Ecosystems

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Chapter 51

• Ecosystems

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Ecosystems

• Population all the individuals of a certain
  species that live in a particular area
• Community all the different species that
  interact together within a particular area
• Ecosystems consist of all the organisms that live
  in an area along with the nonbiological
  (abiotic) components.

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Ecosystems

• Many global environmental problems have emerged
  recently.
• Ecosystem ecology follows the flow of energy and
  nutrients through ecosystems
• Humans have artificially affected the flow of
  these components

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Energy Flow within Ecosystems

• Energy enters an ecosystem primarily though
  sunlight

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Energy Flow and Trophic Structure

• Species within an ecosystems are classified into
  different trophic levels
• Primary producers autotrophs, photosynthetic-
  plants, algae, some bacteria
• Consumers
• Primary consumers herbivores that eat producers
  (plants)- deer, rabbits, etc.
• Secondary consumers carnivores that eat
  herbivores wolf eating a deer
• Tertiary consumers carnivores that eat
  carnivores a hawk eating a snake that ate a
  mouse
• Decomposers fungi, bacteria that break down
  organic material (dead plants and animals)

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Different Trophic Levels in an Ecosystem
Trophic level 4 3 2 1
Feeding strategy Secondary carnivore Carnivore Her
bivore Autotroph
Grazing food chain
Decomposer food chain
Coopers hawk
Owl
Shrew Earthworm Dead maple leaves
Robin
Cricket Maple tree leaves
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Energy Flow in an ecosystem
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Decomposers
Predators of decomposers
Spider
Salamander
Centipede
Puffball
Puffball
Mushroom
Earthworm
Millipede
Nematodes
Primary decomposers
Bacteria and archaea
Pillbugs
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Energy Flow and Trophic Structure

• Key points about energy flow through ecosystems.
• Plants use only a tiny fraction of the total
  radiation that isavailable to them.
• Most energy fixed during photosynthesis is used
  for respiration, not synthesis of new tissues.
• Only a tiny fraction of fixed energy actually
  becomes availableto consumers.
• Most net primary production that is consumed
  enters the decomposer food web.

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Ecological Efficiency percent of energy
transferred from one trophic level to the next
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Ecosystem Processes

• Production rate at which energy/nutrients are
  converted into growth
• Includes Primary Production growth by autotrophs
• Includes Secondary Production - growth by
  heterotrophs
• Consumption - the intake and use of organic
  material by heterotrophs
• Decomposition - the chemical breakdown of organic
  material

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Figure 51.3a
Terrestrial productivity
0100 100200 200400 400600 600800 gt800
Productivity ranges (g/m2/yr)
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Figure 51.3b
Marine productivity
lt35 3555 5590 gt90
Productivity ranges (g/m2/yr)
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Very little of the energy consumed by primary
consumers are used for secondary production
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Pyramid of productivity
Example 100g of plant becomes 5-20g of
grasshopper then 0.25-1g of mouse
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The Different Trophic levels in an ecosystem is
often pictured as a Food chain
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Energy Flow and Trophic Structure

• Food chains and food webs
• Food chains are typically embedded in more
  complexfood webs.
• Many organisms feed at more than one trophic
  level

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Food web
Pisaster
Thais
Limpets
Gooseneck barnacles
Acorn barnacles
Chitons
Bivalves
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Energy Flow and Trophic Structure

• Food chains and food webs
• The maximum number of links in any food chain or
  web ranges from 1 to 6.
• Hypotheses offered to explain this
• Energy transfer may limit food-chain length.
• Long food chains may be more fragile.
• Food-chain length may depend on environmental
  complexity.

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Food chains tend to have few links.
10 8 6 4 2 0
Streams Lakes Terrestrial
Average number of links 3.5
Number of observations
Number of links in food chain
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Biogeochemical Cycles

• The path an element takes as it moves from
  abiotic systems through living organisms and back
  again is referred to asits biogeochemical cycle.
  
• Examples nitrogen cycle, carbon cycle,
  phosphorus cycle

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Figure 51.8
Plants
Consumption
Herbivore
Assimilation
Feces or urine
Death
Death
Detritus
Uptake
Soil nutrient pool
Decomposer food web
Loss to erosion or leaching into groundwater
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Biogeochemical Cycles

• A key feature in all cycles is that nutrients are
  recycledand reused.
• The overall rate of nutrient movement is limited
  most by decomposition of detritus.

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Boreal forest nutrients are put back into the
soil slowly, so organic material builds up
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Tropical rain forest decomposition is rapid so
there is very little organic build up
Result if living material is removed from
tropical rain forests, the soil is nutrient poor
to support new growth
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The rate of nutrient loss is a very important
characteristic inany ecosystem.
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Control
Clearcut
Devegetate one watershed and leave the other
intact. Monitor the amount of dissolved
substances in streams.
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Nutrient export increases dramatically in
devegetated plot
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Biogeochemical Cycles

• Nutrient flow among ecosystems links local cycles
  into one massive global biogeochemical cycle.
• The carbon cycle and the nitrogen cycle are
  examples of major, global biogeochemical cycles.
• Humans are now disrupting almost all
  biogeochemical cycles. This can have very harmful
  effects.

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Humans are adding significant amounts of carbon
into the atmosphere
THE GLOBAL CARBON CYCLE All values in gigatons of
carbon per year
Atmosphere 750 (in 1990) 3.5 per year
Photosynthesis 102
Respiration 50
Fossilfuel use 6.0
Deforestation 1.5
Physical and chemical processes 92
Decomposition 50
Physical and chemical processes 90
Land, biota, soil, litter, peat 2000
2
Rivers 1
Ocean 40,000
Aquatic ecosystems
Terrestrial ecosystems
Humaninduced changes
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Human-induced increases in CO2 flux over time
6 5 4 3 2 1 0
Fossil fuel use
Annual flux of carbon (1015g)
Land use
Year
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Figure 51.12b
360 350 340 330 320 310
Atmospheric CO2
CO2 concentration (ppm)
1960
1970
1980
1990
Year
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THE GLOBAL NITROGEN CYCLE

• Only nitrogen-fixing bacteria can use N2
• make ammonia (NH3) or nitrate (NO3)
• limiting nutrient (demand exceeds supply) for
  plants
• All organisms require nitrogen to make protein
• Animals get nitrogen from their diets, not the
  air

Industrial fixation
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Human activities now fix almost as much nitrogen
each year as natural sources