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
• Post hoc ergo propter hoc danger
• 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 co-evolution of disease and host
• 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
There Goes the Neighborhood
Humans Show Up and Megafaunas Go
Extinct
• Australia 40,000 years ago
• Americas 15,000 years ago
• Madagascar 1000 years ago
• New Zealand 1000 years ago
Did Humans Cause the
American Mass Extinction?
• Contentious: Threatens Image of Early
Humans As Stewards of Environment
• Immigrants From Arctic Wouldn’t Have
Fine-tuned Cultural Sense of How to
Manage Temperate Environment
• American Fauna Not Accustomed to
Humans
What Caused the American
Mass Extinction?
• Climate Change?
– Rode out 20+ Previous Glacial Cycles
• Change in Ecology?
– C3 and C4 Grasses
C3 and C4 Grasses
• Refers to chemical reactions during
photosynthesis (3- versus 4-carbon
molecules)
• C3 Grasses are cool climate, C4
grasses are warm climate
• C4 grasses are richer in silica particles
and wear teeth faster
What Caused the American
Mass Extinction?
• Why Didn’t All Megafauna go Extinct?
– Bison, Pronghorn, Deer, Grizzly Bears
• Did Humans Really Hunt Megafauna?
– Central Asian Mammoth-bone Huts, but
Rabbits Are Main Bones in Food Dumps
– What killed off Saber-Tooth Cats?
• Did Humans Kill Off Some Keystone
Species?
• Timing is Sure Suspicious
Eating Our Way to Extinction
• Steller’s Sea Cow
– Cold-Water Relative of Manatee
– Extinct 1768
• Great Auk
– Flightless, Penguin-like North Atlantic Bird
– The Original “Penguin”
– Nice Example of Convergent Evolution
– Extinct 1844
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
Disloyalty
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
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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
• 1907, Sanctuary established
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 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 assemblages of
communities (Fox River watershed)
• landscape -- diversity of assemblages 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.
Island Biodiversity
• Theory of island biogeography has been
termed the 'First Law of Conservation
Biology.'
• Because of human actions, natural habitats
are becoming increasingly isolated and
island-like.
• By identifying potential mechanisms
underlying the loss of species diversity, Island
Biogeography Theory may help suggest ways
in which we can design nature reserves to
maximize their ability to maintain diversity.
Habitat Fragmentation
• Biodiversity often increases when
habitats are fragmented
• Many species need large areas
– Typically large ranges
– Availability of food
– Protection from predators and invaders
(Example: cowbirds and songbird decline)
• Corridors as solution?
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
Island Biodiversity and
Reserves
• A large reserve is better than a small reserve
• A single undivided reserve is better than a
number of small reserves
• A few large reserves are better than a
number of small reserves
• Reserves should be spaced equally from
another, not linearly
• Linear reserves should be connected with
corridors
• If reserve is small and isolated, it should be
circular and not linear
The Sixth Extinction?
• Sixth Extinction by Richard Leakey and
Roger Lewin 1995
• Are we creating a mass extinction to rival
the other major events in the geologic
past?
Mass Extinctions
Mass Extinctions
• The higher the taxonomic level, the
lower the extinction level
• Easy to wipe out a species, hard to wipe
out a family
• 250 m.y. ago: 90% of species lost, 50%
of families, some orders, no phyla
Why High-Order Taxa Survive
Lazarus Taxa
• Groups that vanish during mass
extinctions and then reappear
• Where do they go?
• Why don’t they change?
Extinct Species
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About 2100 dinosaur fossils in museums
285 genera, 336 species
May have been 1000-1300 genera total
Compare to 1300 living mammal genera
About 30,000 marine invertebrate
genera (more genera living now)
Diversity and the Fossil
Record
• Incomplete
• Many organisms will never be fossilized
– No hard parts
– Rare or very restricted
– Environments where fossilization unlikely
• Often impossible to distinguish species
– Have to rely on skeletons, shells, hard
parts
– No information on coloration
– No information on internal organs
Fossilization
• Most sediment is transported by running
water
• Most fossils are in water-laid rocks
• Bias toward aquatic organisms
– Shells
– Favorable setting
• Terrestrial fossils preserved erratically
What We Wouldn’t Find in the
Fossil Record
• Dusky seaside sparrow (color variant
only)
• Ivory-Billed Woodpecker, California
Condor, Steller’s Sea Cow (never
abundant)
• Most rain forest species (too restricted,
not likely to be fossilized)
What We Would Find in the
Fossil Record
• Extinction of Pleistocene megafauna
• Extinction of Passenger Pigeon
• Reduction in range of bison, large
carnivores
• Expansion of human domestic animals
• Reduction in rain forest, changes in land
cover
• Humans and artifacts
The Sixth Extinction – So Far
• The biggest change so far (Pleistocene
extinction) was prehistoric
• Have been very significant shifts in
vegetation and fauna
• Not many extinctions would show up in
the fossil record
• Little change in easily fossilized marine
faunas