primary consumer Primary consumer Grasshopper Harris’s antelope squirrel Desert kangaroo rat Harvester ants Figure A food web (step 3) Prickly pear cactus Saguaro cactus Mesquite Producers (plants) Brittlebush Nutrient Transfer From To Producers Primary consumers Primary consumers Secondary consumers

Producers provide the chemical energy and nutrients used by all other members of the food web. Red-tailed hawk Secondary, tertiary, and quaternary consumer Secondary and tertiary consumer Elf owl Gila woodpecker Western diamondback Primary and secondary consumer Grasshopper mouse Praying mantis Secondary consumer Collared lizard Primary consumer Primary consumer Grasshopper Harris’s antelope squirrel Desert kangaroo rat Harvester ants Figure A food web (step 4) Prickly pear cactus Saguaro cactus Mesquite Producers (plants) Brittlebush Nutrient Transfer From To Producers Primary consumers Primary consumers Secondary consumers Secondary consumers Tertiary consumers Tertiary consumers Quaternary consumers

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  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.  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.

Figure 37.10a Figure 37.10a Species composition of woodlot A

Figure 37.10b Figure 37.10b Species composition of woodlot B

Table 37.10 Table Relative abundance of tree species in woodlots A and B

Plant species diversity in a community often has consequences for the species diversity of animals in the community. Species diversity also impacts pathogens. Most pathogens infect a limited range of host species or may even be restricted to a single host species. When many potential hosts are living close together, it is easy for a pathogen to spread from one to 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  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.  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.

Low species diversity is characteristic of most modern agricultural ecosystems. To combat potential losses, many farmers and forest managers rely heavily on chemical methods of controlling pests. Modern crop scientists have bred varieties of plants that are genetically resistant to common pathogens, but these varieties can suddenly become vulnerable, too. 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  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.  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.

37.11 SCIENTIFIC THINKING: Some species have a disproportionate impact on diversity
Ecologist Robert Paine hypothesized that the species diversity of a community is directly related to the ability of predators to prevent any one species from monopolizing local resources. To test this hypothesis, Paine manually removed a predatory sea star known as Pisaster from certain areas of the intertidal zone, left comparable areas intact as controls, and determined the species richness of these experimental and control areas over the next several years. 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  Many keystone species have been identified in ecosystems, including sea otters, elephants, freshwater bass, and Pisaster, a sea star noted in Figure 37.11C. 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?  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.

Figure 37.11a Figure 37.11a A rocky intertidal zone on the coast of Washington state

Number of species present
Figure 37.11b 20 15 With Pisaster (control) Number of species present 10 Without Pisaster (experimental) 5 Figure 37.11b Species richness in control and experimental areas after Pisaster removal 1963 ’64 ’65 ’66 ’67 ’68 ’69 ’70 ’71 ’72 ’73 Year Data from R.T. Paine, Food web complexity and species diversity, American Naturalist 100:65–75 (1996).

In the absence of Pisaster, species richness dropped from more than 15 species to fewer than 5. What accounted for the dramatic change? A mussel of the genus Mytilus proved to be a superior competitor for the available space, eliminating most other invertebrates and algae. In the control areas, population growth of Mytilus was suppressed by Pisaster, a voracious predator on the mussel. Thus, interspecific interactions can be an important factor in the species diversity of 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  Many keystone species have been identified in ecosystems, including sea otters, elephants, freshwater bass, and Pisaster, a sea star noted in Figure 37.11C. 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?  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.

Figure 37.11c Figure 37.11c A Pisaster sea star, a keystone species, eating a mussel

Paine’s experiment and others like it gave rise to the concept of a keystone species, defined as a species whose impact on its community is larger than its biomass or abundance indicates and that occupies a niche that holds the rest of its community in place. Examples 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  Many keystone species have been identified in ecosystems, including sea otters, elephants, freshwater bass, and Pisaster, a sea star noted in Figure 37.11C. 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?  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.

The word “keystone” comes from the wedge- shaped stone at the top of an arch that locks the other pieces in place. If the keystone is removed, the arch collapses. A keystone species occupies a niche that holds the rest of its community in place. 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  Many keystone species have been identified in ecosystems, including sea otters, elephants, freshwater bass, and Pisaster, a sea star noted in Figure 37.11C. 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?  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.

