LS_5 Chapter 18 TE 2024 - Exploring the Biosphere

The image on this page was chosen to con- vey the idea that the earth is one large bio- sphere of interacting ecosystems. And God has given humans the responsibility and privilege of managing it. 370 UNIT 5  Unit 5 INTERACTING WITH THE...

The image on this page was chosen to con- vey the idea that the earth is one large bio- sphere of interacting ecosystems. And God has given humans the responsibility and privilege of managing it. 370 UNIT 5  Unit 5 INTERACTING WITH THE BIOSPHERE 18 Exploring the Biosphere 372 19 Rhythms in Ecosystems 397 20 Managing God’s Creation 419 ROB CARTER’S TESTIMONY FROM A MARINE BIOLOGIST TO YOU A lot of Christians don’t think it’s a big deal to mix evolution into the Bible, but I could I love science! But when I was younger there was a Studying the natural world has become a lifelong not do that. I like consistency, and evolu- conflict between what I was being taught in school passion. I have had the pleasure of studying coral tion introduces a giant contradiction that about evolution and what I read about science in the reefs for my doctoral work. After hundreds of scuba causes problems all the way through. For Bible. Everyone I knew, as far as I was aware, believed dives and thousands of hours learning about the example, the Bible clearly teaches that the in evolution. When I got to college, my professors had weird and wonderful creatures that live first people were Adam and Eve and that a lot of hard questions for me! When I finally met some there, I can testify with the psalmist, people who did not accept evolution, I could hardly “For thou, Lord, hast made me glad we did not descend from apes. Jesus also believe it. But with their encouragement I began to through thy work: I will triumph believed this, as did all the New Testament rethink what I believed. in the works of thy hands” (Ps. authors. Therefore, it is not a simple thing 92:4). to reject the beginning of the Bible without causing problems in the rest of the Bible. It Dr. Rob Carter took a couple of years, but in the end I re- alized that evolution was wrong and that there was not a giant contradiction be- tween science and the Bible. INTERACTING WITH THE BIOSPHERE 371  The people in this photo have gathered to view Yosemite Falls in Yosemite National Park. Setting aside land as a park is one way of managing natural resources. 18 EXPLORING THE BIOSPHERE CHAPTER 18 OBJECTIVES Analyze the relationship between biotic and abiotic factors in the envi- ronment. Classify biomes on the basis of distin- guishing characteristics. Evaluate man’s role in the environ- ment on the basis of biblical teaching. BWS OVERVIEW PARKS IN PERIL Chapter 18 is foundational for you and your America’s national parks are places where people can get students as you begin your overview of back to nature. In places like Yosemite, Yellowstone, and the ecology. Grand Canyon, folks can find fresh air, scenic beauty, and plenty of open space. These days, there’s something else peo­ 18A FACTORS IN THE ple can find in our national parks—lots of other people! How can we keep wild places wild and still have them be accessible ENVIRONMENT to millions of visitors? All those visitors can have a lasting and 18.1 Ecosystems and Ecology harmful impact on the ecology of the parks they visit. Exer­ cising good and wise dominion over God’s creation includes 18.2 Factors in the Environment exploring ways to protect natural places for people to enjoy. 18B BIOMES AND ECOSYSTEMS 18.3 Modeling the Environment 18.4 Types of Biomes 18.5 Zones, Habitats, and Niches LAB ACTIVITY Lab 18C, Backyard Ecosystems—Stu- dents study the interactions between abi- otic and biotic factors in a local outdoor area. 18A Factors in the Environment 373 18B Biomes and Ecosystems 379 TEACHING THE MATERIAL In-Text Lab: Carp Question (p. 378), Lab 18C: Backyard Ecosystems —Inquiring into Ecology Right Outside Your Door ESSENTIAL QUESTION STRATEGIES What makes one environment different from another? Class Opener: Use the Chapter opener to begin a discussion of the ways OBJECTIVES that people interact with ecosystems. 18A1 Describe the factors that define an ecosystem. Discussion: Use the Group Discussion: Possible Factors and Group Dis- cussion: Abiotic Factors teacher notes on pages 373 and 375 respectively 18A2 Distinguish between biotic and abiotic factors in the environment. to engage students in thinking about biotic and abiotic factors. RESOURCES Worldview Shaping: Use the Rejoice in the Wonder of God’s Creation Careers: Protecting Parks and People: Serving as a Park Ranger teacher note on page 374 to help students recognize that the splendor of creation points us to the God who created it. Review 18A: Factors in the Environment 372 CHAPTER 18 18A NATURE’S HOUSEHOLDS FACTORS IN THE The prefix eco- in “ecosystem” comes from 18A Questions ? the Greek word oikos, meaning “house- ENVIRONMENT What is an ecosystem? hold.” Just as a household consists of a What things make up an ecosystem? dwelling shared by a number of people, What makes one environment different from another? an ecosystem is made up of a dwelling 18.1 ECOSYSTEMS AND ECOLOGY place and all the organisms that live there. Let’s think for a moment about the things you can expect to find in a national park like Yosemite. There are natural features like moun- GROUP DISCUSSION: tains, rivers, and glaciers. There are also living things like bears, trout, and pine trees. These particular organisms and the place where they POSSIBLE FACTORS live together make up an ecosystem—a limited area in which living Have students brainstorm a list of all the and nonliving things interact. The study of the interactions between things that might affect the trout living in those living and nonliving things is called ecology. a stream. They might be surprised at how 18-1 long the list can get! What things affect the life of this trout? WHAT DO ECOLOGISTS STUDY? Make sure that students understand that At first, the study of ecology might not seem very complicated. Think the study of ecology always involves a of