BioUnit2 Readings PDF

~ KEY QUESTIONS Why is ecology important? What methods are used in ecological studies? What are biotic and abiotic factors? How can we model global systems? VOCABULARY biosphere ecology...

~ KEY QUESTIONS Why is ecology important? What methods are used in ecological studies? What are biotic and abiotic factors? How can we model global systems? VOCABULARY biosphere ecology Early astronauts made many scientific discoveries about the moon species population and space. But they also made some unexpected emotional discov- community ecosystem eries when they saw Earth suspended in lifeless space. "We came biotic factor abiotic all this way," Astronaut William Anders wrote, "to study the moon, factor atmosphere hydrosphere geosphere and the most important thing is that we discovered the Earth." Scott Carpenter added, "It's small. It's isolated, and there is no resupply." Wally Schirra summed it up: "I left Earth three times and found no other place to go. Please take care of Spaceship Earth." How might we care for Spaceship Earth? To start we need to understand the global systems that shape our planet, and the ways those systems are changing as a result of human activity. Ecology: Studying Our Living Planet Astronauts were impressed with Earth's beauty, and they knew that our planet is covered with a thin skin of life that biologists call the biosphere. The biosphere includes all life on Earth, from underground bacteria, rain forest trees, ocean-going whales, airborne mold spores, (!) VIDEO and humans. All forms of life are tightly connected with their sur- roundings, so the biosphere includes everywhere life exists. Watch this video to learn about various sampling The Science of Ecology All forms of life interact with each techniques. other and with their environments.~ Ecology is the scientific study of interactions among organisms, populations, and communities, "'EP&Cllb: Students should be developing of organisms' effects on their environment, and of their responses an understanding that methods used to extract, harvest, transport, and consume to changes in their environment. The root of the word ecology is the natural resources influence the Greek word oikos, meaning "house." Ecology is the study of nature's geographic extent, composition, biological diversity, and viability of natural "houses," organisms that live in those houses, and interactions systems. EP&Cllla: Students should be developing among organisms based on energy and nutrients. Importantly, oikos an understanding that natural systems is also the root of the word economics. Economics studies human proceed through cycles and processes that are required for their functioning. "houses" and interactions among people based on money or trade, energy, and nutrients. 78 Chapter 3 The Biosphere Why Study Ecology? Although ecology studies nature's Individual Organism economy, and economics studies human economy, those two A species is a group of fields developed independently. For much of history, that similar organisms that can breed and produce wasn't a global problem. Human populations were small and fertile offspring. scattered. Our environmental impacts were local. In many cases, ----' human economies could function more or less independently from nature's economy... or so people thought. Recently we've learned that economics and ecology are A population is a actually tightly linked. As human populations have grown, group of individu- and as the power of our technology has increased, our impacts als that belong to the same species on local and global environments have also grown. Our world and live in the is changing around us, largely because of human activity, same area. including industrialization, auto and industry emissions, and _j air pollution. As the effects of human-caused global change become more clear, some economists are discovering what biologists have known for years: Human economies depend on nature's economy. Healthy ecological systems provide essential needs such as drinkable water and fertile soil. We need to understand ecology so that we can design lage of opulations human economies that are sustainable-which means that they gether in a can function without degrading the environment. We also need ea is called to learn to design our economies in ways that offer resilience, which means that they can adapt and continue to function as global ecology changes around us. Levels of Ecological Organization Ecologists study organisms and their environments on several levels as shown in Figure 3-1. Some ecologists study individual organisms... Others study communities, ecosystems, or the entire }. :, :,., biosphere. Ecological studies on a global scale are vital l i t e organisms that to charting a sustainable course for humanity..,i' e in a place, together ,.., 8l~IIJ.Jl!!l~j ith their physical envi- nment, are known as CHECK POINT Summarize What is the difference s stem. between a population and a community? Figure 3-1 Levels of Organization The kinds of questions that ecologists may ask about the living environment can vary, depending on the level at which the ecologist works. oystems lar climates and ms. 3.1 Introduction to Global Systems 79  Gathering Ecological Data To study such a wide range of systems and levels of organization, ecologists use many different tools and methods. ~ Ecologists generally rely on three main approaches, all of which are part of scientific methodology: observation, experimentation, and mod- eling. Many studies involve all three approaches, with ecologists using tools ranging from DNA analysis to data gathered from satellites. Observation Observation is often the first step in asking ecologi- s:ruov cal questions. Some observations are simple, such as: Which species live here? How many individuals of each species are there in a com- Figure 3-2 munity? Other observations are more complex: What happens if a Studying Environmental particular species is removed from a community? How will organisms Conditions respond to climate changes? If these questions are asked properly, they can lead to the development of testable scientific hypotheses. Scientists gather ecological data in many ways. In this particular Experimentation Experiments are designed to test hypoth- experiment, scientists are studying the effects of elevated levels of eses by gathering data that support or reject those hypotheses. carbon dioxide on plant growth. Some ecological experiments, such as the one shown in Figure 3-2, Data collected in experiments carefully monitor conditions in selected parts of natural environ- such as this, can be used to ments. These experiments can be difficult to do, because some model, make inferences, or apply variables, such as weather, cannot be controlled. to larger-scale experiments. Alternatively, ecologists may design artificial environments, like Biosphere 2. Experiments in artificial environments show how plants, bacteria, animals, or artificial communities react to changes such as temperature, lighting, or carbon dioxide concentration. Modeling Many ecological processes, such as climate change, occur over long periods of time or occur over areas as large as our entire planet. Ecologists often make models to help them under- stand these phenomena. Many ecological models consist of math- ematical formulas based on data that have been collected through observation and experimentation. Useful models make predictions that lead to the development of additional hypotheses. Those hypotheses, in turn, may lead to the design of new experiments to test them. Additional data may also lead to changes in models that improve their ability to make useful predictions. ~ CHECK POINT Apply Concepts When have you used the skills of observation, experimentation, or