Ecosystems: What Are They and How Do They Work?

Ecosystems: What Are They and How Do They Work?
Chapter 4 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?

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

Biosphere Ecosystems Realm of ecology Communities Populations
Universe Galaxies Biosphere Solar systems Planets Earth Biosphere Ecosystems Ecosystems Communities Populations Realm of ecology Organisms Communities Organ systems Organs Figure 3.2 Natural capital: levels of organization of matter in nature. Ecology focuses on five of these levels. Tissues Cells Populations Protoplasm Molecules Atoms Organisms Subatomic Particles Fig. 3-2, p. 51

Organisms and Species Organisms, the different forms of life on earth, can be classified into different species based on certain characteristics. Figure 3-3

Other animals 281,000 Known species 1,412,000 Insects 751,000 Fungi
69,000 Prokaryotes 4,800 Figure 3.3 Natural capital: breakdown of the earth’s 1.4 million known species. Scientists estimate that there are 4 million to 100 million species. Plants 248,400 Protists 57,700 Fig. 3-3, p. 52

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

(living and dead organisms) (crust, top of upper mantle)
Oceanic Crust Continental Crust Atmosphere Vegetation and animals Biosphere Lithosphere Soil Upper mantle Crust Rock Asthenosphere Lower mantle Core Mantle Figure 3.6 Natural capital: general structure of the earth. Crust (soil and rock) Biosphere (living and dead organisms) Hydrosphere (water) Lithosphere (crust, top of upper mantle) Atmosphere (air) Fig. 3-6, p. 54

Biosphere Atmosphere Stratosphere Hydrosphere Lithosphere
Membrane of air around the planet. Stratosphere Lower portion contains ozone to filter out most of the sun’s harmful UV radiation. Hydrosphere All the earth’s water: liquid, ice, water vapor Lithosphere The earth’s crust and upper mantle.

What Sustains Life on Earth?
Solar energy, the cycling of matter, and gravity sustain the earth’s life. Figure 3-7

Carbon cycle Phosphorus cycle Nitrogen cycle Water cycle Oxygen cycle
Biosphere Carbon cycle Phosphorus cycle Nitrogen cycle Water cycle Oxygen cycle Figure 3.7 Natural capital: life on the earth depends on the flow of energy (wavy arrows) from the sun through the biosphere and back into space, the cycling of crucial elements (solid arrows around ovals), and gravity, which keeps atmospheric gases from escaping into space and helps recycle nutrients through air, water, soil, and organisms. This simplified model depicts only a few of the many cycling elements. 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 Lower Stratosphere (ozone layer) Greenhouse effect
Energy in = Energy out Reflected by atmosphere (34% ) Radiated by atmosphere as heat (66%) UV radiation Lower Stratosphere (ozone layer) Absorbed by ozone Greenhouse effect Visible Light Troposphere Heat Figure 3.8 Solar capital: flow of energy to and from the earth. Absorbed by the earth 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

Average annual precipitation
100–125 cm (40–50 in.) 75–100 cm (30–40 in.) 50–75 cm (20–30 in.) 4,600 m (15,000 ft.) 25–50 cm (10–20 in.) 3,000 m (10,000 ft.) below 25 cm (0–10 in.) 1,500 m (5,000 ft.) Coastal mountain ranges Sierra Nevada Mountains Great American Desert Rocky Mountains Great Plains Mississippi River Valley Appalachian Mountains Figure 3.9 Natural capital: major biomes found along the 39th parallel across the United States. The differences reflect changes in climate, mainly differences in average annual precipitation and temperature. Coastal chaparral and scrub Coniferous forest Desert Coniferous forest Prairie grassland Deciduous forest Fig. 3-9, p. 56

Nonliving and Living Components of Ecosystems
Ecosystems consist of nonliving (abiotic) and living (biotic) components. Figure 3-10

