Answers to Open-Ended Questions Hoefnagels Essentials 2/e Chapter 19 Answers to Mastering Concepts Questions 19.1 1. Distinguish among ecosystems, communities, and populations. An ecosystem is all of the communities in an area, plus the abiotic environment. A community is all of the populations that live together in one habitat. Populations are interbreeding individuals of one species living in an area. 2. Which abiotic components influence the distribution of species in the biosphere? Water availability, temperature, salinity, nutrient availability, fire, and light are examples of abiotic factors that regulate species distribution. 3. What is the relationship between an organism’s habitat and its niche? A habitat is where a species lives. A niche is all the resources and conditions a species requires to survive, grow, and reproduce. The niche includes biotic and abiotic factors. Habitat is just one facet of a species’ niche. 19.2 1. Explain this statement: “If Earth’s axis were not tilted, there would be no seasons.” The tilt of the Earth on its axis means that the northern hemisphere receives direct sunlight during part of the year and the southern hemisphere receives direct sunlight during another part of the year. Because direct sunlight delivers more heat than sunlight hitting the Earth at an angle, each hemisphere has summer as it tilts toward the sun and has winter as it tilts away from the sun. 2. How do prevailing winds, ocean currents, and mountain ranges affect climate? Prevailing winds move air masses and moisture around the globe. Ocean currents influence temperature and moisture in coastal regions. Mountain ranges affect climate on a local scale by interrupting the movement of air and moisture. 19.3 1. How do climate and soil composition determine the characteristics of terrestrial biomes? Climate and soil composition determine which plants can grow in a particular area. The plants, in turn, influence the animals and other organisms that live there. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 2. Infer one adaptation of plants and one adaptation of animals to the abiotic conditions in any four biomes. Answers will vary but should include specific adaptations to climate, fire, or other abiotic conditions that characterize the biome. 3. Describe the types of organisms that live in each zone of a lake. The shallow water houses rooted plants and phytoplankton, along with many kinds of animals, including invertebrates, fishes, and amphibians. In the open water are phytoplankton, zooplankton, and fishes. Scavengers and decomposers live in the deeper water, where light does not penetrate. 4. How does a river change from its headwaters to its mouth? Near the headwaters, streams are small, fast-moving, turbulent, low in nutrients, and high in dissolved oxygen. As the river flows from its headwaters toward the mouth, it accumulates water, sediments, and nutrients from numerous streams. Meanwhile, the channel becomes wider. The water is slower-moving and less turbulent, so it has less dissolved oxygen. The murky water restricts photosynthesis to the banks and the water surface. 5. Describe some of the adaptations that characterize organisms in the open ocean, estuaries, intertidal zones, and coral reefs. All organisms in the open ocean tolerate high salinity. In the photic zone, floating phytoplankton carry out photosynthesis. Consumers scoop up the plankton, eat other animals, or rely on dead material that falls toward the ocean floor. Organisms living in estuaries have adaptations that allow them to cope with the daily tides, which bring extreme changes in salinity and moisture. Intertidal organisms can withstand wave action and daily periods of extreme dryness, wetness, heat, and cold. Coral reef organisms have adaptations that allow them to live in the nooks and crannies of the reef. 19.4 1. What is the competitive exclusion principle? The competitive exclusion principle states that two species cannot coexist indefinitely in the exact same niche. Sooner or later, the one with the greater reproductive rate will replace the other. 2. List three examples of symbiotic relationships. In a symbiotic relationship, one species lives in or on another. Three types of symbiosis include mutualism, commensalism, and parasitism. In mutualism, both partners benefit; an example is a cow plus the cellulose-digesting microbes in its rumen. In Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. commensalism, one partner benefits and the other neither benefits nor is harmed by the relationship; an example is the tiny mites that live, eat, and breed in a human’s hair follicles. In parasitism, one partner benefits and the other is harmed. Mistletoe growing on a tree illustrates parasitism because the mistletoe uses water and nutrients that the tree has acquired. 3. Describe some adaptations that protect against herbivory and predation. Thorns, milky sap, and poisonous or distasteful chemicals protect against herbivory; camouflage, warning coloration, weapons, and defensive behaviors protect against predation. 