modeling? Describe an example of how you have used this skill. Biotic and Abiotic Factors When we talk about an organism's environment, we are referring to all the conditions, or factors, around the organism that affect it in any way. Traditionally, these factors have been divided into biotic factors and abiotic factors. RO C"'.h;ont1>r3 Th" Biosohere Biotic Factors Living things affect one another, and are therefore parts of each others' environment. ~ A biotic factor is any living part of the environment with which an organism might interact. Biotic factors important to a heron, for example, might include the fish and frogs it eats, predators that eat herons, and other spe- cies that compete with them for food or space. Abiotic Factors Physical factors also affect organisms. ~ An abi- () INTERACTIVITY otic factor is any nonliving part of the environment, such as sun- Measure how various abiotic light, heat, precipitation, humidity, wind or water currents, and soil factors affect organisms in a type. For example, a heron could be affected by abiotic factors such pond. as water availability and quality, temperature, and humidity. Biotic and Abiotic Factors Together The difference Figure 3-3 between biotic and abiotic factors may seem clear. But many so-called Biotic and Abiotic abiotic factors are strongly influenced by organisms, which means that Factors they aren't entirely abiotic! Bullfrogs, for example, often hang out in soft "muck" along the shores of ponds. You might think that muck is Like all ecosystems, this pond is affected by a combination of a strictly abiotic factor, because it contains nonliving particles of sand biotic and abiotic factors. Some and mud. But typical pond muck also contains decomposing organic environmental factors are a mix material from plants and animals that live in and around the pond. of biotic and abiotic compo- Those remains decompose because they serve as "food" to bacte- nents. Biotic and abiotic factors ria and fungi that break down organic matter. That's a lot of "biotic" are dynamic, meaning that they mixed in with "abiotic"! constantly affect each other. Abiotic Factors 3.1 Introduction to Global Systems 81  "Abiotic" condi_tions around a pond's mucky shore are also shaped by organisms. Trees and shrubs around the pond provide shade from strong sun, affecting the amount of sunlight and the range of temperatures the muck experiences. Those plants can also provide protection from dry winds, affecting the humidity of air above the muck. Plant roots determine how much soil washes into the pond during heavy rains. If pine trees grow nearby, decomposing needles make the soil acidic. Decomposing oak leaves, on the other () INTERACTIVITY hand, make soil more alkaline. Figure 3-4 Model of Earth Systems ~ CHECK POINT Explain Give two examples of how abiotic fac- tors are influenced by biotic factors. This model, as we build on it throughout this unit, will show Modeling Global Systems how global events and pro- A constantly-changing mix of biotic and abiotic factors shapes the cesses interact with each other. entire biosphere. So, understanding how the biosphere works is Global systems and cycles challenging. One way to understand global ecology and both local operate across the biosphere, and global change is to develop a model, like the one shown in atmosphere, geosphere, and Figure 3-4. ~ This model shows Earth's global systems, processes hydrosphere. ~ Infer What are some ways that the bio- that operate within those systems, how those systems interact sphere interacts with the other with each other, and how they respond to causes of global change. three components of the Earth This model begins by identifying four global spheres: biosphere, system? atmosphere, hydrosphere, and geosphere. The atmosphere includes all the gases that The biosphere includes all living organisms surround Earth. and the environments they live in. MEASURABLE CHANGES IN THE EARTH SYSTEM The hydrosphere, consists of all Earth's The geosphere includes all the "usually solid fresh water and salt water, including stuff"-rocks, continents, and the ocean water vapor and rain in the atmosphere, floor. Deep inside Earth, portions of the geo- and water underground. sphere are liquid. Adapted from Understanding Global Change, UC Berkeley R? rh,.ntr 3 ThP Biosohere Global Systems and Change Our model has three main BUILD VOCABULARY parts, each of which represents a category of ecological concepts Multiple Meanings In geom- and processes. We will be building this model, step by step, adding etry, a sphere is the shape of icons that represent various phenomena as we describe them. a round ball. In terms such as biosphere and atmosphere, it The model's middle ring, labeled "How the Earth System Works," is a region or area. represents Earth's global systems: events, processes, and cycles within the biosphere, atmosphere, geosphere, and hydrosphere. This part of the model includes phenomena discussed in this chapter, including the global climate system. This model also includes cycles of matter, energy flow, and interactions among organisms that we will discuss in later chapters. The model's outer ring, labeled "Causes of Global Change," rep- resents human activities and nonhuman events and processes that drive changes in those global systems. In this chapter, we discuss several nonhuman causes of global change. We will discuss human causes of global change in Chapter 7. The model's inner circle, "Measurable Changes in the Earth System," contains the kinds of changes in global systems that scientists can measure. These measurements include changes in climate, sea level, air and water quality, and so on. We emphasize "measurable changes" to emphasize that these represent actual data, not hypotheses. This model, like most models, can't describe everything as per- fectly as we would like. For example, the biosphere includes parts of the atmosphere, hydrosphere, and geosphere. The hydrosphere includes water in both the atmosphere and the geosphere. And Figure 3-5 some scientists consider frozen water-snow, ice, glaciers, and so Agricultural Practices on-separately, as the cryosphere. Still, you will see that this model and Greenhouse Gases provides a useful framework for organizing information, demonstrat- ing cause and effect, arguing from evidence, and examining con- These scientists are preparing nections among ecological events and processes. It also pinpoints gas samples for a study investi- changes in global systems that scientists can measure and highlights gating how agricultural prac- the effects of those changes on ecological systems, including tices produce greenhouse gas. human society. "'HS-ESS2-4 8 Modeling Lab Guided Inquiry () INTERACTIVITY Explore a tundra to learn Effects of Greenhouse Gases about the levels of orga- Problem How does the concentration of atmospheric carbon dioxide nization, earth systems, affect climate? and abiotic and biotic Gases such as carbon dioxide are called greenhouse gases because factors that make up this they trap energy from the sun's rays, in a similar way as a greenhouse biome. traps heat energy. In this lab, you will use a model to test whether the concentration of greenhouse gases in the air affects the amount of heat energy trapped by the atmosphere. You can find this lab on line in your digital course. 