Energy in Ecosystems
Energy Flow: Most of the energy that enters a trophic level is used by the organism to stay alive. • 10 % of the energy consumed is retained in the body tissues and is available for the next trophic level. • 90 % of the energy is lost to waste, movement, warmth and metabolism.
Ten Percent Rule­ only ten percent of the energy at a given trophic level is available the next trophic level. Energy Limits:
Energy is lost (used) in four different ways:
1. Plants use energy to carry out life processes such as growth and nutrient­transport.
2. Energy is lost to the environment as waste heat energy. 3. Energy is used by consumers for life processes.
4. Remaining energy is used by decomposers when organisms die.
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Ecological Pyramids
Ecologists use pyramids (graphs) to estimate populations and the flow of energy through various ecosystems.
1. Pyramid of Energy
A pyramid of energy shows the amount of available energy in each trophic level. Usually only 10 % is passed on to each successive level.
The concept is that the energy decreases at each level.
2. Pyramid of Numbers
A pyramid of numbers shows the actual number of organisms at each trophic level in an ecosystem. Most times the graph looks like a true pyramid, but sometimes a smaller number ends up on the bottom.
use the images below to label the pyramid of numbers
How do Ecosystems work: http://www.youtube.com/watch?v=o_RBHfjZsUQ
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Energy Flow Questions
1. Using the spruce ­ deer ­ wolf food chain, explain the factors that account for the loss of energy between the different trophic levels.
2. Create a pyramid of numbers, given the following information: 75000 blades of grass, 7500 beetles, 750 sparrows, 75 snakes, 7 hawks. 3. Create a pyramid of energy based on the following information: Grass captures 67000 kJ of energy from the Sun. Rabbits eat the grass, and snakes eat the rabbits. The wolf, which preys on rabbits and snakes, is the top carnivore. 4. Using the Energy pyramid in the note (flower­grasshopper­mouse­snake) explain why there needs to be a larger number of flowers then snakes for the ecosystem to be sustainable. Use the ten percent rule to help explain your answer.
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