a trout living in one of Yosemite’s streams, for example. What fac- living component. So, for example, the tors affect its life? Simple, right? There’s the trout, and there’s the interspecific competition for resources stream that it lives in. But it’s not actually as simple as that. For in- between two species of fish can be con- stance, where did the water in the stream come from? Originally it sidered a subject for the ecologist, as can fell as either rain or snow. But where did that come from? The water the selection of substrate particle size for vapor that fell as rain or snow had risen into the air through evapo- ration far out over the Pacific Ocean. So the water in the stream is spawning for those same fish. But the affected by events that happen many hundreds of miles away. Com- question of how water velocity helps sort plex, isn’t it? The never-ending tangle of actions and interactions substrate particles by size is one involv- within an ecosystem is what makes ecology fascinating! ing only abiotic factors. It is a question of hydrology but not one of ecology. ExPLorIng thE BIoSPhErE 373 Formative Assessment: Use the Formative Assessment: Biotic and Abi- otic Factors teacher note on page 377 to assess students’ understanding. Discussion: Use the in-text lab and the Group Discussion: The Interplay of Multiple Factors teacher note on page 378 to help students understand the complexity of ecosystems. Class Closer/Ticket Out the Door: “Name a biotic factor and an abiotic factor in your classroom.” EXPLORING THE BIOSPHERE 373  18.2 FACTORS IN THE ENVIRONMENT REJOICE IN THE WONDER Ecosystems consist of many parts that interact with each other. Some OF GOD’S CREATION of those parts are living things and others are not. We call the living While studying the interactions of biotic parts of the ecosystem the biotic factors. The nonliving parts are the and abiotic factors, direct students’ atten- abiotic factors. Let’s take a look at some of these. ABIOTIC FACTORS tion to Psalm 19 and its praise of God for His splendid creation. Sunlight. The amount of sunlight that an ecosystem receives deter­ mines how much energy is available. It controls how much photosyn­ thesis can take place and also affects the daily pattern of temperatures and local climate. Air. Of course, the oxygen that living things need is found in Earth’s atmos­ phere. But air also contains the carbon dioxide that plants need for photo­ synthesis and the water vapor that forms rain or snow. Water. All living things need water. The kinds and numbers of organisms that can live in an ecosystem are gov­ erned by how much water is available and when it is available. 374 ChAPtEr 18 374 CHAPTER 18  Altitude. This mountain peak is bare rock because of its GROUP DISCUSSION: altitude. High­altitude ecosystems are colder than those ABIOTIC FACTORS at lower elevations. Fewer plants and animals are adapted to living in such harsh conditions. Ask students to name the abiotic factors affecting the area around your school. Write each one on the board as they name them. Soil. Whether rich loam or bare rock, the soil or substrate in an ecosystem affects what kinds of plants can grow there. Climate. The climate of an ecosystem is its long­term pattern of weather. Climate is determined mainly by how much sunlight and water an ecosystem receives. ExPLorIng thE BIoSPhErE 375 EXPLORING THE BIOSPHERE 375  FACTORS BIOTIC FACTORS Some students may benefit from looking at a picture of a natural area and listing the abiotic and biotic factors present. Plants. Plants play a crucial role in most eco­ systems by making the sun’s energy available to other organisms in the form of sugars that are produced during photosynthesis. Animals. Only a small number of animals in an ecosystem are as large as this mule deer. Most of the animals in an ecosystem, such as insects, are far smaller. HUMANS AND ECOSYSTEMS Students might be tempted to think that ecosystems are things that are “out there” People. Of course, humans can have a huge impact on an somewhere, but because an ecosystem ecosystem too. Visitors to national parks, such as Yosemite, is any place where a particular organism need transportation, food, and lodging. In 2016 alone, lives in a particular environment, an eco- Yosemite roads, restaurants, hotels, and campgrounds had to accommodate over five million park guests. system can literally be anywhere. A sky- scraper full of office workers is as much an ecosystem as Yosemite is and one whose 376 ChAPtEr 18 interactions are equally as complex. 376 CHAPTER 18  FORMATIVE ASSESSMENT: BIOTIC AND ABIOTIC FACTORS 1. What is an ecosystem? (a limited area in which living and nonliving things interact) 2. What are abiotic factors? (nonliving parts of an ecosystem) 3. What are biotic factors? (living parts of an ecosystem) 4. What are three abiotic factors in an PROTECTING PARKS AND PEOPLE: SERVING AS A PARK RANGER ecosystem? (Accept any three: sunlight, air, water, altitude, soil, climate. Other answers are possible.) “Protect the park from the people, the people from the park, and the people from the people” is an unofficial 5. N  ame three biotic factors. (plants, park ranger motto. Yosemite is a wild and sometimes dangerous place, and people have to be protected. Be­ animals, and people) sides natural hazards such as wild animals, rock falls, icy trails, and cold, swift rivers, some visitors face the extra dangers of high­risk adventures like rock climbing. On REVIEW 18A, FACTORS IN September 11, 1993, a rock climber fell to his death from Yosemite’s Lost Arrow Spire. Ranger Mary Litell Hinson THE ENVIRONMENT was on the job. She was part of the search­and­rescue LAB 18C, team that found the body. Later she broke down in tears as she informed the climber’s friend of the tragedy. BACKYARD ECOSYSTEMS But protecting people from the park isn’t a ranger’s only Once students have an understanding of job. Sometimes they have to protect the park from the people or the visitors from each other. The day’s chal­ the material in Subsection 18.2, they should lenge might be picking up litter, monitoring campfires, be ready to work through Review 18A and or closing trails to protect mother bears and their cubs. Lab 18C. Park rangers have to be ready for anything! 