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.
Energy flow
• Once energy has been captured by
autotrophs it flows through the
ecosystem according to the laws of
thermodynamics.
• These laws state that:
1. Energy can neither be created nor
destroyed. It can only change from one
form to another.
2. Entropy or disorder in the universe is
constantly increasing and all energy
eventually degrades to less useful forms of
heat.
OUTPUT:
INPUT:
HEAT, MOVEMENT,
ENERGY
SOLAR
ENERGY
Producers
(autotrophs)
10%
Primary
Consumers
(heterotrophs)
10%
Secondary
Consumers
(heterotrophs)
Decomposers
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.
SOLAR ENERGY
Primary producer
Primary consumer
HEAT
ENERGY
Secondary consumer
Tertiary consumer
D
E
C
O
M
P
O
S
E
R
S
HEAT
ENERGY
100%
Energy content of first Trophic level
Energy content of
uneaten part
Energy content of
eaten part
Energy
content of
undigested
part
Energy used Energy
for metabolic used for
growth
activity
DECOMPOSERS
HEAT
Energy content
of digested part
90%
10%
Energy available for
next trophic level
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.
Pyramid of Numbers
Quaternary consumer
Tertiary consumer
Secondary consumer
Primary consumer
Primary producer
Pyramid of Numbers
Quaternary consumer
Tertiary consumer
Secondary consumer
Primary consumer
Primary producer
Where the producer is a large organism (a tree?)
Pyramid of Biomass
Quaternary consumer
Tertiary consumer
Secondary consumer
Primary consumer
Primary producer
Key point:
• Show the total dry mass of organisms at each trophic level.
• Does not take into account the energy content of the biomass.
Pyramid of Biomass
Quaternary consumer
Tertiary consumer
Secondary consumer
Primary consumer
Primary producer
This occurs where the primary consumer has a very high
level of productivity – for example phytoplankton
Pyramid of Energy Flow/
Productivity
Quaternary consumer
Tertiary consumer
Secondary consumer
Primary consumer
Primary producer
Key points:
• 10% energy transfer - limit to number of levels
• Show energy built into biomass at each trophic level
• Units are KJm-2yr-1
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.
Task
1. Use your monograph, scholar book and
this PowerPoint to summarise this in your
own words (use diagrams where
appropriate)
2. Use 1 (above) to produce the Extended
Response :
Discuss the flow of energy in a fresh
water ecosystem (15)