1. Big Idea 1, Essential knowledge 4.A.5
Notes – Ch. 54 (Ecology)
Big Idea 1, Essential knowledge 4.A.5

2. Overview: Ecosystems, Energy, and Matter
An ecosystem consists of all the organisms living in a community, as well as the abiotic factors with which they interact (living + nonliving)
Ecosystems range from a microcosm, such as an aquarium or your garden, to a large area such as a lake or forest

3. Overview cont.
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
(food webs vs. water cycles for example)

4. Energy Flow - Trophic Levels
Organisms in a community are related to each other through feeding relationships
Each step up in the transfer of energy is known as a trophic level
All energy ultimately comes from the SUN

5. Trophic Levels Producers Primary consumers Secondary consumers
Convert solar (or chemical) energy into organic compounds
Primary consumers
Eat producers
Secondary consumers
Eat primary consumers
Tertiary consumers
Eat secondary consumers

6. Trophic Relationships
Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) and then to secondary consumers (carnivores)
Energy flows through an ecosystem, entering as light and exiting as heat (still follows the laws of thermodynamics – energy can’t be created or destroyed, but it can be transformed)
Nutrients cycle within an ecosystem

7. Food chains
A food chain is a linear sequence of links starting from a species that are called producers in the web and ends at a species that is called decomposers.
A food chain also shows how the organisms are related with each other by the food they eat.
A straight-line sequence of who eats whom
Simple food chains are rare in nature

8. Food Webs
A food web is a series of connected food chains with complex trophic interactions

9. Tall-Grass Prairie Food Web
marsh hawk
sandpiper
crow
snake
frog
weasel
badger
coyote
spider
sparrow
pocket
gopher
ground
squirrel
vole
earthworms, insects
grasses, composites

10. Pyramid of Numbers/Biomass/Energy
A pyramid of net production represents the loss of energy with each transfer in a food chain
Numbers, energy, & biomass decreases as one moves up the food chain.
(Biomass- dry mass of organic matter)
Most biomass pyramids show a sharp decrease at successively higher trophic levels

11. Trophic Levels Ten-Percent Law
Usable energy is lost through each transfer of energy
Why? (Remember the law of conservation of energy says energy cannot be created or destroyed; it only changes form.)
Only about 10% of the energy at one trophic level is transferred to the next trophic level. 90% is lost as heat with each transfer.

12. Dynamics of energy flow in ecosystems have important implications for the human population
Eating meat is a relatively inefficient way of tapping photosynthetic production
Worldwide agriculture could feed many more people if humans ate only plant material

13. Trophic level Secondary consumers Primary consumers Primary producers

14. Physical and chemical factors limit primary production in ecosystems
Primary production in an ecosystem is the amount of light energy converted to chemical energy (glucose) by autotrophs during a given time period
The extent of photosynthetic production sets the spending limit for an ecosystem’s energy budget
The amount of solar radiation reaching the Earth’s surface limits photosynthetic output of ecosystems
Only a small fraction of solar energy actually strikes photosynthetic organisms

15. Gross and Net Primary Production
Total primary production is known as the ecosystem’s gross primary production (GPP)
GPP: the amount of light energy that is converted to chemical energy by photosynthesis per unit time
Net primary production (NPP) is GPP minus energy used by primary producers for respiration
Only NPP is available to consumers
Ecosystems vary greatly in net primary production and contribution to the total NPP on Earth

17. LE 54-4 Open ocean Continental shelf 65.0 125 24.4 5.2 360 5.6 Estuary
Algal beds and reefs
0.3
0.1
1,500
1.2
2,500
0.9
Upwelling zones
Extreme desert, rock, sand, ice
500
0.1
4.7
3.0
0.04
Desert and semidesert scrub
Tropical rain forest
3.5 90
0.9
3.3
2,200 22
Savanna
Cultivated land
2.9
900
7.9
2.7
600
9.1
Boreal forest (taiga)
Temperate grassland
2.4
800
9.6
1.8
600
5.4
Woodland and shrubland
Tundra
1.7
700
3.5
1.6
140
0.6
Tropical seasonal forest
1.5
1,600
7.1
Temperate deciduous forest
Temperate evergreen forest
1.3
1,200
4.9
1.0
1,300
3.8
Swamp and marsh
Lake and stream
0.4
2,000
2.3
250
0.3 10 20 30 40 50 60
500
1,000
1,500
2,000
2,500 5 10 15 20 25
Key
Percentage of Earth’s
surface area
Average net primary
production (g/m2/yr)
Percentage of Earth’s net
primary production
Marine
Terrestrial
Freshwater (on continents)

