Chapter 54: Ecosystems

1. What is an ecosystem?- All the organisms living within an area & all the abiotic factors

they interact with- Energy flows through while chemicals cycle within an ecosystem

Figure 54.2 An overview of energy and nutrient dynamics in an ecosystem

Microorganismsand other

detritivores

Detritus

Primary producers

Primary consumers

Secondaryconsumers

Tertiary consumers

Heat

Sun

Key

Chemical cycling

Energy flow

Chapter 54: Ecosystems

1. What is an ecosystem?- All the organisms living within an area & all the abiotic factors

they interact with- Energy flows through while chemicals cycle within an ecosystem

2. What is primary productivity?- Amount of light energy converted to chemical energy by autotrophs

3. What is the difference between Gross PP & Net PP?- GPP = total primary productivity - NPP = GPP – respiration (energy used by organisms)

- Storage of chemical energy available to consumers

Figure 54.4 Net primary production of different ecosystems

Lake and stream

Open ocean

Continental shelf

Estuary

Algal beds and reefs

Upwelling zones

Extreme desert, rock, sand, ice

Desert and semidesert scrubTropical rain forest

Savanna

Cultivated land

Boreal forest (taiga)

Temperate grassland

Tundra

Tropical seasonal forestTemperate deciduous forest

Temperate evergreen forestSwamp and marsh

Woodland and shrubland

0 10 20 30 40 50 60 0 500 1,000 1,500 2,000 2,500 0 5 10 15 20 25

(a) Percentage of Earth’ssurface area

(b) Average net primaryproduction (g/m2/yr)

(c) Percentage of Earth’s netprimary production

Key

Marine

Freshwater (on continents)Terrestrial

5.20.30.10.1

4.73.53.32.92.72.41.81.71.61.51.31.00.40.4

125360

1,5002,500

5003.090

2,200900

600800

600700

1401,600

1,2001,300

2,000250

5.61.20.9

0.10.040.9

227.9

9.19.6

5.43.5

0.67.1

4.93.8

2.30.3

65.0 24.4

Figure 54.5 Regional annual net primary production for Earth

180 120W 60W 0 60E 120E 180

North Pole

60N

30N

Equator

30S

60S

South Pole

Chapter 54: Ecosystems

1. What is an ecosystem?- All the organisms living within an area & all the abiotic factors

they interact with- Energy flows through while chemicals cycle within an ecosystem

2. What is primary productivity?- Amount of light energy converted to chemical energy by autotrophs

3. What is the difference between Gross PP & Net PP?- GPP = total primary productivity

- Amount of light energy converted to chemical energy by photosynthesis

- NPP = GPP – respiration (energy used by organisms)- Storage of chemical energy available to consumers

4. What happens to energy at each trophic level?

Figure 54.10 Energy partitioning within a link of the food chain

Plant materialeaten by caterpillar

Cellularrespiration

Growth (new biomass)

Feces100 J

33 J

200 J

67 J

Chapter 54: Ecosystems

1. What is an ecosystem?- All the organisms living within an area & all the abiotic factors

they interact with- Energy flows through while chemicals cycle within an ecosystem

2. What is primary productivity?- Amount of light energy converted to chemical energy by autotrophs

3. What is the difference between Gross PP & Net PP?- GPP = total primary productivity

- Amount of light energy converted to chemical energy by photosynthesis

- NPP = GPP – respiration (energy used by organisms)- Storage of chemical energy available to consumers

4. What happens to energy at each trophic level?5. What does the “Pyramid of Net Production” look like?

Figure 54.11 An idealized pyramid of net production

Tertiaryconsumers

Secondaryconsumers

Primaryconsumers

Primaryproducers

1,000,000 J of sunlight

10 J

100 J

1,000 J

10,000 J- <1% harnessed by autotrophs

Rule of 10 = only 10% of energy reaches the next trophic level

Figure 54.12 Pyramids of biomass (standing crop)

(a) Most biomass pyramids show a sharp decrease in biomass at successively higher trophic levels, as illustrated by data froma bog at Silver Springs, Florida.

Trophic level Dry weight(g/m2)

Primary producers

Tertiary consumers

Secondary consumers

Primary consumers

1.5

11

37809

(b) In some aquatic ecosystems, such as the English Channel, a small standing crop of primary producers (phytoplankton)supports a larger standing crop of primary consumers (zooplankton).