18A REVIEW QUESTIONS 1. What is an ecosystem? 2. What is ecology? 3. List three abiotic factors in an ecosystem. 4. Would bacteria living in a stream be an abiotic or biotic factor in an eco­ system? Explain. 5. Choose one factor in an ecosystem and describe how it might affect one other factor in the same ecosystem. ExPLorIng thE BIoSPhErE 377 18A REVIEW ANSWERS 1. An ecosystem is a limited area in which living and nonliving things interact. (p. 373) 2. Ecology is the study of the interactions between living and nonliving things in an ecosystem. (p. 373) 3. Accept any three: sunlight, air or atmosphere, water, altitude, soil or substrate, climate. (Other answers are possible.) (pp. 374–75) 4. Bacteria are living things, so they are a biotic factor in an ecosystem. (p. 374) 5. Answers will vary. Example: Altitude affects the temperature of an ecosystem. (pp. 374–76) EXPLORING THE BIOSPHERE 377  LAB EXERCISE CARP QUESTION PROBEWARE OPTIONS E Equipment Can one abiotic factor affect another? There is no quick and cheap way to test bowls or beakers (2) Both trout and carp can be found in lakes that ice over during winter. for dissolved oxygen. For more informa- probeware with temperature and But carp are also perfectly happy in warm ponds and lakes where no tion on probeware, see Appendix F in dissolved oxygen probes trout can live. Is there another abiotic factor besides temperature that BJU Press Biology Lab Manual 5th Edition. affects each fish’s ability to survive in either warm or cold water? If you have access to a water quality test ProCEDUrE kit that includes the necessary items to test for DO, you may substitute that for Day 1: probeware. 1 Fill two bowls or beakers with water. Allow one to chill in a re- frigerator overnight; keep the other at room temperature. Day 2: LAB CONSIDERATIONS 2 Copy Table 18-1 on a separate sheet of paper. Gas exchange in any body of water takes 3 Use the probeware to measure the temperature and the dissolved place mostly at its surface-air interface, oxygen concentration of the water in each container. Record so for this experiment a container with a your results in the Day 2 row of Table 18-1. large surface area is more desirable than 4 Place the container of room-temperature water in the refrigera- one that is deep but narrow. tor and allow it to chill overnight. Leave the container of chilled It is important to let the samples set for water out to achieve room temperature. a time in order to allow any excess dis- 1. Why is oxygen important for living things like trout and carp? solved gases in your local water supply to 2. Do both containers have the same dissolved oxygen concentra- gas off. tion? If not, which container of water has a lower dissolved oxy- gen concentration? Day 3: SAMPLE DATA 5 Measure the temperature and dissolved oxygen concentration of The sample data shown in Table 18-1 is each container. Record your results in the Day 3 row of Table 18-1. based on the actual solubility of oxygen 3. Are your results the same as those obtained on Day 2? in water. Student results will vary, but the DO concentration in warm water should 4. What appears to be the relationship between the temperature of the water and its dissolved oxygen concentration? be significantly lower than it is in chilled water. 5. On the basis of your results, give two possible reasons why carp can survive in warm water while trout cannot. 6. Imagine you work for a company that raises trout to sell for GROUP DISCUSSION: stocking ponds and lakes. A farmer comes to you in the spring THE INTERPLAY OF and asks about the possibility of stocking trout in his farm pond. MULTIPLE FACTORS Using the results in your experiment, what do you think you would need to know before making a recommendation to the You can use this lab activity as a spring- farmer? Explain. board for a discussion on how multiple 7. Why do you think it was important for this experiment to switch abiotic and biotic factors interact to af- the two samples and retest them on Day 3? fect living things. Ask students whether table 18-1 there might be other factors that affect Dissolved oxygen Concentration Versus temperature in Water how much dissolved oxygen is available Chilled room temperature for fish. For example, saprophytic bacteria Temperature Dissolved Oxygen Temperature Dissolved Oxygen also require oxygen, and their activity in (°C) (mg/L) (°C) (mg/L) the lower levels of lakes and ponds often Day 2 5 12.8 20 9.2 creates an anoxic zone where fish cannot Day 3 5 12.8 20 9.2 survive. Aquatic plants produce oxygen 378 CHAPTER 18 during photosynthesis, offsetting their IN-TEXT LAB ANSWERS 1. Trout and carp need oxygen for cellular respiration. 2. No. The container with room-temperature water has less oxygen. 3. Yes. 4. Cold water can dissolve more oxygen than warm water can. 5. The warm temperature—that carp can tolerate—itself may be lethal to trout. And since warm water holds less oxygen, the lower oxygen level may also be lethal to trout. 6. You would need to know what the pond’s temperatures are like dur- ing the summer since spring is not the warmest part of the year. 7. Retesting the samples strengthens the conclusion that the difference in temperature caused the difference in dissolved oxygen concentra- tion. 378 CHAPTER 18 18B own biological oxygen demand (BOD), BIOMES AND but only during daylight hours. At night, in the absence of such oxygen produc- ECOSYSTEMS tion, the BOD in heavily planted ponds can exceed the amount of available oxy- How do scientists study the environment? 