Fig. 55-1

ECOSYSTEMS AP CHAP 55

An ecosystem consists of all the organisms living in a community, as well as the abiotic factors with which they interact

Fig. 55-2

Regardless of an ecosystem’s size, its dynamics involve two main processes: energy flow and chemical cyclingEnergy flows through (one way) ecosystems while matter cycles within them

Physical laws govern energy flow and chemical cycling in ecosystems

• The first law of thermodynamics states that energy cannot be created or destroyed, only transformed• Energy enters an ecosystem as solar radiation, is conserved, and is lost from organisms as HEAT!• The second law of thermodynamics states that every exchange of energy increases the entropy of the

universe• In an ecosystem, energy conversions are not completely efficient, and some energy is always lost as HEAT!

Conservation of Mass

• The law of conservation of mass states that matter cannot be created or destroyed

• Chemical elements are continually recycled within ecosystems

• Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products.

Energy, Mass, and Trophic Levels

• Autotrophs build molecules themselves using photosynthesis or chemosynthesis as an energy source; heterotrophs depend on the biosynthetic output of other organisms

• Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) to secondary consumers (carnivores) to tertiary consumers (carnivores that feed on other carnivores)

• Detritivores, or decomposers, are consumers that derive their energy from detritus, nonliving organic matter

• Prokaryotes and fungi are important detritivores

• Decomposition connects all trophic levels

Fig. 55-3

Fig. 55-4

Microorganismsand other

detritivores

Tertiary consumers

Secondaryconsumers

Primary consumers

Primary producers

Detritus

Heat

SunChemical cycling

Key

Energy flow

Decomposition connects all trophic levels

Energy and other limiting factors control primary production in

ecosystems

• Primary production in an ecosystem is the amount of light energy converted to chemical energy by autotrophs during a given time period….ie….amount of PHOTOSYNTHESIS

In primary producers the main energy input is from the solar energy. In a plant, not all

of the solar energy available actually makes it into the leaf.

Only about 1% of

visible light that

strikes

photosynthetic

organisms is

converted to

chemical energy in

photosynthesis.

• It is the energy that is incorporated into the biomass that is available for the next trophic level.

In the consumer a further series of energy losses occur. The consumer will take in a certain amount of energy from the trophic level beneath it.

• It is generally accepted that only around 10% of the energy gained from the previous trophic level is passed on to the next level. All other energy is lost as described above. This limits the number of trophic levels in any food chain.

Gross and Net Primary Production

• Total primary production is known as the ecosystem’s gross primary production (GPP)

• Since autotrophs also have to respire to obtain energy, their GPP is reduced by the amount of energy used for fuel in cell respiration.

• Net primary production (NPP) is GPP minus energy used by primary producers for cell respiration

• Only NPP is available to consumers

SO…

NPP = GPP - R

Only NPP is available to consumers

• It’s like Gross Pay – what you make• Net Pay – what you bring home

• NPP = GPP from photosynthesis – R from cellular respiration

• Or GPP = NPP + R

• In many ecosystems, NPP is about ½ of GPP.

• NPP represents the storage of chemical energy that will be available to consumers.

• NPP can be expressed as energy per unit area per unit time (J/m2 yr) or as biomass added per unit area per unit time (g/m2 yr) added in that unit of time.

Solar Radiation

Reflected

Transmitted

Absorbed

Energy

lost

Energy

accumulated as

biomass

Tree

Layer

Shrub layer

Herb Layer

Energy cannot be created or destroyed

so all of this has to add up.

Our LabWe are calculating the NPP for our Fast Plants by measuring their biomass

accumulated. Remember some energy is

lost as heat and used in respiration.

Then we are measuring the transfer of energy from plants to butterfly larvae in “Secondary Production”.

• Primary productivity can also be determined by measuring oxygen being produced

• Or the amount of carbon compounds being produced

• Think photosynthesis.

• This can be done by measuring the amount of oxygen in samples of water in bottles in light and dark.

Experiment we used to do:

Remember…the difference between gross and net primary productivity.

Gross productivity is the total amount of productivity in the environment. Net productivity is the average productivity produced at a certain period of time.

Gross primary productivity is the total amount of something made in an area. Net primary productivity is the amount of that energy that can actually be used.

