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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?
 …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
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).
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
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
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
ECOSYSTEM COMPONENTS
 Life
exists on land systems called biomes
and in freshwater and ocean aquatic life
zones.
Figure 3-9
Nonliving and Living Components of
Ecosystems
 Ecosystems
consist of nonliving (abiotic) and
living (biotic) components.
Figure 3-10
Factors That Limit Population Growth
 Availability
of matter and energy resources
can limit the number of organisms in a
population.
Figure 3-11
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:
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
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
Solutions
 Goals,
strategies
and tactics for
protecting
biodiversity.
Figure 3-16
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.
SOIL: A RENEWABLE RESOURCE
Figure 3-23
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.
The Water Cycle
Figure 3-26
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
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


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
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?
 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
Systems Analysis
 Ecologists
develop
mathematical and
other models to
simulate the
behavior of
ecosystems.
Figure 3-34
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).