1. CH 55 & 56 – Energy flow in Ecosystems

2. Overview: Ecosystems
An ecosystem consists of all the organisms living in a community, as well as the abiotic (non-living) factors with which they interact
Ecosystems range from a small, such as an aquarium, to a large, such as a lake or forest

3. Figure 55.2
Figure 55.2 A desert spring ecosystem. 3

4. Energy flows through ecosystems Matter cycles within them
Ecosystem dynamics involve two main processes: energy flow and chemical cycling
Energy flows through ecosystems
Matter cycles within them
Physical laws govern energy flow and chemical cycling in ecosystems
Conservation of Energy (first law of thermodynamics)
Energy enters from solar radiation and is lost as heat
Conservation of matter - Chemical elements are continually recycled within ecosystems
Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products

5. Energy, Mass, and Trophic Levels
Autotrophs build molecules themselves using photosynthesis or chemosynthesis as an energy source
Heterotrophs depend on the biosynthetic output of other organisms

6. Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) to secondary consumers (omnivores & carnivores) to
tertiary consumers (carnivores that feed on other carnivores)
Detritivores, or decomposers, are consumers that derive their energy from detritus
Prokaryotes and fungi are important detritivores
Decomposition connects all trophic levels

7. Microorganisms and other detritivores Secondary and tertiary consumers
Figure 55.4
Sun
Key
Chemical cycling
Energy flow
Heat
Primary producers
Primary consumers
Detritus
Figure 55.4 An overview of energy and nutrient dynamics in an ecosystem.
Microorganisms and other detritivores
Secondary and tertiary consumers
Arrows represent energy flow so they go from prey TO predator 7

8. Concept 55.3: Energy transfer between trophic levels is typically only 10% efficient
Net Primary Production (NPP) is the amount of new biomass added in a given time period
Only NPP is available to consumers
Ecosystems vary greatly in NPP and contribution to the total NPP on Earth
Limited by light, nutrients and other abiotic factors
Secondary is the amount of chemical energy in food converted to new biomass

9. Production Efficiency
When a caterpillar feeds on a leaf, only about one-sixth of the leaf’s energy is used for secondary production
An organism’s production efficiency is the fraction of energy stored in food that is not used for respiration

10. Plant material eaten by caterpillar
Figure 55.10
Plant material eaten by caterpillar
200 J
67 J
Figure Energy partitioning within a link of the food chain.
Cellular respiration
100 J
Feces
33 J
Not assimilated
Growth (new biomass; secondary production)
Assimilated 10

11. Interesting Energy production facts:
Birds and mammals have efficiencies in the range of 13% because of the high cost of endothermy
Fishes have production efficiencies of around 10%
Insects and microorganisms have efficiencies of 40% or more

12. Trophic Efficiency and Ecological Pyramids
Trophic efficiency is the percentage of production transferred from one trophic level to the next
It is usually about 10%, with a range of 5% to 20%
Trophic efficiency is multiplied over the length of a food chain

13. Approximately 0.1% of chemical energy fixed by photosynthesis reaches a tertiary consumer
A pyramid of net production represents the loss of energy at each level
Tertiary consumers
10 J
Secondary consumers
100 J
Primary consumers
1,000 J
Primary producers
10,000 J
1,000,000 J of sunlight

14. In a biomass pyramid, each level represents the dry mass of all organisms in each level
Most biomass pyramids show a sharp decrease at successively higher trophic levels

15. Role of Humans in Energy flow:
Dynamics of energy flow in ecosystems have important implications for the human population
Eating meat is a relatively inefficient in terms of utilizing photosynthetic production
Worldwide agriculture could feed many more people if humans ate only plant material
Fossil fuels used to
Produce foods

16. Biological and geochemical processes cycle nutrients and water in ecosystems
Life depends on recycling chemical elements
Nutrient cycles in ecosystems involve biotic and abiotic components and are often called biogeochemical cycles

17. Biogeochemical Cycles
Gaseous carbon, oxygen, sulfur, and nitrogen occur in the atmosphere and cycle globally
Less mobile elements include phosphorus, potassium, and calcium
These elements cycle locally in terrestrial systems but more broadly when dissolved in aquatic systems

18. Burning of fossil fuels Formation of sedimentary rock
Figure 55.13
Reservoir A
Organic materials available as nutrients
Reservoir B Organic materials unavailable as nutrients
Fossilization
Living organisms, detritus
Peat
Coal
Oil
Respiration, decomposition, excretion
Burning of fossil fuels
Assimilation, photosynthesis
Reservoir D Inorganic materials unavailable as nutrients
Reservoir C Inorganic materials available as nutrients
Figure A general model of nutrient cycling.
Weathering, erosion
Atmosphere
Minerals in rocks
Water
Formation of sedimentary rock
Soil 18

19. In studying cycling of water, carbon, nitrogen, and phosphorus, ecologists focus on four factors
Each chemical’s biological importance
Forms in which each chemical is available or used by organisms
Major reservoirs for each chemical
Key processes driving movement of each chemical through its cycle

20. The Carbon Cycle
Carbon-based organic molecules are essential to all organisms
Photosynthetic organisms convert CO2 to organic molecules that are used by heterotrophs
Carbon reservoirs include fossil fuels, soils and sediments, solutes in oceans, plant and animal biomass, the atmosphere, and sedimentary rocks
CO2 is taken up and released through photosynthesis and respiration
Volcanoes and the burning of fossil fuels also contribute CO2 to the atmosphere

21. Burning of fossil fuels and wood
Figure 55.14b
CO2 in atmosphere
Photosynthesis
Photo- synthesis
Cellular respiration
Burning of fossil fuels and wood
Phyto- plankton
Consumers
Figure Exploring: Water and Nutrient Cycling
Consumers
Decomposition 21

22. Figure 55.UN03
Figure 55.UN03 Appendix A: answer to Concept Check 55.4, question 1 22

23. The Nitrogen Cycle
Nitrogen is a component of amino acids, proteins, and nucleic acids
The main reservoir of nitrogen is the atmosphere (N2), though this nitrogen must be converted to NH4+ or NO3– for uptake by plants, via nitrogen fixation by bacteria

24. Decomposition and sedimentation
Figure 55.14c
N2 in atmosphere
Reactive N gases
Industrial fixation
Denitrification
N fertilizers
Fixation
Runoff
Dissolved organic N
NO3–
Terrestrial cycling N2
NH4+
NO3–
Aquatic cycling
Denitri- fication
Figure Exploring: Water and Nutrient Cycling
Decomposition and sedimentation
Assimilation
Decom- position
NO3–
Fixation in root nodules
Uptake of amino acids
Ammonification
Nitrification
NH3
NH4+
NO2– 24

25. The Phosphorus Cycle
Phosphorus is a major constituent of nucleic acids, phospholipids, and ATP
Phosphate (PO43–) is the most important inorganic form of phosphorus
The largest reservoirs are sedimentary rocks of marine origin, the oceans, and organisms
Phosphate binds with soil particles, and movement is often localized

26. Wind-blown dust Geologic uplift Weathering of rocks Runoff Consumption
Decomposition
Plant uptake of PO43–
Plankton
Dissolved PO43–
Uptake
Leaching
Figure Exploring: Water and Nutrient Cycling
Sedimentation
Decomposition 26