Topic Outline

• Ecology

• Population,

community and

ecosystem

• Biotic and abiotic

environment

• Relationships

• Food chain and web

• Energy transfer

between trophic

levels

• Carbon cycle

• Pyramid of numbers

and biomass

• Water pollution

• Conservation and

biodiversity

ECOLOGY

Pyramids of

energy, numbers

and biomass

Lesson Outline

• Pyramid of energy

• Pyramid of numbers

• Pyramid of biomass

Ecological Pyramids

• Pyramid of energy – shows energy flow through the trophic levels of a

food chain.

• Pyramid of numbers – shows the number of organisms at each trophic

level at a particular time.

• Pyramid of biomass – shows the mass of organisms at each trophic level

at a particular time.

Pyramid of energy

• shows energy flow through the trophic

levels of a food chain.

Pyramid of numbers

• shows the number of organisms at each

trophic level at a particular time.

Pyramid of numbers

• Consider the following food chain:

• If there is 1 lion in an area and it feeds on 7

giraffes in a month.

• Each giraffe feeds on 2 trees in a month.

• What would a pyramid of numbers look

like?

tree giraffe lion

Pyramid of numbers

• This pyramid is broad

at the bottom and

narrow towards the

top.

Pyramid of biomass

• Consider the following food chain:

• Biomass of 1 lion = 20kg

• Biomass of 1 giraffe = 20kg

• Biomass of 1 tree = 30kg

• What would a pyramid of biomass look like?

tree giraffe lion

Pyramid of biomass

• For this food chain,

the pyramid of

biomass has a similar

shape to the pyramid

of numbers.

Worksheet time

• Let’s try constructing our own pyramids!

• Pyramids need not always be broad at the

bottom and narrow at the top!

– Use rectangles.

– Producers are always at the bottom,

consumers at the top.

Grass rabbit snake hawk

Pyramid of numbers Pyramid of biomass

Tree aphid protozoa

Pyramid of numbers Pyramid of biomass

Tree aphid ladybird small bird

Pyramid of numbers Pyramid of biomass

grass zebra tsetse fly

Pyramid of numbers Pyramid of biomass

Comparison – which pyramid to use?

• If the producer is a large plant, then the second layer of the pyramid will be much larger than the base.

• It would make more sense to draw a pyramid of biomass

A pyramid of

numbers

A pyramid of

biomass

Conclusion

• Pyramids of biomass are a more accurate

representation of the food chain.

• Pyramids of biomass (almost) always have

a broader base and narrower tip.

– What is the exception?

References

• http://www.globalchange.umich.edu/gctext/I

nquiries/Inquiries_by_Unit/Unit_4.htm