Download Primary Production

Ecosystem
• all the organisms
living in a
community, as
well as the
abiotic factors
with which they
interact
Energy Flow and Chemical Recycling
• Energy flows through
ecosystems, whereas
matter cycles within
them
Energy Flow
• Energy: the ability to do work
• Behavior describe by:
• 1st Law of Thermodynamics
Energy may be transformed from one
type into another but is never created or
destroyed.
2nd Law of Thermodynamics
States that when energy is
transferred or transformed, part of
the energy assumes a form that can
not pass on any further.
This means….
With the passage of time, closed systems tend
to move toward maximum entropy,
eventually no energy available to do work.
But…
Living systems, like us, are open systems with
a constant input of energy.
Energy, Mass, and Trophic Levels
• Energy in
– from the Sun
– captured by autotrophs
= producers (plants)
• Energy through
– food chain
• transfer of energy
from autotrophs to
heterotrophs
(herbivores to carnivores)
• heterotrophs =
consumers
– herbivores
– carnivores
2005-2006
Figure 42.4
Sun
Key
Chemical cycling
Energy flow
Heat
Primary producers
Primary
consumers
Secondary and
tertiary
consumers
Detritus
Microorganisms
and other
detritivores
Figure 42.3
Detritivores, or
decomposers, are
consumers that
derive their energy
from detritus,
nonliving organic
matter.
Prokaryotes and
fungi are important
detritivores
Primary Production
• The amount of light energy converted to
chemical energy by an ecosystem’s autotrophs
in a given time period.
• Sets the budget for the ecosystem.
• Only 1% of the energy striking the earth is
converted to chemical energy.
Energetics
• Study of how energy get from the sun to
organisms
Energetics
• Chemosynthesis
Productivity
Figure 42.6
Where are the most productive areas on Earth?
Net primary production
(kg carbon/m2 • yr)
3
2
1
0
What do you notice about Primary Production in the Oceans?
Gross and Net Primary Production
– Total primary production is known as gross
primary production (GPP).
• This is the amount of light energy that is
converted into chemical energy in an ecosystem.
– The net primary production (NPP) is equal to
gross primary production minus the energy
used by the primary producers for respiration
(R):
• NPP = GPP – Ra
• NPP is expressed as
– Energy per unit area per unit time (J/m2  yr), or
– Biomass added per unit area per unit time
(g/m2  yr)
• Net ecosystem production (NEP) is a measure of
the total biomass accumulation during a given
period
• NEP is gross primary production minus the total
respiration of all organisms (producers and
consumers) in an ecosystem (RT)
NEP = GPP − RT
In aquatic ecosystems, light and nutrients
limit primary production
• Production in Marine
ecosystems.
– Light is the first
variable to control
primary production
in oceans, since
solar radiation
can only penetrate
to a certain depth
(photic zone).
2005-2006
•In the open ocean, nitrogen and
phosphorous levels are very low
in the photic zone, but high in
deeper water where light does
not penetrate.
Phytoplankton density
(millions of cells per mL)
Which nutrient limits phytoplankton?
30
Ammonium
enriched
24
Phosphate
enriched
18
Unenriched
control
Ecologists use the term limiting
nutrient to define the nutrient that
must be added for production to
increase.
12
6
0
A
B
C
D
E
Collection site
F
G
• Upwelling of nutrient-rich waters in parts of the
oceans contributes to regions of high primary
production
• Production in Freshwater Ecosystems.
– Solar radiation and temperature are
closely linked to primary production in
freshwater lakes.
– During the 1970s, sewage and fertilizer
pollution added nutrients to lakes,
which shifted many lakes from having
phytoplankton communities to those
dominated by cyanobacteria.
2005-2006
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• This process is
called
eutrophication,
and which can
lead to
loss of most fish
species
2005-2006
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Primary Production in Terrestrial Ecosystems
• In terrestrial ecosystems, temperature and
moisture affect primary production on a large
scale
• Primary production increases with moisture
Figure 42.8
Net annual primary production
(above ground, dry g/m2 • yr)
1,400
1,200
1,000
800
600
400
200
0
20
40
60
80
100 120 140 160 180 200
Mean annual precipitation (cm)
• Actual evapotranspiration is the water transpired
by plants and evaporated from a landscape
• It is affected by precipitation, temperature, and
solar energy
• Actual evapotranspiration can be used as a
predictor of net primary production
• Soil nutrients are often the limiting factors in
primary production (nitrogen and
phosphorus)
– adaptations help plants access limiting nutrients
from soil.
• Nitrogen Fixing Bacteria
• mycorrhizal fungi
– these fungi supply plants with
phosphorus and other limiting
elements
• Roots have root hairs that
increase surface area
• Many plants release enzymes
that increase the availability
of limiting nutrients.
• Secondary production of an ecosystem is the
amount of chemical energy in food converted to
new biomass during a given period of time
Net secondary production is
the energy stored in
biomass
An organism’s production
efficiency is the fraction
of energy stored in food
that is not used for
respiration
Energy transfer between trophic levels is
typically only 10% efficient
Trophic structure
• Food chains
– feeding relationships
– food chain usually 4
or 5 links = trophic
levels
– length of food chain
limited by
inefficiency of energy
transfer
2005-2006
Why are big, fierce animals rare?
The nitrogen cycle
The phosphorous cycle
The carbon cycle
The water cycle