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Chapter 3
 Ecosystems: What Are
They and How Do They
Work?

Ecology is a study of connections
in nature.

How organisms interact with one
another and with their nonliving
environment.
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.
Food webs show
us the complex
interactions
between many
food chains.
Figure 3-18
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
Producers: Basic Source of All Food

Most producers capture sunlight to produce
carbohydrates by photosynthesis:
Chemosynthesis:
Some organisms such as deep ocean bacteria draw
energy from hydrothermal vents and produce
carbohydrates from hydrogen sulfide (H2S) gas .

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
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.
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.
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.
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
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
 …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.
Figure 3-1
THE EARTH’S LIFE SUPPORT
SYSTEMS

The biosphere
consists of several
physical layers that
contain:





Air
Water
Soil
Minerals
Life
Figure 3-6
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
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
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
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
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