Biodiversity and Extinction

1
Biodiversity and Extinction

• Nothing is Forever

2
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, whats the mechanism?

3
Natural Extinctions

• Habitat Disruption
• Volcanic Eruptions
• Asteroid Impact
• Habitat Modification
• Climate Change
• Mountain-Building
• Sea Level Change
• Exotic Species
• Continental Drift

4
Things that Probably Dont Cause Natural
Extinctions

• Epidemics
• Rapid co-evolution of disease and host
• Evolution of New Competitors in Place
• Existing organisms already well-adapted

5
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

6
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

7
Did Humans Cause the American Mass Extinction?

• Contentious Threatens Image of Early Humans As
  Stewards of Environment
• Immigrants From Arctic Wouldnt Have Fine-tuned
  Cultural Sense of How to Manage Temperate
  Environment
• American Fauna Not Accustomed to Humans

8
What Caused the American Mass Extinction?

• Climate Change?
• Rode out 20 Previous Glacial Cycles
• Change in Ecology?
• C3 and C4 Grasses

9
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

10
What Caused the American Mass Extinction?

• Why Didnt 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

11
Eating Our Way to Extinction

• Stellers 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

12
The Passenger Pigeon

• The First High-Tech Extinction

13
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

14
Disloyalty
15
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.

16
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

17
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

18
The Heath Hen

• When Your Best Just Isnt Good Enough

19
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 Marthas Vineyard,
  Massachusetts
• By 1906, only 50 left
• 1907, Sanctuary established

20
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?

21
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

22
Carolina Parakeet

• Too Adaptable for its Own Good

23
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 1880s
• Last Seen in Florida about 1920

24
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

25
When You Cant 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

26
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)

27
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.

28
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.

29
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?

30
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

31
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

32
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?

33
Mass Extinctions
34
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

35
Why High-Order Taxa Survive
36
Lazarus Taxa

• Groups that vanish during mass extinctions and
  then reappear
• Where do they go?
• Why dont they change?

37
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)

38
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

39
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

40
What We Wouldnt Find in the Fossil Record

• Dusky seaside sparrow (color variant only)
• Ivory-Billed Woodpecker, California Condor,
  Stellers Sea Cow (never abundant)
• Most rain forest species (too restricted, not
  likely to be fossilized)

41
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

42
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