Lesson 4: Ecosystems
Big Question:
What Is Necessary to Sustain Life on Earth?
Lesson Goals
After reading Chapter 4 and hearing/reading this lesson, you
should be able to explain
why the ecosystem is the basic system that supports life and
enables it to persist;
what food chains, food webs, and trophic levels are;
how energy enters ecosystems and determines biological
productivity;
what a community-level effect is;
what ecosystem management involves; and
how conservation and management of the environment might be
improved through ecosystem management.
Lesson 4/ ESRM 100 / University of Washington
How Populations Change Over
Time and Interact with Each Other
How and why does the abundance of a species change even
without human influence?
Interactions include competition, symbiosis, and
predation/parasitism
Would nature remain in balance if we didn’t interfere?
Long term study of wolves and moose of Isle Royale National
Park, Michigan
Lesson 4/ ESRM 100 / University of Washington
The populations of wolves and moose change over time, even
without human interference.
Lesson 4/ ESRM 100 / University of Washington
American Chestnut Blight
For more information, see "Chestnut Blight" and the Wikipedia
article on Chestnut Blight.
Lesson 4/ ESRM 100 / University of Washington
Professions and Places: The
Ecological Niche and the Habitat
What is a habitat, and what is a niche?
Where a species lives is its habitat
What it does for a living (its profession) is its ecological niche
Will a change in land use affect a species’ niche?
A species’ habitat may be damaged to the point where its niche
requirements are no longer available
Lesson 4/ ESRM 100 / University of Washington
Measuring Niches
Can species share a niche?
Two flatworm species: some streams have just one of the species,
others have both
Temperature is key
Lesson 4/ ESRM 100 / University of Washington
How Species Coexist
Flour Beetle Experiments
In a uniform environment, one species always wins
Lesson 4/ ESRM 100 / University of Washington
Two Examples of Symbiosis
Elk-ruminant bacteria to digest cellulose
Red alder – Frankia to fix Nitrogen from air
Lesson 4/ ESRM 100 / University of Washington
The Community Effect – Sea Otter
Lesson 4/ ESRM 100 / University of Washington
The Effect of Sea Otters on the Community
Lesson 4/ ESRM 100 / University of Washington
The Ecosystem: Sustaining Life
on Earth
The oldest fossils are more than 3.5 billion years old
Ecosystems are crucial to sustaining life
An ecosystem is comprised of the individuals of various species
and their nonliving environment.
Lesson 4/ ESRM 100 / University of Washington
A Simple Ecosystem:
Yellowstone Hot Spring
Lesson 4/ ESRM 100 / University of Washington
A Food Web
Lesson 4/ ESRM 100 / University of Washington
Food Webs
Some food webs appear simple and neat.
Lesson 4/ ESRM 100 / University of Washington
Food Web of the Harp Seal
In reality, many food webs are complex because most creatures
feed on several trophic levels.
Lesson 4/ ESRM 100 / University of Washington
Ecosystem Energy Flow
Energy is the ability to do work, and to move matter through an
ecosystem.
Lesson 4/ ESRM 100 / University of Washington
Life and the Laws of Thermodynamics
The law of conservation of energy: energy is neither created nor
destroyed but merely changed from one form to another
Why can’t the same energy continually cycle through an
ecosystem?
Lesson 4/ ESRM 100 / University of Washington
The Law of Entropy
The law of entropy: energy always changes from a more useful,
more highly organized form to a less useful, disorganized form
Whenever useful work is done, heat is released to the
environment and that energy can never be recycled
The net flow of energy through an ecosystem is a one-way flow
Lesson 4/ ESRM 100 / University of Washington
Producing New Organic Matter
Primary production: Some organisms make their own organic
matter from a source of energy and inorganic compounds
Autotrophs: include green plants, algae, some bacteria
Secondary production: Other organisms cannot make their own
organic compounds from inorganic ones and must feed on other
living things
Heterotrophs: all animals, fungi, most bacteria
Lesson 4/ ESRM 100 / University of Washington
Respiration
Living things use energy from organic matter through
respiration
Organic compound are combined with oxygen to release energy
and produce carbon dioxide and water
Involves organic chemicals called enzymes
Lesson 4/ ESRM 100 / University of Washington
Gross and Net Production
Autotroph production involves
• producing organic matter within the body--gross
production;
• using some of this new organic matter as a fuel in
respiration; and
• storing some of the newly produced organic matter for
future use--net production.
Most primary production takes place through photosynthesis.
Lesson 4/ ESRM 100 / University of Washington
Practical Implication I: Human Domination of
Ecosystems
Human domination is not yet a global catastrophe, although
serious environmental degradation has resulted.
Earth’s ecological and biological resources have been and will
continue to be greatly modified by human use of the
environment
An important human-induced alteration of Earth’s ecosystems is
land modification
We can act to cause less damage.
Lesson 4/ ESRM 100 / University of Washington
Practical Implication II:
Ecosystem Management
Ecosystems can be natural or artificial or a combination of both.
The ecosystem concept is central to management of natural
resources.
We must focus on their ecosystem and make sure that it
continues to function.
Lesson 4/ ESRM 100 / University of Washington
Chapter 4: Ecosystems
Question? E-mail your TA. eschelp@u.washington.edu