5,4,3,2,1 go… can you talk about food chains and food webs for 60 seconds mentioning as many as the key words

as possible?Producer Consumer

Food chain

Food web

Omnivore

Habitat

Trophic level

Energy loss

Heat

Quarternary

Decomposer

Respiration

Tertiary consumer

Secondary consumer

Primary consumer Detritivore

CarnivoreHerbivore

Ecological pyramids

About how energy moves and is lost between trophic levels

WAL:

All

Most

Some

• What are the different types of ecological pyramid?

• What are the relative merits and disadvantages of each?

•What percentage of energy is transferred from one level to the next?

Today we are covering from the specification:

Pages 70-72 of your textbook

Pyramids of numbers

• Food chains and food webs are a useful means of showing what different organisms eat and therefore energy flow. They do not provide quantitative information – ecological pyramids

• Usually they look like this:

7

Pyramids of Numbers

What can be the problem?

They can look odd

8

Pyramids of Numbers

1)No account is taken of size – one tree is given the same value as 1 aphid therefore they can look inverted.

2)The number of individuals s so great that it is impossible to represent them accurately on the same

scale as other species in the food chain – one tree and 1 million aphids

They can look odd

Pyramids of Numbers

Pyramids of biomass

• More reliable, quantitative description of a food chain is provided when their biomass is measured.

• Biomass is the total mass of the plants and/or animals in a particular place.

11

Biomass = dry mass of

organisms

Given as gm-2 for an area

Or

gm-3 for a volume

Pyramids of Biomass

12

Measuring biomass

Problem: finding the biomass of worms

Why is this so hard?How would you do it?

13

To eliminate the problem of variability due to moisture content, you can dry your earthworms at 60°C for 24-48 hours to get “dry earthworm

biomass”.

Problem the variability due to gut contents:Answer?

• Keep the live earthworms in containers until they empty their guts (24-48 hours, if they don’t

die in the process);• Dissect the preserved earthworm and flush their

opened gut;• “ash” dry worms leaving only mineral gut

contents.

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The answer?A statistical relationship between length & dry biomass

Dry worm & weigh

“ash” dry @ 500 oC

Remove ash

Weigh gut contents

Subtract gut contents weight from dry

weightQ. Why is the graph so useful?

Pyramids of biomass

• Fresh mass is quite easy to access but varying amounts of water makes it unreliable.

• Use dry mass but the organisms must be killed, therefore only small sample, which may not be representative.

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Anomaly from pyramid of biomass with aquatic food

chain

Q. Why is there less biomass in producers than primary consumers?

Pyramids of Biomass

A. Sample is made at a single point in time and plant biomass may vary with season. Phytoplankton may also be reproducing quickly and so large turnover of biomass.

Pyramids of energy

• Most accurate representation of energy flow through an ecosystem.

• Collecting data can be difficult and complex.• Data are collected in a given area (e.g one

square metre) and in a set time (e.g. a year).• Results are more reliable than those for

biomass as 2 organisms of the same biomass may store different amounts of energy.

• 1g of fat stores 2x amount of energy of 1g carbohydrate.

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Pyramid of Energy

Energy stored in each trophic level

of a Florida ecosystem

Q. Why might deriving energy content be difficult?

Energy KJ m-2 y-1

A. Two organisms of the same dry mass may have different energy contents e.g. more or less fat which is high in energy.

Task

Do application questions and summary questions

Ecological pyramids

About how energy moves and is lost between trophic levels

WAL:

All

Most

Some

• What are the different types of ecological pyramid?

• What are the relative merits and disadvantages of each?

•What percentage of energy is transferred from one level to the next?