1. Chapter 54
Ecosystems

2. An ecosystem consists of all the organisms living in a community + the abiotic factors with which they interact

3. Ecosystems can range from a microcosm, e.g. aquarium to a large area e.g. a lake or forest
Figure 54.1

4. 2 main processes: energy flow and chemical cycling
Energy flows through ecosystems
While matter cycles within them

5. Ecosystems and Physical Laws
Energy is conserved
But degraded to heat during ecosystem processes

6. Trophic Relationships
Energy and nutrients pass from primary producers (autotrophs) primary consumers (herbivores)  secondary consumers (carnivores)

7. Energy flows through an ecosystem
Entering as light and exiting as heat
Figure 54.2
Microorganisms
and other
detritivores
Detritus
Primary producers
Primary consumers
Secondary
consumers
Tertiary consumers
Heat
Sun
Key
Chemical cycling
Energy flow

8. Detritivores, (bacteria and fungi)
Recycle essential chemical elements by decomposing organic material and returning elements to inorganic reservoirs
Figure 54.3

9. Primary production
amount of light energy converted to chemical energy by autotrophs

10. Ecosystem Energy Budgets
Photosynthetic production sets the spending limit for the energy budget of the entire ecosystem

11. The Global Energy Budget
Amount of solar radiation reaching the surface of the Earth limits the photosynthetic output of ecosystems
Only a small fraction of solar energy actually strikes photosynthetic organisms

12. Gross Production (GPP)
Total primary production in an ecosystem

13. Net primary production (NPP)
GPP minus the energy used by the primary producers for respiration
Only NPP is available to consumers

14. Net primary production
Lake and stream
Open ocean
Continental shelf
Estuary
Algal beds and reefs
Upwelling zones
Extreme desert, rock, sand, ice
Desert and semidesert scrub
Tropical rain forest
Savanna
Cultivated land
Boreal forest (taiga)
Temperate grassland
Tundra
Tropical seasonal forest
Temperate deciduous forest
Temperate evergreen forest
Swamp and marsh
Woodland and shrubland 10 20 30 40 50 60
500
1,000
1,500
2,000
2,500 5 15 25
Percentage of Earth’s net
primary production
Key
Marine
Freshwater (on continents)
Terrestrial
5.2
0.3
0.1
4.7
3.5
3.3
2.9
2.7
2.4
1.8
1.7
1.6
1.5
1.3
1.0
0.4
125
360
3.0 90
2,200
900
600
800
700
140
1,600
1,200
1,300
250
5.6
1.2
0.9
0.04 22
7.9
9.1
9.6
5.4
0.6
7.1
4.9
3.8
2.3
65.0
24.4
Figure 54.4a–c
Percentage of Earth’s
surface area
(a)
Average net primary
production (g/m2/yr)
(b)
(c)

15. Terrestrial ecosystems contribute about two-thirds of global NPP and marine ecosystems about one-third
Figure 54.5
180
120W
60W 0
60E
120E
North Pole
60N
30N
Equator
30S
60S
South Pole

16. Primary Production in Marine and Freshwater Ecosystems
Both light and nutrients control primary production

17. Light Limitation
The depth of light penetration affects primary production

18. Nutrient Limitation
Limit primary production more than light

19. Limiting nutrient
Element that must be added in order for production to increase
Nitrogen and phosphorous typically the nutrients that most often limit marine production

20. Nutrient enrichment experiments
Pollution from duck farms concentrated near Moriches Bay adds both nitrogen and phosphorus to the coastal water off Long Island. Researchers cultured the phytoplankton Nannochloris atomus with water collected from several bays.
Figure 54.6
Coast of Long Island, New York. The numbers on the map indicate
the data collection stations.
Long Island
Great South Bay
Shinnecock Bay
Moriches Bay
Atlantic Ocean 30 21 19 15 11 5 4 2

21. Figure 54.6 (a) Phytoplankton biomass and phosphorus concentration
(b) Phytoplankton response to nutrient enrichment
Great
South Bay
Moriches
Bay
Shinnecock
Starting
algal
density 2 4 5 11 30 15 19 21 24 18 12 6
Unenriched control
Ammonium enriched
Phosphate enriched
Station number
(millions of cells per mL)
Phytoplankton 8 7 3 1
Inorganic phosphorus
(g atoms/L)
(millions of cells/mL)
CONCLUSION
Since adding phosphorus, which was already in rich supply, had no effect on Nannochloris growth, whereas adding nitrogen increased algal density dramatically, researchers concluded that nitrogen was the nutrient limiting phytoplankton growth in this ecosystem.
Inorganic
phosphorus
RESULTS
Phytoplankton abundance parallels the abundance of phosphorus in the water (a). Nitrogen, however, is immediately taken up by algae, and no free nitrogen is measured in the coastal waters. The addition of ammonium (NH4) caused heavy phytoplankton growth in bay water, but the addition of phosphate (PO43) did not induce algal growth (b).

