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Ecology
March 2013
Pre AP biology
What is an ecosystem?
Ecology is the study of
organisms and their
interactions with their
living and nonliving
environment .
Where we start this study is
with an ecosystem which
is an area of study that
includes living and non
living parts.
What makes up an ecosystem?
• An Ecosystem has
two parts:
1. Biotic factors – all
the living organisms
2. Abiotic factors –
physical, nonliving
aspects
Use the picture below to list all the biotic
factors you see or can assume are there
•
Use the picture below to list all the abiotic
factors you see or can assume are there
•
Habitat, Population, Community
• A habitat is the place
where a particular
population lives.
• A population is all the
individuals in a
particular species
living in one place
• A community is all the
populations living in
one habitat
Biomes
A large region
composed of similar
ecosytems; biomes
have a specific
climate and animal
and plant
communties.
Where does an ecosystem fit in?
Individual organisms make up
populations which make up 
communities which make up 
ecosystems which make up 
biomes
Energy Flow in Ecosystems
• Everything that
organisms do in an
ecosystem requires
energy.
• How much energy is
available directly
influences biodiversity
• Our ultimate source of
energy is the SUN.
Producers and Consumers
Producers are organisms
that first capture energy
They include: some
bacteria, all plants, and
algae. Producers make
energy-storing molecules
Consumers are
organisms that consume
producers or other
organisms in order to
obtain the energy they
need.
Trophic Levels
Sun
Producer
Consumer
Consumer
Organisms are assigned to a trophic level (feeding
level) based on the organism’s source of energy.
Energy moves from one trophic level to the next.
Trophic Levels
Sun
Producer
1st Trophic Level
Consumer
Consumer
Producers are always on the 1st trophic level.
They receive the sun’s energy and, through
photosynthesis, convert it to organic molecules.
Trophic Levels
Sun
Producer
Consumer
1st Trophic Level 2nd trophic level
Consumer
Consumers are on all levels except the first.
Anything that eats a producer is on the 2nd trophic
level. All herbivores are on the 2nd trophic level.
Herbivores are also called primary consumers
Trophic Levels
Sun
Consumer
Producer
nd
1st Trophic Level 2 trophic level
Consumer
3rd trophic level
Any consumer that eats herbivores is on the 3rd
trophic level and is called a secondary consumer.
Trophic Levels
Sun
Consumer
Producer
nd
1st Trophic Level 2 trophic level
Consumer
3rd trophic level
Consumers either eat both producers and
consumers (called an omnivore), or they eat only
organisms in the 2nd trophic level and above
(called carnivore).
Above the
rd
3
trophic level
• Some organisms like
humans, sharks and hawks
are carnivores that eat
other carnivores and can
be placed on the 4th
trophic level.
• They are called tertiary
consumers.
It is very rare for an ecosystem to have more than
four trophic levels
Food chain
• The path of energy
through the trophic
levels of an ecosystem
is called a food chain
• In a food chain the
arrows always point to
the organism doing the
eating. (Imagine an
arrow pointing into the
eater’s mouth)
Detritivores
• Detritivores are organisms that
obtain their energy from the
organic wastes and dead
bodies that are produced at all
trophic levels.
• They include worms, fungus
and bacteria
• Bacteria and fungus are known
as decomposers because they
cause decay.
• They are important because
they recycle nutrients back into
the environment
Food Web
• Most ecosystems do
not follow simple
straight paths because
individual animals
often feed at several
trophic levels.
• This creates a series of
interconnected chains
called a food web.
Loss of energy
• A plant stores only a small amount of the energy it
absorbs. The rest is given off as heat or used by
the plant to support its daily processes.
• The same is true for a primary consumer. It will
take in energy stored in the plant, but will either
use the energy immediately or it will be given off
as heat. It will only store 10% of the energy it
took in.
• During every transfer of energy in an ecosystem,
energy is lost as heat or used by the organism and
only about 10% is stored at each step.
The 10% Rule
• You can calculate the amount of energy available
to each trophic level by remembering the 10%
rule.
• Sun – 100,000 kcal (kilocalories)
• Grass 10,000 kcal is available to the next trophic
level
• Zebra 1,000 kcal is available to the next trophic
level
• Lion 100 kcal is available to the next trophic level
• Humans 10 kcal is available to the next trophic
level
Energy Pyramid
• The flow of energy in
an ecosystem can be
illustrated using an
energy pyramid
• It is a diagram in
which each trophic
level is represented by
a block that represents
the amount of
available energy.
Energy Pyramid
• If you ate a snake,
how much energy
would be available in
you?
• If a falcon ate the
snake and then a wolf
ate the falcon, how
much energy would be
available in the wolf?
Limitations of Trophic Levels
• Read page 349 and explain why we can’t
depend on the beef industry as the solution
to feeding the world. Why do they always
ship grain to countries experiencing famine?
Should we give them calves so they can
have ranches? Why not?
Cycling of Materials in
Ecosystems
• Certain nutrients cycle through the
environment and get reused over and over.
• The most important nutrients to cycle are
water, carbon, nitrogen and phosphorus.
• Biogeochemical cycle – the cycling of these
materials from the living to nonliving
aspects of an environment
• This DOES NOT apply to energy