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WHAT IS AN ECOSYSTEM?
• Community + all abiotic factors affecting• “Ecosystem” first proposed by Arthur Tansley • Boundaries not fixed• Energy flows• Cycle nutrients
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LAWS OF THERMODYNAMICS
• 1st LAW
• 2nd LAW:
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ENERGY SOURCES IN BIOSPHERE
• Sunlight energy – driving force– Energy distribution and
carbon dioxide in atmosphere shape ecosystems and biosphere
• Biosphere energy and CO2
shape world climate and weather
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CHARLES ELTON & FOOD WEBS
• 1920s, Charles Elton and others proposed:– Organisms living in same place not only have
similar tolerances of physical factors, but– Feeding relationships link these organisms
into single functional entity• Food web
http://www.history.vt.edu/Barrow/Hist3144/readings/ecology/index.html
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http://www.nature.ca/ukaliq/images/a196_fwb_e.jpg
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Feeding relationships of the snowshoe hare-dominated food web in the boreal forest of northwestern Canada
Dominantspecies inyellow
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ALFRED J. LOTKA AND THE THERMODYNAMIC
CONCEPT• Alfred J. Lotka
– Ecosystem as an energy-transforming machine
– Equations representing exchanges of matter and energy among components
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LINDEMAN’S SYNTHESIS• 1942 – Raymond Lindeman
brought Lotka’s ideas of ecosystem as an energy-transforming machine to attention of ecologists
• Incorporated:– Lotka’s thermodynamic concepts– Elton’s food web concept– Tansley’s ecosystem concept
http://www.cedarcreek.umn.edu/people/photo/LindemanRaymond1942.jpg
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LINDEMAN’S FOUNDATIONS OF ECOSYSTEM ECOLOGY
• Ecosystem is fundamental unity of ecology• Within an ecosystem, energy passes through
many steps or links in food chain• Each link in the food chain is a trophic level
(feeding level)
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ODUM’S ENERGY FLUX MODEL
• Recognized utility of energy and masses of elements as common “currencies” in comparative analysis of ecosystem structure and function
Eugene Odum
http://www.researchmagazine.uga.edu/summer2002/odum.htm
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ODUM EXTENDED HIS MODELS TO INCORPORATE NUTRIENT
CYCLING
• Fluxes of energy and materials are closely linked in ecosystem function
• But:– Energy enters ecosystems as light and is
degraded into heat– Nutrients cycle indefinitely, converted from
inorganic to organic forms and back again• Studies of nutrient cycling provides index of energy
fluxes
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AUTOTROPHS - PRODUCERS• Photoautotrophs - Sunlight energy, Green plants• Chemoautotrophs - Chemical energy, certain
bacteria• Primary producers – • Transform sunlight energy to chemical energy
– Sugars, starch, ATP
http://www.scienceclarified.com/images/uesc_01_img0028.jpg http://141.150.157.117:8080/prokPUB/figures/normal/p323-006.jpg
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PRIMARY PRODUCTION• Producers capture energy of light• Transform sunlight energy into energy of chemical
bonds in carbohydrates• 6CO2 + 6H2O → C6H12O6 + 6O2
– For each g of C assimilated, 39 kj energy stored• Gross primary production = • Net primary producion = • GPP – NPP = Respiration
– Energy consumed by producers for maintenance and biosynthesis
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Partitioning gross primary productivity into respiration and net primary productivity
Energy lost and unavailable to consumers
NPP
GPP
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NUTRIENTS STIMULATE PRIMARY PRODUCTION
• Terrestrial production may be nutrient limited
• Aquatic systems often strongly nutrient-limited– Open ocean– Addition of nutrients may
stimulate unwanted production
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GLOBAL PRIMARY PRODUCTION
• Correlates with annual precipitation (when light not limiting)
• Note relationship among tundra, deserts, and tropics– Oceans – nutrient poor
• CO2 Source of carbon
– Follows 1st Law of Energy
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Grams carbon/m2/yr for globe, as calculated from satellite imagery. Oceans = 46%, land = 54%
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PRIMARY PRODUCTION VARIES AMONG ECOSYSTEMS
• Maximum under favorable conditions– Intense sunlight– Warm
temperatures– Abundant
precipitation– Nutrients
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NPP vs. Temperature + Precipitation
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Decomposers
Primary consumers
Primary producers
Secondary consumers
Tertiary consumers
HETEROTROPHS - CONSUMERS
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Decomposers
Primary consumers
Primary producers
Secondary consumers
Tertiary consumers
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ECOLOGICAL PYRAMIDS• Elton• Trophic levels placed in order• Reflects:
– Numbers of organisms at each level– Biomass of each level– Energy at each level
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# PRIMARY PRODUCERS
# HERBIVORES
# CONSUMERS
# CONSUMERS=TOP CARNIVORES
# DECOMPOSERS
PYRAMID OF NUMBERS
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kg PRIMARY PRODUCERS
kg HERBIVORES
kg CONSUMERS
kg CONSUMERS=TOP CARNIVORES
kG DECOMPOSERS
PYRAMID OF BIOMASS
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kJ PRIMARY PRODUCERS
kJ HERBIVORES
kJ CONSUMERS
kJ CONSUMERS=TOP CARNIVORES
kJ DECOMPOSERS
PYRAMID OF ENERGY
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ENERGY TRANSFER EFFICIENCY
• ~10% Efficient between trophic levels• What happens to other 90%
– How is it dispersed?– Is it lost?– Account for it
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ENERGY BUDGET
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ECOLOGICAL EFFICIENCY
• Ecological Efficiency– Percentage of
energy transferred from one trophic level to the next:
– Range of 5-20% typical (avg = 10%)
– Must understand the utilization of energy within a trophic level
Not all food components can be assimilated - Undigested
fibrous material from elephant dung
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FUNDAMENTAL ENERGY RELATIONSHIPS
• Components of an animal’s energy budget are related by:
• Assimilated Energy = Ingested Energy – Egested Energy
• Production = Assimilated Energy – (Respiration-Excretion)
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ASSIMILATION EFFICIENCY• Assimilation Efficiency = Assimilation/Ingestion• Function of Food Quality:
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NET PRODUCTION EFFICIENCY
• Net production efficiency = production/assimilation
• depends on metabolic activity:
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What limits the length of the food chain?
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Food chain length may be limited by:
• Energy constraint hypothesis– Energy is lost with each transfer– Food chain length should be related to productivity– Not supported by research
• Dynamic stability hypothesis– Long food chains easily disrupted– Support is tentative
• Ecosystem size– Species diversity higher
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Do aquatic or terrestrial ecosystems have more trophic levels? What factor contributes most to variation in food chain length among these ecosystems?
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http://www.yale.edu/post_lab/images/FCL_ecosize_large.gif
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SOME GENERAL RULES• Assimilation efficiency increases at higher
trophic levels.• GPP and NPP efficiencies decrease at higher
trophic levels.• Ecological efficiency ~ 10%.• ~ 1% of NPP ends up as production on the third
trophic level – the energy pyramid narrows quickly.
• To increase human food supplies means eating lower on the food chain!
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Readings
• Quantifying Ecology 14.1, pp 293-294
• Field Studies, pp 300-301
• Ecological Issues p 315
• Quantifying Ecology 17.1, p 355
• Field Studies, pp 402-403
• Ecological Issues pp 638-639
• Sections 19.2, 19.3, 19.4; pp 394-401