By the end of this session I should be able to:
(a) define the term ecosystem;
(b) state that ecosystems are dynamic systems;
(c) define the terms biotic factor and abiotic factor, using
named examples;
(d) define the terms producer, consumer decomposer and
trophic level;
(e) describe how energy is transferred though
ecosystems;
(f) outline how energy transfers between trophic levels
can be measured;
(g) discuss the efficiency of energy transfers between
trophic levels;
(h) explain how human activities can manipulate the flow
of energy through ecosystems (HSW6b);
On the piece of paper in front of
you there are 10 different
ecosystems. Name as many as
you can by labelling the pictures
and adding the selection
pressure that would have the
biggest effect on the organisms
living there.
What is lurking in your eyelashes?
Use your texts to complete the following
Key Word
Ecosystem
Abiotic
factor
Biotic factor
Producer
Consumer
Decomposer
Trophic level
Definition
Examples
Link across the
spec
What selection pressures does Ethan have to cope
with? Think biotic and abiotic factors.
Biotic  living / Abiotic  non living
Biotic factors that Ethan needs to
consider
Biotic factors that Ethan needs to
consider
What limits the length of the food chain?
What limits length of food chain?
• H1: Energetics
• Availability of energy limits to 5-7 levels
• Depends on:
NPP
energy needed by consumers
average ecological efficiency
• H2: Dynamic stability
Longer chains less stable because:
Fluctuations at lower trophic levels magnified at
higher levels --->
extinction of top predators.
• A food web is a
branching food chain
with complex trophic
interactions
• Species may play a role
at more than one
trophic level
• Food webs can be
simplified by isolating a
portion of a community
that interacts very little
with the rest of the
community
Biomass available at
• About one order of
the next trophic level
magnitude of available
energy is lost from one
trophic level to the next
– Reason why food chains
generally consist of only 3
or 4 steps
How heterotrophs use food
energy
Cayuga Lake
In NY
Energy loss in an ecosystem
How can we calculate the amount of energy?
each trophic level?
Consumers
(heterotrophs)
Producers (autotrophs)
How is energy lost between trophic level?
Lost in the transfer of light energy
into chemical energy in
photosynthetic organisms
•
•
•
•
•
•
•
Lost in the transfer from one
consumer the next
•
•
•
•
•
•
•
Primary productivity
• Gross Primary Productivity (GPP):
– total amount of photosynthetic energy captured in a given
period of time.
• Net Primary Productivity (NPP):
– the amount of plant biomass (energy) after cell respiration
has occurred in plant tissues.
NPP
=
plant growth/
unit area/
unit time
GPP
–
Plant respiration
total photosynthesis/
unit area/unit time
Primary productivity – marine ecosystems
Global variation in estimated NPP
Figure 9
Mr Moore set the
homework on
‘increasing efficiency in
the production of food
by manipulating
trophic levels’