Download II. Trophic Levels

Outline 3-2: Energy Flow
I. Primary Productivity
A. The rate at which organic
material is produced by
photosynthesis in an
ecosystem.
1. Determines the amount of
energy available in an
ecosystem
2. Other organisms are limited
by this initial amount of
energy
II. Trophic Levels
A. Organisms are assigned to a
particular level in an ecosystem
based on their source of energy
1. What an organism eats and
what it is eaten by
B. Three main levels:
1. Producers
2. Consumers
3. Decomposers
C. Producers
1. Autotrophs who use energy
from environment to assemble
organic molecules from
inorganic molecules.
2. There are 2 types of autotrophs
based on type of energy used.
Those that do:
a. Photosynthesis - use sunlight
b. Chemosynthesis - use energy
in bonds of chemicals
Photosynthesis
Done by plants on land,
algae in water &
photosynthetic
bacteria
Chemosynthesis - done by several types
of bacteria
2. Consumers
a. Heterotrophs that need to feed
on other organisms to obtain
energy
b. Levels:
 Primary consumers - eat
producers
 rabbits, mice, etc.
 Secondary consumers - eat
primary consumers
 wolf, coyote, lion, snake
 Tertiary consumers - eat
secondary consumers
 hawks, eagles, etc.
c. Consumers classified by type of
food eaten:
 Herbivores - eat producers
 Carnivores - eat consumers
 Omnivores - eat both producers
& consumers
 Detritivores - feed on organic
wastes & dead
bodies
3. Decomposers
a. Cause decay of dead bodies &
their waste back into inorganic
minerals
b. Recycle nutrients back into soil
& water for producers to use.
c. Fungi & bacteria are examples
III. Paths of Energy Flow
A. Food Chain
1. Specific sequence in which
organisms obtain energy in an
ecosystem
a. Producers  consumer
levels  decomposers
Grass  grasshopper  mouse  snake  hawk
(decomposers frequently left out of food chain lists)
In some marine food chains, the
producers are microscopic algae and
the top carnivore is four trophic levels
from the producer.
B. Food Web
1. A diagram of all the many interconnected food chains in an
ecosystem
Feeding Relationships
• This food
web shows
some of the
feeding
relationships
in a saltmarsh
community.
IV. Energy is Lost in Ecosystems
A. Energy Transfer
1. An animal eating a plant is
acquiring energy
a. Some of this energy is turned into
new tissues in the animal
b. Some helps the deer in its
activities: running, eating, etc.
c. Most (almost half) is lost as heat to
the environment after the process
of cellular respiration is complete
 Heat is not useful energy
B. Amount of Energy Lost
1. Plants store about ½ of energy
they capture from sun.
2. Herbivores turn about 10% of
the energy they consume into
their own body tissue
3. About 90% of the energy that
carnivores consume is used up & lost
as useful energy for other organisms
(Same concept as #2 in reverse)
 Only about 10% of the energy stored in
one trophic level is transferred to
organisms in the next trophic level 
C. Energy Pyramids
1. Diagram which shows each
trophic level as a block stacked
on top of other blocks.
a. Width of each block is related
to amount of energy in all the
organisms at that level
2. Usually shaped like a pyramid
because higher trophic levels
have less energy
Energy Pyramid:
Shows the relative
amount of energy
available at each
trophic level.
Only part of the
energy that is stored
in one trophic level is
passed on to the next
level.
0.1% Third-level
consumers
1% Second-level
consumers
10% First-level
consumers
100% Producers
D. Other Kinds of Pyramids
1. Numbers pyramids
a.Compares numbers of
organisms at each trophic
level
b. May not be pyramid shaped
2. Biomass pyramids
a. Compares amount of
biomass at each level
 Biomass is total dry
weight of organisms
Ecological Pyramids
Pyramid of
Numbers:
Shows the relative
number of individual
organisms at each
trophic level.
Ecological
Pyramids
Biomass Pyramid:
Represents the amount of
living organic matter at each
trophic level. Typically, the
greatest biomass is at the base
of the pyramid.
50 grams of
human tissue
500 grams of
chicken
5000 grams
of grass
E. Trophic Levels are Limited
1. Most ecosystems on land involve
only 3 or 4 trophic levels
2. This is due to the progressive loss
of energy at each transfer
3. Eventually there is not enough
energy left to support a large
population of organisms at the
next higher level
4. Eating lower on the food chain is
more energy efficient
a. Eating plants instead of meat
would support more people on Earth