Ecosystem Dynamics
Food Chains and Food
Webs
Maroochydore SHS
Energy in Ecosystems
Energy that sustains
majority of living
systems is solar
energy
Solar energy is
converted to chemical
energy in
photosynthesis and is
held briefly in the
biosphere before it is
radiated into space as
heat
Getting Energy
Autrotrophs (Producers) produce their
own food using the suns energy
(Photosynthesis)
Autrotrophs are eaten by other organisms,
which in turn are eaten
This is how food passes through ecosystem
Food chain = the path that food takes from
organism to organism
Based on the way they obtain food, the
organisms can be classified in three
groups:
1.Producers
2.Consumers
3.Decomposers
Producers (Autotrophs)
Convert simple inorganic chemicals to
complex organic molecules (food)
Most use solar radiation (sun) as a source
Productivity = measured by the amount of
energy that is fixed in chemical compounds
or by increase in biomass in a particular
length of time
Example of a Producer…
Plants…
Utilize energy from the sun and nutrients
from the abiotic environment (carbon
dioxide from the air or water, other
nutrients from the soil or water)
Result = photosynthesis
Consumers
Used food by other organisms as
their energy source
Three levels of consumers:
1. First-order (Primary) are herbivores
2. Second-order (Secondary) eat firstorder consumers (carnivores which eat
herbivores)
3. Third (Tertiary) and higher order eat
second-order consumers (carnivores
which eat other carnivores)
Decomposers
Most are simple forms of life
(bacteria, fungi and some protozoans)
These break down the dead bodies
and waste products of other living
things
Convert complex organic molecules
into simple inorganic chemical which
are then released into the
environment and can be reused
Food Chain
Simple linear series that shows the series
of organisms existing in any ecosystem
Can be described as a transfer of energy
Each organism in the series feeds on and
obtains energy from the preceding organism
and provides energy to the next organism
Trophic (feeding) levels describe the
relative positions of producers and
consumers in a food chain
Food Chains
A food chain shows what a set of organisms in an
ecosystem eats with each organism acting as a link
in the chain.
Each link is called a trophic level.
Arrows connect each level and point in the
direction in which the food is going.
Energy flows through an ecosystem from plants
(producers) to herbivores (primary consumers to
carnivores (secondary consumers)
The ant is eaten by the bird.
There are rarely more than 6 links in
any food chain
This is because energy is lost to the
environment in the form of heat at
each level of a food chain
The closer a consumer is to the
producer, the more efficient is the
energy transfer
Food chains always start with
the sun and then a plant.
The lettuce is eaten by the slug, the slug is eaten by the
bird.
The top of the food chain.
Some animals are said to be at the top of the
food chain. This is because they are not hunted
by other animals.
No other animal hunts the
lion. The lion is at the top of
the food chain. Can you think
why?
Food Webs
Displays the interactions between
organisms in a community
In a food web there is greater stability
since a variety of food sources
compensates for seasonal fluctuations
All waste and dead materials are acted
upon by decomposers
Law of Conservation of Matter
and Energy
Ecosystems conform to this law which
states that:
“matter and energy cannot be created
or destroyed but can be changed to
other forms”
Ecological Pyramids
May be:
Pyramid of numbers
Showing the #s of individual organisms at each
level
Pyramid of biomass
Based on the total dry mass of the organisms
at each level
Pyramid of energy
Showing the productivity of the different levels
Large amounts of energy and biomass are dissipated at every trophic level
Pyramid of Numbers
This pyramid illustrates that when the primary
producers (leaves) are small, a large quantity of them
is required to support the primary consumers
(herbivores)
Pyramid of Energy availability
The relationship of the flow of Energy in the ecosystem represented here by an inverted pyramid. Generally only 10% of
the energy of each trophic level is passed on as energy to the next,
higher level