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
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
The First High-Tech
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
• 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
• 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
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,
• By 1906, only 50 left
The Heath Hen – Back From the
• 1907: Sanctuary established for
last 50 birds
• By 1915, number had grown to
• 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
• By 1927, only 13 left, mostly male
• Last bird died, 1932
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
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
• 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
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
• landscape -- diversity of ecosystems (Western
Great Lakes)
Island Biodiversity
• Single islands (mountain tops) always have fewer
species than areas on the “mainland” of similar
• Because islands are isolated, it will be harder for
species to immigrate to them, lowering the rate of
• 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
• 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