Trophic level

Primary producers (phytoplankton)

Primary consumers (zooplankton)

Dry weight(g/m2)

21

4

Figure 54.13 A pyramid of numbers

Trophic level Number of individual organisms

Primary producers

Tertiary consumers

Secondary consumers

Primary consumers

3

354,904

708,624

5,842,424

Fig. 54.14 Relative food energy available to the human population at different trophic levels

Trophic level

Secondaryconsumers

Primaryconsumers

Primaryproducers

- energy is more directly available to vegetarians than carnivores

Chapter 54: Ecosystems

1. What is an ecosystem?- All the organisms living within an area & all the abiotic factors

they interact with- Energy flows through while chemicals cycle within an ecosystem

2. What is primary productivity?- Amount of light energy converted to chemical energy by autotrophs

3. What is the difference between Gross PP & Net PP?- GPP = total primary productivity

- Amount of light energy converted to chemical energy by photosynthesis

- NPP = GPP – respiration (energy used by organisms)- Storage of chemical energy available to consumers

4. What happens to energy at each trophic level?5. What does the “Pyramid of Net Production” look like?6. Let’s consider chemical cycling within an ecosystem….

Figure 54.17 Nutrient Cycles

Transportover land

Solar energy

Net movement ofwater vapor by wind

Precipitationover ocean

Evaporationfrom ocean

Evapotranspirationfrom land

Precipitationover land

Percolationthroughsoil

Runoff andgroundwater

CO2 in atmosphere

Photosynthesis

Cellularrespiration

Burning offossil fuelsand wood

Higher-levelconsumersPrimary

consumers

DetritusCarbon compounds in water

Decomposition

THE WATER CYCLE THE CARBON CYCLE

N2 in atmosphere

Denitrifyingbacteria

Nitrifyingbacteria

Nitrifyingbacteria

Nitrification

Nitrogen-fixingsoil bacteria

Nitrogen-fixingbacteria in rootnodules of legumes

Decomposers

Ammonification

Assimilation

NH3 NH4+

NO3

NO2

Rain

Plants

Consumption

Decomposition

Geologicuplift

Weatheringof rocks

Runoff

SedimentationPlant uptakeof PO4

3

Soil

Leaching

THE NITROGEN CYCLE THE PHOSPHORUS CYCLE

Chapter 54: Ecosystems

1. What is an ecosystem?2. What is primary productivity?3. What is the difference between Gross PP & Net PP?4. What happens to energy at each trophic level?5. What does the “Pyramid of Net Production” look like?6. Let’s consider chemical cycling within an ecosystem….7. What happened at the Hubbard Brook Experimental Forest?

- Nutrients stayed within an ecosystem due to plants

Figure 54.19 Nutrient cycling in the Hubbard Brook Experimental Forest: an example of long-term ecological research

(a) Concrete dams and weirs built across streams at the bottom of watersheds enabled researchers to monitor the outflow of water and nutrients from the ecosystem.

Nitr

ate

conc

entr

atio

n in

run

off

(mg/

L)

Deforested

ControlCompletion of

tree cutting

1965 1966 1967 1968

80.060.040.020.0

4.03.02.01.0

0

The concentration of nitrate in runoff from thedeforested watershed was 60 times greater than in a control (unlogged) watershed.

(c)

One watershed was clear cut to study the effects of the loss of vegetation on drainage and nutrient cycling.

(b)

Chapter 54: Ecosystems

1. What is an ecosystem?2. What is primary productivity?3. What is the difference between Gross PP & Net PP?4. What happens to energy at each trophic level?5. What does the “Pyramid of Net Production” look like?6. Let’s consider chemical cycling within an ecosystem….7. What happened at the Hubbard Brooks Experimental Forest?

- Nutrients stayed within an ecosystem due to plants8. What is biological magnification?

- Concentration of toxins increase in higher trophic levels

Fig. 54.23 Biological magnification of PCBs in a Great Lakes food web

Co

nce

ntr

atio

n o

f P

CB

s

Herringgull eggs124 ppm

Zooplankton 0.123 ppm

Phytoplankton 0.025 ppm

Lake trout 4.83 ppm

Smelt 1.04 ppm