4. Define coevolution and describe an example. In coevolution, two species influence the directions of each other’s evolution and subsequent adaptations. An example is the relationship between a flowering plant and its pollinator. The flower’s shape may accommodate only one or a few types of pollinators. In turn, those pollinators have mouthparts that fit only that type of flower. 19.5 1. How do ecologists measure species diversity in a community? Two measures of species diversity are species richness and relative abundance. Species richness is the total number of species in a habitat. Relative abundance describes the proportion of the community that each species represents. 2. How is natural selection apparent in ecological succession? Succession is a change in species composition over time, and it occurs because one set of species alters the environmental conditions in such a way that other species can begin to exploit the habitat. In changing the conditions, they alter the selective forces that determine which other organisms can survive and reproduce in the habitat. 3. Distinguish between primary and secondary succession. Primary succession begins in a pristine habitat with no previous soil or community, and secondary succession occurs in locations that are disturbed but not destroyed. 4. What processes and events contribute to primary and secondary succession? Primary succession begins with the emergence of a new habitat; secondary succession begins with disturbance to an existing community. In both cases, pioneer species are the first to arrive. These species change the environment in ways that permit other species to thrive. Secondary succession is fastest because the soil-building required for primary succession takes a long time. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 5. How do disturbances prevent true climax communities from developing? Pockets of local disturbance create patches in different successional stages throughout the habitat. These disturbances (fires, trees falling, storm damage) happen frequently enough to prevent a true climax community. 19.6 1. Identify the trophic levels in a food chain. Primary producers are plants and other autotrophs that can produce their own organic matter. Primary consumers eat primary producers, secondary consumers eat primary consumers, and tertiary consumers eat secondary consumers. Decomposers eat dead organisms and organic wastes. 2. What roles do primary producers and decomposers play in ecosystems? Primary producers use inorganic nutrients to build organic material, which all consumers in the ecosystem rely on as an energy source. Decomposers recycle inorganic nutrients to the ecosystem as they decay organic matter. 3. How efficient is energy transfer between trophic levels? About 2% to 30% of the energy available to a trophic level is fixed into tissue and made available to the next higher trophic level, with an overall average of 10%. The rest is lost to the surroundings as heat. 4. Draw an energy pyramid for an ecosystem with three levels of consumers. Answers will vary, but the pyramid might include producers (100 kcal), primary consumers (10 kcal), secondary consumers (1 kcal), and tertiary consumers (0.1 kcal). 5. Explain how biomagnification disproportionately affects organisms at the top of a food chain. Biomagnified chemicals are stored in fatty tissues and are not biodegradable. The chemicals from one trophic level therefore become concentrated into the much smaller biomass that makes up the next highest level. This accumulation happens in each trophic level, so top consumers acquire the highest concentrations in their tissues. 19.7 1. Describe the main abiotic reservoirs for the water, carbon, nitrogen, and phosphorus cycles. For the water cycle, the main storage reservoirs are large water bodies such as the oceans, lakes, and rivers. Soil and the atmosphere also store a significant amount of water. For the carbon cycle, the main abiotic reservoir is the atmosphere. Oceans, carbonate rocks, Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. soil organic matter, and fossil fuels are other large carbon reservoirs. For the nitrogen cycle, the main abiotic reservoir is the atmosphere; soil and ocean sediments also store large amounts of inorganic nitrogen. For the phosphorus cycle, the main abiotic reservoir is phosphate-rich rocks. 2. What unique roles do microbes play in the nitrogen cycle? Nitrogen-fixing bacteria and archaea are the only organisms that can transform N2 from the atmosphere into a form that plants can use. Nitrification and denitrification are also critical processes that are unique to bacteria and archaea. 