Download Energy Webs and Chains

Energy in Ecosystems
Definitions
Population: All of the members of the same species, living in the same ecosystem or
habitat.
Community: The collection of all populations of all the species in an ecosystem or
habitat.
Energy
-All organisms need energy to live: to grow, to run, to reproduce, etc.
-A major part of ecology is the study of how energy flows in ecosystems.
-All energy on Earth originally comes from the Sun, but most of it is not used by
organisms to create food:
 30% is reflected back into space
 44% heats the Earth’s surface and air
 25% evaporates water
 1% makes wind
 0.023% is used for photosynthesis
Trophic Levels
 Organisms can be classified into different trophic levels according to how they receive
their energy.
 Organisms that use the Sun’s energy to make their own food are on the 1st trophic
level and are called Producers or Autotrophs (trees, algae, grass, etc.)
 Organisms that eat producers are on the 2nd trophic level and are called Primary
Consumers (aphids, caterpillars, rabbits, etc.).
 Organisms that eat primary consumers are called Secondary Consumers and are on
the 3rd trophic level (foxes, snakes, sparrows, etc.).
 All consumers could also be called Heterotrophs.
 The final organism in any food system is called the Top Carnivore or Apex
Predator, and could be on any trophic level.
Energy Webs and Chains
There are 2 graphic ways to show which organism eats which other organism(s) and how
they get their energy. They are the Food Chain and the Food Web.
Energy Webs and Chains Continued
 A Food Chain shows one possible path for energy in an ecosystem. It starts with a
producer and uses arrows to show who eats whom.
-Ex: Spruce Tree  Deer  Wolf
 A Food Web shows ALL possible paths for energy. It is a more realistic
representation since all food sources are shown. (See diagram).
 Note that both graphics can be used to place different organisms on trophic levels.
Stable ecosystems have complex food webs so that the removal of one organism does
not cause the ecosystem to crash.
Trophic Levels
 Trophic Level: The number of steps an organism is from the start of the food chain.
Food chains start at trophic level 1 with primary producers such as plants, move to
herbivores at level 2, predators at level 3 and typically finish with carnivores or apex
predators at level 4 or 5.
1. Energy
2. Producer
3. Primary Consumer
4. Secondary Consumer
5. Tertiary Consumer
6. Apex Predator
Limits on Energy Transfer
 In most ecosystems, there are usually not more than four or five trophic levels. Why?
There is a limit to how many times energy can be transferred. Consider the food chain
below:
o Grass  Grasshopper  Frog  Heron
 We know that the grass gets its energy from the Sun and the grasshopper gets its
energy from the grass. However, not all the energy that the grass absorbed is available
to the grasshopper. Most of the energy was used by the grass to produce important
chemicals, to grow, produce heat, etc. The frog, in turn, gets even less of the original
energy from that Sun.
Displaying Energy – Food Pyramids
Energy in Ecosystems
Definitions
Population: All of the members of the
ecosystem or habitat.
species, living in the same
Community: The collection of all
ecosystem or habitat.
of all the species in an
Energy
-All organisms need
to live: to grow, to run, to reproduce, etc.
-A major part of ecology is the study of how energy
-All energy on Earth originally comes from the
organisms to create food:
 30% is reflected back into space
 44% heats the Earth’s surface and air
 25% evaporates water
 1% makes wind
 0.023% is used for photosynthesis
in ecosystems.
, but most of it is not used by
Trophic Levels
 Organisms can be classified into different trophic levels according to how they
their energy.
 Organisms that use the Sun’s energy to make their own food are on the 1st trophic
level and are called
or
(trees, algae, grass, etc.)
 Organisms that eat producers are on the 2nd trophic level and are called
(aphids, caterpillars, rabbits, etc.).
 Organisms that eat primary consumers are called
and are on the 3rd trophic level (foxes, snakes, sparrows, etc.).
Consumers

.
consumers could also be called
 The final organism in any food system is called the
,and could be on any trophic level.
or
Energy Webs and Chains
There are 2 graphic ways to show which organism eats which other organism(s) and how
they get their energy. They are the
and the
Energy Webs and Chains Continued
 A
shows one possible path for energy in an ecosystem. It
starts with a producer and uses arrows to show who eats whom.
-Ex: Spruce Tree  Deer  Wolf
 A
shows
possible paths for energy. It is a more realistic
representation since all food sources are shown. (See diagram).
 Note that both graphics can be used to place different organisms on trophic levels.
Stable ecosystems have complex food webs so that the removal of one organism does
not cause the ecosystem to crash.
Trophic Levels
 Trophic Level: The number of
an organism is from the start of the food
chain. Food chains start at trophic level 1 with primary producers such as plants, move
to herbivores at level 2, predators at level 3 and typically finish with carnivores or
apex predators at level 4 or 5.
1. Energy
2. Producer
3. Primary Consumer
4. Secondary Consumer
5. Tertiary Consumer
6. Apex Predator
Limits on Energy Transfer
 In most ecosystems, there are usually not more than four or five trophic levels. Why?
There is a limit to how many
energy can be transferred. Consider the
food chain below:
o Grass  Grasshopper  Frog  Heron
 We know that the grass gets its energy from the Sun and the grasshopper gets its
energy from the grass. However, not all the
that the grass absorbed is
available to the grasshopper. Most of the energy was used by the grass to produce
important chemicals, to grow, produce heat, etc. The frog, in turn, gets even less of
the original energy from that Sun.
Displaying Energy – Food Pyramids