Ecosystems

Overview

• Flow of energy

• Feeding relationships and feeding modes

• Trophic levels

• Food chains/webs

• Pyramids of biomass, numbers, energy

• Flow of nutrients

• Biogeochemical cycles

Ecosystem definition

• An ecosystem all the populations within a defined area along with the abiotic environment

• An ecosystem is an open system. It obtains energy and recycles nutrients.

The flow of energyThe flow of energy

• Energy enters the ecosystem as radiant energy from the sun

• 1% of the solar energy, that reaches the earth, makes it through the atmosphere to the earth surface.

photosynthesis

Sugar issynthesizedand used inplant tissues.

planttissues,Growth

Energy iscapturedfromsunlight.

Carbon dioxideis absorbedfrom the air.

Oxygen isreleased.

Water is absorbedfrom soil, used inphotosynthesis, andstored in cells.

Inorganic mineral nutrients(nitrate, phosphate) areabsorbed from soil andused in plant tissues.

The process of The process of photosynthesis photosynthesis captures solar energy captures solar energy and results in primary and results in primary productivity:productivity:

= conversion of inorganic carbon into organic carbon

(Primary) Producers do primary productivity

1-3% of solar energy on the earth surface is absorbed by producers

grassland(600)

temperatedeciduous forest(1200)

coniferousforest(800)

tundra(140)

tropicalrain forest(2200)

continentalshelf(360)

openocean(125)

estuary(1500)

desert(90)

Comparison of ecosystem productivitiesComparison of ecosystem productivities

Numbers in g organic carbon/m2/year

Trophic levelsTrophic levels• A trophic level refers to the position of an A trophic level refers to the position of an

organism in the food chainorganism in the food chain

• As organisms of one trophic level become the As organisms of one trophic level become the food source of organisms of the trophic level food source of organisms of the trophic level above them.above them.

• Producers =Producers = self nourishingself nourishingphotoautotroph or chemoautotrophphotoautotroph or chemoautotrophoccupy the 1occupy the 1stst trophic level trophic level

• Consumers = Consumers = rely on other organisms for foodrely on other organisms for foodoccupy all other trophic levelsoccupy all other trophic levelsherbivores, carnivores, omnivoresherbivores, carnivores, omnivores

•

2 categories of organisms:2 categories of organisms:

Heterotrophic Feeding ModesHeterotrophic Feeding Modes

• Herbivores = primary consumers, plant eaters (e.g. grasshoppers, giraffes)

• Carnivores = secondary, tertiary, consumers etc… meat eaters (spiders, eagle wolf)

• Omnivores = can act as primary, secondary, or tertiary consumers (raccoons, bears, rats, humans)

11stst trophic level trophic level

higher trophic levelhigher trophic level

22ndnd trophic level trophic level

het

erot

rop

hs

het

erot

rop

hs

auto

trop

hs

auto

trop

hs

Kelp community Kelp community food chainfood chain carnivorecarnivore

herbivoreherbivore

TERTIARY CONSUMER(4th trophic level)

PRIMARY CONSUMER(2nd trophic level)

SECONDARY CONSUMER(3rd trophic level)

PRODUCER1st trophic level

Simple terrestrial food chainSimple terrestrial food chain

TERTIARY CONSUMER(4th trophic level)

ZooplanktonPRIMARY CONSUMER

(2nd trophic level)

SECONDARY CONSUMER(3rd trophic level)

PhytoplanktonPRODUCER

(1st trophic level)

Simple marine food chainSimple marine food chain

Energy transfer between trophic Energy transfer between trophic levels is inefficientlevels is inefficient

• 5%-20%, avg:10%5%-20%, avg:10%

• Because each organism uses energy Because each organism uses energy for itself: maintenance, activities, heat, for itself: maintenance, activities, heat, etc. This energy is lost to the next etc. This energy is lost to the next trophic level as it is not stored in trophic level as it is not stored in biomass ( plant and animal bodies)biomass ( plant and animal bodies)

Energy is limited Energy is limited

Because of low energy transfer efficiency from one Because of low energy transfer efficiency from one trophic level to the next:trophic level to the next:

1. Each succeeding trophic level contains less 1. Each succeeding trophic level contains less energyenergy

Consequence:Consequence: – each feeding population is smaller then the population each feeding population is smaller then the population

it feeds uponit feeds upon

2. Energy runs out eventually 2. Energy runs out eventually

Consequence:Consequence: – Limits the number of trophic levels in a food chain/webLimits the number of trophic levels in a food chain/web

1 calorie

10 calories

100 calories

1000 calories producer

primary consumer

secondary consumer

tertiary consumer

Nutrient flow is cyclic

• Nutrients are elements and small molecules that form building blocks of life

• Nitrate Phosphate Calcium …..

