Download Sixth 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
• Silica: Not biologically used, but isolated as
inert particles
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
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 first extinction we can time to
the hour
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
How Long Do Taxa Survive?
• Species, Genera: Many Historic Extinctions
• Families: Some Historic Extinctions, Many In
Last Few Million Years
• Orders: Most Recent 20-30 M.Y. Ago
• Class: Trilobites, 220 M.Y. Ago
• Phylum: 500 M.Y. Ago? Maybe Never
• Kingdom: 500+ M.Y. Ago? Maybe Never
Lazarus Taxa
• Groups that vanish during mass extinctions
and then reappear
• Where do they go?
• Why don’t they change?
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 – so far - would show
up in the fossil record
• Little change in easily fossilized marine
faunas