Unformatted text preview: Chapter 3
Ecosystems: What Are They and How Do They Work? Chapter Overview Questions What is ecology? What basic processes keep us and other organisms alive? What are the major components of an ecosystem? What happens to energy in an ecosystem? What are soils and how are they formed? What happens to matter in an ecosystem? How do scientists study ecosystems? Updates Online
The latest references for topics covered in this section can be found at the book companion website. Log in to the book's e-resources page at to access InfoTrac articles. InfoTrac: Rescuers race to save Central American frogs. Blade (Toledo, OH), August 6, 2006. InfoTrac: Climate change puts national parks at risk. Philadelphia Inquirer, July 13, 2006. InfoTrac: Deep-Spied Fish: Atlantic Expeditions Uncover Secret Sex Life of Deep-Sea Nomads. Ascribe Higher Education News Service, Feb 21, 2006. Environmental Tipping Points NatureServe: Ecosystem Mapping U.S. Bureau of Land Management: Soil Biological Communities Core Case Study: Have You Thanked the Insects Today? Many plant species depend on insects for pollination. Insect can control other pest insects by eating them Figure 3-1 Core Case Study: Have You Thanked the Insects Today? ...if all insects disappeared, humanity probably could not last more than a few months [E.O. Wilson, Biodiversity expert]. Insect's role in nature is part of the larger biological community in which they live. THE NATURE OF ECOLOGY Ecology is a study of connections in nature. How organisms interact with one another and with their nonliving environment. Figure 3-2 Organisms and Species Organisms, the different forms of life on earth, can be classified into different species based on certain characteristics. Figure 3-3 Case Study: Which Species Run the World? Multitudes of tiny microbes such as bacteria, protozoa, fungi, and yeast help keep us alive.
Harmful microbes are the minority. Soil bacteria convert nitrogen gas to a usable form for plants. They help produce foods (bread, cheese, yogurt, beer, wine). 90% of all living mass. Helps purify water, provide oxygen, breakdown waste. Lives beneficially in your body (intestines, nose). Populations, Communities, and Ecosystems Members of a species interact in groups called populations. Populations of different species living and interacting in an area form a community. A community interacting with its physical environment of matter and energy is an ecosystem. Populations A population is a group of interacting individuals of the same species occupying a specific area. The space an individual or population normally occupies is its habitat.
Figure 3-4 Populations Genetic diversity In most natural populations individuals vary slightly in their genetic makeup. Figure 3-5 THE EARTH'S LIFE SUPPORT SYSTEMS The biosphere consists of several physical layers that contain: Air Water Soil Minerals Life
Figure 3-6 Biosphere Atmosphere Membrane of air around the planet. Lower portion contains ozone to filter out most of the sun's harmful UV radiation. All the earth's water: liquid, ice, water vapor The earth's crust and upper mantle. Stratosphere Hydrosphere Lithosphere What Sustains Life on Earth? Solar energy, the cycling of matter, and gravity sustain the earth's life. Figure 3-7 Biosphere Carbon cycle Phosphorus cycle Nitrogen cycle Water cycle Oxygen cycle Heat in the environment Heat Heat Heat Fig. 3-7, p. 55 What Happens to Solar Energy Reaching the Earth? Solar energy flowing through the biosphere warms the atmosphere, evaporates and recycles water, generates winds and supports plant growth.