3. How can nutrient pollution lead to O2-depleted water? In the presence of sunlight, nutrients such as nitrogen and phosphorus stimulate the growth of algae. Initially the algae release O2 in photosynthesis, but soon their cells die and sink to the bottom of the water column. There, decomposers consume O2 from the water as they decompose the dead cells of the algae. Write It Out 1. How does a community differ from an ecosystem? A community is a group of interacting populations that inhabit the same region. An ecosystem includes a community plus its nonliving environment. 2. How does the fact that Earth is a sphere tilted on its axis influence the distribution of life? Temperature and moisture largely determine which organisms can live in each region of the globe. The tilt of Earth’s axis and its spherical shape affect these variables. Solar energy is most intense at the equator, where the sun is nearly overhead all year. The average temperature falls with distance from the equator because the same amount of solar energy is distributed over a larger area. The intense sunlight at the equator also drives the major convection cells, which largely determine how much precipitation falls in each region. And because the axis is tilted, the northern and southern hemispheres experience seasonal variations in temperature and moisture. 3. How can the poor soil of the tropical rain forest support such diverse and abundant life? The poor soil of the tropical rain forest supports diverse and abundant life because decomposers and plants constantly recycle nutrients without returning them to the soil. 4. List adaptations of desert and polar ice animals to the climate of their respective biomes. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Desert animals have adaptations that reduce water loss and that allow them to acquire the water they need from their food. Animals that live at Earth’s poles face below-freezing temperatures almost year round. Many of these animals therefore have thick insulation (fat, feathers, and/or fur) and antifreeze chemicals that prevent ice from forming in their cells. 5. Use the clues provided to determine which biome houses each of the following four fish. Yellowfin tuna require salt water; young sea bass occupy areas where fresh and salt water mix; brook trout require clear, cool, oxygen-rich fresh water; and catfish prefer warm, quiet fresh water with a slow current. Yellowfin tuna live in the open ocean; young sea bass live in estuaries; brook trout occupy mountain streams; catfish live in the slow-moving rivers that characterize flat land. 6. Three Galapagos finch species have different beak sizes and specialize in different types of food. Explain how these three species can share the same habitat without driving each other to extinction. Since the finches have different diets, they occupy different niches. Competition is therefore unlikely between these finch species. 7. List examples of adaptations that enable an organism to compete with other species, live inside another species, find food, and avoid herbivory or predation. How does each adaptation contribute to the organism’s fitness? Answers will vary; here are some samples. An example of an adaptation that enables an organism to compete is the rapid growth of a seedling, which may shade out others as it acquires light energy. More photosynthesis means more energy for reproduction. An adaptation that enables one organism to live inside another is the head of a tapeworm, which has hooks that keep the worm from being flushed out of an animal’s digestive tract. A worm with such hooks acquires more food than one without, which means more energy is available for reproduction. An example of an adaptation that helps an animal find food is an eagle’s keen eyesight. An eagle that can spot small animals acquires more food than one with poor eyesight. An example of an adaptation that helps an organism avoid predation is camouflage. An animal that can avoid being eaten (at least before reproductive age) has a chance at reproductive success. 8. Mountain yellow-legged frogs live in the Sierra Nevada range. Their tadpoles mainly eat algae. One predator of adult frogs is a garter snake, which is eaten by bullfrogs. Recently, a chytrid fungus has killed many adult mountain yellow-legged frogs. How might this change affect the algae, garter snakes, and bullfrogs? With fewer tadpole grazers, algae populations might increase. When numbers of adult mountain yellow-legged frogs decline, less food is available to garter snakes, which Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. might decrease garter snake population size. Fewer garter snakes might lead to lower numbers of bullfrogs. 9. Suppose a plot of forest is cleared of trees in anticipation of a new shopping mall. However, after the bulldozers are gone, the company runs out of money, and the land sits undisturbed for many years. Describe the events that may occur in the years following the damage to the forest. What are these community changes called? The land was disturbed but not destroyed. The soil was left intact, and many smaller plants likely remained. The events of secondary succession would therefore commence. Fast-growing species like weeds and herbs would be the first to become abundant. Then grasses and shrubs would become more common. Finally, slower-growing trees would begin to shade the weeds and grasses. After a few decades, the forest would again be mature. 