Chapter 3 Ecosystems

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 www.thomsonedu.com 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

Universe Galaxies Solar systems

Biosphere

Planets Earth Biosphere Ecosystems

Ecosystems

Communities Populations Organisms Organ systems

Realm of ecology Communities

Organs Tissues Cells

Populations

Protoplasm Molecules Atoms Subatomic Particles

Organisms 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

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

Oceanic Crust

Atmosphere Vegetation Biosphere and animals Soil Crust Rock

Continental Crust Lithosphere Upper mantle Asthenosphere Lower mantle

Core Mantle Crust (soil and rock) Biosphere Hydrosphere (living and dead (water) organisms) Lithosphere Atmosphere (crust, top of upper mantle) (air) Fig. 3-6, p. 54

Biosphere  Atmosphere 

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

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

Absorbed by ozone

Visible Light Absorbed by the earth

Radiated by atmosphere as heat (66%)

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

Average annual precipitation 100–125 cm (40–50 in.) 75–100 cm (30–40 in.) 50–75 cm (20–30 in.) 25–50 cm (10–20 in.) below 25 cm (0–10 in.)

4,600 m (15,000 ft.) 3,000 m (10,000 ft.) 1,500 m (5,000 ft.)

Coastal mountain ranges

Sierra Nevada Mountains

Great American Desert

Coastal chaparral Coniferous and scrub forest

Rocky Mountains

Desert

Great Plains

Coniferous forest

Mississippi River Valley

Prairie grassland

Appalachian Mountains

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

Oxygen (O2)

Sun

Producer Carbon dioxide (CO2) Secondary consumer Primary (fox) consumer (rabbit) Precipitation Falling leaves and twigs

Producers Soil decomposers

Water

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

Abundance of organisms

Upper limit of tolerance Few No organisms organisms

Population size

Lower limit of tolerance No Few organisms organisms

Zone of intolerance

Low

Zone of physiological stress

Optimum range

Temperature

Zone of physiological stress

Zone of intolerance

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

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

Chlorophyll H2O

Light-dependent Reaction

Chloroplast in leaf cell O2

Energy storage and release (ATP/ADP)

CO2 6CO2 + 6 H2O

Lightindependent reaction Sunlight

Glucose

C6H12O6 + 6 O2

Fig. 3-A, p. 59

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

Scavengers

Longhorned beetle holes

Decomposers

Termite and Bark beetle Carpenter carpenter ant engraving galleries ant work Dry rot fungus

Time progression

Wood reduced to Mushroom powder 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

Heat

Abiotic chemicals (carbon dioxide, oxygen, nitrogen, minerals)

Heat

Solar energy

Heat

Producers (plants)

Decomposers (bacteria, fungi)

Heat

Consumers (herbivores, carnivores)

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 Preserve sufficient areas of habitats in different biomes and aquatic systems

Strategies

Tactics

•Protect habitat areas through private purchase or government action •Eliminate or reduce populations of nonnative species from protected areas •Manage protected areas to sustain native species •Restore degraded ecosystems

•Identify endangered species •Protect their critical habitats

Tactics •Legally protect endangered species •Manage habitat •Propagate endangered species in captivity •Reintroduce species into suitable habitats 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

First Trophic Level

Second Trophic Level

Third Trophic Level

Producers (plants)

Primary consumers (herbivores)

Secondary consumers (carnivores)

Heat

Heat

Fourth Trophic Level

Tertiary consumers (top carnivores) Heat

Solar energy

Heat Heat Heat

Heat

Heat Detritivores (decomposers and detritus feeders)

Fig. 3-17, p. 64

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

Petrel

Fish

Squid

Carnivorous plankton

Krill Phytoplankton

Herbivorous plankton Fig. 3-18, p. 65

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

Tertiary consumers (human)

Heat Decomposers Heat

10

Secondary consumers (perch) Heat

100

1,000

Primary consumers (zooplankton)

Heat

10,000 Producers Usable energy (phytoplankton) Available at Each tropic level (in kilocalories) 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) 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

Sun Ph nth sy

oto is es

Respiration Gross primary production Growth and reproduction

Energy lost and unavailable to consumers Net primary production (energy available to consumers)

