1. How do ecosystems work? Part 1!
Chapter 41

2. Overview: Pathways of energy and nutrients
Materials cycle
Note complete cycles for purple arrows.
Energy flows one way!
Energy (red) arrows in direction of energy flow
Note heat loss at each step.

3. Energy flow through communities
Energy enters communities through photosynthesis
Carbon dioxide, water and sun’s energy used directly for photosynthesis
Inorganic mineral nutrients needed to build other molecules (proteins, lipids, carbohydrates)

4. Energy flow through communities
Trophic levels
Autotrophs
Which Domains/Kingdoms include at least some autotrophs?
Heterotrophs or consumers
Primary consumers = herbivores: consume primary producers
Secondary consumers and higher = carnivores: consume other consumers…
Detritus feeders and decomposers
Consume dead organic matter
Convert organic molecules back to inorganic ones so primary producers can use them (bacteria mostly do this step.)
What if there were no decomposers?

5. Energy flow through communities
Terrestrial food chain and trophic levels
What is missing here?

6. Energy flow through communities
Marine food chain and trophic levels
What is missing here?

7. Energy flow through communities
Trophic levels (cont.)
Many consumers cannot be strictly categorized
Omnivores: Feed as both herbivores and carnivores
Many carnivores feed at multiple levels
Example: Leopard seal in Antarctic marine food web

8. Antarctic marine food web (simplified)

9. Energy flow through communities
Energy transfer is inefficient
On average, only 10% of energy gets transferred from one trophic level to the next (red arrows)
Most of the rest is lost as heat (yellow arrows)
Some converted to unusable form (i.e. indigestible for the consumer, such as cellulose for us.)

10. Energy pyramid shows inefficiency of energy transfer

11. Biomagnification: Unlike energy, toxins become concentrated up the food web
Top predators are most affected by toxins
At the peak of DDT use, predatory birds contained DDT concentrations up to 1 million times the concentration in water.

12. Cycling of nutrients: Carbon
CO2 sinks
Primary producers (via photosynthesis)
Terrestrial
Marine (>50%)
Ocean water
Ocean sediments
Carbonification
Fossil fuels formed from phytoplankton (oil and gas) and plants (coal, peat)

13. Cycling of nutrients: Carbon
CO2 sources
Respiration: All organisms
Decomposition
Fires
Natural
For agriculture
Burning of fossil fuels*
Use 1 million times as fast as it is formed!

14. In sum, decrease of CO2 sinks and increase of CO2 sources
Increase in global CO2 correlates with global warming

15. Highest temperature increases are along the Antarctic Peninsula