Keystone Keystone absent Figure 37.11d
Figure 37.11d Arch collapse with removal of keystone

37.12 Disturbance is a prominent feature of most communities
Disturbances are events that damage biological communities and include storms, fires, floods, drought, and human activity. The types of disturbances and their frequency and severity vary from community to community. Student Misconceptions and Concerns  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.  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  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.  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.  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.

Small-scale disturbances often have positive effects. However, communities change drastically following a severe disturbance that strips away vegetation and removes significant amounts of soil. Student Misconceptions and Concerns  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.  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  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.  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.  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.

The disturbed area may be colonized by a variety of species, which are gradually replaced by a succession of other species, in a process called ecological succession. Student Misconceptions and Concerns  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.  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  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.  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.  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.

Primary succession begins in a virtually lifeless area with no soil. Examples of such areas are the rubble left by a retreating glacier or fresh volcanic lava flows. Student Misconceptions and Concerns  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.  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  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.  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.  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.

Figure 37.12a Figure 37.12a Primary succession on a lava flow

Secondary succession occurs when a disturbance destroys an existing community but leaves the soil intact. Whenever human intervention stops, secondary succession begins. Numerous studies have documented the stages by which an abandoned farm field returns to forest. Student Misconceptions and Concerns  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.  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  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.  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.  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.

Annual plants Perennial plants and grasses Shrubs Softwood trees
Figure 37.12b Annual plants Perennial plants and grasses Shrubs Softwood trees Hardwood trees Figure 37.12b Stages in the secondary succession of an abandoned farm field Time

37.13 CONNECTION: Invasive species can devastate communities
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  Numerous U.S. government agencies have websites devoted to invasive species. These include: - The United States Department of Agriculture at - The National Invasive Species Council at - The following California Department of Fish and Wildlife website lists more than 10 federal government websites devoted to invasive species.  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 website addresses this example  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. Details of this ongoing crisis can be found at the North America Brown Tree Snake Control site,  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.

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  Numerous U.S. government agencies have websites devoted to invasive species. These include: - The United States Department of Agriculture at - The National Invasive Species Council at - The following California Department of Fish and Wildlife website lists more than 10 federal government websites devoted to invasive species.  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 website addresses this example  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. Details of this ongoing crisis can be found at the North America Brown Tree Snake Control site,  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.

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

Figure 37.13b Figure 37.13b A familiar sight in early 20th-century Australia

Figure 37.13c Figure 37.13c A cane toad (Bufo marinus)

Ecosystem Structure and Dynamics

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  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.  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.

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  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.  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.

Energy flow Light energy Chemical energy Heat energy Chemical elements
Figure 37.14 Energy flow Light energy Chemical energy Heat energy Figure A terrarium ecosystem Chemical elements Bacteria, protists, and fungi

37.15 Primary production sets the energy budget for ecosystems
The amount of solar energy converted to chemical energy (in organic compounds) by an ecosystem’s producers for a given area and during a given time period is called primary production. Ecologists call the amount, or mass, of living organic material in an ecosystem the biomass. Different ecosystems vary in their primary production and contribution to the total production of the biosphere. Active Lecture Tips  Challenge students to work in small groups or pairs 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.)

Algal beds and coral reefs Desert and semidesert scrub Tundra
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 production (g/m2/yr) Data from R.H. Whittaker, Communities and Ecosystems, second edition, New York: Macmillan (1975).

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 converted to caterpillar biomass. Active Lecture Tips  Ask your students to work in pairs or small groups to explain why food chains and food 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.

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

A pyramid of production illustrates the cumulative loss of energy with each transfer in a food chain. Only about 10% of the energy stored at each trophic level is available to the next level. The efficiencies of energy transfer usually range from 5 to 20%. Active Lecture Tips  Ask your students to work in pairs or small groups to explain why food chains and food 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.

