1. Chapter 55
Ecosystems

2. Overview: Ecosystems, Energy, and Matter
An ecosystem consists of all the organisms living in a community
As well as all 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 IN ONE DIRECTION ONLY while matter CYCLES within them

3. Visual Overview: Energy Flow

4. Ecosystems and Physical Laws
Ecosystem ecology emphasizes energy flow and chemical cycling
Ecosystem ecologists view ecosystems As transformers of energy and processors of matter
The laws of physics and chemistry apply to ecosystems particularly in regard to the flow of energy
Energy is conserved but degraded to heat during ecosystem processes

5. Trophic Relationships
Energy and nutrients pass from primary producers (autotrophs)
To primary consumers (herbivores) and then to secondary consumers (carnivores)
Energy flows IN ONE DIRE CTION ONLY through an ecosystem entering as light and exiting as heat – decomposition connects all trophic levels
Nutrients CYCLE within ecosystems

6. Energy Flow & Nutrient Cycles
Figure 54.2
Microorganisms
and other
detritivores
Detritus
Primary producers
Primary consumers
Secondary
consumers
Tertiary consumers
Heat
Sun
Key
Chemical cycling
Energy flow

7. Recycling Nutrients
Detritivores, mainly bacteria and fungi, recycle essential chemical elements
By decomposing organic material and returning elements to inorganic reservoirs
Figure 54.3

8. Primary Production in Ecosystems
Photosynthesis
Involves the use of light energy in the conversion of inorganic carbon into organic carbon.
Photosynthetic organisms include:
terrestrial plants,
seaweeds,
phytoplankton,
blue-green algae,
and zooxanthellae.

9. Primary Productivity in Ecosystems
Physical and chemical factors limit 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
The extent of photosynthetic production sets the spending limit for the energy budget of the entire ecosystem
The 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

10. Fate of Solar Energy

11. Gross Primary Productivity (GP)
The rate of production of organic matter from inorganic materials by autotrophic organisms
Respiration (R)
The rate of consumption of organic matter (conversion to inorganic matter) by organisms.
Net Primary Productivity (NP)
The net rate of organic matter produced as a consequence of both GP and R.

12. Primary Productivity: Formula

13. Gross and Net Primary Production
Total primary production in an ecosystem
Is known as that ecosystem’s gross primary production (GPP)
Not all of this production
Is stored as organic material in the growing plants
Net primary production (NPP)
Is equal to GPP minus the energy used by the primary producers for respiration
Only NPP
Is available to consumers

14. NPP of Varying Ecosystems
Different ecosystems vary considerably in their net primary production 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)

15. Terrestrial Ecosystems
Overall, 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. Environmental Factors Effect Production

17. Primary Production in Marine and Freshwater Ecosystems
Both light and nutrients are important in controlling primary production
The depth of light penetration
Affects primary production throughout the photic zone of an ocean or lake
More than light, nutrients limit primary production
Both in different geographic regions of the ocean and in lakes

18. Limits to Marine & Freshwater Ecosystems
A limiting nutrient is the element that must be added
In order for production to increase in a particular area
Nitrogen and phosphorous
Are typically the nutrients that most often limit marine production
The addition of large amounts of nutrients to lakes has a wide range of ecological impacts

19. Algal Blooms
When an aquatic ecosystem receives a large input of a limiting nutrient, the result is often an immediate increase in the amount of algae & other producers
Leads to algal blooms
Algal blooms occur because there are suddenly more nutrients available…so producers can grow and reproduce more quickly…and if there aren’t enough consumers to eat the producers, then algal blooms can cover the surface of the water.
Runoff from heavy fertilizers can lead to algal blooms

20. Eutrophication
In some areas, sewage runoff has caused eutrophication of lakes, which can lead to the eventual loss of most fish species from the lakes
Figure 54.7

21. Primary Production in Terrestrial and Wetland Ecosystems
In terrestrial and wetland ecosystems climatic factors
Such as temperature and moisture, affect primary production on a large geographic scale
On a more local scale
A soil nutrient is often the limiting factor in primary production

22. Efficiency of Energy Transfer in Ecosystems
Energy transfer between trophic levels is usually less than 20% efficient
The secondary production of an ecosystem
Is the amount of chemical energy in consumers’ food that is converted to their own new biomass during a given period of time

