Communities 7 Ecosystem Metabolism Secondary Production Chapter 26 Krebs

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Communities 7Ecosystem Metabolism Secondary
ProductionChapter 26 - Krebs
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Lecture Topics

• Characteristics and measurement of secondary
  production
• Ecological efficiencies
• Limits on secondary production

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Limits on secondary production

• Rates of primary production
• Second law of thermodynamics
• No process of energy conversion is 100 efficient

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Fate of Primary Production
Net Primary Production 56 x1015g produced
annually (by 830 billion tons of plant biomass)
Herbivores
Sediments
Detritivores
Fire
Decomposers
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Net Ecosystem Production

• Net ecosystem production (NEP) the amount of
  carbon accumulated over a time period (NPP) less
  the carbon used in heterotrophic respiration (Rh)
• NEP NPP - Rh

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Net Biome Production

• Net biome production (NBP) the amount of carbon
  accumulated in a region (biome) over a time
  period (NEP) less the carbon used in
  heterotrophic respiration and losses from fire
  (Fl) (3 x1015g / year).
• NBP NEP Fl

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Primary production and heterotrophic respiration
can clearly be seen in the fluctuation of
atmospheric concentrations of CO2
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Odum brothers developed an approach to study how
communities were structured by energy. Red lines
represent energy flows. Blue lines represent
material flows. Except for primary producers,
energy is transmitted through the exchange of
material (organic chemicals).
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Fate of Primary Production in Herbivores the
energetics approach

• M energy removed from lower trophic level
• C -Gross energy intake Energy not used (NU)

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Fate of Primary Production in Herbivores the
energetics approach

• M energy removed from lower trophic level
• C -Gross energy intake Energy not used (NU)
• D-digested energy F Egested energy (feces)

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Fate of Primary Production in Herbivores the
energetics approach

• M energy remove from lower trophic level
• C -Gross energy intake Energy not used (NU)
• D-digested energy F Egested energy (feces)
• A - Assimilated energy U - Metabolic waste

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Fate of Primary Production in Herbivores the
energetics approach

• M energy remove from lower trophic level
• C -Gross energy intake Energy not used (NU)
• D-digested energy F Egested energy (feces)
• A - Assimilated energy U - Metabolic waste

Resting energy Activity Growth Reproduction
R- Maintenance respiration P -
Production
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Mammals, marsupials and birds (warm blooded) have
similar field metabolic rates. Each requires
energy just to maintain metabolism (U). Lizards
have extremely low metabolism (do not thermally
regulate). Thus 250 g mammal uses 320 kJd-1, but
reptiles only 19 kJd-1
250g
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• Secondary production of populations is difficult
  to measure directly since different processes
  contribute.
• Sampling techniques have been developed to
  estimate secondary production
• Need to monitor
• Growth of individuals
• Mortality rates and weights of individuals at
  death
• Natality rates
• Episodes of weight loss

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Secondary production of elephants in Ugandan
National Park

• Process is very similar to constructing life
  tables, but in this case add the weight of the
  individuals.
• Life table provides estimate of the growth rate
  as a function of age of the animal.
• The average growth per elephant in the population
  was 110.8 kg per year 695,381 kJ per year.
• Density of the elephant population was 2.077
  elephant per sq. km.
• Energy content of elephants is 6.26 kJ/g dry
  weight.
• Hence elephant secondary production was 1.44
  kJ/sq m/ yr

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Growth in biomass Sall ages(no. alive in age
range x average weight for age range)
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Energy dynamics of elephant population of Queen
Elizabeth National Park, Uganda

• Production units used - allows comparisons
  across trophic levels.
• Elephants have access to 3125 kJ of NPP per sq
  m/yr
• Consume about 10 of the NPP
• Only 0.3 of what the elephant consumes goes
  into growth
• Rest goes into waste or metabolism
• Standing crop of elephants is about 1 of the NPP

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Problems with estimating secondary production

• Species do not always fit into one trophic level
• What to do with detritus feeders?
• Adequate sampling of communities difficult
• Complex food webs
• Nonequilibrium communities

Percent plant and animal materials fed upon by
430 species of NA birds. About 50 of bird
species are strict carnivores, and 5 strict
herbivores, the rest fall somewhere between.
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Approaches to addressing measurement problems

• Study individual or groups of species that are
  representative of trophic levels
• Study parts of food webs or chains, not the
  entire system
• Develop food web models to study key factors that
  influence processes

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Changes in food chain of N Pacific as influence
of keystone species (sea otter) was reduced by
switching of killer whales from seals and sea
lions to otters.
An example of how studying a single part of a
food web can help understand the interactions
between grazing, predation and production.
With Killer whales
Without Killer whales
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Food web
3 Guilds of herbivores
Use of food webs and guilds simplifies study of
complex energetic relationships in communities
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Lecture Topics

• Characteristics and measurement of secondary
  production
• Ecological efficiencies
• Limits on secondary production

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Ecological efficiencies
Net Production at of species
n Production efficiency Assimilation of

species n

• Net Production at
• Trophic Level ( i 1)
• Trophic
• efficiency Net Production at
• Trophic Level ( i)

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Production efficiency P / (R P)
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Production efficiencies of major groups of animals
93-99 respiration
homeothermic
59-90 respiration
poikilothermic
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Ecological efficiencies
Net Production at of species
n Production efficiency Assimilation of

species n

• Net Production at
• Trophic Level ( i 1)
• Trophic
• efficiency Net Production at
• Trophic Level ( i)

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• Trophic efficiencies in aquatic systems 2 24
  (mean 10)
• About 2 million tons of tuna harvested annually,
  which represents 0.1 gram of tuna carbon for each
  square meter of ocean
• If we assume a 10 trophic efficiency, then this
  harvesting of .1 g of tuna requires
• 1 gram of pelagic fishes
• 10 grams of zooplankton to feed the pelagic
  fishes
• 100 grams of production of phytoplankton to feed
  the zooplankton

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NPP required to support global fisheries

• On average 8 aquatic net primary production
  goes to support fisheries harvesting - but great
  variability

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Lecture Topics

• Characteristics and measurement of secondary
  production
• Ecological efficiencies
• Limits on secondary production

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Or why is the world green-in spite of herbivory?
Limits on secondary production

• Plant defenses secondary plant substances and
  non-digestible material (lignin) limit
  herbivory.
• Nutrient limit theory nutrients required for
  growth by animals are actually in short supply in
  plants.
• Abiotic factors limit growth seasonal
  variations in temperature, precipitation, and
  other climatic factors limit herbivore numbers.

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Limits on secondary production
Or why is the world green-in spite of herbivory?
(continued)

• Heterogeneity theory because of patchiness of
  ecosystems, foods are not in constant supply -
  leads to instability in herbivore populations.
• Self-limitations through competition, especially
  interference, so herbivores limit themselves.