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Information obtained from: Holt Science and Technology: Life Science. Austin: Holt Rinehart & Winston, 2007. Print.
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Chapter 18 Section 2
Describe the functions of producers, consumers, and decomposers in an ecosystem
Distinguish between a food chain and a food web
Explain how energy flows through a food web
Describe how the removal of one species affects the entire food web
Living things need energy to survive
How does energy pass through an ecosystem?
Organisms can be divided into 3 groups based on how they get energy:◦ PRODUCERS◦ CONSUMERS◦ DECOMPOSERS
Organisms that use sunlight to make food
Photosynthesis (plants, some algae and bacteria)
Ex: grasses in a prairie; algae in the ocean
Organisms that eat other organisms
Eat producers or other animals to obtain energy
Several kinds: ◦ HERBIVORE: eats only plants (ex: grasshoppers,
bison)◦ CARNIVORE: eats animals (ex: coyotes, hawks)◦ OMNIVORES: eat both plants and animals (ex:
mouse) – Scavengers: eat dead plants and animals
Organisms that get energy by breaking down dead organisms
Bacteria and fungi (remove stored energy from dead organisms)
Nature’s recyclers
Food Chain: ◦ how energy flows from one organism to another ◦ Simple food chains are rare; organisms eat many
kinds of foods◦ Pathway of energy transfer through various
stages as a result of the feeding patterns of a series of organisms
Food Web:◦ Shows energy connections in nature◦ A diagram that shows feeding relationships
between organisms in an ecosystem◦ One-way direction
http://pack152.net/AcademicsAndSports/WildlifeConservation/FoodChain.gif
LAND FOOD WEBS
AQUATIC FOOD WEBS
http://classes.dma.ucla.edu/Winter06/161B/projects/tonyau/ps2/1/images/FoodWeb.JPG
A triangular diagram that shows an ecosystem’s loss of energy, which results as energy passes through the ecosystem’s food chain
More energy is available at the base that at the top
Can you create an energy pyramid?
http://www.mlms.logan.k12.ut.us/~mlowe/EnergyPyramid.gif
One species can be very important for the flow of energy in an environment
Ex: Gray Wolves ◦ Consumers◦ Predators◦ Control the populations of many other animals◦ Top of the food pyramid
http://www.panhala.net/Archive/Gray%20Wolves.jpg
Population was almost wiped out by settlers
Elk species were no longer controlled
Overpopulation of elk occurred, leading to overgrazing
Too little grass was left to support other organisms
All populations became affected by the loss of the Gray Wolves
Gray Wolves were brought back to Yellowstone in 1995
Restore the natural energy flow
Not everyone approves
Concerns over safety of livestock
As wolves were reintroduced, the elk population decreased
Wolves killed off old, sick, injured, or diseased elk
Increased plant growth
Hare & fox population increased
All animals are important for balance in the food web
How might an omnivore be a link both at the beginning of a food web and near the end?
How does the energy in a fish get into the fish? How does the energy stored in the fish get released from the fish?
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