Energy Flow in Ecosystems Lesson 2, Lecture notes of Thermodynamics

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Energy Flow in

Ecosystems

Lesson 2

Learning Intentions

Today we will be:

• Looking at the roles of producers,

consumers and decomposers have in the

flow of energy through an ecosystem.

• Looking at why only 10% of energy is

transferred from one trophic level to

another.

• Looking at pyramids of Numbers,

Biomass and Productivity.

Producers (autotrophs)

Primary Consumers (heterotrophs)

Secondary Consumers (heterotrophs)

Decomposers

INPUT:

SOLAR ENERGY

OUTPUT: HEAT, MOVEMENT, ENERGY

Trophic Efficiency = 10%

Trophic Efficiency

• Only about 10% of energy can be passed

on to next trophic level because:

1. Not all the material at any trophic level is

consumed.

2. Not all material consumed is digested and

used.

3. Most of the material digested is used for

metabolic processes and released as heat.

Energy content of first Trophic level

Energy content of uneaten part

Energy content of eaten part

Energy content of digested part

DECOMPOSERS

Energy used for growth

HEAT Energy available for 90% 10% next trophic level

Energy content of undigested part

Energy used for metabolic activity

Saprotrophs

• Are made up of detritivores (e.g.

earthworms) and decomposers (e.g.

bacteria and fungi)

• Saprotrophs break down or degrade

detritus and release nutrients and other

substance for recycling.

• Saprotrophs are largely aerobic species

which means the process of

decomposition can leave environments

depleted of oxygen.

Primary consumer

Pyramid of Numbers

Secondary consumer

Tertiary consumer

Quaternary consumer

Primary producer

Where the producer is a large organism (a tree?)

Primary producer

Primary consumer

Pyramid of Biomass

Secondary consumer

Tertiary consumer

Quaternary consumer

Key point:

• Show the total dry mass of organisms at each trophic level.
• Does not take into account the energy content of the biomass.

Primary producer

Primary consumer

Pyramid of Energy Flow/

Productivity

Secondary consumer

Tertiary consumer

Quaternary consumer

Key points:

• 10% energy transfer - limit to number of levels
• Show energy built into biomass at each trophic level
• Units are KJm-2yr-

In a food web the number (or biomass)

of stages is limited because the

energy reduces by 90% each time.

There are never usually more than

five stages in any food chain in a

food web.