Ecosystem Ecology: Energy Flow & Nutrient Cycling

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ECOSYSTEM ECOLOGY
Ecosystem:
• The organisms in a particular area and the
physical environment with which they
interact.
• All the biotic and abiotic factors in a community.
(Abiotic factors: energy, water, carbon,
nitrogen, phosphorous)
Fig. 55-4
Tertiary consumers
Microorganisms
and other
detritivores
Detritus
Secondary
consumers
Primary consumers
Primary producers
Heat
Key
Chemical cycling
Energy flow
Sun
Energy Flow through Ecosystems
• Energy flows through ecosystems as
organisms capture and store energy, then
transfer it to organisms that eat them.
• These organisms are grouped into trophic
levels...
Trophic Levels:
Route of energy flow
- food chain
- food web
- pyramid of numbers
Pyramid of Numbers
Question:
“Why are big fierce animals rare?”
Charles Elton, 1927
Answer:
Because of the way energy flows
through communities...
Ecosystem Energy Budgets:
Primary Productivity (PP)
Secondary Productivity (SP1, SP2)
Primary Productivity (PP)
• Rate at which energy or biomass is produced
per unit area by plants (primary producers)
• Photosynthesis powers primary
productivity.
• The annual productivity of an area is
determined primarily by sunlight,
temperature, and moisture.
Distribution of Primary Production Worldwide
Figure
56.5
Figure 56.5
Positive Correlation Between Productivity and Sunlight
Positive Correlation Between Productivity and...
Precipitation
Temperature
Fig. 55-8
Net primary production (g/m2·yr)
·
3,000
Tropical forest
2,000
Temperate forest
1,000
Mountain coniferous forest
Desert
shrubland
0
Temperate grassland
Arctic tundra
0
500
1,500
1,000
Actual evapotranspiration (mm H2O/yr)
Secondary Productivity (SP1, SP2…)
• rate of production of new biomass from PP
by heterotrophic organisms
(primary and secondary consumers)
• positively correlated with rainfall...
Fig. 55-10
Tertiary
consumers
Secondary
consumers
10 J
100 J
Primary
consumers
1,000 J
Primary
producers
10,000 J
1,000,000 J of sunlight
Where does all the energy go???
Fig. 55-9
Plant material
eaten by caterpillar
200 J
67 J
Feces
100 J
33 J
Growth (new biomass)
Cellular
respiration
Ecological Efficiency:
Percent of energy transferred from
one trophic level to the next.
Three categories of transfer efficiency are
required to predict energy flow from PP to
SP1 to SP2...
1) consumption efficiency
2) assimilation efficiency
3) production efficiency
1) consumption efficiency (CE)
% of total productivity at one trophic level
that is consumed by the next highest level
(remainder not eaten)
Green World Hypothesis
• Plants have many defenses against herbivores
2) assimilation efficiency (AE)
% of ingested food energy that is assimilated
(i.e. digested), and thus potentially available
for growth, reproduction
(remainder lost as feces)
Elephant dung
3) production efficiency (PE)
% of assimilated energy that is incorporated
into new biomass (growth, reproduction)
(remainder lost as respiratory heat)
Implications?
• SP1 is the % of PP that is incorporated at the
next highest trophic level. (Ditto for SP2…)
This is NEVER 100%.
• Thus, energy loss at each trophic level limits the
length of a food chain...
And that is why big fierce
animals are rare!
Biogeochemical Cycles
Nutrients exist in pools of chemical elements
FOUR main reservoirs where these nutrients exist are:
1) Atmosphere - carbon in carbon dioxide, nitrogen in
atmospheric nitrogen
2) Lithosphere - the rocks - phosphates, calcium in
calcium carbonate, potassium in feldspar
3) Hydrosphere - the water of oceans, lakes, streams and
soil - nitrogen in dissolved nitrate, carbon in carbonic
acid
Atmosphere
Living
Organisms
+
Detritus
Lithosphere
Hydrosphere
4) Living Organisms and Nutrient Cycles
• Living organisms are a reservoir in which carbon
exists in carbohydrates (mainly cellulose) and fats,
nitrogen in protein, and phosphorus in ATP
• In studying cycling of water, carbon, nitrogen,
and other chemicals, ecologists focus on four
factors:
– Biological importance of each chemical
– Major reservoirs for each chemical
– Forms in which each chemical is available or used
by organisms
– Key processes driving movement of each chemical
through its cycle
The Water Cycle
• Water is essential to all organisms
• 97% of the biosphere’s water is
contained in the oceans, 2% is in
glaciers and polar ice caps, and
1% is in lakes, rivers, and
groundwater
• Water moves by the processes of evaporation, transpiration,
condensation, precipitation, and movement through surface and
groundwater
The Carbon Cycle
• Carbon-based organic molecules
are essential to all organisms
• Carbon reservoirs include fossil
fuels, soils and sediments,
solutes in oceans, plant and
animal biomass, and the
atmosphere
• CO2 is taken up via photosynthesis and released via respiration
• Volcanoes and the burning of fossil fuels contribute CO2 to the
atmosphere
Fig. 55-21
14.9
390
14.8
380
14.7
14.6
370
Temperature
14.5
360
14.4
14.3
350
14.2
340
14.1
CO2
330
14.0
13.9
320
13.8
310
300
13.7
13.6
1960
1965
1970
1975
1980 1985
Year
1990
1995
2000
2005
… and Global Temperature
The Nitrogen Cycle
• Nitrogen is a component of
amino acids, proteins, and
nucleic acids
• The main reservoir of nitrogen
is the atmosphere (N2)
• N2 is converted to NH3 via
nitrogen-fixing bacteria
• Organic nitrogen is decomposed to NH4+ by ammonification, and
NH4+ is decomposed to NO3– by nitrifying bacteria; NH4+ and NO3–
assimilated by plants
• Denitrifying bacteria convert NO3– back to N2
How Bears Feed Salmon to the Forest
• The run of salmon leads to a major flow of nutrients
into estuaries and coastal watersheds
• Bears catch salmon in river and consume them in
forest; on average, half the carcass is not eaten.
• Bears’ fat tissue is virtually nitrogen-free, so most of
nitrogen in salmon protein is excreted as urine and feces.
• Nitrogen 14 from atmosphere
• Nitrogen 15 from salmon
• Measurements of nitrogen isotope ratios in tree rings
shows that nitrogen from salmon is incorporated into
trees and enhances their growth
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