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?
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.
Universe
Galaxies
Solar systems
Biosphere
Planets
Earth
Biosphere
Ecosystems
Ecosystems
Communities
Populations
Realm of ecology
Organisms
Organ systems
Communities
Organs
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
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).
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
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
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
Producers: Basic Source of All Food
 Most
producers capture sunlight to produce
carbohydrates by photosynthesis:
Photosynthesis:
A Closer Look
 Chlorophyll
molecules in the
chloroplasts of plant cells
absorb solar energy.
 This initiates a complex
series of chemical reactions
in which carbon dioxide and
water are converted to
sugars and oxygen.
Figure 3-A
Consumers: Eating and Recycling to
Survive
 Consumers
(heterotrophs) get their food by
eating or breaking down all or parts of other
organisms or their remains.

Herbivores
• Primary consumers that eat producers

Carnivores
• Primary consumers eat primary consumers
• Third and higher level consumers: carnivores that eat
carnivores.

Omnivores
• Feed on both plant and animals.
Decomposers and Detrivores


Decomposers: Recycle nutrients in ecosystems.
Detrivores: Insects or other scavengers that feed
on wastes or dead bodies.
Figure 3-13
Aerobic and Anaerobic Respiration:
Getting Energy for Survival
 Organisms
break down carbohydrates and
other organic compounds in their cells to
obtain the energy they need.
 This is usually done through aerobic
respiration.

The opposite of photosynthesis
Aerobic and Anaerobic Respiration:
Getting Energy for Survival
 Anaerobic


respiration or fermentation:
Some decomposers get energy by breaking
down glucose (or other organic compounds) in
the absence of oxygen.
The end products vary based on the chemical
reaction:
•
•
•
•
Methane gas
Ethyl alcohol
Acetic acid
Hydrogen sulfide
Two Secrets of Survival: Energy Flow
and Matter Recycle
 An
ecosystem
survives by a
combination of
energy flow and
matter recycling.
Figure 3-14
BIODIVERSITY
Figure 3-15
Biodiversity Loss and Species
Extinction: Remember HIPPO
H
for habitat destruction and degradation
 I for invasive species
 P for pollution
 P for human population growth
 O for overexploitation
Why Should We Care About
Biodiversity?
 Biodiversity



provides us with:
Natural Resources (food water, wood, energy,
and medicines)
Natural Services (air and water purification, soil
fertility, waste disposal, pest control)
Aesthetic pleasure
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
Food Webs
 Trophic
levels are
interconnected
within a more
complicated food
web.
Figure 3-18
Energy Flow in an Ecosystem: Losing
Energy in Food Chains and Webs
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.
 In
Energy Flow in an Ecosystem: Losing
Energy in Food Chains and Webs
 Ecological
efficiency:
percentage of
useable energy
transferred as
biomass from
one trophic level
to the next.
Figure 3-19
Productivity of Producers:
The Rate Is Crucial
 Gross
primary
production
(GPP)

Rate at which an
ecosystem’s
producers
convert solar
energy into
chemical energy
as biomass.
Figure 3-20
Net Primary Production (NPP)
 NPP

= GPP – R
Rate at which
producers use
photosynthesis to
store energy minus
the rate at which they
use some of this
energy through
respiration (R).
Figure 3-21
 What
are nature’s three most productive and
three least productive systems?
Figure 3-22
SOIL: A RENEWABLE RESOURCE
 Soil
is a slowly renewed resource that
provides most of the nutrients needed for
plant growth and also helps purify water.

Soil formation begins when bedrock is broken
down by physical, chemical and biological
processes called weathering.
 Mature
soils, or soils that have developed
over a long time are arranged in a series of
horizontal layers called soil horizons.
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
Parent
material
Nematode
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
Some Soil Properties
 Soils
vary in the size
of the particles they
contain, the amount
of space between
these particles, and
how rapidly water
flows through them.
Figure 3-25
MATTER CYCLING IN
ECOSYSTEMS
 Nutrient



Cycles: Global Recycling
Global Cycles recycle nutrients through the
earth’s air, land, water, and living organisms.
Nutrients are the elements and compounds that
organisms need to live, grow, and reproduce.
Biogeochemical cycles move these substances
through air, water, soil, rock and living organisms.
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
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.
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
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
mining
excretion
Fertilizer
Guano
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.
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.
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).