Food Chains & Food Webs

Energy Roles Energy enters as sunlight Some organisms capture energy and store it as food energy Organisms that can make their own food are producers Are the source of all food in ecosystem Organisms that obtain energy by feeding on other organisms are consumers

Decomposers break down wastes and dead organisms & return raw materials to the ecosystem Know as nature’s recyclers

Transfer of Energy When a zebra eats the grass, it does not obtain all of the energy the grass has (much of it is not eaten) When a lion eats a zebra, it does not get all of the energy from the zebra (much of it is lost as heat)

This shows that no organism EVER receives all of the energy from the organism they just ate Only 10% of the energy from one trophic level is transferred to the next – this is called the 10% law

Trophic Levels Energy moves from one organism to another when the organism is eaten Each step in this transfer of energy is know as a trophic level The main trophic levels are producers, consumers, and decomposers

- Energy Flow in Ecosystems

Food Chains & Food Webs Food Chain – series of events in which one organism eats another and obtains energy First organism in the food chain is always a PRODUCER The second organism in the chain feeds on the producer and is called the PRIMARY CONSUMER The third organism = SECONDARY CONSUMER The fourth organism = TERTIARY CONSUMER

Food chains only show one path that energy can move, BUT… Food Web – consists of many overlapping food chains in an ecosystem Food webs can interconnect in what is called a global food web Think of it as how we don’t eat the same thing every day, neither do other organisms

ENERGY PYRAMIDS Energy Pyramid shows the amount of energy that moves from one feeding level to another When an organism in an ecosystem eats, it obtains energy The organism uses some of the energy to move, grow, etc… This means only SOME of the energy is available for the next organism in the food web

The other 90% of the energy is used or lost Only about 10% of the energy at one level of the food web is transferred to the next highest level The other 90% of the energy is used or lost As you move up the pyramid, each level has less energy available than the level below Most energy is available at the producer level of the pyramid.

Since so much energy is lost at each level, the amount of energy available at the producer level limits the number of consumers that an ecosystem can support SO…usually there are fewer organisms at highest levels of the food web

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