3.1 Introduction to Global Systems 83  Building and Using The Model How do we build and use our model? In this unit, you will learn about many events, processes, and interactions. If Visual Analogy that was all you learned, you would be left with a list Figure 3-6 of facts to memorize, but no clear way to understand how facts relate to one another. An Earth Systems Jigsaw Puzzle To use an analogy, you would have many pieces You can think of Earth systems as a kind of jigsaw of a complicated jigsaw puzzle... without any idea of puzzle. Each piece of the puzzle represents a how those pieces fit together. It would also be dif- different event or process in biology or earth sci- ficult for you to relate individual events and processes ence, represented by a visual symbol, or icon. As you work through this unit, you will learn how all to important crosscutting concepts in biology. these phenomena interact to shape conditions in That's where the Understanding Global Change both local and global environments. model comes in. The model serves as an "informa- tion organizer." Whenever we discuss ecological events and processes, each will be assigned a visual symbol, or icon, like those shown in Figure 3-6. Some icons represent processes in Earth's systems. Other icons represent causes of global change. Still other icons represent measurable changes. As we learn about these events and processes, we will add their icons to the model like you would assemble a puzzle. As we build the model, you will see how all these pieces fit together to make a picture of the way our planet operates. It will help you create concept maps that show how different aspects of weather and cli- mate influence organisms, and how various causes of global change can influence climate. You will notice that this model includes phenomena and crosscut- ting concepts from both biology and earth science, because those phenomena are always interacting on a global scale. When the model is complete, you can use it to explore connections among causes and effects in global change. '"'EP&Cllb, EP&Cllla LESSON 3.1 Review ~ KEY QUESTIONS CRITICAL THINKING 1. What is the definition of ecology? 5. L-.&.11.M.._.iaWhich approach to ecological investigations is illustrated by Biosphere 2? 2. Describe the three basic methods of ecological Defend your classification. research. 6. CCC Systems and System Models In creating a 3. How are biotic and abiotic factors related? model of our living planet, scientists need to con- How do these factors differ? sider four major Earth systems. Briefly describe 4. Describe an approach for understanding global these four systems, and then explain why it is systems and the changes they undergo. difficult to study these systems individually. 84 Chapter 3 The Biosphere Whatcauses algal blooms? ) Phenomenon Green slime. Toxic muck. Green scum that kills marine life and can cause liver, ) kidney, and nervous system damage in humans. A science fiction movie? Nope. These are descrip- tions of toxic, foul smelling "algal blooms" that seem to appear without warning along both coasts of ) the United States, and in some of the most beautiful places in California. What's behind these sudden ( explosions of microscopic life that cause so much trouble? Algal blooms appear naturally in some fresh- there, thick, floating mats of algae spread water and marine ecosystems at certain times along rivers and into coastal areas along both of year, when available nutrients combine the Atlantic and Gulf Coasts. These poison- with favorable temperatures and other fac- ous mats, so large that they could be seen tors. In lakes, natural blooms often occur from space, fouled beaches and marinas and in springtime. In coastal oceans, they often killed fish. Freshwater blooms also occur in occur in summer. Usually, natural blooms pro- lakes and streams, and some recent blooms vide extra input into the food chain, and color have covered many square kilometers in both water green for a while. Lake Erie and Lake Michigan. But not-so-natural blooms, either caused What's going on? or made worse by local or global human Researchers hypothesize that the Florida activity, can cause serious problems. Toxic blooms-which involved both freshwater and blooms are happening more frequently, in salt-water ecosystems-were triggered by more places, are growing larger, and are last- unusually heavy rains. California's blooms, on ing longer. In 2015, the biggest algal bloom the other hand, seem to have been caused ever recorded along the west coast stretched by unusually warm water in the Pacific, along all the way from California's Channel Islands to with changes in ocean current patterns. the Alaskan Peninsula. That bloom-and other But why would higher temperatures trig- marine blooms since then-forced closures ger a bloom in the eastern Pacific? And why of fish and shellfish industries in California, would heavy rains trigger a bloom in Florida? Oregon, and Washington for months, causing Despite their different triggers, did those losses of millions of dollars. And in 2016 and blooms have anything in common? Could 2017, offshore blooms poisoned dozens of those triggers have been the last straw for sea lions and other marine organisms. Some ecosystems already stressed by local human blooms in California's lakes and streams have activities? If so, do we know enough to act in sickened swimmers and have even killed dogs! ways that could head off future blooms? These California blooms weren't isolated Throughout this chapter, look for events. In 2016, for example, a giant bloom connections to the W.i4ii M1to help you in Florida started in Lake Okeechobee. From answer these questions.  ~ KEY QUESTIONS What are primary producers? How do consumers obtain energy and nutrients? VOCABULARY autotroph primary producer photosynthesis chemosynthesis Life requires energy. You think about energy in your life all the heterotroph consumer detritus time, whether you realize it or not-and not just when you grab an "energy bar" before exercise. To control your weight, you must balance energy you take in, energy your body burns at rest, energy you use during exercise, and energy your body stores as fat. And when we burn fossil fuels, we release energy captured and stored by organisms millions of years ago! But where does all this energy come from? And how is it transferred from one organism to another? Primary Producers No organisms can create energy, but organisms called autotrophs can capture energy from nonliving sources and convert it into forms living cells can use. Autotrophs also store energy in ways that make it available to other organisms, which is why they are also called primary producers. ~ Primary producers are the first producers of energy-rich compounds that can be used later by other organ- isms. All life depends on one or another kind of primary producer. Energy From the Sun Algae and plants are called photosyn- thetic primary producers, because they harness solar energy through photosynthesis. That energy powers the conversion of carbon dioxide and water into energy-rich carbohydrates such as sugars and starches. Photosynthesis produces oxygen that is released into the atmosphere and removes (and stores) carbon dioxide. Without pho- tosynthesis, there would be no oxygen to breathe! On land, plants are the main primary producers. In freshwater ecosystems, plants share that role with algae. In sunlit parts of the ocean, algae do most "'HS-LS2-3: Construct and revise an of the heavy lifting. In tidal flats, salt marshes, and mangrove forests, explanation based on evidence for the certain bacteria are important primary producers that harness sun- cycling of matter and flow of energy in aerobic and anaerobic conditions. light through a different kind of photosynthesis. Life Without Light In 1979, biologists made an extraordinary BUILD VOCABULARY discovery that revolutionized our understanding of deep-sea life. In Prefixes The prefix chemo- the pitch-black depths of the ocean, strange animals thrive around means "chemical," or volcanic vents that spew superheated water. Where do those animals "chemistry." The process of get energy? Water