Ecosystems

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Chapter 54

• Ecosystems

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Ecosystems

• Ecosystems are all of the organisms living in a
  community along with the abiotic factors with
  which they interact.
• Ecosystems can be thought of as transformers of
  energy and processors of matter.

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Ecosystems

• Grouping species into trophic levels allows us to
  follow the transformation of energy and the
  movements of chemical elements through the
  community.

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Autotrophs

• Autotrophs ultimately support all organisms and
  they are called primary producers.
• Plants, algae and photosynthetic prokaryotes are
  the biospheres main primary producers.
• They synthesize sugars and other organic
  compounds from sunlight.

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Primary Production

• Primary production is the amount of light energy
  converted to chemical energy during a given time.
• Huge amounts of solar energy hit the earth each
  day.
• Only a small proportion of this hits a primary
  producer.

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Primary Production

• Of the light that hits a primary producer, only
  about 1 is converted into chemical energy.
• 170 billion tons of organic material is created
  each year.

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Primary Production

• Gross Primary Production (GPP) is the total
  primary production in an ecosystem.
• It is all of the light energy that is converted
  into chemical energy by photosynthesis in a given
  time period.

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Primary Production

• Net Primary Production (NPP) is the gross primary
  production minus the energy used by the primary
  producers for respiration.
• NPP GPP - R
• NPP is important because it represents the
  storage of chemical energy available to consumers.

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NPP

• It is always the total new biomass added in a
  given time.
• Always calculated as dry weight.
• Standing crop is the total biomass of an
  ecosystem.
• Rainforests, estuaries, and coral reefs have a
  high net primary production.

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Primary Production

• Factors which control primary production
• 1. Light limitations
• 2. Nutrient limitations

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Primary Production

• 1. The depth of light penetration controls
  production.
• More than half of the total solar energy is
  absorbed in the first meter of water.
• Light isnt the only factor which controls
  primary production.
• The lack of a production gradient between the
  equator and the poles demonstrates this.
• Something else must be occurring.

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Primary Production

• 2. Nutrient limitations must be overcome in
  order for a lake or ocean to increase its
  production.
• Nitrogen and phosphorous are the 2 elements that
  most limit marine production.

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Primary Production

• Nutrient limitations are also common in
  freshwater lakes.
• This was first noticed and studied by David
  Schindler.

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David Schindler

• He noticed that runoff from farms and yards added
  a lot of nutrients to lakes.
• He also documented the idea of eutrophication--the
  increased numbers of cyanobacteria.

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Eutrophication

• As a result of eutrophication, many fish die due
  to decreased levels of O2.

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David Schindler

• He conducted a lot of research on eutrophication.
• Discovered that phosphorous was the main limiter
  of cyanobacteria growth.
• He is the reason why phosphorous was removed from
  detergents and other water reform measures were
  adopted.

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Heterotrophs

• The trophic level above the primary producer.
  Feeds on autotrophs.
• Herbivores are primary consumers.
• Carnivores eat herbivores and are secondary
  consumers.
• Carnivores that eat other carnivores are tertiary
  consumers and so on...

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Detritivores

• An important group of heterotrophs.
• They feed on and break down dead organic matter.
• The prokaryotes, fungi, and animals that feed as
  detritivores are a major link between primary
  producers and consumers in an ecosystem.

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Detritivores

• Make chemical elements available to other
  organisms.

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Global Productivity

• When looking at productivity on a global scale,
  many areas are very unproductive
• Tundra, deserts, polar regions.
• Equatorial regions are very productive.
• Midlatitude temperate regions are moderately
  productive.

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Global Productivity

• To assess productivity levels, we look at
  evapotranspiration rates.
• The more rainfall in a given area, the higher the
  amounts of evapotranspiration.
• There is a positive relationship between
  evapotranspiration and NPP.

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Secondary Production

• The amount of energy in a consumers food source
  that gets converted into biomass.
• Most primary production is not consumed because
  consumers can only eat so much.

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Trophic Efficiency

• This is the percentage of production transferred
  from one trophic level to the next.
• To see how much production is actually lost, we
  can look at trophic efficiency.

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Trophic Efficiency

• Trophic efficiencies are usually between 5-20.
• So, they are 80-95 unproductive.
• Because of this, most food webs only have 4 or 5
  trophic levels.
• This contributes to pyramids of numbers.

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Trophic Efficiency

• Pyramids of numbers represent the number of
  individuals present at each trophic level.