22. Experiments in another ocean region
Showed that iron limited primary production
Table 54.1

23. Addition of nutrients to lakes has a wide range of ecological impacts

24. e.g. sewage runoff eutrophication loss of fish species
Figure 54.7

25. Live, above-ground biomass
Soil nutrients often the limiting factor in primary production (usually nitrogen)
Figure 54.9
EXPERIMENT
Over the summer of 1980, researchers added phosphorus to some experimental plots in the salt marsh, nitrogen to other plots, and both phosphorus and nitrogen to others. Some plots were left unfertilized as controls.
RESULTS
Experimental plots receiving just phosphorus (P) do not outproduce the unfertilized control plots.
CONCLUSION
Live, above-ground biomass
(g dry wt/m2)
Adding nitrogen (N) boosts net primary
production.
300
250
200
150
100 50
June
July
August 1980
N  P
N only
Control
P only
These nutrient enrichment experiments confirmed that nitrogen was the nutrient limiting plant growth in this salt marsh.

26. Energy transfer between trophic levels is usually 10% efficient

27. Production Efficiency
Figure 54.10
Plant material
eaten by caterpillar
Cellular
respiration
Growth (new biomass)
Feces
100 J
33 J
200 J
67 J

28. Pyramids of Production
Figure 54.11
Tertiary
consumers
Secondary
Primary
producers
1,000,000 J of sunlight
10 J
100 J
1,000 J
10,000 J

29. Certain aquatic ecosystemsh have inverted biomass pyramids
Figire 54.12b
Trophic level
Primary producers (phytoplankton)
Primary consumers (zooplankton)
(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).
Dry weight
(g/m2) 21 4

30. Number of individual organisms
Pyramids of Numbers
Figure 54.13
Trophic level
Number of individual organisms
Primary producers
Tertiary consumers
Secondary consumers
Primary consumers 3
354,904
708,624
5,842,424

31. Worldwide agriculture could successfully feed many more people if humans ate only plant material
Trophic level
Secondary
consumers
Primary
producers
Figure 54.14

32. Most terrestrial ecosystems
Have large standing crops despite the large numbers of herbivores
Figure 54.15

33. The green world hypothesis proposes several factors that keep herbivores in check
Plants have defenses against herbivores
Nutrients, not energy supply, usually limit herbivores
Abiotic factors limit herbivores
Intraspecific competition can limit herbivore numbers
Interspecific interactions check herbivore densities

34. Life on Earth depends on the recycling of essential chemical elements
Nutrient circuits that cycle matter through an ecosystem
Involve both biotic and abiotic components and are often called biogeochemical cycles

35. A General Model of Chemical Cycling
Gaseous forms of carbon, oxygen, sulfur, and nitrogen
Occur in the atmosphere and cycle globally
Less mobile elements, including phosphorous, potassium, and calcium
Cycle on a local level

36. General model of nutrient cycling
Figure 54.16
Organic
materials
available
as nutrients
Living
organisms,
detritus
unavailable
Coal, oil,
peat
Inorganic
Atmosphere,
soil, water
Minerals
in rocks
Formation of
sedimentary rock
Weathering,
erosion
Respiration,
decomposition,
excretion
Burning
of fossil fuels
Fossilization
Reservoir a
Reservoir b
Reservoir c
Reservoir d
Assimilation, photosynthesis

37. Biogeochemical Cycles
The water cycle and the carbon cycle
Figure 54.17
Transport
over land
Solar energy
Net movement of
water vapor by wind
Precipitation
over ocean
Evaporation
from ocean
Evapotranspiration
from land
Percolation
through
soil
Runoff and
groundwater
CO2 in atmosphere
Photosynthesis
Cellular
respiration
Burning of
fossil fuels
and wood
Higher-level
consumers
Primary
Detritus
Carbon compounds
in water
Decomposition
THE WATER CYCLE
THE CARBON CYCLE

38. Water moves in a global cycle
Driven by solar energy
The carbon cycle
Reflects the reciprocal processes of photosynthesis and cellular respiration

39. The nitrogen cycle and the phosphorous cycle
Figure 54.17
N2 in atmosphere
Denitrifying
bacteria
Nitrifying
Nitrification
Nitrogen-fixing
soil bacteria
bacteria in root
nodules of legumes
Decomposers
Ammonification
Assimilation
NH3
NH4+
NO3
NO2 
Rain
Plants
Consumption
Decomposition
Geologic
uplift
Weathering
of rocks
Runoff
Sedimentation
Plant uptake
of PO43
Soil
Leaching
THE NITROGEN CYCLE
THE PHOSPHORUS CYCLE

