Energy and Nutrient Relations

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

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 • 1977 - 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