Ecosystem energetics

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Ecosystem energetics

• Outline
• Limits on primary production
• Relationship between primary and secondary
  productivity
• Trophic efficiency
• Readings Chapters 20

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Laws of thermodynamics govern energy flow
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Laws of thermodynamics govern energy flow
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Energy flow in ecosystems
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Ecosystem energetics - terminology

• Standing crop biomass amount of accumulated
  organic matter found in an area at a given time
  g/m2
• Productivity rate at which organic matter is
  created by photosynthesis g/m2/yr
• Primary productivity autotrophs
• Secondary - heterotrophs
• Gross versus net primary productivity

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Estimating primary productivity in aquatic
ecosystems
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Factors limiting primary productivity in
terrestrial ecosystems

• Temperature
• Precipitation
• Light
• Nutrients

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Controls on primary production in terrestrial
ecosystems
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Controls on primary production in terrestrial
ecosystems
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Controls on primary production in terrestrial
ecosystems
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Controls on primary production in terrestrial
ecosystems
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Controls on primary production in terrestrial
ecosystems
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Primary production as a function of latitude
Despite much variation, there is a general trend
of increasing net primary productivity with
decreasing latitude. a), Grassland and tundra
ecosystems. b) Cultivated crops. c) Lakes
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Global map of primary productivity
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Factors limiting primary productivity in aquatic
ecosystems

• Light
• Nutrients

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Controls on primary production in aquatic
ecosystems
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Controls on primary production in aquatic
ecosystems
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Controls on primary production in aquatic
ecosystems
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Global map of primary productivity
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Energy allocation
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Primary production varies with time
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Primary production varies with time
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Primary production varies with time
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Primary productivity limits secondary productivity
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Primary productivity limits secondary productivity
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Secondary production by trophic level n
Amt respired by trophic level n
Production efficiency 14/70
Amt egested as feces (waste) by trophic level n
Amt assimilated (i.e. absorbed into body) by
trophic level n
Assimilation efficiency 70/200
Amt ingested by trophic level n
Consumption efficiency 200/1000
Amt produced by trophic level n-1
Efficiency of energy transfer
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Efficiency of production
I ingested A assimilated through
gut wall W expelled as waste product Of A,
R respired P production
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Food chains
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Consumption efficiency determines pathways of
energy flow through ecosystem
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FOREST

• Note
• Detrital food chain accounts for most biomass
  produced in a community
• LCS plays greatest role in phytoplankton-based
  food chains

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GRASSLAND
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PLANKTON - OCEAN
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STREAM COMMUNITY
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Energy loss between trophic levels
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Secondary production by trophic level n
Amt respired by trophic level n
Amt egested as feces (waste) by trophic level n
Amt assimilated (i.e. absorbed into body) by
trophic level n
Amt ingested by trophic level n
Amt produced by trophic level n-1
Example a herbivore (level n) feeding on a
plant (level n-1) values kilocalories. Trophic
Efficiency 0.20.350.2 14/1000 0.014
Efficiency of energy transfer
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Decomposition and Nutrient cycling

• Outline
• Process of decomposition
• Types of decomposers
• Controls on decomposition
• Decomposition in lakes and rivers
• Nutrient cycling generalities
• Nutrient cycles
• Carbon
• Nitrogen
• Phosphorus
• Readings Chapters 21, 22

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Decomposition

• Most material plant
• Involves
• Release of chemical energy
• Mineralization ( organic --gt inorganic)
• Note immobilization reverse of mineralization
• Net mineralization rate mineralization -
  immobilization

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Decomposition involves a variety of organisms

• Microfauna microflora lt100 µm bacteria and
  fungi nematodes, protozoa
• Mesafauna 100 µm 2mm mites, potworms
• Macrofauna 2-20 mm - millipedes
• Megafauna gt 20 mm- earthworms, snails

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Fungi microfauna
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Mites mesofauna
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Megafauna
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Vertebrate scavengersConsumers of animal carrion
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Factors influencing decomposition rates
(highest lignin content)
(lowest lignin content)
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Factors influencing decomposition rates
Decomposition of straw
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Factors influencing decomposition rates
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Factors influencing decomposition rates
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Factors influencing decomposition rates
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Immobilization vs. mineralization
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Decomposition in aquatic environments
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Rate of nutrient cycling
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Rate of nutrient cycling
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Zones of production and decomposition
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Nutrient spiraling in rivers
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Nutrient spiraling in rivers
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Terrestrial communitiesNutrient sources

• Weathering of rock (K, P, Ca and many others)
• Fixation of CO2 (photosynthesis) and N2
• Dryfall (particles in the atmosphere)
• Wetfall (snow rain) contains
• Oxides of S, N
• Aerosols
• particles high in Na, Mg, Cl, S
• produced by evaporation of droplets
• Dust particles from fires, volcanoes
• Ca, K, S

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Terrestrial communitiesNutrient losses

• Release to atmosphere
• CO2 from respiration
• Volatile hydrocarbons from leaves
• Aerosols
• NH3 (decomposition), N2 (denitrification)
• Loss in streamflow
• Dissolved nutrients
• Particles

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Oceans

• No outflow
• Detritus sinks --gt mineralization --gt nutrients
  end up
• Being carried back to surface in upwelling
  currents, or
• Trapped in sediment
• E.g. phosphorus 1 lost to sediment with each
  cycling

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The Carbon Cycle
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Daily variation in CO2
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Annual variation in CO2
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The nitrogen cycle
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The phosphorus cycle
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Nitrogen saturation
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Nitrogen saturation
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For next lecture

• Please read Chapter 6