Feeding Relationships - Pyramids

Showing feeding relationships quantitatively (in numbers).

What Food Chains and webs don’t tell us

• A food chain tells us what eats what and shows the movement of energy

• Food chains do not tell us how many organisms are involved, how much their mass is, or how much energy is transferred from organism to organism.

• We use pyramids to show us values associated with each organism.

Pyramids of number

Pyramids of number • This shows us how many

organisms are involved at each feeding (trophic) level.

• Like a food chain a pyramid always starts (at the bottom) with a producer (plant) and builds itself up in the same order as a food chain.

• Each block is in scale to show the numbers in each level.

Practicing Perfect Pyramids Please!

• Try the following on graph paper. Go back and check the rules.

• 1. 8000 rose leaves 1000 greenfly (aphids)200 ladybirds100 spiders

• 2. 5000 oak leaves, 2000 caterpillars, 100 sparrows, 3 sparrow hawks

• 3. 3000 blades of grass, 200 rabbits, 20 foxes, 400 fleas

Pyramid of biomass

More biomass pyramids

• Pyramids of Biomass show the mass of each organism on each level. The more the mass the wider the level.

• For instance one pike has a similar mass to 3 water beetles which is why it's level is almost the same as the beetles.

Pyramid of number Pyramid of biomass

Pyramid of number Pyramid of biomass

Pyramids of energy

• These always are pyramid shaped.

• These show the transference of energy up the feeding levels.

• Energy should be lost as you move up the pyramid. Can you remember why?.

What happens to energy?

• Flow of energy through a food chain. As energy passes to a higher tropic level, approximately 90% of the useful energy is lost. • High tropic levels contain less energy

and fewer organisms than lower levels.

What happens to energy?

• At each tropic level in a food chain, energy is used by the organisms at that level to maintain their own life process.

• It is estimated that in going from one tropic level to the next, about 90 % of the energy is lost.In moving to the next tropic level, only 10 % of the original energy is available. By the third tropic level only 1% of the energy is available.