Ecosystem Ecology

Chapter 55

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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

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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

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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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Energy Pyramids

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Biomass Pyramids

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Numbers Pyramids

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Hydrologic Cycle

Evapotranspiration – takes into account plant transpiration & evaporation from landscape + animals

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Carbon Cycle

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Nitrogen Cycle

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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

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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)

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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