Ecology

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Ecosystems
Energy and Nutrient Cycling
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Outline

• I. Ecosystems
• A. Definition
• B. Energy Flow within Ecosystems
• 1. Trophic Relationships
• 2. Energy Budgets
• 3. Ecological Pyramids
• C. Nutrient Cycling
• 1. Biogeochemical Cycles
• 2. Nutrient Pollution

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Ecosystem

• All of the organisms living in a particular place
  as well as the chemical/physical factors with
  which they interact.
• Range in size from small (like aquarium) to large
  (like forest)
• E.g. desert ecosystem organisms that live there
  (cacti, snakes, rodents), soil chemistry, average
  rainfall, temperatures etc.

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Energy Flow

• Energy flows through ecosystems, while matter
  cycles within them
• Resources critical to human survival and welfare,
  ranging from the food we eat to the oxygen we
  breathe, are products of ecosystem processes

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Energy Flow

• Energy in ecosystems follows the rules of
  thermodynamics
• Ecosystems are open systems where energy
  (generally from the sun) is input, is
  transformed, and is ultimately released as heat
  from organisms
• Heat lost from organisms is disordered, unusable
  energy and therefore has increased entropy of the
  system
• Energy transfers between organisms are not
  completely efficient
• Without energy input (sun) ecosystems collapse

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Trophic Relationships

• Trophic level how an organism gets its
  nutrition (energy)
• All organisms at a particular trophic level are
  the same number of transfer steps away from the
  energy input into the system
• Food Web who eats whom in the ecosystem
• Interconnected food chains
• Energy flows through ecosystems via trophic
  levels within the food web

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Trophic Levels

• Primary producers 1st trophic level-the
  autotrophs-capture sun energy (the initial energy
  source for almost all of earths ecosystems)
• Primary consumers heterotrophs-herbivores
  (caterpillars, cows etc), feed on primary
  producers
• Secondary consumers carnivores (birds, wolves
  etc), feed on primary consumers
• Tertiary consumers carnivores that feed on
  other carnivores

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Decomposers

• aka detritivores -consumers that get their energy
  from detritus-nonliving organic material
• Dead organisms, feces, leaf litter, wood
• Bacteria, fungi, animals which feed on detritus
  like earthworms
• Decompose organic material in ecosystem and
  transfer chemical elements in inorganic forms to
  reservoirs such as soil, water, and air
• Decomposition by bacteria and fungi accounts for
  most conversion of organic materials from all
  trophic levels to inorganic compounds usable by
  primary producers (thereby closing the loop of
  nutrient cycling)

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Ecosystem Energy Budgets

• Primary production amount of light energy
  converted to chemical energy by autotrophs in a
  given time period.
• Sets the spending limit for the energy budget
  of the ecosystem
• Of the visible light that reaches the earth, only
  about 1 is converted to chemical energy by
  photosynthesis
• Biomass amount of biological material in a
  group of organisms in an ecosystem (ex. weight of
  all trees)

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Ecological Pyramids

• A good portion of the energy produced by primary
  producers is used to fuel their life
  functions-cellular respiration, growth,
  reproduction-this is true at every trophic level
• General rule only about 10 of the energy
  contained in a particular trophic level is
  available for transfer to the next trophic level

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Ecological Pyramids

• The only generalization in an ecosystem that
  always holds true energy decreases with each
  successive trophic level
• Some generalizations that are often true
• of individuals decreases as you increase
  trophic level
• Size of individuals increases as you increase
  trophic level

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Nutrient Cycling in Ecosystems

• Within an ecosystem nutrients are cycled
  internally, there are leaks (outputs) like
  erosion and timber/crop harvest
• Must be replaced by nutrient inputs
• Weathering of rocks
• Windblown dust
• Precipitation
• Decomposition into form available to plants

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Nutrient Cycling in Ecosystems

• Nutrients are carried from terrestrial ecosystems
  by movement of water and deposited in aquatic
  ecosystems and associated lowlands
• If inputs exceed outputs, the nutrient cycle in
  the ecosystem becomes stressed or overloaded
  resulting in pollution (nutrient levels exceed
  capability of the ecosystem to process them)

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Nutrient Cycling in Ecosystems

• Nutrients eroded from agricultural lands, sewage,
  industrial wastes drain into streams, rivers,
  lakes and estuaries
• These pollutants destroy plants and animals that
  cannot tolerate their presence or the changed
  environmental conditions caused by them