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

Fig. 3-2, p. 51

Communities

Subatomic Particles

Atoms

Molecules

Protoplasm

Cells

Tissues

Organs

Organ systems

Organisms

Populations

Populations

Communities

Ecosystems

Biosphere

Earth

Planets

Solar systems

Galaxies

Universe

Organisms

Realm of ecology

Ecosystems

Biosphere

Organisms and Species Organisms, the different forms of life on

earth, can be classified into different species based on certain characteristics.

Figure 3-3

Fig. 3-3, p. 52

Insects751,000

Other animals281,000

Fungi69,000

Prokaryotes4,800

Plants248,400

Protists57,700

Known species1,412,000

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

Fig. 3-6, p. 54

Lithosphere (crust, top of upper mantle)

RockSoil

Vegetation and animals

Atmosphere

OceanicCrust

Continental Crust

LithosphereUpper mantle

AsthenosphereLower mantle

Mantle

Core

Biosphere

Crust

Crust (soil and rock)

Biosphere (living and dead

organisms)

Hydrosphere (water)

Atmosphere (air)

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

Fig. 3-7, p. 55

Nitrogencycle

Biosphere

Heat in the environment

Heat Heat Heat

Phosphoruscycle

Carboncycle

Oxygencycle

Watercycle

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

Fig. 3-8, p. 55

Absorbed by ozone Visible

Light

Absorbed by the earth

Greenhouse effect

UV radiation

Solarradiation

Energy in = Energy out

Reflected by atmosphere (34% ) Radiated by

atmosphere as heat (66%)

Heat radiated by the earth

Heat

Troposphere

Lower Stratosphere(ozone layer)

ECOSYSTEM COMPONENTS Life exists on land systems called biomes

and in freshwater and ocean aquatic life zones.

Figure 3-9

Fig. 3-9, p. 56

100–125 cm (40–50 in.)

Coastal mountain

ranges

SierraNevada

Mountains

GreatAmerican

Desert

Coastal chaparraland scrub

Coniferous forest

Desert Coniferous forest

Prairie grassland

Deciduous forest

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

4,600 m (15,000 ft.)

Average annual precipitation

MississippiRiver Valley

AppalachianMountains

GreatPlains

RockyMountains

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

Nonliving and Living Components of Ecosystems

Ecosystems consist of nonliving (abiotic) and living (biotic) components.

Figure 3-10

Fig. 3-10, p. 57

SunOxygen (O2)

Carbon dioxide (CO2)

Secondary consumer(fox)

Soil decomposers

Primaryconsumer

(rabbit)

PrecipitationFalling leaves

and twigs

Producer

Producers

Water

Factors That Limit Population Growth Availability of matter and energy resources

can limit the number of organisms in a population.

Figure 3-11

Fig. 3-11, p. 58

Zone of intolerance

Optimum rangeZone of physiological

stress

Zone of physiological

stress

Zone of intolerance

TemperatureLow High

Noorganisms

Feworganisms

Upper limit of tolerance

Po

pu

lati

on

siz

e

Abundance of organismsFew organisms

Noorganisms

Lower limit of tolerance

Factors That Limit Population Growth

The physical conditions of the environment can limit the distribution of a species.

Figure 3-12

Fig. 3-12, p. 58

Sugar Maple

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

Fig. 3-A, p. 59

Sun

Chloroplastin leaf cell

Light-dependentReaction

Light-independent

reaction

Chlorophyll

Energy storage and release

(ATP/ADP)

Glucose

H2O

Sunlight

O2

CO2

6CO2 + 6 H2O C6H12O6 + 6 O2

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

Fig. 3-13, p. 61

Scavengers

Powder broken down by decomposers into plant nutrients in soil

Bark beetle engraving

Decomposers

Long-horned beetle holes

Carpenter ant

galleries

Termite and

carpenter ant work Dry rot

fungus

Wood reduced to powder

Mushroom

Time progression

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

Fig. 3-14, p. 61

Abiotic chemicals(carbon dioxide,

oxygen, nitrogen, minerals)

Heat

Heat

Heat

Heat

Heat Solarenergy

Consumers(herbivores, carnivores)

Producers(plants)

Decomposers(bacteria, fungi)

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

Fig. 3-16, p. 63

The Ecosystem Approach

Protect populations of species in their natural habitats

Goal

The Species Approach

Goal

Protect species from premature extinction

Preserve sufficient areas of habitats in different biomes and aquatic systems

Strategy

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

Tactics• Legally protect endangered species

• Manage habitat

•Propagate endangered

species in captivity

•Reintroduce species into

suitable habitats

Strategies

• Identify endangered species• Protect their critical habitats

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

Fig. 3-17, p. 64

Heat

Heat

Heat

Heat

Heat

Heat Heat Heat

Detritivores (decomposers and detritus feeders)

First Trophic Level

Second TrophicLevel

Third Trophic Level

Fourth Trophic Level

Solar energy

Producers(plants)

Primary consumers(herbivores)

Secondary consumers(carnivores)

Tertiary consumers

(top carnivores)

Food Webs

Trophic levels are interconnected within a more complicated food web.