40. Decomposers (detritivores) play a key role in chemical cycling
Figure 54.18
Consumers
Producers
Nutrients
available
to producers
Abiotic
reservoir
Geologic
processes
Decomposers

41. Nitrate concentration in runoff
Net losses of water and minerals were greater in disturbed area
Figure 54.19c
(c) The concentration of nitrate in runoff from the deforested watershed was 60 times greater than in a control (unlogged) watershed.
Nitrate concentration in runoff
(mg/L)
Deforested
Control
Completion of
tree cutting
1965
1966
1967
1968
80.0
60.0
40.0
20.0
4.0
3.0
2.0
1.0

42. As the human population has grown in size
Our activities have disrupted the trophic structure, energy flow, and chemical cycling of ecosystems in most parts of the world

43. Nutrient Enrichment
Transporting nutrients from one location to another & added new materials, some of them toxins, to ecosystems

44. Agriculture and Nitrogen Cycling
Agriculture constantly removes nutrients from ecosystems
That would ordinarily be cycled back into the soil
Figure 54.20

45. Nitrogen is the main nutrient lost through agriculture
Thus, agriculture has a great impact on the nitrogen cycle
Industrially produced fertilizer is typically used to replace lost nitrogen
But the effects on an ecosystem can be harmful

46. Contamination of Aquatic Ecosystems
The critical load for a nutrient
Is the amount of that nutrient that can be absorbed by plants in an ecosystem without damaging it

47. When excess nutrients are added to an ecosystem, the critical load is exceeded
And the remaining nutrients can contaminate groundwater and freshwater and marine ecosystems

48. Sewage runoff contaminates freshwater ecosystems
Causing cultural eutrophication, excessive algal growth, which can cause significant harm to these ecosystems

49. Acid Precipitation
Combustion of fossil fuels is the main cause

50. North American and European ecosystems downwind from industrial regions have been damaged by rain and snow containing nitric and sulfuric acid
Figure 54.21
4.6
4.3
4.1
Europe
North America

51. By the year 2000 the entire contiguous United States was affected by acid precipitation
Figure 54.22
Field pH
5.3
5.2–5.3
5.1–5.2
5.0–5.1
4.9–5.0
4.8–4.9
4.7–4.8
4.6–4.7
4.5–4.6
4.4–4.5
4.3–4.4
4.3

52. Toxins in the Environment
Humans release an immense variety of toxic chemicals including thousands of synthetics previously unknown to nature
One of the reasons such toxins are so harmful is that they become more concentrated in successive trophic levels of a food web

53. Biological magnification
Toxins concentrate at higher trophic levels because at these levels biomass tends to be lower
Figure 54.23
Concentration of PCBs
Herring
gull eggs
124 ppm
Zooplankton
0.123 ppm
Phytoplankton
0.025 ppm
Lake trout ppm
Smelt
1.04 ppm

54. In some cases, harmful substances persist for long periods of time in an ecosystem

55. CO2 concentration (ppm) Temperature variation (C)
Rising Atmospheric CO2
Mostly due to the increased burning of fossil fuels and other human activities
Correlation w/ increase in temp.
Figure 54.24
CO2 concentration (ppm)
390
380
370
360
350
340
330
320
310
300
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
1.05
0.90
0.75
0.60
0.45
0.30
0.15
0.15
 0.30
 0.45
Temperature variation (C)
Temperature
CO2
Year

59. How Elevated CO2 Affects Forest Ecology: The FACTS-I Experiment
Influences tree growth, carbon concentration in soils, and other factors over a ten-year period
Figure 54.25

60. The Greenhouse Effect and Global Warming
Caused by atmospheric CO2 but is necessary to keep the surface of the Earth at a habitable temperature

61. Increased levels of atmospheric CO2 are magnifying the greenhouse effect which contributes to global warming and significant climatic change

62. Life on Earth is protected from the damaging effects of UV radiation by a protective layer or ozone molecules present in the atmosphere

63. Depletion of Atmospheric Ozone
Ozone layer has been gradually thinning since 1975
Figure 54.26
Ozone layer thickness (Dobson units)
Year (Average for the month of October)
350
300
250
200
150
100 50
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005

64. The destruction of atmospheric ozone
Probably results from chlorine-releasing pollutants (CFC) produced by human activity
Figure 54.27 1 2 3
Chlorine from CFCs interacts with ozone (O3), forming chlorine monoxide (ClO) and
oxygen (O2).
Two ClO molecules react, forming chlorine peroxide (Cl2O2).
Sunlight causes Cl2O2 to break down into O2 and free chlorine atoms. The chlorine atoms can begin the cycle again.
Sunlight
Chlorine O3 O2
ClO
Cl2O2
Chlorine atoms

65. Figure 54.28a, b
Scientists first described an “ozone hole” over Antarctica in 1985; it has increased in size as ozone depletion has increased
(a) October 1979
(b) October 2000