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 Habitat Modification 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 First High-Tech Extinction 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 only extinction we can time to the minute

When Your Best Just Isn’t Good Enough 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

Too Adaptable for its Own Good 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 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 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