WHAT IS AN ECOSYSTEM?

• Community + all abiotic factors affecting• “Ecosystem” first proposed by Arthur Tansley • Boundaries not fixed• Energy flows• Cycle nutrients

LAWS OF THERMODYNAMICS

• 1st LAW

• 2nd LAW:

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

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

http://www.nature.ca/ukaliq/images/a196_fwb_e.jpg

Feeding relationships of the snowshoe hare-dominated food web in the boreal forest of northwestern Canada

Dominantspecies inyellow

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

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

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)

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

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

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

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

Partitioning gross primary productivity into respiration and net primary productivity

Energy lost and unavailable to consumers

NPP

GPP

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

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

Grams carbon/m2/yr for globe, as calculated from satellite imagery. Oceans = 46%, land = 54%

PRIMARY PRODUCTION VARIES AMONG ECOSYSTEMS

• Maximum under favorable conditions– Intense sunlight– Warm

temperatures– Abundant

precipitation– Nutrients

NPP vs. Temperature + Precipitation

Decomposers

Primary consumers

Primary producers

Secondary consumers

Tertiary consumers

HETEROTROPHS - CONSUMERS

Decomposers

Primary consumers

Primary producers

Secondary consumers

Tertiary consumers

ECOLOGICAL PYRAMIDS• Elton• Trophic levels placed in order• Reflects:

– Numbers of organisms at each level– Biomass of each level– Energy at each level

# PRIMARY PRODUCERS

# HERBIVORES

# CONSUMERS

# CONSUMERS=TOP CARNIVORES

# DECOMPOSERS

PYRAMID OF NUMBERS

kg PRIMARY PRODUCERS

kg HERBIVORES

kg CONSUMERS

kg CONSUMERS=TOP CARNIVORES

kG DECOMPOSERS

PYRAMID OF BIOMASS

kJ PRIMARY PRODUCERS

kJ HERBIVORES

kJ CONSUMERS

kJ CONSUMERS=TOP CARNIVORES

kJ DECOMPOSERS

PYRAMID OF ENERGY

ENERGY TRANSFER EFFICIENCY

• ~10% Efficient between trophic levels• What happens to other 90%

– How is it dispersed?– Is it lost?– Account for it

ENERGY BUDGET

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

FUNDAMENTAL ENERGY RELATIONSHIPS

• Components of an animal’s energy budget are related by:

• Assimilated Energy = Ingested Energy – Egested Energy

• Production = Assimilated Energy – (Respiration-Excretion)

ASSIMILATION EFFICIENCY• Assimilation Efficiency = Assimilation/Ingestion• Function of Food Quality:

NET PRODUCTION EFFICIENCY

• Net production efficiency = production/assimilation

• depends on metabolic activity:

What limits the length of the food chain?

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

Do aquatic or terrestrial ecosystems have more trophic levels? What factor contributes most to variation in food chain length among these ecosystems?

http://www.yale.edu/post_lab/images/FCL_ecosize_large.gif

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!

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