ECOLOGICAL
PYRAMIDS
 AS A RESULT OF THE SECOND LAW
OF THERMODYNAMICS, MOST OF
THE ENERGY GOING FROM ONE
TROPHIC LEVEL TO THE NEXT IN A
FOOD CHAIN OR FOOD WEB IS LOST
TO THE ENVIRONMENT.
ECOLOGICAL PYRAMIDS
 ARE A WAY TO GRAPHICALLY
REPRESENT THE RELATIVE ENERGY
VALUES OF EACH TROPHIC LEVEL.
 THERE ARE THREE MAIN TYPES:
PYRAMID OF NUMBERS
 SHOWS THE NUMBER OF
ORGANISMS AT EACH TROPHIC
LEVEL
 IN MOST PYRAMIDS, THE
ORGANISMSAT THE BASE OF THE
FOOD CHAIN ARE THE MOST
ABUNDANT, AND EACH SUCCESSIVE
TROPHIC LEVEL IS OCCUPIED BY
FEWER OFGANISMS.
© 2004 Brooks/Cole – Thomson Learning
Abandoned Field
Ocean
Tertiary consumers
Secondary consumers
Primary consumers
Producers
 Pyramids of numbers
have limited
usefulness because
they DO NOT
indicate the biomass
of the organisms at
each level. A baby
rabbit does not have
the biomass as an
adult rabbit.
PYRAMID OF BIOMASS
 Illustrates the total biomass at each trophic
level
 BIOMASS is a quantitative estimate of the total
amount of living material
 It indicates the total amount of fixed energy at
a particular time
 Can be dry weigh or live weight
 Generally represent a reduction of biomass at
each trophic level
Assuming that there is on average a 90% reduction of
biomass in each succeeding trophic level:

10,000 kg of grass

1,000 kg grasshoppers

100 kg of toads
 Toad eaters, such as snakes, at most,could be only
about 10 kg
 Even though carnivores do not eat vegetation, it takes
a great deal of vegetation to support them.
 Give an example of an inverted pyramid of biomass
Pyramid of Energy
 Illustrates the energy content
(kilocalories/square meter/per year) of the
biomass of each trophic level.
 Always have large energy bases and get
smaller with each trophic level
 Shows that energy disipates into the
environment
 Approximately 90% of the energy is lost at
each trophic level.
 Is it possible to have an inverted pyramid of
energy? Why or why not?