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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).