1. Ecosystems Chapter 55
AP Biology

2. Objectives…I can… Describe the flow of energy in an ecosystem.
Explain how decomposition connects all trophic levels in an ecosystem.
Define gross and net primary production.
Distinguish among pyramids of net production, of biomass, and of numbers.
Describe the water cycle, the nitrogen cycle, the carbon cycle, and the phosphorous cycle.

3. Objectives…I can…
Describe how agricultural practices can interfere with nitrogen cycling.
Describe the causes and consequences of acid precipitation.
Explain why toxic compounds have a greater effect on top level carnivores.
Describe how increased carbon dioxide in the atmosphere could affect the Earth.
Describe the causes and consequences of ozone depletion.

4. 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.

5. Ecosystems can range from a microcosm, such as an aquarium to a large area such as a lake or forest.
Figure 54.1

6. Energy flows through ecosystems, while matter cycles within them.
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.

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. Trophic Relationships
Primary producers – autotrophs (make their own food) ex: plants
Heterotrophs – consumers (eat other organisms) ex: animals, fungi
Primary consumers – herbivores (eat plants)
Secondary consumers – carnivores (eat primary consumers)
Tertiary consumers – carnivores (eat secondary consumers)
Omnivores – eat producers and other consumers

9. Also called decomposers
Detritivores - mainly bacteria and fungi, recycle essential chemical elements
Also called decomposers
Figure 54.3

10. Primary Productivity
Primary production in an ecosystem is the amount of light energy converted to chemical energy by autotrophs during a given time period.
It is the photosynthetic output of an ecosystem’s producers.
Physical and chemical factors limit primary production in ecosystems.

11. 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 (to make energy for their own life processes).
Only NPP is available to consumers.

12. CFU
1. True or False – Matter flows through an ecosystem, where as energy is recycled.
2. What are three terms that most photosynthetic organisms are known by?
3. Why are detritovores necessary in any ecosystem.
4. What is the difference between gross and net primary productivity?

13. Different ecosystems vary considerably in their 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)

14. Secondary Production 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.
Energy transfer between trophic levels is usually around 10% efficient. (Rule of Ten – only 10% of the energy is “passed on” to the next level)

15. 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

16. 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

17. 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

18. Laws of Thermodynamics and Ecosystems
First Law of Thermodynamics – energy cannot be created or destroyed, it can be transformed
Second Law of Thermodynamics – in each energy transformation some energy is lost (usually as heat)

19. CFU
1. What happens to the amount of biomass as you move up an ecological pyramid?
2. Describe the efficiency of the energy transfer between trophic levels.
3. How does the Second Law of Thermodynamics apply to an ecological pyramid?

20. 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.

21. Biogeochemical Cycles
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

22. Water moves in a global cycle
driven by solar energy.
The carbon cycle
reflects the reciprocal processes of photosynthesis and cellular respiration.

23. THE NITROGEN CYCLE THE PHOSPHORUS 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

24. Chemical Cycles in Ecosystems Chart

25. Nitrogen Cycle
Nitrogen Fixation – (assimilation) – bacteria on the roots of legumes (Ex: bean plants) fix atmospheric nitrogen as ammonium
-Also can also be done by lightning and UV radiation
Nitrification – (assimilation) – done by nitrifying bacteria, ammonium becomes nitrite

26. Nitrogen Cycle
Denitrification – (release) - done by denitrifying bacteria,
nitrogen is released back to the atmosphere
Ammonification – bacteria convert organic compounds back to ammonium

27. 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.

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

29. 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.

30. Sewage and fertilizer runoff contaminates freshwater ecosystems
causing eutrophication, excessive algal growth, which can cause significant harm to these ecosystems.

31. Acid Precipitation
Combustion of fossil fuels is the main cause of acid precipitation.
Figure 54.21
4.6
4.3
4.1
Europe
North America

32. By the year 2000
the entire contiguous United States was affected by acid precipitation.

33. 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 some toxins become more concentrated in successive trophic levels of a food web. This is called biological magnification.

34. 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

35. 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

36. The Greenhouse Effect and Global Warming
The greenhouse effect is caused by atmospheric CO2 trapping heat in the atmosphere.
It 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.

37. 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.

38. 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

39. The destruction of atmospheric ozone
probably results from chlorine-releasing pollutants (chloroflourocarbons) produced by human activity (arosal spray cans, freon use)
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

40. Scientists first described an “ozone hole” over Antarctica in 1985;
1987 –Montreal Protocol – limited use of CFC’s worldwide
Good News! It is showing signs of recovery at this time.

41. What can you do to help preserve the Earth’s ecosystems?