18B Questions ? gen, causing sudden fish die-offs. How do ecologists model the 18.3 MODELING THE ENVIRONMENT environment? God designed Earth to be a home for living things. And there is What kinds of biomes are there? life almost everywhere on Earth. Protists live 11,000 m deep in the How are habitats and niches related? Marianas Trench, and bar-headed geese fly 6500 m high through the Himalayas. Saharan silver ants forage in one of the world’s hottest deserts, while polar bears patrol the pack ice of the Arctic Ocean. These places, along with all the other habitable portions of the earth, are called the earth’s biosphere. But the biosphere is extremely large and diverse. At present, it’s im- possible to model every interaction that takes place between all the biotic and abiotic elements within the entire biosphere. There’s just too much information out there! It makes sense then for ecologists WATER DECIDUOUS BIOMES to break down the earth into smaller chunks for study. One way to FOREST do this is to group together parts of the biosphere that have simi- Regions on different continents that can ICE TROPICAL lar biotic and abiotic factors. These smaller parts of the biosphere RAINFOREST be categorized as the same biome regu- that share similar climates and kinds of living things are known larly have organisms that fit in similar as biomes. niches. For instance, grasslands will often Of course, there are some factors that can affect the entire biosphere. GRASSLANDS/ have large herbivores that live on the TUNDRA SAVANNA But thinking about the biosphere as a collection of different types of grasses. biomes makes it easier for ecologists to learn about and model the DESERT interactions within each type. Even so, biomes can still be dauntingly CONIFEROUS large and complex. To really understand what happens in them, FOREST GROUP DISCUSSION: scientists can define even smaller parts of biomes for study. You’ll see THE MODELING some of these in Subsection 18.5. NATURE OF BIOMES Ask students to name several animals that live in several different biomes. Ex- amples include white-tailed deer and red foxes. After they name several animals, lead them in a group discussion about the modeling nature of biomes. 379 TEACHING THE MATERIAL RESOURCES ESSENTIAL QUESTION Ethics: Fish Fight (p. 396) How do scientists study the environment? Case Study: Riparian Zones (p. 395) Ethics Rubric OBJECTIVES 18B1 Explain how ecologists use models to study the environment. BWS Review 18B: Biomes and Ecosystems 18B2 Describe the various types of biomes. STRATEGIES 18B3 Explain the relationship between biomes, ecosystems, habitats, and Class Opener: Use the Biomes teacher note on this page to open the class niches. with a discussion of biomes and the niches of the organisms that live in 18B4 Recommend a solution to an issue regarding environmental usage. them. BWS Class Discussion: Use the Group Discussion: The Modeling Nature of Bi- omes on this page to lead students in a discussion of the fact that biomes are models. (continued) EXPLORING THE BIOSPHERE 379  18.4 TYPES OF BIOMES LUMPERS VERSUS SPLITTERS Coniferous Forest In far northern North America, Europe, and Asia, winters are long, Defining and delineating biomes is an- snowy, and cold, while the short summers are warm and moist. Co- other fine example of the difficulties that niferous forests, also called boreal forests or taiga in that part of the can accompany some kinds of modeling. world, cover vast areas of the region. In fact, coniferous forests are Biomes don’t suddenly change from one Earth’s largest land biome. Remember that coniferous trees are those kind to another as the borders shown that bear their seeds in cones. The needles and scales of conifers are on a map might suggest. The change is designed to survive the cold of winter. Downward-sloping branches effectively shed snow. Thickly wooded coniferous forests typically gradual. Even within areas of one kind of allow little light to reach the forest floor. And their fallen needles also biome, there are smaller pockets of other create poor soil conditions. As a result, few other kinds of plants can biomes. Scientists don’t even agree on all grow on the forest floor. of the parameters that should be used to gree nis h Only very hardy animals, such as lynxes, moose, and great gray owls, define biomes. Depending on the num- w can live and remain active in the northern forests year-round. Less ber of different criteria that are used to ar sturdy residents, such as mice and squirrels, may spend the winter ble define them, a model might identify as months hibernating. Many migratory birds, such as warblers, spend r few as a half-dozen biomes or well in ex- only their summers here. They come to take advantage of the huge cess of a hundred. swarms of flies, gnats, and mosquitos that breed in the forest’s abun- dant bogs and marshes. Quite a bit of confusion can result from the names assigned to different biomes. For instance, many people associate the term savanna with the tropical grasslands of eastern and southern Africa. Some sci- entists, though, regard savannas as any grasslands with tree coverage between 5% and 25% (and sometimes as high as 80%). By this definition, many other parts of the world could be classified as savan- nas. The oak woodlands of California’s Si- erra Nevada foothills corridor, for example, match this description, but few Califor- nians would think of them as a savanna. BOGS When the winter snows of the boreal forests are temporarily banished by the warmth of the short northern summer, many treeless areas within the forest are moose revealed to be bogs. Bogs are places where acidic, water-saturated soil promotes slow plant growth—and even slower decay. In such conditions, partially de- cayed plant material known as peat can accumulate to a depth of many meters. Flammable peat has historically been im- portant as a fuel source for humans and is 380 still used for that purpose in some areas Formative Assessment: Use the Formative Assessment: Biomes teacher note on page 391 to gauge students’ understanding. Worldview Shaping: Use the ethics box on page 396 to allow students to grapple with the issue of using natural resources. Class Closer/Ticket Out the Door: Writing Prompt: “Identify the biome that you live in and give two characteristics to support your choice.” 