1. Ecosystems (a PIB Bio Review)
An ecosystem consists of all the organisms living in a community as well as all the abiotic factors with which they interact.

2. Ecosystems - Abiotic Factors Overview
How are the abiotic factors different for each of the ecosystems on the right?

3. Gross and Net Primary Production
Total primary production in an ecosystem is known as that ecosystem’s gross primary production (GPP).
But, since not all of this production is stored as organic material in the growing plants, only net primary production (NPP) is available to consumers.
NPP = GPP - Respiration
An Echinus sp. in a Laminaria sp. forest

4. Ecosystems - Biotic Factors Overview
Net Primary Production is a way to compare the biotic potential of ecosystems (Kg Carbon/m2 ∙ yr)

5. Ecosystems - Biotic Factors Overview
What proportion of global NPP do terrestrial ecosystems contribute? Marine ecosystems?
What role could open ocean and tropical rain forests play in mitigating global warming? How?
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)

6. Ecosystem Cycles and Flows
Regardless of an ecosystem’s size, its dynamics involve two main processes: energy flow and chemical cycling.

7. Biogeochemical Cycles
The water cycle and the carbon cycle:
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

8. Biogeochemical Cycles
The nitrogen cycle and the phosphorous cycle
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
Which of the four biogeochemical cycles only cycles locally?

9. The Nutrient Cycle is completed by Decomposition
Decomposition connects all trophic levels in an ecosystem and detritivores, mainly bacteria and fungi (saprotrophs), recycle essential chemical elements by decomposing organic material and returning elements to inorganic reservoirs.

10. The Non-Anthropogenic Nitrogen Cycle
What processes are occurring in the soil that result in forms of nitrogen that can be assimilated by plants?

11. The Non-Anthropogenic Nitrogen Cycle
Complete this figure:

12. The Non-Anthropogenic Nitrogen Cycle
Complete this figure:
Nitrogen fixation
Denitrification
Ammonification
Assimilation
Nitrification
Decomposition!

13. The Nutrient Cycle is completed by Decomposition!
Nitrogen-fixing bacteria form symbiotic associations with the roots of legumes like clover and lupine. The plants supplies simple carbon compounds to the bacteria, and the bacteria convert nitrogen (N2) from air into a form the plant host can use.
Nitrifying bacteria are CHEMOAUTOTROPHS and oxidize ammonium (NH4+) to nitrite (NO2-) then to nitrate (NO3-) – a preferred form of nitrogen for grasses and most row crops. Nitrifying bacteria are suppressed in forest soils, so that most of the nitrogen remains as ammonium. Forest soils don’t work for crop production.
Denitrifying bacteria convert nitrate to nitrogen (N2) or nitrous oxide (N2O) gas. Denitrifiers are anaerobic, meaning they are active where oxygen is absent, such as in saturated soils.
Actinomycetes are Fungi SAPROTROPHS responsible for the characteristically “earthy” smell of freshly turned, healthy soil. Actinomycetes decompose a wide array of substrates, but are especially important in degrading recalcitrant (hard-to-decompose) compounds, such as chitin and cellulose, and are active at high pH levels.

14. Vegetation and Nutrient Cycling: The Hubbard Brook Experimental Forest
What evidence do we have that nutrient cycling is strongly regulated by vegetation?
The Hubbard Brook Experimental Forest has been used to study nutrient cycling in a forest ecosystem since 1963.

15. Vegetation and Nutrient Cycling
What do you see?
What does it mean?

16. Vegetation and Nutrient Cycling
What part of the Nitrogen Cycle was affected?

17. Nutrient Inputs and Primary Production in Ecosystems: the Critical Load Hypothesis
Both light and nutrients are important in controlling primary production, but nutrients have recently become an important area in ecosystem research, especially because of anthropogenic inputs—exceeding an ecosystems critical load of nutrients—and eutrophication.

18. Nutrient Inputs and Primary Production in Ecosystems: the Critical Load Hypothesis
On 13 October 1908, Fritz Haber filed his patent on the “synthesis of ammonia from its elements” for which he was later awarded the 1918 Nobel Prize in Chemistry. A hundred years on we live in a world transformed by and highly dependent upon Haber–Bosch nitrogen.

