is Ecosystems
Ecosystems
What an ecosystem?
Ecosystems are:
Ecosystems
self-contained
self-contained
assemblages of
organisms that, together with their
physical environments, move energy
and nutrients among the component
parts.
parts.
Ecosystems
Ecosystems
Ecosystem
Ecosystem
ecology focuses
on energy flow
and nutrient
cycles as parts of
a coordinated
whole.
whole.
Ecosystems
Ecosystems
Advantages of the ecosystem concept:
1.
Provides a mechanism for integrating
Provides
information from many different
ecosystems. Organisms are assigned
functional roles.
functional
Ecosystems
Ecosystems
2.
Easier to compare ecosystems
Easier
using the functional roles rather than
taxonomic classifications.
For example we can compare nitrogen
For
cycles in tropical versus temperate
versus boreal ecosystems.
versus
Ecosystems
Ecosystems
3.
Ecosystems can be modeled
Ecosystems
more easily than populations or
communities in many cases.
communities
Ecosystems
Ecosystems
4.
The ecosystem approach has many
The
applications.
Resource
Resource management (fisheries,
forestry) and pollution monitoring.
Global scale problems need an
Global
ecosystem approach to be effective.
Recall the First Two General
Principles of Ecology
Principles
1.
Ecological systems function
Ecological
according to the laws of
thermodynamics (Ecosystems).
thermodynamics
2.
The physical environment exerts a
The
controlling influence on the
productivity of ecological systems
(Ecosystems).
(Ecosystems).
Ecosystems:
Energy Flow Begins with Primary
Production
Production
Primary Production
Solar radiation is the principle source of
energy.
energy.
It arrives in a variety of wavelengths.
Ecosystems:
Primary Production
Primary
Only 400 to 700 nanometers are
Only
effective in photosynthesis.
effective
Solar radiation has dual properties:
Solar
1.
1.
2.
wave lengths
particles (photons)
Ecosystems:
Primary Production
Primary
Photons of different wavelengths have
Photons
different energy values
long
wave lengths = less energy
Short wave lengths = more energy
Ecosystems:
Primary Production
Primary
An Einstein (e) = energy content of
An
one mole of photons
one
1e of red (0.7) llight = 42,000
ight
1e red
calories
calories
1e of blue (0.5) llight = 60,000
ight
1e blue
calories
calories
Ecosystems:
Primary Production
Primary
Gram calorie = amount of heat energy
Gram
needed to raise the temperature of 1g
of water 1o C.
of
Most ecosystem units are in
Most
kilocalories =1,000 gram calories
= 1g of food calorie.
1g
Ecosystems:
Primary Production
Primary
Energetic units are usually expressed as
Energetic
rates: kcal/m2/day.
rates
By contrast:
Standing crop = an energy unit
converted to a biomass equivalent at a
given point in time (kg of carbon/m2)
given
Ecosystems:
Primary Production
Primary
Rate of energy input via solar
radiation:
radiation:
Amount of energy entering Earths
Amount
atmosphere is estimated at 15.3 X 108
atmosphere
cal/m2per year or 15.3 X 105 kcal/m2
cal/m
kcal/m
year-1.
year
Ecosystems:
Primary Production
Primary
Much of this energy is scattered by
Much
dust, used in heating the ground,
water, and air and in evaporating
water.
Amount available to plants varies by
Amount
latitude and climate as we discussed
latitude
climate
earlier.
earlier.
Ecosystems:
Primary Production
Primary
Primary Production defined:
The accumulation of energy by
autotrophs (photosynthesis or
autotrophs
chemosynthesis) per unit area per
unit time.
unit
Ecosystems:
Secondary Production
Secondary
Secondary Production defined:
The accumulation of energy by
heterotrophs (herbivores,
decomposers etc.) per unit area per
unit time.
unit
Ecosystems:
Primary Production
Primary
Gross production (GP) = total amount
of energy accumulated at a trophic
level.
level.
