2.2.2.3
Ecological
Pyramids
Ecological Pyramids
 Ecological
pyramids represent numerical
relationships between successive trophic
levels in a community.
 Which pyramid is chosen for examination
depends on the type and quantity of
data collected.
Pyramids
 Graphic
models of quantitative
differences between trophic levels
 By second law of thermodynamics energy
decreases along food webs
 Pyramids are thus narrower as one
ascends
Losses in the pyramid
 Energy
is lost between each trophic level,
so less remains for the next level

Respiration, Homeostasis, Movement, Heat
 Mass

is also lost at each level
Waste, shedding, …
Pyramids of Numbers
 One
way to simplify food webs is to assign
the organisms to trophic levels and then
count the number of organisms in each
trophic level.
Pyramids of Numbers
 Needs
sampling similar to Biomass and
therefore has the same limitations
 Also measures the storages
Pyramids of Numbers
 Represents
the numbers of individual
plants and animals present in the food
web.
 It does not take into account the relative
size of any organisms.
 Consequently, it is possible to have an
inverted pyramid of numbers.
© 2004 Brooks/Cole – Thomson Learning
Pyramids of Numbers
Grassland
(summer)
Tertiary consumers
Secondary consumers
Primary consumers
Producers
Temperate Forest
(summer)
Pyramids of Biomass
A
pyramid of biomass takes body size into
account
 You have to find the dry mass of the
organisms in your sample and their energy
content (this must be measured in a fixed
area).
 However, it does seem to be logical i.e.
big organisms support lots of little ones.
Pyramids of Biomass
 Represents
the standing stock of each
trophic level (in grams of biomass per unit
area g / m2)
 Represent storages along with pyramids
of numbers
How do we get the biomass of
a trophic level to make these
pyramids?
 Why
can’t we measure the biomass of
an entire trophic level?
 Take quantitative samples – known
area or volume
 Measure the whole habitat size
 Dry samples to remove water weight
 Take Dry mass for sample then
extrapolate to entire trophic level
How do we get the biomass of
a trophic level to make these
pyramids?
 Evaluation
 It is an estimate
based on assumption that
 all
individuals at that trophic level are
the same
 The sample accurately represents the
whole habitat
Pyramids of Biomass
 Biomass
decreases at each trophic level
because the transfer of energy from the
primary producer to the primary
consumer and between the consumers is
inefficient. Energy is lost at each stage,
that is, at each of the transfers.
Pyramids of Biomass
 See
example on your sheet
 green plant
zebra lion
© 2004 Brooks/Cole – Thomson Learning
Abandoned Field
Pyramids of Biomass
Tertiary consumers
Secondary consumers
Primary consumers
Producers
Ocean
Pyramids of productivity
 Pyramids
of productivity require much
more data to construct since many
samples, separated by intervals of time,
are needed to estimate productivity,
 They provide a coherent view of how an
ecosystem works.
Pyramids of productivity
 Production
by primary producers must be
greater than production by secondary
consumers and so on.
 Do not need to consider numbers or
differences in size because all organisms
can be converted to their energy
equivalent.
Pyramids of productivity
 Flow
of energy through trophic levels
 Energy decreases along the food chain

Lost as heat
 Productivity
pyramids ALWAYS decrease
as they go higher – 1st and 2nd laws of
thermodynamics
Pyramids of productivity
 Shows
rate at which stock is generated at
each level
 Productivity measured in units of flow
(J / m2 yr or g / m2 yr )
© 2004 Brooks/Cole – Thomson Learning
Energy
Input:
1,700,000
kilocalories
Incoming solar energy
not harnessed
1,679,190
(98.8%)
Energy
Transfers
Waste,
remains
20,810
(1.2%)
Producers
4,245
Metabolic heat,
export
3,368 13,197
Herbivores
Top carnivores
21
Carnivores
Herbivores
383
3,368
720
383
2,265
Carnivores
90
21
Top
carnivores
5
272
16
Decomposers,
detritivores
Energy Output
Total Annual Energy Flow
20,810 + 1,679,190
1,700,000 (100%)
Decomposers/detritivores
Producers
20,810
5,060
Figure 54.11 An idealized pyramid of net production
Figure 54.14 Food energy available to the human population at different trophic levels
Efficiency of trophic levels in relation to the total energy
available decreases with higher numbers
But efficiency of transfer always remains around that 10% rule
How does pyramid structure
effect ecosystem function?
Limited length of food chains
1.
•
•
•
Rarely more than 4 or 5 trophic levels
Not enough energy left after 4-5 transfers
to support organisms feeding high up
Possible exception marine/aquatic
systems b/c first few levels small and little
structure
How does pyramid structure
effect ecosystem function?
Vulnerability of top carnivores
2.
•
•
•
Effected by changes at all lower levels
Small numbers to begin with
Effected by pollutants & toxins passed
through system