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Lesson 4: Ecosystems
Big Question:
What Is Necessary to Sustain Life on Earth?
Lesson 4/ ESRM 100 / University of Washington
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 OverTime and Interact with Each OtherHow 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: TheEcological Niche and the HabitatWhat 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 Lifeon EarthThe 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 ThermodynamicsThe 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 EcosystemsHuman 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 ManagementEcosystems 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.
