chapter 55 ecosystems. copyright © 2008 pearson education, inc., publishing as pearson benjamin...

Chapter 55Chapter 55

Ecosystems

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Overview: Ecosystems

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

• Regardless of an ecosystem’s size, its dynamics involve two main processes: energy flow and chemical cycling.

• Energy flows through ecosystems while matter cycles within them.


I. Conservation of Mass

• Matter cannot be created or destroyed.

• Chemical elements are recycled

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


• Autotrophs build organic molecules (photosynthesis or chemosynthesis)

• Heterotrophs depend on other organisms.

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


• Detritivores (decomposers) are consumers that derive their energy from detritus, nonliving organic matter.

– Prokaryotes and fungi

• Decomposition connects all trophic levels.

Fungi decomposing a dead tree

Energy and Nutrient Dynamics in an Ecosystem

Microorganismsand other

detritivores

Tertiary consumers

Secondaryconsumers

Primary consumers

Primary producers

Detritus

Heat

SunChemical cycling

Key

Energy flow


II. Energy controls production

• Primary production = amount of light energy converted to chemical energy by autotrophs. Amount of photosynthetic production sets the spending limit for an ecosystem’s energy budget. (amount of sunlight = amount of output)


A. Gross and Net Primary Production

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

• Net primary production = NPP

• GPP - energy used by producers for respiration. NPP = GPP - Respiration

• Only NPP is available to consumers.

• Standing crop = total biomass of photosynthetic autotrophs at a given time.

Net primary production (kg carbon/m2·yr)

0 1 2 3

·

Global net primary production in 2002

Global net primary production in 2002


III. Production in Aquatic Ecosystems

• Both light and nutrients control primary production.

• Depth of light penetration affects primary production in the photic zone of an ocean or lake.


A. Nutrient Limitation

• More than light, nutrients limit primary production in geographic regions of the ocean and in lakes.

• Limiting nutrient = 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.


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

• In some areas, sewage runoff has caused eutrophication (high levels of algae, decay, low oxygen) of lakes, which can lead to loss of most fish species.


IV. Production in Terrestrial Ecosystems

• Temperature and moisture affect primary production on a large scale.

• Actual evapotranspiration is the water annually transpired by plants and evaporated from a landscape.

• Locally, soil nutrient is often the limiting factor in primary production.

Net

pri

mar

y p

rod

uct

ion

(g

/m2 ·

yr)

Relationship between net primary production and actual evapotranspiration in six terrestrial ecosystems

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·


V. Energy transfer is 10% efficient

• Secondary production = the amount of chemical energy in food converted to new biomass during a given period of time.

– Ex. When a caterpillar feeds on a leaf, only about one-sixth of the leaf’s energy is used for secondary production.

• Production efficiency = fraction of energy stored in food that is not used for respiration.

• Approximately 0.1% of chemical energy fixed by photosynthesis reaches a tertiary consumer.

Energy partitioning within a link of the food chain

Cellularrespiration100 J

Growth (new biomass)

Feces

200 J

33 J

67 J

Plant materialeaten by caterpillar

Primaryproducers

100 J

1,000,000 J of sunlight

10 J

1,000 J

10,000 J

Primaryconsumers

Secondaryconsumers

Tertiaryconsumers


• Biomass pyramid – amount of living matter in an area

– Sharp decrease at successively higher levels

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

Pyramids of biomass = standing crop:

(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


• Ecosystems – Andersen – 14 min

http://www.bozemanscience.com/047-ecosystems

Nutrient CyclingReservoir 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


VI. Water Cycle

• 97% oceans, 2% ice, and 1% is in lakes, rivers, and groundwater.

• evaporation, transpiration, condensation, precipitation, and surfacewater and groundwater.

Nutrient Cycles: Water Cycle

Precipitationover land

Transportover land

Solar energy

Net movement ofwater vapor by wind

Evaporationfrom ocean

Percolationthroughsoil

Evapotranspirationfrom land

Runoff andgroundwater

Precipitationover ocean


VII. Carbon Cycle

• C stored in 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; volcanoes and burning of fossil fuels add CO2 to the atmosphere.

Nutrient Cycles:Carbon Cycle

Higher-levelconsumersPrimary

consumers

Detritus

Burning offossil fuelsand wood

Phyto-plankton

Cellularrespiration

Photo-synthesis

Photosynthesis

Carbon compoundsin water

Decomposition

CO2 in atmosphere


VIII. Nitrogen Cycle

• The main reservoir of nitrogen is the atmosphere (N2), though this nitrogen must be converted to NH4

+ or NO3

– for uptake by plants, via nitrogen fixation by bacteria.

