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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

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Biodiversity and Extinction

Nothing is Forever

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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?

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Natural Extinctions

  • Habitat Disruption

    • Volcanic Eruptions

    • Asteroid Impact

  • Habitat Modification

    • Climate Change

    • Mountain-Building

    • Sea Level Change

  • “Exotic” Species

    • Continental Drift

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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

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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

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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

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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

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What Caused the American Mass Extinction?

  • Climate Change?

    • Rode out 20+ Previous Glacial Cycles

  • Change in Ecology?

    • C3 and C4 Grasses

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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

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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

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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

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The Passenger Pigeon

The First High-Tech Extinction

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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

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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….

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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

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The Heath Hen

When Your Best Just Isn’t Good Enough

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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

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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?

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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

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Carolina Parakeet

Too Adaptable for its Own Good

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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

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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

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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

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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)

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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.

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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.

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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?

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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

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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

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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?

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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

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Lazarus Taxa

  • Groups that vanish during mass extinctions and then reappear

  • Where do they go?

  • Why don’t they change?

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Extinct Species

  • 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)

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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

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  • 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

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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)

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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

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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