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

An important implication of this stepwise decline of energy in a trophic structure is that the amount of energy available to top-level consumers is small compared with that available to lower-level consumers. Only a tiny fraction of the energy stored by photosynthesis flows through a food chain all the way to a tertiary consumer. This explains why top-level consumers such as lions and hawks require so much geographic territory. Active Lecture Tips  Ask your students to work in pairs or small groups to explain why food chains and food 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.

37.17 CONNECTION: A pyramid of production explains the ecological cost of meat
As omnivores, people eat plant material and meat. When humans eat grain or fruit, we are primary consumers, beef or other meat from herbivores, we are secondary consumers, and fish like trout or salmon, we are tertiary or quaternary consumers. Student Misconceptions and Concerns  The environmental impact of eating farm animals is little appreciated by most students who otherwise may be concerned about global climate change and the conservation of natural ecosystems. This chapter section helps explain the basis of the increased costs associated with a diet that includes meat. Teaching Tips  Some students might be interested in eating more proteins and fewer carbohydrates because of popular diet plans. But do high-protein diets always require the consumption of more meat? The many sources of plant proteins might be surprising to students. Some high-protein vegetarian options are described by the Vegetarian Society at its website,

37.17 CONNECTION: A pyramid of production explains the ecological cost of meat
Only about 10% of the chemical energy available in a trophic level is passed to the next higher trophic level. Therefore, the human population has about 10 times more energy available to it when people eat plants than when they eat the meat of herbivores. Eating meat of any kind is expensive economically and environmentally. Student Misconceptions and Concerns  The environmental impact of eating farm animals is little appreciated by most students who otherwise may be concerned about global climate change and the conservation of natural ecosystems. This chapter section helps explain the basis of the increased costs associated with a diet that includes meat. Teaching Tips  Some students might be interested in eating more proteins and fewer carbohydrates because of popular diet plans. But do high-protein diets always require the consumption of more meat? The many sources of plant proteins might be surprising to students. Some high-protein vegetarian options are described by the Vegetarian Society at its website,

Trophic level Secondary consumers Primary consumers Producers
Figure 37.17 Trophic level Secondary consumers Meat-eaters Primary consumers Vegetarians Cattle Producers Corn Corn Figure Food energy available to people eating at different trophic levels

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.

37.18 Chemicals are cycled between organic matter and abiotic reservoirs
Biogeochemical cycles include biotic components, abiotic components, and abiotic reservoirs, where chemicals accumulate or are 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.

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

37.19 The carbon cycle depends on photosynthesis and respiration
Carbon is the major ingredient of all organic molecules and found in the atmosphere, in fossil fuels, and dissolved in carbon compounds in the ocean. The reciprocal metabolic processes of photosynthesis and cellular respiration are mainly responsible for the cycling of carbon between the biotic and abiotic worlds. 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 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 climate change, consider including a brief discussion of the topic here.  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.

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

37.19 The carbon cycle depends on photosynthesis and respiration
On a global scale, the return of CO2 to the atmosphere by cellular respiration closely balances its removal by photosynthesis, but the increased burning of wood and fossil fuels (coal and petroleum) is raising the level of CO2 in the atmosphere. 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 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 climate change, consider including a brief discussion of the topic here.  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.

37.20 The phosphorus cycle depends on the weathering of rock
Organisms require phosphorus, usually in the form of the phosphate ion (PO43−), for nucleic acids, phospholipids, ATP and as a mineral component of bones and teeth. 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  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.  As noted in Module 37.20, phosphate contamination of aquatic systems typically leads to increased algal growth and potentially disastrous fish kills.  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.

In contrast to the carbon cycle and the other major biogeochemical cycles, 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  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.  As noted in Module 37.20, phosphate contamination of aquatic systems typically leads to increased algal growth and potentially disastrous fish kills.  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.

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

Because phosphates are transferred from terrestrial to aquatic ecosystems much more rapidly than they are replaced, the amount in terrestrial ecosystems gradually diminishes over time. Soil erosion from land cleared for agriculture or development accelerates the loss of phosphates. Farmers and gardeners often use crushed phosphate rock, bone meal (finely ground bones from slaughtered livestock), or guano, the droppings of seabirds and bats, to add phosphorus to the 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  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.  As noted in Module 37.20, phosphate contamination of aquatic systems typically leads to increased algal growth and potentially disastrous fish kills.  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.

