Chapter 3
Ecosystems: What Are
They and How Do They
Work?
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?
 What
would happen if all of the insects on
Earth disappeared?
THE NATURE OF ECOLOGY
 Ecology

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
Realm of ecology
Organisms
Organ systems
Communities
Organs
Tissues
Cells
Populations
Protoplasm
Molecules
Atoms
Organisms
Subatomic Particles
Fig. 3-2, p. 51
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
 Individuals
 Populations

Members of a species interact in groups
 Community

Populations of different species living and
interacting in an area
 Ecosystem

A community interacting with its physical
environment of matter and energy
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.
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
warms the
atmosphere
evaporates and
recycles water
generates winds
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
limits population size
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 (i.e. deep ocean bacteria)
draw energy from hydrothermal vents and
produce carbohydrates from hydrogen sulfide
(H2S) gas
Photosynthesis:
A Closer Look
 Chlorophyll
(within)
chloroplasts of plant cells
absorb solar energy


initiates a complex series of
chemical reactions
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
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
 aerobic




respiration
break down carbohydrates and other organic
compounds
obtain the energy they need
Occurs in the presence of oxygen
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
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
How can we protect biodiversity?
GOALS
•Don’t kill of as many species
•Preserve as many resources as
possible.
•Reduce pet trade
•Less pollution
•Promote use of native species in yards
STRATEGIES/TACTICS
•Protesting
•Rat them out
•Physically remove illegal pets
•Remove invasive plant species
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
 How
are food chains and webs different?
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
Herbivorous
plankton
Phytoplankton
Fig. 3-18, p. 65
Energy Flow in an Ecosystem: Losing
Energy in Food Chains and Webs
 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 will be lost as heat
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




slowly renewed
provides most of the nutrients needed for plant
growth
helps purify water
Soil formation begins when bedrock undergoes
weathering
broken down by physical, chemical and biological
processes
 Mature


soils
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
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
The Water Cycle
Figure 3-26
Water’ Unique Properties
 Cohesion

attraction between molecules of 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
 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
The Nitrogen Cycle:
Bacteria in Action
Figure 3-29
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
The Phosphorous Cycle
Figure 3-31
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
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?

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?
 Collect

and analyze data
Geographic Information Systems (GIS)
Allows for the collection of data over a large area
Allows the simultaneous overlay of many layers of
data

Remote Sensing
 use
controlled indoor and outdoor chambers
to study ecosystems
 Develop mathematical models to simulate
behavior of ecosystems
Critical nesting site
locations
GIS
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
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
 baseline
data on the world’s ecosystems is
necessary to



see how they are changing
develop effective strategies for preventing or
slowing their degradation
Scientists currently have less than half of the
basic ecological data needed to evaluate the
status of ecosystems in the United Sates