380 CHAPTER 18  today. Bogs can be quite large—one ex- ample in Western Siberia covers more than a million square kilometers! ck aco pe Deciduous Forest The trees in a deciduous forest lose their leaves at the end of each growing season. These forests are found across large portions of INTERACTIVE BIOME North America, Europe, and Asia. Deciduous forests have four sea- sons, mild temperatures, and around 100 cm of rainfall each year. For an interactive website that challenges The decayed leaves of deciduous trees make rich soil. Good soil and students to connect each major biome ample rainfall combine to produce a thick and often tangled under- with the appropriate biotic and abiotic story (the plants of the forest that grow beneath the canopy formed factors, conduct an Internet search using by tall trees). the keywords “build a biome.” The far-flung deciduous forests of eastern North America are home to many kinds of animals. Here you might see black bears, white- tailed deer, opossums, and turkeys. The same sort of forest in India may be home to tigers, gaurs (similar to bison), Asian elephants, and peacocks. gaur ExPLorIng thE BIoSPhErE 381 EXPLORING THE BIOSPHERE 381  Tundra If you were to travel northward through the boreal forests of the Northern Hemisphere, in time you would reach what’s called the tree line. North of this line is a region where only a few inches of soil thaw out during the short summer growing season. Beneath that is a layer called permafrost, which remains frozen year-round. Rainfall is also scarce here. The thin soil and lack of rain prevent the growth of tree roots. Instead of trees, huge areas are covered by low- growing shrubs, grasses, and lichens. This biome is called tundra. In the north it’s known as Arctic tundra, but it also exists in high moun- tains. There it is known as alpine tundra. ANTARCTIC TUNDRA Though it is a harsh environment, the Arctic tundra supports a sur- prising amount of wildlife. Gray wolves prey on caribou and musk Most of Antarctica is permanently cov- oxen. Arctic foxes pursue smaller prey such as lemmings and tun- ered by ice, but a few islands off its coast dra voles. Small ponds and streams formed by summer meltwater and some parts of the Antarctic Peninsula produce vast clouds of insects. Astonishing numbers of ducks, geese, are ice-free part of the year. These places and other migratory birds take advantage of this seasonal abundance support an Antarctic tundra biome. Its of food and nesting habitat to raise their young. Before the winter cold returns, these birds take wing for warmer climes, sometimes total area is very small in comparison with as far away as South America. Their annual migrations often cover the two types mentioned in the Student many thousands of kilometers. Edition. ox sk u m rns c te cti Ar 382 ChAPtEr 18 382 CHAPTER 18 Grasslands Grasslands are often found in the interiors of continents, especially in North and South America and Asia. Interior summers tend to be warm, while winters can be cold and windy. Also called prairies or plains, these areas don’t receive enough rainfall to support the growth of forests. Many grasslands receive 25–75 cm of rain each year. Some grasslands get more than this, but dry-season fires prevent tree growth. Yearly rainfall determines what kinds of grasses will grow on a grassland. Less rain normally permits only shorter grass species to grow. Deep, fertile grassland soils have often served humans well as productive farmland. Grasslands provide plenty of food for grazing animals. Bison and pronghorns once roamed the Great Plains of North America in large numbers. In the South American pampas, one can find gua- nacos, while the Eurasian steppes support wild horses and gazelles. Sometimes the herds aren’t mammals—instead, they’re large, swift- ger running birds such as emus or rheas. Abundant grains also feed large ad nb numbers of rodents like mice, gophers, and prairie dogs. These in ica turn are preyed upon by foxes, badgers, and other small carnivores. er Am From the air, or perched on a rare tree or utility pole, hawks and fal- cons also scan the seas of grass for unwary rodent meals. k aw h n’s Swainso bison ExPLorIng thE BIoSPhErE 383 EXPLORING THE BIOSPHERE 383  Desert Would it surprise you to learn that high temperatures are not the de- fining feature of a desert? It’s true! Deserts are biomes that receive very little water. Each year they can expect to see about 25 cm or less. The Sahara in Africa is perhaps the world’s most famous desert. When we think of it, we often imagine scenes of blistering-hot sand dunes. But the frigid interior of Antarctica is also a desert. It receives only about 5 cm of water each year in the form of snow. The extreme temperatures of the scorching Sahara dunes and the frozen heart of Antarctica limit the kinds of life that can survive there. But the more temperate deserts found elsewhere are home to a wide variety of plants and animals. All of them have special fea- tures or behaviors designed for living in an environment short on liquid water. Desert plants often have thick, fleshy stems and leaves for storing water. Many also conserve water by not blooming every year. Instead, they produce flowers only during rare wet years. Des- ert mammals can keep cool by being more active at night. Reptiles warm their bodies in the morning sun, then seek shade as the day- time heat increases. Only a few large mammals are suited for desert life. These include mountain lions, oryx, and, of course, camels. Most desert mammals, like jackrabbits, jerboas, and kangaroo rats, are smaller. Small- to medium-sized desert hunters, such as jackals and bobcats, take ad- vantage of these food sources. Desert birds include hawks, owls, and a rd quail. But deserts are perhaps best known for their diverse kinds of i liz an reptiles. Among these are two well-known species of poisonous liz- bi ards—the Gila monster and Mexican beaded lizard. Fa vicunas 384 ChAPtEr 18 384 CHAPTER 18 Tropical Rainforest nb il l TEMPERATE RAINFORESTS r Tropical rainforests combine year-round warmth and large amounts ho of rainfall with a lack of a dry season. They get a lot of rain—over When we think of rainforests, we often 170 cm per year and often much