Energy Flow 1

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Energy Flow 1

• BS111
• Ecology Biodiversity

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Learning objectives

• describe energy flow in ecosystems

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Ecosystem dynamics

• Regardless of ecosystems size, its dynamics
  involve 2 processes that cannot be fully
  described by population or community phenomena
• Energy flow
• Chemical cycling
• Energy enters most ecosystems as sunlight
  converted to chemical energy by autotrophs
  passed to heterotrophs in the organic compounds
  of food dissipated as heat

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Revision energy

• common currency living world
• Stored in chemical bonds released slowly to drive
  biological activity
• Maintenance of life metabolism
• Capacity to do work (joule amount of energy in
  a force moving 1 kg 1 m/ calorie amount of heat
  to raise 1 g water 1C (1 joule 4.2 calories)

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Laws of thermodynamics

• 1. Energy can be changed from one form to another
  (transferred or transformed), but it cannot be
  created or destroyed
• 2. Energy transformations lead to a reduction in
  usable energy (i.e. energy transformed from type,
  e.g. movement, to another, e.g. electrical
  energy, some dissipated as heat)

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More on energy..

• Energy at work kinetic energy
• Stored energy potential energy
• Activity of living systems synthesising
  structural molecules to build new cells, gametes,
  creating molecules to store energy and drive
  metabolic processes. Detected as heat lost
  through respiration
• Energy fixed in tissues production

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Energy sources

• 3 main energy sources light, organic molecules
  (carbohydrates, proteins, lipids, nucleic acids)
  inorganic molecules (mineral, salts)
• Organisms classified by evolutionary histories
• Can also be classified by trophic (feeding)
  biology

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Energy dark orange enters from sun as
radiation, moves as chemical energy transfers
through the food web Exits as heat radiated into
space nutrients blue arrows most transfers
through the trophic levels lead eventually to
detritus then cycle back to primary consumers
An overview of energy and nutrient dynamics in an
ecosystem. Energy flows through and exits an
ecosystem Chemical nutrients primarily cycle
within it
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• Autotrophs capable of synthesising organic
  compounds from inorganic molecules using energy
  from light or inorganic chemical reactions
• Photosynthetic autotrophs use CO2 as source of
  carbon and light as source of energy synthesise
  organic compounds, e.g. sugars, amino acids, fats

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• Chemosynthetic autotrophs synthesise organic
  molecules using CO2 as carbon source inorganic
  chemicals, e.g. hydrogen sulphide (H2S) as source
  of energy, e.g. bacteria
• Heterotrophs (other-feeders) use organic
  molecules both as carbon energy source take
  in autotrophs as food - almost all animals,
  fungi, most bacteria, protozoa depend on
  autotrophs for the energy and raw materials they
  need.

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The producers

• Photosynthesis is a metabolic pathway -converts
  light energy into chemical energy.
• Plants Chloroplasts within leaves use radiant
  energy to split water molecules and combine the
  products with CO2 to form glucose (or other
  simple sugars)
• So, substrates are CO2 water - energy source
  sunlight - end-products O2 carbohydrates, e.g.
  sucrose, glucose, starch
• Productivity of autotrophs 99 living biomass on
  planet

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Primary production

• Primary production production of new organic
  matter, or biomass, by autotrophs
• Rate of primary production amount of biomass
  produced over interval of time
• Gross primary production total amount of biomass
  produced by all autotrophs
• Net prim. prod. amount of biomass left after
  autotrophs have met their energetic needs
  (gross-respiration by prim. Prod.)

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Links in the chain

• Food chain describes route by which energy
  passes through community feeding relationships
  between some of its species
• Trophic levels position in food web. Determined
  by number of transfers of energy from prim.
  producers

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Pyramid of net production Little energy fixed in
tissues of carnivore. Inefficiency of energy
transfer losses means little available to
higher trophic levels Here, trophic efficieny of
10 for each link/ PP convert only about 1 of
energy available to them to net PP.
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Biomass pyramid each tier represents standing
crop (total dry mass of all organisms) in one
trophic level
Narrow sharply from PPs at the base to the top
level carnivores energy transfers so inefficient
Some aquatic ecosystems inverted biomass
pyramid. Primary consumers outweigh producers
Phytoplankton grow, reproduce and are consumed
so quickly by zooplankton they never develop a
large pop. Size or standing crop phytoplankton
short turnover time because phytoplankton
continually replace their biomass they can
support a biomass of zooplankton bigger than
their own biomass
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The web

• Food chain follows one possible route food web
  maps all possible (sig. chains of comm. linked as
  network)
• Oak tree comm. Birds mammals mostly omnivorous
• Can be used as ecological road maps to track
  route of pollutants, e.g. pesticides, heavy
  metals

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Patterns of terrestrial PP
Terrestrial PP generally limited by temperature
moisture Highest rates under warm, moist
conditions (precipitation, soil
fertility) Majority of PP on land comes from
larger plant forms like grasses or trees
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Evapotranspiration

• Temp. moisture combined in a single measure
  evapotranspiration
• Total amount of water that evaporates and
  transpires off a landscape in 1 yr (AET)
• This is ve correlated with net PP
• Notesig. variation in terrestrial PP results
  from diffs. In soil fertility (nutrient avail.
  N/P)

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Relationship between net primary production and
actual evapotranspiration in six terrestrial
ecosysytems.
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Patterns of aquatic PP

• Generally limited by nutrient availability
• Marine nitrogen
• FW phosphorus
• Margins of continents over continental
  shelves/areas of upwelling
• Majority of PP by small, dispersed pelagic
  phytoplankton rather than marine plants (plants
  only account for 5-10 of total marine
  productivity)

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Consumer influence

• Consumers influence rates of PP in aquatic and
  terrestrial systems
• E.g. piscivorous fish can indirectly reduce rates
  of PP in lakes by reducing density of plankton
  eating fish
• Reduced density of planktivorous fish can lead to
  increased density of herbivorous zooplankton,
  which can reduce densities of phytoplankton
  hence PP! (an effect called trophic cascade)

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Summary

• Revision energy terms
• Laws of thermodynamics
• Energy sources autotrophs, heterotrophs etc
• Primary production
• Food chains
• Food webs
• Patterns of terrestrial PP
• Patterns of aquatic PP
• Consumer influence

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Recommended reading

• Campbell Reece, Chapter 55, pp1222-1230
• Mackenzie et al . Instant notes, Section P,
  pp169-179