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Transcript
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 • • • • • 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