19. Nutrient Inputs and Primary Production in Ecosystems: the Critical Load Hypothesis
Erisman, J. W., Sutton, M. A., Galloway, J., Klimont, Z., & Winiwarter, W. (2008). How a century of ammonia synthesis changed the world. Nature Geoscience, 1(10),
“In 2005, approximately 100 Tg N from the Haber–Bosch
process was used in global agriculture, whereas only 17 Tg N was consumed by humans in crop, dairy and meat products.”
Approximately 80% of the Nitrogen in our bodies was fixed by the Haber-Bosch process.
What do you see in the graph?
What does it mean?

20. Nutrient Inputs and Primary Production in Ecosystems: the Critical Load Hypothesis
Anthropogenic inputs of N and P and Aquatic Eutrophication are responsible for the Gulf of Mexico Dead Zone

21. Dead Zones Around the World
Nutrient Inputs and Primary Production in Ecosystems: the Critical Load Hypothesis
Dead Zones Around the World

22. Acid Precipitation and the Terrestrial Critical Load
Combustion of fossil fuels is the main cause of acid precipitation: inputs of hydrogen ions (H2CO3, H2SO4, HNO3) beyond the critical load that an ecosystem can naturally buffer against.
What is the explanation for the soil pH pattern below?

23. Acid Precipitation
What is the explanation for the soil pH pattern below?
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

24. The Threat of Acid Precipitation
Acid precipitation and ecosystem damage in SE Canada. 1 2 3 4 5 6 7 8 9 10 11 12 13 14
More acidic
Acid rain
Normal rain
More basic

25. Atmospheric CO2 Critical Load

26. Food Chain Critical Load and Bioaccumulation
In biological magnification (accumulation), toxins concentrate at higher trophic levels because at these levels biomass tends to be lower.
Concentration of PCBs
Herring
gull eggs
124 ppm
Zooplankton
0.123 ppm
Phytoplankton
0.025 ppm
Lake trout ppm
Smelt
1.04 ppm
Polychlorinated biphenyls (PCBs) were used to enhance the fire resistant properties of PVC wire coatings, among other things.
Liver failure and impaired reproduction in animals.
What is the relationship between trophic level biomass and chemical concentration?

27. Trophic Level Energy Transfer Efficiency
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. This energy transfer between trophic levels is usually less than 20% efficient, and generally around 10% efficient.

28. Pyramids of Production
Why doesn’t this energy pyramid have smooth sides?
The 10% rule
Energy production is represented by:
KJ/m2 • yr

29. Pyramids of Biomass
One important ecological consequence of low trophic efficiencies can be represented in a biomass (dry weight) pyramid.
Why do most biomass pyramids show a sharp decrease at successively higher trophic levels?

30. Most biomass (especially plant biomass) is inedible.
Pyramids of Biomass
One important ecological consequence of low trophic efficiencies can be represented in a biomass (dry weight) pyramid.
Why do most biomass pyramids show a sharp decrease at successively higher trophic levels?
Most biomass (especially plant biomass) is inedible.

31. The Green World Hypothesis
Most terrestrial ecosystems have large standing crops despite the large numbers of herbivores.
According to The Green World Hypothesis, (e.g. Hairston et al. 1960) why do terrestrial herbivores consume relatively little plant biomass?

32. The Green World Hypothesis
The Green World Hypothesis of today 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.
Most plant biomass is inedible.

33. Why is it difficult to classify organisms into trophic levels?
Soil Food Web
Trophic Ecology
Why is it difficult to classify organisms into trophic levels?

34. Why is it difficult to classify organisms into trophic levels?
Marine Food Web
Trophic Ecology
Why is it difficult to classify organisms into trophic levels?

35. Why is it difficult to classify organisms into trophic levels?
Terrestrial Food Web
Trophic Ecology
Why is it difficult to classify organisms into trophic levels?

36. Humans and Trophic Ecology
Worldwide, why is it true that agriculture could successfully feed many more people if humans all fed more efficiently, eating mostly or only plant material?
Trophic level
Secondary
consumers
Primary
producers

37. Critical Load: Climate Stress and Local Food Webs