Food Chains, Food Webs, and
Ecological Pyramids
• A food chain is the simplest path that
energy takes through an ecosystem.
• Energy enters from the sun.
• Each level in the transfer of energy is a
trophic level.
• Organisms at each level use energy in
cellular respiration and heat loss and store
the rest.
The 1st Trophic Level
• Consists of primary producers
(autotrophs).
• Primary producers include land plants and
phytoplankton in aquatic environments.
2nd Trophic Level
• Consists of primary consumers
(heterotrophs)
• Primary consumers that eat green plants
are herbivores.
• Examples: grasshoppers, rabbits,
zooplankton
The 3rd and Any Higher Trophic
Level
• Consists of consumers.
• Carnivores and omnivores
• Examples: Humans, wolves, frogs, and
minnows
Food Chains
• Arrows
represent the
flow of
energy …Not
Who Eats
Who.
Food Web
• A food web
represents may
interconnected food
chains describing
various paths that
energy takes through
an ecosystem.
Ecological Pyramids
• Models that show how energy flows through
ecosystems.
• Pyramids can show the relative amounts of
energy, biomass, or numbers of organisms at
each trophic level in an ecosystem.
• The base of the pyramid represents producers.
• Each step up represents a different level of
consumer.
• The number of trophic levels in the pyramid is
determined by the number of organisms in the
chain or web.
Energy pyramids compare energy used by
producers and other organisms on trophic
levels.
• Between each tier of an
energy pyramid, up to 90
percent of the energy is
lost into the atmosphere
as heat.
• Only 10 percent of the
energy at each tier is
energy
energy transferred
lost
transferred from one
trophic level to the next.
Other pyramid models illustrate an
ecosystem’s biomass and distribution of
organisms.
• Biomass is a measure of the total dry mass of organisms in
a given area.
Biomass
pyramid
tertiary
consumers
75 g/m2
150g/m2
secondary
consumers
primary
consumers
producers
producers
675g/m2
2000g/m2
• Even though a biomass pyramid shows
the total mass of organisms at each level,
it doesn’t necessarily represent the
amount of energy available at each level.
• For example, the skeleton and beak of a
bird will contribute to the biomass but
aren’t available for energy.
• A pyramid of numbers shows the numbers
of individual organisms at each trophic level
in an ecosystem.
tertiary
consumers
5
secondary
consumers
5000
primary
consumers
500,000
producers
producers
5,000,000
• A vast number of producers are required to support even a
few top level consumers.