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Trophic Efficiency

• Pyramids of numbers represent the number of
  individuals present at each trophic level.

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Recycling of Nutrients

• Life on earth depends on the recycling of
  nutrients.
• The assimilation of nutrients and their removal
  from the body through waste is a way in which
  many nutrients are recycled.
• When organisms die, detritivores recycle many of
  their nutrients.

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Biogeochemical Cycles

• The nutrient recycling which involves both biotic
  and abiotic components.
• There are 2 general categories
• 1. Global
• 2. Local

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Biogeochemical Cycle

• Gaseous forms of C, N, O, S are found in the
  atmosphere--globally.
• These elements are more mobile.
• K, P, Ca are found in different concentrations on
  a more local scale in the soil.
• They are less mobile.

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Model for Nutrient Cycling

• We have to look at
• The main reservoirs for elements.
• Processes that transfer the elements between
  reservoirs.

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Model for Nutrient Cycling

• Each reservoir has two questions that need to be
  answered
• Does it contain organic or inorganic materials?
• Are the materials directly available for use by
  organisms?

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Water Cycle

• Rates of 1-2 production depend on the water
  cycle as well as decomposition.
• The liquid phase is the important phase available
  to most organisms.
• 97 of H2O is in the oceans.
• 2 is in glaciers and polar ice caps.
• 1 is in lakes and streams.

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Water Cycle

• Evaporation by solar energy and wind are the main
  processes driving the water cycle.
• Condensation into clouds and precipitation make
  up the rest of the water cycle.

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Carbon Cycle

• Carbon is important because it forms the
  framework for organic molecules essential to all
  life.
• Photosynthesis makes use of CO2 by converting it
  into forms used by consumers.

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Carbon Cycle

• Carbon is found in great proportions in fossil
  fuels, sediments of aquatic ecosystems, the
  oceans, plants and animal biomass, and the
  atmosphere.

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Carbon Cycle

• The largest carbon reservoir is found in
  sedimentary rocks like limestone.

Bob Krist/Corbis
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Carbon Cycle

• Key processes concerning the carbon cycle
• The fixing of CO2 by plants
• The return of CO2 to the atmosphere through cell
  respiration.

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Carbon Cycle

• Volcanoes contribute a lot of CO2 to the
  atmosphere over geologic time.
• The burning of fossil fuels is also adding a lot
  of CO2 to the atmosphere.

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Nitrogen Cycle

• Nitrogen is important to the building of amino
  acids, proteins, and nucleic acids.
• It is the crucial and limiting nutrient to
  plants.
• Plants and algae use NH4 and NO3-
• Bacteria use NH4, NO3-, and NO2-
• Animals can only use organic forms of
  nitrogen--aas and protein.

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Nitrogen Cycle

• The atmosphere is the main reservoir of nitrogen
  80.
• It is also found dissolved in the various water
  sources on the planet and locked in living
  organisms.

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Phosphorous Cycle

• Phosphorous is a major constituent of nucleic
  acids, phospholipids, and ATP.
• It is important to living organisms for bone and
  teeth too.
• PO43- is the only biologically important form of
  phosphorous.
• Plants use it to synthesize organic compounds.

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Phosphorous Cycle

• Sedimentary rock of marine origin is the largest
  source of PO43-. It is also found in the soil.
• The weathering of rock ads phosphorous to the
  soil in the form of phosphate.

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Phosphorous Cycle

• Phosphate taken up by producers can get
  distributed throughout the ecosystem when
  organisms excrete it or they die and decompose.
• Only small amounts of phosphorous are found in
  the atmosphere because there are no significant
  phosphate gases.

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Nutrient Cycles

• These are generally faster in the tropics where
  temperatures are warmer and more moisture falls.
• 10 of nutrients are available in the detritus
  of tropical forests.
• It is slower in temperate regions.
• 50 of nutrients are available in temperate
  forests.

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Nutrient Cycles

• In aquatic ecosystems, nutrient cycling is
  generally much slower and only occurs during the
  turnover.
• Generally due to the lack of oxygen in the water.

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Nutrient Cycles

• Human activities have greatly disrupted the
  nutrient flows within ecosystems.
• One example
• Normally, organisms grow and die in the same
  spot and their nutrients are cycled there.
• Now, many crops are grown and shipped all across
  the globe.