gushing from those vents carries energy-rich inor- chemosynthesis uses chemi- ganic compounds such as hydrogen sulfide. Some bacteria not only cal energy to produce organic tolerate high temperatures near the vent, but can harness chemical compounds in an organism. energy from those inorganic molecules. They use a process called chemosynthesis (kee moh SIN thuh sis) in which chemical energy powers production of carbohydrates as shown in Figure 4-1. Around ~ INTERACTIVE VIDEO J the vents, chemosynthetic bacteria live inside the tissues of certain Compare the flow of energy and the roles of producers types of worms and large clams. Those bacteria supply their animal and consumers in two eco- hosts with carbohydrates, which the hosts use as energy sources. systems: a kelp forest and a This discovery opened researchers' eyes to the ecological signifi- hydrothermal vent. cance of chemosynthesis. Thanks to studies inspired by this work, we now know that chemosynthetic primary producers are more com- mon, and live in many more environments, than anyone expected. Figure 4-1 Recent studies have shown that chemosynthetic bacteria thrive deep within Earth's crust, in total darkness and exposed to extremely high Photosynthesis and Chemosynthesis temperatures. They are also found closer to the surface in under- ground streams and caves previously thought to be lifeless. Still Plants use the energy from other chemosynthetic bacteria live buried in the mud of tidal flats sunlight to carry out the proc- all over the world. We have a great deal more to learn about these ess of photosynthesis. Other alternate forms of primary production which are both fascinating and autotrophs, such as sulfur ecologically important. bacteria, use the energy stored in chemical bonds in a process called chemosynthesis. In both G?C;:j@lj4 )i~il Compare How are and Contrast cases, energy-rich carbohy- photosynthesis and chemosynthesis similar? How are they different? drates are produced. Carbon dioxide + Carbon dioxide Water + + Oxygen Carbohydrates + + Carbohydrates Hydrogen sulfide Sulfur Light Energy Chemical Energy compounds ---~ + Oxygen Photosynthesis Chemosynthesis 4.1 Energy, Producers, and Consumers 115 () INTERACTIVITY Consumers Animals, fungi, and many bacteria cannot harness energy directly Explore producers and from the environment as primary producers do. These organisms, consumer types such as known as neterotrophs, must acquire energy from other organisms, herbivores, omnivores, car- usually by eating them. Heterotrophs are also called consumers. nivores, scavengers, decom- posers, and detritivores. ~ Consumers are organisms that rely on other organisms for _J energy and nutrients. Types of Consumers Consumers are classified by the way they acquire energy and nutrients from other organisms as shown in Figure 4-2. You can see that the definition of "food" varies a lot! Beyond Consumer Categories Many organisms do not fit neatly inside the tidy categories ecologists try to place them in. 0 INTERACTIVITY For example, some animals usually described as carnivores, such as hyenas, will scavenge if they get a chance. Many aquatic ani- Figure 4-2 mals eat a mixture of algae, bits of animal carcasses, and tiny bits Consumers of organic matter-including the feces of other animals! Toucans use their razor-sharp bills to cut up fruit, but they also can swallow Consumers rely on other frogs, small mammals, and even baby monkeys! Consumers often organisms for energy and lumped together may also differ from one another in more subtle nutrients. The Amazon ways. Herbivores may eat different parts of the plants they eat. That's rain forest shelters examples of each type of consumer, as important because different plant parts often contain very different shown here. amounts of available energy. Herbivores like this military macaw obtain energy and nutrients by eating plant leaves, roots, seeds, or fruits. Common herbivores include Omnivores are animals that he carcasses of oth eat both plants and other ave been killed by animals. Humans, bears, ave died of other c pigs, and this white-nosed his king vulture is coati are omnivores. posers ee y such as this giant own organic matter. This earthworm chew or grind detritus etritus, or small pieces o particles into smaller pieces. Many ecaying plant and animal types of mites, snails, shrimp, and crabs emains. Bacteria and fun are detritivores. They commonly digest ike these mushrooms, decomposers that live on, and in, detritus particles.  Fruits, such as berries are easy to digest and are usually rich in energy and nutrients. So it isn't surprising that many birds and mam- mals search them out. Much of the world's human population also gets most of its energy from the seeds of grasses: rice, corn, wheat, oats, and barley. Leaves are plentiful in many ecosystems, but are low in energy and tough to digest. Why? Leaves are composed largely of cellulose. Interestingly, no multicellular organism can manufacture an enzyme that can break down cellulose molecules. Only fungi, certain bacte- ria, and some single-celled organisms manufacture those enzymes. So how can any animal eat leaves? Those animals cultivate microor- ganisms inside their guts that digest cellulose for them! Cattle and many other grazing animals spend a long time chew- ing food into a pulp. When they swallow this pulp, it enters a com- plex digestive tract, part of which supports microorganisms that can break down cellulose. In cows, bacteria do that job. Many grazers periodically regurgitate the mixture of food and bacteria back up into their mouths, chew it again, and re-swallow it. This is called "chewing the cud." Even with all this extra work, grazers can extract relatively little energy from each mouthful of leaves. They therefore spend a lot of their time eating. What's more, the kind of digestive system needed to extract energy and nutrients from leaves is very heavy. That's why only a handful of birds including the hoatzin bird shown in Figure 4-3, eat leaves. Figure 4-3 Herbivores The desert goat is a typical grazing animal that needs to spend a lot of time chewing its food in order to extract the nutrients. The hoatzin bird digests leaves by fermentation in an unusually large swelling in their esophagus. That enlarged digestive organ is so big that it takes up room normally occupied by the bones and muscles used for flight, so hoatzins are weak fliers. In fact, the fermentation process makes these birds smell like manure, and the birds have the nickname "stinkbird." Proboscis monkeys have large guts, and regurgitate, rechew, and swallow their food, much like other more familiar grazing animals. "'HS-LS2-3 LESSON 4.1 Review ~ KEY QUESTIONS 4. SEP Construct an Explanation Termites are insects that feed on wood, which contains cellu- 1. What are the two primary sources of energy that lose. Scientists have observed that some termite power living systems? species prefer wood that has been attacked 2. How do consumers obtain energy? by fungi. Construct an explanation for this CRITICAL THINKING observation. 3. SEP Develop Models Draw a model to illustrate the flow of energy from a nonliving source to an herbivore. A 1 c:....,..........,, o.......J,,,,.. ___ __ _. r ________ -.. ".,.-,  ~ KEY QUESTIONS How does energy flow through ecosystems? How do ecological pyramids help analyze energy flow through trophic levels? VOCABULARY food chain phytoplankton food web trophic level Once energy is captured and stored in a form organisms can use, ecological pyramid biomass what happens next? When one organism eats another, energy moves from the "eaten" to the "eater." That sounds simple, but you would be surprised at how complicated it can be! Food Chains and Food Webs Primary producers and consumers are linked through feeding relation- ships that vary a lot among ecosystems. But energy always flows in similar ways.