Figure 3-8 Solar radiation Energy in = Energy out Reflected by atmosphere (34% ) UV radiation Radiated by atmosphere as heat (66%) Absorbed by ozone Visible Light Absorbed by the earth Lower Stratosphere (ozone layer) Troposphere Greenhouse effect Heat Heat radiated by the earth Fig. 3-8, p. 55 ECOSYSTEM COMPONENTS Life exists on land systems called biomes and in freshwater and ocean aquatic life zones. Figure 3-9 Nonliving and Living Components of Ecosystems Ecosystems consist of nonliving (abiotic) and living (biotic) components. Figure 3-10 Factors That Limit Population Growth Availability of matter and energy resources can limit the number of organisms in a population. Figure 3-11 Factors That Limit Population Growth The physical conditions of the environment can limit the distribution of a species. Figure 3-12 Producers: Basic Source of All Food Most producers capture sunlight to produce carbohydrates by photosynthesis: Producers: Basic Source of All Food Chemosynthesis: Some organisms such as deep ocean bacteria draw energy from hydrothermal vents and produce carbohydrates from hydrogen sulfide (H2S) gas . Photosynthesis: A Closer Look Chlorophyll molecules in the chloroplasts of plant cells absorb solar energy. This initiates a complex series of chemical reactions in which carbon dioxide and water are converted to sugars and oxygen.
Figure 3-A Consumers: Eating and Recycling to Survive Consumers (heterotrophs) get their food by eating or breaking down all or parts of other organisms or their remains. Herbivores Primary consumers that eat producers Carnivores Primary consumers eat primary consumers Third and higher level consumers: carnivores that eat carnivores. Omnivores Feed on both plant and animals. Decomposers and Detrivores Decomposers: Recycle nutrients in ecosystems. Detrivores: Insects or other scavengers that feed on wastes or dead bodies. Figure 3-13 Aerobic and Anaerobic Respiration: Getting Energy for Survival Organisms break down carbohydrates and other organic compounds in their cells to obtain the energy they need. This is usually done through aerobic respiration. The opposite of photosynthesis Aerobic and Anaerobic Respiration: Getting Energy for Survival Anaerobic respiration or fermentation: Some decomposers get energy by breaking down glucose (or other organic compounds) in the absence of oxygen. The end products vary based on the chemical reaction: Methane gas Ethyl alcohol Acetic acid Hydrogen sulfide Two Secrets of Survival: Energy Flow and Matter Recycle An ecosystem survives by a combination of energy flow and matter recycling. Figure 3-14 BIODIVERSITY Figure 3-15 Biodiversity Loss and Species Extinction: Remember HIPPO H for habitat destruction and degradation I for invasive species P for pollution P for human population growth O for overexploitation Why Should We Care About Biodiversity? Biodiversity provides us with: Natural Resources (food water, wood, energy, and medicines) Natural Services (air and water purification, soil fertility, waste disposal, pest control) Aesthetic pleasure Solutions Goals, strategies and tactics for protecting biodiversity. Figure 3-16 ENERGY FLOW IN ECOSYSTEMS Food chains and webs show how eaters, the eaten, and the decomposed are connected to one another in an ecosystem. Figure 3-17 Food Webs Trophic levels are interconnected within a more complicated food web. Figure 3-18 Energy Flow in an Ecosystem: Losing Energy in Food Chains and Webs In accordance with the 2nd law of thermodynamics, there is a decrease in the amount of energy available to each succeeding organism in a food chain or web. Energy Flow in an Ecosystem: Losing Energy in Food Chains and Webs Ecological efficiency: percentage of useable energy transferred as biomass from one trophic level to the next.
Figure 3-19 Productivity of Producers: The Rate Is Crucial Gross primary production (GPP) Rate at which an ecosystem's producers convert solar energy into chemical energy as biomass.
Figure 3-20 Net Primary Production (NPP) NPP = GPP R Rate at which producers use photosynthesis to store energy minus the rate at which they use some of this energy through respiration (R). Figure 3-21 What are nature's three most productive and three least productive systems?
