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 : 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 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