more. Some rainforests receive over think of lush jungles. But there are actu- 10 meters of rain in a year! ally two types of rainforest—tropical and The many and varied plants in a rainforest make up four distinct, temperate. Because tropical rainforests vertical zones. The highest zone, the emergent layer, consists of the occur over a greater area of the globe, the tops of the tallest trees. Beneath this is a thick canopy layer made of Student Edition concentrates on them. the crowns of shorter trees. Little sunlight can get through this layer, so the lower layers exist in perpetual shade. Closer to the ground is Temperate rainforests are coniferous or the understory made of small trees, bushes, and large-leafed plants. deciduous forests that experience much- Finally there is the forest floor itself, rich in fungi and bacteria that higher-than-average annual rainfall, usu- decompose the abundant plant and animal material. ally in excess of 140 mm annually. This is Rainforests are well known among the world’s biomes for having a relatively uncommon biome normally the greatest diversity of living things. A few hectares of rainforest found near mid-latitude coastlines with may have hundreds of species of trees. Insects, birds, amphibians, mild temperatures. and reptiles each show their greatest variety of form and color here. Most of these creatures live in the rainforest’s trees. Knowing that, it’s no surprise then to learn that some of the most common rainforest mammals are tree-dwelling primates (monkeys, lemurs, and apes) and bats. In the rainforest, even plants live on other plants! Held high above the soil by their host plants, epiphytes such as orchids and bro- meliads obtain moisture and nutrients from the damp rainforest air. o ro ga kan tr e e ExPLorIng thE BIoSPhErE 385 EXPLORING THE BIOSPHERE 385  Chaparral Chaparrals are found in coastal areas with mild, wet winters and hot, dry summers. Dry summers mean that chaparrals are also sub- ject to cycles of wildfires and regrowth. One of the largest regions of chaparral is the coastlands around the Mediterranean Sea. For this reason, chaparrals are often said to have a Mediterranean climate. Chaparral plants and animals must be able to cope with both fire and drought. The most common plants in chaparrals are shrubs. They often have tough, waxy leaves to conserve water. Many have thorns that deter browsing animals. Unlike other biomes, a chaparral’s growing season is in winter and early spring when water is available. Many chaparral plants depend on fires to return nutrients to the soil b bit ra and to clear the ground for new growth. ck MORE ON TORPOR Chaparral animals are adapted to seasonal changes. Large animals ja like deer may escape summer heat by migrating to cooler elevations Different types of torpor are known by in the mountains. Smaller mammals, such as jackrabbits, become various names. Students are probably fa- less active during the summer or restrict their activities to the cool- miliar with winter-induced torpor, known ness of night. Amphibians survive the dry weather by entering a dor- as hibernation. Torpor induced by dry mant state called torpor. They find a damp, sheltered place to hide summertime weather is referred to as es- until the winter rains return. tivation. Many animals experience daily cycles of torpor, that is, sleep, in addition to seasonal cycles, being active only by day (diurnal) or night (nocturnal). As chil- dren enter into puberty, their developing q uail bodies require lengthier periods of tor- rn ia por, producing the sleeping-in teenagers lifo Ca that parents are familiar with. 386 386 CHAPTER 18 Savanna The savannas of the world are regions that are not quite either for- ests or grasslands, but rather something in between. Their widely spaced trees don’t form a closed canopy like those in a forest. The understory is mostly grasses. Like chaparrals, savannas have a wet season and a dry season. Rainfall totals are modest. Savannas near the Equator have warm temperatures throughout the year. They are sometimes called tropical grasslands. Tropical savannas cover large portions of South America, but the best-known examples are in Africa. Here one finds endless seas of grass dotted by acacia and baobab trees. The savanna supports a wondrous variety of grazing animals. Wildebeests, zebras, giraffes, rhinoceroses, and many kinds of antelope abound. These are preyed upon by prides of lions, stealthy leopards, and swift cheetahs. Life on the African savannas is strongly linked to the changing avail- CONFUSED ABOUT BIOMES? ability of water. Wet-season rains refill lakes and streams and allow new grasses to grow. Grazing animals can forage over wide areas. As Some students may be confused about the dry season arrives, water supplies dry up. Animals are forced to the differences between grasslands, des- linger near the few remaining watering holes or migrate to find other erts, chaparrals, and savannas. Compare sources of water. The yearly migration of wildebeest alone involves rainfall and give examples of regions. Per- about 1.5 million animals! haps make a note about certain animals that live in one of these biomes but not se c ret in the others. a r y bi rd Afri ca n w ild do g ExPLorIng thE BIoSPhErE 387 EXPLORING THE BIOSPHERE 387  Freshwater Biomes Freshwater biomes are diverse, but they cover less than 2% of the earth’s surface. These biomes can be split into two types according to water flow. The first includes biomes composed of standing water, such as lakes, ponds, swamps, and bogs. The second includes biomes that contain running water (streams and rivers). The differences be- tween the two types can be great. In many cases, species that live in one type cannot survive in the other. On top of the factors that affect land biomes, aquatic biomes (those consisting of water) are greatly affected by two added factors. One is depth. The sunlight needed for photosynthesis is quickly scattered as it passes through water. The deeper the water, the less light that is available for photosynthesis. Depth also determines how much