Falling leaves and twigs Soluble mineral nutrients
Oxygen (O2) Sun Producer Carbon dioxide (CO2) Secondary consumer (fox) Primary consumer (rabbit) Precipitation Producers Falling leaves and twigs Figure 3.10 Natural capital: major components of an ecosystem in a field. Soil decomposers Water Soluble mineral nutrients Fig. 3-10, p. 57

Factors That Limit Population Growth
Availability of matter and energy resources can limit the number of organisms in a population. Figure 3-11

Lower limit of tolerance Upper limit of tolerance
No organisms Few organisms Few organisms No organisms Abundance of organisms Population size Figure 3.11 Natural capital: range of tolerance for a population of organisms, such as fish, to an abiotic environmental factor—in this case, temperature. These restrictions keep particular species from taking over an ecosystem by keeping their population size in check. Zone of intolerance Zone of physiological stress Optimum range Zone of physiological stress Zone of intolerance Low Temperature High Fig. 3-11, p. 58

Factors That Limit Population Growth
The physical conditions of the environment can limit the distribution of a species. Figure 3-12

Sugar Maple Fig. 3-12, p. 58 Figure 3.12
The physical conditions of the environment can limit the distribution of a species. The green area shows the current range of sugar maple trees in eastern North America. (Data from U.S. Department of Agriculture) Fig. 3-12, p. 58

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

Sun Chloroplast in leaf cell Chlorophyll H2O Light-dependent Reaction
Figure 3.A Simplified overview of photosynthesis. In this process, 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, such as glucose, and oxygen. H2O Light-dependent Reaction O2 Energy storage and release (ATP/ADP) Glucose Light-independent reaction CO2 Sunlight 6CO2 + 6 H2O C6H12O6 + 6 O2 Fig. 3-A, p. 59

Animation: Linked Processes

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

Termite and carpenter ant work Bark beetle engraving
Scavengers Decomposers Termite and carpenter ant work Bark beetle engraving Carpenter ant galleries Long-horned beetle holes Dry rot fungus Wood reduced to powder Figure 3.13 Natural capital: various scavengers (detritivores) and decomposers (mostly fungi and bacteria) can “feed on” or digest parts of a log and eventually convert its complex organic chemicals into simpler inorganic nutrients that can be taken up by producers. Mushroom Time progression Powder broken down by decomposers into plant nutrients in soil Fig. 3-13, p. 61

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

Abiotic chemicals (carbon dioxide, Heat oxygen, nitrogen, Solar Heat
minerals) Heat Solar energy Heat Heat Producers (plants) Decomposers (bacteria, fungi) Figure 3.14 Natural capital: the main structural components of an ecosystem (energy, chemicals, and organisms). Matter recycling and the flow of energy—first from the sun, then through organisms, and finally into the environment as low-quality heat—links these components. Consumers (herbivores, carnivores) Heat Heat Fig. 3-14, p. 61

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

The Ecosystem Approach The Species Approach
Goal Goal Protect populations of species in their natural habitats Protect species from premature extinction Strategy Strategies Preserve sufficient areas of habitats in different biomes and aquatic systems Identify endangered species Protect their critical habitats Tactics Tactics Protect habitat areas through private purchase or government action Figure 3.16 Solutions: goals, strategies, and tactics for protecting biodiversity. Legally protect endangered species Manage habitat Eliminate or reduce populations of nonnative species from protected areas Propagate endangered species in captivity Manage protected areas to sustain native species Reintroduce species into suitable habitats Restore degraded ecosystems Fig. 3-16, p. 63

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

(decomposers and detritus feeders)
First Trophic Level Second Trophic Level Third Trophic Level Fourth Trophic Level Producers (plants) Primary consumers (herbivores) Secondary consumers (carnivores) Tertiary consumers (top carnivores) Heat Heat Heat Solar energy Heat Heat Figure 3.17 Natural capital: a food chain. The arrows show how chemical energy in food flows through various trophic levels in energy transfers; most of the energy is degraded to heat, in accordance with the second law of thermodynamics. Heat Heat Detritivores (decomposers and detritus feeders) Heat Fig. 3-17, p. 64