Gross primary production is the overall total of production.

Primary productivity is the amount of light energy converted to chemical energy during a period of time. It is the photosynthetic output of an ecosystem’s autotrophs.

The NPP is an ecosystem’s GPP minus the energy used by producers in their own cellular respiration (R).

So NPP = GPP – R

GPP = NPP + R

• Tropical rain forests, estuaries, and coral reefs are among the most productive ecosystems per unit area

• Marine ecosystems are relatively unproductive per unit area, but contribute much to global net primary production because of their volume

Fig. 55-6

Net primary production (kg carbon/m2·yr)

0 1 2 3

·

Primary Production in Aquatic Ecosystems

In marine and freshwater ecosystems, both light and nutrients control primary production

Nutrient Limitation

• More than light, nutrients limit primary production in the ocean and in lakes

• A limiting nutrient is the element that must be added for production to increase in an area

• Nitrogen and phosphorous are typically the nutrients that most often limit marine production

Fig. 55-7

Atlantic Ocean

Moriches Bay

ShinnecockBayLong Island

Great South Bay

A

BC D

EF G

EXPERIMENT

Ammoniumenriched

Phosphateenriched

Unenrichedcontrol

RESULTS

A B C D E F G

30

24

18

12

6

0

Collection site

Ph

yto

pla

nkt

on

den

sity

(mill

ion

s o

f ce

lls p

er m

L)

Nutrient enrichment experiments confirmed that nitrogen was limiting phytoplankton growth off the shore of Long Island, New York

Ammonium NH3

Table 55-1

What is the limiting factor in this area?IRON

• Upwelling of nutrient-rich waters in parts of the oceans contributes to regions of high primary production

• The addition of large amounts of nutrients to lakes has a wide range of ecological impacts

• In some areas, sewage runoff has caused eutrophication of lakes, which can lead to loss of most fish species

Why do the fish die?

Primary Production in Terrestrial Ecosystems

• In terrestrial ecosystems, temperature and moisture affect primary production on a large scale

• Evapotranspiration is related to net primary production

Net

pri

mar

y p

rod

uct

ion

(g

/m2 ·

yr)

Fig. 55-8

Tropical forest

Actual evapotranspiration (mm H2O/yr)

Temperate forest

Mountain coniferous forest

Temperate grassland

Arctic tundra

Desertshrubland

1,5001,00050000

1,000

2,000

3,000·

On a more local scale, a soil nutrient is often the limiting factor in primary production

What is the limitingfactor in this soil example?

Energy transfer between trophic levels is typically only 10% efficient

• Secondary production of an ecosystem is the amount of chemical energy in food converted to new biomass during a given period of time

Production Efficiency• When a caterpillar feeds on a leaf, only

about one-sixth of the leaf’s energy is used for secondary production

• An organism’s production efficiency is the fraction of energy stored in food that is not used for respiration or other processes that do not lead to biomass in the organism.

Fig. 55-9

Cellularrespiration100 J

Growth (new biomass)

Feces

200 J

33 J

67 J

Plant materialeaten by caterpillar

200 6

When a caterpillar feeds on a

leaf, only about one-sixth of

the leaf’s energy is used for

secondary production

Trophic Efficiency and Ecological Pyramids

• Trophic efficiency is the percentage of production transferred from one trophic level to the next

• It usually ranges from 5% to 20%• Trophic efficiency is multiplied over the length of a

food chain• Approximately 0.1% of chemical energy fixed by

photosynthesis reaches a tertiary consumer• A pyramid of net production represents the loss of

energy with each transfer in a food chain

Fig. 55-10

Primaryproducers

100 J

1,000,000 J of sunlight

10 J

1,000 J

10,000 J

Primaryconsumers

Secondaryconsumers

Tertiaryconsumers

Energy transfer between trophic levels is typically only 10% efficient

• In a biomass pyramid, each tier represents the dry weight of all organisms in one trophic level

• Most biomass pyramids show a sharp decrease at successively higher trophic levels

• Certain aquatic ecosystems have inverted biomass pyramids: producers (phytoplankton) are consumed so quickly that they are outweighed by primary consumers