Decomposers

• Recycle nutrients• Feed on dead organic matter and reduce

these wastes to CO2, water, minerals

• Decomposers: bacteria and fungus, earthworms, mites, centipedes, nematode worms, some insects

Carbon cycleCarbon cycle

• Carbon enters the ecosystem as CO2

• Atmosphere: 0.036%• Dissolved in the ocean and freshwater as

H2CO3 ( carbonic acid)

Carbon cycle Carbon cycle

• 3 pathways:

• 1. CO2-> organic carbon (biomass: plants and animals) -> CO2

• 2. CO2+ Ca -> CaCO3 (coral skeleton, shells) deposits after death, converts into limestone

• 3. Fossil fuels: dead remains of plants and animals transformed into coal, oil and natural gas through pressure and high temperatures Coal, oil -> Combustion ->CO2

CO2 dissolvedin ocean

respiration

burning of fossil fuels fire

consumers producers

wastes, deadbodies

fossilfuels

limestone

reservoir

processes/locations

trophic levelsCO2 in

atmosphere

CARBON CYCLECARBON CYCLE

Nitrogen cycleNitrogen cycle• Major reservoir: atmosphere: 79%• Used only by nitrogen-fixing bacteria in soil & water

• N-fixers: N2-> NH3 (ammonia), fertilize the soil

• Rhizobium: symbiotic N2-fixing bacteria in legumes (beans and peas) roots

• Plants use: NH3 and NO3 (nitrate)

• Fertilizer: washed into the ocean->eutrophication-> algal blooms->O2 depletion due to decomposing bacteria->threatens survival of heterotrophs( animals)

reservoir

processes/locations

trophic levels/organisms

nitrogen inAtmosphere

electrical stormsproduce nitrate

producersconsumers

wastes, deadbodies

Ammonifying, nitrifying bacteria

Ammonium and nitrate in soil

and water

denitrifyingBacteria

fertilizerfactories

uptakeby

plants nitrogen-fixingbacteria in

legume rootsand soil

burning producesnitrogen oxides

Nitrogen cycleNitrogen cycle

Phosphorus cyclePhosphorus cycle

• Reservoir: rocks ; as PO4 dissolved into H2OPathway: – Absorbed by plants -> – Passed on along the food chain -> – PO4 excretion (e.g. guano = bird droppings) by

animals -> – decomposition of dead organisms converts

organic P into PO4

Phosphate pollutionPhosphate pollution

• Fertilizer: washed into the ocean-> eutrophication-> algal blooms->

• O2 depletion due to decomposing bacteria->

• threatens survival of heterotrophs (animals)

phosphatein

rock

geologicaluplift

reservoir

processes/locations

trophic levels

consumers

detritusfeeders

producers

phosphatein

soil

phosphatein

sediment

runofffrom rivers

runoff fromfertilized

fields

phosphatein

water

Phosphorus cyclePhosphorus cycle

Hydrolytic cycleHydrolytic cycle

• Reservoir: ocean: contains 97% of the available water

• The hydrolytic cycle is driven by solar energy -> evaporation and precipitation

• Ground water is used for irrigation of cropland in dry areas (India, China, Western US) -> ground water levels have dropped. Groundwater loss in India can jeopardize 25% of the grain harvest

reservoirs

processes/locations

water vaporin atmosphere

precipitationoverland

lakes andstreams

groundwater

surfacerunoff

water inocean

Precipitationover

ocean

evaporation fromland and

transpirationfrom plants

evaporationfrom

ocean

Hydrolytic Hydrolytic cyclecycle

Acid rain /acid depositionAcid rain /acid deposition• Sulfur dioxide:

– 2/3 from burning of coal and oil• nitrogen oxides:

– Vehicles, power plants and industry• nitrogen oxides: • Sulfur and nitrogen oxides + water vapor -> nitric acid +

sulfuric acid • Returns to the surface as acid rain, fog and snow• Affects:

– Trees: get killed – crops: leaches out calcium and potassium and destroys

decomposing bacteria – lakes: kills the aquatic community – buildings, statues are eaten away– all organism as many toxic metals dissolve better in acidic water:

e.g. lead mercury

Global warmingGlobal warming• Green house gases trap heat in the atmosphere: allow

solar Energy to come in, but absorb longer–wavelength Energy, that radiates back from the earth surface.

• Greenhouse gases: CO2!– also: methane, nitrous oxide, water vapor

• CO2 increase: – by more than 30% since 1850: 280ppm -> 370ppm– now: 1.5ppm/year

• Major CO2 sources: – Fossil fuel burning– deforestation: burning (tropics, rainforest for agricultural

land)

Consequences of global warmingConsequences of global warming• Increase in the average global temperature

• Prediction: increase by 2.5oC (10.4oF) in 2100• Last ice age: global decrease by 5oC• -> dramatic effect on weather and climate

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tem

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°C)

CO2temperature

[CO

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pm

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ObservationsObservations• Melting of polar ice caps and glaciers:

E.g. Artic sea and Iceland ice caps - Glacier national park (150 glaciers->35)- Mount Everest Glacier retreated 3 miles over 50y y

• Sea level will rises:- Coastal cities and wetlands flood

• Ocean and air currents alter path:- precipitation patterns change -> more extreme

droughts and rain falls -> crop losses• Coral reefs are affected:• Living systems: already change ranges towards

poles• Spring time events: such as breeding are shifted

to earlier dates

Your decision makes a differenceYour decision makes a difference

• U.S. population: 5% of the world population• U.S. greenhouse gas generation: 20% of the

world population• What can we do?What can we do?

– Fuel-efficient vehicles, public transportation, car pool– Conserve electricity– Insulate and weatherproof house– Recycle : e.g. 95% of the E to make an aluminum can

be preserved if made from a recycled one