Net production (NP) = gross
production minus losses due to
respiration.
respiration
NP = GP - R
Ecosystems:
Primary Production
Primary
Net Production is the energy that will
Net
be stored in the ecosystem as
stored
biomass.
biomass
That is, when organisms accumulate
That
energy, this energy is stored as mass
and we refer to it as biomass.
biomass
Ecosystems:
Primary Production
Primary
Biomass serves
as a handy
measure of
accumulated net
production in an
ecosystem.
ecosystem.
Ecosystems:
Primary Production
Primary
Global Patterns of Net Production
Global
(Biomass):
(Biomass):
Terrestrial: 115 X 109 metric
tons/year (67% of total)
tons/year
Aquatic: 55 X 109 metric tons/year
(33% of total)
(33%
Ecosystems:
Primary Production
Primary
Conclusion:
Oceans cover 2/3
Oceans
of Earths surface
but only produce
1/3 of the Net
Production.
Production.
Ecosystems:
Primary Production
Primary
Ecosystems with low production (NP):
Terrestrial:
Deserts and
Deserts
Tundras, which make up 30% of
which
the land surface area of the
world.
world.
Aquatic: Open Oceans, which
Open
which
make up 90% of the total marine
surface area.
surface
Ecosystems:
Primary Production
Primary
Ecosystems with high production
Ecosystems
high
(NP):
(NP):
Tropical
Shallow
wet forests
aquatic areas
(marshes, estuaries, coral
marshes,
reefs)
reefs
Terrestrial Net Production
Terrestrial
The limits to terrestrial net
The
terrestrial
production in natural ecosystems
are due to availabilities of:
are
1.
2.
3.
Temperature
Moisture
Light
Light
Ecosystems:
Primary Production
Primary
The log of evapotranspiration
The
evapotranspiration
predicts accurately the above
ground biomass (NP) of terrestrial
ecosystems.
Evapotranspiration is defined as:
The total amount of water vapor
The
returned to the atmosphere as a
result of direct evaporation or plant
transpiration
transpiration
Terrestrial Net Production
Evapotranspiration is a surrogate
for:
for:
moisture availability,
moisture
light and
temperature.
Ecosystems:
Secondary Production
Secondary
Primary production predicts
secondary production (herbivore
secondary
biomass, for example).
biomass,
Recall the Second Principle of
Ecology
Ecology
The physical environment exerts a
The
controlling influence on the
productivity of ecological systems
(Ecosystems).
(Ecosystems).
Ecosystems:
Primary Production
Primary
Although primary production is
Although
regulated in a similar fashion
everywhere, there is a fundamental
difference between terrestrial and
terrestrial
aquatic ecosystems.
aquatic
Ecosystems:
Primary Production
Primary
Terrestrial ecosystem primary
Terrestrial
production is determined by moisture,
light, and temperature (as measured
by evapotranspiration).
by
Nutrient availability, especially P
especially
and N are the most important
regulators of aquatic productivity.
aquatic
Ecosystems:
Primary Production
Primary
In temperate freshwater lakes,
In temperate
seasonal fluctuations in NP are tied to
the seasonal changes in temperature.
These seasonal changes in turn affect
These
thermal stratification.
This determines the availability of
This
nutrients in the surface waters where
photosynthesis takes place.
photosynthesis
Ecosystems:
Primary Production
Primary
Aquatic Ecosystems
Aquatic
These changes are driven by the fact
These
that the density of water varies with
temperature.
Warm water is less dense than cool
Warm
water.
However, water reaches its
However,
maximum density at 4o C.
maximum
C.
Ecosystems:
Primary Production
Primary
Aquatic Ecosystems
In the summer warm water stays near
In
the surface and cool water remains
near the bottom of lakes. This
produces thermal stratification.
thermal
In the winter, very cold water remains
In
at the surface, and the warmer, 4o
at
water sinks to the bottom.
Ecosystems:
Primary Production
Primary
Aquatic Ecosystems
In the spring and fall there are times
In
when the lakes become isothermal.
isothermal
That is, temperatures are the same
from top to bottom.
