1. Energy and Nutrient Relations
Chapter 6

2. Outline
Energy Sources
Solar-Powered Biosphere
Photosynthetic Pathways
Using Organic Molecules
Chemical Composition and Nutrient Requirements
Using Inorganic Molecules
Energy Limitation
Food Density and Animal Functional Response
Optimal Foraging Theory

3. Energy Sources
Organisms can be classified by trophic levels.
Autotrophs use inorganic sources of carbon and energy.
Photosynthetic: Use CO2 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.

4. Solar - Powered Biosphere
Light propagates through space as a wave.
Photon: Particle of light bears energy.
Infrared (IR) Long-wavelength, low energy.
Interacts with matter, increasing motion.
Ultraviolet (UV) Short wavelength, high energy.
Can destroy biological machinery.
Photosynthetically Active Radiation (PAR)
Between two extremes.

5. Photosynthetically Active Radiation

6. Solar - Powered Biosphere
PAR
Quantified as photon flux density.
Number of photons striking square meter surface each second.
Chlorophyll absorbs light as photons.
Landscapes, water, and organisms can all change the amount and quality of light reaching an area.

7. Photosynthetic Pathways
C3 Photosynthesis
Used by most plants and algae.
CO2 + ribulose bisphosphate (5 carbon sugar) = phosphoglyceric acid (3 carbon acid)
To fix carbon, plants must open stomata to let in CO2 .
Water gradient may allow water to escape.

8. C3 Photosynthesis

9. Photosynthetic Pathways
C4 Photosynthesis
Reduce internal CO2 concentrations.
Increases rate of CO2 diffusion inward.
Need fewer stomata open.
Conserving water
Acids produced during carbon fixation diffuse to specialized cells surrounding bundle sheath.

10. C4 Photosynthesis

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

12. CAM Photosynthesis

13. Using Organic Molecules
Three Feeding Methods of Heterotrophs:
Herbivores: Feed on plants.
Carnivores: Feed on animal flesh.
Detritivores: Feed on non-living organic matter.

14. Chemical Composition and Nutrient Requirements
Five elements make up 93-97% of biomass of plants, animals, fungi and bacteria:
Carbon
Oxygen
Hydrogen
Nitrogen
Phosphorus

15. Essential Plant Nutrients
Potassium
Calcium
Magnesium
Sulfur
Chlorine
Iron
Manganese
Boron
Zinc
Copper
Molybdenum

16. Herbivores
Substantial nutritional chemistry problems.
Low nitrogen concentrations.
Must overcome plant physical and chemical defenses.
Physical
Cellulose; lignin; silica
Chemical
Toxins
Digestion Reducing Compounds

17. Detritivores
Consume food rich in carbon and energy, but poor in nitrogen.
Dead leaves may have half nitrogen content of living leaves.
Fresh detritus may still have considerable chemical defenses present.

18. Carnivores
Consume nutritionally-rich prey.
Cannot choose prey at will.
Prey Defenses:
Aposomatic Coloring - Warning colors.
Mullerian mimicry: Comimicry among several species of noxious organisms.
Batesian mimicry: Harmless species mimic noxious species.

19. Carnivores
Predators are usually selection agents for refined prey defense.
Usually eliminate more conspicuous members of a population (less adaptive).
Must catch and subdue prey - size selection.
Predator and prey species are engaged in a co-evolutionary race.

20. Using Inorganic Molecules
Organisms found living on sea floor.
Near nutrients discharged from volcanic activity through oceanic rift.
Autotrophs depend on chemosynthetic bacteria.
Free-living forms.
Living within tissue of invertebrates.

21. Energy Limitation
Limits on potential rate of energy intake by animals have been demonstrated by studying relationship between feeding rate and food availability.
Limits on potential rate of energy intake by plants have been demonstrated by studying response of photosynthetic rate to photon flux density.

22. 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 generally level off at different maximum photosynthesis rates.

24. Food Density and Animal Functional Response
Holling described (3) basic functional responses:
1. Feeding rate increases linearly as food density increases - levels off at maximum.
Consumers require little or no search and handling time.
2. Feeding rate rises in proportion to food density.
Feeding rate partially limited by search/handling time.

25. Food Density and Animal Functional Response
3. Feeding rate increases most rapidly at intermediate densities
(S-shaped).

26. Optimal Foraging Theory
Assures if energy supplies are limited, organisms cannot simultaneously maximize all life functions.
Must compromise between competing demands for resources.
Principle of Allocation

27. Optimal Foraging Theory
All other things being equal,more abundant prey yields larger energy return. Must consider energy expended during:
Search for prey
Handling time
Tend to maximize rate of energy intake.

28. Optimal Foraging in Bluegill Sunfish

29. 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.

30. Review
Energy Sources
Solar-Powered Biosphere
Photosynthetic Pathways
Using Organic Molecules
Chemical Composition and Nutrient Requirements
Using Inorganic Molecules
Energy Limitation
Food Density and Animal Functional Response
Optimal Foraging Theory