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Energy and Nutrient Relations

Chapter 7

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Outline• Photosynthetic Autotrophs• Solar-Powered Biosphere• Photosynthetic Pathways• Using Organic Molecules• Chemical Composition and Nutrient

Requirements• Heterotrophs• Energy Limitation• Food Density and Animal Functional

Response• Optimal Foraging Theory

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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.

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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.

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Photosynthetically Active Radiation

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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.

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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.

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C3 Photosynthesis

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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.

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C4 Photosynthesis

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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.

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CAM Photosynthesis

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Chemosynthetic Autotrophs

• 1977 - Organisms found living on sea floor. Near nutrients discharged from volcanic

activity through oceanic rift. Chemosynthetic bacteria are the

autotrophs that the communities depend on.

Free-living forms. Living within tissue of invertebrates.

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Heterotrophs

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

matter.

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Chemical Composition and Nutrient Requirements

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

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Essential Plant Nutrients

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

• Manganese• Boron• Zinc• Copper• Molybdenum

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Herbivores

• Substantial nutritional chemistry problems. Low nitrogen concentrations.

• Must overcome plant physical and chemical defenses. Physical

Cellulose; lignin; silica Chemical

Toxins Digestion Reducing Compounds

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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.

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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.

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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.

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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.

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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.

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Photon Flux and Photosynthetic Response Curves

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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.

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Food Density and Animal Functional Response

3. Feeding rate increases most rapidly at intermediate densities

(S-shaped)

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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

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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.

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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.

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Review• Energy Sources• Solar-Powered Biosphere• Photosynthetic Pathways• Using Organic Molecules• Chemical Composition and Nutrient

Requirements• Heterotrophs• Energy Limitation• Food Density and Animal Functional

Response• Optimal Foraging Theory

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