~ Energy flows through an ecosystem in a one-way direction, from primary producers through various consumers. Food Chains The simplest way to think of energy moving through an ecosystem is to imagine it flowing along a food chain. A food chain is a series of organisms in which energy is transferred from one organ- ism to another. Some food chains are very short. In Gorongosa National Park in Mozambique, an antelope feeds on a primary producer, such as grass. Carnivores, such as lions feed on antelope. The lion is thus two steps removed from the primary producers. In the Pacific Ocean and other aquatic ecosystems, most pri- mary producers are tiny floating algae called p ytoplankton, which are eaten by small animal plankton called zooplankton. Here, food chains usually involve two or three more steps between primary producers and large fish. So big marine animals are often four or five steps from primary producers. 0HS-LS2-4: Use mathematical representations to support claims for the Food Webs In most ecosystems, feeding relationships are much cycling of matter and flow of energy among organisms in an ecosystem. more complicated than a simple chain. Why? Because many animals EP&Cllla: Students should be developing eat more than one kind of food. For example, in the food web shown an understanding that natural systems proceed through cycles and processes in Figure 4-4, raccoons and moorhens eat several species of plants. that are required for their functioning. EP&Clllc: Students should be developing Several predators, such as alligators and panthers, in turn, often prey an understanding that human practices upon these animals. Ecologists call this network of feeding interactions, can alter the cycles and processes that operate within natural systems. through which both energy and matter move, a food web. 11 a ra................ A i:::,............,C'+c,.,,,c 0 INTERACTIVITY Figure 4-4 Food Web This illustration of a food web shows some of the feeding relationships within a typical marsh ecosystem along the Gulf Coast. One food chain within 0 INTERACTIVITY Food Chains Within Food Webs Look back at Figure 4-4. A food web is a network that includes all the food chains in an ecosys- Use the interactive food tem. Starting with a primary producer, see how many different routes, web activity to explore the or food chains, you can take to reach the vulture, panther, or alliga- effects of invasive species tor. Each route is a food chain. A food web, therefore, is a network on food webs. that includes all the food chains in an ecosystem. Note that this is a highly simplified representation of this food web, in which many spe- cies have been left out. Now, you can appreciate how complicated food webs can be! Decomposers and Detritivores in Food Webs Decomposers and detritivores have vital roles in the movement of energy and matter through food webs. Look again at the food web. Although white-tailed deer, raccoons, shrimp, and flagfish feed at least partly BUILD VOCABULARY on primary producers, most producers die without being eaten. In Academic Words The word the detritus pathway, decomposers convert that dead material to convert means "to change detritus, which is eaten by detritivores, such as shrimp and crayfish. from one form to another." Decomposition also releases matter in the form of nutrients that Decomposers convert, or can be used by primary producers as shown in Figure 4-5. Without change, uneaten dead plant decomposers, nutrients would remain locked within dead organisms. matter into detritus. Food Webs and Disturbance Food webs often contain so many different organisms, interacting in so many different ways, that it is difficult to predict how they will respond to disturbance. Food webs have different responses to different kinds of disturbances. Short-term natural disturbances, such as a flood, may cause dramatic short-term changes, but have little or no long-term effect. Long- Visual Analogy term human-caused disturbances, such as climate change or habitat Figure 4-5 destruction, can transform ecosystems in lasting ways. Even some "short-term" human disturbances, such as oil spills, can have serious Earth's Recycling effects that last for years, or even decades. Center Look again at Figure 4-4. Imagine what would happen if an oil Decomposers break down spill washed into this marsh, causing a drop in the numbers of bacte- dead and decaying matter and ria and fungi that break down detritus. What effect might that have release nutrients that can be on shrimp and crayfish? Would those populations decline? If they reused by primary producers. did, how might alligators and pelicans change their feeding behav- ~Use Analogies How are ior? And how might those changes affect other species? decomposers like a city's recy- cling center? Decomposers Primary Producers 120 Chapter 4 Ecosystems Ecological Pyramids Each step in a food chain or food web is called a trophic level. Primary producers make up the first trophic level. Various con- sumers occupy other levels. We can illustrate trophic levels in an ecosystem with a model called an ecological pyramid. Ecological Plramids model the relative amount of energy or mat- ter contained within each trophic level in a food chain or food web. There are three different types of ecological pyramids: pyramids of energy, pyramids of biomass and pyramids of numbers. Figure 4-6 Pyramids of Energy Theoretically, there is no limit to the Pyramid of Energy number of trophic levels in a food web, or the number of organ- isms on each level. But there's a catch. Only a small portion of the Pyramids of energy show the energy stored in any trophic level is available to organisms at the amount of energy available at each trophic level. An ecosys- next level. This is because organisms use up much of the energy they tem requires a constant supply acquire for life processes, such as respiration, movement, growth, of energy from photosynthetic and reproduction. Most of the remaining energy is released into the or chemosynthetic producers. environment as heat-a byproduct of these activities.~ Pyramids of energy show the relative amount of energy available at each Third-level trophic level of a food chain or food web. 0.1% consumers The shape of a pyramid of energy depends on the efficiency Second-level of energy transfer from one trophic level to the next. On average, 1% consumers about 10 percent of the energy available within one trophic level is transferred to the next trophic level, as shown in Figure 4-6. For First-level instance, one tenth of the solar energy captured and stored in the 10% consumers leaves of grasses ends up stored in the tissues of cows and other grazers. One tenth of that energy-10 percent of 10 percent, or Primary 1 percent of the original amount-gets stored in the tissues of producers humans who eat cows. "'HS-LS2-4 Quick Lab 4 Open-Ended Inquiry How Can You Model ANALYZE AND CONCLUDE Energy Flow in Ecosystems? 1. SEP Use Models About how much 1. Using materials of your choice, develop a mathematical energy is transferred from one trophic model of energy flow through four trophic levels in an eco- level to the next? How does your system. To start, decide what will represent one energy unit. model show this flow of energy? Then, decide what will represent the trophic levels. 2. Evaluate Claims A classmate claims 2. Model the amount of available that energy is conserved as it flows energy in the first trophic level. through an ecosystem. Use your model and scientific reasoning to Set up a data table to record the number of energy units available support or refute this claim. in your model. 