Food Chains, Food Webs,
and the Transfer of Energy
Symbiosis and Succession too!
Autotrophs
• A groups of organisms that can use the
energy in sunlight to convert water and
carbon dioxide into Glucose (food)
• Autotrophs are also called Producers because
they produce all of the food that heterotrophs
use
• Without autotrophs, there would be no life on
this planet
• Ex. Plants and Algae
Autotrophs
Autotrophs
• Chemotrophs
– Autotrophs that get their energy from inorganic
substances, such as salt
– Live deep down in the ocean where there is no
sunlight
– Ex. Bacteria and Deep Sea Worms
Heterotrophs
• Organisms that do not make their own food
• Another term for Heterotroph is consumer
because they consume other organisms in
order to live
• Ex. Rabbits, Deer, Mushrooms
Heterotrophs
Heterotrophs
• Consumers
– 1. Scavengers/Detritivores – feed on the tissue of
dead organisms (both plans and animals)
• Ex. – Vultures, Crows, and Shrimp
Heterotrophs
• Consumers
– 2. Herbivores – eat ONLY plants
• Ex. – Cows, Elephants, Giraffes
Heterotrophs
• Consumers
– 3. Carnivores – eat ONLY meat
• Ex. – Lions, Tigers, Sharks
Heterotrophs
• Consumers
– 4. Omnivores – eat BOTH plants and animals
• Ex. – Bears and Humans
Heterotrophs
• Consumers
– 5. Decomposers – absorb any dead material and
break it down into simple nutrients or fertilizers
• Ex. – Bacteria and Mushrooms
Transfer of Energy
• When a zebra eats the grass, it does not
obtain all of the energy the grass has (much
of it is not eaten)
• When a lion eats a zebra, it does not get all
of the energy from the zebra (much of it is
lost as heat)
Transfer of Energy
• The two (2) previous examples of energy
transfer show that no organism EVER
receives all of the energy from the organism
they just ate
• Only 10% of the energy from one trophic
level is transferred to the next – this is called
the 10% law
Trophic Levels
• Energy moves from one organisms to another
when it is eaten
• Each step in this transfer of energy is know
as a trophic level
– The main trophic levels are producers, consumers,
and decomposers
Food Chains
• The energy flow from one trophic level to the
other is know as a food chain
• A food chain is simple and direct
• It involves one organism at each trophic level
–
–
–
–
Primary Consumers – eat autotrophs (producers)
Secondary Consumers – eat the primary consumers
Tertiary Consumers – eat the secondary consumers
Decomposers – bacteria and fungi that break down
dead organisms and recycle the material back into the
environment
Food Chain
Food Web
• Most organisms eat more than JUST one
organism
• When more organisms are involved it is
known as a FOOD WEB
• Food webs are more complex and involve lots
of organisms
Food Web
Food Web
• Notice that the arrow points in the
direction of the energy transfer,
NOT “what ate what”
Food Web
Biomass
• The total mass of the organic matter at each
trophic level is called biomass
• Biomass is just another term for potential
energy – energy that is to be eaten and used.
• The transfer of energy from one level to
another is very inefficient (10% Law)
Biomass
Ecological Pyramid
• An ecological pyramid shows the relationship
between consumers and producers at
different trophic levels in an ecosystem
• Shows the relative amounts of energy or
matter contained at each trophic level
• The Pyramid shows which level has the most
energy and the highest number of organisms
Ecological Pyramid
Ecological Pyramid
Ecological Pyramid
•
•
•
•
Which
Which
Which
Which
level
level
level
level
has
has
has
has
the
the
the
the
most energy?
most organisms?
least organisms?
least energy?
Symbiosis
• A close and permanent association between
organisms of different species
– Mutualism – a relationship in which both
organisms benefit from each other
• Example: Birds eating pest off a rhino’s back
– Commensalism – a relationship in which one
organism benefits and the other is not affected
• Example: Barnacles on a whale
– Parasitism – A relationship in which one organism
benefits and the other is harmed
• Example: Ticks on a dog
In your Lab notebook
complete the following:
Symbiotic
Relationship
Commensalism
Textbook
Definition
a relationship in
which one
organism
benefits and the
other is not
affected
Mutualism
a relationship in
which both
organisms
benefit from
each other
Parasitism
A relationship in
which one
organism
benefits and the
other is harmed
My definition
(less than 4
words)
My example
Ecological Succession: Some
Definitions
• the gradual and directional process of species
change in a community
• biotic communities change through time in
response to many influences:
– climatic change
– disturbances
– invasion of species from other areas
• Eventually, succession leads to a climax
community
Primary Succession
• the processes and progress involved in changing an
area from one lacking any community (no plants, no
animals, no insects, no seeds, etc.) to one consisting
of individuals, populations, communities, and
ecosystems.
• the arrival of life in an area where no community
previously existed.
Example of Primary
Succession
Secondary Succession
• The arrival of new species in an area that already has
life.
• Results in the transition of a community from pioneer
species to climax species.
• Because soil may already be present, the rate of
secondary succession is faster than primary
succession.
• Secondary succession also indicates changes in
community composition following disturbances.
Example of Secondary
Succession
This is an
example of a
secondary
succession
following a
disturbance (fire).
It does not
completely wipe
out life.
What is a Pioneer Species?
• The first species to colonize an area
(usually lichens and mosses but
sometimes higher plants), beginning
the process of soil formation.
What is Climax Community?
A community that remains fairly
constant in species composition if
the land and climate are
undisturbed. These are the
communities that characterize the
various biomes.
A summary of changes that occur
during succession:
• Pioneer species colonize a bare or disturbed site. Soil building.
• Changes in the physical environment occur (e.g., light, moisture).
• New species of plants displace existing plants because their seedlings
are better able to become established in the changed environment.
• Newly arriving species alter the physical conditions, often in ways that
enable other species to become established.
• Animals come in with or after the plants they need to survive.
• Eventually a climax community that is more or less stable will become
established and have the ability to reproduce itself.
• Disturbances will start the process of succession again.
“Food Web of Biome_____”
this is your title
1. Choose a Biome from 4. Must label organisms as:
pg 99-104) to draw a
– Method of nutrition
food web
• Producer
• Herbivore
2. Draw, Color and Label
• Carnivore
your Food Web
– Example on pg 71
– A food web shows how
two or more food chains
interact
3. Must show arrows
showing energy flow
– What eats what
• Omnivore
– Tropic Level
•
•
•
•
•
Producer
1st Consumer
2nd Consumer
3rd Consumer
Decomposer or Scavenger
• Don’t forget about the
SUN!