18. Overall, terrestrial ecosystems contribute about two-thirds of global NPP
Marine ecosystems contribute about one-third

19. LE 54-5
North Pole
60°N
30°N
Equator
30°S
60°S
South Pole
180°
120°W
60°W 0°
60°E
120°E
180°

20. Energy transfer between trophic levels
Secondary production of an ecosystem is the amount of chemical energy in food converted to new biomass during a given period of time
An organism’s production efficiency is the fraction of energy stored in food that is not used for respiration
When a caterpillar feeds on a leaf, only about one-sixth of the leaf’s energy is used for secondary production

21. Decomposition Decomposition connects all trophic levels
Detritivores, mainly bacteria and fungi, recycle essential chemical elements by decomposing organic material and returning elements to inorganic reservoirs
Eat detritus (organic waste/remains of dead organisms)
Can fit in to a food chain or web at any location

22. Limiting Nutrients What limits primary production? Aquatic Ecosystems
Light (depth penetration)
Nutriens/Minerals
Nitrogen
Phosphorus
Terrestrial Ecosystems
Temperature
Moisture
Minerals (N & P are the main limiting factors for plants.)

23. 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 scale
On a more local scale, a soil nutrient is often the limiting factor in primary production
Actual evapotranspiration is the water annually transpired by plants and evaporated from a landscape

24. The addition of large amounts of nutrients to lakes has a wide range of ecological impacts
In some areas, sewage runoff has caused eutrophication (the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system) of lakes, which can lead to loss of most fish species
Can cause a lowering of the oxygen content
Can cause an increase the numbers of one species that may harm others

25. Net primary production (g/m2/yr) Actual evapotranspiration (mm/yr)
3,000
Tropical forest
2,000
Net primary production (g/m2/yr)
Temperate forest
1,000
Mountain coniferous forest
Desert
shrubland
Temperate grassland
Arctic tundra
500
1,000
1,500
Actual evapotranspiration (mm/yr)

26. Chemical cycles Life depends on recycling chemical elements
Biogeochemical cycles-The flow of a nutrient from the environment to living organisms and back to the environment

27. LE 54-16
Reservoir a
Reservoir b
Organic
materials
available
as nutrients
Organic
materials
unavailable
as nutrients
Fossilization
Living
organisms,
detritus
Coal, oil,
peat
Respiration,
decomposition,
excretion
Assimilation,
photosynthesis
Burning
of fossil fuels
Reservoir c
Reservoir d
Inorganic
materials
available
as nutrients
Inorganic
materials
unavailable
as nutrients
Weathering,
erosion
Atmosphere,
soil, water
Minerals
in rocks
Formation of
sedimentary rock

28. Water cycle
1. Water vapor rises and begins to cool in the atmosphere (it’s a lot colder the higher up in elevation you go – which is why there is snow in the mountains but not in the valley)
2. Clouds form when the cooling water vapor condenses into droplets around dust particles in the atmosphere
3. Water falls from clouds in the form of rain or snow, which transfers water to Earth’s surface.
4. Groundwater and runoff from land surfaces flow into streams, rivers, lakes, and oceans, where they evaporate into the atmosphere to continue through the water cycle
Approx. 90% of water vapor evaporates from oceans, lakes, and rivers, and the rest comes from the surfaces of plants (through a process called transpiration)
Freshwater makes up only about 3% of all water on earth; of that, only about 31% of that is available, because 69% is frozen in ice caps and glaciers
Some environmentalists have stated water will soon be more valuable than oil, due to its scarcity and the fact that so much of it is being polluted (a bottle of water is already more expensive than a similar amount of oil)

29. Hydrologic (Water) Cycle
Atmosphere
precipitation onto land 111,000
wind-driven water vapor
40,000
evaporation from ocean
425,000
precipitation into ocean 385,000
evaporation from land plants (evapotranspiration) 71,000
surface and groundwater flow 40,000
Ocean
Land

30. The Carbon Cycle All living things contain carbon
Carbon and oxygen often make up molecules essential for life
During photosynthesis, plants convert carbon dioxide (made of carbon and oxygen) into sugar (glucose) and release oxygen back into the air
These sugars are used as a source of energy for all organisms in the food web.
Carbon dioxide is recycled when autotrophs and heterotrophs release it back into the air during cellular respiration (the process that is the opposite of photosynthesis – remember?)