Animation: Prairie Trophic Levels

Food Webs Trophic levels are interconnected within a more complicated food web. Figure 3-18

Humans Blue whale Sperm whale Crabeater seal Elephant seal
Killer whale Leopard seal Adelie penguins Emperor penguin Squid Figure 3.18 Natural capital: a greatly simplified food web in the Antarctic. Many more participants in the web, including an array of decomposer organisms, are not depicted here. Petrel Fish Carnivorous plankton Krill Herbivorous plankton Phytoplankton Fig. 3-18, p. 65

Animation: Categories of Food Webs

Animation: Prairie Food Web
PLAY ANIMATION

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

Heat Heat Tertiary consumers Decomposers (human) Heat 10 Secondary
(perch) Heat 100 Primary consumers (zooplankton) Figure 3.19 Natural capital: generalized pyramid of energy flow showing the decrease in usable energy available at each succeeding trophic level in a food chain or web. In nature, ecological efficiency varies from 2% to 40%, with 10% efficiency being common. This model assumes a 10% ecological efficiency (90% loss in usable energy to the environment, in the form of low-quality heat) with each transfer from one trophic level to another. QUESTION: Why is it a scientific error to call this a pyramid of energy? 1,000 Heat 10,000 Usable energy Available at Each tropic level (in kilocalories) Producers (phytoplankton) Fig. 3-19, p. 66

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

Gross primary productivity (grams of carbon per square meter)
Figure 3.20 Natural capital: gross primary productivity across the continental United States based on remote satellite data. The differences roughly correlate with variations in moisture and soil types. (NASA’s Earth Observatory) Gross primary productivity (grams of carbon per square meter) Fig. 3-20, p. 66

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

and unavailable to consumers Respiration
Sun Photosynthesis Energy lost and unavailable to consumers Respiration Gross primary production Net primary production (energy available to consumers) Figure 3.21 Natural capital: distinction between gross primary productivity and net primary productivity. A plant uses some of its gross primary productivity to survive through respiration. The remaining energy is available to consumers. Growth and reproduction Fig. 3-21, p. 66

What are nature’s three most productive and three least productive systems?
Figure 3-22

Average net primary productivity (kcal/m2 /yr)
Terrestrial Ecosystems Swamps and marshes Tropical rain forest Temperate forest North. coniferous forest Savanna Agricultural land Woodland and shrubland Temperate grassland Tundra (arctic and alpine) Desert scrub Extreme desert Aquatic Ecosystems Estuaries Figure 3.22 Natural capital: estimated annual average net primary productivity per unit of area in major life zones and ecosystems, expressed as kilocalories of energy produced per square meter per year (kcal/m2/yr). QUESTION: What are nature’s three most productive and three least productive systems? (Data from Communities and Ecosystems, 2nd ed., by R. H. Whittaker, New York: Macmillan) Lakes and streams Continental shelf Open ocean Average net primary productivity (kcal/m2 /yr) Fig. 3-22, p. 67

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

Wood sorrel Oak tree Organic debris builds up Lords and ladies
Dog violet Rock fragments Grasses and small shrubs Earthworm Millipede Fern Moss and lichen Honey fungus O horizon Mole Leaf litter A horizon Topsoil B horizon Bedrock Subsoil Immature soil Regolith Young soil C horizon Figure 3.23 Natural capital: soil formation and generalized soil profile. Horizons, or layers, vary in number, composition, and thickness, depending on the type of soil. (Used by permission of Macmillan Publishing Company from Derek Elsom, Earth, New York: Macmillan, Copyright © 1992 by Marshall Editions Developments Limited) Pseudoscorpion Mite Parent material Nematode Root system Actinomycetes Red Earth Mite Fungus Mature soil Bacteria Springtail Fig. 3-23, p. 68