Figure 3-18

Fig. 3-18, p. 65

HumansBlue whale Sperm whale

Crabeater seal

Elephant seal

Killer whale

Leopard seal

Adelie penguins Emperor

penguin

Petrel FishSquid

Carnivorous plankton

Krill Herbivorous plankton

Phytoplankton

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

Fig. 3-19, p. 66

Heat

Heat

Heat

Heat

Heat

DecomposersTertiary

consumers(human)

Producers(phytoplankton)

Secondaryconsumers

(perch)

Primaryconsumers

(zooplankton)

10

100

1,000

10,000Usable energy

Available atEach tropic level(in kilocalories)

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

Fig. 3-20, p. 66

Gross primary productivity(grams of carbon per square meter)

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

Fig. 3-21, p. 66P

hotosynthesis

Sun

Net primary production (energy available to consumers)

Growth and reproduction

RespirationEnergy lost and unavailable to consumers

Gross primary production

What are nature’s three most productive and three least productive systems?

Figure 3-22

Fig. 3-22, p. 67

Average net primary productivity (kcal/m2 /yr)

Open ocean

Continental shelfLakes and streams

EstuariesAquatic Ecosystems

Extreme desert

Desert scrub

Tundra (arctic and alpine)Temperate grassland

Woodland and shrublandAgricultural land

Savanna

North. coniferous forestTemperate forest

Terrestrial Ecosystems

Tropical rain forest

Swamps and marshes

Background Stratigraphy Study of rock (ohhh, exciting) A grouping exercise Rock layers provide a quick look at regional climates and geological events throughout

history Windows into climate conditions during specific times Ex. Of sedimentary rock layer: Grand Canyon (pre-cambian and Paleozoic)

Rock-stratigraphic unit or rock unit Individual band with its own specific characteristics and position Formation: rock units stacked up vertically; composed of many rock units grouped into a

section with same physical properties (takes thousands to millions of years to create) Lithology

Visual study of rock’s physical characteristics using a handheld magnifying glass or low-power microscope

Three Main rock type: Igneous, sedimentary, metamorphic

Rock formations can be matched by their physical characteristics: Grain size and shape Grain orientation Mineral content Sedimentary structure Color weathering

Igneous Rock Rock formed by the cooling and hardening of molten rock (magma), deep in the Earth, blasted out

during an eruption; 95% of the first 10 mi of crust six minerals: quartz, feldspar, pyroxene, olivine, amphibole, and mica (Si, Ca, Na, K, Mg, Fe, Al, H, O) Two type:

• Felsic: affected by heat (magma rising or friction b/t plates); lots of Si minerals (quartz and granite)• Mafic: high levels of Mg and Fe containing minerals

Sedimentary Rock Formed from rocks and soils from other locations compressed with the remains of dead organisms Fine-grained texture b/c they are layered or settled by water or wind Lithification: process that makes lithified soil (made of silt, sand, and organic compounds) by

compaction and cementation Diagenesis: process that lithifies sediments; controlled by temperature (200’C); unstable minerals

recrystallize into more stable matrix form or are chemically changed, like organic matter, into coal or hydrocarbons.

• 1. Compaction, 2. cementation, 3. recrystallization, 4. chemical changes (ex oxidation and reduction)

Detritus: any type of rock that has been moved from its original location Metamorphic Rock

Formed when rocks (igneous or sedimentary) originally of one type change into a different type by heat and/or pressure

3 main causes/forces: internal heat of earth, weight of overlying rock, and horizontal pressures from previously changed rock

Example: MARBLE and SLATE

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 Basics Renewable but very slowly (climate is factor) 1 cm of soil can take 15-100 years to form Mixture of six components

