1. ECOSYSTEM ECOLOGY
: Energy Flow, food chains

2. Ecosystem:
The organisms in a particular area and the physical environment with which they interact.
All the biotic and abiotic factors in a community.
(Abiotic factors: energy, water, carbon,
nitrogen, phosphorous)

3. An ecosystem has abiotic and biotic components:
ABIOTIC components:
Solar energy provides practically all the energy for ecosystems.
Inorganic substances, e.g., sulfur, boron, tend to cycle through ecosystems.
Organic compounds, such as proteins, carbohydrates, lipids, and other complex molecules, form a link between biotic and abiotic components of the system.

4. BIOTIC components:
The biotic components of an ecosystem can be classified according to their mode of energy acquisition.
In this type of classification, there are:
Autotrophs
and
Heterotrophs

5. Autotrophs Autotrophs (=self-nourishing) are called primary producers.
Photoautotrophs fix energy from the sun and store it in complex organic compounds
(= green plants, algae, some bacteria)
light
complex
organic
compounds
photoautotrophs
simple
inorganic
compounds

6. (typically sulfur and ammonia compounds)
Chemoautotrophs (chemosynthesizers) are bacteria
that oxidize reduced inorganic substances
(typically sulfur and ammonia compounds)
and produce complex organic compounds.
oxygen
reduced
inorganic
compounds
complex
organic
compounds
chemoautotrophs

7. Chemosynthesis near hydrothermal vents

8. Other chemoautotrophs:
Nitrifying bacteria in the soil under our feet!

9. Heterotrophs
Heterotrophs (=other-nourishing) cannot produce their own food directly from sunlight+ inorganic compounds. They require energy previously stored in complex molecules.
heat
complex
organic
compounds
simple
inorganic
compounds
heterotrophs
(this may include several steps, with
several different types of organisms)

10. Heterotrophs can be grouped as:
consumers
decomposers

11. Consumers feed on organisms or particulate organic matter.
Decomposers utilize complex compounds in dead protoplasm.
Bacteria and fungi are the main groups of decomposers.
Bacteria are the main feeders on animal material.
Fungi feed primarily on plants, although bacteria also are important in some plant decomposition processes.

13. Microorganisms and other detritivores Secondary consumers
Fig. 55-4
Tertiary consumers
Microorganisms
and other
detritivores
Secondary
consumers
Primary consumers
Detritus
Primary producers
Figure 55.4 An overview of energy and nutrient dynamics in an ecosystem
Heat
Key
Chemical cycling
Sun
Energy flow

14. Energy Flow through Ecosystems
Energy flows through ecosystems as organisms capture and store energy, then transfer it to organisms that eat them.
These organisms are grouped into trophic levels...

15. Trophic Levels: Route of energy flow food web - pyramid of numbers
food chain
food web
- pyramid of numbers

16. Pyramid of Numbers

17. Question:
“Why are big fierce animals rare?”
Charles Elton, 1927

18. Answer:
Because of the way energy flows
through communities...

19. Ecosystem Energy Budgets:
Primary Productivity (PP)
Secondary Productivity (SP1, SP2)

20. Primary Productivity (PP)
Rate at which energy or biomass is produced
per unit area by plants (primary producers)
Photosynthesis powers primary productivity.
The annual productivity of an area is determined primarily by sunlight, temperature, and moisture.

21. Distribution of Primary Production Worldwide
Figure 56.5
Figure 56.5

22. Positive Correlation Between Productivity and Sunlight

23. Positive Correlation Between Productivity and...
Temperature
Precipitation

24. Net primary production (g/m2·yr)
Fig. 55-8
3,000
Tropical forest
2,000
Net primary production (g/m2·yr)
Temperate forest
1,000
Mountain coniferous forest
Figure 55.8 Relationship between net primary production and actual evapotranspiration in six terrestrial ecosystems
Desert
shrubland
Temperate grassland
Arctic tundra
500
1,000
1,500
Actual evapotranspiration (mm H2O/yr)

25. Secondary Productivity (SP1, SP2…)
rate of production of new biomass from PP
by heterotrophic organisms
(primary and secondary consumers)
positively correlated with rainfall...