This encourages mixing of nutrient
This
laden bottom water with oxygenated
surface waters.
Lake Productivity
Lake
Oligotrophic = A lake with low
productivity; usually a young lake with
few nutrients, often deep with clear
water.
water.
Mesotrophic = A middle-aged lake
with higher productivity and a higher
nutrient level.
nutrient
Ecosystems:
Ecosystems:
Lake Productivity
Eutrophic = An old lake or a lake
heavily affected by pollutants. Very
high nutrient levels; highly productive,
but often poor in species.
The term cultural eutrophication
refers to lakes aging very quickly due
to human pollutants.
to
Eutrophic versus
Oligotrophic Lake
Eutrophic
Ecosystems:
Primary Production
Primary
Productivity is often measured as
Productivity
changes in standing crop over a unit
of time.
of
SCt+1= SCt + NPt-(t+1) H D
NPt-(t+1) = NP in the time period t to t+1
H = losses due to herbivores
D = llosses due to death and decomposition of
osses
plant parts
plant
Ecosystems:
Primary Production
Primary
Photosynthetic Efficiency, PE
PE = NP/PAR
NP = Net Production = GP R
PAR = Photosynthetically Active
PAR
Radiation
Radiation
Gross versus Net Productivity in Some Crop Plants
(kcal/m2/day)
NP
PE(%) PG (%)
PAR
GP
Sugar Cane,
Hawaii
4000
306
190
4.8
62
Maize, Israel
6000
405
190
3.2
47
Sugar Beets,
England
2650
202
144
5.4
71
Respiration Losses
Respiration
GP NP = R
Sugar Cane: R = 306190 =116 Kcal/m2/day
Sugar
306190
Maize: R= 405 190 = 215 Kcal/m2/day
Maize:
Sugar Beets: R= 202144 = 58 Kcal/m2/day
Sugar
Respiration Losses
Respiration
Therefore, English sugar beets have
Therefore,
an NP that equals 75% of the other
crops even with only 44% of the PAR
of the maize in Israel, because the
losses due to R are so low.
losses
low
Respiration Losses
Respiration
In both homothermic and
In
heterothermic organisms:
heterothermic
Respiration losses increase with
temperature.
temperature.
In many green plants:
As
As
photosynthesis rates go up with
temperature, so do respiration rates.
temperature,
Adaptations:
Adaptations:
High Temperatures and High Light
Conditions
Conditions
At least three different photosynthetic
At
pathways have been evolved by
plants, allowing them to adapt to
different light and temperature
regimes.
regimes.
These are C3, C4 and Crassulacean
Acid Metabolism (CAM).
Acid
Atriplexpatula
Atriplexrosea
Figure 7.1
Differences Among C3, C4, and CAM Plants
Characteristic
C3 Plants
C4 Plants
CAM Plants
Light-saturation point
3000 - 6000
footcandles
8000 - 10000+ ?
footcandles
Optimum temperature
16o 25o
40o 50o
30o 35o
CO2 compensation
30 70 ppm
0 10 ppm
0 4 ppm
Maximum
photosynthetic rate
15 35
30 45
3 - 13
1
4
0.02
Photorespiration
High
Low
Low
Stomata Behavior
Open day,
closed night
Open day,
closed night
Closed day,
open night
(mg CO2/dm2 leaf area/hr)
Maximum growth rate
(g/dm /day)
2
Ecosystems:
Energy Budgets
Energy
Energy Budgets:
Illustrate
Illustrate
where
major energy drains
are in natural and
agricultural
ecosystems.
ecosystems.
Ecosystems:
Secondary Production
Secondary
Secondary production is higher systems in
marine because a much
higher fraction of photoysynthetic NP
is consumed by animals in oceans
than in terrestrial systems.
Consumption efficiency averages 2550% (as high as 90%) in marine
50%
systems, but is 5-10% in terrestrial
forests.
forests.
