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.

4Fig. 6.2

5

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 (visible light). Wave length between about 400 and 700 nm

6

Solar - Powered Biosphere

• PAR Quantified as photon flux density.

Number of photons striking square meter surface each second.

Expressed in µmole, where 1 mole is Avogadro's number of photons 6.023X10²³.

• Chlorophyll absorbs light as photons. Landscapes, water, and organisms can all

change the amount and quality of light reaching an area.

7

Photosynthetically Active Radiation

8

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.

9

C3 Photosynthesis

10

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.

11

C4 Photosynthesis

12

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.

13

CAM Photosynthesis

14

Using Organic Molecules

• Three Feeding Methods of Heterotrophs: Herbivores: Feed on plants. Carnivores: Feed on animal flesh. Detritivores: Feed on non-living organic

matter.

15

Chemical Composition and Nutrient Requirements

• Five elements make up 93-97% of biomass of plants, animals, fungi and bacteria: Carbon Oxygen Hydrogen Nitrogen Phosphorus

16

Fig. 6.7

17

Essential Plant Nutrients

• Potassium• Calcium• Magnesium• Sulfur• Chlorine• Iron

• Manganese• Boron• Zinc• Copper• Molybdenum

18Fig. 6.9

19Fig. 6.10

20

Herbivores

• Substantial nutritional chemistry problems. Low nitrogen concentrations.

• Must overcome plant physical and chemical defenses. Physical

Cellulose; lignin; silica Chemical

Toxins Digestion Reducing Compounds

21Fig. 6.11

22

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.

23Fig. 6.12

24

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.

25Fig. 6.13

26

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. (mountain lion Puma concolor)• Predator and prey species are engaged in a

co-evolutionary race.

27Fig. 6.14

28Fig. 6.15

29

Fig. 6.16

30

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.

31

Fig. 6.17

32

Fig. 6.18

33

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.

34

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.

35

36Fig. 6.20

37

Food Density and Animal Functional Response

• Functional response: when amount of food available to animal is increased, its rate of feeding will increase and then levels off.

• 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.

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Food Density and Animal Functional Response

• 3. Feeding rate increases most rapidly at intermediate densities (S-shaped).

39Fig. 6.22

40Fig. 6.23

41

Optimal Foraging Theory

• Optimal forging theory: Natural selections will favor individuals within population that are more effective at acquiring energy.

• Assures if energy supplies are limited, organisms cannot simultaneously maximize all life functions. Must compromise between competing

demands for resources. Principle of Allocation

42

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.• Optimization: The animal will adjust its diet

(preys) until the rate of energy intake reaches a maximum.

• Need to know the formula and application

43

Model for Prey Choice

44

Optimal Foraging in Bluegill Sunfish

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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.

46Fig. 6.25

47Fig. 6.26

48

Application and Tools

• Bioremediation-using the tropic diversity of bacteria to solve environmental problems.

• Sewage treatment-using bacteria for degrading organic

matters at different temperatures .

• Cyanide and Nitrates in mine spoil-using soil bacteria in breaking down CN, and Nitrates.

49Fig. 6.27

50Fig. 6.28