3_ Support Claims Support the claim that matter is conserved when one 3. Next, model how this energy transfers to the second, third, and organism eats another. fourth trophic levels. Record your data in your data table. 4.2 Energy Flow in Ecosystems 121  Pyramids of Biomass and Numbers The total amount of living tissue within a given trophic level is called its biomass. Biomass is usually measured in grams of organic matter per unit area. The amount of biomass a given trophic level can support is deter- mined, in part, by the amount of energy available to the organisms in that trophic A pyramid level.~ of biomass is a model that illustrates the relative amount of living organic matter in each trophic level of an ecosystem. Ecologists interested in the number of organisms at each trophic level often use a pyramid of numbers. ~ A pyramid of numbers is a model that shows the relative number of individual organisms at each Figure 4-7 trophic level in an ecosystem. In most ecosystems, the pyramid of numbers is similar in shape to the pyramid Pyramids of Biomass and Numbers of biomass. The numbers of individuals on each level In most cases, pyramids of biomass and num- decrease from the level below it. To understand this bers follow the same general pattern. In the point more clearly, imagine that an ecologist marked field modeled here, there are more individual off a large field, and then weighed and counted every primary producers than first-level consumers. organism in that area. The result might look something Likewise, the primary producers collectively like the pyramid in Figure 4-7. have more mass. The. same patterns hold for the second and third-level consumes. With In some cases, however, consumers are much each step to a higher trophic level, biomass smaller in size and mass than the organisms they feed and numbers decrease. upon. Thousands of insects may graze on a single tree, for example. In such cases, the normal pyramid of 0 INTERACTIVITY numbers may be turned upside down, but the pyramid of biomass usually has the normal orientation. Even a Learn more about how energy flows single tree has a lot more biomass than the insects that through ecosystems by interacting with feed on it! ecological pyramids. "HS-LS2-4, EP&Cllla, EP&Clllc LESSON 4.2 Review ~ KEY QUESTIONS 4. Calculate Imagine you have a five-step food chain. If 100 percent of the energy is available at 1. Energy is said to flow in a "one-way" direction the first trophic level, what percentage of energy through an ecosystem. In your own words, is available at the highest trophic level? describe what that means. 5. SEP Use Models Choose one of the food chains 2. What are the three types of ecological pyramids? shown within the food web in Figure 4-4. Write Explain how each type of pyramid models energy a paragraph describing the feeding relation- and matter in ecosystems. ships among the organisms in the food chain. CRITICAL THINKING Hint: Use the terms producers, consumers, and decomposers in your description. 3. SEP Construct an Explanation Suppose there was a sudden decrease in the number of crayfish 6. SEP Construct an Explanation Why are decom- in the food web shown in Figure 4-4. Construct posers and detritivores essential parts of all an explanation to explain how this change may food webs? affect the food web. 122 Chapter 4 Ecosystems  Whatcan we learn from China? Phenomenon China has had a sophisticated culture and economy for centuries. A combination of natural resources and technology has long supported a large and growing population. Between 1650 and 1800, China's population doubled from 150 million to 300 million. By the late 1800s, it reached 450 million, and China began reaching the limits of available natural resources. Fertile soil and water good enough for farming and drinking were running out. What could be done to ensure that there were enough resources to go around? Despite problems with resource availability, and government jobs. Couples with more battles with Western powers, and civil war, than one child were heavily fined. This policy China's population kept increasing. Ever-more has been reworked several times and has had limited resources made living conditions for several unintended results. In 2005, there farmers and poor families worse and worse. were 32 million more males under the age Those hardships periodically fueled social of 20 than females. (In traditional Chinese unrest. Then between 1958 and 1962, China's society, sons are preferred because they sup- leader, Mao Zedong, enforced agricultural port aging parents.) In 2016, the government policies called "The Great Leap Forward." relaxed the policy and allowed families to The result was the one of worst catastrophes have two children. in Chinese history. Farmers couldn't supply These efforts have finally slowed popula- enough food for the population, and as many tion growth in China. Most women in China as 45 million people died. today have fewer than two children on aver- Almost immediately after that disaster age. This puts China in a better position ended, population growth began again! On to handle its economic and environmental average, Chinese women were bearing nearly problems. The country still faces shortages of _ six children each. By 1970, China's population fertile land and adequate water. And failure had grown to 790 million, and resource short- to treat air as a shared resource has led to ages caused serious social and ecological some of the worst air pollution in the world. problems. Unable to provide more resources, Meanwhile, global society still faces chal- the government tried to control growth with lenges and resource shortages created by a population control program. They encour- rapidly growing population. Are there lessons aged people to marry later and have fewer to be learned from China's experience? How children. Birthrates fell, but not enough to do environmental conditions affect popula- meet government goals. tion growth in general? And how do popula- In 1979, the Chinese government estab- tions affect their environment? lished a strict "one child" policy. It awarded Throughout this chapter, look for families that had only a single child better connections to the to help you access to schools, medical care, housing, answer these questions.  ~ KEY QUESTIONS How do ecologists study populations? What factors affect population growth? What happens during exponential growth? What happens during logistic growth? VOCABULARY population density population distribution Off the coast of California, southern sea otters are making a come- age structure immigration back. These adorable mammals, along with the closely-related emigration exponential northern sea otters, once lived in an area that stretched from Baja growth logistic growth California all the way up to Alaska. They were nearly wiped out by fur carrying capacity hunters during the eighteenth century. In 1911, otters were pro- tected by international treaty, and their numbers have been increas- ing. Southern sea otters are still endangered because they live only along a short stretch of the California coastline. A single large oil spill could cause their extinction. Why does that matter ecologically? Sea otters are important in maintaining the balance of the ecosystem. Otters help maintain the kelp forests by preying on sea urchins and other invertebrates that eat the kelp. Meanwhile, divers off the coast of North Carolina couldn't believe their eyes. They were certain they'd seen a lionfish. Why was that observation surprising? Because lionfish are native to the tropical Pacific Ocean, not the Atlantic ocean! Recently, more and more lion- fish have been reported around Florida, throughout the Caribbean, and all around the Gulf of Mexico. Lionfish are still spreading. Fisheries and biologists are worried, because lionfish are predators that eat at least 70 species of native fishes. How did they get here? Why are their numbers increasing so rapidly? Can we control lionfish? Describing Populations Imagine that you're investigating an endangered species like sea a HS-LS2-1: Use mathematical and/or computational representations to support otters or an aggressively invading species like lionfish. Among the explanations of factors that affect carrying first questions you ask might be "How many individuals of this spe- capacity of ecosystems at different scales. HS-LS2-2: Use mathematical cies live here?" "Where else do they live?" or "Are those populations representations to support and revise explanations based on evidence about stable, increasing, or decreasing?" Welcome to population biology! factors affecting biodiversity and ~ Ecologists study populations by examining their geographic populations in ecosystems of different scales. range, growth rate, density and distribution, and age structure. 