31. Carbon Cycle cont.
Carbon enters a long term cycle when organic (living) matter is buried underground and converted into coil, oil, or gas deposits.
The carbon might remain as fossil fuel for millions of years (we call them fossil fuels because they are literally made from long-dead material like dinosaurs and ancient plants)
Carbon is released from fossil fuels when they are burned, which adds carbon dioxide to the atmosphere
While carbon is naturally released into the atmosphere through this cycle, because we are digging up and burning these fuels, we are releasing carbon at a much faster rate than is natural, and the earth cannot reabsorb it from the atmosphere fast enough
We are giving off the equivalent of 4 atomic bombs a second

32. LE 54-17b Higher-level consumers Primary consumers Carbon compounds
CO2 in atmosphere
Photosynthesis
Cellular
respiration
Burning of
fossil fuels
and wood
Higher-level
consumers
Primary
consumers
Carbon compounds
in water
Detritus
Decomposition

33. Carbon in Atmosphere
One pressing problem caused by human activities is the rising level of atmospheric carbon dioxide
Atmospheric carbon is mainly carbon dioxide
Carbon dioxide is added to atmosphere
Aerobic respiration, volcanic action, burning fossil fuels
Removed by photosynthesis

34. The Nitrogen Cycle Nitrogen is an element found in proteins
The largest concentration of nitrogen is found in the atmosphere
Plants and animals can’t use it directly from the atmosphere; it’s captured from the air by bacteria that live in water, soil, or grow on the roots of some plants.

35. Nitrogen cycle cont.
The process of capture and conversion of nitrogen into a form that is usable by plants is called nitrogen fixation
Nitrogen enters the food web when plants absorb nitrogen from the soil and convert them it into proteins
Consumers (heterotrophs that eat other organisms) get nitrogen by eating plants or animals that contain nitrogen;
they reuse the nitrogen and make their own proteins
Because the supply of nitrogen in a food web depends on the amount of nitrogen that is fixed, nitrogen is often a factor that limits the growth of producers (so it’s used in a lot of fertilizers, or you could use nitrogen-fixing plants like beans)
Nitrogen is returned to the soil in several ways:
when an animal urinates,
when organisms die and decomposers convert it into usable material,
and bacteria convert it back into a gas which returns it to the atmosphere

36. LE 54-17c N2 in atmosphere Denitrifying bacteria Nitrogen-fixing
Assimilation
Denitrifying
bacteria
NO3–
Nitrogen-fixing
bacteria in root
nodules of legumes
Decomposers
Nitrifying
bacteria
Ammonification
Nitrification
NH3
NH4+
NO2–
Nitrogen-fixing
soil bacteria
Nitrifying
bacteria

37. Decomposition and Nutrient Cycling Rates
Decomposers (detritivores) play a key role in the general pattern of chemical cycling
Rates at which nutrients cycle in different ecosystems vary greatly, mostly as a result of differing rates of decomposition

38. Nutrient Enrichment
In addition to transporting nutrients from one location to another, humans have added new materials, some of them toxins, to ecosystems

39. Agriculture and Nitrogen Cycling
Agriculture removes nutrients from ecosystems that would ordinarily be cycled back into the soil
Nitrogen is the main nutrient lost through agriculture; thus, agriculture greatly impacts the nitrogen cycle
Industrially produced fertilizer is typically used to replace lost nitrogen, but effects on an ecosystem can be harmful

40. Contamination of Aquatic Ecosystems
Critical load for a nutrient is the amount that plants can absorb without damaging the ecosystem
When excess nutrients are added to an ecosystem, the critical load is exceeded
Remaining nutrients can contaminate groundwater and freshwater and marine ecosystems
Sewage runoff causes cultural eutrophication, excessive algal growth that can greatly harm freshwater ecosystems (red tides)