Ecosystems:
Secondary Production
Secondary
Secondary production is also higher
production
in tropical terrestrial ecosystems as
compared to equivalent temperate
systems.
systems.
The accumulation of dead organic
The
matter (litter) is highest in cold forests
(especially Boreal forests).
(especially
Decomposition
Decomposition
Dead organic
Dead
matter (DOM)
provides energy
for decomposers
of the detrital
food chain.
food
Decomposition
Decomposition
Unless organic material is
Unless
accumulating (as it did during the
previous geological eras, leading to
the deposition of our fossil fuels),
then
then
NP = Decomposition plus losses to
herbivores
herbivores
Decomposition
Decomposition
During decomposition,
During
organic matter is
reduced, ultimately to
CO2 and H2O, and
CO
O,
nutrients are released.
nutrients
DecompositionbyJessicaLangley
Decomposition
Decomposition
Without decomposition, supplies of
Without
essential nutrients would be locked up
in organic matter and dwindle to the
point that GP would decline even
though solar radiation remained
available.
This actually happens in many
This
aquatic systems.
aquatic
Decomposition
Decomposition
1.
2.
Trends in litter (plant organic
Trends litter
matter) production and
production and
decomposition:
decomposition
Litter production is linked to NP.
Litter production
More in the tropics, least in deserts.
More
Litter accumulation, however, is
accumulation however,
highest in high latitude Boreal
forests because of slow
decomposition rates.
decomposition
Decomposition
Decomposition
3.
Litter is not uniform in composition.
Litter
The ratio of C/N determines the rate of
decomposition. The higher the ratio
decomposition The
the slower the decomposition, because
N is usually a rate limiting factor for
decomposing organisms, just as it is for
photosynthesis. Fresh litter has a high
C/N ratio and decomposes slowly.
C/N
Different species have different C/N ratios
and differences in secondary compounds.
and
Decomposition
Decomposition
4.
Cellulose
The higher the
The
proportion of
cellulose, woody
fibers, lignin, and
resins, the slower
the decomposition.
the
Decomposition
Decomposition
5.
Very acidic or basic pHs also slow
Very
decomposition rates. Acid pHs
are common in bogs, for example,
leading to an accumulation of
peat.
peat.
Peat Bog in Ireland
Bog People from Ireland
Bog Artifacts
ShinroneDress
Goldbeadsandtorques
Decomposition
Decomposition
6.
Oxygen levels can also limit
Oxygen
decomposition, especially in aquatic
environments. Anoxic conditions
Anoxic
are found in some soils, many lakes,
and in ocean sediments.
The Chesapeake Bay suffers from
The
anoxic zones due to pollution.
anoxic
Because of pollution there are even
Because
dead zones in the Gulf of Mexico.
dead
Decomposition
Decomposition
Organic material is
Organic
ultimately broken down in
its final stages by bacteria
bacteria
and fungi.
and fungi
Final degradation to
Final
carbon dioxide and water
is carried out by these
organisms, called the
ultimate decomposers.
ultimate
Decomposition
Decomposition
However, a wide variety of organisms
However,
prepare the way for bacteria and fungi.
These are called reducer-decomposers.
These
reducer-decomposers
Decomposition
Decomposition
RedSpiderMite
For example, plant
For
material is first processed
by microarthropods, such
as mites, spring-tails
(Collembolans), as well
as by nematodes, earth
worms, millipedes and
slugs.
slugs.
Earthworms
Decomposition
Decomposition
Animal material is first attacked by
Animal
carrion flies, a wide variety of beetles,
and carrion eaters such as crows,
vultures and some mammals.
vultures
Decomposition
Decomposition
These reducer-decomposers shred,
These reducer-decomposers
tear and grind up the organic material,
increasing its surface area and/or
chemically processing the material in
their guts.
This improves oxygen penetration of
This
the organic material and opens up
these tissues to ultimate
decomposition by bacteria and fungi.
decomposition
Dermestid Beetles Cleaning a Skull:
Used for conservation of skeletons.
