Trophic Levels
&
Ecological Pyramids
1
Energy Flow in Ecosystems
March 24, 2016
Trophic Levels
2
Each step in a food chain or food web is called a trophic level.
 Primary producers always make up the first trophic level.
 Various consumers occupy every other level. Some examples
are shown.

Energy Flow in Ecosystems
March 24, 2016
Trophic Levels
3
Quaternary Consumers
Tertiary Consumers
Secondary Consumers
Primary Consumers
Producers
Energy Flow in Ecosystems
March 24, 2016
Ecological Pyramids
4
 Ecological
pyramids show the relative amount of
energy or matter contained within each trophic level in
a given food chain or food web.
 There are three different types of ecological pyramids:
pyramids
of energy,
 pyramids of biomass, and
 pyramids of numbers
Energy Flow in Ecosystems
March 24, 2016
Ecological Pyramids
5
1.
What do the three types of ecological pyramids
illustrate?



Pyramids of energy show the relative amount of energy
available at each trophic level.
A pyramid of biomass illustrates the relative amount of
living organic matter at each trophic level.
A pyramid of numbers shows the relative number of
individual organisms at each trophic level in an ecosystem.
Energy Flow in Ecosystems
March 24, 2016
1. Pyramids of Energy
6




There is theoretically no limit to the
number of trophic levels in a food
web or the number of organisms that
live on each level.
However, only a small portion of the
energy that passes through any given
trophic level is ultimately stored in the
bodies of organisms at the next level.
Organisms expend much of the energy
they acquire on life processes, such as
respiration, movement, growth, and
reproduction.
Most of the remaining energy is
released into the environment as
heat—a byproduct of these activities.
Energy Flow in Ecosystems
March 24, 2016
Pyramids of Energy
7
On average, about 10 percent of the energy available within one
trophic level is transferred to the next trophic level (trophic
efficiency)
 The more levels that exist between a producer and a consumer,
the smaller the percentage of the original energy from
producers that is available to that consumer.

Energy Flow in Ecosystems
March 24, 2016
Pyramids of Energy
8
Tertiary
consumers
10 kcal
Secondary
consumers
100 kcal
Primary
consumers
Producers
Energy Flow in Ecosystems
1,000 kcal
10,000 kcal
March 24, 2016
Pyramids of energy
9
 Advantages
 Takes into account the PRODUCTIVITY
 Addresses the fact that weight for weight, two species do not
necessarily have the same energy content
 Disadvantages
 Very difficult to obtain data
 Destructive
 Problems identifying trophic level
Energy Flow in Ecosystems
March 24, 2016
2. Pyramids of Biomass
10
The total amount of living tissue within a given trophic level is
called its biomass.
 The amount of biomass a given trophic level can support is
determined, in part, by the amount of energy available.

Energy Flow in Ecosystems
March 24, 2016
2. Pyramids of Biomass
11
Illustrates the relative
amount of living organic
matter at each trophic level.
 Indicates the total dry
mass of the organisms in
each trophic level
 Typically, the greatest
biomass is at the base of the
pyramid, as is seen in the
field ecosystem modeled
here.

Energy Flow in Ecosystems
March 24, 2016
Pyramids of Biomass
12
 How might this data be
collected?
a) Individual organisms
weighed and counted.
b) Dry mass should be
compared to eliminate
errors due to water
content
Energy Flow in Ecosystems
 Advantages
The data is more accurate.
 Eliminates misleading
problems of producer size
differences
 Disadvantages
 Laborious and expensive
 Destructive
 Can also be misleading in
some circumstances

March 24, 2016
3. Pyramids of Numbers
13

A pyramid of numbers shows the relative number of individual
organisms at each trophic level in an ecosystem.
3rd level carnivore
2nd level carnivore
1st level Carnivore
Herbivores
Producers
Log numbers
Energy Flow in Ecosystems
March 24, 2016
3. Pyramids of Numbers
14
In most ecosystems, the shape of the pyramid of numbers is
similar to the shape of the pyramid of biomass for the same
ecosystem, with the numbers of individuals on each level
decreasing from the level below it.
Energy Flow in Ecosystems
March 24, 2016
3. Pyramids of Numbers
15



In some cases, however, consumers are much smaller than organisms they
feed upon.
Thousands of insects may graze on a single tree, for example. The tree has a
lot of biomass, but represents only one organism.
In such cases, the pyramid of numbers may be turned upside down, but the
pyramid of biomass usually still has the normal orientation.
2nd level carnivore
1st level carnivore
herbivores
Producers
numbers
Energy Flow in Ecosystems
March 24, 2016
Pyramids of Number
16
 Advantage
 Data relatively easy to collect using simple sampling
 Disadvantages
 Producers vary in size
 Large range of numbers
 Trophic level difficult to work out
Energy Flow in Ecosystems
March 24, 2016
Associated terms with energy production and
energy17 flow.
 Primary production:
 Fixation of energy by autotrophs in an ecosystem.
 Rate of primary production:
 Amount of energy fixed over a given period of time.
 Gross primary production (GPP):
 Total amount of energy fixed by autotrophs.
 Net primary production (NPP):
 Amount of energy leftover after autotrophs have met their
metabolic needs.
Energy Flow in Ecosystems
March 24, 2016
Primary Productivity in Ecosystems
18
 Gross primary productivity (GPP)
• The rate at which an ecosystem's producers capture and store a
given amount of chemical energy as biomass in a given length of
time.
 Net primary productivity (NPP)
• Rate at which all the plants in an ecosystem produce net useful
chemical energy; equal to the difference between the rate at
which the plants in an ecosystem produce useful chemical
energy (gross primary productivity) and the rate at which they
use some of that energy through cellular respiration.
•
(NPP = GPP – Respiration)
Energy Flow in Ecosystems
March 24, 2016
Coral reefs and Marine ecosystems have the
highest primary19productivity?
WHY?
 Highest rates of primary production by marine
phytoplankton are generally concentrated in areas with
higher levels of nutrient availability.
 Highest rates found along continental margins.


Nutrient run-off from land.
Sediment disturbance
 Open ocean tends to be nutrient poor.
 Vertical mixing main nutrient source.
Energy Flow in Ecosystems
March 24, 2016
What controls primary productivity?
20
Terrestrial primary production
generally increases with moisture and
temperature
•Rosenwitz studied net primary production
across biomes
•Compare NPP to actual evapotranspiration
Energy Flow in Ecosystems
March 24, 2016
What controls primary productivity?
21
Terrestrial and aquatic primary
production is also limited by nutrient
availability
Energy Flow in Ecosystems
March 24, 2016