Chapter 57
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Flow of Energy in Ecosystems
• First Law of Thermodynamics: energy is neither created nor destroyed; it changes forms
• Second Law of Thermodynamics : whenever organisms use chemical-bond or light energy some is converted to heat (entropy)
• Sun our major source of energy (E)
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Flow of Energy in Ecosystems
• Trophic levels: level an organism “feeds” at
• Producers (autotrophs): “self-feeders” make organic compounds (photosynthesis)
• Consumers (heterotrophs): must take in food
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Flow of Energy in Ecosystems
• Consumers are classified by their diet
• Herbivores : first consumer level, eat plants
• Primary carnivores : eat herbivores
• Secondary carnivores : eat primary carnivores or herbivores
• Detritivores : eat decaying matter
– Decomposers : microbes that break up dead matter – “CHONPS”
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Trophic levels within an ecosystem
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Flow of Energy in Ecosystems
• Productivity: the rate at which the organisms in the trophic level collectively synthesize new organic matter
• Primary productivity: producers
• Respiration: rate producers use org. compounds
• Net primary productivity (NPP) = PP – respiration
• Secondary productivity: productivity of a heterotroph trophic level
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Flow of Energy in Ecosystems
• biomass: the amount of organic matter present at a particular time
• Only small fraction of incoming solar energy is captured by producers ~ 1%/year
– Used to make chemical-bond energy
– As energy passes up the food chain, most is lost as heat and waste
– Less biomass/fewer individuals at each trophic level
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Flow of Energy in Ecosystems
• 50% of chemical-bond energy is not assimilated and is egested in feces
• 33% of ingested energy is used for cellular respiration
• 17% ingested energy is converted into insect biomass
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Flow of Energy in Ecosystems
Flow of energy through the trophic levels of Cayuga Lake
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Human Impacts:
Pollution
• Biomagnification: becomes more concentrated at higher trophic levels
• predatory bird species’ eggshells so thin that the shells broke during incubation
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Ecosystem productivity per year
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Flow of Energy in Ecosystems
• Trophic level interactions
– Trophic cascade: process by which effects exerted at an upper level flow down to influence two or more lower levels
– Top-down effects: when effects flow down
– Bottom-up effects: when effect flows up through a trophic chain
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Flow of Energy in Ecosystems
Trophic cascade in a large-scale ecosystem
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Example: Top-down
• Human removal of carnivores produces topdown effects
– Over fishing of cod - 10% their previous numbers
– Jaguars and mountain lions absent on Barro
Colorado Island
– Smaller predators become abundant
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Example: bottom-up
• When primary productivity is low, producer populations cannot support herbivore populations
• As primary productivity increases, herbivore populations increase
• Increased herbivore populations lead to carnivore populations increasing
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Flow of Energy in Ecosystems
Bottom up effects
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Biodiversity and Stability
• Species richness is influenced by ecosystem characteristics
– Primary productivity
– Habitat heterogeneity
• Accommodate more species
– Climatic factors
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Biodiversity and Stability
Factors that affect species richness
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Biodiversity and Stability
• Tropical regions have the highest diversity
– Evolutionary age of tropical regions
– Increased productivity
– Stability/constancy of conditions
– Predation
– Spatial heterogeneity
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Latitudinal cline in species richness
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