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Nutrient Cycles

• To combat this problem, we apply fertilizers.
• One problem with this, however, is adding too
  much.
• Nitrogen has become a large problem.
• It contaminates ground water, water ways, and
  freshwater and marine ecosystems.

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Nutrient Cycles

• High concentrations of nitrogen containing
  compounds--NH4, NO3- and other biologically
  usable nitrogen containing compounds accumulate.
• The problem is that aquatic ecosystems get
  overgrown and use up all of the dissolved O2.
• This chokes out many organisms.

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Nutrient Cycles

• Recall what we discussed about lakes
• Oligotrophic lakes--have a low primary
  production.
• Eutrophic lakes--have a high primary production.
• Humans have contributed to cultural
  eutrophication due to runoff.

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Nutrient Cycles

• The burning of fossil fuels has increased the
  amount of acid producing compounds in the
  atmosphere (SO42-, NO3-, etc.).

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Acid Precipitation

• This becomes the problem.
• Normal pH of rain is 5.6 due to dissolved CO2 in
  the water.
• Any precipitation lower than 5.6 is considered to
  be acidic
• Soil pH decreases as a result, and calcium and
  other nutrients get leached from the soil in an
  attempt to buffer the soil pH.
• This limits plant growth.

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Acid Precipitation

• Many plants and freshwater ecosystems have been
  altered as well.
• The acidity damages the plants, and lowers the pH
  of the water of lakes, streams and rivers.

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Human Activities

• The activities of humans is producing a wide
  variety of changes to the global environment.
• As a result, there are a variety of consequences.

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Biological Magnification

• Biological magnification is a process by which
  toxic chemicals accumulate in higher
  concentrations the higher up we go in the trophic
  ladder.
• The top level feeds on the level below it, so you
  can see the problem.

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Biological Magnification

• PCBs and the Great Lakes.
• Herring Gulls are the top level carnivores and
  they feed mainly on fish.
• The concentration of PCBs in these gulls is
  about 5000x higher than at the base of the food
  chain.

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Biological Magnification

• DDT is also a problem.
• It was used as a pesticide in the 1940s and
  50s.
• Many bird populations began to decline shortly
  after its use began.
• This is because DDT interferes with calcium
  deposition in egg shells.
• Egg shells were weaker and the weight of the
  parents crushed the eggs.

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Biological Magnification

• Mercury is another big problem.
• Its main source in the atmosphere is from coal
  fired power plants and plastic production.
• It finds its way into lakes, rivers and streams.
• Bottom level decomposers break it down into a
  compound called methyl mercury which is very
  toxic.

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Biological Magnification

• Accumulation within the food chain contributes to
  a variety of problems.
• Mainly neurological problems.

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Human Activities

• Human activities have contributed to a wide
  variety of gases being released into the
  atmosphere.
• CO2 is a main gas.
• Comes from the burning of fossil fuels and
  deforestation.

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Human Activities

• Elevated CO2 levels contribute to global warming.
• Higher CO2 levels trap radiant energy from the
  sun which would normally escape back into space.

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Global Warming

• Global warming does do some good. The
  temperature of earth would be about 60F cooler
  if it were not for greenhouse gases.

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Global Warming

• The environmental implications of increased CO2
  levels are dramatic.
• A 1.3C increase in average surface temperature
  will mean that the earth will be warmer than at
  any time during the past 100,000 years.

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Global Warming

• Worst case scenario is that the polar ice caps
  will melt and coastal regions will become
  inundated with water.

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Global Warming

• Some of the early signs of global warming is that
  the ice shelf in the Antarctica is melting and
  collapsing.

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Ozone Layer

• The ozone layer is like the earths sunscreen.
• It acts to protect us from harmful UV rays.
• An accumulation of CFCs in the atmosphere is the
  main contributor to the destruction of the ozone.

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Ozone Layer

• Fluctuations in the size of the hole in the ozone
  layer is somewhat seasonal.
• Examination of the fluctuations in the hole in
  the ozone layer shows that the hole is gradually
  getting larger.

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Ozone Layer

• This allows more UV in which causes a variety of
  problems.
• Increased rate of skin cancer
• Increased rate of cataracts
• Increased problems with phytoplankton and crop
  production.
• The Montreal Protocol has been signed by a number
  of nations to stop the production of chemicals
  that deplete the ozone layer.

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Ozone Layer

• There is enough chlorine in the atmosphere to
  affect the ozone layer for another 100 years.