Extinction
Extinction occurs when all individuals of a species are gone and
have left no descendants. If all the species within a genus are
extinct then the genus is extinct.
extinct If all genera in a family are
extinct then the family is extinct. Extinction removes a potential
branch on the evolutionary tree.
Extinction is Forever
We can conclude a species has gone extinct when the last
member
b off that
h species
i has
h died.
di d
Tecopa pupfish - 1977
Dodo - 1581
Elephant Bird
(Madagascar) ~ 1500
Moa (New Zealand) –
4 species ~ 1400
Quagga - 1883
Passenger Pigeon – 1914
Once the most common
bird in North America.
Tasmanian Tiger or Thylacine - 1936
Caribbean Monk Seal - 1952
Golden Toad - 1989
Pyrenean Ibex - 2000
Baiji River Dolphin - 2006
It is often difficult to prove that no individuals of a species
remain
i in
i the
h wild.
ild It
I is
i easier
i to prove for
f large
l
animals.
i l
Ivorybilled Woodpecker - ?
What makes a species vulnerable
to extinction?
• Vulnerability to introduced exotics
• Overexploitation
• Rarity
• Habitat loss / Fragmentation
S ll population
Small
l ti size
i makes
k extinction
ti ti more likely
lik l
• A small ppopulation
p
is pprone to ppositive-feedback loops
p
that draw it down an extinction vortex
• The key factor driving the extinction vortex is loss of
the genetic variation necessary to enable evolutionary
responses to environmental change
Small
population
Inbreedingg
Genetic
drift
Lower
p
reproduction
Higher
mortality
Loss off
L
genetic
variability
Reduction in
individual
fitness and
population
adaptability
Smaller
population
Natural Extinctions
• Habitat Disruption
– Volcanic Eruptions
– Asteroid Impact
• Habitat
H bi M
Modification
difi i
– Climate Change
– Mountain-Building
– Sea Level Change
• “Exotic” Species
– Natural Dispersal
p
– Continental Drift
Extinctions are most easily seen in species that have restricted
distributions – endemic species.
Hotspots of biodiversity are also hotspots of extinction…
Human-Caused Extinction
• Overexploitation (Food, fur, collecting, pest
eradication etc.)
eradication,
etc )
• Habitat Degradation/Destruction
• Destruction of keystone species
• Introduction of Exotic Species
– Competitors
– Predators
– Diseases
• Pollution,
Pollution Contamination,
Contamination Climate Change
Overexploitation
• Human harvesting of wild plants or animals at rates
exceeding ability of populations of those species to rebound
• Large organisms with low reproductive rates are
especially vulnerable
• Overexploitation by the fishing industry has greatly reduced
populations of some game fish,
fish such as blue-fin
blue fin tuna
• World
World’ss fish stocks have been reduced by 90%
since the start of industrial fishing
Human exploitation of other species increases with our
population size.
Humans Arrivals are Linked to Large Mammal
Extinctions
• Australia 40,000 years ago
• Americas
A
i
15
15,000
000 years ago
• Madagascar 1000 years ago
• New Zealand 1000 years ago
Habitat Degradation
• Destruction of Habitat
– “Save the Rainforests!”
– Elimination
Eli i i off living
li i space
– Change in habitat
• Rainforest
R i f
to pasture lands
l d
– Leads to diminishing resources
• Increases
I
competition
titi
– Can also be caused by natural processes
• Volcanoes,
Volcanoes floods
floods, dro
drought,
ght etc…
etc
Satellite Images of Amazon Deforestation
between 1975 and 2001
Climate Change alters habitats over the entire Earth.
Habitat Fragmentation
Smaller fragments have:
• fewer habitat types
• fewer species
• smaller
ll populations
l ti
• higher
g
extinction rates
Predation
• Introduction of predators can impact natives
– Invasive alien species
• Can
C eatt other
th species
i
• Compete for food sources
• Introduce diseases
Predators reduce the population size of prey species. Predators
that are very effective can reduce the size of prey populations
to the point of extinction.
The introduction of cats to areas that formerly lacked
mammalian predators has caused the extinction of many
species of birds, reptiles, and mammals. Introduced rats have
caused the extinction of many birds and egg-laying
egg laying reptiles.
reptiles
Lake Victoria had over 150
endemic species of fish belonging
to one family. Each had
specialized feeding adaptations.
The introduction of a large predator,
the Nile perch, has caused the
extinction of about half the species.
Coextinction
• Everything is Connected to Everything ECE
• The loss of one species
p
leads to the loss of
another – loss of a prey species impacts
p
predators
• Chain of extinction
• Can be caused by small impacts in the
beginning