Nutrient Cycles:Nitrogen Cycle

Decomposers

N2 in atmosphere

Nitrification

Nitrifyingbacteria

Nitrifyingbacteria

Denitrifyingbacteria

Assimilation

NH3 NH4 NO2

NO3

+ –

–

Ammonification

Nitrogen-fixingsoil bacteria

Nitrogen-fixingbacteria


IX. Phosphorus Cycle

• Phosphate (PO43–) is the most important

inorganic form of phosphorus.

• Stored in sedimentary rocks of marine origin, oceans, and organisms.

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

Nutrient Cycles:PhosphorousCycle

Leaching

Consumption

Precipitation

Plantuptakeof PO4

3–

Soil

Sedimentation

Uptake

Plankton

Decomposition

Dissolved PO43–

Runoff

Geologicuplift

Weatheringof rocks


X. Decomposition and Nutrient Cycling Rates

• Decomposers = play a key role in chemical cycling.

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

• Rapid decomposition = low levels of nutrients in the soil.

How does temperature affect litter decomposition in an ecosystem?

Ecosystem typeEXPERIMENT

RESULTS

Arctic

Subarctic

Boreal

TemperateGrassland

Mountain

P

O

D

J

RQ

K

B,C

E,FH,I

LNUS

TM

G

A

A

80

70

60

50

40

30

20

10

0–15 –10 –5 0 5 10 15

Mean annual temperature (ºC)

Per

cen

t o

f m

ass

lost

B

CD

E

F

GH

I

JK

LMN

O

P

QR

S

T

U


A. Agriculture and Nitrogen Cycling

• Agriculture removes nutrients from the soil.

• Nitrogen is the main nutrient lost through agriculture

• Fertilizer is typically used to replace lost nitrogen, but effects on an ecosystem can be harmful.


B. Contamination of Aquatic Ecosystems

• Critical load for a nutrient is the amount that plants can absorb without damaging the ecosystem.

• When have excess nutrients, critical load is exceeded.

• Remaining nutrients can contaminate groundwater and ecosystems.

– Sewage runoff causes eutrophication

The dead zone arising from nitrogen pollution in the Mississippi basin

Winter Summer


XI. Acid Precipitation

• Combustion of fossil fuels is the main cause

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

• Effects areas downwind from industry

Changes in the pH of precipitation at Hubbard Brook

Year200019951990198519801975197019651960

4.0

4.1

4.2

4.3

4.4

4.5p

H


XII. Toxins

• Humans release many toxic chemicals

• Toxins are harmful because they become more concentrated in successive trophic levels.

• Biological magnification concentrates toxins at higher trophic levels.

– Ex PCBs and many pesticides such as DDT

Biological Magnification of PCBs in a Great Lakes food web

Lake trout4.83 ppm

Co

nce

ntr

ati

on

of

PC

Bs

Herringgull eggs124 ppm

Smelt1.04 ppm

Phytoplankton0.025 ppm

Zooplankton0.123 ppm


XIII. Greenhouse Gases and Global Warming

• Burning of fossil fuels and other human activities, the [CO2] has been steadily increasing.


• Greenhouse effect = CO2, water vapor, and other greenhouse gases reflect infrared radiation back toward Earth

• Increased levels of CO2 are magnifying the greenhouse effect, which could cause global warming and climatic change.

• A warming trend would also affect the geographic distribution of precipitation.


XIV. Depletion of Ozone

• Ozone protects life on Earth from damaging effects of UV radiation

• Destruction of ozone probably results from chlorine-releasing pollutants such as CFCs (chloroflorocarbons) produced by human activity.

• Causes DNA damage, hole is getting smaller bc of an international agreement in 1987

How free chlorine in the atmosphere destroys ozone

O2

Sunlight

Cl2O2

Chlorine

Chlorine atom

O3

O2

ClO

ClO

Erosion of Earth’s ozone shield

(a) September 1979 (b) September 2006

Ecosystem Changes – Andersen

Biodiversity - Andersen

http://www.bozemanscience.com/051-ecosystem-change

http://www.bozemanscience.com/055-biodiversity


You should now be able to:

1. Explain how the first and second laws of thermodynamics apply to ecosystems.

2. Define and compare gross primary production, net primary production, and standing crop.

3. Explain why energy flows but nutrients cycle within an ecosystem.

4. Explain what factors may limit primary production in aquatic ecosystems.


5. Distinguish between the following pairs of terms: primary and secondary production, production efficiency and trophic efficiency.

6. Explain why worldwide agriculture could feed more people if all humans consumed only plant material.

7. Describe the four nutrient reservoirs and the processes that transfer the elements between reservoirs.


8. Explain why toxic compounds usually have the greatest effect on top-level carnivores.

9. Describe the causes and consequences of ozone depletion.

chapter 55 ecosystems. copyright © 2008 pearson education, inc., publishing as pearson benjamin...

Documents

gppnet primary production

photosynthetic production

production efficiency

marine production

efficientsecondary production

pearson education

pearson benjamin cummingsa

light energy