Energy flow in ecosystems Section 3.3 Energy flow in ecosystems

How does energy move through an ecosystem? Energy flows like a one way stream in an ecosystem

Food chains Steps by which energy is transferred - through eating!

Aquatic food chains Often start with phytoplankton and algae In this chain, the top carnivore is 4 steps removed from the primary producer

Food webs Often there are many links between different food chains

Decomposers and detritivores Detritivores and decomposers are as important as other consumers Provide a food sauce for other primary consumers Release nutrients Without decomposers nutrients stay locked up in dead organisms

Why might scientists use models such as food chains or a food web Why might scientists use models such as food chains or a food web? What kind of predictions can be made? Unethical to experiment on animals Feeding relationships can be difficult to observe A Food web can be used to predict what might happen if a particular species increases or decreases in number.

Disturbing a food web Algae for krill grow beneath Antarctic sea ice? What effect might global warming have?

Trophic levels Each step in a food chain or food web is called a trophic level Primary producers are always first trophic levels Displayed in ecological pyramids

Pyramid of energy Only a small portion of energy will move from one trophic level to another

Pyramid of biomass Illustrates the relative amount of of living organic matter available at each trophic level Biomass is measured by grams of organic matter per unit area

Pyramid of numbers Often a very similar shape to pyramid of biomass, but this is not always the case…