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A pyramid of numbers shows how many organisms are consumed at each stage (trophic level) of a food web.
Generally, there are more organisms consumed at earlier stages.
This is because most of the energy consumed is used for movement or staying warm. Little is used to build body mass. |
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How is a pyramid or number arranged? Circle map before and after watching the video:
https://www.youtube.com/watch?v=TZk6vcmLcKw
Draw to scale
(1 mm : 1 Organism)
1 Barn owl eats
10 Frogs,
Each frog eats 20 aphids
These numbers are far too low, but will fit nicely on a page.
A Barn Owl has a mass of 500g
A Frog has a mass of 25g
An Aphid has a mass of 0.001g
If 1% of the mass of the eaten animal makes up the consumer, then the numbers should be:
1 Barn owl
2000 Frogs
5,000,000,000 Aphids
Each frog eats 2,500,000 Aphids |
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Organisms on low levels of the food web can ingest small amounts of toxic materials and survive.
When multiple low level organisms are ingested by higher level organisms the toxic materials accumulate to levels that are dangerous.
This is called bioaccumulation. |
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What is bioaccumulation and what levels of the food chain will it affect the most? DDT example:
If each aphid has 0.01 micrograms of DDT in it:
How much DDT does a frog have? (25 milligrams)
How much DDT does an Owl have? (50 grams) |
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