Decomposition
Decomposition
The result is that the rate of
The
decomposition by the ultimate
decomposers is vastly increased once
the surface area is increased.
the
Ecological Efficiencies
Ecological
Energy flow from one trophic level to
Energy
another is never 100% efficient.
another
Efficiencies allow ecologists to
Efficiencies
measure rates of energy transfer and
make comparisons among
ecosystems as well as estimate the
number of tropic levels that can be
supported.
supported.
Ecological Efficiencies
Ecological
As energy moves from one trophic
As
level to another, there are a number
of stages where energy is dissipated
of
See the following diagram.
Ecological Efficiencies
Ecological
At the end of the last step is the NP of
At
the new trophic level.
the
Recall that secondary production is
Recall
secondary
the formation of heterotrophic
biomass in terms of kcal/unit
area/time.
area/time.
Ecological Efficiencies
Ecological
In a study of elephants
In
at Queen Elizabeth
Park in Uganda, the
plant NP was 747
kcal/m2/year.
kcal/m
Ecological Efficiencies
Ecological
Of that the elephants:
Consumed
71.5 kcal/m2/year.
Lost in urine and feces = 40.2
Assimilation = 31.3
Respiration = 30.96
NP2 = 0.34 kcal/m2/year
NP1= 747 Kcal
NP 747
675.5 (not consumed)
consumed)
Consumption = 71.5
Assimilation = 31.3
40.2 (feces)
Respiration = 30.96
NP2 = 0.34 Kcal
Ecological Efficiencies
Ecological
Standing crop estimated as 7.1
Standing
kcal/m2/year.
kcal/m /year.
Ecological Efficiencies
Ecological
These figures allow us to examine three
These
efficiencies related to the movement of
energy within a trophic level.
energy
1.
Photosynthetic efficiency
PE = NP/PAR
NP/PAR
PAR = photosynthetically active radiation.
For example, the cattail marsh had a PE of 2.2%.
Photosynthetic Efficiencies
Photosynthetic
Japanese Rice
Japanese
Scots Pine, Britain
Scots
Beech Forest, Denmark
Beech
Sugar Cane, Java
Sugar
Sugar Cane, Hawaii
Sugar
Maize, Israel
Maize,
Sugar Beets, England
Sugar
=
=
=
=
=
=
=
2.2%
2.2%
2.4%
2.4%
2.5%
2.5%
1.9%
1.9%
4.8%
4.8%
3.2%
3.2%
5.4%
5.4%
Secondary Production:
Secondary
Assimilation Efficiency
2.
Among heterotrophs, assimilation efficiency:
Among heterotrophs
EA = A/I
A = amount of energy assimilated
I = amount of energy ingested
Secondary Production:
Secondary
Assimilation Efficiency
For the Uganda elephants:
Consumed
= 71.5 kcal/m2/year.
Lost in urine and feces = 40.2
Assimilation = 31.3
Therefore, assimilation efficiency =
Therefore,
31.3/71.5 = 44%
31.3/71.5
Growth or Production
Efficiency
Efficiency
EG = NP/A or
EG = 1 R/A
R
= respiration rate at this trophic level
A = amount of energy assimilated
NP = A R
Growth or Production
Efficiency
Efficiency
For the elephant
For
herd:
herd:
R = 30.96
A = 31.3
31.3
NP = 0.34
EG = 0.34/31.3 = 1.1%
Assimilation Efficiency
Assimilation
Determined by:
Determined
1)
1)
2)
2)
1.
type of organism (heterotherm versus
type
homeotherm) and
type of food consumed.
Homeotherms (birds and mammals) have,
Homeotherms
in general, higher assimilation efficiencies
than heterotherms (insects and reptiles for
example).
example).
Assimilation Efficiency:
Types of Food
Types
2.
High quality easily assimilated foods:
Flesh of vertebrates and arthropods
Plant sap, nectar and seeds
Assimilation Efficiency:
Types of Food
Types
Spittlebug(heterotherm)eatingnectar(highqualityfood).