Fig. 55-11

(a) Most ecosystems (data from a Florida bog)

Primary producers (phytoplankton)

(b) Some aquatic ecosystems (data from the English Channel)

Trophic level

Tertiary consumersSecondary consumers

Primary consumersPrimary producers

Trophic level

Primary consumers (zooplankton)

Dry mass(g/m2)

Dry mass(g/m2)

1.5

1137

809

214

Biological and geochemical processes cycle nutrients between organic and inorganic parts of

an ecosystem

• Life depends on recycling chemical elements

• Nutrient circuits in ecosystems involve biotic and abiotic components and are often called biogeochemical cycles

Biogeochemical Cycles• Gaseous carbon, oxygen, sulfur, and

nitrogen occur in the atmosphere and cycle globally

• Less mobile elements such as phosphorus, potassium, and calcium cycle on a more local level

Fig. 55-13Reservoir A Reservoir B

Organicmaterialsavailable

as nutrientsFossilization

Organicmaterials

unavailableas nutrients

Reservoir DReservoir C

Coal, oil,peat

Livingorganisms,detritus

Burningof fossil fuels

Respiration,decomposition,excretion

Assimilation,photosynthesis

Inorganicmaterialsavailable

as nutrients

Inorganicmaterials

unavailableas nutrients

Atmosphere,soil, water

Mineralsin rocks

Weathering,erosion

Formation ofsedimentary rock

All elements cycle between organic and inorganic reservoirs

In studying cycling of water, carbon, nitrogen, and phosphorus, ecologists focus on four factors:

– Each chemical’s biological importance– Forms in which each chemical is available

or used by organisms– Major reservoirs for each chemical– 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

Fig. 55-14a

Precipitationover land

Transportover land

Solar energy

Net movement ofwater vapor by wind

Evaporationfrom ocean

Percolationthroughsoil

Evapotranspirationfrom land

Runoff andgroundwater

Precipitationover ocean

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 and released through photosynthesis and respiration; additionally, volcanoes and the combustion of fossil fuels contribute CO2 to the atmosphere

Fig. 55-14b

Higher-levelconsumersPrimary

consumers

Detritus

Burning offossil fuelsand wood

Phyto-plankton

Cellularrespiration

Photo-synthesis

Photosynthesis

Carbon compoundsin water

Decomposition

CO2 in atmosphere

The Terrestrial Nitrogen Cycle

• Nitrogen is a component of amino acids, proteins, and nucleic acids

• The main reservoir of nitrogen is the atmosphere (N2), though this nitrogen must be converted to ammonia or nitrate for uptake by plants, via nitrogen fixation by bacteria

• Organic nitrogen is decomposed to ammonia by ammonification, and ammonia is decomposed to nitrate in soil by nitrification

• Denitrification converts nitrates back to N2

in the atmosphere.

BACTERIA

NITROGEN

NitrogenFixation

ammonia, nitrates

Organic nitrogen from metabolism

ammonification ammonia

nitrification nitrates

denitrification

N2

BACTERIA

BACTERIA

BACTERIA

DECOMPOSITION

Fig. 55-14c

Decomposers

N2 in atmosphere

Nitrification

Nitrifyingbacteria

Nitrifyingbacteria

Denitrifyingbacteria

Assimilation

NH3 NH4 NO2

NO3

+ –

–

Ammonification

Nitrogen-fixingsoil bacteria

Nitrogen-fixingbacteria

BACTERIA aresuper important here!

Nitrogen accumulation in a pond

The Phosphorus Cycle

• Phosphorus is a major constituent of nucleic acids, phospholipids, and ATP

• Phosphate (PO43–) is the most important

inorganic form of phosphorus• The largest reservoirs are sedimentary

rocks of marine origin, the oceans, and organisms

• Phosphate binds with soil particles, and movement is often localized

• DOES NOT CYCLE IN THE ATMOSPHERE

Fig. 55-14d

Leaching

Consumption

Precipitation

Plantuptakeof PO4

3–

Soil

Sedimentation

Uptake

Plankton

Decomposition

Dissolved PO43–

Runoff

Geologicuplift

Weatheringof rocks

Decomposition and Nutrient Cycling Rates

• Decomposers (detritivores) play a key role in the general pattern of chemical cycling

• Rates at which nutrients cycle in different ecosystems vary greatly, mostly as a result of differing rates of decomposition

• The rate of decomposition is controlled by temperature, moisture, and nutrient availability

• Rapid decomposition results in relatively low levels of nutrients in the soil

Human activities now dominate most chemical cycles on Earth

• As the human population has grown, our activities have disrupted the trophic structure, energy flow, and chemical cycling of many ecosystems

How have humans impacted our ecosystems?