146 Chapter 5 Populations Geographic Range The places a population lives make up its geographic range. Knowing an organism's range today, as well as its historic range, is important in understanding its relationships with other species in its habitat. A population's range can vary enormously in size. The range of a bacterial population in a rotting pumpkin is smaller than a cubic meter. The original range of sea otters (which include two or three subspecies) stretched thousands of kilometers around the Pacific Ocean, as shown in Figure 5-1. That range shrank dramatically when they were hunted. Even after a century of recov- ery, ranges of both northern and southern sea otters are only a frac- tion of their original sizes. The range of invading lionfish population in the Atlantic, on the other hand, now stretches from as far north as Boston to at least as far south as Venezuela. Figure 5-1 J--~ ~ Geographic Ranges RUSSIA The geographic range of the CANADA sea otter (top map) is decreas- ing while the geographic range of the lionfish (bottom map) is increasing. In the sea otter map, note how the range PACIFIC OCEAN UNITED has decreased from the gold STATES area to the purple area. On the other hand, the lionfish KEY range has increased from the D Historical Range green areas to the red areas. Current Range ~ Populations (ii;\ Species \2]j) ranges Adapted from Understanding Global Change, UC Berkley KEY 0 Native range of lionfish -- _,._J-l. ;,.__ New range of lionfish ~ Predicted future range '---:--~,-------~~~- ___, -'""3= Source: U.S. Geological Survey Department of the lnterior/USGS 5.1 How Populations Grow 147  In a random population, indi- In a uniform population, such In a clumped population, viduals are spaced unevenly. as this king penguin popula- such as these striped cat- These trees show a random tion, individuals are spaced fish, several individuals are population distribution. evenly from one another. packed closely together. Figure 5-2 Density and Distribution The number of individuals per Patterns of Distribution unit area is called an area's population density. Different species can have very different densities, even in the same environment. A The dots in the inset illustrations population of ducks in a pond may have a very low density, while represent individual members of fishes in the pond have a much higher density. Why does population a population. ~Compare How density matter? A few, widely spaced lionfish entering a new environ- do the three types of distribution ment might not disturb existing communities very much, but these differ from one another? invaders can reach densities of over 200 adults per acre. At this high density, lionfish can eat more than 460,000 other fish each year! In () INTERACTIVITY some places, lionfish have already devoured as much as 90 percent of the local species they eat! Learn about the ways popu- lations may be described. Population distribution describes the way individuals are spaced... out across their range. Figure 5-2 shows three main distribution patterns: random, uniform, and clumped. Some patterns serve a purpose. When the location of an individual is independent of other individuals, they may be distributed randomly. When individuals compete with one another for space or other resources, uniform distribution can result. Clumping into schools or herds can help indi- viduals avoid predators. Age Structure To fully understand a population, researchers need to know more than just the number of individuals. They need to know the ages of those individuals, how many of them are male, and how many are female. Those data describe the age structure of the population. Why is that information important? Because most plants and animals cannot reproduce until they reach a certain age. Also, among animals, only females can produce offspring, and the number of offspring they produce can vary with age. CHECKPOINT Summarize What is the difference between population density and population distribution? 148 Chapter 5 Populations Population Growth ~ INTERACTIVE VIDEO When will a population increase, decrease, or stay the same size? Changes in population size depend on how many individuals are Explore the effect of birthrate and death rate as it applies to added to it or removed from it, as shown in Figure 5-3. ~ Birthrate, population growth of pandas death rate, and the rate at which individuals enter or leave a in this interactive video. population all affect population growth. Birthrate and Death Rate Populations can increase if more individuals are born in any time period than die during that same period. In other words, a population can increase when its birthrate is higher than its death rate. Note that birth means different things in dif- ferent species, and that species vary wildly in the amount of young they produce. Sea otters, much like humans are usually born one at a time. Lionfish, on the other hand, release as many as 15,000 eggs at once! It is important to note that not all 15,000 eggs will hatch or survive to reproductive age. If the birthrate equals the death rate, a population may stay the same size. But if the death rate is greater than the birthrate, the population will decrease. That's what happened to sea otters. Otters breed once every year or two, and usually give birth to only one pup each time. Intensive hunting during the eighteenth century raised Figure 5-3 the otter death rates so high that births couldn't keep up. Factors That Affect Lionfish, by contrast, appear to have no predators or other natural Population Growth enemies in the Atlantic. So their death rate in the Atlantic is lower than in their native range, and their "birth" rate is very high. Many The numbers of individuals that are born, die, or enter scuba diving groups have launched campaigns to hunt the invading or leave a population affect lionfish, trying to increase their death rate and cause the population the growth of a population. to decrease. Lionfish, as it so happens, are quite tasty, and several ~SEP Use Models How chefs have produced "Lionfish Cookbooks" in an effort to encourage would you expand this model hunting these invasive animals. Human lionfish hunting can barely to include the effects of fishing make a dent in a population with a high birthrate. on this population? A population increases when new individuals are born. A population may decrease in size if individuals move away from it. Births Emigration Immigration ~~ Fish population Deaths A population may increase in size if individuals arrive from elsewhere. A population decreases when individuals die. 5.1 How Populations Grow 149  Immigration and Emigration A population may increase if