Food Chains Food Webs Food Pyramids March 30

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 Grasshopper Frog Snake Hawk Producer Primary Consumer Secondary Consumer Tertiary Consumer Top Consumer Trophic Level 1 st 2 nd 3 rd 4 th 5 th

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 food 2) 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 web 1) Grass Rabbit Hawk 2) Clover Rabbit Fox 3) Grass Mouse Snake Hawk Fox Snake Mouse Grass Rabbit Clover

Food Pyramids • Show the quantity of organisms involved • There are three types 1) Pyramid of Numbers 2) Pyramid of Biomass 3) 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