1. Ecosystems and Energy Structure

2. Ecosystems
An ecosystem comprises a community and its physical environment
Both biotic and abiotic components make up an ecosystem

3. Energy Flow and Chemical Cycling
One way to look at ecosystems is as systems that cycle life-sustaining chemicals and allow energy to flow between trophic levels
Trophic levels describe the levels of the food chain

5. Energy Flow
All energy used for life must originally come from autotrophs
Autotrophs obtain carbon from inorganic compounds
Photoautotrophs obtain energy from light
Chemoautotrophs obtain energy from inorganic compounds

6. Primary production
Autotrophs are responsible for primary production, the creation of sugars and other energy-rich compounds from inorganic matter

7. Heterotrophs Heterotrophs obtain carbon from organic sources
Chemoheterotrophs obtain energy from sources such as carbohydrates
Photoheterotrophs obtain energy from light

8. Consumers Heterotrophs act as consumers
Organisms that eat primary producers are primary consumers
Organisms that eat primary consumers are secondary consumers, and so on (tertiary, quaternary)

9. Decomposition
Decomposers (also called saprotrophs) include fungi, bacteria.
Primary difference between decomposers and consumers is that decomposers break down dead matter while consumers eat still living or recently deceased matter.
Similar to detritivore

10. Decomposers play a vital part in chemical recycling, allowing producers to continue producing.
Fungi (rot) and some bacteria are the only known organisms able to digest lignin, a primary component of wood.

12. Laws of Physics
The laws of physics still apply when dealing with biology
Of particular importance are the Laws of Thermodynamics and Conservation of Mass

13. Laws of Thermodynamics
1st – Energy cannot be created or destroyed, only transformed.
2nd – Energy transformations are never completely efficient.
Combined the two laws have a variety of implications for life. Life could not exist without the constant addition of energy, primarily from the Sun, to our ecosystems.

14. Law of Conservation of Mass
Mass cannot be created or destroyed, only converted into new forms
For ecosystems the implication of this law is that carbon, nitrogen, phosphorus, and other nutrients cannot be destroyed and will be continuously recycled

15. Primary Production
The sun provides approximately 1022 J (2.39 x 1021 cal) of energy to the Earth per day
However most of this energy is absorbed or deflected by Earth’s atmosphere, or land places without any photosynthetic organism around
In the end, approximately 1% actually makes it into chemical energy

16. Gross vs Net
Gross primary productivity (GPP) is the total about of light energy converted into chemical energy in a given time period
Net Primary Productivity (NPP) = GPP – R (energy used by primary producers for respiration)
NPP is the amount of energy that is available to consumers

17. Measuring energy production
Most commonly energy production is measured by biomass added to the ecosystem in a given time
Note that it’s the biomass added. The total biomass (called the standing crop) is not a useful indicator of energy production,

19. What limits productivity?
The limiting nutrient is the nutrient that most limits primary production
Put another way, the limiting nutrient is the nutrient that most increases production when added to an ecosystem

20. The limiting nutrient depends upon the ecosytem in question
In ocean ecosystems the limiting nutrients tend to be either light or nitrogen
Light limits productivity in deep water where little light penetrates
Near the ocean surface nutrients, such as nitrogen, limit productivity

21. Nitrogen is the most common limiting nutrient in open water
Addition of nitrogen to open water often results in eutrophication and algal blooms

22. Upwelling can cause natural increase in nutrients
Wind driven motion of water can cause nutrient rich upwellings

23. Freshwater tends to lack phosphorus

24. Terrestrial ecosystems
Water can be a very important limiting nutrient in terrestrial systems
Temperature also varies more on land than in water and can limit growth in colder months
Nitrogen and phosphorus may be local limiters on productivity.