Animation: Soil Profile
PLAY ANIMATION

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

Desert Soil (hot, dry climate) Grassland Soil semiarid climate)
Mosaic of closely packed pebbles, boulders Weak humus-mineral mixture Alkaline, dark, and rich in humus Dry, brown to reddish-brown with variable accumulations of clay, calcium and carbonate, and soluble salts Figure 3.24 Natural capital: soil profiles of the principal soil types typically found in five types of terrestrial ecosystems. Clay, calcium compounds Desert Soil (hot, dry climate) Grassland Soil semiarid climate) Fig. 3-24a, p. 69

Tropical Rain Forest Soil (humid, tropical climate)
Acidic light-colored humus Figure 3.24 Natural capital: soil profiles of the principal soil types typically found in five types of terrestrial ecosystems. Iron and aluminum compounds mixed with clay Tropical Rain Forest Soil (humid, tropical climate) Fig. 3-24b, p. 69

Deciduous Forest Soil (humid, mild climate)
Forest litter leaf mold Humus-mineral mixture Light, grayish-brown, silt loam Figure 3.24 Natural capital: soil profiles of the principal soil types typically found in five types of terrestrial ecosystems. Dark brown firm clay Deciduous Forest Soil (humid, mild climate) Fig. 3-24b, p. 69

Coniferous Forest Soil
Acid litter and humus Light-colored and acidic Figure 3.24 Natural capital: soil profiles of the principal soil types typically found in five types of terrestrial ecosystems. Humus and iron and aluminum compounds Coniferous Forest Soil (humid, cold climate) Fig. 3-24b, p. 69

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

0.05–2 mm diameter 0.002–0.05 mm diameter less than 0.002 mm Diameter
Sand Silt Clay 0.05–2 mm diameter 0.002–0.05 mm diameter less than mm Diameter Water Water Figure 3.25 Natural capital: the size, shape, and degree of clumping of soil particles determine the number and volume of spaces for air and water within a soil. Soils with more pore spaces (left) contain more air and are more permeable to water than soils with fewer pores (right). High permeability Low permeability Fig. 3-25, p. 70

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

Condensation Transpiration Evaporation Precipitation Precipitation
Rain clouds Transpiration Evaporation Precipitation to land Transpiration from plants Precipitation Precipitation Evaporation from land Evaporation from ocean Surface runoff (rapid) Runoff Precipitation to ocean Infiltration and Percolation Surface runoff (rapid) Figure 3.26 Natural capital: simplified model of the hydrologic cycle. Groundwater movement (slow) Ocean storage Fig. 3-26, p. 72

Animation: Hydrologic Cycle

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

Figure 3.27 Natural capital: simplified model of the global carbon cycle. Carbon moves through both marine ecosystems (left side) and terrestrial ecosystems (right side). Carbon reservoirs are shown as boxes; processes that change one form of carbon to another are shown in unboxed print. QUESTION: What are three ways in which your lifestyle directly or indirectly affects the carbon cycle? (From Cecie Starr, Biology: Concepts and Applications, 4th ed., Pacific Grove, Calif.: Brooks/Cole, © 2000) Fig. 3-27, pp

Animation: Carbon Cycle

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

(billion metric tons of carbon equivalent)
High projection Low projection (billion metric tons of carbon equivalent) CO2 emissions from fossil fuels Figure 3.28 Natural capital degradation: human interference in the global carbon cycle from carbon dioxide emissions when fossil fuels are burned and forests are cleared, 1850 to 2006 and projections to 2030 (dashed lines). (Data from UN Environment Programme, British Petroleum, International Energy Agency, and U.S. Department of Energy) Year Fig. 3-28, p. 74

