Ecosystem Ecology

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Ecosystem Ecology
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Ecosystem Studies

• An ecosystem consists of all the organisms living
  in a community as well as all the abiotic factors
  with which they interact.
• The dynamics of an ecosystem involve two
  processes that cannot be fully described by
  population or community processes and phenomena
  energy flow and chemical cycling.
• Energy enters most ecosystems in the form of
  sunlight.
• It is converted to chemical energy by autotrophs,
  passed to heterotrophs in the organic compounds
  of food, and dissipated as heat.
• Chemical elements are cycled among abiotic and
  biotic components of the ecosystem.

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Variation in Ecosystem Size
Pitcher plant to Planet Earth
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Ecosystem Function

• Ecosystem ecologists view ecosystems as
  transformers of energy and processors of matter.
• We can follow the transformation of energy by
  grouping the species in a community into trophic
  levels of feeding relationships.

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Trophic Levels
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Great Lakes Food Web
Primary Producers
Decomposers
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Energy Flow

• Most primary producers use light energy to
  synthesize organic molecules, which can be broken
  down to produce ATP.
• The amount of photosynthetic production sets the
  spending limit of the entire ecosystem

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The Ecocycle at Cellular Level
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Global Energy Input

• Every day, Earth receives approximately 1023
  joules of solar radiation.
• The intensity of solar energy striking Earth
  varies with latitude, with the tropics receiving
  the greatest input.
• Most of this radiation is scattered, absorbed, or
  reflected by the atmosphere.
• Much of the solar radiation that reaches Earths
  surface lands on bare ground or bodies of water
  that either absorb or reflect the energy.
• Only a small fraction actually strikes algae,
  photosynthetic prokaryotes, or plants, and only
  some of this is of wavelengths suitable for
  photosynthesis.
• Of the visible light that reaches photosynthetic
  organisms, only about 1 is converted to chemical
  energy.

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Global Energy Input

• Although only a small amount of light reaches
  plants, primary producers produce about 170
  billion tons of organic material per year.
• Total primary production in an ecosystem is known
  as gross primary production (GPP).
• This is the amount of light energy that is
  converted into chemical energy per unit time.

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The Two Most Important Biological Reactions

• Photosynthesis
• Energy
• 6CO2 12H2O gt C6H12O6 6O2 6 H2O
• Respiration
• C6H12O6 6O2 6H2O gt 6CO2 12 H2O energy

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Energy Flow and Nutrient Cycling

• Nutrients and matter are cycled among abiotic and
  biotic components of the ecosystem.
• Energy, unlike matter, cannot be recycled.
• An ecosystem must be powered by a continuous
  influx of energy from an external source, usually
  the sun.
• Energy flows through ecosystems, while matter
  cycles within them.

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Energy and Material Flow in Ecosystems
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Energy Storage
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Ecosystem Roles for Organisms

• Organisms can be broadly classified based on how
  they get their energy
• Producers (autotrophs) - these organisms
  manufacture complex organic molecules from simple
  inorganic molecules using some source of energy -
  solar or chemical for some bacteria
• Consumers (heterotrophs) - they eat other living
  things to get their nourishment
• consumers that eat producers (plants) are primary
  consumers or herbivores
• consumers that eat primary consumers are
  secondary consumers or carnivores, etc.
• Detritovores consume the organic matter in plant
  or animal remains
• Decomposers break down organic molecules into
  simple inorganic molecules for their nourishment
  - bacteria and fungi

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A Simple Ecological Pyramid
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A More Complex Food Web
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Productivity

• GPP - The total amount of energy assimilated by
  plants during photosynthesis is known as gross
  primary production.
• The rate of GPP depends upon availability of
  water, temperature, and availability of
  nutrients - thus we see the highest rates of GPP
  in systems that are supplied with large amounts
  of water and which have fairly warm temperatures.
• NPP - The amount of energy that is stored in
  plant bodies and thus available to consumers is
  called net primary production.
• NPP GPP - respiration

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Productivity by Global Area
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Productivity Relative to Temperature and
Precipitation
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Aquatic Productivity

• In aquatic systems, GPP depends upon availability
  of light and nutrients
• Vast areas of tropical open ocean have low
  productivity while areas near coast near polar
  regions have high productivity - why is this?
  main limit to productivity in oceans is due to
  availability of nutrients

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Marine Net Primary Productivity
Red most productive, Purple least productive
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Light Penetration in Water
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Upwelling and Productivity
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Energy Flow in Grazer and Decomposer Food Webs
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Energy Flow in Four Types of Ecosystems