1. Chapter 54
Ecosystems

2. Ecosystems
Microcosm: aquarium
Lakes, forests
Figure 54.1

3. Dynamics
Energy flows
Matter cycles

4. Ecosystem ecologists
Monitor energy & matter

5. Energy flows Light - heat Figure 54.2 Tertiary consumers
Microorganisms
and other
detritivores
Detritus
Primary producers
Primary consumers
Secondary
consumers
Tertiary consumers
Heat
Sun
Key
Chemical cycling
Energy flow

6. Decomposition – connects levels
Detritivores, (bacteria, fungi) recycle chemical elements
Figure 54.3

7. Primary production
Amount of light energy converted to chemical energy by autotrophs during a given time period

8. Ecosystem Energy Budgets
The extent of photosynthetic production
Sets the spending limit for the energy budget of the entire ecosystem

9. The Global Energy Budget
Only a small fraction of solar energy
Actually strikes photosynthetic organisms

10. Gross and Net Primary Production
GPP – total production
Not all stored as organic material in growing plants

11. Only NPP is available to consumers
GPP minus energy used by 1o producers for respiration
Only NPP is available to consumers

12. NPP varies in ecosystems
And in their contribution to the total NPP on Earth
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)

13. Gobal NPP Terrestrial 2/3 Marine 1/3 Figure 54.5 180 120W 60W 0
North Pole
60N
30N
Equator
30S
60S
South Pole

14. Primary Production in Marine and Freshwater Ecosystems

15. Light Limitation light penetration
Affects primary production throughout the photic zone of an ocean or lake

16. Limiting nutrient: element that must be added
Nutrient limitation
Limiting nutrient: element that must be added
for production to increase in a particular area
Nitrogen and phosphorous
most often limit marine production

17. Nutrient enrichment

18. Iron may limit PP
Table 54.1

19. The addition of large amounts of nutrients to lakes
Has a wide range of ecological impacts

20. Eutrophication
Sewage runoff may cause eutrophication
Figure 54.7

21. Primary Production in Terrestrial and Wetland Ecosystems
Climate factors such as temperature and moisture affect primary production on a large geographic scale

22. Evapotranspiration measurements
Actual evapotranspiration
amount of water annually transpired by plants and evaporated from a landscape
related to net primary production
Figure 54.8
Actual evapotranspiration (mm H2O/yr)
Tropical forest
Temperate forest
Mountain coniferous forest
Temperate grassland
Arctic tundra
Desert
shrubland
Net primary production (g/m2/yr)
1,000
2,000
3,000
500
1,500

23. Live, above-ground biomass
Nutrients
local scale
soil nutrient often limiting
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.

24. Between trophic levels < 20% efficient 2o production
Energy transfer
Between trophic levels < 20% efficient
2o production
amount of chemical energy in consumers’ food converted to own new biomass during a given period of time

25. Production Efficiency
When a caterpillar feeds on a plant leaf
Only about one-sixth of the energy in the leaf is used for secondary production
Figure 54.10
Plant material
eaten by caterpillar
Cellular
respiration
Growth (new biomass)
Feces
100 J
33 J
200 J
67 J

26. Production efficiency of organism
Fraction of energy stored in food that is not used for respiration

27. Trophic Efficiency and Ecological Pyramids
percentage of production transferred from one trophic level to the next
ranges from 5% to 20%

28. Pyramids of Production
Shows energy loss
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. Biomass pyramids
Show a sharp decrease at successively higher trophic levels
Figure 54.12a
(a) Most biomass pyramids show a sharp decrease in biomass at successively higher trophic levels, as illustrated by data from a bog at Silver Springs, Florida.
Trophic level
Dry weight
(g/m2)
Primary producers
Tertiary consumers
Secondary consumers
Primary consumers
1.5 11 37
809

30. Certain aquatic ecosystems
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

31. 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

32. Energy flow dynamics Eating meat important for human population
Is a relatively inefficient way of tapping photosynthetic production

33. Worldwide agriculture could successfully feed many more people
If humans all fed more efficiently, eating only plant material
Trophic level
Secondary
consumers
Primary
producers
Figure 54.14

34. The Green World Hypothesis
Terrestrial herbivores consume relatively little plant biomass because they are held in check by a variety of factors

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

36. Several factors keep herbivores in check
Plant defenses
Nutrients
Abiotic factors
Intraspecific competition
Interspecific interactions

37. Biogeochemical cycles
Biological and geochemical processes move nutrients between organic and inorganic parts of the ecosystem
Life on Earth
Depends on recycling of essential chemical elements

38. 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 more local level

39. Model of nutrient cycling
Includes main reservoirs of elements and processes that transfer elements between reservoirs
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

40. All elements
Cycle between organic and inorganic reservoirs

41. 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

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

43. 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

44. Decomposition and Nutrient Cycling Rates
Decomposers (detritivores) play a key role
Figure 54.18
Consumers
Producers
Nutrients
available
to producers
Abiotic
reservoir
Geologic
processes
Decomposers

45. Nutrient cycling rates
Are extremely variable, mostly as a result of differences in rates of decomposition

46. Vegetation and Nutrient Cycling: The Hubbard Brook Experimental Forest
Is strongly regulated by vegetation

47. The research team constructed a dam on the site
Hubbard Brook
The research team constructed a dam on the site
To monitor water and mineral loss
Figure 54.19a
(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.

48. Trees in one valley were cut down Sprayed with herbicides
Figure 54.19b
(b) One watershed was clear cut to study the effects of the loss of vegetation on drainage and nutrient cycling.

49. Nitrate concentration in runoff
Net losses of water and minerals
Were found to be 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

50. We are disrupting chemical cycles throughout the biosphere
With human population increase
Our activities disrupted trophic structure, energy flow, and chemical cycling of ecosystems in most parts of the world

51. Nutrient Enrichment
Transporting nutrients
Adding new materials (some toxic)

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

53. Agriculture has a great impact on nitrogen cycle
Fertilizer used to replace nitrogen
But the effects on an ecosystem can be harmful

54. 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

55. When critical load exceeded
Remaining nutrients can contaminate groundwater and freshwater and marine ecosystems

56. Sewage runoff contaminates freshwater ecosystems
Eutrophication
Change in species composition or species loss

57. Combustion of fossil fuels
Acid Precipitation
Combustion of fossil fuels
Is the main cause of acid precipitation

58. 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

61. Environmental regulations and new industrial technologies
Have allowed many developed countries to reduce sulfur dioxide emissions in the past 30 years

62. 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

63. In 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

64. In some cases, harmful substances
Persist for long periods of time in an ecosystem and continue to cause harm

65. Atmospheric Carbon Dioxide
One pressing problem caused by human activities
Is the rising level of atmospheric carbon dioxide

66. Rising Atmospheric CO2
Due to the increased burning of fossil fuels and other human activities
The concentration of atmospheric CO2 has been steadily increasing
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

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

68. The Greenhouse Effect and Global Warming
The greenhouse effect is caused by atmospheric CO2
But is necessary to keep the surface of the Earth at a habitable temperature

69. Increased levels of atmospheric CO2 are magnifying the greenhouse effect
Which could cause global warming and significant climatic change

70. Depletion of Atmospheric Ozone
Life on Earth is protected from the damaging effects of UV radiation
By a protective layer or ozone molecules present in the atmosphere

71. Satellite studies of the atmosphere
Suggest that the 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

72. The destruction of atmospheric ozone
Probably results from chlorine-releasing pollutants 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

73. 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
Figure 54.28a, b