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: the atmosphere, of which about 80% is nitrogen gas, and 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.

Nitrogen fixation converts N2 to compounds of nitrogen that can be used by plants and is carried out by some bacteria. Figure 37.21 illustrates the actions of two types of nitrogen-fixing 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.

Nitrogen (N2) in atmosphere
Figure 37.21 Nitrogen (N2) in atmosphere 8 Plant Animal 6 Organic compounds Organic compounds Assimilation by plants Nitrogen fixation 1 5 Death; wastes 3 Denitrifiers Nitrogen-fixing bacteria in root nodules Detritus Nitrates in soil (NO3−) Figure The nitrogen cycle Decomposers Free-living nitrogen-fixing bacteria 4 Nitrifying bacteria 7 Decomposition Nitrogen fixation Ammonium (NH4+) in soil 2

Human activities are disrupting the nitrogen cycle by adding more nitrogen to the biosphere each year than natural processes. Combustion of fossil fuels in motor vehicles and coal-fired power plants produces nitrogen oxides (NO and NO2). Modern agricultural is another major source of nitrogen. Some nitrogen escapes to the atmosphere, where it forms NO2 or nitrous oxide (N2O), an inert gas that lingers in the atmosphere and contributes to global warming. 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.

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 at and in a 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.

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 at and in a 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.

Video: Cyanobacteria (Oscillatoria)

Figure 37.22a Figure 37.22a Algal growth on a pond resulting from nutrient pollution

Nitrogen runoff from Midwestern farm fields has been linked to a “dead zone” observed each summer in the Gulf of Mexico. Vast algal blooms extend outward from where the Mississippi River deposits its nutrient-laden waters. As the algae die, decomposition of the huge quantities of biomass diminishes the supply of dissolved oxygen over an area that ranges from 13,000 to 22,000 km2, or roughly 5,000 to 8,500 square miles. 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 at and in a 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.

Figure 37.22b Winter Figure 37.22b Concentrations of phytoplankton in winter and summer. Red and orange indicate highest concentrations. Summer

37.23 CONNECTION: Ecosystem services are essential to human well-being
Humans rely upon natural ecosystems to supply fresh water and some foods, recycle nutrients, decompose wastes, and regulate climate and air quality. 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  Most human communities include at least one golf course where heavy chemical applications of fertilizers occur. Discuss with your students the environmental impact of replacing a natural prairie or forested ecosystem with a golf course, noting the change in species diversity and broader ecological impacts of applications of fertilizers and pesticides and the related increase in fossil fuel consumption. Immediate examples from your local community help students immediately relate to the topics of this chapter.

Wetlands buffer coastal populations against tidal waves and hurricanes, reduce the impact of flooding rivers, and filter pollutants. Natural vegetation helps to retain fertile soil and prevent landslides and mudslides. 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  Most human communities include at least one golf course where heavy chemical applications of fertilizers occur. Discuss with your students the environmental impact of replacing a natural prairie or forested ecosystem with a golf course, noting the change in species diversity and broader ecological impacts of applications of fertilizers and pesticides and the related increase in fossil fuel consumption. Immediate examples from your local community help students immediately relate to the topics of this chapter.

Ecosystems that we create are also essential to our well-being. Agricultural ecosystems supply most of our food and fibers, make use of ecosystem services, such as control of agricultural pests by natural predators and pollination of crops, and rely upon nutrient cycling to maintain soil fertility, the foundation for crop growth. 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  Most human communities include at least one golf course where heavy chemical applications of fertilizers occur. Discuss with your students the environmental impact of replacing a natural prairie or forested ecosystem with a golf course, noting the change in species diversity and broader ecological impacts of applications of fertilizers and pesticides and the related increase in fossil fuel consumption. Immediate examples from your local community help students immediately relate to the topics of this chapter.

