Energy Flow (4.2)
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Notes & Review:Ecology NotesEcology Review Game |
Energy Flow & Loss in an Ecosystem
First Law of Conservation says that energy can be neither created nor destroyed. So the question is where does the energy found in an ecosystem come from?
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Energy is transferred or transformed throughout the ecosystem. Once it is transformed into a usable form through photosynthesis, it can then be transferred. But the transferring of energy is not very efficient.
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Why is there inefficient transfer of energy?
- Not all of the organism is consumed (leaving energy behind)
- Some die before they are eaten (leaving energy behind)
- Some parts of organisms are indigestible (unable to be converted into energy)
- MOST is lost via cellular respiration converted to heat for the purpose of living.
- Heat is lost energy from the ecosystem. While it stays within the universe (law of conservation), it is lost from the ecosystem.
Energy Pyramids
An energy pyramid is a visible way of showing energy loss through an ecosystem. Units are measured in kilojoules per meter squared per year. (KJm-2yr-1). See diagram below of completed energy pyramid from the problem with steps and calculations seen below that
Food Chains vs Food Webs
Food chains and food webs allow us to see consumer interaction within an ecosystem. Although some can show detrivores and saphrotrophs, it is harder to demonstrate trophic levels for these organisms as they technically occupy all levels, hence they are usually left off food webs.
Food webs and food chains
Food webs and food chains
Food Chains help us identify tropic levels:
Note that the arrows in a food web or food chain represent the direction of energy movement, so the arrows go towards what is gaining the energy.
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Food Webs allow us to the see the complexity of the interactions of an ecosystem. Few organisms only fall into a single trophic level.
The following food web has been color coordinated with trophic levels.
Learn to build a food web Food Web Game- can you decipher the parts? |
Why does the loss of energy up a food chain limit the length of the chain (or biomass) an ecosystem can contain?
The amount of energy available to an entire ecosystem is found in its autotrophs. The less energy you begin with the less energy available at the higher trophic levels because it is lost as it moves up the food chain. The less energy available at the higher levels, the more organisms the higher trophic levels must eat in order to gain the energy needed for survival. At some point the amount of energy needed to survive and the amount of energy available are no longer helpful. It becomes more advantageous for an organism to occupy lower trophic levels, or in some cases multiple trophic levels, to ensure their energy requirements are met.
The amount of energy available to an entire ecosystem is found in its autotrophs. The less energy you begin with the less energy available at the higher trophic levels because it is lost as it moves up the food chain. The less energy available at the higher levels, the more organisms the higher trophic levels must eat in order to gain the energy needed for survival. At some point the amount of energy needed to survive and the amount of energy available are no longer helpful. It becomes more advantageous for an organism to occupy lower trophic levels, or in some cases multiple trophic levels, to ensure their energy requirements are met.