Extinctions

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Extinctions
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Estimates of Organisms

• Fossil record from Precambrian period estimate
  total number of species on Earth at 500 million
• Current numbers of named species is 1.5 2
  million
• Current estimates of total species ranges between
  10 100 million

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Loss of Biodiversity

• EXTINCTION - the disappearance of a species
• Extinctions have been occurring constantly at a
  low 'background rate', usually matched by the
  rate at which new species appear - resulting in
  an overall increase in biodiversity
• A world without extinction would be really
  crowded!!

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Mass Extinction

• Sudden loss of species in a short time
• These are usually attributed to a rapid climate
  change, a meteorite impact, a large volcanic
  explosion

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There are 5 mass extinctions in the fossil record
See page 95
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Mass Extinctions

• There have been five major extinctions since the
  beginning of life on Earth 3.5 billion years ago

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Late Ordovician (440 mya)

• 2nd most devastating in Earths history
• 25 of all families were lost
• Probably due to glaciation and sea level changes

Sourcehttp//www.palaeos.com/Paleozoic/Ordovician
/Ordovician.htm
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Devonian (365 mya)

• Effecting marine and terrestrial species
• Possibly due to global cooling since many warm
  water species were lost
• Occurred over a span of 500,000 -15 million years

Source http//www.palaeos.com/Paleozoic/Devonian/
Devonian.2.htm
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Permian -Triassic (250 mya)

• Largest extinction
• estimated that as many as 95 of all marine
  species were lost
• 54 of all families were lost
• Possible causes
• continents merging to
• form Pangaea
• global cooling caused
• by volcanic eruptions
• Ice age may
• have followed

Source http//www.palaeos.org/Permian
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Late Triassic (200 mya)

• 23 of all terrestrial families
• Possible causes
• Climate change as Pangeae broke apart

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Cretaceous-Tertiary (65 mya)

• Also known as the K-T extinction
• Effecting ½ of all marine species
• Many terrestrial plants, dinosaurs, and reptiles
  became extinct.
• Gave rise to mammals

Source http//www.worldbook.com/wb/Students?conte
nt_spotlight/dinosaurs/world_mesozoic
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K T Extinction Continued

• Possible causes
• Impact hypothesis
• meteor collided with
• the Earth on the Yucatan in Mexico and/or
  eruption of volcanoes in the Deccan Plateau in
  India, causing dust clouds, stopping
  photosynthesis

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Pleistocene (11, 000 ya)

• Start of the 6th extinction event (Holocene)
• Ice age period
• Loss of 75 of large genus (mammals)
• Possible causes
• Hunting
• Climate change

Source http//www.msnbc.msn.com/id/12721432/
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Holocene extinction event

• The 6th and current mass extinction
• Started at the end of the last ice age 10,000
  years ago with the extinction of the large
  mammals
• The rate of extinction has increased in the past
  100 years
• Humans!

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Background Extinction Rate

• The natural extinction rate of all species over
  time
• Current estimates 1 species per million species
  per year.
• Determine the background extinction rate given
  the current estimate of 10-100 million species

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Current Extinction Rates

• 10 100 species per year Did you get this?
• Todays extinction rate is much higher than this!
• Some experts estimate that the current extinction
  rate is 1000 times the background extinction rate
• According to E.O. Wilson 3 extinct species per
  hour

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Recent Extinction Rates continued

• By the year 2010 over 500,000 species of plants
  and animals will have become extinct since the
  Pleistocene
• The current rate of extinction is caused by one
  species Humans!

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Past causes of extinction

• Climate change
• Volcanic events
• Magnetic reversal of the poles
• Sea level changes
• Collision of Meteorites
• Glaciations
• Plate tectonics
• Competition / predation

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Present causes of extinction/loss of biodiversity
-

• human impact
• HIPPO
• Habitat destruction
• Introduced species invasive species
• Pollution
• Population
• Over exploitation

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Habitat destruction

• Degradation
• e.g. stream siltation caused by deforestation
• Fragmentation
• e.g.highways through national parks
• Loss of habitat
• e.g. new strip mall on Hanes Mall Blvd

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Introduced species (invasive)

• Non-native species
• e.g. green crab, zebra mussel, ctenophore in
  Mediterranean Sea
• Genetically modified species that invade natural
  areas.

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Pollution

• Air
• Water
• Land
• Major sources
• Fossil fuels
• Domestic waste
• Industrial waste
• Manufacturing processes
• Agriculture

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Population

• With the global population increasing at a rate
  of 3 people per second there are
• Increasing use of resources
• Increasing habitat destruction
• Increasing waste production and pollution

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Over exploitation

• Hunting, collecting, harvesting
• e.g. Atlantic cod for food
• e.g. sea otter for fur
• Wildlife trade e.g. bear gallbladders as
  aphrodisiacs
• Indirectly through over consumption of resources
  e.g. water, land

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Resources

• Course Companion
• Text by Miller