41. Acid Precipitation
Combustion of fossil fuels is the main cause of acid precipitation
North American and European ecosystems downwind from industrial regions have been damaged by rain and snow containing nitric and sulfuric acid
By the year 2000, acid precipitation affected the entire contiguous United States

42. LE 54-22
5.3
5.0
5.4
5.1
5.6
5.2
5.5
5.3
6.1
5.3
5.2
5.3
4.8
4.5
4.7
5.2
5.2
5.5
5.4
5.2
5.1
4.6
5.2
5.0
4.7
4.8
5.2
4.9
4.8
4.5
4.6
5.2
4.3
5.5
4.5
4.5
5.6
5.5
4.5
5.2
4.7
4.9
4.5
5.6
5.3
4.7
4.5
4.6
5.4
5.3
5.5
4.5
4.3
4.4
4.6
5.1
4.7
4.6
4.5
5.4
4.7
6.0
4.1
4.4
4.5
5.5
5.3
5.3
4.8
4.4
4.4
5.9
4.6
4.3
5.3
5.4
4.6
4.6
4.5
4.6
6.3
5.1
4.7
4.4
4.5
4.5
5.2
5.3
5.0
4.5
4.5
4.7
4.7
5.3
4.6
5.0
5.1
4.9
5.6
5.7
5.4
4.8
5.4
4.6
4.6
5.4
5.0
4.8
4.9
4.6
4.5
4.5
4.9
4.8
4.7
4.5
4.5
5.4
4.6
5.3
4.5
Field pH
5.7
5.0
4.5
4.7
4.7
4.8
4.7
4.7
5.0
4.8
5.1
4.7
5.0
5.3
5.2
4.7
4.7
5.0
5.0
5.4
5.0
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
4.9
4.7
4.6
4.7
5.4
5.1
4.8
5.1
4.8
4.7
5.3
4.9
4.8
4.8
4.7
5.7
4.7
4.8
4.9
5.1
5.0
4.8
4.7
4.7
5.0
4.7
4.9

43. Toxins in the Environment
Humans release many toxic chemicals, including synthetics previously unknown to nature
In some cases, harmful substances persist for long periods in an ecosystem
One reason toxins are harmful is that they become more concentrated in successive trophic levels
In biological magnification, toxins concentrate at higher trophic levels, where biomass is lower

44. LE 54-23 Herring gull eggs 124 ppm Lake trout 4.83 ppm
Concentration of PCBs
Smelt
1.04 ppm
Zooplankton
0.123 ppm
Phytoplankton
0.025 ppm

45. Greenhouse Effect
Greenhouse gases impede the escape of heat from Earth’s surface
Figure 48.18, Page 880

46. The Greenhouse Effect and Global Warming
The greenhouse effect caused by atmospheric CO2 keeps Earth’s surface at a habitable temperature
Increased levels of atmospheric CO2 are magnifying the greenhouse effect, which is causing global warming and climatic change

47. Long-term increase in the temperature of Earth’s lower atmosphere
Global Warming
Long-term increase in the temperature of Earth’s lower atmosphere
Figure 48.19, Page 881

48. Depletion of Atmospheric Ozone
Life on Earth is protected from damaging effects of UV radiation by a protective layer or ozone molecules in the atmosphere
Satellite studies suggest that the ozone layer has been gradually thinning since 1975

49. Ozone layer thickness (Dobson units)
LE 54-26
350
300
250
200
Ozone layer thickness (Dobson units)
150
100 50
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Year (Average for the month of October)

50. Destruction of atmospheric ozone probably results from chlorine-releasing pollutants produced by human activity

51. Two CIO molecules react, forming chlorine peroxide (Cl2O2).
Chlorine from CFCs interacts with ozone (O3), forming chlorine monoxide (CIO) and oxygen (O2).
Chlorine atoms O2
Chlorine O3
CIO O2
Sunlight causes Cl2O2 to break down into O2 and free chlorine atoms. The chlorine atoms can begin the cycle again.
CIO
Cl2O2
Two CIO molecules react, forming chlorine peroxide (Cl2O2).
Sunlight

52. Scientists first described an “ozone hole” over Antarctica in 1985; it has increased in size as ozone depletion has increased

53. LE 54-28
October 1979
October 2000