Food Chains, Food Webs & Food Pyramids

1. Food Chains, Food Webs & Food Pyramids March 30, 2011

2. Review from last day • Producer: makes its own food (e.g., plants) • Consumer: feeds on other organisms (e.g., humans)

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

4. 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

5. 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

6. Food Chain Example

7. 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

8. Food Webs • Most feeding relationships are more complex than just a single chain because: • Most organisms eat more than 1 type of food • Most organisms are eaten by more than 1 type of consumer • Food webs show many connected food chains

9. Food Web Example

10. Practice Food Web • Arrange these food chains into a single food web • Grass  Rabbit  Hawk • Clover  Rabbit  Fox • Grass  Mouse  Snake  Hawk Hawk Fox Snake Mouse Rabbit Grass Clover

11. Food Pyramids • Show the quantity of organisms involved • There are three types • Pyramid of Numbers • Pyramid of Biomass • Pyramid of Energy

12. 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

13. 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

14. 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