Secondary Production
Energy Removed From Lower Trophic Level
Energy
Not Used
Gross Energy
Intake
Egested
Energy
Digested
Energy
Urinary
Waste
Resting Energy
Activity
‘Maintenance’ (or
respiration)
Assimilated
Energy
Growth
Reproduction
‘Production’
Energy Budget
Maintenance
Net Production
C = (Mr + Ma + SDA) + (F + U) + (Gs + Gr)
Metabolism
Waste
Growth
C = rate of energy consumption
Mr = standard metabolic rate (resting energy)
Ma = metabolic rate increase due to activity (above Mr)
SDA = metabolic rate increase due to specific dynamic action (digestion)
F + U = waste losses due to egestion (feces) and excretion (urine) rates
Gs = somatic growth rate due to protein synthesis and lipid deposition
Gr = growth rate due to gonad (reproductive) synthesis
Energy partitioning is not
equal among species and
can change depending on
season.
Herbivorous mammals:
Log (FMR) = 0.774 + 0.727(log body mass)
Larger animals
require more energy
Mammals and birds
(warm blooded) need
more than reptiles
(cold blooded)
Trophic Levels
Heat
First Trophic
Level
Second Trophic
Level
Third Trophic
Level
Fourth Trophic
Level
Producers
(plants)
Primary
consumers
(herbivores)
Secondary
consumers
(carnivores)
Tertiary
consumers
(top carnivores)
Heat
Heat
Heat
Solar
energy
Heat
Heat
Detritvores
(decomposers and detritus feeders)
Heat
Measuring Net Production
net change
losses by
• Production =
+
in biomass
mortality
• Need to estimate change in biomass,
natality (birth rate), and loss due to death
(including harvesting) or emigration
Net Productivity
of species n
Production Efficiency =
Assimilation
of species n
Group
Mammals and birds
Insects
Production
Efficiency
Respiration
1 – 3%
97 – 99%
10 – 41%
59 – 90%
Why the difference?  Homeothermy (it takes a lot of
energy to keep warm)
Net Production at
trophic level i + 1
Trophic Efficiency =
No. of Cases
Net production
at trophic level i
Energy not transferred
is lost as respiration
or to detritus.
40
35
30
25
20
15
10
5
0
For aquatic systems,
average ~ 10.
2
6
10
14
16
Transfer Efficiency (%)
20
24
How much primary production is required to support
a particular fishery?
Tuna are top predators operating at trophic level 4.
In 1990 2,975,000 tons of tuna were taken. This is
equivalent to 0.1 g carbon per m2 of open ocean
per year!!!! How much production is needed to
sustain this fishery assuming a 10% transfer
efficiency?
Tuna 0.1
Pelagic Fishes 1.0
Zooplankton
10
Phytoplankton 100
Need 1.0 g pelagic fish, 10 grams
zooplankton, and 100 grams of
phytoplankton per m2/year of
open ocean to support this fishery
– and this is just harvested
tuna!!!!!
When all of the data for worldwide fisheries are
aggregated, on average 8% of global aquatic primary
production is being used to produce the global
fisheries catch. But, production varies with
ecosystem type:
Area
(106km2)
NPP
(gCm-2yr-1)
Open Ocean
332.0
103
0.012
1.8
Upwellings
0.8
973
25.560
25.1
Tropical Shelves
8.6
310
2.871
24.2
Temperate Shelves
18.4
310
2.306
35.3
Coastal/reef systems
2.0
890
10.510
8.3
Rivers and Lakes
2.0
290
4.3
23.6
126
0.330
8.0
Ecosystem Type
Weighted Means
Fishery Catch P. Production
(gCm-2yr-1)
required (%)
Estimates of Energy Flow in a
Temperate Deciduous Forest
Aquatic ecosystem
herbivores consume a
higher fraction of the
primary production
than in terrestrial
ecosystems (red
arrows = average)
Herbivory
Ecosystem
NPP going to
consumption (%)
Tropical rain forest
7
Temperate deciduous forest
5
Grassland
10
Open ocean
40
Oceanic upwelling zones
35
Reduction in standing crop of
vascular plants from herbivores
Terrestrial ecosytems
26%
Marine ecosystems
65%
Freshwater ecosystems
31%
Low Ecological Efficiency
• Organisms at the base of the food web are
much more abundant than those near the
top
• Eltonian pyramid – a diagram
demonstrating the number, biomass, or
energy distributions across size classes
Heat
Heat
Tertiary
consumers
(human)
Decomposers
Heat
10
Secondary
consumers
(perch)
100
1,000
10,000
Usable energy
Available at
Each tropic level
(in kilocalories)
Heat
Primary
consumers
(zooplankton)
Producers
(phytoplankton)
Heat
Biomass
Why does the ocean have such a low biomass of
primary producers?
• Phytoplankton such as diatoms reproduce
by dividing and can divide every few
hours.
– Because of their fast population growth rate,
they are able to support a large number of
primary consumers.
• Plants are the primary producers in an
abandoned field.
– Have a much longer lifespan than
phytoplankton
• Need a much larger biomass of plants to
support the primary consumers.
Number of Organisms
Why does a temperate forest have so few individual
primary producers compared to a grassland?
• In a temperate forest, a single tree can
support many primary consumers
because of its large size.
• It takes a lot of individual grasses to = the
biomass of a large tree.
Number of Organisms
Limits to Secondary
Primary Production
• Primary production is an
obvious limiter
– Also include the 2nd law of
thermodynamics
Above ground PP and
herbivore biomass
• Carrying Capacity – the number or weight
of animals of a single or mixed population
that can be supported permanently on a
given area
• Ecological Carrying Capacity – maximum
density of animals that can be sustained
without inducing negative effects on
vegetation
• Economic Carrying Capacity – density of
animals that enables maximal sustained
harvesting and is always lower than the
ecological carrying capacity