1) Agriculture and N cycling

• In agriculture, we have depleted our N resources and added back with fertilizers which have harmed our ecosystems.

2) Contamination of Aquatic Ecosystems

• When excess nutrients are added to an ecosystem, the critical load (minimal amt plants can absorb) is exceeded

• Remaining nutrients can contaminate groundwater as well as freshwater and marine ecosystems and cause eutrophication

3) Acid Precipitation

• Combustion of fossil fuels is the main cause of acid precipitation

• North American and European ecosystems downwind from industrial regions have been damaged by rain and snow containing nitric and sulfuric acid

• Acid precipitation changes soil pH and causes leaching of calcium and other nutrients

Fig. 55-19

Year200019951990198519801975197019651960

4.0

4.1

4.2

4.3

4.4

4.5p

H

4) Toxins in the Environment

• Humans release many toxic chemicals, including synthetics previously unknown to nature

• One reason toxins are harmful is that they become more concentrated in successive trophic levels

• Biological magnification concentrates toxins at higher trophic levels, where biomass is lower

Fig. 55-20

Lake trout4.83 ppm

Co

nce

ntr

ati

on

of

PC

Bs

Herringgull eggs124 ppm

Smelt1.04 ppm

Phytoplankton0.025 ppm

Zooplankton0.123 ppm

Brier Creek fish kill report looks at material used in mining, wastewater

treatment

• In a status report on the incident, Savannah River keeper said the characteristics of the fish kill are indicative of poisoning by aluminum sulfate – used as a coagulant in kaolin mining and sewage treatment.

5) Greenhouse Gases and Global Warming

• One pressing problem caused by human activities is the rising level of atmospheric carbon dioxide

• Due to the burning of fossil fuels and other human activities, the concentration of atmospheric CO2 has been steadily increasing

Fig. 55-21

CO2

CO

2 c

on

ce

ntr

ati

on

(p

pm

) Temperature

1960300

Av

era

ge

glo

ba

l te

mp

era

ture

(ºC

)

1965 1970 1975 1980Year

1985 1990 1995 2000 200513.6

13.7

13.8

13.9

14.0

14.1

14.2

14.3

14.4

14.5

14.6

14.7

14.8

14.9

310

320

330

340

350

360

370

380

390What we know for sure:

The concentration of atmospheric CO2 has been steadily increasing.

The Greenhouse Effect and Climate

• CO2, water vapor, and other greenhouse gases reflect infrared radiation back toward Earth; this is the greenhouse effect

• could cause global warming and climatic change

• Northern coniferous forests and tundra show the strongest effects of global warming

Depletion of Atmospheric Ozone• Life on Earth is protected from damaging

effects of UV radiation by a protective layer of ozone molecules

• Destruction of atmospheric ozone probably results from chlorine-releasing pollutants such as CFCs produced by human activity

• Ozone depletion causes DNA damage in plants and poorer phytoplankton growth

Ozo

ne

lay

er

thic

kn

ess

(D

ob

so

ns)

Fig. 55-23

Year’052000’95’90’85’80’75’70’65’601955

0

100

250

200

300

350

Satellite studies suggest that the ozone layer has been gradually thinning since 1975

Fig. 55-24

O2

Sunlight

Cl2O2

Chlorine

Chlorine atom

O3

O2

ClO

ClO

How free chlorine in the atmosphere destroys ozone.

ozone

• Ozone depletion causes DNA damage in plants and poorer phytoplankton growth

Fig. 55-25

(a) September 1979 (b) September 2006

Scientists first described an “ozone hole” over Antarctica in 1985; it has increased in size as ozone depletion has increased

An international agreement signed in 1987 has resulted in a decrease in ozone depletion

DO YOUR PART!