oxy- gen is available for living things. Deep water contains very little oxy- gen. In deep lakes, enough oxygen and sunlight to support much life is found only in the topmost layers. WHEN IS A CREEK The other major factor in aquatic biomes is the supply of nutrients needed by protists and algae. Nutrients tend to collect in low-elevation NOT A CREEK? aquatic biomes, so they are often thick with algae and have murky Answer: when it’s a stream, brook, run, or water as a result. In contrast, high mountain lakes and streams tend one of several other words that are used to be crystal clear because few nutrients are available for algae and to identify watercourses that are consid- other organisms. ered smaller than rivers. There is gener- ally a lot of overlap in the definitions of these terms, and the use of them often varies regionally. To add to the confusion, many watercourses tagged with the name “river” are smaller than some that are called creeks. 388 388 CHAPTER 18 Marine Biomes SALTWATER WEDGES About 70% of the earth is covered by salt water. In the ocean, living things can be found from the shoreline to the bottoms of the deep- AND DECREASED SALINITY est trenches (over 10 km below the surface). Like freshwater biomes, The mixing of fresh and salt water de- marine biomes are largely governed by depth and the supply of nu- scribed on this page is not thorough. Be- trients for photosynthesis. Because of this, most marine life is found cause fresh water is less dense than salt in the upper layers of the world’s oceans. Along ocean shores, rising and falling tides also regularly cover and then uncover areas of land. water, it tends to flow over the surface Organisms that live in this intertidal zone must be fit for life both in of salt water as it approaches the sea. and out of water. Also along the coasts, rivers empty fresh water into Likewise, the denser salt water may push the sea. This creates bays and marshes where the two waters mix. upstream beneath the freshwater layer, The water here is brackish—its salt level is somewhere between that creating a saltwater wedge, sometimes of fresh water and seawater. for many kilometers. Because the mixing Marine organisms can be placed into four large groups according process is not immediate, the freshwater to their manner of living and location in the ocean. Animals such discharge of rivers often lowers the salin- as worms and clams form part of the benthos. They live on the ity of ocean waters near their mouths. In ocean’s bottom. Plankton are animals that drift in the ocean’s cur- rents, mainly near the surface. Plankton include tiny algae and small the extreme case of the Amazon River, animals such as copepods and larval squid. Animals that can move this region of decreased salinity extends about freely, the ocean’s nekton, are those such as whales and adult hundreds of kilometers offshore. fish. Transient animals spend only part of their time in the ocean but depend on it in some way. These include animals like seals and ma- rine birds. Because of the ocean’s vast size and the great variety of interactions between its abiotic factors, ocean biomes occur in many forms. At one extreme are brightly colored coral reefs, rich in number and va- riety of life forms. At the other extreme are the deep abyssal plains, rab nearly devoid of oxygen and cloaked in lasting darkness. Here, one id er c may search endless hectares of sea floor and happen upon only a few sp urchins or crinoids. ExPLorIng thE BIoSPhErE 389 EXPLORING THE BIOSPHERE 389  18.5 ZONES, HABITATS, AND NICHES Breaking down the biosphere into biomes helps to make modeling it easier. Still, different regions of a biome can be very different from each other. Australian savannas, for example, have very different plants and animals than savannas in Africa. This is where the defini- tion of ecosystems (p. 373) comes in handy. Australian and African savannas are the same kind of biome, but their unique combinations of biotic and abiotic factors make them distinct ecosystems. One has eucalyptus trees and kangaroos, while the other has baobabs and rhi- noceroses—very different! 390 390 CHAPTER 18  alpine tundra (3500 m) Zonation subalpine forest You don’t have to travel from one continent to another to see a (3000 m) change from one kind of ecosystem to another. Take the mountains of California’s Sierra Nevada for instance. Their elevations range from just above sea level in the foothills to over 4000 m at the tallest upper montane forest peaks. As one travels up into the mountains, the scenery gradually (2500 m) changes from grassland, to forest, and lastly to mountain peaks of mid montane forest bare rock. This gradual change caused by increasing elevation is an (1500 m) example of zonation. The creation of distinct zones within an eco- system can be caused by other abiotic factors besides elevation. You saw earlier that tropical rainforests have distinct zones governed by lower montane forest the heights of the forest trees and plants. Rivers can be divided into (1000 m) pools and riffles that are based on the speed of flowing water. Ocean zones are determined in part by the sea’s depth. oak woodland Habitat (150 m) A single ecosystem can be huge! Just think of the Amazon jun- gle or the East African savanna. Most animals don’t use all the grasslands FORMATIVE ASSESSMENT: space within an ecosystem to find food, shelter, and mates. They SIERRA NEVADA BIOTIC ZONES BIOMES use only some part of it. The portion that they use is their hab- itat. In the Sierra Nevada, an example of this is the American 1. I n what biome do you live? (Answers pika, a small, rabbit-like animal. The pika makes its home will vary depending on location.) only in the boulder fields found high in the subalpine 2. What biome is defined by its significant forest. Pikas make their nests in the nooks and crannies be- tween the boulders. Nearby grasses serve as food. Every- lack of water? (desert) thing the pika needs to survive can be found in this rocky 3. What are the main producers in the portion of the subalpine zone. tundra? (shrubs, grasses, and