The Nitrogen Cycle: Bacteria in Action
Figure 3-29

Excretion, death, decomposition
Gaseous nitrogen (N2) in atmosphere Food webs on land Nitrogen fixation Fertilizers Uptake by autotrophs Figure 3.29 Natural capital: simplified model of the nitrogen cycle in a terrestrial ecosystem. Nitrogen reservoirs are shown as boxes; processes changing one form of nitrogen to another are shown in unboxed print. QUESTION: What are three ways in which your lifestyle directly or indirectly affects the nitrogen cycle? (Adapted from Cecie Starr, Biology: Today and Tomorrow, Brooks/Cole © 2005) Loss by denitrification Excretion, death, decomposition Uptake by autotrophs Ammonia, ammonium in soil Nitrogen-rich wastes, remains in soil Nitrate in soil Nitrification Ammonification Loss by leaching Loss by leaching Nitrite in soil Nitrification Fig. 3-29, p. 75

Animation: Nitrogen Cycle
PLAY ANIMATION

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

Global nitrogen (N) fixation
Nitrogen fixation by natural processes Global nitrogen (N) fixation (trillion grams) Figure 3.30 Natural capital degradation: human interference in the global nitrogen cycle. Human activities such as production of fertilizers now fix more nitrogen than all natural sources combined. (Data from UN Environment Programme, UN Food and Agriculture Organization, and U.S. Department of Agriculture) Nitrogen fixation by human processes Year Fig. 3-30, p. 76

The Phosphorous Cycle Figure 3-31

mining Fertilizer excretion Guano agriculture weathering uptake by
autotrophs uptake by autotrophs leaching, runoff Marine Food Webs Dissolved in Ocean Water Dissolved in Soil Water, Lakes, Rivers Land Food Webs death, decomposition death, decomposition Figure 3.31 Natural capital: simplified model of the phosphorus cycle. Phosphorus reservoirs are shown as boxes; processes that change one form of phosphorus to another are shown in unboxed print. QUESTION: What are three ways in which your lifestyle directly or indirectly affects the phosphorus cycle? (From Cecie Starr and Ralph Taggart, Biology: The Unity and Diversity of Life, 9th ed., Belmont, Calif.: Wadsworth © 2001) weathering sedimentation settling out uplifting over geologic time Marine Sediments Rocks Fig. 3-31, p. 77

Animation: Phosphorous Cycle
PLAY ANIMATION

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

Acidic fog and precipitation
Water Sulfur trioxide Sulfuric acid Acidic fog and precipitation Ammonia Ammonium sulfate Oxygen Sulfur dioxide Hydrogen sulfide Plants Dimethyl sulfide Volcano Industries Animals Ocean Figure 3.32 Natural capital: simplified model of the sulfur cycle. The movement of sulfur compounds in living organisms is shown in green, blue in aquatic systems, and orange in the atmosphere. QUESTION: What are three ways in which your lifestyle directly or indirectly affects the sulfur cycle? Sulfate salts Metallic sulfide deposits Decaying matter Sulfur Hydrogen sulfide Fig. 3-32, p. 78

Animation: Sulfur Cycle
PLAY ANIMATION

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

USDA Forest Service Private owner 1 Habitat type
Critical nesting site locations USDA Forest Service USDA Forest Service Private owner 1 Private owner 2 Topography Habitat type Forest Wetland Figure 3.33 Geographic information systems (GISs) provide the computer technology for organizing, storing, and analyzing complex data collected over broad geographic areas. They enable scientists to overlay many layers of data (such as soils, topography, distribution of endangered populations, and land protection status). Lake Grassland Real world Fig. 3-33, p. 79

Systems Analysis Ecologists develop mathematical and other models to simulate the behavior of ecosystems. Figure 3-34

Identify and inventory variables Obtain baseline data on variables
Define objectives Systems Measurement Identify and inventory variables Obtain baseline data on variables Make statistical analysis of relationships among variables Data Analysis Determine significant interactions System Modeling Objectives Construct mathematical model describing interactions among variables Figure 3.34 Major stages of systems analysis. (Modified data from Charles Southwick) Run the model on a computer, with values entered for different Variables System Simulation System Optimization Evaluate best ways to achieve objectives Fig. 3-34, p. 80

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).

Ecosystems: What Are They and How Do They Work?

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