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?