1. Food Webs and Ecosystem Ecology
CHAPTER 20 CONTINUED

2. Trophic Structure Feeding relationships among organisms
Determines passages of energy and nutrients from producers (autotrophs) to consumers (heterotrophs)
Sequence of this food transfer is called the food chain

3. What is missing from this food chain?
Omnivores,
Scavengers,
Detritivores,
Decomposers

4. Scavengers
Secondary
Secondary
Decomposers
Primary
Primary
Detritivore
Producer
Primary

5. Food Webs

6. Biomagnification
The increasing concentration of a substance, such as a toxic chemical, in the tissues of organisms at successively higher levels in a food chain.

7. Birds of Prey and DDT

8. What happened? DDT Long-lived: half life of 15 years
Mobile: transported in water, soil, organisms
Soluble in fats: builds up in fatty tissues

9. Eggshell thinning Birds were crushing their own eggs
Populations dropped

10. Why do we care? Still happening today Know your area!
Can’t regulate what you don’t know
New chemicals being manufactured
Know your area!
cfpub.epa.gov

11. Ecosystem Ecology Ecosystems: community + abiotic components
Energy flow – the passage of energy through the components of the ecosystem
Chemical cycling – the use and reuse of chemical elements within an ecosystem

12. Transfer of materials through all abiotic and biotic components
Constant input of E from sun

13. Ecological Pyramid
Shows cumulative loss of E with each transfer in the food chain
80–95% of the energy at one trophic level never reaches the next
This explains why top-level consumers such as lions and hawks require so much geographic territory. It takes a lot of vegetation to support trophic levels. Most food chains are limited to three to five levels.

14. Biogeochemical Cycling
Components
Biotic (living)
Abiotic (non living) from an abiotic reservoir, where chemicals are stored outside of living organisms

15. Three types of abiotic reservoirs

17. The Carbon Cycle
Photosynthesis removes CO2 from atmosphere, incorporating it into organic molecules
Organic molecules are passed along food chain via consumers
Cellular respiration returns CO2 to atmosphere
4. Decomposers break down carbon in detritus eventually releasing it into the atmosphere
Burning wood and fuels releases carbon back into the atmosphere

19. The Phosphorus Cycle - P as PO4-3
Breakdown of rock adds inorganic phosphate to the soil
Plants absorb dissolved phosphate from soil, build phosphorus atoms into organic compounds
Consumers obtain organic phosphorus by eating plants
4. Phosphates returned to soil via decomposition
Phosphates drain into water where they settle
Geologic processes lift rock and expose it to weathering

21. The Nitrogen Cycle
Nitrogen fixation – conversion of gaseous N2 to ammonia (NH3) and then to ammonium (NH4+), which can be used by plants
This process is essential because atmospheric nitrogen is not readily usable

22. The Nitrogen Cycle
Some bacteria live on roots, a mutualistic relationship that supplies its host with direct source of usable nitrogen
Free living bacteria fix nitrogen, resulting in NH4+
Some fixed N is absorbed by plants
Nitrifying bacteria convert NH4+ to nitrate (NO3- )

23. The Nitrogen Cycle Nitrate is also readily absorbed by plants
Animals form N containing waste products
Decomposition of organic compounds releases ammonium into the soil (refilling reservoir)
Denitrifying bacteria strip nitrates of their oxygen atom, releasing N2 back into the atmosphere

24. Helpful review videos Carbon and Nitrogen cycles
Phosphorus cycle