Food Chains, Food Webs & Food Pyramids

March 30, 2011

Review from last day

• Producer: makes its own food (e.g., plants)• Consumer: feeds on other organisms (e.g.,

humans)

Scavenger

• Do not kill their own food• Eats abandoned carcasses (e.g., vultures)

Food Chains

• Feeding relationships that describe eating patterns of organisms

• Placement of the organism in the food chain depends on what role they play in the ecosystem

Food Chains (con’t)

• Each step in a food chain is called a trophic level

• Approximately 90% energy loss at each step• Any change in one level affects all other levels

Food Chain Example

Organism Role Trophic Level

Grass Producer 1st Grasshopper Primary Consumer 2ndFrog Secondary Consumer 3rd Snake Tertiary Consumer 4thHawk Top Consumer 5th

Practice Drawing Food Chains

• In an alpine meadow, clover is eaten by a ground squirrel. The ground squirrel is eaten by a grizzly. Create the appropriate food chain.

• Clover Ground Squirrel Grizzly

Food Webs

• Most feeding relationships are more complex than just a single chain because:1) Most organisms eat more than 1 type of food2) Most organisms are eaten by more than 1 type

of consumer• Food webs show many connected food chains

Food Web Example

Practice Food Web• Arrange these food chains into a single food web1) Grass Rabbit Hawk2) Clover Rabbit Fox3) Grass Mouse Snake Hawk

Hawk Fox

Snake

Mouse Rabbit

Grass Clover

Food Pyramids

• Show the quantity of organisms involved• There are three types

1) Pyramid of Numbers2) Pyramid of Biomass3) Pyramid of Energy

Pyramid of Numbers• Shows the number of organisms at each trophic level •Easy to construct• Not useful to show amount of energy because it does not take into account the sizes of individual organisms

Pyramid of Biomass• Shows total mass of the

organisms at each trophic level• Takes number and size into

consideration• Good estimate of energy in

ecosystem• Does not take reproductive

rates into consideration• Reduction of biomass in

pyramid occurs because:– Not everything in the lower

levels gets eaten– Not everything that is eaten is

digested– Energy is always being lost as

heat

weasels

Pyramid of Energy• Shows available energy at each level• Most accurate but very to difficult to model• Energy is lost as heat along the food chain• Energy decreases as you move up the food chain