Fig. 3-21, p. 66

 What are nature’s three most productive and

three least productive systems? Figure 3-22

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 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

Oak tree

Wood sorrel Lords and ladies

Fern O horizon Leaf litter

Dog violet Grasses and small shrubs Earthworm Millipede Honey fungus Mole

Organic debris builds up Rock fragments Moss and lichen

A horizon Topsoil B horizon Subsoil

Bedrock Immature soil Regolith Young soil Pseudoscorpion

C horizon

Mite Nematode

Parent material Root system Mature soil

Red Earth Mite Springtail

Actinomycetes Fungus Bacteria Fig. 3-23, p. 68

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

Mosaic of closely packed pebbles, boulders Weak humusmineral mixture

Desert Soil (hot, dry climate)

Dry, brown to reddish-brown with variable accumulations of clay, calcium and carbonate, and soluble salts

Alkaline, dark, and rich in humus Clay, calcium compounds Grassland Soil semiarid climate)

Fig. 3-24a, p. 69

Acidic light-colored humus Iron and aluminum compounds mixed with clay Tropical Rain Forest Soil (humid, tropical climate) Fig. 3-24b, p. 69

Forest litter leaf mold Humus-mineral mixture Light, grayishbrown, silt loam Dark brown firm clay

Deciduous Forest Soil (humid, mild climate)

Fig. 3-24b, p. 69

Acid litter and humus Light-colored and acidic 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

Sand 0.05–2 mm diameter

Silt 0.002–0.05 mm diameter

Water

High permeability

Clay less than 0.002 mm Diameter

Water

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

Rain clouds

Transpiration Evaporation Transpiration

Precipitation to land

from plants

Precipitation

Runoff

Surface runoff (rapid)

Precipitation

Evaporation from land Evaporation from ocean

Precipitation to ocean

Surface runoff (rapid)

Infiltration and Percolation Groundwater movement (slow)

Ocean storage

Fig. 3-26, p. 72

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

Fig. 3-27, pp. 72-7

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

CO2 emissions from fossil fuels (billion metric tons of carbon equivalent)

High projection Low projection

Year Fig. 3-28, p. 74

The Nitrogen Cycle: Bacteria in Action

Figure 3-29

Gaseous nitrogen (N2) in atmosphere

Food webs on land Nitrogen fixation

Fertilizers

Uptake by autotrophs Excretion, death, decomposition Ammonia, ammonium in soil

Nitrogen-rich wastes, remains in soil

Ammonification Loss by leaching

Nitrification

Uptake by Loss by autotrophs denitrification Nitrate in soil Nitrification Nitrite in soil

Loss by leaching

Fig. 3-29, p. 75

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 (trillion grams)

Nitrogen fixation by natural processes

Year

Fig. 3-30, p. 76

The Phosphorous Cycle

Figure 3-31

mining excretion

Guano

Fertilizer agriculture

uptake by uptake by weathering autotrophs autotrophs leaching, runoff Dissolved Land Marine Dissolved in Soil Water, Food Food in Ocean Lakes, Rivers Webs Webs Water death, death, decomposition decomposition weathering sedimentation settling out uplifting over geologic time Rocks Marine Sediments

Fig. 3-31, p. 77

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

Sulfur trioxide

Water

Acidic fog and precipitation

Sulfuric acid Ammonia

Oxygen Sulfur dioxide

Ammonium sulfate

Hydrogen sulfide Plants

Dimethyl sulfide

Volcano Industries

Animals

Ocean Sulfate salts Metallic sulfide deposits

Decaying matter

Sulfur Hydrogen sulfide

Fig. 3-32, p. 78

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

Critical nesting site locations

USDA Forest Service

USDA Private Forest Service owner 1 Private owner 2

Topography

Forest

Habitat type

Wetland 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

Systems Measurement

Define objectives Identify and inventory variables Obtain baseline data on variables

Data Analysis

Make statistical analysis of relationships among variables Determine significant interactions

System Modeling

Objectives Construct mathematical model describing interactions among variables

System Simulation

System Optimization

Run the model on a computer, with values entered for different Variables

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).