But agricultural methods introduced over the past several decades have pushed croplands beyond their natural capacity to produce food. Nutrient runoff affects freshwater and marine ecosystems as fertilizer use increases. Pesticides may kill beneficial organisms as well as pests. Clearing and cultivation expose land to wind and water that erode the rich topsoil. In China, for example, overgrazing and other poor agricultural practices are turning 900 square miles of land—an area the size of Rhode Island—into desert each year. 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  Most human communities include at least one golf course where heavy chemical applications of fertilizers occur. Discuss with your students the environmental impact of replacing a natural prairie or forested ecosystem with a golf course, noting the change in species diversity and broader ecological impacts of applications of fertilizers and pesticides and the related increase in fossil fuel consumption. Immediate examples from your local community help students immediately relate to the topics of this chapter.

Figure 37.23a Figure 37.23a A dust storm in Changling, China

Human activities also threaten many forest ecosystems and the services they provide. Forests are also cut down to provide timber and fuel wood. Many people in nonindustrialized countries use wood for heating and cooking. 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  Most human communities include at least one golf course where heavy chemical applications of fertilizers occur. Discuss with your students the environmental impact of replacing a natural prairie or forested ecosystem with a golf course, noting the change in species diversity and broader ecological impacts of applications of fertilizers and pesticides and the related increase in fossil fuel consumption. Immediate examples from your local community help students immediately relate to the topics of this chapter.

Figure 37.23b Figure 37.23b A woman in Haiti gathering wood to process into charcoal

The growing demand of the human population for food, fibers, and water has largely been satisfied at the expense of other ecosystem services, but these practices cannot continue indefinitely. Sustainability is the goal of developing, managing, and conserving Earth’s resources in ways that meet the needs of people today without compromising the ability of future generations to meet theirs. 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  Most human communities include at least one golf course where heavy chemical applications of fertilizers occur. Discuss with your students the environmental impact of replacing a natural prairie or forested ecosystem with a golf course, noting the change in species diversity and broader ecological impacts of applications of fertilizers and pesticides and the related increase in fossil fuel consumption. Immediate examples from your local community help students immediately relate to the topics of this chapter.

You should now be able to
Define a biological community. Explain why the study of community ecology is important. Define interspecific competition, mutualism, predation, herbivory, and parasitism and provide examples of each. Define an ecological niche. Explain how interspecific competition can occur when the niches of two populations overlap. Describe the mutualistic relationship between corals and dinoflagellates. Define predation. Describe the protective strategies potential prey employ to avoid predators.

Explain why many plants have chemical toxins, spines, or thorns. Define coevolution and describe an example. Explain how parasites and pathogens can affect community composition. Identify and compare the trophic levels of terrestrial and aquatic food chains. Explain how food chains interconnect to form food webs. Describe two components of species diversity. Define a keystone species.

Explain how disturbances can benefit communities. Distinguish between primary and secondary succession. Explain how invasive species can affect communities. Compare the movement of energy and chemicals within and through ecosystems. Compare the primary production of tropical rain forests, coral reefs, and open ocean. Explain why the differences between them exist. Describe the movement of energy through a food chain.

Explain how carbon, nitrogen, and phosphorus cycle within ecosystems. Explain how rapid eutrophication of aquatic ecosystems affects species diversity and oxygen levels. Explain how human activities are threatening natural ecosystems.

Quaternary consumers Killer whale Tertiary consumers Tuna Secondary
Figure 37.UN01 Quaternary consumers Killer whale Tertiary consumers Tuna Secondary consumers Herring Primary consumers Figure 37.UN01 Reviewing the concepts, 37.8 Zooplankton Producers Phytoplankton An aquatic food chain

Autotrophs Heterotrophs Producer Herbivore (primary consumer)
Figure 37.UN02 Autotrophs Heterotrophs Producer Herbivore (primary consumer) Carnivore (secondary consumer) Energy Light Chemical elements Detritus Figure 37.UN02 Reviewing the concepts, 37.14 Decomposer Inorganic compounds (chemical elements)

Approximately 90% loss of energy at each trophic level Energy
Figure 37.UN03 Approximately 90% loss of energy at each trophic level Figure 37.UN03 Reviewing the concepts, 37.16 Energy

Figure 37.UN04 Figure 37.UN04 Connecting the concepts, question 1

Figure 37.UN05 Figure 37.UN05 Connecting the concepts, question 2

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