individuals move into its range from elsewhere, a process called immigration. Suppose that an oak grove produces a bumper crop of acorns one year. The squirrel population in that grove may increase as squirrels from nearby areas immigrate in search of food. If there is a food shortage or a lack of another limiting resource, individuals may move out of the population's home range. This process, called emigration, can cause a population to decrease in size. Young animals may emigrate from the area where they were born to find mates or to establish new territories. How quickly organisms immigrate and emigrate depends, in part, on how far they travel, how quickly they move, and whether or not human activity moves them around. Lionfish, for example, didn't immigrate into the Atlantic on their own. They were released by home aquarium keepers who had bought them as pets. Additionally, newly-hatched lionfish can live for several weeks as larvae (immature or juvenile fish) able to float on ocean currents. That's why lionfish show up as far north as Boston! Their larvae are carried north from Florida by the Gulf Stream. Sea otters, on the other hand, don't migrate or travel far from their home turf. Exponential Growth If you provide a population with all the food and space it needs, protect it from predators and disease, and remove its waste prod- ucts, the population will increase faster and faster over time. Why? By meeting all the above needs, many members of the population will survive and produce offspring. Later, those offspring will produce their own offspring. Then, the offspring of those offspring will repro- BUILD VOCABULARY duce. Each generation, therefore, contains more individuals than the Related Words An prior generation. exponent indicates the That's why the rate of population growth changes, even though number of times a number is the birthrate may be more or less constant. The population increases multiplied by itself. The adjec- more and more rapidly as more and more offspring are produced in a tive exponential describes situation called exponential growth.~ Under ideal conditions with something that is expressed using exponents-such as the unlimited resources, a population will increase exponentially. This rate of growth. means that the larger the population gets, the faster it grows. e "HS-LS2-1 Argument-Based Inquiry Guided Inquiry Estimating Population Size Problem How can you estimate the size of a large population of plants, animals, or other living things? In this lab, you will estimate the size of various populations in a model ecosystem. Then you will use mathematical representa- tions to explain the factors that affect the carrying capacity of the model ecosystem for the species. Find this lab on line in your digital course. 150 Chapter 5 Populations Organisms That Reproduce Rapidly Exponential Growth Let's say that we begin a hypothetical experiment with a single bacterium that divides to produce two t Vl cells every 20 minutes. We supply the bacterium E with ideal conditions-and watch. After 20 minutes,.!!? C Ill the bacterium divides to produce two bacteria. After... 0) another 20 minutes, those two bacteria divide to 0 '+- produce four cells. At the end of the first hour, those 0... (I) four bacteria divide to produce eight cells...a E Do you see what is happening? After three :::, 20-minute periods, we have 2 x 2 x 2, or 8, cells. Z ~._....,_.,.a,4~!::§:~~~------' Another way to demonstrate this result is to use an Time~ exponent: 2 3 cells. In another hour (six 20-minute periods), there will be 26 , or 64, bacteria. In just one Figure 5-4 more hour, there will be 29 , or 512. In one day, this bac- Exponential Growth terial population will grow to an astounding 4720 quin- tillion individuals (A quintillion is written as the digit In the presence of unlimited resources and in the "1" followed by 18 zeroes!) What would happen if this absence of predation and disease, populations will growth continued without slowing down? In a few days, increase exponentially. The characteristic J-shape of this bacterial population would cover the planet! the graph shows exponential growth. If you plot the size of this population on a graph over time, you get a curve shaped like the letter "J." This J-shaped curve rises slowly at first, and then rises faster and faster, as shown in Figure 5-4. If nothing interferes with this exponential growth, the population will become larger and larger, faster and faster. Organisms That Reproduce Slowly Of course, many organ- isms grow and reproduce much more slowly than bacteria. A female elephant can produce a single offspring only every two to four years, and newborn elephants take about ten years to mature. But, if expo- nential growth continued indefinitely, the result would still be impos- sible. In the unlikely event that all descendants of a single elephant pair survived and reproduced, after 750 years there would be nearly 20 million elephants! Invasive Species Sometimes, when an organism migrates or is moved to a new environment, its population grows exponentially for a time. That's happening with lionfish in the Atlantic. This growth rate was also observed when a few European gypsy moths were acciden- tally released from a laboratory near Boston. Their population grew exponentially, and within a few years, these plant-eating pests had spread across the northeastern United States. In peak years, gypsy moth caterpillars devour the leaves of thousands of acres of forest. In some places, the caterpillars form a living blanket that covers the ground, sidewalks, and cars! ~ CHECK POINT Calculate How many bacteria will there be after four hours from a single bacterium that divides to produce two cells every 15 minutes? 5.1 How Populations Grow 151  Logistic Growth Exponential growth presents a puzzle. Bacteria, lionfish, and gypsy moths don't cover Earth or fill the oceans! This fact or observation means that natural populations don't grow exponentially for long. Sooner or later, something-or several "somethings"-stop, or slow down, exponential growth. What causes the slowdown in population growth rate? Phases of Growth One way to begin answering this question is to watch how populations behave in nature. Figure 5-5 traces the phases of growth that a population goes through after a few indi- viduals are introduced into a real-world environment. Phase 1: Population Grows Rapidly After a short time, the population begins to grow exponentially. Individuals grow and reproduce rapidly. Many offspring are produced with few individuals dying with unrestricted access to necessary resources resulting with increases in population size and rapid growth rate. Phase 2: Growth Slows Down In real-world populations, expo- 0 INTERACTIVITY nential growth does not continue for long. At some point, the rate of population growth begins to slow. This change in rate does not Figure 5-5 mean that population size decreases. The population still increases, Logistic Growth but the rate of increase slows down, so the population grows more slowly. This slowdown can be used by a variety of factors that will be Real-world populations show discussed in the next lesson. the characteristic S-shaped curve of logistic growth. As Phase 3: Growth Stops At some point, the rate of population resources become limited, growth drops to zero. This change means that the population's size population growth slows or levels off. Under some conditions, the population can remain at or stops, leveling off at the carry- near this size indefinitely. ing capacity. Logistic Growth The Logistic Growth Curve The curve in Figure 5-5 is shaped like the letter Phase II: "S." This S-shaped curve represents what is Growth slows. called logistic growth.~ Logistic growth __