Extinction
1. Extinction Case Histories
2. Definitions of Extinction
3. Rates of Extinction: Geological
Past, Historical Past, Current
4. Extinction Causes
11/24/2011
What is extinction?
• A common and widespread process
– 99% of species that have ever lived on
earth are now extinct
• The end of an evolutionary line
• The opposite of “extant”
Extinction case histories
• Dodo
• Hawaiian fauna
• Passenger Pigeon
The Dodo (Raphus cuculatus)
• “Discovered” in 1598 on island of Mauritius
• Biology
– ate fruit
– large (100 lbs.)
– flightless
Reconstruction of dodo
from skeleton,American
Museum of Natural
History
Raphus skeleton from Artistic representation of
American Museum of dodo, 1686.
Natural History
Extinction of the Dodo
• Extinct by 1681 (80 years after discovery)
• Causes of extinction
– exploitation by sailors for food
– habitat destruction of forest/food supply
– introduced predators--rats, monkeys, pigs
Hawaiian fauna
• Overview from Bishop museum
• Example:
– Black mamo
• Causes:
– habitat destruction
– competition from exotic species
– introduction of exotic diseases and
predators
Passenger Pigeon
• Range was eastern U.S. (bred in north,
wintered in south)
• Migrated in huge numbers
– "a column, eight or ten miles in length . . .
resembling the windings of a vast and
majestic river."
– In 1808 a single flock in Kentucky was
estimated to contain over 2 billion birds.
Passenger pigeon biology
made it a “sitting duck”
• Fed on “mast”: huge • Nested in trees in
crops of eastern large breeding
chestnut and oak colonies (100’s of
trees pairs)
Pasenger pigeon extinction
• “Martha” died in
• Causes linked to
Cincinnati Zoo, westward expansion
September 1, 1914.
• Forest clearing
• Birds thought to be a
menace to crops
• Adults and nestlings
taken for food
• Railroad expansion led
to shipping to city
markets via refrigerated
freight
Extinctions in Geological Time
• BBC “The Extinction Files”
Background rate of extinction:
marine invertebrates
5-10 families per million years
Source:
University of
Rochester, Earth
Sciences
Department
Mass extinctions:
10-20 families per million years
Source: University
of Rochester,
Earth Sciences
Department
Problems with determining past extinctions
Incomplete fossil record
– only certain features
fossilize
Track of
theropod
dinosaur, Dinosaur-bearing formations from
Sundance Wyoming (Jurassic and Cretaceous
Formation, periods)
Wyoming
(Jurassic Some environments do not result
period). in preservation of fossils
Photos: U.S. Bureau Land
Management
Lazarus taxa: 'rise from the dead’
e.g. Coelacanth, Latimeria chalumnae
• known from fossils
400 mya
• disappeared from
fossil record 80 mya
• live coelacanth
discovered, South
Africa, 1938
• another population of Sulawesi Coelacanth
live coelacanths, History of South African
Coelacanth discovery
Indonesia,1998
“Elvis” taxa
• species that disappear from fossil record
• only to be replaced by unrelated, but
strikingly similar impersonators
Thylacosmilus,, Meicocene
Smilodon, Pleistocene
(20,000 y.a.), South America
(10,000 y.a.), California
Extinctions in Historical Period
• How to document a species is extinct?
– # total species unknown
– have to prove doesn't exist (compare to
proving does)
• search every known locality
• insufficient funds, scientists
Definitions used by
World Conservation Monitoring
Centre
• EXTINCT - A taxon is Extinct when there is no
reasonable doubt that the last individual has died.
• EXTINCT IN THE WILD (EW) - A taxon is extinct in
the wild when:
– it is known only to survive in cultivation, in
captivity or as a naturalised population (or
populations) well outside the past range.
– A taxon is presumed extinct in the wild when
exhaustive surveys have failed to record an
individual.
Operational Definition of
Extinct:
• Not seen in wild by reliable observer in
50 years
Recorded Extinctions Since 1600
300
250 continental island oceanic
200
# species
150
100
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Figures on extinctions
Causes of Bird Extinctions
70
60 continental
oceanic islands
50
% of total
40 Continents Islands
Number of species 11 92
30 Number of subspecies 2 83
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Current Extinction Rates
• How to estimate?
– Rate of habitat loss
– Known patterns of species occurrence
From:
Pimm and
Raven,
2000,
Nature 403,
843 - 845
Causes of extinction
• Ecological
– Ultimate
– Proximate
• Human influences
– overexploitation
– Habitat destruction
– Introductions and exterminations
– Pollution
– Ecosystem cascades
– Mismanagement and or confusion
Ultimate Ecological Causes of Extinctions
• Population abundance naturally low
• Geographic range small
• Patchy distributions within overall range
• Body size large
• Top predators (high trophic position)
• Highly specialized
– habitats
– breeding sites
– food
– migratory species
Proximate Ecological Causes of
Extinctions
• Demographic stochasticity
• Environmental stochasticity
• Genetic failure
• Natural catastrophes
More Extinction Case Histories
• From Wilson CD:
– Heath hen
– North American burying beetle
– Hawaiian fauna