23. 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

24. Production & Trophic Efficiency
The production efficiency of an organism
Is the fraction of energy stored in food that is not used for respiration
Trophic efficiency
Is the percentage of production transferred from one trophic level to the next
Usually ranges from 5% to 20%
Decreases moving between trophic levels because much energy is used for metabolism and life processes, and much is lost as entropy (heat waste)

25. Pyramids of Production
This loss of energy with each transfer in a food chain
Can be represented by a pyramid of net 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

26. Pyramids of Biomass
One important ecological consequence of low trophic efficiencies can be represented in a biomass pyramid
Most 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

27. Certain aquatic ecosystems have inverted biomass pyramids
Pyramids of Biomass
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

28. Number of individual organisms
Pyramids of Numbers
A pyramid of numbers represents the number of individual organisms in each trophic level
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

29. Biogeochemical Cycles
Biological and geochemical processes move nutrients between organic and inorganic parts of the ecosystem
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

30. 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

31. Biogeochemical Cycles
A general model of nutrient cycling
Includes the main reservoirs of elements and the 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

32. 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

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

34. Biogeochemical Cycles
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

35. Biogeochemical Cycles
Most of the nitrogen cycling in natural ecosystems
Involves local cycles between organisms and soil or water
The phosphorus cycle
Is relatively localized

36. Decomposition and Nutrient Cycling Rates
Decomposers (detritivores) play a key role
In the general pattern of chemical cycling
Figure 54.18
Consumers
Producers
Nutrients
available
to producers
Abiotic
reservoir
Geologic
processes
Decomposers

37. As the human population has grown in size
The human population is disrupting chemical cycles throughout the biosphere
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

38. In addition to transporting nutrients from one location to another
Nutrient Enrichment
In addition to transporting nutrients from one location to another
Humans have added entirely new materials, some of them toxins, to ecosystems
Agriculture constantly removes nutrients from ecosystems
That would ordinarily be cycled back into the soil

39. 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

40. 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
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

41. Contamination of Ecosystems
Sewage runoff contaminates freshwater ecosystems
Causing cultural eutrophication, excessive algal growth, which can cause significant harm to these ecosystems
Combustion of fossil fuels
Is the main cause of acid precipitation

42. Contamination of Ecosystems
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

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

44. 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

45. Biological Magnification
In biological magnification toxins concentrate at higher trophic levels because at these levels biomass tends to be lower
In some cases, harmful substances persist for long periods of time in an ecosystem and continue to cause harm
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

46. Dichloro-diphenyl-trichloro-ethane (DDT):
Toxins can become concentrated in successive trophic levels of food webs!
Halogenated hydrocarbons or organochlorines:
Include DDT and PCBs, which are slow to biodegrade
Dichloro-diphenyl-trichloro-ethane (DDT):
used as a pesticide from 1939-late 1960s
fat soluble compound
the world’s production has substantially decreased since it was banned in the West
detected in mud of deep sea and snow & ice of Antarctica

47. Effect of PCBs & DDT Polychloronated biphenyls (PCBs)
Toxins can become concentrated in successive trophic levels of food webs!
Effect of PCBs & DDT
Polychloronated biphenyls (PCBs)
produced since 1944
banned in U.S. by 1979
used in production of electrical equipment, paints, plastics, adhesives, and coating compounds…
found everywhere in the ocean
released in env. by unregulated incineration of discarded products
DDT & PCBs affects:
copepod and oyster development
death of shrimp and a variety of fish

48. Biomagnification
In biomagnification, there is a tendency for pollutants to concentration as they move from one link in a food chain to another…top level carnivores suffer the most harmful effects of biomagnification.

49. Atmospheric Carbon Dioxide
One pressing problem caused by human activities
Is the rising level of atmospheric carbon dioxide
Due to the increased burning of fossil fuels and other human activities
The concentration of atmospheric CO2 has been steadily increasing

50. Rising Atmospheric CO2 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

51. 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
Increased levels of atmospheric CO2 are magnifying the greenhouse effect
Which could cause global warming and significant climatic change

52. 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
Satellite studies of the atmosphere
Suggest that the ozone layer has been gradually thinning since 1975

53. Depletion of Atmospheric Ozone
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

54. Depletion of Atmospheric Ozone
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

55. Depletion of Atmospheric Ozone
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