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