Figure 3-22 SOIL: A RENEWABLE RESOURCE Soil is a slowly renewed resource that provides most of the nutrients needed for plant growth and also helps purify water. Soil formation begins when bedrock is broken down by physical, chemical and biological processes called weathering. Mature soils, or soils that have developed over a long time are arranged in a series of horizontal layers called soil horizons. SOIL: A RENEWABLE RESOURCE Figure 3-23 Layers in Mature Soils Infiltration: the downward movement of water through soil. Leaching: dissolving of minerals and organic matter in upper layers carrying them to lower layers. The soil type determines the degree of infiltration and leaching. Soil Profiles of the Principal Terrestrial Soil Types Figure 3-24 Some Soil Properties Soils vary in the size of the particles they contain, the amount of space between these particles, and how rapidly water flows through them. Figure 3-25 MATTER CYCLING IN ECOSYSTEMS Nutrient Cycles: Global Recycling Global Cycles recycle nutrients through the earth's air, land, water, and living organisms. Nutrients are the elements and compounds that organisms need to live, grow, and reproduce. Biogeochemical cycles move these substances through air, water, soil, rock and living organisms. The Water Cycle Figure 3-26 Water' Unique Properties There are strong forces of attraction between molecules of water. Water exists as a liquid over a wide temperature range. Liquid water changes temperature slowly. It takes a large amount of energy for water to evaporate. Liquid water can dissolve a variety of compounds. Water expands when it freezes. Effects of Human Activities on Water Cycle We alter the water cycle by: Withdrawing large amounts of freshwater. Clearing vegetation and eroding soils. Polluting surface and underground water. Contributing to climate change. The Carbon Cycle: Part of Nature's Thermostat Figure 3-27 Effects of Human Activities on Carbon Cycle We alter the carbon cycle by adding excess CO2 to the atmosphere through: Burning fossil fuels. Clearing vegetation faster than it is replaced.
Figure 3-28 The Nitrogen Cycle: Bacteria in Action Figure 3-29 Effects of Human Activities on the Nitrogen Cycle We alter the nitrogen cycle by: Adding gases that contribute to acid rain. Adding nitrous oxide to the atmosphere through farming practices which can warm the atmosphere and deplete ozone. Contaminating ground water from nitrate ions in inorganic fertilizers. Releasing nitrogen into the troposphere through deforestation. Effects of Human Activities on the Nitrogen Cycle Human activities such as production of fertilizers now fix more nitrogen than all natural sources combined.
Figure 3-30 The Phosphorous Cycle Figure 3-31 Effects of Human Activities on the Phosphorous Cycle We remove large amounts of phosphate from the earth to make fertilizer. We reduce phosphorous in tropical soils by clearing forests. We add excess phosphates to aquatic systems from runoff of animal wastes and fertilizers. The Sulfur Cycle Figure 3-32 Effects of Human Activities on the Sulfur Cycle We add sulfur dioxide to the atmosphere by: Burning coal and oil Refining sulfur containing petroleum. Convert sulfur-containing metallic ores into free metals such as copper, lead, and zinc releasing sulfur dioxide into the environment. The Gaia Hypothesis: Is the Earth Alive? Some have proposed that the earth's various forms of life control or at least influence its chemical cycles and other earth-sustaining processes. The strong Gaia hypothesis: life controls the earth's life-sustaining processes. The weak Gaia hypothesis: life influences the earth's life-sustaining processes. HOW DO ECOLOGISTS LEARN ABOUT ECOSYSTEMS? Ecologist go into ecosystems to observe, but also use remote sensors on aircraft and satellites to collect data and analyze geographic data in large databases. Geographic Information Systems Remote Sensing Ecologists also use controlled indoor and outdoor chambers to study ecosystems Geographic Information Systems (GIS) A GIS organizes, stores, and analyzes complex data collected over broad geographic areas. Allows the simultaneous overlay of many layers of data.
Figure 3-33 Systems Analysis Ecologists develop mathematical and other models to simulate the behavior of ecosystems. Figure 3-34 Importance of Baseline Ecological Data We need baseline data on the world's ecosystems so we can see how they are changing and develop effective strategies for preventing or slowing their degradation. Scientists have less than half of the basic ecological data needed to evaluate the status of ecosystems in the United Sates (Heinz Foundation 2002; Millennium Assessment 2005). ...
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