1. 1 Energy and Nutrient Relations Chapter 6

2. 2 Energy Sources Organisms can be classified by trophic levels.  Autotrophs use inorganic sources of carbon and energy.  Photosynthetic: Use CO 2 as carbon source, and sunlight as energy.  Chemosynthetic: Use inorganic molecules as source of carbon and energy.  Heterotrophs use organic molecules as sources of carbon and energy.

3. 3 Oxygenic Photosynthesis (There are anoxygenic photosynthetic bacteria!)

4. 4 Photosynthetic Pathways C 3 Photosynthesis  Used by most plants and algae.  CO 2 + ribulose bisphosphate (RuBP; 5 carbon sugar) = 2x phosphoglyceric acid (3PGA; 3 carbon acid)  To fix carbon, plants must open stomata to let in CO 2.  Water gradient may allow water to escape. http://ntri.tamuk.edu/bio/photo/

5. 5 C 3 Plant Photorespiration: “Too much of a good thing.”

6. 6 Photosynthetic Pathways C 4 Photosynthesis  First CO 2 fixed to phosphoenolpyruvate (3 carbons) to form 4 carbon acid.  Reduces internal CO 2 concentrations.  Increases rate of CO 2 diffusion inward.  Need fewer stomata open.  Conserves water

7. 7 C 4 Photosynthesis e.g. grasses, corn, sugar cane

8. 8 Photosynthetic Pathways CAM Photosynthesis  (Crassulacean Acid Metabolism)  Limited to succulent plants in arid and semi-arid environments.  Carbon fixation takes place at night.  Reduces water loss.  Low rates of photosynthesis.  Extremely high rates of water use efficiency.

9. 9 CAM Photosynthesis

10. 10 Energy Limitation Liebig’s Law of the Minimum:  The resource in least supply relative to an organism’s needs will control growth.  It is the growth limiting resource. Limits on the potential rate of energy intake by plants (hence growth) have been demonstrated by studying response of photosynthetic rate (P) to photon flux density (light intensity or irradiance; I). The P versus I curve.

11. 11 P versus I curve

12. 12 Photon Flux and Photosynthetic Response Curves Rate of photosynthesis increases linearly with photon flux density at low light intensities, rises more slowly with intermediate light intensities, and tends to level off at high light intensities.  Response curves for different species may:  level off at different maximum P.  respond differently at lower levels of I.

13. 13 http://www.marietta.edu/~spilatrs/biol103/photolab/sunexpl.gif Which P vs I curve would favor a sunny as opposed to shady habitat?

14. 14 Using Organic Molecules for Energy and Growth Three Feeding Methods of Heterotrophs:  Herbivores: Feed on plants.  Carnivores: Feed on animal flesh.  Detritivores: Feed on non-living organic matter that becomes colonized by microbes (detritus)

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16. 16 Herbivores Substantial nutritional chemistry problems.  Low N:C ratio compared to plants.  Carbon mostly as cellulose & NO cellulases of their own. Must overcome plant physical and chemical defenses.  Physical: structures, woody parts, silica  Chemical: toxins, inhibitors of digestion.

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18. 18 Detritivores Consume food rich in carbon and energy, but very poor in nitrogen.  Dead leaves may have half nitrogen content of living leaves. Fresh detritus may still have considerable chemical defenses present. Microbial colonization of plant derived detritus increases nutritional value.

19. 19 Carnivores Consume nutritionally-rich prey. Carnivore C:N is equivalent to prey C:N.

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21. 21 Energy Limitation Limits on potential rate of energy intake by animals (hence growth) have been demonstrated by studying relationships between feeding rate and food availability. Holling described (3) basic functional responses to food density:  1. Feeding rate increases linearly as food density increases - levels off at maximum.  Consumers require little or no search and handling time.

22. 22  2. Feeding rate rises in proportion to food density.  Feeding rate partially limited by search/handling time.  3. Feeding rate increases most rapidly at intermediate densities.  S-shaped curve.

23. 23 http://www.tnstate.edu/ganter/Functional.Response.JPG

24. 24 06_22.jpg Which type of response?

25. 25 06_23.jpg

26. 26 Optimal Foraging Theory All other things being equal, more abundant prey yields larger energy return. What about different prey types and sizes as well as densities (real world complexity)? Must consider energy expended during:  Search for prey  Handling time Consumers choose prey that maximize rate of energy intake per unit of foraging energy expenditure.

27. 27 Optimal Foraging in Bluegill Sunfish

28. 28 Optimal Foraging By Plants Limited supplies of energy for allocation to leaves, stems and roots. Bloom suggested plants adjust allocation in such a manner that all resources are equally limited.  Appear to allocate growth in a manner that increases rate of acquisition of resources in shortest supply.  E.g. shading of some plants causes increased stem growth (spindly looking).

29. 29 06_25.jpg Which stand of birch trees grows on infertile (nutrient poor) soil?

30. 30 Using Reduced Inorganic Molecules 1977 - Organisms found living on sea floor.  Near nutrients discharged from volcanic activity through oceanic rift.  Autotrophs depend on chemosynthetic bacteria that oxidize reduced inorganics.  Free-living forms.  Living within tissue of invertebrates.