Transcript Extinction

Biodiversity and Extinction
Nothing is Forever
Natural Extinctions
• Surprisingly enough, we know very little
about natural extinctions
• In the past, known only from fossil records
• Physical evidence of cause rarely preserved
• Cause and Effect hard to establish
• Even if cause established, what’s the
mechanism?
Natural Extinctions
• Habitat Disruption
– Volcanic Eruptions
– Asteroid Impact
• Habitat Modification
– Climate Change
– Mountain-Building
– Sea Level Change
• “Exotic” Species
– Continental Drift
Things that Probably Don’t Cause
Natural Extinctions
• Epidemics
– Rapid evolution of disease
• Evolution of New Competitors in Place
– Existing organisms already well-adapted
Human-Caused Extinction
• Excessive Predation (Food, fur, collecting,
pest eradication, etc.)
• Habitat Destruction
• Destruction of keystone species
• Introduction of Exotic Species
– Competitors
– Predators
– Diseases
• Pollution and Contamination
The Passenger
Pigeon
The First High-Tech
Extinction
The Passenger Pigeon
• May once have been the most numerous
bird on the planet
• Estimated 5 billion
• Made up 30-40% of all North American
birds
• Flocks 1 mile wide, 300 miles long
• Evolved to travel and breed en masse
• Protection against most predators
Humans and the Passenger Pigeon
• Unlike other predators, humans exploited
the mass flocks of the passenger pigeon
• Netting, mass shooting
• Railroads shipped pigeons to market,
created demand
• Declines noted by 1860
• Species could probably have survived even
this predation, except….
Extinction of the Passenger Pigeon
• Pigeons were hunted in nesting sites
• Hunters used telegraph to learn of
colonies
• Conservation laws too little, too late
• Last wild pigeons shot Wisconsin,
1899 and Ohio, 1900
Extinction of the Passenger Pigeon
• Scattered birds could not breed
• Captive breeding attempts failed
• Last bird died in Cincinnati Zoo,
September 14, 1914, 1 PM
• The only extinction we can time to
the minute
The Heath Hen
When Your Best Just Isn’t Good
Enough
The Heath Hen
• Eastern race of the prairie chicken
• Once ranged from Maine to Virginia
• Hunting caused visible decline by 1800,
steep by 1830
• By 1870, restricted to Martha’s Vineyard,
Massachusetts
• By 1906, only 50 left
The Heath Hen – Back From the
Brink?
• 1907: Sanctuary established for
last 50 birds
• By 1915, number had grown to
2000
• Species had been rescued?
The Heath Hen – Over the Brink
• 1907-1915: Heath hen had grown from 50
to 2000 birds
• 1916: Fire destroyed most of refuge
• Harsh winter and influx of hawks further
damaged species
• Flock attacked by disease from domestic
turkeys
• By 1927, only 13 left, mostly male
• Last bird died, 1932
Carolina
Parakeet
Too Adaptable for
its Own Good
Carolina Parakeet
• Only Parrot Native to U.S.
• Once ranged from Virginia to Texas
• Adapted readily to agriculture and became
regarded as a pest
• Widely hunted
• Rare by 1880’s
• Last Seen in Florida about 1920
Recovering From Near Disaster
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Cheetahs once ranged worldwide
Remaining 20,000 are genetically identical
Near extinction 10,000 years ago
Generations of close inbreeding
Were able to re-occupy large range because
nothing had filled ecological niche
When You Can’t Go Home Again
• American Chestnut tree was once a major
food crop and lumber source
• Accounted for half the value of eastern
timber
• Devastated by blight 1904-30
• Isolated trees and viable roots still survive
• Research on blight immunization
• Even if blight cured, other trees have filled
ecological niche
Biodiversity
Scales of organization
• genetic -- diversity of genetic information found
within species and populations
• species -- diversity of species
• community -- diversity of community composition
• ecosystem -- diversity of communities (Fox River
watershed)
• landscape -- diversity of ecosystems (Western
Great Lakes)
Island Biodiversity
• Single islands (mountain tops) always have fewer
species than areas on the “mainland” of similar
size
• Because islands are isolated, it will be harder for
species to immigrate to them, lowering the rate of
immigration.
• Because of limited resources on islands, carrying
capacity will be lower, decreasing population sizes
and increasing extinction rates.
Exotic Species
• Volunteers – natural chance immigrants (cattle
egrets)
• Unintentional (rats, English sparrows)
• Escaped ornamentals (kudzu, purple loosestrife)
• Escaped pets (feral cats, house finches)
• Escaped domestic animals (pigs, goats)
• Bio-control gone haywire (mongooses)
• Most exotics not street smart
• Vigorous exotics have no natural predators
• Hawaii: 80% overrun by exotic species