10. Imagine that you could build a covered enclosure around a small ecosystem, blocking out all light and preventing gas exchange with the environment. How would the total amount of organic material, available energy, and nutrients in the ecosystem change over time? Without light, most or all primary production would cease (some autotrophs do not use light energy to produce food, but most do). With no energy entering the ecosystem, producers would soon die. Without food, herbivores would also die, followed by consumers. Decomposers would break down the dead bodies, converting organic matter into CO2 and H2O and releasing heat. After the last decomposer died, all of the energy in the ecosystem would have been released as heat and all of the organic material would have been converted into CO2, H2O, and other inorganic substances. However, the total amount of nutrients in the ecosystem would not have changed throughout this process. All of the phosphorus that was once in producers, consumers, and decomposers would end in the soil. Nitrogen and carbon would be distributed between the atmosphere and the soil. 11. Alaska salmon spend much of their adult lives in the ocean, eating crustaceans and small fish. When it is time to mate, they swim upstream to spawn in the rivers where they hatched. Along the way, bears and other predators catch and eat many salmon. What does this story tell us about the source and fate of nutrients in ecosystems? The adult salmon form a link between the biogeochemical cycles of the ocean and the land. Nutrients therefore move between ecosystems within the biosphere. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Pull It Together 1. What factors determine the location of each biome on Earth? For terrestrial biomes, temperature and moisture are most important; these depend, in turn, on latitude, altitude, and distance from the ocean. Fire also maintains some biomes on land. For aquatic biomes, important factors include latitude, distance from shore, light penetration, depth/pressure, nutrient availability, dissolved oxygen, and salinity. 2. What types of forests occur on Earth, and what combination of conditions favors each type? The main types of forests are rainforests, temperature deciduous forests, temperate coniferous forests, and taiga. High rainfall and warm temperatures throughout the year favor the rainforest. In temperate deciduous forests, rainfall is evenly distributed throughout the year, summers are warm, and winters are cold. Temperate coniferous forests usually grow where winters are milder and summers are cooler. Taiga forests grow where winters are very long and cold. 3. What types of terrestrial biomes are likely to have standing and running water? Make connections between terrestrial and aquatic biomes in the concept map. Tundra, chaparral, and desert biomes seldom receive precipitation, so standing and running water are uncommon in these biomes. Grasslands and savannas have seasons during which rainfall is abundant, so seasonal streams and ponds are likely. Forests often receive significant precipitation; permanent lakes, streams, and rivers are common. Many connections between terrestrial and aquatic biomes are possible. They include the runoff of nutrients from land to water; the ocean currents that moderate the temperature of nearby land; the animals that occupy both water and land; the oxygen produced by aquatic producers that replenishes the atmosphere above both water and land; and the food that humans harvest from the water to consume on land. 4. Add mutualism, commensalism, and parasitism to this concept map. “Symbiosis” connects with “when both species benefit, is called” to “Mutualism”. “Symbiosis” connects with “when one species benefits and the other is unharmed, is called” to “Commensalism”. “Symbiosis” connects with “when one species benefits and the other is harmed, is called” to “Parasitism”. 5. Make another concept map that shows nutrient cycling on land. Include producers, consumers, decomposers, carbon, nitrogen, phosphorus, atmosphere, and soil. You may also add other concepts. The concept map should show that producers obtain carbon from the atmosphere and nitrogen and phosphorus from the soil. Producers release carbon to the atmosphere. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Consumers obtain all of these nutrients from producers. Consumers release nitrogen and phosphorus to the soil and release carbon to both the atmosphere and soil. Decomposers obtain carbon, nitrogen, and phosphorus from dead organic matter and organic wastes. Decomposers release nitrogen and phosphorus to the soil and release carbon to the atmosphere. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.