lichen) Niches 4. What is zonation? (a gradual change in Of course, pikas aren’t the only things that live in their habitat. The ecosystems caused by increasing eleva- plants that the pikas feed on grow there. Predators such as golden tion) eagles and long-tailed weasels hunt there—especially for pikas! Each of these organisms plays a different role in the daily life of 5. What is the niche of a grass in a grass- the mountains. The parts played by pikas and plants and preda- land? (They are eaten by the herbivores tors within their habitat are their niche—their role within the in the grassland.) ecosystem. By eating grasses and being eaten in turn by pred- ators, pikas serve as an important link in the transfer of energy through an ecosystem. Golden eagles have a different niche. They REVIEW 18B, don’t eat plants, but they do help keep the pika population in check. Every organism in an ecosystem has a slightly different niche. BIOMES AND ECOSYSTEMS Once students have an understanding of the material in Subsection 18.5, they should 391 be ready to work through Review 18B. EXPLORING THE BIOSPHERE 391  18B REVIEW QUESTIONS 1. What is the biosphere? 2. What do different parts of the world that are classified as a particular type of biome have in common? 3. The floor of Yosemite Valley within Yosemite National Park is dominated by coniferous forest. Would it be more correct to define Yosemite Valley as a biome or an ecosystem? Explain. 4. Copy Table 18­2. Fill in your copy with the missing descriptors for each biome. table 18-2 Coniferous Deciduous tropical tundra grassland Desert Chaparral Savanna Forest Forest rainforest cold cold warm mild warm winters, mild winters, summers, can be hot warm winters, year­round temperatures warm year­round short cold or cold year­round hot near summers summers winters summers Equator wet moist about 100 25–75 cm over 170 wet and Precipitation scarce very little winters, dry year­round cm per year per year cm per year dry seasons summers plants grasses shrubs, coniferous deciduous with fleshy many and and widely Plants grasses, grass shrubs trees trees stems and varied spaced lichens leaves trees 5. Sea turtles spend their entire adult lives at sea except for when females briefly return to land to lay their eggs. Are the beaches where they lay their eggs part of their habitat? Explain. 6. Mountain lions are the top predators in the mountains of the American West. Jaguars are the top predators in the rainforests of Central America. Which of the following statements is true for both mountain lions and jaguars? a. They live in the same kind of biome. b. They live in the same kind of habitat. c. They have the same niche within their ecosystems. 392 ChAPtEr 18 18B REVIEW ANSWERS 1. The biosphere refers to all the parts of the earth where life exists. (p. 379) 2. They have similar abiotic and biotic factors, such as climate and kinds of organisms. (p. 379) 3. Yosemite Valley is a limited area within the larger coniferous forest biome, so it is more correctly considered an ecosystem. (pp. 373, 379) 4. See reduced student page above. (pp. 380–89) 5. Yes. Since sea turtles require beaches for reproduction, they are part of the sea turtle’s habitat. (p. 391) 6. c (p. 391) 392 CHAPTER 18  CHAPTER 18 CHAPTER SUMMARY 18A FACtorS In thE EnVIronMEnt Ecosystems are defined by particular combinations of biotic and abiotic factors. Biotic factors are the living parts of an ecosystem; abiotic factors are the nonliving parts. 18A tErMS ecosystem 373 ecology 373 biotic factor 374 abiotic factor 374 climate 375 18B tErMS 18B BIoMES AnD ECoSYStEMS biome 379 To make modeling easier, Different regions within a coniferous forest 380 ecologists break down the biome type can be composed biosphere into smaller units of different ecosystems. deciduous forest 381 including biomes, ecosystems, An organism’s habitat is the tundra 382 and habitats. portion of its ecosystem that grassland 383 Biomes are regions within the it uses to find food, shelter, biosphere that have similar and mates. desert 384 climates and kinds of living things. An organism’s niche is the sum of tropical rainforest 385 all its roles within its ecosystem. chaparral 386 savanna 387 habitat 391 niche 391 ExPLorIng thE BIoSPhErE 393 EXPLORING THE BIOSPHERE 393  CHAPTER 18 CHAPTER REVIEW QUESTIONS Recalling Facts In Questions 1–6, match each term with its definition. a. ecosystem b. biosphere c. biome d. habitat e. niche f. zone 1. the habitable portion of the earth 2. a distinct area within an ecosystem caused by a gradual change in an abiotic factor 3. the parts of an ecosystem that an organism uses to find food, shelter, and mates 4. regions of the earth that have similar climates and kinds of living things 5. a limited area in which living and nonliving things interact 6. the role of an organism within its ecosystem 7. (True or False) An ecosystem is affected only by events that happen within that ecosystem. 8. In what ways does the amount of sunlight received affect life in an eco­ system? 9. Why are fewer organisms adapted to living in mountain ecosystems? Understanding Concepts QUESTION 10: 10. Which of the following things would an ecologist study? Choose all that apply. WHY NOT CHOICE D? a. the effect of cosmic rays on gases in Earth’s upper atmosphere Students may reason that because snow- b. the competition for food between pikas and long­tailed voles fall is an abiotic factor in an ecosystem, c. the patterns of seed distribution by migratory birds the Sierra Nevada, choice d should be in- d. the long­term changes in annual snowfall in the Sierra Nevada cluded in their answers. Point out to them 11. Briefly describe three ecosystems near where you live. that ecology studies the interactions be- 12. Is an aquarium filled with fish an ecosystem? Explain. tween factors, and choice d describes the study of only a single factor in isolation. 13. Classify the following factors in a tropical rainforest as biotic or abiotic. a. humidity b. breezes from a waterfall c. vegetation of varying heights d. nutrient­poor soil e. predators like the jaguar