5 ENERGY FLUXES AND CYCLES
FOOD WEBS AND SUBSYSTEMS
The cascade effect is a series of secondary extinctions that are triggered by the primary extinction of
a key species in an ecosystem.
Keystone species is an organism that helps define an entire ecosystem. Without its keystone
species, the ecosystem would be dramatically different or cease to exist.
We can distinguish different tropic levels and subsystems in the ecosystem.
- Primary producers: plants à Autotrophic subsystem
- Secondary producers: the rest of the organisms. à Herbivorous subsystem
- Decomposers: those organisms that get rid of the dead organic material. à Detritivore subsystem
Pool: amount of biomass in a specific area. A pool is a measure of a flux.
A pool has its residence time, which is the time that energy remains stored in a pool (dimension
hour day year). How long does it stay?
And has a turnover rate, which is a fraction of the pool that is replaced annually (dimension hour1
day-1 year-1)
Primary production definitions
NPP = Net Primary Production (productivity).
It has two components:
- GPP = Gross Primary production (effectively is photosynthesis).
- R = Respiration (of plants)
NPP = GPP – R
For ecosystems as a whole (not only plants)
NEP = Net Ecosystem Production
It has two components:
-GEP = Gross Ecosystem production (effectively is photosynthesis) = so it’s like GPP
-Re (Ecosystem respiration) = R (autotrophic) + R (heterotrophic)
NEP = GEP – Re
1
, AMOUNT OF PRIMARY PRODUCTION
Primary production (NPP) is related to:
• latitude (exposure to the sun and length of growing season, temperature)
• rainfall
• terrestrial or aquatic environment
area primary production
land 1/3 54%
ocean 2/3 46%
The productivity of land is bigger.
ENERGY FLUXES: SECONDARY PRODUCTION
Secondary production: energy flux
The gain by consumers in energy or biomass per unit area per unit time remaining after allowing for
respiratory losses. R= respiration (respiration – loss of heat - energy).
H=herbivore
C=Carnivore
V=vertebrate
M=microbivores
D=Detritivores
I=invertebrates
There is no energy cycle because it’s all driven by sunlight.
At every trophic level, we lose elements. The flux starts
big, but part of it is lost to dead organic material and
then to respiration.
There is a production pyramid that describes this
situation.
Production in the ecosystem, the flux of
energy with 3 trophic levels:
NE = not eaten
F = faeces
2
FOOD WEBS AND SUBSYSTEMS
The cascade effect is a series of secondary extinctions that are triggered by the primary extinction of
a key species in an ecosystem.
Keystone species is an organism that helps define an entire ecosystem. Without its keystone
species, the ecosystem would be dramatically different or cease to exist.
We can distinguish different tropic levels and subsystems in the ecosystem.
- Primary producers: plants à Autotrophic subsystem
- Secondary producers: the rest of the organisms. à Herbivorous subsystem
- Decomposers: those organisms that get rid of the dead organic material. à Detritivore subsystem
Pool: amount of biomass in a specific area. A pool is a measure of a flux.
A pool has its residence time, which is the time that energy remains stored in a pool (dimension
hour day year). How long does it stay?
And has a turnover rate, which is a fraction of the pool that is replaced annually (dimension hour1
day-1 year-1)
Primary production definitions
NPP = Net Primary Production (productivity).
It has two components:
- GPP = Gross Primary production (effectively is photosynthesis).
- R = Respiration (of plants)
NPP = GPP – R
For ecosystems as a whole (not only plants)
NEP = Net Ecosystem Production
It has two components:
-GEP = Gross Ecosystem production (effectively is photosynthesis) = so it’s like GPP
-Re (Ecosystem respiration) = R (autotrophic) + R (heterotrophic)
NEP = GEP – Re
1
, AMOUNT OF PRIMARY PRODUCTION
Primary production (NPP) is related to:
• latitude (exposure to the sun and length of growing season, temperature)
• rainfall
• terrestrial or aquatic environment
area primary production
land 1/3 54%
ocean 2/3 46%
The productivity of land is bigger.
ENERGY FLUXES: SECONDARY PRODUCTION
Secondary production: energy flux
The gain by consumers in energy or biomass per unit area per unit time remaining after allowing for
respiratory losses. R= respiration (respiration – loss of heat - energy).
H=herbivore
C=Carnivore
V=vertebrate
M=microbivores
D=Detritivores
I=invertebrates
There is no energy cycle because it’s all driven by sunlight.
At every trophic level, we lose elements. The flux starts
big, but part of it is lost to dead organic material and
then to respiration.
There is a production pyramid that describes this
situation.
Production in the ecosystem, the flux of
energy with 3 trophic levels:
NE = not eaten
F = faeces
2
