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Slide 2 of 27
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
Ecological Succession – the process of sequential rebuilding of an ecosystem following a dramatic destruction
2 Types of succession: Primary Succession Secondary Succession
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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
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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
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Keystone SpeciesOccupy an important ecological niche in an ecosystem
Dramatically affect the diversity of an ecosystem
Dominant speciesHighest dry biomass in the community
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Ecosystems
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
Slide 9 of 27
Energy
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
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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
Slide 11 of 27
How would we measure _____?
You are given: 1. A number of aquatic photosynthetic organisms2. Opaque foil to completely block out light3. 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?
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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
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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
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Hydrologic Cycle
Evapotranspiration – takes into account plant transpiration & evaporation from landscape + animals
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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
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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
Slide 22 of 27
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!?!
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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
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Toxins
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
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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)
Slide 26 of 27
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
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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