back to basics food chain: a representation of the passage of energy across trophic levels (from...
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Back to basics
• Food chain: a representation of the passage of energy across trophic levels (from primary producers through consumers) – Trophic level: trophic position in the food chain
• Food web: a representation of the passage of energy through populations within a community; emphasizes biodiversity
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Food chain
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Humans
Baleen whales
Crab-eater seals
Birds Fishes Squids
Leopardseals
Elephant seals
Smaller toothed whales
Sperm whales
Carnivorous plankton
Euphausids (krill)
Copepods
Phyto-plankton
Food web
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Secondary production
• Definition
• Secondary producers have dual roles as producers and consumers
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• Percentage of energy transferred from one trophic level to the next
• Typically between 5-20%
• Another way of looking at it is, at each step in the food chain, 80-95% of energy is lost
Ecological efficiency or food chain efficiency
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Components of energy transfer between trophic levels
Energy from lower trophic level
Energy not used Gross energy intake
Egested energy Digested energy
Urinary waste Assimilated energy
Resting energy Activity Growth Reproduction
Maintenance orrespiration
Production
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Elephant dung
Assimilation =
Production =
Egested energy
Reproduction
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Ranges from 15-90%
Variability due to:
Differences between herbivores/carnivores/decomposers – what are they?
Elephant dung
Assimilation efficiency =
Egested energy
Reproduction
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Ranges from 1-6% in homeothermsUp to 75% in ectothermic poikilotherms
Net production efficiency=
Egested energy
Reproduction
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Ranges from 1-5% in homeotherms5-15% for insects
Some aquatic animals exceed 30%
Gross production efficiency=
Egested energy
Reproduction
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Exploitation efficiency
• When production and consumption are not balanced energy accumulates in ecosystem
• Exploitation efficiency is the proportion of production on one trophic level that is consumed by organisms in next higher level
• Ecological = gross production x exploitationefficiency efficiency efficiency
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Residence time
Biomass accumulation ratio
Detritus and residence time
Differences between aquatic and terrestrial ecosystems
Energy moves through ecosystems at different rates
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Detritus food chains
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Energy as currency
• Aids in comparing ecosystems
• Helps define connections across ecosystems
• Helps define generalities in energy flow
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Biotic effects on energy flow