Assimilation Efficiency:
Types of Food
Types
3.
Low quality poorly
Low
assimilated foods:
assimilated
Anything with large
Anything
amounts of cellulose,
lignin and fiber
(leaves, wood, bark
etc.).
etc.).
Cellulose
Lignin
Assimilation Efficiency
Assimilation
Growth Efficiency
Growth
Homeotherms use large amounts of
energy in respiration, thus have low
growth efficiencies.
growth
Heterotherms have higher growth
efficiencies.
efficiencies.
Growth Efficiency:
Growth
Heterotherms
Heterotherms
Grasshoppers
Spittlebug
Lepidopteran
Harvester Ant
Spittlebug
36.7%
41.5%
41.8%
0.7%
0.7%
Californiabutterfly,Lycaenahelloides
Growth Efficiency:
Growth
Homeotherms
Homeotherms
MeadowVole
Old Field Mouse
Meadow Vole
Uganda Cob
African Elephant
UgandaCob
1.8%
2.9%
1.5%
1.5%
Consumption Efficiency
Consumption
How much of plant NP do herbivores
How
gather?
gather?
Answer differs greatly among ecosystems.
Four types:
Four
1. Forests
1.
= low consumption
2. Grasslands = moderate consumption
Consumption Efficiency
Consumption
3.
Aquatic/oceanic = high consumption.
Aquatic/oceanic
4. Streams
Streams
= energy flow dominated by
detritus with very little plant NP within the
stream ecosystem.
stream
General Rules for the Proportion of Primary
Production Harvested by Grazers as Contrasted with
Decomposers (Grazing Food Chain versus
Decomposer Food Chain
Type of Ecosystem
Percent of Primary
Production Processed
by Grazers/Herbivores
Percent of Primary
Production Processed by
Decomposers
Forests
1 10
90 99
11 60
40 89
60 99
1 - 40
Grasslands
Aquatic Ecosystems
Efficiencies: Review
Efficiencies:
1.
Photosynthetic Efficiency:
PE = NP/PAR
2.
Assimilation Efficiency:
EA = A/I
A/I
Efficiencies: Review
Efficiencies:
3.
Growth Efficiency:
EG = NP/A or
EG = 1 R/A
NP = A R
R = respiration rate at this trophic level
Sample Problem
Sample
Farmer John has a fishpond. He
Farmer
wishes to increase his fish yield. He
hires an ecologist who measures net
primary production of the pond. The
figure is 3200 kcal/m2 of pond surface
figure
area.
Sample Problem
Sample
If solar radiation (PAR) is measured at
If
10,000 kcal/m2/year, what is the
10,000
/year,
photosynthetic efficiency of this pond?
Sample Problem
Sample
The ecologist next drains the pond
The
and finds that it primarily contains one
species of herbivorous fish. When
tested in an aquarium the ecologist
finds that it assimilates 45% of what it
eats.
eats.
Sample Problem
Sample
If this is correct, and the fish
If
consumes 2000 kcal/m2/year, what is
consumes
/year,
the expected net production of fish if
the R/A ratio is 65%? What is the
growth efficiency?
growth
Sample Problem: Answers
Sample
Part one.
Part
Given the equation:
Given
PE =
NP/PAR
NP/PAR
We have:
PE = 3200/10,000 = 32.0%
Sample Problem: Answers
Sample
Part two.
First we have:
EA
= A/I
or 0.45 = A/2000 and A=900
or
kcal/m2/yr.
kcal/m
Next we have:
NP
NP
= A - R.
But 0.65 = R/A and R = 0.65 A.
Sample Problem: Answers
Sample
Substituting 0.65A for R
We have:
NP = A - 0.65A = 0.35A
NP
Since A = 900.
We have:
NP
= (.35)(900) = 315 kcal/m2/yr.
Finally:
EG = NP/A = 35%
EG
Questions?