27. Tertiary consumers 10 J Secondary consumers 100 J Primary 1,000 J
Fig
Tertiary
consumers
10 J
Secondary
consumers
100 J
Primary
consumers
1,000 J
Figure An idealized pyramid of net production
Primary
producers
10,000 J
1,000,000 J of sunlight

28. Where does all the energy go???

29. Plant material eaten by caterpillar 200 J 67 J Cellular respiration
Fig. 55-9
Plant material
eaten by caterpillar
200 J
Figure 55.9 Energy partitioning within a link of the food chain
67 J
Cellular
respiration
100 J
Feces
33 J
Growth (new biomass)

30. Ecological Efficiency:
Percent of energy transferred from
one trophic level to the next.

31. Three categories of transfer efficiency are
required to predict energy flow from PP to
SP1 to SP2...
consumption efficiency
assimilation efficiency
production efficiency

32. 1) consumption efficiency (CE)
% of total productivity at one trophic level
that is consumed by the next highest level
(remainder not eaten)

33. Green World Hypothesis
Figure A green ecosystem
Plants have many defenses against herbivores

34. 2) assimilation efficiency (AE)
% of ingested food energy that is assimilated
(i.e. digested), and thus potentially available
for growth, reproduction
(remainder lost as feces)

35. Elephant dung

36. 3) production efficiency (PE)
% of assimilated energy that is incorporated
into new biomass (growth, reproduction)
(remainder lost as respiratory heat)

37. Implications? SP1 is the % of PP that is incorporated at the
next highest trophic level. (Ditto for SP2…)
This is NEVER 100%.
Thus, energy loss at each trophic level limits the
length of a food chain...

38. And that is why big fierce
animals are rare!

40. Biogeochemical Cycles
Nutrients exist in pools of chemical elements
FOUR main reservoirs where these nutrients exist are:
1) Atmosphere - carbon in carbon dioxide, nitrogen in atmospheric nitrogen
2) Lithosphere - the rocks - phosphates, calcium in calcium carbonate, potassium in feldspar
3) Hydrosphere - the water of oceans, lakes, streams and soil - nitrogen in dissolved nitrate, carbon in carbonic acid

41. Atmosphere
Living
Organisms +
Detritus
Lithosphere Hydrosphere

42. 4) Living Organisms and Nutrient Cycles
Living organisms are a reservoir in which carbon exists in carbohydrates (mainly cellulose) and fats, nitrogen in protein, and phosphorus in ATP

43. In studying cycling of water, carbon, nitrogen, and other chemicals, ecologists focus on four factors:
Biological importance of each chemical
Major reservoirs for each chemical
Forms in which each chemical is available or used by organisms
Key processes driving movement of each chemical through its cycle

44. The Water Cycle Water is essential to all organisms
97% of the biosphere’s water is contained in the oceans, 2% is in glaciers and polar ice caps, and 1% is in lakes, rivers, and groundwater
Figure Nutrient cycles
Water moves by the processes of evaporation, transpiration, condensation, precipitation, and movement through surface and groundwater

45. The Carbon Cycle
Carbon-based organic molecules are essential to all organisms
Carbon reservoirs include fossil fuels, soils and sediments, solutes in oceans, plant and animal biomass, and the atmosphere
Figure Nutrient cycles
CO2 is taken up via photosynthesis and released via respiration
Volcanoes and the burning of fossil fuels contribute CO2 to the atmosphere

46. CO2 concentration (ppm) Average global temperature (ºC)
Fig
14.9
390
14.8
380
14.7
14.6
370
Temperature
14.5
360
14.4
350
14.3
CO2 concentration (ppm)
Average global temperature (ºC)
14.2
340
14.1
CO2
330
14.0
Figure Increase in atmospheric carbon dioxide concentration at Mauna Loa, Hawaii, and average global temperatures
13.9
320
13.8
310
13.7
300
13.6
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Year

47. … and Global Temperature

48. The Nitrogen Cycle
Nitrogen is a component of amino acids, proteins, and nucleic acids
The main reservoir of nitrogen is the atmosphere (N2)
N2 is converted to NH3 via nitrogen-fixing bacteria
Figure Nutrient cycles
Organic nitrogen is decomposed to NH4+ by ammonification, and NH4+ is decomposed to NO3– by nitrifying bacteria; NH4+ and NO3– assimilated by plants
Denitrifying bacteria convert NO3– back to N2

49. How Bears Feed Salmon to the Forest
The run of salmon leads to a major flow of nutrients into estuaries and coastal watersheds

50. Bears catch salmon in river and consume them in forest; on average, half the carcass is not eaten.
Bears’ fat tissue is virtually nitrogen-free, so most of nitrogen in salmon protein is excreted as urine and feces.

51. Nitrogen 14 from atmosphere
Nitrogen 15 from salmon
Measurements of nitrogen isotope ratios in tree rings shows that nitrogen from salmon is incorporated into trees and enhances their growth