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11/28/2013 Following Energy Movement in Ecosystems Understanding Energy Flows In order to understand energy flows, we categorize living things by their “Trophic Level”. What is a Trophic Level? – A Trophic Level is a measure of how living things get their energy. Classification of Organisms There are TWO main classes of organisms: 1) AUTOTROPHS 2) HETEROTROPHS Autotrophs – Organisms that make their own food from basic nutrients and light from the sun. -These organisms are also called PRODUCERS. -They belong in the FIRST trophic level (they form the base of any food web). Example: Plants and algae Heterotrophs What is a Heterotroph? – Organisms that cannot make their own food. -They must obtain their food and energy from autotrophs or other heterotrophs. Heterotrophs are also known as CONSUMERS -Consumers can belong to the second, third, or any higher trophic level. Autotrophs We know that autotrophs make their own food – but there are TWO ways that they can make food. In order to tell the difference – we put them in different categories: Photosynthetic Organisms Chemosynthetic Organisms – Use the energy from the sun to make their own food. – Use energy from chemical reactions to make food Example: Grass and other plants Example: Certain types of bacteria Heterotrophs There are 5 types of heterotrophs: -Omnivores -Carnivores -Herbivores -Scavengers -Decomposers 1) Omnivores – Eat plants AND animals Example: The Black Bear eats a variety of foods including fruit, nuts, small deer and fish. 1 11/28/2013 Heterotrophs Heterotrophs 2) Carnivores– Eat animals only 5) Decomposers – Breaks down dead organisms -This completes the circle of life by returning nutrients into the soil. Example: Lions – A male lion can eat up to 75 pounds of meat during one meal! Example: Bacteria, maggots, worms, etc 3) Herbivores– Eat plants only Example: Cows – they can eat different plants such as grass, grains, and hay. 4) Scavengers– Eat dead animals Example: Vultures – they aren’t very picky about what they eat, as long as it is dead and rotting. Food Chains Food Chains Food chain– A way of showing a step-by-step sequence of who eats whom in an ecosystem. What does this food chain tell us? The plant is eaten by the slug. The slug is eaten by the frog. The frog is eaten by the heron. What is happening in this food chain? Insect Frog •The slug receives its energy 2 steps away from the original source (sunlight). •Therefore it is in the 2nd trophic level. The direction of the arrow indicates the FLOW OF ENERGY and can be read as “eaten by” (example – Insect is eaten by the frog) Slug *If the slug is in the 2nd trophic level which level is the frog in? Food Chains Ok – so, since the frog is in the 3rd trophic level then the Heron who eats the frog is a member of the 4th trophic level? Plants Frog Food Webs Heron -The heron is the FINAL carnivore in this food chain. *The final carnivore in any food chain is called the TOP CARNIVORE Heron Plants Frog Slug Food Web – a picture representation of the feeding relationships among organisms in an ecosystem. - In this food web, you can see that the fox and the owl have many different food sources. - The loss of any one member in this web will have a serious effect on all of the other organisms. It is important to remember that: decomposers can be found at any level in the food chain, even if they are not shown! 2 11/28/2013 Trophic Levels 3