1) Eroded rock

2) Mineral nutrients

3) Decaying organic matter

4) Water

5) Air

6) Living organisms (microscopic decomp) 3 major roles of soil

Provides Nutrients Filters water Stores water

3 Soil Horizons (Horizon 0)

Surface litter layer Freshly fallen/partially decomposed (leaves, twigs,

crop wastes, animal waste) Brown or black color

Horizon A Topsoil Porous mix of partially decomposed organic matter

(HUMUS) Horizon B Horizon C

SOIL: A RENEWABLE RESOURCE

Figure 3-23

Fig. 3-23, p. 68

Fern

Mature soil

Honey fungus

Root system

Oak tree

Bacteria

Lords and ladies

Fungus

Actinomycetes

Nematode

Pseudoscorpion

Mite

RegolithYoung soil

Immature soil

Bedrock

Rockfragments

Moss and lichen

Organic debrisbuilds upGrasses and

small shrubs

Mole

Dog violet

Woodsorrel

EarthwormMillipede

O horizonLeaf litter

A horizon

Topsoil

B horizonSubsoil

C horizon

Parent material

Springtail

Red Earth Mite

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

Fig. 3-24a, p. 69

Mosaic of closely packed pebbles, boulders

Weak humus-mineral mixture

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

Desert Soil(hot, dry climate)

Grassland Soilsemiarid climate)

Fig. 3-24b, p. 69

Tropical Rain Forest Soil(humid, tropical climate)

Acidic light-colored humus

Iron and aluminum compounds mixed with clay

Fig. 3-24b, p. 69

Deciduous Forest Soil(humid, mild climate)

Forest litter leaf moldHumus-mineral mixtureLight, grayish-brown, silt loamDark brown firm clay

Fig. 3-24b, p. 69

Coniferous Forest Soil(humid, cold climate)

Light-colored and acidic

Acid litter and humus

Humus and iron and aluminum compounds

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

Fig. 3-25, p. 70

0.05–2 mmdiameter

High permeability Low permeability

WaterWater

Clayless than 0.002 mm

Diameter

Silt0.002–0.05 mm

diameter

Sand

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

Fig. 3-26, p. 72

PrecipitationPrecipitation

Transpiration

Condensation

Evaporation

Ocean storage

Transpiration from plants

Precipitation to land

Groundwater movement (slow)

Evaporation from land Evaporation

from ocean Precipitation to ocean

Infiltration and Percolation

Rain clouds

RunoffSurface runoff

(rapid)

Surface runoff (rapid)

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. 72-73

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

Fig. 3-28, p. 74

CO

2 em

issi

on

s fr

om

fo

ssil

fu

els

(bil

lio

n m

etri

c to

ns

of

carb

on

eq

uiv

alen

t)

Year

Lowprojection

Highprojection

The Nitrogen Cycle: Bacteria in Action

Figure 3-29

Fig. 3-29, p. 75

Gaseous nitrogen (N2)in atmosphere

Ammonia, ammonium in soil Nitrogen-rich wastes,remains in soil

Nitrate in soil

Loss byleaching

Loss byleaching

Nitrite in soil

Nitrification

Nitrification

Ammonification

Uptake by autotrophsUptake by autotrophsExcretion, death,

decomposition

Loss bydenitrification

Food webs on land

Fertilizers

Nitrogen fixation

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

Fig. 3-30, p. 76

Nitrogen fixation by natural processes

Glo

bal

nit

rog

en (

N)

fixa

tio

n(t

rill

ion

gra

ms)

Year

The Phosphorous Cycle

Figure 3-31

Fig. 3-31, p. 77

Dissolvedin Ocean

Water

Marine Sediments Rocks

uplifting overgeologic time

settling out weatheringsedimentation

LandFoodWebs

Dissolvedin Soil Water,Lakes, Rivers

death,decomposition

uptake byautotrophs

agriculture

leaching, runoff

uptake byautotrophs

excretion

death,decomposition

mining Fertilizer

weathering

Guano

MarineFoodWebs

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

Fig. 3-32, p. 78

Hydrogen sulfide

Sulfur

Sulfate salts

Decaying matter

Animals

Plants

Ocean

IndustriesVolcano

Hydrogen sulfideOxygen

Dimethyl sulfide

Ammoniumsulfate

Ammonia

Acidic fog and precipitationSulfuric acid

WaterSulfurtrioxide

Sulfur dioxide

Metallicsulfidedeposits

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

Fig. 3-33, p. 79

Critical nesting sitelocations

USDA Forest ServiceUSDA

Forest ServicePrivateowner 1 Private owner 2

Topography

Habitat type

LakeWetlandForest

Grassland

Real world

Systems Analysis

Ecologists develop mathematical and other models to simulate the behavior of ecosystems.

Figure 3-34

Fig. 3-34, p. 80

SystemsMeasurement

Define objectivesIdentify and inventory variablesObtain baseline data on variables

Make statistical analysis of relationships among variables

Determine significant interactions

Objectives Construct mathematical model describing interactions among variables

Run the model on a computer, with values entered for differentVariables

Evaluate best ways to achieve objectives

DataAnalysis

SystemModeling

SystemSimulation

SystemOptimization

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).