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Ecosystem Ecology. Chapter 55. Succession. Populations ebb & flow over time, but sometimes there is a dramatic disturbance that destroys an ecosystem Called a blowout Such as forest fires, volcanic eruptions, flooding Human activity: clear cutting of a forest or strip mining

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  • Populations ebb & flow over time, but sometimes there is a dramatic disturbance that destroys an ecosystem
  • Called a blowout
    • Such as forest fires, volcanic eruptions, flooding
    • Human activity: clear cutting of a forest or strip mining
  • Ecological Succession – the process of sequential rebuilding of an ecosystem following a dramatic destruction
  • 2 Types of succession:
    • Primary Succession
    • Secondary Succession
primary succession
Primary Succession
  • When ecosystem is rebuilt from a lifeless area
    • Characterized by lack of soil
  • The essential operation is soil replenishment

1. Lichens & mosses occupy the land

    • called Pioneer organisms

2. Weathering and decay begins to build soil

3. Pioneer organisms are overrun by other organisms, such as grasses & brushes

  • Finally, there is a climax community
    • Final stable community
secondary succession
Secondary Succession
  • Blowout event that does NOT destroy the soil
    • Technically, this disaster does not “denude” the soil
  • Since soil is intact, the regeneration process occurs relatively quickly
    • In 1988, Yellowstone forest fire occurred, the ecosystem began to recover in less than a year
    • By contrast, primary succession takes about 10,000 years to fully recover

Keystone Species

  • Occupy an important ecological niche in an ecosystem
  • Dramatically affect the diversity of an ecosystem
  • Dominant species
  • Highest dry biomass in the community
  • Def. – Community + abiotic factors
  • Def. – sum of all the organisms in the area + the abiotic factors with which they interact
  • Ecosystems ecology has 2 unique processes:
    • 1. Energy Flow
    • 2. Chemical Cycling
  • Energy comes into most ecosystems from the sun
  • Energy cannot be recycled
  • Energy flows through trophic levels in food chains and food webs
  • Primary Producers are the autotrophs
    • Most important level
    • Support all the other organisms in the ecosystem
primary production
Primary Production
  • Def. – Amount of light energy converted to chemical energy by autotrophs in an ecosystem
  • Sets the limit on available energy in an ecosystem
    • Less primary production = less energy for the higher trophic levels
  • Gross Primary Productivity
    • Total photosynthesis or primary production in an ecosystem
  • Net Primary Productivity
    • Photosynthesis – Respiration
    • Energy available to consumers
how would we measure
How would we measure _____?
  • You are given:

1. A number of aquatic photosynthetic organisms

2. Opaque foil to completely block out light

3. A device that measures dissolved oxygen concentration.

  • How would you measure gross primary production?
  • How would you measure respiration?
  • How would you measure net primary production?

 Only 10% of energy in 1 trophic level passes to the next level.

 This is one of the main constraints on the number of trophic levels

3 types of pyramids
3 Types of Pyramids
  • Energy Pyramid
    • Aggregate measure of energy in different trophic levels
  • Biomass Pyramid
    • Aggregate mass in different trophic levels
  • Number Pyramid
    • Total number of individuals in a trophic level

Hydrologic Cycle

  • Evapotranspiration – takes into account plant transpiration & evaporation from landscape + animals
nitrogen cycle
Nitrogen Cycle
  • Nitrogen-fixing bacteria
    • Nodules in roots of legumes which convert free nitrogen into the ammonium ion
    • N2 + 4H2  2NH4
  • Nitrifying bacteria
    • Convert NH4 to nitrites then to nitrates
  • Denitrifying bacteria
    • Convert nitrates  free atmospheric nitrogen
biological magnification
Biological Magnification
  • DDT – popular pesticide in 1950’s
    • Responsible for malaria control
    • Rachel Carson wrote Silent Spring about DDT proliferation
      • Eventually led to a ban on DDT usage in the US
      • ONLY in the US, many other countries still use DDT
    • DDT is on every square kilometer on Earth
    • DDT enters the food chain at a low level but then bioaccumulates in the tissues of organisms consuming the organisms that ingested DDT
    • Most severe effects in tertiary consumers or organisms at the top of a food chain
biological magnification page 2
Biological Magnification (Page 2)
  • Bald Eagle
    • Symbol of America almost became extinct because of biological maginification of DDT
    • DDT entered the food chain with the bald eagle at the top
    • DDT interferes with the deposition of calcium in eggshells
    • Thin-shelled eggs were easily broken, which led to a substantial decrease in the number of eagle hatchlings
    • Hence the bald eagle (symbol of America) was saved from extinction by human intervention (stopping DDT spraying)

What is the definition of irony!?!

acid precipitation
Acid Precipitation
  • Humans are altering the Biosphere, is it a bad thing?
    • Threat of inhabitability due to population explosion
    • Natural resources are being exploited at an astronomical rate
    • Air & water are being rapidly polluted
  • Acid rain
    • Caused by airborne pollutants
    • These pollutants emanate from combustion of fossil fuels
    • Nitrogen & sulfur pollutants become nitric, nitrious, sulfurous, and sulfuric acid
    • Precipitates kills organisms & damages stonework
  • Cattle & chickens contain antibiotics & hormones which accelerate animal growth, but may have serious ill affects on humans who consume the meat
  • Carcinogens or teratogens accumulate in human fatty tissue due to biological magnification
ozone layer
Ozone Layer
  • CFCs (Chlorofluorocarbons) released into the air caused the formation of a hole in the ozone layer
    • Ozone layer protects the Earth’s surface from ultraviolet (UV) light
  • It is thought that increased UV exposure is associated with increased incidence of skin cancer (melanomas)
global warming
Global Warming
  • Excessive burning of fossil fuels has increased concentrations of atmospheric CO2
  • Causes greenhouse effect
    • CO2 and water vapor trap infrared radiation reflected off the Earth’s surface in the atmosphere
    • Leads to increase in temperature (global warming)
    • An increase in 1.0°C could cause polar ice caps to melt, raising the sea level
    • Which may lead to major coastal cities being flooded away
exotic species
Exotic Species
  • Introduction of exotic species can have dramatic consequences for the ecosystem
  • The zebra mussel (Balkan native) that found its way to the Great Lakes, USA
  • Clogged intake pipes for local water supply
  • Caused millions of dollars in damage & brought native species to extinction